The microstructure evolution related to the L12 (supersaturated Ni3Al1-xVx) → L12 (Ni 3Al)+D022 (Ni3V) phase separation of the Ni3Al0.50V0.50 alloy, with the addition of a small amount of Si (less than 0.2 mol%), was examined by transmission electron microscopy. The data showed that the L12 single phase was formed via the appearance and subsequent disappearance of the D022 regions under an isothermally holding process, as in the case of the Ni3Al 0.50V0.50 alloy without Si. A striking feature of the microstructure evolution of the present alloy was that the formation of the final L12 single phase was accomplished within an extremely brief period of less than 10 min. Such a brief period indicated that the microstructure evolution was not accompanied by atomic diffusion, which was quite different from the case of the Si-free alloy. On this basis, we propose that the Si addition induced a pinning effect on atomic migration (i.e., suppression of long-range atomic diffusion) in the supersaturated L12 matrix and thus accelerated the formation of the final L12 single phase.
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