The performance of SiC/SiC continuous-fiber ceramic composites (CFCCs) will depend on the service environment. Reaction between the environment and the fiber/matrix interphase is of primary concern
because this will affect the structural properties of these composites. The effects of Ar+O2 and Ar+H2 environments on the weight loss and crack growth rates of SiC/SiC CFCCs have been determined and a model that correlates the time-dependent debonding resulting from the
environmental reactions and the crack growth rates is presented. Boron nitride (BN) interphases were shown to be more stable than carbon (C) in Ar+O2 environment for concentrations up to 2% O2 as observed by a
factor of 10 slower crack velocity at 1373 K for a CFCC with a
BN-interphase as compared to a C-interphase. A factor of 10 lower weight loss was found for a CFCC with a C-interphase in Ar+H2
environments of 100 and 1000 Pa H2 as compared to an Ar+10 Pa O2 environment. A limited amount of data on material with a BN interphase is included in this paper for comparison to that with C interphase.
Interactions with the environment will introduce a number of design issues for the application of SiC/SiC CFCCs including: 1) time-dependent elastic properties, 2) reduced matrix cracking stress,
3) accelerated creep rates, 4) reduced fatigue strength, 5) increased subcritical crack growth rates and 6) reduced hermetic properties. The novel properties of these materials can be used beneficially by the
designer but will also provide a challenge in their application while environmental interactions will increase the challenge in their use.
Keywords: ceramic composite, high-temperature, oxygen, crack-growth