金属ガラスの熱的構造若返り

抄録

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 T_a/T_g and V_c/V_i to evaluate the rejuvenation behavior. A rejuvenation map was actually constructed using these two parameters. It is important to satisfy the condition of T_a/T_g ≥ 1.2 during annealing because of the resetting the thermal history of metallic glasses over 1.2T_g 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 T_a/T_g ~ 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.