Influence of Cr content on hot corrosion behavior of Nickel-based alloy coatings at high temperature

Three coatings were deposited on 20G steel by high velocity arc spay technique. Microstructures of these coatings were characterized by optical microscope, scanning electric microscope equipped with EDS. Phases were identified by X-ray diffraction analysis. Hot corrosion trials of these high Cr content coatings were conducted under the mixed sulfates Na₂SO₄+K₂SO₄ layer at 650 ℃. The results showed that hot corrosion kinetic curves fitted well to the parabolic laws, NiO and Cr₂O₃ protective oxide scales have been formed on the surface of four corroded coatings. As the increasing Cr content, the Cr₂O₃ content in the protective oxide scales was gradually increased and the NiO content was reduced, resulted in a significantly enhance in hot corrosion resistance. The corrosion resistance properties of the Ni-30Cr, Ni-45Cr and Ni-50Cr were approximately 10, 15 and 20 times higher than that of 20G steel. In addition, the hot corrosion resistance of Ni-50Cr coating was about 1.4 times of that of Ni-Cr-Ti coating (Tafa 45CT).