Effect of aluminum addition on microstructure, mechanical properties and high temperature tribological properties of nickel-rich NiTi alloy

The nickel-rich 60NiTi alloy with high strength, excellent corrosion resistance and low elastic modulus, is expected to be the next generation of bearings in aerospace applications. However, it needed the heat treatment to enhance its hardness, and the poor performance in wear and oxidation resistance at higher temperatures also limit its wide application. In this study, the effects of Hf and Al on the microstructure, mechanical properties, high-temperature tribological properties and oxidation resistance of 60Ni-40Ti alloys were studied. The results showed the Al addition reduced the precipitation of the second phases such as Ni₃Ti and Ni₃Ti₂ in the matrix, and formed the new NiTi₂, which helped improve the microhardness of the alloy. Tribological results proved that the 54Ni-40Ti-3Hf-3Al alloy obtained better tribological performance in almost all test conditions than 60NiTi and 57Ni-40Ti-3Hf, this was attributed to the formation of the dense and stable oxide glaze layer on the wear surface. The wear mechanism transitioned from abrasive wear and adhesive wear at room temperature to oxidation wear and delamination wear at 300 °C. This work provided a method to improve the wear resistance of 60NiTi alloy at high temperature.