Influence of Manufacturing Route on the Oxidation Resistance of Platinum-Modified Aluminide Bond Coatings and Their Performance in Thermal Barrier Coatings Deposited on a Ni-Based Superalloy

The importance of manufacturing route of Pt-aluminide bond coatings in determining the life of thermal barrier coatings on Ni-based superalloys is demonstrated. It is shown that bond coatings aluminized by chemical vapor deposition exhibit higher resistance to oxidation in comparison with the pack cementation route, which results in about twofold increase in the life of the thermal barrier coating as determined under cycling oxidation conditions. This difference in behavior is correlated with the initial microstructures of the bond coatings and their effect on thermal stability and oxidation resistance. However, thermal barrier coatings utilizing the two types of bond coatings are found to fail by the same mechanism involving spallation of the top coating due to loss of adhesion between the thermally grown oxide and underlying bond coating. It is concluded that manufacturing by the CVD route with low Al activity decelerates the kinetics of the processes leading to degradation of the coating system in comparison with the pack cementation route with high Al activity.