Two-step relaxations in metallic glasses during isothermal annealing

Isothermal annealing is a very useful strategy in modulating the properties and structures of metallic glasses, which has been regarded as a single relaxation progress. In this work, the enthalpy relaxation of Au-based metallic glasses are studied using a high-precision calorimetry. An intriguing transition from β relaxation to α relaxation was confirmed during isothermal annealing. Energy landscape model is proposed to quantitatively explain how the relaxation modes transform. It is found that a small enthalpy decrease (about 0.8 kJ/mol) in initial state causes an extremely large increase (about 100 kJ/mol) in relaxation barrier, which is attributed to the enhanced cooperative atomic motion. These results open a gate for precisely understanding the role of different relaxation modes in modifying the properties of metallic glasses.