SiC Ceramic Sintering Method

1. Pressureless Sintering

Sic pressureless sintering can be divided into solid phase sintering and liquid phase sintering. Solid-phase sintering was first invented by American scientist Prochaka in 1974. A small amount of P and C were added to sub-micron β-SiC to achieve pressureless sintering of SiC, and a sintered body with a theoretical density of 95% was obtained. w. Btcker uses a -SiC as raw material, and adding P and c can also densify SiC. P and its compounds and Al and its compounds can form a solid solution with SiC to promote sintering. C reacts with SiO2 on the surface of siC to increase the surface energy, which is beneficial to sintering. In solid-phase sintered SiC, the grain boundaries are relatively clean, there is basically no liquid phase, and the crystal grains are easy to grow at high temperatures. Therefore, the fracture is transgranular fracture, and the strength and toughness are usually low, generally between 300 ~ 450 MPa and 3.5 ~ 4.5 MPa. m/h. SiC liquid phase sintering was proposed by M. MA in the 1990s, and the selected additives were Y2O3-Al2O3 and a combination of rare earth oxides. The reaction of oxide Y203 and Al203 will generate three different eutectic compounds, such as YAG (Y3A1, O1s, melting point 1760°C), YAP (YAIO3, melting point 18509C) and YAM (Y, Al2O, melting point 1940C), YAG is often used as an additive for SiC sintering.

2. Reaction Sintering

Reaction sintering technology is a near-net-size manufacturing technology with simple process and low cost. It can achieve sintering of SiC through siliconizing reaction at a lower temperature of 1450 ~ 1600C and a short period of time, and can produce large-sized and complex-shaped parts. The preparation process of reaction sintered SiC ceramics is relatively simple. Due to the inherent defects of siliconizing reaction sintering, there is 8%~12% of free Si in SiC, which reduces high-temperature mechanical properties, corrosion resistance and oxidation resistance, and the use temperature is limited to below 1350C . SiC with a certain particle size is directly used, mixed with C to form a green body, and then infiltrated at high temperature. Part of Si reacts with C to form SiC and combine with SiC in the green body to achieve the purpose of sintering. There are two methods for siliconizing: ①The temperature reaches the melting temperature of Si, and the liquid phase of Si is produced. Through the action of the capillary, Si directly enters the green body and reacts with C to form SiC to achieve the purpose of sintering; ②The temperature is greater than the melting temperature of Si, Si vapor is generated, and sintering is achieved through the penetration of Si vapor into the green body.