Дисертації: "Microstructure defects"

1

Yi, Jianzhang. "Effect of microstructure and defects on the fatigue behaviour of cast A356-T6 aluminium-silicon alloy." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405613.

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2

Hayward, Erin G. "Atomistic studies of defects in bcc iron: dislocations and gas bubbles." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44761.

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The structure and interactions of the defects in material on an atomistic scale ulti- mately determine the macroscopic behavior of that material. A fundamental understanding of how defects behave is essential for predicting materials failure; this is especially true in an irradiated environment, where defects are created at higher than average rates. In this work, we present two different atomistic scale computational studies of defects in body centered cubic (bcc) iron. First, the interaction energies between screw dislocations (line defects) and various kinds of point defects will be calculated, using anisotropic linear elastic theory and atomistic simulation, and compared. Second, the energetics and behavior of hydrogen and hydrogen-helium gas bubbles will be investigated.

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3

Adegoke, Olutayo. "Processability of Laser Powder Bed Fusion of Alloy 247LC : Influence of process parameters on microstructure and defects." Licentiate thesis, Högskolan Väst, Avdelningen för avverkande och additativa tillverkningsprocesser (AAT), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-16114.

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This thesis is about laser powder bed fusion (L-PBF) of the nickel-based superalloy: Alloy 247LC. Alloy 247LC is used mainly in gas turbine blades and processing the blades with L-PBF confers performance advantage over the blades manufactured with conventional methods. This is mainly because L-PBF is more suitable, than conventional methods, for manufacturing the complex cooling holes in the blades. The research was motivated by the need for academia and industry to gain knowledge about the processability of the alloy using L-PBF. The knowledge is essential in order to eventually solve the problem of cracking which is a major problem when manufacturing the alloy. In addition, dense parts with low void content should be manufactured and the parts should meet the required performance. Thus, the thesis answered some of the important questions related to process parameter-microstructure-defect relationships. The thesis presented an introduction in chapter 1. A literature review was made in chapter 2 to 4. In chapter 2, the topic of additive manufacturing was introduced followed by an overview of laser powder bed fusion. Chapter 3 focused on superalloys. Here, a review was made from the broader perspective of superalloys but was eventually narrowed down to the characteristics of nickelbased superalloys and finally Alloy 247LC. Chapter 4 reviewed the main research on L-PBF of Alloy 247LC. The methodology applied in the thesis was discussed in chapter 5. The thesis applied statistical design of experiments to show the influence of process parameters on the defects and microstructure, so a detail description of the method was warranted. This was given at the beginning of chapter 5 and followed by the description of the L-PBF manufacturing and the characterization methods. The main results and discussions, in chapter 6, included a preliminary investigation on how the process parameters influenced the amount of discontinuity in single track samples. This was followed by the results and discussions on the investigation of voids, cracks and microhardness in cube samples (detail presentation was given in the attached paper B). Finally, the thesis presented results of the microstructure obtainable in L-PBF manufactured Alloy 247LC. The initial results of the microstructure investigation were presented in paper A.

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4

Lee, Soon Gi. "Quantitative Characterization of Processing-Microstructure-Properties Relationships in Pressure Die-Cast Mg Alloys." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11552.

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The central goal of this research is to quantitatively characterize the relationships between processing, microstructure, and mechanical properties of important high-pressure die-cast (HPDC) Mg-alloys. For this purpose, a new digital image processing technique for automatic detection and segmentation of gas and shrinkage pores in the cast microstructure is developed and it is applied to quantitatively characterize the effects of HPDC process parameters on the size distribution and spatial arrangement of porosity. To get better insights into detailed geometry and distribution of porosity and other microstructural features, an efficient and unbiased montage based serial sectioning technique is applied for reconstruction of three-dimensional microstructures. The quantitative microstructural data have been correlated to the HPDC process parameters and the mechanical properties. The analysis has led to hypothesis of formation of new type of shrinkage porosity called, gas induced shrinkage porosity that has been substantiated via simple heat transfer simulations. The presence of inverse surface macrosegregation has been also shown for the first time in the HPDC Mg-alloys. An image analysis based technique has been proposed for simulations of realistic virtual microstructures that have realistic complex pore morphologies. These virtual microstructures can be implemented in the object oriented finite elements framework to model the variability in the fracture sensitive mechanical properties of the HPDC alloys.

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5

Sun, Qianying. "Conducting ceramics based on ZnO co-doped by (Al, Ti, Mg) : microstructure, electronic active defects and electrical properties." Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1014.

