Understanding the mechanism for the embrittlement of a monolithic Zr-based bulk metallic glass by oxygen

Monolithic bulk metallic glasses (BMGs) with a nominal composition of Zr₆₅Cu_27.5Al_7.5 and the oxygen concentrations of 0.06 at.% and 0.68 at.% were prepared respectively. Oxygen effects on the deformation behavior and as-cast structural state were investigated. Although no crystalline phases were found in the BMG with higher oxygen concentration, the compressive plasticity was dramatically decreased. It was found that there is no direct correlation between the notable embrittlement and the initial free-volume content in the BMG. Geometrically-constrained compression tests for the BMGs shown that the processes of free-volume accumulation and shear band propagation during plastic deformation were obviously retarded by oxygen. It appears that the mechanism for the oxygen-induced embrittlement was closely related with the decreased atomic mobility by oxygen. As an indicator of atomic mobility, activation energy may be used as a parameter to evaluate the plasticity of monolithic Zr-based BMGs with different dissolved oxygen concentrations.