Structure and properties of electrodeposited silver-bismuth alloys

The elemental and phase compositions, the deposition rate, the structure, and some physico- mechanical properties, such as hardness, wear resistance, roughness and internal stress of electrodeposited coatings of silver - bismuth alloy have been studied. The possibility of deposition of alloy coatings of desired composition depending on the electrolysis conditions and on the composition of the electrolyte used has been demonstrated. With increase in the Bi content in the coatings, hardness and wear resistance decrease, and at Bi contents higher than 50 wt.% the wear resistance remains unchanged. The roughness of the coatings is independent of their Bi content. The alloy coatings reveal a negative ( compressive) internal stress. They consist of two phases and are heterogeneous both in the bulk and in the surface layer. A clearly expressed columnar structure is observed, the columns being of different phase composition. This structure is sometimes accompanied by a lamellar structure. The simultaneous deposition of phases with different Bi content leads to self- organization phenomena and formation of wave, spiral and target structures on the electrode surface.