Scale Surface and Scale/Alloy Interface for Alumina-Forming Alloys with Noble Metal and Yttrium

Scale surface and scale/alloy interface for alumina-forming (Fe-20Cr-4Al) alloys with noble metal (palladium, platinum) and yttrium were studied in oxidizing atmospheres (oxygen, oxygen-water vapor) for 18ks at 1473, 1573 and 1673K, by mass gain measurements, amount of spalled oxide, X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission-transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS). After oxidation at 1473K for 18ks in oxygen, the mass gains of the FeCrAl, FeCrAlPd and FeCrAlPt alloys showed almost the same values. Those of the FeCrAlY alloys decreased with increasing yttrium of up to 0.1% followed by an increase with the yttrium content. The mass gain of the FeCrAlPtY alloys with appropriate additions of platinum and yttrium were lower than that of the FeCrAlY alloy with 0.1mass% yttrium, and alumina/alloy interface of the alloy showed good coherency by TEM. The scale surface of the FeCrAl, FeCrAlPd and FeCrAlPt alloys were rough, however, those of the FeCrAlY and FeCrAlPtY alloys were smooth. After oxidation at 1673K for 18ks in water-vapor (47vol%), FeCrAlPt alloy with 0.5mass% platinum showed good oxide adherence. Platinum concentration was observed at alloy side of the alumina/alloy interface by FE TEM/EDS.