Microstructure of a heat treated nickel-aluminum bronze and its corrosion behavior in simulated fresh and sea water

Nickel-aluminum bronzes (NAB) are a family of alloys with excellent mechanical and corrosion resistance properties, even in highly corrosive environments, attributed to the complex as-cast microstructures. Heat treatment, in-service conditions or welding procedures induce microstructural transformations resulting in changes of the properties. To evaluate the corrosion behavior of one selected NAB alloy, different heat treatments were performed and the relation between microstructural changes and corrosion behavior was studied. Under common casting conditions, CuAl10Fe5Ni5 bronze consists of the α-phase, β-phase, and several intermetallic phases, collectively referred to as j-phases. The microstructures of the as-cast and heat treated samples were characterized by metallographic methods. After grinding and polishing, the samples were etched with FeCl3-as well as Cu(NH4)2Cl4-solutions and examined by light optical and scanning electron microscopy. Finally, electrochemical corrosion tests of both as-cast and heat treated samples were carried out in simulated fresh water and sea water under potentiostatic conditions. Four specimens of each sample type were polarized simultaneously at different potentials for 70 h. These specimens were used to study the corrosion progress of the different specific microstructural features and constituents by metallographic investigations. © 2016 by ASTM International.