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（CMC）增强纤维的SiC纤维有三种类型；Nicalon (SiC_ < 1.34 > O_ < 0.36 >), Hi-Nicalon (SiC_ < 1.39 > 0 _ < 0.01 >)和Hi-Nicalon-Type年代(SiC_ < 1.05 >)。第一种纤维为非晶碳化硅（SiC_XO_Y）相，第二种纤维为微晶低氧纤维，最后为近化学计量烧结碳化硅纤维。这种氧含量和微观结构的差异会极大地影响纤维在不同高温环境下的性能。在高和中等的氧分压下，SiC纤维被被动氧化，由此产生的稳定的二氧化硅膜保护材料免受进一步氧化。在低氧分压下，SiC纤维发生活性氧化并形成气态产物，对SiC纤维造成严重的破坏。在1773K下，在Ar-O_2混合气体中氧化这些SiC纤维，并在1 ~ 10^5 Pa的分压（po_2）下进行氧化，以研究其从主动到被动的氧化转变。Nicalon的活性氧化发生在po^2 < 100 Pa， Hi-Nicalon的活性氧化发生在po^2 < 10 Pa， Hi-Nicalon- s型的活性氧化发生在po^2 < 1 Pa， po^2值取决于SiC_XO_Y相的量。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重要的。在1573 ~ 1723 K的空气和氩气中对单丝进行了拉伸蠕变试验，施加的载荷为0.35 ~ 0.75 Gpa。蠕变仪最初是在科学研究资助基金(（B)(2)）的支持下生产的。从应力指数和在空气和氩气中的蠕变活化能来看，Nicalon、Hi-Nicalon和Hi-Nicalon- S型合金的蠕变变形机制分别与晶界扩散、晶界滑动和位错移动有关。这些纤维在空气和氩气中的蠕变参数几乎没有差别。因此，目前，hi - nicalon - S型将是大多数CMC应用的最佳选择。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