Single‐ and Multilayered Interphases in SiC/SiC Composites Exposed to Severe Environmental Conditions: An Overview

Abstract

Pyrocarbon (PyC), the common interphase for SiC/SiC, is not stable under severe environmental conditions. It could be replaced by boron nitride more resistant to oxidation but poorly compatible with nuclear applications. Other materials, such as ternary carbides seem promising but their use in SiC/SiC has not been demonstrated. The most efficient way to improve the behavior of PyC interphase in severe environments is to replace part of PyC by a material displaying a better compatibility, such as SiC itself. Issues related to the design and behavior of layered interphases are reviewed with a view to demonstrate their interest in high‐temperature nuclear reactors.

Tensile fracture behavior and strength distribution of SiCf/SiC composites with different SiBN interface thicknesses

“…So far, the successful interfaces for SiC f /SiC composites are pyrolytic carbon (PyC) interface and hexagonal boron nitride (BN) interface. But PyC interface is oxidation prone even at very low temperatures ( $ 400 1C) [6].…”

Initial assessment of environmental effects on SiC/SiC composites in helium-cooled nuclear systems

“…For example, the lifetime in air at 700 o C under static loading of 1D SiC (HiNicalon)/SiC minicomposite is improved when the classical PyC 100 single layer interphase is replaced by a (PyC 20 -SiC 50 ) 10 multilayer hybrid interphase (the subscripts stands for layer thickness in nm). 51 A different approach for improved oxidation stability of SiC/SiC composites is using environmental barrier coatings (EBC). It is known for example that SiC-based systems are not suitable for long term use at high temperatures (above 1200 o C) in high steam environments, such as that found in gas turbines.…”

“…Such severe radiation conditions are known to change the structure of materials, and hence their properties. 51 Irradiation of monolithic SiC causes moderate swelling. Irradiation of SiC fibers causes different effects, depending on the composition and structure.…”

“…Irradiation of PyC is known to induce anisotropic dimensional changes, which would induce residual thermal stress and might affect the fibermatrix bonding upon prolonged irradiation exposure. 51 To avoid unwanted effects, the thickness of PyC interphase should be as low as possible, but large enough to allow matrix crack deflection. This can be achieved by using hybrid multilayered (PyC-SiC) n interphase with thin (only a few nanometers) PyC sublayers.…”

Creep behavior in interlaminar shear of a Hi-NicalonTM/ SiC-B4C composite at 1200∘C in air and in steam

“…The issue of improving the oxidation resistance of the SiC/SiC composites has been addressed through the design of innovative multilayered interphases [10][11][12] and of self-healing multilayered matrices [10,[12][13][14][15][16]. The multilayered matrices contain phases that facilitate glass formation at high temperature thus healing the cracks and preventing oxygen from diffusing further into the composite and reaching the oxidation-prone fibers.…”