Selective oxidation behavior of Ag-49Cu-xGa precious metal alloys

Abstract

Novel Ag-49Cu-xGa (x = 5, 7, 10, wt%) ternary alloys were designed to overcome cost-performance limitations of conventional Ag-28Cu through compositional engineering. By reducing silver content to less than 46 wt% while incorporating 5–10 wt% Ga, we achieve a duplex phase microstructure consisting of Ag and Cu-rich phases with good oxidation resistant property. The outward Cu diffusion and subsequent CuO formation drive the development of porous oxide scale, which creates rapid pathways for enhanced Cu-O interdiffusion, and scattered distribution of Ga₂O₃ under sample surface cannot suppress internal oxidation. Increased Ga content enables the oxidation process to reach a kinetically stable state in a shorter time. Crucially, Ga preferentially dissolves in Cu-rich phase, enabling a unique atomic redistribution mechanism during oxidation. Higher Ga content in Cu-rich phase facilitates outward diffusion of Ga, promoting formation of a continuous Ga₂O₃ barrier with hundreds of nanometers. This nanoscale protective layer, characterized by a favorable Pilling-Bedworth ratio (1.33), effectively suppresses oxygen inward diffusion and maintains integrity of Ga₂O₃ scale. The above results benefit the expanding of new application areas of cost-effective precious metal alloys with low solidus and liquidus temperatures.