NSUF 19-1747: Nano-precipitate Stability and a'-Precipitation in ODS and Wrought FeCrAl Alloys
The primary objectives of this project are (1) to track the stability of ODS FeCrAl nanoprecipitates and (2) to assess the ability for the nanoscale precipitate distribution in the ODS FeCrAl alloy to impede the formation of Cr-rich α'-precipitates that contribute significantly to hardening in wrought FeCrAl alloys. In the context of these two project objectives, the only previous post-irradiation examination (PIE) work that has been conducted on lower-Cr (12 wt.%) ODS FeCrAl only reached 1.8 dpa in dose. The stability of the fine-scale precipitates will be a function of their resistance to ballistic dissolution in competition with the tendency for these precipitates to re-form through back-diffusion of solute atoms to the precipitates in an attempt to regain thermodynamic equilibrium in an irradiation environment. An additional layer of complexity exists for the Cr-rich α'-precipitates in the sense that irradiation-enhanced diffusion is supplementing the already thermodynamically favorable Fe-Cr unmixing during extended irradiation times consistent with higher dose irradiation campaigns. It is thus important to extend the previous results on low-dose irradiation to higher doses to more effectively probe these different aspects of nanoprecipitate stability. Specifically, this work involves the characterization of low-Cr ODS FeCrAl alloy 125YF (nominally Fe-12Cr-5.6Al) and other wrought FeCrAl alloys of similar composition (Fe-10Cr-6Al, Fe-13Cr-5Al, Fe-13Cr-5Al) after neutron irradiation to 7 dpa at 335°C, characteristic of the temperature regime expected in an LWR environment. A secondary 200°C irradiated specimen of 125YF is also included in the sample matrix to provide information regarding the aforementioned ballistic dissolution vs. solute back-diffusion argument for nanoprecipitate stability. To perform the PIE, this project requires the use of focused ion beam (FIB) sample preparation, as well as atom probe tomography (APT). APT analysis provides a way not only to quantify the size and number density of nanoprecipitates, but it also allows for the visualization of the precipitate morphologies. The precipitate size, number density, and composition results obtained from these techniques will indicate the irradiation stability of nanoprecipitates in the Fe-12Cr-5.6Al+FeO+Y2O3 (125YF) alloy to higher irradiation doses. Furthermore, the APT results will also help to determine the effects the fine scale ODS FeCrAl nanoprecipitate population has on Cr segregation and precipitation in this class of alloys. The information then has wide reaching impacts on ferrous-based alloy development for the nuclear industry, specifically with regards to the applicability of ODS FeCrAl alloys as an ATF cladding concept. This project is predicted to take no more than 6 months to complete. Fabrication of APT samples using FIB techniques is estimated to take no more than 1 month. APT data collection is expected to take less than 1 month after sample preparation. Data analysis and reporting will take approximately 4 months from the date of initial data collection.
Additional Info
| Field | Value |
|---|---|
| Abstract | The primary objectives of this project are (1) to track the stability of ODS FeCrAl nanoprecipitates and (2) to assess the ability for the nanoscale precipitate distribution in the ODS FeCrAl alloy to impede the formation of Cr-rich α'-precipitates that contribute significantly to hardening in wrought FeCrAl alloys. In the context of these two project objectives, the only previous post-irradiation examination (PIE) work that has been conducted on lower-Cr (12 wt.%) ODS FeCrAl only reached 1.8 dpa in dose. The stability of the fine-scale precipitates will be a function of their resistance to ballistic dissolution in competition with the tendency for these precipitates to re-form through back-diffusion of solute atoms to the precipitates in an attempt to regain thermodynamic equilibrium in an irradiation environment. An additional layer of complexity exists for the Cr-rich α'-precipitates in the sense that irradiation-enhanced diffusion is supplementing the already thermodynamically favorable Fe-Cr unmixing during extended irradiation times consistent with higher dose irradiation campaigns. It is thus important to extend the previous results on low-dose irradiation to higher doses to more effectively probe these different aspects of nanoprecipitate stability. Specifically, this work involves the characterization of low-Cr ODS FeCrAl alloy 125YF (nominally Fe-12Cr-5.6Al) and other wrought FeCrAl alloys of similar composition (Fe-10Cr-6Al, Fe-13Cr-5Al, Fe-13Cr-5Al) after neutron irradiation to 7 dpa at 335°C, characteristic of the temperature regime expected in an LWR environment. A secondary 200°C irradiated specimen of 125YF is also included in the sample matrix to provide information regarding the aforementioned ballistic dissolution vs. solute back-diffusion argument for nanoprecipitate stability. To perform the PIE, this project requires the use of focused ion beam (FIB) sample preparation, as well as atom probe tomography (APT). APT analysis provides a way not only to quantify the size and number density of nanoprecipitates, but it also allows for the visualization of the precipitate morphologies. The precipitate size, number density, and composition results obtained from these techniques will indicate the irradiation stability of nanoprecipitates in the Fe-12Cr-5.6Al+FeO+Y2O3 (125YF) alloy to higher irradiation doses. Furthermore, the APT results will also help to determine the effects the fine scale ODS FeCrAl nanoprecipitate population has on Cr segregation and precipitation in this class of alloys. The information then has wide reaching impacts on ferrous-based alloy development for the nuclear industry, specifically with regards to the applicability of ODS FeCrAl alloys as an ATF cladding concept. This project is predicted to take no more than 6 months to complete. Fabrication of APT samples using FIB techniques is estimated to take no more than 1 month. APT data collection is expected to take less than 1 month after sample preparation. Data analysis and reporting will take approximately 4 months from the date of initial data collection. |
| Award Announced Date | 2019-05-14T15:58:47.213 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Caleb Massey |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1747 |