Corrosion mechanism of an Al–BN abradable seal coating system in chloride solution

• Galvanic corrosion occurred within the three parts of the Al–BN coating system.
• The Al matrix of Al–BN suffered spontaneous pitting due to galvanic interaction.
• Hydrogen evolution during corrosion compensated 13% of the current for Al–BN.

The corrosion mechanism of an Aluminum–Boron Nitride (Al–BN) abradable coating system (with NiAl bond layer and 0Cr17Ni4Cu4Nb substrate) in chloride solution has been investigated by potentiodynamic polarization and volumetric tests. Galvanic interaction of the coating system during corrosion has been confirmed. Upon coupling, the Al–BN layer assumes anodic character, while the bond NiAl and substrate act as cathodes. Spontaneous pitting is aroused on the Al matrix of the Al–BN layer due to the galvanic interaction. The Negative difference effect (NDE) of the Al–BN has been discussed.