Determination of N-body potential for Fe-Cr alloy system and its application to defect study

Attempts have been made to construct the N-body potential for Fe-Cr alloy system by mixing Finnis-Sinclair potential for Fe and that for Cr under the rule for the electron density given by Ackland and Vitek and the rule for the pair term given by Johnson through the adjustment of the heat of the solution of Fe-Cr alloy and the size factor of the Cr atom in the Fe matrix to the experimental values. The obtained potential was used for the determination of the defect structures, e.g., a vacancy-Cr complex (V-Cr) and a self-interstitial atom (SIA-Cr) complex (I-Cr). The binding energy of this complex is very small, i.e., 26 meV, which is not contradictory to the experimental result, namely, less than 105 meV obtained in the muon experiment and the vacancy migration temperature obtained by the positron annihilation lifetime experiment, i.e., about 200 K for both pure Fe and Fe-Cr alloy. Calculations were made for the various types of I-Cr complexes, but mixed dumbbell type complex is not the most stable structure. The most stable configuration is the structure where Cr atom sits beside the 〈1 1 1〉 Fe crowdion and the binding energy for this structure is 0.12 eV.