Characterization of Zirconium Oxides Part I: Raman Mapping and Spectral Feature Analysis

Raman mapping of sectioned zirconium cladding oxides was performed to analyze different spectral features before and after breakaway, as well as between zirconium and its alloys Zr-2.65Nb, Zry-3, and Zry-4. Oxide phase composition, or percent tetragonality, was defined to compare tetragonal to monoclinic zirconia. Percent tetragonality was spatially mapped to support distinction of zirconia phase distribution. A tetragonal-rich layer was seen at the metal/oxide interface, while post-breakaway samples exhibited increased amount of tetragonal phase in the bulk of their oxides. Spatial mapping of spectral peak location and half-width at half-maximum was accomplished to distinguish differences in stability mechanisms of tetragonal-rich zirconia phase. Shifts in monoclinic peak positions provided mapping of relative stress state, supporting the differences in stabilization of tetragonal phase near the metal/oxide interface and tetragonal phase in the bulk of the oxide. Tetragonal phase near the metal/oxide interface is stabilized through support of oxygen sub-stoichiometry and compressive stress. Tetragonal phase observed in the bulk of the oxide is stabilized through oxygen sub-stoichiometry, void of compressive stress. A linear trend between percent tetragonality and stress state was determined. This resulted in a connection between mechanism of tetragonal to monoclinic phase transformation and a cladding\u27s ability to resist oxidation and breakaway. Poor performing samples displayed greater stress gradients, driven by lattice mismatch at the metal/oxide interface, as well as between tetragonal and monoclinic phase boundaries. Tetragonal phase at the metal/oxide interface for superior performing samples have reduced epitaxial growth of tetragonal grains, lowering compressive stress gradients and provided more resistant inner-oxide layers. With increased utility of Raman spectroscopy for characterizing zirconium cladding materials, different degradation mechanisms can be further understood

Determination of residual stress fields in a thermally grown oxide under thermal cycling loadings, using XRD and Raman spectroscopy. Correlations with microstructural states

Abstract. The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromia oxide are determined either by XRD or Raman spectroscopy. In addition, the microstructure of the chromia films is investigated ant its influence on the evolution of the stress release processes is analyzed. Introduction NiCr alloys are currently used at high temperatures because it develops a dense chromia surface oxide film which slows down the oxidation process. In turn, the material durability depends on the ceramic film integrity. The isothermal oxide layer growth or the cooling steps usually induce the development of high residual stress in the ceramic film. The determination of such growth or residual stress has already been undertake

Determination of residual stress fields in a thermally grown oxide under thermal cycling loadings, using XRD and Raman spectroscopy. Correlations with microstructural states

Abstract. The presence of residual stresses in thermal oxide layers has been recognized for a long time. In the present work, the mechanical fields for chromia oxide are determined either by XRD or Raman spectroscopy. In addition, the microstructure of the chromia films is investigated ant its influence on the evolution of the stress release processes is analyzed. Introduction NiCr alloys are currently used at high temperatures because it develops a dense chromia surface oxide film which slows down the oxidation process. In turn, the material durability depends on the ceramic film integrity. The isothermal oxide layer growth or the cooling steps usually induce the development of high residual stress in the ceramic film. The determination of such growth or residual stress has already been undertake

Residual stress determination in oxide layers at different length scales combining Raman spectroscopy and X-ray diffraction: Application to chromia-forming metallic alloys

In oxidizing environments, the protection of metals and alloys against further oxidation at high temperature is provided by the oxide film itself. This protection is efficient only if the formed film adheres well to the metal (substrate), i.e., without microcracks and spalls induced by thermomechanical stresses. In this study, the residual stresses at both macroscopic and microscopic scales in the oxide film adhering to the substrate and over the damaged areas have been rigorously determined on the same samples for both techniques. Ni-30Cr and Fe-47Cr alloys have been oxidized together at 900 and 1000 °C, respectively, to create films with a thickness of a few microns. A multi-scale approach was adopted: macroscopic stress was determined by conventional X-ray diffraction and Raman spectroscopy, while microscopic residual stress mappings were performed over different types of bucklings using Raman micro-spectroscopy and synchrotron micro-diffraction. A very good agreement is found at macro- and microscales between the residual stress values obtained with both techniques, giving confidence on the reliability of the measurements. In addition, relevant structural information at the interface between the metallic substrate and the oxide layer was collected by micro-diffraction, a non-destructive technique that allows mapping through the oxide layer, and both the grain size and the crystallographic orientation of the supporting polycrystalline metal located either under a buckling or not were measured

