Effect of B on hot corrosion behavior of silicide coatings under different corrosive environments at 900 °C

Abstract

Silicide coatings and B-modified silicide coatings were prepared on Nb-Si based alloys using halide activated pack cementation. The hot corrosion behavior of the coatings exposed to Na2SO4 and Na2SO4 + NaCl mixture salts at 900 °C was investigated. The results show that B-modified silicide coatings possess better hot corrosion resistance than the silicide coatings. The hot corrosion products of silicide coatings show a regional microstructure, including uplift regions of AlNaSiO4 imbedded with Al2O3 phases, and depressed silica regions with NaNbO3 and TiO2 particles. The addition of B to the silicide coatings promotes the formation of the uniform and dense boroaluminosilicate scale with better fluidity during hot corrosion, which impedes the self-sustaining cyclic chlorination/sulfidation reactions, and thus, improves the hot corrosion resistance of the silicide coatings.