Internal Oxidation of Silver-Based Alloys: Strengthening–Toughening Mechanisms and Microstructural Control

Silver-based alloys are irreplaceable in high-reliability electrical contacts because silver has the highest electrical conductivity of all metals, yet its low strength and the intrinsic strength–ductility trade-off limit their use under increasingly severe service conditions. Internal oxidation—the selective in situ oxidation of reactive solutes in a chemically inert Ag matrix—converts these solutes into fine, dispersed oxides, thereby strengthening the alloy. This review critically assesses internal oxidation in silver-based alloys. The thermodynamic and kinetic criteria for selective oxidation are summarized, together with the Wagner diffusion-controlled framework describing the oxidation front. Using Ag-Mg and Ag-Sn as archetypal systems, we trace the microstructural evolution from coherent Mg-O nanoclusters and dispersed SnO2 particles to deleterious banded oxides, identifying band formation and under-oxidized cores as the two characteristic microstructural defects. The roles of temperature, time, oxygen partial pressure and third-element additions (Te, In, Sb, Bi, Ni) in widening the process window and refining the oxide dispersion are examined. Orowan bypassing, coherency strain and Hall–Petch grain refinement, and their coupling with microstructural characteristics, are discussed to provide guidelines for alloy design. Finally, outstanding questions and opportunities, including atomic-scale in situ characterization, predictive multiscale modeling and novel processing routes, are outlined.