Effects of Cu, Re, and Mo ternary additions on the tribological and electrochemical properties of NiTi-based alloys fabricated by mechanical alloying and spark plasma sintering

The toxicity of Ni²⁺ ions has been the bane of NiTi shape memory alloy (SMA) in various applications, such as biomedical. However, the formation of TiO₂ film, which doubles as a resistance to corrosion and wear in frictional applications, has been reported as unstable when exposed for a long period, further causing the mobility of Ni²⁺ to the surface. Therefore, this study investigated the enhancement in corrosion and tribological resistance of NiTi-based ternary alloys incorporated with two of the Cu, Re, and Mo for a given sample. The NiTi-based ternary alloys were fabricated via spark plasma sintering (SPS). The microstructure and crystal phases of the sintered sample were investigated using a scanning electron microscope and X-ray diffractometer, respectively. Their electrochemical responses in H₂SO₄ and NaCl solutions and their tribological features were determined, which showed different enhancement levels compared to the NiTi alloy. For the tribological properties, a combination of NiTi-0.5Re-0.8Mo gave the best wear resistance with a wear rate of about 1.219 × 10⁻⁷ mm³/N·m at 15N. The electrochemical test also revealed that the NiTi-Re-Mo ternary alloy group has the lowest corrosion rate, which can be attributed good chemical resistance of the combined Re and Mo that aided in TiO₂ film stability in both acidic and saline environments.