Soutenance de thèse : Meng LIANG

Analysis of small-scale plasticity of bulk Cu-Zr metallic glasses under deformation by atomistic simulations

Doctorante : Meng LIANG

Laboratoire INSA : MATEIS

Ecole doctorale : ED34 : Matériaux de Lyon

Metallic glasses (MGs) are one of the most attractive new materials with excellent mechanical properties. They have wide applications for micromechanics microelectronics, jewelry, biomaterials, aerospace and other fields. However, the poor plasticity of MGs at room temperature limits their industrial applications. Therefore, the improvement of ductility of MGs has become an important issue in the field of materials science. The focus of this thesis is to investigate the plasticity of MGs prepared under different conditions by Molecular Dynamics (MD) simulations and to characterize the plastic events at the microscopic scale in order to understand how plasticity evolves and ultimately assess under which conditions the ductility can be improved.
The system investigated in this thesis is a model binary Cu-Zr MG. We study the effect of quenching rate, composition, strain rate and temperature on the plasticity of Cu-Zr MG. After quasi-static shear deformation, it can be concluded that the plasticity of Cu-Zr MGs is more homogeneous, i.e. strain localization and shear bands are hindered, when the materials are prepared with the highest quenching rate, when they contain less Cu, and when they are submitted to the highest strain rate and temperature.
In order to understand the microscopic mechanisms involved in the plasticity, we have developed a method to identify and characterize individual plastic events. By this way,  we can evaluate their number, their plastic intensity, their average size and their orientation. Furthermore, we are able to reconstruct the mechanical behavior by considering the plastic events as Eshelby’s inclusions in an infinite elastic matrix.
Finally, we show that thermal cycling below the glass temperature can be an effective way to improve the ductility of MG by rejuvenating them.