| 1. |
- Canovic, Sead, 1979, et al.
(författare)
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Microstructural Investigation of the Initial Oxidation of the FeCrAlRE Alloy Kanthal AF in Dry and Wet O-2 at 600 and 800 degrees C
- 2010
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 157:6, s. C223-C230
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Tidskriftsartikel (refereegranskat)abstract
- The FeCrAlRE (where RE is reactive element) alloy Kanthal AF was exposed isothermally at 600 and 800 degrees C for 72 h in dry O-2 and in O-2 with 10 vol % H2O. The mass gains were 3-5 times higher at the higher temperature. The presence of water vapor increased the oxidation rate at 800 degrees C, while no significant effect was observed at 600 degrees C. A thin two-layered oxide formed at 600 degrees C: an outer (Fe, Cr)(2)O-3 corundum-type oxide, containing some Al, and an inner, probably amorphous, Al-rich oxide. At 800 degrees C a two-layered oxide formed in both environments. The inner layer consisted of inward grown alpha-Al2O3. In dry O-2 the originally formed outward grown gamma-Al2O3 had transformed to alpha-Al2O3 after 72 h. Water vapor stabilized the outward grown gamma-Al2O3 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 degrees C the Y-rich RE particles were surrounded by thick oxide patches in both dry and humid O-2.
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| 2. |
- Canovic, Sead, 1979, et al.
(författare)
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Oxidation of Co- and Ce-nanocoated FeCr steels: A microstructural investigation
- 2013
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 215, s. 62-74
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Tidskriftsartikel (refereegranskat)abstract
- The effect of novel Co and Ce nanocoatings on oxidation behaviour and chromium volatilization from a commercial Fe-22Cr steel (Sanergy HT) developed for solid oxide fuel cell interconnect applications is investigated. Three different coatings (10 nm Ce, 640 nm Co and 10 nm Ce + 640 nm Co) are studied. Uncoated and nanocoated samples are exposed isothermally at 850 C in the air with 3% H2O for 168 h. The detailed microstructure of the different coatings is investigated. The surface morphology and microstructure of the oxide scales are characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and energy dispersive X-ray analysis (EDX). Cross-section TEM thin foils are prepared by using a combined FIB/SEM (focused ion beam/scanning electron microscope) instrument. A 640 nm cobalt coating strongly inhibits Cr volatilization but has only minor effects on oxidation rate. In contrast, a 10 nm Ce coating decreases the oxidation rate but has no significant effects on chromium volatilization. Combining the two coatings, i.e., applying a 640 nm Co coating on top of the 10 nm Ce, effectively reduces Cr evaporation and slows down the rate of alloy oxidation.
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| 3. |
- Engkvist, Josefin, 1972, et al.
(författare)
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Alumina scale formation on a powder metallurgical FeCrAl alloy (Kanthal APMT) at 900-1100°C in dry O2 and in O2 + H2O
- 2010
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 73:1, s. 233-253
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Tidskriftsartikel (refereegranskat)abstract
- A Rapidly Solidified Powder (RSP) metallurgical FeCrAl alloy, Kanthal APMT, was exposed in dry and humid O-2 for 72 h at 900-1,100 A degrees C. The formed oxide scales were characterized using gravimetry in combination with advanced analysis techniques (SEM, EDX, TEM, XRD, AES and SIMS). The oxide scales were at all exposures composed of two-layered alpha-Al2O3 scales exhibiting a top layer of equiaxed grains and a bottom layer containing elongated grains. A Cr-rich zone, originating in the native oxide present before exposure, separated these two layers. The top alpha-Al2O3 layer is suggested to have formed by transformation of outwardly grown metastable alumina, while the inward-grown bottom alpha-Al2O3 layer had incorporated small Zr-, Hf- and Ti-rich oxide particles present in the alloy matrix. The scale also contained larger Y-rich oxide particles. Furthermore, in the temperature range studied, the presence of water vapour accelerated alloy oxidation somewhat and affected scale morphology.
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| 4. |
- Engkvist, Josefin, 1972, et al.
