Effect of Thermal Treatment on Composite Coatings of Electroless Ni-P/Nano-Diamond on Pure Aluminum Substrate

Recently, researches of composite coatings deposited on the aluminum substrate have been increasing. The Ni-P/nano-diamond composite coating deposited by means of direct electroless deposition on pure aluminum substrate was investigated. The effects of thermal treatment on the surface morphology, microstructure, micro-hardness, and adhesion and elements diffusion of composite coating were examined. Results show that the structure transformation of composite coating from amorphous/microcrystalline into crystalline occurs after thermal treatment and that its micro-hardness increases with the heating temperature and its maximal hardness is 1254Hv after being treated at 350°C for 1h. A diffusion layer forms after thermal treatment due to the inter-diffusion of Al, Ni and P elements at the interface, which leads to the improvement of adhesion strength between the coating and the substrate.