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Pressureless Sintering of Silicon Carbide Ceramics
Silicon carbide is a strongly covalently bonded compound, therefore, the diffusion rate during sintering is rather low. Silicon carbide is difficult to sinter. Densification must be achieved with the aid of additives or external pressure or reaction. The high cost of silicon ceramics has seriously hindered its application. At present, the methods for preparing high-density silicon carbide ceramics mainly include pressureless sintering, hot pressing sintering, hot isostatic pressing and reaction sintering. Pressureless sintering can prepare complex Silicon carbide parts with different shapes and large sizes. And it is relatively easy to realize industrialization, so it is considered to be the most promising sintering method for silicon carbide ceramics. This paper briefly introduces the latest progress of pressureless sintering technology.
1 Silicon carbide ceramic B/C series pressureless sintering
It is generally believed that B/C series sintered silicon carbide belongs to the category of solid-state sintering. When B and C are added at the same time, B is solidified into SiC, and the addition of B and C creates favorable conditions for the densification of silicon carbide. The disadvantage is that it requires more High sintering temperature (>2000°C). The purity of the raw powder material is high. And the fracture toughness of the sintered body is low. It has a strong crack strength sensitivity. The structure shows coarse grains and poor uniformity. Fracture The mode is a typical transgranular fracture.
2 Liquid phase sintering and its toughening mechanism
That is, a certain amount of multi-component eutectic oxides are used as sintering aids. It reacts with the SiO2 layer on the surface of silicon carbide particles to form part of the grain boundary liquid phase at high temperature, resulting in the weakening of interface bonding. Because of its mass transfer mode and Solid-phase sintering is completely different. The liquid phase flows viscous in the form of capillary transport, requiring less energy than diffusive mass transfer, enabling SiC densification at lower temperatures. Liquid phase sintering reduces the sintering temperature, greatly reduces the requirements for sintering equipment and sintering costs. If industrial production can be formed, the application field of high-performance silicon carbide ceramics will be greatly expanded. Liquid phase sintering can also be achieved by adding different sintering aids. Change the composition and properties of materials, and design materials according to different needs to meet the requirements of special parts. For example, ultra-dense materials with a density of 3.22 and high-tough ceramics with a fracture toughness greater than 1 GPa can be obtained by liquid phase sintering. Due to different additive systems It forms a different liquid phase composition from SiC, which makes the sintering process more complicated. The influencing factors are more diversified.
3 Conclusion
Since the 1970s, people have been exploring ways to reduce the cost of silicon carbide sintering. Research on the industrial production technology of silicon carbide ceramic products is easy and feasible. Due to the development of new industries, the requirements for new materials have increased. High-performance silicon carbide ceramic structural materials are more More and more people’s attention has been paid to it. The research of various sintering methods has opened up new ways to overcome the shortcomings of poor toughness of silicon carbide, improve the comprehensive properties of sintered bodies, broaden the application scope of silicon carbide ceramics, and make the design according to user requirements. The performance of silicon carbide sintered body becomes possible.
4 Selection of sintering equipment:SIMUWU has a lot of experience in vacuum furnace manufacturing and heat treatment. Answer all kinds of questions from customers from the selection stage, and complete the sales and after-sales service of the equipment responsibly. The RVS series silicon carbide vacuum sintering furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tooling and molds. The good vacuum system and temperature control system ensure the effective progress of the vacuum heat treatment process. Silicon carbide vacuum sintering furnace is used for reaction sintering, pressureless sintering, hot isostatic pressing sintering of SiC ceramic products, and can also be used for sintering other ceramic products such as silicon nitride.
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