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Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Evaluation of Alumina-Forming Austenitic Foil for Advanced Recuperators

[+] Author and Article Information
Bruce A. Pint

Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831-6156pintba@ornl.gov

Michael P. Brady, Yukinori Yamamoto, Michael L. Santella, Philip J. Maziasz

Oak Ridge National Laboratory, Materials Science and Technology Division, Oak Ridge, TN 37831-6156

Wendy J. Matthews

 Capstone Turbine Corporation, Chatsworth, CA 91311

J. Eng. Gas Turbines Power 133(10), 102302 (May 06, 2011) (6 pages) doi:10.1115/1.4002827 History: Received May 27, 2010; Revised July 19, 2010; Published May 06, 2011; Online May 06, 2011

A corrosion- and creep-resistant austenitic stainless steel has been developed for advanced recuperator applications. By optimizing the Al and Cr contents, the alloy is fully austenitic for creep strength while allowing the formation of a chemically stable external alumina scale at temperatures up to 900°C. An alumina scale eliminates long-term problems with the formation of volatile Cr oxy-hydroxides in the presence of water vapor in exhaust gas. As a first step in producing foil for primary surface recuperators, three commercially cast heats have been rolled to 100μm thick foil in the laboratory to evaluate performance in creep and oxidation testing. Results from initial creep testing are presented at 675°C and 750°C, showing excellent creep strength compared with other candidate foil materials. Laboratory exposures in humid air at 650800°C have shown acceptable oxidation resistance. A similar oxidation behavior was observed for sheet specimens of these alloys exposed in a modified 65 kW microturbine for 2871 h. One composition that showed superior creep and oxidation resistance has been selected for the preparation of a commercial batch of foil.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 2

Light microscopy of polished cross sections of foils after final annealing at 1200°C for ((a)–(c)) 7 min and ((d)–(f)) 12 min. ((a) and (d)) AFA F1, ((b) and (e)) AFA F2, and ((c) and (f)) AFA F4.

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Figure 3

Specimen mass change for commercial 347 and 120 foil (80–100 μm thick) compared with AFA foils during 100 h cycles in humid air at 650°C

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Figure 4

Specimen mass change for commercial alloy 120 foil (80 μm thick) compared with AFA foils during 100 h cycles in humid air at 700°C

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Figure 5

Specimen mass change for commercial alloy 120 foil (80 μm thick) compared with AFA foils during 100 h cycles in humid air at 800°C

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Figure 7

Light microscopy of polished cross sections of sheet specimens after 2871 h at 720°C in microturbine exhaust. (a) AFA F1, (b) AFA F2, and (c) AFA F4.

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Figure 8

Tensile creep behavior of AFA foils with strain % plotted versus exposure time at 677°C(1250°F) in air with a load of 117 MPa (17 ksi)

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Figure 9

Creep rupture behavior of AFA foils compared with two commercial foils with strain percent plotted versus exposure time at 750°C(1382°F) in air with a load of 100 MPa (14.5 ksi). Alloy grain size is noted for each foil.

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Figure 6

Light microscopy of polished cross sections of sheet specimens after 1558 h at 720°C in microturbine exhaust. (a) AFA F1, (b) AFA F2, and (c) AFA F4.

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Figure 1

Electron microprobe measured Cr loss from 90 μm foil specimens of alloy 120 exposed in laboratory wet air experiments at 650–800°C and to microturbine exhaust at 720°C. A 40 kW h lifetime is shown for reference.

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