Enhancement of the superelastic behavior of the Ti–Au–Cr–based shape memory alloys via the manipulations of annealing–treatments and Ta additions

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Shape memory alloys (SMAs) have attracted much attention due to their applicability to biomaterials, such as surgery tools, in this rapid population aging years. Promising Ti–Au–Cr–Ta SMAs, which possess high biocompatibility, good X–ray contrast, proper mechanical properties, and functionality (i.e., superelasticity), were systematically studied in this work. Alloys were successfully manufactured by the physical metallurgy methods; in addition, their phase constituents, fundamental mechanical properties, shape recovery behaviors were also examined. The phase constituents, which was successfully manipulated by annealing–treatments at various temperatures, composed of the parent β–phase majorly and the Ti3Au intermetallic compound minorly. Superelasticity was revealed in certain specimens due to the well–manipulated phase constituents, phase stability, and the amount of Ti3Au precipitates. Followed by the annealing–treatments, Ta addition concentrations were systematically fine–tuned for further enhancement of the mechanical properties and the functionalities. It was found that the annealing–treated alloys performed better than the solution–treated specimens in the literature in terms of mechanical properties. An excellent superelasticity, which exhibited almost 100% shape recovery rate during unloading of the externally applied stress, was practiced in the both thermally and compositionally optimized Ti–Au–Cr–Ta SMAs.