Analytical electron microscopy of cast Au-Ag-Cu alloys

Abstract

The microstructure in an as-cast Au-Ag-Cu-Pd alloy has been examined by electron microscopy (TEM) combined with quantitative X-ray microanalysis (EDS). The primary phase formed during solidification is enriched in silver and palladium, while gold and copper segregate to grain boundaries, where substantial amounts of lamellar eutectic colonies are formed. The compositions of the lamellae were determined by EDS analysis to be 56% Au-13% Ag-26% Cu-6% Pd and 50% Au-42% Ag-5.5% Cu-2.5% Pd (wt%). Ordering and decomposition reactions take place during cooling in the solid state: plate-like precipitates of tetragonal AuCu-I on {001} planes were found within the primary phase and in silver-rich lamellae in eutectic colonies.