NSUF 21-4350: Correlative TEM and APT approach to elucidate hydride morphology and behavior in ex-service pressure tube material

Through this RTE, we propose to examine ex-service hydrides in Zr-2.5Nb pressure tube material using a correlative APT and TEM method where TEM analysis is followed by destructive APT analysis on the same specimen. The authors are not aware of any previous correlative work of this type on ex-service hydrides. The significant advantage of using CANDU reactor material is that deuterium is the dominant hydrogen isotope, allowing for the APT analysis to separate the deuterium in the sample from the hydrogen contamination in the vacuum chamber without artificial hydriding. The analyses outlined in must be confirmed using more representative material to ensure the discussion and conclusions apply to in-reactor hydrides. Additionally, a large number of hydrides should be analyzed to assess the hydride to hydride variation within a single sample and ensure good statistics given the small volumes involved. Combining APT and TEM analysis on same specimen allows to accomplish the best of both techniques to elucidate features such as dislocation for their chemical segregation and to determine local structure, especially the hydride-matrix interface region. TEM is known to provide accurate crystallographic structure from the specimen with no distortion of 2D image, however, accurate chemical quantification is challenging. APT has ability to provide 3D element distribution in materials but it suffers from small field of view and ion trajectory aberrations near chemical and structural heterogeneities. Thus combining TEM and APT analysis on hydrides formed in Zr-2.5 alloy would provide detailed local microstructure and chemistry of different precipitates and further enhance understanding of hydride formation in Zr-Nb alloys. Further observation of hydride morphology and chemistry, specifically at hydride-matrix interfaces, using multiple techniques could help substantiate and extend the proposed correlations between dislocations (memory effect), solid solubility hysteresis, and the kinetics and thermodynamics of hydride formation.

Additional Info

Field	Value
Abstract	Through this RTE, we propose to examine ex-service hydrides in Zr-2.5Nb pressure tube material using a correlative APT and TEM method where TEM analysis is followed by destructive APT analysis on the same specimen. The authors are not aware of any previous correlative work of this type on ex-service hydrides. The significant advantage of using CANDU reactor material is that deuterium is the dominant hydrogen isotope, allowing for the APT analysis to separate the deuterium in the sample from the hydrogen contamination in the vacuum chamber without artificial hydriding. The analyses outlined in must be confirmed using more representative material to ensure the discussion and conclusions apply to in-reactor hydrides. Additionally, a large number of hydrides should be analyzed to assess the hydride to hydride variation within a single sample and ensure good statistics given the small volumes involved. Combining APT and TEM analysis on same specimen allows to accomplish the best of both techniques to elucidate features such as dislocation for their chemical segregation and to determine local structure, especially the hydride-matrix interface region. TEM is known to provide accurate crystallographic structure from the specimen with no distortion of 2D image, however, accurate chemical quantification is challenging. APT has ability to provide 3D element distribution in materials but it suffers from small field of view and ion trajectory aberrations near chemical and structural heterogeneities. Thus combining TEM and APT analysis on hydrides formed in Zr-2.5 alloy would provide detailed local microstructure and chemistry of different precipitates and further enhance understanding of hydride formation in Zr-Nb alloys. Further observation of hydride morphology and chemistry, specifically at hydride-matrix interfaces, using multiple techniques could help substantiate and extend the proposed correlations between dislocations (memory effect), solid solubility hysteresis, and the kinetics and thermodynamics of hydride formation.
Award Announced Date	2021-06-07T16:11:20.117
Awarded Institution	None
Facility	None
Facility Tech Lead	Alina Zackrone
Irradiation Facility	None
PI	Mukesh Bachhav
PI Email	[email protected]
Project Type	RTE
RTE Number	4350