(författare)
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Oxidation of FeCrAl foils at 500-900 degrees C in dry O-2 and O-2 with 40% H2O
- 2009
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Ingår i: Materials at High Temperatures. - 0960-3409 .- 1878-6413. ; 26:2, s. 199-210
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Tidskriftsartikel (refereegranskat)abstract
- High temperature resistant FeCrAl alloys are frequently used in high temperature applications Such as heating elements and metal based catalytic converter bodies. When exposed to high temperatures an adherent, slowly growing, dense aluminium oxide layer forms on the surface, which protects the underlying alloy from severe degradation. The composition, structure and properties of the formed oxide layer are strongly dependent on the alloy composition, temperature and oxidation environment. In this study, the Sandvik 0C404 FeCrAl alloy, in the form of 50 mu m thick foils, was exposed isothermally in the temperature range 500-900 degrees C for 168 hours in dry O-2 and in O-2 with 40 vol.% H2O. The surface morphology, composition and microstructure of the grown oxide scales were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), grazing incidence X-ray diffraction (GI-XRD), Auger electron spectroscopy (AES), and time of flight secondary ion mass spectrometry (TOF-SIMS). The oxidation process was faster at 900 degrees C than at 500 and 700 degrees C. At 500 degrees C a thin (10-20 nm) mixed oxide of Fe, Cr and Al was formed. Exposure at 700 degrees C resulted ill a similar (40-50 nm) duplex oxide, in both dry O-2 and in O-2 With 40 vol.% H2O. These oxide scales consisted of all inner and an outer relatively pure alumina separated by a Cr-rich band. This type of duplex oxide scale also formed at 900 degrees C with a thin inward growing alpha-Al2O3 at the oxide/metal interface and an outward growing layer outside a Cr-rich band. However, at 900 degrees C the Outward growing layer showed two types of oxide morphologies; a thin smooth base oxide and a much thicker nodular oxide grown on top of substrate ridges. In dry O-2 atmosphere, the main part of this outward growing layer had transformed to alpha-Al2O3. Only in the outer part of the thick oxide nodules, metastable alumina was found. When exposed in the presence of water vapour the main pall of the metastable alumina remained untransformed.
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| 5. |
- Froitzheim, Jan, 1981, et al.
(författare)
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Long term study of Cr evaporation and high temperature corrosion behaviour of Co coated ferritic steel for solid oxide fuel cell interconnects
- 2012
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 220, s. 217-227
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behaviour of the uncoated ferritic Fe-22Cr steel Sanergy HT is compared with an 640 nm Co coated version of the same material. The materials have been subject to corrosion and Cr volatilization measurements in air for up to 3000 h at 850 degrees C. Oxidation tests have been carried out both isothermal and discontinuously. The volatilization measurements were carried out using a recently developed denuder technique, which allows to quantify Cr evaporation in a time resolved manner. The oxidation process is studied from very initial phases (>15 s) to long term behaviour (3000 h). The formed oxide scales are analysed by XRD, SEM/EDX as well as TEM/EDX.The results show that both materials form an oxide scale with an inner layer of Cr2O3 and a spinel layer on top. In the case of the uncoated material, the spinel layer is of (Cr,Mn)(3)O-4 type while in the presence of a Co coating a (Co,Mn,Fe)(3)O-4 is formed. The Cr evaporation measurements show that despite the fact that the Co coating is very thin (640 nm) it effectively blocks Cr evaporation for at least 3000 h. This is in line with TEM analysis showing that after 3000 h there is only a low Cr content in the outer oxide scale. This long term stability indicates the suitability of the coated material as solid oxide fuel cell (SOFC) interconnect.
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| 6. |
- Hellström, Kristina M, 1971, et al.
(författare)
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Oxidation of a Dispersion-Strengthened Powder Metallurgical FeCrAl Alloy in the Presence of O2 at 1,100°C: The Influence of Water Vapour
- 2015
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 83:5-6, s. 533-558
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behaviour of the FeCrAl alloy Kanthal(A (R)) APMT in O-2 + N-2 and O-2 + N-2 + H2O environments at 1,100 A degrees C was investigated using thermogravimetry and detailed analyses of the scale morphology with SEM/EDX and STEM/EDX. Wrought FeCrAl alloy Kanthal(A (R)) AF was used as a reference. Exposure time was up to 168 h. Water vapour influenced the early oxide growth kinetics. This effect is explained in terms of water acting as an oxidant, simultaneously with O-2. During later stages of the exposures, H2O had no effect on the kinetics of oxidation.
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| 7. |
- Hellström, Kristina M, 1971, et al.
