Effect of Mechanical Alloying Parameters on the Formation of Ni-Cu Solid Solution Coating on the Ni Balls

Mechanical alloying is a viable technique to produce coatings of limited thickness on a solid substrate. Elemental copper powder was mechanically alloyed with nickel balls in a planetary ball mill under various milling times and rotation speeds. The mutual diffusion of the elements during milling which led to the formation of a Ni-Cu solid solution and the creation of Ni-Cu coating on the surface of Ni balls was studied. The maximum hardness of the coating increased to threefold (HV(0.01)594) that of the substrate. Micro-structural characterization of the coating surface using optical microscope, scanning electron microscope (SEM), and electron probe micro-analyzer (EPMA) indicates that, by using appropriate processing conditions, a thick, fully-dense coating can be metallurgically bonded to the nickel balls. X-ray diffraction (XRD) results revealed the formation of nanocrystalline solid solutions. (C) 2011 The Japan Society of Applied Physics