Cubic boron nitride-base sintered ceramics for cutting tool

Abstract

The ceramics of the present invention comprises a composition having a bonding phase constituent component, a dispersed phase constituent component, and unavoidable impurities. The bonding phase constituent component has one or more of titanium and aluminum carbide, nitride and carbonitride compounds including oxygen, and 20% to 48% by volume of decomposed reaction phase cubic crystal boron nitride. The dispersed phase constituent component comprises cubic crystal boron nitride, and the decomposed reaction phase comprises one or more of titanium carbide, titanium nitride and titanium carbonitride, and one or more of aluminum oxide and aluminum nitride, as well as titanium boride. The crystal grain sizes in the bonding phase comprising the decomposed reaction phase, and the crystal grain sizes in the dispersed phase comprising the cubic boron nitride are all substantially less than 1 micron. The titanium and aluminum carbide compound is preferably Ti.sub.2-3 AlC, the titanium and aluminum nitride compound is substantially Ti.sub.2-3 AlN, and the titanium and aluminum carbonitride compound is substantially Ti.sub.2-3 AlCN. The decomposed reaction phase substantially comprises one or more of TiC, TiN, TiCN, Al.sub.2 O.sub.3, AlN and TiB.sub.2.