Stoichiometry effects on core structure and mobility in B2 NiAl

Abstract

Abstract The effects of stoichiometry deviation on the core structure and motion of dislocations in B2 NiAl are studied. Vacancies and antisites are introduced into numerous positions in embedded atom simulation blocks containing [100](001) as well as [100](011) pure edge dislocations. The interaction of these point defects with the dislocation is quantified by calculating the change in total energy experienced by the simulated lattice. An off-stoichiometry Ni-rich alloy is generated by randomly substituting Ni atoms for Al atoms as well as simply deleting Al atoms from the perfect lattice structure. It was found that a 2% deviation from stoichiometry affects the shapes of 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 as visualized using the strain invariant method. It was found that Al vacancies are strongly attracted to the dislocation core and produce much more significant changes in the core structure than antisites or Ni vacancies do. The Peierls stresses were found to increase significantly for the alloy when off-stoichiometry. The interaction of antisites with the dislocation core is not as strong, although the Peierls stress is still found to increase. The simulations suggest that an entirely different core structure may be stable for the off-stoichiometric alloys.