Oxide reduction effects in SPS processing of Cu atomized powder containing oxide inclusions

The SPS sintering of a commercial copper atomized powder was investigated for analyzing the effects of the oxides reduction reactions on densification and microstructure. This powder, with a mean particle size close to 12 μm, contains copper oxides (Cu₂O mainly) located at the particle surface and inside the particles. Beforehand, the reduction of the oxides was studied by means of TGA, XPS analyses and pressureless sintering in atmosphere containing 4 percent of hydrogen. CuO and Cu₂O were reduced at 280 and 425 °C respectively. The reduction of Cu₂O located inside particles induced the swelling of these latter. The SPS sintering under vacuum did not allow removing the oxides, even using low heating rate during the cycle. Under hydrogen containing atmosphere, the oxide reduction is significant, but requires time, typically through low heating rates, to be efficient. Densification is not achieved in this case because of the development of pores related to the hydrogen sickness phenomenon. No particular effect is observed on neck formation and contacts strengthening. - Highlights: • Cu powders with internal oxides were sintered by SPS under vacuum and hydrogen atmosphere. • During sintering, densification is competing with particle swelling which may result from oxide reduction. • Despite the carbon matrix, oxides are not removed during SPS processing under vacuum. • Oxides can be reduced when hydrogen is used but this needs long processing times and induces porosity.