NSUF 16-737: Microstructural recovery in irradiated nanostructured ferritic alloys
I have samples of 14YWT nanostructured ferritic alloy that have been ion-irradiated at cryogenic temperature. As a result, in the ~1500 nm deep irradiated zone, the grain boundary segregation (typically Cr-W) and the nano-oxide particles (Y-Ti-O, along with smaller amounts of Al-Y-O and Ti(O,C,N) ) have been homogenized into the matrix, leaving a chemically homogeneous single-phase structure. (This has been verified by atom probe and scanning/transmission electron microscopy [S/TEM]). This is a very non-equilibrium situation; solutes such as Y and Ti are thermodynamically driven to combine with oxygen and precipitate out of the supersaturated matrix, and other solutes such as Cr and W (along with significant precipitation) will be thermodynamically driven to go to the grain boundaries. Essentially, this structure has cryogenically locked-in the structure arising after the quench of the damage cascades, resulting in a situation that can be used to explore the underlying physics of recovery from radiation damage. I hypothesize that re-heating the as-irradiated structure will result in precipitation of the excess solutes and formation of a structure similar to the original, as-fabricated state. What is not clear is how this recovered structure will differ from the as-fabricated state, and quantitative analysis of the differences between the as-fabricated and recovered state should help inform physical models of the recovery of radiation damage in structural materials. Our overarching scientific goal is to measure quantitatively the differences in nano-oxide and grain boundary segregation in the as-fabricated material vs. the annealed + recovered material, with strong attention to the influence of grain boundary character (high-angle, low-angle, or coincident-site-lattice special boundary). Specific technical objectives are to (1) perform focused ion beam preparation of the cryogenically irradiated 14YWT. (2) Use transmission Kikuchi diffraction (tKD) and S/TEM to measure the grain boundary character and chemistry of a large ensemble of grains in the irradiated and unirradiated material. (3) Use in-situ heating in the S/TEM to drive recovery of the ion irradiated material. (4) Repeat the tKD and S/TEM measurements on the exact same areas to determine, first, the differences between the as-fabricated and damage-recovered states, and second, to determine the influence of grain boundary character on damage. The impact on the scientific state of knowledge will be to provide direct quantitative measurements of undamaged, radiation-damaged, and thermally-recovered states. This comprehensive and high-resolution data will provide the fundamental microstructural physics for expanding and validating models of radiation damage and recovery in complex structural alloys.
Additional Info
| Field | Value |
|---|---|
| Abstract | I have samples of 14YWT nanostructured ferritic alloy that have been ion-irradiated at cryogenic temperature. As a result, in the ~1500 nm deep irradiated zone, the grain boundary segregation (typically Cr-W) and the nano-oxide particles (Y-Ti-O, along with smaller amounts of Al-Y-O and Ti(O,C,N) ) have been homogenized into the matrix, leaving a chemically homogeneous single-phase structure. (This has been verified by atom probe and scanning/transmission electron microscopy [S/TEM]). This is a very non-equilibrium situation; solutes such as Y and Ti are thermodynamically driven to combine with oxygen and precipitate out of the supersaturated matrix, and other solutes such as Cr and W (along with significant precipitation) will be thermodynamically driven to go to the grain boundaries. Essentially, this structure has cryogenically locked-in the structure arising after the quench of the damage cascades, resulting in a situation that can be used to explore the underlying physics of recovery from radiation damage. I hypothesize that re-heating the as-irradiated structure will result in precipitation of the excess solutes and formation of a structure similar to the original, as-fabricated state. What is not clear is how this recovered structure will differ from the as-fabricated state, and quantitative analysis of the differences between the as-fabricated and recovered state should help inform physical models of the recovery of radiation damage in structural materials. Our overarching scientific goal is to measure quantitatively the differences in nano-oxide and grain boundary segregation in the as-fabricated material vs. the annealed + recovered material, with strong attention to the influence of grain boundary character (high-angle, low-angle, or coincident-site-lattice special boundary). Specific technical objectives are to (1) perform focused ion beam preparation of the cryogenically irradiated 14YWT. (2) Use transmission Kikuchi diffraction (tKD) and S/TEM to measure the grain boundary character and chemistry of a large ensemble of grains in the irradiated and unirradiated material. (3) Use in-situ heating in the S/TEM to drive recovery of the ion irradiated material. (4) Repeat the tKD and S/TEM measurements on the exact same areas to determine, first, the differences between the as-fabricated and damage-recovered states, and second, to determine the influence of grain boundary character on damage. The impact on the scientific state of knowledge will be to provide direct quantitative measurements of undamaged, radiation-damaged, and thermally-recovered states. This comprehensive and high-resolution data will provide the fundamental microstructural physics for expanding and validating models of radiation damage and recovery in complex structural alloys. |
| Award Announced Date | 2016-12-16T07:44:12.777 |
| Awarded Institution | Massachusetts Institute of Technology |
| Facility | Massachusetts Institute of Technology Reactor |
| Facility Tech Lead | Gordon Kohse, Kory Linton |
| Irradiation Facility | None |
| PI | Chad Parish |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 737 |