Effects of Ni and Cr addition on the wear performance of NiTi alloy

Development of hard materials for structural and bearing applications is a challenging task due to complexities in materials processing. Nickel-based intermetallics are a choice for the wear resistance applications. In this study, in order to examine the effects of Ni and Cr addition on the wear performance of Ni-rich alloys, 60Ni, 55Ni-5Cr, 50Ni-5Cr, and 50Ni-10Cr (at.%) alloys were developed through arc melting technique. The aim was to conduct a microstructural and phase analysis study and their effects on hardness and wear behavior. Samples were solution treated at 900 °C for 5 h under vacuum followed by equilibrium cooling. Microstructural and phase analysis revealed the presence of B2 cubic NiTi austenite along with Ni-rich hexagonal Ni₃Ti and Cr-rich tetragonal Cr₃Ni₂ phases throughout the microstructure of alloys. The Cr developed phase was not present in binary composition because of Cr absence. Ternary compositions possessed higher hardness and wear resistance than the binary alloy. Hardness and wear resistance of 50Ni-5Cr and 50Ni-10Cr were comparable with tool steels and conventional 440C martensitic stainless steel bearing material; this high hardness and wear resistance was attributed to the strong solid solution strengthening and precipitation hardening effects of Cr along with the combined effect of Ni-rich Ni₃Ti and NiTi austenite phases. Improvement in hardness and wear resistance were correlated with the Cr addition in the developed alloys.