Structural-Phase Transformations in the Cu3Pt5 Alloy During Atomic Ordering

Using the Monte Carlo approach, it is found out that a complex structural-phase transformation is observed in the Cu3Pt5 alloy in the course of an order – disorder transition, which is a combination of atomic ordering and structural transformation. Cooling of the alloy gives rise to horizontal sections appearing in the temperature curve of configurational energy, which correspond to different structural states of the alloy, the difference between their energies being very small. This is an indication of low stability of these states with respect to structural-phase mutual transformations. In this case, structure defects, e.g., antiphase boundaries, significantly affect the structural-phase state of the entire system. Thus, structure defects predetermine a channel for a transition in this low-stability state. Under thermal cycling, there are hysteresis loops in the temperature dependence of the configurational energy in the vicinity of the order – disorder transition in the low-stability state of the alloy: during heating and cooling the system undergoes differing structural-phase states. At low and high temperatures, its atomic and phase structures are quite well defined, while at intermediate temperatures they are principally indefinite. Under conditions of thermal cycling, the phase structure in the region of low-stability states exhibits peculiar features: a principal difference between the structural-phase states during heating and cooling.