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“Advanced TEM investigation of the plasticity mechanisms in nanocrystalline freestanding palladium films with nanoscale twins”. Wang B, Idrissi H, Galceran M, Colla MS, Turner S, Hui S, Raskin JP, Pardoen T, Godet S, Schryvers D, International journal of plasticity 37, 140 (2012). http://doi.org/10.1016/j.ijplas.2012.04.003
Abstract: Nanocrystalline palladium thin films deposited by electron-beam evaporation and deformed by on-chip tensile testing reveal a surprisingly large strain hardening capacity when considering the small similar to 25 nm grain size. The as-grown films contain several coherent single and multifold twin boundaries. The coherency of the twin boundaries considerably decreases with deformation due to dislocation/twin boundary interactions. These reactions are described based on a detailed analysis of the number and the type of dislocations located at the twin boundaries using high-resolution TEM, including aberration corrected microscopy. Sessile Frank dislocations were observed at the twin/matrix interfaces, explaining the loss of the TB coherency due to the Burgers vector pointing out of the twinning plane. Grain boundary mediated processes were excluded as a mechanism dominating the plastic deformation based on the investigation of the grain size distribution as well as the crystallographic texture using Automated Crystallographic Orientation Indexation TEM. Other factors influencing the plastic deformation such as impurities and the presence of a native passivation oxide layer at the surface of the films were investigated using analytical TEM. The twin boundaries observed in the present work partly explain the high strain hardening capacity by providing both increasing resistance to dislocation motion with deformation and a source for dislocation multiplication. (C) 2012 Elsevier Ltd. All rights reserved.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.702
Times cited: 44
DOI: 10.1016/j.ijplas.2012.04.003
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“Texture-dependent twin formation in nanocrystalline thin Pd films”. Wang B, Idrissi H, Shi H, Colla MS, Michotte S, Raskin JP, Pardoen T, Schryvers D, Scripta materialia 66, 866 (2012). http://doi.org/10.1016/j.scriptamat.2012.01.038
Abstract: Nanocrystalline Pd films were produced by electron-beam evaporation and sputter deposition. The electron-beam-evaporated films reveal randomly oriented nanograins with a relatively high density of growth twins, unexpected in view of the high stacking fault energy of Pd. In contrast, sputter-deposited films show a clear 〈1 1 1〉 crystallographic textured nanostructure without twins. These results provide insightful information to guide the generation of microstructures with enhanced strength/ductility balance in high stacking fault energy nanocrystalline metallic thin films.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 3.747
Times cited: 19
DOI: 10.1016/j.scriptamat.2012.01.038
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“Ultrahigh strain hardening in thin palladium films with nanoscale twins”. Idrissi H, Wang B, Colla MS, Raskin JP, Schryvers D, Pardoen T, Advanced materials 23, 2119 (2011). http://doi.org/10.1002/adma.201004160
Abstract: Nanocrystalline Pd thin films containing coherent growth twin boundaries are deformed using on-chip nanomechanical testing. A large work-hardening capacity is measured. The origin of the observed behavior is unraveled using transmission electron microscopy and shows specific dislocations and twin boundaries interactions. The results indicate the potential for large strength and ductility balance enhancement in Pd films, as needed in membranes for H technologies.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 19.791
Times cited: 57
DOI: 10.1002/adma.201004160
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“Effect of deposition rate on the microstructure of electron beam evaporated nanocrystalline palladium thin films”. Amin-Ahmadi B, Idrissi H, Galceran M, Colla MS, Raskin JP, Pardoen T, Godet S, Schryvers D, Thin solid films : an international journal on the science and technology of thin and thick films 539, 145 (2013). http://doi.org/10.1016/j.tsf.2013.05.083
Abstract: The influence of the deposition rate on the formation of growth twins in nanocrystalline Pd films deposited by electron beam evaporation is investigated using transmission electron microscopy. Statistical measurements prove that twin boundary (TB) density and volume fraction of grains containing twins increase with increasing deposition rate. A clear increase of the dislocation density was observed for the highest deposition rate of 5 Å/s, caused by the increase of the internal stress building up during deposition. Based on crystallographic orientation indexation using transmission electron microscopy, it can be concluded that a {111} crystallographic texture increases with increasing deposition rate even though the {101} crystallographic texture remains dominant. Most of the TBs are fully coherent without any residual dislocations. However, for the highest deposition rate (5 Å/s), the coherency of the TBs decreases significantly as a result of the interaction of lattice dislocations emitted during deposition with the growth TBs. The analysis of the grain boundary character of different Pd films shows that an increasing fraction of high angle grain boundaries with misorientation angles around 5565° leads to a higher potential for twin formation.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 1.879
Times cited: 13
DOI: 10.1016/j.tsf.2013.05.083
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“Single layer graphene controlled surface and bulk indentation plasticity in copper”. Bahrami F, Hammad M, Fivel M, Huet B, D'Haese C, Ding L, Nysten B, Idrissi H, Raskin JP, Pardoen T, International Journal Of Plasticity 138, 102936 (2021). http://doi.org/10.1016/J.IJPLAS.2021.102936
Abstract: The impact of graphene reinforcement on the mechanical properties of metals has been a subject of intense investigation over the last decade in surface applications to mitigate the impact of tribological loadings or for strengthening purposes when dispersed into a bulk material. Here, the effect on the plastic indentation response of a single graphene layer grown on copper is analyzed for two configurations: one with graphene at the surface, the other with graphene sandwiched under a 100 nm thick copper cap layer. Nanoindentation under both displacement and load control conditions show both earlier and shorter pop-in excursions compared to systems without graphene. Atomic force microscopy reveals much smoother pile-ups with no slip traces in the presence of a surface graphene layer. The configuration with the intercalated graphene layer appears as an ideal elementary system to address bulk hardening mechanisms by indentation testing. Transmission electron microscopy (TEM) cross-sections below indents show more diffuse and homogeneous dislocation activity in the presence of graphene. 3D dislocation dynamics simulations allow unraveling of the origin of these 3D complex phenomena and prove that the collective dislocation mechanisms are dominantly controlled by the strong back stress caused by the graphene barrier. These results provide a quantitative understanding of the impact of graphene on dislocation mechanisms for both surface and bulk applications, but with an impact that is not as large as anticipated from other studies or general literature claims.
