炭素繊維およびC/C複合材料の熱処理によるヤング率の変化

Abstract

高温構造用途向けの高度C/C複合材料(炭素繊維強化型炭素複合材料)の最も重要な基本的力学特性の1つとしてヤング率の温度依存性を室温から1,373Kまで正確に測定した。使用した材料は2種類の1方向強化型C/C複合材料で、その違いは複合材料製作に先立つ焼成(前焼成として表示)によって導入したC/C複合材料中の炭素繊維の微細構造である。これらの複合材料はついで1,473Kと3,073Kの間で焼成(後焼成として表示)を行った。微細構造の検査はX線回折解析,TEM(透過型電子顕微鏡)観察およびラマン分光分析法で行った。ヤング率の温度依存性は後焼成による炭素繊維の微細構造変化を反映して正負の傾向すなはち2方向の温度依存性を示した。全試験片について、これらの温度依存性は炭素繊維の黒鉛化が全試験片の最低と最高であった2つの典型的試験片の1次関数により表すことができた。ヤング率の温度依存性はラマン分光法の結果から推定可能であることが分かった。微細構造とヤング率の相関についてもTEMの結果と炭素繊維およびC/C複合材料の製造過程における熱履歴とともに論じた。

As one of the most important basic mechanical properties of advanced C/C (Carbon/Carbon fiber) composites for high temperature structural applications, temperature dependence of Young's modulus was precisely studied from room temperature up to 1,373 K. Materials used were two kinds of unidirectional C/C composites, where the variables were microstructure of carbon fibers in C/C composites introduced by heat treatment prior to composite fabrication (denoted as prior heat treatment). Those composites were, then, heat treated between 1,473 K and 3,073 K (denoted as post heat treatment). Microstructural inspections were performed with X-ray diffraction analysis, TEM (Transmission Electron Microscopy) observation and Raman spectroscopy. The temperature dependence of Young's modulus showed positive and negative trends, i.e. two way temperature dependence, reflecting microstructure changes of carbon fibers by post heat treatments. For all the specimens, these temperature dependence could be written by a linear function of two typical specimens, in which the graphitization of carbon fiber were the lowest and the highest of all specimens. And the temperature dependence of Young's modulus was considered to be predictable from the results of Raman spectroscopy. Also the correlation between microstructure and Young's modulus was discussed together with the TEM results and thermal history during the fabrication of carbon fibers and C/C composites.