Impact of an Applied Stress on C-Component Loops under Zr Ion Irradiation in Recrystallized Zircaloy-4 and M5®

Recrystallized zirconium alloys are used as cladding and structural components materials for the Pressurized Water Reactor (PWR) fuel assemblies. Under neutron irradiation, they undergo deformation and especially irradiation growth which takes place in the absence of any applied stress. This phenomenon, referred as "stress-free" growth, accelerates for high irradiation doses. The breakaway growth is correlated to the formation of a specific irradiation defect: the c-component dislocation loops.In the present work, 600 keV Zr+ ion irradiations at 573 K were performed on recrystallized Zircaloy-4 and M5 (R)(1) in order to investigate the impact of a macroscopic stress, applied under irradiation, on the evolution of c-loop microstructure. Two loading histories were considered, using a four point bending device specifically designed to apply a tensile or a compressive stress under irradiation. During the first loading experiment, the external stress was applied at an early stage of irradiation. Transmission Electron Microscopy (TEM) observations showed that the initial applied stress has no effect on the incubation dose of c-loops. For the second loading experiment, the macroscopic stress was applied when c-loops are already created. A clear but slight effect of the applied stress on the evolution of the c-loop microstructure was observed on both recrystallized Zircaloy-4 and M5 (R). Indeed, the c-loop linear density is lower when a tensile stress is applied parallel to the c-axis, which is in good agreement with the Stress Induced Preferential Absorption (SIPA) mechanism. (C) 2015 Elsevier B.V. All rights reserved.