Hot Corrosion of Nickel-Chromium and Nickel-Chromium-Aluminum Thermal-Spray Coatings by Sodium Sulfate-Sodium Metavanadate Salt Available to Purchase

The hot corrosion behavior of low-pressure plasma-sprayed (LPPS) 80 wt% Ni-20 wt% Cr and flame-sprayed (FS) 75 wt% Ni-20 wt% Cr-4.0 wt% Al coatings on type 304 (UNS S30400) stainless steel (SS) by thin fused films of sodium sulfate (Na₂SO₄) and 0.7 mol fraction Na₂SO₄-0.3 mol fraction sodium metavanadate (NaVO₃) at 900°C in a 1% sulfur dioxide (SO₂)-oxygen (O₂) atmosphere was studied using an electrochemical method. The 80% Ni-20% Cr coatings were tested in the as-sprayed condition. 75% Ni-20% Cr-4% Al coatings were tested under as-sprayed and laser-glazed conditions. Evolution of the fused salt film chemistry, in terms of the thermodynamic activities of O₂ and sodium oxide (Na₂O), was monitored using a zirconia O₂ probe and a fused-silica Na sensor. Results permitted qualitative evaluation of the corrosion resistance of the coatings and could be interpreted in terms of previously proposed hot corrosion mechanisms.