BEHAVIOR OF NICALON(TM)-FIBER-REINFORCED GLASS-MATRIX COMPOSITES UNDER THERMAL CYCLING CONDITIONS

The damage evolution of commercially available SiC Nicalon((TM))-fiber -reinforced glass-matrix composites under thermal cycling conditions i n oxidizing atmosphere has been investigated. The samples were alterna ted quickly between high-temperature (T = 700 degrees C) and room-temp erature air for different numbers of cycles. Thermal aging experiments were also conducted by exposing the samples in air at 700 degrees C f or long periods of up to 250 h. Both destructive and non-destructive m easurement techniques were employed to characterize the samples and to detect differences in behavior for the various thermal loading condit ions. The flexural strength and Young's modulus decreased, while the i nternal friction increased with increasing numbers of cycles. Material degradation was attributed to phenomena related to viscous flow of th e glass matrix, and to oxidation of the fiber, which occurred as a con sequence of the extended exposures at high temperatures. The microstru ctural damage observed includes porosity formation (cavitation) within the matrix and at the fiber/matrix interfaces. The experimental resul ts also suggest degradation of the in situ fiber strength due to fiber surface oxidation and damage, fiber displacement and consequent fiber -to-fiber contact. (C) 1998 Elsevier Science Ltd. All rights reserved.