Effect of heat treatment on corrosion behaviour of additively manufactured Inconel 718 superalloy in NaCl solution

Nickel-based superalloys, particularly Inconel 718, are extensively employed in gas turbine blade applications owing to their excellent high-temperature strength and corrosion resistance. However, these alloys remain susceptible to degradation in aggressive marine environments. This study investigates the corrosion behaviour of laser-bed powder fusion processed Inconel 718 subjected to two post-processing heat treatment conditions: solution-treated (ST) and solution-aged (SA). Electrochemical performance was evaluated in 3.5 wt-% NaCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy. The results revealed that the SA condition exhibited inferior corrosion resistance than the ST condition. The corrosional potential shifted from approximately – 57 mV (ST) to – 129 mV (SA), while the corrosion current density increased from about 3 to 10 μA cm−2, indicating more than three times increase in corrosion after aging. EIS measurements further confirmed the reduced stability in the SA condition through low impedance response. Although passive film formation was observed in both conditions, the SA alloy exhibited a significantly higher density of corrosion pits. Scanning electron microscopy revealed needle-like δ-phase precipitates in the SA condition, which promoted micro-galvanic interactions and enhanced localised pitting corrosion. These findings highlight the critical influence of heat treatment-induced microstructural evolution on the corrosion behaviour of additively manufactured Inconel 718.