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Les céramiques conductrices à base de ZnO suscitent un important intérêt pour leurs applications comme varistances, capteurs de gaz, électrodes transparentes, dispositifs piézoélectriques, électro-optiques ou thermoélectriques. Le dopage de ZnO confère aux céramiques formées des propriétés électriques et optiques remarquables caractérisées par une transparence optique modulée, des énergies de liaison élevées pour les excitons, et des conductivités électriques atteignant 0.1 MS.m-1. La grande conductivité de ZnO est intimement liée aux éléments dopants, à la microstructure des céramiques et aux conditions de synthèse et traitements. Les joints de grains, la structure cristalline, le désordre structural et les défauts électroniques contribuent au comportement électrique des matériaux. Le présent travail de thèse s'inscrit dans ce contexte et porte sur la mise en œuvre de méthodes de fabrication de céramiques à base de ZnO co-dopées par des éléments (Al, Ti, Mg) et l'étude de leurs caractéristiques physiques incluant la structure cristalline, la microstructure et le comportement électrique. Ainsi, des études exhaustives ont été menées par des méthodes structurales (RX, Raman), microscopies (MET, MEB) et de résonance magnétique (RPE, RMN) sensible à l'ordre local et aux défauts électroniques actifs. La conductivité est ajustée par la nature des éléments dopants, l'atmosphère de frittage et les méthodes de fabrication par solutions solides ou par frittage flash (SPS). La corrélation "Préparation - Structure - Conductivité" a été établie pour la réalisation de céramiques à base de ZnO avec de fortes conductivités ouvrant la voie à des applications technologiques potentielles
ZnO based ceramics with appropriate doping elements show excellent electrical and optical properties such as high exciton binding energies, a modulated optical transparency and high electrical conductivities. Therefore, ZnO based conducting ceramics have been extensively investigated in the aim of their application as resistors, visitors, gas sensors, transparent electrodes, solar cell windows, piezoelectric, electro-optical and thermoelectric devices. The high conductivity of ZnO ceramics up to 0.1MS·m-1 is closely related to the doping elements along with the ceramic microstructure and the processing conditions with particular effects of grain boundaries, crystalline structure and structural disorder within the ceramics. Thus, the present thesis is devoted to the fabrication by sintering under defined conditions (sintering atmospheres, processes) of ZnO based ceramics co-doped by (Al, Ti, Mg) , the investigations and deep analysis of their related properties including crystalline structure, micro-structure and the electrical behavior. Exhaustive studies were developed on the doped ceramics by using structural methods (XRD, Raman), microscopy (TEM, SEM) and magnetic resonance (EPR, NMR) probing the local order and electronic active defects. The conductivity is adjusted by the nature of the structure influenced by the doping elements, the sintering atmosphere, and the sintering method. The correlation "Preparation - Structure - Conductivity" has been established to pave the way for the potential technological applications of highly conducting ZnO-based ceramics

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6

Vecchi, Pierpaolo. "Defect analysis in directionally solidified multicrystalline silicon." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21177/.

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This project studies how the microstructure and metallic impurities affect the electrical properties of mc-Si wafers, to improve the efficiency and the production yield of photovoltaic solar cells. Dislocations and impurities in silicon are recombination centres that reduce free carrier lifetime and thus efficiency of solar cells. The quality of the material can be improved by finding optimal growth conditions and a threshold value for the contamination that does not compromise the device efficiency. Two sets of p-type mc-Si wafers located at different heights and lateral positions of two directionally solidified ingots, one contaminated with iron and one with aluminum, were analysed with several characterization techniques. The two ingots show similar microstructure, but the top of the iron contaminated ingot has a significantly lower lifetime, as it contains more dislocation clusters decorated with segregated iron. Aluminum is less detrimental at this low concentration level and it is more homogeneously distributed along the ingot height. A Mott-Schottky analysis after evaporation of aluminum contacts confirmed the p-type nature of the samples and estimated the free charge carrier concentration. Current profiles and local I-V curves measured with Conductive Atomic Force Microscopy show that decorated grain boundaries are a preferential path for electrical conduction compared to the grain regions and iron precipitates affect more heavily the electrical properties of the wafer compared to aluminum precipitates. The shape of the current profile at the boundary was justified with a theoretical model that assumes a redistribution of charge density due to a Coulombic potential introduced by a spherical and positively charged precipitate, that can be identified with b-FeSi2. The results from this characterization show that metallic contamination at grain boundaries in Si is responsible for enhanced free carrier recombination and thus efficiency reduction in mc-Si cells.

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7

MARINUCCI, GERSON. "Desenvolvimento, fabricacao e analise de falha e fratura de cilindros de fibra de carbono colapsados por pressao interna." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10913.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

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8

Chauhan, Vinay Singh. "Impact of Nanoscale Defects on Thermal Transport in Materials." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586440154974469.

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9

Sugar, Joshua D. "Mechanisms of microstructure development at metallic-interlayer/ceramic interfaces during liquid-film-assisted bonding." Berkeley, Calif. : Oak Ridge, Tenn. : Lawrence Berkeley National Laboratory ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/825347-j6A0Su/native/.

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Thesis (M.S.); Submitted to the University of California, Berkeley, CA (US); 1 Dec 2003.
Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--54185" Sugar, Joshua D. USDOE Director. Office of Science. Basic Energy Sciences (US) 12/01/2003. Report is also available in paper and microfiche from NTIS.

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10

Mokhtari, Hossein. "Transmission electron microscopy of defects and internal fields in GaN structures." Thesis, University of Bristol, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368206.

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11

Morco, Stephanie Renee. "Characterizing Bacterial Resistance and Microstructure-Related Properties of Carbon-Infiltrated Carbon Nanotube Surface Coatings with Applications in Medical Devices." BYU ScholarsArchive, 2021. https://scholarsarchive.byu.edu/etd/8909.

