Electrodeposition of Fe-Ni alloy coating on ferritic stainless steel

Fe-Ni alloy coatings were electrodeposited on ferritic stainless steel (FSS) in solutions containing FeSO₄ and NiSO₄. The effects of pH, [Fe²⁺]/[Ni²⁺] (molar ratio) of electroplating solutions and cathode current density on deposition rate and surface appearances of the coatings were investigated. The results indicated that the deposition rate of the coating in solution with [Fe²⁺]/[Ni²⁺] of 0.4 slightly increased with increasing pH from 2.5 to 3.5 under the current density of 5.5 mA/cm², and then the deposition rate of the coating in solution with pH 4.0 began to decrease. The deposition rate also slightly increased with pH up to 3.5 under higher cathode current densities of 13.5 and 27 mA/cm². Under 13.5 mA/cm², however, the coating deposited in solution with pH 4 was prone to crack or flake. The deposition rate increased and the surface of coatings became less smooth with increasing cathode current density. The effect of the ratio of [Fe²⁺] to [Ni²⁺] on deposition rate was not obvious. With increasing the ratio of [Fe²⁺] to [Ni²⁺] in plating solution, the content of Fe in the coatings increased; while the Ni content in the coatings decreased with the increase in the ratio of [Fe²⁺] to [Ni²⁺]. The deposited coating consisted of Fe-Ni alloy phase.