Study On Microstructures And Prorerties Of Ni-based WC Composite Coatings

Wear is one of the main forms of material consumption and failure, it starts from the material surface. Therefore, the improvement of surface properties of materials is of great significance to resist wear and prolong the service life of materials. The wear resistance of materials can be effectively improved by coatings on the surface of materials. The WC reinforced Ni-based alloys have excellent wear resistance performance, are widely used in the occasions of wear resistance.In this paper, Ni60+35%WC metal-ceramic composite coatings was prepared by oxygenacetylene flame spaying on 40 Cr substrate, then flame remelting and induction remelting were carried on the coatings. In order to improve the strength of the substrate and excavate the potential of Ni-based WC coatings further at the same time, the remelted coatings were quenched at the temperature of 850℃ and tempered at different temperatures(200℃,400℃,600℃). The microstructure and phase composition of the coatings were characterized and analyzed by optical microscope, scanning electron microscope, and X ray diffraction. The microhardness and wear performance of the coatings were determined by microhardness tester and friction and wear testing machine. The microstructure and properties of the coatings prepared with the different processes were compared.The results show that the coating prepared by oxygen-acetylene flame spraying has laminated structure and some defects such as porosity and inclusions, its compactness is poor. There is a interface between the coatings and the substrate and the combination between them is mechanical.The coating’s application occasions are limited. After flame remelting or induction remelting,defects in coatings reduced, the microstructure of the coatings is compact and there exists metallurgical bonding between the coatings and substrate. Remelting makes the quality of the coatings and the bonding strength between the coatings and the substrate enhanced significantly.There is no obvious differences between the phases composition of the coatings after two different ways of remelting. Remelting make the precipitation of hard phases such as Cr23C6,Cr7C3 and Cr2 B occurred, in addition to the dispersion strengthening effect of WC particles, the hardness of the coating reaches a high level. The values of microhardness of flame remelted coatings and induction remelted coatings are 783 HV and 806 HV respectively. The microhardness and wear resistance of the coatings is significantly higher than substrate. In comparison of coatings remelted by two different ways, the microhardness and wear resistance of coatings after induction remelting is higher than that of coatings after flame remelting.When the induction remelted coatings quenched at 850℃ and tempered at 200℃, 400℃ and600℃, transition zone near the interface becomes wider and smooth, the WC particles in the coating decomposed with different degree and there exists whisker microstructure around. The microhardness of remelted coatings is improved after quenching and tempering. When quenched at 850℃ and tempered at 400℃, the coatings’ microhardness is the highest, up to 866 HV, and its wear resistance is better than the coatings induction remelted.