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Carbon-infiltrated carbon nanotube (CICNT) forests are carbon nanotube (CNT) forests infiltrated with pyrolytic carbon to increase durability by becoming a solid material. This material can be tuned to maintain the nanotube geometry of a CNT forest and can also be fabricated on a variety of materials and geometries. Additionally, the present work has indicated that CICNT forests may resist bacterial proliferation and biofilm formation. This phenomenon is not due to the CICNT chemistry; it is presumably due to the CICNT nanostructure morphology. Thus, both silicon and stainless steel substrates were used to investigate CICNT's structural resistance to Methicillin-resistant Staphylococcus aureus (MRSA) biofilm. From in vitro experimental testing, CICNT on both these substrates resisted MRSA cell attachment and biofilm proliferation. The discovery of this non-pharmaceutical biofilm resistance expands the potential applications of CICNT to include medical devices that are prone to infection and/or devices that contribute to infection. Two representative applications were investigated: external fixator pins and scalpel blades. CICNT-coated versions of these applications underwent additional MRSA biofilm resistance testing as well as mechanical testing. In particular, external fixator pins were identified as a high potential application of CICNT surface coating technology. Previous work on both CNT and CICNT forests has largely been performed on planar structures. However, any potential medical device applications involve curved substrates. In particular, concave curvatures are challenging due to the potential for stress-related CICNT forest defects. Thus, the present work also included a study of the incidence rates and determining factors of these defects. SEM images of the cross-sections revealed different types of microscale forest defects while the top surface showed morphologies that are largely consistent with flat substrates. CICNT forest height and substrate curvature were identified as contributing factors to CICNT forest defect incidence rates. Thus, the present work advances the understanding of bacterial resistance and microstructure-related properties of CICNT surface coatings, with applications in medical devices.

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12

Gilmore, Annette Clare. "Microscopic studies of doped and electron irradiated CVD diamond." Thesis, University of Bristol, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313357.

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13

Silva, Elisa Cadete Quadros. "Defect sources in brasses and new low lead compositions." Master's thesis, Universidade de Aveiro, 2016. http://hdl.handle.net/10773/17111.

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Mestrado em Ciência e Engenharia de Materiais
Este estágio curricular foi realizado na empresa Grohe Portugal – Indústria de Componentes Sanitários S.A, localizada na zona industrial do Areeiro (Albergaria-a-Velha), distrito de Aveiro. A empresa Grohe foi fundada na Alemanha no século XX com o objetivo de produzir torneiras. Atualmente, a Grohe é reconhecida como a maior produtora de componentes sanitários da Europa, bem como pela qualidade dos seus processos produtivos e eficiência do sistema logístico e entrega de produtos. A nível de processos produtivos, a Grohe está dividida em cinco departamentos: Fundição, Maquinagem, lixamento e polimento, Galvânica e Montagem. O departamento da Fundição, por sua vez, é constituído pela Fusão Central, Vazamento por Gravidade, Vazamento por Baixa Pressão e pela Macharia. Este trabalho teve como objetivos principais a caracterização microestrutural das três ligas de cobre de baixo teor de chumbo que a Grohe produz e identificação de possíveis origens dos defeitos mais comuns nestas ligas, sobretudo no Vazamento por Baixa Pressão. A Grohe prepara e controla quimicamente as suas próprias composições de latão num forno central de fusão, compostas maioritariamente por cobre e zinco (60% Cu, 40% Zn) e por pequenas adições de outros elementos de liga. Foi feita uma caracterização microstrutural às três ligas por microscopia ótica. Os materiais envolvidos no processo de vazamento como os revestimentos cerâmicos dos moldes, os filtros cerâmicos utilizados, a escória resultante do processo como também o tubo de vazamento constituinte da máquina de vazamento por baixa pressão foram submetidos a uma caracterização química por microscopia eletrónica de varrimento e difração de raios-X. Realizou-se uma análise química e microestrutural por SEM/EDS às inclusões presentes em sucata de torneiras de latão. As microestruturas das três ligas fabricadas em Grohe apresentam diferenças significativas. O latão Grohe 0 com o menor teor de Zn e a menor quantidade de elementos afinadores de grão tem uma morfologia do tipo de Widmanstatten com placas grandes de fase α (97 μm x 17 μm) e a fase β presente entre os grãos de fase α. O latão Grohe 0 Light é uma liga hiperperitética com fase α na forma de agulhas finas (24 μm x 3 μm) no seio dos grãos-mãe β e ao longo dos seus limites de grão. A microestrutura da liga DZR consiste numa morfologia equiaxial mais fina (16 μm) de grãos de α numa matriz de β devido à maior quantidade de afinadores de grão e teor intermédio de Zn. O maior tamanho de grão do latão Grohe 0 explica por que este tem uma dureza menor (HRB 39) do que as ligas Grohe 0 Light e DZR (HRB 59), com microestruturas mais finas. Os resultados da análise SEM/EDS aos defeitos da liga de latão Grohe 0 permitiram a sua divisão em quatro classes: (1) Defeitos ricos em Al, Si e O, tendo como possível origem o revestimento cerâmico BC11; (2) defeitos ricos em Al, Si, O e Pb, uma fase vítrea com origens no revestimento cerâmico ou em sucata reciclada; (3) defeitos ricos em Si e O, tendo como fontes prováveis a escória, partículas dos filtros cerâmicos ou sucata com restos de filtros cerâmicos, revestimento BC 15 ou mesmo areia dos machos; (4) defeitos ricos em Fe, Cr, V e Mo, muito provavelmente resultado de uma contaminação pontual com uma ferramenta fraturada usada para o processamento de matérias-primas.
This work was done at Grohe Portugal – Sanitary Components S.A, located in the industrial zone in Albergaria-a-Velha, district of Aveiro. This company was founded in Germany in the 20th century with the goal of manufacturing faucets for sanitary industries. At present time, Grohe is distinguished as the largest manufacturer of sanitary components in Europe, as well as by the quality in their productive processes and efficiency of their logistics system and product delivery. In terms of productive processes, Grohe has five departments: Foundry, Machining, Surface sanding and polishing, Galvanic and Assembly. In the foundry unit there is a central melting, sand core processing, two gravity casting units and six low pressure die casting machines. The copper-beryllium molds are manufactured in the company. The work was based on the characterization of three low lead brass alloys that the industry produces and possible sources of defects. Since Grohe owns their own central melting station, where the manufactured brass is made primarily of copper and zinc (60% Cu, 40% Zn), the company does not buy previously fabricated brass for the casting process, this means there is total control of the content of the alloys. Ultimately, this work aims in characterizing brass alloys at microstructural level, the presence of defects (pores or inclusions) and the study of the alloys that originate the larger amount of wastes. A preliminary microstructural characterization was performed on the three brasses by optical microscopy. The materials involved during the processing of casting such as ceramic coatings, ceramic filters, produced slag, as well as the riser tube in the low-pressure die casting machine, were submitted to a chemical characterization by scanning electron microscopy and X-ray diffraction. A chemical analysis was performed by energy dispersive X-ray spectroscopy on specimens of inclusions detected in waste of brass faucets. The microstructures of the three alloys manufactured in Grohe are markedly different. Grohe 0 brass with lowest Zn content and smallest amount of grain refining elements has a coarse Widmanstatten structure (97 μm length x 17 μm width) with the β phase present in the periphery of the plate-like α grains. Grohe 0 Light is a hyperperitectic alloy with a finer needle-like α phase (24 μm length x 3 μm width) inside the β mother grains and along their grain boundaries. The microstructure of the DZR composition consists of a finer equiaxed morphology (16 μm) of α grains in a β matrix due to the larger amounts of grain refining elements and intermediate Zn content. The coarseness of the microstructure of the Grohe 0 brass differences explains why it has a lower hardness (HRB 39) than Grohe 0 Light and DZR brasses (HRB 59). SEM/EDS analysis of the defects of the brass alloy Grohe 0 allowed their division into four different classes: (1) Defects rich in Al, Si and O, having as a possible origin the ceramic coating BC11; (2) defects rich in Al, Si, O and Pb, a vitreous phase with origins in the ceramic coating or from recycled scrap materials; (3) defects rich in Si and O, having as likely sources the slag, particles from the ceramic filters or scraps with ceramic filters, the ceramic coating BC 15 or even sand from the cores and (4) defects rich in Fe, Cr, V and Mo, extemporaneous, and most likely a contamination from a fractured tool used in the processing of raw materials.

