Evaluation of Nanostructured coating layers formed on Ni balls during mechanical alloying of Cu powder

A novel coating method utilizing mechanical alloying was used to deposit a nickel–copper solid solution on the surface of nickel balls in a planetary ball mill. Mechanically milled copper powders were deposited by cold welding on the activated surface of the nickel balls. The impact of the nickel balls causes surface wear, leading to formation of mixed layered particles of copper–nickel and rewelding. In addition, diffusion takes place through the coating layer to form a Ni–Cu solid solution. The hardness of the coating reached a threefold increase (HV0.01594) in comparison with the substrate hardness. Microstructural characterization of the coating surface performed using an optical microscope, SEM, and EPMA indicates that, with appropriate processing conditions, a thick, fully dense coating can be metallurgically bonded to the nickel balls. XRD results revealed the presence of a solid solution and nanocrystalline structure.