NSUF 21-4233: IVEM Investigation of Defect Evolution in FCC Compositionally Complex Alloys under Dual-beam Heavy-ion Irradiation
The proposed study will investigate the microstructural evolution under irradiation by Kr++ heavy ions and He co-implantation of three candidate compositionally complex alloy (CCA) compositions from two alloy systems 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 CCA. 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 NiFeCr and NiFeMn conventional counterparts. Improvements in material properties are attributed to the compositional complexity related to the number and choice of constituent elements. Since Co-free FCC CCA have been found to show similar irradiation hardening and microstructural evolution to 316SS, 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 is predicted by CALPHAD to phase separate at ~760 ̊C, while the latter is predicted to be a single FCC phase down to ~575 ̊C. Although both were found to phase separate after ageing at 700 ̊C, sluggish diffusion slows phase separation in all these CCA for the duration of an IVEM irradiation. To advance fundamental understanding of the radiation resistance of compositionally complex base matrices, 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 and void formation, growth, migration, and stability. These CCA have already been studied by the PI at IVEM, and results indicate that defect cluster formation under single-beam irradiation is reduced at 50K in CCA compared to less compositionally complex materials. At high temperature, interstitial loop growth kinetics were slowed in Cr15Fe35Mn15Ni35. This study builds upon that work with co-implantation experiments at elevated temperatures to observe defect clustering and void growth behavior in a He-producing environment. Arc-melted or vacuum-induction melted samples are homogenized and formed into disks for electro-polishing before 1MeV Kr++ and 12 keV He+ irradiation at 773 and 873K to a dose of 10 dpa and 0.5% He/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 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 microstructural evolution under irradiation by Kr++ heavy ions and He co-implantation of three candidate compositionally complex alloy (CCA) compositions from two alloy systems 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 CCA. 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 NiFeCr and NiFeMn conventional counterparts. Improvements in material properties are attributed to the compositional complexity related to the number and choice of constituent elements. Since Co-free FCC CCA have been found to show similar irradiation hardening and microstructural evolution to 316SS, 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 is predicted by CALPHAD to phase separate at ~760 ̊C, while the latter is predicted to be a single FCC phase down to ~575 ̊C. Although both were found to phase separate after ageing at 700 ̊C, sluggish diffusion slows phase separation in all these CCA for the duration of an IVEM irradiation. To advance fundamental understanding of the radiation resistance of compositionally complex base matrices, 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 and void formation, growth, migration, and stability. These CCA have already been studied by the PI at IVEM, and results indicate that defect cluster formation under single-beam irradiation is reduced at 50K in CCA compared to less compositionally complex materials. At high temperature, interstitial loop growth kinetics were slowed in Cr15Fe35Mn15Ni35. This study builds upon that work with co-implantation experiments at elevated temperatures to observe defect clustering and void growth behavior in a He-producing environment. Arc-melted or vacuum-induction melted samples are homogenized and formed into disks for electro-polishing before 1MeV Kr++ and 12 keV He+ irradiation at 773 and 873K to a dose of 10 dpa and 0.5% He/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 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 | 2021-06-07T15:52:45.21 |
| 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 | 4233 |