Investigation of the Synergistic Effect of Cr and CeO₂ on the Mechanical, Oxidation, and Tribological Properties of Ni-Based Self-lubricating Composites

To improve the tribological properties of sulfur-containing Ni-based self-lubricating composites, FGH97-WS₂-Cr-CeO₂ (FWCC) were prepared by spark plasma sintering technique. All composites prepared obtained new phases Cr_xS_y and M₆C, originating from the decomposition of WS₂. Homogenization and fine microstructure resulted in the best mechanical properties of the FWCC composites, with the microhardness of 542 ± 12 HV, compressive yield strength of 1910 ± 52 MPa, and flexural strength of 954 ± 34 MPa. When the composites exposed to 600 °C, the oxidation of Cr_xS_y dominated the oxidative weight gain. The coefficient of friction and wear rate of FWCC composites both tend to decrease with increasing temperature. The optimum tribological properties of FWCC composites are obtained at 600 °C with the coefficient of friction of 0.23 and the wear rate of 0.22 × 10^-5 mm³ N^-1 m^-1. The wear rate is two orders of magnitude lower than that of FGH97-WS₂ composites (FW). This is mainly due to the synergistic effect of Cr and CeO₂. The addition of Cr promotes the formation of enough Cr₂O₃ oxide particles during friction, while the addition of CeO₂ not only enhances the adhesion of the oxide enamel layer, but also improves the high-temperature stability of the sulfide.