NSUF 24-4849: Radiation Tolerance of MX-Type Precipitates Revealed Through In-Situ Ion Irradiations

Nanoprecipitates play a key role in preventing material degradation during irradiation by providing trapping sites for point defects and by pinning dislocations at elevated temperatures. Particularly, MX-type nanoprecipitation in advanced steels have been of interest to provide beneficial material properties for advanced fission reactors. However, the evolution of MX precipitation as a function of irradiation parameters has not been systematically studied, particularly effects leading to dissolution. In-situ TEM offers a unique ability to understand the dynamic effects of various irradiation parameters on precipitate behavior and saves time and resources as compared to ex-situ irradiations. No systematic study of precipitate dissolution using in-situ TEM investigations has been conducted and open questions remain on best practices and its applicability to precipitate behavior in bulk materials. In previous research, the effect of TEM lamella thickness has been shown to greatly affect both dislocation loop and cavity formation and evolution. If the TEM lamella is too thin, the free surfaces of the lamella act as the strongest sinks for point defects, preventing microstructural evolution that is correlated to bulk material evolution. The main outcome of this proposal will be guidance for systematic in-situ TEM ion irradiation studies of precipitate for advanced fission structural materials. This work will dynamically capture the effects of ballistic dissolution, damage cascade size and morphology, and back diffusion as a function of TEM sample thickness on the critical dose to dissolution of TiC nanoprecipitates in an advanced steel known as Castable Nanostructured Alloy – Heat Treatment 7 (CNA-HT7). CNA-HT7 has a high pre-existing distribution of TiC nanoprecipitates on the order of ~1021 m-3. This density will allow for in-situ precipitate imaging with the use of EFTEM Fe jump-ratio maps and DF-TEM images in low, medium, and high thickness areas of the specimens. The EFTEM jump-ratio technique is a well-established method for chemical mapping of precipitates, and previous unpublished work performed at MIBL by authors of this proposal has proved the ability to image nanoprecipitates in EFTEM during in-situ ion irradiation. In addition, STEM-EDS will be performed before and after irradiation for precipitate characterization. DF-TEM is a more conventional imaging technique enabling direct correlations on imaging method to the final quantitative results generated from this study. It is calculated that approximately 1-20 precipitates, 4-47 precipitates, and 6-68 precipitates will be observed in the regions of interest during in-situ irradiation in the low, medium, and high thickness areas, respectively. After the critical dose is established in samples at two temperatures, in-situ post-irradiation annealing (PIA) experiments at the irradiation temperature will allow for real-time observation of the thermodynamic pathways of the reprecipitation process and will assess the effects of free surfaces on reprecipitation. Imaging will be conducted at discrete time intervals for fine spatial and temporal resolution of the reprecipitation behavior. This work is expected to be completed by Quarter 4 of Fiscal year 2024.

추가 정보

필드	값
Award Announced Date	2024-02-02T12:16:44.14
Awarded Institution	Oak Ridge National Laboratory
Facility Tech Lead	Kevin Field
Irradiation Facility
PI	Weicheng Zhong
PI Email	[email protected]
Project Type	RTE
RTE Number	None