The effects of hydrogen on viscoelastic relaxation in Zr–Ti–Ni–Cu–Be bulk metallic glasses: implications for hydrogen embrittlement

Abstract The effects of hydrogen on the viscoelastic relaxation behavior of a Zr–Ti–Ni–Cu–Be bulk metallic glass have been investigated in an attempt to elucidate hydrogen-affected flow and fracture behavior. Dynamic mechanical testing was performed to study relaxation behavior near the glass transition temperature. Relaxation time constants were increased in the presence of hydrogen with a concomitant increase of thermal activation energy. In addition, the glass transition temperature was increased and crystallization kinetics retarded in the presence of hydrogen leading to enhanced thermal stability. Positron annihilation spectroscopy was employed to study the interaction of hydrogen and open-volume regions. While hydrogen charging was found to decrease the open-volume regions in the amorphous phase, an increase in free volume was observed in the crystalline counterpart. The amorphous phase was found to have a greater hydrogen absorption capacity compared to its crystalline counterpart. Relaxation behavior, crystallization kinetics and the interaction of hydrogen with the amorphous microstructure are discussed. Finally, the effects of retarded relaxation processes on fracture resistance are considered.