超重力下燃烧合成TiB_2-TiC共晶复合陶瓷

采用超重力下燃烧合成技术,制备出TiB2-TiC共晶复合陶瓷。XRD、SEM与EDS结果表明,复合陶瓷主要由大量细小的TiB2片晶均匀分布于TiC基体上的共晶组织构成,而富钛ε碳化物(Ti,Cr)C1-x则断续分布于TiC基体间,同时在基体中还孤立分布着少量的、形态不规则的α-Al2O3晶粒或Al2O3-ZrO2共晶团组织。高温化学反应使所有产物均呈液态,且超重力的引入诱发熔体内部Stocks流,从而获得液态Ti-Cr-C-B与液态氧化物的分层熔体,液态Ti-Cr-C-B在远离平衡态下发生共晶反应生成TiB2-TiC共晶复合陶瓷。性能测试表明,随着B4C+Ti+C在燃烧体系中质量分数增加,TiB2-TiC共晶复合陶瓷相对密度和断裂韧性变化不大,分别为97%~99%与6.5~7.1 MPa.m1/2,而维氏硬度与弯曲强度则逐渐增加,最高可达28.6 GPa与615 MPa。

TiB_2-TiC eutectic composite ceramics prepared by combustion synthesis under high gravity

TiB_2-TiC eutectic composite ceramics were prepared by combustion synthesis under high gravity. XRD, SEM and EDS results show that TiB_2- TiC composites are mainly composed of the eutectic microstructures of TiC matrix, in which a large number of the fine TiB_2 platelet grains are dispersed uniformly; meanwhile, at the boundaries of the eutectic microstructures there discontinuously disperse the ε-carbides with the enrichment of Ti atoms, and a few of isolated, irregular α-Al_2O_3 grains and Al_2O_3-ZrO_2 colonies are also observed. Because high-temperature chemical reaction results in the full-liquid products, and the introduction of high gravity induces the Stocks flow in the melts, leading to the formation of layered melts consisting of liquid Ti - Cr - C - B and liquid oxides, it is considered that TiB_2-TiC composites grow through eutectic transformation far away from the equilibrium state. The results of properties indicate that with increasing mass fraction of B_4C+Ti+C in combustion systems, the relative density and fracture toughness of TiB_2-TiC composites are all among 97% ～99 % and 6.5～values of 28. 6 GPa and 615 MPa, respectively.