烧结助剂对HfB_2-SiC基超高温陶瓷组织和性能的影响研究

The Effect of Sintering Aids on Microstructure and Mechanical Properties of HfB_2-SiC Composites

采用热压烧结工艺制备出HfB_2-20%SiC(HS)、HfB_2-20%SiC-5%Si_3N4(HSS)和HfB_2-20%SiC-5%AIN(HSA) (体积分数,下同)3种超高温陶瓷基复合材料,对材料进行了微结构表征和力学性能测试,并对Si_3N_4、AIN烧结助剂的作用机理进行了初步分析。结果表明,与HfB_2-20%SiC相比,Si_3N_4和AIN烧结助剂的引入使材料的烧结温度从2200℃降低到1850℃,相对密度从95%提高到99%左右。材料的平均晶粒尺寸显著降低,形成了相应的晶粒边界相。力学性能测试结果表明,HfB_2-20%SiC-5%Si_3N_4和HfB_2-20%SiC-5%AIN的抗弯强度和断裂韧性均比HfB_2-20%SiC获得一定程度的提高。烧结助剂的引入使SiC/HfB_2超高温陶瓷材料的断裂模式从单纯的穿晶断裂转变为穿晶/沿晶混合的断裂模式。

Three kinds of HfB2 based ultra-high temperature ceramics, HfB2-20vol%SiC （HS）, HfB2-20vol%SiC-5vol%Si3N4 （HSS） and HfB2-20vol%SiC-5vol%A1N （HSA） were fabricated from commercially available powders by hot-pressing in a graphite element furnace at high temperature under 30 MPa. The mechanical properties, microstructures and phase constitutions of HS, HSS and HSA were investigated. The results show that the introduction of Si3N4 and AIN as sintering aids, can markedly decrease the sintering temperature from 2200℃ to 1850℃. The relative densities of the three kinds of ultra high temperature ceramics also increased from 95% to 99%. The microstructure analysis of the three composites all revealed homogeneous microstructures with regularly dispersion of SiC particles, and some secondary grain-boundary phases were found mainly at the triple junctions of the diboride grains of HSS and HSA. The introduction of Si3N4 or AIN into HfB2-SiC composite resulted in the change of fracture mode from the trans-granular to the inter/trans-granular fracture mode.