Ophiolites - thrust sheets of oceanic lithosphere that have been emplaced onto the continental margin - provide the opportunity to explore the structure and genesis of oceanic crust. As many ophiolites formed above subduction zones, they also allow for the investigation of mantle wedge and subduction interface processes. This the- sis examines the Oman-United Arab Emirates (UAE) ophiolite, which is the largest and most intensely studied ophiolite on Earth. Three distinct problems are addressed. (1) Recent research has proposed that the architecture and tectonic evolution of the ophiolite in the UAE differs from in Oman. In Chapter 2, I test this hypothesis by integrating new geological mapping and field observations with previously published maps of the ophiolite in the UAE. My results indicate that the ophiolite is gently folded, but otherwise largely intact. I demonstrate that the architecture of the ophi- olite in the UAE is not significantly different from in Oman. Thus, there is no basis for a different tectonic evolution as recently proposed. (2) Observations from exper- iments and small-scale natural shear zones indicate that volumetrically-minor phases can control strain localization. In Chapter 3, I test the hypothesis that minor phases control strain-localisation at plate boundaries. To do so, I analyzed peridotites from the base of the ophiolite, a palaeosubduction interface. My results demonstrate that minor phases limited olivine grain growth, which led to rheological weakening. (3) The mechanisms by which metamorphic soles detached from the downgoing slab and accreted to the hanging-wall mantle is unclear. In Chapter 4, I examine a transect across the metamorphic sole in the UAE. My results reveal that granulite formation was more extensive than is typically considered. I propose that granulite formation resulted in rheological strengthening, which caused the subduction interface to migrate into the downgoing slab and accrete the metamorphic sole.

<p>The goal of this work has been to evaluate the different experimental techniques used for quantitative analysis of multi-phase materials systems. </p><p>Powder based specimens containing two-phases, austenite and ferrite , were fabricated and quantified. The volume fraction of ferrite varied from 2 Vol% to 50 Vol%. </p><p>X ray powder diffraction (XRD) measurements were based on two peak analysis. Computer based software Topas was used for quantitative analysis, which is believed to be the most advanced in this field. XRD results were found within the absolute limit of +/- 4% of given ferrite volume fraction. Volume fraction as low as 2 Vol% was successfully detected and quantified using XRD. However, high statistical error was observed in case of low volume fraction, such as 2 Vol% and 5 Vol% ferrite volume fraction. </p><p>Magnetic balance (MB) measurements were performed to determine the volume fraction of magnetic phase, ferrite. MB results were found in good agreement with given volume fractions. As low as 2 Vol% volume fraction was detected and quantified with MB. MB results were within the absolute limit of +/- 4% of given ferrite volume fraction. </p><p>Image analysis (IA) was performed after proper sample preparation as required by electron backscatter diffraction (EBSD) mode of Scanning electron microscopy (SEM). IM results were found within the absolute limit of +/- 2 % of given ferrite volume fraction. However, high statistical error was observed in case of 2 Vol% volume fraction.</p>

Plagioclase is the most abundant mineral in the lower crust and it is thus important to constrain the behaviour of plagioclase during deformation. Anorthosites, which are plagioclase-rich rocks, are common in Archaean cratons but their origin and rheological importance is still debated. The aims of this thesis are to 1) describe a newly discovered Archaean anorthosite complex (Naajat Kuuat, SW Greenland), investigate its origin and a possible genetic relationship between the anorthosite and associated mafic-ultramafic rocks and 2) to study the rheology and deformation mechanisms in plagioclase-rich rocks. The main focus of this thesis is on the deformation studies. (1) Geochemical whole-rock analyses from the Naajat Kuuat complex are indicative for an origin near a subduction zone setting. A genetic link by crystal fractionation between the anorthosite and associated mafic-ultramafic units is inferred. (2) Deformation behaviour of plagioclase is assessed from analyses of three anorthosite units deformed during different conditions. Samples were analysed using the electron backscatter diffraction technique (EBSD) in combination with optical and chemical analyses. All three case studies show significant strain localisation related to grain size reduction. A wet anorthosite deformed at dry conditions (T ~675-700°C) was dynamically recrystallised. Continuous bands of recrystallised grains developed a texture yet display microstructures and grain relationships indicative for grain size sensitive creep, suggesting that the rheology followed a Newtonian flow law. In the other two studies, samples with initially dry and wet composition, respectively, have experienced deformation during fluid present conditions at T ~550-620°C. These two samples show that fluids effectively caused reactions, replacements and aided strain localisation during deformation at mid crustal conditions. / At the time of the doctoral defence the following papers were unpublished and had a status as follows: Paper 1: Manuscript; Paper 2 Manuscript; Paper 3 Manuscript.

