Self-Lubricating Ni-Based Composite Coating with Core-Shell Structured Mo@Ag@Ni Addition: Tribological Behaviors and Interface Evolution over Multi-Thermal Cycles

The rapid dissipation of soft metal lubricants would deteriorate the self-lubricating properties of the coatings at elevated temperatures. In this study, the core-shell structured Mo@Ag@Ni particles were prepared via electroless plating to suppress the rapid dissipation of Ag and facilitate tribochemical reactions at high temperatures. The NiCrAlY-Mo@Ag@Ni composite coating was sprayed on the substrate of Inconel 718 alloy using atmospheric plasma spraying technology. The results of this study show that the structural design of Mo@Ag@Ni can enhance the bonding strength of the particle interface, resulting in a high microhardness of approximately 332.2 HV. During high-temperature friction tests, Mo@Ag@Ni can provide excellent tribological properties by promoting the silver molybdate formation on the worn surface. At 800 °C, the friction coefficient and wear rate are only about 0.32 and 1.58 × 10−5 mm3N−1m−1, respectively. Moreover, the Ni shell layer can inhibit the rapid diffusion of Ag and provide sufficient Ag2O to maintain the continuity of Ag2MoO4 lubricating film, which endows the coating with a longer lubrication life. Over multi-thermal cycles, the friction coefficient and wear rate constantly maintain at about 0.3 and 2.5 × 10−5 mm3N−1m−1, respectively.