The Ni/Ni3Al diffusion-couple interface was examined by using the techniques of analytical electron microscopy and high-resolution electron microscopy. It was shown that the Ni-rich solid solution phase (γ phase) was transformed from the Ni3Al-based intermetallic phase (γ′ phase) and that it extended into the γ′ phase during diffusion annealing. The orientations of the γ and γ′ phases remained the same. Coherency existed across the γ/γ′ phase boundary. The position of the boundary was not well-defined but was in an equilibrium condition in terms of composition.

Electron Microscopy Study of Ni/Ni3Al Diffusion-Couple Interface - I. Microstructural Observation and Microchemical Analysis. Watanabe, M., Horita, Z., Smith, D.J., McCartney, M.R., Sano, T., Nemoto, M.: Acta Metallurgica et Materialia, 1994, 42[10], 3381-7