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Papers by Author: Alain Galerie

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The Effect of Water Vapor on Thermal Oxide Grown on Inconel 690

Authors: Anusara Srisrual, Jean Pierre Petit, Yves Wouters, Alain Galerie

Abstract: Nickel based alloys are well considered materials for uses in high temperature applications. Inconel 690 is the one of outstanding candidate with the superior properties. The aim of this report is to present the influence of water vapor on thermal oxide film. Inconel 690 was oxidized under dry and wet atmosphere at 900°C for 30 hours. The oxidized samples were characterized by SEM/EDS, Raman spectroscopy, and photoelectrochemical technique. The results illustrated that typical thermal oxides grown on alloy composed of Cr, Fe, Ni, in forms of Cr₂O₃, NiFe₂O₄, NiCr₂O₄, Fe₂O₃, Fe₂_–_xCr_xO₃ and/or solid solution of NiFe₂O₄−NiCr₂O₄. The presence of water vapor affected on oxide morphology, its stoichiometry, and also semiconducting behavior. Oxide film grown under water vapor atmosphere show the homogeneity. Water vapor promoted the predominated oxide of Cr₂O₃ with n−type semiconducting. Moreover the characterization revealed the effect of surface orientation on oxidation mechanism in case of sample which oxidized in oxygen atmosphere.

Effect of Humidity on the Corrosion Kinetics of Ferritic Stainless Steels Subjected to Synthetic Biogas

Authors: Piyorose Promdirek, Gobboon Lothongkum, Yves Wouters, Somrerk Chandra-Ambhorn, Alain Galerie

Abstract: Ferritic stainless steels have nowadays been used as materials for interconnectors in solid oxide fuel cells (SOFCs) at intermediate temperatures (800°C). Their degradation in contact with dry synthetic biogas used instead of other fuel gas has already been studied. In such biogas atmosphere, humidity may play an important role. The objective of this study is therefore to understand the effect of H₂O on the corrosion kinetics of the ferritic stainless steels type AISI441 (18CrTiNb) under synthetic biogas (70%CH₄ and 30%CO₂) mixed with 3%H₂O. The thermodynamic analysis by FactSage was used to determine the partial pressure of oxygen and the activity of carbon in the humid biogas. The results showed that the partial pressure of oxygen is in the range 10^–24.8 to 10^–21.2 bar for temperatures between 600-800°C and that the formation of solid carbon can occur in these conditions. This was not different compared with the conditions in dry biogas. These conditions lead to the stability of some important oxides such as Cr₂O₃ and Cr-Mn spinel and to carbon deposition and/or carbide formation. The surface morphology of 441 subjected to humid biogas showed oxide scale composed mainly of Cr₂O₃ topped with Cr-Mn spinel. Some carbide such as Cr₇C₃ was found in chromia scale. Kinetic experiments under both dry and humid biogas at temperatures between 600 and 800°C showed linear weight changes. Arrhenius law was followed and the rate-determining steps were identified as parallel oxidation and carburization limited by oxide-gas interface reactions.

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Water Vapour Effects on the Oxidation of Chromia-Forming Alloys

Authors: Alain Galerie, Jean Pierre Petit, Yves Wouters, Julie Mougin, Anusara Srisrual, Peggy Y. Hou

Abstract: The electronic properties of chromia scales grown between 800°C and 900°C on chromium metal and chromia-forming ferritic stainless steels were determined using room temperature PhotoElectroChemistry (PEC) experiments and the relative importance of the n- and p-character of the scales could be assessed. According to the thermodynamic previsions of defects structures, the external part of all the scales grown in oxygen exhibits band gap energy around 3.5 eV, with a marked p-type character on chromium and a possibly n-type behaviour on stainless steels. On the contrary, the internal part of the scales is always n-type, with predominant interstitial chromium defects. A major change appears when chromium or stainless steels are oxidised in water vapour-argon mixtures, where the absence of a p‑type semiconductor in the scales could be evidenced. Hydrogen defects are thought to be responsible of this particular behaviour which leads to a strong reduction of residual stresses due to increased high temperature relaxation. Moreover, the inversion of the growth direction resulting from high mobility of the OH defects makes the chromia scales grown in water vapour more adherent than when grown in oxygen.

