What is Tungsten Carbide?

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Definitionen

The name "tungsten carbide" or "Hartmetall" (German for hard metal) generally describes a material group that is characterized by high hardness and metallic properties. Due to their metallic luster and their relatively good electrical and thermal conductivity, these materials differ very clearly from the non-metallic hard materials that were used as abrasives long before the introduction of metallic hard materials. Some of them, such as corundum and diamond, occur naturally, others, such as silicon carbide and boron carbide, have to be produced artificially, which, by the way, is also practiced today with corundum and diamond.

Nomenclature and Delimitation of Terms

Although the German term "Hartmetall" (hard metal) can basically be used for all hard metallic substances, i.e. also for pure metallic hard materials and their combinations, if they have been brought into compact form in any way (by sintering, melting, or hot pressing), "Hartmetall" is understood to mean in a narrower sense the combination of metallic hard materials, which can be described as very brittle due to their high hardness, with relatively soft, tough metals, mainly the iron group (iron, cobalt, nickel), the so-called binders or binding metals . The predominant amount of hard material particles are cemented or "cemented" together in thin layers of binding metal in the manner of brazing, just as the aggregate particles are firmly bonded to one another in concrete. In the English-language literature, the expression "cemented carbides" is therefore also commonly used for "Hartmetall" based on hard metallic carbides, although it should be noted immediately that there are other metallic hard materials in addition to metallic carbides.

In carbide, the high hardness of the metallic hard material is combined with the toughness of a binder metal. One speaks therefore of a "composite material". The hard material and the binding metal are essentially retained as two structural components separated by defined grain boundaries. The picture shows such a typical carbide structure. The gray grains are the hard material tungsten carbide, which are held together by the white binder cobalt metal. As the content of metallic hard materials increases, the carbide becomes harder, and as the content of binding metal increases, it becomes tougher.

Je nachdem, ob das Hartmetall durch Schmelzen und Gießen oder auf pulvermetallur­gischem Weg mittels der sogenannten Sintertechnik in seine kompakte Form gebracht wurde, spricht man von Gusshartmetallen bzw. von Sinterhartmetallen. Zur Erzielung der erwähnten besonderen Struktur von Hartmetall wird heute überwie­gend die Sintertechnik angewendet. Dabei wird das zu Formen gepresste Gemisch von Hartstoff und Binder weit unterhalb des Schmelzpunktes der Hartstoffe, meist im Be­reich des Schmelzpunkts der Bindemetalle, erhitzt. Der schmelzflüssige Binder benetzt die Hartstoffteilchen wie ein Hartlot, bewirkt das Zusammenziehen dieser Hartstoff­teilchen auf kleinstem Raum und damit die Verdichtung zu einem festen Körper.

Mit „Hartmetall“ meint man daher im üblichen Sprachgebrauch die Sinterhartmetalle, meist sogar nur die Sinterhartmetalle auf Karbidbasis.