The temporal evolution of microstructures during structural transition of D022 and L12 involved with transient phases

A microscopic phase-field method was employed to study the evolution in microstructure of Ni-Al-V alloys during the ordering process. The FCC → L12/D022 phase transition proceeds with an intermediate transient L10/L10 (M = 1) phase at the critical Al level where the two phases co-exist. Additionally, L12 may act as a transient phase of D022 at compositions not in favor of D022, and vice versa. The rearrangement of atoms during the structural transition undergoes three classical stages: a respective disorder stage with atoms distributing uniformly; a second transient phase with atoms aligning in either L10/L10 (M = 1) configuration with slight atom fluctuation, or in L12-Ni3Al/D022-Ni3V configuration, with atoms highly aligned, and lastly; a third equilibrium L12-Ni3Al/D022-Ni3V phase. Further studies on the atomic occupancy probability demonstrated that L10 and L10 (M = 1) are low-ordered phases with atomic occupancy probability fluctuation within a narrow range; conversely, L12 and D022 are ordered phases showing significant atomic occupancy probability fluctuations when ordering as well as when act as a transient phase.