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Sintering of B4C by Pressureless Liquid Phase Sintering
Boron carbide ceramic materials have many excellent properties, such as: high melting point (2450C, ultra-high hardness (HV>30GPa), low density (2.51g/cm3), high modulus, good wear resistance, oxidation resistance, acid and alkali resistance Strong and good neutron absorption capacity, and has a large tensile strength at high temperature, so it has been widely used in industry, military and other aspects, but the fracture toughness of boron carbide ceramics is very low, Krc<2.2MPa, a total of The valence bond content is as high as 94%, so it is an extremely difficult to sinter ceramic material. The relatively mature process for preparing high-density boron carbide is hot pressing sintering, and there are also hot isostatic pressing, microwave sintering, reaction sintering, pressureless Sintering or spark plasma sintering and other technologies are used for boron carbide sintering. Among them, pressureless sintered B4C ceramics are widely valued due to their simple preparation process, superior product performance and low cost.
1 Determination of material pressureless sintering process
In order to determine the reasonable sintering temperature and holding time of the pressureless sintered B4C ceramic material, the sintering process of the B4C ceramic material with a carbon mass fraction of 4% and a SiC mass fraction of 8% was taken as the research object. Keep warm for 30min. Experimental Figure 1 shows the influence of different sintering processes on the density of B4C ceramic materials when the carbon mass fraction is 4%, SiC, and the mass fraction is 8%. It can be seen from Figure 1a that when the sintering temperature is 1975°C, the density of the material has a maximum value, and the density increases significantly from 1950 to 1975°C, so the sintering temperature is a very sensitive factor for the sintering process . It can be seen from Figure 1b that when the sintering temperature is 1975°C, the density of the sample with a holding time of 30 min appears the maximum. Therefore, it can be obtained from Fig. 1 that the best sintering process of pressureless sintered B4C ceramic material is 1975°C for 30min.
1) The best sintering process for pressureless sintered B4C ceramic material is 1975°C for 30min.
2) The effects of the addition of sintering aids SiC and C on the density, hardness and flexural strength of the material all increase first and then decrease. The fracture toughness of the material increases with the increase of the mass fraction of C. The increase of SiC decreases first, and increases slightly after the SiC mass fraction is higher than 6%.
3) When the addition of sintering aids SiC and C is 6% and 5% respectively, the obtained pressureless sintered B4C ceramic material has the best mechanical properties: the bulk density is 2.45g/cm3, the Vickers hardness is 35GPa, the resistance Bending strength 240MPa.
3 Equipment recommendation
SIMUWU pressureless sintering furnace is mainly used in the field of pressureless sintering of emerging composite ceramic silicon carbide such as silicon carbide sealing rings, heat exchange tubes, shaft sleeves and shaft tubes, nozzles, impellers and bulletproof products. Furnace basic configuration: maximum temperature 2200°C, heating element: SGL graphite rod or tube, plate, graphite felt for heat insulation, domestic pump and Leybold pump for vacuum system are optional.
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