Abstract
Cycling of a metallic glass between ambient and cryogenic temperatures can induce higher-energy states characteristic of glass formation on faster cooling. This rejuvenation, unexpected because it occurs at small macroscopic strains and well below the temperatures of thermally induced structural change, is important, for example, in improving plasticity. Molecular-dynamics simulations elucidate the mechanisms by which thermal cycling can induce relaxation (reaching lower energy) as well as rejuvenation. Thermal cycling, over tens of cycles, drives local atomic rearrangements progressively erasing the initial glass structure. This arises mainly from the heating stage in each thermal cycle, linked to the intrinsic structural heterogeneity in metallic glasses. Although, in particular, the timescales in MD simulations are shorter than in physical experiments, the present simulations reproduce many physically observed effects, suggesting that they may be useful in optimizing thermal cycling for tuning the properties of metallic glasses and glasses in general.
Highlights
For any type of glass of given composition, its properties can vary widely, depending on the structure reached by varying the production process and subsequent treatments [1]
Rejuvenation can be induced by mechanical deformation [2,3,4,5,6], by reheating and rapid quenching [7], or irradiation [8], but among such methods, cryogenic thermal cycling (CTC) [9] is straightforward to apply
As described in Methods, we focus on the vibrational density of states (VDOS) g(E) and the atomic participation ratio Pi in low-frequency modes (Supplementary Fig. S3)
Summary
For any type of glass of given composition, its properties can vary widely, depending on the structure reached by varying the production process and subsequent treatments [1]. For metallic glasses (MGs), annealing-induced relaxation (ageing) can lead to severe embrittlement, and there is a focus on the reverse process of rejuvenation. Rejuvenation can be induced by mechanical deformation [2,3,4,5,6], by reheating and rapid quenching [7], or irradiation [8], but among such methods, cryogenic thermal cycling (CTC) [9] is straightforward to apply. The underlying atomistic mechanisms of the effects of CTC clearly merit investigation
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