INFLUENCE OF RE OXIDE ADDITIONS ONHOT CORROSION BEHAVIORS OF NiAl COATINGS￣①
(Corrosion Science Laboratory; Academia Sinica ; Shenyang 110015)
Abstract: The influence of rare-earth(RE) oxide additions, e. g. Y2O3 and Gd2O3 on the hot corrosion behaviors of the NiAl coatings exposed to the Na2SO4+25wt.- % K2SO4 fused salt at 850℃ was studied. The experimental results show that the RE oxide additions can not only reduce the corrosion rates of the coatings, but also lighten the corrosion degree of the sulfides on the coatings through the formation of stable RE-oxygen-sulfides which are aggregated in the surface corrosion areas of the coatings. With increasing additions , the effect of the RE oxides against hot corrosion will improve. Furthermore, the corrosion form of the sulfides will change from imhomogeous corrosion , in which case the intracrystalline local corrosion is predominant , to mixed type corrosion ,in which case the transgranular corrosion is predominant.
Key words: rare earth oxides NiAl based coatings hot corrosion