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Small scale mechanical behaviour of interfaces: bridging experimental and computational modelling methods

Recent advances in fabrication processes with precise control of microstructures down to the nanometer level catalyzed the emergence of new materials with extreme mechanical performances. This requires the development of advanced experimental characterization and computational methods for the prediction of material properties at small scales.


The overall objective of this symposium is to improve our understanding of the fundamental mechanisms controlling the mechanical properties involving the strength, ductility, fracture, creep and wear resistance at small scales in advanced inorganic 3D bulk and small dimension systems with microstructures dominated by interfaces. The core questions concern the competing deformation and failure mechanisms, involving grain, twin and phase boundaries processes, dislocations/interface interactions, diffusion, shear transformation zones and shear bands in metallic glasses, cavitation and fracture or local decohesion. Special attention will be paid to the importance of rate dependent behaviour and back stresses originating from the abundance of the interfaces, the stress/strain driven formation and mobility of these interfaces, their interactions with fracture mechanisms, and the resulting size effects. Investigations dedicated to new hybrid material systems combining crystalline and amorphous metals, oxides and graphene are also welcome. Of particular interest are enhancements of mechanical properties of such systems by proper tuning of internal/external dimensions and constituents. Advanced micro/nanocharacterization methods (ex-situ and in-situ TEM and SEM micro/nanomechanical testing, residual stress measurement, aberration corrected HR(S)TEM and EELS, automated orientation, phase and nanostrain mapping in SEM and TEM, etc) as well as simulation methods on the corresponding scales (ab-initio, DD, MD, etc) will be in the core of the present symposium in order to reveal the fundamental plasticity mechanisms, the competition or synergy between these mechanisms and their impact on the macroscopic property level.

Hot topics to be covered by the symposium:

  • Advances in processing and fabrication of nanostructured materials;
  • Nano- and microscale characterization of interfaces;
  • Contributions of interface glide and migration to deformation of nanoscale structures;
  • Fundamental aspects of dislocation-interface interactions;
  • Role of interfaces in rate dependent deformation and back stress;
  • Influence of interfaces on damage and fracture;
  • Intrinsic and extrinsic size effects on mechanical properties;
  • Advances in ex-situ and in-situ micro/nanomechanical testing;
  • Advances in numerical technical methods;
  • Bridging scales: from small scale mechanics to bulk behavior.

Invited speakers

  • Daniel Kiener (University of Leoben, Austria) 
  • Erdmann Spiecker, (University of Erlangen, Germany)
  • Frédéric Mompiou (University of Toulouse, France)
  • Rebecca Janisch (University of Bochum, Germany)
  • William Curtin (École polytechnique fédérale de Lausanne, Switzerland)

Scientific committee:

  • Peter Fratzl (Max Planck Institute, Germany)
  • Otmar Kolednik (Erich Schmid institute, Austria)  
  • Thomas Antretter (University of Leoben, Austria)
  • Pascal Jacques (Université catholique de Louvain, Belgium)
  • Dominique Schryvers (University of Antwerp, Belgium)​
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Session 1 : H. Idrissi
Authors : R. Fritz, D. Wimler, A. Leitner, V. Maier-Kiener, D. Kiener
Affiliations : Department Materials Physics, Montanuniversität Leoben, Leoben, Austria; Department Materials Physics, Montanuniversität Leoben, Leoben, Austria; Department Materials Physics, Montanuniversität Leoben, Leoben, Austria; Department of Physical Metallurgy and Materials Testing, Montanuniversität Leoben, Leoben, Austria; Department Materials Physics, Montanuniversität Leoben, Leoben, Austria

Resume : The interface influence on the thermally activated deformation behavior in bcc metals is addressed for a more fundamental understanding on the mechanisms that dominate plastic deformation. Therefore, scale-bridging experiments at variable strain rate and temperatures are performed on chromium and tungsten, encompassing uniaxial macroscopic compression tests in direct correlation to local in-situ SEM micro-compression experiments on taper-free pillars, as well as to advanced multiaxial nanoindentation testing. We assess the strain-rate sensitivity and activation volume and demonstrate that, independent of stress state, sample volume and surface fraction, a distinct temperature-dependent transition occurs from lattice resistant to interface dominated characteristics. Considering the fraction of grain boundaries in the sample volume, a simple model is provided towards a unified picture of the deformation of bcc samples.

Authors : In-Chul Choi, Christian Brandl, Ruth Schwaiger
Affiliations : Karlsruhe Institute of Technology, Institute for Applied Materials, Eggenstein-Leopoldshafen, Germany

Resume : High-temperature nanoindentation is a novel technique to characterize also the rate-dependent mechanical properties of free surface of materials, when the thermal drift is precisely controlled. Here high-temperature nanoindentation experiments have been performed on body-centered cubic (bcc) chromium, which is one of candidate materials for high-temperature application. Contrary to intuitive and well-known behavior of face-centered cubic metals, where the plastic deformation of materials becomes time-dependent at elevated temperature, the rate-sensitive deformation in bcc Cr is observed at room temperature and disappears at high temperature. These phenomena are closely related to the kink-pair nucleation-limited mobility of non-planar screw dislocations in bcc metals, which governs the slip and the plastic resistance. The signatures of the temperature- and rate-dependent plastic relaxation mechanisms (e.g., strain-rate, sensitivity, activation volume and activation energy) are discussed in context of the above-mentioned thermally-activated motion of screw dislocations. Additionally, the sensitivity on interstitial impurities (e.g. N) is studied and is consistent with solute-drag effects on the kink-drift below the Knee temperature superimposed on the thermally activated kink-pair nucleation.

Authors : T.W. Cornelius1, J. Shin1, 2, S. Labat1, F. Lauraux1, M.-I. Richard1,3, G. Richter4, D.S. Gianola2, O. Thomas1
Affiliations : 1Aix-Marseille Université, CNRS, IM2NP UMR 7334, 13397 Marseille Cedex 20, France; 2University of California, Santa Barbara, CA 93106-5050 CA, USA; 3European Synchrotron (ESRF), ID01 beamline, 38043 Grenoble Cedex 9, France; 4MPI for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany

Resume : In the recent past, the mechanical properties of low-dimensional materials have attracted enormous attention showing yield strengths that approach the ultimate limit of the respective material for defect free nanostructures [1, 2]. Despite numerous experimental and theoretical works the mechanical behavior and the onset of plasticity on the nanoscale such as the influence of surface stress on defect nucleation is still not fully understood. To shed additional light on this topic, in situ experimental setups are being designed for monitoring the evolution of the structures during mechanical deformation. So far, most in situ mechanical tests coupled with X-ray diffraction techniques concentrated on micrometer sized samples [3-6]. For in situ nano-mechanical tests, we coupled for the first time a MEMS based tensile testing stage with nanofocused coherent X-ray diffraction imaging (CDI) that gives access both to defects and to the displacement field in a specimen with a resolution of 1 pm [7]. By measuring several independent Bragg peaks, this technique enables 3D visualization of individual crystal defects as well as determination of the complete elastic tensor. Here, we will present in situ nano-mechanical studies on individual defect-scarce Au nanowires combining the MEMS based tensile testing stage and CDI. This work has been carried out thanks to the support of the A*MIDEX grant (ANR-11-IDEX-0001-02) funded by the French Government « Investissements d’Avenir » program. [1] B. Wu et al., Nature Materials 4 (2005) 525 [2] G. Richter et al., Nano Lett. 9 (2009) 3048 [3] C. Kirchlechner et al., Acta Materialia 60 (2012) 1252 [4] R. Maaß et al., Mater. Sci. Eng. A 524 (2009) 40 [5] Z. Ren et al., J. Synchrotron Radiation 21 (2014) 1128 – 1133 [6] C. Leclere et al., J. Appl. Crystal. 48 (2015) 291 – 296 [7] S. Labat et al., ACS Nano 9 (2015) 9210 - 9216

Authors : Julien Godet, Clarisse Furgeaud, Laurent Pizzagalli, Michael J. Demkowicz
Affiliations : Julien Godet, Pprime Institute – CNRS – University of Poitiers, FRANCE: Clarisse Furgeaud - Pprime Institute – CNRS – University of Poitiers, FRANCE: Laurent Pizzagalli, Pprime Institute – CNRS – University of Poitiers, FRANCE: Michael J. Demkowicz- Materials Science and Engineering, Texas A&M University, College Station, TX 77843, USA

Resume : In order to evaluate the role of a hard amorphous silicon (a-Si) shell on the deformation of a soft crystalline gold core, we have investigated the mechanical properties of the Au@a-Si core-shell nanowire (NW) by molecular dynamics simulations. We have first optimized an existing parametrization of the MEAM potential to better reproduce the mechanical properties of gold and silicon as well as the Au-Si interactions. The comparison of the tensile tests performed on pristine Au NW, a-Si shell and Au@a-Si core-shell NW reveals that the hard amorphous shell works against the growth of ledges left by localized plasticity. In consequence, the localized plasticity and the expansion of nano-twin are reduced. The confinement of the dislocations in the core due to the hard shell do not lead to an apparent hardening of the nanostructure. But a homogeneous plastic deformation of the core-shell nanowire is observed at almost a constant flow stress equal to the yield stress. This behavior is characteristic of an elastic-perfect plastic material.

10:15 Coffee break    
Session 2 : D. Kiener
Authors : Christian Brandl
Affiliations : Karlsruhe Institute of Technology (KIT) Institute for Applied Materials Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen, Germany email:

Resume : With decreasing dimensions of metals, the strength is increasing with decreasing dimensions can approach the theoretical strength limit – even down to a regime, where the strength is theoretically predicted to be flaw insensitive. Using atomic simulation, we investigate the effect of predefined flaws, i.e. notches, in intrinsic brittle Si nanowires and intrinsic ductile Au nanowires. The defect evolution, flow stresses and the strain hardening in the MD simulations of single crystal Au nanowires is compared to experimental studies, where gold nanowires were structured by He-ion beams with sub-50 nm diameter well-defined holes. The experimental microstructure after deformation - as seen by (high-resolution) transmission electron microscopy - suggests the formation of a nano-grained substructure at the failure location, which is also consistently observed in our MD simulation. The striking similarities between MD simulations and the experimental data are critically discussed and explained by strain hardening in a strength regime of theoretical shear strength in Au. More generally, the quantitative assessment of different models for dislocation nucleation at free surfaces points to contradicting predictions. Together with the observed flaw insensitivity the later analysis are discussed in context of thermally activated dislocation nucleation and grain boundary motion at high stresses to challenge our current notion of defect nucleation and mobility at the nanoscale.

Authors : O. Glushko, M. J. Cordill
Affiliations : Erich Schmid Instiute, Leoben, Austria; Montanuniversität Leoben, Austria

Resume : In this contribution the room-temperature grain coarsening induced by cyclic tensile strain in polymer-supported ultra-fine grained Au films with three different thicknesses (250 nm, 500 nm, and 1 µm) is investigated by means of a detailed electron backscatter diffraction analysis. All three sample types demonstrate an increase of the average grain size with the cycle number by up to one order of magnitude. The evolution of the microstructure with the cycle number can be described by two stages. During the first stage the grain coarsening occurs without any topological changes of the surface of the film. Within the second stage further grain coarsening is accompanied by grain rotation as well as by formation of slip bands, extrusions and cracks. By means of quasi in-situ EBSD characterization it will be demonstrated that the grain coarsening is isotropic and coarsened grains do not exhibit any specific crystallographic orientations or misorientations to the neighboring grains. A thermodynamic-based model where the driving force appears due to the difference in yield stresses between the grains with different sizes is shown to provide an adequate explanation of the experimental data.

Authors : Zhuocheng Xie, Jakob Renner, Aruna Prakash, Erik Bitzek
Affiliations : Friedrich-Alexander-Universität Erlangen-Nürnberg, Materials Science & Engineering, Institute I, Erlangen, Germany

Resume : Metallic nanowires (NWs) receive currently much attention due to their often superior mechanical properties compared to bulk materials. Similarly, nanotwinned metals have lately attracted a lot of interest because they combine high strength with high ductility, two properties which have been thought to be mutually exclusive. Recently, nanotwinned nanowires were reported, which could combine both strengthening mechanisms, namely surface dislocation nucleation controlled plasticity and hardening due to dislocation - twin interactions. Here, we report on molecular dynamics simulations of tensile tests on single and multi-twinned Au nanowires with <110> and <112> orientations. The interactions of partial dislocations nucleated at the surfaces with the twin boundaries parallel to the wire axis are analyzed in detail and the resulting deformation behavior is compared to recent experiments.

