First-principles density functional theory calculations were used to study Al diffusion in β-NiAl. The activation energy and diffusion constant pre-exponential factors were calculated for five previously postulated Al diffusion mechanisms: next-nearest-neighbour Al jumps, the triple defect mechanism and three variants of the six-jump cycle mechanism beginning with an Al vacancy. It was predicted that the triple defect mechanism had the lowest activation energy and was the mechanism by which Al diffusion occurs in NiAl. In order to elucidate why Pt has a beneficial effect on thermal barrier coating lifetime, the effect of Pt on each of these mechanisms was also examined. In all cases, Pt decreases the diffusion activation energy, which should enhance Al diffusion in the coatings.

The Effect of Platinum on Al Diffusion Kinetics in β-NiAl - Implications for Thermal Barrier Coating Lifetime. K.A.Marino, E.A.Carter: Acta Materialia, 2010, 58[7], 2726-37