NSUF 20-4095: ChemisSTEM Characterization of Bulk Heavy Ion Irradiated Complex Concentrated Alloys
The proposed study will investigate the formation of extended defects after irradiation by Ni++ heavy ions in two complex concentrated 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 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 conventional NiFeCr and NiFeMn 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, Cr18.1Fe27.3Mn27.3Ni27.3 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 and maintained a single-phase after ageing. Although the former was 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, high dpa irradiations have been performed and require post-irradiation examination using advanced microscopy tools such as ChemiSTEM on the FEI Titan at INL. This equipment allows for the high-resolution defect characterization and chemical mapping necessary to measure chemical ordering and segregation near extended defects. These CCA have already 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 CCA compared to less compositionally complex materials. At 500 ̊C, interstitial loop growth kinetics were slowed in Cr15Fe35Mn15Ni35. This study builds upon that work with 5 MeV Ni++ irradiations performed also at 500 ̊C to observe defect evolution and void growth behavior at 50, 100, and 200 dpa. Arc-melted or vacuum-induction melted samples were homogenized and polished prior to irradiation at the Texas A&M University Accelerator Laboratory. A total of 4 days at IMCL to use the Titan 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 complex concentrated 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 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 conventional NiFeCr and NiFeMn 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, Cr18.1Fe27.3Mn27.3Ni27.3 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 and maintained a single-phase after ageing. Although the former was 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, high dpa irradiations have been performed and require post-irradiation examination using advanced microscopy tools such as ChemiSTEM on the FEI Titan at INL. This equipment allows for the high-resolution defect characterization and chemical mapping necessary to measure chemical ordering and segregation near extended defects. These CCA have already 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 CCA compared to less compositionally complex materials. At 500 ̊C, interstitial loop growth kinetics were slowed in Cr15Fe35Mn15Ni35. This study builds upon that work with 5 MeV Ni++ irradiations performed also at 500 ̊C to observe defect evolution and void growth behavior at 50, 100, and 200 dpa. Arc-melted or vacuum-induction melted samples were homogenized and polished prior to irradiation at the Texas A&M University Accelerator Laboratory. A total of 4 days at IMCL to use the Titan 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 | 2020-07-14T14:03:49.317 |
| Awarded Institution | Idaho National Laboratory |
| Facility | Advanced Test Reactor |
| Facility Tech Lead | Alina Zackrone |
| Irradiation Facility | None |
| PI | Calvin Parkin |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 4095 |