Surface rumpling of a (Ni, Pt)Al bond coat induced by cyclic oxidation

The surface of an initially flat, platinum-modified nickel aluminide bond coat formed on a single crystal superalloy is shown to progressively roughen ("rumple") with thermal cycling in air. Far less surface roughening occurs after isothermal oxidation or after the same number of thermal cycles but with a shorter high-temperature exposure in each cycle. Mechanisms of the observed rumpling and the implications of the bond coat surface evolution leading to the failure of thermal barrier coatings are discussed. It is concluded that local volume changes in the bond coat, caused by aluminum depletion and subsequent decomposition of the beta-(Ni, Pt)Al phase, are responsible for the observed rumpling. (C) 2000 Published by Elsevier Science Ltd on behalf of Acta Metallurgica Inc.