Amorphous multielementary alloys: A preparation route for shape memory alloys

Abstract

Rapid solidification methods (planar flow casting and twin roll casting) have been used to improve and simplify processing of shape memory alloys. Our goal is to synthesize amorphous as-cast materials and then near-net shaping can be obtained while working in the supercooled liquid temperature region. Materials are thereafter crystallized in order to recover a reversible austenite–martensite transformation. Alloying equiatomic Ni–Ti intermetallic compound with selected elements leads to better glass forming ability (GFA). Despite the fact that compositional requirements for obtaining thermoelastic reversible martensitic transformation and glass formation are different and contradictory, the pseudo-binary alloys developed by substitution of Zr, Hf for Ti, and Cu, Co, Pd, Sn for Ni are good candidates to exhibit both phenomena. We report here a choice of compositions, which after fast cooling, are amorphous and demonstrate a superplastic behaviour in the Δ T ( T x − T g) region. After an adequate thermal treatment, a martensitic phase is obtained for some compositions, and such alloys demonstrate shape memory and superelastic properties.