Atomic-scale computer simulation for ternary alloy Ni-Cr-Al during early precipitation process

The aging behaviors of Ni-Cr-Al ternary alloy are studied at temperature 873 K based on the mean-field theory, and the early precipitation process is simulated at atomic-scale with microscopic phase-field model. The precipitation mechanism of the low supersaturated alloy Ni-12.2at. %Cr-7.8at. %Al is non-classical nucleation and growth, the L1₂ structure (Ni₃Al) and D0₂₂ structure (Ni₃Cr) phases precipitate simultaneously, a part of D0₂₂ phase transmits to L1₂ structure phase, and other part retains its previous structure. For high supersaturated alloy, congruent ordering appears first, then followed by spinodal decomposition, the nonstoicheometric ordered phases are produced in this process, which occurs before clustering. The precipitation mechanism of Ni-8at. %Cr-18at. %Al alloy is similar to Ni-10at. %Cr-12at. %Al alloy, but the ordering process of the former is ahead of the latter.