High temperature wear behavior of Ni-rich NiTi-based alloys

Ni-rich NiTi-based alloys have been regarded as promising candidates for tribological applications because of their high hardness and excellent corrosion resistance. In this work, the effects of aging and Hf addition on microstructure and unlubricated wear properties of Ni-rich NiTi alloys, Ni 55 Ti 45 and Ni 55 Ti 40 Hf 5 alloys, were investigated. Both the aging and addition of Hf increase the microhardness of Ni 55 Ti 45 alloy. The aged Ni 55 Ti 40 Hf 5 alloy shows the largest value of microhardness resulting from the combination of the precipitation strengthening of Ti 3 Ni 4 and H phases, and the solid-solution strengthening of Hf atom. The wear resistance of the studied alloys can be improved by the aging and Hf addition. The coefficient of friction values obtained at 400 °C are lower than that obtained at room temperature. Among the studied alloys, the aged Ni 55 Ti 40 Hf 5 alloy shows the lowest coefficient of friction. The studied alloys show the same wear mechanisms, i.e. abrasive and oxidative wear at 400 °C.