The sintering process of tungsten carbide is divided into pre-sintering (deforming agent), solid phase sintering, liquid phase sintering, cooling and so on. During the sintering, the volume of the block will shrink, and the pores decrease greatly, which is so called the sintering densification. Liquid phase flow and particle rearrangement during the stage of liquid sintering do contribute a lot to densification. The liquid-solid wetting angle and the content of cobalt are two of the most important influence factors.

 

Capillary action of liquid phase and flow resistance of particles are the main effects of liquid phase flow and particle rearrangement. As a result, all the factors that affect the above two effects will affect the speed and degree of sintering densification.

 

 

1, Liquid-Solid Wetting Angle

According to the capillary action formula (1), the capillary pressure of the liquid is increased with the decrease of the wetting angle of WC. In industrial applications, an appropriate amount of TiC is often added to the conventional WC-Co tungsten carbide. Because the wetting angle of Co and TiC is greater than the wetting angle between Co and WC, the tungsten carbide containing TiC is more difficult than the pure WC-Co tungsten carbide in sintering densification.

 

h=2γcosθ/(ρgr)（1）

γ= Surface tension,

θ= Contact angle,

ρ= Contact angle,

g= Acceleration of gravity,

r= Radius of tube.

 

2, Content of Cobalt (Take Cobalt as An Example, Other Bonding Metals are Similar)

The higher amount of cobalt and more the liquid phase will lead to the accelerate of the contraction. For example, the liquid phase volume fraction of WC-6Co is 14%, while WC-15Co is 32%. Experiment shows that the increase of cobalt content in the block not only does not promote the contraction of the solid phase in the phase of the solid phase. But it greatly promotes the contraction of the second stage. Reason is that the capillary pressure increases with the increase of the liquid phase. Obviously, the increase of cobalt content will promote the liquid phase flow.