Calculations were made of the properties which were needed in order to evaluate the tendency of a face-centered-cubic metal to deform plastically by forming crystallographic twins rather than by dislocation-mediated slip. This property was referred to as being twinability. A formulation of twinability was used which was derived by coupling continuum mechanics to an atomistic stress-slip relation. The essential quantities required for evaluating the twinability were the elastic constants, which were measurable experimentally, and the energies of various stacking sequences of the face-centered cubic (111) planes. These stacking sequences included intrinsic stacking-fault configurations as well as the unstable-stacking energy and unstable-twinning energy configurations which could only be determined computationally. A tight-binding model was used to evaluate the necessary stacking energies, as well as the extrinsic stacking fault energy and twin-boundary energy, for 8 face-centered cubic metals. The accuracy of the tight-binding parameters was established by comparing them with first-principles values found from an extensive study of the literature. It was shown that the ranking of these metals, in order of twinability, agreed with available experimental results. The low incidence of deformation twinning in Al was reproduced, and was explained in terms of the material parameters by using an approximation to the twinability expression. It was predicted that Pd, which was not studied experimentally here, should twin as easily as Cu.

Tight-Binding Calculations of Stacking Energies and Twinability in FCC Metals. N.Bernstein, E.B.Tadmor: Physical Review B, 2004, 69[9], 094116 (10pp)