Transient regimes during high-temperature deformation of a bulk metallic glass: a free volume approach

The homogeneous deformation of a zirconium-based bulk metallic glass is investigated in the glass transition range. Compression and stress-relaxation tests have been conducted. The stress-strain curves are modeled in the framework of the free volume theory, including transient phenomena (overshoot and undershoot). This approach allows several physical parameters (activation volume, flow defect creation and relaxation coefficient) to be determined from a mechanical experiment. This model is able to rationalize the dependency of stress overshoot on relaxation time. It is shown that, due to the relationship between flow defect concentration and free volume model, it is impossible to determine the equilibrium flow defect concentration. However, the relative variation of flow defect is always the same, and all the model parameters depend on the equilibrium flow defect concentration. The methodology presented in this paper should, in the future, allow the consistency of the free volume model to be assessed.