Microstructure and Tribological Properties of Laser Cladded Co-WC/Cu Composite Coatings on IN718

IN718 superalloy displays outstanding comprehensive properties within a certain temperature range, but its limitations hinder the widespread apply to related moving parts in a wide temperature range. The best solution to this problem is laser cladding, which not only allows for the flexible design of high-performance coatings, but also effectively improves economic benefits. Therefore, to enhance the service life of the IN718 superalloy moving parts in extreme environments, three wear-resistant and friction-reducing composite coatings was laser-cladded onto its surface: Co (S1)、Co-5%WC-5%Cu (S2)and Co-5%WC-15%Cu (S3) (mass fraction). The microhardness of the three coatings and their tribological performance at room temperature and 600 ℃ were analyzed systematically. The results indicated that the S1 coating mainly consisted of the solid solution γ-Co and (Fe, Ni), as well as the intermetallic compound Fe_xNb_y. The S2 and S3 coatings exhibited carbides such as Cr₂C₃ and WC, as well as a lubricating phase Cu. The dissolved WC re-solidifies and forms carbides, which enhanced dispersion, and the undissolved WC acted as a high-hardness framework that firmly combined with the coating solvent. A suitable amount of Cu could act as a solid lubricant (Cu film) at RT, and the CuO oxide film functioned as a friction reducer at 600 ℃. Additionally, both CuO and Cu films could prevent the oxidation and depletion of WC. Thus, the microhardness and tribological properties of the three coatings had been improved. The microhardness of the composite coatings were more than 1.7 times that of the substrate (268.89 HV_0.5), which were 478.69 HV_0.5、481.73 HV_0.5 and 458.51 HV_0.5, respectively. And the composite coatings also exhibited excellent tribological performance, the S2 coating showed excellent wear resistance at both RT and 600 °C, with improvements of 84.4% and 64.9%, respectively. The S2 coating (RT) and the S3 coating (600 ℃) had the best anti-friction effects, with improvements of 26.9% and 26.7%, respectively. The main wear mechanisms of coatings were found to be oxidative and fatigue wear at RT; oxidative and adhesive wear at 600 ℃.