Structure and stability of δ-UZr2 phase in U-50 wt% Zr alloy

Abstract

ABSTRACT Thermodynamic stability of the hexagonal delta phase has been discussed for the U-50 wt% Zr alloy composition based on the XRD, FESEM, and EDS results, further corroborated by the ab-initio calculations. It has been shown that U-50 wt% Zr composition falls into a two-phase region in the U–Zr phase diagram at about 573 K, in contradiction to the published phase diagram. Crystallographic structure of the delta phase in terms of the atomic occupation has been elucidated using the near-neighbour analysis obtained from the EXAFS results. It is shown here that the (111) plane collapse mechanism of the parent bcc phase is not complete in the delta phase even after the sample was aged for 864 ks (240 h) at 573 K.