Simultaneously increasing strength and electrical conductivity in nanostructured Cu-Ag composite

This study demonstrates how to increase the hardness, the mechanical strength, the ductility and the electrical conductivity of Cu-8 wt%Ag alloy by engineering the precipitation kinetics of Ag. Discontinuous and continuous precipitation phenomena were shown by differential scanning calorimetry (DSC) to correspond to two distinct exothermic reactions in this alloy. Activation energy was found to be 63.7±0.1 kJ/mol for discontinuous and 68.7±2.3 kJ/mol for continuous precipitation. At higher temperatures (475-580 °C), both continuous and discontinuous precipitation occurred, but at lower temperatures (410 °C), only discontinuous precipitation was observed. Because of higher density and very fine continuous precipitation, the microhardness and tensile strength of a sample aged at 475 °C was up to 22% higher than samples aged at other temperatures (e.g. 170 °C, 410 °C, 580 °C, and 680 °C). Optimized microstructure also enhances the ductility in addition to the tensile strength and the hardness. Because the formation of precipitation reduces Ag dissolved in Cu matrix, the electrical resistivity of aged samples began to decrease above 410 °C. The size, volume fraction, and spacing of continuous Ag precipitates apparently play important roles in maximization of total strength and electrical resistivity.