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2020 Spring Meeting

Nanomaterials and advanced characterization


Advanced small-scale mechanical characterization: strength, plasticity, fracture and fatigue

Thin films, coatings, welds, flexible electronics, sensors and MEMS rank among the most critical components made of small volumes of materials used in a variety of applications (automotive, energy, nuclear, microelectronics, aerospace...). Ensuring their service performance and lifetime requires detailed knowledge about the small-scale mechanical behaviour of materials, which can only be gained through advanced experimental and/or simulation methods.


The small-scale mechanical characterization of materials relies upon the development and use of a wide range of highly specialized experimental and simulation techniques, aimed at investigating different mechanical aspects. Past research has mostly focused on the yield behavior of single crystalline microsized structures. Although they represent a big initial step toward a better understanding of mechanical size effects, these investigations were very limited in scope regarding both the kind of failure and the type of microsamples. The present symposium will focus on recent developments aimed at expanding our knowledge to the behavior of more complex specimens (for instance nano-objects, thin films and bulk nanostructured materials) and/or under more complex loading conditions (including cyclic fatigue, fracture testing...). To date, the most promising investigations build upon the combination of mechanical testing either with in-situ characterization methods (such as TEM, SEM, AFM, micro-XRD, synchrotron, electrical measurements) or with simulation methods (such as for instance atomistic simulations and discrete dislocation dynamics).

The symposium highly welcomes such contributions, which are well suited for gaining a deep insight into the mechanisms responsible for mechanical size effects. Direct applications of these methods to solve complex engineering issues are also warmly welcomed.

Hot topics to be covered by the symposium:

  • Small-scale plasticity, fracture and fatigue testing
  • Advances in in-situ and ex-situ micro/nanomechanical testing
  • Recent advances in characterization methods, including TEM, SEM, AFM, synchrotron techniques
  • Advances in numerical technical methods
  • Complex loading situations
  • Applications to nuclear materials
  • Applications to nano-objects, thin films and bulk nanostructured materials
  • Applications to crystalline, amorphous or hybrid materials
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09:45 Coffee break    
10:00 Welcome address    
Mechanical properties across length scales : B. Merle
Authors : Gerhard Dehm
Affiliations : Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany

Resume : Small scale mechanical measurements did not only lead to new insights on size scaling effects in single crystal metals, but also opened new insights on fundamentals of plasticity, fatigue and fracture of bulk materials. In steels, for example, the different phases like ferrite, martensite, and/or cementite have a complex interaction, but often little is known about the performance of the individual phases. Small scale mechanical testing can be used to determine critical resolved shear stresses of different glide systems, study brittle-to-ductile transitions, deformation mechanisms and fracture toughness of brittle phases like cementite or Laves phases. Similarly, understanding environmental impact on mechanical properties of engineering alloys, like hydrogen embrittlement, where numerous phenomena are reported in literature, could benefit from small scale mechanical testing by focusing on different microstructure components. In that case it is important to ensure hydrogen charging of the small samples and avoiding surface roughening by chemical attack during electro-chemical exposure. In this presentation, recent advances on small scale testing of phases, grain boundaries and hydrogen embrittlement will be presented. Acknowledgement Major contributions by H. Tsybenko, C. Tian, F. Stein, J. Rao, N. Malyar, W. Luo, C. Kirchlechner, M. Kini, J. Duarte, S. Brinckmann are gratefully acknowledged. Part of this project was funded by the DFG within the project KI-1889/1-1. GD acknowledges financial support from the European Research Council (ERC) through Grant No. 787446 — GB-CORRELATE

Authors : Wenzhen Xia, Gerhard Dehm, Steffen Brinckmann
Affiliations : Department of Structure and Nano-/Micromechanics of Materials; Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf 40235, Germany

Resume : Due to the complex collective interaction of tribological metallic contacts, the microstructure – tribological property relationship is still largely unresolved . The rise of nano- and micro-mechanical instrumentation allows separating the interacting tribological processes. For instance, single microasperity wear, i.e. nano/micro-scratch, testing has become a useful technique for understanding the mechanisms during the very initial run-in stage of tribology [1, 2]. Although the tribological contact has been dramatically simplified, the understanding of abrasion-induced plasticity is still incomplete. In this work, we introduce a novel micro-wall wear test that aims at 1) further simplifying the stress state in the contact zone and 2) better identifying the active slip system in the entire deformation zone. Initially, we utilize the advanced Focused Ion Beam (FIB) to produce micro-walls with different wall directions in the {111} and {100} grains. We indent and scratch on the micro-walls using a wedge nanoindenter tip. We observe that the dislocations prefer to be activated on the positively inclined slip-planes [3] and then on the negatively inclined slip-planes. After abrasion, the active slip-planes remain activated while the dislocation activity moves closer to the top surface. Interestingly, high-resolution electron backscatter diffraction (EBSD) results show that single dislocation-walls form after indentation in some of micro-walls. In all micro-walls, dislocation walls are formed during abrasion. Both sides of the dislocation-wall are misoriented by a large angle (~30°). The electron channeling contrast imaging (ECCI) and transmission electron microscopy (TEM) confirm the high density of dislocations in the dislocation-walls. These results are compared to the work of Greiner at al.[4, 5], who investigated dislocation trace formation under macroasperity contacts in a bulk material. The present study shows the grain orientation dependence of the dislocation-wall formation and is the first to produce a dislocation-wall in a single grain during tribology. This micro-wall wear test has the potential to better study the origin of tribology-induced grain refinement in metals. [1] S. Brinckmann, G. Dehm, Nanotribology in austenite: Plastic plowing and crack formation, Wear 338 (2015) 436-440. [2] S. Brinckmann, C.A.C. Fink, G. Dehm, Nanotribology in austenite: Normal force dependence, Wear 338 (2015) 430-435. [3] W. Xia, G. Dehm, S. Brinckmann, Unraveling indentation-induced slip steps in austenitic stainless steel, Mater Design (2019). [4] C. Greiner, J. Gagel, P. Gumbsch, Solids Under Extreme Shear: Friction-Mediated Subsurface Structural Transformations, Adv Mater 31(26) (2019). [5] X. Chen, R. Schneider, P. Gumbsch, C. Greiner, Microstructure evolution and deformation mechanisms during high rate and cryogenic sliding of copper, Acta Mater 161 (2018) 138-149.

Authors : Alekseev, P.A.*(1), Dunaevskiy, M.S.(1), Borodin, B.R.(1), Cirlin, G.E.(2), Khayrudinov, V.(3), Lipsanen, H.(3) & Lähderanta, E.(4).
Affiliations : (1) Ioffe Institute, 194021 Saint-Petersburg, Russia; (2) Alferov University, 194021 Saint-Petersburg, Russia; (3) Department of Electronics and Nanoengineering, Aalto University, Espoo FI-00076, Finland; (4) Laboratory of Solid-state Physics, Lappeenranta University of Technology, 53850 Lappeenranta, Finland;

Resume : GaP nanowires (NWs) are promising materials for flexible devices. Bulk GaP has the zinc blende (ZB) structure, GaP NWs may have a wurtzite structure (WZ) with a direct band gap. During the growth planar defects (stacking faults and twinning) may occur. Mechanical properties of the WZ GaP NWs and an impact of the planar defects on the Young’s modulus almost have not been studied. Here, we studying these features by atomic force microscopy (AFM). Pure WZ GaP NWs were grown by MBE on a graphene/SiC substrate. NWs with high density of the planar defects were grown by MOVPE on Si substrate. We investigated inclined NWs with diameters of 60 to 100 nm and with the length up to 3 microns. Previously, we have developed an AFM method based on the PeakForce technique (Bruker) for determining the Young's modulus of single NWs obliquely grown on substrate [1]. This technique allows measuring the force-distance curves at each point of the scan, as well as the deformation of the object by the probe with a well-controlled force. By analyzing the deformation profiles along the axis of a NW one can determine its stiffness and Young's modulus. The Young's modulus of the NWs with a pure WZ structure was 160±20 GPa which is close to the theoretical value (167 GPa). Planar defects led to the decreasing of the modulus to 140 ±20 GPa. Reasons of the softening are discussed. [1] M. Dunaevskiy et al.// Nano Lett., 17, 3441 (2017) This work is supported by Russian Presidential Grant МК-1543.2020.2

12:00 Lunch break    
Small-scale plasticity : N/A
Authors : Jeffrey M.Wheeler*, Ming Chen, Laszlo Pethö, Alla S.Sologubenko, Huan Ma, Johann Michler, Ralph Spolenak
Affiliations : ETH Zürich, Laboratory for Nanometallurgy, Department of Materials Science, Vladimir-Prelog-Weg 5, Zürich CH-8093, Switzerland Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Mechanics of Materials and Nanostructures Feuerwerkerstrasse 39, Thun CH-3602, Switzerland Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Transport at Nanoscale Interfaces Ueberlandstrasse 129, Dübendorf CH-8600, Switzerland

Resume : As the backbone material of the information age, Si is extensively used as a functional semiconductor and structural material in microelectronics and microsystems. At ambient temperature, the extreme brittleness of Si handicaps its manufacturing and performance in devices and systems. Here, we demonstrate Si processed by modern lithography procedures exhibits an ultrahigh elastic strain limit, near ideal strength (shear strength ~4 GPa) and plastic deformation at the micron-scale, one magnitude larger than previous observations, due to superior surface quality. This extended elastic regime enables enhanced functional properties by allowing higher elastic strains to modify the band structure. Further, the micron-scale plasticity of Si allowed us to investigate the intrinsic size effects and dislocation behavior in diamond-structured materials. This revealed a transition in deformation mechanisms from full to partial dislocations upon increasing specimen size at ambient temperature. This study demonstrates a surface engineering pathway for the fabrication of more robust Si-based structures and microdevices with enhanced semiconductor functionality.

Authors : Nicoló della Ventura, Szilvia Kalácska, Amit Sharma, Daniele Casari, Jakob Schwiedrzik, Johann Michler, Xavier Maeder
Affiliations : Empa, Swiss Federal Laboratories for Materials Science and Technology, Feuerwerkerstrasse 39, 3602 Thun, Switzerland

Resume : The mechanism of twin nucleation and propagation in single crystal Mg is investigated at the micron-scale for different crystallographic loading direction, both in tension and compression, with in-situ HR-EBSD characterizations during deformation. Orientation mapping, strains, stresses and GNDs evolutions are given for different deformation steps, which allow investigating in detail the interplay between slip activities and twin formation in the materials during progressive deformation. Post-mortem 3D HR-EBSD characterizations with FIB slicing can reveal the twin shape and GNDs distribution inside the deformed materials. This offers a better understanding of the twin-twin and twin–slip interactions during deformation. The HR-EBSD measurements are supported by post-mortem TEM characterizations for more detailed investigations of the dislocations and twins in the material.

Authors : Salomé Parent1, Christophe Tromas1, Anne Joulain1, Hadi Bahsoun1, Ludovic Thilly1, Patrick Villechaise1, Thierry Ouisse2
Affiliations : 1 Institut Pprime, - Université de Poitiers, Chasseneuil Futuroscope, France E-mail: 2 LMGP, Grenoble, France

Resume : Mn+1AXn phases are hexagonal materials with a nanolaminar structure consisting in an alternation of metallic planes and carbide or nitride layers. Basal plane dislocation mechanisms are widely reported in MAX phases (e.g. dislocations walls, dislocations pile ups and kink bands) but they cannot account for all the deformation processes. Furthermore, since the grains are platelets elongated along the basal plane, the macroscopic mechanical response is not only related to the crystallographic structure. The analysis of the elementary deformation mechanisms required thus mechanical testing experiments at small scale. In this way, spherical nanoindentation tests have been performed in single crystal platelets of Cr2AlC, oriented with the basal plane edge on in order to inhibit basal slip below the indent. Transmission Electron Microscopy (TEM) thin foils have been prepared by focussed ion beam (FIB) in cross section through the indents and the deformation structures have been characterized at small scale in a same region both by Atomic Force Microscopy (AFM) surface observation and by TEM Weak Beam. The correlation between AFM and TEM analysis on a same deformation structure has allowed to identify deformation twinning in this material and to characterize the twinning system. This study has been strengthened by an extensive analysis of the twinning deformation below an indent using ACOM (Automatic Crystal Orientation Mapping) ASTAR technique on a second MAX phase: Ti2AlN.

Authors : Peter Schall
Affiliations : Van der Waals-Zeeman Institute, University of Amsterdam, The Netherlands

Resume : Ductile fracture, the slow dissipation-controlled propagation of cracks, remains a key unsolved challenge in the mechanics of amorphous materials, currently limiting their strength and lifetime. Structural weakening within the highly focused strain field preceding the crack tip is thought to play the central role during ductile fracture. However, no consensus exists on the magnitude and nature of this dissipation as its dynamics remain elusive as atomic-scale observations continue to be prohibitively difficult. Colloidal glasses allow direct particle-scale insight into the structure and dynamics of deformation and fracture. Here, by direct particle-scale observation of a cohesive colloidal glass during slow fracture, we reveal remarkable spatio-temporal organization in the structural weakening process. Direct local measurement of the strain at the crack tip during crack propagation shows the intriguing interplay between elastic energy and dissipation behind these complex spatio-temporal correlations. We also use colloidal glasses to elucidate the mechanism behind plastic deformation of an amorphous solid, and find intriguing signs of criticality: local plastic regions grow until they percolate across the sample and the material yields. These results shed new light on the small-scale mechanical behaviour and dynamics.

Authors : Erkka J. Frankberg* (1,2,3), Janne Kalikka (4), Francisco García Ferré (3), Lucile Joly-Pottuz (2), Turkka Salminen (5), Jouko Hintikka (1), Mikko Hokka (1), Siddardha Koneti (2), Thierry Douillard (2), Bérangère Le Saint (2), Patrice Kreiml (6), Megan J. Cordill (6), Thierry Epicier (2), Douglas Stauffer (7), Matteo Vanazzi (3), Lucian Roiban (2), Jaakko Akola (4,8), Fabio Di Fonzo (3), Erkki Levänen (1) & Karine Masenelli-Varlot* (2)
Affiliations : (1) Unit of Materials Science and Environmental Engineering, Tampere University, Tampere, Finland; (2) Université de Lyon, INSA-Lyon, UCBL, MATEIS, CNRS UMR 5510, Villeurbanne, France; (3) Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia, Milano, Italy; (4) Computational Physics Laboratory, Tampere University, Tampere, Finland. (5) Tampere Microscopy Center, Tampere University, Tampere, Finland; (6) Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Leoben, Austria; (7) Bruker Nano Surfaces, Bruker Inc., Eden Prairie, MN, USA; (8) Department of Physics, Norwegian University of Science and Technology, Trondheim, Norway.

Resume : Oxide glasses are an integral part of the modern world, but their usefulness can be limited by their characteristic brittleness at room temperature. Using in situ TEM and numerical simulations, we show that amorphous aluminum oxide can permanently deform without fracture at room temperature and high strain rate by a viscous creep mechanism [1]. These thin-films can reach flow stress at room temperature and can flow plastically up to a total elongation of 100%, provided that the material is dense and free of geometrical flaws coupled with an effective activation energy that allows sufficient bond-switching activity in the atom network. Our study demonstrates a much higher ductility for an amorphous oxide at low temperature than previous observations and we formulate a criterion that can help to find other oxides with similar behavior. This discovery may facilitate the realization of damage-tolerant glass materials that contribute in new ways, with the potential to improve the mechanical resistance and reliability of applications such as electronic devices and batteries. Moreover, the results indicate that amorphous oxides have potential to be used as high-strength, damage-tolerant engineering materials. The results reveal new aspects of glass thermodynamics below glass transition temperature and could lead to a new paradigm on how glass materials can be used in engineering. [1] Frankberg et al. Science Vol. 366, Issue 6467, pp. 864-869 (2019)

Authors : Haug, C.*(1,2), Ruebeling, F.(1,2), Kashiwar, A.(3,4), Gumbsch, P.(1,3,5), Kübel, C.(3,4,6), Greiner, C.(1,2)
Affiliations : (1) Karlsruhe Institute of Technology (KIT), Institute for Applied Materials (IAM), Germany (2) KIT IAM-CMS MicroTribology Center (µTC), Germany (3) Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology, Germany (4) Department of Materials and Earth Sciences, Technical University of Darmstadt (TUD), Germany (5) Fraunhofer Institute for Mechanics of Materials (IWM), Germany (6) Karlsruhe Nano Micro Facility, Karlsruhe Institute of Technology (KIT), Germany

Resume : Friction and wear in mechanical systems cause a substantial contribution to global energy consumption. Studying fundamental mechanisms governing dislocation mediated plasticity as well as friction at metal sliding interfaces may greatly help advance the development of materials tailored for low friction and little wear. As the stress state in ball-on-flat contacts is notoriously complex and makes quantitative analysis difficult, deformation mechanisms in such systems warrant further investigation. This work therefore analyzes microstructural changes occurring on the micron scale as a result of sliding a sapphire sphere over high-purity copper in the vicinity of a twin boundary. Two characteristic horizontal line features (dislocation trace lines, DTL) are observed parallel to the sliding interface. Their interaction with the twin boundary is studied using automated crystal orientation mapping (ACOM). Making use of the twin boundary as a marker, three complementary fundamental deformation mechanisms are identified: A simple shear process affecting the immediate subsurface area and a localized plastic shear process occurring at the lower DTL as well as a crystal rotation of the areas between the sliding interface and both DTLs. Analysis reveals that the three processes are physically compatible. They can be considered decisive for guiding future experiments as well as computational modeling efforts.

16:00 Coffee break    
X-ray diffraction : T. Cornelius
Authors : W. Ludwig(1,2)*, N. Vigano(2), P. Reischig(3), H. Proudhon(4), J. Wright(2)
Affiliations : (1) MATEIS, INSA Lyon, UMR5510 CNRS, Villeurbanne, France (2) ESRF, Grenoble, France (3) Innocryst Ldt. , Leicester, UK (4) CdM, Mines ParisTech, Evry, France

Resume : Over the last years, a number of X-ray diffraction based characterization techniques have reached a level of maturity that enables us to interrogate microstructural variables (i.e. local orientation, elastic strain, damage) in the bulk of 100µm up to ~1mm sized polycrystalline sample volumes. With the upgrade of the ESRF storage ring and the availability of faster detector systems time-lapse observation of deforming metallic microstructures at the (sub-)micrometer length-scale will become possible. In this talk we will review and illustrate the complementary possibilities offered by monochromatic beam 3D scanning micro-diffraction and full-field imaging based characterization approaches. The comparison with concomitant simulations (e.g. crystal plasticity, discrete dislocation dynamics, phase field) on the digital clone of the experimentally observed sample volumes may be an avenue for improving current material models and for inferring difficult to measure materials parameters.

Authors : Pierre Godard, Julien Drieu La Rochelle, Cristian Mocuta, Dominique Thiaudiere, Pierre-Olivier Renault
Affiliations : University of Poitiers France; University of Poitiers France; Synchrotron SOLEIL, France; Synchrotron SOLEIL, France; University of Poitiers France

Resume : Ductile crystalline materials can deform by dislocation slip and/or by twinning, and the leading mechanism depends on the applied stress conditions like temperature and strain-rate, but also on geometric conditions like the grain size. For example, twinning has been found to occur even in high stacking fault energy metals like aluminum [1]. In this work, we aim at quantifying through in situ pole figure measurements the twins’ evolution as a function of the applied strain in gold single crystals. The 50 nm-thick gold thin film is deposited on NaCl single crystal by physical vapor deposition technique at 400°C. The film is then transferred on a polyimide cruciform substrate to be deformed on a biaxial tensile tester in situ during synchrotron x-ray diffraction measurements. The as-deposited single crystal contains an initial twin fraction of a few %. The typical twins’ thickness and size are 5-10 nm and 50-100 nm, respectively. We will present the first results obtained on in situ uniaxial applied deformation in the [110] direction. The twins' volume evolution is quantified as a function of applied deformation ε thanks to the intensity of the diffracting pole. In particular, we show that the twins’ volume is constant up to ε=1%, but increases drastically by ~400% at ε=4% applied strain [2]. [1]: M. Chen et al, Science 300 (2003) 1275 [2]: J. Drieu La Rochelle et al, Surf. Coat. Technol 377 (2019) 124878

Authors : A. Davydok, C. Krywka
Affiliations : Institute for Materials Research, Helmholtz Zentrum Geesthacht, Hamburg, Germany

Resume : Composite materials attract a huge scientific interest as materials with a wide spectrum of controlled properties. In particular, organically-linked Fe3O4 nanocomposites based supercrystals demonstrate unique combination of strength and stiffness [1]. Nevertheless it is not fully clear if the "smaller is stronger" trend is also relevant for such new materials. Better understanding of the mechanical properties requires in-situ deformation experiments with nano- and micro-specimens. Such kind of studies can only be performed using nanoprobes with high spatial resolution and sensitive to small structural changes, such as nanofocused, high energy X-ray beams. The P03 Nanofocus Endstation at PETRA III at DESY (Hamburg, Germany) is operated by Helmholtz Zentrum Geesthacht and offers unique conditions for mechanical tests coupled with X-ray nanodiffraction [2]. The highly stabile experimental setup is dedicated to structural analysis with sub-micron precision. The X-ray beam is focused down to a size of only 250 x 250 nm^2 by means of KB-mirrors with focal distance of ~10cm which provides space for extended, in-situ sample environment implementation. The strong focus on materials science at P03 is demonstrated by the wide range of in-situ experiments already performed, such as mechanical testing with strain resolution of 10^-5 [3]. In this presentation the applicability of P03 instrumentation for in-situ mechanical tests will be presented. Combining scanning X-ray nanodiffraction with a self-developed nanoindenter we have performed unique experiments separating the influence of organic and non-organic components to the mechanical properties of a microsized supercrystal. Detailed technical specification of the beamline will be shown as well as results obtained during the experiment. References: [1] Dreyer A., Feld A., Kornowski A.,Yilmaz E., Noei H., Meyer A., Krekeler T., Jiao C., Stierle A., Abetz V., Weller H. Schneider G., Nature Materials 15 5 (2016); [2] Krywka C., Neubauer H., Priebe M., Salditt T., Keckes J., Buffet A., Stephan Volkher Roth S., Döhrmann R., Müller M., J.Appl.Cryst.45, 85 (2012); [3] Zeilinger A., Todt J., Krywka C., Müller M., Ecker W., Sartory B., Meindlhumer M., Stefenelli M., Daniel R., Mitterer C. Keckes J., Sci. Rep. 6,22670 (2016).

