Computational Materials Design of Castable SX Ni-based Superalloys for IGT Blade Components
In order to raise the inlet gas temperatures to improve thermal efficiency of industrial gas turbines (IGT), turbine blade materials are required to have superior creep rupture resistance. Ni-base single crystal (SX) blades have higher creep strength in comparison with directionally solidified blades, and are widely used in aerospace engines. However, their use in IGTs, which require larger size castings (2-3X compared to aerospace), is limited due to casting related defects such as freckling, high angle boundary (HAB) formation, grain nucleation, and shrinkage/porosity; and post-cast defects such as incipient melting and recrystallization during high temperature solution heat treatment. Current techniques for developing new SX alloys are empirical in nature and are inadequate in identifying unique alloy compositions that can satisfy both the processing and property objectives for gas turbine blades. In this SBIR program, QuesTek Innovations LLC, a leader in computational materials engineering, will design a castable SX Ni- based superalloy that can be cast effectively as large IGT blade components providing superior creep performance comparable to state-of-the-art SX aeroturbine blades, thereby allowing higher gas inlet temperatures and increased thermal efficiency. The systems engineering materials design framework is based on existing CALPHAD multicomponent tools, and will invoke reliable physics-based models to predict intrinsic freckling potency as a function of the solidification pathway, alloy hot-tearing tendency, and other casting related defects. The computational materials design considers trade-offs between the blade property requirements such as creep strength, resistance to TCP formation, tensile strength, corrosion resistance, grain-boundary strength and SX processing requirements such as freckling resistance, hot-tearing resistance, incipient melting etc. In the program QuesTek will leverage its previous experience in modeling Ni-based superalloys (DARPA-AIM Contract#F33615-00-2-5216; NASA Contract# NNC07CB01C; etc) and use in-house models that have been developed to predict Ni SX castability. The Phase I focus will be on computationally designing candidate alloys that can achieve enhanced castability while achieving increased metal temperature capability of 1050-1100 C. The predicted behavior of the designs will be benchmarked against current SX alloys such as CMSX-4 and PWA1484. Concept feasibility will be demonstrated by comparing the casting behavior of commercial alloys against QuesTeks predictions. The Phase II program will focus on developing the entire systems- based materials design and validation through casting complex blade components with internal cooling passages using actual OEM blade tooling. In the SBIR program QuesTek will work with a leading energy turbine manufacturer and a leading SX casting house to provide the voice of the customer and define property and processing requirements. QuesTek has a vast experience in working with various materials suppliers and processing facilities, accelerating testing and qualification for a wide range of specifications and requirements, and delivering flight critical hardware for government and commercial applications. IGCC turbines operating at higher temperatures, enabled by new high yield SX castings, can operate at higher efficiency and thus reduce electricity-generation costs and CO2 emissions. The high yield of the new SX alloys will accelerate their adoption by the IGT community, and their enhanced temperature capability will allow hydrogen-fueled turbines and ultra-high temperature steam turbines to be developed, thus making the vision of zero-emission fossil-fuel power plants possible.
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Questek Innovations Llc
1820 Ridge Avenue Evanston, IL 60201-3621
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