Effect of Y Addition on Isothermal Oxidation Behavior of Ti50Ni50 Shape Memory Alloy at 700 °C

The effect of Y addition on the microstructure and isothermal oxidation behaviour of an equal-atomic Ti-Ni shape memory alloy at 700 °C in air was investigated. The results show that the grains of the Ti-Ni alloy are evidently refined with Y addition. The oxidation rate significantly declines with the addition of 0.5 at%Y and 1.0 at%Y because the fast outward diffusion of Ti is inhibited by the segregated Y ions. However, the oxidation rate increases with 5.0 at%Y addition since the formation of oxide along the NiY phase breaks the continuity of the TiO2 scale.