CVD-produced ZrO2- and C/ZrO2-fiber coatings for mullite/mullite composites

The outstanding thermal-mechanical properties make mullite fiber/mullite ma trix composites a favorite candidate for high temperature applications, e.g . in turbines. In order to realize crack deflection and fiber pull-out, a c oating of the mullite fibers is necessary to obtain a weak bonding between fibers and matrix. ZrO2 coatings were produced by a CVD-process using Zr(ac ac)(4) as precursor. The substrates were Nextel 720 fiber fabrics, which we re in some experiments precoated with carbon. The diffusion into the fiber bundle was described. Composites were fabricated by infiltration of coated fibers with a pre-mullite slurry and hot-pressing at < 1300 degrees C. Expe riments have shown that C/ZrO2 double layers yield favorable thermo-mechani cal properties, while porous ZrO2 single layers did not.