《The oxidation of iron-aluminum alloys》.pdf

Oxidation of Metals, Vol. 38, Nos. 1/2, 1992 The Oxidation of Iron-Aluminum Alloys R. Prescott* and M. J. Graham* Received June 1, 1991 Thispaper briefly summarizes studies related to the oxidation of Fe-Al alloys. Emphasis isplaced on oxide phase composition, morphology, and the develop- ment ofprotective c~-A1203scales on oxidation-resistant Fe-Al alloys both with and without ternary additions. KEY WORDS: Fe-A1 alloys; oxidation; scale morphology; ternary additions. I N T R O D U C T I O N In order to develop an understanding of the mechanisms involved in the oxidation of alumina-forming alloys, it is reasonable to begin by examining the binary Fe-A1 system. Fe-A1 alloys have been of interest since the early 1930% when it was realized that additions of A1 led to improvements in the scaling resistance of iron and steels. Hauttman I reported that the heat resistance of steels at 1000~ improved markedly when the A1 content was raised to between 4-9%. Ziegler 2 noted an improvement in performance with increasing A1 content in studies on Fe-A1-C alloys and claimed that alloys with 8% A1 were comparable in oxidation resistance to Ni-Cr alloys. Other workers also noted that addition of A1 brought about improved scaling properties in the range 900-1200~ 3 and it was observed that oxidation took place in accordance with a parabolic rate law. 4 Sykes and Bampfylde 5 concluded that the percentage of A1 required to give complete protection is dependent on temperature, with 6% A1 being sufficient at 900-1000~ 9% is necessary at ll00~ and 11% at 1300~ *Institute for Mi