Oxide/oxide Re-Crystallized Fiber Composites for Use at > 1400°C

A. Krell (Sp), H. Klemm, T. Hutzler, A. Bales, Fraunhofer-Institut für Keramische Technologien und Sinterwerkstoffe, Dresden (Germany) 
 
Oxide fiber/matrix composites are derived from polycrystalline fibers with subsequent re-crystallization annealing at > 1700 °C in order to associate the ease of processing of commercially available thin fibers with a high creep stability and a sufficiently high thermal shock tolerance. It is estimated that with a length of single-crystalline segments in the range of 100 µm the creep rate of the re-crystallized fiber will come close to that of sapphire.
Tube demonstrators (diameter 40 mm x 100 mm, wall thickness ~ 1 mm) have been manufactured and exhibit "strong" or "weak" interfaces depending on the annealing conditions and on the matrix (different grades of mullite, ZrO2). Deformation curves of the as-sintered tubes and after thermal shock indicate different degrees of damage tolerance depending on annealing. At 1400 °C, the creep rate of these composites is lower than known for the most creep-resistant compact mullite ceramics.
The stability in wet hot-gas environments was investigated at high streaming velocities, and it turned out that the corrosion resistance is improved when mullite matrices were replaced by zirconia.