Heterogeneous ordering and antiphase domain morphology in Cu₃Pt (19 at.%Pt)

Abstract

The ordering process in a Cu[sbnd]19at.% Pt alloy has been investigated. Differential thermal analysis revealed that the ordering occurs in two stages, a low-temperature stage I and a higher-temperature stage II. Examination of the stage I ordering during isothermal annealing by X-ray analysis showed that the variation in lattice constant and domain size with annealing time exhibit a step for annealing temperatures above 540 K, and that line broadening of both fundamental and superlattice peaks is observed irrespective of the annealing temperature. Combining this information with observations of the morphology of antiphase domains by transmission electron microscopy, it is confirmed that stage I ordering is a process of heterogeneous nucleation and growth of the ordered domain from the grain boundary, assisted by the migration of excess vacancies introduced by quenching. It is concluded that the kinetics of stage I ordering is controlled by the stability of the defect formed by the clustering of excess vacancies in the ordered region. The observed phenomena can be well interpreted by the proposed ordering mechanism.