NSUF 23-4680: Investigation of Void Swelling and Chemical Segregation in Heavy Ion Irradiated Compositionally Complex Alloys
The proposed study will investigate the formation of extended defects after irradiation by Ni++ heavy ions in two compositionally complex alloy (CCA) compositions of interest for sodium fast reactor claddings and core applications. Conventional alloys optimized for claddings and ducts such as austenitic D9 and ferritic-martensitic G92 and 9-12Cr steels show dramatic degradation after hundreds of displacements per atom (dpa), far short of the needs of advanced reactors, triggering exploration of CCAs. Preliminary studies have shown that these alloys exhibit excellent strength, temperature resistance, and improved tolerance to radiation damage, promoting their candidacy for cladding and core applications. Especially interesting are recent findings that complex Ni-based alloys show a reduction in defect formation and void swelling compared to their single-element constituents and to their conventional NiFeCr and NiFeMn counterparts. Improvements in material properties are attributed to the number, choice, and ratio of constituent elements. Since Co-free FCC CCAs have shown similar irradiation hardening and microstructural evolution to 316 stainless steel (SS), the benefit of compositional complexity may be of similar magnitude to dilute alloying element additions, and thus demands fundamental mechanistic understanding. This study has identified two compositions in the FCC CrFeMnNi family, Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35. The former has mechanical properties comparable to 316SS and was found to undergo phase separation after ageing at 700 ̊C, while the latter is predicted by CALPHAD to be a single FCC phase at 600 ̊C. Although the former was found to phase separate after ageing at 700 ̊C, sluggish diffusion slows phase separation in both CCAs for the duration of an IVEM irradiation. To advance fundamental understanding of the radiation resistance of compositionally complex base matrices, high-dpa irradiations are being performed and will require post-irradiation examination using advanced microscopy tools such as Super-X EDS on the ThermoFisher Spectra300 at CAES. This equipment allows for the high-resolution defect characterization and chemical mapping necessary to measure chemical redistribution and segregation near extended defects. These CCAs have been studied by the PI at the IVEM-Tandem facility, and results indicate that defect cluster formation under single-beam irradiation is reduced at 50 K in CCAs compared to less compositionally complex materials. At 500 ̊C, interstitial loop growth kinetics were slowed in Cr15Fe35Mn15Ni35 compared to Cr18Fe27Mn27Ni28. This study builds upon previous bulk irradiations at 500 ̊C with 4.0 MeV Ni++ irradiations performed at 600 and 650 ̊C to compare defect evolution and void growth behavior to 316H SS at 150 dpa, which is included as a control. Vacuum-induction melted samples were homogenized and polished prior to irradiation at the Wisconsin Ion Beam Laboratory (WIBL). A total of 8 days at CAES to use the Spectra300 are requested over the next year. The goal of this effort is three-fold: to compare the radiation tolerance of these alloys to simple metals and model alloys; to inform future CCA design and improvements by mapping the physical response of the alloys under these conditions; and finally, to characterize the effect of compositional complexity on the mobility of point defects and larger defect structures.
Additional Info
| Field | Value |
|---|---|
| Abstract | The proposed study will investigate the formation of extended defects after irradiation by Ni++ heavy ions in two compositionally complex alloy (CCA) compositions of interest for sodium fast reactor claddings and core applications. Conventional alloys optimized for claddings and ducts such as austenitic D9 and ferritic-martensitic G92 and 9-12Cr steels show dramatic degradation after hundreds of displacements per atom (dpa), far short of the needs of advanced reactors, triggering exploration of CCAs. Preliminary studies have shown that these alloys exhibit excellent strength, temperature resistance, and improved tolerance to radiation damage, promoting their candidacy for cladding and core applications. Especially interesting are recent findings that complex Ni-based alloys show a reduction in defect formation and void swelling compared to their single-element constituents and to their conventional NiFeCr and NiFeMn counterparts. Improvements in material properties are attributed to the number, choice, and ratio of constituent elements. Since Co-free FCC CCAs have shown similar irradiation hardening and microstructural evolution to 316 stainless steel (SS), the benefit of compositional complexity may be of similar magnitude to dilute alloying element additions, and thus demands fundamental mechanistic understanding. This study has identified two compositions in the FCC CrFeMnNi family, Cr18Fe27Mn27Ni28 and Cr15Fe35Mn15Ni35. The former has mechanical properties comparable to 316SS and was found to undergo phase separation after ageing at 700 ̊C, while the latter is predicted by CALPHAD to be a single FCC phase at 600 ̊C. Although the former was found to phase separate after ageing at 700 ̊C, sluggish diffusion slows phase separation in both CCAs for the duration of an IVEM irradiation. To advance fundamental understanding of the radiation resistance of compositionally complex base matrices, high-dpa irradiations are being performed and will require post-irradiation examination using advanced microscopy tools such as Super-X EDS on the ThermoFisher Spectra300 at CAES. This equipment allows for the high-resolution defect characterization and chemical mapping necessary to measure chemical redistribution and segregation near extended defects. These CCAs have been studied by the PI at the IVEM-Tandem facility, and results indicate that defect cluster formation under single-beam irradiation is reduced at 50 K in CCAs compared to less compositionally complex materials. At 500 ̊C, interstitial loop growth kinetics were slowed in Cr15Fe35Mn15Ni35 compared to Cr18Fe27Mn27Ni28. This study builds upon previous bulk irradiations at 500 ̊C with 4.0 MeV Ni++ irradiations performed at 600 and 650 ̊C to compare defect evolution and void growth behavior to 316H SS at 150 dpa, which is included as a control. Vacuum-induction melted samples were homogenized and polished prior to irradiation at the Wisconsin Ion Beam Laboratory (WIBL). A total of 8 days at CAES to use the Spectra300 are requested over the next year. The goal of this effort is three-fold: to compare the radiation tolerance of these alloys to simple metals and model alloys; to inform future CCA design and improvements by mapping the physical response of the alloys under these conditions; and finally, to characterize the effect of compositional complexity on the mobility of point defects and larger defect structures. |
| Award Announced Date | 2023-06-01T09:07:06.213 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Calvin Parkin |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |