Corrosion Behavior of High Energy–High Rate Consolidated Graphite/Copper Metal Matrix Composites in Chloride Media

The corrosion behavior of particulate reinforced graphite/copper (Gr_p/Cu) metal matrix composites (MMCs) was studied in 3.5 wt.% sodium chloride solution using electrochemical techniques, ionic solution analysis, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) techniques. The materials under investigation were high energy-high rate (HEHR) consolidated Gr_p/Cu metal matrix composites. HEHR processing employs a 10 MJ homopolar generator that supplies a 100 kA pulse to rapidly heat and solidify the composite powder compact. This short time at high temperature and the preferential heating and melting at the graphite-copper interface serve to encapsulate the graphite reinforcement, thus providing a highly densified composite product. Initially the open circuit potential corrosion behavior of 1.2, 5, 15, 25, and 40 volume percent Gr_pCu composites was studied in aerated and deaerated 3.5 wt.% NaCl solution using SEM and EDX. Subsequently, the environmental stability of these composites was studied using electrochemical techniques such as polarization resistance and potentiodynamic polarization. The severity of corrosive attack increased with increasing graphite content and in aerated solutions. In addition, solutions from these tests were analyzed to determine the relative amounts of copper and carbon present in the electrolyte after polarization tests. Microscopic analysis techniques were used to characterize the corrosion morphologies and the extensive localized corrosion occurring at the graphite-copper interface. The effectiveness of benzotriazole as a corrosion inhibitor for the copper MMCs was also studied.