Thermal cycling-induced evolution of structure and local mechanical properties in metallic glass

The influence of thermal treatment on the long-term mechanical properties of two different kinds of metallic glasses was investigated in this study. As model systems, bulk metallic glasses (BMGs) with the composition of Pd43Cu27Ni10P20 cycled 60, 200, and 500 times between 77K and room temperature and Zr44Ti11Cu10Ni10Be25 cycled 300, 500, and 700 times have been employed. To ensure that meaningful steady-state properties have been reached, experiments have been performed three years after sample preparation. It was found that the thermal cycling of the Pd-based BMGs had induced rejuvenation when compared to the non-cycled sample, including a higher relaxation enthalpy, lower modulus, hardness, activation volume, and shear transformation zone volume. However, for Zr-BMGs, a rejuvenation to relaxation behavior is observed. Also, while Zr-BMGs showed significantly changes in yielding behavior upon thermal cycling, fluctuations in Pd-BMGs were negligible. We speculate that the observed substantial differences between these two samples might originate because Pd-BMG has a denser structure and higher fragility, making it more difficult to induce excess free volumes.