Equation of state and phase evolution of U-7.7Nb with implications for the understanding of dynamic behavior of U-Nb alloys

Abstract

In this work, we conducted in-situ high P-T neutron diffraction experiments on U-7.7Nb. Our results show that the tetragonal γo phase is substantially more compressible than the monoclinic α′′ phase. As the pressure increases, this leads to increased volume collapse and stress relaxation for the reverse martensitic transformation, α′′ → γo. At moderately elevated temperatures, a substantial strain-induced stabilization against transformation into a body centered cubic γphase was observed in the γo phase. We also found that the ability to retain the metastable γphase, formed from rapid heating of thermally reset γo, has subtle dependence on the austenitization temperature. The present findings provide a direct test for the hypotheses proposed to explain the low-pressure shock behaviors of the U-Nb alloys.