Silicon carbide pressureless sintering furnace

The pressureless sintering of silicon carbide can be divided into two types: solid phase sintering and liquid phase sintering.

Solid phase sintering was first invented by American scientist Prochazka in 1974. He added a small amount of B and C to the sub-micron β-SiC to achieve pressureless sintering of SiC, and produced a dense sintered body close to the theoretical density of 95%. Many subsequent studies have shown that compounds of B and B and Al and Al can form solid solutions with SiC to promote sintering. The addition of carbon reacts with SiO2 on the surface of SiC to increase the surface energy, which is beneficial to sintering. The solid-phase sintered SiC has relatively “clean” grain boundaries and basically no liquid phase. The grains are easy to grow at high temperature. Therefore, the fracture is transgranular fracture, their strength and fracture toughness are generally not high, between 300 ~ 450MPa and 3.5 ~ 4.5MPa · m1 / 2. However, its grain boundary is relatively “clean”, the high temperature strength does not change with the increase of temperature, generally 1600 ℃ can be used, and the strength does not change. In solid phase sintering, the SiC-AlN system is worth noting. Because of its good electrical resistance and thermal conductivity, it may be an inexpensive substrate material for large-scale integrated circuits.

Liquid-phase sintering of silicon carbide was solved by American scientist Mulla.M.A in the early 1990s. Its main sintering additive is Y2O3-Al2O3. According to its phase diagram, there are three eutectic compounds, YAG (Y3Al5O15, melting point 1760 ℃), YAP (YAlO3, melting point 1850 ℃), YAM (Y4Al2O9, melting point 1940 ℃). In order to reduce the sintering temperature, YAG is generally used as SiC sintering additive. When the composition of YAG reaches a mass fraction of 6%, the silicon carbide material has basically reached densification. During the sintering process, the mass loss of the main component of Al2O3 will occur, so that the additive component cannot reach the composition of YAG. Therefore, the composition of Al2O3 should be appropriately increased, and the composition of YAG should be changed to YAG · Al2O3. At this time, the relative density of the material is increased from 98% to 99%, which is almost completely dense. The strength of the material is increased from 600MPa to 707MPa. Fracture toughness increased from 8.1MPa · m1 / 2 to 10.7MPa · m1 / 2. This result is very compelling. Its appearance has opened up new application areas of pressureless sintered SiC, especially the working conditions with high performance requirements.

Vacuum Sintering Furnace Technical Parameter :