Comparison of the reciprocating sliding wear of 58Ni39Ti-3Hf alloy and baseline 60NiTi

Hardened 60NiTi, due to combination of high compressive strength, high Rockwell hardness, low stiffness and large elastic compressive strain, is a desirable alloy to be employed in different load bearing applications. However, a more complex ternary NiTi-Hf alloy (similar to 58 wt% Ni-similar to 39 wt% Ti-similar to 3 wt% Hf) designated as 58Ni39Ti-3Hf, shows improved properties over baseline 60NiTi and is recently receiving recognition as an alternative for this intermetallic. Nevertheless, it is not yet understood how the sliding wear properties of 58Ni39Ti-3Hf differ from those of baseline 60NiTi. In this research, a series of ball (WC)-on-plate reciprocating sliding wear tests are conducted under moderate and extreme sliding induced stress conditions to illustrate how 58Ni39Ti-3Hf responds as compared to 60NiTi. In addition, to fully understand the reasons causing divergence in the wear response of both materials, mechanical and micro-tribological properties of these two alloys were investigated and compared through indentation, hardness and scratch tests. Obtained results, other than confirming the possibility of employing 58Ni39Ti-3Hf as an alternative for 60NiTi, emphasize the role of good lubrication and stress design in sliding applications where 58Ni39Ti-3Hf and 60NiTi are exploited as wear resistant alloys. Fatigue wear, adhesion and abrasion are different wear mechanisms causing damage in these NiTi alloys. 58Ni39Ti-3Hf, due to its improved fatigue properties, shows a slightly improved unlubricated sliding wear behavior than 60NiTi. However, 58Ni39Ti-3Hf appears to be slightly more prone to cracking and brittle fracture than 60NiTi in the single pass scratch tests showing its inferiority to resist wear under abrasive modes.