Effect of vacancy concentration on low-stability pre-transitional structural phase states and energy characteristics of the NiAl intermetallic compound

Using the Monte-Carlo method, using the example of the NiAl intermetallic compound, the effect of vacancy concentration on the structure-phase states and energy characteristics in the process of heating and cooling is considered. The analysis showed that the presence and concentration of vacancies are significant factors in the pre-transition low-stability structural-phase states before transformation. On the one hand, the presence of vacancies and their concentration do not affect the temperature ranges of structural phase transformations, on the other hand, they have a significant effect on the pre-transition low-stability structural phase states and the rate of diffusion processes. From the temperature behavior of the parameter of the short-range order, the higher the concentration of vacancies (i.e., the higher the system’s defectiveness), the higher the temperatures tend to increase in atomic order due to the intensification of diffusion processes. This testifies, in turn, to an increase in the temperature of the onset of structural transformations with an increase in its defectiveness during cooling. Analysis of the temperature dependences of the long-range order parameter of the intermetallic leads to the conclusion that an increase in the concentration of vacancies (i.e., an increase in the alloy imperfection) leads to a natural result - a decrease in the long-range order in the system in the region of low-stability pre-transition states and an increase in the onset temperature of the transformation.

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