Why Cobalt Is Used in Tungsten Carbide?

Tungsten carbide, WC in short, is the hardest metal alloy known to man. Sintered and finished tungsten carbide has a combination of compressive strength, extreme hot hardness at high temperatures, and resistance to abrasion, corrosion, and thermal shock. Tungsten carbide has a compressive strength greater than any other metal or alloy, and it is three times more rigid than steel. The abrasion resistance of tungsten carbide is up to 100 times greater than that of steel. And it also has lower thermal expansion. Tungsten carbide can resist thermal shock and oxidation, even under a temperature of around 650℃. The tungsten carbide can resist galling and is easy to weld. It can still retain its toughness and abrasive qualities even under a temperature of around -300℃. Since tungsten carbide is nearly inert, it is suitable for wear applications in corrosive environments. Tungsten carbide has more properties, like extremely high compressive strength. Among these performances, the most significant one should be the ability to resist abrasion.

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In fact, these properties can be adjusted by changing the ratio of binder, the grain size of tungsten carbide, and the grain distribution.

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As we all know, tungsten carbide products are made of the main raw material, tungsten carbide powder, and the binder phase, cobalt powder. Cobalt is not the only kind of binder powder used in manufacturing tungsten carbide.

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Iron, nickel, chrome, and cobalt can be used as a binder. When they are used as pure elemental materials, they all have a susceptibility to chemical attack. However, these can be handled in manufacturing tungsten carbide products. First, they can be used as a part of an alloy to form a material with corrosion resistance. And then, sintering can greatly improve its resistance to corrosion.

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Nickel, as binders, is used but will make the finished parts expensive and the nickel oxides make the workpiece hard to braze.

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Cobalt is the most widely and the easiest one to use as a binder. The melting point of cobalt is up to around 1500℃, which forms a liquid phase and draws tungsten carbide in on itself by surface tension to eliminate voids and porosity.

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