Adu: Composite Mate. VoL 8, No I, Pp. 3-16(1999) Materials design and processing of high temperature ceramic matrix composites: state of the art and future trends R. NASLAIN Laboratory for Thermostructural Composites. UMR-580/(CNRS-SEP/SNECMA-UB1) University of Bordeaux- 1. 3 Allee de La Boetie, 3 3600 Pessac, france Abstract-The material design of ceramic matrix composites(CMCs)is discussed in terms of fiber nature and architecture, interphases(pyrocarbon, BN, multilayers), matrices and seal-coating taking into account lifetime considerations. CMCs are processed by liquid or gas phase routes Besides the well established processing routes, such as polymer impregnation and pyrolysis (PIP) slurry impregnation/hot pressing(SIHP)and isothermal/isobaric chemical vapor infiltration(I-CvI) techniques, emerging processes allowing densification times of the order of a day, are discussed Keywords: CMC: C/C: SiC/SiC: design: interphase: processing L INTRODUCTION The ceramic matrix composites(CMCs) considered here consist of continuous (or semi-continuous ceramic fibers embedded in a ceramic matrix, such as carbon, silicon carbide, silicon nitride or a refractory oxide. They are usually designed for applications in severe environments. It is now well established that CMCs are tough materials when the fiber-matrix(FM)bonding is properly controlled during processing, i. e. through the use of a thin layer of a compliant material with a low shear strength, referred to as the interphase. It has been recently suggested that the best interphase materials might be those with a layered crystal structure, e.g pyrocarbon, or with a layered microstructure, such as(PyC-SiC)n multilayers [lI The design of a CMC, in terms of materials, is dictated by the nature of the application. It usually includes: (i) the choice of a proper fiber and fiber architecture: (ii) the selection of suitable interphase and matrix materials and, when necessary: (iii) the use of an external seal coating. As the composition of the CMC is fixed, a processing technique has to be selected on the basis of everal considerations, including the size and shape of the part as well as the