Mechanical properties and corrosion resistance of pulse electrodeposited Ni-B/B4C composite coatings

Ni-B/B4C composite coatings on N80 steel were achieved by pulsed electrodeposition (PED). The optimal condition for obtaining composite coating is investigated via studying the effects of different content B4C on the performance of Ni-B/B4C coatings, including the surface morphology, microstructure, hardness and electrochemical properties. Scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectrometer (EDS) were used to analyze the surface morphology, crystal morphology and element type and content of the composite coatings. The hardness of coatings was investigated by micro-hardness test. The electrochemical properties of coatings were demonstrated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscope (SECM). Results show that the grain was uniformly deposited on the surface of N80 steel, and no pinholes and microcracks were captured. Besides, the average Vickers hardness of the Ni-B/B4C was the highest (1030.61 HV), and the average coefficient of friction (COF) is 0.22 (the average COF of Ni-B is 0.49). In 3.5 w% NaCl solution, Ni-B/B4C (2 g L−1) exhibits good corrosion resistance, with a corrosion voltage of −0.30−0.010+0.010 V, and a corrosion current of −1.15−0.220+0.219 μA.