Keywords: A1 Journal article; Electron microscopy for materials research (EMAT)
Impact Factor: 5.702
DOI: 10.1016/J.IJPLAS.2021.102936
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“Rheology of amorphous olivine thin films characterized by nanoindentation”. Baral P, Orekhov A, Dohmen R, Coulombier M, Raskin JP, Cordier P, Idrissi H, Pardoen T, Acta Materialia 219, 117257 (2021). http://doi.org/10.1016/J.ACTAMAT.2021.117257
Abstract: The rheological properties of amorphous olivine thin films deposited by pulsed laser deposition have been studied based on ambient temperature nanoindentation under constant strain-rate as well as re-laxation conditions. The amorphous olivine films exhibit a viscoelastic-viscoplastic behavior with a significant rate dependency. The strain-rate sensitivity m is equal to similar to 0 . 05 which is very high for silicates, indicating a complex out-of-equilibrium structure. The minimum apparent activation volume determined from nanoindentation experiments corresponds to Mg and Fe atomic metallic sites in the (Mg,Fe)(2)SiO4 crystalline lattice. The ambient temperature creep behavior of the amorphous olivine films differs very much from the one of single crystal olivine. This behavior directly connects to the recent demonstration of the activation of grain boundary sliding in polycrystalline olivine following grain boundary amorphization under high-stress. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of Acta Materialia Inc.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 5.301
DOI: 10.1016/J.ACTAMAT.2021.117257
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“On-chip very low strain rate rheology of amorphous olivine films”. Coulombier M, Baral P, Orekhov A, Dohmen R, Raskin JP, Pardoen T, Cordier P, Idrissi H, Acta materialia 266, 119693 (2024). http://doi.org/10.1016/J.ACTAMAT.2024.119693
Abstract: Recent observations made by the authors revealed the activation of stress induced amorphization and sliding at grain boundary in olivine [1], a mechanism which is expected to play a pivotal role in the viscosity drop at the lithosphere-asthenosphere boundary and the brittle -ductile transition in the lithospheric mantle. However, there is a lack of information in the literature regarding the intrinsic mechanical properties and the elementary deformation mechanisms of this material, especially at time scales relevant for geodynamics. In the present work, amorphous olivine films were obtained by pulsed laser deposition (PLD). The mechanical response including the rate dependent behavior are investigated using a tension -on -chip (TOC) method developed at UCLouvain allowing to perform creep/relaxation tests on thin films at extremely low strain rates. In the present work, strain rate down to 10-12 s- 1 was reached which is unique. High strain rate sensitivity of 0.054 is observed together with the activation of relaxation at the very early stage of deformation. Furthermore, digital image correlation (DIC), used for the first time on films deformed by TOC, reveals local strain heterogeneities. The relationship between such heterogeneities, the high strain rate sensitivity and the effect of the electron beam in the scanning electron microscope is discussed and compared to the literature.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/J.ACTAMAT.2024.119693
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“Grain boundary-mediated plasticity in aluminum films unraveled by a statistical approach combining nano-DIC and ACOM-TEM”. Baral P, Kashiwar A, Coulombier M, Delannay L, Hoummada K, Raskin JP, Idrissi H, Pardoen T, Acta materialia 276, 120081 (2024). http://doi.org/10.1016/J.ACTAMAT.2024.120081
Abstract: Nanomechanical on-chip testing is combined with nanoscale in situ digital image correlation and automated crystal orientation mapping in TEM to deliver novel statistically representative quantitative data about the deformation mechanisms in nanocrystalline aluminum films. The films are very ductile, with a rare stable multiple necking process with local strains reaching up to 0.45 and macroscopic elongation up to 0.17. The strain fields with resolution below 100 nm are related to the underlying microstructure and crystallographic orientation maps. This reveals nanoscopic shear bands forming preferentially along GB with high misorientations, tilted at +/− 45° with respect to loading direction. The analysis of these data prove that the strong strain delocalization process is promoted by GB migration and grain rotation, leading to large strain rate sensitivity. The distribution of misorientation angles between grains evolve during deformation. The GBs with misorientation between 20° and 40°, which are the GBs with highest energy, involve the largest strains.
Keywords: A1 Journal article; Engineering sciences. Technology; Electron microscopy for materials research (EMAT)
Impact Factor: 9.4
DOI: 10.1016/J.ACTAMAT.2024.120081
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