氧化气氛对B_4C-SiC/C复合材料自愈合抗氧化性的影响

EFFECTS OF OSIDATIVE ATMOSPHERES ON SELFHEAL-ING PROPERTIES OF B4C - SiC/C COMPOSITES

考察了氧化气氛（空气流量、空气湿度和氧化介质等）对Ｂ４Ｃ－ＳｉＣ／Ｃ复合材料自愈合抗氧化性的影响。对复合材例的恒温氧化行为进行了实验研究。结果发现：在某个临界值以下。空气流量的增加主要是加速氧气向材料内部扩散。导致氧化质量损失增加；高于临界值，空气流量的增加可以加速复合材料表面陶瓷粒子的氧化转化，从而促进实现自愈合抗氧化。湿空气在低温下（１０００℃）主要是促进了复合材料表面的Ｂ２Ｏ３以硼酸和偏硼酸的形式挥发，对自愈合抗氧化性不利；但在高温（１２００℃）下，湿空气反而可以促进ＳｉＣ粒子的氧化转化，时自愈合抗氧化有利。在强的氧化介质（如氧气）中氧化时，复合材料内部大量的炭基体颗粒和Ｂ４Ｃ粒子首先发生强烈的选择性氧化反应，自愈合抗氧化性较差。

The isothermal oxidation behavior of B4C - SiC/C composites were investigated in order to determine the effects of oxidative atmosphere on the selfhealing properties of the composites. Results demonstrate thatwhen the air flow rate is below a critical value, increasing its rate mainly accelerates the diffusion of oxygen intothe interior of the composites, which causes steady weight - loss due. to oxidation of the carbon substrate; andwhen the air flow rate is above the critical value, increasing its rate would speed up the oxidation of ceramics,which can accelerate the realization of selfhealing to resist oxidation for the composites. At lower temperatures(1O00 ), moist air could speed up the volatilization of B2O3 in the form of HBO2 and H3BO3, which are dis-advantageous to self - healing properties of the composites: At higher temperatures(1 200 ), moist air canaccelerate the oxidation of SiC particles. which is favorable to the selfhealing properties instead. In oxygen at-mosphere. a large amount of carbon substrate and B4C particles had been oxidized before an effective protectionlayer was formed on the surface of the composites.