Structural-Phase Features of the Order – Disorder Transition in an Fcc-Alloy with В2 Superstructure in the Presence of a Complex of Thermal Antiphase Boundaries

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Using the Monte Carlo method, it is shown that the presence of a dual defect in the form of a pair of thermal antiphase boundaries in an ordered FCC-alloy with В2 supersructure (CuZn alloy taken as an example) gives rise to considerable structural-phase variations in the system during the order – disorder transition compared to the defect-free system. The availability and character of the observed peculiarities largely depend both on the temperature and the distance between thermal antiphase boundaries. It is underlined that the boundaries of the Cu–Cu and Zn–Zn types differ both in linear dimensions and in the degree of ordering of near-theboundary regions. For a boundary of the Cu–Cu type, this region is smaller and less ordered in contrast to linear dimensions and ordering degree of the Zn–Zn type boundary. At low temperatures, linear dimensions of the near-the-boundary disordered regions increase with the temperature, while the overall order in the system decreases. In the range of low-stability states of the system, the dimensions of the near-the-boundary disordered regions are maintained at approximately 10 interplanar distances for a boundary of the Cu–Cu type and about 12 interplanar distances for a boundary of the Zn–Zn type. It is noted that ordering degrees in these regions become similar, antiphase boundaries become smeared and get faceted; the first disordered regions invariably appear in the vicinity of the Zn–Zn type boundary.