Electrical and tribological properties of a Ni–18%Ru alloy for contact applications

A study of the microstructure, development of contact resistance during oxidation, and abrasive wear behavior for a Ni–18 at.%Ru alloy is presented in this article. It is shown that the alloy can be solutionized and aged, resulting in a fine lamellar mixture of FCC a-Ni and HCP b-Ru phases. Upon oxidation in air for 400 h, the measured contact resistance of the alloy is two orders of magnitude lower than that of pure Ni after 400-h oxidation. This behavior results from the formation of a low-resistivity rutile RuO2 scale on the b phase lamellae, which gives conducting pathways through the insulating NiO scale that forms on the a phase. After an initial run-in period, the steady-state abrasive wear rate measured for the Ni–Ru alloy is an order of magnitude less than that of pure Ni. Since the micro-cutting and flaking wear mechanisms are the same, the differences in the wear rates are ascribed to the presence of the well-dispersed hard Ru-rich b phase. The combination of a low-resistivity self-healing native oxide scale and good wear properties makes the alloy an excellent candidate for electrical contact applications.