|Budget Amount *help
¥3,500,000 (Direct Cost : ¥3,500,000)
Fiscal Year 2000 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1999 : ¥1,400,000 (Direct Cost : ¥1,400,000)
Fiscal Year 1998 : ¥1,500,000 (Direct Cost : ¥1,500,000)
The purpose of this study is to clarify the effect of sulfur and reactive elements to the microstructure of alumina scale on heat-resistant alloys.
1. Oxidation behavior of Fe-20Cr-4Al alloys with 3, 35, 53, 104, 171, 185, 491, 1300 and 6300ppmS was studied for 18ks at 1273, 1373, 1473, 1573 and 1673K in oxygen. Oxide scales on 3ppmS showed good oxide adherence at any oxidation temperatures. Oxide scales on 35, 53, and 104ppmS spalled extensively during cooling after oxidation at 1473K.Oxide scales on 3ppmS showed a planar morphology, however, oxide scales on 7, 35 and 53ppmS showed a convoluted morphology after oxidation at 1473K.
2. Oxidation behavior of Fe-20Cr-4Al alloys (185ppmS), and the alloys with yttrium (10, 300, 800 and 3700ppmY), or hafnium (500, 900, 1900 and 4300ppmHf) was studied for 18ks at 1273, 1373, 1473, 1573 and 1673K in oxygen. Yttrium-doped alloys showed an improved oxide adherence because of removal of sulfur and formation of yttrium-sulfide particles into the substrate. On the othe hand, oxide scales on hafnium-doped alloys spalled after oxidation at 1573K.
3. Oxidation behavior of Fe-20Cr-4Al (3, 7, 53, 104, 171, 185 and 1300ppmS, 10, 300, 800 and 3700ppmY, 500, 900, 1900 and 4300ppmHf) was studied for 360ks at 1373, 1473 and 1573K in air. After oxidation at 1573K, oxide scales on 7 and 53ppmS showed good oxide adherence, however, oxide scales on 104, 171, 185 and 1300ppmS spalled during cooling. On the other hand, yttrium-doped alloys showed good oxide adherence, and oxide scales on hafnium-doped alloys spalled. The microstructure of oxide scales on the alloys depended on temperature and time of oxidation, and contents of sulfur, yttrium or hafnium.