Kinetic process of the phase separation in the alloy Ni₃Al _0.52V_0.48

In the Ni₃Al_0.52V_0.48 alloy, D0 ₂₂ precipitation in the supersaturated L1₂ matrix has been found to stagnate due to the occurrence of the L1₂ → L1 ₂ + D0₂₂ → L1₂ structural change in an isothermal process. In this paper, we experimentally show the variation of the L1₂ and D0₂₂ chemical compositions during the structural change. Our results reveal that the transient D0₂₂ formation accompanies a large concentration fluctuation, while the final L1₂ composition reverts back to the initial L1₂ one. It is also found that the average V content of the D0₂₂ regions decreases together with the change in the L1₂/D0₂₂ habit planes from the {100} to {110} ones. These experimental results are indicative of the suppression of atomic diffusion and subsequent redistribution of Al and V in the L1₂ matrix, resulting in D0₂₂ annihilation. It is proposed that jump site selectivity and cooperative atomic migration in the L1₂ structure are important factors in the suppression of atomic diffusion. Because the appearance of these factors correlates well with the vacancy concentration of the L1₂ matrix, it is concluded that the stagnation of D0₂₂ precipitation represents one kinetic process under the present thermodynamic path.