Multilayered ruthenium-modified bond coats for thermal barrier coatings

Diffusional approaches for fabrication of multilayered Ru-modified bond coats (BCs) for thermal barrier coatings (TBCs) have been developed via low-activity (LA) chemical vapor deposition and high-activity (HA) pack aluminization. Both processes yield BCs comprising two distinct B2 layers, based on NiAl and RuAl; however, the position of these layers relative to the BC surface is reversed when switching processes. The structural evolution of each coating at various stages of the fabrication process and subsequent cyclic oxidation is presented, and the relevant interdiffusion and phase equilibria issues are discussed. Evaluation of the oxidation behavior of these Ru-modified BC structures reveals that each B2 interlayer arrangement leads to the formation of alpha-Al2O3 TGO at 1100 degrees C, but the durability of the TGO is somewhat different and in need of further improvement in both cases.