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

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 beta-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.