r./. App Ceram. Technol, 7/ 3/263-275(2010) International Journal o Applied p p Ceramic TECHNOLOGY ceramic Product D Single-and Multilayered Interphases in SiC/SiC Composites Exposed to Severe Environmental Conditions An overview Roger R. Naslain, Rene J -F. Pailler, and Jacques L. Lamon Laboratory for ThermoStructural Composites(LCTS), University of Bordeaux, 33600 Pessac, france 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 Py C 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. Introduction residual thermal stresses. The interphase protects fibers against chemical reactions that could occur during pre The interphase plays a key role in the behavior of cessing and use of CMCs in aggressive environments ceramic matrix composites(CMCs). It prevents the early It has been postulated that the best failure of the fibers, matrix microcracks being arrested terials for SiC/SiC might be those with a layered structure, or/and deflected parallel to fiber axis(the so-called the layers being parallel to fiber surface, weakly bonded to mechanical fuse"function). It also transfers load from one another but strongly adherent to fibers. Pyrocar the fibers to the matrix and eventually releases part of bon(PyC) was thought to be the best interphase material for sic/sic in terms of their mechanical behavior -5 Unfortunately, Py C is oxidation prone even at low This paper was presented in part ar the 33rd Annual International Conference on Advanced temperatures with the result that PyC interphase can be consumed and the FM coupling nce, that C 200) The American Ceramic Society interphase becomes the weak point of SiC/SiC wheSingle- and Multilayered Interphases in SiC/SiC Composites Exposed to Severe Environmental Conditions: An Overview Roger R. Naslain,* Rene´ J.-F. Pailler, and Jacques L. Lamon Laboratory for ThermoStructural Composites (LCTS), University of Bordeaux, 33600 Pessac, France 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. Introduction The interphase plays a key role in the behavior of ceramic matrix composites (CMCs). It prevents the early failure of the fibers, matrix microcracks being arrested or/and deflected parallel to fiber axis (the so-called ‘‘mechanical fuse’’ function). It also transfers load from the fibers to the matrix and eventually releases part of residual thermal stresses. The interphase protects fibers against chemical reactions that could occur during pro￾cessing and use of CMCs in aggressive environments. It has been postulated, that the best interphase ma￾terials for SiC/SiC might be those with a layered structure, the layers being parallel to fiber surface, weakly bonded to one another but strongly adherent to fibers.1–4 Pyrocar￾bon (PyC) was thought to be the best interphase material for SiC/SiC in terms of their mechanical behavior.1–5 Unfortunately, PyC is oxidation prone even at low temperatures with the result that PyC interphase can be consumed and the FM coupling degraded. Hence, that interphase becomes the weak point of SiC/SiC when Int. J. Appl. Ceram. Technol., 7 [3] 263–275 (2010) DOI:10.1111/j.1744-7402.2009.02424.x Ceramic Product Development and Commercialization This paper was presented in part at the 33rd Annual International Conference on Advanced Ceramics and Composites, Daytona Beach, FL, January 18–23, 2009 *naslain@lcts.u-bordeaux1.fr r 2009 The American Ceramic Society