NSUF 17-1118: IVEM investigation of defect evolution in FCC and BCC HEAs during heavy ion irradiation
The proposed study will investigate the microstructural evolution of two candidate high entropy alloys (HEA) for sodium fast reactor claddings and core applications under irradiation by Kr++ heavy ions in the IVEM. Optimized conventional alloys for applications as claddings and ducts such as austenitic D9 and ferritic-martensitic G92 and 9-12Cr steels show dramatic degradation under environments of hundreds of dpa, falling far short of the needs of next generation reactors. Limitations in conventional alloying design have triggered a shift to exploring new, more compositionally complex alloys: HEAs. While HEAs embody a rather new approach to alloying, preliminary studies have already shown that these alloys exhibit properties of excellent strength, temperature resistance, and tolerance to radiation damage, thus promoting their candidacy for cladding and core applications. Especially of interest are the recent findings that Ni-based complex 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 alloy counterparts. The 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 increasing and adjusting the compositional complexity of an alloy to control how energy is deposited into a material to mitigate the number of surviving defects, and manipulate subsequent defect growth and cascade events to reduce damage with increasing fluence. This study has identified two promising alloys: an fcc Cr0.66FeMnNi HEA with high ductility, and a bcc light refractory NbTiVZr HEA with high strength and limited softening. The former has mechanical properties which are comparable to that of 316-type stainless steel (316SS), but with the promise of mitigated void swelling; and the latter should exhibit lower void swelling rates than the fcc HEA. In order 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. While the end interest in these alloys will be to observe void growth behavior in a He producing environment, the first steps are to isolate and characterize the defect evolution under heavy ion irradiation – 1MeV Kr++ at 50K and 873K to a dose of 10 dpa. A total of 4 days on the IVEM are requested over the next year to perform these irradiations. The goal of this effort is three-fold: to compare the radiation tolerance of these alloys to conventional ferritic-martensitic alloy candidates; to inform future design and improvements of HEAs by mapping the physical response of the HEA alloys under these conditions; and finally, to act as a precursor study for the anticipated addition of a He gun to the IVEM studies, which will enable the co-implantation of He+ ions and heavy K++ ions for the study of void swelling under helium production.
Additional Info
| Field | Value |
|---|---|
| Abstract | The proposed study will investigate the microstructural evolution of two candidate high entropy alloys (HEA) for sodium fast reactor claddings and core applications under irradiation by Kr++ heavy ions in the IVEM. Optimized conventional alloys for applications as claddings and ducts such as austenitic D9 and ferritic-martensitic G92 and 9-12Cr steels show dramatic degradation under environments of hundreds of dpa, falling far short of the needs of next generation reactors. Limitations in conventional alloying design have triggered a shift to exploring new, more compositionally complex alloys: HEAs. While HEAs embody a rather new approach to alloying, preliminary studies have already shown that these alloys exhibit properties of excellent strength, temperature resistance, and tolerance to radiation damage, thus promoting their candidacy for cladding and core applications. Especially of interest are the recent findings that Ni-based complex 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 alloy counterparts. The 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 increasing and adjusting the compositional complexity of an alloy to control how energy is deposited into a material to mitigate the number of surviving defects, and manipulate subsequent defect growth and cascade events to reduce damage with increasing fluence. This study has identified two promising alloys: an fcc Cr0.66FeMnNi HEA with high ductility, and a bcc light refractory NbTiVZr HEA with high strength and limited softening. The former has mechanical properties which are comparable to that of 316-type stainless steel (316SS), but with the promise of mitigated void swelling; and the latter should exhibit lower void swelling rates than the fcc HEA. In order 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. While the end interest in these alloys will be to observe void growth behavior in a He producing environment, the first steps are to isolate and characterize the defect evolution under heavy ion irradiation – 1MeV Kr++ at 50K and 873K to a dose of 10 dpa. A total of 4 days on the IVEM are requested over the next year to perform these irradiations. The goal of this effort is three-fold: to compare the radiation tolerance of these alloys to conventional ferritic-martensitic alloy candidates; to inform future design and improvements of HEAs by mapping the physical response of the HEA alloys under these conditions; and finally, to act as a precursor study for the anticipated addition of a He gun to the IVEM studies, which will enable the co-implantation of He+ ions and heavy K++ ions for the study of void swelling under helium production. |
| Award Announced Date | 2017-09-20T12:37:11.99 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Todd Allen |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1118 |