Microstructure and Tensile Properties of Fine-Grained Bulk Copper Fabricated by Thermomechanical Consolidation of Copper Nanopowder/Micron-Sized Powder Blend

Samples of fine structured Cu were fabricated by spark plasma sintering (SPS) of compacts of Cu nanopowder/micron-sized powder blend with a ratio of 3:7 by weight, and one of the SPSed samples was further processed by hot extrusion. The microstructures of the as-SPSed and the as-extruded samples and the tensile properties and fracture behavior of the as-extruded sample were studied. It was found that the microstructures of the samples consist of a concoction of ultrafine and coarse grains with high dislocation densities ( ~ 1015 m^-2) as a result of microstructural evolution during material processing. Some nanograins were oxidized to form Cu₂O particles residing around the coarse grains. Extrusion of the SPSed sample increases its microhardness from 70 HV to 90 HV. The electrical conductivity of the as-extruded sample reaches 87% international annealed copper standard (IACS), and its tensile properties are 200 MPa for yield strength, 218 MPa for ultimate tensile strength and 9% for elongation to fracture. The tensile test specimens from the as-extruded sample exhibit nearly ideal plastic deformation and undergo ductile fracture, suggesting that the fine-grained copper is a highly desirable material for high strength electrical conductors.