Synthesis And Mechanical Properties Of Electroless Ni-P/WC Coatings

Ni-P-WC coatings which phosphorus content was 5.99% were prepared by electroless method with neutral formula on 45 steel. A series of experimental projects was confirmed through optimizing the technics. The connection among properties of composite coating and WC concentration in bath was studied. The composite coatings properties were studied after heat treatment and laser treatment. The microstructure of coatings was studied by metallographic microscope, SEM and AFM. The phase and component content were studied by XRD and EDS. The results show that, when WC addition increased, the deposition rate decreased and the appearance quality of films proved to be poor, the AFM Micrographs show that the max fluctuation of films was from 2μm to 3.7μm and the hardness of films present increased at first and decreased at last. When the WC addition was 3g/l, the hardness of the film can reach the maximum. The porosity of Ni-P-WC coating was small and the adhesion was good.After heat treatment at 200℃,300℃,400℃ and 500℃, the hardness of coatings increased. The highest hardness was obtained by heat treatment at 300℃. It was found that for all samples annealed at different temperature, the thermal stability of WC particles in the coatings is evident, since there are no changes in the shape and intensity of the diffraction profile of the WC phase. The structure of coatings changed from amorphous state to crystal state and intermetallic compound Ni3 P was precipitated. For laser cladding coating processing, the self corrosion potential of coatings after treatment by nanosecond lasers was high, the self corrosion current was low, the coatings had higher corrosion resistance. The hardness of coatings after treatment by fiber laser decreased. The XRD result show that Ni was precipitated. The results of friction-wear test show that the coatings after impulse laser has the best abrasive resistance. The composite Ni-P-WC plating growth mechanism was discussed, the cellular structure preferential deposite where contains the WC, the first increase in the number of cellular structure began to grow up and touch each other gradually. Nickel phosphorus cell stacked with each other, grew step by step.