On the Microstructures of Platinum Aluminide Bond Coatings Produced by Different Aluminizing Methods: Effects on the Performance of Thermal Barrier Coatings on Ni-Based Superalloys

Abstract

It is shown that aluminizing of platinum-modified aluminide bond coatings by an external vapor source of aluminum in an open retort (chemical vapor deposition) can substantially enhance the performance of thermal barrier coatings in comparison with aluminizing by an internal vapor source in a closed retort (pack cementation). This is demonstrated by about twofold increase in life as determined from cyclic oxidation tests at 1150 °C. The difference in behavior is explained with reference to variations in the initial microstructure of each bond coating, particularly the platinum distribution and thickness of the interdiffusion zone. However, in both cases, it is found that decohesion of the top ceramic coatings during cyclic oxidation occurs by spallation of the oxides developed by the bond coatings. It is concluded that aluminizing by chemical vapor deposition improves the thermal stability and resistance to oxidation of the bond coating.