For a detailed interpretation of experimental results on self-diffusion in NiAl molecular static calculations were applied to compute the energy barriers corresponding to general six-jump cycles in NiAl. It was found that the [110] six-jump cycle involved the lowest migration barriers among other possible cycles in the B2 structure of NiAl and had the highest probability to be accomplished. The attempt frequencies of different jumps were calculated within the quasi-harmonic approximation. The Monte Carlo approach with residence-time algorithm was then applied to compute the diffusional correlation effects. The temperature dependence of the Ni diffusion coefficient by the six-jump mechanism was found to obey the Arrhenius law D0exp{-Q/kT} with D0 ≅ 1.3 x 10-5m2/s and Q ≅ 3.12eV at 800 to 1500K. These values agreed well with experimental results for 63Ni tracer diffusion [Do ≅ 3.6 x 10-5 m2/s, Q ≅ 3.01eV], in monocrystalline NiAl samples of stoichiometric composition. However, the analysis predicted that the six-jump cycles may be easily broken if the vacancy met specific configurations. The resulting contribution of the six-jump cycle mechanism to the total Ni diffusivity was estimated to be smaller than about 30% at lower temperatures (≤ 1100K) and perfect stoichiometric composition. With deviation from the stoichiometry and/or increase of temperature the effectiveness of the six-jump cycles decreased rapidly

On the Six-Jump Cycle Mechanism of Self-Diffusion in NiAl. S.Divinski, C.Herzig: Intermetallics, 2000, 8[12], 1357-68