Texture Evolution and Ultrafine Grain Formation in Cross-Cryo-Rolled Zircaloy-2

Abstract

The texture and mechanical properties of cross-rolled zircaloy-2 at 77 and 300 K were investigated. Cross-rolling at 77 K was performed to impart different thickness reductions of 25% and 50%, while at 300 K with 25%, 50%, 75% and 85% reductions to the sample. EBSD analysis of deformed sample showed that near-basal orientation is not deformed completely after 50% rolling reduction. The activation of prismatic silp, $\{ 11\bar{2}2\}$ contraction twin and $\{ 10\bar{1}2\}$ extension twin were evident from the deformed microstructure at 77 K. The propensity for activation of basal slip <a> at 77 K was also observed. The deformation of the sample at 300 K occurs by prismatic, basal <a> and pyramidal <c + a> slips, which were predicted by pole figures. After annealing, the tensile strengths (735 and 710 MPa) are almost the same for 50% cryo-cross-rolled and room-temperature cross-rolled zircaloy-2 with almost 2.7% difference in their ductility. KAM analysis of the deformed samples was made to estimate the stored strain energy and dislocation density. Annealing of deformed sample at 673 K for 30 min results in recrystallization, which leads to the formation of ultrafine grains.