HIGH-TEMPERATURE CREEP BEHAVIOR OF REINFORECEMENT FIBERS FOR CERAMIC MATRIX COMPOSITES AND CHARACTERISTICS FOR SEVERE ENVIRONMENTS

用于陶瓷基复合材料增强纤维的碳化硅纤维有三种：尼卡隆(碳化硅)、高尼卡隆(碳化硅1.39；0.01)和高尼卡隆型S(碳化硅)。第一种纤维含有非晶态碳化硅(SiCxOY)相，第二种纤维是微晶的低氧纤维，最后是近化学计量比的烧结碳化硅纤维。氧含量和微观结构的这种差异可能会在很大程度上影响纤维在不同环境下的高温性能。在中高氧分压下，碳化硅纤维被被动氧化，生成的稳定的二氧化硅薄膜保护材料免受进一步氧化。在低氧分压下，碳化硅纤维会发生活性氧化并生成气态产物，从而对碳化硅纤维造成严重的损伤。在本工作中，这些碳化硅纤维在含氧…的Ar-O_2混合气体中于1773K被氧化较高的En分压(PO2)(从1到10^5Pa)来研究活性到被动的氧化转变。活性氧化发生在高尼卡隆的po^2≦100Pa.高Nicalon的po^2≦10Pa.高NicalonS型的po^2≦1Pa.另一方面，为了更好地了解高温CMC加固的可靠性，研究这些纤维的蠕变行为是很重要的。单丝在空气和Ar气体中的拉伸蠕变试验在1573-1723K之间进行，载荷为0.35-0.75 GPA。蠕变装置最初是在科学研究补助金((B)(2))的支持下生产的。从空气和Ar气体中的应力指数和蠕变激活能来看，尼卡隆、高尼卡隆和高尼卡龙型S的蠕变变形机制分别与晶界扩散、晶界滑动和位错运动有关。这些纤维在空气和Ar中的蠕变参数几乎没有差别。因此，目前高尼卡龙型S将是最适合广大CMC应用的。较少

Three types of SiC fibers for reinforced fibers of ceramic-matrix composites (CMC) are commercially available ; Nicalon (SiC_<1.34>O_<0.36>), Hi-Nicalon (SiC_<1.39>0_<0.01>) and Hi-Nicalon-Type S (SiC_<1.05>). The first fiber contains an amorphous silicon oxycarbide (SiC_XO_Y) phase, next one is low-oxygen contained fiber and is microcrystalline, and finally, nearly stoichiometric sintered SiC fiber. Such differences in oxygen content and microstructure may greatly affect the properties of the fibers at high temperatures in different environments. Under high and moderate oxygen partial pressures, the SiC fibers are passively oxidized and the resulting stable silica film protects the material from further oxidation. Under low oxygen partial pressures, the SiC fibers are subjected to active-oxidation accompanied by the formation of gaseous products, resulting in serious damage to the SiC fibers. In the present work, these SiC fibers were oxidized at 1773K in Ar-O_2 gas mixtures with oxyg … More en partial pressures (po_2) from 1 to 10^5 Pa to investigate the active-to-passive oxidation transition. The active-oxidation occurred at po^2≦100 Pa for Nicalon, po^2≦10 Pa for Hi-Nicalon and po^2≦1 Pa for Hi-Nicalon-Type S. The po^2 values are dependent upon the amounts of SiC_XO_Y phase. On the other hand, it is important to investigate creep behavior of these fibers in order to obtain a better understanding of the reliability for reinforcement of high temperature CMC. Tensile creep tests were performed on single filaments in air and Ar gas at 1573-1723 K with an applied load of 0.35-0.75 Gpa. The creep apparatus was originally produced with the support by Grant-in-Aid for Scientific Research ((B)(2)). From the values of the stress exponents and the activation energies for creep in air and Ar gas, the creep deformation mechanisms of Nicalon, Hi-Nicalon and Hi-Nicalon-Type S are associated with the grain-boundary diffusion, grain-boundary sliding and the movement of dislocations, respectively. The differences between the creep parameters of these fibers in air and Ar were not almost observed. Thus, at the present time Hi-Nicalon-Type S will be best for the majority of CMC applications. Less