Authors : Srinivasan Mahendran, Philippe Carrez, Patrick Cordier
Affiliations : UMET, UMR-CNRS 8207, University of Lille, Villeneuve d’Ascq, 59655 France

Resume : Knowledge of the deformation mechanisms of Mg2SiO4 olivine is important for the understanding of flow in the Earth’s upper mantle. Plastic deformation of olivine has thus been the subject of numerous experimental studies highlighting the importance of dislocations of Burgers vector [100] and [001]. Recently, in situ TEM nanomechanical testing provided new information regarding the dependence of the critical resolved shear stress on temperature (Idrissi et al., 2016) for [001] dislocations. In this study, we focus on the dislocation core properties at the atomic scale by using a semi-empirical potential library with inclusion of coulombic interaction for ions and core-shell model description of oxygen ions. Our results demonstrate that [100] or [001] are characterized by different core structures which help to a better understanding of experimental data. In particular, we show that [100] screw dislocation exhibit a planar screw core spreading into (010) plane. By contrast, [001] dislocations show a non-planar stable narrow core, but also several high-energy transient planar cores. The occurrence of transient cores for [001] dislocations suggests that [001] glide may undergo a typical locking-unlocking mechanism. Idrissi, H., Bollinger, C., Boioli, F., Schryvers, D. and Cordier, P. 2016 Low-temperature plasticity of olivine revisited with in situ TEM nanomechanical testing Science Advances 2(3)

Authors : Witold Chrominski, Malgorzata Lewandowska
Affiliations : Faculty of Materials Science and Engineering, Warsaw University of Technology, Woloska 141, 02-507 Warsaw, Poland

Resume : Severe plastic deformation is frequently applied to reduce grain size in order to provide efficient strengthening effect. Microstructure obtained this way always feature heterogeneities related with the crystallographic texture, activation of different slip systems or heating during the process. Thus, it is reasonable to expect that plastic deformation mechanisms (at local scale) will be related with local microstructural characteristics like dislocation substructure, misorientation angle of grain boundaries. In this study pure aluminium was subjected to hydrostatic extrusion which produces double fiber texture with axes of <001> and <111> parallel to extrusion direction. Both orientations contain grains with different local characteristics of grain boundaries. Such samples were then compressed to evaluate mechanical properties. EBSD and TEM investigations in initial and post-mortem states were performed to evaluate micorstructural response on the external stress. Results indicate that texture did not changed but shape of grains did. Then, in-situ straining experiments were done to follow dislocation activities, which can be responsible for previously discovered microstructure changes after the bulk deformation. Results showed that depending on the grain orientation (and its substructure) different deformation mechanisms can be observed. In fine grains with a size of approx. 600 nm, boundary assisted mechanisms are preferred while in relatively big grains (size of about 1 µm) with dislocation substructure transgranular deformation dominates. These results were combined with simple estimation of strengthening mechanisms expected to occur in pure aluminium after severe plastic deformation. In summary it can be stated that aluminium with strong microstuctural heterogeneities can be treated as a complex in which different parts (grain types) provide strength or ductility depending on local structure

Authors : Aviral Vaid, Aruna Prakash, Julien Guénolé, Sandra Korte-Kerzel, Erik Bitzek
Affiliations : Aviral Vaid, Aruna Prakash, Julien Guénolé, Erik Bitzek: Materials Science and Engineering Institute I, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany Sandra Korte-Kerzel: Institut für Metallkunde und Metallphysik, RWTH Aachen, 52056 Aachen, Germany

Resume : Complex intermetallic phases play an important role in improving the mechanical properties of many alloys. Mg17Al12 is one of the most commonly occurring complex intermetallics in the Mg-Al alloy system. In the present work, the deformation behavior of Mg17Al12 and the Mg-Mg17Al12 system was studied using classical atomistic simulations. Several semi-empirical potentials for this system were investigated and a suitable modified embedded-atom method potential was chosen to develop a mechanistic understanding of the influence of crystallography and interfaces on deformation mechanisms. Dislocations in the complex intermetallic Mg17Al12 were studied by performing deformation tests using molecular dynamics simulations and by calculating the generalized stacking fault energy surface (or γ-surface). The results are compared to micromechanical testing. Additionally, the structure and the properties of the Mg-Mg17Al12 interface were studied for the experimentally observed Burgers crystallographic orientation relationship: (0001)Mg || (011)Mg17Al12 and [2-1-10]Mg || [1-11]Mg17Al12. Finally, the interaction of dislocations on the basal plane of Mg with the Mg17Al12 precipitate was studied and compared to experiments.

12:05 Lunch    
Session 3 : R. Janisch
Authors : F. Mompiou, N. Combe, M. Legros
Affiliations : CEMES-CNRS and Université de Toulouse

Resume : Grain boundaries have a large impact on the plastic accommodation processes. The GB mechanisms usually act in combination with intragranular mechanisms but in small grained metals new activated mechanisms can supplant classical dislocation mechanisms. Indeed in such materials, the absence of lattice dislocations and/or the increasing difficulty to nucleate them in the grain interior, impose the activation of GB based plasticity. This phenomena has been thoroughly studied in nanostructured metals in the last years, motivated by potential applications requiring exceptional specific strength for fuel/structural efficiency and in a large variety of microelectronics, coatings, MEMS, or stretchable device applications. However, many aspects have still to be unfolded first because of the inherent complexity of GB. Secondly, the impact of GB mechanisms at the microstructure scale is expected to be profound because they can induce grain growth and rotation. Thus the interplay between GB mechanisms and intragranular ones at a broader scale needs to be fully characterized. In this talk, i would like to show few results highlighting GB-based mechanisms studied in real time under stress in different sample types with submicronic grains. Observations were obtained at nanoscale by in-situ straining TEM experiments. I will show that GB can migrate under stress, leading to grain growth, in agreement to many previous observations. This can be explained by a mechanism called "Shear coupled GB migration". It can act in addition to GB sliding and grain rotation. In-situ observations, especially in well-defined bicrystals, revealed that these mechanisms can be explained by the motion of GB boundary dislocations. In parallel to in-situ observations, atomistic models in which the minimum energy path of the shear-coupled GB migration was computed. They confirmed this mechanism and allow to explore competition between different "modes" of coupling.

Authors : Zakaria EL OMARI, Sylvain QUEYREAU, Charlie KAHLOUN, Brigitte BACROIX
Affiliations : LSPM CNRS UPR 3407, Université Paris 13, Sorbonne-Paris-Cité, 93430 Villetaneuse, France

Resume : Grain boundaries (GB) have the capability to migrate in certain conditions of applied temperature and loading. The mobility M is often simply stated as v = MP where v is the velocity of GBs and P the driving force. Mobility is intimately related to the atomic structure of GBs. Molecular Dynamics (MD) technique has proven useful to estimate GB mobility thanks to a well-controlled application of motive forces in connection with the details of GB atomic structures. Recent MD simulations are capable of efficiently explore the 5D parametric space associated to GB geometry [1-3]. In this work, we employ MD to investigate the impact of the GB plane orientation on the migration of selected high angle GBs in Ni. We focus on close-to 40° <111> GBs that are considered to be highly mobile [4]. Interatomic interactions are described by an EAM potential [5]. We approximate 40° <111> GBs with two CSL type GBs: a ∑7 GB of 38.21° around <111> and a ∑103 40.34° <111>. PBC are applied in the GB plane. Periodicity is exactly ensured in the GB plane thanks to the use of CSL vectors to orient the simulation box [6]. Our simulations show that GB energy and mobility are strongly affected by the GB plane orientation. Simulations cover an extensive range of configurations in term of temperature, applied driving force and of mixed tilt-twist GBs including symmetrical and asymmetrical cases. Similarly to results obtained for GBs considered in [1], pure twist GBs are immobile. For a given misorientation, mobility of mixed tilt-twist GBs strongly correlates with the tilt component of the GB plane orientation. These results are interpreted in correlation with the observed elementary mechanisms at the origin of the GB migration. [1] D Olmsted et al., Acta Materialia, 57(13) [2] Bulatov et al. , 2014, Acta Materialia, 65 [3] A. D. Banadaki et al., 2015, Computational Materials Science, 112(2016) [4] RB Godiksen et al., 2007, Acta Mater, 55, 6383 [5] Foiles et al., 1986, Physical Review B, 33(12) [6] A. D. Banadaki et al., 2015, Journal of Applied Crystallography, 48

Authors : I. Braems
Affiliations : Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS, 2 rue de la Houssinière, BP 32229, 44322 Nantes cedex 3, France

Resume : By segregating at its grain boundaries, sulphur favors the embrittlement of a polycristalline nickel sample that is undergoing a tensile test. Atomic-scale computations performed on the well-documented S5(012) bicrystal related this to a strong decrease of both tensile and shear strengths [1, 2]. Yet NanoSIMS experiments on a polycrystalline sample showed that the S concentration varies strongly with the Grain Boundary (GB) type, so that clean coherent-twin GBs can coexist with fully segregated other GBs [3]. Consequently, not all interfaces are expected to participate in failure, so that the description of their interfacial properties (structure, configuration) as a function of S composition is out of experimental reach via classical techniques such as AES, and we aim at developing an atomic-scale approach for all GBs that would complete experimental observations. To understand this anisotropy-dependent segregation and determine which interfaces will participate in failure, we study the energetics of the segregation of S atoms and the energetics related to decohesion for 4 different GBs (S5(012), S5(013), S11(113) and the coherent-twin GB S3(111)) using both the ReaxFF potential [2] and DFT computations. This allows to define the prominent parameters of this anisotropic segregation and rule on the ability of the ReaxFF potential in describing segregated internal interfaces. This work has been supported by ANR 15 – CE30 – 0016 (GiBBS). 1] M. Yamaguchi, M. Shiga and H. Kaburaki, Science 307, 393-397 (2005). [2] H. P. Chen, R.K. Kalia, E. Kaxiras, G. Lu, A. Nakano, K.I. Nomura, A.C.T. Van Duin, P. Vashishta and Z. Yuan, Physical Review Letters 104, 155502 (2010). [3] F. Christien, C. Downing, K.L. Moore and C.R.M Grovenor, Surface and Interface Analysis 3, 377-387.

Authors : V.I. Razumovskiy*, S.V. Divinski**
Affiliations : * Materials Center Leoben Forschung GmbH, Roseggerstraße 12, A-8700 Leoben, Austria; ** Institute of Materials Physics, University of Münster, Wilhelm-Klemm-Str. 10, D-48149 Münster, Germany

Resume : This work is devoted to a combined theoretical and experimental (radiotracer measurements) investigations of impurity segregation to a sigma 5 grain boundary (GB) in Cu and its effect on the mechanical strength of the interface. Ag, Au, Se, Ge, Ni, Co and Bi have been chosen as solutes for the investigation. The segregation energies obtained by means of density functional theory (DFT) calculations and by evaluation of the radiotracer diffusion experiments will be compared and analyzed in detail. While Ag segregation at Cu sigma 5 grain boundary was measured experimentally for dilute limit and beyond it, segregation of Au, Se, Ge, Ni, Co and Bi at general high-angle grain boundaries was evaluated experimentally. A short overview of the state-of-the-art theoretical methods for the evaluation of the effective segregation energy from DFT calculations will be given and some aspects of the fundamental problems related to a direct comparison between 0K DFT and experimental results obtained at elevated/ambient temperatures will be discussed. In addition, we will present a theoretical analysis of the influence of the selected impurities on the mechanical strength of the GB in the framework of the Rice-Thompson-Wang theory.

