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Abstract
Pure nickel and nickel-based binary and ternary materials containing tungsten carbide and graphite dispersions have been studied. Three types of carbide powder and six types of graphite, different in size, shape, and structure (one in each group being nickel-coated) were studied to varying degrees. The smallest carbide powder (0·35 μm) possessed the best wear-resistance and the lowest coefficient of friction. The larger and coated types of graphite are somewhat superior; however, considerable amounts (∼ 40 vol.-%) are needed to improve wear-resistance substantially and reduce the coefficient. Use of the coated type of carbide leads to rather high coefficients (0·58-0·76) under dry testing conditions. Several effects of the presence of a small amount of oxygen in the sintering atmosphere are discussed; a most interesting result is the marked improvement in the wear-resistance of pure nickel treated to produce a dispersion of nickel oxide. With some powders blending can lead to reduced wear-resistance, while with others increasing the blending time has no effect. Several of the findings confirm the interpretation of the results of the previous study regarding the dependence of wear on the ratio of the volume fraction of tungsten carbide to that of graphite, based on microstructural considerations. Wear-resistance cannot be correlated with high hardness.
Notes
* Manuscript received 2 June 1969. Contribution to a Symposium on “Lubrication, Friction, and Wear (Tribology) in Powder Metallurgy” to be held in Eastbourne on 24-26 November 1969.