Structure study of a metallic glass using positron annihilation methods

Abstract

The effects of vitrification and cold rolling on the structure in a metallic glass of Pd.775Cu.06Si.165 alloy and crystalline Pd have been investigated using positron lifetime and angular correlation measurements. It is concluded that: A) the metallic glass contains a negligible concentration of vacancy-like defects and the crystallite model may be excluded as a possible structure of metallic glasses, B) the glass-crystalline boundaries contain a very small fraction of vacancy-like defects and exhibit a smooth transition structure from glassy to crystalline regions, C) the cold rolling of the metallic glass induces no vacancy or dislocation-like defects and plastic flow in metallic glasses is accompanied by cooperative atomic regroupings somewhat analogous to the visco flow of glasses near the glass transition temperature, D) the electronic structure of the Pd-Cu-Si alloy alters little upon disordering from a crystalline to glassy state, but exhibits a large change from that of crystalline Pd. This is attributed to the valence electrons transferred from Si to the d-shell of Pd in the Pd-Cu-Si alloy.