Electron microscopy study of Ni/Ni₃Al diffusion-couple interface-I. Microstructural observation and microchemical analysis

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.