Microstructural analysis and surface studies on Ag-Ge alloy coatings prepared by electrodeposition technique

Abstract

Among the main characteristics of silver and its alloys, tarnish resistance as well as surface brightness is essential. Alloying these materials with germanium has been shown to have considerable potential in providing tarnish protection. However, studies regarding the electrodeposited silver-germanium (Ag–Ge) alloy coatings are limited. The main objective of this study is to investigate the electrodeposition process of Ag-Ge alloy coatings with different Ge contents. In this regard, co-electrodeposition of Ag and Ge as an alloy coating was performed on pure copper substrates from a cyanide-based electrolyte. The effect of Ge incorporation on alloy composition, surface morphology, topography, texture, crystalline structure and cathodic efficiency of the obtained electrodeposits was investigated. Also corrosion properties of coatings were perused by polarization curves. Evaluation of the coatings was performed using different characterization techniques including XPS, SEM, FESEM, EDS, XRD, AFM, ICP, GIXRD, XRF, FTIR and electrochemical analysis. Results indicated that the optimum content of Ge in the coating was found to be 6 wt% regarding dense and uniform microstructure along with the best corrosion resistance. In addition, the X-ray diffraction patterns exhibited a shift in lattice parameter of Ag that was attributed to the Ag-Ge biphasic alloy formation. Moreover, the surface studies revealed a morphological transformation from nodular to cauliflower-like by increasing the Ge content of coating. The obtained polarization curves represent a remarkable decrease in Ag-6Ge alloy corrosion current density, about 20 times compared to Ag-0.5Ge and about 6 to pure silver. Discrepancies in characteristics between the Ag-Ge and pure Ag coatings were addressed and discussed.