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14

Merabet, Amina. "Etude par microscopie électronique du silicium aux petites échelles : comportement mécanique et structure atomique des défauts." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0554/document.

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De récents travaux consacrés à l’étude des propriétés des matériaux aux petites échelles ont souligné des différences exceptionnelles dans le comportement mécanique des nano-objets par rapport aux matériaux massifs. Dans le cas du silicium, une transition fragile-ductile à température ambiante a été observée lorsque la taille des échantillons est réduite. Cependant, les défauts et les mécanismes à l’origine de ce changement de comportement n’ont pas été clairement identifiés. Ce travail repose sur l’étude post mortem de nanopiliers déformés, en utilisant différentes techniques de microscopie électronique. Les nanopiliers étudiés ont été préparés par gravure plasma et déformés en compression à température ambiante. Les résultats obtenus durant cette thèse, confirment la différence de comportement des nano-objets par rapport au matériau massif. Par ailleurs, une grande variété de défauts produits lors de la compression a été observée. L’orientation cristallographique de l’axe de sollicitation semble avoir un impact important sur les mécanismes à l’origine du comportement ductile observé. La comparaison entre images HRTEM expérimentales et simulées témoigne de la propagation simultanée de dislocations partielles et parfaites dans les plans {111}. De plus, des événements plastiques ont également été observés dans des plans {115}. Divers mécanismes de déformation possibles impliqués lors de la compression des piliers sont décrits à partir des observations microscopiques. Un modèle tenant compte de l’influence sur la mobilité des dislocations des interactions entre systèmes de glissement est proposé afin d’expliquer la transition fragile-ductile observé aux petites échelles
Several recent works devoted to the study of the properties of materials at small scales have revealed exceptional differences in the mechanical behavior of nano-objects as compared to bulk material. In the case of silicon, a brittle-ductile transition at room temperature has been observed when the sample size decreases. However, the extended defects and mechanisms behind this behavioral change have not been clearly identified. This work is based on the post mortem study of deformed nanopillars, using different electron microscopy techniques. The studied nano-pillars of 100 nm in diameter were prepared by plasma etching (RIE) and deformed in compression at room temperature. The results obtained during this thesis confirm the difference in the behavior of nano-objects compared to bulk material. Moreover, a large variety of defects produced during plastic deformation has been observed. The crystallographic orientation of the deformation axis seems to have a significant impact on the mechanisms behind the observed ductile behavior. The comparison between experimental and simulated HRTEM images notably evidences the simultaneous propagation of partial and perfect dislocations in {111} planes. In addition, unexpected plastic events have also been observed in {115} planes. Various possible deformation mechanisms involved during the nano-compression of the pillars are described, based on the microscopic observations. Finally, a model considering the influence of interactions between various activated systems on the mobility of dislocations is proposed to explain the brittle-ductile transition observed at small scales in silicon

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15

Schnur, Christopher. "Electron Beam - Powder Bed Fusion Of Alloy 718 : Influences Of Contour Parameters On Surface And Microstructural Characteristics." Thesis, Högskolan Väst, Avdelningen för Industriell ekonomi, Elektro- och Maskinteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-14318.