Authors : Gunnar Lumbeeck (1), Behnam Amin-Ahmadi (1), Hosni Idrissi (1,2), Joris Proost (2), Dominique Schryvers (1)
Affiliations : (1) Electron Microscopy for Materials Science (EMAT), Department of Physics, University of Antwerp, Belgium; (2) Institute of Mechanics, Materials and Civil Engineering, Université catholique de Louvain, Belgium

Resume : Pd has been known as an enabling material for future hydrogen (H) technology like H purification and sensing applications. However, the mechanical stability and response to H pressure of Pd thin films is still insufficiently understood. It is already reported that in nanocrystalline (nc) Pd films, intrinsic or extrinsic stacking faults (SFs), Shockley partial loops and 9R phase are formed after hydriding to β-phase indicating a clear effect of H on the SF energy of Pd [1]. The stability of glissile intrinsic SF loops in nc Pd films after dehydriding was also attributed to the presence of large internal stress heterogeneities typical of nc materials. In the present research, the effect of these defects on the mechanical properties and corresponding nanoplasticity mechanisms is investigated. In-situ HR TEM nanomechanical testing was performed on a Pd film containing SFs and 9R phase (hydrided to β phase). The results show the shrinkage of the 9R phase, formation of nanotwins from partial dislocations and loss of twin boundary coherency. Furthermore, in-situ nanomechanical testing was combined with Automated Crystal Orientation Mapping TEM to gain an overall perspective on the grain growth, rotation and the behaviour of twinning/detwinning initiated by the tensile deformation. The observed mechanisms are in agreement with mechanical softening revealed by nanoindentation experiments performed on (de)hydrided Pd films. [1] B. Amin-Ahmadi et al. (2016), Acta Materialia, 111, 253-261.

15:30 Coffee break    
Session 4 : F. Mompiou
Authors : Rebecca Janisch
Affiliations : ICAMS, Ruhr-Universität Bochum, Germany

Resume : Interfaces in metallic micro- and nanostructures play a role during plastic deformation in many respects. Besides accomodating part of the plastic strain by means of grain boundary sliding and migration they can act as sources, sinks, or barriers for dislocations, as well as as crack nucleation sites. Especially in interface dominated microstructures such as lamellar TiAl, they thus can rule the overall mechanical behaviour. High resolution experimental methods exist to analyze the underlying atomistic processes. However, since these processes are not independent, often several of them occur at the same time. To isolate the intrinsic deformation mechanisms of grain boundaries we have carried out molecular statics and molecular dynamics simlations of bicrystal shear at different interfaces in Al and TiAl. Four distinct mechanisms could be identified, namely rigid grain sliding, grain boundary migration, coupled sliding and migration, and dislocation nucleation and emission. Depending on the loading direction different mechanisms can occur at one and the same grain boundary, i.e. there is a pronounced anisotropy in the interfacial shear behaviour. This anisotropy is suggested as the explanation for seemingly contradicting experimental results (e.g. [1],[2]). By varying the geometry and chemistry of the interfaces we could relate the observed mechanisms to structural features of the grain boundaries as well as physical properties of the material. The influence of external factors such as strain and temperature will be discussed in the presentation. [1] W.Marketz, F.Fischer, and H.Clemens, ``Deformation mechanism in TiAl intermetallics - experimental and modeling'', Int. J. Plasticity, vol. 19, pp. 281-321, 2003. [2] L.Hsiung and T.Nieh, ``Creep deformation of fully lamellar TiAl controlled by the viscous glide of interfacial dislocations'', Intermetallics, vol. 7, pp. 821-827, 1999.

Authors : Andriy Ostapovets, Jiří Buršík, Karel Krahula, Lubomír Král, Anna Serra
Affiliations : Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 61662 Brno, Czech Republic;Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 61662 Brno, Czech Republic;Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 61662 Brno, Czech Republic;Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Žižkova 22, 61662 Brno, Czech Republic;Universitat Politecnica de Catalunya, Jordi Girona 1-3, 08034 Barcelona, Spain

Resume : Twinning is important deformation mode in materials with hexagonal close packed structure. This kind of plastic deformation is naturally related to migration of twin boundaries. In the simplest case, the twin boundary coincides with the plane invariant to twinning shear. However, invariant plane condition cannot be satisfied for all boundaries of three-dimensional twin. Consequently, other types of twin boundaries are possible. For instance, basal-prismatic boundaries were observed for {1 0 -1 2} twins in magnesium. The double twinning represents another interesting case. The interfaces of double twinned regions can be different from interfaces of single twin. We will provide experimental observation and theoretical analysis of double extension twin boundaries in magnesium. We will also discuss possible mechanism of migration for such boundaries.

Authors : Maxime Mieszala(1), Gaylord Guillonneau(2), Madoka Hasegawa(1), Rejin Raghavan(3), Jeffrey M. Wheeler(4), Stefano Mischler(5), Johann Michler(1), Laetitia Philippe(1)
Affiliations : (1) Laboratory for Mechanics of Materials and Nanostructures, Empa - Materials Science and Technology, Switzerland ; (2) Université de Lyon, Ecole Centrale de Lyon, Laboratoire de Tribologie et Dynamique des Systèmes, UMR 5513 CNRS/ECL/ENISE, France ; (3) Max-Planck-Institut für Eisenforschung GmbH, Structure and Nano-/Micromechanics of Materials, Germany ; (4) Laboratory for Nanometallurgy, Department of Materials, ETH Zürich, Switzerland ; (5) Tribology and Interface Chemistry Group, EPFL, Ecole Polytechnique Fédérale de Lausanne, Switzerland

Resume : Grain boundary engineering by nanoscale twinning in fcc metals is an effective way to enhance the mechanical properties while preserving the electrical conductivity. In this presentation, the mechanical properties of electrodeposited copper films with nanoscale twins will be presented. Copper films with highly-oriented nanoscale twins were produced by electrodeposition. By controlling the deposition parameters, deposits with a preferred twin growth orientation, either horizontal or vertical, were achieved. Microcompression tests were conducted on micropillars fabricated by focused ion beam to measure the effect of the twin orientation. Results show an increase in strength with the addition of twins as compared to a coarse grained sample. The twin orientation causes a strong mechanical anisotropy between vertically and horizontally aligned twins (an increase in stress of 44% and 130% at 5% offset strain, respectively). A larger activation volume, derived from micropillar strain rate jump tests, is measured for horizontal twins compared to vertical twins. These observations will be discussed with regard to the preferred deformation mechanism as a function of the twin orientation. At last, the potential of combining grain boundary engineering with micro-architectured materials to develop high performance structural and functional materials is addressed.

Authors : Romuald Béjaud, Sandrine Brochard, Julien Durinck
Affiliations : INSTITUT P’ - UPR 3346 - University of Poitiers - CNRS - ISAE ENSMA

Resume : At the nano-scale, nanostructured materials can induce surprising mechanical properties when compared to bulk behaviour. Nanolayered or nanotwinned metals for example, are known to have ultra-high mechanical strength, thermal stability and radiation resistance. As the interface spacing decreases to the nanometer-scale the density of interfaces increases significantly and subsequently these properties become largely governed by the interface-defect interactions. Under a mechanical stress, the plastic response of these materials is generally controlled by the interfaces. As examples, some studies showed for bimetallic nanolamellar composites that interfaces can come into play for the nucleation of deformation twins leading to the increase of twinning activity (Han, W. Z. et al., Appl. Phys. Lett., 2012, 100), whereas others demonstrated that the interface structures have a key role in twin propagation (An, X. H. et al., Appl. Phys. Lett., 2015, 107). In this context, we chose to use atomistic simulations, which are particularly well suited to determine the elementary events involved in plastic deformation, in order to investigate how different interface types may influence twin propagation and thickening. Some particular crystallographic orientations have been considered in order to enable the most common interfaces observed in the Ag-Cu multilayered material and to promote the dislocation nucleation. The chosen orientations also allow the introduction of specific surface defects, which can act as dislocation sources under mechanical stress. Our study highlights the role of the interface structures for twin propagation and the role of misfit dislocations on twin thickening. We show in particular that depending on the interface structure, new twins can be nucleated via a mechanism implying Lomer dislocations. We also show for the first time the non negligible role played by misfit dislocations in the thickening of twins.

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Session 5 : M. Fivel
Authors : F. Maresca, W. A. Curtin
Affiliations : Laboratory for Multiscale Mechanics Modeling EPFL

Resume : In next-generation high-strength/high-toughness steels, the austenite/martensite (fcc/bcc) interface is the dominant microstructural feature controlling important properties. In spite of decades of research, the fundamental structure and mechanism of motion of this interface have remained uncertain. Here, an atomistic fcc-bcc iron interface is constructed that has a structure that completely matches experimental observations. The interface reveals a defect structure differing from longstanding theory assumptions and violating conditions believed essential for a glissile interface. Based on the atomistically-observed interface defect structure, we (i) revise the conditions for achieving a glissile interface, (ii) revise the crystallographic double-shear theory of lath martensites, and (iii) develop a mesoscale model for lath martensite plasticity that accounts for retained austenite. The new parameter-free theory provides predictions in near-perfect agreement with both simulations and experiments and thus allows for guided design of materials with larger fcc to bcc transformation strain and, hence, higher toughening. The mesoscale model demonstrates how the nanoscale insights translate into understanding of macroscopic plasticity in these interface-controlled steels. The adroit application of atomistic modeling tools thus expands the possibilities for design and control of mesoscale architecture in high-performance steels.

Authors : A. Sannikov*, T. Antretter**, M. Petersmann**
Affiliations : * Materials Center Leoben Forschung GmbH, Roseggerstrasse 12, 8700 Leoben, Austria; ** Institute of Mechanics, Montanuniversitaet Leoben, Franz-Josef Strasse 18, 8700 Leoben, Austria

Resume : Transformation induced plasticity is an essential feature of the class of martensitically transforming steels and its analysis is of great interest to material researchers as well as to industry. The commercial steel grade MarvalX12 - a maraging steel - has been chosen as a reference for characterizing the TRIP behavior. A meso-scale representative volume element (RVE) based on earlier work [1] has been set up and discretized where each element represents an initially austenitic domain that is subjected to martensitic transformation simulated by an instantaneous toggling of the element's properties. The evolution of the phase fraction rate, which is a function of temperature, stress and strain, determines the sequence of elements to be transformed. The transformation hardening relation determines the shape of the kinetics. The presented model is capable of reproducing the experimentally determined behavior of MarvalX12 for a certain range of loading cases including non-proportional loading paths. It can be used also to calibrate the macroscopic mean-field model developed in [1]. A closer look at a smaller scale is required to understand the material behavior within the austenitic grain just before martensitic transformation. To this end, another RVE has been developed on the micro-scale representing a sub-domain of a grain, where crystallographically different martensitic variants are nucleating and growing, thereby forming the block- and packet-structure, which can be observed using electron backscatter diffraction (EBSD). This model allows to investigate TRIP effects on the micro level, where the interaction of martensite variant formation with crystal plasticity comes into play.   [1] M. Fischlschweiger, G. Cailletaud and T. Antretter, International Journal of Plasticity, pp. 53-71, (2012)

Authors : Adrien Gola, Peter Gumbsch, Lars Pastewka
Affiliations : Karlsruhe Institute of Technology

Resume : We use a combination of atom-swap Monte-Carlo (MC) and molecular dynamics (MD) to study the equilibrium structure and mechanical properties of Cu(1-x)Ag(x)|Ni multilayers with 6nm layer width. We find that Cu|Ni multilayers form a semi-coherent interface with a network of partial dislocations arranged in a regular triangular pattern. Ag is then alloyed to the Cu layers in order to tune the lattice misfit in a controlled manner. A combination of MC and MD was used to equilibrate Cu(1-x)Ag(x)|Ni with x=0%, 5% and 10% towards their thermodynamic equilibrium. We find segregation of Ag within the Cu layers at 300K and 600K and alloying of Cu and Ni at 600K in good agreement with the experimental binary phase diagrams of the Cu-Ag and Cu-Ni systems. The resulting structures were then sheared parallel and perpendicular to the normal of the bilayer interface. We generally find initial sliding at the Cu|Ni interface within the misfit dislocation network, followed by emission of partial dislocations into the Cu layer, and finally an increase of flow stress with increasing Ag content. Additional calculations of biaxial tension that suppress sliding at the heterointerface show a similar trend. Hardening can be traced back to the formation of sessile stacking-fault tetrahedra whose density increases with the density of the interfacial misfit dislocation pattern that is controlled by the amount of Ag in the Cu layer.

