Formation of Ni₅Al₃ phase in Ni₃Al/NiAl diffusion couples

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.