Electroless Ni–P–(nano-MoS 2 ) 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.