Authors : Darjan Kozic, Ruth Konetschnik, Hans-Peter Gänser, Roland Brunner, Daniel Kiener, Thomas Antretter, Otmar Kolednik
Affiliations : Materials Center Leoben Forschung GmbH, Leoben, Austria; Department Materials Physics, Montanuniversität Leoben, Austria; Materials Center Leoben Forschung GmbH, Leoben, Austria; Materials Center Leoben Forschung GmbH, Leoben, Austria; Department Materials Physics, Montanuniversität Leoben, Austria; Institute of Mechanics, Montanuniversität Leoben, Austria; Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Austria

Resume : A microelectronic component incorporates a variety of materials with very different properties. Following the trend of ongoing miniaturization, single films of such components have typically a thickness between a few nanometers and a micrometer. It is an important fact that materials arranged in a stack or composite behave different to homogeneous materials. Reasons for this behavior are sharp interfaces between the materials and a non-uniform residual stress state, which arises during film deposition. It is clear that physically correct predictions about the reliability of such components are a very demanding task. In this work, we present an important step into this direction. We are investigating the influence of interfaces and locally resolved residual stresses on the crack driving force for a crack extending through stacks consisting of tungsten (W) and copper (Cu) layers deposited on a silicon (Si) wafer. To calculate the crack driving forces in the material systems, we use the concept of configurational forces. With this approach, we are able to determine the impact of each material inhomogeneity and of the residual stresses on the crack driving force. The analysis shows that there are critical positions in each stack where the crack driving force is high or low, i.e. where crack growth can occur at low or high loads, respectively. Certain stack arrangements are preferable to others. For example, the introduction of a 500 nm Cu-layer between two W-layers decreases the crack driving force and reduces the propensity to fracture, as well as compressive residual stresses in the W-layers. The presented procedure is very helpful for the design of future thin film microelectronic components with high reliability and damage tolerance.

10:15 Coffee break    
Session 6 : W. Curtin
Authors : Na-Ri Kang1, Young-Cheon Kim1, Hansol Jeon1, Seong Keun Kim2, Ju-Young Kim1
Affiliations : 1 School of Materials Science and Engineering, UNIST (Ulsan National Institute of Science and Technology), Ulsan 44919, Republic of Korea; 2 Center for Electronic Materials, KIST (Korea Institute of Science and Technology), Seoul 02792, Republic of Korea;

Resume : Nano-sized tubular structures have attracted considerable interest because they make possible the study of fundamental physical properties. In particular, the semiconductor zinc oxide (ZnO) has been widely studied due to its thermal stability, high mechanical strength and electron mobility, and wide application range. The high strength-to-weight ratio of interconnected tubular networks makes this a creative design strategy for reducing the linear decrease in strength and stiffness of low-density materials with increasing porosity. So we fabricate nanotubular ZnO with wall thickness of 45, 92, 123 nm using nanoporous gold (np-Au) with ligament diameter at necks of 1.43 μm as sacrificial template. Through micro-tensile and micro-compressive testing of nanotubular ZnO structures, we find that the exponent m in σ ̅∝ρ ̅^m, where σ ̅ is the relative strength and ρ ̅ is the relative density, for tension is 1.09 and for compression is 0.63. Both exponents are lower than the value of 1.5 in the Gibson-Ashby model that describes the relation between relative strength and relative density where the strength of constituent material is independent of external size, which indicates that strength of constituent ZnO increases as wall thickness decreases. We discuss that this wall-thickness-dependent strength of nanotubular ZnO is caused by strengthening of constituent ZnO by size reduction at the nanoscale or by the structure effect.

Authors : Yao Han, Zhipeng Xie
Affiliations : School of Materials Science and Engineering, Tsinghua University, Beijing, China

Resume : A novel oscillatory pressure-assisted sintering (OPS) process is reported to fabricate high-quality nanostructured ceramics. Compared with the nano-zirconia ceramics prepared by conventional pressureless sintering (PS) and hot-pressing (HP), the samples prepared by OPS process exhibited a higher density (99.9%), smaller grain size (120 nm), and more homogeneous microstructure. More remarkably, the OPS samples showing higher strength, hardness and elastic modulus compared with the samples prepared by other two techniques were obtained at relatively lower heating temperature and less holding time for 1300°C and 0.5 hour than other two techniques at 1450°C and 1 hour. The XRD patterns indicate that the samples with three preparation methods consist of single phase of tetragonal zirconia. The OPS samples were also analyzed by SEM, Raman and nanoindentation methods. In addition, the fracture model of OPS samples slightly changed from transgranular fracture to intergranular fracture. These results suggest that OPS is an effective technique for fabricating high-quality nanostructured zirconia ceramics with low heating temperature and less sintering time, which is beneficial to prolong working life of graphite molds and sintering devices, what’s more, it significantly reduces cost.

Authors : Erkka J. Frankberg 1), Lucile Joly-Pottuz 2), Francisco Garcia 3), Turkka Salminen 4), Janne Kalikka 5,6), Siddardha Koneti 2), Lucian Roiban 2), Thierry Douillard 2), Bérangère Le Saint 2), Jaakko Akola 5,6), Erkki Levänen 1), Fabio Di Fonzo 3), Karine Masenelli-Varlot 2)
Affiliations : 1) Laboratory of Materials Science, Tampere University of Technology, Korkeakoulunkatu 6, 33720 Tampere, Finland; 2) Univ. Lyon, INSA-Lyon, CNRS UMR 5510, MATEIS, 7 Avenue J. Capelle, 69621 Villeurbanne, France; 3) Center for Nano Science and Technology, Istituto Italiano di Tecnologia, Via G. Pascoli 70/3, 20133 (MI), Italia; 4) Optoelectronics Research Center, Tampere University of Technology, Korkeakoulunkatu 6, 33720 Tampere, Finland; 5) Department of Physics, Tampere University of Technology, P.O. Box 692, FI-33101 Tampere, Finland; 6) COMP Centre of Excellence, Department of Applied Physics, Aalto University, FI-00076 Aalto, Finland

Resume : Recent TEM in situ mechanical experiments on single alumina nanoparticles have shown unexpected plasticity in room temperature alumina [1, 2]. These results push the theoretical boundaries of ceramics mechanical ductility towards comparable levels with metals. The important questions for materials science now are: (i) whether the plastic behaviour can be transferred into polycrystalline, continuous material; (ii) what is the microstructure of such plastic material and (iii) what is the mechanism behind the hypothetical plasticity of the material. Relatively cheap and abundantly available engineering ceramic, such as alumina, with room temperature plasticity would be a breakthrough in the engineering ceramics field. We report the findings of room temperature plasticity on our model material, alumina thin films produced by pulsed laser deposition. Alumina produced this way has an exotic, nanocrystalline microstructure, and is a strong candidate for having the capability for room temperature plasticity. We show the latest results of our In situ TEM studies and atomistic simulations that are focused on analysing and explaining the material’s mechanical response (strain, dislocation activity, fracture etc.) to compression and indentation forces and look for evidence of the mechanism behind the mechanical response. [1] E. Calvié et al. Journal of European ceramic society, Vol. 32, No. 10, p. 2067-2071, 2012 [2] E. Calvié, et al. Materials Letters, Vol. 119, p. 107-110, 2014

Authors : Si-Hoon Kim1, Sang Yun Lee1, Myoung Hoon Song1, Eun-chae Jeon2 and Ju-Young Kim1
Affiliations : 1 School of Materials Science and Engineering, UNIST (Ulsan National Institute of Science and Technology), Ulsan 44919, Republic of Korea; 2 Department of Nanomanufacturing Technology, Korea Institute of Machinery and Materials, Daejeon 34103, Republic of Korea

Resume : Perovskite has been widely used as active material of light-emitting diode (LED) due to its advantage such as high luminous efficiency and low cost of production. Current research of perovskite focused on applied in deformable electronics since demand for flexible and stretchable electronics increases. Since LED consists of component materials of thin films, stress distribution varies depending on position from neutral axis. It is important to analyze critical bending radius by stress concentration point of component materials because fracture will occur at this point. In this work, flexibility of perovskite LEDs was evaluated by mechanical properties of component materials. Hole-indentation was performed on thin films suspended over circular hole to measure elastic properties of component materials. We conducted uniaxial tensile test in SEM for perovskite samples, the weakest material of perovskite LEDs, to measure accuracy tensile properties. Critical bending radius was analyzed using stress distribution analysis of multilayer during bending with mechanical properties of component materials.

Authors : A. Etiemble1,2, G.I. Nkou Bouala2, C. Lopes3,C. Langlois 2, B. Freitas3,4, M.S. Rodrigues3, J. Rethoré5, J.F. Pierson1, F. Vaz3,6, P. Steyer2
Affiliations : 1 Institut Jean Lamour (UMR CNRS 7198), Université de Lorraine, Parc de Saurupt, 54011 Nancy, France 2 Univ. Lyon, INSA-Lyon, MATEIS UMR CNRS 5510, 21 Avenue Jean Capelle, 69621, Villeurbanne cedex, France 3 Centro/Departamento de Física, Universidade do Minho, Campus de Gualtar, 4710 - 057 Braga, Portugal 4 Instituto Pedro Nunes, Laboratório de Ensaios, Desgaste e Materiais, Rua Pedro Nunes, 3030-199 Coimbra, Portugal 5 LaMCoS, INSA de Lyon, Villeurbanne, FRANCE 6 SEG-CEMUC, Mechanical Engineering Department, University of Coimbra, 3030-788 Coimbra, Portugal

Resume : Recent investigations in biomaterials showed the advantages in the use of polymeric substrates coated with thin films in order to functionalize the surface to provide conductive, biocompatible and/or antibacterial activity. Ti-Ag thin films display, for example, excellent biocompatibility and reveal great potential to be used as conductive materials for prosthesis pressure sensors [1]. On the other hand, Zr-Cu-Ag thin film metallic glasses could combine promising antibacterial activity and high durability to be used as coating of medical instruments to fight hospital acquired-infections [2]. In both cases, the film deformation on flexible substrate needs to be better understood to optimize the mechanical durability of the devices. In this study, microscale characterization of Ti-Ag and Zr-Cu-Ag thin films was followed in situ using a tailored micro-tensile test machine implanted into a SEM chamber. In addition, to quantify the local deformation, we proposed an original approach involving the Digital Image Correlation. Finally, the influence of the thin film composition and structure was investigated. [1] C. Lopes et al. TiAgx thin films for lower limb prosthesis pressure sensors: effect of composition and structural changes on the electrical and thermal response of the films. Appl Surf Sci 2013; 285: 10-8. [2] A. Etiemble et al., Innovative Zr-Cu-Ag thin film metallic glass deposited by PVD magnetron sputtering for antibacterial applications, J. Alloys and Comp. (2016), doi: 10.1016/j.jallcom.2016.12.259

Affiliations : INSTITUT P’ UPR 3346 CNRS Université de Poitiers ISAE-ENSMA

Resume : When a solid is immersed into a liquid solution, whatever their nature (dielectric or conductive), physicochemical phenomena lead to polarize a solid—liquid interface. Two zones with opposite sign of charge appear, one in the solid and the other in the liquid, forming thus the electric double layer (EDL). Various electrical and electrochemical methods have been combined in this work to determine the characteristics of the EDL at the interface between polycrystalline austenitic stainless steel 304L immersed in NaCl aqueous solution (0.01M, 0.1M and 1M). Its effective capacity Cdl was determined by both cyclic voltammetry (CV), for various electric fields and with different voltage scan speeds [1], and by electrochemical impedance spectroscopy (EIS) using an electrical equivalent circuit (EEC) [2]. Another electrical method by flow electrification allows to measure the space charge density ρw at the wall [3]. The results demonstrate that the double layer capacitance depends mainly on the concentration of the electrolyte and the applied potential and that the space charge density is also proportional to the concentration. The influence of the surface roughness (various preparations with SiC papers 240 or 800, or with diamond paste 0.25 µ) on the EDL was then studied by EIS and CV. It appeared that on a macroscopic scale, the roughness has a little influence on the capacity of the EDL at the 304L / NaCl (0.01M) interface. These results were discussed in regards with physical and chemical characterisations operated by XPS, MEB, AFM and WLI. Bibliography [1] Allen J. Bard, Electrochemical Methods. Fundamentals and Applications (1983) [2] G.J. Brug, A.L.G. van den Eeden, J. Electroanal. Chem 176, p275 (1984) [3] Thierry Paillat, Eric Moreau, Gérard Touchard, Journal of electrostatics 53, p171 (2001)

12:05 Lunch    
Session 7 : E. Bitzek
Authors : Erdmann Spiecker
Affiliations : Lehrstuhl für Mikro- und Nanostrukturforschung & Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander Universität Erlangen-Nürnberg, Cauerstr. 6, 91058 Erlangen, Germany

Resume : Modern electron microscopes provide an ideal platform for in situ mechanical testing and manipulation of materials at small length scales owing to high flexibility in realizing special sample geometries and loading scenarios without compromising microscope performance. This holds true for both, combined focused ion beam scanning electron microscopes (FIB-SEM) as well as transmission electron microscopes (TEM) with the former providing highest flexibility and the latter highest resolution. In this contribution we report on new approaches of in situ mechanical testing and manipulation in FIB-SEM and TEM that have been developed and applied to various materials systems within Erlangen's DFG Research Training Group GRK1896 “In situ Microscopy with Electrons, X-rays and Scanning Probes”. Examples include sliding friction experiments and defect manipulation in layered crystals and 2D materials, combined mechanical testing and 3D characterization of nanoporous metals as well as new preparation routines for in situ compression and tensile testing of glass structures. Wherever possible, modeling simulation aspects are also addressed.

