The effect of grit blasting on the oxidation behavior of a platinum-modified nickel-aluminide coating

The surface of platinum-modified nickel-aluminide bond coats on superalloys is usually roughened by grit blasting prior to deposition of thermal barrier coatings (TBCs). Analysis of the grit-blasted surface by secondary ion mass spectrometry (SIMS) reveals that this pretreatment leads to contamination of the bond coat by various impurities, in particular, the alkali and alkaline-earth metals and titanium. These impurities then become incorporated into the growing alumina scale and adversely affect the oxidation behavior of the bond coat. In particular, it is shown that grit blasting results in about a tenfold increase of the oxidation rate and extensive scale spallation during cyclic oxidation at 1150 degreesC.