Effect of Ni, W and Mo on the microstructure, phases and high-temperature sliding wear performance of CoCr matrix alloys.

CoCrNi, CoCrW and CoCrMo alloys were fabricated by powder metallurgy technology. The effect of nickel, tungsten and molybdenum, as alloying elements, on the microstructure, phase, mechanical and high-temperature tribological properties of CoCr matrix alloys were systematically studied. The wear and friction behaviors were investigated from room temperature (23 °C) to 1000 °C. The alloys were found to contain different ratios of γ(fcc) and ε(hcp) phases; Ni stabilized γ(fcc), while W and Mo stabilized ε(hcp). The hardness measurements showed that the strengthening effect increased with the addition of Ni, W, and Mo, respectively. Addition of Mo and W resulted in the lowest and highest friction coefficients with the addition of Ni resulting in a friction coefficient between the two. The wear and friction behaviors of the three alloys depended on the phase, alloying elements and oxidation from room temperature to 1000 °C. Coefficients of friction of the alloys were not directly correlated with the wear rates. CoCr matrix alloys reinforced with Mo showed the highest hardness and the best high-temperature tribological performance. It was attributed to the high hardness, stable oxide film, and in situ formed high-temperature solid lubricants. With an increase in temperature, the wear mechanism was found to change from abrasive wear to oxidative wear.