NSUF 17-1115: Heavy ion irradiation and ex situ transmission electron microscopy study of the effectiveness of twin boundaries in alleviating radiation damage in 316 austenitic stainless steels
Interfaces can act as radiation defect sinks and thus reduce defect density (or slow down defect accumulation with dose). In addition to grain boundaries, polycrystalline austenitic stainless steels can contain interfaces such as twin boundaries, formed during annealing or cold work. Twin boundaries have a high orientation coincidence (S3) compared to random boundaries, and they can be coherent or incoherent depending on the boundary plane. The surface area of twin boundaries can be adjusted by varying parameters such as the composition, fabrication process, or cold-work treatment. In particular, cold work can under appropriate conditions induce a very large surface area of deformation twin boundaries (comparable or larger than the surface area of grain boundaries), which might provide a large defect sink area.
Several experimental and simulation studies in He-irradiated Cu observed that coherent twin boundaries are poor sinks for radiation defects but that incoherent twin boundaries can be much more efficient. Analyses of radiation-induced segregation at boundaries in austenitic stainless steel tend to confirm this difference in sink strength. Some authors observed in Kr-irradiated Ag that coherent twin boundaries could be distorted by neighboring defect clusters, thus becoming partially incoherent and able to capture stacking fault tetrahedra and dislocation loops. These authors also showed the existing of a twin boundary affected zone with reduced defect accumulation, which had been previously described by in an Fe-15Ni-15Cr alloy. Recent work by the co-PI on in situ TEM (Transmission Electron Microscopy) Au ion irradiation of 316 stainless steel seems to confirm the ability of twin boundaries to capture point defect clusters/loops and dislocations (see Fig.1 in narrative). Further work is needed to confirm these preliminary results.
The project objective is to provide compelling observations of the effectiveness of twin boundaries as effective point defect sinks in 316 stainless steels. As summarized above, some existing results in pure metals and preliminary observations on these steels seem to support this hypothesis. The observations will address the following questions pertaining to 316 stainless steels: is there a twin boundary affected zone with reduced defect accumulation? In terms of sink strength, how do twin boundaries compare to high-angle grain boundaries, and how do their sink strengths evolve with time? What is the difference in sink strength between annealing (typically more coherent) and deformation (typically less coherent) twin boundaries? The project will use heavy ion irradiation and TEM to study radiation defects near annealing and deformation twin boundaries in austenitic stainless steels, and will add to the corpus of existing data on pure metals. The measurements of defect denuded zones in the vicinity of twin boundaries could be used to improve radiation damage models of stainless steel in nuclear reactor environment. They would complement the growing body of research on RIS at twin boundaries, motivated by the promising low-RIS behavior of those boundaries compared to high angle grain boundaries. Results could also help design thermo-mechanical or cold-work treatments for austenitic stainless steels promoting twin structures that alleviate radiation damage for components in LWR.
The period of performance will be 4 days of ion beam and 10 days of TEM.
Additional Info
| Field | Value |
|---|---|
| Abstract | Interfaces can act as radiation defect sinks and thus reduce defect density (or slow down defect accumulation with dose). In addition to grain boundaries, polycrystalline austenitic stainless steels can contain interfaces such as twin boundaries, formed during annealing or cold work. Twin boundaries have a high orientation coincidence (S3) compared to random boundaries, and they can be coherent or incoherent depending on the boundary plane. The surface area of twin boundaries can be adjusted by varying parameters such as the composition, fabrication process, or cold-work treatment. In particular, cold work can under appropriate conditions induce a very large surface area of deformation twin boundaries (comparable or larger than the surface area of grain boundaries), which might provide a large defect sink area. Several experimental and simulation studies in He-irradiated Cu observed that coherent twin boundaries are poor sinks for radiation defects but that incoherent twin boundaries can be much more efficient. Analyses of radiation-induced segregation at boundaries in austenitic stainless steel tend to confirm this difference in sink strength. Some authors observed in Kr-irradiated Ag that coherent twin boundaries could be distorted by neighboring defect clusters, thus becoming partially incoherent and able to capture stacking fault tetrahedra and dislocation loops. These authors also showed the existing of a twin boundary affected zone with reduced defect accumulation, which had been previously described by in an Fe-15Ni-15Cr alloy. Recent work by the co-PI on in situ TEM (Transmission Electron Microscopy) Au ion irradiation of 316 stainless steel seems to confirm the ability of twin boundaries to capture point defect clusters/loops and dislocations (see Fig.1 in narrative). Further work is needed to confirm these preliminary results. The project objective is to provide compelling observations of the effectiveness of twin boundaries as effective point defect sinks in 316 stainless steels. As summarized above, some existing results in pure metals and preliminary observations on these steels seem to support this hypothesis. The observations will address the following questions pertaining to 316 stainless steels: is there a twin boundary affected zone with reduced defect accumulation? In terms of sink strength, how do twin boundaries compare to high-angle grain boundaries, and how do their sink strengths evolve with time? What is the difference in sink strength between annealing (typically more coherent) and deformation (typically less coherent) twin boundaries? The project will use heavy ion irradiation and TEM to study radiation defects near annealing and deformation twin boundaries in austenitic stainless steels, and will add to the corpus of existing data on pure metals. The measurements of defect denuded zones in the vicinity of twin boundaries could be used to improve radiation damage models of stainless steel in nuclear reactor environment. They would complement the growing body of research on RIS at twin boundaries, motivated by the promising low-RIS behavior of those boundaries compared to high angle grain boundaries. Results could also help design thermo-mechanical or cold-work treatments for austenitic stainless steels promoting twin structures that alleviate radiation damage for components in LWR. The period of performance will be 4 days of ion beam and 10 days of TEM. |
| Award Announced Date | 2017-09-20T12:36:19.57 |
| Awarded Institution | Center for Advanced Energy Studies |
| Facility | Microscopy and Characterization Suite |
| Facility Tech Lead | Kumar Sridharan, Yaqiao Wu |
| Irradiation Facility | None |
| PI | Kumar Sridharan |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1115 |