The role of vacuum furnace in cemented carbide sintering
Vacuum furnaces play an extremely important role in the field of cemented carbide sintering, which is mainly reflected in the following aspects:
1. **Exclude harmful gases and impurities**:
- **Exclude adsorbed gases**: Some gases, such as air and moisture, are usually adsorbed in cemented carbide powder compacts. Sintering in a vacuum environment can effectively remove these gases. The discharge of gases reduces the porosity, increases the density of cemented carbide products, and thus enhances their mechanical and physical properties. For example, in the absence of a vacuum environment, residual gases may form pores or defects inside the alloy, reducing the hardness and strength of the alloy; after sintering in a vacuum furnace, these problems can be effectively avoided.
- **Exclude impurities**: Vacuum is conducive to removing impurities or their oxides in cemented carbide, which plays a role in purifying materials. Some volatile impurities can evaporate quickly and be discharged from the furnace in a vacuum environment, thereby improving the purity and quality of cemented carbide. For example, some low-melting-point metal impurities will evaporate during vacuum sintering, making the composition of cemented carbide purer.
2. **Improve the organizational structure of the sintered body**:
- **Promote liquid phase sintering**: Liquid phase will appear during the sintering process of cemented carbide. In a vacuum environment, the wettability of the liquid phase to the solid phase is improved, which is conducive to the shrinkage during the sintering process and the improvement of the alloy organizational structure. The liquid phase can better fill the gaps between the solid phase particles, making the structure of the cemented carbide more dense and uniform, and improving its performance. For example, in a normal sintering environment, the flow and filling of the liquid phase may be hindered by the gas, resulting in an uneven alloy structure; while in a vacuum environment, the liquid phase can flow fully, making the organizational structure of the alloy more ideal.
- **Inhibit grain growth**: Vacuum sintering can reduce the sintering temperature and reduce the growth rate of grains in cemented carbide compared to sintering in a normal atmosphere. This is because in a vacuum environment, heat transfer is more uniform, and there is no convection and oxidation of gas to affect the growth of grains. Smaller grain size can improve the hardness, toughness and wear resistance of cemented carbide.
3. **Improve product quality and stability**:
- **Reduce oxidation and decarburization**: In a vacuum environment, there is almost no oxygen and other oxidizing gases, so the oxidation of cemented carbide during the sintering process can be completely eliminated, avoiding the formation of an oxide layer on the alloy surface. At the same time, for some cemented carbide materials that are prone to decarburization, vacuum furnaces are also ideal sintering equipment, which can prevent the loss of carbon elements and ensure the stability of the alloy's composition and performance.
- **Precise control of temperature and atmosphere**: The vacuum furnace is equipped with an advanced temperature control system and vacuum system, which can accurately control the sintering temperature, insulation time and furnace atmosphere. This makes the sintering process of cemented carbide more stable and controllable, and the quality and performance of the product have a high consistency. For example, for some cemented carbide formulas that have strict requirements on temperature and atmosphere, only in a vacuum furnace can a precise sintering process be achieved to produce high-quality products.
4. **Adapt to the sintering of a variety of cemented carbide materials**: Different types of cemented carbide materials, such as tungsten-cobalt, tungsten-titanium-cobalt, tungsten-titanium-tantalum (niobium), etc., as well as cemented carbide with different additives, have different requirements for sintering environment and process. The vacuum furnace can adjust the sintering parameters according to the characteristics of different materials to meet the sintering requirements of various cemented carbide materials.
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