Phase and structural transformations in U and U-Nb alloy upon severe deformation and heat treatments

Transmission electron microscopy was used to analyze the twin and dislocation structure of samples of commercial uranium in the initial (undeformed) state and after severe deformation using explosive loading by plane and spherical waves of various intensity. It has been shown that an increase in the intensity of explosive loading by a plane wave leads, first, to an increase in the density of randomly distributed dislocations and twins and, then, to the development of polygonization processes with the formation of a subgrain structure of the α phase. Crystallographic analysis of the initial and deformation-induced twins in uranium has shown the presence of predominantly {130} twins of mixed type and, in singular cases, {172} and {176} twins of the second kind. It has been established that the retained spherical shells have a distinctly pronounced zonal structure, which contains information on the forward and reverse martensitic phase transformations of uranium (α ? β(γ) ? L, etc.) that occur under shock-wave loading by spherical waves. Conditions are determined for the manifestation of structural heredity in the U-6 wt % Nb alloy with recovery of the size and shape of grains of the initial high-temperature γ phase during the forward γ → α″ martensitic transformation upon cooling and during reverse α″ → γ transformation upon heating. Elimination of the structural heredity with significant grain refinement of the high-temperature γ phase occurs in the process of repeated quenching from 700°C after one type of preliminary treatments (cold deformation of α″ martensite, recrystallization of the deformed α″ phase, high-temperature aging of the initial α″ martensite, and eutectoid decomposition).