Analysis of small-scale plasticity of bulk Cu-Zr MGs under deformation by atomistic simulations ; Analyse de la plasticité à petites échelles des verres métalliques massifs à base Cu-Zr sous déformation par simulations atomistiques

Metallic glasses (MGs) are very promising new materials because of their excellent mechanical properties. They have many potential applications in micromechanics, microelectronics, jewelry, biomedical, aerospace and many other fields. However, their low plasticity at room temperature limits their wide diffusion in the industry for the moment. Therefore, the improvement of their ductility has become a major issue in materials science. The objective of this thesis is to study the plasticity of metallic glasses prepared under different conditions, by molecular dynamics (MD) simulations and to characterize the plastic events occurring at the microscopic scale during their deformation in order to understand how the plasticity evolves, and finally to evaluate under which conditions the ductility can be improved. The system studied in this thesis is a binary Cu-Zr model. We studied the effect of quenching rate, composition, strain rate and temperature. Our simulations show that during quasi-static shear deformation, the plasticity of Cu-Zr glasses is more homogeneous, i.e., the localization of deformation and the formation of shear bands are more limited, when these materials are prepared with higher quenching rates, when they contain less copper, and/or when they are subjected to higher deformation rates and/or temperatures. In order to understand the microscopic mechanisms involved in this plasticity, we have developed a method to identify and characterize individual plastic events. In this way, we can evaluate their number, plastic intensity, average size and orientation. Moreover, we are able to reconstruct the simulated mechanical behavior by considering the plastic events as Eshelby inclusions in an infinite elastic matrix. Finally, we show that thermal cycling below the glass transition temperature can be, under certain conditions, an efficient way to improve the ductility of metallic glasses, via their rejuvenation. ; Les verres métalliques (MGs) sont de nouveaux matériaux très prometteurs du fait de leurs ...