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

Herein, 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 700celcius 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.

Automated summary

The NiCrMoFeCoAl-30%Cr3C2 coating exhibited the best corrosion stability on T22 steel, with the highest charge transfer resistance. The post-heat-treated HVOF coatings hindered electrolyte access to the base alloy, subsequently improving corrosion stability.