NSUF 23-4756: Understanding the role of nanostructuring in enhancing phase stability of 304 austenitic steel during irradiation via in-situ ion irradiation in transmission electron microscope
The proposed project will involve in-situ ion irradiation of coarse-grained (CG), ultra-fine grained (UFG), and nanocrystalline (NC) stainless steel 304 in a transmission electron microscope (TEM) at different temperatures, as well as examination of the irradiation-induced microstructure changes in these samples in real time and post irradiation. 300 series austenitic steels undergo irradiation-induced polymorphic phase transformation (PMPT) from γ-austenite to α-ferrite resulting in the reduction of ductility and corrosion resistance, which together leads to stress corrosion cracking (SCC). Our recent study has observed enhanced resistance to irradiation-induced phase transformation in nanostructured 300 series stainless steels as opposed to their CG counterpart. Explanations for the influence of nanostructuring on the inhibition of phase transformation have been made in our previous study, however, they were derived from ex-situ characterization. In order to better understand the underlying mechanisms, it is important to address the following questions: 1) How does irradiation-induced defect accumulation vary with grain size? 2) How do such defects interact with grain boundaries (GBs) in nanostructured 304? 3) How does irradiation-induced solute segregation and precipitation vary with grain size? We hypothesize that hindered irradiation-induced segregation of Ni and decreased precipitation of Ni-rich precipitates (Ni is an austenite stabilizer), as well as reduced irradiation-induced dislocation loops and accordingly strain, in UFG and NC 304 as compared to those in CG 304, will impede the irradiation-induced austenite to ferrite transformation; the reduced irradiation effects in nanostructured 304 is owing to the increased density of GBs, which serve as sinks to absorb irradiation-induced defects. The main irradiation defects we will study include irradiation-induced cavities and dislocation loops, and the main irradiation effects to be investigated encompass irradiation-induced solute segregation and precipitation, PMPT, and grain growth. The project will only involve three sets of samples (CG, UFG, and NC 304) and a relatively small set of well-designed experiments despite the study of several phenomena. In-situ ion irradiation in TEM is a powerful technique that provides real-time information about the microstructural response to irradiation, which is anticipated to shed light onto the underlying mechanisms for irradiation effects. An extremely limited number of in-situ irradiation studies of CG 304 were found in the literature, and this proposed work will be the first investigation, using in-situ ion irradiation in TEM, to study the irradiation-induced PMPT in UFG and NC 304. The effects of grain size and temperature on the irradiation behavior of UFG and NC 304 will be investigated, focusing on irradiation-induced solute segregation and precipitation, PMPT and grain growth, and the underlying mechanisms for the irradiation effects will be studied via in-situ and ex-situ detailed microstructural examination. The establishment of irradiation performance of nanostructured austenitic steels with appealing properties will impact the life extension of current reactors and the development of advanced reactors. Hence, the proposed research is highly relevant to DOE-NE’s Light Water Reactor Sustainability Program and Advanced Reactor Technologies Program.
Additional Info
| Field | Value |
|---|---|
| Abstract | The proposed project will involve in-situ ion irradiation of coarse-grained (CG), ultra-fine grained (UFG), and nanocrystalline (NC) stainless steel 304 in a transmission electron microscope (TEM) at different temperatures, as well as examination of the irradiation-induced microstructure changes in these samples in real time and post irradiation. 300 series austenitic steels undergo irradiation-induced polymorphic phase transformation (PMPT) from γ-austenite to α-ferrite resulting in the reduction of ductility and corrosion resistance, which together leads to stress corrosion cracking (SCC). Our recent study has observed enhanced resistance to irradiation-induced phase transformation in nanostructured 300 series stainless steels as opposed to their CG counterpart. Explanations for the influence of nanostructuring on the inhibition of phase transformation have been made in our previous study, however, they were derived from ex-situ characterization. In order to better understand the underlying mechanisms, it is important to address the following questions: 1) How does irradiation-induced defect accumulation vary with grain size? 2) How do such defects interact with grain boundaries (GBs) in nanostructured 304? 3) How does irradiation-induced solute segregation and precipitation vary with grain size? We hypothesize that hindered irradiation-induced segregation of Ni and decreased precipitation of Ni-rich precipitates (Ni is an austenite stabilizer), as well as reduced irradiation-induced dislocation loops and accordingly strain, in UFG and NC 304 as compared to those in CG 304, will impede the irradiation-induced austenite to ferrite transformation; the reduced irradiation effects in nanostructured 304 is owing to the increased density of GBs, which serve as sinks to absorb irradiation-induced defects. The main irradiation defects we will study include irradiation-induced cavities and dislocation loops, and the main irradiation effects to be investigated encompass irradiation-induced solute segregation and precipitation, PMPT, and grain growth. The project will only involve three sets of samples (CG, UFG, and NC 304) and a relatively small set of well-designed experiments despite the study of several phenomena. In-situ ion irradiation in TEM is a powerful technique that provides real-time information about the microstructural response to irradiation, which is anticipated to shed light onto the underlying mechanisms for irradiation effects. An extremely limited number of in-situ irradiation studies of CG 304 were found in the literature, and this proposed work will be the first investigation, using in-situ ion irradiation in TEM, to study the irradiation-induced PMPT in UFG and NC 304. The effects of grain size and temperature on the irradiation behavior of UFG and NC 304 will be investigated, focusing on irradiation-induced solute segregation and precipitation, PMPT and grain growth, and the underlying mechanisms for the irradiation effects will be studied via in-situ and ex-situ detailed microstructural examination. The establishment of irradiation performance of nanostructured austenitic steels with appealing properties will impact the life extension of current reactors and the development of advanced reactors. Hence, the proposed research is highly relevant to DOE-NE’s Light Water Reactor Sustainability Program and Advanced Reactor Technologies Program. |
| Award Announced Date | 2023-09-14T13:35:29.323 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Wei-Ying Chen |
| Irradiation Facility | None |
| PI | Haiming Wen |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | None |