The effect of grain size on the low-stability pre-transitional structural phase states of the NiAl intermetallic compound

The effect of grain size (model cell size) on the features of pre-transition low-stability structural phase states of the NiAl intermetallic compound in the region of structural phase transformations during thermal cycling (heating and cooling) is studied using the Monte Carlo method. Analysis of the temperature dependences of the parameters of the long-range order found that when heated, the highest long-range order is observed in the alloy with the largest grain size, and the smallest - with the smallest grain size. In order to disorder the alloy with increasing grain size, increasing overheating of the alloy is necessary. When cooled, the long-range order appears primarily in the fine grain alloy. As the grain size increases, the temperature of the appearance of the long-range order decreases, i.e. as the grain size increases, more and more super cooling is required to realize the atomically ordered states of the system. The larger the grain size, the wider the temperature range of the structural phase transformation. Features of the formation of structural-phase states in the cooling process depending on the grain size (cell size of the model) indicate that the first ordered regions appear in the alloy with a fine grain. As the grain size increases, the temperature of the appearance of the long-range order decreases, i.e. as the grain size increases, more and more super cooling is required to realize the atomically ordered states of the system.

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