Nickel-aluminium bronze pitting corrosion in seawater

摘要

Cast nickel-aluminium bronze (UNS C95800), CuAl9Fe5Ni4Mn, is extensivelyused in seawater environments because of its castability, high toughness anderosion-corrosion resistance. This investigation has for the first time studied theevolution of nickel-aluminium bronze pitting corrosion during prolonged exposure tonatural (estuarial) seawater. The corrosion performance has been linked to thecomplex nickel-aluminium bronze microstructure, principally the influence of the a+Kiiieutectoid on the initiation of selective phase corrosion. Initially, a protective oxidefilm forms as the copper-rich a-phase corrosion penetrates further into themicrostructure leaving the unattacked k-phases to create an adherent skeletal lattice.At localised sites selective phase corrosion can also occur and due to the continuousnature of the Kiii-phase develops into a 'pitting' type phenomenon after prolongedexposures. The pitting mechanism is characterised by very wide although relativelyshallow corrosion features. This mechanistic understanding provides further insightsinto the development of pitting corrosion experienced by NAB after long-termexposures to natural seawater for up to 3 years.