Interdiffusion analysis for NiAl versus superalloys diffusion couples

Solid-to-solid diffusion couples, beta-NiAl (B2) versus various commercial superalloys (i.e., CM247, GTD-111, IN-939, IN-718, and Waspalloy) were examined to quantify the rate of Al interdiffusion as a function of initial superalloy composition. The diffusion couples were assembled with Invar steel jig encapsulated in Ar by sealing in quartz capsules and annealed at 1050 degrees C for 96 h. Concentration profiles measured by electron probe microanalysis in the single-phase beta-NiAl region were used to determine interdiffusion fluxes and effective interdiffusion coefficients of individual components in the single-phase beta-NiAl side of the couple. The values determined using experimental concentration profiles of the single-phase beta-NiAl side of the couple were used to predict effective interdiffusion coefficients in multiphase superalloy side of the couple based on mass balance and local continuity of interdiffusion fluxes. Microstructural and compositional stability of protective coatings (e.g., NiCoCrAlY and NiAl) as a function of superalloys composition are discussed based on effective interdiffusion coefficients predicted from diffusion couple studies