X-ray diffraction (continuation) : M. Cordill
Authors : T.W. Cornelius1, F. Lauraux1, S. Labat1, M.-I. Richard1, 2, S.J. Leake2, O. Kovalenko3, E. Rabkin3, T.U. Schülli2, O. Thomas1
Affiliations : 1Aix Marseille Univ., Université de Toulon, CNRS, IM2NP, Marseille, France; 2ID01/ESRF – The European Synchrotron, 71 Avenue des Martyrs, 38000, Grenoble, France; 3Department of Materials Science and Engineering, Technion – Israel Institute of Technology, 32000 Haifa, Israel

Resume : The mechanical properties of micro- and nanostructures differ significantly from those of their bulk counterparts. Despite numerous studies, plasticity at the nanoscale is, however, not fully understood yet. In situ experiments are perfectly suited for the fundamental understanding of the onset of dislocation nucleation. We developed a scanning force microscope which allows for in situ nano-mechanical tests in combination with Bragg coherent X-ray diffraction imaging (BCDI) [1]. This lensless imaging method retrieves the far-field amplitude scattered from the sample using computational inversion algorithms. The retrieved phase in direct space is directly related to the strain within the crystal. Our BCDI studies on indented Au crystals demonstrated the capability to imaging a single prismatic loop induced by nano-indentation [2]. Here, we report about in situ nano-indentation of Au crystals where the evolution of strain and defects was imaged by multi-wavelength (mw) BCDI [3]. With increasing mechanical load, prismatic dislocation loops appear at about half-height of the indented crystal, and disappear upon unloading [4]. This is the first time that mw-BCDI has been successfully employed during in situ experiments providing direct insight into the plasticity at the nanoscale. [1] Z. Ren et al., J. Synchrotron Radiat. 21 (2014) 1128-1133 [2] M. Dupraz et al., Nano Lett. 17 (2017) 6696-6701 [3] F. Lauraux et al., J. Appl. Cryst. (2020) in press [4] F. Lauraux et al., in preparation

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09:45 Coffee break    
Machine learning : N/A
Authors : Sandra Korte-Kerzel*, Carl Kusche, Setareh Medghalchi, Talal Al-Samman, Ulrich Kerzel
Affiliations : Kusche: Institute of Physical Metallurgy and Materials Physics, RWTH Aachen University, Aachen, Germany; Medghalchi: Institute of Physical Metallurgy and Materials Physics, RWTH Aachen University, Aachen, Germany Al-Samman: Institute of Physical Metallurgy and Materials Physics, RWTH Aachen University, Aachen, Germany Kerzel: IUBH International University of Applied Sciences, Erfurt, Germany AND Institute of Physical Metallurgy and Materials Physics, RWTH Aachen University, Aachen, Germany Korte-Kerzel: Institute of Physical Metallurgy and Materials Physics, RWTH Aachen University, Aachen, Germany

Resume : High performance materials, from natural bone over ancient damascene steel to modern superalloys, typically possess a complex structure at the microscale. Their properties exceed those of the individual components and their knowledge-based improvement therefore requires understanding beyond that of the components? individual behaviour. Electron microscopy has been instrumental in unravelling the most important mechanisms of co-deformation and in-situ deformation experiments have emerged as a popular and accessible technique. However, a challenge remains: to achieve high spatial resolution and statistical relevance in combination. Here, we overcome this limitation by using panoramic imaging and machine learning to study damage in dual phase steels. This high-throughput approach now gives us strain and microstructure dependent insights into the prevalent damage mechanisms across a large area of this heterogeneous material. Aiming for the first time at automated classification of the majority of damage sites rather than only the most distinct, the new method also encourages us to expand current research past interpretation of exemplary cases of distinct damage sites towards the less clear-cut reality. A transfer to other materials, such as dual phase magnesium or high stiffness steels, has also been begun, as has the exploration of the third dimension of these complex microstructures to further expand the physical interpretation of the large datasets of electron micrographs now available.

Authors : Durmaz, Ali Riza (1,2,3), Schmitz-Elbers, Manuel (1), Straub, Thomas (1), Eberl, Christoph (1,2)
Affiliations : (1) Fraunhofer Institute for the Mechanics of Materials IWM, Germany; (2) University of Freiburg, Germany; (3) KIT Karlsruhe Institute of Technology, Germany

Resume : A characteristic crack formation process, starting from damage accumulation in individual grains, micro crack initiation, and finally short crack formation determines the fatigue lifetime of a material. In the past years, our group has developed a fatigue damage evolution testing methodology, which exploits a strong correlation between resonant frequency changes and early damage initiation. So far, this method could only detect damage initiation on the global scale of the tested micro samples. Building on this work, we developed a multi modal approach employing in-situ optical images of the sample surface, ex-situ EBSD measurements processed with MTEX and complementary crystal plasticity FEM (CPFEM). We used the processed optical image data to locate single damage initiation sites (cracks and extrusions) and to create labels for machine learning (ML) methods. Simultaneously, EBSD measurements and CPFEM served to extract various microstructure characteristics as ML features. We attained feature importance and relationships using a random forest model. Additionally, deep learning (DL) semantic segmentation of post-mortem SEM images using a UNET architecture allowed us to distinct between extrusions and crack regions in the fatigued micro samples. Here we will present the first comparison between experimentally obtained damage initiation sites, CPFEM and ML-predictions.

Authors : Hadzic, N.(1,2,3), Durmaz, A.(1,2,3), Jünger, F.(2), Straub, T.(1,2), Rohrbach, A.(2), Eberl, C.(1,2)
Affiliations : (1) Fraunhofer Institute for Mechanics of Materials IWM, Germany; (2) University of Freiburg, Germany; (3) Karlsruhe Institute of Technology KIT, Germany

Resume : The lifetime of materials is a critical parameter for the reliability of devices. Further, rising requirements on materials lead to the necessity of a more distinct understanding of microstructural influences on the fatigue mechanisms. The progress of fatigue in alloys can be divided in several stages driven by cyclic irreversibilities, such as the occurrence of dislocation structures, formation of PSBs, growth of extrusions at the surface and crack initiation and growth. The lifetime of stress scenarios beyond the high cycle fatigue regime is mainly dominated by early stage fatigue mechanisms until crack initiation. Currently used in-situ characterization methods mostly operate either under vacuum or with complex stop and go practice. A combination of a micro fatigue setup designed for the detection of the early stages of fatigue occurrence and a novel microscopy technique would represent an alternative method allowing in-situ observation of formation of extrusions on the surface of samples. The ROCS-microscopy (Rotating Coherent Scattering Microscopy), up to now developed and used for the observation of biological cells, allows time and position dependent imaging independent of any atmospheric conditions. This method employs illumination of the sample’s surface with a collimated laser beam with a defined tilt and a variation of the azimuthal angle and integrates the back scattered light from different angles into an image. The aim was to implement an in-situ ROCS-microscopy based characterization method, to measure the formation of extrusions and performing first fatigue tests on martensitic steel, SAE 4150 subsequently. A preliminary study of the combined setup showed higher contrast for bright field images, while dark field images reproduced the topography of the sample surface. A comparison of obtained ROCS-microscopy images with alternative imaging methods showed higher image contrast for ROCS and resolvable structures of 190 nm distance. The formation of extrusions could be monitored by the evaluation of the accumulated peak intensity from the obtained in-situ ROCS images. Additionally, occurred extrusions and microcracks were characterized by scanning electron microscopy. Microstructural analysis showed ferritic areas, ascribed to high annealing temperatures, in the predominantly martensitic microstructure where a cumulated occurrence of extrusions could be observed. A link between the slip orientations of the extrusions with the slip plane traces of the damaged grain could be observed. Further, the observation of intragranular misorientations at extrusion borders, present already before the fatigue process, points to them acting as barriers against the growth of extrusions. The potential use of the in-situ ROCS fatigue setup allows a fast and simple characterization method to investigate the occurrence and propagation of extrusions. The influence of the microstructure under ambient conditions throughout early stages of fatigue can be investigated.

Authors : Fang Zhou
Affiliations : ZEISS Research Microscopy Solutions, Carl Zeiss Microscopy GmbH, Carl-Zeiss-Straße 22, 73447 Oberkochen, Germany

Resume : The recent development of in-situ mechanical testing and heating in SEM leads to linking the mechanical properties to the microstructures of materials by means of direct observation, strain analysis and EBSD misorientation measurement. An understanding of the connection between microstructures and mechanical properties helps researchers to design novel advanced materials in a highly effective way. Furthermore, such in-situ materials testing approaches deliver experimental datasets for the validation and the improvement of computational materials models, which is essential in designing novel high-performance materials by means of optimizing their microstructures and manufacture processes. The integration of in-situ testing accessories into a SEM up to now is, however, far from seamless and user friendly. The output is, on the other hand, very sobering in terms of the scale of sample area interrogated, throughput and reproducibility of results or datasets. For example, to validate and refine computational materials models, a large amount of highly resolved strain maps at precise mechanical loadings and temperatures of the sample are required which are, however, hardly available using the in-situ solutions at present. Another example is to determine grain misorientations through EBSD, defect formation and grain boundary migration caused by mechanical loading and subsequent tempering. There is, however, no real automated workflow for such long-term demanding experiments. To address these shortcomings, a well-integrated solution for demanding in-situ testing, combining high resolution surface sensitive SEM imaging and EDS/EBSD analytical methods with materials testing stages is under development. In this work, a solution which enables tailored in-situ automated workflows based on Python scripting is introduced. The automated workflow can generate meaningful data with utmost reproducibility and precision. On the other hand, such automated workflows make high throughput data acquisition at high image resolution and precise loading parameters in the SEM possible. The high quality of the acquired datasets facilitates post processing and data analysis, for e.g. high-resolution strain mapping by means of digital image correlation (DIC). By correlating the high-resolution images of the sample surface before and after its deformation during the in-situ experiment, the local surface strain can be evaluated by means of DIC. A selected area close to the center of the Cu sample is imaged with a high pixel density of 4000 x 3000 pixels at different nominal strain levels using the chamber SE detector. The DIC analysis performed by means of GOM Correlate is introduced. In this selected area, the local normal strain in the x direction is significantly larger than the nominal strain value, and the strain is mainly concentrated around the micrometer sized cracks which grow and propagate during the in-situ experiment. Further advancements such as automated feature tracking, autofocus and multiple regions of interest (ROIs) help to realize true one-button-start workflows and experiments. A heating element is integrated for high temperature in-situ testing up to 800°C. The temperature in the range of room temperature to 800°C can be kept constant for more than 24 hours for long-term in-situ testing combined with EBSD. Results such as grain boundary transition or grain deformation imaged using backscattered electron detection (BSD) at high temperatures will be shown. Examples of measuring grain misorientation during mechanical loading by means of high-resolution EBSD as well as high resolution strain mapping using DIC will also be discussed.

Authors : E.V. Podryabinkin, A.G. Kvashnin, M.A. Khansary, A.V. Shapeev
Affiliations : Skolkovo Institute of Science and Technology, Skolkovo Innovation Center 121025, 3 Nobel Street, Moscow, Russian Federation

Resume : Hardness is one of the most complicated and important property of materials from a practical point of view. It refers to the property of a material to resist pressing-in or scratch of an indenter made of a much harder material than tested one. The determination of hardness is traditionally based on the experimental measurement procedure, during which the test material is indented with a small piece of another very hard material (usually diamond). In this case, the hardness value itself is calculated as the ratio of the maximum indentation force to the area of the imprint left on the test sample. However, the measured hardness depends not only on the shape of the indenter, but also on the depth of its penetration (or the scale of the measurements)[1,2]. In addition to complexity and high cost, the experimental determination of hardness does not allow it to be used in the computer design of new materials. Therefore, in computational materials science, hardness is calculated by empirical models based on various other available material characteristics [3–6]. Such models are typically constructed as explicit formulas approximating known experimental data and generally nit very accurate. We proposed a technique which is based on atomistic modeling of the indentation similarly to the experimental procedure. A crucial aspect in this case is the model of interatomic interaction used. The empirical potentials traditionally used for atomistic modeling, as a rule, do not have sufficient accuracy to ensure the predictive power of this method, and, in addition, are developed only for a limited class of materials. Quantum-mechanical models, on the other hand, having acceptable accuracy, do not allow calculating structures with more than 200 atoms without special efforts, which makes it practically impossible to directly use them for calculating hardness. In this situation, machine-learning interatomic potentials (MLIPs) have direct indications for use. Here we use moment tensor potentials (MTP) to solve this issue [7,8]. These models are trained on the results of quantum mechanical calculations and reproduce the behavior of ab-initio models after that. Performance of MLIPs is comparable with empirical potentials, and the accuracy is close to that of quantum-mechanical models. Thus, we calculated the hardness for several known covalent materials, namely diamond, SiC etc, and obtained nanohardness for different crystallographic surfaces. Obtained data is consistent with numerous experimental results. References 1. Fischer-Cripps A.C. Analysis of Nanoindentation Test Data // Nanoindentation. New York, NY: Springer New York, 2011. P. 39–75. 2. Broitman E. The nature of the frictional force at the macro-, micro-, and nano-scales // Friction. 2014. Vol. 2, № 1. P. 40–46. 3. Chen X.-Q. et al. Modeling hardness of polycrystalline materials and bulk metallic glasses // Intermetallics. 2011. Vol. 19. P. 1275–1281. 4. Mazhnik E., Oganov A.R. A model of hardness and fracture toughness of solids // J. Appl. Phys. 2019. Vol. 126, № 12. P. 125109. 5. Oganov A.R., Lyakhov A.O. Towards the theory of hardness of materials // J. Superhard Mater. 2010. Vol. 32, № 3. P. 143–147. 6. Gao F. et al. Hardness of Covalent Crystals // Phys Rev Lett. 2003. Vol. 91. P. 015502–015506. 7. Shapeev A. Moment Tensor Potentials: A Class of Systematically Improvable Interatomic Potentials // Multiscale Model. Simul. 2016. Vol. 14, № 3. P. 1153–1173. 8. Podryabinkin E.V., Shapeev A.V. Active learning of linearly parametrized interatomic potentials // Comput. Mater. Sci. 2017. Vol. 140. P. 171–180.

12:10 Lunch break    
High-temperature applications : N/A
Authors : Jon Molina-Aldareguia*, Na Li, Jingya Wang, Javier Llorca
Affiliations : IMDEA Materials Institute,

Resume : High-throughput materials characterization is an emerging area in materials science. Starting from cheap raw materials, annealing of diffusion couples or multiples at elevated temperature allows the fabrication of specimens with a wide range of chemical compositions at small scales. This way, a single specimen can provide an enormous amount of data for database construction of novel alloys, including properties such as lattice parameters, phase stability and other physical properties. Considering the length scale of the composition profiles generated by interdiffusion, the determination of mechanical properties requires the use of advanced nanomechanical testing techniques. In this study, Mg/Mg-Zn and Mg/Mg-Al diffusion couples were produced with the aim of fast screening the composition-microstructure-mechanical properties relationships, for Mg-Al-Zn magnesium alloys. A range of techniques, like nanoindentation and micropillar compression, were used to determined the local mechanical properties, including strength and creep behavior at elevated temperature, over the available composition and grain orientation spectra in the diffusion zone, while the deformation mechanisms were determined by focused ion beam (FIB) and transmission electron microscopy (TEM). The outcome of this study and the feasibility of the approach to construct a quantitative composition-microstructure-property relationship for Mg-Al-Zn alloys will be discussed.

Authors : Sebastian Moser (1), Gerald Zernatto (1), Manuel Kleinbichler (1), Michael Nelhiebel (1), Johannes Zechner (1), Megan J. Cordill (2)
Affiliations : (1) KAI Kompetenzzentrum Automobil- und Industrieelektronik GmbH, Europastrasse 8, 9524 Villach, Austria; (2) Erich Schmid Institute for Materials Science, Austrian Academy of Sciences, Jahnstrasse 12, Leoben 8700, Austria

Resume : When a multilayer system is thermally cycled it undergoes a corresponding stress/strain cycle due to the different coefficients of thermal expansion of the respective materials. For thin metal films on silicon substrates it is known that the heating rate used for such a thermo-mechanical treatment has a significant influence on the system’s mechanical response. For microelectronic applications, it is indispensable to replicate application-typical heating conditions, which are characteristic pulses of sub-millisecond duration. In this study, the thermo-mechanical fatigue behavior of copper on silicon is investigated under repetitive thermal pulsing. In order to achieve extreme thermal conditions, special microheaters with a copper metallization are used. Due to the low thermal mass, the microheaters allow quasi-adiabatic heating with heating rates on the order of 106 K/s reaching peak temperatures above 400°C. This corresponds to relative strain rates >10 s-1 in the Cu films. A novel in-situ setup is used to actuate the devices inside a scanning electron microscope to allow one to study the gradual deformation of the metallization on a microscopic scale, while applying several thousands of thermal pulses. In-situ electrical resistance monitoring and intermittent roughness measurements serve as additional means for characterizing degradation and deformation. For a more comprehensive understanding, tests have been performed with pulses of different temperature spans.

Authors : Comby-Dassonneville, S. *(1), Tiphene, G. (2), Borroto, A. (3), Baral, P. (2), Douillard, T. (1), Langlois, C. (1), Roiban, L. (1), Pierson, J.-F. (3), Kermouche, G. (4), Guillonneau, G. (2), Loubet, J.-L. (2), Steyer, P. (1)
Affiliations : (1) MATEIS, INSA de Lyon ; (2) LTDS, Ecole Centrale Lyon ; (3) IJL, Université de Lorraine ; (4) Laboratoire Georges Friedel, Ecole des Mines des Saint Etienne

Resume : Metallic glasses (MGs) have been intensively studied since the 60’s, due to their amorphous structure, intrinsic chemical homogeneity and lack of crystallographic defects, resulting in unique characteristics in comparison with conventional polycrystalline materials. Their mechanical behavior is characterized by an outstandingly high elastic domain and maximal strength. Although they are macroscopically weak at room temperature, they are highly ductile under high temperature [1], with a so-called “superplastic” deformation behavior. Thin film metallic glasses (TFMGs) deposited by magnetron sputtering show particular interest in terms of wide range of accessible chemical composition and enhanced ductility [2]. Zr-Cu based TFMGs are of particular interest for their good antibacterial and corrosion properties [3]. In this work, the mechanical behavior of Zr-Cu based TFMGs at high temperature is studied. Thanks to high temperature nanoindentation, the superplastic behavior of TFMGs is studied from hardness response during isothermal as well as temperature ramp experiments. Based on the work of Baral et al. [4], high temperature nanoindentation is also used as an original technique to evaluate the crystallization kinetic of metallic glasses. Results are correlated to high temperature X-Ray Diffraction measurements and microstructure imaging. [1] Spaepen, Acta Mater. 1977 [2] Chu et al., JOM 2010 [3] Nkou Bouala et al., Surf Coat Tech. 2018 [4] Baral et al., Mater. Des. 2018

Authors : Christian Minnert, Warren C. Oliver, Karsten Durst
Affiliations : Physical Metallurgy, Technische Universität Darmstadt, Germany; Nanomechanics Inc./ KLA, Oak Ridge, USA; Physical Metallurgy, Technische Universität Darmstadt, Germany

Resume : In recent years, nanoindentation systems have been developed which can operate at ever higher temperatures in order to characterize the local mechanical properties and thermally activated mechanisms of high temperature materials such as nickel-based superalloys at their operating temperature. In this work a new ultra-high temperature nanoindentation system for testing at up to 1100 °C will be presented. The system is capable to perform indents from small scale up to large indentation depths due to the combination of a 1 N actuator and a high frame stiffness of > 106 N/m even at 1100 °C. Dynamic testing allows a continuous determination of the contact stiffness which is essential for determining the depth dependent material properties, like hardness and modulus. Low drift rates can be achieved by an independent tip and sample heating, the active actuator cooling ensures that the machine properties will not change during ultra-high temperature or long term testing. Operating the nanoindenter inside a scanning electron microscope equipped with a high temperature backscattered electron detector opens the possibility of in-situ observations, as high vacuum prevents oxidation effects. Tests were performed on fused silica, molybdenum and single crystalline nickel using a constant strain rate, strain rate jump as well as a step-load and hold creep method to show the capability of the system at high temperatures.

