NSUF 18-1610: IVEM Investigation of Defect Evolution in Bulk High Entropy Alloys under Single- and Dual-beam Heavy-ion Irradiation
The proposed study will investigate the microstructural evolution under irradiation by Kr++ heavy ions and He+ ions in the IVEM of three candidate high entropy alloy (HEA) compositions from the two alloy systems selected 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 sustaining hundreds of displacements per atom (dpa), far short of the needs of next generation reactors. Limitations in conventional alloying design have triggered exploration of HEAs. Preliminary studies have shown that these alloys exhibit excellent strength, temperature resistance, and 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 of their Ni-Fe-Cr and Ni-Fe-Mn conventional counterparts. Improvements in material properties are attributed to the compositional complexity related to the number and choice of constituent elements. The HEA design process focuses on tuning the compositional complexity of an alloy to mitigate the number of surviving defects and manipulate defect growth and cascade events to reduce damage with increasing fluence. This study has identified two promising compositions in the FCC CrFeMnNi family, 18.1Cr-27.3Fe-27.3Mn-27.3Ni and 15Cr-35Fe-15Mn-35Ni. The former has mechanical properties comparable to 316-type stainless steel (316SS), but with the possibility of mitigated void swelling, while the latter is predicted by CALPHAD to be a single FCC phase at 600 °C. The equimolar quaternary HEA NbTaTiV has also been identified due to its single-phase BCC crystal structure. Arc-melted samples heat treated for recrystallization are formed into disks for electro-polishing. To confirm candidacy and inform future tailoring of these alloys, in situ IVEM studies are necessary for the dynamic observation of defect formation and evolution under irradiation. This technique provides the high temporal and spatial resolution needed for characterizing loop formation, growth, migration, and stability. 316SS and 18.1Cr-27.3Fe-27.3Mn-27.3Ni have already been studied by the PI at ANL using IVEM, with preliminary results suggesting that defect clustering is not suppressed in the HEA relative to 316SS. This study builds upon that work by including model alloy E-90, pure Ni, one new FCC and one new BCC HEA composition. This study will also include observation of void growth behavior in a He-producing environment, the next step being characterization of the defect evolution under newly-available dual-beam heavy-ion irradiation– 1MeV Kr++ at 50K, 300K, 873K to a dose of 10 dpa. A total of 10 days on the IVEM 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 design and improvements of HEAs by mapping the physical response of the HEA alloys under these conditions; and finally, to characterize the difference in radiation resistance behavior in HEAs vs conventional alloys.
Additional Info
| Field | Value |
|---|---|
| Abstract | The proposed study will investigate the microstructural evolution under irradiation by Kr++ heavy ions and He+ ions in the IVEM of three candidate high entropy alloy (HEA) compositions from the two alloy systems selected 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 sustaining hundreds of displacements per atom (dpa), far short of the needs of next generation reactors. Limitations in conventional alloying design have triggered exploration of HEAs. Preliminary studies have shown that these alloys exhibit excellent strength, temperature resistance, and 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 of their Ni-Fe-Cr and Ni-Fe-Mn conventional counterparts. Improvements in material properties are attributed to the compositional complexity related to the number and choice of constituent elements. The HEA design process focuses on tuning the compositional complexity of an alloy to mitigate the number of surviving defects and manipulate defect growth and cascade events to reduce damage with increasing fluence. This study has identified two promising compositions in the FCC CrFeMnNi family, 18.1Cr-27.3Fe-27.3Mn-27.3Ni and 15Cr-35Fe-15Mn-35Ni. The former has mechanical properties comparable to 316-type stainless steel (316SS), but with the possibility of mitigated void swelling, while the latter is predicted by CALPHAD to be a single FCC phase at 600 °C. The equimolar quaternary HEA NbTaTiV has also been identified due to its single-phase BCC crystal structure. Arc-melted samples heat treated for recrystallization are formed into disks for electro-polishing. To confirm candidacy and inform future tailoring of these alloys, in situ IVEM studies are necessary for the dynamic observation of defect formation and evolution under irradiation. This technique provides the high temporal and spatial resolution needed for characterizing loop formation, growth, migration, and stability. 316SS and 18.1Cr-27.3Fe-27.3Mn-27.3Ni have already been studied by the PI at ANL using IVEM, with preliminary results suggesting that defect clustering is not suppressed in the HEA relative to 316SS. This study builds upon that work by including model alloy E-90, pure Ni, one new FCC and one new BCC HEA composition. This study will also include observation of void growth behavior in a He-producing environment, the next step being characterization of the defect evolution under newly-available dual-beam heavy-ion irradiation– 1MeV Kr++ at 50K, 300K, 873K to a dose of 10 dpa. A total of 10 days on the IVEM 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 design and improvements of HEAs by mapping the physical response of the HEA alloys under these conditions; and finally, to characterize the difference in radiation resistance behavior in HEAs vs conventional alloys. |
| Award Announced Date | 2018-09-17T12:10:23.6 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Calvin Parkin |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1610 |