Pulse electrodeposition of nickel-nitride composite coating and its oxidation under heating treatment

Nickel-based composite coatings exhibit increased mechanical and oxidation properties due to utilization of reinforced particles as co-deposits within the nickel matrix. Meanwhile, pulse current electrodeposited composite coatings have higher mechanical properties compared to direct current electrodeposited coatings, since they provide a smaller electric force by which nickel ions are captured by particles and inhibit the grain growth of nickel. However, particles near the cathode surface cannot be reloaded in time, leading to lower adsorption of nickel ions on the particle surfaces. In this study, Ni-AlN composite coatings were developed using pulse current electrodeposition at 0.4 to 0.8 mA mm-2. The surface modification of the composite coating was performed by using microwave heating at a temperature of 700 °C for 2 hours. The results showed that Ni and AlN reveal cubic crystal structures of the composite coating. The highest hardness coating was obtained by the sample deposited at 8 mA mm-2. After microwave heating, the surface morphology is composed of microspheres and irregular particles. XRD analysis results suggested that the high temperature oxidation of Ni-AlN composite coating causes the formation of nickel and aluminium oxide. Post-heated coating samples showed a higher hardness than pre-heated. However, for samples deposited at the highest pulse current density, the hardness is lower due to the formation of a weak particle-matrix interface.