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Galvanic compatibility between graphite/epoxy (Gr/epoxy) composites and metals (HY80 and nickel aluminum bronze (NAB)) was evaluated in galvanic couple tests and in accelerated electrochemical tests in seawater for 180 days. Results indicate that significant galvanic corrosion of NAB and HY80 can occur when each material is coupled to a Gr/epoxy composite containing exposed graphite fibers, with the rate of the metallic corrosion increasing as the graphite fiber area in the composite is increased. The extent of corrosion attack is greater for NAB than HY80 when coupled to Gr/epoxy; however, the magnitude of the galvanic corrosion is largely influenced by the formation and maintenance of corrosion product films. Galvanic corrosion can also occur between Gr/epoxy composites with no graphite fibers initially exposed to the environment and a metal as a result of moisture absorption through the epoxy outerlayer to the graphite fibers. The electrochemical results suggest that short-term electrochemical testing is not a reliable method for assessing long-term galvanic corrosion behavior of Gr/epoxy-metal couples in seawater but is effective in evaluating differences in corrosion resistance with varying cathode: anode area ratios.
graphite/epoxy composites, metals, galvanic corrosion, seawater
Materials engineer, David Taylor Research Center, Annapolis, MD