NSUF 23-4744: Understanding fundamental effect of grain structure on microstructure evolution in HT9 via in-situ irradiation and TEM
Ferritic/martensitic (F/M) HT9 steels are being considered as potential structural materials for next generation nuclear reactors. Previous PI and team’s research showed that the radiation resistance of the HT9 steel can be significantly improved by composition engineering (varying N contents) [1]. Inspired by the previous work, the efforts on improving the alloy performance via grain engineering have been continued on the HT9 steel. Our previous ex-situ irradiation study revealed that the fine grain HT9 showed excellent radiation resistance up to 200 peak dpa and started to show similar performance to the coarse grain HT9 afterwards due to radiation induced grain growth and grain boundary carbide dissolution. Radiation resistance of the fine grain HT9 has never been studied and we do not have good understanding on the fundamentals yet. If successful, we will be able to understand why grain boundary carbides in the fine grain HT9 are more susceptible to irradiation compared to the ones in the coarse grain HT9 and apply the knowledge when designing next-generation HT9 steels. In this proposed research, samples will be all prepared at LANL for the in-situ ion irradiation and TEM at ANL-IVEM facility using a focused ion beam (FIB). Two to three TEM samples will be prepared for each coarse and fine grain HT9 which include one pristine and 1-2 pre-irradiated samples at different doses (e.g. 200 and 300 dpa). The purpose of using pre-irradiated samples is to expedite the damage up to the level where we started to see the dissolution of the carbides and significant grain growth (~200 dpa). By adding 50-100 dpa damage using Kr2+ beam at 450 C, we will be able to observe significant changes in the microstructure which can help us understand fundamentals. The samples were already irradiated at LANL through other DOE NE program and no extra effort is needed. Due to high dose level required for each sample, 10-days of IVEM time is requested to reduce the load on each day. Microstructure characterization will be conducted using a TEM. Videos will be obtained for general in-situ recording, and bright field, scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) will be used for further characterization. Along with the carbide dissolution, other chemical changes such as grain boundary segregation and precipitation will be monitored. When the damage level reaches ~300 dpa for the pre-irradiated sample, void swelling is also anticipated. [1] H. Kim et. al., JNM 560 (2022) 153492. https://doi.org/10.1016/j.jnucmat.2021.153492
Additional Info
| Field | Value |
|---|---|
| Abstract | Ferritic/martensitic (F/M) HT9 steels are being considered as potential structural materials for next generation nuclear reactors. Previous PI and team’s research showed that the radiation resistance of the HT9 steel can be significantly improved by composition engineering (varying N contents) [1]. Inspired by the previous work, the efforts on improving the alloy performance via grain engineering have been continued on the HT9 steel. Our previous ex-situ irradiation study revealed that the fine grain HT9 showed excellent radiation resistance up to 200 peak dpa and started to show similar performance to the coarse grain HT9 afterwards due to radiation induced grain growth and grain boundary carbide dissolution. Radiation resistance of the fine grain HT9 has never been studied and we do not have good understanding on the fundamentals yet. If successful, we will be able to understand why grain boundary carbides in the fine grain HT9 are more susceptible to irradiation compared to the ones in the coarse grain HT9 and apply the knowledge when designing next-generation HT9 steels. In this proposed research, samples will be all prepared at LANL for the in-situ ion irradiation and TEM at ANL-IVEM facility using a focused ion beam (FIB). Two to three TEM samples will be prepared for each coarse and fine grain HT9 which include one pristine and 1-2 pre-irradiated samples at different doses (e.g. 200 and 300 dpa). The purpose of using pre-irradiated samples is to expedite the damage up to the level where we started to see the dissolution of the carbides and significant grain growth (~200 dpa). By adding 50-100 dpa damage using Kr2+ beam at 450 C, we will be able to observe significant changes in the microstructure which can help us understand fundamentals. The samples were already irradiated at LANL through other DOE NE program and no extra effort is needed. Due to high dose level required for each sample, 10-days of IVEM time is requested to reduce the load on each day. Microstructure characterization will be conducted using a TEM. Videos will be obtained for general in-situ recording, and bright field, scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) will be used for further characterization. Along with the carbide dissolution, other chemical changes such as grain boundary segregation and precipitation will be monitored. When the damage level reaches ~300 dpa for the pre-irradiated sample, void swelling is also anticipated. [1] H. Kim et. al., JNM 560 (2022) 153492. https://doi.org/10.1016/j.jnucmat.2021.153492 |
| Award Announced Date | 2023-09-14T13:41:56.937 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Hyosim Kim |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |