Platinum Effect on Durability of Aluminide Coatings: Mechanics-Based and Density Functional Theory Investigation

A new mechanism describing the effect of Pt addition on the enhanced oxidation and durability of aluminide coatings was studied using combined mechanics-based model and density functional theory calculations. The coefficients of thermal expansion (CTE) of _-NiAl and Ptdoped _-NiAl were calculated using density functional theory combined with thermal physical formula. The calculated CTEs of NiAl and NiAl-Pt were then compared with the measured CTEs of NiAl and also with that of Al2O3. The wavy profile of the NiAl/Al2O3 interface was generated and described approximately using the trigonometry sinusoidal function characterized by a ratio of the wave amplitude over the wave length. The calculated and measured CTEs were then inserted into the mechanics-based interfacial stress model to evaluate thermal residual stresses at

the NiAl/Al2O3 interface. The results indicate that addition of Pt to NiAl significantly reduces the thermal residual tensile stress, and consequently may reduce the interface crack nucleation and propagation, thus leading to improvement of aluminide coating oxidation resistance and durability. The calculated interfacial residual tensile stresses showed the dependence of the oxide scale thickness, elastic moduli of both NiAl and Al2O3, and the interface amplitude and wave length. The implications associated with the performance of aluminide coating due to addition of Pt were discussed.

Key words: Platinum effect, aluminide coating, first principles calculations, oxidation resistance, residual stress, durability.