Friction and Wear Characteristics of Hot-Pressed NiCr–Mo/MoO3/Ag Self-Lubrication Composites at Elevated Temperatures up to 900 °C

Abstract

NiCr-based high-temperature self-lubricating composites with Ag/Mo/Ag–MoO3/Ag–Mo were prepared by the powder metallurgy method, respectively. The mechanical and tribological properties of the composites rubbing against alumina balls were investigated from room temperature to 900 °C. The tribo-chemical reaction films formed on the sliding surface and their effects on the tribological properties of composites at different temperatures were analyzed by SEM and Micro-Raman. The results showed that the triboloical properties of NiCr-based composites were improved by adding alloying elements or a solid lubricating phase; meanwhile, the composites containing Ag–MoO3 or Ag–Mo exhibited even better triboloical properties than those with Mo or Ag at high temperatures. The lowest friction coefficient of the NCr–MoO3–Ag composite is around 0.19 and that of the NiCr–Mo–Ag composite is around 0.20; both composites exhibited an optimal wear rate in the order of magnitude of 10−6 mm3 N−1 m−1 at high temperatures. XRD and Micro-Raman results indicated that the composition of the tribo-layers formed on the worn surface of the composites varies with different testing temperatures. Compounds such as Ag2MoO4, NiCr2O4 and NiO, which formed on the rubbing surface at high temperature, worked synergistically to improve the tribological properties of the NiCr-based composite at high temperatures.