NSUF 23-4685: The effects of high-temperature creep on irradiation damages of 316H stainless steel made by laser additive manufacturing
Being simultaneously exposed to the temperature and stress in service for a long time, AM microstructure evolves, resulting in dislocation cell recovery, dislocation interaction, low angle boundary formation, and chemical redistribution. These changes will further affect the irradiation resistance and impact the component life. However, it is unclear how these substructural changes will affect radiation defect formation, especially void swelling and loop formation at the operating temperatures of advanced reactors (500-700ºC).
LPBF AM 316H SS and DED AM 316H SS were fabricated by Concept Laser MLab and Optomec LENS 500, respectively. The materials will be evaluated under as-built condition. Dog-bone specimens will be machined along the build direction. Creep test will be conducted at 650°C with the stress level 20% below the yield strength at 650°C (200 MPa for LPBF AM 316H SS and 110 MPa for DED AM 316H SS). The testing conditions are selected under the dislocation creep regime (10-4<σ/G<10-2). This region is of particular interest due to the thermally activated movement of dislocations as well as vacancies and interstitials. Specimens will be stopped in the middle of the creep test within the steady state creep regime at 3 incremental times. Including the as-received materials without creep testing, the total 8 samples will be studied through in-situ ion-irradiation and TEM characterization (4 creep conditions and 2 AM process methods). TEM samples will be pre-prepared and subjected to 1 MeV Kr ion irradiation up to a peak dose level of 5 dpa at 650°C inside a Hitachi H-9000NAR TEM at IVEM facility. The displacement damage from Kr is calculated by SRIM simulation using K-P model. Both loop formation and void swelling have been reported at a dose of 3 dpa at high temperatures. TEM characterization of structural and chemical changes of dislocation cells at different stages of creep will be conducted at Purdue. Post-irradiation TEM work at IVEM facility will quantify (1) structural and chemical changes of dislocation cells at different radiation levels; (2) the size, density, and distribution of voids and dislocation loops near cell boundaries and inside cells. TEM work will be done at 4 incremental dose steps (0, 1, 3, and 5 dpa) to study microstructural evolution during irradiation.
We believe the recovery of dislocation cells during creep will decrease the sink strength, thus producing more radiation damage. However, on the other hand, we should not rule out the possibility that the removal of chemical heterogeneity and the formation of uniform dislocation structures towards the later stage of creep can help inhibit defect formation. The competition between these two processes at the different stages of creep deformation determines the overall radiation resistance at the time. As such, the outcome from this research is to understand the relationship between dislocation substructure and radiation damage as the function of creep time.
Additional Info
| Field | Value |
|---|---|
| Abstract | Being simultaneously exposed to the temperature and stress in service for a long time, AM microstructure evolves, resulting in dislocation cell recovery, dislocation interaction, low angle boundary formation, and chemical redistribution. These changes will further affect the irradiation resistance and impact the component life. However, it is unclear how these substructural changes will affect radiation defect formation, especially void swelling and loop formation at the operating temperatures of advanced reactors (500-700ºC). LPBF AM 316H SS and DED AM 316H SS were fabricated by Concept Laser MLab and Optomec LENS 500, respectively. The materials will be evaluated under as-built condition. Dog-bone specimens will be machined along the build direction. Creep test will be conducted at 650°C with the stress level 20% below the yield strength at 650°C (200 MPa for LPBF AM 316H SS and 110 MPa for DED AM 316H SS). The testing conditions are selected under the dislocation creep regime (10-4<σ/G<10-2). This region is of particular interest due to the thermally activated movement of dislocations as well as vacancies and interstitials. Specimens will be stopped in the middle of the creep test within the steady state creep regime at 3 incremental times. Including the as-received materials without creep testing, the total 8 samples will be studied through in-situ ion-irradiation and TEM characterization (4 creep conditions and 2 AM process methods). TEM samples will be pre-prepared and subjected to 1 MeV Kr ion irradiation up to a peak dose level of 5 dpa at 650°C inside a Hitachi H-9000NAR TEM at IVEM facility. The displacement damage from Kr is calculated by SRIM simulation using K-P model. Both loop formation and void swelling have been reported at a dose of 3 dpa at high temperatures. TEM characterization of structural and chemical changes of dislocation cells at different stages of creep will be conducted at Purdue. Post-irradiation TEM work at IVEM facility will quantify (1) structural and chemical changes of dislocation cells at different radiation levels; (2) the size, density, and distribution of voids and dislocation loops near cell boundaries and inside cells. TEM work will be done at 4 incremental dose steps (0, 1, 3, and 5 dpa) to study microstructural evolution during irradiation. We believe the recovery of dislocation cells during creep will decrease the sink strength, thus producing more radiation damage. However, on the other hand, we should not rule out the possibility that the removal of chemical heterogeneity and the formation of uniform dislocation structures towards the later stage of creep can help inhibit defect formation. The competition between these two processes at the different stages of creep deformation determines the overall radiation resistance at the time. As such, the outcome from this research is to understand the relationship between dislocation substructure and radiation damage as the function of creep time. |
| Award Announced Date | 2023-06-01T09:02:28.87 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | John Snitzer |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |