Triple-defect complexes in the B2 intermetallic compound NiAl -: art. no. 054113

The present study combines a theoretical model on the basis of the Bethe-Bragg-Williams approximation with literature data on the pair-interaction energies in beta'-NiAl with B2 (CsCl) structure. In this intermetallic compound, the most interesting point defect complexes are the triple defects since they have been supposed to be mainly responsible for the concentration dependence of the Ni self-diffusion coefficient in the temperature range between 1000 and 1300 K, which is nearly constant for Al-rich and stoichiometric alloys and shows a pronounced increase with increasing Ni content on the Ni-rich side of the composition range. The theoretical composition dependence of the concentration of triple-defect complexes, derived in the present work, and the experimental Ni diffusivities from the recent literature show excellent correlation, thus pointing to an important contribution of the triple-defect diffusion mechanism in B2 NiAl.