The effect of deposition and processing variables on the oxide structure of MCrAl coatings

The protection afforded by a high temperature coating is known to be strongly influenced by the structure of the surface oxide. In a previous study of cast alloys and MCrAl coatings applied by electron beam physical vapor deposition a marked effect of the structure, the type and location of the “active element” and the substrate on the oxide structure and the protection afforded by the coating was found. This study has been continued and expanded to include the additional deposition techniques of plasma spraying and sputtering. Extensive use of the deep etching technique is made to characterize the oxide and to determine the presence and morphology of “pegs”. A description of the technique and the results of the study are presented.