Determination of the AuCu Superlattice Formation Region in Gold-Copper-Silver Ternary System

Abstract

The composition and temperature range of the AuCu-type superlattice formation in the Au-Cu-Ag ternary system was determined by X-ray powder diffraction. Four distinguishable phase transformations were detected, i.e., 1) α (disordered FCC phase) → AuCu I, 2) α → AuCu II, 3) α → α1 (Cu-rich FCC phase) + α 2 (Ag-rich FCC phase), and 4) α → AuCu3. The stable temperature range of the AuCu I-type superlattice was restricted to a lower temperature range by adding silver to stoichiometric and off-stoichiometric Au-Cu alloys. Depending on the increase in silver content, the co-existing region of the AuCu II-type superlattice and the silver-rich α2 phase extended to the lower temperature and over a wide composition range.