Approaching the universal yield point of bulk metallic glasses from molecular dynamics simulations

Li, J.*; Shimizu, Futoshi ; Ogata, Shigenobu*; Kaburaki, Hideo

Most bulk metallic glasses yield at about 2% strain in uniaxial tension/compression tests. A careful analysis of the elementary shear behavior in contrast to crystalline concepts such as the generalized stacking fault energy reveals a simple explanation. We perform molecular dynamics simulations on 2-component model systems and a 5-component BMG system, observing and characterizing the nucleation and evolution of shear bands. Despite gross uncertainties in the interatomic interactions and the predeformation glass structure, our MD results give a reasonable account of the 2% universal yield point. The general concepts of glass rejuvenation and aging, which we call alienation and recovery processes in the context of intense localized shear, and occurring mainly within a timescale of 1-100 atomic vibration periods, is postulated to play a critical role. This mechanistic model can explain why the yield point is relatively insensitive to the interatomic potential and the structure of the pre-deformed glass.