Contribution à l'étude des mécanismes de relaxation de contraintes dans les films de chromine formés sur Ni-30Cr et Fe-47Cr : approche multi-échelle par spectroscopie Raman et microdiffraction Synchrotron

Chromia-former alloy are mainly used for high temperature applications. Their ability to form a protective thermal oxide scale allows reducing oxidation kinetics of the materials. In particular, Ni-Cr and Fe-Cr alloy forms a α-Cr2O3 scale at the surface. Durability of the metal/ceramic system depends on the mechanical integrity of this scale, and also of the scale damage which could appear during oxidation or cooling. These scale damages are closely correlated to the residual stress magnitude in the oxide and to the microstructure. In this work, Ni-30Cr and Fe-47Cr alloys oxidized in air at 800, 900 and 1000°C and a multi-scale approach is proposed to a analyse with accuracy residual stress magnitude both at macroscopic scale in the adherent oxide and at local scale through delaminated area.At macroscopic scale, residual stress magnitudes are determined thanks to conventional X-Ray diffraction and Raman spectroscopy. Delamination rate in the oxide scale and diffusional creep phenomena are quantified in function of metallurgical parameters leadings to different microstructural state of the system. The influence of competition between these two stress release modes on scale damage is discussed. At microscopic scale, residual stress map through different types of delamination are performed thanks to Raman microspectroscopy and Synchrotron microdiffraction. Raman microspectroscopy is particularly appropriated to analyze delamination locally formed, due to its lateral resolution. Observations by atomic force microscopy have been performed to describe the different delamination type (dimension, height). These morphological information and associated residual stresses allows confrontation to buckling mechanic and calculation of the interface toughness. Diagrams and maps concerning the scale damages have been done thanks to these analyses.Les alliages à base de chrome sont couramment utilisés pour des applications à haute température. Leurs capacités à former une couche d’oxyde thermique protectrice permet de réduire les cinétiques d’oxydation de ces matériaux. En particulier, les alliages Ni-Cr et Fe-Cr forment une couche continue de α-Cr2O3 en surface. La durabilité du système métal/céramique résultant dépend de l’intégrité mécanique de cette couche, et donc des mécanismes d’endommagement susceptibles de se produire lors de l’oxydation ou du refroidissement. L’endommagement est étroitement corrélé au niveau de contraintes résiduelles dans l’oxyde mais aussi à sa microstructure. Dans ces travaux, des alliages Ni-30Cr et Fe-47Cr sont oxydés à l’air à 800, 900 et 1000°C et une approche multi-échelle est proposée pour analyser rigoureusement les contraintes résiduelles aussi bien à des échelles macroscopiques dans le film d’oxyde adhérent qu’à des échelles locales au travers de régions délaminées.A l’échelle macroscopique, les niveaux de contraintes résiduelles sont déterminés grâce à la diffraction des Rayons X conventionnelle et à la spectroscopie Raman. Les taux de délamination des couches d’oxyde et les phénomènes de fluage diffusionnel sont quantifiés en fonction de paramètres métallurgiques conduisant à différents états microstructuraux du système. L’influence de la compétition entre ces deux modes de relaxation de contrainte sur l’endommagement est discutée. A l’échelle microscopique, des cartographies de contraintes résiduelles au travers de différents types de délaminations sont réalisées grâce à la microspectroscopie Raman et à la microdiffraction Synchrotron. En raison de sa résolution latérale, la microspectroscopie Raman est particulièrement appropriée pour analyser les délaminations formées localement. Des observations par microscopie à force atomique ont également été menées afin de décrire la géométrie (dimensions, hauteur) des différents types d’objets délaminés. Ces informations morphologiques complémentaires couplées aux niveaux de contraintes associés permettent une confrontation aux lois de la mécanique du cloquage, et l’extraction de l’adhérence interfaciale. A partir de ces analyses, des schémas et cartes de l’endommagement des couches de chromine sont proposés

