Oxidation Properties of Fe‐Al Alloys (1.5–5 a/o Al) in Oxygen at 1173 K

Abstract

Oxidation properties of Fe-l.5, 3, and 5 atomic percent (a/o) A1 alloys were investigated at 1173 K in oxygen at 1 bar pressure. The reaction kinetics were represented by two limiting parabolic stages, a rapid initial stage and slow final stage separated by a transient period. The initial oxidation rate was more rapid with increasing alloy aluminum content. The reaction products of the 1.5 and 3 a/o A1 alloys formed a duplex scale consisting of an outer Fe~O:~ and an inner (Fe, A1):,O4 layers with FeAlzO,-A120:~ platelet precipitates which extended across the internal oxidation zone in the alloys. In the case of the Fe-5 a/o A1 alloy, a triplex Fe2OJ(Fe, A1):~OJAI~O:~ scale ultimately developed as the internal oxidation zone was completely converted to oxide upon growth of an AI~O~ film at the internal oxidation front.Oxidation resistance of steels is generally achieved by incorporating metallic elements which are selectively oxidized such as chromium and silicon to form adherent and slow growing oxide films. Aluminum is a prospective alloying element to protect iron from oxidation by forming a protective A120:~ film. Binary Fe-A1 alloys, nonetheless, have been the subject of only a few oxidation investigations (1-9); in consequence, the conditions and mechanisms for growth of various types of scales and internal precipitation of oxides are not yet understood. An attempt is made in this paper to more adequately define the mechanisms of scaling with concurrent internal oxidation and of the transition with increasing alloys aluminum content from internal oxidation to scale growth solely by examining the oxidation properties of iron alloys containing from 1.5 to 5 a/o Al. Experimental Alloys of nominal compositions 1.5, 3, and 5 atomic percent (a/o) A1 were prepared by electric arc melting of iron (99.95% pure) and aluminum (99.98% pure) containing impurity contents as published elsewhere (10) in an argon atmosphere gettered of oxygen by titanium chips. Actual compositions of these a-solid solution phase alloys were 1.56, 3.02, and 5.50 a/o A1. 3 and 5 a/o A1 were homogenized at 1473 K for 24h and the Fe-l.5 A1 alloy was homogenized at 1173 K for 170h in argon. Specimens 1.5 • 10-3m thick and of 0.01m diam were cut from these alloy ingots and subjected to metallographic polishing finishing with 1 ~m diamond paste.Oxidation runs were carried out in flowing oxygen (ultrapure grade) at 1 bar and 1173 K using a gravimetric assembly described previously (11). Oxide phases were identified by x-rays using Ni-filtered Cu-Ka radiation. Morphologies of reaction products were examined by light and electron (SEM) microscopy. Specimens were mounted in room setting epoxy resin, and, whenever etching was difficult, fracture cross sections were prepared. Energy dispersive x-ray analyses (EDAX) were used to determine distributions of elements in the various solid phases. Results

AlN formation in Fe‐Al alloys in N2‐O2 atmospheres

“…Continuous alumina scales have long been known to be protective against further oxidation in iron‐aluminum alloys. Several studies have been done to determine the critical aluminum content at which the alumina scale becomes protective . This value varies depending on temperature and oxygen partial pressure.…”

The Effect of the Third Element Cr on Oxidation Behavior of Fe-xCr-10Al (at.%) Alloys at 900°C

“…The present authors have studied the roughness effects on the oxidation properties of Fe-xCr-10Al alloys containing 0 10 at.% Cr [26], and the results indicated that the alloy surface conditions played important roles on the formation of nodular Fe-rich oxides. Duplex or triplex scales were found to form on Fe-Al alloys after oxidation at high temperatures [1][2][3]. The cross section of the oxidized Fe-10Al alloy revealed that layered scales composed of the mixture oxides of Fe and Al were developed during the oxidation.…”

“…Surface morphologies of oxidation products were examined with a scanning electron microscope (SEM, Philips XL30). The specimen was mounted in a cold-setting epoxy resin for examining the Ahmed et al [1] Saegusa et al [2] Ahmed et al [3] Boggs [4] Kubaschewski et al [5] Tomaszewicz et al [6] Miner et al [7] Al oxides mixed Fe and Al oxides Huntz et al [8] Hou et al [9] Golightly et al [10] Lambertin et al [11] Stott et al [12] Quadakkers et al [13] KeeSun Lee et al [14] Quadakkers et al [15] Borner et al [16] Quadakkers et al [17] Miner et al [7] cross-section. EDS were used to determine distributions of elements in the various solid phases.…”

“…Iron-based alloys are commercially important hightemperature materials, among which the Fe-Al [1][2][3][4][5][6][7] and Fe-Cr-Al [7][8][9][10][11][12][13][14][15][16][17] alloys are of very great interest in the studies of high temperature oxidation. Fig.…”

Nano Al2O3 Rod Array Structure Produced by Using Internal Oxidation of Dilute Ni(Al) Alloys

“…Internally oxidized alloys were ground by SiC abrasive papers and then electropolished in H 2 SO 4 solution at 50ºC to remove the Ni in the internally-oxidized zone (IOZ) for developing the oxide rod array structure. Some other alloys having a small amount of Al also shows internal oxidation with rod-like or needle-like Al 2 O 3 , such as Fe(Al) (25,26). The proposed method to fabricate nano Al 2 O 3 rod array structure can be applied to other alloys including Al in which rodlike Al 2 O 3 precipitates appear.…”