Selective dissolution of the γ phase in a binary Ni(γ)/Ni3Al(γ′) two-phase alloy

Selective dissolution of Ni(γ) in a binary Ni(γ)/Ni3Al(γ′) two-phase alloy was performed in an aqueous electrolyte including 1 wt.% (NH4)2SO4 and 1 wt.% citric acid to obtain a rough, γ′-terminated surface. The electrochemical potential for the selective dissolution was determined from the polarization curves of the γ and γ′ single-phase alloys. The selective dissolution tests proved that γ was precisely removed above 1.7 VSCE, resulting in the formation of a rough, γ′-terminated surface. Surface analyses revealed that a passive AlOx, which retarded the dissolution, was preferentially formed on γ′, resulting in a successful selective dissolution.

Research highlights
► Selective dissolution of γ in the γ/γ′ two-phase alloy is due to the difference in the dissolution rate between the γ and γ′ phases.
► Selective dissolution of γ in the γ/γ′ two-phase alloy is successfully achieved in the higher transpassive region above 1.7 VSCE, resulting in the formation of a rough, γ′-terminated surface.
► The passive AlOx is preferentially formed on the γ´ in the γ/γ′ two-phase alloy and retards the dissolution of the γ′ phase, resulting in the selective dissolution of γ.