Carbon Nanotube Reinforced Silver-Copper Hybrid Metal Matrix Composites as Bimetallic Electrodes

This work proposes and optimizes the sintering process to produce hybrid metal matrix composites (HMMC) electrodes with optimal performance while minimizing the required energy input and production times. Four sets of carbon nanotube (CNT)-reinforced HMMC were manufactured via powder metallurgy and sintered via hot uniaxial pressing, techniques which are easily scalable and produce near-net shape components. The sintering temperature and time were optimized using relative density to determine if the parameters were satisfactory. Following sintering, metallographic cross sections of the HMMC (i.e., Ag/Cu, Ag/Cu+CNT, Ag+CNT/Cu, and Ag+CNT/Cu+CNT) were prepared and characterized via confocal laser and scanning electron microscopy. A qualitative assessment of the elemental distribution near the interface was conducted via energy dispersive X-ray spectroscopy linear and map scans. Moreover, load- and current-dependent electrical contact resistance was evaluated. The sintering times and temperatures required for the HMMC are lower than those required for pure metals due to the decreased eutectic temperature of the silver-copper mixture. Sintering at 550°C for 2.5 hours is sufficient to achieve densities above 90%. The CNT act as diffusion barriers, slowing down the formation of Kirkendall voids. The Ag/Cu+CNT and Ag+CNT/Cu+CNT samples exhibited the most promising results, based on their low resistance and exceptional contact elasticity.