Degradation Mechanism of Amorphous Silicon Carbide Fiber due to Air-Exposure at High Temperatures
Degradation Mechanism of Amorphous Silicon Carbide Fiber due to Air-Exposure at High Temperatures
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DOI：
10.2320/matertrans.48.111
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发表时间：
2007-02
影响因子：
1.2
通讯作者：
K. Morishita;Tasuku Matsumoto;Shojiro Ochiai;H. Okuda;T. Ishikawa;Mitsuhiko Sato
中科院分区：
文献类型：
--
作者：
K. Morishita;Tasuku Matsumoto;Shojiro Ochiai;H. Okuda;T. Ishikawa;Mitsuhiko Sato
研究了非晶碳化硅纤维Tyranno-ZMI在1173 ~ 1873 K温度下暴露20 ks后的降解机理。通过腐蚀去除光纤表面的氧化层制备的裸光纤，其平均强度随暴露温度的升高而降低，尤其是在高于1673 K的温度下暴露时。采用Sherrer法对纤维中β SiC晶粒尺寸的测量表明，在1773 K以上的温度下，纤维中的β SiC晶粒发生粗化。纤维表面的扫描电镜观察表明，纤维表面形成了许多缺陷。通过使用聚焦离子束在纤维试样中直接引入人工缺口，测定了在1673和1773 K下暴露的纤维的断裂韧性值分别为1：8 - 0：3、1：9 - 0：4和1：3 - 0：4 MPa ffffiffi p。基于这些结果，纤维的劣化的原因归因于表面缺陷的扩展，该表面缺陷由于β-SiC晶体的粗化而导致断裂韧性的降低而增强。[doi：10.2320/matertrans.48.111]
The degradation mechanism of the amorphous silicon carbide fiber, Tyranno-ZMI � , exposed in air at 1173 � 1873 K for 20 ks were studied. The average strength of the bare fiber, which was prepared by etching away the oxidation layer on the fiber surface, decreased with increasing exposure temperature, especially when exposed at the temperature higher than 1673 K. The measurement of the crystallite size of � SiC in the fiber with Sherrer method revealed that coarsening of the crystalline occurred in the fiber exposed at the temperatures higher than 1773 K. The scanning electron microscope observation of the fiber surface showed that the many defects formed on the fiber surface. By introducing an artificial notch directly into the fiber specimens using a focused-ion(Ga þ )-beam, the fracture toughness values of the as-supplied fiber and of the fiber exposed at 1673 and 1773 K were determined to be 1:8 � 0:3, 1:9 � 0:4 and 1:3 � 0:4 MPa ffiffiffiffi p , respectively. Based on these results, the reason for the degradation of the fiber was attributed to the extension of the surface defect which was enhanced by the reduction in fracture toughness due to coarsening of the � -SiC crystalline. [doi:10.2320/matertrans.48.111]