Continuous hot corrosion behaviour of an FeCrAlSi coating prepared by laser cladding

Abstract FeCrAlSi coatings were prepared using laser cladding technology and subjected to a continuous hot corrosion test in a eutectic 75 wt% Na2SO4 + 25 wt% K2SO4 salt at 800 °C in air. The FeCrAlSi coating consists of mainly the Fe Cr solid solution, AlFe intermetallic compound and little FeAl2 phase, and the microhardness and tribological properties improved over those of the untreated substrate. In the earliest stage of hot corrosion, a protective Al2O3 film is formed. During the subsequent hot corrosion process, the O2− concentration gradually increases. The alkalinity of the molten salt/coating interface then increases to the level at which it reacts with Al2O3, and the newly formed porous Al2O3 film is less protective. In the mid-stage of hot corrosion, Cr continues to diffuse upward through the porous Al2O3 film, and petal-like Cr2O3 forms on the pores, gradually forming a continuous Cr2O3 film. In the subsequent hot corrosion process, the internal oxidation of the Al intensifies, and the phenomenon of Al2O3 phase diffusing into the interior is more obvious. In the last stage of hot corrosion, the SiO2 film exists in the internal corrosion layer, which is passivated in the molten sulphate. Additionally, Al2O3 no longer penetrates the coating, thus forming a protective oxidation film with the (Cr, Fe)2O3 + Al2O3 in the external corrosion layer, which effectively slows oxidation and sulphuration reactions.