Common Cemented Carbide Sintering Defects and Their Causes

Sintering refers to a process in which powdery materials are transformed into dense bodies, and is a very important step in the production process of cemented carbide. The cemented carbide sintering process can be divided into four basic stages: removal of forming agent and pre-sintering stage; solid phase sintering stage (800 ℃ - eutectic temperature); liquid phase sintering stage (eutectic temperature - sintering temperature); Cooling stage (sintering temperature - room temperature). However, because the sintering process is very complicated and the conditions are harsh, it is easy to produce defects and reduce the quality of the product if you are not careful. Common sintering defects and their causes are as follows:

1. Peeling

Cemented carbide with peeling defects is prone to burst cracking and chalking. The main reason for peeling is: the contact of cobalt in the briquette causes carbon-containing gas to decompose free carbon in it, resulting in a decrease in the local strength of the briquette, resulting in peeling.

2. Holes

Void refers to pores over 40 microns in size. The main reason for the generation of holes is that there are impurities in the sintered body that are not wetted by the solution metal or there is a serious segregation of the solid phase and the liquid phase, which may form holes.

3. Bubble

Blistering will cause a raised surface to appear on the surface of the cemented carbide, thereby reducing the performance of the product. The main reasons for the generation of blister are: 1) Air accumulates in the sintered body. During the sintering shrinkage process, the sintered body appears liquid phase and densifies, which will prevent the air from being discharged, and then form blister on the surface of the sintered body with the least resistance; 2 ) There is a chemical reaction that generates a large amount of gas in the sintered body, and the gas is concentrated in the sintered body, and the blister is naturally generated.

4. Deformation

The common deformation phenomena of cemented carbide are blister and concave. The main reasons for the deformation are: uneven density distribution of the compact; severe carbon deficiency in the sintered body; unreasonable boat loading; uneven backing plate.

5. Black Heart

The black center refers to the part with loose organization on the alloy fracture. The main reason for black hearts is: the carbon content is too low or too high.

6. Crack

Crack is a relatively common phenomenon in the sintering process of cemented carbide. The main reasons for cracks are: 1) The pressure relaxation does not show immediately when the briquette is dried, and the elastic recovery is faster during sintering; 2) The briquette is partially oxidized when it is dried, and the thermal expansion of the oxidized part is different from that of the unoxidized part.