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Additive Manufacturing (AM) is an uprising manufacturing process for parts with complex geometries and low production quantities. Within the layer-wise building process, less additional processes are needed, to produce the parts. This allows a building of parts within a reasonable time- and costs-range. Especially industries, such as aerospace industry, can profit from AM. Electron beam – Powder bed fusion (EB-PBF) is a common technique, within AM, to produce metallic parts out of special alloys such as Alloy 718. This superalloy is a Nickle-Iron based alloy that has high mechanical properties, even in elevated temperatures (up to 650ºC). The combination of such material properties with high geometrical freedom creates new opportunities for the industry. However, it must be noted that a significant drawback of AM-techniques is the need for post-processing because of surface roughness- and microstructural characteristics. Commonly, the produced parts utilize mechanical post process such as milling to provide good surface roughness and dimensional accuracy. To reduce the surface roughness in the contour region, and therefore reduce the amount of mechanical post-processing, the present survey elaborates the effect of relevant parameters on contours such as the number of contours, scanning speed, focus offset and beam current. By using Design of Experiments (DOE), two batches were carried out: one screening batch and a two-level-full factorial design. In those batches, 15×15×15 mm cubes were printed with various parameters and, after that, analysed by using White light interferometry (WLI), Optical microscopy (OM) and Scanning electron microscopy (SEM). Furthermore, the program ImageJ was used to perform porosity and melt pool measurements. It had been observed that the number of contours had quite a considerable impact on the final surface roughness and the number of defects. Samples with two contours, instead of only one, tend to have a lower surface roughness. Nevertheless, the parameters and their interaction were found to have fundamental effects on the resulting surface roughness and microstructure.

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16

Hradil, David. "Mechanicko strukturní charakteristiky materiálů vyrobených metodou SLM." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-254320.

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The master's diploma thesis deals with the mechanical and structural characteristics of aluminium-base alloy 2000 series, produced by selective laser melting (SLM). The experimental part of the thesis deal with selection of SLM processing parameters, influence of scanning strategy and evaluation of mechanical and structural characteristics of fabricated materials. Mechanical characteristics were evaluated based on results of tensile tests and microhardness measurement. Structural characteristics of materials produced by SLM were evaluated using metallographic analysis.

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17

Lee, Yousub. "Simulation of Laser Additive Manufacturing and its Applications." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440360229.

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18

Pushparasah, Anitha. "Interactions hydrogène - matériaux dans les aciers TRIP de 3ème génération." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEM022.

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Face aux normes environnementales de plus en plus exigeantes, l’allègement des véhicules est devenu un enjeu majeur pour l’industrie de l’automobile, qui cherche à réduire l’émission de gaz à effet de serre par la réduction de la consommation. C’est dans cette optique qu’ont été développés les aciers de 3ème génération à effet TRIP (TRansformation-Induced Plasticity). Ces aciers multiphasés contiennent une fraction importante d’austénite résiduelle (15 30 % mass.), qui peut se transformer en martensite au cours de la déformation. Cette caractéristique confère à ces aciers un très bon compromis résistance-ductilité. Au cours de leur procédé d’élaboration, ces aciers subissent un traitement thermique sous atmosphère réductrice et un électrozingage, deux étapes au cours desquelles de l’hydrogène peut être incorporé aux matériaux. L’hydrogène ainsi absorbé peut modifier les propriétés mécaniques des aciers et conduire à leur rupture prématurée.Ce travail de thèse vise à caractériser les phénomènes de diffusion et de piégeage de l’hydrogène incorporé au cours du procédé d’élaboration de deux aciers TRIP de 3ème génération et d’évaluer son impact sur les propriétés mécaniques de ces aciers. Il s’agit d’un acier austénito-ferritique riche en manganèse et en aluminium (Mn-Al) et d’un acier austénito-martensitique riche en manganèse et en silicium, trempé et revenu (« Quenched and Partitionned » - Q&P). L’incorporation de l’hydrogène au cours du traitement thermique et de l’électrozingage a été simulée par des chargements à hautes températures et à plus basse température (par voie cathodique), respectivement.Des essais de thermodésorption (TDS) couplés à des essais de perméation électrochimique ont permis une meilleure compréhension des phénomènes de diffusion et de piégeage de l’hydrogène dans ces aciers multiphasés. Il a été montré que la diffusion et le piégeage de l’hydrogène dépendent du mode de chargement de celui-ci, justifié par une cinétique de désorption à température ambiante plus lente et un piégeage plus profond identifiés dans le cas du chargement à hautes températures. La formation d’un nouveau type de piège a également été identifiée lorsque l’acier subit une transformation de phase en présence d’hydrogène. Les potentiels sites de piégeage identifiés sont : les sites interstitiels de l’austénite, les dislocations/interfaces et les défauts nouvellement créés au cours de la transformation de phase.Enfin, des essais de traction uniaxiale réalisés sur des éprouvettes plates pré-chargées en hydrogène ont montré une sensibilité de ces aciers vis-à-vis de l’hydrogène incorporé par voie cathodique
Lighter vehicles with lower fuel consumption and CO2 emissions became a major stake for the automotive industry. In this context, 3rd generation TRIP steels have been developed. These multiphase steels contain an important fraction of residual austenite (15 30 wt.%) which can transform into martensite under deformation. This characteristic give the steels a better compromise strength-ductility. During their elaboration, these steels are subjected to a heat treatment under reducing atmosphere and an electro-galvanisation, two steps during which hydrogen can enter the material. The absorbed hydrogen can modify the mechanical properties of the steels and lead to their premature failure.This work aims to characterize the diffusion and trapping of hydrogen incorporated during the elaboration process of two 3rd generation TRIP steels: an austenitic-ferritic Mn-Al steel and an austenitic-martensitic quenched and partitioned (Q&P) steel. The incorporation of hydrogen during the heat treatment and the electro-galvanisation has been simulated by high temperature and low temperature (cathodic) charging, respectively.Thermal desorption mass spectroscopy (TDMS) analyses combined with electrochemical permeation tests have permitted a better comprehension of diffusion/trapping phenomena in these multiphase steels. It has been showed that diffusion and trapping of hydrogen depends on its introducing mode: high temperature charging induces a slower desorption kinetic at room temperature and a deeper trapping of hydrogen in the microstructure. Transformation-induced defects have been identified when a phase transformation occurs with hydrogen in the steel. The potential trapping sites identified are: the interstitial sites of austenite, the dislocations/interfaces and transformation-induced defects.Finally, tensile tests realized on pre-charged samples have showed a sensitivity of these steels to cathodic hydrogen charging

