OXIDATION SULFIDATION OF IRON-ALUMINUM ALLOYS

A principal reason for the interest in iron aluminides is their potent ial to resist corrosion in aggressive high-temperature environments. A ccordingly, the development programme for this class of alloys has inc luded an investigation of the corrosion properties in mixed oxidant (H 2S-H-2-H2O) environments. Corrosion studies were initially directed at Fe3Al and FeAl, including effects of third element additions such as Cr, Nb, Mo, Zr and Y. Iron-aluminium alloys with lower aluminium conce ntrations (between 16 and 22 atom%) were next investigated to establis h the minimum aluminium concentration needed to resist sulfidation and oxidation. The results have shown that alloys containing greater than or equal to 18% Al are uniquely resistant to H2S-containing environme nts at 800 degrees C. Chromium adversely affected the corrosion resist ance in this mixed gas environment, although this effect was partially offset by the addition of molybdenum. Zirconium and yttrium had no si gnificant effect on the corrosion rate under the same temperature and environmental conditions. Metallographic and chemical analyses of the corrosion product scales and underlying alloy were performed to determ ine the roles of the respective metallic elements in the corrosion pro cess in H2S-H-2-H2O. These results, together with weight change determ inations, are discussed in terms of the apparent corrosion mechanisms and optimization of alloy composition for exposure to gasifier environ ments.