热压温度对C-SiC-B_4C复合材料性能的影响

Effect of hot pressing temperature on the microstructure and properties of C-SiC-B_4C composite

用热压烧结法制备C-SiC-B_4C复合材料,研究了热压温度对其显微组织和力学性能的影响.结果表明,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提高.在2000℃烧结的复合材料综合力学性能最佳,其体积密度、气孔率、抗折强度和断裂韧性分别达到2.81 g/cm^3、2.4%、236.7 MPa和5.4 MPa·m^(1/2).随着热压温度的提高,材料的组织经历了陶瓷相长大、C相变薄、C相和SiC逐渐致密化等过程.利用鳞片石墨C_(fg)易在压力下滑动在陶瓷基体上形成C_(fg)条状组织的特性,实现了材料的显微组织设计.碳陶复合材料的界面结合状态改善、C_(fg)条状结构和C_(fg)与陶瓷相的热膨胀不匹配是材料力学性能提高的主要原因.

C-SiC-B4C composites were prepared with flake graphite Cfg, SiC, B4C and TiO2 and the effects of sintering temperature on the microstructures and properties of C-SiC-B4C composites were investigated. The result showed that the bulk density, bending strength and fracture toughness of the composites increase obviously with the increasing of sintering temperature. The composite has the best comprehensive mechanical properties where the bulk density 2.81 g/cm^3, apparent porosity 2.4%, bending strength 236.7 MPa and fracture toughness 5.4 MPa.m^1/2 at 2000 ℃ The microstructure of composite experiences the process of ceramic phase growing up, carbon phase being compressed, carbon phase and SiC being densified with the increasing of hot pressing temperature. The Cfg lamellar structure forms in the ceramic basis in the end because of its sliding under the pressure, and the composite microstructure designing was realized. It was found that the main reasons of improvement of the composites mechanical property are the interfacial adhesion of carbon phase and ceramic phase is improved, Cfg lamellar structure distribution which is better than the carbon partial distribution from the petrol coke and black pigment as raw materials, and mismatch of heat expansion of carbon phase and ceramic phase.