Surface-toughened cemented carbide bodies and method of manufacture

Abstract

A process for producing a ceramic-metal composite body exhibiting binder enrichment and improved fracture toughness at its surface. The process involves forming a shaped body from a homogeneous mixture of: (a) about 2-15 w/o Co or about 2-12 w/o Ni binder, (b) excess carbon, (c) optionally, 0 to less than 5.0 v/o B-1 carbides, and (d) remainder tungsten carbide. The mixture contains sufficient total carbon to result in an ASTM carbon porosity rating of C06 to C08 at the core of the densified body. The weight ratio of excess carbon to binder is about 0.05:1 to 0.037:1. The shaped body is densified in a vacuum or inert atmosphere at or above about 1300.degree. C. and slow cooled, at least to about 25.degree. below the eutectic temperature. Alternatively, the sintered body may be cooled to a holding temperature at or slightly above the eutectic temperature, isothermally held for at least 1/2 hr, and further cooled to ambient. The core zone of the resulting densified body exhibits an ASTM carbon porosity rating of about C02-C08, while its surface zone exhibits an ASTM carbon porosity rating of about C00. The surface zone has an outer surface layer enriched in binder content to a depth of about 5-200 .mu.m, improving the surface fracture toughness of the body. Sintering temperature and pressure may be tailored to produce efficiently either a tool suitable for coating or a tool suitable for brazing.