Synthesis and microstructure control of bride-nitride composite ceramics by solid-state displacement reaction

研究了B_4C-Ti、BN-Ti和BN-Zr体系的反应工艺，确定了合成微观结构良好的TiB_2-TiC-C、TiB_2-TiN和ZrB_2-ZrN复合材料的最佳反应温度和保温时间。对TiB_2-TiC-C复合材料进行了反应热压致密化试验。在2000℃下对B_4C和Ti粉末混合物进行反应热压，不同的Ti/B_4C混合比例分别为：B_4C-TiB_2-C在0<x<2时，TiB_2-C在x=2时，TiB_2-TiC- c在2<x<3时，TiB_2-TiC在x=3时形成不同的反应产物。相对密度在x=2时最小值为97.0%。除该混合比例外，各烧结体密度均较高，相对密度均在98.4%以上。1100℃下，Ti与BN反应，TiB首先作为中间产物生成，然后TiB与BN反应生成TiB_2。TiB_2-TiN复合材料中TiN_x的N/Ti比值略低于混合比估算值。由于这种现象，反应后总会有少量BN残留。完美的TiB_2-TiN复合材料的合成需要大量的Ti加入。Zr与BN在1100℃下的反应，反应时间为144 h后反应停止。在Ar流中合成优于在真空或真空胶囊中合成。ZrN_x的非化学计量量随反应时间的延长而降低。

Reaction processes in the B_4C-Ti, BN-Ti and BN-Zr systems were examined for determining the most suitable reaction temperature and holding time for the syntheses of TiB_2-TiC-C, TiB_2-TiN and ZrB_2-ZrN composites with fine microstructure. For the TiB_2-TiC-C composites, their densification was tried by reactive hot pressing.For reactive hot pressing of powder mixtures of B_4C and Ti at 2000℃, different reaction products were formed by varying the Ti/B_4C mixing ratio x : B_4C-TiB_2-C at 0<x<2, TiB_2-C at x=2, TiB_2-TiC-C at 2<x<3 and TiB_2-TiC at x=3. Relative density had the minimum value 97.0% at x=2. Except for this mixing ratio, every sintered body was highly dense and had a relative density more than 98.4%.For the reaction between Ti and BN at 1100℃, TiB was first formed as an intermediate product and then TiB_2 was formed by the reaction between TiB and BN.N/Ti ratios of TiN_x in TiB_2-TiN composites were a little lower than those estimated from the mixing ratios. Because of this phenomenon, a little amount of BN always remained after reaction. The synthesis of a perfect TiB_2-TiN composite will need excessive addition of Ti.For the reaction between Zr and BN at 1100℃, the reaction ceased after a reaction time of 144 h. Syntheses in an Ar stream prefer to those in vacutun or in vacuumized capsule. The nonstoichiometry of ZrN_x decreased with the reaction time.