METASTABLE STRUCTURES IN LIQUID QUENCHED AND VAPOR QUENCHED AG-CU ALLOYS

The phases and structures of liquid quenched (substrate temperatures of -150°, 20° and 50°C) and vapor quenched (substrate temperature 20°C) Ag-Cu alloys were investigated by X-ray and electron diffraction and by electron transmission microscopy. A single phase FCC solid solution with a maximum deviation of about +1% from Vegard's law was obtained for the thinnest regions (1000-3000 Å) of the liquid quenched alloys with a substrate temperature of -150°C. For the thicker regions and for higher substrate temperatures, segregated silver-rich FCC metastable structures were obtained, the degree of segregation increasing with increase in substrate temperature. A metastable copper-rich FCC phase was only observed for the highest substrate temperature of 50°C. A new hexagonal phase was suggested in the liquid quenched alloys. The crystal structure and lattice parameter of the vapor quenched alloys on a substrate at 20°C were the same as those for liquid quenching. Annealing of liquid quenched Ag 50-Cu 50 alloys in the range of 25°C to 250°C produced a gradual increase in segregation with increase in temperature, finally yielding the α + β equilibrium phases at 200°C. © 1969.