On the Microstructure and the Phase of Electrodeposited Au-Sn and Ag-Sn Alloys

Abstract

The microstructure and the phase of Au-Sn and Ag-Sn alloys electrodeposited from cyanide baths were investigated by X-ray diffraction and transmission electron microscopy. On the solubility of α solid solution and the range of intermediate phase ζ Au-Sn and ζ Ag-Sn of the electrodeposited Au-Sn and Ag-Sn alloys in room temperature, the solubility was decreased and the range was shifted to Sn side by about 10at% as alloy composition in comparison with the thermally equilibrium alloys. The intermetallic compounds of AuSn, AuSn₂, and AuSn₄ were electrodeposited, but the superlattice ε phase in the Ag-Sn alloy was not formed. In both of electrodeposited Au-Sn and Ag-Sn alloys, coring structure by peritectic reaction could not be observed, instead, the homogeneously mixed structure consisting of α and ζ phase was observed. These α and ζ crystallites grew epitaxially with substrates, and no specific habit relationship between α and ζ crystallites was found. The morphology of the crystallites was also influenced by substrates; that is the slender ζ-crystallites in the Au-Sn alloy deposited on the (011) Cu substrate were elongated in the [011] Cu substrate direction. This phenomenon was caused by misfit between (200) Cu and (0111) ζ plane along the [100] Cu direction.