Microstructure and mechanical properties of Ni-P-Si3N4 nanowire electroless composite coatings

•The Ni-P-Si3N4 nanowire composite coating has been successfully prepared.•The composite coating has a fine nodular microstructure without porosity.•The Si3N4 nanowire can greatly increase the hardness of composite coating.•The Si3N4 nanowire can greatly reduce friction coefficient of the coating.•The Si3N4 nanowire can significantly improve the wear resistance. In this paper, a new Ni-P-Si3N4 nanowire composite coating has been successfully prepared on AZ31 Mg substrate through electroless deposition technique. The effect of Si3N4 nanowire concentration in the plating bath on the surface morphology, hardness and wear behavior of the composite coatings have been investigated. The results show that when the concentrations of Si3N4 nanowire is 1.5g/L, the morphology of composite coating appears the fine nodular structure. Moreover, the Si3N4 nanowire is uniformly dispersed in the coating at the 1.5g/L concentrations of Si3N4 nanowire. But when the concentrations of Si3N4 nanowire in bath over 1.5g/L, the coatings surface morphology become roughness and some pores appear on the coating surface because of the agglomeration of Si3N4 nanowire. As seen from the experiments results, the microhardness of the composite coating were significantly increased to about 790HV200 as plating, the friction coefficient and wear weight loss of the composite coating is both decreased to the 1/6 of conventional Ni-P electroless coating. These improvements have been attributed to the dispersion strengthening effect of Si3N4 nanowire.