Time dependence of Mg-incorporation in alumina scales on FeCrAl alloys studied by FIB-prepared TEM cross sections

Penkalla, H. J.; Dimyati, Arbi; Dani, Mohammad; Untoro, Pudji; Naumenko, D.; Quadakkers, Willem J.

doi:10.1179/mht.2003.048

Cited by 19 publications

(8 citation statements)

References 11 publications

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“…As expected, the morphology shows that the a-Al 2 O 3 grains in the outer oxide have grown outwards. The directions of growth of the two subscales are in accordance with several reports in literature [5,26]. The promotion of a-Al 2 O 3 formation at 700°C by chromia in the oxide scale was reported previously [3].…”

Section: Oxidation Kineticssupporting

confidence: 89%

The Effect of Water Vapor on the Initial Stages of Oxidation of the FeCrAl Alloy Kanthal AF at 900 °C

et al. 2007

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The effect of water vapor on the initial stages of oxidation of the FeCrAl alloy Kanthal AF is reported. Polished samples were exposed isothermally at 900°C for 1, 24, 72 and 168 h in a well-controlled environment consisting of dry O 2 or O 2 + 40% H 2 O. The samples were investigated using a combination of gravimetry and several surface-analytical techniques, including XRD, SEM, EDX, FIB, AES and TEM. The presence of water vapor significantly accelerates oxidation during the first 72 h. A two-layered oxide forms in both the dry and wet environments. The bottom layer consists of inward-growing a-Al 2 O 3 while the outer layer initially consists of outward-growing c-Al 2 O 3 . A straight and narrow Cr-enriched band is present at the top of the lower (a-Al 2 O 3 ) oxide, corresponding to the original sample surface. In dry O 2 , the top (c-Al 2 O 3 ) layer is converted into a mixture of c-Al 2Àx (Mg,Fe) x O 3À(x/2), MgAl 2 O 4 and a-Al 2 O 3 . This transformation does not occur in O 2 + H 2 O. The initial acceleration of oxidation by H 2 O is attributed to the stabilization of the outward-growing c-alumina layer by the hydroxylation of the c-Al 2 O 3 surface. A schematic mechanism of the early stages of oxidation of FeCrAl alloys is presented, emphasizing the influence of water vapor.

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Section: Oxidation Kineticssupporting

confidence: 89%

The Effect of Water Vapor on the Initial Stages of Oxidation of the FeCrAl Alloy Kanthal AF at 900 °C

et al. 2007

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“…A power law curve fit was applied to experimental data, indicating that the thermal oxidation process follows a sub-parabolic time dependence. This subparabolic relation during the oxidation of FeCrAl material was observed by several researchers [ 8 , 24 , 28 ]. The difference in the rate of weight change for all FeCrAl fibers increases with time.…”

Section: Resultssupporting

confidence: 76%

“…Whittle and Stringer [ 22 ] presented various theoretical models explaining the effect and importance of rare earth elements in reducing the growth rate and improving the adhesion between the scale-oxide layer and the base metal alloy. Various experimental studies have investigated the effects of rare earth elements on oxidation behavior [ 23 , 24 , 25 , 26 , 27 , 28 ]. However, the literature survey reveals few technical papers on FeCrAl fibers [ 17 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ].…”

Section: Introductionmentioning

confidence: 99%

The Microstructure Formation of a Protective Oxide-Scale Layer on Small-Diameter FeCrAl Fibers

Alazemi

Ibrahim

2022

Materials

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FeCrAl fibers, at high temperatures, form a protective oxide-scale layer dominated by aluminum oxide on the surface to prevent further oxidation of the base metal alloy. This study investigates the effects of heat treatment on the microstructure formation of the oxide-scale layer on small-diameter FeCrAl fibers, 12 and 17 µm, produced using a bundle drawing process. The morphology examination and chemical analyses of the small-diameter fibers exhibit the microstructure and chemical compositions of the surface and cross-section areas, revealing a distinctive interface layer with a high aluminum concentration between the base metal and the oxide-scale layer. Furthermore, thermogravimetric analysis results show that the 12 µm fibers have about a 60% higher oxidation rate than the 17 µm fibers—caused by the high outward diffusion of aluminum to the surface of the fibers due to their high surface-area-to-weight ratio. Consequently, the high growth rate of the nonuniform oxide-scale layer and the limited aluminum reservoir of the 12 and 17 µm diameter fibers lead to faster depletion of aluminum from the base metal alloy—limiting the lifetime and durability of the smaller-diameter fibers in high-temperature applications.

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“…In many cases sophisticated sample preparation methods have to be used, such as focused ion beam ͑FIB͒ milling of transmission electron microscopy ͑TEM͒ specimens. 5,6 The oxidation of alumina forming alloys at temperatures below ϳ1000°C initially results in the formation of metastable "transient" aluminas ͑e.g., ␥-, ␦-, and -Al 2 O 3 ͒ in addition to the stable ␣-Al 2 O 3 . 7,8 This is because the nucleation of ␣-Al 2 O 3 is slow at these temperatures.…”

mentioning

confidence: 99%

Microstructural Investigation of the Initial Oxidation of the FeCrAlRE Alloy Kanthal AF in Dry and Wet O[sub 2] at 600 and 800°C

Canovic¹,

Engkvist

Liu³

et al. 2010

J. Electrochem. Soc.

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The FeCrAlRE (where RE is reactive element) alloy Kanthal AF was exposed isothermally at 600 and 800°C for 72 h in dry normalO2 and in normalO2 with 10 vol % normalH2O . The mass gains were 3–5 times higher at the higher temperature. The presence of water vapor increased the oxidation rate at 800°C , while no significant effect was observed at 600°C . A thin two-layered oxide formed at 600°C : an outer (Fe,Cr)2normalO3 corundum-type oxide, containing some Al, and an inner, probably amorphous, Al-rich oxide. At 800°C a two-layered oxide formed in both environments. The inner layer consisted of inward grown α-Al2normalO3 . In dry normalO2 the originally formed outward grown γ-Al2normalO3 had transformed to α-Al2normalO3 after 72 h. Water vapor stabilized the outward grown γ-Al2normalO3 and hence no transformation occurred after 72 h in humid environment. RE-rich oxide particles with varying composition (Y, Zr, and Ti) were distributed in the base oxide at both temperatures and in both environments. The RE-rich particles were separated from the alloy substrate by a layer of Al-rich oxide. At 800°C the Y-rich RE particles were surrounded by thick oxide patches in both dry and humid normalO2 .

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Time dependence of Mg-incorporation in alumina scales on FeCrAl alloys studied by FIB-prepared TEM cross sections

Cited by 19 publications

References 11 publications

The Effect of Water Vapor on the Initial Stages of Oxidation of the FeCrAl Alloy Kanthal AF at 900 °C

The Effect of Water Vapor on the Initial Stages of Oxidation of the FeCrAl Alloy Kanthal AF at 900 °C

The Microstructure Formation of a Protective Oxide-Scale Layer on Small-Diameter FeCrAl Fibers

Microstructural Investigation of the Initial Oxidation of the FeCrAlRE Alloy Kanthal AF in Dry and Wet O[sub 2] at 600 and 800°C

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