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 °C, 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. The nickel-base composites containing silver, MoS2 and CeO2 were prepared by powder metallurgy (P/M) method. The friction and wear properties of composite were tested from room temperature to 600 °C by a pin-on-disk tribometer with alumina, high speed steel, and Ti2AlNb alloy as counterfaces. The microstructure and morphology of composites were analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The worn surfaces were observed by optical microscope and SEM. The composite is mainly consisted of free phase of Cr3S4, CeS, silver and a little amount of MoS2. The friction coefficient at room temperature is decreased after adding silver in the composite. Meanwhile, the wear rates at high temperature are reduced by adding cerium oxide. The friction coefficients of silver and CeO2 containing Ni-base composite from room temperature to 600 °C are in the range of 0.16–0.26. The wear rates are reduced by more than one order of magnitude after adding silver and CeO2, especially the wear rates at 600 °C are even two orders of magnitude lower. The SEM analysis of worn surface after rubbing at 600 °C shows that the rare earth compound is helpful for the formation of smooth ‘glaze’ layer, which improves the wear resistance at high temperature.