Evaluation of the microstructure, mechanical and tribological properties of nickel-diamond nanocomposite coatings

This study investigates the feasibility of a two-step process for the deposition of wear resistant, nickel-diamond nanocomposite coatings onto steel substrates. The steps involve the spray deposition onto stainless steel substrates, of nickel nanoparticles (40 - 60 nm diameter) and nanodiamonds (approx. 100 nm diameter). This is followed by the sintering of the nanoparticle coating using a microwave plasma. The 0.2 - 2 µm thick nanocomposite coatings exhibited very good adhesion on the steel substrates, based on Rockwell C indentation tests. The morphology and roughness of the coatings was found to be significantly influenced by the sintering temperature, which was investigated in the range 711 to 885 ᵒC. The effect of nanodiamond concentration and spray duration were also investigated. Of the parameters studied, the concentration of nanodiamond in the composite was the dominant factor controlling the wear performance of the coatings, when assessed based on pin-on-disc wear tests. Compared to the nickel coating and the steel substrate, the nickel-diamond nanocomposite coatings exhibited a 126 and 55-fold enhancement respectively, in wear performance.