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

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.