Atomistic modelling of stoichiometry effects on dislocation core structure in NiAl

Dislocation core structures in stoichiometric and non-stoichiometric NiAl have been analyzed. Atomistic computer simulation with embedded atom method potentials was used for the study of the configuration of the material in the vicinity of dislocation cores. The results were analyzed in terms of the stress tensor as a function of position, giving the detailed shape of the dislocation core. A non-stoichiometric Ni-rich alloy was generated by random substitution of Al atoms by Ni atoms in the perfect lattice structure. The results show that a 2% deviation from stoichiometry affects the shapes of the dislocation cores, in that they tend to lose their preference for the well-defined crystallographic planes seen in the stoichiometric alloy. Stoichiometry deviations also increase the non-planar spreading of the core. This increased non-planar spreading of the core in Ni-rich NiAl is in agreement with the experimental results of high resolution electron microscopy. In addition, it was found that Al vacancies are greatly attracted to the distribution core and produce more significant changes in the core structure. The Peierls stresses were found to increase significantly for the non-stoichiometric alloys. The interaction of antisites with the dislocation core is not as strong, although the Peierls stress is still found to increase.