Effect of Si Addition to Improve the Performance of Type II and Type I Hot Corrosion Resistance of Aluminide Coating

Microstructure and hot corrosion resistance of four aluminide coatings with different Si contents ranging from 0 at % to 30 at% are studied. Si primarily exists as CrSi2 and (Cr,Ti)5Si3 in the upper zone of Si-modified aluminide coatings; CrSi2 transforms into Cr3Si phase during corrosion process. These silicides hinder the inward diffusion of the corrosive elements, resulting in enhanced corrosion resistance of Si-modified aluminide coatings at 700 degrees C. Mechanisms of severe corrosion in coatings with Si at 900 degrees C was disclosed; high content of Si leads to insufficient Al to renovate Al2O3 scale, as well as high temperature causes fast depletion of Al.