Diffusion experiments have been conducted using the Ni3Al/NiAl couples at annealing temperatures of 873 and 923 K. It is shown that the Ni5Al3 phase forms between the Ni3Al and NiAl phases during the diffusion annealing. Optical microscopy, transmission electron microscopy and electron probe microanalysis (EPMA) are employed for the identification of the Ni5Al3 phase. Concentration profiles of Al across the diffusion-couple interfaces are measured using EPMA to determine the region of the Ni5Al3 single-phase in the Ni-Al binary phase diagram. Interdiffusion coefficients in the Ni5Al3 phase are also determined from the concentration profiles.
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