What are the characteristics of cobalt-based cemented carbide commonly used in mechanical seal materials

Cobalt-based tungsten carbide is the most widely used cemented carbide for mechanical seals. It is made of extremely hard tungsten carbide (WC) plus cobalt (Co) or other iron group metals as a binder, and is pressed and sintered by powder metallurgy. Its biggest feature is high hardness, high thermal conductivity and low linear expansion coefficient. Hard phases such as WC in cemented carbide have strong corrosion resistance and are very stable in corrosive media such as acid and alkali. However, the corrosion resistance of the bonding metal is poor, and the sealing medium of mechanical seals often corrodes the bonding metal first, so that the hard phase WC and the like are isolated and lost, and are quickly worn away in relative friction. So WC-Co cemented carbide is not suitable for corrosive occasions. However, it has strong corrosion resistance in media such as sulfuric acid at ordinary temperatures and caustic soda below the boiling point. WC-Co material has low impact toughness and high brittleness, and the machining cost is expensive.

The physical and mechanical properties of commonly used cobalt-based cemented carbides in making mechanical seals are shown in the table below.