(författare)
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The Oxide Scales Formed on a Dispersion-Strengthened Powder Metallurgical FeCrAl Alloy at 900 A degrees C in O-2 and in O-2 + H2O
- 2015
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 84:1-2, s. 1-19
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Tidskriftsartikel (refereegranskat)abstract
- Early oxide scale growth on an oxide dispersion strengthened rapidly solidified powder FeCrAl material, Kanthal(A (R)) APMT, was investigated at 900 A degrees C in an O-2 + N-2 and an O-2 + H2O + N-2 environment for up to 168 h. Gravimetry was used to follow oxide growth and the oxide scale was examined with XRD. Scale morphology was investigated in detail with SEM/EDX, TEM/EDX/CBED. The alloy rapidly formed a protective two-layered alpha-alumina scale containing oxide nodules. Between the top and bottom alumina layers there was a zone containing chromia-rich particles 5-20 nm in diameter, corresponding to the original sample surface. The alumina scale mainly grew inward after 1 h of oxidation. Alumina scale growth at 900 A degrees C was initially somewhat faster in an O-2 + H2O + N-2 environment than in an O-2 + N-2 environment.
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| 8. |
- Ingemarsson, Linda, 1972, et al.
(författare)
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Oxidation behavior of a Mo(Si,Al)2 composite at 900–1600 C in dry air
- 2013
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 48:4, s. 1511-1523
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation of a Mo(Si,Al)2-based compositeis investigated in the temperature range 900–1600 C indry air. Exposure time was 72 h. Comparisons are madewith the oxidation behavior of a conventional MoSi2-basedmaterial. Cross-sections are examined with scanning electronmicroscopy and transmission electron microscopy; thephase composition is analyzed by X-ray diffraction andconvergent beam electron diffraction. The material forms acontinuous external a-alumina scale throughout the temperature range. Below the scale, there is a continuousMo5(Si,Al)3 layer that overlies Mo(Si,Al)2 in the bulk. TheMo(Si,Al)2 phase immediately beneath the Mo5(Si,Al)3layer is depleted in Al. No indications of MoO3 volatilization could be found for the Mo(Si,Al)2 material
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| 9. |
- Intiso, Luciana, 1981, et al.
(författare)
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Oxidation Behaviour of Sanicro 25 (42Fe22Cr25NiWCuNbN) in O-2/H2O Mixture at 600 degrees C
- 2012
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 77:5-6, s. 209-235
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates oxidation at 600 A degrees C of alloy Sanicro 25 (42Fe22Cr25NiWCuNbN) in dry and wet O-2 environments. The exposure time was 1-168 h. The oxidized samples were analyzed by grazing incidence X-ray diffraction, glow discharge optical emission spectroscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. Alloy Sanicro 25 showed protective oxidation behaviour under the present conditions. Initially, a thin and smooth corundum-type single layer base oxide formed, featuring a Cr-rich bottom part and a Fe-rich top. With time, double-layered oxide nodules form consisting of inward- and outward-growing parts. Below the oxide scale a 100-200 nm thick oxidation-affected zone formed in the alloy, which was depleted in Cr and enriched in Ni. In this region the chromium carbides and copper-rich particles present in the bulk alloy were dissolved. In O-2 + H2O environment, chromium volatilized from the surface, causing the chromium content of the oxide to be lower than after oxidation in dry O-2. However, under present experimental conditions, the Cr depletion of the scale was not enough to trigger accelerated corrosion of the alloy.
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| 10. |
- Jonsson, Torbjörn, 1970, et al.
(författare)
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Influence of H2O(g) on the Oxide Microstructure of the Stainless Steel 353MA at 900°C in Oxygen.
- 2007
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 154:11, s. C603-C610
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the impact of water vapor on the corrosion behavior of the austenitic Si-containing FeCrNi steel 353MA at 900°C through a detailed microstructural characterization of the oxide scales formed after 168 h in O2 and in O2 with 40% H2 O. The oxidized samples were investigated by focused ion beam and transmission electron microscopy in combination with energy dispersive X-ray analysis. The microstructural investigation showed that the oxide scales were affected by the presence of water vapor. However, there was no significant difference in scale thickness. In both atmospheres a continuous chromia [Cr-rich (Fe,Cr)2 O3] layer was present beneath the spinel oxides. The influence of water vapor on scale composition is attributed to chromia evaporation by the formation of Cr O2 (OH)2 (g). The ability of the alloy to maintain a continuous chromia layer in spite of chromia evaporation and to avoid breakaway oxidation is attributed to several factors. First, the supply of chromium to the scale by diffusion in the alloy must be rapid. Second, the presence of spinel oxides at the oxide/gas interface may decrease chromia evaporation. Third, the high CrFe ratio in the alloy is suggested to make it difficult to convert the protective chromia to poorly protective hematite. © 2007 The Electrochemical Society.
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