Tungsten carbide cobalt is an alloy of a hard ceramic phase, the tungsten carbide (WC) and a ductile metallic phase, the cobalt (Co). Hard metals such as WC-Co are non-natural materials not occurring in nature. They are produced by mixing carbide and metal powders, a forming step and a thermal treatment (sintering).
From hard metals, mainly tools are produced for chipping (turning, milling, drilling) or non-chipping shaping (drawing, rolling, spinning), as well as for cutting (stamping) or breaking of metals, wood, paper, plastic, stone, and coal. Further, surgery equipment is produced from WC-Co.
Likewise, different technical wear-resistant parts like nozzles or reinforcements (e.g. for mills) are made of WC-Co. Well-known products include hard metal driller or hard metal coated circular saw blades for hobby craftsmen as well as the small balls in ball pens.
Important properties of WC-Co are hardness, strength, high breaking and beating ductility as well as high electrical and thermal conductivity. By varying the metallic cobalt content and the tungsten carbide grain size, important properties of the alloy can be specifically adapted. This fact is illustrated in Figure 1 with respect to hardness. By varying the cobalt content between 0 and 20 mass per cent, hard metals can cover a hardness range from tempered steel to super-hard alloys. The smaller the carbide grain the harder an object can penetrate the surface and the higher is its hardness.
In 1999, the task-force `hard metals` of the German industrial union for powder metallurgy suggested a classification of WC-Co hard metals according to grain size, which is today accepted worldwide (Table 1). For hard metal grain sizes below 1 µm, exceptional combinations of hardness and strength are achievable, which makes such alloys interesting for the production of hard materials and very fine tools.
Ground breaking for the development of hard metal industries was the work of the Osram Studiengesellschaft in Berlin and the patent filed in 1923 by Karl Schröter, which was bought by the Krupp company later on. As soon as 1926, Krupp introduced the first alloy under the name WIDIA to the market. WIDIA is short for “wie Diamant” (German for `diamond-like`) and refers to the extraordinary hardness of the material. Nowadays, large production facilities are located in China, the USA, Sweden, Israel, Luxembourg, Austria and Germany.
After use, hard metals are recycled to a large extent, WC-Co containing scrab is either reused completely in hard metal production or used for steel alloys.
- R. Kieffer, F. Benesovsky: Hartstoffe, Wien, Springer-Verlag 1963
- W. Schedler: Hartmetall für den Praktiker, VDI-Verlag GmbH, Düsseldorf 1988
- V. Richter, K. Müller in: Schatt, Wieters, Kieback: Pulvermetallurgie,Technologien und Werkstoffe, Springer Verlag, 2. extended edition 2007
S. Moseley, V. Richter:
Hard metals of the EPMA