Creation of free volume in amorphous Pd40Ni40P20 during high temperature deformation

The deformation of amorphous Pd40Ni40P20 is investigated as a function of temperature and strain rate. The free volume is used as a measure for the state of structural relaxation, and its influence on the material's mechanical properties is investigated using Differential Scanning Calorimetry (DSC) traces as a measure for the frozen-in amount of free volume after heat treatment and deformation. It is found that amorphous Pd40Ni40P20, when preannealed into its metastable equilibrium state, shows a large strain softening effect when deformed at temperatures close to the glass transition temperature. It is shown that the strain softening is caused by the creation of additional free volume due to the deformation, and that the material reaches a new, strain-rate dependent equilibrium slate. In order to understand this effect, the free volume theory is used as a starting point to investigate the mechanism by which deformation in metallic glasses occurs. (C) 1997 Elsevier Science S.A.