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ASTM Selected Technical Papers
Zirconium in the Nuclear Industry: 20th International Symposium
Editor
Suresh K. Yagnik
Suresh K. Yagnik
Symposium Chairperson and STP Editor
1
Electric Power Research Institute (EPRI)
,
Palo Alto, CA,
US
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Michael Preuss
Michael Preuss
Symposium Chair and STP Editor
2
The University of Manchester Manchester
,
GB
;
Monash University
,
Clayton/Melbourne,
AU
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ISBN:
978-0-8031-7737-6
No. of Pages:
928
Publisher:
ASTM International
Publication date:
2023

The microstructural development of Zircaloy-4 during recrystallization annealing has been studied in specimens that have undergone relatively small strains (approximately less than 0.15). Although important work has been completed to understand the formation of coarse grains in Zircaloy in recent years, the objective of this work has been to provide a quantification of the as-deformed state to enable the development of a quantitative relation to the recrystallized condition. Electron backscatter diffraction was used to characterize the as-deformed and annealed conditions of uniaxially compressed specimens cut from a Zircaloy-4 plate. The condition of the microstructure is characterized for the region in which the partially recrystallized sporadic coarse grains form. Initiation of recrystallization is observed above thresholds of in-grain misorientation (1.0–1.5° grain orientation spread) and twin fraction (∼2%). This threshold behavior (the twin-fraction threshold in particular) is consistent across specimens deformed along different principal directions (longitudinal and transverse). Above these thresholds, the grain size is observed to rise to a peak and subsequently decrease with further strain. Similar grain size variation is observed as a function of strain between specimens compressed along different plate directions despite distinct differences in the way in which deformation has been accommodated between the two cases (relative activity of slip and twinning). An interrupted annealing study has attempted to directly observe nucleation and growth events to relate these to the observed thresholds. Initial results have shown behavior that is consistent with the strain-induced boundary-migration mechanism proposed by other workers.

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