The goal of this work has been to evaluate the different experimental techniques used for quantitative analysis of multi-phase materials systems. Powder based specimens containing two-phases, austenite and ferrite , were fabricated and quantified. The volume fraction of ferrite varied from 2 Vol% to 50 Vol%. X ray powder diffraction (XRD) measurements were based on two peak analysis. Computer based software Topas was used for quantitative analysis, which is believed to be the most advanced in this field. XRD results were found within the absolute limit of +/- 4% of given ferrite volume fraction. Volume fraction as low as 2 Vol% was successfully detected and quantified using XRD. However, high statistical error was observed in case of low volume fraction, such as 2 Vol% and 5 Vol% ferrite volume fraction. Magnetic balance (MB) measurements were performed to determine the volume fraction of magnetic phase, ferrite. MB results were found in good agreement with given volume fractions. As low as 2 Vol% volume fraction was detected and quantified with MB. MB results were within the absolute limit of +/- 4% of given ferrite volume fraction. Image analysis (IA) was performed after proper sample preparation as required by electron backscatter diffraction (EBSD) mode of Scanning electron microscopy (SEM). IM results were found within the absolute limit of +/- 2 % of given ferrite volume fraction. However, high statistical error was observed in case of 2 Vol% volume fraction.

La compréhension et la simulation des mécanismes de déformation dans la croûte supérieure sont des enjeux scientifiques et techniques importants. La calcite étant un minéral commun de la croûte supérieure se déformant essentiellement par maclage sous 200 °C, c'est pour cette raison que l'on s'intéresse plus particulièrement au maclage de la calcite dans le cadre de cette thèse. L'utilisation du maclage de la calcite n'en est pas à son coup d'essai et de nombreuses méthodes d'inversions existent que ce soit pour remonter aux tenseurs des contraintes comme aux tenseurs des déformations. Cette thèse propose une nouvelle méthode d'inversion basée sur l'inversion d'Etchopar permettant de reconstruire 5 sur 6 paramètres du tenseur des contraintes avec une quantification fine des incertitudes. Cette méthode permet de détecter automatiquement l'existence d'un ou de plusieurs évènements tectoniques enregistrés par le maclage de la calcite. Un deuxième volet de la thèse consiste en l'amélioration de la méthode d'acquisition des données de macles en utilisant un EBSD (electron backscatter diffraction). En effet, l'utilisation traditionnelle de la platine universelle a des limitations techniques et amène aussi à un doute visuel sur l'appréciation du statut non-maclé de certains plans, en plus du côté long et fastidieux. Le dernier volet de la thèse consiste à déterminer le seuil de maclage de la calcite pour différentes tailles de grains à l'aide de tests mécaniques sous une presse uniaxiale. Qui plus est, le suivi en continu des déformations sur les monocristaux de calcite a permis de mettre en évidence le comportement macroscopique d'un cristal de calcite et la séquence de maclage. / The understanding and modelling of deformation mechanics in the upper crust are important scientific and technical issues. The calcite is a common mineral in the upper crust and mainly deforms by twinning under 200°C. That is why we are interested by calcite twinning as part of this thesis. It is not the first time that calcite twinning is used to reconstruct paleostress or paleostrain tensors. This thesis propose a new inversion method based on the Etchecopar’s one allowing to reconstruct 5 among 6 parameters of the stress tensor with an accurate quantification of the uncertainties. This method allows to automatically detect the realness of one or several tectonic events recorded by calcite twinning. A second part of the thesis consists in the improvement of the data acquisition by using EBSD (electron backscatter diffraction). In fact, the traditional use of the universal stage has technical limitations and brings some optical doubt about the untwinned status of few planes in addition to the long and tedious side. The last part of the thesis consists in the establishing the threshold of calcite twinning for different grain sizes by mechanical tests under a uniaxial press. Moreover, the continuous monitoring of the experiments using single crystals of calcite allowed to highlight the macroscopic behavior of a single crystal and the sequence of twinning.

