The morphology of alumina scales formed on Fe-20Cr-4Al-S alloys with reactive element (Y, Hf) additions at 1273 K

摘要

The morphology of alumina scales formed on Fe-20Cr-4Al-S (185 ppm) alloys with reactive elements (10, 300, 800, and 3700 ppmY, 500, 900, 1900, and 4300 ppmHf) was studied in oxidizing atmospheres at 1273 K for 18, 1800 and 3600 ks by mass gain measurements, X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). No spalling of the oxide scales was observed on any of the alloys after any of the oxidation times. Mass gain decreased for alloys with small additions of reactive elements, and then increased with increasing reactive element content. Oxide scales on the 185 ppmS, the 500 and 900 ppmHf alloys showed a wavy morphology. On the other hand, oxide scales on the other alloys with reactive elements changed from small wavy to planar morphologies with increasing reactive elements after any of the oxidation times studied. Oxide scales formed on all of the alloys were recognized as mainly -Al_2O_3. After oxidation for 3600 ks, Y_3Al_5O_(12) particles were observed for the 800 and the 3700 ppmY alloys, and HfO_2 particles were also detected for the 1900 and the 4300 ppmHf alloys.