Influence of bimodal copper grain size distribution on electrical resistivity and tensile strength of silver- copper composite wires

In order to obtain the best compromise between high strength and low resistivity it was decided to introduce a controlled content of copper (Cu) large grains in copper-silver (Ag-Cu) composite wires. Composite powders are prepared by mixing of 1 vol% Ag nanowires and bimodal Cu powder. The so-obtained composites powders are consolidated into cylinders (8 mm in diameter and 30 mm long) by Spark Plasma Sintering (SPS) at only 450 degrees C. The cylinders served as starting materials for room temperature wire-drawing (WD) for the preparation of fine wires (1-0.2 mm diameter). The microstructure of the cylinders and the wires was investigated by scanning electron microscopy imaging and electron backscattered diffraction analysis. The electrical resistivity and the tensile strength were measured at 293 K and 77 K. The electrical resistivity of the wires is the lowest when the large Cu grain content is the highest. Cu large grains greatly limit the electronic scattering, forming areas with few grain boundaries and no Ag/Cu interfaces and therefore can be considered as fast conduction channels. Conversely, the addition of Cu large grains leads to a moderate decrease in mechanical strength. By presenting a 12 % lower electrical resistivity and an equivalent ultimate tensile strength (UTS) wires with bimodal Cu matrix show a better compromise between low electrical resistivity and high UTS (0.45 mu omega cm, 1082 MPa at 77 K) compared to wires with a fine-grained Cu matrix (0.51 mu omega cm, 1138 MPa at 77 K).

Automated summary

To achieve the best balance between high strength and low resistivity, the introduction of controlled content of large copper grains in copper-silver composite wires can create fast conduction channels and result in lower resistivity. However, it also leads to a moderate decrease in the mechanical strength of the wires.