Authors : Benoit Merle, Jan P. Liebig, Mirza Mackovic, Olivier Pierron, Gunther Richter, Erdmann Spiecker, Mathias Göken
Affiliations : Materials Science & Engineering 1, Friedrich-Alexander-University Erlangen-Nürnberg (FAU); Materials Science & Engineering 1, Friedrich-Alexander-University Erlangen-Nürnberg (FAU); Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander-University Erlangen-Nürnberg (FAU); G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology; Max Planck Institute for Intelligent Systems; Institute of Micro and Nanostructure Research, Friedrich-Alexander-University Erlangen-Nürnberg (FAU); Materials Science & Engineering 1, Friedrich-Alexander-University Erlangen-Nürnberg (FAU);

Resume : A novel method was developed for the preparation of thin film microtensile specimens. Unlike other techniques, it does not rely on expensive cleanroom photolithographic equipment, but it is based on a combination of focused ion beam (FIB) milling and electron-beam-assisted etching with xenon difluoride precursor gas. The new method furthermore ensures that the area of interest is never exposed to ion beam irradiation so that a pristine microstructure is preserved. This is achieved by using a special shadow milling geometry with a thin silicon membrane simultaneously serving as a substrate and protective layer for the thin film of interest. A further advantage of the new method is that it enables the target preparation and mechanical testing of individual microstructural defects. The method was applied to nanotwinned Cu-Al as well as Au thin films. The fabricated tensile specimens were mounted on a push-to-pull mechanical conversion device and subsequently tested in-situ in the transmission electron microscope (TEM). [1] Liebig, J. P., Göken, M., Richter, G., Mačković, M., Przybilla, T., Spiecker, E., Pierron, O.N., Merle, B.: A flexible method for the preparation of thin film samples for in situ TEM characterization combining shadow-FIB milling and electron-beam-assisted etching. Ultramicroscopy, 171:82-88 (2016).

Authors : Anton Davydok, Christina Krywka
Affiliations : Institute for Materials Research, Helmholtz-Zentrum Geesthacht, outstation at DESY, Notkestraße 85, 22607 Hamburg, Germany

Resume : The size dependent plastic behavior of micro and nano-scaled non-organic materials has attracted enormous interest during the last decade. When the object size becomes comparable to intrinsic length scales, finite-size and quantum size effects occur influencing the physical properties. For complete understanding of the deformation process in-situ experiments are necessary. X-ray nanodiffraction in combination with nanoindeter provides unique information on stress-strain response during mechanical testing with strain resolution of 10^-5. In this presentation the setup for in-situ experiments at the Nanofocus Endstation of P03 beamline (PETRA III, DESY) will be presented with technical characteristic and examples of successful experiments will be shown.

Authors : M.J. Cordill, A.A. Taylor
Affiliations : Erich Schmid Institute for Materials Science, Austrian Academy of Sciences

Resume : Interfacial properties of thin films on compliant substrates are important to understand in order to design reliable flexible electronic devices. Due to the compliance of the substrates, measuring the adhesion energies of these systems is difficult with existing techniques and models. A new method and mechanics-based model have been developed to measure the adhesion energy of metal films on compliant substrates using an in situ uniaxial tensile test inside a scanning electron microscope. With this technique, the initial fracture and buckling of the film can be observed and correlated to the strain. Once buckling of the film has been achieved, the height and width of the buckles are then used in the new model to calculate the adhesion energy. To demonstrate the technique and model, titanium films on polyimide are studied before and after annealing. It will be shown that annealing decreases the adhesion because the interface structure changes.

15:15 Coffee break    
Session 8 : E. Spiecker
Authors : Miroslav Popovic, Kai Chen, Mark Asta, Jan Schroers, Peter Hosemann
Affiliations : Department of Nuclear Engineering, University of California Berkeley, Berkeley CA 94720 (USA); School of Materials Science & Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049 (P. R. China); Department of Materials Science & Engineering, University of California Berkeley, Berkeley CA 94720 (USA); School of Engineering & Applied Science, Yale University, New Haven, CT 06511 (USA); Department of Nuclear Engineering, University of California Berkeley, Berkeley CA 94720 (USA);

Resume : The oxidation of Fe-based alloys in liquid Pb-Bi eutectic, with oxygen dissolved in liquid phase, leads to oxide formation on the surface. These structures are primarily determined by oxygen concentration and diffusion properties of cations from solid and oxygen anion from liquid phase. In this work, the influence of temperature and oxygen concentration on oxides growth dynamics and their diffusion properties is examined in oxidation of ferritic Fe-Cr-Al-alloys in liquid lead-bismuth at high temperatures. The order of oxide phases, and their structure, determined by XRD, EDS, TEM and Raman spectroscopy, are correlated with model predictions of dynamics of their formation and degradation. The ultimate goals have been to determine the oxide phases present in the scales, and to understand their evolution (as a function of temperature and oxygen concentration) and origins of strain induced in oxide and in bulk.

Authors : Maxim N. Popov,1 Jürgen Spitaler,1 and Claudia Draxl2
Affiliations : 1 Materials Center Leoben (MCL) Forschung GmbH, Roseggerstr. 12, A-8700 Leoben, Austria 2 Institut für Physik and IRIS Adlershof Theoretische Festkörperphysik, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, 12489 Berlin, Germany

Resume : Layered materials present a promising route for achieving attractive combinations of properties, e.g., high hardness and toughness at the same time [1]. In this work, we evaluate the mechanical moduli of an Al2O3-TiO2 superlattice using effective elastic constants as well as a a more advanced direct ab initio approach which involves calculations of stress-strain curves of the superlattice. The effective elasticity is derived by means of the Grimsditch-Nizzoli [2] method, which allows to estimate the elasticity of a superlattice from the elasticity of the constituents. The ab initio calculations are performed in the framework of density functional theory, using the structural information (epitaxial relationships and interface structure) obtained in our previous work [3]. We compare the outcomes of the two approaches and discuss the performance of the Grimsditch-Nizzoli method when evaluating the bulk, Young's, and shear moduli. In particular, we demonstrate that the transverse Young's modulus obtained in the Grimsditch-Nizzoli method gives reasonable results, while a reliable description of the shear modulus is only obtained when applying the direct ab-initio approach. References: [1] Abadias, G. et al., Surface and Coatings Technology 202, 844 (2007) [2]Grimsditch, M. and Nizzoli, F., Phys. Rev. B 33, 5891 (1986) [3] Popov, M.N. et al., Phys. Rev. B 86, 205309 (2012)

Authors : Daniele Stradi, Umberto Martinez, Anders Blom, Mads Brandbyge, Søren Smidstrup, Kurt Stokbro
Affiliations : QauntumWise A/S, Center for Nanostructured Graphene (CNG), Department of Micro- and Nanotechnology (DTU Nanotech)

Resume : Here we introduce an atomistic approach based on density functional theory and non-equilibrium Green’s function, which includes all the relevant ingredients required to model realistic metal-semiconductor interfaces and allows for a direct comparison between theory and experiments via I -V bias curve simulations. We apply this method to characterize an Ag/Si interface relevant for photovoltaic applications and study the rectifying-to-Ohmic transition as a function of the semiconductor doping. We also demonstrate that the standard “activation energy” method for the analysis of I -V bias data might be inaccurate for nonideal interfaces as it neglects electron tunneling, and that finite-size atomistic models have problems in describing these interfaces in the presence of doping due to a poor representation of space-charge effects. Finally, we will describe a novel surface Green’s function (SGF) method where the surface is described as a true semi-infinite system and present a number of examples to illustrate how the SGF method gives a number of benefits compared to the slab approach as well as enables new type of studies.

Authors : Masashi Yoshida
Affiliations : National Institute of Technology, Ube College

Resume : Titanium diboride (TiB2) has many desirable properties such as high hardness (Hv=3400), high melting point (3000K), low density, high electrical resistivity and good corrosion resistance. However, a high sintering temperature above 2000K is required to obtain dense TiB2 specimens. Grain growth occurs by the sintering at such high temperatures which causes the degradation of the mechanical properties. In order to obtain dense and hard TiB2 based materials by the sintering at lower temperatures, sintering of TiB2 with various intermetallics as sintering aid has been investigated. In the present study, it has been shown that AlTi-TiB2 composites in which sub-micron sized TiB2 particles are dispersed in AlTi matrix can be formed by the reaction sintering of Al, Ti and boron powders using the spark plasma sintering method at 1573K. The Vickers hardness of AlTi-TiB2 composites increases as the amount of TiB2 increases up to 85vol%. The highest Vickers hardness of 2200Hv has been obtained for AlTi-85vol%TiB2. No crack has been observed near the corners of the Vickers indentation indicating excellent fracture toughness of composites of sub-micron sized TiB2 particles. On the other hand, in the AlTi-TiB2 composites fabricated using micron sized TiB2 particles, cracking occurs in TiB2 particles and at the interface between TiB2 and AlTi matrix.

Authors : V. Carnevali [1,2], Z. Zhiyu [3], M. Jugovac [1,#], L. Patera [1,§], G. Soldano [4], M. Mariscal [4], C. Africh [4], G. Comelli [1], M. Peressi [1]
Affiliations : [1] Università di Trieste, Via A. Valerio 2, Trieste, Italy [2] CNR-IOM TASC, Trieste [3] ICTP, Trieste [4] Universidad Nacional de Cordoba, and INFIQC CONICET-UNC, Argentina [#] present address: Peter Grünberg Institut, Forschungszentrum Jülich, Deutschland [§] present address: Faculty of Physics, University of Regensburg, Deutschland

Resume : Epitaxial graphene on metallic surfaces can form a variety of moiré superstructures due to interfacial lattice parameter and/or symmetry mismatch [1][2]. The latter characterizes graphene on Ni(100), where the hexagonal carbon network accommodates onto a square surface lattice. The interfacial mismatch leads to moiré patterns with stripe-like or rhombic-network morphology and with periodicity depending on the relative misorientation angle between graphene and the Ni surface. Different moiré patterns are characterized by high resolution scanning tunneling microscopy (STM) images and successfully described by atomistic models which consider the geometric registry. Ab-initio density functional theory (DFT) simulations well reproduce the observed STM images and shed further light on the spatial corrugation of graphene and the interfacial interactions, indicating that, depending on the misorientation angle, graphene can be alternately physi- and chemisorbed or uniformly chemisorbed. The interaction is modulated periodically by the (sub)nanometer-sized moiré superstructures. [1] Vinogradov, N.A. et al., Phys. Rev. Lett., 109 (2012) 026101 [2] Murata, Y. et al., ACS Nano, 4 (2010) 6509-6514

16:50 Poster session: H. IDRISSI    
Authors : Chang Su Woo
Affiliations : Korea Institute of Machinery & Materials

Resume : we developed rubber material that is environment-friendly and superior in mechanical property using rubber-clay nanocomposites. Typical modifiers to enhance dynamical properties of rubber material were carbon black and silica. Recently, nano-clay was popular as modifiers. Many researches on nanocomposites are being actively carried out because they are excellent in modification even with a small quantity of them while nano-clay is difficult to diffuse. Fillers or modifiers used when manufacturing polymer nanocomposites include layered silicate, POSS nanoparticles, CNT and nanoparticles of metal or inorganic matters, among which layered silicate is now being most actively developed as polymer nanocomposites. The key technology of development of polymer nanocomposites is how to change layered clay so as to easily insert polymers into it. When organic matters are inserted using inorganic material like clay silicate that has a uniform structure with nano scale, in particular, nanocomposites are attracting great concerns in their application. The basic structure of clay, as it is well known, consists of silica tetrahedral and alumina octahedral sheets: it is classified into several groups including vermiculite and montmorillonite depending on its negative charge. 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. Thermal resistance was estimated through material tests of developed material at room temperature and aged condition. Fatigue durability was estimated after we developed a new method that could estimate fatigue lifetime of rubber parts in a short period in the initial stage. As results, fatigue lifetime evaluation by the fatigue lifetime 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 rubber component made by the developed material was longer than the existing material.

