Microstructural and elemental evolution of directed energy deposited inconel 825 under hot corrosion

This study investigates the hot corrosion behaviour of Inconel 825 wall under high-temperature environments using a eutectic mixture of sodium sulphate (Na₂SO₄) and vanadium pentoxide (V₂O₅). The wall was fabricated using cold metal transfer (CMT)-based directed energy deposition (DED) process. Specimens were exposed to temperatures of 700°C and 900°C to simulate conditions encountered in industrial applications such as marine engineering and power generation. At 700°C, the alloy exhibited a weight gain of approximately 0.15 mg/cm² over 50 hours, attributed to the formation of a dense and adherent Cr₂O₃ oxide layer. SEM/EDS analysis confirmed a uniform chromium-enriched oxide scale with limited incorporation of vanadium and sulphur, maintaining parabolic corrosion kinetics. At 900°C, the weight gain increased significantly to 0.7 mg/cm², reflecting a shift to linear kinetics. SEM/EDS analysis at this temperature indicated extensive incorporation of vanadium and sulphur into the oxide layer, forming non-protective compounds such as NiV₂O₆, CrVO₄, Cr₂S₃, and Ni₃S₂. Elemental mapping demonstrated chromium depletion in the oxide scale and substrate, compromising the formation of a continuous Cr₂O₃ layer. This study emphasizes the temperature-dependent nature of hot corrosion mechanisms of Inconel 825 and highlights the need for surface engineering techniques to enhance its performance in aggressive environments.