A Review of Investigations on Microstructure and Mechanical Properties of the Present Achievements of the Ti-Au-based Shape Memory Alloys

Owing to the worldwide growth of aging population, the biomedical materials, such as implantation materials, are greatly demanded in these decades. Shape memory alloys (SMAs) and superelastic (SE) alloys, whose shape deformation could be manipulated by controlling the stress and temperature applied, are considered as promising materials to practice the biomedical applications. In this article, the β-Titanium (β-Ti) alloys were chosen for their high biocompatibility and appropriate shape deformation behaviors. First, Gold (Au) element was chosen as the tailoring element to functionalize the β-Ti alloys for its high X-ray contrast, which is a crucial prerequisite for the biomedical materials. Second, to impose the phase transformation temperature to be around the human body temperature, various transition metals were examined and introduced into the Ti-Au-based alloys. Based on the screening results of the transition metals, chromium (Cr) was determined to be the addition element. To further enhance the X-ray contrast and biocompatibility as well as conduct the fine-tune of phase stability of the Ti-Au-Cr-based alloys, Tantalum (Ta), which possesses high X-ray contrast and excellent biocompatibility, was served as the fourth element in this system and its addition concentration was optimized. Besides to the selection of the elements, the annealing temperature and annealing time length were both investigated to optimize the transformation temperature, phase stability, and microstructures. It was found that the Ti-4Au-5Cr-5Ta alloy, which was annealed at 1073 K for 1.8 and 3.6 ks performed a room temperature superelasticity, showed almost 100% shape recovery upon unloading.