R. narain number of parts to be produced. Because ceramic remains brittle within a broad range of temperature, CMCs should be fabricated according to processes that do not damage the fibers, which generally means pressureless techniques and use of matrix precursors. Further, in order to avoid strong chemical reactions between the constituents or detrimental change in the fiber microstructure, low temperature processing techniques are often preferred. The starting material can be a simple continuous fiber tow (or tape), fiber fabrics or, more often, a multidirectional nD fiber preform. The interphase material is classically deposited on the fiber surface by chemical vapor deposition(CVD)or infiltration(CVD). Then the fiber archite densified according to liquid or gas phase routes, or a combination of both(h processes)[21 2. MATERIALS DESIGN 2. Fiber architecture In the field of CMCs, carbon fibers are by far the most attractive reinforcements Carbon is one of the most refractory materials and one of the very few materials whose mechanical properties increase as temperature is raised. Further, a variety of carbon fibers are available, some of them being relatively cheap. Unfortunately carbon reacts with oxygen at temperatures as low as 400-500oC, with formation f gaseous oxides(active oxidation). As a result, the use of carbon fibers in CMCs that will be exposed to oxidizing atmospheres, demands internal/external oxidation protection. Hence, non-oxide fibers, such as silicon carbide or related fibers, known to undergo passive oxidation with formation of a protective silica scale are more appropriate. During many years, the SiC-based fibers available on the market such as the Si-C-O Nicalon fibers(from Nippon Carbon) or the Si-C-O(Ti) Tyranno fibers from Ube Industries, were limited in thermal stability, undergoing decomposition at 1100-1200C 13-111. As a result, their use was limited to low temperature processing techniques and applications. Modern oxygen-free fibers with a stoichiometry close to C/Si (at)= I and displaying a much higher thermal stability (Hi-Nicalon S from Nippon Carbon. Tyranno(SA)from Ube Industries or Sylramic from Dow Corning )are now available [12-17. Such fibers might become attractive for CMCs if their cost is reduced significantly. Finally, refractory oride fibers would be the best reinforcements for CMCs used in a prolonged manner at high temperature in oxidizing atmospheres. These fibers actually exist on the market, as pure alumina(Nextel 610 from 3M)or as mixed alumina-mullite(Nextel 720 also from 3M) fibers, but their high temperature mechanical properties are relatively poor beyond 1000-1 100C due to grain growth and creep[18-231 Ceramic yarn fibers are sometimes employed as continuous single tows. After im pregnation with a liquid precursor of the matrix and winding, they yield a prepreg type or semi-product material, which is used to produce laminates according to techniques similar to those developed for their polymer matrix counterparts. How ever, ceramic fibers are more generally employed as self-standing multidirectional