Structure changes of melt-spun and mechanically alloyed AgCuCd eutectic alloy

Structural changes of melt-spun ribbons and mechanically alloyed AgCuCd alloy powders of ternary eutectic composition 17 wt.% Ag, 29.5 wt.% Cu and 53.5 wt.% Cd were studied using X-ray diffraction, and transmission and scanning electron microscopy. The equilibrium eutectic consists of α, β and γ phases. Rapidly quenched ribbon consists of metastable β(AgCd) phase showing B2 ordering with modulations following the 〈100〉 direction originating from spinodal decomposition. A small fraction of a fine mixture of randomly oriented α and γ crystallites (about 40 nm in size) with large β inclusions was found in very thin areas transparent for the transmission electron microscope observations. Fine globular clusters of γ(Ag, Cu)5Cd8 precipitates of the same crystallographic orientation as the β matrix were observed in thicker areas. The mechanical alloying of mixed powders caused both formation of supersaturated α solid solutions after 32 h of milling and secondary crystallisation of γ(Ag, Cu)5Cd8 and β2(Cu2Cd) phases after 64 h of milling. A decrease of the amount of initial elements is accompanied by refinement of its grain size. Transmission electron microscopy observations performed using the samples milled for 32 and 64 h revealed the nanocrystalline structure of α solid solution and γ and β2 particles of about 15 nm size.