Authors : Anand H.S. Iyer, Krystyna Stiller, Magnus Hörnqvist Colliander
Affiliations : Department of Physics, Chalmers University of Technology, 41296 - Gothenburg, Sweden.

Resume : High temperature materials depend on formation of a protective oxide scale for corrosion prevention. Variation of mechanical and thermal loads during operation causes scale cracking and can initiate damage in the material. It is therefore imperative to study oxide scale fracture and evaluate their mechanical properties. Despite chromia being the protective oxide for many materials, limited number of fracture studies have been performed. Our recent study on microscale fracture of chromia scales using at room temperature and 600 °C revealed the presence of transgranular fracture, though stress concentrations were present at grain boundaries, which implies that grain orientation also plays a role in fracture. However, the complex microstructure makes cleavage plane determination difficult. Microcantilever experiments were designed on single crystal wafers of known orientation, such that tensile direction was perpendicular to known cleavage planes for corundum structure. Fracture testing followed by SEM imaging of fracture surface was used to identify the cleavage plane, which showed pyramidal and rhombohedral fracture, though surface energy studies show only the latter. Notched cantilevers used for fracture toughness evaluation also did not show a trend for preferred cleavage planes. This shows that neither surface energy nor cleavage fracture toughness can be used as a criterion for determination of preferred cleavage planes in chromia.

Authors : Ude D. Hangen, Yuling Chang, Wolfgang Bleck
Affiliations : Bruker Nano GmbH, Aachen; Steel institute, RWTH Aachen University; Steel institute, RWTH Aachen University

Resume : Complex-phase (CP) steels attract more attention from the automobile industry due to their better stretch-flangeability compared with dual-phase steels in the same strength level. The microstructure of CP steels normally consists of ferrite, martensite and various forms of bainite. We investigate a commercial hot-rolled complex-phase steel (CP800), which is characterized by high strength and excellent hole expansion ratio. The metallographic preparation of these microstructures for high resolution investigations is limited to a very smooth polish of the sample. The microstructure of CP800 is then characterized as a ferritic-bainitic matrix with the dispersion of hard martensite islands through the EBSD and EPMA combined method. The local dispersion of mechanical properties is then observed through accelerated property mapping (XPM) of a Hysitron TI980 Triboindenter equipped with a cube-corner indenter. Over fifty thousand indents are located in an 60*60 µm2 area. The high-resolution nanohardness profile coupled with electron microscopic results shows that isolated high nanohardness peaks are caused by either hard constituents (martensite or precipitations) or extreme fine grain clusters. Besides these few peaks, the majority of the microstructure exhibits homogeneous nanohardness distribution with only smooth gradients. This hardness distribution leads to homogeneous plasticity distribution during deformation and consequently prevents the strain localization and early crack initiation during hole expansion test. Based on the results of this study, the XPM and high-resolution nanohardness map are effective in identifying microstructural constituents and presenting the gradient of hardness distributions in complex-phase microstructure.

16:00 Coffee break    
Poster session : N/A
Authors : Doina RADUCANU*, Vasile Danut COJOCARU*, Vlad Andrei RADUCANU**, Anna NOCIVIN***, Elisabeta Mirela COJOCARU*, Nicolae SERBAN*, Ion CINCA*
Affiliations : *-University POLITEHNICA of Bucharest, Romania **-National University of Arts from Bucharest, Romania ***-University OVIDIUS of Constanta, Romania

Resume : For developing performant medical devices the biomechanical adaptation play a key role for both, the bulk material (at macro scale) and for surfaces (at micro/nano scale). As concerning the interaction of living cells with artificial surfaces, cellular mechanosensitivity has direct effects on tissue structure and functions. In this work, surfaces archirectures, similar of the cancellous bone, obtained by self-nano-crystallization, were realized on a gum-alloy as substrate, Ti-31.7Nb-6.21Zr-1.4Fe-0.16O (wt. %) (TNZFO), using silicone masks with micrometric patterns/perforations, on which was applied a Nano Surface-Severe Plastic Deformation (NS-SPD) process. For finding the 3D suitable geometries of the perforations and their distribution on the masks, the Generative Design algorithms were developed using dedicated software tools (Rhinoceros). The masks were obtained by 3D printing using the Fused Filament Fabrication method. The NS-SPD involves the multidirectional repeated mechanical impacts on the sample surface with high velocity balls at high strain rates of approximately 102-103 s-1. Deeper compressive residual stresses are generated beneath the NS-SPD surface, creating a superficial self-nanocrystallized structure, on un-covered areas due to the small volume-multidirectional local plastic deformation. NS-SPD parameters have a direct effect on the plastically deformed micro-volumes at the surface, affecting the local micro-topography and the microstructure evolution.

Authors : Jingxian Wang1, Mohammad Arab Pour Yazdi 2, Fernando Lomello 3, Alain Billard 2, András Kovács 4, Frederic Schuster 5, Claude Guet 1, Timothy J. White1, Yves Wouters 6, Celine Pascal 6, Frederic Sanchette 7, ZhiLi Dong 1
Affiliations : 1 School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore; 2 Univ. Bourgogne Franche-Comté, UTBM, IRTES EA7274, F-90100 Belfort, France; 3 Den–Service d’Etudes Analytiques et de Réactivité des Surfaces (SEARS), CEA, Université Paris-Saclay, 91191, Gif sur Yvette, France; 4 PGI-5, Forschungszentrum Julich GmbH in the Helmholtz Association, 52425 Julich, Germany; 5 CEA Cross-Cutting program on Advanced Materials Saclay, 91191 Gif-sur-Yvette, France; 6 SiMaP, UMR CNRS/UJF/Grenoble INP, 38402 Saint-Martin d’Hères, France; 7 LRC CEA-ICD-LASMIS-UTT, Antenne de Nogent-52, 52800 Nogent, France

Resume : Nanocomposite coatings have attracted attention from industries due to their enhanced mechanical properties, tribological performance, thermal stability and oxidation resistance. However, it is challenging to tailor the structure of nanocomposite coatings and further improve the properties to meet some special needs in applications with extreme environments. In this study, (Ti0.6Al0.4)1-xYxN multilayer coatings were fabricated by the physical vapour deposition (PVD) method. The influence of yttrium on the crystal structures, mechanical properties and high temperature oxidation resistance were investigated in detail [1]. In the PVD process, the period and yttrium concentration were controlled by varying substrate rotation speed and power applied on the yttrium target respectively, which could modify the coating hardness, adhesion, wear resistance and durability against oxidation. Results showed that for a fixed period, doping 2.4 at% yttrium into Ti-Al-N coatings delivered enhanced hardness and improved the oxidation resistance without deterioration of adhesion and wear resistance compared to yttrium-free Ti-Al-N. Such type of hard protective coatings have potential applications in areas that exploit high-speed machining, casting and hot-forming. [1] Jingxian Wang et al, Metallurgical and Materials Transactions A, 2017, 48A, 4097 – 4110.

Authors : Te-Hua Fang1*, Yu-Cheng Wei1, I-Tseng Tang2
Affiliations : 1 Department of Mechanical Engineering, National Kaohsiung University of Science and Technology, Kaohsiung 80778, Taiwan 2 Department of Greenergy, National University of Tainan, Tainan 701, Taiwan

Resume : In this study, we perform a quasi-continuous simulation of nanoimprint on a rough inclined surface. The effects of crystal orientation, surface roughness, and inclined plane on the contact and imprinting mechanics are studied using quasi-continuum simulations. These effects are investigated in terms of strain distribution and the stress–strain curve. The results show that the contact interference leads to the formation of the defects and slip inside the material. The number of defects increases with increasing imprinting interference. The internal stress of the material become more intense, the more seriously affected as the surface roughness of the contact increase. When embossing an inclined surface, the smaller the angle of inclination, the deeper the imprinting depth when larger imprinting variation occurs. Here proposed method of rough contact behavior can help not only to significantly reduce the cost of experiments but also help to explain the contact behavior of imprinted inclined plane.

Authors : Younghyun Cho
Affiliations : Department of Energy Systems, Soonchunhyang University, Asan 31538, Korea

Resume : High-aspect-ratio polymer pillars have been of great interest in wetting and dry adhesion due to their unique surface topography. Specifically, tunable dry adhesion as manifested in gecko foot hairs has been attributed to millions of hierarchical fibrillar structures on gecko toe pads, allowing for adhesive attachment and rapid detachment. Here, we report on the preparation of tapered nanorods from epoxy with various cross-sections and study the shape effect on normal and shear adhesion strength. Cone-shaped, stepwise, and pencil-like structures (300 nm in diameter at the base of the pillars and 1.1 μm in height), are prepared from epoxy resin templated by nanoporous anodic aluminum oxide (AAO) membranes. The adhesion force was measured by nanoindentation. It showed that depending on the shapes of the nanorods, the adhesion force significantly changes and the adhesion in normal and shear direction are quite different. To understand the deformation mechanism of the tapered nanorods and the resulting adhesion behaviors, we performed quantitative in-situ indentation experiments in SEM. We confirmed that different nanorods exhibited different deformation, depending on the load applied in the normal and shear direction. The results from in-situ indentation imaging corroborated well with finite element analysis and nanoindentation measurements, suggesting that the shape of the nanorods played a key role in mechanical response, thus, dry adhesion strength.

Authors : M.J. Cordill, J. Sträußnigg, G. Richter
Affiliations : Erich Schmid Institute for Material Science, Austrian Academy of Sciences; Erich Schmid Institute for Material Science, Austrian Academy of Sciences; Max Planck Institute for Intelligent Systems

Resume : One of the most common methods to measure the elastic modulus and hardness of thin films is to use nanoindentation. In order to remove the influence of a substrate the well-known “10% rule of thumb” is utilized. This “rule” states that the elastic modulus and hardness can be taken at 10% of the film thickness with no or little influence from the substrate. While this guideline may hold true for some film-substrate systems (hard-on-soft or soft-on-hard) and film thicknesses (greater than 100 nm), it cannot and should not, be applied universally. It will be shown on single crystalline copper films on sapphire, grown by thermal evaporation (50, 100, and 300 nm thick) that the hardness can be evaluated but the elastic modulus cannot be properly measured when compared to bulk single crystal copper. It will be demonstrated that the elastic modulus is a long range property that is substantially influenced by the substrate even at indentations of 10% of the thickness. For example, using the initial Hertzian elastic portion of the load-displacement curve before a pop-in occurs does not allow for the elastic modulus of copper to be measured. The findings reveal that the 10% rule should not be applied to evaluating the elastic modulus of thin films.

Authors : Changsu Woo, Hyunsung Park
Affiliations : Korea Institute of Machinery & Materials

Resume : We developed rubber-clay nano-composites that are environment-friendly and excellent in mechanical properties and fatigue life. In this study, acrylonitrile butadiene rubber (NBR) was used as rubber in combination, ZnO and stearic acid were used as vulcanization activators and 3C was used as an additive, sulfur of purity 99.9% was used as a vulcanizing agent, TT and CZ were used as vulcanization accelerators and carbon black, clay, and nano-clay were used as reinforced compound. Polymer layered silicate was made by the melted intercalation method in which polymers in the melted state were inserted between silicate layers. This method is advantageous in mass production and does not need to use solution. Mechanical tests on the developed material were performed at room temperature and aging condition and we verified that mechanical properties of the developed material such as tensile strength, elongation, and modulus change were superior to the existing material. Fatigue durability was evaluated througth we developed a new method that could fatigue life prediction of rubber parts in a short period in the initial stage. Fatigue life of rubber material estimated by the fatigue life prediction equation was exactly consistent with that obtained by fatigue tests of actual engine mounts. In addition, we verified that the developed material was superior in fatigue durability as well as mechanical properties because the lifetime of engine mounts made by developed material was longer than the existing material. In this study, advance of related technologies was achieved by constructing complete technologies including design, analysis, and estimation of rubber parts. We expect that these results will contribute to enhance performance and reliability of rubber parts.

Authors : P. Milana (1), S. Mostoni (1), C. Marano (2), B.Di Credico (1), M. D’Arienzo (1), A.Susanna (3), R. Donetti (3), R. Scotti (1) .
Affiliations : (1) Department of Materials Science, University of Milano Bicocca, Via R. Cozzi 55, 20125 Milano, Italy (2) Department of Chemistry, Materials and Chemical Engineering” Giulio Natta”, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133, Italy (3) Pirelli Tyre S.p.A., Viale Sarca, 222, 20126 Milano, Italy

Resume : The density and distribution of sulfur crosslinks between the polymer chains promoted by the vulcanization process, combined with the use of reinforcing fillers, affect the mechanical properties of rubber nanocomposites (NCs). Activators and accelerators are used to improve the vulcanization rate and among them ZnO is the most used activator, due to its highly kinetic and crosslinking efficiency. Since the catalytic activity of zinc has a central role in the formation of crosslinks, this study focuses on the effect that the structure and the localization of the catalytic site inside the polymer matrix have on the mechanical behavior of rubber materials. To do this, a novel efficient activator, Zn@SiO2 based on zinc single sites anchored onto the silica surface, was used as double function filler, acting as both activator and reinforcing filler. The microscopic structure and the mechanical behavior of rubber NCs cured with Zn@SiO2 were studied by performing TEM analysis, DMA (Dynamic mechanical analysis), uniaxial tensile and fracture tests, and compared to those of rubber NCs conventionally cured with ZnO particles. Regarding rubber NCs cured with Zn@SiO2, TEM analysis showed a higher crosslink density close to the silica particles, while the mechanical tests showed enhanced mechanical properties. The results suggest that localizing the catalytic sites in the rubber matrix could be a promising tool to tune the crosslink distribution and the mechanical properties of rubber NCs.

Authors : Hyun-Hee Choi, Eun-Hee Kim, Bong-Gu Kim, SeungCheol Yang, Yeon-Gil Jung
Affiliations : Changwon National University;Changwon National University;Changwon National University;Changwon National University;Changwon National University

Resume : In this study, new organic-inorganic binder conversion process, which can be applied in 3D printing technique, was introduced for preparing the ceramic mold and core with improved mechanical strength using two organic binders with different chemical properties, and one inorganic binder. Green body was fabricated with a 3D printer and ceramic slurry prepared by mixing the starting powder and two organic binders (non-aqueous and aqueous polymers). The green body was immersed in water at 60℃ for 5 min to remove the aqueous polymer, leaving space for penetrating an inorganic binder in the green body. After removing the aqueous polymer, the sample was immersed in the inorganic binder solution composed of tetraethyl orthosilicate (TEOS, SiO2 precursor) and sodium methoxide (NaOMe, Na2O precursor), and then dried at 80℃ for 1h. The prepared sample was heat-treated at 1000℃ for 1h for converting the inorganic binder to glass phase. The application of the dual polymer increased the penetrating amount of the inorganic binder in the green body, and finally the strength of the ceramic mold and core increased after the heat treatment. The novel organic-inorganic binder conversion process in the 3D printing process could confirm the feasibility of manufacturing a ceramic mold and core with effective strength for investment casting.

Authors : Daniel E. Martínez-Tong [1,2], René I. Rodríguez-Beltrán [3,4,5], Tiberio A. Ezquerra [6], Pablo Moreno [4], Esther Rebollar [5]
Affiliations : [1] Departamento de Física de Materiales, Basque Country University (UPV/EHU). P. Manuel de Lardizábal 3, E-20018 San Sebastián – Spain. [2] Centro de Física de Materiales (CSIC – UPV/EHU). P. Manuel Lardizábal 5, E-20018 San Sebastián – Spain. [3] CONACyT - Unidad Monterrey. Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE). Alianza centro 504, PIIT, 66629 Apodaca - Mexico [4] Grupo de Aplicaciones del Láser y Fotónica (ALF-USAL), Universidad de Salamanca, Pl. de la Merced s/n, 37008, Salamanca, Spain [5] Instituto de Química Física Rocasolano (IQFR-CSIC), C/Serrano 119, 28006, Madrid, Spain [6] Instituto de Estructura de la Materia (IEM-CSIC), C/Serrano 121, 28006, Madrid, Spain

Resume : Organic materials are key candidates for the development of future technologies. In particular, polymer-based systems present outstanding mechanical properties, allowing the preparation of flexible and resistant components. They are of utmost interest in the fabrication of micro and nanodevices as a result of ease of processing down to nanoscales. A current challenge consists in studying the nanometric features of these materials using laterally-resolved techniques. In this work, we present a nanomechanical study of nanostructured polyesters films, using Atomic Force Microscopy (AFM). The nanostructures were formed by pulsed laser irradiation (Laser Induced Periodic Surface Structures, LIPSS). The nanomechanical properties were studied using a combination of techniques. We mapped the surface mechanical contrast using PeakForce Quantative Nanomechanical Mapping. Then, on selected areas of the films we performed force spectroscopy measurements. A detailed analysis of the force-distance curves allowed extracting quantitative values of the Young’s modulus, stiffness, indentation depth, and adhesion force. It was possible to determine that laser irradiated polymer surfaces presented enhanced properties, for example higher Young’s modulus, compared to their non-irradiated counterparts. Finally, on selected samples we performed Lateral Force Microscopy (LFM) measurements to study the impact of laser structuring on surface friction.

Authors : Guanlin Lyu, Jun-Seong Kim, Janghyeok Pyeon, SeungCheol Yang, Yeon-Gil Jung*, Dowon Song, Taeseup Song, Ungyu Paik.
Affiliations : Guanlin Lyu; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam51140, Republic of Korea. Jun-Seong Kim; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam51140, Republic of Korea. Janghyeok Pyeon; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam51140, Republic of Korea. SeungCheol Yang; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam51140, Republic of Korea. Yeon-Gil Jung*; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam51140, Republic of Korea. Dowon Song; Department of Energy Engineering, Hanyang University, Seoul 04763, Republic of Korea Taeseup Song; Department of Energy Engineering, Hanyang University, Seoul 04763, Republic of Korea Ungyu Paik; Department of Energy Engineering, Hanyang University, Seoul 04763, Republic of Korea

Resume : Calcium magnesium alumina-silicate (CMAS) attack on thermal barrier coatings (TBCs) is one of the reasons for the early delamination of TBCs in jet engine and gas turbine in high temperature environments. The increased operating temperature results that the finer CMAS debris tends to adhere to the coating surface and form molten CMAS which eliminates the void spaces within the TBC. In this study, we evaluated the effects of CMAS on the microstructure evolution in yttria-stabilized zirconia (YSZ), lanthanum zirconate (LZ), and composite coating with a 50:50 volume ratio of YSZ and LZ (LZ–YSZ). YSZ was easily to be deteriorated by CMAS due to the de-stabilization of t’-YSZ. LZ showed the mitigated penetration of CMAS by reaction products (Ca2La8(SiO4)6O2, CaAl2Si2O8, and MgAl2O4), which originated from high reactivity between LZ and molten CMAS. The LZ–YSZ composite showed a denser microstructure in the surface, resulting in retarding the penetration of CMAS. Therefore, the TBC with the LZ–YSZ composite will prolong the lifetime performance and protect the further corrosive degradation of TBCs in high temperature environments. The infiltration behavior and the reaction mechanism of molten CMAS for the YSZ, LZ, and LZ–YSZ composite were discussed after CMAS attack for 5, 10, and 20 h at 1250 °C.

