On the structural relaxation of bulk metallic glass under warm deformation

The influence of both isothermal annealing and warm deformation on the structural relaxation behavior of Zr44Ti11Cu9.8Ni10.2Be25 (LM1B) bulk metallic glass (BMG) was investigated. The structurally relaxed samples were obtained from warm extrusion to introduce different amounts of free volume annihilation. We employed density measurements as well as differential scanning calorimetry to study free volume changes in these structurally relaxed samples. The results demonstrated that isothermal annealing within the supercooled liquid region (SLR) caused annihilation of free volume by ∼0.1%, but a small amount of in situ deformation promoted the annihilation process. In contrast to the conventional belief that annealing induced embrittlement caused by the reduction of free volume and densification, it is interesting to note that, in this study, when material was relaxed at the mid-temperature within the SLR (673 K for LM1B) plastic strain actually increased as compared to the as-received counterpart. This indicates that proper warm deformation can improve the room temperature plasticity of BMG as a result of subtle atomic-scale structural changes.