3D Microscopy to Assess the Effect of High Temperature Cyclic Oxidation on the Deformation of Cast and ODS FeCrAlY Alloys
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Specimen deformation, oxide scale growth, and scale cracking were monitored for cyclic oxidation exposures at 1200 °C of three cast FeCrAlY(Hf) alloys and two oxide dispersion strengthened (ODS) FeCrAl alloys. Evolution of both the specimen geometry and surface deformation was quantified using 3D optical microscopy. The stress in the alumina scale was also measured using photo-stimulated luminescence piezospectroscopy. The goal was to assess the effect of stress generation and stress relaxation on scale spallation for FeCrAl materials with drastic differences in terms of high temperature strengths. After 1000, 1-h cycles, the cast alloys exhibited significant deformation with a convoluted oxide scale, leading for the two Hf-free FeCrAlY alloys to undergo crack formation and spallation. For the Hf-containing FeCrAlY, limited spallation was observed due to the localization of spallation at grain boundaries, the large grain structure, and the beneficial effect of Hf on scale adhesion. In contrast, limited deformation was measured for the ODS FeCrAl alloys, with minimal cracking and scale spallation for alloy PM2000 after 1000 h. A higher spallation rate was observed for ODS MA956, which was attributed to a high defect concentration in the alumina scale that formed. The mechanisms leading to spallation during cyclic oxidation for the cast and ODS FeCrAlY alloys are described.
KeywordsODS FeCrAlY Oxide scale 3D microscopy Deformation Cracking
The authors would like to thank G. Garner, M Stephens, T. Lowe, T. Jordan, and C. Cox for their help with the experimental work. They also would like to acknowledge M. Brady and B. Thiesing for reviewing the manuscript. This research was sponsored by the US Department of Energy (DOE), Fossil Energy Crosscutting Research Program and the DOE Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office (Combined Heat and Power). This manuscript has been authored by UT–Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the US Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the US Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
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