On the rumpling mechanism in nickel-aluminide coatings: Part I: an experimental assessment Original Research Article

Progressive roughening (rumpling) of the surface of platinum-modified nickel aluminide bond coats during cyclic oxidation at 1150 °C is studied. A series of microstructural observations and quantitative results, for different experimental conditions, are used to describe the surface evolution of the bond coats and a bulk aluminide alloy of similar composition. Possible rumpling mechanisms, discussed in the literature, are examined and compared to the actual characteristics of the observed rumpling. The effects of various factors, specifically oxidation conditions, cycle length, surface roughness, thermal expansion mismatch, and phase transformation in the bond coat are explored and briefly discussed. Analysis of the experimental data suggests that the underlying mechanism of surface rumpling of the aluminide bond coats still remains to be established.