Rapid solidification of silver-rich Ag-Cu-Zr-Al alloys

In this work amorphous/crystalline Ag-Cu-Zr-Al composites with 80 wt.% Ag were obtained by rapid solidification exploiting the presence of a miscibility gap in the liquid. Undercooling favored the separation of a silver-rich liquid, that solidifies as f.c.c.-Ag solid solution, and a remaining liquid that falls in the glass forming compositional range of the Cu-Zr-Ag-Al system. Alloys with nominal composition (at.%) Ag73.0Cu12.7Zr12.1Al2.2 (alloy A), Ag73.1Cu17.2Zr9.7 (alloy B0), Ag72.5Cu16.7Zr9.4Al1.4 (alloy B1), Ag71.8Cu16.2Zr9.1Al2.8 (alloy B2) were studied. All the alloys have a silver content (80 wt.%) corresponding to the one required for commercial precious alloys. The effect of the cooling rate and the composition on phase selection and microstructures was evaluated by comparing slowly cooled master ingots and rapidly quenched ribbons. In alloys B0, B1 and B2, the amorphous fraction progressively reduces when increasing the Al content. For alloy A, amorphization of the silver poor liquid can be obtained only at high quenching rate. A ductile fracture behavior of the as-spun ribbons is combined with high hardness values (260-290 HV).