Studies of the nobility of phases using scanning Kelvin probe microscopy and its relationship to corrosion behaviour of Ni–Al bronze in chloride media

• As-cast Ni–Al bronze was subjected to friction-stir processing.
• Nobility of phases in the microstructure was characterised by SKPFM.
• Phases with lower nobility were preferentially corroded in acidic chloride media.
• Correlation between nobility of phases and real corrosion behaviour was discussed.

An as-cast Ni–Al bronze (NAB) was subjected to friction-stir processing. The microstructure, nobility of the phases and corrosion behaviour of the as-cast and friction-stir processed NAB were studied using EPMA, scanning Kelvin probe force microscopy (SKPFM) and SEM, respectively. SKPFM results revealed that the κ phase in the as-cast NAB and the small-sized phases inside β′ in the friction-stir processed NAB exhibited relatively lower nobility. These phases were preferentially corroded in acidic chloride solution but protected in neutral chloride solution. The correlation between the nobility of the phases and the practical corrosion behaviour was also discussed.