What are the characteristics of cobalt-based cemented carbides?

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Tungsten carbide based on cobalt is the most widely used material for mechanical seals; it is formed by compressing and sintering tungsten carbide (WC), which has extremely high hardness, along with cobalt (Co) or other ferrous metals that serve as binders, using powder metallurgy methods. Its main features are high hardness, high thermal conductivity, and a low linear expansion coefficient. Hard phases such as WC in cemented carbides have excellent corrosion resistance and remain very stable in corrosive media such as acids and bases. However, the corrosion resistance of the bonded metal is poor; often, the sealing medium corrodes the bonded metal first, isolating phases such as WC and leaving them without support, causing them to wear away rapidly due to relative friction. Therefore, WC-Co cemented carbide is not suitable for corrosive environments. However, it exhibits strong corrosion resistance in sulfuric acid at normal temperatures and in media such as sodium hydroxide below its boiling point. WC-Co materials have low impact toughness and high brittleness, and their machining is expensive. The physical and mechanical properties of commonly used cemented carbides are shown in Table 12.