Authors : Lord Jaykishan Nayak, Gour Gopal Roy
Affiliations : Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, India

Resume : The present study deals with effect of welding speed on transient temperature distribution and its correlation with microstructure and mechanical properties during bead-on-plate experiment of electron beam welded Zircaloy-4 plate. Experimentally temperature was measured by K-type thermocouple at some selected location. Numerical analysis was investigated using finite element model (FEM) and found good correlation between experiment and simulated temperature data. Joint prepared with high welding speed (lower heat input) demonstrated lower peak temperature and faster cooling rate that resulted in decrease in the size of fusion and heat affected zone. Also the grain size of fusion zone and HAZ decreased with increase in welding speed. Widmanstätten type structure developed in fusion zone and randomly oriented acicular type structure developed in HAZ. Hardness of fusion zone and heat affected zone was found to be higher than base metal and it varied linearly with welding speed.

Authors : Chaebeen Kwon, Taeyoon Lee*
Affiliations : Nanobio Device Laboratory, School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-Gu, Seoul, Korea 03722

Resume : Textile-based electronics have pointed out as a fundamental technology for the next generation of smart wearable devices. These trends for textile-based electronics have led to the development of conductive fibers with various materials and manufacturing methods such as metal wires, conducting polymer coated wires, carbon nanotubes (CNTs) fibers and graphene fibers. Each type of conductive fibers has different electrical, mechanical, electrochemical properties. Metal wires stand out high electrical conductivity, but they have limited flexibility, causing early rupture strain. Both conducting polymer coated wires and CNTs fibers show relatively low electrical conductivity and inherent degradation under applied tensile strain. However, the composite fibers which consist of elastic and conductive regions enable to retain their high electrical conductivity under high tensile strain. This is because the electrical pathways of electron were effectively remained during the stretching of the fiber. Herein, we presented a facile method to fabricate ultra-stretchable surface-enriched Ag nanoparticles (NPs) / polyurethane (PU) hybrid conductive composite fibers by modulating diffusion process. To control diffusivity of Ag precursor, hydroxyl group solvents with varied molecular weights including Methanol, Ethanol, Isopropyl alcohol (IPA), and Butanol were used. The limited liquid precursor permeating reduction process results in formation of Ag-rich outer shell and PU core fibers. The lowest diffusive solvent, butanol with the largest molecular weight (74.12 g/mol) leads to clear local segregation between Ag NPs in outer shell and PU in core : Ag abundant conductive outer shell was formed while remaining pure polymeric characteristic core in fiber. Due to stable electrical pathways in Ag rich shell, the fiber exhibits the highest conductivity (30485 Scm-1) with 300% tensile strain. To improve the performance of butanol-solvent based stretchable conductive fibers, the self-healing polymers (SHPs) were used by wrapping on the fibers. The SHP-encapsulated stretchable conductive fibers showed higher conductivity, and stability about 1000 stretching cycles. The SHP-encapsulated stretchable fiber was used for connection between light emitting diodes (LEDs) to light them up, showing the fiber can be applied as an excellent interconnect in textile-based electronics.

Authors : Junseong Kim, Dowon Song, Yun kon Joo, Guanlin Lyu, SeungCheol Yang, Yeon-Gil Jung.
Affiliations : Junseong Kim ; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 641-773, Republic of Korea Dowon Song ; Department of Energy Engineering, Hanyang University, Seoul 133-791, Republic of Korea Yun kon Joo ; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 641-773, Republic of Korea Guanlin Lyu ; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 641-773, Republic of Korea SeungCheol Yang ; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 641-773, Republic of Korea Yeon-Gil Jung ; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 641-773, Republic of Korea

Resume : In this study, the applicability of the superalloy fabricated by additive manufacturing (i.e. 3D printing) was investigated in comparison to the conventionally forged superalloy. The microstructure and mechanical properties of the 3D printed Inconel 718 alloy before and after hot isostatic pressing (HIP) were characterized and compared to the conventionally forged alloy. The as-printed alloy showed lower mechanical properties in hardness and elastic modulus than the HIP-treated and forged alloy due to its large amounts of defects, showing a lot of pores at the melt pool boundary on the fractured surface after tensile test. The HIP-treated alloy showed denser microstructure with less pores, implying lower fracture toughness. The yield strength was almost doubled after HIP-treatment, while the tensile strength showed a slight increase. However, the elongation property was evidently deteriorated after HIP treatment. The plastic deformation of the HIP-treated alloy after yielding was markedly low, resulting in a rapid fracture. Also, the surface properties for the superalloy prepared by 3D printing were improved by applying the diffusion coating.

Authors : Hye-Yeong Park, Eun-Hee Kim, SeungCheol Yang, Yeon-Gil Jung
Affiliations : School of Materials Science and Engineering, Changwon National University

Resume : A single-crystal casting has been performed to improve the thermomechanical properties of turbine blade, which is the key component of gas turbine. Ceramic core employed in the single-crystal casting process should endure for a long time at casting temperatures above 1500 C because of direct contact with a molten metal. In the fabrication of the core applied to a conventional casting, it takes a lot of time and energy because it requires dozens of hours at heat treatment to develop strength in the core. In this work, an inorganic binder was applied to a conventional injection-molding method to produce a core having enough strength and completely elution property during the casting process. The starting powders for the core used a mixture of three kinds of fused silica with different particle sizes, zircon flour, and silicon carbide. The mixed ceramic powder was coated with a silica precursor, and then dried at 80 °C for 1 h. The dried powder was mixed with wax and injection-molded. The injected core was heat-treated at 1200 and 1500 C for 1 h. The additional heat treatment at 1550 C for 3 h was conducted to investigate the applicability of the core coated with the inorganic binder in the casting process. The inorganic binder-coated core with a superior firing strength had no cracks or surface defects after the heat treatment, compared with the core without the inorganic binder. In addition, the turbine blade of 150 mm length was well-cast as a single crystal and the internal core was completely eluted.

Authors : Deepak Sharma, David Parfitt, Bo Chen, Sitarama Raju Kada, Daniel Fabijanic, Matthew Robert Barnett, Michael Fitzpatrick
Affiliations : Deepak Sharma; David Parfitt; Bo Chen; Michael Fitzpatrick - The Institute for Future Transport and Cities, Coventry University, Coventry, CV1 5FB, UK Deepak Sharma; Sitarama Raju Kada; Daniel Fabijanic; Matthew Robert Barnett - The Institute for Frontier Materials, Deakin University, Victoria, 3216, Australia; Bo Chen - Department of Engineering, University of Leicester, Leicester, LE1 7RH, UK

Resume : Metastable β-Ti alloys are known for their high specific strength and deep hardenability. These remarkable properties are influenced by the size, shape and volume fraction of α-phase precipitates. The refinement of α-phase precipitates due to their heterogeneous nucleation from precursor nanoscale isothermal ω-phase (ωiso) precipitates has led to improved mechanical properties for these alloys. Therefore, it is important to understand the precipitation kinetics of ωiso precipitates to precisely control and optimise the mechanical properties of the alloy. The precipitation of ωiso precipitates is influenced by the cooling rate used during the solution treatment of the alloy. Hence, a small-angle neutron scattering study was done to understand the precise pathway of ωiso precipitates transformation from the β-phase matrix in Ti-5Al-5Mo-5V-3Cr (wt%) alloy during the ageing of the sample at 300 °C up to 8 h. For solution treatment of the alloy, two cooling rates, air cooling and water quenching, were used. The SANS data analysis showed the presence of ellipsoidal ωiso during the ageing period. The alloy samples after air cooling showed the delayed nucleation of ωiso precipitates. The precise pathway of transformation was clarified, and evolved microstructure was quantified.

Authors : Mihaela COSNITA; Maria VISA; Cristina CAZAN
Affiliations : Transilvania University of Brasov, Romania

Resume : Abstract: The current issue related to global warming and limited conventional energy resources has pushed the energy sector to renewable energy resources. The photovoltaic technology–low carbon energy resource is one of the most used renewable energy technology. The largest market share (over 80 %) photovoltaic technology is based on silicon photovoltaic modules (Si-PV). The Si-PV power plants are in continuous growth for covering the high energy demands. Therefore the Si-PV waste amounts in the future decades are expected to become an environmental and economically issue. The forecasts in this regard estimates the PV waste amount to reach 1.957.099 t by 2038, therefore the PV recycling represents an important targets worldwide. This paper investigates the durability of Si-PV composite materials especially regarding their stability in water, UV radiations and saline environment. The paper continues a previous research on Si-PV recycling in novel composite materials with waste rubber and high density polyethylene (HDPE). That work concluded the possibility of recycling up to 35-40 wt% Si-PV module wafers in all-waste polymer composites. The mechanical performance of the all-waste composites were measured in terms of tensile, compression and impact strength before and after ageing tests. The interface properties before and after ageing tests were determined by FTIR analysis, contact angle measurements and by SEM investigation. The crystalline structure was determined by X-ray diffraction (XRD). After water immersion the best combination of tensile, compression and impact strength was noticed for 35 wt% Si-PV composites 190 0C processed. The mechanical characteristics before water immersion were tensile strength of 2.65 MPa; compressive strength of 210.40 MPa; impact resistance of 44.70 kJ/m2 and after water immersion: tensile strength of 2.85 MPa; compression strength of 208.17 MPa and the impact strength of 42.97 kJ/m2. The best water stability for 40 wt% Si-PV composites was noticed for that 210 0C processed with the following mechanical characteristics-before water immersion: tensile strength of 2.86 MPa; compressive strength of 198.55 MPa and impact strength of 36.05 kJ/m2 and after water immersion: 2.89 MPa; 196.18 MPa and impact strength of 48.98 kJ/m2. Acknowledgements: This work was supported by a grant of Ministery of Research and Innovation, CNCS - UEFISCDI, project number PN-III-P1-1.1-PD-2016-0286, within PNCDI III, ctr. 101/02.05.2018.

Authors : Glöß, M.* (1,3), Pütt, R. (2), Moors, M. (1), Monakhov, K. Y. (3)
Affiliations : (1) Forschungszentrum Jülich GmbH, Peter Grünberg Institut, Wilhelm-Johnen-Str., 52425 Jülich, Germany; (2) RWTH Aachen University, Institute of Inorganic Chemistry, Landoltweg 1, 52074 Aachen, Germany; (3) Leibniz Institute of Surface Engineering (IOM), Permoserstraße 15, 04318 Leipzig, Germany

Resume : Polyoxometalates (POMs), especially those containing vanadium are of great interest for a broad range of applications due to their structural diversity and tunable electronic properties. The opportunity of switching between multiple redox states without significant changes of the metal–oxo skeleton architecture makes them suitable for usage as molecular redox-active units in resistive switching memory cells. One prerequisite for the integration of POMs into nanoelectronic devices is the investigation of their adsorption behavior and the associated chemical processes on conductive substrates. Therefore we used the droplet deposition from organic solution of different organically derivatized Wells-Dawson-type POMs on HOPG and Au(111). We characterized the adsorption behavior with surface-sensitive methods such as scanning tunneling microscopy (STM), X-ray photoelectron microscopy (XPS) and grazing-incidence small-angle X-ray scattering (GISAXS). Additionally we investigated the influence of an increasing water amount in solution with SAXS and observed that it affects crucially the surface adsorption.

Authors : Ting. Wang, Xiaodong. Chen, Alfred Tok
Affiliations : Department of Materials Science and Engineering, Nanyang Technological University, Singapore

Resume : The stretchable strain sensor is an essential component in wearable electronics and demanded in recent years that can be used for personalized healthcare monitoring, movement detection, human-machine interfaces, soft robotics and other several areas. Therefore, strain sensors with tunable electromechanical performance in terms of stretchability and sensitivity are necessary to meet different mechanical deformations and various sensing ranges from such a broad application. Large research works have been done based on different mechanisms of stretchable strain sensors. Among them, crack-based strain sensors have attracted much attention. Although crack formation in material and structure is often regarded as undesired process to be avoided, researchers played with crack initiation and propagation and were able to fabricate stretchable strain sensors with different stretchability and sensitivity. However, previous works only investigated the crack patterns in the strain sensor with a uniform flat structure, we are curious about the crack pattern in a gradient structure. Herein, the purpose of this work is to study the crack pattern in the strain sensor with a thickness-gradient structure and evaluate its electromechanical performance. A thickness-gradient conductive thin film on the elastic substrate was fabricated via thermal evaporation at various tilted angles ranging from 0deg to 75deg. Thin films with different gradient-thickness were verified by AFM. The electromechanical performance of stretchable strain sensors were characterized by a semiconductor characterization system and mechanical tester. The crack patterns were observed by SEM and conformal microscopes. We obtained thickness-gradient strain sensor (gradient-thickness = 20%) with high sensitivity (GF=1400) at stain ( ɛ =20%) which was much higher than that of the uniform flat thickness (gradient-thickness= 0%, GF=100 at strain ɛ =20% ). We also found the electromechanical performance of strain sensors can be tuned by changing the percentage of thickness-gradient. Besides, the crack morphologies were also different by stretching the thickness-gradient strain sensors in the longitudinal and the transverse direction which cannot be observed in uniform-thickness strain sensors. The achievement of this work was to investigate the difference of crack patterns in thickness-gradient strain sensors and the uniform-thickness strain sensors, studied the mechanism and proposed a new strategy to fabricate strain sensors with high sensitivity and stretchability by using gradient structure through a simple method.

Authors : Reza Abbassi, Nigel Jennett, Vit Janik
Affiliations : Institute of Future Transport and Cities, Coventry University

Resume : Indentation resulting in a permanent impression injects an amount of plastic strain that requires the creation of geometrically necessary dislocations. The applied indentation stress required is a function of the combination of both test and material length scales. Variation of indent size, therefore, can be used to determine the effective plastic zone size and dislocation density. Stacking Fault Energy is a lattice property dependent on the bond strength, coordination (lattice type) and lattice spacing (and so burgers vector). In high SFE materials, it is less probable for dislocations to move off the slip plane or form partials and so the probability of dislocations tangling and pinning is reduced leading to lower work hardening. It is expected, therefore that dislocations in high SFE materials will have longer mean free paths and larger plastic zones, and this will lead to lower dislocation densities and longer pinning length scales. Very little experimental validation of this exists. The success of equation 1 in describing hardness and uniaxial tensile tests and scratch test results suggests that this could be used to validate this expectation. We, therefore, have obtained a large number of different metal single crystals with stacking fault energies ranging from ~20 mJ/m2 to ~200 mJ/m2 . We performed Berkovich indentations into these single crystals to determine mean indentation pressure as a function of indent size and have determined the parameters k1 and k3√ρs in equation 1 (for a single crystal k2/d = zero). From this data, the relative size of plastic zone and the relative fraction of dislocations that are mobile were calculated after Hou & Jennett (2012). Preliminary results indicate that, as SFE increases, k1 does decrease, i.e. the plastic zone gets bigger and k3√ρs also decreases, I,e, separation of pinning dislocations increases. We intend to validate these estimates of plastic zone size using FIB cross-section and to investigate the effects of indenter geometry (strain field distribution), lattice type (FCC vs BCC) and crystal orientation (100) vs. (110) vs. (111) in selected materials.

Authors : Barnasree Chanda, Jayanta Das
Affiliations : Department of Metallurgical and Materials Engineering, Indian Institute of Technology Kharagpur, West Bengal 721302, India

Resume : High entropy alloys are a new class of alloys which consists of five or more major element in the range of 5-35 at.%. The ever increasing demands for new structural applications, high entropy alloys (HEA) are transpire as a new paradigm shift in material society. Nano-eutectic HEAs exhibit superior mechanical properties over the single-phase high entropy alloys. The optimum combination of strength and ductility are the key features of eutectic HEAs. In this work, the novel CoCrFeNiTax (0.2 ≤ x ≤ 0.5) HEAs with eutectic microstructure were designed and cast by arc melting. The phase composition, mechanical properties and stability of these alloys were investigated. The evolved microstructure in all the HEAs consist of eutectic lamellae with alternating α (γ-Ni)-FCC phase and β (Co2Ta)-type Laves phase. It was observed that x= 0.2, and 0.5 alloys contains eutectic microstructure along with proeutectic phase and at x= 0.4 homogenous eutectic microstructure was obtained. The CoCrFeNiTa0.4 HEA with the eutectic microstructure exhibited a relatively high combination of yield strength (~1820 MPa) and ductility (~21 %). Further, analysis regarding the eutectic phase stability in terms of different thermodynamic and electronic parameters considering the synergistic effect atomic size difference (δr), mixing enthalpy (ΔHmix) and valence electron concentration (VEC) were carried out. Also, from literature EHEAs comprising of FCC /BCC solid solution phases and intermetallic compound/topologically closed packed (TCP) phases have been surveyed thoroughly. The assessment predict the existence of stable eutectic/near eutectic phases in all surveyed and present EHEAs when −18 ≤ ΔHmix ≤ −6, 6 ≤ VEC ≤ 8.5 and δr > 3%. References: [1] B. Chanda, J. Das, Composition Dependence on the Evolution of Nanoeutectic in CoCrFeNiNbx (0.45≤ x ≤ 0.65) High Entropy Alloys, Adv. Eng. Mater., 1700908 (2017)1-9. [2] B. Chanda, J. Das, An assessment on the stability of the eutectic phases in high entropy alloys. J. Alloys Compd., 798 (2019) 163-173.

Authors : Minseop Kim 1, Songhee Choi 2, Soonhee Park 1, Jiho Kim 3, Shinbuhm Lee 2, Boknam Chae 3, and Jongseok Lee 1*
Affiliations : 1 Department of Physics and Photon Science, School of physics and chemistry, Gwangju Institute of Science and Technology (GIST), Gwangju 61005, South Korea; 2 Department of Emerging Materials Science, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu 42988, South Korea; 3 Pohang Accelerator Laboratory, Pohang University of Science and Technology (POSTECH), Pohang 37673, South Korea;

Resume : Physical properties of thin-film oxides, such as electrical transport and crystal structures, can be controlled by the strain induced by the lattice mismatch with a substrate. Therefore, it is an important issue in the fabrication of thin-film oxide-based devices to control the strained condition, for example, by changing a film thickness and crystallographic orientation of substrate. Meanwhile, microcracks in a film can be formed accompanied by a local strain relaxation and impede a current flow. In the case of VO2, electrical and possibly structural phases can be distributed inhomogeneously during an insulator-to-metal transition around room temperature. In particular, the VO2 film grown on TiO2(001) substrate can have microcracks and make position-dependent electrical and structural phases. In this presentation, we discuss the effect of the cracks in the strain relaxation along the lateral directions by using nano infrared imaging technique. The variations of infrared scattering amplitude and phase are clearly observed and they will be discussed with the distribution of structural and electrical properties.

Authors : Martin Šilhavík*, Zahid Ali Zafar, Prabhat Kumar, Jiří Červenka
Affiliations : FZU Institute of Physics of the Czech Academy of Sciences, Prague 16200, Czech Republic

Resume : Graphene aerogel is a three-dimensional porous form of graphene with a high surface-to-volume ratio. Graphene aerogels have attracted a significant amount of interest in recent years due to their unique mechanical and electrical properties that show great potential for numerous applications in engineering, electrochemistry, and biology. Here, we investigate the mechanical properties of graphene aerogels prepared via hydrothermal reduction of graphene oxide. The as-fabricated graphene aerogels, however, contain a lot of defects and oxygen groups which cause poor elastic properties. For this reason, we have thermally annealed the samples in a furnace in an inert gas atmosphere. The high-temperature annealing enabled a complete oxygen removal from the samples, resulting in a significant improvement of the elasticity of the graphene aerogels. The annealed graphene aerogels demonstrate superelastic compression up to a GPa pressure regime. To better understand the deformation mechanism in the samples we have performed in situ SEM measurements that visualized the deformation of individual graphene pores. Based on the observation we developed a model that is able to describe the stress-strain curves of the graphene aerogels. Our study provides new insights into the superelastic behavior and deformation mechanism of the porous graphene aerogels.

