高温氧化对再结晶碳化硅陶瓷断裂强度的影响

研究了在1500℃空气中的高温氧化对再结晶碳化硅(recrystallized silicon carbide,RSiC)陶瓷断裂强度的影响。用X射线衍射仪、扫描电镜分析了RSiC样品氧化后表面的物相组成及显微结构。结果表明:在1500℃下RSiC陶瓷的氧化质量增加遵循抛物线规律,氧化速率常数为3.77×10-5g2/(cm4·h1),其线性相关系数r2为0.998。RSiC陶瓷的室温抗弯强度随氧化时间增加呈现出先升后降的变化趋势,当氧化21h时,材料的室温抗弯强度最高,达到87MPa。氧化初期由于样品表面生成致密的非晶态SiO2,对样品表面的缺陷起到了钝化作用,导致材料室温断裂强度升高;氧化后期由于非晶态SiO2膜的析晶而产生裂纹以及循环氧化导致裂纹扩展,从而使材料的断裂强度降低。

EFFECT OF HIGH TEMPERATURE OXIDATION ON THE FRACTURE STRENGTH OF RECRYSTALLIZED SILICON CARBIDE

The effect of high temperature oxidation at 1 500 ℃ in air on the fracture strength of recrystallized silicon carbide （RSiC） was investigated. The phase composition and microstructure of the surface of RSiC sample after oxidation were analyzed by X-ray diffraction and scanning electron microscopy. It was found that the mass gain of RSiC is a parabolic relationship with oxidation time at 1 500 ℃. Its oxidation rate constant is 3.77 × 10-5 g2/（cm4·h1） and the linear correlation coefficient r2 is 0.998. The fracture strength of RSiC increases at first and then decreases with the oxidation time increases. A maximal strength of 87 MPa can be obtained after oxidation at 1 500 ℃ for 21 h. The compact amorphous silica is formed on surface of the RSiC at the earlier stage of oxidation causing a passitive action for the recovery of the surface defects,resulting in the increase of fracture strength. The fracture strength decreases at the later stage of oxidation due to the crystallization of amorphous silica and the formation of cracks on the surface of samples during oxidation cycles.