An investigation has been done to study the evolution of the microstructure, mechanical and electrical properties of AlMgSi alloy destined for the transport of electric energy, in function of the deformation caused by the cold drawing process. We identified that drawing of aluminum wire causes development of a fibrous texture of type < 111 > and < 100 >. We notice also that the electrical resistivity and mechanical resistance increases with the increasing of the deformation level. Characterization methods used in this work is: The Electron Back Scattered Diffraction EBSD, X-Ray diffraction, Vickers microhardness, Tensile test, Measuring electrical resistivity, the Scanning Electron Microscope (SEM) and Energy Diffraction Spectrum (EDS).

The aim of the present work, made up of two parts, consists in studying the behaviour of the local environment of the doping zirconium, in the polycrystalline α-alumina related to the material microstructure. At first, the kinetics of grain growth has been studied, and local chemical analyses on thin foils at grain boundaries using the energy dispersive X-ray spectroscopy (EDXS) technique, were performed. In the second part, we shall consider the evolution of the local order around the doping element, related to the microstucture, by X-ray absorption spectroscopy (XAS) measurements. This study was performed on doped α-polycrystalline alumina (0.03 wt% ZrO2) samples. According to the experimental results, we can show a great interaction between the zirconium and the grain boundaries of the alumina: during the grain growth, grain boundaries drag most of the doping element in solid solution. A transition in the environmental configuration around the doping in grain boundaries is observed, when the segregation ratio of the zirconium in grain boundaries reaches the value of about (4±2)×103. In these conditions, a change in the local order is observed, around the segregated zirconium. This change varies from a statistical disorder to an ordered state, and can be described as an assembly of nanocrystalline metastable, tetragonal zirconia particles. This transition of the environmental configuration in grain boundaries is correlated to the increase of the grain growth velocity, according to the kinetics studies.

Le travail que nous presentons ici a pour objectif l'etude de l'evolution de l'environnement local autour du zirconium dans l'alumine en relation avec la microstructure du materiau. Cette etude est realisee sur de l'alumine-α polycristalline dopee a 300 ppm en poids de ZrO 2 ayant des microstructures differentes. Pour cela trois techniques d'analyse ont ete utilisees: l'analyse d'images (MEB), la spectroscopie-X a dispersion d'energie (EXDS) sur lames minces pour la determination des heterogeinites de composition chimique aux joints de grains, et la spectroscopie d'absorption-X (X.A.S) pour la determination de l'ordre local autour du dopant Les resultats montrent l'existence d'une forte interaction du zirconium avec les joints de grains de l'alumine. Dans les joints de grains, et pour un taux d'enrichissement de l'ordre de ≃ 8×10 3 , le zirconium forme des particules de zircone metastable, tetragonale, de taille nanometrique.

Yttrium bulk diffusion in single crystals of α-alumina is investigated by the SIMS technique, in the temperature range 1150–1500 °C. The bulk diffusion coefficients obey the relation: D(Y)(1150–1500 °C) = 1.2 10−10 exp (−295(kJ mol−1)/RT) (m2 s−1). These values are close to those of chromium diffusion in alumina, although the size of Y3+ ion is significantly higher than that of Cr3+ ion. The results are used to calculate the parameters of yttrium grain boundary diffusion in alumina, from the penetration profiles obtained in a previous work in polycrystals by the radiotracer technique.

The transport properties of alumina scales formed on undoped and Y-doped β-NiAl have been characterized at 1100°C by diffusion measurements, either by isotopic exchange (16O2–18O2) or from a thin film of chromium, in order to simulate the cationic inward diffusion. The penetration profiles have been established by secondary ion mass spectrometry (SIMS). To determine anionic and cationic diffusion coefficients, the microstructure, determined by transmission electron microscopy (TEM), and the surface roughness of the scale have been considered. The diffusion coefficients determined on scales are compared to results on massive alumina extrapolated to 1100°C. The oxidation constant is then calculated, using the theory of Wagner, and compared either with the values experimentally obtained by thermogravimetry, or with the oxidation constant calculated from electrochemical measurements. The value calculated from the electrochemical results is in good agreement with the experimental value, while the calculation from diffusion data leads to an oxidation constant smaller than the experimental value. The yttrium effect on transport properties is small.

(Attention for corrosion science, the abstract must not exceed more than 100 words)In this research, first a multi-analytical approach was carried out to propose a mechanistic model for the formation of the thermal oxide film on low Cr stainless steel. It describes the effects of kinetically and thermodynamically driven phenomena on the growth of a Fe-Cr complex oxide film at 950℃. Second, the behavior of the thermal oxide film in the presence of fluoride ions, as a relevant pickling agent in conversion treatment, was investigated. It was shown that fluoride ions enter the oxide film and form a complex with Fe and preferentially dissolve hematite islands through a complexation mechanism.

The chemical state and local structure around zirconium in doped alpha-polycrystalline alumina (300 wt. ppm %. ZrO2) was studied by Extended X-Ray Absorption Fine Structure (EXAFS) measurements at zirconium K-edge energy and by STEM analysis on thin foils. It appared that most of the zirconium is located in grain boundaries as nanocrystalline tetragonal zirconia particles. This allotropic tetragonal zirconia form is stabilised at room temperature because of the important contribution of the surface free energy.

