Understanding irradiation-induced nanoprecipitation in zirconium alloys using parallel TEM and APT

摘要

We investigate nano-scale irradiation-induced precipitation in a Zr-Sn-Fe-Cr-Ni-alloy (Zircaloy-2) by combining atom probe tomography (APT) for chemical detail with scanning transmission electron microscopy (STEM) and high resolution energy dispersive X-ray (EDX) spectroscopy for wider context and complimentary and correlative TEM diffraction techniques for crystallographic relationships. We find that Fe- and Cr-rich nano-rods precipitate in Zircaloy-2 following proton irradiation at 350 degrees C to a low dose of similar to 2 dpa. The long-axis of the nano-rods are aligned in a direction 12-15 degrees from the Zr matrix 0001 , align in the basal plane and are of width 1.5-5 nm. Smaller rods are of APT-determined composition Zr-4(Fe0.67Cr0.33), tending towards Zr-3(Fe0.69Cr0.31) as the rod volume increases to similar to 400 nm(3), in agreement with STEM-EDX determination of composition resembling that of Zr3Fe with Cr replacing some of the Fe. The Fe/Cr ratio has been shown to increase with distance from the nearest partially-dissolved Zr(Fe,Cr)(2) phase particle. The nucleation of nano rods has implications for macroscopic irradiation-induced deformation phenomena, irradiation-induced hardening and the evolution of dislocation loops and other defects. (C) 2018 Published by Elsevier B.V.