熔体变质对超高重力场燃烧合成TiC-TiB_2组织均匀性的影响

Effect of Melt Modification on Microstructure Homogeneity of TiC-TiB_2 Composites Prepared by Combustion Synthesis in Ultrahigh Gravity Field

通过在(Ti+B4C)反应体系中相应增加(CrO3+Al)高能铝热剂添加量,使燃烧体系绝热温度依次达到3000℃、3200℃、3400℃、3600℃与3800℃,进行加速度2000 g的超高重力场燃烧合成实验,制备出系列TiC-TiB2复合陶瓷,探讨高能铝热剂的引入对陶瓷显微组织、凝固行为与力学性能的影响。经XRD、FESEM与EDS测试,发现陶瓷显微组织均由TiB2基体相、不规则TiC第二相、少量的Cr基合金相及Al2O3夹杂物构成,增加高能铝热剂的引入量,通过提高反应熔体温度并增加金属液相,对陶瓷合成过程进行耦合控制,不仅急剧降低Al2O3夹杂含量与尺寸,而且明显细化陶瓷组织、改善其均质性,进而当绝热温度超过3600℃,出现TiB2片晶平均尺寸1μm的超细晶组织,使陶瓷致密性、抗弯强度与断裂韧性均显著提升。

By introducing （CrO3 ＋ A1） high-energy thermit into （Ti ＋ B4C） system and increasing adiabatic temperature of reactive system from 3000 ℃ to 3800℃ at intervals of 200 ℃, a series of solidified TiC-TiB2 were prepared by combustion synthesis in ultrahigh gravity field of 2000 g （ where g represents the gravitational acceleration）. XRD, FESEM and EDS results showed that the solidified TiC- TiB2 are mainly composed of a number of TiB2 primary platelets, irregular TiC secondary grains, and a few of isolated Al2O3 inclusions and Cr-based alloy. Increasing the addition amount of high-energy thermite in combustion system imposes a coupled control on the solidified TiC-TiB2 composite by increasing both actual temperature and metallic liquid in TiC-TiB2 melt, thereby not only reducing AlzO3 inclusions sharply but also refining the microstructure and improving the homogeneity of the ceramic, and ultrafine-grained microstructure of average thickness of TiB2 platelets smaller than 1 μm begin to appear in near-full-density ceramic as the adiabatic temperature of reaction system exceed 3600 ℃, so the enhanced densification, flexural strength and fracture toughness of the ceramic are presented with the increasing of the thermit in reaction system.