Ni-based composite coating doped with nano-Al_2O_3 particulates was prepared making use of
electro-brush plating. The tribological
properties of the resulting composite coating sliding against Si_3N_4 under the lubrication of 50 cc oil for diesel engine containing SiO_2 and Al_2O_3 contaminant were comparatively investigated on a T-11 ball-on-disk friction and wear tester, using quick speed nickel coating as the reference. The worn surface morphologies of the quick speed nickel coating and composite coating were observed on a scanning electron microscope, while the morphological features of the wear debris in the residue lubricating oil were analyzed by means of ferrograph. It was found that the composite coating doped with Al_2O_3 particulates had much higher hardness and better wear resistance than the quick speed nickel coating, which was attributed to the fine-particle strengthening and dispersive strengthening functions of the nano particulates. The composite coating was dominated by abrasive wear as it slid against the ceramic counterpart at a relatively smaller load, while it was mainly characterized by adhesion wear at a relatively higher load.