Polygonized structure formation in polymorphic transitions in uranium
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Polymorphic transformations in uranium are considered in relation to the formation of polygonized structures in the α and β phases. Dislocational polygonized structures arise in γ→β and β→α transitions in a fashion that on the whole is subject to the laws found for other polymorphic metals, while the differences are associated in the main with the uniquely complicated crystal structures of the uranium β and α phases. Metallography has been applied to determine the conditions of continuous cooling that produce a polygonized structure in the β grains in the γ→β transition (network substructure), and also the conditions for subgrains to arise in the α grains. The continuous cooling conditions govern whether the β→α transition occurs with normal kinetics or martensite kinetics. A bainite type of transition is characteristic of the γ→β transition. The defectiveness in the polygonized structure in α-uranium is such that the gridded substructure of the β grains is retained after cooling from the γ region (grain boundaries and subboundaries containing segregations of impurity particles), and this favors hardening of the α phase, but it reduces the plasticity.
KeywordsUranium Polymorphic Transition Recrystallization Temperature Grid Substructure Titanium Foil
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