The effects of yttrium addition on high-temperature oxidation of heat-resistant alloy with sulfur

The effects of yttrium (10, 300 and 3700 ppmY) addition on high-temperature oxidation of Fe-20Cr-4Al alloy with sulfur (185 ppmS) were studied in air for 1800 ks at 1273, 1373 and 1473 K by mass-change measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Oxide scales on all of the alloys showed good adherence after oxidation at 1273 K. On the other hand, oxide scales on the 185 ppmS and 10 ppmY alloys spalled from the entire surface, and those on other alloys did not spall after oxidation at 1373 and 1473 K. Mass gains of the alloys with yttrium addition tended to increase with increasing content of yttrium. Oxide scales on the 185 ppmS alloy showed a convoluted morphology, however, surface morphologies of those on the other alloys with yttrium changed to planar with increasing yttrium content after oxidation at 1273 K. Oxide scales on all of the alloys were almost planar after oxidation at 1373 and 1473 K. Behavior of sulfur and yttrium will be presented after oxidation. (C) 2002 Elsevier Science B.V. All rights reserved.