Microstructural development of α alumina scales developed on FeCrAl alloys

Prior, David J.; Al‐Badairy, H.; Seward, Gareth; Veltkamp, C. J.; Tatlock, G. J.

doi:10.1179/174328406x131091

Cited by 8 publications

(6 citation statements)

References 32 publications

(46 reference statements)

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“…2(e)) and long axes perpendicular to the foil orientation. Similar findings were included in the paper by Prior et al [16]. This two layer structure is observed for α-alumina in all the EBSD analysed samples.…”

Section: Resultssupporting

confidence: 90%

Void Formation and Filling under Alumina Scales Formed on Fe-20Cr-5Al Alloy Thin Foils

Potter

Tatlock

2008

MSF

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The oxidation behaviour and the subsequent chemical failure of a Fe-20Cr-5Al based alloy were studied at 1200°C in laboratory air, at times of up to 700 hours. Tests on 70 micron thick foils, showed void formation at the metal/oxide interface soon after the aluminium content in the alloy dropped below a critical level (≤0.5 wt%). At this stage, the alloy could no longer sustain alumina scale formation and resulted in the initiation and development of a Cr-rich sub-layer. This chromia layer was found to be continuous and of a uniform thickness. As the sub-layer formed, voids were also observed at the metal/oxide interface. The voids were found to fill with chromia after further exposure. It is thought that the change in oxide growth mechanism from alumina to chromia growth is responsible for the void formation. This also explains the lack of void formation during the sustainable growth of the alumina scale. The introduction of silicon to the Fe-20Cr-5Al based alloy via a diffusion couple was found to significantly influence the oxidation behaviour of the thin foils. Void formation was observed directly beneath the alumina scale and filled voids were now found to contain silicon oxide rather than chromia. The void filling mechanism also appeared to be different. With chromia filled voids, the filling commenced from the underside of the oxide, with the oxide growing inwards, while silica containing voids were filled by silica growing outwards into the void from the substrate. Throughout the study, optical and scanning electron microscopes were used to analyse all stages of oxidation and the subsequent failure of the thin foil samples. EBSD was also used to generate a more comprehensive analysis of selected locations.

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Section: Resultssupporting

confidence: 90%

Void Formation and Filling under Alumina Scales Formed on Fe-20Cr-5Al Alloy Thin Foils

Potter

Tatlock

2008

MSF

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“…FeCrAl alloy's resistance to high-temperature oxidation is based on the properties of the oxide-scale layer formed on the alloy surface. Thermal oxidation of FeCrAl alloy can also lead to interesting Al 2 O 3 morphology formations with a high surface area such as platelets or whiskers [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] . Pint et al 12 study cited that the metastable chemical conversion, which contains most of θ-Al 2 O 3 , into stable α-Al 2 O 3 leads to volume change.…”

mentioning

confidence: 99%

Multistage heat treatment and the development of a protective oxide-scale layer on the surface of FeCrAl sintered-metal-fibers

Ibrahim

Alazemi

Naji

2021

Sci Rep

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This study investigates the effects of Multistage Heat Treatment (MSHT) on the development of an oxide-scale layer on the surface of FeCrAl sintered-metal-fibers. The oxide-scale layer was developed using an MSHT cycle at 930 °C for 1 h, followed by 960 °C for 1 h, and finally at 990 °C for 2 h. In this study, three samples were considered: Sample 1 was kept without thermal oxidation, while Samples 2 and 3 were exposed to one and eighteen MSHT cycles. Thermo-gravimetric analyses show that the weight gain of the heat-treated sample slows with time, confirming the growth of the protective oxide-scale layer. Scanning electron microscope images, after one MSHT cycle, reveal nonuniform oxide-scale growth with platelet-like on the surface. After eighteen MSHT cycles, however, clumped particles formed on the surface of the fibers. Atomic force microscopy was utilized to study the surface topography of the fibers. The results show that MSHT increases the surface roughness, where the surface roughness of one and eighteen MSHT cycles are the same. The x-ray diffraction analyses of the baseline sample and the sample with one MSHT cycle show pattern peaks of crystalline Fe2CrAl. In contrast, the results of eighteen MSHT cycles displayed diffraction pattern peaks of crystalline Cr and stable α-Al2O3. In summary, the results of this study reveal the changing nature of the oxide-scale layer. The findings of this study form the foundation for new techniques to protect and prepare the FeCrAl fibers as a support for catalysts.

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“…[7][8][9][10] Although the role of RE in enhancing oxidation resistance properties for an alloy is widely acknowledged, there remains a lack of consensus regarding the action mechanism of RE due to its multiple effects on the alloy-oxide system. It is generally believed that the influence of RE elements on the Al 2 O 3 oxide film is primarily exerted through several mechanisms: 1) RE segregation at grain boundaries (GBs) within the oxides alters the diffusion mechanism from mixed transport of oxygen and aluminum to oxygen-dominated transport; [11][12][13] 2) RE induces changes in microstructures, grain size, and growth direction of oxides; [14][15][16] and 3) desulfurizing by RE reduces S-segregation at the oxide-alloy interface, mitigates interfacial void formation, enhances interfacial strength, and improves adhesion of the oxide film. [17][18][19] Moreover, in the commercial production of a FeCrAl alloy, besides intentionally added trace elements, there are inevitably other impurity elements present.…”

Section: Introductionmentioning

confidence: 99%

Grain Size Effect and Spinel Transition for Alumina Scale Thermally Grown on Rare Earth–Mg Codoped FeCrAl Alloy

Duan,

Zhang,

Liu

et al. 2024

steel research int.

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The synergistic effects of rare earth (RE) and Mg elements on the high‐temperature oxidation resistance of Fe–20Cr–6Al alloy are investigated in‐depth. The scale on RE–Mg codoped alloy mainly consists of α‐Al2O3/MgAl2O4, with many pores caused by spinel transition. Owing to the segregation of RE ion at the grain boundaries, there is a significant refinement effect of oxide grains, which improves the spallation resistance of scale and offers more grain boundary diffusion pathways for ion transport, resulting in an obvious increase of oxidation weight gain. The findings indicate that RE is beneficial for inhibiting the grow‐up of oxide grains, whereas Mg can weaken the compactness of scale.

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Microstructural development of α alumina scales developed on FeCrAl alloys

Cited by 8 publications

References 32 publications

Void Formation and Filling under Alumina Scales Formed on Fe-20Cr-5Al Alloy Thin Foils

Void Formation and Filling under Alumina Scales Formed on Fe-20Cr-5Al Alloy Thin Foils

Multistage heat treatment and the development of a protective oxide-scale layer on the surface of FeCrAl sintered-metal-fibers

Grain Size Effect and Spinel Transition for Alumina Scale Thermally Grown on Rare Earth–Mg Codoped FeCrAl Alloy

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