Thermal shock resistane and thermal cycling beh- oviour of SiC-fiber reinforced glass matrix composites

摘要

The damage evolution of commercially available SiC-Nicalon~TM fiber-reinforced glass matrix composites under thermal shock and thermal cycling conditions in oxidizing atmospheres was investigated. The thermal shock tests involved quenching the samples from high temperatures (590-710℃) to room temperature in a water bath. For the thermal cycling tests the samples were quickly alternated between high temperature (T = 700℃) and room temperature air for different number of cycles. Both destructive and non-destructive techniques were employed to characterize the samples and to detect dif ferences in behavior for the various thermal loading con- ditions. In thermally shocked samples, damage in the form of matrix microcracks was induced by quenching from intermediate temperatures, e.g. 660℃. The extent of damage increased with the number of thermal shock cy- cles, as detected by a decrease in the Young's modulus and a simultaneous increase in the internal friction measured non-destructively be a mechanical force resonance tech- nique. In thermally cycled samples, material degradation was ascribed to porosity formation in the matrix as a consequence of the extended exposures at high tempera- tures. With increasing number of cycles, also interfacial oxidation was detected. An attempt was made also to ex- plore the possibility of healing the induced microcracks in thermally shocked samples by an optimized post-thermal shock heat--treatment (annealing) schedule, exploiting the viscous flow of the glass matrix.