Preparation of boron carbide ceramics （一)

Hot press sintering

Hot pressing sintering causes the particles to rearrange and produce plastic flow due to the pressure at high temperature, resulting in grain boundary slip and strain-induced twinning, creep and volume diffusion. The combined effect of these mechanisms can obtain boron carbide ceramics with high density and high strength. Hot press sintering is carried out in an inert atmosphere or vacuum. Generally, the hot press temperature is 2200 ℃ ~ 2300 ℃, the pressure is 20MPa ~ 40MPa, and the holding time is 0.5h ~ 2h. However, boron carbide is a compound with strong covalent bond. It is difficult to obtain high-density, high-performance products. In order to reduce the sintering temperature of boron carbide and improve the performance of boron carbide, sintering aids must be added to promote sintering. Because boron carbide has poor thermal shock resistance, it is necessary to cool down slowly, and hot pressing sintering can only prepare products with simpler shapes.

Hot isostatic pressing

The use of hot isostatic sintering boron carbide can achieve densification without additives, and obtain fine crystal microstructure and high bending strength. Hot isostatic pressing is the use of inert gases such as N2, Ar, etc. as a medium for transmitting pressure. The boron carbide powder compact or the powder packed in the package is placed in a high-pressure container to subject the powder to high temperature and balanced pressure to reduce sintering Temperature, to avoid grain growth, can obtain high density boron carbide ceramic materials. Compared with the general hot pressing method, it can make the material receive isotropic pressure, so the microstructure of the ceramic is uniform. The disadvantage is that the equipment cost is higher and the size of the workpiece to be processed is limited.