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