Processing and Microstructure of Cr-Ta and Cr-Ta-Mo Composites

The Cr-Ta alloy with an eutectic structure has a good combination of high strength and oxidation resistance at elevated temperatures up to 1,200°C. It is an ideal candidate for ultrahigh-temperature applications. However, the material shows low ductility and fracture toughness at room temperature. An effective way to improve the ductility and fracture toughness is to obtain an aligned microstructure of eutectic Cr-based alloys, using a directional-solidification (DS) process, in which the feed materials with eutectic compositions are preferred. In the present work, a quantitative technique was developed to assist in monitoring and controlling the composition of the Cr-based alloys throughout the processing at elevated temperatures. The eutectic compositions of the Cr-Ta and Cr-Ta-Mo alloy systems were determined to be Cr-9.7 at. % (atomic percent) Ta and Cr-9.7 at. % Ta-1.0 at. % Mo, respectively. Research sponsored by the Fossil Energy Advanced Research and Technology Development (AR&TD) Materials Program, U. S. Department of Energy, under subcontract, 11X-SP173V, to the University of Tennessee, and by the AR&TD Materials Program, under contract with DE-AC05-000R22725 with UT-Battelle, LLC.