WC-Co tungsten carbide is widely used because of its mature technology. In sintering, its components will change as the temperature changes. It is necessary to make a thorough understanding of the composition changes in the holding and cooling stage which will have a great influence on tungsten carbide. Generally, the WC-Co pseudo binary phase diagram is needed, as shown in the following figure.

 

 

Holding Stage

At this stage, WC continues to dissolve into the liquid phase and changes the average component of the liquid phase from the b to the c point. At the same time, the WC particles that have not been dissolved at this time can achieve a real balance with the liquid phase of the c point.

 

Then, the prolongation of heat preservation only sends WC through the solution and re precipitation process through the liquid phase, The WC grains grow up while the composition and proportion of the two phases remain unchanged. In this stage, the amount of liquid phase increases with the increase of cobalt content.

 

Cooling to Eutectic Temperature

WC (along the cd line) is precipitated from the liquid phase, and the amount of liquid phase decreases. When the eutectic temperature is cooled to the eutectic temperature, the composition of the liquid is back to the eutectic temperature point, making the eutectic reaction occur. At the same time, the γ phase (WC solid solution based on Co) and WC are precipitated.

 

Cooling below Eutectic Temperature

The components of the γ phase in the eutectic change from a' to a'' along the solid solution line of the γ phase, and the WC crystal is continuously precipitated. Some of these precipitated WC crystals will precipitate on the WC grain of the raw material. When the temperature is reduced to the room temperature, the microstructure of the alloy is composed of the original undissolved WC crystal and the WC crystal precipitated from the liquid phase and the γ phase. At this time, the alloy is still WC+γ two-phase structure. Therefore, some people call the original WC particles as α phase, and call the WC crystal precipitated by the cooling crystallization α1 phase.