热震条件下Al_(2)O_(3)-O’-SiAlON-SiC复合材料氧化行为研究

Oxidation Behavior of Al_(2)O_(3)-O’-SiAl_(2)O_(3)N-SiC Composite under Thermal Shock Condition

以板状刚玉(骨料和细粉)、α-Al_(2)O_(3)微粉和硅粉等为原料,在1500℃下埋炭保温3 h烧结制备了Al_(2)O_(3)-O’-SiAlON-SiC复合材料。研究了热震及不同热震次数对复合材料氧化行为的影响。研究结果表明:在无热震和热震条件下,试样氧化增重率在900~1300℃均随温度升高而增加;热震氧化条件下的增重率大于无热震条件,且随热震次数增加,氧化增重率略有增加。无热震条件下,试样恒温氧化曲线类似于抛物线型,而热震条件下,试样氧化曲线接近直线型。因此,热震明显促进了复合材料的氧化,其原因在于热震使试样表面的氧化保护膜破裂,试样产生微裂纹,为氧气进入试样内部提供通道,进而加速材料氧化。

Al_(2)O_(3)-O’-SiAlON-SiC composite was prepared from tabular corundum(aggregates and fines), ultra-fine α-Al_(2)O_(3) and Si powder as starting materials at 1 500 ℃ for 3 h in carbon embedded condition. The effects of thermal shock and thermal shock cycle on oxidation behavior of the composite were investigated. The results show that the weight gain ratio of the composite increases with temperature increasing from 900 ℃ to 1 300 ℃ with and without thermal shock condition. The weight gain ratio with thermal shock is more than that without thermal shock, and the weight gain ratio increases with the increase of thermal shock cycle, indicating that thermal shock can promote the oxidation of Al_(2)O_(3)-O’-SiAlON-SiC composite. The oxidation curves exhibit parabolic-like without thermal shock, and the curves are linear-like with thermal shock. O’-SiAlON and SiC are oxidized on the surface of sample to form a dense protective film which retards oxygen diffusion into the inner of sample without thermal shock. However, the oxidation protective film is broken under thermal shock condition, which provides passages for oxygen to enter the inner part of the samples, accelerating the oxidation of the composite.