Four sintering methods of silicon carbide

Pressureless sintering
Pressure-free sintering is considered as a promising sintering method for SiC sintering. According to the different sintering mechanism, pressure-free sintering can be divided into solid phase sintering and liquid phase sintering.S. roehazka sintered SiC with a density higher than 98 at 2020℃ by adding an appropriate amount of B and C to ultrafine SiC powder (oxygen content less than 2).A.M. Ulla et al. used Al2O3 and Y2O3 as additives to sintering 0.5 m -sic (particle surface containing a small amount of SiO2) at 1850-1950℃, and the relative density of SiC ceramics obtained was greater than the theoretical density of 95, and the grain size was small, with an average size of 1.5 m.

Hot pressing
Nadeau pointed out that without any sintering additives, pure SiC can only sintering densification at extremely high temperature, so many people practice hot pressing sintering process on SiC.There have been many reports on hot pressing sintering of SiC by adding sintering additives.Alliegro et al. studied the effects of metal additives such as B, Al, Ni, Fe and Cr on the densification of SiC and found that Al and Fe were effective additives to promote the hot pressing and sintering of SiC.F.f.lange studied the effect of adding different amounts of Al2O3 on the properties of hot-pressed sintered SiC, and believed that the hot-pressed sintering densification was based on the dissolution-reprecipitation mechanism.However, the hot pressing sintering process can only produce SiC components with simple shape, and the number of products prepared in the process of hot pressing sintering is very small, so it is not conducive to industrial production.

Hot isostatic sintering
In order to overcome the defects of the traditional sintering process, Duna adopted the hot isostatic sintering process with B and C as additives to obtain the fine crystal SiC ceramics with a density greater than 98 and a bending strength of up to 600MPa at room temperature at 1900℃.Although dense SiC products with complex shapes can be obtained by hot isostatic sintering, and the products have good mechanical properties, HIP sintering requires the inclusion of raw materials, so it is difficult to achieve industrial production.

Reaction sintering
Reaction sintering SiC, also known as self-binding SiC, is a process in which the mass of the billet increases, the porosity decreases, and the finished product with certain strength and dimensional accuracy is sintered through the chemical reaction between the porous billet and the gas or liquid phase.It is formed by mixing p-sic powder and graphite in a certain proportion and heating it to about 1650 ℃. At the same time, it penetrates Si or penetrates into the p-sic through the gas phase to form a reaction with graphite and combine the existing p-sic particles.If the Si is completely permeated, the reaction sintered body with complete density and no size shrinkage can be obtained.Compared with other sintering processes, the size change of reactive sintering in the densification process is small, and the size of products can be manufactured, However, due to the existence of a considerable amount of SiC in the sinter, the high temperature properties of reaction sintered SiC ceramics are poor.