High temperature isostatic pressing sintering of silicon carbide ceramic

Using glass or metal foil (low-carbon steel, nickel, molybdenum) as a mold and hydrogen or inert gas as a pressurized medium, sintering the powder inside the mold under high temperature and pressure; It is also possible to first burn a non dense body with a certain shape under atmospheric pressure, and then conduct high-temperature isostatic pressing sintering, without the need for metal foil molds, which is the technology of no wrapping. In the HIPS process, using Ar or N2 as the medium gas temperature is about 100 ℃ lower than the sintering temperature; There are two pressurization sequences: one is to first pressurize to about 60% of the required final pressure, and then raise the temperature to increase the pressure in the cylinder body to the final pressure; Another method is to raise the temperature first and then apply pressure. The key to HIPS technology is the selection of different packaging materials. The main requirements for the package are: (1) good high-temperature performance, without reacting with SiC and its composite components at sintering temperature; (2) Good deformability, using a melt type sheath material with sufficient viscosity to prevent infiltration into the sintered body. Glass encapsulation has good effect, low cost, and is easy to shape, making it easy to directly prepare complex shaped products without the need for mechanical processing. It is very meaningful for the preparation of silicon carbide ceramic and their composite materials; Using a glass casing, divided into two layers, the inner layer is high melting point glass, and the outer layer is low melting point glass, with thicknesses of 0.05 and 1mm, respectively. The high pressure of the HIPS method can reach several thousand atmospheres, which enables the sintering of silicon carbide ceramic and its composite materials at extremely low temperatures that cannot be sintered under normal pressure. Although hot isostatic pressing sintering can obtain dense silicon carbide ceramic with complex shapes and good mechanical properties, HIPS sintering requires the encapsulation of the blank, making it difficult to achieve industrial production.

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