The iron effect on hot corrosion behaviour of MCrAlX coating in the presence of NaCl at 900 °C

Abstract

Cyclic hot corrosion tests of two MCrAlX coatings with different Fe contents were carried out in a molten salt (75 wt% Na2SO4 + 25 wt% NaCl) environment at 900 °C under type I hot corrosion. The positive effect of high Fe addition which reduces the advancing of corrosion front in the coating was discussed. The experimental results showed that the main corrosion reaction is the basic fluxing of Al, while Fe is relatively inert. Combined with thermodynamic modelling, it was demonstrated that a high Fe addition in MCrAlX coatings shifts the equilibrium Al content of the γ phase towards a low level and also reduces the loss of Cr from coating to the substrate. Both effects contributed to a higher “effective” Al supply of the coating to resist basic fluxing and thereby enhance the coating resistance to hot corrosion by reducing the rate of advancing of the corrosion front.