Pores after Sintering

Cemented carbide is a kind of compound consisting of equal tungsten and carbon, which has a hardness near to diamond. Cemented carbide has high toughness and high hardness at the same time. Cemented carbide is made by powder metallurgy, and sintering is the most important process during manufacturing a cemented carbide product. It is easy to cause pores after tungsten carbide sintering if it is not properly controlled. In this article, you will get some information about the pores after tungsten carbide sintering. 

The tungsten carbide powder and binder powder are mixed in a certain proportion. Then the mixture powder is made into green compact after wet milling in a ball mill machine, spray drying, and compacting. The green tungsten carbide compacts are sintered in a HIP sintering furnace. 

The main sintering process can be divided into four stages. They are the removal of molding agent and pre-sintering stage, solid-phase sintering stage, liquid-phase sintering stage, and cooling sintering stage. During sintering, the temperature is increasing slowly. In factories, there are two common methods for sintering. One is hydrogen sintering, in which the composition of parts is controlled by phase reaction kinetics in hydrogen and atmospheric pressure. And the other one is vacuum sintering, which is using a vacuum environment or a reduced environment. The gas pressure controls the cemented carbide composition by slowing down the reaction kinetics.

Only when workers control each stage carefully, the tungsten carbide final products can obtain desired microstructure and chemical composition. Some pores may exist after sintering. One of the important reasons is about sintering temperature. If the temperature rises so fast, or the sintering temperature is too high, the grain growth and movement will be uneven, resulting in the generation of pores. Another significant reason is the forming agent. The binder must be removed before sintering. Otherwise, the forming agent will volatilize during the increasing sintering temperature, which will result in pores.

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