in order not to damage the fibers and to reduce the cost. The choice of a given processing technique is dictated by the size, the shape and the number of parts to be 3. Lie ase routes 3 /.. Reactive melt infiltration (RMI). RMI processes can be used when one of the elements of the matrix has a low(or relatively low)melting point and readily wets the fiber preform. In the DIMOX process(Lanxide). the molten element such as an aluminum alloy(mp a 650C), reacts with the atmosphere, e.g. the air, as it climbs by capillary forces in the fiber preform pore network, yielding an alumina matrix composite [44-47]. The alumina matrix grows in the fiber preform open pore network, from the molten alloy, according to a complex dissolution (of oxygen)/precipitation(of alumina) process, in which Mg(present in the alloy) plays a key role. A layer of Mgo(permeable to oxygen diffusion) formed at the liquid metal surface as the result of the oxidation of Mg, prevents the formation of a dense protective scale of alumina that would stop the in-depth diffusion of oxygen. With a processing temperature 1200C, a variety of fibers including Nicalon-type fibers, can be utilized(Fig 3). In the SILCOMP process( General Electric), a ceramic fiber preform which has been first consolidated with carbon, is impregnated with liquid silicon at N 1450C Liquid silicon readily reacts with carbon to yield a SiC based matrix. In this latter process, only fibers with a high thermal stability, such as carbon or Hi-Nicalon-type fibers, can be used [48-52]. Furthermore, as both liquid aluminum and liquid silicon are very corrosive, the fibers have to be protected. Dual BN-SiC coatings, BN being the mechanical fuse and SiC a diffusion barrier, have been successfully used in Nicalon/Al2O, and Hi-Nicalon/SiC composites [531 Some residual Al or Si is usually present in the matrix, but this can be removed by wicking(Al)or entrapped in the matrix as refractory silicide(Si), when necessary oth processes yield near net-shape composites 3.1.2. Polymer impregnation and pyrolysis (PIP). In the PIP-process, a fiber preform is impregnated with a liquid thermosetting organic (or organometallic) precursor of the matrix. After curing, the material is pyrolyzed, a weight loss and GROWI PHASE CTION Figure 3. Fabrication of a near net shape alumina matrix composite by the DIMOX process (schematic), according to [441