The environment factors affecting the performance of nickel-aluminum bronze (NAB)

Corrosion and galvanic compatibility studies of a cast nickel-aluminum bronze, NAB (UNS C95800), coupled with an area ratio 1:1 to titanium and a cupronickel (Cu-15Ni) alloy, have been made in brackish seawater. The galvanic currents and mixed-potentials have been routinely monitored for a period of 6 months (from January ’03 to June ’03) as part of a 3 year program. Additionally, environmental factors including dissolved oxygen, seawater temperature and salinity, have been studied in order to assess their affects on the corrosion performance of NAB in natural seawater. Accelerated corrosion rates for the NAB coupled to titanium or Cu-Ni alloy have occurred compared with the uncoupled NAB. Subsequent testing has shown the accelerated corrosion rates are linked to the biofouling season and the local test environment. Corrosion rates decrease at the end of the fouling season. Decoupled potentials indicate a significant polarization of the cathode component, which has been attributed to a surface modification of the titanium and Cu-Ni alloy by the formation of a biofilm. In the case of the Cu-Ni, an enrichment in iron and nickel within the oxide film may also be involved