Journal
CORROSION SCIENCE
Volume 48, Issue 3, Pages 741-765Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.corsci.2005.01.012
Keywords
FeCrAl; ternary alloys; oxidation; Cr effect
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The conditions for the formation of external alumina scales on binary Fe-Al alloys and the nature of the third-element effect due to chromium additions have been investigated by studying the oxidation at 1000 degrees C in 1 atm O-2 of a binary Fe-10 at.% Al alloy (Fe-10Al) and of two ternary Fe-Cr-10 at.% Al alloys containing 5 and 10 at.% chromium (Fe-5Cr-10Al and Fe-10Cr-10Al, respectively). An Al-rich scale developed initially on Fe-10Al was subsequently replaced by a multi-layered scale containing mixtures of Fe and Al oxides plus a large number of Fe-rich oxide nodules: internal aluminum oxidation was essentially absent from this alloy. Addition of 5 at.% chromium to Fe-10Al did not suppress the formation or nodules, but they were eventually healed by the growth of all alumina layer at their base, resulting in a significant reduction of the oxidation rate. Finally, the alloy with 10 at.% Cr formed continuous external alumina scales without any Fe-rich nodule. Thus, the addition of sufficient amounts of chromium to Fe-10Al produces a third-element effect as expected. However, the process found in this alloy system does not involve a prevention of the internal oxidation of Al. Instead, it shows a transition from the growth of mixed Fe- and Al-rich external scales directly to all external Al2O3 scale formation. An interpretation of this kind of mechanism involving a third-element is presented along with a prediction of the critical Al contents required to produce the various possible scaling modes on binary Fe-Al alloys. (C) 2005 Elsevier Ltd. All rights reserved.
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