Abstract
Structural rejuvenation in metallic glasses by a thermal process (i.e. through recovery annealing) was investigated experimentally and theoretically for various alloy compositions. An increase in the potential energy, a decrease in the density, and a change in the local structure as well as mechanical softening were observed after thermal rejuvenation. Two parameters, one related to the annealing temperature, Ta/Tg, and the other related to the cooling rate during the recovery annealing process, Vc/Vi, were proposed to evaluate the rejuvenation phenomena. A rejuvenation map was constructed using these two parameters. Since the thermal history of metallic glasses is reset above 1.2Tg, accompanied by a change in the local structure, it is essential that the condition of Ta/Tg ≥ 1.2 is satisfied during annealing. The glassy structure transforms into a more disordered state with the decomposition of icosahedral short-range order within this temperature range. Therefore, a new glassy structure (rejuvenation) depending on the subsequent quenching rate is generated. Partial rejuvenation also occurs in a Zr55Al10Ni5Cu30 bulk metallic glass when annealing is performed at a low temperature (Ta/Tg ~ 1.07) followed by rapid cooling. This behavior probably originates from disordering in the weakly bonded (loosely packed) region. This study provides a novel approach to improving the mechanical properties of metallic glasses by controlling their glassy structure.
Highlights
Metallic glasses have been applied in industry owing to their attractive mechanical, physical, and chemical properties [1,2,3], which originate from the intrinsic random atomic configuration
We examined the properties of the rejuvenated metallic glass samples using the normalized recovery annealing temperature, Ta/Tg, and the cooling rate, Vc/Vi, for a universal evaluation, as both parameters dominantly affect the rejuvenation process [33]
We investigate the structural rejuvenation in metallic glasses by a simple thermal process based on experimental and simulation studies performed for various alloy compositions
Summary
Metallic glasses have been applied in industry owing to their attractive mechanical, physical, and chemical properties [1,2,3], which originate from the intrinsic random atomic configuration. With respect to this random structure, relaxation phenomena have been recognized as important subjects in fundamental and applied research [4]. Controlling the relaxation state of metallic glasses is very important for improving their mechanical properties. It has been regarded that the recovery of a less relaxed state (i.e. rejuvenation) is very difficult, since the relaxation process is a non-reversible reaction. Rejuvenation has been induced only by introducing severe plastic
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