Alumina Fiber/Alumina Matrix Composites Prepared by a Chemical Vapor Infiltration Technique

Ceramic/ceramic composites made of alumina fibers embedded in an alumina matrix were obtained from fibrous alumina preforms (Vf = 0.12 to 0.40) using a chemical vapor infiltration technique based on gaseous alumina precursors (AICI3-H2-CO2). Low deposition temperatures (950° to 1000°C) and total pressures (2 to 3 kPa) must be used to preferentially deposit alumina within the pores rather than on the external surface of the preform. Different fiber orientations were studied; i.e. randomly oriented short fibers and one- and two-dimensional preforms. Densification was performed down to residual open porosity of the order of 10 to 15%. For a one-dimensional α-alumina fiber composite (residual porosity ≅10%), flexural strengths of 250 MPa and ≅ 100 MPa were obtained at room temperature and 1200°C, respectively. Most composites exhibited brittle failure at room temperature.