Electrochemical studies of heat‐treated NiCrMoFeCoAl and NiCrMoFeCoAl‐30%Cr3C2 HVOF coatings on T22 boiler steel

Abstract

AbstractHerein, we present the corrosion behavior of NiCrMoFeCoAl and NiCrMoFeCoAl‐30%Cr3C2 high‐velocity oxy fuel (HVOF) coatings on the ASTM‐SAE213‐T22 boiler tube steel alloy. The samples exposed to molten salt (Na2SO4–60%V2O5) environment at 700℃ under thermocyclic conditions were investigated in conjunction with electrochemical techniques. The surface structures and morphologies of heat‐treated samples suggest the extent of corrosion is least for the NiCrMoFeCoAl‐30%Cr3C2‐coated steel. Room‐temperature electrochemical analysis of heat‐treated samples demonstrate the good stability with NiCrMoFeCoAl‐30%Cr3C2 layers on T22 steel at solid/liquid interface under neutral pH conditions. The potentiodynamic and impedance analyses reveal that the higher charge transfer resistance was observed for NiCrMoFeCoAl‐30%Cr3C2‐coated steel, followed by NiCrMoFeCoAl‐coated steel and bare T22 steel. The chromium carbide containing the HVOF coating exhibit a highly dense layer and the metal chromites/chromates on the post‐heat‐treated coatings provide poor access for the electrolyte to base alloy and subsequently improve corrosion stability.