hot pressing sintering silicon carbide ceramic

Hot pressing sintering of pure SiC powder can achieve densification, but it requires high temperature (>2000 °C) and high pressure (>35 MPa). Alliegro of Norton studied the effect of metal additives such as B, Al, Ni, Fe and Cr on the densification of sic ceramic, and proved that Al and Fe are the best additives to promote the hot pressing sintering of sic ceramic. Lange studied the effect of Al2O3 addition on the hot pressing performance of SiC and found that SiC densification was achieved by liquid-phase dissolution and reprecipitation mechanism. Jiang Dongliang et al. investigated the hot pressing sintering process of α-SiC with B4 C and C as additives and obtained silicon carbide ceramic with close to theoretical density at 2050 ℃.

Although hot pressing sintering reduces the sintering temperature and results in denser sic ceramic with high flexural strength, the hot pressing process is inefficient and makes it difficult to manufacture SiC components with complex shapes, which is not conducive to industrial production.

Since pure SiC is difficult to achieve densification by atmospheric pressure sintering and hot-pressure sintering, the addition of additives can affect some properties of silicon carbide ceramic. In order to further solve the above contradiction, many researchers have adopted hot isostatic pressure (HIP) sintering process to prepare SiC ceramics, and achieved good results. Kofune’s experiments showed that when the particle size of SiC powder was less than 0.6 nm, the dense silicon carbide ceramic could be obtained by HIP sintering process at 1950 ℃ without any additives. The study of Shanghai Institute of Silicon Research, Chinese Academy of Sciences showed that Al2O3 can effectively promote the densification of sic ceramic during the HIP sintering process, and that silicon carbide ceramic with a relative density of 93.7% and flexural strength of 582 MPa can be obtained by the HIP sintering process at 1850 ℃ and 200 MPa for 1 h when SiC is added with 3-5% Al2O3. Although hot isostatic sintering can obtain dense SiC products with complex shapes and good mechanical properties, HIP sintering requires encapsulation of the billet, so it is difficult to achieve industrial production at present.

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