Microstructure and mechanical properties of SiC‐polycrystalline fiber and new defect‐controlling process
Microstructure and mechanical properties of SiC‐polycrystalline fiber and new defect‐controlling process
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DOI：
10.1111/ijac.12719
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发表时间：
2017-11
影响因子：
2.1
通讯作者：
H. Oda;T. Ishikawa
中科院分区：
文献类型：
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作者：
H. Oda;T. Ishikawa
化学计量SiC多晶纤维（Tyranno SAR）显示出高达2000°C的优异耐热性和约3 GPa的相对高的强度。然而，目前，为了扩大应用领域，迫切需要更高的强度。要实现实力的提升，就必须对实力的主导因素有一个全面的了解。我们通过检测第一断裂表面和断裂起源来确定主导因素（缺陷）。发现这种类型的纤维包含几种类型的缺陷，并且表明强度与缺陷尺寸的二分之一幂成反比地降低。通过实际的实验分析和计算结果，阐明了缺陷产生的原因。Tyranno SA是通过从非晶Si-Al-C-O纤维到SiC多晶结构的转化过程产生的，伴随着CO气体的释放。在转化过程中，发生不希望的组成变化（SiO气体的蒸发），这导致残余碳（缺陷之一）的增加。为了防止SiO气体的蒸发，我们通过改变转化过程的平衡状态，新开发了一个有利的条件，然后可以显着减少异常SiC晶粒生长和残余碳。
A stoichiometric SiC-polycrystalline fiber (Tyranno SAR) shows excellent heat-resistance up to 2000°C and relatively high strength around 3 GPa. However, presently, the higher strength has been eagerly required to extend the application field. To achieve increase in the strength, we have to perfectly understand the dominating factors of the strength. We specified the dominating factors (defects) by detecting the first fracture surface and the fracture origin. This type of fiber was found to contain several types of defects, and showed that the strength was decreased in inverse proportion to one-half power of the defect size. The causes of the defects were clarified by an actual experimental analysis and calculation results. Tyranno SA was produced by a conversion process from an amorphous Si-Al-C-O fiber to SiC polycrystalline structure accompanied by a release of CO gas. During the conversion process, undesirable change in the composition (vaporization of SiO gas), which causes an increase in the residual carbon (one of defects), occurs. To prevent the vaporization of SiO gas, we newly developed a favorable condition by shifting the equilibrium state of the conversion process, and then could remarkably reduce both an abnormal SiC grain growth and the residual carbon.