Preparation and mechanical properties of Ni–P–Al2O3–SiO2 composite coatings by pulsed electrodeposition

Ni–P-based composite coatings have been widely used in the field of surface protection of metal materials due to their excellent physical and chemical properties. This study selected hard Al₂O₃ and SiO₂ nanoparticles as strengthening phases and uniformly doped them into the Ni–P matrix using pulsed electrodeposition technology. The surface quality and mechanical properties of the composite coating were improved by optimizing the duty cycle parameters, and the effect of duty cycle on the deposition behaviour of the composite coating was revealed. The microstructure, composition, wear resistance and elastoplasticity of the composite coatings were characterized by scanning electron microscope, energy dispersive spectrometer, X-ray diffraction analyzer and nano-indentation instrument. The research results indicate that the reduction of pulse duty cycle has significant grain refinement and concentration polarization reduction effects, but this seriously sacrifices the deposition rate. Under direct current conditions, there are numerous defects such as pores and micro cracks on the surface of composite coatings. When the duty cycle is 40%, the surface of the composite coating is smooth and dense, and its micro hardness and elastic recovery ratio (h_e/h_max) reach their maximum values of 806 HV and 0.48, respectively, while the average friction coefficient reaches its minimum value of 0.27, which indicates that it has good mechanical properties. This study provides a theoretical basis for the efficient preparation of Ni–P–based composite coatings and improve its application value in surface engineering.