In Situ Neutron Diffraction Study of Crystallographic Evolution and Thermal Expansion Coefficients in U-22.5 at.%Zr During Annealing

A uranium-22.5 at.%zirconium (U-10 wt.%Zr) ingot was manufactured by traditional arc casting. The sample was characterized by high-pressure preferred-orientation time-of-flight neutron diffractometry with in situ heating reaching 900 degrees C. The phase transitions, lattice parameter ratios, and linear coefficients of thermal expansion were investigated experimentally. Contradictory to commonly referenced phase diagrams, the results of this work showed that the beta-U+gamma ''-UZr dual-phase region is not present in U-22.5 at.%Zr. Rather, only two phase transformations were observed upon cooling. These transformations occurred at 655 degrees C and 600 degrees C and corresponded to gamma-UZr -> alpha-U+gamma ''-UZr -> alpha-U+delta-UZr2, respectively. The linear coefficients of thermal expansion were measured for alpha-U, delta-UZr2, and gamma-UZr. The thermal expansion of alpha-U was shown to be anisotropic in nature with significant lattice contraction in the 010(b) direction. Similar anisotropy albeit to a lesser extent was observed in delta-UZr2 with contraction in the 001(c) direction.