Deformation and stored energy of polycrystalline bismuth

Stress-strain curves of polycrystalline bismuth deformed in compression were obtained at 78, 193, 243, 273, 298 and 353 K at strain rates of 2.2 × 10^-4, 2.2 × 10^-3 and 2.2 × 10^-2 s^-1. The strain rate sensitivity was measured by strain rate change tests. Activation volumes and activation enthalpies of deformation were determined. The stored energy of cold work was measured by liquid metal solution calorimetry. The flow stress shows a large strain rate dependence except at 78 K; its strain rate sensitivity goes through a maximum in the range of 243 to 273 K. The interpretation of the activation volume and activation enthalpy suggests that the deformation mechanism changes between 193 and 243 K and between 298 and 353 K. The stored energy of cold work increases at first linearly with strain and at a strain of approximately 0.5 levels off to a saturation value of about 420 J .g-atom^-1. The stored energy and the ratio of the stored to the expended energy are unusually large. Some conclusions are drawn regard-ing the deformation mechanism of bismuth.