A theoretical model, based upon the Bethe-Bragg-Williams approximation, was combined with published data on pair-interaction energies in β’-phase material with the B2 structure. The most interesting point defect complexes were triple defects, and were thought to be largely responsible for the concentration-dependence of Ni self-diffusion at 1000 to 1300K. This was nearly constant for Al-rich and stoichiometric alloys, and exhibited a marked increase with increasing Ni content on the Ni-rich side of the composition range. The present theoretical composition-dependence of the concentration of triple-defect complexes, and experimental Ni diffusivities, exhibited excellent correlation. This indicated the large contribution which was made by the triple-defect diffusion mechanism in the B2 material.

Triple-Defect Complexes in the B2 Intermetallic Compound NiAl. R.Krachler, H.Ipser: Physical Review B, 2004, 70[5], 054113 (7pp)