Electrical Characterization of Carbon Nanotube Reinforced Silver and Copper Composites for Switching Contacts

Carbon nanotube (CNT)-reinforced silver and copper metal matrix composites—at three different reinforcement phase concentrations (0.5 wt.%, 0.75 wt.%, and 1 wt.%)—were produced via powder metallurgy and sintered via hot uniaxial pressing. Optical and electron microscopy techniques were used to characterize the powder mixtures and sintered composites. The latter were also electrically characterized via load-dependent electrical contact resistance (ECR) and surface fatigue tests. Particle size and morphology play a crucial role in CNT deposition onto the metallic powder. CNT were deposited exceptionally well onto the dendritic copper powder regardless of its larger size (compared with the silver flakes) due to the higher surface area caused by the grooves and edges of the dendritic structures. The addition of CNT to the metallic matrices improved their electrical performance, in general outperforming the reference material. Higher CNT concentrations produced consistently low ECR values. In addition, high CNT concentrations (i.e., 1 wt.%) show exceptional contact repeatability due to the elastic restitutive properties of the CNT. The reproducibility of the contact surface was further evaluated by the fatigue tests, where the composites also showed lower ECR than the reference material, rapidly reaching steady-state ECR within the 20 fatigue cycles analyzed.