Study on the high-temperature tribological behaviors of NiCrAlY-ZrO2-Cr2O3-CaF2 self-lubricating and wear-resistant coatings

NiCrAlY coatings are widely used in high-temperature moving components of aero-engines, and their high-temperature tribological properties have a significant impact on the high-performance service of components. In this study, to improve the tribological properties of NiCrAlY coatings, a NiCrAlY-ZrO2-Cr2O3-CaF2 high-temperature self-lubricating and wear-resistant coating is prepared, and the tribological tests are conducted on coatings under different temperatures by using a high-temperature friction test apparatus. Then, the microscopic morphology, elemental composition, phase constitution, and wear degree of the coating are characterized and analyzed based on scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), and white light interferometry (WLI), revealing the effect and mechanism of high temperature on the tribological behavior of the coating. The results show that in the range of room temperature to 700 °C, the CaF2 phase on the coating surface continuously provides lubrication. Additionally, after 400 °C, the coating surface undergoes oxidation reaction to generate NiO, CaCrO4, and NiCr2O4 lubricating phases. At the same time, the proportion of ZrO2 and Cr2O3 compounds with high hardness and wear resistance increases with the rise of temperature, resulting in a decrease in the friction coefficient and wear rate of the coating. Therefore, the coating has excellent friction-reducing and wear-resistant properties under high-temperature conditions. When the temperature exceeds 700 °C, the CaF2 lubricating phase and high wear-resistant ZrO2 and Cr2O3 compounds on the coating surface decrease, resulting in a weakened friction-reducing and wear-resistant effect of the coating. Correspondingly, the friction coefficient and wear rate slightly increase. In addition, the coating mainly undergoes adhesive wear under high-temperature conditions, and abrasive wear is also observed in the range of 700 ~ 800 °C.