Segregation of alloying elements to planar faults in gamma'-Ni3Al

Systematic first principles calculations are performed to determine the interaction energies between solutes (Co, Cr, Nb, Ta) and stable stacking faults in gamma'-Ni3Al. Our results show that there is no obvious driving force for segregation to already formed SISF, SESF, or twin boundaries, which is in contrast to direct experimental evidence for segregation as provided by high spatial resolution structure and chemical analysis using scanning transmission electron microscopy techniques. This apparent discrepancy provides evidence for possible formation mechanisms of these planar faults via metastable precursor structures that are found to be attractive for solutes. In addition, we study the underlying reasons for the segregation in terms of size and chemical mismatch and find that a favorable change in bonding environment, rather than the solute misfit volume, dominates the solute/fault interaction energy. (c) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.