Formable Advanced High-Strength Steels (AHSS) have a unique combination of strength and ductility, making them ideal in the effort to lightweight vehicles. The AHSS in this study, Quenched and Partitioned 1180, rely on the Transformation Induced Plasticity (TRIP) effect, in which retained austenite (RA) grains transform to martensite during plastic deformation, providing extra ductility via the transformation event. Understanding the factors involved in RA transformation, such as local strain and grain attributes, is therefore key to optimizing the microstructure of these steels. This research seeks to increase understanding of those attributes and the correlations between microstructure and RA transformation in TRIP steels. To measure local strain, the viability of using forescatter detector (FSD) images as the basis for DIC study is investigated. Standard FSD techniques, along with an integrated EBSD / FSD approach (Pattern Region of Interest Analysis System), are both analyzed. Simultaneous strain and microstructure maps are obtained for tensile deformation up to around 6% strain. The method does not give sub-grain resolution, and surface feature evolution prevents DIC analysis across large strain steps; however, the data is easy to obtain and provides a natural set of complementary information for the EBSD analysis. In-situ tensile tests combined with EBSD allow RA grain and neighboring attributes to be characterized and corresponding transformation data to be obtained. However, pseudo-symmetry of the ferrite (BCC) and martensite (BCT) phases prevents EBSD from accurately identifying all phases. Measuring the relative distortion of the crystal lattice, tetragonality, is one approach to identifying the phases. Unfortunately, small errors in the pattern center can cause significant errors in tetragonality measurement. Therefore, this research utilizes a new approach for accurate pattern center determination using a strain minimization routine and applies it to tetragonality maps for phase identification. Tetragonality maps based on dynamically simulated patterns result in the most accurate maps and can also be used to predict approximate local carbon content. Machine learning is then used on the collected data to isolate key attributes of RA grains and provide a decision tree model to predict transformation based on those attributes. Among the most relevant attributes found, RA grain area, RA grain shape aspect ratio, a “hardness” factor, and major axis orientation are included. Possible correlations between these factors and transformation improve understanding of relevant attributes and show the advantage that machine learning can have in unravelling complex material behavior.

One conventional method for studying dislocations uses the Transmission Electron Microscope (TEM), a complex and expensive piece of equipment which requires extensive specimen preparation in order to thin the specimens to electron transparent thickness. Newer High Resolution Electron Backscatter Diffraction (HREBSD) methods of determining geometrically necessary dislocation content via cross-correlation promise to be able to produce estimates of the dislocation density of the sample over a larger area with considerably less preparation time and using a much more accessible instrument. However, the accuracy of the new EBSD technique needs more experimental verification, including consideration of possible changes in the specimen dislocation density due to the different preparation methods. By comparing EBSD and TEM dislocation measurements of Electron Transparent platinum specimens prepared using the Focused Ion Beam (FIB), along with EBSD dislocations measurements of specimens prepared by both FIB and mechanical polishing techniques, this paper seeks to verify the accuracy of the new method and identify any changes in the specimens’ apparent dislocation density caused by the different preparation processes.

No description available.

