Ni and Al diffusion in Ni-rich NiAl and the effect of Pt additions

First-principles density functional theory calculations are used to examine long-range Ni and short-range Al diffusion in Ni-rich NiAl. Since Ni diffusion in Ni-rich NiAl has been observed to have a lower activation energy than Ni diffusion in stoichiometric NiAl, another diffusion pathway, the antistructure bridge (ASB) mechanism, is believed to be activated once a threshold concentration of Ni antisite atoms has been reached. Our calculated activation energies for Ni diffusion via the ASB mechanism agree well with experimental data, confirming the ASB mechanism is likely operating in the Ni-rich region of the phase diagram, providing a means of long-range Ni diffusion. Since the ASB mechanism does not involve Al atoms, no long-range transport of Al occurs via this mechanism. Instead we looked at short-range Al transport via next-nearest-neighbor Al jumps into Al vacancies created during the ASB mechanism. The effect of Pt on these mechanisms was also examined; we predict that the presence of Pt enhances the rate of the ASB mechanism, which has implications for the lifetime of jet engine thermal barrier coatings.