High-temperature corrosion behavior of iron-aluminide alloys and coatings Page: 3 of 13
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OXIDATION OF ODS Fe3Al ALLOYS
As described elsewhere,4 ODS Fe3Al alloys are currently being developed to increase the
operating temperature regime of these uniquely sulfidation-resistant materials. Determining
the effects of a dispersion of oxides on the high-temperature oxidation resistance of Fe3A1 is
a key part of this effort. Use of a reactive element (RE) oxide may further improve the
adhesion of alumina scales on iron aluminides, as has been shown for the FeCrAI, NiCrAl, and
NiAI systems (see, for example, refs. 5-7). The initial results on the effects of Y203, CeO2,
and La2O3 on high-temperature cyclic oxidation of Fe-28% Al-2% Cr (FAS) are summarized
here. More details of the work with the Y203 and CeO2-doped FAS can be found in ref. 8.
Powders of gas-atomized FAS and submicron oxides (Y203, CeO2, or La2O3) were
mechanically blended in a flowing Ar atmosphere using a high-speed attritor and stainless
steel balls. (Unless otherwise noted, all concentrations are in at.%). The blended powder was
canned, degassed, and extruded at 1100*C. For comparison, a FAS powder extrusion without
an oxide addition, ingot-processed Fe-28% Al-5% Cr-0.1% Zr (FAL), and a commercial
ZrO2-dispersed (0.06% Zr) Fe-20% Cr-10% Al alloy (Kanthal alloy APM) were also tested.
Coupons (about 15 mm diam x 1 mm thick) were polished with 0.3 gm alumina prior to
oxidation. Cyclic oxidation experiments were conducted at 1200*C in air and in dry, flowing
02. Admittedly, the exposure temperature of 1200*C is significantly higher than most
potential applications for iron aluminides, but it is a convenient way to assess the potential
lifetime of these materials based on aluminum consumption. A similar approach was
previously used to predict oxidative lifetimes for ingot-processed iron aluminides and for
comparison with FeCrAl alloys.9 In short-term cyclic testing (2 h cycles), specimens were
hung in a furnace in flowing 02 and weight changes were measured continuously using a
microbalance to check for any indication of isothermal spallation. (However, spallation was
only observed upon cooling.) In long-term testing (100 h cycles), specimens were placed in
a static air furnace inside individual alumina crucibles so that any spalled oxide was collected
and weighed. In both types of tests, the specimen weight changes were measured before and
after oxidation. After oxidation, specimens were examined using scanning electron
microscopy (SEM) with energy dispersive x-ray (EDX) analysis.
Specimen weight change data for the various alloys exposed to 2 h cycles are shown in
Fig. 1. A fine powdery alumina scale formed on the undoped FAS alloy and led to large
weight losses after just a few cycles. In contrast, rapid weight gains were observed for the
CeO2- and La203-dispersed alloy specimens. The CeO2-dispersed alloy exposure was
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Tortorelli, P. F.; DeVan, J. H.; Pint, B. A.; Wright, I. G. & Saunders, S. R. J. High-temperature corrosion behavior of iron-aluminide alloys and coatings, report, July 1995; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc794788/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.