Powder-based methods that are used to make porous metals are relatively simple and scalable, and porosity can be controlled by interparticle spacing as well as the addition of a sacrificial template. A relatively new process based on reducing oxides in a metal matrix has been demonstrated to produce microscale porosity within individual powder particles and thereby may be used to enhance other powder metal techniques. Templating methods require relatively large quantities of powder, but oxide-reduction feedstock powders have only been produced by small-batch ball milling processes (e.g., 10 s of grams). Planetary ball milling is capable of processing larger quantities of powder (e.g., 100 s of grams) but has significantly different milling characteristics. To successfully apply this technique, it was systematically studied in terms of composition, milling conditions, and the addition of stearic acid to control powder size and morphology along with final porosity. It was found that by controlling basic parameters, such as oxide levels and milling time, a relatively high porosity (25%) and powder percentage (99%) can be achieved in Cu-2 mol% CuO with only 0.035 wt% stearic acid and only 90 min of milling.
Keywords: additive expansion by reducing oxides; copper; copper oxide; planetary milling; porous metals; solid-state foaming.