Authors : Wafa Maftuhin 1, Maximilian Raisch 2, Michael Sommer 2, Michael Walter 1,3,4
Affiliations : 1 Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT) Georges-Köhler-Allee 105, 79110 Freiburg, Germany; 2 TU Chemnitz, Institute for Chemistry, Chair for Polymer Chemistry, Str. der Nationen 62, 09111 Chemnitz, Germany; 3 Cluster of Excellence livMatS @ FIT; 4 Fraunhofer IWM, Wöhlerstraße 11, D-79108 Freiburg

Resume : Mechanocromic polymers which produce an optical signal in response to a mechanical force, hold the promise to act as molecular mechanosensors, which can be used to image stress or strain. Most mechanocromic systems relie on homogeneous or heterogeneous bond scission and therefore show intrinsic limitations that are typically related to their two-state nature and the associated barrier between the two forms. A barrierless, simple and robust mechanochromic system still remains to be designed. Here we reported the new concept of donor-acceptor (D/A) torsional springs for force sensing and stress imaging. We investigated the force dependent D/A properties of the diketopyrrolopyrole (DPP) polymer with DFT and TDDFT. We found that these molecules should indeed be usable for force sensing and stress imaging in that their optical absorption properties change reversibly under the application of force. This can be traced back to change in the electronic properties due to changes in the dihedral angle and therefore in the coupling between the donor acceptor parts in the molecules. Application of external forces on DPP leads to force-induce planarization and a resulting shift of the optical spectra to longer wavelengths. Increased steric hindrance in ortho-DPP leads to a larger dihedral angle and larger optical shifts, making this polymer a more effective force sensor. Our mechanochromic system is barrierless could open opportunities and application of unprecedented extent.

Authors : Yugyeong Je, Dong-Hoon Shin, SangWook Lee
Affiliations : Department of Physics, Ewha Womans University, Seoul, 03760, Korea

Resume : We have constructed a graphene nanoelectromechanical resonator array systems and studied its basic electromechanical properties. Drum-like suspended graphene structures with various diameter were fabricated using micro contact transfer method combined with conventional lithography processes. Mechanical resonance frequencies of the suspended graphene radio were measured by laser interferometry technique. The resonance frequency of graphene radio has been shown in megahertz range, which can be tuned by applying electromechanical strain to the resonator. Duffing type mechanical oscillation behavior was observed as the driving force of graphene resonator was increased. Non-linear resonance behavior of graphene has been investigated for sensing a small variation of its mechanical resonance frequencies. Graphene based nanoelectromechanical radio was demonstrated as a proof of concept for measuring low frequency variation using non-linear behavior of electromechanical resonator. We will introduce our plan to estimate the mass change of single-molecule protein on graphene resonators with a sensitivity of less than a few daltons by measuring its resonance frequency variation.

Authors : Ai Serizawa, Tomoya Takahashi, Yusuke Ito
Affiliations : Department of Materials Science and Engineering, College of Engineering, Shibaura Institute of Technology; Graduate School of Materials Science and Engineering, Faculty of Engineering, Shibaura Institute of Technology

Resume : Films, which are fabricated on metallic materials, exhibit a different kinds of function such as corrosion resistance, wear resistance and surface hardening. In this study, the novel anti-corrosive film was fabricated on Al alloy substrates using steam. The resultant film was characterized and evaluated by electrochemical measurements. In addition, the mechanical property of the thin-film was evaluated by tensile test and nanoindentation system. FE-SEM images of the film surfaces showed that plate-like or block type nanocrystals, which were densely formed over the entire surface. XRD patterns indicated that the film was composed mainly of AlO(OH) crystals. The potentiodynamic polarization curves revealed that the corrosion current density of the film-coated substrates significantly decreased, and that the pitting corrosion was completely suppressed. The film was also fabricated on the plate-like tensile test sample. The crack was initiated on the surface of the film when the introduced strain reached 2%, however, the delamination of the film was not observed even if the tensile test sample was fractured. The fracture strain of 2% was much higher compered to aluminum oxide, confirmed that the strong adhesion between the film and Al alloy substrate. Acknowledgement: This research was supported by JST under Program on Open Innovation Platform with Enterprises, Research Institute and Academia (OPERA) (No. 18072116), JSPS KAKENHI, Grant-in-Aid for Scientific Research(B) (No. 19H02482), and the light metal educational foundation, Inc.

Authors : R. Pietruszka1, B.S. Witkowski1, S. Zimowski2, T. Stapinski3, M. Godlewski1
Affiliations : 1Institute of Physics, Polish Academy of Sciences, Aleja Lotnikow 32/46, PL-02668 Warsaw, Poland 2AGH University of Science and Technology, Faculty of Mechanical Engineering and Robotics, Mickiewicza Av. 30, 30-059 Krakow, Poland 3AGH University of Science and Technology, Mickiewicza Av. 30, 30-059 Krakow, Poland

Resume : Thin films of selected oxides deposited by Atomic Layer Deposition (ALD) are intensively studied for applications in electronics (including transparent electronics), optoelectronics (transparent electrodes), photovoltaics (mostly as transparent electrodes and passivation layers), and also as a barrier layers (organic photovoltaics, organic diodes). For some of the above mentioned applications thin films of ZnO and ZnO:Al (AZO) are deposited on transparent substrates, such as glass or foils. In this work we report on advantageous properties of ZnO-based films deposited on a glass substrate using low temperature ALD process. Hardness and Young modulus are determined and compared with the ones reported for similar films deposited by a sputtering. The results obtained - hardness H (8220 ± 786 GPa (for AZO); 9182 ± 815 GPa (for ZnO)) and Young modulus E (87 ± 7 GPa (for AZO); 93 ± 5 GPa (for ZnO)) confirm advantageous properties of the ALD-deposited films. For scratching tests we used MCT system by the CSEM Instruments, Switzerland. First scratches were observed when applying a 6N force for ZnO and 3,2 N force in the case of AZO. Even at larger forces, when first cracks occurred, no traces of delamination are found, confirming a very good adhesion of deposited films. New results for Al2O3 and HfO2 thin layers (used for gate oxides applications) will be discussed. These results indicate better mechanical properties of HfO2 films, as compared to Al2O3. This work was partially supported by the National Centre for Research and Development TECHMATSTRATEG1/347012/NCBR/2017, and AGH grant number,

Authors : Amarish Kumar Shukla and J. Dutta Majumdar
Affiliations : Dept. of Met. & Mat. Engg., Indian Instituite of Technology Kharagpur- 721302, India

Resume : Aluminium foam is a promising material for light weight applications, because of its high specific strength and good damping capacity. In the present study, aluminium foam has been developed using cenosphere as space holder by spray forming route. The porous structure has been characterised by field emission electron microscopy (FESEM) to observe the microstructure, micro-computer tomography (µ-CT) to find the distribution of porosity throughout the matrix. The localised mechanical properties of the matrix and interface have been evaluated by Nano indentation (NI) study. The microstructure of the foam consists of presence of cenosphere dispersed in grain refined aluminium matrix. The density of the foam is 1.896 g/cm3 as compared to 2.7 gm/cm3 of commercially pure aluminium. The µ-CT results show that the spray formed foam introduces microporosity up to 8%, and the pore has spherical in nature. The nanoindentation results show that the addition of cenosphere enhanced nanohardness from 538.28±24.34 MPa (for as-received aluminium) to 672.86±54.5 MPa (for aluminium foam) and increases the energy absorption from 86.48 nJ (for as-received aluminium) to 93.70 nJ (for aluminium foam) of foam, however; it decreases elastic modulus of foam from 58 GPa (for as-received aluminium) to 46 GPa (for aluminium foam). Key words: Aluminium foam; porosity; microcomputer tomography (µ-CT); Nano-Indentation; spray forming.

Authors : Sina Zare Pakzad(1), Mohammad Nasr Esfahani(2), Zuhal Tasdemir(3), Mustafa Yilmaz(1), Nicole Wollschläger(4), B. Erdem Alaca(1)(5)
Affiliations : (1) Department of Mechanical Engineering, Koç University, Rumelifeneri Yolu, 34450 Sariyer, Istanbul, Turkey; (2) Department of Electronic Engineering, University of York, YO10 5DD, UK; (3) Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland; (4) Bundesanstalt für Materialforschung und-prüfung (BAM), Unter den Eichen 87, D-12205 Berlin, Germany; (5) Surface Science and Technology Center, Koç University, Rumelifeneri Yolu, 34450 Sariyer, Istanbul, Turkey.

Resume : There has been a vast effort towards the characterization of materials behavior at the nanoscale. Mechanical characterization of nanowires (NWs) is mainly carried out through tensile or bending tests. The interpretation of test data via comprehensive modeling is equally important to address the current challenge of understanding the size-dependent behavior of NWs. For instance, modeling of NW deformation at the atomistic level predicts size-dependent elastic properties for NWs only with cross-sectional dimensions less than ~10 nm. We undertake such a study by investigating the elastic modulus of Si NWs with a critical dimension of 28 nm via three-point bending test. Testing effort is accompanied by a comprehensive non-linear model of NW bending, including surface and intrinsic stress effects. The model considers all relevant effects including large deformations, intrinsic stresses and surface effect. The presence of intrinsic stresses is verified through scanning X-ray diffraction microscopy, while native oxide is characterized through high-resolution transmission electron microscopy. We examine the surface effect by implementing the surface stress and surface elastic modulus through atomistic simulations coupled with the continuum model. Native oxide covering the silicon NW is modeled and two independent surface parameters are quantified verifying that size effect is postulated to be primarily a result of differences in the NW surface and core elastic moduli. A deeper understanding of the surface effect on NW mechanical properties is critical for the control and correct utilization of such nanoscale phenomena.

Authors : Ying ZHOU*, Amélie FILLON, Hamza JABIR, Thierry GLORIANT
Affiliations : University of Rennes, INSA Rennes, CNRS, ISCR-UMR 6226, F-35000 Rennes, FRANCE

Resume : Superelastic alloys are highly regarded for their unique ability to recover large deformations through reversible stress-induced phase transformations. Although NiTi alloy is the most well-known superelastic alloys, some Ni-free metastable ?-titanium alloys also exhibit interesting superelastic performances [1-2]. Due to their functional and mechanical properties, these alloys are attractive for a variety of applications such as actuators, sensors, dampers, sealing, biomedical tools and implantable devices. Their macroscopic deformation behavior including their bulk superelastic response has been extensively studied using macroscopic techniques (tensile and compression experiments) [3]. Much less work exists on the occurrence of a microscopic superelastic effect in a confined geometry during micro- and nano-scale deformations. With the increasing demand for small-scale applications, characterization of the local mechanical behavior is an important issue of extensive interest. Nanoindentation is conducted at the grain scale in Ni-free polycrystalline metastable ?-Ti alloys to study the effect of crystallographic orientations on elastic (elastic modulus), superelastic (strain recovery) and plastic (hardness) properties [4]. Results reflect the large scale mechanical anisotropy measured in bulk single crystals from macroscopic investigations [3]. Nanoindentation, especially using spherical indenters, is useful for probing superelastic response and mechanical anisotropy during nanoscale deformations. [1] Castany P., Ramarolahy A., Prima F., Laheurte P., Curfsd C., Gloriant T., In situ synchrotron X-ray diffraction study of the martensitic transformation in superelastic Ti-24Nb-0.5N and Ti-24Nb-0.5O alloys, Acta Mater. 88, 102?111 (2015). [2] Ijaz M.F., Laillé D., Héraud L., Gordin D.M., Castany P., Gloriant T., Design of a novel superelastic Ti-23Hf-3Mo-4Sn biomedical alloy combining low modulus, high strength and large recovery strain, Materials Letters 177, 39-41 (2016). [3] Zhang Y. W., Li S.J., Obbard E.G., Wang H., Wang S.C., Hao Y.L., Yang R., Elastic properties of Ti?24Nb?4Zr?8Sn single crystals with bcc crystal structure, Acta Mater., 59, 3081?3090 (2011). [4] Jabir H., Fillon A., Castany P., Gloriant T., ?Crystallographic orientation dependence of mechanical properties in the superelastic Ti-24Nb-4Zr-8Sn alloy?, Phys. Rev. Mat. 3, 063608 (2019), DOI: 10.1103/PhysRevMaterials.3.063608

Authors : Dennis Bedorf, Wolfgang Stein, Daniel Habor, Martin Knieps
Affiliations : SURFACE Rheinstr.7 D-41836 Hueckelhoven

Resume : The precise characterization of micro- and nanomechanical material properties is up to now a field of material scientists with fundamental knowledge of contact mechanics. Failure to follow the device-related preparations for the actual measurement can have a major impact on the measurement results and make a quantitative statement often impossible. As digitalization progresses, the need for micro and nanomechanical sensors and actuators increases. This means that the need for quality-assuring analysis technology is growing in order to ensure that such components are of sufficient quality. This also increases the need to adapt the measurement method to the industrial environment. The expertise for the measuring process must pass from the user to the machine. Therefore, the entire chain of effects of the measuring process - the preparation of the measuring device, the sample preparation, the implementation of the measurement and the processing of the measured values ​​must be designed to be variable and error-free. SURFACE has taken with its sm@rt system the first step in this direction. Thanks to its modularity, the new sensor concept can be adapted to the application area - wide load range, large linearity range, high resolution, high measurement quality. All this is paired with very small sensor dimensions. Microcontroller systems with the latest signal processors and scalable software / hardware architecture are also used on the control side. The operating mode of the system is adapted to the operator's know-how by means of variable user levels and the measurement processing and preparation is carried out accordingly, so that the measurement process is finally carried out as a “one button action”. The evaluation of the current measurement results can then be compared and checked using stored material data. The deviations of the current data from the stored material data can then serve as a correction or evaluation of the local measurement. We will show examples to demonstrate the functionality of the system.

Authors : Waters, T.*(1), Hook, J.(1), Evans, A.(1), Ellis, F.(1), Elídóttir K.(1), Ogilvie, S.P.(2), Backes, C.(3), Dalton, A.B.(2) and Jurewicz, I.(1)
Affiliations : (1)Department of Physics, University of Surrey, Guildford, UK (2) Department of Physics and Astronomy, University of Sussex, Falmer, Brighton, UK (3) Applied Physical Chemistry, University of Heidelberg, Germany * Lead presenter

Resume : Despite the enormous potential of two-dimensional nanomaterials (2D-NMs) using them in 3D systems has proven challenging. This can be tackled by using the process of wet-spinning poly(vinyl alcohol) (PVA) fibres. 2D-NMs can be integrated into polymeric fibres to exploit their properties on a bulk scale. However, issues remain with these nanocomposite fibres such as controlling NM flake alignment and orientation. To overcome this the formation of striations in PVA fibres under strain has been investigated. Striations are microscopic fibrils that form perpendicular to the direction strain on the PVA fibre. Limited literature exists on PVA striations, so a model is proposed here where an extending amorphous region pulls lamella crystals into horizontal alignment within the semi-crystalline PVA. It is hypothesised that with control of striations it is possible to manipulate the 2D-NMs incorporated in the fibre. The nanomaterial used (graphene, graphene oxide, black phosphorous and molybdenum disulphide), weight fraction and NM flake size have been varied to determine the effects on mechanical properties, fibre morphology and nanomaterial alignment. Polarised Raman spectroscopy was used to investigate degree of NM alignment within fibres before and after stretching to increasing levels of strain. This work helps to determine the compatibility of various 2D-NMs in PVA fibres and whether the strain induced formation of striations can be used to impart control over the NMs within.

Authors : Alekseeva L.S., Karazanov K.O., Boldin M.S., Lantsev E.A.
Affiliations : Research Institute of Physics and Technology of Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, Russia

Resume : In the present work, the thermal shock resistance was carried out for Y2.5Nd0.5Al5O12 - x SiC composites (x = 10, 20, 30, 40 vol.%). The composites were previously cracked using a diamond pyramid of a hardness tester. To simulate the thermal shock, composites were heated in a muffle furnace and abruptly cooled in air. Heating was carried out in the temperature range from 200 to 1000 °C, in increments of 100 °C, for 20 minutes at each stage. The length of the cracks was measured using optical microscopy. It follows from the obtained data that the crack length practically did not change with increasing heating temperature and did not depend on the content of silicon carbide.

Authors : Gianluca Tozzi 1, Marta Peña Fernández 1, Alexander Kao 1, John Chiverton 2, Fang Zhou 3, Benjamin Tordoff 3, Gordon Blunn 4
Affiliations : 1 Zeiss Global Centre, School of Mechanical and Design Engineering, University of Portsmouth, UK 2 School of Energy and Electronic Engineering, University of Portsmouth, UK 3 ZEISS Research Microscopy Solutions, Carl Zeiss Microscopy GmbH, Germany 4 School of Pharmacy and Biomedical Sciences, University of Portsmouth, UK

Resume : Musculoskeletal conditions (i.e. osteoarthritis) and trauma affect soft tissues, inducing for example articular cartilage deterioration and ligament/tendon injury. Therefore, the need of understanding their morphology and mechanics is of paramount importance to design new biomaterials and treatments. High-resolution X-ray computed tomography (XCT) offers accurate resolution to visualise and quantify morphology in mineralised tissues such as bone. However, XCT setups are typically unable to resolve weakly absorbing soft tissues (i.e. cartilage, ligaments) with sufficient contrast unless stained (i.e. PTA), which can significantly alter their morphology and mechanical properties if not sufficiently developed [1]. This study will report preliminary results on the use of less invasive staining [2] and phase-contrast XCT imaging to resolve features in soft tissues, specifically chondrocyte lacunae in articular cartilage to enable digital volume correlation (DVC) analysis. DVC was performed (zero-strain test) on a fresh cylindrical bone-cartilage plug extracted from a bovine medial tibial plateau in the longitudinal direction, as well as a whole stained mouse tibial plateau. XCT of the bone-cartilage interface in the bovine plug were obtained in phase contrast (Zeiss Versa 510, 2 micrometers voxel size) and stained mouse tibial plateau (GE Nanotom M, 1.12 micrometers voxel size) in absorption. A local multi-pass DVC approach (DaVis, LaVision) with a final sub-volume size of 40 voxels for the bovine and 80 voxels for the mouse specimens was used. A good DVC correlation pattern was found in the articular cartilage. For the phase-contrast images regions rich of chondrocyte lacunae enabled a better correlation, whereas in the stained tibial plateau high correlation in the articular cartilage was achieved. Standard deviation of the error (SDER) of the strain components for both bovine and mice specimens was always <100 microstrains. References: [1] Disney et al. 2017. Sci. Rep. DOI: 10.1038/s41598-017-16354-w; [2] Kerckhofs et al. 2018. Biomaterials. 159, 1–12

Authors : A.C. Costache [1][2], C.V.Doicin[1],G. Moagar-Poladian[2]
Affiliations : [1]University Politehnica of Bucharest; [2]National Institute for Research and Development in Microtechnologies

Resume : During the time, recycled nylon powder attracted the attention due to their multiple applications and can be used as raw material in different industries. Among these, it can be remarked textile, food, music industry, personal care etc. Since the physical properties (e.g. elastic constants or mechanical resistance) of the material are closely related to the applications, an accurate characterization of this become mandatory. Powder was collected from the 3D printer’s tank and the anti-ex vacuum cleaner. After decontamination, further processing is done by melting and solidifying the polymer. Firstly, this paper presents the characterization of the material by means of Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), energy dispersion X-ray spectroscopy (EDX), X-ray diffraction (XRD). Secondly, the mechanical characterization of recycled nylon powder (PA12) is discussed. In this sense, resistance tests of the material were performed for each melting- solidification cycle through two methods. After more cycles, it was observed that the mechanical resistance decreases, and the reusing become possible only in a few areas.

Authors : Anil Kumar, Sapan Kumar Nayak, Atanu Banerjee and Tapas Laha
Affiliations : Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Kharagpur - 721302, India; Research and Development Division, Tata Steel, Jamshedpur - 831007, India

Resume : Deformation behavior of a new series of plasma sprayed Fe-based (Fe-10Cr-4B-4P-2C wt.%) amorphous/nanocrystalline composite coating was investigated by carrying out multi-scale indentation and nano-tribological tests. The coating with optimized spraying parameters exhibited excellent mechanical properties in terms of higher nanohardness, lower sliding friction coefficient (COF) and sliding wear. Decrease in both coefficient of friction and wear rate of the coatings with increasing plasma power was observed from dry sliding wear test, which also helped in understanding the wear mechanism in the coatings. Nanoindentation studies were carried out at various peak loads and loading rates to understand surface deformation behavior of the coating. The coating displayed loading rate dependent “pop-in” events on load-displacement curves and strain sensitivity model was applied to understand the effect of free volume concentration. Further investigation of coating deformation response in a tribological contact was evaluated by nano-scratch, which exhibited shear band formation along the nano-wear track.

Authors : Supriya Patibanda1*, G. Siva Kumar2, Ralph Abrahams3, Krishna Jonnalagadda4
Affiliations : 1. IITB-Monash Research Academy, Indian Institute of Technology Bombay, Mumbai 400076, India. 2. Center for Engineered Coatings, International Advanced Research Center for Powder Metallurgy and New Materials, Hyderabad 500005, India. 3. Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia. 4. Department of Mechanical Engineering, Indian Institute of Technology Bombay, Mumbai 400076, India.