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19

Peeva, A. "Microstructural Characterization and Engineering of Defects in Silicon." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-29062.

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20

Peeva, A. "Microstructural Characterization and Engineering of Defects in Silicon." Forschungszentrum Rossendorf, 2003. https://hzdr.qucosa.de/id/qucosa%3A21734.

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21

Cao, Haiping. "Characteristics of cast magnesium alloys : microstructures, defects and mechanical properties /." Jönköping : Linköping : Div. of Component Technology - Castings ; Dept. of Mechanical Engineering, Univ, 2005. http://www.bibl.liu.se/liupubl/disp/disp2005/tek955s.pdf.

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22

Fanzon, Silvio. "Geometric patterns and microstructures in the study of material defects and composites." Thesis, University of Sussex, 2018. http://sro.sussex.ac.uk/id/eprint/72566/.

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The main focus of this PhD thesis is the study of microstructures and geometric patterns in materials, in the framework of the Calculus of Variations. My PhD research, carried out in collaboration with my supervisor Mariapia Palombaro and Marcello Ponsiglione, led to the production of three papers [21, 22, 23]. Papers [21, 22] have already been published, while [23] is currently in preparation. This thesis is divided into two main parts. In the first part we present the results obtained in [22, 23]. In these two works geometric patterns have to be understood as patterns of dislocations in crystals. The second part is devoted to [21], where suitable microgeometries are needed as a mean to produce gradients that display critical integrability properties.

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23

Frame, Dustin Michael. "Microstructural development and the evolution of defects in constrained and sinter-forged ceramics /." Thesis, Connect to this title online; UW restricted, 2006. http://hdl.handle.net/1773/10607.

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24

Minani, Evariste. "Microstructure, stress and defect evolution under illumination in hydrogenated amorphous silicon (a-Si:H)." Doctoral thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/6540.

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Includes abstract.
Includes bibliographical references (leaves 151-157).
The purpose of this study is firstly to investigate the relation between microstructure, stress and hydrogen distribution in as deposited hydrogenated amorphous silicon (a-Si:H) layers, and secondly the investigation of the influence of illumination on hydrogen evolution and its relationship with the strain in illuminated layers.

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25

Якущенко, Іван Володимирович, Иван Владимирович Якущенко та Ivan Volodymyrovych Yakushchenko. "Структурні характеристики та фізико-механічні властивості багатокомпонентних нітридних покриттів до і після іонної імплантації". Thesis, Сумський державний університет, 2018. http://essuir.sumdu.edu.ua/handle/123456789/67473.

