Fiber-coatings for fiber-reinforced mullite/mullite composites

Mullite-based fiber-reinforced composites are favorite candidates for the application in combustion chambers of gas turbines. The application requires damage tolerance, temperature and oxidation-resistance at high temperatures (> 1200 degreesC) over long terms. In order to realize crack deflection and fiber pull-out, an interphase coating of the mullite fibers (Nextel (TM) 720) is necessary to obtain a weak bonding between fibers and matrix. Two systems of interphases produced by CVD were described. The first system is a carbon/metal-oxide double layer (C/ZrO2, C/Al2O3). Properties of the resulting composites after heat-treatment (1300 degreesC, 1000 h) under cyclic and continuous heating conditions were described. The second system is the codeposition of La2O3 and Al2O3 on the fibers. After heat-treatment at 1300 degreesC lanthanum hexaluminate (LaAl11O18) with a magneto plumbite structure containing sliding planes should be formed.