Shape Memory Effect Controlled by Localized Flow of Liquid-Like Atoms in Metallic Glass

Shape memory effect (SME) usually exists in crystalline alloys, polymers, ceramics, and their composites, induced by phase changes like Martensitic transformation and glass transition. Here, we report SME in metallic glasses (MGs) far below the glass transition temperatures. It is found that the recoverable strain of the trained MG, which reflects SME, increases with training temperature, stress, and time. The SME is interpreted as an intrinsic phenomenon of MGs, in which the local liquid-like regions (LLRs) with viscosities of ∼10¹⁰ Pa s and surrounding elastic matrix serve as the switching and memorizing segments, respectively. The activation of the LLRs, affected by deformation temperature and time in an Arrhenius-type relation, involves the nonaffine displacement of solute atoms and the rearrangement of unstable medium-range ordered (MRO) structure. In contrast, the recovery of the matrix containing more rigid MRO string-like structure is mainly contributed by the reversible variation of short-range atomic distance. Due to the instability of the LLRs, a transition from rejuvenation to aging appears during the shape memory (SM) process. The results reveal a new mechanism of SME linking to the dynamic structural heterogeneity of MGs and could be insightful for designing new types of glassy SM functional materials.