In situ de-wetting of liquid–solid interface to fabricate spherical Ag@Ni immiscible alloys

Abstract

Spherical Ag@Ni immiscible alloy powders were successfully fabricated combining in situ de-wetting of metal droplets from a metalloid solid medium with phase separation of immiscible alloys. The effects of atom ratio and temperature on morphology, structure, and phase separation were investigated. The spherical morphology of alloy powders confirmed the de-wetting of the liquid–solid interface between the liquid Ni–Ag immiscible alloy and the solid alumina powder medium. The Ni-rich phase was scattered in the Ag-rich phase matrix at 1673 K while the spherical Ni-core at the center was surrounded by a ring-shaped shell of Ag at the outer layer with an egg-type structure at 1753 K. The egg-type microstructure of the Ni–Ag particle resulted from the liquid–liquid immiscible phase separation. Such spherical Ag@Ni alloy powders with an egg-type microstructure have a good combination of a high strength Ni-rich phase core and a high electric and thermal conductivity Ag-rich phase shell with many potential advanced applications in electronic packaging.