Advantages of vacuum sintering of cemented carbide

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Vacuum Sintering: Powder sintering under sub-atmospheric pressure conditions. Mainly used for sintering active metals and refractory metals beryllium, thorium, titanium, zirconium, tantalum, niobium, etc.; sintering cemented carbide, magnetic alloys, tool steel and stainless steel; A compound that reacts with gases.

 

The advantage is:

(1) Reduce the adverse effects of harmful components (water, oxygen, nitrogen) in the atmosphere on the product.

(2) Vacuum sintering can be used for materials that are not suitable for reducing or inert gas as a protective atmosphere (such as sintering of active metals), or materials that are prone to decarburization and carburization.

(3) Vacuum can improve the wettability of the liquid to the solid phase, which is conducive to shrinking and improving the structure of the alloy.

(4) Vacuum sintering helps to remove impurities such as silicon, aluminum, magnesium, calcium or their oxides, and plays a role in purifying materials.

(5) Vacuum is beneficial to remove adsorbed gas, residual gas in pores and reaction gas products, and has a significant effect on promoting shrinkage in the later stage of sintering. For example, the porosity of cemented carbide sintered in vacuum is significantly lower than that of cemented carbide sintered in hydrogen.

(6) The temperature of vacuum sintering is lower than that of gas shielded sintering. For example, when sintering cemented carbide, the sintering temperature can be reduced by 100~150°C. This is beneficial to reduce energy consumption and prevent grain growth.

The sintering of cemented carbide is liquid phase sintering, that is, it is carried out under the condition that the rebond phase is in the liquid phase. The compacts are heated in a vacuum furnace to 1350 °C–1600 “C. The linear shrinkage of the compacts during sintering is about 18%, and the volume shrinkage is about 50%. The exact value of the shrinkage depends on the particle size of the powder and the alloy ingredients.

The sintering of cemented carbide is a complex physical and chemical process, which includes plasticizer removal, degassing, solid-phase sintering, liquid-phase sintering, alloying, densification, dissolution and desorption and other processes. The compact is formed under specific sintering conditions to form an article with a certain chemical composition, structure, properties and shape and size. These process conditions vary greatly according to different sintering devices.

Cemented carbide vacuum sintering is a process of sintering below 1atm (1atm=101325Pa). Sintering under vacuum conditions greatly reduces the hindering effect of the gas adsorbed on the powder surface and the gas in the closed pores on densification, which is beneficial to the diffusion process and densification, and avoids the reaction between the metal and some elements in the atmosphere during the sintering process. It can significantly improve the wettability of the liquid binder phase and the hard phase, but vacuum sintering should pay attention to prevent the evaporation loss of cobalt.

Vacuum sintering can generally be divided into four stages, namely plasticizer removal stage, pre-sintering stage, high temperature sintering stage, and cooling stage.