Corrosion Resistance and Mechanical Properties of Nickel Aluminum Bronze Alloys

Nickel aluminium bronze (NAB) alloys represent a class of copper-based materials renowned for their exceptional combination of corrosion resistance and mechanical strength, particularly in marine and offshore environments. The alloy matrix is typically dominated by a ductile α-copper solid solution, interspersed with a series of κ intermetallic phases formed by combinations of iron, nickel, aluminium and sometimes manganese. These κ phases contribute to the overall hardness and tensile yield strength, but also introduce local cathodic sites that may initiate microgalvanic corrosion when exposed to chloride‐rich media. Microstructural control through casting, heat treatments, additive manufacturing or friction stir processing can refine grain size, alter phase morphology and redistribute alloying elements, thereby tuning the trade-off between strength, toughness and corrosion performance. In seawater, NAB alloys develop a protective oxide or hydroxide film on their surface, yet selective phase corrosion of eutectoid regions can undermine this barrier. Mechanical loading and dynamic environments—such as cavitation, erosion or tribocorrosion—exacerbate degradation by combining mechanical wear with electrochemical attack. Recent advances focus on optimising processing routes to achieve uniform microstructures, minimising detrimental intermetallic precipitates and promoting stable passive films. Such developments underpin ongoing efforts to extend component life in naval propulsion systems, offshore oil and gas infrastructure, and renewable-energy applications.

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Technical terms

α-phase: The primary copper-rich solid solution in NAB, characterised by a face-centred cubic lattice and responsible for ductility.

κ-phases: A family of intermetallic precipitates (labelled κI–κV) containing Fe, Ni and Al that strengthen the alloy but can act as cathodic sites in corrosion cells.

Microgalvanic cell: Local electrochemical cell formed between phases of differing electrode potential, driving preferential corrosion of the anodic phase.

Wire arc additive manufacturing (WAAM): A process that deposits metal layer by layer using a welding wire feedstock and electric arc heat source, yielding near-net shapes.

Friction stir processing (FSP): A solid-state technique that uses a rotating tool to refine microstructure, homogenise alloying elements and modify surface properties.

Cavitation erosion-corrosion: Combined material loss mechanism where collapsing vapour bubbles induce mechanical damage while simultaneously accelerating electrochemical attack.

References

1. Corrosion performance of wire arc additively manufactured NAB alloy. npj Materials Degradation (2023).
2. Evolution of the Corrosion Product Film on Nickel-Aluminum Bronze and Its Corrosion Behavior in 3.5 wt % NaCl Solution. Materials (2019).
3. A Study of Erosion–Corrosion Behaviour of Friction Stir-Processed Chromium-Reinforced NiAl Bronze Composite. Materials (2022).
4. Understanding the Corrosion Behavior of Nickel–Aluminum Bronze Induced by Cavitation Corrosion Using Electrochemical Noise: Selective Phase Corrosion and Uniform Corrosion. Materials (2023).