Stored energy, microstructure, and flow stress of deformed metals

The stored energy of plastic deformation has been estimated from transmission electron microscope measurements of dislocation boundary spacings and misorientation angles using Al (99.99 pet) cold rolled to reductions of 5 to 90 pet as an example system. In order to obtain the most accurate estimate of stored energy, it is necessary to take into account the presence of two classes of dislocation boundary, considering the boundary misorientation angle distribution and the stereology of each class independently. Stereological relationships are developed to predict the stored energy estimates that would result from electron backscatter pattern (EBSP) investigations on these microstructures. The calculations show that EBSP investigations can be used to estimate the stored energy, but that at low strains, the limited angular resolution will lead to a significant underestimation. A relationship between the flow stress (0.2 pet offset) and the stored energy is found, though the relationship differs significantly for the low and high strain regimes. At low strains, the flow stress is linearly related to the quare root of the stored energy (E-S) according to sigma - sigma(0) = M alpha[(G/K)E-S](0.5), where G is the bulk modulus, M is the Taylor factor, and K and alpha are constants.