Microstructure and wear behaviour of Ni-based surface coating on copper substrate

The Ni-based surface coatings were prepared by a vacuum infiltration casting technique on copper substrate. The surface coatings were fabricated through copper melt penetrating into thin preforms whose thickness could change. By optimizing the processing parameters, compact surface coatings were achievable as confirmed through SEM observation. The surface coating was mainly composed of solid solution of Ni, solid solution of Cu and CrB. The macro-hardness of the coating was about HRC 58, and the micro-hardness of the coating shows a gradient distribution. The average micro-hardness of the coating was about HV450. Wear behaviour was investigated by using block-on-ring dry sliding linear contact at several loads (50 N-300 N) and two different sliding speeds (0.424 m/s and 0.848 m/s). Wear rate and friction coefficient were estimated using a method founded upon the PV factor theory. The surface oxidation predominated as the principle wear mechanism at low load. Meanwhile, adhesion and oxidation mechanism were observed when the coatings were tested at higher load more than 200 N. Friction coefficient decreased with increasing load and sliding speed.