Diffusional Interactions and their Applications in Reducing Interdiffusion in Bond Coat Systems Used in Turbine Blades

Interdiffusion analysis in multicomponent alloy systems plays a pivotal role in controlling various processes and in designing materials. Interdiffusion of elements also leads to changes in microstructure and properties during service, especially for the materials operating at elevated temperatures. The urge of increasing efficiency of gas turbine engines has led to the demand of higher service temperatures and longer life, which is achieved by the application of thermal barrier coatings (TBC) on Ni based superalloys. To prevent oxidation damage to the superalloy substrate, bond coats are used in which diffusion acts as a key factor influencing the stability and durability of the engine components. Over the last few decades, β-(Ni,Pt)Al coatings have been widely employed as bond coat materials because the presence of Pt enhances oxidation resistance by accelerating diffusion of Al to generate a continuously growing TGO (Thermally grown oxide) layer. However, this also encourages the interdiffusion of Ni and Al between the bond coat and the substrate, which weakens the TBC system. Therefore, a thorough understanding of diffusion behaviour is required in the bond coat materials. In the present study, ternary interdiffusion coefficients are determined in β-(Ni,Pt)Al at 1100 °C. Knowledge of such diffusional interactions would further open new avenues to design bond compositions and process sequences in order to minimize the microstructural changes caused by interdiffusion processes in service.