Deformation twinning in Cr2AlC MAX phase single crystals: A nanomechanical testing study

In a recent study [1], we observed and characterized for the first time deformation twinning in the Ti2AlN MAX phase deformed at high temperature (800°C) by Berkovich nanoindentation. Since plastic deformation in these nanolayered materials was believed to be governed only by basal plane dislocations involved in kink band mechanisms, this result has shed a new light on the mechanical behavior of MAX phases. In order to go further in the understanding of twinning deformation mechanisms in MAX phases, we performed a study in Cr2AlC single crystal, deformed at room temperature by spherical nanoindentation and by micropillar compression tests, in such an orientation that the basal plane was edge on, to inhibit basal dislocations and to promote twinning. Please click Download on the upper right corner to see the full abstract

On the possible role of hydrogen in the formation of fatigue striation in a moist atmosphere

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Couplage fort des transitions électronique de matériaux moléculaires en phase liquide

This thesis contributes to the fundamental understanding of the phenomenon of strong coupling of light with organic molecules by implementing new systems and techniques in order to investigate property modifications of molecules coupled with photonic resonances. State-of-the-art nanofabrication techniques for the formation of large hole-array gratings in metals and nanofluidic Fabry-Perot (FP) cavities are presented. These systems were then invested to study, under strong coupling, surface and bulk properties modifications of organic molecules in the solid and liquid phase. In particular, electronic transitions of cyanine dye molecules in liquid solutions were coupled to resonant photonic modes of specially designed nanofluidic FP cavities. Their strong coupling has led to an enhancement of the emission quantum yield, highlighting the radiative nature of the associated polaritonic states.Cette thèse contribue à la compréhension fondamentale du phénomène de couplage fort de la lumière avec des molécules organiques en mettant en œuvre de nouveaux systèmes et de nouvelles techniques, afin d'étudier les modifications de propriétés de molécules couplées à des résonances photoniques. Nous présentons des techniques de nanofabrication avancées pour la création de grands réseaux de trous sur des métaux et de cavités de Fabry-Pérot (FP) nanofluidiques. Ces systèmes sont ensuite utilisés pour étudier, sous régime de couplage fort, les modifications des propriétés de surface et de volume de molécules organiques en phase solide et liquide. En particulier les transitions électroniques de molécules du colorant cyanine en solution liquide ont été couplées à des modes photoniques résonants de cavités FP nanofluidiques spécialement conçues. Leur couplage fort a conduit à une amélioration du rendement quantique d'émission, mettant en évidence la nature radiative des états polaritoniques

Loss of ductility in optimized austenitic steel at moderate temperature: A multi-scale study of deformation mechanisms

International audienceA Ti-stabilized cold-worked 15Cr-15Ni steel, called AIM1 (Austenitic Improved Material #1), has been selected as a candidate for the fuel cladding tubes of sodium-cooled fast reactors. This steel exhibits an unusual loss of ductility between 20 and 200 °C for both solution-annealed and cold-worked conditions, which is similar to that observed for Twinning Induced Plasticty steels and for the 200 and 300 series stainless steels. Therefore, a multi-scale study has been carried out to determine the deformation mechanisms that are active at different temperatures. Tensile tests have been performed to characterize the macroscopic material behavior, and Electron Backscattered Diffraction and Transmission Electron Microscopy characterization techniques have been used to investigate the meso and micro-scale phenomena, such as the deformation microstructures and the evolution of the lattice defects. The parameters governing the deformation mechanisms have been examined, with particular attention paid to the conditions for mechanical twinning activation. This work required an original study of the variation of Stacking Fault Energy with temperature, based on the measurement of the dissociation extension of dislocation nodes. An increase in the SFE was observed between 20 and 200 °C. After reviewing the existing models for predicting twinning, the present study proposes an approach based on the minimization of the total energy of the material to explain why twinning is not favorable at high temperatures. At 20 °C, both dislocation slip and twinning are active and efficient mechanisms to release the strain energy. However, at 200 °C, only dislocation slip is favorable and is often associated with dislocation cross-slip

Electronic Light–Matter Strong Coupling in Nanofluidic Fabry–Pérot Cavities

Electronic light–matter strong coupling has been limited to solid molecular films due to the challenge of preparing optical cavities with nanoscale dimensions. Here we report a technique to fabricate such Fabry–Pérot nanocavities in which solutions can be introduced such that light–molecule interactions can be studied at will in the liquid phase. We illustrate the versatility of these cavities by studying the emission properties of Chlorin e6 solutions in both the weak and strong coupling regimes as a function of cavity detuning. Liquid nanocavities will broaden the investigation of strong coupling to many solution-based molecular processes