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Microstructural Changes in Inconel® 740 After Long-Term Aging in the Presence and Absence of Stress

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Abstract

The Ni-based alloy, Inconel® 740, is being extensively examined for use in advanced ultrasupercritical steam boilers because its precipitation-strengthened microstructure appears to offer the necessary creep strength under the high temperatures and pressures (up to 760°C and 35 MPa) needed for high efficiency power generation. However, because this application requires extremely long lifetimes under these conditions (up to 30 years), long-term microstructure stability is a major concern. In this paper, results from microstructural analyses of Inconel 740 specimens aged at 700 and 750°C in the presence and absence of creep loading for times up to ~31,000 h are presented. The primary focus was on the development of the eta η (Ni3Ti) phase and coarsening of coherent γ′-Ni3(Al,Ti) precipitates and its depletion near eta/matrix interfaces. However, despite these processes, Inconel 740 showed adequate long-term microstructural stability to assure adequate creep strength for the intended application.

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Acknowledgements

This research was sponsored by the U.S. Department of Energy (DOE), Office of Fossil Energy, Crosscutting Research Program in support of the DOE project on boiler materials for advanced ultrasupercritical steam conditions. G.J. Pillitiere, T. Lowe, T. Geer, K.S. Reeves, K. Powers, and J. Moser assisted with the experimental work. The authors thank D.T. Hoelzer and Y. Yamamoto for comments on the results and manuscript.

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Authors and Affiliations

  1. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA

    K. A. Unocic & P. F. Tortorelli

  2. Electric Power Research Institute, Charlotte, NC, 28262, USA

    J. P. Shingledecker

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  1. K. A. Unocic
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  2. J. P. Shingledecker
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  3. P. F. Tortorelli
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Correspondence to K. A. Unocic.

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Unocic, K.A., Shingledecker, J.P. & Tortorelli, P.F. Microstructural Changes in Inconel® 740 After Long-Term Aging in the Presence and Absence of Stress. JOM 66, 2535–2542 (2014). https://doi.org/10.1007/s11837-014-1208-4

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  • DOI: https://doi.org/10.1007/s11837-014-1208-4

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