可加工B4C/BN复相陶瓷的制备及其高温抗氧化性能

Preparation of Machinable B_4C/BN Composites and Their Oxidation Resistances at High Temperature

采用热压烧结工艺制备单相B4C陶瓷、B4C/BN微米复相陶瓷和B4C/BN纳米复相陶瓷。研究了其在1 000～1 300℃的等温氧化性能,通过对氧化后试样表面的物相组成和显微结构的分析,探讨了氧化机理。结果表明:单相B4C陶瓷、B4C/BN微米复相陶瓷和B4C/BN纳米复相陶瓷的高温抗氧化性能随氧化温度提高和氧化时间增加而逐渐降低,试样氧化过程中质量损失逐渐明显。对试样在不同氧化温度下得到的氧化曲线进行了线性拟合分析,试样在1 000℃时抗氧化性能较好,但在1 300℃时抗氧化性能较差。氧化后试样表面的物相组成主要为B4C相、h-BN相,以及少量的B2O3相和Al4B2O9或Al18B4O33相。氧化后试样表面存在一层厚度约为100μm的氧化层,氧化层中存在许多微孔和少量玻璃相物质。氧化生成的B2O3挥发是导致试样质量随着氧化温度和氧化时间增加而显著减少的主要原因。

The B4C monolith, B4C/BN microcomposites and B4C/BN nanocomposites were fabricated by hot-pressing process. Oxi- dation resistance of the hot-pressed specimens at 1 000--1 300 ℃ were investigated. The phase composition and microstructure of the sample＇s surface after oxidation process were analyzed. The oxidation mechanism of specimens was discussed. The results showed that the oxidation resistances of BaC monolith, B4C/BN microcomposites and B4C/BN nanocomposites at high temperature decreased gradually with the increase of oxidation temperature and oxidation time. The mass-loss of composites samples became remarkably. The oxidation resistance curve of specimens obtained from different oxidation temperatures was analyzed by linear regressive meth- ods. The specimens exhibited excellent oxidation resistance at 1 000 ℃, but the oxidation resistance of specimens decreased remarka- bly at 1 300 ℃. The X-ray diffraction patterns showed that there existed the BaC phase and h-BN phase on surface of the oxidized specimens, and low content of B2O3 phase and AlaB2O9 or A118B4O33 phase also existed on surface of the oxidized specimens. There existed an oxidized layer with the thickness of about 100 pm on the surface of oxidized specimens. The microstructure showed that there existed some small pores and glass phase on the surface of the oxidized specimens. The specimen＇s mass decreased gradually with the increase of oxidation temperature and oxidation time due to the evaporation of the produced B2O3 during the high tempera- ture oxidation process.