Resume : Thermal barrier coatings (TBCs) consisting of top coat, bond coat and thermally grown oxide are used to provide thermal insulation for the hot sections of aerospace engines and other high temperature components. Mechanical properties of TBCs are highly influenced by the specific microstructural characteristics of its individual layers. Of all the components, the ceramic top coat layer is in direct exposure to the elevated temperatures of the engine and hence plays a major role in deciding the overall life of TBCs. The aim of the present study is to evaluate and comprehend the tensile behaviour of the most widely used top coat material, plasma sprayed ZrO2 7wt.% Y2O3 (7YSZ), of ~300µm thickness. An in situ uniaxial tensile setup was developed in conjunction with high resolution optical microscopy to characterize the YSZ freestanding thin films. Strains upto an accuracy of 0.01% were measured using digital image correlation technique which provided major insights into the deformation and failure of these coatings. The tensile stress vs. strain curves of the coatings exhibited a non-linear behavior, with an elastic modulus of 12±4 GPa and failure strength of ~16±4 MPa. Successive unloading-reloading experiments were performed at different stress levels to deconvolute the elastic behavior of these brittle ceramics. The role of microstructural features like crack density and porosity on the fracture of these films was observed using fractographs. Hence, a finite element based numerical model replicating the non-linear tensile behaviour including the influence of microcrack density and porosity on tensile stress was developed. The observations in this study experimentally strengthen the proposed theoretical micromechanisms for the failure of YSZs in literature. This study also enables the prediction of probability of failure of YSZ using Weibull parameters developed herein. Keywords: Yttria Stabilized Zirconia; Insitu tensile properties; Digital image correlation; Fractography; Finite element method.

Authors : F. Bergner, C. Heintze, K. Vogel, P. Chekhonin, S. Akhmadaliev
Affiliations : Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany

Resume : Nanoindentation of ion-irradiated materials has received considerable attraction because of the potential capability to efficiently derive the effect of displacement damage on the hardness. In order to reach this goal, several assumptions have to be made within the analysis of the measured nanoindentation response. These include the shape and size of the indentation plastic zone, the separation of the irradiation effect from the indentation size effect and the type of superposition of individual hardness contributions. The aim of the study is to experimentally verify given sets of assumptions by way of variations of the ion energy. To this end, several Fe-Cr-based alloys were exposed to irradiations with Fe ions of energies between 1 and 8 MeV and the nanoindentation response was measured as function of the contact depth. The same procedure of analysis including assumptions was applied to all irradiations. The presentation will show, to what extent the results of the analysis, namely hardness versus displacement damage, depend on the ion energy. As a criterion, they should be invariant against variations of the ion energy.

Authors : Sebastian Krauß, Jan Philipp Liebig, Mathias Göken, Benoit Merle
Affiliations : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)

Resume : Nanotwinned metals display a remarkable strength due to the high effectiveness of twin boundaries as obstacles to dislocation motion. In order to further characterize these interactions, micropillars containing single coherent twin boundaries with different orientations were compressed with a flat punch and subsequently investigated in the scanning electron microscope. The crystal orientations for compression were selected to activate different slip modes. The aim is to probe the different barrier effects that can act on gliding dislocations. The investigations concentrated on copper and α-brass. The latter is a low stacking-fault energy alloy exhibiting a high density of recrystallization twins. Coherent twin boundaries were selected from an EBSD orientation mapping of the sample and oriented by means of a custom sample holder. FIB-milling at these interfaces yielded micropillar samples containing a single twin boundary. Single crystal reference samples were obtained from the bulk of the grain located on both sides of the twin boundary. The microcompression tests enabled the quantification of the influence of the twin boundary barrier on the strength of each sample. The tests evidenced a strong dependency of the strength of the sample on crystal orientation and stacking-fault energy. The activated glide systems were subsequently identified from slip trace analysis and STEM mapping of lamellas obtained by FIB lift-out from the bulk of the tested micropillars.

Authors : Stefan Gabel, Sven Giese, Benoit Merle, Ioannis Sprenger, Martin Heilmaier, Steffen Neumeier, Erik Bitzek, Mathias Göken
Affiliations : Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; KIT, Karlsruhe, Germany; KIT, Karlsruhe, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany

Resume : Lamellar eutectic NiAl-Cr(Mo) alloys show an increase of the fracture toughness based on different toughening mechanisms. These mechanisms result from the fibrous or lamellar microstructure of the two constituting phases α-Cr(Mo) and β-NiAl. However, the influence of the fracture toughness of the individual phases and the evolution from early crack growth to the toughening mechanisms has not yet been systematically studied. Here bending tests on FIB-notched microcantilever beams are used to characterize the small scale fracture properties. The micromechanical investigations revealed that the fracture toughness of the α-Cr(Mo) phase (7.5-9.1 MPa√m) is much higher than the fracture toughness of β-NiAl (2.2-2.9 MPa√m). Larger cantilevers in the crack arresting orientation had an enhanced fracture toughness with up to 14.4 MPa√m, which is lower than that one of bulk lamellar samples. This is attributed to the small interaction volume which hinders the full exploitation of potential extrinsic toughening mechanisms. Further results of these alloys will be discussed in the paper.

Authors : Bentejui Medina-Clavijo, Gorka Ortiz-de-Zarate, Andres Sela, Iñaki M. Arrieta, Aleksandr Fedorets, Pedro J. Arrazola, Andrey Chuvilin
Affiliations : CIC nanoGUNE: Bentejui Medina-Clavijo; Andrey Chuvilin; Mondragon Unibertsitatea: Gorka Ortiz-de-Zarate; Andres Sela; Iñaki M. Arrieta; Pedro J. Arrazola; Far Eastern Federal University: Aleksandr Fedorets; Ikerbasque, Basque Foundation for Science: Andrey Chuvilin;

Resume : This work shows the applicability of direct observation of metal cutting (down to sub-micron scales) combined with the measurement of the cutting force in-operando in an electron microscope (SEM). A prototypic device to perform linear cutting inside the vacuum chamber of an SEM has been designed, constructed and utilized to study intimate details of the machining process. Experiments on in-situ machining have shown that all the main structural features of deformation during cutting, such as the material’s shear zones, are preserved in the sub-micrometer cutting regime. A few peculiar features of the cutting process have been noticed by in-operando microscopic observation: It has been observed that before the nucleation of any shear band in front of the tool, the cutting force is ~50% higher as compared to the shearing steady state. Additionally it was observed that the local thickness of the area deformed under the tool showed a clear dependence of the underlying grain orientation. The process of machining at small scales typically leads to increasing cutting energies, well over the values found on the macro scale. In this work, availability of extremely small feeds and cutting tool apex radii in SEM micromachining allowed to analyze and discriminate the different sources for the size effect on the cutting energy. A model that discriminates between the different sources behind the increase of cutting energy has been developed which accurately predicts experimental values. It has been shown that at an industrially relevant range of feeds and tool radii, the size effect is determined primarily by geometrical factors, while at a sub-micrometer range the contribution of increasing geometrically necessary dislocation density becomes relevant.

Authors : Kukro Yoon, Taeyoon Lee*
Affiliations : NanoBio Device Laboratory, School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea

Resume : Recently, the metal nanoparticle formation technology has attracted a vast amount of interest due to its simplicity and practicality. Specifically, the metal nanoparticle networks are extremely useful in wearable electronics because they can maintain electrical properties under strong external deformation. Previously, we have developed a novel method to form Ag nanoparticles inside polymer based textiles using chemical reduction process. The Ag nanoparticle networks provoke change in the resistance of textile due to external mechanical stimulus, and this property allows the textiles embedded with Ag nanoparticle to be applied onto wearable electronics as a sensor. To improve the performance of this sensor, nano-/micro-scale architectures inspired by nature have been proposed. In our study, hierarchical microsized hairy architectures was developed to exhibit remarkable stretchability (<200%) and sensitivity of textile based sensor. The regularly ordered microhairy structures constructed with polyurethane-carbon black-silver nanowire (PU/CB/AgNW) composite mixtures are layered onto the Ag nanoparticle embedded textiles using imprinting technique. We analyzed the correlation between the aspect ratio and electrical conductivity of the microsized hairy architectures, and proposed a fabrication method of the optimized condition. Additionally, finite element method (FEM) simulation was modeled to understand the linear resistance changes by the microsized hairy architectures in pressure/strain condition. Consequently, the Ag nanoparticle embedded textiles with hierarchical microsized hairy architecture was applied to wearable electronics, which can monitor human movements.

Authors : Chihyeong Won, Sanggeun Lee, Taeyoon Lee
Affiliations : Nanobio Device Laboratory, School of Electrical and Electronic Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea

Resume : One-dimensional electrodes and devices using nanomaterials and nanostructures have been developed due to a lot of advantages, such as highly flexible, low cost and light weight. Precious studies, however, presented limited structure of certain metals and could only sense one property like mechanical stress. Herein, we fabricated Palladium (Pd) nanoparticles on polyurethane (PU) based fiber using a novel method that immersed elastomeric fibers into metal precursor chemical solutions. Pd nanoparticle shells were fabricated on the PU fiber, which acts as a conducting path and lowers electrical resistance of polymer. When the fiber was stretched, nano-cracks of Pd nanoparticle shells were formed on the fiber surface. The formation of Pd nano-cracks can be controlled by the number of chemical solution processes. Depending on the stretching rate (10 ~ 110%), the connection between Pd nanoparticle shells was changed which determine conductivity of fiber. In addition, exposure to hydrogen (H2) gas changes the conducting network of Pd nano-cracks since Pd reacts with H2 gas to form PdHx. We could also detect very small amounts of H2 gas (5 ppm) by analyzing variation in Pd nano-cracks. To conclude, an unprecedented process was used to fabricate the Pd nanostructures on fiber and simultaneously detect H2 gas concentration and mechanical strains through crack network analysis between Pd nanoparticles.

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09:45 Coffee break    
Fracture mechanics : M. Cordill
Authors : David Armstrong
Affiliations : University of Oxford

Resume : InIndentation based fracture toughness measurements remain one of the fastest and most convenient ways of measuring fracture toughness and are widely used even though there are known inaccuracies with the methodologies used. In this work we use single crystal and polycrystalline silicon carbide to study the effects of temperature on crack propagation and morphologies. SiC is being widely developed as a structural material for use in the nuclear and aerospace power generation industries such as nuclear fuel cladding and combustion chamber linings for aero engines. However its lack of ductility means in must be used in the form of a SiC SiC composite. In this work we compare fracture processes in single crystal SiC and nanocrystalline SiC around Berkovich indents from RT to 750oC. Hardness is seen to drop from 45GPa to 20GPa and reduced modulus from 300GPa to 200GPa across this temperature range, in good agreement with other studies. At room temperature the fracture occurs on the expected <112 ̅0> planes (fig 1). By 400oC this fracture has transitioned to the <101 ̅0> planes. FIB-SEM tomography shows that there is significant changes to the subsurface cracking between the two test temperatures. Whilst at room temperature the cracks run perpendicular to the surface and link up sub surface (similar to the so called half penny cracks seen around Vickers indents), at 400oC significant lateral cracking is seen with cracks running parallel to the surface. Having demonstrated the ability to use multiple microscopy methods to understand fracture in a simple compound such as SiC I will demonstrate the methods can be extended to understanding fracture processes in air sensitive materials used in energy storage such as LAPG and LLZO.

Authors : J.T. Pürstl, N.G. Jones, R.P. Thompson, T.E.J. Edwards, P. Chartier, W.J. Clegg
Affiliations : Department of Materials Science and Metallurgy, University of Cambridge; Department of Materials Science and Metallurgy, University of Cambridge; Department of Materials Science and Metallurgy, University of Cambridge; EMPA – Swiss Federal Laboratories for Materials Science and Technology; Département de Physique et Mécanique des Matériaux, Institut P', Université de Poitiers; Department of Materials Science and Metallurgy, University of Cambridge

Resume : High temperature applications require structural materials that can provide the necessary high temperature stability and corrosion resistance. While ceramics are highly suitable candidates in that regard, their use in structural components is often restricted due to their intrinsic brittleness. MAX phases, a group of ternary carbides that show unusually good damage tolerance, are a possible basis for the design of tougher ceramics. The origin of this toughness is believed to lie in the layered crystal structure of the hexagonal MAX phases, and it is believed that on this basis tougher ceramics can be designed using other structures also. The link between enhanced toughness and layered crystal structure can be explained by electron density shifts that occur between the atomic layers. These affect the local elastic properties, effectively easing the onset of plastic flow via dislocation movement parallel to the layers. The extent of these electron density shifts, and thus improved toughness, is linked to the electronegativity difference between the layers, and can therefore be adjusted via the layer composition. In the current study, we demonstrate how changes in layer composition can affect the flow behaviour in the form of basal plane slip in MAX phases. Testing of different MAX phases is carried out in the form of single crystal micropillar compression with digital image correlation, and a method is presented that allows for a more consistent extraction of the flow stresses. It is shown that the differences in flow stresses due to the above effect can vary significantly in MAX phases. Based on this outcome, nanoindentation was carried out in different components of the layered fcc Th6Mn23 structure type to demonstrate how the effect might take shape in other crystal systems.

Authors : Stefan Gabel, Erik Bitzek, Mathias Göken, Benoit Merle
Affiliations : Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany; Institute I: General Materials Properties, FAU Erlangen-Nürnberg, Erlangen, Germany

Resume : Body-centered cubic (bcc) metals like Cr and W have a high melting point and high strength. However, their fracture toughness at room temperature is low. This is due to their rather high ductile to brittle transition temperature. At room temperature the fracture toughness is limited by dislocation mobility or by the inability to activate nucleation sources. Focused Ion Beam milled cantilevers were used to investigate the facture toughness on the microscale and to study the influence of the loading rate and the initial dislocation density of the sample. In order to introduce dislocations into the material by pre-deformation, the sample surface was indented with a Vickers punch prior to testing. A Finite Element based estimation of the resulting strain field was used to select positions corresponding to different amounts of pre-deformation, where microcantilevers were fabricated. The Continuous Stiffness Measurements allowed tracking the ongoing crack growth, which is correlated to a change of the cantilever stiffness. The measurements showed that an increase of the initial dislocation density leads to a toughening of the sample. This toughening effect saturates at around 14% pre-deformation. The dependence of the brittle to ductile transition on the availability of dislocations and activity of dislocations sources was investigated via TEM-lamella lift-outs and Transmission Kikuchi Diffraction mapping. The physical origins of these behaviors will be discussed in the paper.

Affiliations : 1 Université Lyon, INSA-Lyon, MATEIS UMR CNRS 5510, Villeurbanne Cedex, France 2 CEA, DEN, DEC, Cadarache, 13108 St Paul Lez Durance, France

Resume : Among micromechanical tests, bending of micro-cantilever specimens milled with FIB is particularly attractive as it offers several advantages. Specimens can be prepared directly from the surface of the bulk material, tests can be carried out using a nanoindenter, and the analysis can be relatively straightforward. This study investigates the use of this method to evaluate the fracture properties of different ceramic materials: zirconium dioxide ZrO2, uranium dioxide UO2, UO2 irradiated in commercial nuclear reactors, and nacre-like alumina Al2O3. Each of these oxide ceramics has different microstructures and mechanical properties. For example, UO2 shows bubbles of fission gas after use in a nuclear reactor, while nacre-like Al2O3 has platelet shaped grains and a weaker secondary phase at grain boundaries. The application of the micro-bending method to these ceramics has not only enabled to bring mechanical data on each material, but also to study the different parameters related to their microstructure: ‐ The influence of elastic anisotropy on mechanical properties at the grain scale ‐ The influence of defects on the measured fracture properties ‐ The local strength of an individual grain boundary ‐ The tensile and shear strength of an individual interface The analysis of these experimental data provides answers on the size effect observed on the fracture strength measured at a local scale, which is of the order of several GPa, i.e. an order of magnitude above macroscopic values.

Authors : Joan Sendra, Micha Calvo, Marco Volpi, Henning Galinski, Ralph Spolenak
Affiliations : Laboratory for Nanometallurgy, Department of Materials, ETH Zurich

Resume : Microstructure strongly influences the mechanical properties of thin films. Consequently, the characterization of mechanical behavior at small length scales is fundamental. In particular, stress mapping is of great interest since it allows the study of fracture mechanics, e.g. visualizing the stress distribution around a crack tip. Conventional lab scale stress mapping techniques are based on electron microscopy (EM) and Raman spectroscopy (RS). Common drawbacks are the required high vacuum for EM and the need of Raman active materials for RS, hindering the range of materials that can be analyzed. Here, we present an advanced reflectance anisotropy spectroscopy (RAS) microscope based on a super continuum laser source as a non-destructive stress mapping technique for a wide range of materials. Our microscope enables insight into the electronic band structure, phase and crystal orientation. We demonstrate strain mapping in sputtered thin films on flexible substrates and outline the potential of the technique for mapping grain orientation using polycrystalline copper. The simultaneous stress and grain orientation mapping will enable future studies on the fracture mechanics of thin films and novel materials with different microstructure and environmental conditions.

12:10 Lunch break    
Thin films mechanics : B. Merle
Authors : Damien Faurie* 1, Fatih Zighem1, Skander Merabtine1, Pierpaolo Lupo2, Adekunle Adeyeye2
Affiliations : 1/ LSPM-CNRS, Université Sorbonne Paris Nord, France 2/ National University of Singapore

Resume : Nanoscale systems fabricated on flexible or stretchable substrates are being studied more and more because of their ability to adapt to non-planar surfaces, particularly in confined environments. In addition, these systems have the advantage of being lighter and less expensive than their counterparts deposited on more conventional rigid substrates. In recent years, many magneto-electronic devices have been made on different polymer substrates. The ability of these magnetic thin films on polymer substrates to be folded or stretched is essential, but their use is still delicate, which is a brake on the industrialization of these systems. The main issues are to understand how the applied strains to the flexible magnetic systems impact their magnetic properties. Obviously, when a thin film is deposited on a flexible substrate, it is usually submitted to high stresses due to the stretching or the curvature of the whole system and to the mechanical contrast between the film and the substrate. These stresses may have an important effect on the static and dynamic magnetic properties of thin films, especially on the resulting magnetic anisotropy. In particular, it is important that the large strains to which they are subject are not harmful to their functional properties. In fact, beyond the classical magnetoelastic effects observable at small strains, the phenomenon of multi-cracking and associated localized buckling observed for inorganic thin films on organic substrates tensily stressed lead to heterogeneous strains must have effects on the magnetic properties. However, these are rarely discussed in the case of flexible magnetic systems, and have never been studied in depth. In this work, we focused on experimentally identifying the cracking mechanisms for different magnetic alloys (Co40Fe40B20, Ni80Fe20) deposited on Kapton® substrate. The phenomena of multi-cracking but also buckling of thin films have been studied. Thin films surface was probed by atomic force microscopy during in situ tensile tests to clearly identify these mechanisms. Subsequently, we have identified the effects of these irreversible phenomena on the magnetic properties of thin films (anisotropy and Gilbert damping coefficient). References : [1] S Merabtine, F Zighem, D Faurie, A Garcia-Sanchez, P Lupo, AO Adeyeye, Nano letters 18 (5), 3199-3202 (2018). [2] S Merabtine, F Zighem, A Garcia-Sanchez, V Gunasekaran, M Belmeguenai, X Zhou, P Lupo, AO Adeyeye, D Faurie, Scientific reports 8 (1), 13695 (2018). [3] D Faurie, F Zighem, P Godard, G Parry, T Sadat, D Thiaudière, P-O Renault, Acta Materialia 165, 177 (2019)

Authors : Matteo Ghidelli (1,2), Hosni Idrissi (3,4), Andrey Orekhov (4), Jean-Pierre Raskin (5), Jang-Ung Park (6), Andrea Li Bassi (2), Thomas Pardoen (3)
Affiliations : (1) Department of Structure and Nano/-Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany. (2) Micro- and Nanostructured Materials Laboratory, Department of Energy, Politecnico di Milano, Milan, Italy. (3) Institute of mechanics, materials and civil engineering, Université catholique de Louvain, Louvain-la-Neuve, Belgium. (4) EMAT, University of Antwerp, Antwerp, Belgium (5) Institute of information and communication technologies, electronics and applied mathematics, Université catholique de Louvain, Louvain-la-Neuve, Belgium. (6) Nano Science Technology Institute, Department of Materials Science and Engineering, Yonsei University, Seoul, Republic of Korea

Resume : Thin film metallic glasses (TFMGs) are emerging materials characterized by a unique combination of mechanical/electrical properties involving large yield strength close to the theoretical limit, large ductility (> 10%) and metallic-like electrical conductivity. Nevertheless, the synthesis of advanced TFMGs with engineered microstructure and the understanding of their mechanical/electrical properties is barely tackled, limiting potential applications for stretchable electronics. Here, we report the use of Pulsed Laser Deposition (PLD) as a novel technique to synthetize nanostructured Zr50Cu50 (%at.) TFMGs. We show how the control of PLD process parameters (background gas pressure and laser fluence) enables to synthetize a variety of film microstructures among which compact fully amorphous and amorphous nano-granular resulting from cluster-assembled growth showing lower density and large free volume interfaces. Compact TFMGs show large elastic modulus (140 GPa) and hardness (10 GPa) which decreases for nanogranular films, while in-situ TEM tensile tests reveal an outstanding and tunable yield strength (3 GPa) and ductility (> 9%) product. Finally, we developed a stretchable transparent electrode based on nanogranular TFMGs nanotrough network showing excellent stretchability (70%) and low sheet resistance (~3 Ω/sq) which is then integrated in wirelessly rechargeable transparent heater, demonstrating the potential of these films for novel stretchable electronic devices.

