The ordering rate in Au-Cu binary alloys can be modified by gallium addition. In order to investigate the effect of the Au/Cu ratio and gallium content on the ordering rate, the free energy change associated with the order-disorder transformation was estimated. A Rietveld analysis of the X-ray diffraction patterns of the AuCuI ordered phase was made to investigate the site preference of the gallium atoms in the AuCuI ordered structure. Our main results are as follows. In the Au-Cu binary and Au-Cu-Ga ternary alloys, the age-hardening rate strongly decreased for large deviations of the Au/Cu or Au/(Cu+Ga) ratio from 1. It was caused by a decrease in the driving force for atomic ordering. Gallium addition caused an increase in the driving force for ordering and a decrease of the liquidus temperature, which resulted in the acceleration of age-hardening rate. Gallium atoms occupied the Cu site rather than the Au site in the Au-Cu-Ga ordered phase.
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Mechanical Engineering
- Metals and Alloys
- Materials Chemistry