Authors : Yang Zhang*, C.H. Zheng, Z.X. Lei
Affiliations : School of Sciences, Nanjing University of Science and Technology, Nanjing 210094, China

Resume : Duo to the unique and highly valuable properties, graphene sheets has attracted increasing attention. In this paper, the nonlocal elastic theory and classical plate theory (CLPT) are used to derive the governing equations. The element-free kp-Ritz method is employed to analyze the buckling behaviors of double layer circular graphene sheets (DLGSs) embedded in an elastic medium. Pasternak-type model is adopted to simulate the functioning of the elastic medium. Then, the effects of boundary conditions, aspect ratio, size of graphene sheets, nonlocal parameters on the buckling behavior of DLGSs are investigated.

Authors : Jong-Ha Lee, Jong Seob Choi, Hyung Jin Kim
Affiliations : 1. Department of Biomedical Engineering, Keimyung University, South Korea 2, Convergence Medical Devices Research Center, Electronic Medical Technology Research Division, Gumi Electronics & Information Technology Research Institute, South Korea

Resume : Falls are dangerous for the elderly population; therefore, many fall detection systems have been developed. However, previous methods are bulky for elderly people or only use a single sensor to isolate falls from daily living activities, which makes a fall difficult to distinguish. We present a cost-effective and easy-to-use portable fall-detection sensor and algorithm. Specifically, to detect human falls, we used a three-axis accelerator and a three-axis gyroscope in a mobile phone. We used the Fourier descriptor-based frequency analysis method to classify both normal and falling status. To calculate the classification accuracy, the K-fold cross-validation method was used and K was set as 10. The performance indices were evaluated by five performance indices, including classification accuracy (TP+TN)/(TP+TN+FP+FN), sensitivity (TP/[TP+FN]), specificity (TN/[TN+FP]), positive predictive value (TP/[TP+FP]), and negative predictive value (TN/[TN+FN]), where TP is the number of true positive findings correctly classified as positive; TN = true negative; FP = false positive; and FN = false negative [8]. From the results, we noticed that the proposed method detects 384 data (falling or walking) out of 414 original data (falling or walking). The statistical analysis shows that the resulting accuracy was 96.14%, sensitivity was 100%, specificity was 92.08%, positive predictive value was 92.98%, and negative predictive value was 100%. In this paper, we propose a mobile phone-based falling detection sensor and algorithm. We used a three-axis accelerator and three-axis gyroscope to determine the direction and rotation of the subjects’ bodies. The support vector machine classifier was used to analyze the sensor’s signal. From the experimental results, the proposed method detects falling status with 96.14% accuracy, which indicates that human activity can be classified using a mobile phone. These detection methods can warn others of a user’s fall.

Authors : A. Ruiz Moreno, Z. Szaraz, S. Ripplinger, I. Simonovski
Affiliations : European Commission, Joint Research Centre, Directorate G: Nuclear Safety and Security. Westerduinweg 3, 1755 LE Petten, The Netherlands

Resume : Single-grain mechanical properties have been measured with the aim of calibrating the material parameters of a crystal plasticity finite element model to a single-crystal response. Such simulation-oriented experiments allow the investigation of the deformation behaviour of individual grains in plastically deforming metals, which underpins the bridging of scales in multiscale modelling approaches to predict the mechanical behaviour of nuclear structural materials and support the elaboration of materials design rules for nuclear energy applications. Preliminary computations of 316L stainless steel pillars using macroscopically calibrated material properties indicated that applying a 100mN compressive force (the maximum allowed by the nanoindentation system where micropillar compression is performed) to pillars of diameter below 10 µm results in average compressive strains above 10 %, a sufficient amount of plastic deformation for an initial calibration of crystal plasticity material properties, while 20 µm pillars would result in mainly elastic deformation. On that basis, a series of micropillars have been fabricated by Focused Ion Beam inside single grains of polycrystalline steels, and compressed by a flat punch using a nanoindentation system. This work will present the results of the combination of compression tests and crystal plasticity finite element simulations.

Authors : Suji Gim, Hyung-Kyu Lim, Hyungjun Kim
Affiliations : Graduate School of Energy, Environment, Water, and Sustainability (EEWS), Korea Advanced Institute of Science and Technology

Resume : Hydrophobicity of graphene has been investigated for the first time using multiscale simulation, i.e. combined quantum mechanics / molecular mechanics (QM/MM). Wettability of graphene was determined by using a concept of work of adhesion; free energy gap of a two-phase system (liquid and solid) between a sum of each solitary states and a neighbored state. Two phase thermodynamics (2PT) analysis was used for free energy calculations. Interfacial interactions from not only van der Waals, electrostatic potential but also perturbed or reorganized states were reproduced by potential feedback cycles in QM/MM simulation. Here, we investigate a consequence of various chemo-physical conditions in graphene such as layer thickness, corrugated structure, and nitrogen doping. The microscopic wettability of graphene and geometric alignment of waters on the surface were studied.

Authors : Julien Godet, Firas Abed El Nabi, Sandrine Brochard, Laurent Pizzagalli
Affiliations : Julien Godet, Pprime Institute – CNRS – University of Poitiers, FRANCE: Firas Abed El Nabi, Pprime Institute – CNRS – University of Poitiers, FRANCE: Sandrine Brochard, Pprime Institute – CNRS – University of Poitiers, FRANCE: Laurent Pizzagalli, Pprime Institute – CNRS – University of Poitiers, FRANCE

Resume : While bulk silicon is brittle at temperatures below 600-700K, the compression of nanopillars has shown that a decrease of the diameter below few hundreds of nanometers could change the silicon behavior from brittle to ductile [1]. As silicon is free of initial defect, this size effect should be controlled by the cracks and/or the dislocations nucleation from the surface. The identification of the parameters governing the brittle to ductile transition in size and the understanding of the mechanisms are the key points to prevent the failure of microelectronic components based on the silicon strained technology. Nowadays the respective improvements in simulations and experiments allow to investigate the mechanical properties of objects of similar sizes, close to hundreds of nanometers. We considered atomistic simulations based on two different semi-empirical potentials fitted to better reproduce the ductile and brittle properties of bulk silicon. The simulations under tensile load show the nucleation of perfect dislocations from the surface that can lead to cavity opening when they interact [2]. Second, we show that the brittle to ductile transition is not abrupt and mainly controlled by the diameter of the nanopillars, as observed experimentally in compression. The underlying mechanisms will be detailed, and a criterion based on the quantification of the plastic deformation before cracks opening will be presented to measure the degree of ductility of the breaking. [1] F. Oestlund et al. AFM 19 (2009) 1 [2] F. Abed El Nabi et al MSMSE 23 (2015) 025010

Authors : A. Titenko1, L. Demchenko2, S. Sidorenko2
Affiliations : 1Institute of Magnetism NAS of Ukraine and MES of Ukraine; 2Metal Physics Department, Igor Sikorsky Kyiv Polytechnic Institute, Ukraine.

Resume : The report is devoted to mechanisms that may operate influence of nanoparticles interaction with bulk matrix on phase transformations and in such way – on mechanical properties formation. By direct experimental control, it was shown that ferromagnetic nanoparticles, formed in Cu-Al-Mn alloys under 473 K for 3 h aging in a magnetic field of 1.5 kOe having different orientation, provide: 1) stress reduction, arising during phase (martensite) transformations; 2) superelasticity increasing. Oriented growth of precipitated nanoparticles in an applied field direction and their volume fraction increasing favor of induced martensitic transformation reversibility. The model of established effect has been proposed. When martensitic transformations take place the internal stresses arise as a result of austenite phase shear deformation. From other side, austenite aging before martensite transformation results in nanoparticles Cu2AlMn coherently connected with a matrix precipitation, that reduces internal stresses during transformation. This leads to thermal hysteresis of martensitic transformation narrowing and superelasticity increasing. The competition between these processes driving forces on bulk-, micro- and nanolevels is discussed. Thus, bridging scales (from nanoscale mechanisms to bulk behavior, mechanical properties formation due to intrinsic nanosize effects) is illustrated in this report through the role of ferromagnetic nanoparticles in Cu-Al-Mn alloy phase transformations.

Authors : Ye-Seol Ha, Hyeyoung Shin, Hyungjun Kim
Affiliations : Dept. of Energy, Environment, Water and Sustainability (EEWS) Korea Advanced Institute of Science and Technology (KAIST), Daejeon, South Korea

Resume : The power conversion efficiency of perovskite solar cells has remarkably increased in the past few years. However, there are some drawbacks for perovskite solar cells to be commercialized. The main drawback is degradation of the perovskite structure by moisture. And spiro-OMeTAD, which is hole transporting layer (HTL) located between electrode and perovskite layer, is well known for hygroscopic characteristics. In this study, we investigated the behaviors of oxygen and water in spiro-OMeTAD using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The spiro-OMeTAD with oxygen and water loaded models were used. Mean square displacements (MSD) and other physical properties were calculated to understand the behavior of oxygen and water in spiro-OMeTAD. Understanding hygroscopic characteristics of spiro-OMeTAD with computational simulations were attempted to offer an insight for developing high stability perovskite solar cells.

Authors : I. Guizani, K. Chakir, M. M. Habchi and A. Rebey*
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications, 5019 Monastir, Tunisia

Resume : We have theoretically investigated the 1.55 µm p-type doped GaNAsBi-based Double Quantum Wells (DQWs) using the (16x16) BAC model combined with a self-consistent calculation. We have found that the coupling effect becomes more pronounced by reducing barriers width. The optical performance of the structure is enhanced when the DQWs are coupled and doped. Moreover, a p-i-n heterojunction based on GaNAsBi/GaAs (DQWs) designed for infrared photodetection was developed. The computed gain can reach the value 4.2 〖10〗^4 〖cm〗^(-1). The optimization of well parameters such as the Bismuth composition, the well width and the doping densities give rise to p-i-n heterojunction emitting at the wavelength 1.55 µm. The quantum confined stark effect on the optical properties of studied structures is also discussed.

Authors : I.Guizani, H. Fitouri I. Zaied and A. Rebey*
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro-Epitaxies et Applications, 5019 Monastir, Tunisia

Resume : We have experimentally studied the multicomponent responses of photoreflectance spectrum using selective phase analysis. After several experimental tests, the phase diagram of GaAs substrate in region of fundamental energy shows only one component. On the other hand, the PR spectrum of GaAsBi/GaAs structure reveals at least two contributions relative to fundamental band-band transition and Franz-Keldysh oscillations for GaAs and/or GaAsBi layers. A successful separation of different components is realized by the help of adequate phase angle. We seem that the separation of contributions combined with multilayers model is useful to extract the values of the physical parameters for each region of each structure. We have detailed the methodology and experimental procedure to identify each contribution.

