Comprehensive deformation of polycrystalline uranium at low temperatures

Polycrystalline α-uranium was tested in compression from 20 to 300 K and, with the exception of the 20 K tests, no cracking was observed during extensive plastic deformation (epsilon<=-3.0). Alpha uranium was found to be a strongly work hardening material; the dislocation and twinning structures developed, however, are not stable and resulted in unexpectedly weak material when samples were tested at temperatures above the initial deformation temperature. On the other hand, the results obtained suggest that large strain deformation at warm temperatures should lead to high yield strength uranium at room temperature. The stress-strain curves for annealed polycrystalline α-U from 78 to 300 K can be predicted accurately from the phenomenological relation: sigma=sigmasub(s) - exp[-(Nepsilon)sup(p)].(sigmasub(s)-sigmasub(g)), where N and p are material constants equal to 0.613 and 0.58, respectively, and sigmasub(y) is the yield strength. The saturation flow stress, sigmasub(s), is predicted to be 6200 MPa (900 ksi) at 78 K and 2900 MPa (420 ksi) at room temperature. (Auth.)