Surface Dimples Composite MoS2 Nickel-based Coating and Its Friction and Wear Properties

In order to solve the problem that the anti-wear and friction reduction properties of hard coatings are difficult to balance, this study proposes and prepares the surface micro-pits composite MoS2 nickel-based coating structure with excellent anti-wear and anti-friction properties, which provides an important basis for the coating design with unified anti-wear and anti-friction properties. Taking 42CrMo bearing steel as substrate, nickel-based coating was prepared by laser melting on the surface of 42CrMo bearing steel, and micro-pits composite MoS2 nickel-based coating was prepared by EDM on the surface of nickel-based coating. The tribological properties of 42CrMo bearing steel, 42CrMo bearing steel surface nickel-based coating and surface micro-pits composite MoS2 nickel-based coating under three loads (2 N, 4 N, 6 N) were tested by ball-on-disc friction and wear test (GCr15 ball). The microstructure and wear scar morphology of the composite coating were analyzed by advanced test techniques (XRD and SEM). The surface of the prepared nickel-based coating has no pores, cracks and other defects. The coating is metallurgically bonded with the substrate, which provides high bearing capacity and good wear resistance for the substrate under external load. A series of complex compounds such as FeNi3, (Cr,Fe)7C3, CrB, and BFe2 were generated in the coating using γ-Ni (Fe) solid melt as the matrix phase. Under the dispersion strengthening of (Cr,Fe)7C3, CrB and other hard phases, the hardness of the coating reached 545HV0.2, 3.5 times that of the matrix. The surface micro-pits of the surface micro-pits composite MoS2 nickel-based coating are well formed, and there are no large cracks at the edge of the micro-pits. The solid lubricant is completely filled at the bottom of the micro-pits, and the filling effect is good. Under different load conditions, the wear rate of nickel-based coating is much lower than that of 42CrMo bearing steel. The friction coefficient and wear rate of surface micro-pits composite MoS2 nickel-based coating are lower than those of nickel-based coating and 42CrMo bearing steel. The friction coefficient decreases first and then increases with the increase of load. Oxidation wear and abrasive wear occur in the sliding process of substrate and coating. Under 4 N load condition, the surface micro-pits composite MoS2 nickel-based coating has the lowest friction coefficient of 0.36, which is 40.9% lower than that of the substrate sample and 21.7% lower than that of the coating sample. The wear rate is 7.41´10‒7 mm3/(N·m). Compared with the Ni-based coating sample (26.62´10‒7 mm3/(N·m)), it decreased by 72.09%. In the process of friction and wear, the solid lubricant in the micro-pits was extruded and dragged onto the surface under the action of stress, transferred and spread along the sliding direction, and formed a stable and continuous lubricating film on the friction surface, so as to obtain a stable friction coefficient and lower wear rate. The coating and solid lubricant in the surface micro-pits composite MoS2 nickel-based coating structure can independently and efficiently play their own wear resistance and friction reduction characteristics, and play a synergistic effect under different loads. The surface with good friction reduction and wear resistance can be obtained by the composite treatment of the two methods. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.