Non-isothermal short-range-ordering by excess vacancies in αCu−Zn alloys

Abstract

The kinetics short-range-order (SRO) in quenched Cu-30 at.% Zn, Cu-25 at. %Zn and Cu-20 at. %Zn was investigated by differential scanning calorimetry (DSC). It was evidenced a growing atomic mobility with increasing Zn content. From the DSC traces it is inferred that ordering is established in one stage, assisted by excess vacancies. As the quenching temperature increases considerable reordering occurs during cooling from the quenching temperature. The variation in the SRO non-isothermal behaviour with quenching temperature and composition is interpreted in terms of the atomic mobility and the degree of disorder together with the concentration of vacancies retained by quenching. Activation energies which control the mean life of vacancies and those which control the ordering rate were very similar, indicating that the mobility of vacancies is highly effective in generating SRO. Such activation energies are somewhat lower than the effective energies which control the kinetics of the process obtained from the DSC traces, suggesting that the presence of solute-vacancy complexes may be important as the Zn concentration increases. This feature was confirmed by an estimation of the solute-vacancy binding energy. It was also inferred that divacancy formation is unlikely in the alloys under study.