Precipitation kinetics of ordered γ′ phase and microstructure evolution in a NiAl alloy

•Kinetics of γ′ phase from nucleation to coarsening in NiAl alloy is studied.•Non-stoichiometric ordered phase and initial cluster are quantitatively described.•Time exponent of particle radius decreases from nucleation and growth to coarsening.•Average aspect ratio of γ′ phase shows three stages with respect to average radius.

The precipitation kinetics of ordered γ′ (L12-Ni3Al) phase from nucleation and growth to coarsening in a NiAl alloy is studied by phase field simulation. The initial nucleation of the γ′ phase is quantitatively described by the variations of composition and order parameter profiles of the initial Al-enriched cluster, and the coarsening kinetics is clarified with the time exponent of the average particle radius of γ′ phase. The precipitation of the γ′ phase from the supersaturated γ solid solution goes through the non-stoichiometric ordered phase, stoichiometric ordered phase, growth and coarsening. The time exponent of the average radius of the γ′ phase with coherent equilibrium is smaller than that indicated by the Lifshitz–Slyozov–Wagner theory at the coarsening stage, and it decreases from 1.35 of the nucleation and growth stage to 0.22 of the coarsening stage. The peak of the particle size distribution decreases and the width of the particle size distribution increases as the aging progresses. As the average radius of the γ′ phase increases, the average aspect ratio of the γ′ phase undergoes a slowly increase to a fast increase from nucleation to growth stage, then goes into a relatively stable state at the coarsening stage.