NANOstructures induced by elementary PLASTic mechanisms – NANOPLAST

The emergence process of moving dislocations is characterised by the appearance of steps at the free surface of crystalline materials, with an elementary height equal to the component of the activated dislocation Burgers vector projected on the surface normal, i.e. only few tens of nanometre. Recent developments of scanning probe microscopes, such as atomic force and scanning tunnelling microscopy (AFM and STM), enable nano-scale surface features to be routinely imaged, measured and analysed, even under deformation conditions. A home made device allowing in situ AFM observation of the surface of specimens under deformation has been built at the Laboratoire de métallurgie physique (LMP). Significant experimental results have already been obtained, as for instance concerning the operating mode of Frank-Read sources, individual and collective dislocation movements. This equipment, which is supporting one of the main research topic of the LMP, is however limited to atmospheric working conditions leading to potential surface contaminations and low lateral scanning probe microscopy analysis. These drawbacks restrict the investigations to materials that do not suffer too much from oxidation (such as oxides, superalloys, ionic crystals...). - In this context, the ambitious project that is outlined in this proposal is aimed at developing in situ deformation devices (uniaxial compression and tension set-up and nanoindentation working at variable temperatures) coupled with AFM-STM facilities under UHV environment. This unique UHV experimental equipment especially dedicated to mechanical testing will considerably improve the performances of our existing equipment under atmospheric conditions and gives us a leadership position in the domain of surface plasticity. - From a general point of view, this project intends to answer to one of the main existing objectives in materials science that consists to describe the mechanical properties of materials in terms of their micro-structural defects by relating various length scales of observations, starting from nano- to meso-scale. It is expected that the new experimental results with 3D atomic level resolution will allow a better understanding of basic deformation mechanisms controlling deformation kinetics and will establish the foundation for theoreticians to propose and/or develop more reliable models for describing the plastic response of crystalline materials under stress. ...