Attempts have been made to improve the thermal and wear resistance of electroplated nickelsilicon carbide composite coatings. Coating methods have been investigated by adopting an up-flow bath system, and the coated surfaces have been examined by using scanning electron microscopy. The amount of co-deposited silicon carbide was reduced by increasing the electrolyte flow rate. Films with 2.5-4.0 wt% co-deposit of silicon carbide were obtained at a current density of 30A/dm2, in the bath containing 200g/l of dispersed silicon carbide with 100cm/sec of flow rate. Addition of 0.2g/l of phosphorous, e.g. phosphorous acid, hypophosphorous acid, or sodium phosphite, to the electrolyte provided the film with greater thermal resistance. In the application of this composite film to a cylinder bore of 2-stroke engine, it turned out that wear loss of this coating was approximately 60 percent of that of conventional cast iron sleeve cylinder. After more than 20, 000km test running, the wear loss of the cylinder bore was less than 2.5μm in depth, around the top end position of the piston. Both the protruded silicon carbide powders on the nickel matrix surface produced by electrolyticpolishing and the hard nickel matrix obtained by adding phosphorous compounds have thus made the improvement of wear resistance possible.
