The achievement of room-temperature (RT) superelasticity in a Ti-Mo-Al ternary alloy system through the addition of a relatively high concentration of Al to manipulate the phase stability of the ω phase is realized in this study. The composition of the Ti-6 mol% Mo (Ti-11.34 mass% Mo) alloy was designated as the starting alloy, while 5 mol% Al (=2.71 mass% Al) and 10 mol% Al (=5.54 mass% Al) were introduced to promote their superelastic behavior. Among the alloys, Ti-6 mol% Mo-10 mol% Al alloy, which was investigated for the very first time in this work, performed the best in terms of superelasticity. On the other hand, Ti-6 mol% Mo and Ti-6 mol% Mo-5 mol% Al alloys exhibited a shape memory effect upon heating. It is worth mentioning that in the transmission electron microscopy observation, ω phase, which appeared along with β-parent phase, was significantly suppressed as Al concentration was elevated up to 10 mol%. Therefore, the conventional difficulties of the inhibited RT superelasticity were successfully revealed by regulating the number density of the ω phase below a threshold.
In order to develop high performance biomedical shape memory alloy having both good biocompatibility and high X ray radiography resolution, effects of Al and Cu contents on the martensitic transformation, microstructure and mechanical properties of AuCuAl ternary alloys were studied. Differential scanning calorimetry revealed that the martensitic transformation start temperature decreased with a rate of -7 K/molAl in the Au 30 molCu Al alloys. Besides, the M s increased with a rate of 18 ~53 K/molCu in the Au Cu 15~20 molAl alloys in the Cu poor side of stoichiometry, while the M s was almost constant in Cu rich side. By taking into account of the estimated defect structures, the number of Au Al atomic bonds is important for the stabilization of the parent b phase. Corresponding microstructural change due to the martensitic transformation was confirmed by optical microscopy. Vickers hardness of the Au 30 molCu Al alloys decreased with increasing Al content, and a minimum was reached at 20~25 molAl and then the Vickers hardness increased at 25 molAl. The alloys at a limited composition range around Au 30~31 molCu 14~15 molAl possessed both high strength and ductility in addition to pseudoelasticity, while the other alloys exhibited poor ductility.
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