How does the ratio of tungsten carbide (WC) to cobalt (Co) in cemented carbide button bits affect their performance?

The ratio of tungsten carbide (WC) and cobalt (Co) in cemented carbide button bits has the following impacts on their performance:

Hardness: Tungsten carbide is a hard phase with extremely high hardness. An increase in the cobalt content will lead to a decrease in the hardness of the alloy. For example, when the cobalt content in industrial WC-Co alloys increases from 2% to 25%, the hardness of the alloy in HRA decreases from 93 to around 86. Approximately, for every 3% increase in cobalt, the hardness of the alloy decreases by 1 degree.

Toughness: Cobalt, as a binder, can closely connect tungsten carbide particles together, providing good toughness. As the cobalt content increases, the toughness of the alloy will be enhanced, and the impact resistance will be improved. Most of the cemented carbide alloys used in mines are coarse-grained alloys with a relatively high cobalt content, in order to obtain better impact toughness to adapt to harsh working environments.

Flexural Strength: Generally speaking, within a certain range, the flexural strength of the alloy increases with the increase of the cobalt content. However, when the cobalt content exceeds 25%, the flexural strength instead decreases with the increase of the cobalt content. For industrially produced WC-Co alloys, within the cobalt content range of 0-25%, the flexural strength usually increases with the increase of the cobalt content.

Compressive Strength: The compressive strength of WC-Co alloys decreases with the increase of the cobalt content in the alloy, and increases with the refinement of the tungsten carbide phase grains in the alloy. Therefore, fine-grained alloys with a low cobalt content have a higher compressive strength.

Wear Resistance: A high content of tungsten carbide results in good wear resistance of the alloy. Since tungsten carbide itself has extremely high hardness and wear resistance, it is a key factor for the wear resistance of cemented carbide button bits. If the cobalt content is too high, the relative content of tungsten carbide in the alloy will decrease. During the wear process, the softer cobalt phase is more likely to be worn away, thus reducing the overall wear resistance.

Elastic Modulus: Due to the high elastic modulus value of tungsten carbide, WC-Co alloys also have a high elastic modulus. The elastic modulus decreases with the increase of the cobalt content in the alloy.

Thermal Conductivity and Coefficient of Thermal Expansion: WC-Co alloys have a relatively high thermal conductivity, and the thermal conductivity is generally only related to the cobalt content in the alloy, increasing with the decrease of the cobalt content; the linear coefficient of thermal expansion increases with the increase of the cobalt content.