In-situ TiC-reinforced Ni-based composite coatings fabricated by ultrasonic-assisted electrospark powder deposition

ABSTRACT In this study, a (Ti + graphite)-Ni composite powder serving as a coating material was deposited on H13 steel to fabricate an in-situ TiC-reinforced Ni-based composite coating by a new type of ESD process, which was named ultrasonic-assisted electrospark powder deposition (UEPD). The composite coating has an average thickness of approximately 45.5 μm and metallurgically bonds with the substrate. The ultrasonic vibration exerted on the UEPD electrode can effectively improve the forming quality of the composite coating, which produces better compactness and thickness uniformity as well as few defects. The microstructure mainly consisted of submicron dendrites due to the rapid solidification of the molten pool. TiC particles as reinforcements were successfully synthesized in the coating via an in-situ reaction due to their low Gibbs free energy and high melting point. The formation of refined grains and in-situ reinforcements prompts the average hardness of the coating to reach 1400.5 HV0.05, which is approximately 2.5 times that of the substrate. The tribological properties of the composite coating are greatly improved in comparison with those of the substrate. The wear rate and friction coefficient of the composite coating decrease by two orders of magnitude and 46.2%, respectively.