In the kinetic process of the fcc → L12 + D022 phase transition of the Pd3Al0.2V0.8 alloy, the suppression of atomic diffusion in the L12 regions during the evolution from the fcc + L12 intermediate state occurred under a certain thermodynamic process. Owing to this suppression, the L12 regions underwent no L12 + D022 evolution and were closed to atomic exchanges with the fcc regions. As for the fcc regions, the L12 + D022 state indeed formed but the L12 chemical composition deviated from that of the L12 regions due to a lack of mutual atomic exchange. Such independent evolutions eventually led to a formation of the metastable state with partially closed regions. From the viewpoint of the stochastic process, the L12 and fcc regions act as independent closed ensembles with different time averages along the respective probabilistic trajectories during the evolutions. Because the starting state (the fcc single phase) of the phase transition can be regarded as one canonical ensemble, the evolution to the present metastable state indicates a translation from one to two statistical ensembles in one solid state during the phase transition, the trigger for which is the suppression of atomic diffusion in the L12 regions.
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