Processing of all-oxide ceramic matrix composites with RBAO matrices
A methodology to produce full-scale, all-oxide composites with porous reaction-bonded aluminum oxide (RBAO) matrices is presented. Composites are produced by a two-step impregnation route, in which alumina fiber fabrics are first infiltrated with an ethanol-based slurry of the RBAO particles and then laminated between layers of an RBAO-loaded paraffin-based suspension to produce thermoplastic prepregs. The composition of the RBA Oprecursor powders is tailored for each of these suspensions, so that low-to-zero shrinkage is achieved during sintering and alloxide composites with a reduced amount of shrinkage-related matrix cracks are produced. Processing challenges faced during the development of these composites are presented and discussed. These include the formation of matrix voids owing to the evaporation of volatile species from the RBAO powder surfaces that remain entrapped in the paraffinbased suspension during lamination. Despite these voids, composites containing ∼ 36 vol% fibers exhibit a flexural strength of ∼ 240 MPa, together with a non-catastrophic, stepwise failure, similar to that of layered ceramics.
Ceramic matrix composites