Authors : (a,b) F. Bahrami, (a,b) M. Hammad, (c) M. Fivel, (b) B. Huet, (d) C. D’Hease, (e) L. Dinge, (d) B. Nystend, (a,e) H. Idrissi, (b) J.P. Raskin, (a) T. Pardoen
Affiliations : a: Institute of Mechanics, Materials and Civil engineering (iMMC) UCLouvain, B-1348 Louvain-la-Neuve, Belgium b: Information and Communication Technologies, Electronics and Applied Mathematics (ICTEAM), UCLouvain, B-1348 Louvain-la-Neuve, Belgium c: Univ. Grenoble Alpes, CNRS, Grenoble INP, SIMaP, 38000 Grenoble, France d: Institute of Condensed Matter and Nanosciences – Bio-and Soft Matter (IMCN/BSMA), UCLouvain, B-1348 Louvain-la-Neuve, Belgium e: Electron Microscopy for Materials Science (EMAT), Department of Physics, University of Antwerp, Groenenborgerlaan 171, B-2020, Belgium

Resume : The enhancement of the mechanical properties of metals by graphene additions has been demonstrated over the last decade for surface applications to mitigate the impact of tribological loadings or for strengthening purposes through bulk dispersion. This research is investigated the effect of the presence of a single layer graphene grown on Cu on the development of the contact plasticity for two configurations: one with graphene at the surface, the other with graphene sandwiched under a 100nm thick Cu cap layer. As a matter of fact, a film of copper (deposited on a quartz wafer) is the substrate used in the CVD process for graphene production, there is no need for transferring graphene which avoids any possible artifacts. Moreover, the adhesion between CVD-grown graphene and the underlying Cu film is larger than transferred graphene, since during transfer, wrinkles and ripples may form, thus weakening the interaction between graphene and the substrate. For the first configuration, nanoindentation under both displacement and load control conditions show earlier and shorter pop-in excursions compared to systems without graphene. The presence of graphene caused a marked effect on the indentation response in the second configuration as well, even larger than in the first one. Atomic force microscopy reveals much smoother pile-ups with no slip traces when graphene layer is present on the surface. In order to understand better the root causes of the observed effects on the plastic flow, transmission electron microscopy is used to compare samples after nanoindentation in terms of dislocation structures. Furthermore, 3D discrete dislocation dynamics (DDD) simulations are conducted to unravel more quantitatively how dislocations interact and multiply under the indent with and without the presence of graphene. These results provide a more quantitative understanding of the impact of graphene on dislocation mechanisms for both surface and bulk applications.

Authors : Hui Wang1, Hosni Idrissi1,2, Michaël Coulombier1, Jean-Pierre Raskin3, Thomas Pardoen1
Affiliations : 1 Institute of Mechanics Materials and Civil Engineering, IMAP, UCLouvain, 1348 Louvain-la-Neuve, Belgium 2 EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020, Antwerp, Belgium 3 Department of Electrical Engineering, UCLouvain, 1348 Louvain-la-Neuve, Belgium

Resume : The nanolaminate (NL) systems, highly applauded in recent literature for their extreme strength, often suffer from a lack of ductility, with a negative impact on the transfer to engineering applications. There are only very few examples of NL with alternating crystalline layers, like the Cu/Nb system, in which the crystallography and the structural properties of the interfaces have been successfully tailored in order to improve the plastic deformability without significantly sacrificing the high strength. Efforts to ‘‘ductilize’’ another class of NLs made by alternating crystal/amorphous layers are even more rare, involving only attempts to tune the layer thickness in order to suppress catastrophic shear banding. However, several questions remain regarding the role of the crystal/amorphous interface and of the mechanisms controlling the interaction between dislocations and GBs with the amorphous phase. In this research, we explore the mechanical properties and nanoscale plasticity mechanisms in a tri-layer model system of Al/Al2O3/Al film deposited on Si substrate at room temperature by DC magnetron sputtering. The mechanical response of the films is investigated using nanoindentation as well as a UCLouvain lab-on-chip tensile method based on the relaxation of internal stresses in an actuator beam to pull on the specimen after chemical etching of the underlying sacrificial layers. The results of the nanoindentation confirm the occurrence of creep. Furthermore, by reducing the thicknesses of the alumina layer, a small decrease of theYoung’s modulus and hardness is observed. Preliminary in-situ TEM nanotensile tests show activation of intense GB processes in the Al layers, correlated with significant plastic deformation in the amorphous alumina layer.

Authors : C.O.W. Trost, M.J. Cordill, H.P. Gänser, R. Hammer
Affiliations : Erich Schmid Institute of Materials Science of the Austrian Academy of Sciences, Erich Schmid Institute of Materials Science of the Austrian Academy of Sciences and Dept. of Materials Science of Montanuniversität Leoben, Materials Center Leoben, Materials Center Leoben

Resume : Metallic foils are non-trivial to mechanically test due to their thickness. With straining clamping problems and proper orientation as well as quasi instant plastification hinder the proper evaluation of the mechanical behavior. Usually the “problematic areas” at the beginning of the stress-strain curve are not shown nor discussed but simply removed from analysis and the values are extrapolated back to zero. Since the data is altered by this procedure, the reproducibility of the experiment is also decreased, thus strongly influencing both the evaluated elastic modulus and the calculated yield stress. In literature it has been reported that elastic modulus of metallic foils measured by tensile testing strongly deviates from the elastic moduli measured by ultrasonic testing. To counter the imperfect way of cutting and data extrapolation, new ways of testing and advanced data evaluation combined with finite element calculations have to be used to extract sufficient data from the experiment. A new testing procedure that uses repeated loading and unloading within the elastic regime will be introduced. This procedure allows for the elastic modulus of the thin foils to be accurately measured and also does not influence the yield stress or elongation to failure. The measured elastic modulus values will be compared to nanoindentation and ultrasonic measurements as well as calculated modulus based on pole figures.

Authors : Micha Calvo, Ralph Spolenak
Affiliations : Laboratory of Nanometallurgy Department of Materials ETH Zurich

Resume : At small scales, materials often exhibit unique behavior. These size effects, often summarized as “smaller is stronger”, have been extensively studied during the last two decades using various methods such as nano-indentation, synchrotron based x-ray diffraction, wafer-curvature, micropillar compression, bulge testing, cantilever bending, nanowire tensile experiments, and recently also by reflectance anisotropy spectroscopy (RAS). Most of these methods have issues with the characterization of ultra-thin polycrystalline films with thicknesses below 50 nm. Nevertheless, these ultra-thin films are widely used in industry as reflection- or diffusion-barriers. Therefore, the importance of understanding their mechanical properties, to avoid failures in service, is expected to increase with the rise of flexible electronics. RAS operates by probing the dielectric function in two orthogonal directions, and this makes it highly sensitive small changes in lattice spacing or elastic strain. Unlike Raman spectroscopy, RAS is not limited to any particular materials class, so nearly any continuous film can be investigated if the material has an electronic transition within the detection range: 1.5 - 5.5 eV. In this work, we demonstrate how to qualitatively and reliably test ultra-thin films on flexible substrates in uniaxial tension in-situ with RAS on film thicknesses below 50 nm. This allowed a new size effect study on Gold polycrystalline films with sizes down to 20 nm.

16:00 Coffee break    
In situ TEM investigations : H. Idrissi
Authors : Eita Tochigi*, Takaaki Sato, Naoya Shibata, Hiroyuki Fujita, Yuichi Ikuhara
Affiliations : The University of Tokyo; Pennsylvania University; The University of Tokyo, Tokyo City University; The University of Tokyo

Resume : Deformation and fracture of crystalline materials are essentially originated from atomic structure changes. Therefore, to understand deformation and fracture mechanisms, it is important to gain knowledge based on experimental observations in atomic level. In situ transmission electron microscopy (TEM) mechanical testing is useful to examine microstructural evolution of crystalline materials upon loading. However, there have been still challenges to perform in situ TEM mechanical testing at the atomic resolution because of some technical difficulties. In particular, development of a miniaturized mechanical actuator with subnanometer stability is indispensable. Using microelectromechanical systems (MEMS) technology, we developed a mechanical testing device with electrostatic actuators, which is compatible with a double-tilt biasing TEM holder. The performance of the MEMS device was evaluated in an aberration-corrected scanning TEM (STEM), and it was confirmed that the MEMS device has good stability to acquire atomic-resolution images during loading. Using this system, in situ loading experiments for several crystalline materials were performed. In the presentation, we will demonstrate atomic structure evolution of crystalline materials upon loading and discuss their local deformation and fracture phenomena.

Authors : Patrick Cordier1,2, Vahid Samaee3, Thomas van der Werf3,4, Gunnar Lumbeeck3, Thomas Pardoen4, Dominique Schryvers3, Hosni Idrissi3,4
Affiliations : 1Univ. Lille, CNRS, INRAE, ENSCL, UMR 8207 - UMET - Unité Matériaux et Transformations, F-59000 Lille, France; 2 Institut Universitaire de France, 1 rue Descartes, F-75005 Paris, France; 3 Electron Microscopy for Materials Science, University of Antwerp, Antwerp, Belgium; 4 Institute of Mechanics, Materials and Civil Engineering, Université Catholique de Louvain, Louvain-la-Neuve, Belgium

Resume : It is now recognized that large earthquakes are preceded and followed by a wide range of events, e.g. bursts of low-frequency earthquakes (LFEs), tremors, which can release as much strain as megathrust earthquakes. These events are related to creeping parts of the fault interface for which some recent models have inferred the possibility of viscosities of the order of some 1017 Pa.s. However, the detailed mechanisms associated with these events are poorly known. In this study we adopt the mineral physics point of view and address the issue of the mechanical properties of antigorite which, among serpentines, is an important component of fault rheology. Given its particular crystal structure and its complex microstructure, the rheology of antigorite is still poorly understood. Standard ductile processes involving dislocation glide have been reported, but other mechanisms like kinking, delamination, which can lead to a semi-brittle behaviour are likely to contribute as well. Consequently, the type of rheological law that is adapted to this mineral is still a matter of debate. Recently, the development of a new generation of advanced instruments for quantitative in situ TEM nanomechanical testing has open a new field of investigation of mechanical properties in the transmission electron microscope (TEM). The major advantage of this technique is to provide a direct, visual access, to the deformation mechanisms as they operate. In the present work, it will be demonstrated that a step forward in the investigation of the plasticity mechanisms of antigorite can be made by using original sample preparation methods. Small beams (410.1 µm3) of antigorite are prepared by Focused Ion Beam and deformed in tension in the TEM. Cyclic deformation is applied in the load control mode using the PI-95 TEM picoindenter holder and the Push-to-Pull (PTP) device (Bruker.Inc). Automated crystal orientation mapping in TEM (ACOM-TEM) was used prior to the in situ TEM tests in order to obtain statistical information regarding the local orientation of the grains and the nature of the interfaces. Despite applied stresses close to 1 GPa, no dislocation activity could be observed. In contrast, significant plasticity, largely recoverable, resulted from the development of damage at interfaces. We propose that due to the crystal structure of antigorite, the interfaces represent a key factor in controlling its mechanical properties.

Authors : Vahid Samaee 1, Patrick Cordier 2 3, Gunnar Lumbeeck 1, Ralf Dohmen 4, Nick Schryvers 1, Hosni Idrissi 1 2,
Affiliations : 1- Electron Microscopy for Materials Science, University of Antwerp, Antwerp, Belgium; 2- Univ. Lille, CNRS, INRA, ENSCL, UMR 8207 - UMET - Unité Matériaux et Transformations, F-59000 Lille, France; 3- Institut Universitaire de France, 1 rue Descartes, F-75005 Paris, France; 4- Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, 44801 Bochum, Germany; 5- Institute of Mechanics, Materials and Civil Engineering, Université Catholique de Louvain, Louvain-la-Neuve, Belgium;

Resume : Olivine is a silicate with orthorhombic symmetry and (Mg, Fe)2SiO4 composition which is the dominant phase of the Earth’s mantle down to 410 km depth. There are evidence that in the convective mantle, olivine deformation involves dislocation glide and climb. However, due to low symmetry, this mineral does not possess enough slip systems to satisfy the Von Mises criterion. Several recent studies have focused on the possible contribution of grain boundaries (sliding, migration) to the deformation of olivine aggregates, but so far, the mechanisms at play are not clarified. The deformation of ultra-fine grains materials represents an opportunity to enhance grain boundary sliding (GBS) and in-situ nanomechanical testing in the transmission electron microscope (TEM) provides further opportunity to gain information on the acting mechanisms. In this study, we use the PI-95 TEM Picoindenter holder and the Push-to-Pull (PTP) device (Bruker.Inc) to perform quantitative in-situ tensile tests in the TEM. To carry on this study, olivine aggregates with very small grains are needed that are not available in nature. Here we start from amorphous thin films of Mg2SiO4 forsterite (the Mg-rich end member of the olivine solid solution) deposited by Pulsed laser deposition (PLD). First, small beams from this amorphous film ware heated in-situ in the TEM to crystallize olivine. Heating up to 900°C induces crystallization of the thin films with a final grain size of the order of 100 nm. These recrystallized beams were used to prepare the final nanotensile test specimens. We present the results of the tensile tests performed on these specimens with a special attention to the grain boundary activity.

Authors : Andrey Orekhov1,2, Matteo Ghidelli3,4, Armand Béché2, Magnus Nord2, Johan Verbeeck2, Jean-Pierre Raskin5, Dominique Schryvers2, Thomas Pardoen1, Hosni Idrissi1,2
Affiliations : 1 Institute of Mechanics, Materials and Civil Engineering, UCLouvain, B-1348, Louvain-la-Neuve, Belgium. 2 EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium 3 Micro- and Nanostructured Materials Laboratory, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, MI, Italy 4 Structure and Nano/-Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-straße 1, 40237 Düsseldorf, Germany 5 Institute of information and communication technologies, electronics and applied mathematics, ICTEAM, Université catholique de Louvain, B-1348, Louvain-la-Neuve, Belgium.

Resume : Bulk metallic glasses (BMGs) exhibit some outstanding mechanical properties involving high fracture strength, and high elastic strain arising from the liquid-like atomic structure with no grain boundaries, dislocations, and phase segregations, contrary to crystalline materials. Recent reports have shown that thin film metallic glasses (TFMGs) are even more promising due to their mechanical properties with a unique combination of high strength (close to the theoretical limit) and ductility (> 10%). However, despite extensive research over recent years, the origin of the mechanical size effect in TMGFs is not fully unravelled yet and it can result either from geometric confinement or from a change of atomic arrangement in the films. In the present work, the fundamental mechanisms controlling the plastic deformation are investigated in Zr50Cu50 (%at.) TMGFs deposited by Pulsed Laser Deposition (PLD). The microstructure of the films is analysed using advanced TEM techniques including spatially resolved fluctuation electron microscopy (FEM) combined with state-of-the-art aberration corrected imaging and spectroscopy techniques. The deformation mechanisms are analysed by combining FEM and quantitative in-situ nanotensile testing using the Bruker PI 95 TEM PicoIndenter. The results reveal that the films exhibit a well-controlled nanoscale density/chemical heterogeneities and a very promising yield strength (~3 GPa) and ductility (>9%) product which depends on the nano-porosity content, with large/low plasticity and low/high yield strength obtained for nanoporous/compact metallic glass films.

18:30 AWARD CEREMONY followed by SOCIAL EVENT    
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09:45 Coffee break    
Small-scale fatigue : M. Cordill
Authors : O. Castelnau*, V. Jacquemain, D. Vinci, N. Ranc, T. Ors, V. Michel, V. Favier, D. Thiaudière, C. Mocuta
Affiliations : Laboratoire PIMM, Arts et Métiers ParisTech, 151 Bd de l?Hopital, 75013 Paris, France Synchrotron Soleil, L'Orme des Merisiers, 91190 Saint-Aubin, France

Resume : We investigate the fatigue behaviour of metallic alloys when submitted to a very high number of fatigue cycles (VHCF), typically above one billion. This corresponds to many industrial applications in which rupture is observed although the specimens are submitted to stresses well below the yield stress. A new in situ method based on time-resolved X-ray diffraction is proposed to measure the elastic strain evolution during ultrasonic fatigue experiments operating at 20kHz. Pure Cu and perlitic steel are chosen as illustrative materials. The ultrasonic fatigue machine was mounted on the diffractometer of the DiffAbs beamline at synchrotron SOLEIL. A 2d hybrid pixel X-ray detector (XPAD3.2) was triggered by the strain gage signal in a synchronous data acquisition scheme (pump?probe). The method enables achieving a temporal resolution of 1 microsecond. From the diffraction patterns, the position of the peaks, their shifts and their respective broadening can be deduced during the 50 microseconds loading cycles. The diffraction peak shift allows to estimate the lattice strain with a resolution of ~10-5. The associated effective stress is calculated using an adapted homogenization scheme. The amplitudes of the cyclic stresses are found to vary linearly with respect to the displacement applied by the ultrasonic machine. Moreover, the experimental results highlight an increase of the diffraction peak broadening with the number of applied cycles.

Authors : Hu Zhao, Chongguang Liu, Alex Eggeman, Brian Derby,
Affiliations : Hu Zhao, University of Manchester; Chongguang Liu, University of Manchester; Alex Eggeman, University of Manchester; Brian Derby, University of Manchester;

Resume : Ag nanowires (NWs) have applications in flexible electronics because of their excellent electrical and optical properties. The polyol process used to fabricate Ag NWs leads to a distinctive penta-twinned structure containing five {111} twin planes sharing a common axis along [110]. Here we study the mechanical performances of these wires through TEM analysis of individual NWs after cyclic deformation. This is achieved by spraying Ag NWs onto 3mm porous polycarbonate disks covered by an electron transparent collodion thin film, selected fibres suspended over pores in the disks can be identified for repeated TEM study after deformation. The disks are repeatedly cycled from 0 – 8% tensile strain and individual NWs are selected and characterized before and after fatigue tests. A bamboo defect structure, defined as repeated narrow regions of contrast difference across the diameter of the penta-twinned Ag wires that repeat along a wire at distances significantly greater than the wire diameter, is observed under TEM observation. An increase in density of bamboo defects in the Ag NW networks is observed after increasing numbers of fatigue cycles. Further characterization using precession assisted scanning nanobeam electron diffraction (NBED) suggests that the bamboo structure is caused by crystal rotation in the penta-twinned NWs around the [110] growth direction. We propose that the torque that generates rotation is induced by the presence of NW/NW joints within the network allowing circumferential loading of individual NWs when the network is in global tension. Fewer bamboo structures are observed after fatigue when examining lower density NW networks, supporting the network joint hypothesis.

