Time-resolved phase and compositional homogenization of segregated uranium-niobium alloys above the monotectoid temperature

In-situ time-resolved synchrotron wide-angle and small-angle x-ray scattering (WAXS/SAXS) were conducted to study the homogenization of phase and composition in segregated U-6Nb. The sub-second time resolution data collected during heating to 750 degrees C and subsequent isothermal holds show that the integrated SAXS intensities correlate well with variations of lattice parameter, solute redistribution, and phase fraction, especially the volume fractions of orthorhombic alpha-uranium in the segregated alloy. Based on the combined datasets, the phase and compositional homogenization processes within the similar to 0.01 mm(3) volume probed by x-rays are rapid during heating above the monotectoid temperature, completed within approximately 15 s and 60 s, respectively. For the same alloy pre-aged at different time-at-temperatures, our data reveal subtle differences in the time domain for the completion of homogenization, indicating that the initial microstructures of the segregated U-Nb alloys, such as volume fraction of alpha-U, Nb content in the bcc phase, and possibly the lamellar morphologies, have discernible effects on homogenization. Overall, the present observations provide detailed real-time insight into the homogenization dynamics leading to equilibrium in the high temperature phase. (C) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

In-situ time-resolved synchrotron wide-angle and small-angle x-ray scattering (WAXS/SAXS) were used to study the homogenization of phase and composition in segregated U-6Nb. The results show that the integrated SAXS intensities correlate well with variations of lattice parameter, solute redistribution, and phase fraction, especially the volume fractions of orthorhombic alpha-uranium in the segregated alloy. The combined datasets reveal that the phase and compositional homogenization processes within the probed volume are rapid during heating above the monotectoid temperature, completed within approximately 15 s and 60 s, respectively.