Effects of heavy ion irradiation on Zr-2.5Nb pressure tube alloy. II. Orientation dependent dislocation loop propagation and elemental redistribution

Abstract

The irradiation induced microstructure of heavy ion irradiated Zr-2.5Nb alloy has been characterized by X-ray diffraction and transmission electron microscopy (TEM). Diffraction line profile analysis is used to analyze the X-ray diffraction data and anisotropic responses to irradiation in terms of peak broadening in axial direction (AD; sample surface normal aligned with axial direction) and transverse direction (TD; sample surface normal aligned with transverse direction) samples. More specifically, AD samples demonstrate a significantly higher peak broadening than TD for the same irradiation dose level. TEM characterization shows that heavy ion irradiation induces small <a> type dislocation loops in the range of 2-10 nm in diameter. However, up to 0.2 dpa, the dislocation densities calculated from X-ray diffraction and TEM characterization both show comparable quantities for AD and TD samples. The considerable additional peak broadening of AD samples is attributed to an intergranular strain distribution. Chemi-STEM analysis shows that Fe is depleted from β-phase to α-β phase boundary and then into the α matrix, mainly due to ion sputtering during heavy ion irradiation.