Spark plasma sintering of a Cu–Cu2O powder obtained by partial oxidation of electrolytic copper

Abstract

Studies of consolidation of pre-oxidized powders are interesting from the viewpoint of gaining an understanding of the features of sintering of metallic core-oxide shell particles and the formation of oxide-reinforced composites. If spark plasma sintering (SPS) is selected as a consolidation method, the possibility of the oxide interacting with graphite tooling/foil should be taken into account in the development of metal-oxide composites. In the present work, materials fabricated by SPS of a partially oxidized copper powder containing Cu2O were studied. The pre-oxidized powder obtained by annealing an electrolytic copper powder in air was subjected to SPS in contact with a graphite foil. Pressureless SPS at 700 °C resulted in the formation of a porous structure, in which the morphology of the ligaments was similar to that of the particles of the oxidized powder. The grain structure of the oxide layers could be well distinguished. After SPS at 700 °C and 40 MPa, the Cu2O phase was preserved even in the subsurface layer of the compact. The oxide reduction to metal was observed after SPS at 900 °C and occurred only in the vicinity of the graphite foil. The Cu–Cu2O composites sintered under a pressure of 40 MPa at 700 °C and 900 °C had a porosity of 5% and a Vickers hardness of 140 ± 5 HV0.3 and 120 ± 5 HV0.3, respectively. A reduction in hardness of the composites can be explained by grain growth in the material sintered at a higher temperature.

Keywords

• Copper
• Microstructure
• Oxidation
• Hardness
• Graphite foil