Preparation and high temperature tribological properties of laser in-situ synthesized self-lubricating composite coating on 304 stainless steel

Abstract

An in-situ synthesized self-lubricating anti-wear composite coating was prepared with mixed Ni60-TiC-WS2 precursor powders on the surface of 304 stainless steel by high-energy laser beam. The microstructure and microhardness of the composite coating and substrate were characterized by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), and Vickers hardness test. The tribological properties and the related wear mechanisms of the composite coating and the substrate were systematically studied at RT, 300, 600 and 800 °C, respectively. The correlative results reveal that solid solution Cr0.19Fe0.7Ni0.11, self-lubricating sulfides Ti2CS/CrS/WS2 and hard ceramic particle Fe2C/Cr7C3 are in-situ synthesized in molten pool during laser process. Microstructure of the upper area of the coating is primarily composed of long strip structure, continuous matrix, white granular structure and rod structure. However, the cellular dendrites that formed during the solidification process were aggregated in the bottom area of the coating, which deteriorate the mechanical properties of the coating. The average microhardness of the composite coating (302.0 HV0.5) is slightly higher than that of the substrate (257.2 HV0.5), this is due to the more sulfides and iron compounds were in-situ synthesized in the molten pool, which was formed by the irradiation of the high-energy laser beam. At all test temperatures, the coefficient of friction (COF) and wear rate of the coating are lower than that of the substrate. The minimum COF of the coating (0.3031) appears at 300 °C, and the wear resistance of the coating is the best at 600 °C, with a wear rate of 9.699 × 10−5 mm3/Nm.