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 -> L1(2)/D0(22) phase transition proceeds with an intermediate transient L1(0)/L1(0) (M = 1) phase at the critical Al level where the two phases co-exist. Additionally, L1(2) may act as a transient phase of D0(22) at compositions not in favor of D0(22), 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 L1(0)/L1(0) (M = 1) configuration with slight atom fluctuation, or in L1(2)-Ni3Al/D0(22)-Ni3V configuration, with atoms highly aligned, and lastly; a third equilibrium L1(2)-Ni3Al/D0(22)-Ni3V phase. Further studies on the atomic occupancy probability demonstrated that L1(0) and L1(0) (M = 1) are low-ordered phases with atomic occupancy probability fluctuation within a narrow range; conversely, L1(2) and D0(22) are ordered phases showing significant atomic occupancy probability fluctuations when ordering as well as when act as a transient phase. (C) 2013 Elsevier Ltd. All rights reserved.