High-temperature oxidation resistance of Al2O3-forming heat-resisting alloys with noble metal and rare earth additions

Abstract

High-temperature oxidation behavior of Al2O3-forming heat-resisting alloys with noble metal (palladium, platinum, gold) and rare earth (yttrium) additions was studied in oxidizing atmospheres (oxygen, oxygen-water vapor) for 18 ks at 1473, 1573, and 1673 K, by mass gain measurements, amount of spalled oxide, observation of surface appearance, X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). Mass gains of all the Al2O3-forming Fe-20Cr-4Al alloys increased with increasing oxidation temperatures in both oxidation conditions. After oxidation in oxygen, the mass gains of the alloys with noble metal were almost the same values after any oxidation temperature. The mass gain of the alloys with yttrium decreased with increase in yttrium addition up to 0.1 mass%, and then tended to increase with 0.5 mass% yttrium addition at all oxidation temperatures studied. The amount of spalled oxide from the Fe-20Cr-4Al (A4) alloy showed the biggest value at 1573 K-oxidation, and then decreased in the order of 1473 K, 1673 K. On the other hand, the amount of spalled oxide from the other alloys decreased compared with the A4 alloy. No spalled oxide from 0.5Pt, 0.05Y, and 0.5Y alloys was observed at any oxidation temperature. After oxidation in an oxygen-water vapor mixture (dew point: 353 K), the mass gain of all the alloys showed similar values to that obtained in oxygen after any oxidation temperature. The amount of spalled oxide from the A4 alloy was about the same after oxidation at 1473 and 1573 K in oxygen, but then was higher when oxidized at 1673 K. The amount of spalled oxide from the other alloys obtained in oxygen–water vapor increased compared with those obtained in oxygen. On the other hand, the amount of spalled oxide from the 0.5Y alloy was zero after any oxidation temperature, and that from the 0.5Pt alloy was also zero after 1673 K-oxidation.