Single‐ and Multi‐Layered Interphases in SiC/SiC Composites Exposed to Severe Conditions: An Overview

Pyrocarbon (PyC), which is presently the best interphase material for SiC/SiC composites is not stable under conditions encountered in advanced applications: it is sensitive to oxidizing atmospheres or to neutron irradiation, even at moderate temperatures. Attempts have been pursued to replace PyC-interphase by boron nitride, which is more resistant to oxidation but poorly compatible with nuclear applications. Other interphase materials, such as ternary carbides (MAX-phases) seem promising but their use in SiC/SiC has not been demonstrated. Hence, the most efficient way to improve the behavior of PyC-interphase in severe environments is presently to replace part of the pyrocarbon by a second material displaying a better compatibility with the environment, such as SIC itself ((PyC-SiC)(n) multilayered interphases). Important issues related to the design and behavior of layered interphases are reviewed on the basis of LCTS-experience and recent data published by others with a view to demonstrate their potential interest in HT-nuclear reactors.