Fiber/Matrix Interphases for Silicon Carbide Fiber Reinforced Titanium Matrix Composites

Silicon carbide fiber reinforced titanium matrix (SiC/Ti) composites offer lightweight, high strength replacement materials for superalloys in gas turbine engines and airframes. Titanium matrices tend to react with SiC and form reaction products that exhibit properties which are very different from the starting constituents. This mismatch in properties generates large residual thermal stresses after fabrication and high temperature exposure of the composites. These stresses can damage the material, resulting in poor strengths and unacceptable thermomechanical fatigue characteristics. The proposed program seeks to improve the properties of SiC/Ti composites by designing and demonstrating fiber/matrix interphase barrier coatings. The proposed effort will first employ unique, coupled thermomechanical and micromechanical models to select barrier materials, thicknesses, morphologies, and application methods. Then to demonstrate the improvements, a minimum of two of the most attractive barrier coating materials will be applied to commercial SiC monofilaments. Titanium alloy matrix composite compacts will be fabricated using the experimental coated fibers and compared with composites that use state of the art metallized or carbon-coated fibers. The compacts will be examined before and after thermal exposure to evaluate the reaction products and residual stresses. The results of the Phase I program will demonstrate two or more specific barrier coatings that improve the composite strength and fatigue behavior. The project will be performed with the assistance of Pratt & Whitney-Florida.