Experimental-size specimens of two different compositions of nickel-aluminum bronze were cast, subjected to five different heat treatments and were exposed to seawater. Both alloys were in compliance with UNS C95800 and MIL-B -244 80, except that the aluminum content of one alloy, at 8.1%, was below the lower limit of the specified compositional range. Their microstructures were characterized and correlated with corrosion resistance. Selective phase attack was seen in both alloys, although it was much more pronounced in the alloy with the lower aluminum content, to the point where entire grains fell out. It was observed that the higher aluminum-containing alloy had markedly superior corrosion resistance. Thus it is important to maintain the aluminum level in alloy UNS C95800 at or above the lower limit, and within the specified range of 8.5-9.5%.
Keywords: Aluminum Bronze, Nickel-Aluminum Bronze, Seawater, Microstructure, Martensite, Bainite, Eutectoid, Alpha, Widmanstatten, Phase, Corrosion, Localized Corrosion, Selective Phase Corrosion, Selective Attack, Depth of Attack, Depth of Penetration, UNS C95800, MIL-B-24480.