Effect of initial orientation on dynamic recrystallization of a zirconium alloy during hot deformation

The present study investigated the influence of the initial orientation on the dynamic recrystallization (DRX) behavior of a Zr-1Sn-0.3Nb alloy. A hot-rolled and annealed Zr sheet was compressed along two directions: along the normal direction so that the grains' < c >-axis was nearly parallel to the loading direction (0 sample) and along the transverse direction so that the grains' < c >-axis was nearly perpendicular to the loading direction (90 degrees sample). The samples were compressed at 700 degrees C at a strain rate of 1 s(-1). The microstructures at different strains were characterized by the electron backscatter diffraction (EBSD) technique, and conventional dislocation analysis using transmission electron microscope (TEM) was performed. A threshold value of grain orientation spread (GOS) equaled to 5 degrees was used to distinguish the dynamically recrystallized grains from the deformed matrix. The results revealed that the DRX behavior strongly depended on the initial orientation. The Schmid factor analysis and TEM observation confirmed that pyramidal < c + a > slip operated from the first stage of deformation in the 0 degrees sample but not in the 90 degrees sample. For the 0 degrees sample, in the early and medium stages of deformation, due to the high stored energy caused by the operation of pyramidal < c + a > slip, DDRX was mainly contributed to the formation of new fine grains. However, in the later stage of deformation, the DRX mechanism changed from DDRX to CDRX. In the 90 degrees sample, although DDRX featured by grain boundary bulging occurred, the main DRX mechanism was CDRX in the whole deformation processing. Moreover, texture induced hardening in the early stage of deformation hides the softening induced by DDRX.