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Дисертаційна робота присвячена дослідженню впливу імплантації негативних іонів Au- на фазовий склад, структурно-напружений і дефектний стан, механічні й трибологічні властивості п'яти- та шести- елементних нітридних покриттів (TiZrAlYNb)Nx і (TiZrHfVNbTa)Nx і вплив на них технологічних умов осадження (тиску робочого газу, і потенціалу зсуву підкладки). Результати дослідження елементного, фазового і напружено-деформованого стану покриттів свідчать про те, що в покриттях відбувається формування двух основних кристалічних фаз – ГЦК і ОЦК в залежності від тиску робочого газу. Фазовий стан змінюється від аморфного до нанокристалічного, а покриття знаходяться під напруженням стиску. Проведення іонної імплантації (однозарядними негативними іонами золота Au-) призводить до наступних наслідків. Поверхневий шар покриття сильно розупорядкований із підвищеною долею ОЦК фази у результаті балістичної взаємодії іонів золота і матеріалу покриття. Також, відбувається значне збільшення кількості дефектів у покритті: дислокацій, пустот, нанопор, бі- і тривакансій, а також вакансійних комплексів. Дослідження механічних та трибологічних властивостей покриттів показали, що імплантація іонами золота приводить до зростання твердості покриттів у імплантованому шарі (до величини 39,05 ГПа), а також індекс в’язкопластичності збільшується до 0,123. Спостерігається збільшення зносостійкості покриттів (у 2,5 рази) і зменшення коефіцієнту тертя. Таким чином, проведення іонної імплантації іонами золота, за рахунок внутрішніх процесів дефектоутворення, зменшення розміру зерен і збільшення об’ємної долі меж зерен призводить до покращення фізико-механічних властивостей покриттів (TiZrAlYNb)Nx і (TiZrHfVNbTa)Nx.
Диссертационная работа посвящена исследованию влияния имплантации отрицательных ионов Au- на фазовый состав, структурно-напряженное и дефектное состояние, механические и трибологические свойства пяти- и шести- элементных нитридных покрытий (TiZrAlYNb)Nx и (TiZrHfVNbTa)Nx и влияние на них технологических условий осаждения (давления рабочего газа, и потенциала смещения подложки). Результаты исследования элементного, фазового и напряженнодеформированного состояния покрытий свидетельствуют о том, что в покрытиях происходит формирование двух основных кристаллических фаз – ГЦК и ОЦК в зависимости от давления рабочего газа. Фазовое состояние изменяется от аморфного до нанокристаллического, а покрытия находятся под напряжениями сжатия. Проведение ионной имплантации (однозарядными отрицательными ионами золота Au-) приводит к следующим последствиям. Поверхностный шар покрытия сильно разупорядочен, с повышенной долей ОЦК фазы в результате баллистического взаимодействия ионов золота и материала покрытия. Также, происходит значительное увеличение количества дефектов в покрытии: дислокаций, пустот, нанопор, би- и тривакансий, а также вакансионных комплексов. Исследования механических и трибологических свойств покрытий показали, что имплантация золота приводит к возрастанию твердости покрытий в имплантированном шаре (до величины 39,05 ГПа), а также индекс вязкопластичности увеличивается до 0,123. Наблюдается увеличение износостойкости покрытий (в 2,5 раза) и уменьшение коэффициента трения. Таким образом, проведение ионной имплантации ионами золота, за счет внутренних процессов дефектообразования, уменьшения размера зерен и увеличения объемной доли границ зерен приводит к улучшению физико-механических свойств покрытий (TiZrAlYNb)Nx и (TiZrHfVNbTa)Nx.
The thesis is devoted to investigation of the influence of ion implantation by negative ions Au- on the phase composition, structure-stress and defect state, mechanical and trybological properties of five- and six- elements nitride coatings (TiZrAlYNb)Nx and (TiZrHfVNbTa)Nx, and influence on them of the deposition technological parameters – pressure of working state, and substrate bias voltage. The results of the investigation of element, phase and structure-deformated state of the coatings show that, two main crystalline phases are formed in the coatings – FCC and BCC; depending on the working gas pressure phase state is changed from amorphous to nanocrystalline; and coatings are under the compressive stress. Ion implantation (by one-charge negative ions gold Au-) leads to the following. Subsurface layer is disordered a lot, and has higher rate of BCC phase – based on ballistic collisions of ions of Au with the coating’s material. Also, number of defects in the coating is increased significantly – dislocations, holes, nanopores, bi- and triplevacancies, and also vacancy clusters are found. Investigation of mechanical and trybological properties of the coatings showed, that ion implantation leads to increasing of hardness of the coatings in the implanted layer (up to 39,05 GPa), and index of viscoplasticity is increased to 0,123. Wear resistance is increased (up to 2,5 times), and friction coefficient is decreased. Thus, ion implantation by Au- ions, leads to improving of physical and mechanical properties of the investigated coatings (TiZrAlYNb)Nx and (TiZrHfVNbTa)Nx, because of internal processes of defects formation, decreasing of grains sizes, and increasing of volume rate of grain boundaries.

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26

Selmi, Mayada. "Textures à la surface libre de cristaux liquides smectiques : étude en géométrie films librement suspendus et sur substrats structurés." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0098/document.

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Ces travaux concernent l’étude expérimentale des textures se développant dans les ménisques de films smectiques de cristaux liquides thermotropes. Ces fluides complexes nous servent de système modèle pour l’étude des couplages élasto-capillaires qui se manifestent dans certaines conditions par des déformations périodiques de l’interface cristal liquide-air. Dans un premier temps, à partir de l’étude détaillée de la topographie de l’interface par une méthode interférométrique, nous caractérisons les différents types de structures, puis, identifions les principaux paramètres impliqués dans le processus d'apparition des défauts dans le ménisque de films libres suspendus. Ces résultats nous servent de base pour discuter des mécanismes physiques qui génèrent les différents types de défauts observés. Nous regardons en particulier, comment la diminution d’épaisseur de couche associée à une transition de phase va induire une instabilité mécanique responsable de l’apparition des ondulations de l’interface. Dans un deuxième temps, afin d’aller plus loin dans la compréhension des mécanismes, nous avons utilisé des films minces de cristaux liquides déposés sur des substrats solides microstructurés par des plots fabriqués par des techniques photolitographiques. Une telle géométrie permet de générer un ménisque autour de chaque plot et surtout de faire varier un plus grand nombre de paramètres comme par exemple l’ancrage sur le substrat via un traitement chimique de surface. L’ensemble de nos résultats apportent un éclairage nouveau sur la caractérisation et la compréhension des déformations spécifiques aux ménisques de fluides complexes
The present work is an experimental study of the textures that appear in the meniscus of free standing smectic films with thermotropic liquid crystals. These complex fluids serve as model systems to investigate elasto-capillary phenomena which, under certain conditions, manifest themselves through periodic deformations of the liquid crystalair interface. In the first part of the thesis, we focus our attention on meniscus structures whose interfacial topographies are thoroughly characterized thanks to an in-house optical interferometry technique. Our study allows us to identify the main parameters involved in the development of meniscus structures and to discuss the physical mechanisms that are likely to be responsible for their formation. In particular, we show how a phase transition-induced layer shrinkage triggers a mechanical instability leading to interfacial undulations of the smectic free surface. In the second part of the manuscript, we address the case of thin liquid crystal films deposited on solid patterned solid substrates. The latter consist of regular arrays of microposts fabricated through photolithographic techniques. Such a geometry allows a meniscus to be formed around each micropost and makes it possible to examine the influence of other parameters such as the anchoring conditions on the solid substrate. The results gathered so far are able to shed some light on the characterization and the understanding of the specific deformations and textures that appear in the menisci of complex fluids

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27

Reece, M. J. "An electron microscope study of defect microstructures in synthetic and natural ferrite crystals." Thesis, University of Essex, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375644.

