Abstract
Supercritical CO2 (sCO2) has attractive aspects as a working fluid, however, above ~550°C it carburizes conventional Fe-based alloys. Evaluations of Fe-based alloys found that advanced austenitic alloys like alloy S31025 with higher Cr and Ni contents have better sCO2 compatibility than conventional stainless steels at 650°C in sCO2 for up to 2000 h exposures. To further understand the protective scale formed on alloy S31025 in 300 bar research grade sCO2 at 650°C, the thin Cr-rich scale was analyzed after 500 h using analytical transmission electron microscopy and compared to scales formed on model Fe-20Cr20Ni and Fe-20Cr-25Ni. Typical Mn and Si rich layers were observed but a recurring observation was an O depleted region in the scales. Characterization identified a mixed O-C phase with Cr and Fe within the scale formed on both commercial and model alloys. This phase did not form after a similar 500 h exposure at 650°C in 1 bar CO2,.
| Original language | English |
|---|---|
| State | Published - 2024 |
| Event | Association for Materials Protection and Performance Annual Conference and Expo 2024 - New Orleans, United States Duration: Mar 3 2024 → Mar 7 2024 |
Conference
| Conference | Association for Materials Protection and Performance Annual Conference and Expo 2024 |
|---|---|
| Country/Territory | United States |
| City | New Orleans |
| Period | 03/3/24 → 03/7/24 |
Funding
The authors would like to thank B. Johnston, T. M. Lowe and D. Newberry for assistance with the experimental work at ORNL. S. Bell and T. Lach at ORNL provided helpful comments on the manuscript. This research was sponsored by the U.S. Department of Energy, Office of Fossil Energy and Carbon Management, Advanced Materials Program. The Talos STEM was supported by the Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States 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 United States 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).
Keywords
- austenitic steels
- supercritical carbon dioxide
- transmission electron microscopy