Formation of Ni5Al3 Phase in Ni3Al/NiAl Diffusion Couples

Diffusion experiments have been conducted using the Ni 3 Al/NiAl couples at annealing temperatures of 873 and 923 K. It is shown that the Ni 5 Al 3 phase forms between the Ni 3 Al and NiAl phases during the diffusion annealing. Optical microscopy, transmission electron microscopy and electron probe microanalysis (EPMA) are employed for the identification of the Ni 5 Al 3 phase. Concentration profiles of Al across the diffusion-couple interfaces are measured using EPMA to determine the region of the Ni 5 Al 3 single-phase in the Ni-Al binary phase diagram. Interdiffusion coefficients in the Ni 5 Al 3 phase are also determined from the concentration profiles.