Sintering densification of tungsten carbide is the most prominent change in the sintering process. There are many kinds of statements about the mechanism of densification. Views include diffusion control, flow control, physical and chemical reaction process control, etc. At present, the mainstream view regards the whole densification process as a complex process of the three stages of diffusion - flow - rearrangement.

 

The sintering of tungsten carbide is a kind of typical liquid phase sintering, which can be roughly divided into 3 stages: stage of liquid phase flow and particle rearrangement, stage of solid phase dissolution and reprecipitation stage and stage of solid phase sintering. Most of the densification process is completed in the first two stages. Especially, the maximum amount of sintering shrinkage occurs in the stage of particle rearrangement.

 

 

Diffusing Stage

Before the mass formation of liquid phase, this stage mainly occurs through the diffusion mode between solid particles. In this stage, a small amount of shrinkage occurs. With the increase of temperature, the surface atoms of the powder particles spread through the contact between particles. Then, with the further increase of temperature, the process of volume diffusion (gap concentration difference) occurs inside and outside of the particles. At this time the strength of the body has a certain increase.

 

Fluid Phase

The temperature of this stage is close to the eutectic temperature. The binder metal produces the phenomenon of high temperature creep and plastic flow, promoting the movement of solid particles. Particles are close together and are rearranged. At the same time, the sintering body produces a sharp contraction. The densification of this stage is the largest in the whole sintering process.

 

Rearrangement Stage

At this stage, due to the chemical position difference (saturated concentration difference) in different parts of the particle, the carbide dissolves and precipitates in the liquid phase, which makes the sintered body shrink further.