The influence of powder properties and additives on the densification sintering of materials: the particle size of the original boron carbide powder, the particle size distribution, the shape of the powder particles, the purity, etc. have a greater impact on the organization and properties of boron carbide ceramic. The reduction of surface energy is the driving force of ceramic sintering. The smaller the particle size of the powder , the larger the specific surface area, the greater the driving force of sintering, while the finer the powder, the more structural defects produced in the preparation process, high sintering activity, which can promote sintering and densification. Pure B4C is generally sintered by solid-phase sintering, which has a high sintering temperature and a narrow sintering temperature range. It has been found that the activation of grain boundaries and bulk diffusion can be improved by adding sintering additives to increase the density of point defects or dislocations.
Hot pressure sintering of B4C: The unpressurized sintering of B4C can be used to prepare products with complex shapes, but it tends to result in overgrowth of grains and porosity of 3-7Vol.%, so the strength and toughness of the material are low.
Hot Isostatic Pressure Sintering of B4C: The use of hot isostatic pressure (HIP) sintering of boron carbide ceramic allows for densification without additives, as well as the achievement of fine grain microstructures and high bending strength. Successful use of special boron oxide glass envelope filled with submicron pure B4C powder, at 1700 ℃ above, 200MPa pressure insulation for 60min, the relative density of the production of 100% boron carbide ceramic, the three-point bending strength of 714MPa, Weber touch number m of 8.3. In the case of metal envelope, B4C decomposition of the formation of metal borides and graphite, will make the envelope brittle. In addition, boron oxide gas may be released from the envelope and the sample at the same time, thus rupturing the envelope. Therefore, it is common to perform unpressurized sintering to obtain B4C without open-ended gas holes, followed by hot isostatic pressing to eliminate the remaining closed-ended gas holes and achieve complete densification, with hot isostatic pressing temperatures in the range of 1950-2050 °C.