In-Situ Functionally Graded Oxide Matrix Composite for Gas Turbine Applications

Currently, ceramic matrix composites (CMCs), which generally are lighter and more thermally stable than their metallic counterparts, are under evaluation for use in industrial gas turbine engines. The use of CMC could permit higher operating temperatures and reduced cooling, thereby contributing to higher fuel efficiency and lower NOx and CO emissions. State-of-the-art oxide-based composites require a thermal protection system (TPS) coating to mitigate the thermal gradients endured by the material during exposure. However, this coating can delaminate or erode, leading to exposure of the underlying composite, which contains a mullite-based fiber that is prone to attack in a moist combustion environment. This project will develop a non-silica-containing composite with a TPS that is integral and fabricated in situ. This oxide-based composite design will be resistant to environmental attack on the hot side, and will support a low thermal gradient on the cold side to minimize thermal stresses. In Phase I, a compositionally graded oxide matrix composite was exposed in a simulated combustion environment for 100 hours. The results provided a clear direction for Phase II, in which two different composite design options will be evaluated. The optimal design will be down-selected based on mechanical and thermal property data. Subscale components of the functionally graded composite material will be fabricated and tested in a subscale test facility, and then a full-scale component will be fabricated and tested. Commercial Applications and Other Benefits as described by the awardee: The functionally graded oxide matrix composite should resist degradation in the moisture-containing combustion environments that exist in high temperature gas turbine engines, providing significant economic and environmental benefits. The market for industrial gas turbine engine applications is expected to grow over the next decade, due to the closing of aging coal plants and the need for increased global power demands, particularly in Asia. The materials also would have potential use in propulsion-related applications in the industrial, military, and commercial sectors.