Phase transformations and thermal expansion coefficients of unirradiated U-X wt.% Zr (X=6, 10, 20, 30) measured via neutron diffraction

This work characterizes the crystallographic evolution of unirradiated U-X wt.% Zr ( X = 6, 10, 20, 30) while cooling from equilibration, single phase gamma-U-Zr, at 900 degrees C to ambient temperature using time-of -flight neutron diffraction. The beta-U phase was unobserved during cooling at 1 degrees C/min in all alloys. All alloys followed the phase transformation pathway of gamma-U-Zr ->gamma-U-Zr +alpha-U ->alpha-U +delta-UZr2 with an ob-served miscibility gap in gamma-U-Zr. The alpha-U and delta-UZr2 transformation took place simultaneously in the U-30 wt.% Zr sample. These findings strengthen the need to re-approach the U-Zr phase diagram in entirety. Bulk volumetric CTEs agree well with published data, strengthening the quantification of lattice-specific CTEs reported in this study. A compositionally dependent discontinuity in thermal expansion, increasing in magnitude with decreasing U content, occurs during the gamma-U-Zr ->alpha-U +delta-UZr2 transformation. The gamma-U-Zr lattice parameter was measured to have a compositional dependency.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

This study characterizes the crystallographic evolution of unirradiated U-X wt.% Zr alloys (X = 6, 10, 20, 30) during cooling from 900 degrees C to ambient temperature. It was found that all alloys followed a phase transformation pathway, with a miscibility gap observed in gamma-U-Zr and simultaneous transformation of alpha-U and delta-UZr2 in the U-30 wt.% Zr sample. These findings highlight the need to reassess the U-Zr phase diagram.