Contribution at the study of stress release mechanism in chromia scales formed on Ni-30Cr and Fe-47Cr : multiscale approach by Raman spectroscopy and Synchrotron microdiffraction

Les alliages à base de chrome sont couramment utilisés pour des applications à haute température. Leurs capacités à former une couche d’oxyde thermique protectrice permet de réduire les cinétiques d’oxydation de ces matériaux. En particulier, les alliages Ni-Cr et Fe-Cr forment une couche continue de α-Cr2O3 en surface. La durabilité du système métal/céramique résultant dépend de l’intégrité mécanique de cette couche, et donc des mécanismes d’endommagement susceptibles de se produire lors de l’oxydation ou du refroidissement. L’endommagement est étroitement corrélé au niveau de contraintes résiduelles dans l’oxyde mais aussi à sa microstructure. Dans ces travaux, des alliages Ni-30Cr et Fe-47Cr sont oxydés à l’air à 800, 900 et 1000°C et une approche multi-échelle est proposée pour analyser rigoureusement les contraintes résiduelles aussi bien à des échelles macroscopiques dans le film d’oxyde adhérent qu’à des échelles locales au travers de régions délaminées.A l’échelle macroscopique, les niveaux de contraintes résiduelles sont déterminés grâce à la diffraction des Rayons X conventionnelle et à la spectroscopie Raman. Les taux de délamination des couches d’oxyde et les phénomènes de fluage diffusionnel sont quantifiés en fonction de paramètres métallurgiques conduisant à différents états microstructuraux du système. L’influence de la compétition entre ces deux modes de relaxation de contrainte sur l’endommagement est discutée. A l’échelle microscopique, des cartographies de contraintes résiduelles au travers de différents types de délaminations sont réalisées grâce à la microspectroscopie Raman et à la microdiffraction Synchrotron. En raison de sa résolution latérale, la microspectroscopie Raman est particulièrement appropriée pour analyser les délaminations formées localement. Des observations par microscopie à force atomique ont également été menées afin de décrire la géométrie (dimensions, hauteur) des différents types d’objets délaminés. Ces informations morphologiques complémentaires couplées aux niveaux de contraintes associés permettent une confrontation aux lois de la mécanique du cloquage, et l’extraction de l’adhérence interfaciale. A partir de ces analyses, des schémas et cartes de l’endommagement des couches de chromine sont proposés.Chromia-former alloy are mainly used for high temperature applications. Their ability to form a protective thermal oxide scale allows reducing oxidation kinetics of the materials. In particular, Ni-Cr and Fe-Cr alloy forms a α-Cr2O3 scale at the surface. Durability of the metal/ceramic system depends on the mechanical integrity of this scale, and also of the scale damage which could appear during oxidation or cooling. These scale damages are closely correlated to the residual stress magnitude in the oxide and to the microstructure. In this work, Ni-30Cr and Fe-47Cr alloys oxidized in air at 800, 900 and 1000°C and a multi-scale approach is proposed to a analyse with accuracy residual stress magnitude both at macroscopic scale in the adherent oxide and at local scale through delaminated area.At macroscopic scale, residual stress magnitudes are determined thanks to conventional X-Ray diffraction and Raman spectroscopy. Delamination rate in the oxide scale and diffusional creep phenomena are quantified in function of metallurgical parameters leadings to different microstructural state of the system. The influence of competition between these two stress release modes on scale damage is discussed. At microscopic scale, residual stress map through different types of delamination are performed thanks to Raman microspectroscopy and Synchrotron microdiffraction. Raman microspectroscopy is particularly appropriated to analyze delamination locally formed, due to its lateral resolution. Observations by atomic force microscopy have been performed to describe the different delamination type (dimension, height). These morphological information and associated residual stresses allows confrontation to buckling mechanic and calculation of the interface toughness. Diagrams and maps concerning the scale damages have been done thanks to these analyses

