Abstract
Kinetic behaviors of ordered Fe–Co and βCuZn alloys have been investigated with basic equations derived on the basis of the Bragg and Williams theory which is extended to a binary alloy of the bcc structure containing vacancies. It is then assumed that atom movements occur in two mechanisms, a direct interchange of atoms and an interchange through vacancies. The order dependence of vacancy concentration is also considered following the method of Girifalco. Both the two mechanisms assumed here for the interchange of atoms play an important role in the ordering process. The interchange through vacancies is dominant particularly in the ordering process for ordered βCuZn alloy. The numerical calculations have been carried out by using the appropriate values estimated from the data on diffusion and other experiments. In ordered Fe–Co alloys the order parameter at room temperature is retained up to about 500°C. Beyond 500°C it begins to vary rapidly with the maximum rate at about 550°C and finally reaches its equilibrium value. This result is in agreement with the interpretation by Yokoyama, Takezawa and Higashida. On the other hand, the temperature dependence of the order parameter in ordered βCuZn alloy exhibits a negligible anomaly near room temperature.
