不同氧化温度下涂覆BN涂层SiC纤维的微观结构及性能研究

Microstructure and properties of SiC fibers coated with BN coating at different oxidation temperatures

通过化学气相渗透(CVI)工艺在典型国产SiC纤维表面沉积BN涂层,并在800~1200℃的氧化环境下处理1 h。对涂覆BN涂层的SiC纤维氧化后的形貌、结构以及成分进行表征,通过单丝拉伸强度评价涂覆BN涂层的SiC纤维氧化后的性能变化。结果表明,氧化温度低于1000℃时,BN涂层及其氧化物层能够有效阻止O_(2)对内部SiC纤维的侵蚀,高于此温度时,SiC纤维被氧化。随着氧化温度的升高,涂覆BN涂层的SiC纤维表面氧化物经历α-B_(2)O_(3)→SiC x O y→非晶SiO_(2)的历程。涂覆BN涂层的SiC纤维单丝拉伸强度随着温度的升高呈衰减趋势,且BN涂层直接暴露在氧化环境下反而降低SiC纤维的抗氧化能力。纤维断裂的失效源先由BN涂层缺陷过渡为B_(2)O_(3)氧化层缺陷最终演变为SiO_(2)氧化层气孔缺陷。

The BN coating was deposited on the surface of typical domestic SiC fibers by chemical vapor permeation(CVI)process,and the fibers were oxidized at 800-1200℃for 1 h.The morphology,structure and composition of BN coated SiC fibers after oxidation were characterized.The property changes of BN coated SiC fibers after oxidation were evaluated by tensile strength of monofilament.The results show that when the oxidation temperature is lower than 1000℃,the BN coating and its oxide can effectively prevent the erosion of the inner SiC fibers by O 2,and when the temperature continues to rise,the SiC fibers are oxidized.With the increase of oxidation temperature,the surface oxide of BN coated SiC fibers goes through the process ofα-B_(2)O_(3)→SiC x O y→amorphous SiO_(2).The tensile strength of BN coated SiC fibers decreases with the increase of oxidation temperature.Direct exposure of BN coating to oxidizing environments reduces the oxidation resistance of SiC fibers.The failure source of fiber fracture first transitions from BN coating defects to B_(2)O_(3)oxide layer defects and finally evolves into SiO_(2)oxide layer porosity defects.