Hot Corrosion Behavior of Low-Pressure Cold-Sprayed CoNiCrAlY Coatings

CoNiCrAlY coatings were deposited by low-pressure cold spraying and pre-oxidized in a vacuum environment, and its hot corrosion behavior in pure Na₂SO₄ and 75 wt.% Na₂SO₄ + 25 wt.% NaCl salts was investigated. The pre-oxidation treatment resulted in the formation of a dense and continuous α-Al₂O₃ scale on the coating surface. After being corroded for 150 h at 900 °C, the pre-oxidized coating exhibited better corrosion resistance to both salts than the as-sprayed coating. The presence of preformed Al₂O₃ scale reduced the consumption rate of aluminum, by delaying the formation of internal oxides and sulfides and promoting the formation of a denser and more adherent Al₂O₃ scale. Moreover, we investigated the corrosion mechanism of cold-sprayed CoNiCrAlY coatings in the two salts and discussed the effect of the pre-oxidation treatment.