Characterization of a grain size refinement process in cast uranium

The refinement of coarse grains in cast uranium can lead to wrought-like properties. In this study, a β-quenched process is coupled with a shock-loading technique and α-annealing to manipulate uranium's grain size and the resulting microstructures have been characterized. Neutron powder diffraction has been used to evaluate the residual strain accumulated from the thermo-mechanical treatments. Optical microscopy and electron backscattering (EBSD) in scanning electron microscopy have been employed to evaluate the grain size variation and the nature of deformation mechanisms, respectively. Large strain anisotropy at the lattice level was observed on shock-loaded specimens. The final stress relief annealing did not eliminate all the residual strain. Slip and twinning were observed optically on the shocked specimens while EBSD indicates that although {130}, {172}, and {112} deformation twins were identified, an unusual type of twinning ‘{176}’/<512> was found to be dominant. It is believed that the magnitude of energy applied favored the occurrence of the {176} twin in the polycrystalline uranium. Average grain size of cast uranium underwent a significant reduction to ∼92 μm at the end of the process. The overall results indicate the shock-loading approach as a promising step toward controlling cast uranium grain size and thus its mechanical properties.