Bien que le silicium ameliore la resistance a la corrosion de couches de Cr 2 O 3 formees sur acier inoxydable dans des atmospheres riches en carbone, il n'en est pas de meme en atmosphere oxydante. Les couches sont alors constituees de Cr 2 O 3 avec une quantite non negligeable d'oxydes de fer et, en surface externe, des oxydes de Mn et Ti. Le silicium est present dans toute la couche en tres faible quantite et empeche la contamination en fer de la partie externe de la couche, en particulier a basse pO 2 . Les courbes de cinetique d'oxydation sont le plus souvent paraboliques avec deux stades, le deuxieme stade correspondant a une modification de la purete ou de la densite de la couche. Les coefficients de diffusion calcules a partir des constantes d'oxydation sont legerement plus eleves que ceux determines sur couches d'oxyde de chrome pures, probablement en raison de l'incorporation des impuretes Fe, Mn, Ti, Si. L'etude en XPS in situ a permis de mettre en evidence une modification des pics lors du chauffage sous ultra-vide, liee a une contamination de surface.

The influence of yttrium on the microstructure and toughness of alpha-alumina is studied as a function of oxygen partial pressure and chemical state of the doping element. For doping amounts higher than 0.03 mol% of Y2O3, Y3Al5O12 garnet precipitates and the alumina grain size is then limited by such a precipitation along grain boundaries. For coping amounts lower than or equal to 0.03 mol% of Y2O3, yttrium ions are in solid solution as defect complexes of the type (2Y(Al)(x) + mV(O)(--) + nO(i)(n))(2(m-n.) and segregates along grain boundaries. The stability of the defect complexes is promoted by low oxygen pressures and the grain size is limited by the yttrium segregation along grain boundaries. At high oxygen pressures, the yttrium solubility decreases and an enrichment in yttrium is observed at the sample surface. Simultaneously, an abnormal alumina grain growth appears. The alumina toughness, estimated by indentation, is improved by the presence of defect complexes at low oxygen pressures while the Y3Al5O12 garnet precipitates increase the alumina brittleness. (C) 1996 Elsevier Science Limited.

The influence of yttrium doping on the alumina microstructure is correlated to the Y amount and to the oxygen pressure. A low oxygen pressure promotes the solubility of yttrium in the bulk, its segregation in grain boundaries and increases the alumina toughness. Moreover alumina grain growth is limited either by garnet precipitation or by yttrium segregation along boundaries.

The influence of yttrium doping on the ionic and electronic conductivities of or alumina developed on a beta NiAl alloy by oxidation at 1100 degrees C was investigated by electrochemical measurements, in order to point out the possible effect of this element on the transport properties of alumina scales. It appears that the yttrium influence is small. It slightly reduces the ionic transport number at low oxygen pressure and increases it at high pO(2): the alumina scale behaves as an ionic conductor near the substrate-oxide interface and progressively becomes a mixed conductor or an electronic conductor near the outer oxide-gas interface. The ionic-electronic transition is sharper for undoped scales.

The influence of yttrium doping on the ionic and electronic conductivities of α alumina developed on a β NiAl alloy by oxidation at 1100[ddot]C was investigated by electrochemical measurements, in order to point out the possible effect of this element on the transport properties of alumina scales. It appears that the yttrium influence is small. It slightly reduces the ionic transport number at low oxygen pressure and increases it at high pO2: the alumina scale behaves as an ionic conductor near the substrate-oxide interface and progressively becomes a mixed conductor or an electronic conductor near the outer oxide-gas interface. The ionic-electronic transition is sharper for undoped

Although the influence of yttrium on transport properties of α alumina has been the object of many studies, the mechanisms by which this element acts have not yet been elucidated. The method of modification by yttrium of the microstructure of α polycrystalline alumina and the nature of the point defects created by this doping element were studied. The results obtained are discussed in relation to alumina transport properties and especially in relation with the effect of yttrium on the oxidation mechanism of alumina former alloys, taking into account the doping amount.

ChemInformVolume 20, Issue 7 Physical Inorganic Chemistry ChemInform Abstract: High-Temperature Corrosion of Fe-Ni-Cr, Fe-Cr-Al, and Fe-Ni-Cr-Al Alloys in Controlled H2/H2O/CH4 Atmospheres. M. K. LOUDJANI, M. K. LOUDJANI Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this authorJ. C. PIVIN, J. C. PIVIN Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this authorA. M. HUNTZ, A. M. HUNTZ Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this authorJ. H. DAVIDSON, J. H. DAVIDSON Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this author M. K. LOUDJANI, M. K. LOUDJANI Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this authorJ. C. PIVIN, J. C. PIVIN Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this authorA. M. HUNTZ, A. M. HUNTZ Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this authorJ. H. DAVIDSON, J. H. DAVIDSON Lab. Metall. Struct., ISMA, CNRS, Univ. Paris-Sud, 91405 Orsay, Fr.Search for more papers by this author First published: February 14, 1989 https://doi.org/10.1002/chin.198907025Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue7February 14, 1989 RelatedInformation

Corrosion tests have been carried out at 1200°C in various H2/H2O/CH4 mixtures, for a range of pre-oxidized materials, including an austenitic Fe45Ni25Cr alloy and a series of ferritic, austenitic and two phase alumina-forming grades. The corrosion process has been studied principally by metallographic examination of the scales and of the underlying alloys, together with local chemical and physical analysis. The results are interpreted with the aid of thermodynamic phase-stability diagrams.

AbstractDer größte Teil des im Al2O3 als Dotierung (l mol‐%) vorhandenen Yttriums wird als Y3Al5O,2 ausgefällt.

Yttrium‐doped a‐poly crystalline alumina was studied by microscopy observations and by extended X‐ray absorption fine‐structure experiments. The latter results were compared to those obtained for a standard Y2O3 powder and to theoretical spectra for Y2O3, and Y3Al5O12 calculated on the basis of crystallographic data. Most of the yttrium in the doped alumina is precipitated as a Y3Al5O12 phase. An observed threshold displacement involves a slight valence electron delocalization for the Y3+ ion.