粉体合成工艺对TiB_2–TiC复相陶瓷微观组织及力学性能的影响

Effect of Powder Synthesis Processing on Microstructure and Mechanical Properties of TiB_2–TiC Composite Ceramics

分别以直接法和间接法碳硼热还原工艺合成的TiB_2–TiC复合粉体为原料,采用热压烧结工艺制备了共晶成分的TiB_2–44%TiC(摩尔分数)复相陶瓷,研究了粉体合成工艺和烧结温度对TiB_2–TiC复相陶瓷显微组织和力学性能的影响。结果表明:以直接法合成粉末为原料烧结的TiB_2–TiC复相陶瓷中,TiB_2晶粒多呈棒状、组织细小均匀;而以间接法合成粉末为原料制备的复相陶瓷中TiB_2晶粒多呈等轴状。随着烧结温度的升高,复相陶瓷致密度提高,晶粒长大,但力学性能变化不明显。以直接法合成复合粉末为原料,在烧结温度为2 000℃、压力为30 MPa、保温时间为1 h工艺条件下制备的TiB_2–TiC复相陶瓷综合性能最佳,其致密度、弹性模量、Vickers硬度、抗弯强度和断裂韧性分别为99.9%、537 GPa、19.0 GPa、598 MPa、5.3 MPa·m^(1/2)(压痕法)和11.6 MPa·m1/2(单边切口梁法)。TiB_2–TiC复相陶瓷主要的增韧机制为裂纹偏转和分叉。

TiB2–44%TiC（in mole fraction） composite ceramics with an eutectic composition were prepared by hot pressing sintering with TiB2–TiC composite powders synthesized by direct and indirect carbon–boron thermal reduction processes, respectively. The effects of the synthesis process and sintering temperature on the microstructure and mechanical properties of TiB2–TiC composite ceramics were investigated. The results show that TiB2 grains in TiB2–TiC composite ceramic sintered with TiB2–TiC composite powder by the direct process are rod–shaped and the microstructure is fine and uniform, while the TiB2 grains in TiB2–TiC composite ceramic sintered with TiB2–TiC composite powder by the indirect processare equiaxed. The density of the composite ceramics increases and the grains grow up, but the mechanical properties changes slightly with the increase of the sintering temperature. The TiB2–TiC composite ceramic prepared by hot pressing sintering at 2 000 ℃ and 30 MPa for 1 h with the direct synthesized composite powder has the optimum comprehensive properties（i.e., relative density of 99.9%, elastic modulus of 537 GPa, the Vickers hardness of 19.0 GPa, flexural strength of 598 MPa, and fracture toughness of 5.3 MPa×m^1/2（by indentation method） and 11.6 MPa×m1/2（by SENB）. The toughening mechanism of TiB2–TiC composite ceramics is due to crack deflection and branching.