Temperature dependence of mechanical properties and pressure sensitivity in metallic glasses below glass transition

An experimental investigation into the variation of the mechanical properties (yield stress, yield strain, elastic moduli, hardness) from sub-ambient temperature (77 K) to that just below the glass transition temperature, of different bulk metallic glasses was conducted. Particular emphasis was on the constraint factor, the ratio of hardness to compressive yield stress, which is taken to be the proxy for the temperature dependence of pressure sensitive plastic flow. All the mechanical properties, except the constraint factor, decrease linearly, throughout the temperature range examined, with temperature and when normalized exhibit certain universal tendencies. The constraint factor was found to increase, monotonically but not necessarily linearly, with temperature. Finite element analyses, with pressure dependent constitutive behaviour, were performed in order to extract pressure sensitivity from the indentation load-displacement curves reported by Schuh et al. in 2004. This, in turn, was used to predict the variation of constraint factor with temperature. A good correlation suggests that the increase in constraint factor with temperature is indeed associated with enhanced pressure sensitivity.