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Application of the Micro-Tensile Testing to Investigate the Adhesion of Thermal Oxide Scales Grown on AISI 441 Stainless Steel Sheet Oxidised in Air and Water Vapour

Authors: Somrerk Chandra-Ambhorn, Thanasak Nilsonthi, Youcef Madi, Alain Galerie

Abstract: A micro-tensile testing has been developed to investigate the adhesion behaviour of the oxide scale thermally grown on AISI 441 stainless steel sheet oxidised at 800 °C in different atmospheres - synthetic air and water vapour. In the test, a sample was placed in a tensile testing machine sitting in the chamber of a scanning electron microscope at room temperature. Evolution of the failure of the oxide scale was monitored in function of the imposed strain. It was found that the scale formed on steel oxidised in synthetic air exhibited the drastically lower spallation ratio in function of strain comparing to the scale on steel oxidised in 20 %v/v H2O/N2. For the sample oxidised in water vapour, it was clearly observed that the scale was primarily failed by the crack perpendicular to the tensile loading direction, followed by the spallation due to the compressive stress generated by the Poisson effect. After the test, precipitates rich in Nb, Si, and possibly Ti were observed at the internal interface between scale and steel substrate. For the oxidised samples that the final polishing direction paralleled to the main sample axis, the strain provoking the first spallation of the samples oxidised in synthetic air and 20%H2O/N2 were 6.23 and 3.52 % respectively. The theoretical model was developed in our previous work to quantify the mechanical adhesion energy. These values were 357 and 68 J.m–2 for the steels oxidised in synthetic air and 20%H2O/N2 respectively.

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Photoelectrochemical Characterisation of Chromia Scales Thermally Grown on Various Metal Substrates

Authors: Yves Wouters, Alain Galerie, Jean Pierre Petit

Abstract: Chromia scales grown on several chromia-forming metallic substrates in various conditions were characterised by photoelectrochemistry (PEC), highlighting the presence of two semiconductor phases signed by their respective bandgaps (3.0 and 3.5 eV) with variations of semiconduction type (n, p and insulator, more or less doped). The protective character of the scale was clearly demonstrated when the highest bandgap phase (3.5 eV), identified as the external subscale was close to an insulator.

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The Role of Zr in the High-Temperature Oxidation of Fe₃Al

Authors: Kazimierz Przybylski, Sébastien Chevalier, P. Juzoń, Alain Galerie, Günter Borchardt, Olivier Heintz, Jean Pierre Larpin

Abstract: The paper describes an examination of the effect of the addition of zirconium as a third element on the heat-resisting properties and explains the high temperature oxidation mechanism of Fe3Al intermetallic compounds. The Fe3Al and Fe3Al-0,05Zr specimens have been isothermally oxidized in the temperature range of 1173-1473 K in synthetic air for 100 hrs. The formed oxide layer, about 1,5-2 μm thick, was Al2O3. An examination of the cross-sectioned scales by SEM-EDS showed that the alumina layer consisted of a small inner columnar layer and an outer equiaxed grain layer. Additionally, very fine (50-150 nm) oxide grains rich in Zr, further identified as ZrO2, were found across the alumina scales. To understand the role of Zr on the growth mechanism of α–Al2O3 oxide scale on Fe3Al materials, two-stage oxidation experiments were performed (16O2/18O2), followed by SIMS and TEM-SAD observations. Particular attention was paid to the use of TEM in order to precisely characterize the products on samples prepared using the FIB (Focused Ion Beam) method. A combination of analytical techniques revealed that ZrO2 particles, most of which were formed along alumina grain boundaries, enhanced oxygen diffusion along grain boundaries due to oxygen-deficient composition of zirconium oxide (ZrO2-y).

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Thermal Alumina Scales on FeCrAl: Characterization and Growth Mechanism

Authors: Sébastien Chevalier, Alain Galerie, Olivier Heintz, Remi Chassagnon, Alexandre Crisci

Abstract: High temperature oxidation resistance of alumina-forming materials is connected to the growth of dense, stable and protective alumina scales. Depending on temperature, impurities present in the base alloys, presence of water vapour in the oxidizing atmosphere, the alumina scales are composed of alpha-alumina (which is the stable phase obtained for temperatures over 1000°C) or of transient alumina (γ,θ,δ obtained for lower temperatures). It is generally considered that γ- Al2O3 grows when T<850°C, that θ-Al2O3 is present for 850°C

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Comments on the Quantification of Mechanical Adhesion Energy of Thermal Oxide Scale on Metallic Substrate Using Tensile Test

