Microscopic phase-field simulation for Ni₃Al precipitation in Ni-Al alloy

Based on the microscopic phase-field dynamic model and the microelasticity theory, the morphology evolution of Ni₃Al (γ′) phase and early precipitation mechanism in Ni-Al alloy were simulated. Simulation results show that γ′ phase morphology changes from initial circular or irregular shape into the quadrate shape and their orientations become more obvious during precipitation process, in the later stage, the γ′ precipitates present quadrate shape with round corner and regularly align along the [10] and [01] directions. Under the effect of elastic strain energy, the coarsening process follows the rule of preferential selection, the particles lying in the elastic soft directions grow and coarsen further; the particles lying out of the elastic soft direction shrink and dissolve, highly preferential selected microstructure is formed in the later precipitation process. The early precipitation mechanism is the non-classical nucleation and growth, the evolution of γ′ phase is in the order: supersaturated solid solution→nonstoicheometric ordered phase→stoicheometric γ′ phase→growth.