The energy of dissociated triangular frank dislocation loops in f.c.c. metals

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Abstract
The energy of a dissociated triangular Frank dislocation loop has been calculated for two models of the way in which the loop may dissociate to form a stacking-fault tetrahedron. By considering the equilibrium between the dissociated Frank dislocation and a complete stacking-fault tetrahedron, a relation between the edge-length of the defect, l, and the stacking-fault energy of the metal, γ, has been obtained. The influence on the l-γ relation of the choice of dislocation core energy and the stress present in the metal has been investigated. The results of the calculations have been applied to the experimental observations of Loretto et al. (1965) on stacking-fault tetrahedra and triangular Frank dislocation loops formed in plastically deformed copper, silver and gold. The values of stacking-fault energy of these metals so determined are γCu = 59 ergs/cm2, γAg= 15 ergs/cm2 and γAu = 45 ergs/cm2. The value for silver is now compatible within experimental error with the value deduced from observations on three-fold dislocation nodes.