Tribological Properties and Oxidation Resistance of Laser Cladded Ni60/SiC Composite Coatings on Inconel 718 Alloy

In this study, in order to improve the service performance of Inconel 718 alloy under severe working conditions such as high temperature and high pressure and strong oxidation, three hybrid powder systems doped with different SiC mass fractions were prepared by laser melting coating, including Ni60-10% SiC (C1), Ni60-20% SiC (C2) and Ni60-30% SiC (C3). The microstructure and evolution of the coatings were analyzed in depth using testing and analysis techniques such as X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The focus of this paper was on the tribological properties and oxidation resistance of the coating surfaces. The average microhardness was tested using Vickers hardness tester. Wear tests were carried out at room and elevated temperatures using a friction and wear tester in a ball-and-disc spinning configuration, and the wear profiles of the samples were measured using a probe-type surface profiler to examine the friction and wear characteristics. The frictional wear processes of three coatings were investigated. In addition, the wear processes and behavioral mechanisms of the surface coatings were further investigated by characterizing the work hardening and morphology of the damaged surfaces. Finally, the oxidative weight gain of the samples was tested using a single-temperature zone tube furnace to investigate the antioxidant properties of the coatings.

The results showed that the main phases of Ni60-SiC composite coatings were (Fe, Ni), CrNi_x, Ni₃Si and Cr₂₃C₆. The microhardness of the coatings was 2.6~3.1 times that of the substrate due to solid solution strengthening, fine grain strengthening and hard phases diffusely distributed within the coatings, with the highest microhardness of 749.5HV_0.5 for the C2 coating. The C2 coating showed the best performance in terms of friction reduction and wear resistance at both room temperature and 600 ℃, with the friction reduction (average coefficient of friction) increased by 20.44% and 46.62% and the wear rate reduced by 75.12% and 63.70%, respectively. Under high temperature conditions, the oxide film generated on the surface of the coating played a lubricating role, which made the friction coefficient at high temperature lower than that at room temperature. The secondary reinforcement of hard phases, such as Ni₃Si led to the wear rate of the composite coatings to be significantly lower than that of the substrate, among which the C2 coating had the optimal abrasion resistance at room temperature and 600 ℃, with the wear rate of 3.07×10⁻⁵ and 10.31×10⁻⁵ mm³/(N∙m), respectively. With the increase of SiC content, the weakening of the plowing effect and the appearance of brittle debonding led to a decrease and then an increase in the average friction coefficient. In addition, the oxidation resistance of all the coatings was better than that of the substrate, with the best oxidation resistance of the C3 coating with an oxidation rate of 5.32 mg²/(cm⁴∙h), which was mainly due to the synergistic effect of the Cr₂O₃ dense oxides and the liquid phase that could be formed to reduce the pore space after the melting of SiO₂.