Ultrafine shape memory alloys synthesized using a metastable metallic glass precursor with polymorphic crystallization

Abstract Metallic glasses have been considered as a precursor for developing nano- or ultrafine-structured alloys based on its crystallization behavior at large undercooled liquid state. However, the multicomponent system, requiring high glass-forming ability, makes it difficult to control the crystallization mechanism, and leads to the formation of brittle intermetallic compounds during crystallization. Here, we present an intermetallic-type metallic glass precursor designed via thermodynamic and physical considerations. The metallic glass precursor polymorphically crystallized into ultrafine-structured single-phase shape memory alloy. The crystallization kinetics and final grain-size strongly depend on isothermal annealing temperatures. The shape memory alloys fabricated using the metallic glass precursor revealed excellent superelastic and shape memory effects, which was affected by the critical stress for martensitic transformation depending on the grain size. Our approach and discovery provide a feasibility of the simple fabrication processing for ultrafine-structured shape memory alloys by one-step heat-treatment technique including thermoplastic forming of metallic glass precursor.