Experimental assessment of fiber-reinforced ceramics for combustor walls

Experimental and theoretical work concerning the application of ceramic com ponents in small high-temperature gas turbines has been performed for sever al years. The significance of some nonoxide ceramic materials for gas turbi nes in particular is based on their excellent high-temperature properties. The application. of ceramic materials allows an increase of the turbine inl et temperature resulting in higher efficiencies and a reduction of pollutio n emissions. Tile inherent brittleness of monolithic ceramic materials can be virtually reduced by reinforcement with ceramic fibers leading to a quas iductile behavior: Unfortunately, some problems arise due to oxidation of t hese composite materials in the presence of hot gas flow containing oxygen. At the Motoren und Turbinen Union, Munchen GmbH, comprehensive investigati ons including strength, oxidation, and thermal shock rests of several mater ials that seemed to be appropriate for combustor liner applications were un dertaken. As a result C/C, SiC/SiC, and two C/SiC composites coated with Si C, as oxidation protection, were chosen for examination in a gas turbine co mbustion chamber To prove the suitability of these materials under real eng ine conditions, the fiber-reinforced flame tubes were installed in a small gas turbine operating under varying conditions. The loading of the flame tu bes was characterized by wall temperature measurements. The materials showe d different oxidation behavior when exposed to the hot gas flow. Inspection of the C/SiC composites revealed debonding of the coatings. The C/C and Si C/SiC materials withstood the tests with a maximum cumulated test duration of 90 h without damage.