包覆工艺制备C—SiC—B4C—TiB2复合材料的组织与性能

以鳞片石墨，B4C，SiC，TiO2为原料，利用包覆工艺在不同热压温度下制备了W（C）=50％的C—SiC—B4C—TiB2复合材料，并详细研究了热压温度对复合材料显微组织和性能的影响规律．结果表明，当热压温度高于1850℃时，复合材料由C，SiC，B4C和TiB2这四相组成；复合材料的体积密度、抗折强度和断裂韧性均随着热压温度的升高而增加．2000oC热压时，复合材料的体积密度、气孔率、抗折强度和断裂韧性分别达到2．41g／cm^3，3．42％，176MPa和6．1MPa·m^1/2；热压温度升高，复合材料的碳相和陶瓷相逐渐致密，碳相最终形成了在陶瓷基体上镶嵌的直径为40μm橄榄球状和条状这两种形貌．碳／陶瓷相的弱界面分层诱导韧化和第二相TiB2与陶瓷基体之间热膨胀系数不匹配所致的残余应力使变形过程中微裂纹的扩展路径发展变化，使复合材料的韧性提高．

Microstructure and properties of C -SiC -B4 C composites prepared by coating processing

C - SiC - B4C carbon/ceramic composites with 50% （ mass fraction） content of graphite flake were prepared from graphite flake, B4C, SiC and TiO2 by the coating and hot -pressing technology at different temperatures. The effects of sintering temperature on the microstructures and properties of C -SiC -B4C composites were studied. Results show that C, SiC, B4C and TiB2 exist in the composite when the temperature is higher than 1 850 ℃. The bulk densiw, flexural strength and fracture toughness of the composites increase with hot - pressing temperature increasing. The bulk density, apparent porosity, flexural strength and fracture toughness are 2. 41g/cm3, 3.42% , 176 MPa and 6. 1 MPa · m1/2 respectively at 2 000℃. During the process of sintering, two kinds of morphology of the carbon phase have been found, olivaryshaped with diameter 40 μm and striated structure. Carbon - ceramic weak boundary condition stratify caused by the micro - crack and the changes in the micro - crack propagation route due to the existence the residual stress by the mismatch of the heat expansion coefficients between the second phase TiB2 and ceramic matrix enhanced the toughening of the composites.