Potential and Perspectives for Oxide/Oxide Composites

The challenge for oxide/oxide composites is to provide an alternative to SiC/SiC composites with the aim of decreasing the cost of manufacture and improving the thermal stability in air at high temperature. Oxide/oxide composites consist of a porous alumina matrix reinforced by fibers of the same nature. Obtaining a controlled rate of porosity in the preparation helps to dissipate the energy associated with the propagation of cracks in the matrix during loading. It follows that the composite is damage-tolerant without requiring a carbon coating on the fibers as in the case of SiC/SiC composites.
Using submicron alumina powders and specific additives necessary for shaping and for control of the sintering shrinkage, the first composites were obtained by developing a method of infiltration into fibrous reinforcements. To increase the fiber volume fraction and thus the mechanical properties, processes based on the prepreg molding in a plastic bag of a suspension in a fiber preform were selected. The development of these various processing routes is outlined in relation with the evolution of properties. The development of thermal barrier coatings based on microporous oxide is also presented, in order to extend the thermostructural potential beyond 1200°C.