Four Sintering Methods for Silicon Carbide (SiC) Sintering Furnaces

2025-04-11 13:58:50

I. Pressureless Sintering

Pressureless sintering is considered a promising method for SiC sintering. Based on different sintering mechanisms, it can be further divided into solid-phase sintering and liquid-phase sintering. S. Proehazka achieved a SiC sintered body with a density exceeding 98% by pressureless sintering at 2020°C using ultrafine β-SiC powder (oxygen content < 2%) with additions of boron (B) and carbon (C). A. Mulla et al. utilized Al₂O₃ and Y₂O₃ as additives to sinter 0.5 μm β-SiC (with trace surface SiO₂) at 1850–1950°C, obtaining SiC ceramics with a relative density >95% of the theoretical value and fine grains averaging 1.5 μm in size.

II. Hot Pressing Sintering

Nadeau noted that pure SiC requires extremely high temperatures for densification without sintering aids, leading to extensive research on hot pressing sintering with additives. Alliegro et al. investigated the effects of metals such as B, Al, Ni, Fe, and Cr on SiC densification, identifying Al and Fe as the most effective promoters. F.F. Lange studied the influence of varying Al₂O₃ additions, concluding that densification in hot pressing sintering occurs via a dissolution-reprecipitation mechanism. However, this method is limited to simple-shaped components, low production yields, and challenges in industrial scalability.

III. Hot Isostatic Pressing (HIP) Sintering

To address the limitations of conventional sintering, Duna employed HIP sintering with B and C additives, achieving >98% dense SiC ceramics with a room-temperature flexural strength of ~600 MPa at 1900°C. While HIP enables complex-shaped, high-performance SiC products, the requirement for green body encapsulation hinders its industrial adoption.

IV. Reaction Sintering

Reaction-sintered SiC, also termed self-bonded SiC, involves infiltrating a porous α-SiC/graphite green body with molten or gaseous silicon (Si) at ~1650°C. The Si reacts with graphite to form β-SiC, bonding the original α-SiC particles. Full densification with near-zero dimensional shrinkage is achievable if Si infiltration is complete. Compared to other methods, reaction sintering offers minimal dimensional changes but suffers from reduced high-temperature performance due to residual free Si in the sintered body.