During the process of sintering, the tungsten carbide press will produce obvious contraction, which is the sintering densification of tungsten carbide. Similar to the densification process, the contraction process can also be divided into three stages, and the contraction and contraction mechanisms at each stage are not the same.

 

 

1, In the first stage, the temperature is below 1150℃. Some shrinkage will occur in the sintering body. If the total contraction of the sintered body is 100%, the contraction of this stage accounts for about a few percent. The contraction at this stage is mainly due to the surface diffusion and volume diffusion.

 

2, At the temperature higher than 1150℃ and before the appearance of liquid phase, it belongs to the second stage. In this stage, the sintering body produces a severe contraction, which approximately accounts 80% of the total shrinkage. The contraction in this stage is mainly caused by the formation of liquid phase and the mechanism of particle rearrangement. Because the sintering temperature is close to the eutectic temperature, the plastic flow will occur in bonded metal, the rearrangement of the particles and the sharp contraction of the volume of the body will occur.

 

3, The third stage occurs when the liquid phase appears, resulting in approximately a few percent of the contraction. Contraction of this stage is mainly caused by the mechanism of dissolving and re precipitation. With the reduce of the gas-liquid surface energy, the size and number of pores decreased, causing carbide particles to move closer direction.

 

Due to the existence of liquid surface tension caused by the pressure, the carbide particles contact points is higher, the chemical (saturated concentration), solubility in the liquid phase than in other parts of the same particles must be high, the contact point is the preferential dissolution and precipitation in other parts. After the contact point dissolves, the distance between the two tungsten carbide particles is shorter and the sintered body is contracted.