generally speaking it is desirable to employ a high cobalt content for enhanced toughness and resistance to breakage the conversion of carbon to diamond in a higher cobalt composite enhances the wear resistance to offset the usual decrease in wear resistance of higher cobalt grades of cemented carbide more than about fifteen percent by volume of graphite is undesirable since decreases in toughness may be observed in applications where the composite cemented carbide article with diamond particles dispersed in the matrix is to be used as a cutting or machining tool higher proportions of excess carbon may be useful graphite contents up to 50 by volume may be employed where the tungsten carbide content of the composite is concomitantly reduced sufficient cobalt should be present for catalyzing substantially complete conversion of graphite to diamond if the carbon content is too high cracking of the composite article may be observed due to differential thermal expansion or excessive shrinkage when such a cemented tungsten carbide article with excess carbon is then processed in a super pressure press at temperatures and pressures where diamond is thermodynamically stable excess carbon in the article is converted to diamond particles dispersed through the cobalt phase in addition to the hardening due to presence of very high hardness diamond particles it appears that such a dispersion of diamond particles has a dispersion hardening effect on the cobalt resulting in a.