Mechanical behaviour and microstructural characterizations of ultrafine grained Zircaloy-2 processed by cryorolling

The mechanical properties and microstructural characteristics of ultrafine grained Zircaloy-2 processed by cryorolling (CR) were investigated in the present work. The solutionised Zircaloy-2 was rolled at liquid nitrogen temperature (77 K) with different thickness reductions (25-85%). The dislocation density (p) in the cryorolled Zircaloy-2 increases with increasing true strain due to the suppression of dynamic recovery. EBSD analysis of CR Zircaloy-2 revealed initial strain hardening, which has occurred due to activation of {10(1)over bar2}<(1)over bar011 > tensile and {11(2)overbar2}<(1)overbar(1)overbar23) compressive twins during deformation of samples up to 50% strain. The prismatic and basal slips were activated during subsequent deformation. The fraction of low angle boundaries has increased with increasing true strain up to 50% thickness reduction but the fraction of high angle grain boundaries has increased for CR85% alloy. The CR 85% alloy showed hardness and yield strength values of 282 HV and 891 MPa, respectively. The annealed CR 85% alloy showed higher ductility (9.5% and 11.2% in rolling and transverse direction, respectively) as compared to CR 85% alloy. The annealed Zircaloy-2 showed heterogeneous microstructure consisting of ultrafine grains and nanograins. (C) 2014 Elsevier B.V. All rights reserved.