Abstract:Dissolution kinetics of δ phase in Inconel 718 at 980, 1000 and 1020℃ respectively was established using the quantitative X-ray diffraction(XRD) method. Microstructure evolution during dissolution process was analyzed with scanning electron microscopy(SEM). Dissolution rate of δ phase during high temperature heating keeps at a high level at the beginning stage, and then decreases gradually with the increase of heating time. A dynamic equilibrium state approaches after being heated at 980℃ for more than 30min and at 1000℃ for more than 2h, and the equilibrium mass fraction are 3% and 0.6% respectively. δ phase fully dissolves into the austenitic matrix after being heated at 1020℃ for more than 2h. The dissolution and fracture effects cause the morphology evolution of δ phase from long needle shape to short bars or particles at high temperature.

Key words: Inconel 718; δ phase; dissolution kinetics; diffusion