NSUF 19-1624: Critical Evaluation of Solute Segregation and Precipitation Across Damage Rates in Dual Ion Irradiated T91 Steel
Prediction of material response to high irradiation damage levels is a key challenge facing the nuclear industry for the life extension of current reactors and the development of advanced Gen IV reactors. The evolution of the irradiation induced microstructure and microstructure-related degradation modes must be understood for reliable materials performance at high displacements per atom (dpa) and high temperatures (> 400°C). Ion irradiation is the only viable means to conduct accelerated materials evaluation using high damage rates to achieve high dpa with relatively low cost and little to no induced radioactivity. Challenges to the implementation of ion irradiation as a surrogate for neutron irradiation include accounting for damage rate effects, accounting for transmutation and the lack of data to establish the equivalence. This work aims to address the effect of irradiation damage rate on the microstructure of a ferritic-martensitic steel T91 and generate data to compare with reactor irradiation. T91 is one of the candidate materials for high dose structural components because of its resistance to swelling compared to austenitic steels. Compared to austenitic steels, little work has been done on the radiation-induced segregation (RIS) of alloying elements with existing work focusing on Cr and Ni segregation. RIS of interstitial impurities can have significant consequences for grain boundary embrittlement. Precipitation of secondary phases act as barriers to dislocation motion and can lead to additional embrittlement. The objective of this study is to develop an understanding of the effect of irradiation damage rate on the microstructural evolution of the Fe9Cr steel T91 focusing on solute clustering and segregation to grain boundaries. Bars of T91 heat 30176 were irradiated using the dual-beam configuration at the Michigan Ion Beam Laboratory at the University of Michigan using 5 MeV Fe2+ ions and simultaneously injected with energy degraded 2.1-2.15 MeV He2+ ions to simulate gas buildup to 16.6 dpa at 600 nm depth from the surface at 445°C. The irradiations were conducted with damage rates ranging from 5 x 10-5 dpa/s to 4 x 10-3 dpa/s with the helium injection rate held at 0.22 appm He/dpa and the samples are ready for analysis. Measurements of RIS and precipitating clusters can be performed using transmission electron microscopy (TEM) with a high angle double tilt holder to rotate the boundary to edge-on conditions and an accurate, high count EDS system for elemental composition mapping. The FEI Talos F200X S/TEM at LAMDA is ideal for this measurement and was used for characterization of BOR-60 irradiated T91. The period of performance is estimated at 7 working days of instrument time. The outcomes of this RTE will provide quantitative RIS profiles and Ni/Si cluster size and density across nearly two orders of magnitude in damage rate, partially spanning the gap between ion and neutron irradiation damage rates. The analysis of this data will provide a comparison to the same heat of material irradiated in a test reactor and through this, provide a path for qualifying materials for service at high doses using ion irradiation as a surrogate to reactor irradiation.
추가 정보
| 필드 | 값 |
|---|---|
| Abstract | Prediction of material response to high irradiation damage levels is a key challenge facing the nuclear industry for the life extension of current reactors and the development of advanced Gen IV reactors. The evolution of the irradiation induced microstructure and microstructure-related degradation modes must be understood for reliable materials performance at high displacements per atom (dpa) and high temperatures (> 400°C). Ion irradiation is the only viable means to conduct accelerated materials evaluation using high damage rates to achieve high dpa with relatively low cost and little to no induced radioactivity. Challenges to the implementation of ion irradiation as a surrogate for neutron irradiation include accounting for damage rate effects, accounting for transmutation and the lack of data to establish the equivalence. This work aims to address the effect of irradiation damage rate on the microstructure of a ferritic-martensitic steel T91 and generate data to compare with reactor irradiation. T91 is one of the candidate materials for high dose structural components because of its resistance to swelling compared to austenitic steels. Compared to austenitic steels, little work has been done on the radiation-induced segregation (RIS) of alloying elements with existing work focusing on Cr and Ni segregation. RIS of interstitial impurities can have significant consequences for grain boundary embrittlement. Precipitation of secondary phases act as barriers to dislocation motion and can lead to additional embrittlement. The objective of this study is to develop an understanding of the effect of irradiation damage rate on the microstructural evolution of the Fe9Cr steel T91 focusing on solute clustering and segregation to grain boundaries. Bars of T91 heat 30176 were irradiated using the dual-beam configuration at the Michigan Ion Beam Laboratory at the University of Michigan using 5 MeV Fe2+ ions and simultaneously injected with energy degraded 2.1-2.15 MeV He2+ ions to simulate gas buildup to 16.6 dpa at 600 nm depth from the surface at 445°C. The irradiations were conducted with damage rates ranging from 5 x 10-5 dpa/s to 4 x 10-3 dpa/s with the helium injection rate held at 0.22 appm He/dpa and the samples are ready for analysis. Measurements of RIS and precipitating clusters can be performed using transmission electron microscopy (TEM) with a high angle double tilt holder to rotate the boundary to edge-on conditions and an accurate, high count EDS system for elemental composition mapping. The FEI Talos F200X S/TEM at LAMDA is ideal for this measurement and was used for characterization of BOR-60 irradiated T91. The period of performance is estimated at 7 working days of instrument time. The outcomes of this RTE will provide quantitative RIS profiles and Ni/Si cluster size and density across nearly two orders of magnitude in damage rate, partially spanning the gap between ion and neutron irradiation damage rates. The analysis of this data will provide a comparison to the same heat of material irradiated in a test reactor and through this, provide a path for qualifying materials for service at high doses using ion irradiation as a surrogate to reactor irradiation. |
| Award Announced Date | 2019-02-08T00:00:00 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | Stephen Taller |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1624 |