A new method was presented for the calculation of the excess energies of line and planar defects in ordered alloys. This method linked the macroscopic thermodynamic concept of a Gibbsian excess energy to the results of total energy calculations at the atomic scale. The method was applied to the calculation of dislocation line energies by using an embedded atom model. Three decomposition reactions were found to be energetically favorable. One was the climb decomposition of the <011>{01¯1} edge dislocation according to:

<011>{01¯1}  <100>{010} + <010>{00¯1}

This climb decomposition was stabilized by the interaction energy between the <100> dislocations. The interaction did not depend upon the distance, and therefore exerted no forces upon the dislocations. There was also a climb decomposition of the <011>{21¯1} edge dislocation into 2 mixed <100> dislocations:

<011>{21¯1}  <100>{101} + <010>{10¯1}

Finally, there was the decomposition of a <111> edge dislocation into 2 mixed dislocations with <100> and <011> Burgers vectors:

<111>{01¯1}  <100>{01¯1} + <011>{01¯1}

This decomposition was suggested to be important with regard to the transition from <111> to <110> slip in so-called hard-oriented NiAl single crystals at high temperatures.

Energies of Defects in Ordered Alloys: Dislocation Core Energies in NiAl R.Schroll, M.W.Finnis, P.Gumbsch: Acta Materialia, 1998, 46[3], 919-26