Hybrid Pore Formation in Copper Spheres by Gas Entrapment and Oxide Reduction

Solid‐state methods for producing porous metals vary greatly in their approaches and outcomes, and they often result in distinctly different pore sizes and/or characteristics. By combining methods in a hybrid process, it is possible that unique porous structures can be made that are simpler to produce, have improved functional properties, or are otherwise superior to any single approach. For the first time, a combination of gas entrapment and oxide reduction to produce microscale porosity in millimeter‐scale copper spheres created by planetary milling is reported. The milling process entraps Ar in micron to submicron pores within the spheres, which are comprised of a Cu 2 mol% CuO metal matrix composite. Upon heating at 800 °C in an inert atmosphere, the individual spheres expand and form ≈29% closed porosity with an average pore size of 1.5 μm. When those spheres are then reheated to 600 °C in a reducing atmosphere, the porosity is converted to being almost entirely open with an average size of 2.3 μm. In addition to the unique nature of the porosity, the processing of the spheres is unusual in that it is completed after only 90 min of milling. Planetary milling is used to create a Cu–CuO metal matrix composite in the form of millimeter‐sized spheres. A hybrid pore formation mechanism allows for closed micron and submicron pores to be formed by gas entrapment. Those pores can then be opened through a secondary‐oxide‐reduction step.