The Oak Ridge National Laboratory (ORNL) and ATI Allegheny Ludlum worked together on a collaborative program for about two years to produce a wide range of commercial sheets and foils of the new AL20-25+ (AL20–25+Nb) stainless alloy for advanced microturbine recuperator applications. There is a need for cost-effective sheets/foils with more performance and reliability at 650–750°C than 347 stainless steel, particularly for larger 200–250 kW microturbines. Phase 1 of this collaborative program produced the sheets and foils needed for manufacturing brazed plated-fin air cells, while Phase 2 provided foils for primary surface air cells, and did experiments on modified processing designed to change the microstructure of sheets and foils for improved creep-resistance. Phase 1 sheets and foils of AL20-25+Nb have much more creep-resistance than 347 steel at 700–750°C, and those foils are slightly stronger than HR120 and HR230. Results for Phase 2 showed nearly double the creep-rupture life of sheets at 750°C/100 MPa, and similar improvements in foils. Creep data show that Phase 2 foils of AL20-25+Nb alloy have creep resistance approaching that of alloy 625 foils. Testing at about 750°C in flowing turbine exhaust gas for 500 h in the ORNL Recuperator Test Facility shows that foils of AL20–25+Nb alloy have oxidation-resistance similar to HR120 alloy, and much better than 347 steel.
Creep Strength and Microstructure of Alloy Sheets and Foils for Advanced Microturbine Recuperators
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Maziasz, P. J., Shingledecker, J. P., Evans, N. D., Yamamoto, Y., More, K. L., Trejo, R., and Lara-Curzio, E. (October 20, 2006). "Creep Strength and Microstructure of Alloy Sheets and Foils for Advanced Microturbine Recuperators." ASME. J. Eng. Gas Turbines Power. July 2007; 129(3): 798–805. https://doi.org/10.1115/1.2718569
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