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）的增强纤维的三种类型的SiC纤维是可商购的; Nicalon（SiC_<1.34>O_<0.36>）、Hi-Nicalon（SiC_<1.39>0_<0.01>）和Hi-Nicalon-Type S（SiC_<1.05>）。第一纤维含有非晶碳氧化硅（SiC_XO_Y）相，第二纤维是低氧纤维并且是微晶的，最后是近化学计量比烧结的SiC纤维。氧含量和微观结构的这种差异可能极大地影响纤维在不同环境中的高温下的性能。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纤维经受活性氧化，伴随着气体产物的形成，导致SiC纤维的严重损伤。在1773 K下，在Ar和O_2混合气体中，对SiC纤维进行了氧化处理。 关于我们 en分压（po_2）从1到10^5 Pa，以研究主动到被动氧化转变。Nicalon、Hi-Nicalon和Hi-Nicalon S型的活性氧化分别发生在p0^2 ~ 100 Pa、p0^2 ~ 10 Pa和p0^2 ~ 11 Pa。po^2值与SiC_XO_Y相的数量有关。另一方面，为了更好地理解高温CMC增强的可靠性，研究这些纤维的蠕变行为是重要的。在空气和氩气中，在1573-1723 K下，施加0.35-0.75 Gpa的载荷，对单丝进行拉伸蠕变试验。蠕变仪最初是在科学研究补助金（（B）（2））的支持下生产的。从应力指数和蠕变激活能的值来看，Nicalon、Hi-Nicalon和Hi-Nicalon S型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。这些纤维在空气和氩气中的蠕变参数几乎没有观察到差异。因此，目前Hi-Nicalon-Type S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