NSUF 20-3032: Microstructural Characterization of Neutron Irradiated HT-UPS steel to Support High-energy X-ray Studies
High-temperature ultrafine precipitation strengthened (HT-UPS) steel is a candidate of structural material for advanced nuclear reactors because of its high-temperature strength and creep resistance. However, little is known regarding its irradiation response. In the present research, HT-UPS steel samples were previously neutron irradiated up to ~0.3 dpa at ~600℃ and were investigated pre- and post-neutron irradiation using non-destructive high-energy X-ray techniques such as far-field high-energy diffraction microscopy (FF-HEDM) and micro-computed tomography (µ-CT). Grain count increase, lattice shrinkage, cavity/precipitate increase and cavity/precipitate coarsening were observed in these experiments. The current literature indicates the presence of various sub-micro and nanometer scale defect structures up to a dose of 3 dpa and a temperature of 700℃. Based on this, it can be hypothesized that the dislocation microstructures can rearrange to form low angle grain boundaries and act as nucleation sites for recrystallization of new grains and thus, increase the grain count. Precipitates and grain boundaries can act as efficient sinks for interstitials, thus lead to lattice shrinkage because of the residual vacancies. Moreover, the precipitates tend to nucleate at the dislocations (as nucleation sites) and act as annihilation sites for vacancies and interstitials. Thus, the current literature and our present research combine to show some relevant microstructural observations related to assessment of irradiation tolerance of HT-UPS steel. However, high-energy X-ray techniques have limitations with respect to the indexing and measuring sizes of small and deformed grains and thus can provide only a few micrometer resolution (~10 μm). In addition, grain shapes and efficient differentiation between precipitates and cavities are not provided. Thus, a comparison of these results with higher resolution techniques can establish the confidence, validate, and provide better insight. Shielded FEI Helios dual-beam SEM-plasma FIB equipment, located in Irradiated Materials Characterization Laboratory (IMCL), Idaho National Laboratory (INL), will be used for the proposed work to capture EBSD grain maps and EDS scans for control and ~0.3 dpa irradiated HT-UPS samples. A “U-pattern” milling will be performed to create a block of interest with the dimension ~200 μm x ~200 μm x ~100 μm, from the samples. A serial sectioning approach will be utilized to sequentially mill and scan the surface of the blocks. A layer of 500 nm will be milled and an approximate size of 200 μm x 200 μm with 0.5 μm step size will be scanned on at least 20 layers of control and 40 sections of irradiated samples. 2D crystallographic orientation maps and EDS spectra will be generated for the scanned regions. These set of investigations can be accomplished over a span of 8 days. Each sample will be allocated with 4 days, of which the carving of the block can be accomplished in 0.5 days and the EBSD/EDS data can be collected in the remaining 3.5 days. “Slice-n-View” software will be utilized to dynamically reconstruct the 3D grain maps. Ultimately, SEM/EBSD/EDS and HEDM in a combination allow for better understanding of grain level neutron irradiation damage in HT-UPS.
Additional Info
| Field | Value |
|---|---|
| Abstract | High-temperature ultrafine precipitation strengthened (HT-UPS) steel is a candidate of structural material for advanced nuclear reactors because of its high-temperature strength and creep resistance. However, little is known regarding its irradiation response. In the present research, HT-UPS steel samples were previously neutron irradiated up to ~0.3 dpa at ~600℃ and were investigated pre- and post-neutron irradiation using non-destructive high-energy X-ray techniques such as far-field high-energy diffraction microscopy (FF-HEDM) and micro-computed tomography (µ-CT). Grain count increase, lattice shrinkage, cavity/precipitate increase and cavity/precipitate coarsening were observed in these experiments. The current literature indicates the presence of various sub-micro and nanometer scale defect structures up to a dose of 3 dpa and a temperature of 700℃. Based on this, it can be hypothesized that the dislocation microstructures can rearrange to form low angle grain boundaries and act as nucleation sites for recrystallization of new grains and thus, increase the grain count. Precipitates and grain boundaries can act as efficient sinks for interstitials, thus lead to lattice shrinkage because of the residual vacancies. Moreover, the precipitates tend to nucleate at the dislocations (as nucleation sites) and act as annihilation sites for vacancies and interstitials. Thus, the current literature and our present research combine to show some relevant microstructural observations related to assessment of irradiation tolerance of HT-UPS steel. However, high-energy X-ray techniques have limitations with respect to the indexing and measuring sizes of small and deformed grains and thus can provide only a few micrometer resolution (~10 μm). In addition, grain shapes and efficient differentiation between precipitates and cavities are not provided. Thus, a comparison of these results with higher resolution techniques can establish the confidence, validate, and provide better insight. Shielded FEI Helios dual-beam SEM-plasma FIB equipment, located in Irradiated Materials Characterization Laboratory (IMCL), Idaho National Laboratory (INL), will be used for the proposed work to capture EBSD grain maps and EDS scans for control and ~0.3 dpa irradiated HT-UPS samples. A “U-pattern” milling will be performed to create a block of interest with the dimension ~200 μm x ~200 μm x ~100 μm, from the samples. A serial sectioning approach will be utilized to sequentially mill and scan the surface of the blocks. A layer of 500 nm will be milled and an approximate size of 200 μm x 200 μm with 0.5 μm step size will be scanned on at least 20 layers of control and 40 sections of irradiated samples. 2D crystallographic orientation maps and EDS spectra will be generated for the scanned regions. These set of investigations can be accomplished over a span of 8 days. Each sample will be allocated with 4 days, of which the carving of the block can be accomplished in 0.5 days and the EBSD/EDS data can be collected in the remaining 3.5 days. “Slice-n-View” software will be utilized to dynamically reconstruct the 3D grain maps. Ultimately, SEM/EBSD/EDS and HEDM in a combination allow for better understanding of grain level neutron irradiation damage in HT-UPS. |
| Award Announced Date | 2020-02-05T14:13:27.577 |
| Awarded Institution | Idaho National Laboratory |
| Facility | Advanced Test Reactor |
| Facility Tech Lead | Alina Zackrone |
| Irradiation Facility | None |
| PI | Sri Tapaswi Nori |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 3032 |