Hot corrosion behaviour of a Ni + CrAlYSiN composite coating in Na2SO4-25 wt.% NaCl melt

► The Ni + CrAlYSiN and NiCrAlYSi coatings improved the hot corrosion resistance of K438. ► An oxide scale composed of α-Al2O3, Cr2O3, NiCr2O4 formed on the Ni + CrAlYSiN coating. ► No spallation or crack of the oxide scales on the Ni + CrAlYSiN coating was observed. ► A α-Al2O3 scale was formed on the NiCrAlYSi coating. ► Internal oxidation and sulphidation were detected in the NiCrAlYSi coating.