Electroless Ni-P-(nano-MoS2) composite coatings and their corrosion properties

Ni-P coatings were co-deposited with MoS2 nanoparticles on medium carbon steel substrate by electroless plating. The effects of incorporation of MoS2 nanoparticles into the Ni-P coating on the morphology of the coating surface and corrosion properties were investigated. X-ray diffraction pattern and X-ray photoelectron spectroscopy spectra showed that the MoS2 nanoparticles were covered in the nickel phosphor matrix. Corrosion tests were conducted in aqueous 10 wt-%HCl, 10 wt-%NaOH and 3.5 wt-% NaCl using a weight loss method, and in aqueous 3.5 wt-% NaCl by electrochemical measurement for bare substrate, Ni-P coating and Ni-P-(nano-MoS2) composite coating, respectively. The experimental results showed that corrosion resistance of the coating containing MoS2 was slightly lower than that of the coating without MoS2. The corrosion rate of Ni-P-(nano-MoS2) composite coating in HCl aqueous solution was found to be increased owing to the corrosion microcells and high porosity and rougher surface. Ni-P-(nano-MoS2) composite coating, however, exhibited significantly enhanced corrosion resistance in both aqueous NaOH and NaCl solutions compared with substrate. The corrosion mechanism of the composite coatings was also discussed.