【作者】 于国强；

【导师】 刘维良；

【作者基本信息】 景德镇陶瓷学院 ， 材料学， 2012， 硕士

【摘要】 碳化硼（B₄C）具有密度小、硬度高、强度高、耐磨损、耐高温、化学稳定性好以及中子吸收能力强等特点，被国内外广泛应用于轻质防弹材料、耐磨和自润滑材料、高级耐火材料、特种耐腐蚀材料、切割研磨材料以及原子反应堆屏蔽材料等诸多领域。但是传统电弧炉冶炼工艺制备的B₄C容易发生包晶分解，并且B₄C本身极高的共价键比例使其在烧结时晶界移动阻力很大，难以烧结致密，又由于其较低的断裂韧性，大大限制了其在更多领域的应用。本论文以H₃BO₃和炭黑为原料，采用碳热还原法在碳管电阻炉中制备B₄C粉体，并对其粒度、总碳含量以及晶相进行了测试和分析，结果表明：当H₃BO₃和炭黑摩尔比为5.2:7、在合成温度为1800℃、合成时间为40min条件下制备的B₄C粉末纯度较高，总碳含量为21.5%，初始粒度为d50=36.19μm；以钢球为球磨介质、在转速为300r/min的全方位行星球磨机上粉碎1h后其d50达到2.49μm，在80℃的浓度为30%的H₂SO₄溶液中酸洗后，球磨引入的Fe等杂质被基本去除。为克服热压烧结B₄C产品的成本高、产量小等缺点，本课题以制备的B₄C粉末为主要原料，通过添加炭黑、 SiC和TiC等烧结助剂，在常压烧结条件下制备了B₄C基复相陶瓷，并对其致密度、力学性能和微观结构进行了测试和分析。结果表明：当以重量比为2:1的水溶性酚醛树脂和环糊精为组合粘结剂，其添加量为粉料的9wt%、粉料中水分含量为1.2wt%、模压压力为150MPa·cm^-2、保压时间为10s时制备的生坯密度最大且表观性能良好，密度为1.73g·cm^-3；通过正交试验优化得到的最佳配方为：2wt%C-12wt%SiC-7wt%TiC-79wt%B₄C，在最高烧成温度为2100℃、保温1.5h的最佳无压烧结工艺下，其断裂韧性、抗弯强度、维氏硬度和相对密度分别达到3.72MPa m1/2、515.7MPa、32.3GPa和96.26%。论文最后结合BSE测试结果和EDS分析结果对B-Si-Ti-C系统的固溶机理和增韧机理进行了分析，结果显示，在一定条件下，SiC与B₄C发生了一定的固溶，TiC与B₄C发生原位反应生成了有利于增强B₄C基体韧性的TiB2，而C的主要作用则是去除B₄C基体表面的氧，提高了其表面能，所以此四元系统固溶性较好；实验中涉及的增韧机理主要是热膨胀系数失配引起的裂纹偏转和第二相粒子加入对裂纹扩展的阻碍作用。更多还原

【Abstract】 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.更多还原