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INTERNATIONAL TUNGSTEN INDUSTRY ASSOCIATION

Information on tungsten: sources, properties and uses

Tungsten Carbide and Cobalt

The high solubility of tungsten carbide (WC) in the solid and liquid cobalt binder at high temperatures provides a very good wetting of WC and results in an excellent densification during liquid phase sintering and in a pore-free structure.

Variations in WC particle size lead to an astonishingly broad band of property relationships and possible applications, which range from high-strength steels on the tough side (Vickers Hardness: about 800 HV10) to hard ceramics on the hard and wear resistant side (Vickers Hardness: 2800 HV10).  However, compared to hard ceramic materials such as aluminium oxide or silicon carbide which show brittle behaviour during loading, cemented carbides always exhibit a considerable toughness, due to the part-metallic nature of the composite.

It is this remarkable relationship between high hardness and considerable toughness, and the high flexibility of the materials in terms of property combinations which make cobalt-based cemented carbide tools so successful in the machining industry.  A too low toughness (resistance against crack propagation) would easily result in premature material failures during working.  Beyond that, even hard materials, such as hardened steel, high strength titanium alloys and ceramics or fibre-reinforced composites, can be machined at a high level of productivity.

So-called straight grades (containing WC and Co only) have maintained their unique position in the tooling industry, due to their outstanding properties.  Additions of other hard carbides or carbonitrides (eg TiC, Ti(C,N), TaC) or alternative binder materials (Ni, NiCr, FeNiCo) have widened the application range in certain directions, for example in the machining of steel (TiC, TaC) or corrosion and oxidation resistant environments (NiCr), but the two phase materials (WC-Co) still demonstrate their predominance in numerous applications.

© 2011 International Tungsten Industry Association
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