Authors : Chongguang Liu, Brian Derby, William Sampson
Affiliations : The University of Manchester; The University of Manchester; The University of Manchester

Resume : Fatigue and Electrical Resistance of Silver Nanowire Networks Transparent conductive thin films (TCF) are widely used in electrical devices, especially for organic light-emitting diodes (OLED), screens & displays, solar cells and touch panels. TCFs must have low sheet resistance and high light transmittance. Generally, the materials used to make TCFs should behave low sheet resistance and high light transparency, typically the sheet resistance, Rs, should be ≤ 100 Ω/m2 with optical transmittance, T ≥ 90 % . Currently, indium tin oxide (ITO) films are the industry standard for TCF applications. ITO thin films show good electrical conductivity, high light transparency and good chemical stability, hence they have been used successfully for over 60 years in TCFs. However, the drawbacks of ITO, such as its brittleness and finite supply of In, have encouraged the exploration of new materials and methods to replace ITO and to extend TCFs to applications in bendable and stretchable electronics. Potential replacements include conductive polymers, carbon nanotubes, metallic grids, graphene, and metallic nanowires. Silver nanowire networks (AgNW) can show lower sheet resistance with higher light transmittance than ITO thin films; they also display a much greater strain to failure and greater resistance to mechanical damage. This project investigates the optoelectric properties and flexibility of AgNW networks with the objective of developing a fuller understanding of their behaviour, damage mechanisms and how these can be developed into predictive models for their properties and lifetime. Silver nanowires have been deposited onto flexible polymer substrates by spray coating to form a continuous stochastic network. Post-spraying treatment of either a low temperature anneal or a normal pressure is used to improve wire-wire electrical contact and reduce the network sheet resistance while maintaining optical transparency. The structural integrity of the film under flexible electronics service conditions has been assessed through repeated bending tests in a high cycle fatigue environment. At a specific bending cycles, the results showed a linear relationship between the square root of the sheet resistance and the inverse of the areal coverage of the network. Under cyclic bending fatigue testing, the gradient of this linear relationship which can be determined as the network resistance RN increases and is related to the number of strain cycles. According to the results, the increase of sheet resistance of networks is mainly caused by the loss of nanowire-nanowire junctions rather than a change of individual nanowires, which is further proved by SEM analysis. Keywords: Silver nanowire networks, transparent conductive films, flexible and stretchable electronics, bending fatigue.

Authors : Sebastian Krauß, Mathias Göken, Benoit Merle
Affiliations : Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Materials Science & Engineering I, Martensstr. 5, 91058 Erlangen

Resume : Microscale experiments enable to isolate microstructural contributions to the global mechanical deformation behavior of a sample. By structuring micropillars at specific regions of interest of a sample, the quasi-static and fatigue behavior of these microstructural features can be analyzed independently. Local fatigue tests were carried out on a bimodal copper sample containing alternating layers of ultrafine and coarse grainsize. Micropillars are fabricated in the plain coarse domain, ultrafine domain and in the interface region. In quasi-static compression, the bimodal micropillars show a 12 % increased strength (at 1 % plastic strain) compared to the ultrafine grained micropillars, revealing the pronounced hardening effect of the bimodal interface. In fatigue testing, the bimodal micropillars show a reduced lifetime compared to the ultrafine grained micropillars. This reduced fatigue lifetime likely originates from extrusions forming in the coarse grained area of the micropillar. In addition, the ultrafine grained part experiences cyclic softening by microstructural coarsening. The cyclic deformation mechanisms will be discussed based on Focused Ion Beam (FIB) cross-sections of the tested micropillars.

11:50 Poster awards session N    
12:00 Lunch break    
Extreme environments and nuclear materials : A. Ruiz-Moreno
Authors : Peter Hosemann*, H. Vo, D. Frazer, A. Dong, S.A. Maloy, A. Aitkaliyeva
Affiliations : University of California Berkeley, Los Alamos National Laboratory, Lawrence Berkeley national Laboratory, University of Florida

Resume : Extracting mechanical property values from small sample volumes has tremendous benefits for nuclear materials evaluations. Reducing materials hazardous levels by reducing the sample volume, making ion beam irradiations accessible to mechanical properties or simply sample regions of specific interest are features one can take advantage of if SSMT is deployed. However, the values measured at small length scales are not the same as values measured at large length scales. Fundamental material science and some knowledge on the materials microstructure must be deployed to understand this translation between the scales. Further new infrastructure and technology today allows for a more rapid sample manufacturing allowing to probe the multiple length scales fast and efficient. This presentation will outline the scientific reasons for scaling effects associated with different testing techniques as well as mitigation strategies specifically for irradiated materials so one can quantify property changes at multiple length scales. Nanoindentation, micro-compression, micro-tensile and micro-bending on ion beam irradiated materials as well as neutron irradiated materials are presented while femto-second laser ablation based techniques for radioactive sample manufacturing is introduced.

Authors : Peter Hähner (1), Lyubomira Veleva (1), Hygreeva Namburi (2), Dmitry Terentyev (3), Ana Ruiz Moreno (1)
Affiliations : (1) European Commission, Joint Research Centre, Nuclear Safety and Security, Westerduinweg 3, 1755 LE Petten, The Netherlands (2) CVR Research Centre Řež, Hlavní 130, 250 68 Husinec-Řež, Czech Republic (3) SCK•CEN, Nuclear Materials Science Institute, Boeretang 200, 2400 Mol, Belgium

Resume : The ability to predict tensile properties from nanoindentation tests is critically important, whenever material availability is too restrictive for tensile testing, for instance when material properties of interest are affected at a shallow surface layer by ion irradiation. This work reports results from quasi-static nanoindentation measurements of pure iron at room temperature, following tensile pre-straining to 15 % strain at ambient and elevated (125°C and 300°C) temperatures, to extract hardness and elastic modulus as functions of indentation depth and their dependence on the prior work hardening in tension. As evidenced by atomic force microscopy, the material exhibited increased disposition for pile-up formation following pre-straining affecting the mechanical properties of the material. When the nanoindentation data were compared with bulk properties from tensile tests performed at room temperature, with and without pre-straining, a significant and systematic mismatch between nano-hardness and tensile test results was observed. This discrepancy could be reconciled by an elastic modulus correction procedure, to compensate for the varying propensity for pile-up formation. It was concluded that strain hardening behaviour and nanoindentation hardness results have to be assessed in relation to the dynamic strain ageing (DSA) behaviour of the material during pre-deformation at intermediate temperature, as DSA impacts the strain hardening rate via dynamic recovery.

Authors : Rohit Sharma, Nigel M. Jennett, Vit Janik, Chris D. Hardie, Alexandra J. Cackett
Affiliations : Rohit Sharma; Nigel M.Jennett; Vit Janik - Research Institute for Future Transport and Cities, Coventry University, Coventry, West Midlands, CV1 5FB, UK; Chris D. Hardie; Alexandra J. Cackett - UK Atomic Energy Authority, Culham Science Centre, Oxfordshire OX14 3DB, UK

Resume : Nuclear energy is the second largest low-carbon energy source contributing >10% of global electricity. Structural health monitoring of nuclear plant is essential for safety. Currently, surveillance samples are placed in the reactor and destructively tested periodically to monitor the effects of radiation damage. This is costly (samples are radioactive) and limits plant life extension as sample supply is fixed at reactor startup. A smaller-scale test would improve safety by reducing sample radioactivity/waste and increasing surveillance frequency and/or number of locations. Instrumented indentation testing (IIT) is a quasi non-destructive test method able to obtain Hardness (H), Modulus (E), and constitutive property (σ - ε) data from a very small volume of material. However, H and σ vs. ε properties are fundamentally length-scale dependent, requiring a size effect (SE) algorithm to translate properties reliably from small to large (plant) length-scale. We ratio key parameters in the Hou and Jennett (2012) SE algorithm to quantify the relationship (not currently possible by direct measurement) between plastic zone size and dislocation interaction distance in IIT spherical indentation data (Cu single crystal) from the EMPIR Strength-ABLE project. We show the plastic zone size of (same ε) indents increases faster with ε for larger radius spherical indenters, but dislocation interaction distance stays constant - indicating that the method is quantifying the material damage state.

Authors : M. Vanazzi1,2, M. Cabrioli1,2, B. Paladino1,2, E. Frankberg1 and F. Di Fonzo1
Affiliations : 1Center for Nano Science and Technology - CNST@PoliMi, Istituto Italiano di Tecnologia, 20133 Milan (MI), Italy. 2 Dipartimento di Energia, Politecnico di Milano, 20133 Milano (MI), Italy.

Resume : We recently demonstrated (E. Frankberg et al. Science, 2019) that defect-free amorphous alumina exhibits an elastoplastic response under both tensile and compressive in situ TEM tests at room temperature. A yield stress as high as 4 GPa (tensile and compressive) has been measured, with a plastic deformation as high as 7% in tension and 100% in compression. The experimental and theoretical work performed so far portraits a scenario in which three conditions seem to be necessary for ductility in amorphous oxides: structural homogeneity; high mass/atomic density; absence of defects down to the nm range; bonds flexible enough to undergo changes in coordination number as well as of neighbour. Preliminary SEM in situ micromechanical tests suggest that this elastoplastic behaviour is maintained even for volumes of several microns cube. These materials, in the form of coatings on structural steels, are key for next generation nuclear systems like liquid metal cooled fast reactors and magnetically confined nuclear fusion. Al2O3 and Y2O3 on AISI316, 1515-Ti and EUROFER-97, has been tested as anti-corrosion, radiation-resistant and insulating tritium permeation barriers. In particular, the compatibility in Pb and Pb-Li has been proven up to 10,000 hours. The tritium permeation reduction of these films is in the order of 104-105, well above the DEMO design requirements. To conclude, amorphous alumina coatings are promising candidates to face the major issues related to future nuclear technologies, potentially enabling the design of innovative and economically attractive power plants.

Authors : Pooyan Changizian, Zhongwen Yao, Mark R. Daymond, Malcolm Griffiths, Steven Xu
Affiliations : Department of Mechanical and Materials Engineering, Queen's University, Kingston, Ontarion Canada; Department of Mechanical and Materials Engineering, Queen's University, Kingston, Ontarion Canada; Department of Mechanical and Materials Engineering, Queen's University, Kingston, Ontarion Canada; Department of Mechanical and Materials Engineering, Queen's University, Kingston, Ontarion Canada; Kinectrics Inc, Ontario, Toronto

Resume : X-750 Ni-based superalloy which is used as spacer material in the fuel channels of the CANada Deuterium Uranium (CANDU) reactor exhibits significant embrittlement after service due to neutron radiation damage effects. In this study an accelerated ion irradiation (Helium and Proton) was employed to simulate the after-service microstructure, coupling with advanced microstructural characterization methods to investigate the deformation, crack initiation\propagation and fracture mechanisms in X-750 superalloy. Small-specimen tensile tests have been carried out and indicate significant ductility reduction for He-implanted material compared to non-irradiated X-750. Also, fracture mode changed from the dimpled-ductile to the brittle fracture after He implantation. Cross-sectional TEM via focused ion beam (FIB) lift-out technique on the fracture surface was employed to trace initiated cracks for understanding the failure mechanisms after irradiation. Grain boundary cracks form preferentially at the interface of chromium carbide particles and propagate through shearing and coalescence of cavities decorate the grain boundary. Cracks also create within the grains that initiate at the interface of pre-existing nano-twins and matrix.

Authors : A. García-Junceda 1, L. Puricelli 2, W. de Weerd 1, P. Hähner 1, F. Rossi 1, A. Valsesia 2, F. Fumagalli 2, P. Colpo 2, A. Ruiz-Moreno 1
Affiliations : 1. European Commission, DG Joint Research Centre, Nuclear Safety and Security Directorate, Westerduinweg 3, 1755 LE Petten, The Netherlands. 2. European Commission, DF Joint Research Centre, Health, Consumers and Reference Materials, Via E. Fermi 2749, 21027, Ispra, VA, Italy.

Resume : The development of new approaches to mechanically test advanced materials at the micro-scale represents a breakthrough in the assessment of the performance of materials for specific cases, such as coated materials, biomaterials and irradiated metallic alloys. In the latter, the use of small-scale mechanical testing techniques requiring reduced volumes of irradiated material may imply the advantage of avoiding the use of hot cells for specimen manipulation and testing. This is particularly relevant for the long-term operation of existing nuclear power plants, as well as future fusion and fission reactors, in which some of the structural alloys need to withstand elevated irradiation doses. Therefore, materials degradation due to radiation damage need to be evaluated and understood. Advanced micromechanical testing usually requires microfabrication techniques for the preparation of the samples. This study proposes the development of novel in situ micromechanical tests based on the deformation of metallic membranes. The micro-samples are produced by high-energy ion sputtering of a ferritic-martensitic T91 steel. The optimization of the parameters for the preparation of the micro-membranes as well as first attempts to determine the mechanical properties by in-situ micro-punching tests are presented.

16:00 Coffee break    
Extreme mechanics : N/A
Authors : J.Rao, G.Dehm, M.J. Duarte
Affiliations : Max-Planck-Institut für Eisenforschung GmbH

Resume : Hydrogen embrittlement, often leading to catastrophic failure, has been widely studied. However, there is still a lack of fundamental understanding and controversy about its specific effects and interaction mechanisms in steels. The investigated single-phase ferritic Fe-Cr binary alloys have high hydrogen diffusivity and low solubility, therefore ideal for in-situ studies. Hydrogen is electrochemically introduced to the specimens by an in-situ nanoindentation set-up developed in-house, which enables collecting mechanical properties and simultaneously charging the sample with hydrogen from the backside. As the surface of the specimen stays intact, it is possible to characterize specific microstructural changes before and after hydrogen charging employing, e.g., transmission electron microscopy, electron channeling contrast imaging, electron backscatter diffraction. During hydrogen charging, the hardness of the alloys increases with increased applied voltage, corresponding to a higher amount of hydrogen charged into the material, while the elastic modulus remains constant. The pop-in load decreases with increased applied voltage, indicating a reduction of the shear stress necessary for dislocation nucleation. Larger variations of both properties with higher Cr concentrations are also observed. The cross-section underneath indentation imprints was examined by TEM to identify the microstructure variations before and after hydrogen charging within specific grain orientations.

Authors : high strain rates Manish Jain1*, R. Ramachandramoorthy1 Marko Knezevic 2, Nenad Velisavljevic3, Nathan A. Mara4, Irene J. Beyerlein5, Johann Michler1, Siddhartha Pathak6
Affiliations : 1 EMPA− Swiss Federal Laboratories for Materials Science and Technology, Thun, Switzerland 2 Mechanical Engineering, University of New Hampshire, Durham, NH 3 Argonne National Laboratory, Argonne, IL 4 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 5 Mechnical Engineering, University of California, Santa Barbara, CA 6 Chemical and Materials Engineering, University of Nevada, Reno, NV *speaker

Resume : We study the response of body centered cubic (bcc) Mg under extreme conditions of pressure, temperature and strain rate. Bcc Mg was stabilized at ambient pressures in a Mg/Nb multilayer nanocomposite where the adjacent Mg/Nb interfaces are spaced within a few nanometers. We investigated the structure of the hitherto-unknown bcc Mg phase in the Mg/Nb multilayer nanocomposite under high pressures in a diamond anvil cell experiment using synchrotron radiation x-ray diffraction (XRD). Additionally, we performed high temperature micro-pillar compression tests and strain rate jump tests on Mg (bcc)/Nb 5nm/5nm and Mg (hcp)/Nb 50nm/50nm nanolaminates to compare the responses of hcp vs. bcc Mg. Results from these tests were analyzed in terms of the measured activation energies and activation volumes from sub-micrometer sized Mg/Nb multilayer nanocomposites.

Authors : Benoit Merle, George M. Pharr,
Affiliations : Materials Science & Engineering 1, Friedrich-Alexander-University Erlangen-Nürnberg (FAU), Department of Materials Science & Engineering, Texas A&M University

Resume : Constant strain rate nanoindentation is a popular method for accessing the local strength of complex materials. However, with currently available testing systems using continuous stiffness measurement (CSM), nanoindentation is so far limited to strain rates of ~0.1 /s, which precludes it from ballistic applications. Here, we show that the current limitation derives primarily from a plasticity issue related to the continuous stiffness measurements. In order to access higher deformation rates, the Oliver-Pharr evaluation method was modified, so as to avoid the need for a measurement of the contact stiffness. With this improvement, the experimental upper strain rate limit is mostly determined by the time constants of the hardware components and lies around 100 /s with most current commercial systems. References: [1] B. Merle, V. Maier-Kiener, G.M. Pharr. Influence of modulus-to-hardness ratio and harmonic parameters on continuous stiffness measurement during nanoindentation. (2017) Acta Materialia, 134, pp. 167-176. [2] 38. B. Merle, W.H. Higgins, G.M. Pharr. Extending the Range of Constant Strain Rate Nanoindentation Testing (2020) Journal of Materials Research, DOI: 10.1557/jmr.2019.408

Advanced applications : N/A
Authors : Andreas Varellas
Affiliations : Prof. Kornyshev Alexei; Prof. Bresme Fernando; Dr. Reddyhoff Tom

Resume : In recent years, there have been important applications envisioned that would require small-scale devices to be implemented. An example of such are microelectromechanical systems (MEMS) used as energy harvesters. A significant challenge in the realisation of such devices is finding novel ways of lubrication, due to the high friction and wear present. In this work, Room Temperature Ionic Liquids (RTILs) are proposed as a solution to this problem, due to their numerous tuneable properties. The vapour pressure of ionic liquids is also very low, thus almost no liquid is lost due to evaporation. Additionally, their ionic behaviour is a topic with major scope for enhancing or controlling the compound’s properties through applied electric fields. Finally, these liquids are also able to be characterised through molecular simulations. In order to explore the friction properties at the nanoscale of RTILs, a MEMS tribometer has been developed. This consists of a miniature thrust pad bearing interface, manufactured using semiconductor fabrication techniques. Furthermore, this experimental rig is to be modified to apply charge on the system. In this way, the charged behaviour of RTILs can be studied. Thanks to previous molecular simulation work done at Imperial, the experimental results can be compared and validated. Following the conclusions of this work, applications will be explored in the nanoscale lubrication properties for MEMS devices and energy harvesters.

Authors : Antje Dollmann (1,2), Christian Greiner(1,2)
Affiliations : 1 Institute for Applied Materials (IAM), Karlsruhe Institute of Technology (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany 2 KIT IAM-CMS MicroTribology Center (µTC), Strasse am Forum 5, 76131 Karlsruhe, Germany

Resume : Metallic materials exhibit microstructural changes in the near subsurface area under a tribological load. As the microstructure itself has a complex and dynamic interplay with the tribological properties, a deep, fundamental understanding of the microstructural evolution is mandatory. High entropy alloys (HEAs) have been considered as promising materials for tribological applications in terms of their high solid solution strengthening and corrosion resistance. Single stroke experiments have been carried out with the coarse-grained model HEA CoCrFeMnNi to learn about the first states of the microstructural evolution. This has been investigated by scanning transmission electronmicroscopy (STEM) and transmission Kikuchi diffraction (TKD). It was found that the resulting microstructure dependents strongly on the stress field, ranging from dislocation self-organization to twinning and even up to the formation of a nano-crystalline layer. The stress field has been varied by using different counter body materials as well as atmospheres, while keeping the normal load constant. As the tribological systems with the thickest deformation layers exhibit material transfer, adhesion is considered as an important factor. Furthermore, a special focus of the talk will be twin formation. So far, it is not known, if the normal or friction force or which kind of combination of these leads to twinning under tribological load; first insights will be presented.

Authors : Amélie FILLON*, Ying ZHOU, Thierry GLORIANT
Affiliations : University of Rennes, INSA Rennes, CNRS, ISCR-UMR 6226, F-35000 Rennes, FRANCE

Resume : The aim of this study is to investigate whether Titanium-based alloys fabricated as films can display superelastic behaviors as their ingot-metallurgy counterparts. Superelastic response originates from the mechanical instability of the beta phase leading to a reversible phase transformation and a remarkable strain recovery. There is little information on the possibility to deposit Ni-free superelastic beta-type Ti-based films through physical vapor deposition methods. Quaternary Ti-Zr-Nb-Sn alloy films were deposited on silicon substrates by magnetron sputtering at room temperature. The morphological, crystallographic and microstructural characteristics of the films were studied by scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Superelastic responses and mechanical properties of films were investigated by nanoindentation using both spherical and Berkovich indenters. Results showed that metastable beta phase of Ti alloy films was stabilized at room temperature during magnetron sputtering. Superelastic effect exists in our nanograined alloy films and can be probed at the local scale by nanoindentation during nanoscale deformations under complex loading conditions.


No abstract for this day

Symposium organizers
Ana Maria RUIZ MORENOEuropean Commission

DG Joint Research Centre, Nuclear Safety and Security Directorate, Westerduinweg 3 - 1755 LE Petten, The Netherlands

+31 224 565097
Benoit MERLE (Main)Friedrich-Alexander-University Erlangen-Nürnberg (FAU)

Materials Science & Engineering I, Martensstr. 5 / 3.OG – 91058 Erlangen, Germany

+49 9131 8570456
Hosni IDRISSIUniversité Catholique de Louvain

IMMC, Place Sainte Barbe 2, 1348 Louvain la Neuve, Belgium
Megan J. CORDILLErich Schmid Institute for Materials Science, Austrian Academy of Sciences

Jahnstrasse 12, Leoben 8700, Austria

+43 3842 804 102
Thomas W. CORNELIUSCNRS, IM2NP UMR 7334, Aix-Marseille Université

Faculté des Sciences, Campus St Jérome - Case 262, Avenue Escadrille Normandie Niemen, 13397 Marseille Cedex 20, France

+ 33 4 91 28 80 13