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The morphology and kinetics evolution of the γ′(Ni3Al) phase during re-dissolution are studied in Ni-15 at% Al alloy, the changes of volume fraction and average particle radius of the γ′ phase were clarified with phase-field simulation. During isothermal aging, the interdistance of the neighboring γ′ phase affects the interface concentration gradient of Al, which dominates the growth or re-dissolution of the γ′ phase particle. After isothermal aging at 700 K, the alloy is continuously heated to 900 K with different heating rates, the re-dissolution lag happens, meaning the coalescence coarsening of adjacent γ′ phase particles still proceeds at the initial heating stage. The pre-dissolution of γ′ phase with cubic shape is re-dissolved firstly at the edges and corners, in continuous heating to 900 K or by second-order aging from 700 to 900 K. Different from continuous heating, in the second-order aging process, the connected particles with band shape are broken initially by re-dissolving. At different heating rates, the similar dynamic relationships are abstracted for the volume fraction and the heating rates, and the average particle radius and the heating rates.

A bimodal precipitation with primary and secondary γ′ phase in Ni-17 at.% Al alloys was produced via preaging and continuous cooling. The morphology and composition evolution of γ′ phase during cooling process were studied by using phase-field simulation, the bimodal precipitation mechanism was declared. The content of Al in secondary γ′ phase is lower than the equilibrium composition because of the slower atom diffusion during continuous cooling. With the increase of cooling rates, the volume fraction and average radius of primary and secondary γ′ phase are reduced, the number density of secondary γ′ phase increases; in addition, the inter-distance of particle size distribution of primary and secondary γ′ phase is widen. A long time of isothermal preaging reduces the precipitation and growth of secondary γ′ phase. The hybrider precipitates with bimodal size distribution of γ′ phase help optimizing the precipitates morphology of nickel based alloys.