Four stages of cemented carbide vacuum sintering

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Cemented carbide vacuum sintering is a process of sintering under sub-atmospheric pressure. This process includes plasticizer removal, degassing, solid-phase sintering, liquid-phase sintering, alloying, densification, and dissolution. Let’s take a look at the four major processes of cemented carbide vacuum sintering:

①Plasticizer removal stage

In the plasticizer removal stage, the temperature is raised from room temperature to about 200 °C, and the gas adsorbed on the surface of the powder particles in the compact is separated from the surface of the particles under the action of heat, and continuously escapes from the compact. The plasticizer in the compact is heated to escape from the compact. Maintaining a high degree of vacuum is conducive to the release and escape of gas. Different types of plasticizers have different performances under heat. The formulation of the plasticizer removal process should be determined by testing according to specific conditions. Generally, the vaporization temperature of plasticizers is below 550°C.

②Pre-sintering stage

The pre-sintering stage refers to pre-sintering before high-temperature sintering, so that the combined oxygen in the powder particles and carbon undergo a reduction reaction, and carbon monoxide gas is generated to leave the compact. In alloys, even if pressure sintering, it is difficult to eliminate. On the other hand, the presence of oxidation will seriously affect the wettability of the liquid to the hard phase, and ultimately affect the densification process of cemented carbide. Before the appearance of the liquid phase, it should be fully degassed and the highest possible vacuum should be used.

③ High temperature sintering stage

The high-temperature sintering stage is the key stage for the densification of the cemented carbide compact, and the sintering temperature and sintering time are important process parameters for the compact to achieve densification, form a uniform structure, and obtain the required properties. The sintering temperature and sintering time depend on factors such as alloy composition, powder particle size, and grinding strength of the mixture, and are also restricted by the overall design of the material.

④ Cooling stage

In the cooling stage, the cooling rate affects the composition and structure of the bonding phase of the alloy, resulting in internal stress. The cooling rate should be under control. Sintering hot isostatic pressing is a new sintering technology, also known as low pressure sintering. After the degassing is completed, the pores on the surface of the compact have been closed, and the binder phase is still in the liquid phase. Product densification.