Computer simulation of the initial precipitation processes of γ′ and θ phases

A kinetic model for ternary systems was developed based on the microscopic diffusion form of the phase-field equations describing the precipitation process in binary alloys. The model was used for atomic simulation of the initial precipitation mechanisms of γ′ and θ ordered phases in Ni₇₅Al₁₁V₁₄ and calculation of the order parameters of γ′(Ni₃Al) phase. The results show: the γ′ ordered phase precipitated from the disordered matrix by a nonclassical nucleation mechanism accompanied by spinodal decomposition, and an initially formed nonstoichiometric ordered phase later transformed into the stoichiometric one; clusters of V atoms appeared at the γ′ phase boundary resulting in the formation of a nonstoichiometric θ ordered phase; the degree of ordering of the O domain decreases with distance from the γ′-phase boundary. There exists two types of DO₂₂ ordered domains: horizontal and vertical, depending on their adjacent γ′ phase boundary.