Selective Spinodal Decomposition at Grain Boundaries in Ultrafine-Grained Ag-Cu Alloys with Sub-Critical Solute Concentration

Abstract

Grain-boundary (GB) segregation effects on chemical spinodal decomposition at low solute concentrations were investigated in sputter-deposited ultrafine-grained Ag-Cu alloys films using scanning transmission electron microscopy and x-ray diffraction. Spinodal decomposition was observed to initiate at GBs as non-crystalline Cu solute clusters, with local solute concentration varying based on the overall Cu content of the alloy and thermal annealing state. Direct experimental evidence demonstrates that heterogeneous GB segregation at low solute concentrations can selectively induce localized spinodal decomposition at GBs, a phenomenon rarely observed in immiscible alloys with higher solute concentrations. This finding provides critical insights into the role of heterogeneous solute segregation at GBs in influencing the properties of nanocrystalline and ultrafine-grained materials.

Keywords: Ultrafine-grained alloys, spinodal decomposition, heterogeneous segregation, magnetron sputtering, STEM