Grain fragmentation and twinning in deformed Zircaloy 2: Response to positron lifetime measurements

Microstructural developments in deformed Zircaloy 2 were studied using techniques ranging from positron annihilation spectroscopy (PAS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD). Grain fragmentation during plastic deformation, which is expected to involve dislocation realignment and recovery, showed a clear correlation with drop in mean PAS lifetime (tau(m)). An increased tau(m), on the other hand, was associated with annihilation of deformation twins. The deformation twins, (1 0 (1) over bar 2)<(1) over bar 0 1 1 > type tensile twins, were identified from axis-angle relationship: 94.8 degrees ((1) over bar 2 (1) over bar 0). A deviation of more than 5 degrees from the exact twin orientation relationship was considered as annihilation. Such annihilation, caused by developments of in-grain misorientations, is expected to involve accommodation through interfacial dislocations. Presence of such dislocations, and associated point defects, offers an explanation for the observed increase in tau(m). (C) 2009 Elsevier B.V. All rights reserved.