Stored energy in nickel cold rolled to large strains, measured by calorimetry and evaluated from the microstructure

High-purity polycrystalline nickel (99.99 pct purity) was cold rolled to equivalent von Mises strains from 1.4 to 4.5 (70 to 98 pct reduction in thickness). The stored energy of the deformed samples was measured using both microstructural parameters obtained from transmission electron microscope (TEM) investigations and differential scanning calorimetry (DSC). For the microstructure-based estimate of the stored energy, the required parameters are the misorientation angles across, and the spacings between the dislocation boundaries and high-angle boundaries present after deformation. It was found that the stored energy determined from both TEM and DSC investigations increased linearly with strain, with the latter being larger by a factor of between 1.9 and 2.7. This difference can be reduced by considering the contribution to the stored energy from other sources.