The dissociation energy of extended dislocations in fcc lattices

Abstract

The dissociation of a dislocation in the {111} plane of a fee crystal into two Shockley partials is studied in the framework of the generalized Peierls model. The interplanar atomic misfit energy (the γ-surface) is represented by a two-dimensional Fourier series in which the ‘stacking fault energy’ γ _g and the maximum stacking energy γ _m can be varied independently. Whereas for Volterra dislocations the separation d ₀ of the Shockley partials depends only on γ _g , it turns out that in the more general treatment the equilibrium separation d depends also on γ _m . Hence previous experimental determinations of γ _g from TEM observations have to be re-evaluated. The energy ΔE _p to recombine the two Shockley partials also depends on the value of ΔE _v. Agreement with the dissociation energy ΔE _v for a Volterra dislocation in screw orientation can only be obtained when the ‘recombination radius’ is chosen r _c ≈ 0.15b.