Recovery of cold-work in extruded Zr-2.5 wt% Nb

X-ray line broadening measurements and electron microscopy have been used to characterize the dislocation substructures in extruded, cold-worked and stress relieved Zr-2.5 wt% Nb pressure tube materials. Variation in dislocation substructure deduced from the X-ray line broadening measurements give good agreement with thin film observations. Recovery of cold-work occurs in three 'stages' in Zr-2.5 wt% Nb. Between 575 and 725 K the dislocation density decreases from approximately 1.5-1.8 x 1015m-2 to approximately 3-4 x 1014m-2 with little change in sub-grain size or dislocation arrangement below 725 K. From 725 K to 875 K the sub-grain size increases from <100nm to approximately 400nm while the dislocation density decreases slowly to approximately 1.4-1.7 x 1014m-2. Above 875 K the sub-grain size increases to >= 800 nm, some grain growth occurs and only a few well defined dislocation networks remain. As-extruded Zr-2.5 wt% Nb has a sub-grain size of approximately 600 nm and a dislocation density of approximately 8 x 1013 m-2. The implications of the measurements are discussed. (Auth.)