Evaluating plasticity of rejuvenated metallic glasses by effective enthalpy

Yang C.; Zhou H.B.; Duan J.; Cai S.L.; Ding G.; Zhang B.B.; Shi C.J.; Dai L.H.; Wilde G.; Jiang M.Q.

Abstract

Structural rejuvenation is a promising strategy to enhance the plasticity of metallic glasses, but quantitatively evaluating the rejuvenation-deformation relationship is challenging. In this work, we systematically investigate the compressive plasticity of a typical Zr-based metallic glass which is rejuvenated by elastostatic compression or cycled twists. Meanwhile, the thermodynamics and structural properties are carefully characterized for these rejuvenated glasses. An obvious gap in the plastic strain εp is observed between two sets of the rejuvenated glasses, although they have very close exothermic enthalpy ∆Hexo before glass transition. This plasticity gap is also reflected by the different modes of shear banding: straight for the elastostatic compression but deflected for the cycled twists. We use the concept of effective enthalpy ΔHeff and find a linear relationship between ΔHeff and εp for all rejuvenated glasses. This implies that the plastic deformability of glasses is determined not only by the existing free volume evaluated by ∆Hexo but also by the creating free volume required to enter the supercooled liquid state, as evaluated by the endothermic glass transition overshoot. Synchrotron high-energy X-ray diffraction reveals that the larger εp in glasses with higher ΔHeff arises from the enhanced structural heterogeneity caused by the decoupling of medium-range orders.