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

• Published in: Corrosion science Vol. 193; p. 109869
• Main Authors: Liu, Hongfei, Tan, Chee Kiang Ivan, Meng, Tzee Luai, Teo, Siew Lang, Liu, Junyi, Cao, Jing, Wei, Yuefan, Tan, Dennis C.C., Lee, Coryl J.J., Suwardi, Ady, Lin, Ming
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Ltd 01.12.2021; Elsevier BV
• Subjects: Chromium; Corrosion prevention; Depletion; Diffusion layers; Diffusion zone; Grain boundaries; Hot corrosion; Inconel 625; Laser beam cladding; Laser-cladding; Molten salts; Molten sulfate salts; Molybdenum; Nickel base alloys; Nucleation; Spallation; Superalloys; Laser-cladding; Inconel 625; Diffusion zone; Hot corrosion; Molten sulfate salts
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2021.109869

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. [Display omitted] •Hot corrosions of laser-cladded inconel 625 in molten salt mixture of Na2SO4-MgSO4.•External dual-layer MgO/Cr2O3 formed with Cr2O3 immediate on inconel 625.•Cr outward-diffused and S inward-diffused, dominantly along the grain boundaries.•Cr depletion promoted δ-precipitations, dislocations, pores and internal spallation.•S-diffusion led to internal sulfide scales without internal oxide scales at all.