Kinetics of Overlapping Precipitation and Particle Size Distribution of Ni₃Al Phase

The precipitation kinetics of overlapping process from nucleation and growth to coarsening of the γ′(Ni₃Al) phase in Ni–Al alloys are investigated quantitatively by using the interface diffusion-controlled phase field model. It is found that the time exponent of average particles radius of the γ′ phase is about 1/3 at the growth and coarsening stage, while the exponent is smaller than 1/3 at the later steady-state coarsening stage. The decrease rate of the number density of the γ′ phase is larger at the steady-state coarsening than that of the growth and coarsening stage. The particle size distribution (PSD) is widened at the nucleation and growth stage, then is narrowed at the growth and coarsening stage, and becomes wide again at the steady-state coarsening stage; the width of PSDs obtained by the quantitative calculation is greater than 0.215 proposed by the LSW theory. Moreover, the position of the PSDs peak moves from 1.0 of the normalized radius at the nucleation and growth stage to less than 1.0 of the growth and coarsening stage, and then moves back to 1.0 at steady-state coarsening stage. The non-monotonically variation of kinetics of the γ′ phase during the precipitation process are reasonable and theoretically significant for the kinetics evolution.