Authors: Somrerk Chandra-Ambhorn, P. Promdirek, Gobboon Lothongkum, Yves Wouters, Alain Galerie

Abstract: The tensile test, accompanied by the corresponding theoretical model, has been developed to quantify the mechanical adhesion energy of the oxide scale on metallic substrate in our previous works. The method to quantify the adhesion energy took into account the effect of residual stress. The effect of the variation of the measured residual stress on the quantified adhesion energy is assessed in this paper. For the scales failed at strains initiating the spallation of 0.018 and 0.011 followed by the transverse crack, it was found that the quantified adhesion energy of the oxide is not sensitive to the variation of the residual stress measured in the range from 0.5 to 2.0 GPa. This is due to the compensation of the decrease in stored energy due to the stress applied in the loading direction (x direction) and the increase in stored energy due to the stress applied in the direction perpendicular to the loading direction (y direction) when the residual stress increases. For the scale failed by the transverse crack followed by the spallation, the quantified adhesion energy tends to be sensitive to the variation of the measured residual stress. The assumption of energy relaxation during the tensile test is alternatively proposed. It is assumed that the energy stored due to the stress in x and y directions is totally released at the first crack. The energy stored due to the stress in y direction from strain initiating the crack to strain initiating the spallation is used in the quantification of the adhesion energy. The scatter of the adhesion energy values quantified by this method and those measured by the inverted-blister test is reduced comparing to the results reported in the previous work.

907

Short Term Oxidation of Stainless Steels during Final Annealing

Authors: Sébastien Gonzales, Lucile Combarmond, Minh Thi Tran, Yves Wouters, Alain Galerie

Abstract: Two ferritic AISI 430 and AISI 441 and two austenitic AISI 304 and AISI 316L stainless steels were submitted to short term oxidation in a complex atmosphere 3% O2, 16% H2O, 8% CO2, 73% N2 to simulate phenomena occurring during the rapid furnace annealing taking place after the final cold rolling. This thermal sequence is devoted to metallurgical aims but generates undesirable oxides which have to be further pickled. Temperature of the furnace was set to the values used in industrial practice: 900°C for 430, 1060°C for 441 and 1120°C for both austenitics. Six different oxidation durations were used between 30 and 300 s. For the shortest times, sample temperature was not constant and heating rate depended on sample thickness. Oxide thickness measured by GDOS was shown to increase monotonically for all grades whereas mass change measurements exhibited initial mass losses for the austenitic grades. XRD and Raman spectroscopy were used for phase characterisation and confirmed the increase of the ratio chromia/haematite with increasing annealing time. Enrichment of manganese (MnCr2O4), silicon (SiO2) and boron (B-containing oxide) at the external (Mn) and internal (Si, B) interfaces was observed on the GDOS profiles (boron for austenitic grades only). Manganese spinel was responsible for blocking chromium (VI) volatilisation after a certain time, and interface oxides for hindering chromium transfer from the steel to the oxide scale. Ferritic grades behaved the same, except that no boron enrichment was detected. Besides, stabilised 441 exhibited Ti and Nb enrichments as oxides at both internal and external interfaces. External TiO2-NbO2 solid solution was assumed to be hardly dissolved in acidic pickling baths. All these results were consistent with the different pickling behaviours of the materials.

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Imaging by Photoelectrochemical Techniques of Laves-Phases γ Zr(Fe,Cr)₂ Thermally Oxidized on Zircaloy-4

Authors: F. Atmani, Yves Wouters, Alain Galerie, Jean Pierre Petit, Yacoub Dali, Marc Tupin, Philippe Bossis

Abstract: The oxidation of γ-Zr(Fe,Cr)2 intermetallic particles during the thermal exposition of Zircaloy-4 at 470°C in oxygen was investigated with PhotoElectroChemical techniques (PEC). Via the measurement of bandgap, haematite Fe2O3 (2.2 eV), rhomboedric solid solution (FexCr1-x)2O3 (2.6 eV) and chromia Cr2O3 (3.0 eV) phases were identified as components of oxidised particles. Evolution of size, lateral distribution and density of these particles was studied in function of zirconia scale thickness. During the first stage of oxidation, the density of oxidised particles increased with thickness but decreased during a second stage, highlighting in an innovative way the phenomenon of haematite and chromia dissolution in the zirconia matrix. It is concluded that PEC techniques represent a sensitive and powerful way to locally analyse the various semiconductor phases in an oxide scale at the micron scale.

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