Thermal rejuvenation in metallic glasses

It is found that metallic glasses can be rejuvenated by a thermal process using experimental and simulation methods. We have reported that an increase in the potential energy, decrease in the density, and change in the local structure as well as mechanical softening were observed after the thermal rejuvenation. We proposed two parameters in the annealing condition of Ta/Tg and Vc/Vi to evaluate the rejuvenation behavior. A rejuvenation map was actually constructed using these two parameters. It is important to satisfy the condition of Ta/Tg = 1.2 during annealing because of the resetting the thermal history of metallic glasses over 1.2Tg for rejuvenation. The glassy structure changes into a more disordered state by rejuvenation, resulting in the disappearance of icosahedral short-range order (SRO). We also investigated that the rejuvenation occurs partially in a Zr55Al10Ni5Cu30 bulk metallic glass (BMG) when it is annealed at Ta/Tg ~ 1.07 followed by rapid cooling. This phenomenon probably originates from disordering in the weakly bonded (loosely packed) region in the heterogeneous local structure model. Such the thermal rejuvenation provides a novel approach for improving the mechanical properties of metallic glasses by controlling their intrinsic glassy structure. © 2019 Society of Materials Science Japan. All rights reserved.