Composites Part A 29A(1998)1145-115 1359-835X/98/S- see front mat c 1998 Elsevier Science Ltd. All rights reserved ELSEVIER PII:S1359835X(9700128-0 The design of the fibre-matrix interfacial zone in ceramic matrix composites Roger R. Naslain Laboratory for Thermostructural Composites, UMR-47(CNRS-SEP-UB1) University of Bordeaux, 3 Allee de La boetie, 33600 Pessac, france atrix interactions or deposited on the fibre surface prior to composite fabrication. It has several key functions, including crack defection, load transfer, diffusion barrier and residual stress relaxation. Four types of interphase are depicted involving weak interfaces, materials with a layered crystal structure(pyrocarbon, BN, micas and phyllosiloxides r materials with the B-alumina/magnetoplumbite structures), multilayers such as(PyC-SiC)n or(BN-SiC), or finally, porous materials. Achieving high mechanical properties and long lifetimes in severe environments require a subtle design of the fibre-matrix interfacial zone, which is depicted for Nicalon/glass-ceramic and Nicalon/SiC matrix composites. C 1998 Elsevier Science Ltd. All rights reserved eywords: A. ceram composites ( CMCs); B interface/interphase; pyrocarbon; boron nitride; multilayers INTRODUCTION FM interfacial zone in CMCs from a processing standpoint The first approach is through the in situ formation of a weak Ceramic matrix composites(CMCs)display, with respect to interphase resulting from some chemical reaction at the FM many other polymer or metal matrix composites, the key interfaces during the high temperature step of composite oroperty of being inverse composites, which is to say that processing. It has been extensively used during the early the strain at failure of the matrix, Em, is much lower than that development of glass-ceramic matrix composites,. The of the fibres, Ef. As a result in such composites the matrix second approach, which offers much more design flexibility undergoes microcracking, Since in CMCs the two inasmuch as it no longer relies on an in situ reaction, is constituents, namely the fibres and the matrix, are brittle, based on the use of precoated fibres, the weak interphase the matrix microcracks should not induce the early failure of being deposited on the fibre surface prior to the deposition he fibres by a notch effect, which means that the matrix of the matrix itself. This second approach was extensively microcracks should be defected at the fibre-matrix(FM) used for non-oxide composites, such as C/SiC and SiC/SiC interfaces. This key function is actually achieved when, composites (the fibre being designated first, as usual) after processing, the FM bonding is weak enough. Further, produced according to the cvi process. A variety of in CMCs the FM interfaces have another key function, i.e interphase materials was suggested, the most studied being that of load transfer as in any fibre-reinforced composite, pyrocarbon, h xagona which supposes conversely a strong enough FM bonding such as micas, B-aluminas and rare-earth phosphates Finally, CMCs are fabricated at relatively high temperatures The aim of the present contribution is, first, to present the (typically, -1000C in the so-called chemical vapour basis of the interphase concept in CMCs(in terms of infiltration (Cvn) process and even higher in the slurry terphase functions and interphase ma aterial nature)and impregnation/hot pressing technique) and they are used in second, to show how such a concept has been used to design severe conditions(high temperatures and oxidizing atmos the FM interfacial zone, focusing on some important pheres), a feature which introduces a constraint of presently used composites thermochemical and thermomechanical compatibilities The design of the FM interfacial zone, or interphase should take into account all these requirements, which are INTERPHASE CONCEPT IN CMCs often contradictory. It becomes an extremely difficult materials science challenge, it the lifetime of the composites Mechanical behaviour of CMCs required in advanced jet engines CMCs are inverse and damageable composites displaying There are two classical approaches to the design of the a non-linear stress-strain behaviour under tensile loading