Grain refinement and solute distribution in Zircaloy-4 following high-pressure torsion.

Abstract

Zirconium (Zr) alloys such as Zircaloy-4 are widely used for structural components and fuel cladding in industrial nuclear fission applications. High-pressure torsion (HPT), a severe plastic deformation process, produces an ultra-fine grain structure with properties that may have benefits in the nuclear industry, but the microstructural implications of processing of Zr alloys using this technique have not yet been extensively explored. Here, electron microscopy and atom probe tomography were used to investigate the microstructure and solute distribution in an as-received Zircaloy-4 and a fine-grained HPT-processed sample. Fe segregates to grain boundaries in both samples, however at much lower concentrations after HPT-processing, indicating that Fe diffuses to the newly formed grain boundaries during the severe plastic deformation. Although Sn segregates to the grain boundaries of the as-received sample, it is distributed almost homogenously in the HPT-processed sample, which may provide advantages for corrosion resistance. Very low concentrations of Cr alloying elements at the matrix and grain boundaries of both samples is attributed to precipitation.