Study On The Preparation And Properties Of B₄C-based Ceramics Composite And Synthesis Of B₄C Powder

Boron carbide （B₄C） ceramic, due to its low density, high hardness, highstrength, abrasion resistance, resistance to high temperature, excellent abilityof corrosion and excellent ability of absorbing neutron, has been widely usedin light bulletproof materials, sharpener materials, lubricate materials,high-grade refractory materials, special corrosion resistant materials andradiation protection materials. However, the B₄C which is prepared by electricarc furnace was easy to peritectic decomposing, the widespread use of boroncarbide was also limited due to the relatively low strength and fracturetoughness as well as poor sinterability caused by strong covalent bond andlow self-diffusion coefficient.The H₃BO₃and carbon black were used as raw material, B₄C powder wasprepared by carbothermal reduction method in carbon tube furnace, and itsparticle size, and crystal phase were tested and analyzed. The results showthat B₄C powder with high purity can be got when the mol ratio of H₃BO₃andcarbon black is5.2:7, the synthesis temperature is1800℃and thesynthesistime is40min, its total carbon is21.5%, the initial particle size isd50=36.19μm. The median diameter could reach2.49μm after be crushed incomprehensive planet ball mill for1h, the Fe in powder could be removed asit was washed in H₂SO₄with the concentration of30%,80℃.In view of the B₄C products which were sintered by hot pressing have thedefect of high-cost and low-yield, in this study, B₄C-based ceramics wereprepared by pressureless sintering with B₄C we got as main raw material, C,TiC, and SiC as sintering aids. And the relative density, mechanical propertiesand microstructure of B₄C-based ceramics were tested and analyzed, theparameters of compression molding were also investigated, water solublephenolic resin and cyclodextrin were selected as binder with the weight ratioof2:1, the green body with density of1.73g·cm-3could be got when theaddition of binder is9wt%, kept10s with the pressure of150MPa·cm-2, andthe moisture content was1.2wt%. The results showed that the best formula is2wt%C-12wt%SiC-7wt%TiC-79wt%B₄C, the relative density, fracturetoughness, bending strength and vickers hardness of the sample could reach96.26%,3.72MPa m1/2,515.7MPa and32.3GPa respectively when it wassintered at the best sintering process of2100℃for1.5h. The solid solubility mechanism and toughening mechanism of the samplewere analysed through the results of BSE and EDS, the results show that someextent solid solution occurred between SiC and B₄C,, in-situ reaction wasoccurred between TiC and B₄C, the product is TiB2, which could enhance thetoughness of the B₄C, the main role of C is to remove the oxygen on the B₄Csurface, and the surface energy of B₄C could be increased, so the solidsolubility of the system is good; In this process, main toughening mechanicalsrefer to crack deflection resulting from unsuitable expanding coefficient andinhibiting crack diffusion for addition of second phase.