Abstract
An outstanding challenge in the manufacturing and joining of oxide dispersion strengthened steels is retaining the nanofeatures in the alloy throughout the fabrication and welding process. MA956 was friction stir welded with two different sets of welding parameters, resulting in a medium and high heat input. After welding, 5 MeV Fe++ ion irradiations were performed at doses ranging from 50 to 200 dpa in the temperature range of 400 to 500 °C. Post-irradiation characterization was performed with scanning transmission electron microscopy and energy-dispersive x-ray spectroscopy to investigate the Y-Al-O dispersoids, voids, and dislocations. After welding, the dispersoid microstructure coarsened, resulting in fewer and larger dispersoids regardless of heat input. After irradiation, the dispersoid behavior in the welded material was sensitive to temperature, exhibiting growth behavior attributed to Ostwald coarsening at 500 °C but a mixture of nucleation and more muted growth at 400 and 450 °C, attributed to competing mechanisms of radiation-enhanced diffusion and Ostwald coarsening. Void swelling correlated to heat input; being more prevalent in the welded conditions occurring at lower doses and in higher values relative to the base material. The low values of swelling despite microstructure coarsening caused by welding demonstrate the excellent swelling resistance of MA956, even after welding with the highest swelling values of 0.5% noted in the stir zone high heat input condition at 450 °C, 200 dpa. The dislocation behavior was inconsistent: the strongest trend was that network density was higher for welded versus base material, and an increase in loop diameter with temperature was observed. A rate theory model based on the observed microstructure suggests at high temperature interstitial loss to sinks was more likely to be dominant compared to mutual annihilation via point defect recombination, because of an increase of the radiation diffusion coefficient with temperature regardless of initial welded microstructure.
| Original language | English |
|---|---|
| Article number | 153530 |
| Journal | Journal of Nuclear Materials |
| Volume | 561 |
| DOIs | |
| State | Published - Apr 1 2022 |
Funding
This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05–00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE 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). Research supported by the Defense Threat Reduction Agency (DTRA). This work was also supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07–051D14517 as part of the Nuclear Science User Facilities’ Rapid Turnaround Experiment program (17–906, 17–1032 and 18–1396). This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy, Department of Defense or the United States Government. The authors gratefully acknowledge the MIBL staff and graduate students for assistance in ion irradiation. We also thank Y. Wu for assistance at CAES and L. He, B. Kombaiah and X. Liu for assistance with characterization studies performed at the MFC. The authors acknowledge the Open Campus program at Army Research Laboratory in Aberdeen, MD for providing access to characterization suite. Partial support for review and editing by ST sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy. Finally, we thank CAPT D. Ruth for several insightful conversations. Research supported by the Defense Threat Reduction Agency (DTRA). This work was also supported by the U.S. Department of Energy, Office of Nuclear Energy under DOE Idaho Operations Office Contract DE-AC07–051D14517 as part of the Nuclear Science User Facilities’ Rapid Turnaround Experiment program (17–906, 17–1032 and 18–1396). This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy, Department of Defense or the United States Government. The authors gratefully acknowledge the MIBL staff and graduate students for assistance in ion irradiation. We also thank Y. Wu for assistance at CAES and L. He, B. Kombaiah and X. Liu for assistance with characterization studies performed at the MFC. The authors acknowledge the Open Campus program at Army Research Laboratory in Aberdeen, MD for providing access to characterization suite. Partial support for review and editing by ST sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy. Finally, we thank CAPT D. Ruth for several insightful conversations.
Keywords
- Friction stir welding
- Ion irradiation
- MA956
- Microstructure characterization
- Oxide dispersion strengthened steel
- Scanning transmission electron microscopy