Anti-Friction and Wear Resistance of Ni-Based Soft and Hard Composite Coatings

In order to solve the difficulties faced by hard coatings in balancing the friction reduction and wear resistance performance and the difficulty in controlling the self-lubricating performance, this study proposed and successfully prepared a new type of composite coating structure with an integrated structure of soft and hard coatings, and this composite coating structure skillfully combined the hard coating with the soft coating, with the main purpose of improving the overall tribological performance of the coating. Through this soft and hard composite coating structure, it could overcome the problem that the coating only focused on hardness and wear resistance but failled to provide good self-lubricating performance, and the optimization of the coating performance was achieved by the interaction between the hard coating and the soft coating. In this experimental study, we used 20CrMo steel as the substrate material, and use the laser cladding technology to melt Ni20 and WC powder on the substrate surface in a certain ratio, and obtain Ni-based hard coatings after fine grinding treatment. In order to further enhance the friction reduction performance of the coating, a polytetrafluoroethylene (PTFE) composite solution containing an appropriate amount of molybdenum disulfide (MoS₂) was prepared using vibratory mixing technology, and a PTFE soft coating was prepared on the surface of the Ni-based hard coating through the spraying-heat curing process, so that a Ni-based soft and hard composite coating with an integrated hard and soft structure was obtained. With this innovative coating structure, in order to expect to realize the excellent friction and wear reduction properties of the material. This study focused on investigating the microstructure of the Ni-based hard coating and Ni-based soft-hard composite coating and their friction and wear performance under different loads. The results showed that the average hardness of the Ni-based hard and soft composite coatings was increased by more than 20% compared with that of the substrate, and the friction experiments showed that the friction coefficient of the Ni-based hard and soft composite coatings was continuously stabilized at a low level of about 0.15 in a wide range of loads (3~15 N). Notably, the Ni-based soft and hard composite coatings showed the best tribological performance under medium load (6 N) conditions; under such conditions, the friction coefficients of the Ni-based soft and hard composite coatings were reduced by 83% and 80%, respectively, compared with those of the matrix and the Ni-based hard coatings. In addition, the wear of the Ni-based soft-hard composite coating was also reduced by 87% relative to the matrix. The enhancement of the friction and wear performance of this material mainly stemed from the synergistic effect of MoS₂ and PTFE inside the soft coating with Ni20 and WC inside the hard coating. The results of the study provided some guidance for the design of friction functional structures.