Early evolution of δ phase and coarse γ′ phase in Inconel 718 alloy with high temperature ageing

The early evolution of the delta phase and coarse gamma ' phase in aged Inconel 718 alloy was studied by transmission electron microscope. The results show that the needle-like delta phase first nucleates at the grain boundary and then grows into the grain interior. It is found that two delta phases with different orientations were combined to form one delta phase as the ageing time extended to 4 h. In addition, the delta phase maintains a good orientation relationship with the matrix during ageing. The coarse gamma ' phase nucleates at the dislocation, and the increase in size leads to the loss of coherence with the matrix, in which the strengthening effect is not obvious.