Structural-Phase Transformations of CuZn Alloy Under Thermal-Impact Cycling

Resumo

Using the Monte Carlo method, special features of structural – phase transformations in β-brass are investigated during thermal impact using thermal cycling as an example (a number of successive order – disorder and disorder – order phase transitions in the course of several heating – cooling cycles). It is shown that a unique hysteresis is observed after every heating and cooling cycle, whose presence indicates irreversibility of the processes, which suggests a difference in the structural – phase states both in the heating and cooling stages. A conclusion is drawn that the structural – phase transformations in the heating and cooling stages occur within different temperature intervals, where the thermodynamic stimuli of one or the other structural – phase state are low. This is also demonstrated both in the plots of configurational energy, long- and short-range order parameter, atomic structure variations, and structural – phase state distributions. Simultaneously, there coexist ordered and disordered phases and a certain collection of superstructure domains. This implies the presence of low – stability states in the vicinity of the order – disorder phase transition. The results of investigations demonstrate that the structural – phase transitions within two successive heating and cooling cycles at the same temperature are different in both stages. These changes, though not revolutionary, occur in every cycle and decrease with the increasing cycle number. In fact, the system undergoes training with a tendency towards a certain sequence of structural – phase states.