Superelasticity over a wide temperature range in metastable β-Ti shape memory alloys

Shape memory alloys (SMAs) offer many technological advantages in various applications due to shape memory effect and superelasticity. Among them, superelasticity persists within a narrow temperature range (<100 K), beyond which, superelasticity disappears due to the loss of reversibility in the thermoelastic martensite. Here we present a unique metastable β-Ti SMA of Ti-19Nb-10Zr-1Fe, showing the classic superelasticity over a wide temperature range from 123 K to 373 K. It is verified experimentally to be originated from two concurrent nano-scale transitions: β → α″ martensitic nanodomains (strain glass transition), and β → nano-sized a-ω precipitates. Requiring no pre-training, a classic superelasticity with stress plateaus was associated with the reversible stress-induced strain glass to martensite transformation by in-situ SXRD. Further, a temperature-stress phase diagram was constructed, which facilitates the understanding of wide temperature superelasticity in metastable β-Ti SMAs, and may serve as a guide map for future designing and application of advanced β-Ti based SMAs.