Change in free volume during the homogeneous flow of Zr-based bulk metallic glass matrix composite

The influence of plastic deformation on the structure of a Zr55.9Cu18.6Ta8Al7.5Ni10 bulk metallic glass composite (BMGC) with a Ta solid solution as the second phase was investigated during a compression test in the supercooled liquid region, as a function of strain rate and the amount of strain. The structure of the BMGC after deformation was characterized by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). It was found that an increase in excess free volume took place during plastic deformation. High strain rate can promote the generation of more free volume, which eventually leads to a reduction of the glass transition temperature and even splitting of the crystallization process. Microhardness measurement indicated that deformation induced softening of the BMG composite, probably due to the formation of nanovoids resulting from the increase of free volume.