Authors: K A Unocic J P Shingledecker P F Tortorelli
Publish Date: 2014/11/18
Volume: 66, Issue: 12, Pages: 2535-2542
Abstract
The Nibased alloy Inconel® 740 is being extensively examined for use in advanced ultrasupercritical steam boilers because its precipitationstrengthened 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 longterm 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 ~31000 h are presented The primary focus was on the development of the eta η Ni3Ti phase and coarsening of coherent γ′Ni3AlTi precipitates and its depletion near eta/matrix interfaces However despite these processes Inconel 740 showed adequate longterm microstructural stability to assure adequate creep strength for the intended applicationThis research was sponsored by the US 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 GJ Pillitiere T Lowe T Geer KS Reeves K Powers and J Moser assisted with the experimental work The authors thank DT Hoelzer and Y Yamamoto for comments on the results and manuscript
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