Authors : K. Chakir, I. Guizani, C. Bilel, A. Rebey
Affiliations : University of Monastir, Faculty of Sciences, Unité de Recherche sur les Hétéro–Epitaxies et Applications, 5019 Monastir, Tunisia

Resume : Electronic band structure of strain-balanced GaAsN/GaAsBi type II double quantum wells (DQWs) was theoretically investigated by using the band anticrossing model combined with the envelope function approximation. The strain-balanced DQWs were coupled by the optimization of the well and barriers widths. We have discussed the coupling effect on the confined states energies and the oscillator strengths of inter-band transitions. The in-plane carrier effective masses and the optical absorption spectra of 1.3 and 1.55 µm GaAsN/GaAsBi type II DQWs are also examined.

Authors : S. Abdeslam
Affiliations : Institute of Optics and Mechanics of Precision, Ferhat Abbas University Sétif 1, 19000 Sétif, Algeria.

Resume : Cu-Ag system has attracted significant attention in recent years because of their applications due to their unusual mechanical and electrical properties ; since it was used as contacts and interconnect layers in microelectronic industry [1] and as material magnets [2]. In the present work, we investigate the effect of silver inclusion on mechanical behaviors of copper nanomaterial during nanoindentation process by means of Molecular Dynamics Simulations, based on the embedded atomic method (EAM), using the LAMMPS code [3]. We investigate how Ag inclusion influences the copper nanoindentation. Simulation results show that the presence of silver inclusion has influenced the material strength. First, hardness of Cu matrix containing Ag inclusion is less larger than of pure Cu. Second, the composite Cu-Ag hardness increases by increasing the depth of the Ag inclusion. This result is in good agreement with previous simulations [4,5]. Keywords : Nanoindentation, MD simulation, Inclusion, Nanomaterial, Hardness. References [1] S. Strehle et al., Microelectron. Eng. 76 (2004) 205-211. [2] C. Zhao et al., Mater. Sci. & Engineer. A 652 (2016) 296–304. [3] S.J. Plimpton,  J. Comput. Phys. 117 (1995) 1–19. [4] C. Wei, C. Yu, Proc. of the Intl. Conf. on Future Trends in Structural, Civil, Environmental and Mechanical Engineering -- FTSCEM 2013 . [5] V.V. Pogorelko, A.E. Mayer, Mater. Scien. Eng. A642 (2015) 351-359.

Authors : Nikoletta Florini, George P. Dimitrakopulos, Joseph Kioseoglou, Thomas Kehagias
Affiliations : Physics Department, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece

Resume : The strong piezoelectric effect of III-V semiconductor nanostructures, renders them important candidates for micro- and opto-electronics applications. In heteroepitaxy, the property that mainly defines the efficiency of such nanostructures is the development of stress-strain fields due to lattice misfit. The present approach is a versatile route to solve elasticity problems at the nanoscale for various growth orientations and compositional profiles using the Finite Elements Method (FEM), in conjunction with High-Resolution Transmission Electron Microscopy (HRTEM) imaging. In our analysis, we modify the elastic characteristics of any (hkl)-oriented system with respect to the conventional <001> coordinate system. Thus, by determining the affine transformation from one coordinate system to another, we address the calculation of the new stiffness tensor C(hkl), in relation to the independent stiffness constants of the <001>-oriented system. This transformation comprises three successive rotations about the three axes of the <001> coordinate system. Simultaneously, the FEM mesh is chosen to be consistent with the bicrystal symmetry as expressed by a dichromatic pattern. Then, in the frame of thermo-elasticity theory and using the anisotropic elastic model, we calculate the elastic properties of any (hkl)-oriented nanostructures of various chemical compositions, thus enabling a direct comparison with quantitative HRTEM results obtained by geometric phase analysis or peak finding. Acknowledgements Work supported by the Research Projects for Excellence IKY/Siemens.

Authors : Brigita Abakevičienė(1,2), Mantas Lukauskas(2), Skirmantas Norkus(2), Aušra Gadeikytė(3), Dalius Jucius(1), Algirdas Lazauskas(1), Viktoras Grigaliūnas(1)
Affiliations : (1) Institute of Materials Science, Kaunas University of Technology, K. Barsausko srt. 59, LT-51423 Kaunas, Lithuania (2) Department of Physics, Kaunas University of Technology, Studentu str. 50, LT-51368 Kaunas, Lithuania (3) Department of Applied Informatics, Kaunas University of Technology, Studentu str. 50, LT-51368 Kaunas, Lithuania

Resume : Fluoropolymers are very attractive compounds because of their versatility and their unique physical and chemical properties. In this work, a piezo-actuated testing device has been developed for measuring the elastic and plastic properties of FEP, ETFE, and PFA fluoropolymers films via uniaxial micro-tensile testing and finite element method simulations. The piezo-actuated micro-tensile setup was able to measure film elongation up to 210 μm with an accuracy of 50 nm. The tensile test results revealed a major difference in the material deformation mechanism as the stress was applied in the different direction of the polymer chains, and at the different measurement conditions (strain rate, temperature). The microstructure changes of the temperature affected fluoropolymers were investigated by XRD. The results confirmed the ability of the custom-built equipment for the measurements of very small load and displacement levels, which are a prerequisite for such type of investigations.

Authors : Deepak Chhabra
Affiliations : Dr. Deepak Chhabra, Assistant Professor, Department of Mechanical Engineering, University Institute of Engineering & Technology, MDU, Rohtak-124001, Haryana, India

Resume : A new approach has been presented to find out optimal number of piezo-patches for the multimodal vibration reduction of smart plate using genetic algorithm. The length of the chromosomes/number of genes in genetic algorithm represents the number of piezopatches on the plate. The length of chromosome remains constant in general GA. Laying–up of varying length of chromosomes still remains a hard task as crossover implementation is more complex in this case. A variable length of chromosomes has been generated in adaptive GA to determine the optimal number of piezo-patches. The finite element model of smart plate is based on the Kirchoff’s plate theory has been utilized. The performance index based on spillover effects has been minimized while maintaining the degree of controllability to determine the optimal number of actuators. The results clearly indicate that present approach performs better in terms of computation effort and processing time.

Authors : Sunil Dhingra
Affiliations : Sunil Dhingra Department of Mechanical Engineering University Institute of Engineering & Technology, Kurukshetra University, Kurukshetra, Haryana, India-136119

Resume : The current work is focused on performance of sunflower biodiesel in a single cylinder direct injection diesel engine. Three engine input parameters are varied in order to predict optimum combinations of performance, combustion and emission parameters. Hybrid RSM-NSGA-II technique is applied to predict the optimal solutions. It is observed that design engineer can select any of the solutions depending upon the requirement of performance, combustion and emission parameters.

Authors : Hossein Azizi, Sebastian Gurevich, Nikolas Provatas
Affiliations : Department of Physics, Centre for the Physics of Materials, McGill University, Montreal, QC, Canada

Resume : We explore numerically the morphological patterns of thermo-diffusive instabilities in combustion fronts with a continuum fuel source, within a range of Lewis numbers and ignition temperatures, focusing on the cellular regime. For this purpose, we generalize the recent model of Brailovsky et al. to include distinct process kinetics and reactant heterogeneity. The generalized model is derived analytically and validated with other established models in the limit of infinite Lewis number for zero-order and first-order kinetics. Cellular and dendritic instabilities are found at low Lewis numbers. These are studied using a dynamic adaptive mesh refinement technique that allows very large computational domains, thus allowing us to reduce finite-size effects that can affect or even preclude the emergence of these patterns. Our numerical linear stability analysis is consistent with the analytical results of Brailovsky et al. The distinct types of dynamics found in the vicinity of the critical Lewis number, ranging from steady-state cells to continued tip-splitting and cell-merging, are well described within the framework of thermo-diffusive instabilities and are consistent with previous numerical studies. These types of dynamics are classified as “quasi-linear” and characterized by low amplitude cells that may be strongly affected by the mode selection mechanism and growth prescribed by the linear theory. Below this range of Lewis number, highly non-linear effects become prominent and large amplitude, complex cellular and seaweed dendritic morphologies emerge. The cellular patterns simulated in this work are similar to those reported by Malchi et al. in experiments of flame propagation over a bed of nano-aluminum powder burning with a counter flowing oxidizer. These resemble the dendritic fingers observed in this study, in the limit of low-Lewis number. It is noteworthy that the physical dimension of our computational domain is roughly close to their experimental setup.

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Session 9 : R. Brunner
Authors : Lukas Lührs, Birthe Müller, Jörg Weissmüller
Affiliations : Hamburg University of Technology, Institute of Materials Physics and Technology; Hamburg University of Technology, Institute of Materials Physics and Technology; Hamburg University of Technology, Institute of Materials Physics and Technology, Institute of Materials Research, Materials Mechanics, Helmholtz-Zentrum Geesthacht;

Resume : Nanoporous metals can take the form of macroscopic bodies that consist of a bicontinuous network of pores and solid ligaments. Owing to their large surface area to volume ratio nanoporous metals exhibit substantial surface induced property modifications. Amid these materials nanoporous gold (NPG) stands out as an ideal model material due to its adjustable surface area and high chemical stability. As a result of NPGs significant electromechanical coupling, electrical tuning of the strength and flow stress, elastic modulus, creep behavior and crack propagation has been reported. Yet, the impact of electrical modulation on the Poisson's ratio, an essential material parameter that links longitudinal and transverse strain, is still unknown. In our contribution we investigate the influence of electrical excitation on the transverse mechanical coupling of NPG through the analysis of a metal/electrolyte hybrid material. We present experiments of NPG under compression testing in 1 M perchloric acid while varying the applied electrical potential, E. Our results reveal a considerable dependence of the plastic Poisson's ratio, νP, on E. We link these findings to the surface tension, γ, a capillary force that promotes a tension/compression asymmetry in the nanostructure. Since γ depends on E, we demonstrate that plastic lateral expansion in NPG is governed by surface effects. In this line of argument we are able to interpret earlier reports showing a ligament size dependence of νP.

Authors : Thomas Przybilla1)*; Erich Thiess1); Florian Niekiel1); Benjamin Winter1); Mirza Mačković1); Zhuocheng Xie2); Arun Prakash2); Stephen T. Kelly3); Hrishikesh A. Bale3); Erik Bitzek2); Erdmann Spiecker1);
Affiliations : 1) Institute of Micro- and Nanostructure Research & Center for Nanoanalysis and Electron Microscopy (CENEM), Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Cauerstrasse 6, 91058 Erlangen, Germany; 2) Institute of General Material Properties, Department of Materials Science and Engineering, Friedrich-Alexander-Universität Erlangen-Nürnberg, Martensstrasse 5, 91058 Erlangen, Germany; 3) Carl Zeiss X-ray Microscopy, 4385 Hopyard Rd, Ste 100, Pleasanton, CA 94588, USA; *

Resume : In this work we present results on in situ small scale testing of nanoporous gold (npg) in scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By combining nano- and micromechanical testing of pillar structures with advanced tomographic imaging, a 3D characterization of the plastic deformation process in different states of deformation is achieved. For small strut sizes 360° electron tomography (ET) is applied enabling high quality reconstructions of the 3D morphology of npg without missing-wedge artefacts. Combining the geometric information with mechanical data from in situ testing in SEM and TEM the yield strength is precisely determined. Furthermore, the experimentally derived 3D data are used as input for large-scale molecular dynamics (MD) simulations in order to understand the role of strain localization and identify predominant defect processes. For larger strut sizes mechanical testing and 3D structure analysis of npg pillars are carried out by in situ SEM and high-resolution X-ray tomography (Nano-CT), respectively. Image correlation analysis applied to in situ SEM image series reveals the evolution of local strain gradients during deformation and, in particularly, local yielding in the very early stages of deformation. The yield strength strongly depends on strut size revealing a clear size effect. The scale-bridging approach is complemented by in situ nanomechanical testing of single struts in TEM.