Structural evolution of HMX during processing operations

International audienceThe impact of processing operations such as chemical synthesis conditions, milling, coating and pressing operations on the crystallographic structure of HMX has been studied using X-ray diffraction and Rietveld analysis. Strong differences in grain morphology and X-ray patterns were first observed after synthesis on two different setups with different washing methods. Diffraction pattern refinements were tentatively performed on the basis of known structures and assuming preferential orientations. The impossibility of achieving satisfactory agreement, even considering the orientation of several planes, could be attributed to the presence of polymorphism or hydrates. The possible new polymorphs or hydrates were metastable since milling led to the stable ß-HMX polymorph. No such transformation occurred during the coating operation, but an increase in structural defects was observed. Finally, the pressing step did not induce any transformation but surprisingly led to a decrease in structural defects, probably due to isotropic deformation of the crystallographic cell and the repairing effect of the associated thermal treatment.L’impact des opérations de traitement telles que les conditions de synthèse chimique, les opérations de broyage, de revêtement et de pressage sur la structure cristallographique du HMX a été étudié à l’aide de la diffraction des rayons X et de l’analyse de Rietveld. De fortes différences dans la morphologie des grains et les rayons X ont été observées pour la première fois après la synthèse sur deux configurations différentes avec des méthodes de lavage différentes. Des raffinements de diagrammes de diffraction ont été provisoirement effectués sur la base de structures connues et en supposant des orientations préférentielles. L’impossibilité d’obtenir un accord satisfaisant, même en tenant compte de l’orientation de plusieurs plans, pourrait être attribuée à la présence de polymorphisme ou d’hydrates. Les nouveaux polymorphes ou hydrates possibles étaient métastables puisque le broyage a conduit au polymorphe ß-HMX stable. Aucune transformation de ce type ne s’est produite pendant l’opération de revêtement, mais une augmentation des défauts structurels a été observée. Enfin, l’étape de pressurage n’a induit aucune transformation mais a étonnamment conduit à une diminution des défauts structurels, probablement dus à la déformation isotrope de la cellule cristallographique et à l’effet réparateur du traitement thermique associé

Tuberculose nosocomiale

GRENOBLE1-BU Médecine pharm. (385162101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

The use of micro-Raman imaging to measure 18O tracer distribution in thermally grown zirconia scales

International audienceHigh temperature Zircaloy-4 oxidation has been studied through two-stage oxidation experiments using 18O isotope. 18O distribution in the oxidation scales was investigated by micro-Raman imaging. First, zirconia standards with known 18O content were prepared and analyzed for calibration purposes. Then, to assess the method on a simple case, 18O tracer penetration patterns were recorded after a 800°C two-stage oxidation. Finally, oxidation at 850°C of a Zircaloy4 cladding tube pre-corroded at 425°C to simulate corrosion during normal reactor operation was studied. These preliminary results give insights on the protective nature of the first formed zirconia scale in case of an accident. © 2015 Elsevier Ltd

Structural evolution of HMX during processing operations

The impact of processing operations such as chemical synthesis conditions, milling, coating and pressing operations on the crystallographic structure of HMX has been studied using X-ray diffraction and Rietveld analysis. Strong differences in grain morphology and X-ray patterns were first observed after synthesis on two different setups with different washing methods. Diffraction pattern refinements were tentatively performed on the basis of known structures and assuming preferential orientations. The impossibility of achieving satisfactory agreement, even considering the orientation of several planes, could be attributed to the presence of polymorphism or hydrates. The possible new polymorphs or hydrates were metastable since milling led to the stable ß-HMX polymorph. No such transformation occurred during the coating operation, but an increase in structural defects was observed. Finally, the pressing step did not induce any transformation but surprisingly led to a decrease in structural defects, probably due to isotropic deformation of the crystallographic cell and the repairing effect of the associated thermal treatment.</p