Effect of Ag and CeO2 on friction and wear properties of Ni-base composite at high temperature

The molybdenum disulfide and metal silver are commonly used solid lubricants at the temperature below 500℃, while the rare earth compound is useful at high temperature but ineffective at room temperature. These solid lubricants are limited in special temperature ranges. When they are combined in the nickel-base alloy, a self-lubrication over a wide temperature range is reached. Silver is attractive because of its large diffusion coefficient, which allows the metal to rapidly provide lubrication with increasing temperature. However, silver is less effective in providing lubrication in the case of above 500 ◦C, because of excessive softening. One approach for obtaining low friction at high temperature (>500 ◦C) is to incorporate with soft oxide compounds that are deformed by plastic flow. This mechanism has been observed previously for ZnO–WS₂ adaptive coatings, whereZnWO₄ was formed during wear at 500 ◦C .The silver, MoS₂ and CeO₂ were incorporated in the nickel-base composite by powder metallurgy (P/M) in order to reach the lubrication over a wide temperature range. The nickel-base composite containing silver, MoS₂ and CeO₂ were prepared by powder metallurgy method. XRD result indicates that the composite is consisted of nickel-based solution, the sulfide of chromium, CeS, single phase tungsten, silver and a little MoS₂. The friction coefficient from room temperature to 400 ◦C is reduced by adding silver in the Ni-base composite. The addition of CeO₂ is favour to the formation of smooth glaze layer during high-temperature friction, which reduces friction and wear at

600 ◦C. With Al₂O₃, high speed steel and Ti₂AlNb as counterfaces, the lower friction coefficient and wear rate are obtained when Ag–MoS₂–CeO2 containing Ni-base composite rubs against Ti₂AlNb.

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