Abstract
The microstructure and phase of Au-Ni alloys electrodeposited from citric acid-cyanide acidified baths were studied by utilizing T. E. M. and S. E. M. and also by measuring microhardness. The electrodeposited alloys were found to form supersaturated solid solutions on the side of Au with a limit up to about 45at. % Ni, and also on Ni side with about 95at. % or more Ni. Over the at. % range of Ni from about 45 to 95, metastable intermediate phases, which probably have similar structures to the phases of AuNi and/or AuNi3 in metallurgically melted Au-Ni alloys, coexisted with the supersaturated solid solutions. Film growth by electrodeposition was of the following process: nucleation→island crystal→network crystal→plate crystal. Also, microcrystallites of 50-200Å in size and many microtwins were observed in the plate crystals of the films. In the initial stage of electrodeposition the film growth took place coherently with Cu substrates. The thick films deposited for 60min, on the other hand, showed smooth surfaces and the smoothness increased with increasing Ni content of the alloys. Formation of supersaturated solid solutions and metastable intermediate phases caused an increase in the film hardness. A maximum value of Hv=400 was obtained at about 80at. % Ni, but the alloys containing about 63-90 at. % Ni were brittle.
