Modification of alumina scale formation on FeCrAlY alloys by minor additions of group IVa elements

Effect of Zr Additions on the Oxidation Kinetics of FeCrAlY Alloys in Low and High pO2 Gases

“…For optimization of the alumina scale properties with respect to growth rate and adherence, the FeCrAl alloys are commonly alloyed with minor amounts (less than 1 wt pct) of reactive elements (REs) such as Y, La, and Ce. [1][2][3][4][5] Numerous articles concerning the oxidation behavior of FeCrAl alloys in gases with high oxygen partial pressures (pO 2 ) exist, e.g., References 1 through 5, but only little information for this class of materials in low pO 2 gases is available. Atmospheres with low pO 2 are frequently encountered in industrial applications of FeCrAl alloys, such as heating elements in furnaces for heat treatment in process atmospheres or in car exhaust gas systems.…”

Effect of Zr Content on the Morphology and Emissivity of Surface Oxide Scales on FeCrAlY Alloys

“…Based on results in ref. [13,16] and the microstructural studies of the 1 050 C specimens (Figure 3-5) it is apparent, that the differences in weight gain for a given temperature are mainly related to differences in the extent of internal oxidation. The differences in oxidation rates for specimens of different thickness for a given alloy and temperature reveal that the extent of (internal) oxidation is more affected by the Zr reservoir in the specimen than by the actual Zr content in the alloy.…”

“…The thermodynamic and kinetic background for this effect was discussed in ref. [16,22] At a given temperature this internal oxidation obviously increases with increasing alloy Zr content and increasing specimen thickness. For getting more detailed insight into the distribution of Zr in the internal oxidation zone and in the external alumina base scale, GDOES depth profiling was carried out using the thick and thin specimens of the medium Zr-doped alloy after 500 h oxidation at 1 050 C (see Figure 4).…”

“…Based on these considerations and the results in ref., [16] the scale formation mechanisms on a thick and thin specimen of a high Zr containing alloy are schematically shown in Figure 7. In both specimens rapid surface enrichment of Zr occurs.…”

“…Schematic illustration of oxide scale formation on a thick and a foil specimen of high Zr-doped FeCrAlY alloy based on the present results and mechanism proposed in ref. [16] Fig. 8.…”