Phase-controlled internal oxidation and solute redistribution in Sb- and Cr-modified Ag-Sn-In-Ni alloys

Internal oxidation of multi-component silver-based alloys is governed by oxygen diffusion in the silver matrix and by the composition and reactivity of enriched-solute secondary phases, yet the phase-specific roles of minor Sb and Cr additions remain unclear. Ag-6.5Sn-2.5In-0.5Ni-0.5Sb and Ag-6.5Sn-2.5In-0.5Ni-0.5Cr alloys were investigated by high-pressure oxidation, quasi-in-situ oxidation, X-ray diffraction, and electron probe microanalysis. After oxidation at 750 °C in pure O 2 under pO 2 ≈ 0.9 MPa, oxidation proceeded inward from both surfaces, leaving a residual Ag-rich core. The Cr-containing alloy showed a larger inward oxidation depth than the Sb-containing alloy, suggesting a higher degree of internal oxidation. Quasi-in-situ observations further indicated distinct representative phase-dependent oxidation trends. In the Sb-containing alloy, early oxygen enrichment was associated mainly with Sn- and In-bearing regions in the Ag matrix, whereas oxidation of Ni-Sb-Sn-rich secondary regions became evident at later representative stages and was accompanied by redistribution of Sn, Sb, and Ni. In the Cr-containing alloy, Cr-rich regions showed a strong local oxidation response once reached by oxygen, whereas Ni-Sn-rich and mixed Ni-Cr-Sn-containing regions exhibited distinct and spatially heterogeneous oxidation behavior. These results suggest distinct representative phase-dependent oxidation trends. Sb is associated with a relatively sequential oxidation pathway involving delayed oxidation of Ni-Sb-Sn-rich secondary regions, whereas Cr introduces reactive Cr-bearing regions and promotes multiphase-coupled oxidation. The present results establish a process–microstructure relationship between minor alloying additions, secondary-phase constitution, and internal oxidation behavior, providing a mechanistic basis for controlling oxidation extent, oxide morphology, and phase distribution during internal-oxidation processing of Ag-SnO 2 -based precursor alloys.