Approach to the fabrication of oxide/oxide single-crystalline-fiber composites from polycrystalline fiber bundles

An important contribution to future more efficient gas turbines is expected from composites that can be exposed to temperatures > 1400°C for > 10.000 h. Under these conditions, difficulties arise both with known non-oxide fibers (because of limited thermodynamic stability) and with polycrystalline oxides (due to limited creep resistance). Single crystalline oxide fibers could be a solution but are not available with thin diameter < 20 µm (important for processing) and as endless fiber bundles (imperative for providing some real component volume when starting with very thin fibers). Therefore, oxide/oxide fiber/matrix composites were derived here from polycrystalline fibers which obtain a high creep stability after re-crystallization annealing at e.g. 1750°C; with a length of single-crystalline segments ~ 100 µm the creep rate will come close to that of a completely single-crystalline sapphire body. Simple processing is enabled by the use of bundles of 10-15 µm thin sintered alumina fibers. First tube demonstrators (40 mm x 100 m, wall thickness 1 mm) have been manufactured and exhibit ?strong? or ?weak? interfaces depending on the annealing conditions and on the matrix (ZrO2, dif ferent grades of mullite, ...). The best combination of creep stability at high temperatures > 1400 °C with the requested damage tolerance on thermal shock is expected for an axially strong fiber/matrix interface.