Approved for public release, distribution is unlimited / The effect of friction-stir processing (FSP) on the microstructure of a cast nickel-aluminum bronze (NAB) material has been characterized by various micro-analytical methods including orientation imaging microscopy (OIM). Cast NAB is widely utilized in the production of propellers for the surface ships and submarines of the U.S. Navy due to excellent corrosion-resistance. New applications require improved mechanical properties that may be attainable using FSP to achieve localized microstructure modification. Friction between a rotating tool and the surface of the material results in a *stirring* action that, in turn, produces adiabatic heating and local softening of the material. The tool rotation results in very large shear deformations in the softened regions and thus microstructure refinement and homogenization; in effect FSP may convert an as-cast microstructure to a wrought condition in the absence of macroscopic shape change. In as-cast material, results of optical and scanning electron microscopy (using energy dispersive analysis) show an ` (FCC) matrix containing globular and particulate dispersions that correspond to the *I, *II and *IV second phases; these represent various morphologies of the Fe3Al intermetallic compound, which has a D03 structure. Also present are lamellar particles of *III, which is NiAl and has a B2 structure. The grain size in the ` matrix is ~ 1 mm. In OIM, the microtexture and microstructure in the ` (FCC) matrix may be readily obtained and analyzed. However, interatom distances in the Fe3Al and NiAl phases differ by only about one percent and so these phases are not distinguishable from one another during OIM. Altogether, microstructure and microtexture analysis showed that there are several regions in the thermomechanically affected zone (TMAZ) of a material subjected to FSP. From base material inward toward the TMAZ, these include: annealing effects in undeformed base material; a region just inside the TMAZ in which grain deformation and C-type shear deformation textures are observed; regions of highly refined and recrystallized grains further inside the TMAZ, wherein the grain size is < 5æm; and, finally, regions of elongated, banded and twinned grain structures that suggest grain growth following recrystalliztion. / Lieutenant, United States Navy

L’évolution de la technologie microélectronique conduit à une densité d’intégration toujours plus forte des transistors. Les structures d’interconnexions en cuivre Damascène suivent cette tendance et doivent être maîtrisées en termes de fabrication, de performance et de robustesse, ces différents aspects étant intimement liés aux contraintes résiduelles et à la résistivité. Cette thèse vise à comprendre les mécanismes de génération de contraintes et identifier les différentes contributions à la résistivité de ces objets en fonction des conditions de recuit et des dimensions (de la centaine de nm à plusieurs µm). Pour ce faire, les rôles respectifs de la microstructure et des dimensions de films et de lignes de cuivre électrodéposés ont été découplés sur la base de modèles analytiques intégrants des paramètres microstructuraux et géométriques. La microstructure a été analysée principalement à partir de cartographies d’orientations cristallines réalisées par EBSD. Dans le cas des lignes de cuivre de 0.2 à 1 µm de large, les contraintes résiduelles ont été déduites de l’exploitation de nano-capteurs pivotants spécialement élaborés. Les résultats obtenus montrent qu’indépendamment de la température de recuit, l’augmentation de résistivité et de contraintes résiduelles observée vers les faibles dimensions est le fruit d’une diminution de la taille moyenne de cristallites et d’un confinement géométrique plus prononcé. En outre, l’augmentation de résistivité résulte également d’une élévation de la probabilité de réflexion des électrons aux joints de grains. Cette dernière a été associée à la réduction de la proportion de joints de grains spéciaux de cohérence atomique élevée. / The evolution of the microelectronic technology leads to a transistors integration density always stronger. The Damascene copper interconnections structures follow this tendency and must be controlled in terms of manufacturing, performance and robustness, these different aspects being intimately related to the residual stresses and resistivity. This thesis aims to understand the mechanisms of the residual stresses generation and identify the different contributions to the resistivity of these objects as a function of annealing conditions and dimensions (from about a hundred of nm to several µm). In order to do this, the respective effects of the microstructure and dimensions of electroplated copper films and lines were separated on the basis of analytical models integrating microstructural and geometrical parameters. The microstructure was principally analysed from mappings of crystalline orientations achieved by EBSD. For the copper lines of width 0.2 and 1 µm, the residual stresses were deduced from the exploitation of nano-rotating sensors specially elaborated. The results obtained show that independently of the annealing temperature, the resistivity and residual stresses increase observed toward the small dimensions arises from the diminution of the average crystallites size and the geometrical confinement more pronounced. Furthermore, the resistivity increase results also of the electrons reflection probability growth at grains boundaries. This last point was associated to the reduction of the proportion of special grains boundaries having a high atomic coherency.