Authors : Katharina Klingan [a], Christian Zafiu [a,b], Christoph Huber [a], Wolfgang Kautek [a]
Affiliations : [a] University of Vienna, Department of Physical Chemistry, Vienna, Austria; [b] Forschungszentrum Jülich, Institute of Complex Systems (ICS-6), Jülich, Germany

Resume : A nanotribological evaluation of the electrochemical double layer at gold/electrolyte interfaces was undertaken by in-situ lateral force measurements. Chemisorption (specific adsorption) of sulphate, bromide and iodide caused a friction increase as has been reported on silver [1]. Chemisorbed bromide showed a greater friction than iodide due to a higher surface coverage, whereas fluoride exhibited no effect, as it did not chemisorb. Low normal forces (<11 nN) led to classical friction behaviour according to the Amonton’s law for non-specifically (in the Outer Helmholtz Plane) and specifically adsorbed anions (in the Inner Helmholtz Plane). At higher normal forces, the cantilever tip displaced the chemisorbed anions leading to a deviation from Amonton’s law. When a two-dimensional gold hydroxide layer was generated at high normal forces (>11 nN), the friction remained on a finite high level because the tip replaced the chemisorbed anions but could not penetrate the hydroxide layer. This study demonstrates that solvated anions in the Outer Helmholtz Plane do not contribute to friction significantly, whereas specifically adsorbed (chemisorbed) anions in the Inner Helmholtz Plane increase the mechanical resistance. Thus, nanotribology of a noble metal can be controlled by electrochemical surface charging conditions, e.g. by a potentiostat, and by the chemical nature of the anions. [1] W. Kautek, S. Dieluweit, and M. Sahre, J. Phys. Chem. 1997, 101, 2709.

Authors : Ali Ghaemi(1); Li Liu(2); Stephan Gekle(1); Seema Agarwal(2)
Affiliations : (1) Biofluid Simulation and Modeling, Fachbereich Physik, and Bayreuth Center for Colloids and Interfaces, Universität Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany. (2) Macromolecular Chemistry II and Bayreuth Center for Colloids and Interfaces, Universität Bayreuth, Universitätsstraße 30, 95440 Bayreuth, Germany.

Resume : A combined numerical-experimental analysis is applied in order to explain the complex behavior of a rare example of one-component dual actuator. The system of interest is a bilayer with aligned and randomly oriented poly(N-isopropyl acrylamide) fibers which displays irreversible change in shape by rolling in contact with water, and reversible size change in response to temperature changes. A combination of anisotropic Young’s modulus and temperature dependent swelling/shrinkage is shown to be responsible for the actuators controllable unique folding.

Authors : Sebastien Pierrat (1), Chanjuan Liu (1), Jan Henk Kamps (1), Chiel Leenders (1), Olivier Guise (1), Xiaoyin Cheng (2), Katja Schladitz (2)
Affiliations : (1) SABIC, Plasticslaan 1, 4612PX Bergen op Zoom, The Netherlands (2) Fraunhofer-Institut für Techno- und Wirtschaftsmathematik ITWM, Fraunhofer-Platz 1, 67663 Kaiserslautern, Germany

Resume : Fiber reinforced plastics (FRP) gained a strong interest in the last decades, finding applications in automotive, mass transportation, water management or consumer electronics. FRPs provide lightweight, design flexibility, cost-effectiveness and represent an attractive alternative for metal replacement. The use of FRP allows to overcome the mechanical limitations of base polymer, by enhancing the tensile strength, the elastic modulus and impact strength of the material. The fiber pull-out length, which is related to the adhesion and friction forces occurring at the interface between the surface of the fibers and the polymer matrix, provides critical information regarding the mechanical properties. However, the assessment of the pull-out length is challenging because SEM provides only a 2D projection of the 3D random orientation of the fibers on the fractured surface. Such projection introduces challenges and inaccuracy in the fiber pull-out length assessment. In order to improve the accuracy of the fiber pull-out length measurement, an algorithm is developed to perform the 3D surface reconstruction with SEM images acquired at different tilling angles. The common features on each image are detected, aligned, and used to estimate the projective geometry of SEM detectors. Based on the estimated geometry, the 3D surface is reconstructed via triangulation. The measured pull-out length with respect to the fractured surface is then correlated to the mechanical properties.

10:15 Coffee break    
Session 10 : H. Idrissi
Authors : Vadim Levin1, Egor Morokov1,2, Yulia Petronyuk1,2, Inna Grigorieva3, Alexander Antonov 3
Affiliations : 1 Emanuel Institute of Biochemical Physics RAS, Russia, Moscow 2 Scientific and Technological Center of Unique Instrumentation RAS, Moscow, Russia 3 Optigraph GmbH, Berlin, Germany

Resume : Highly annealed pyrolytic graphite (HAPG) is a high quality type of graphite with low angle (less than 0.1°) mosaic structure that usually is employed for the fabrication of X-ray optics. HAPG plate consist of large number of individual graphite crystals with size 100 μm, which have a small tilt angle to the plate surface and minimal distance between neighbor crystals. Understanding of HAPG internal crystal structure as initial as after mechanical processing (cutting, polishing) or its applying on substrate is meaning factor in HAPG future application. Investigations of HAPG internal microstructure were carried out by impulse acoustic microscopy. It is shown that high frequency ultrasound wave is sensitive radiation for characterization of crystal orientation, atomic interlayer delimitation inside HAPG plate, adhesive defects of HAPG films to substrate etc.

Authors : Vadim Levin, Yulia Petronyuk, Egor Morokov, Tatiana Ryzhova, Alexander Shanygin, Pavel Shershak
Affiliations : Emanuel Institute of Biochemical Physics RAS, Russia, Moscow; Scientific and Technological Center of Unique Instrumentation RAS, Moscow, Russia; Central Aerohydrodinamic Institute, Zhukovsky, Russia National Institute of Aviation Technology, Moscow, Russia

Resume : Composite materials fabricated with reinforcement of polymer matrix by regular package of carbon, glass or organic fibers are widely used today in aerospace engineering. Carbon fibers are very attractive as reinforcement due to their strength, stiffness, and low weight, high level of damping, good corrosion and heat resistance. Anisotropic properties and multiple boundaries in the bulk structure of polymer reinforced composites as well as technological imperfections result in more complex processes of material destruction. Studying mechanisms of defects formation at micro level are the basis for understanding destruction processes in composites to assess strength and reliability of such materials and constructions of them [1,2]. Optical, electron or probe microcopies are destructive techniques. In the paper the nondestructive high resolution ultrasonic technique for bulk visualization of the composite damaging under the mechanical loading and environment factors is proposed. Using short pulses of focused ultrasound probe (50-100MHz) makes it possible imaging with a lateral resolution of 30μm at a depth of several millimeters. Packaging of reinforced threads and defects of their adhesion to the composite matrix, pockets of polymer binding, interlayer delaminating, localization and distribution of the defects in the material bulk are well seen in acoustic images. Dynamics of microstructural changes under the tensile loading and low-speed impact is studied. Mechanisms of the material destruction are discussed. Research is supported by Russian Scientific Foundation No15-12-00057. [1] Greenhalgh E.S. Failure Analysis and Fractography of Polymer Composites. Woodhead Publishing, Cambridge, 2008; [2] Jollivet T., Walaszek H., Terrien N., JEC Composites Magazine, 81, 2013

Authors : Tobias Cramer, Lorenzo Travaglini, Stefano Lai, Luca Patruno, Stefano de Miranda, Annalisa Bonfiglio, Piero Cosseddu, Beatrice Fraboni
Affiliations : Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Italy; Department of Electric and Electronic Engineering, University of Cagliari, Piazza d’Armi, Italy; DICAM, University of Bologna, Viale Risorgimento 2, Italy;

Resume : Reliable performance under mechanical deformation is a central goal for flexible electronic sensors. The realization of mechanically rugged materials and device architectures depends crucially on the understanding of how strain affects electronic material properties and leads to defect formation. Scanning Kelvin-Probe Microscopy (SKPM) is a formidable technique for nanoelectronic investigations as it combines non-invasive measurement of surface topography and surface electrical potential. Here we show that SKPM becomes feasible on free-standing, deformed flexible samples when operated in the low-interaction regime of non-contact mode thereby providing the opportunity to study strain effects on nano-electronic properties. As an example we apply the technique to investigate strain effects and failure of flexible thin film transistors containing the organic semiconductor TIPS-pentacene during bending.[1] We find that the step-wise reduction of device performance at a critical bending radii is related to the formation of nano-cracks in the microcrystal morphology of the TIPS pentacene film. The cracks are easily identified due to the abrupt variation in SKPM surface potential caused by a local increase in resistance. Importantly, the strong surface adhesion of microcrystals to the elastic dielectric allows to maintain a conductive path also after fracture thus providing the opportunity to attenuate strain effects. We support our findings by numerical simulations of the bending mechanics of the hole transistor structure allowing to quantify the tensile strain exerted on the TIPS-pentacene micro-crystals as the fundamental origin of fracture. [1] T. Cramer, L. Travagli, S. Lai, L. Patruno, S. De Miranda, A. Bonfiglio, P. Cosseddu, B. Fraboni, Sci. Rep. 2016, 6, 38203.

Authors : M. U. Manzoor, H. Zaidi, A. Nadeem, Z. Ali, T. Ahmad, M. Kamran, R. Ahmad
Affiliations : Department of Metallurgy & Materials Engineering, College of Engineering & Emerging Technologies, Quaid-e-Azam Campus, University of the Punjab, Lahore, Pakistan

Resume : Metal matrix composites (MMCs) come under advanced materials that can be used for a wide range of industrial applications. MMCs consist of a non-metallic reinforcement incorporated into a metallic matrix which can enhance advantageous properties over base metal alloys. Copper-Glass fiber reinforced aluminium based hybrid composites were prepared by compo casting method. 4 weight % copper was used as alloying element with Al because of its precipitation hardened properties. Different weight compositions of composites were developed and characterized by mechanical testing. A significant improvement in tensile strength and micro hardness were found, before and after heat treatment of the composite. The SEM analysis of the fractured surfaces showed dispersed and embedded glass fibers within the network leading to the enhanced strength.

Authors : Muhammad M.T.Z. Butt, Tahir T Ahmad, Muhammad M. Kamran, M. U. Manzoor
Affiliations : Department of Metallurgy and Materials Engineering, CEET, Faculty of Engineering & Technology; University of the Punjab, Lahore, Pakistan

Resume : High strength and light weight are the unique properties of Metal Matrix Composites which make them to be used in aerospace and automobile industries. Aluminium-carbon fibers hybrid composites were developed and studied the effect of. 2, 4, 6 and 8 wt.% ratio of carbon fibers with constant amount (2wt.%) of silica sand nanoparticles. Tensile testing and Micro Hardness Tester machines were used to measure the tensile and hardness properties of the developed composites. Changing the wt.% ratio of the reinforcements changed the mechanical as well as electrical properties of the developed hybrid composites. The fracture analysis of tensile tests was studied using Scanning Electron Microscope (SEM).

Authors : Anton Davydok, Christina Krywka
Affiliations : Institute for Materials Research, Helmholtz-Zentrum Geesthacht, outstation at DESY, Notkestraße 85, 22607 Hamburg, Germany

Resume : Huge scientific interest to novel nanostructures with superior properties and characteristics require appropriate experimental techniques with commensurate tools for detail investigations. P03 nanofocus endstation at PETRA III in DESY operated by Helmholtz Zentrum Geesthacht we provide high stability experimental setup with high spatial resolution using a nanosized beam. It is one of only few places in the world where the experimental conditions for scanning X-ray nanodiffraction are provided and it offers a hard X-ray beam with a size of only 250 x 350 nm². The strong focus on materials science at P03 is demonstrated by the wide range of experiments already performed with in situ sample environments: pressure, indentation force, tensile stress, fluid shear, magnetic fields - all of these parameters were successfully modified in situ and combined with the high spatial resolution provided by nanofocused beam.

12:05 Lunch    
14:00 round-table discussion    
15:00 Conclusion Symposium W    
15:30 Coffee break    
16:15 Plenary Session    

No abstract for this day

No abstract for this day

Symposium organizers
Erik BITZEKFriedrich-Alexander-Universität Erlangen-Nürnberg

Department of Materials Science and Engineering, Institute I, Martensstr. 5, 91058 Erlangen, Germany
Hosni IDRISSIUniversité Catholique de Louvain

IMMC, Place Sainte Barbe 2, 1348 Louvain la Neuve, Belgium

101 Rue de la Physique, BP46, 38402 St Martin d’Hères cedex, France
Roland BRUNNERMaterials Center Leoben Forschung GmbH (MCL)

Roseggerstraße 12 , 8700 Leoben, Austria