Liquid metal replacement as a means to form bicontinuous Invar-Ag microcomposites

Invar-Ag composites could combine the low thermal expansion of Invar with the high thermal conductivity of Ag, especially if a bicontinuous microstructure, characteristic of dendritic solidification, can be achieved. However, liquid-phase immiscibility in the Invar-Ag system prevents direct formation of such structures via conventional solidification. This study introduces a liquid-phase replacement approach that selectively replaces the interdendritic Cu-rich network in Invar-Cu precursors with Ag. Ag was successfully infiltrated into millimeter-thick bulk specimens formed by arc melting, substantially improving thermal transport relative to Invar-Cu. Infiltration into additively-manufactured Invar-Cu proved more challenging due to capillary instabilities fostered by the much finer-scale cellular microstructure. This work discusses the infiltration mechanisms, resultant microstructure formation, effect of interfacial segregation on wetting, and thermal performance of Invar-Ag composites.