Study on Microstructure and Micromechanical Properties of Cu - Rich Ni - Cu - P Coating Synthesized by Electroless Plating

In order to explore the microstructure and micromechanical properties of Cu - rich Ni - Cu - P coating synthesized through electroless plating, such coating was synthesized on the 45 steel substrate by electroless plating. The SEM, XRD, EDS, microhardness tester and nanoindenter were used to test the microstructure and micromechanical properties of the coating without heat treatment and after heat treatment. Results showed that a uniform Cu - rich Ni - Cu - P coating was obtained, which showed good adhesion with the 45 steel substrate. With the prolongation of plating time, the content of Cu in the coating decreased while the content of Ni and P increased. The coating without heat treatment was mainly composed of Cu - and Ni - based solid solutions. After a heat treatment at 200 ℃ or 300 ℃ for 2 h, the phase composition of the coating showed no obvious change. However, after a heat treatment at 400 ℃, NiP2 and Cu3P were precipitated from the coating. In the early stage of plating (10 min), the hardness of coating increased obviously with the prolonging of the plating time, but after that a sluggish increase appeared. In all, a heat treatment, especially at 400 ℃ for 2 h, could promote the precipitation of phosphide and thus increase the hardness of coating.