Hot corrosion and internal spallation of laser-cladded inconel 625 superalloy coatings in molten sulfate salts

Abstract Hot corrosions of laser-cladded inconel 625 in molten salt of Na2SO4-MgSO4 mixture have been studied at 900 °C to address its anticorrosion behaviors. Elemental and microstructural characterizations provide direct evidence for the formation of MgO/Cr2O3 external layers and the outward-diffusion of Cr atoms. The Cr-depletion promotes precipitation of δ-Ni3(Nb/Mo), nucleation and accumulation of dislocations, pores, and internal spallation of the corroded alloy. They also provide evidence for the diffusion of sulfur into the near-surface region, leading to the formation of internal sulfide scales (i.e., Nb4-xCrxS6, CrS, and MnCr2S4). Grain boundaries play important roles in the atomic diffusions and sulfide formations.