High-Temperature Flow of SiC Continuous Fiber-Glass Ceramic Matrix Composites: The Effect of Interface/Interphase Ductility

Abstract

ABSTRACTThe elevated temperature rheology of continuous SiC (Nicalon®) calcium aluminosilicate glass-ceramic matrix composites is evaluated in uniaxial compression creep experiments (-σ1 = 20-to-40 MPa; T = 1300–1320°C). The steady state strain rate is demonstrated.to be highly sensitive to the orientation of the reinforcement relative to the maximum compressional stress, with highest bulk specimen strain rates noted for conditions in vWhich the sliding between the fiber and the matrix is optimized as a kinetic flow response (i.e., a fiber orientation of approximately 40-50° from σ1). One further discovers that the temperature sensitivity (i.e., activation energy) of flow increases as the amount of interface flow/sliding increases. The experimental results suggest that the high-temperature, low-stress interface response in this composite system is related to the ductile flow of the “Planar” SiO2 reaction-layer interphase that exists (in addition to the well-recognized planar carbon interphase) in these materials. The results of these simple experiments are used to calibrate a microscale-to-macroscale rheologic model in which the fibermatrix interface is described by a viscous constitutive relationship.