NSUF 23-1845: 4D-STEM strain mapping of radiation induced defects
To characterize irradiation-induced defects, TEM is often the go-to microscope technique because it provides the excellent resolution needed to obtain details on the defect characteristics. In situ TEM mechanical testing and in situ TEM irradiation further expanded the TEM tool box for understanding dislocation-radiation-induced defect interactions and irradiation-induced defect evolution. With the most recent advancement in electron detectors, scanning transmission electron microscopes (STEMs) are now capable of collecting diffraction patterns at each probe position of a STEM image (i.e 4D-STEM.) 4D-STEM datasets provide the ability to measure local strain within a TEM foil with ~2 nm resolution. This capability has not yet been harnessed to study the local strain fields of radiation-induced defects. It is well known that the mechanical stability of the radiation-induced defects can influence the deformation response. However, one outstanding question remaining in the nuclear materials community is how the internal strain associated with these defects influences the deformation and failure response of the irradiated materials. Previous theoretical analyses have shown that the different defect types possess unique local elastic-strain signatures. Recent dislocation dynamics simulation have revealed that the elastic field around defects can control the degree of dislocation climb, hence the creep response of the materials. In particular, the knowledge of the defects’ internal strains can help to better explain how the different defect populations dictate the resulting microscopic dislocation-defect interactions (e.g. cross-slip, shearing, Orowan looping) and macroscopic properties (e.g. creep rate, ductility.) This proposal will focus on understanding and improving the sensitivity of 4D-STEM strain mapping for irradiation-induced defects. We will utilize high temperature in situ irradiation to create well-controlled defect types with known populations and sizes. The following questions regarding 4D-STEM strain-mapping sensitivity will be addressed: can 4D-STEM strain-mapping resolve (a) small defects embedded within the TEM foil (signal-to-background ratio effect), (b) local field of defects that exhibit both tensile and compressive nature (e.g. dislocation loops), and (c) short-range strain fields (bubbles)? We will perform 4D-STEM strain mapping on radiation-induced unfaulted and faulted loops (of different sizes) as well as He bubbles to answer the proposed questions. Furthermore, dislocation dynamics simulations of those defects’ strain fields will be used to compare against the experimental results, to elucidate on the 4D-STEM sensitivity. If the proposed research is successful, we will expand the TEM toolbox for irradiated materials; in particular, we will have the ability to reliably map strain fields of radiation-induced defects at very high resolution for the first time. By coupling with in situ TEM and bulk mechanical testing, the role of defects’ local strain fields can be directly correlated with the plastic deformation response across length scales. This will advance our understanding of the intricate relationship between defects and the mechanical properties of irradiated materials. Given the significant development and rapid adoption of 4D-STEM techniques, the proposed research will have lasting impact on the field of advanced TEM characterization and will open new research avenues to study radiation-induced defect dynamics in situ TEM.
Additional Info
| Field | Value |
|---|---|
| Abstract | To characterize irradiation-induced defects, TEM is often the go-to microscope technique because it provides the excellent resolution needed to obtain details on the defect characteristics. In situ TEM mechanical testing and in situ TEM irradiation further expanded the TEM tool box for understanding dislocation-radiation-induced defect interactions and irradiation-induced defect evolution. With the most recent advancement in electron detectors, scanning transmission electron microscopes (STEMs) are now capable of collecting diffraction patterns at each probe position of a STEM image (i.e 4D-STEM.) 4D-STEM datasets provide the ability to measure local strain within a TEM foil with ~2 nm resolution. This capability has not yet been harnessed to study the local strain fields of radiation-induced defects. It is well known that the mechanical stability of the radiation-induced defects can influence the deformation response. However, one outstanding question remaining in the nuclear materials community is how the internal strain associated with these defects influences the deformation and failure response of the irradiated materials. Previous theoretical analyses have shown that the different defect types possess unique local elastic-strain signatures. Recent dislocation dynamics simulation have revealed that the elastic field around defects can control the degree of dislocation climb, hence the creep response of the materials. In particular, the knowledge of the defects’ internal strains can help to better explain how the different defect populations dictate the resulting microscopic dislocation-defect interactions (e.g. cross-slip, shearing, Orowan looping) and macroscopic properties (e.g. creep rate, ductility.) This proposal will focus on understanding and improving the sensitivity of 4D-STEM strain mapping for irradiation-induced defects. We will utilize high temperature in situ irradiation to create well-controlled defect types with known populations and sizes. The following questions regarding 4D-STEM strain-mapping sensitivity will be addressed: can 4D-STEM strain-mapping resolve (a) small defects embedded within the TEM foil (signal-to-background ratio effect), (b) local field of defects that exhibit both tensile and compressive nature (e.g. dislocation loops), and (c) short-range strain fields (bubbles)? We will perform 4D-STEM strain mapping on radiation-induced unfaulted and faulted loops (of different sizes) as well as He bubbles to answer the proposed questions. Furthermore, dislocation dynamics simulations of those defects’ strain fields will be used to compare against the experimental results, to elucidate on the 4D-STEM sensitivity. If the proposed research is successful, we will expand the TEM toolbox for irradiated materials; in particular, we will have the ability to reliably map strain fields of radiation-induced defects at very high resolution for the first time. By coupling with in situ TEM and bulk mechanical testing, the role of defects’ local strain fields can be directly correlated with the plastic deformation response across length scales. This will advance our understanding of the intricate relationship between defects and the mechanical properties of irradiated materials. Given the significant development and rapid adoption of 4D-STEM techniques, the proposed research will have lasting impact on the field of advanced TEM characterization and will open new research avenues to study radiation-induced defect dynamics in situ TEM. |
| Award Announced Date | 2023-02-08T10:48:12.133 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Hi Vo |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 4519 |