Fretting wear resistance at ambient and elevated temperatures of 316 stainless steel improved by laser cladding with Co-based alloy/WC/CaF₂ composite coating

The coating fabricated by laser cladding on the surface has been an effective way to strengthen and enhance the wear resistance of alloys. However, the traditional Co-based alloy coatings rarely pay attention to the addition of self-lubrication constituents to form the composite coating. In addition, the effects of the Co-based composite coating on fretting wear resistance were few addressed. In this study, a Co-based alloy/WC/CaF₂ composite coating was fabricated by laser cladding on the surface of 316 stainless steel to improve the surface hardness and self-lubrication performance. The microstructure, phase constituents and fretting wear resistance at both room temperature (RT) and 500 °C were investigated. Results confirm that the composite coating is consisting of α-Co, Cr₂₃C₆ and WC phases. And the F element is effectively dissolved into the α-Co phase. The fabricated composite coating is dense and uniform. The microhardness of the composite coating can reach to 600 HV_0.2 due to the presence of WC and Cr₂₃C₆ phase. In addition, the grain refinement is another reason resulting in the higher microhardness. Fretting tests demonstrate that the fretting wear resistance at both RT and 500 °C are significantly improved by the composite coating, which can lead to the decrease of the COF and the wear loss. The lower COF can be ascribed to the dissolved F element in α-Co phase, especially at high fretting temperature. Additionally, the composite coating can effectively prevent the oxidation during fretting both at RT and 500 °C. This work provides an excellent method for the metallic materials to improve fretting wear resistance at both RT and high temperature.