The microstructure of the AuCu-6at.%Ag alloy has been studied by conventional electron microscopy as well as by high resolution electron microscopy. The combination of these techniques with optical diffraction allowed the identification of a face-centred cubic disordered α phase which, depending on the aging temperature, coexists with AuCu I or AuCu II. Precipitates of this α phase are finely dispersed and are sometimes as small as 10 nm × 2 nm. The atomic disorder along the periodic antiphase boundaries in AuCu II and their wavy character can be visualized and semiquantified by comparing high resolution observations with calculated images.
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