Development of a Protective Surface Layer on Orthorhombic Titanium Aluminide Composites

UES is proposing a novel approach for the protection of orthorhombic titanium aluminide matrix composites (OTMCs) from interstitial embrittlement using a ductile surface layer. The surface layer will be composed of a Nb-Ti-al-Cr alloy which offers the following advantages: (a) Excellent ductility, (b) adequate oxidation resistance, (c) good chemical and thermomechanical compatibility with the orthorhombic titanium aluminide matrix, and (d) excellent formability including cold-rollability into foil. The specific objectives of the proposed Phase I effort are to: (1) demonstrate the feasibility of developing a ductile surface layer of a Nb-Ti based alloy on a Ti-22A1-23Nb/SCS-6 composite and fiberless matrix, (2) establish proof-of-concept by tensile testing and out-of-phase thermomechanical fatigue (TMF) testing, (3) characterize the reaction between the Ti alloy substrate and the Nb-Ti alloy surface layer, and (4) evaluate the extent of oxidation and its effect on tensile properties after 500 hr exposure to air at 650 and 700 degree C. In the first part of this program, a Nb-40Ti-10Al-l0Cr (atomic %) alloy surface layer will be used for the proof-of-concept demonstration. In the second part of the program, the layer composition will be refined with Hf addition and evaluated.