Surface-toughened cemented carbide bodies and method of manufacture

A process for producing a ceramic-metal composite body exhibiting binder enrichment and improved fracture toughness at its surface, said process comprising the steps of:

• forming a shaped body from a homogeneous mixture consisting essentially of:
• (a) a metallic binder selected from the group consisting of cobalt, nickel, and alloys thereof, (b) excess carbon in a form selected from the group consisting of elemental carbon and a precursor of carbon, wherein the total carbon present in said mixture is sufficient to result in an ASTM carbon porosity rating at the core of said ceramic-metal composite body of C06 to C08, the weight ratio of said excess carbon to said binder being about 0.05:1 to 0.037:1, (c) optionally, 0 to less than 5.0 volume percent B-1 carbides, and (d) remainder tungsten carbide;
• wherein said metallic binder is present, in the case of cobalt, in an amount of about 2-15 weight percent, in the case of nickel, in an amount of about 2-12 weight percent, and, in the case of said alloy thereof, in an amount between about 2 and 12-15 weight percent, the maximum increasing with the ratio of cobalt to nickel in said alloy;
• sintering said shaped body in a vacuum or inert atmosphere at a temperature of at least about 1300.degree. C., said sintering step being carried out for a time sufficient to produce a fully dense sintered body in which said binder serves as an intergranular bonding agent for said tungsten carbide;
• and
• cooling said sintered body to a holding temperature at or about the eutectic temperature of said mixture, isothermally holding said sintered body at said holding temperature for at least 0.5 hr, and further cooling said sintered body to ambient temperature.

A fully dense ceramic-metal composite body exhibiting improved fracture toughness at its surface, said body comprising:

• a core zone exhibiting an ASTM carbon porosity rating of about C02-C08;
• and
• a surface zone exhibiting an ASTM carbon porosity rating of about C00, said surface zone including an outer surface layer enriched in binder content to a depth of about 5-200 .mu.m and to a degree sufficient to improve fracture toughness at said surface;
• and said body consisting essentially of, overall:
• a metallic binder selected from the group consisting of cobalt, nickel, and alloys thereof;
• wherein said metallic binder is present, in the case of cobalt, in an amount of about 2-15 weight percent, in the case of nickel, in an amount of about 2-12 weight percent, and, in the case of said alloy thereof, in an amount between about 2 and 12-15 weight percent, the maximum increasing with the ratio of cobalt to nickel in said alloy;
• excess carbon in a form selected from the group consisting of elemental carbon and a precursor of carbon, wherein the total carbon present in said body overall is sufficient to result in said ASTM carbon porosity rating of C06 to C08 at said core zone, the weight ratio of said excess carbon to said binder being about 0.05:1 to 0.037:1;
• optionally, 0 to less than 5.0 volume percent of B-1 carbides;
• and
• remainder tungsten carbide.