Study on the Tribological Characteristics of Porous Ni-Graphite Composite Coating

The multilayer Ni-graphite composite coating was made using electrodeposition method after wetting agent treatment of the graphite particles the high porosity of this coating, is beneficial for the other lubricants impregnating the coating. The graphite particles with lamellar structure have the preferential orientation in the coatings. The expanded graphite, in which the water or impurities is absorbed, is of the good lubricating properties. The tribological characteristics of Ni-graphite composite coatings were studied in detail, with the following results: a. The friction coefficient decreases obviously with the increase of graphite content in the coatings, when the content of graphite is 29.1% (vol) the friction coefficient is 0.18, this value is much lower than that of Ni coating(0.64). With higher content of graphite the wear rates of composite coating increase and it is always higher than that of the Ni coatings. b. No remarkable change of friction coefficient, but small reduction in wear rate has been found when increasing of the thickness of composite coating. c. Under the same operating condition, the friction coefficients of Ni-graphite coating and oily (oil wetted) coating are all much less than that of Ni coating; the wear rate of oily Ni-graphite coating is also less than that of Ni coating but the wear rate of the Ni-graphite coating is higher than that of Ni coating, the friction-wear properties of oily Ni-graphite coating are better than that of dry coatings. d. The friction coefficients of the Ni coating, Ni-graphite and oily Ni-graphite decrease along with the increasing of load, under 8N of load the friction factors are 0.61, 0.18 and 0.10 respectively, but their wear rates increase along with the increasing of load. Not only the wear rate of the oily Ni-graphite coating is the lowest when the load is less than 5N but also its change is very small, so under low load conditions oily coating has excellent antifriction-antiwear properties.