Thermal stability of immiscible Cu-Ag/Fe triphase multilayers with triple junctions

Nanostructured metallic multilayers have attracted significant attention due to their high mechanical strength. However, they often have limited thermal stability at elevated temperatures. Multilayers with immiscible constituents also suffer from high temperature microstructure instability due to thermal grooving and subsequent layer pinch-off. Here we report the enhanced thermal stability of immiscible triphase Cu-Ag/Fe multilayer with triple junctions comparing to Cu/Fe multilayers. The immiscible Cu/Fe multilayers experienced drastic thermal grooving and rapid grain growth at 500°C, followed by the complete breakdown of layer structure and spheroidization at 600°C. In comparison, the layer structures of Cu-Ag/Fe triphase multilayers remain stable up to 600°C with insignificant grain coarsening. The grooving kinetics as well as the underlying mechanisms that lead to the excellent thermal stability of the triphase multilayers are discussed. This study provides a fresh perspective on designing thermally stable nanostructured multilayers for high temperature applications.