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28

J, Boeckl John. "Microstructural investigation of defects in epitaxial GaAs grown on mismatched Ge and SiGe/Si substrates." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1116498970.

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Thesis (Ph. D.)--Ohio State University, 2005.
Title from first page of PDF file. Document formatted into pages; contains xxii, 212 p.; also includes graphics. Includes bibliographical references (p. 203-212). Available online via OhioLINK's ETD Center

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Boeckl, John J. "Microstructural investigation of defects in epitaxial GaAs grown on mismatched Ge and SiGe/Si substrates." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1116498970.

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30

Neagu, Dragos. "Materials and microstructures for high temperature electrochemical devices through control of perovskite defect chemistry." Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3606.

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The development of technologies that enable efficient and reliable energy inter-conversion and storage is of key importance for tempering the intermittent availability of renewable energy sources, and thus for developing an energy economy based on sustainable, clean energy production. Solid oxide electrolysis cells (SOECs) may be used to store excess electrical energy as hydrogen, while solid oxide fuel cells (SOFCs) could convert back hydrogen into electricity, thus balancing energy availability and demand. However, the current state-of-the-art hydrogen electrode used in both SOECs and SOFCs, the Ni-yttria-stabilised zirconia cermet (Ni-YSZ), is unreliable in conjunction with intermittent energy sources, in particular due to its innate redox instability. This thesis explores the fundamental properties of various inherently redox stable A-site deficient titanate perovskite systems (A1-αBO3, B = Ti), seeking to uncover the principles that enhance their properties so that they may be used to replace Ni-YSZ. In particular, this work demonstrates that the versatility of perovskites with respect to the introduction of lattice defects such as vacancies and cation substitutions enables considerable improvements in the extent of reduction, electronic conductivity and overall electrochemical activity. Most importantly, the defect chemistry context set by the presence of A-site vacancies was found to trigger the exsolution of electrocatalytically active nanoparticles from the parent perovskite, upon reduction. This is an entirely new phenomenon which was explored and exploited throughout this study to produce perovskite surfaces decorated with uniformly distributed catalytically active nanoparticles. As demonstrated in this study, the exsolution phenomenon excels in terms of producing nanoparticles with uniform size, distribution, diverse composition and ‘unconventional' surface anchorage. The resulting enhanced properties, and especially the exsolution phenomenon, contributed coherently towards improving the suitability of the perovskites developed here towards their application as hydrogen electrode materials. Consequently, when integrated into SOEC button cells as hydrogen electrodes, they exhibited a step-change increase in performance compared to other perovskites considered to date. Many of the principles and perovskite defect chemistry explored and exemplified in this study on perovskite titanates may be extended to other perovskites as well. In particular the advanced control and understanding achieved in this work over the exsolution phenomenon may inspire the formulation of new and sophisticated oxide materials with advanced functionality.

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Simsek, Sanli Ekin. "Investigation of Microstructural Defects in Cu(In,Ga)Se2 Thin Films by Scanning Transmission Electron Microscopy." Phd thesis, TUprints, 2019. https://tuprints.ulb.tu-darmstadt.de/8849/1/Simsek_Sanli_Dissertation_2018.pdf.

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Polycrystalline Cu(In,Ga)Se2 (CIGS) based thin-film solar cells achieve power-conversion efficiencies of almost 23% on the laboratory scale, one of the highest among thin-film solar cells. The aim of further CIGS research and development is to reach conversion efficiencies of 25%, which is currently the efficiency of the best single-crystalline Si based solar cells. To reach this goal, the factors limiting efficiency, e.g. non-radiative recombination of charge carriers, should be minimized. Such recombination processes may occur at line or planar defects present in the CIGS absorbers (among other interfaces, such as absorber and buffer layer). In the present study, the structure and composition of several defects as well as their evolution during the growth were investigated for an enhanced understanding. Highest efficiencies in CIGS solar cells are achieved, when the absorber is fabricated with a three-stage co-evaporation process. During the second stage of this process, Cu and Se are evaporated on the initially formed (In,Ga)2Se3 layer. The composition of the absorber becomes Cu-rich ([Cu]/([In] + [Ga]) > 1) during this stage. The change in composition leads to recrystallization, i.e. grain growth and defect annihilation, thus enabling higher conversion efficiencies. Therefore, it is crucial to investigate the recrystallization and the evolution of the microstructure at the second-stage of the CIGS growth. In the literature, two methods were suggested for this purpose: i) investigating the microstructural evolution of diffusion couples during a heating study; ii) ex-situ comparison of a growth-interrupted and a growth-finished sample. In the first part of this study, a Cu-poor ([Cu]/([In] < 1) CuInSe2 (CIS) precursor layer with a Cu2-xSe capping layer was prepared and heated in a scanning transmission electron microscope (STEM) to mimic the recrystallization. During the Cu diffusion from the Cu-rich Cu2-xSe phase into the Cu-poor CIS phase, the growth of defect-free grains towards the grains with closely-spaced planar defects (PDs) was monitored by low-angle annular dark-field (LAADF) imaging, whereas elemental depth profiles were analyzed by energy-dispersive X-ray spectroscopy (EDXS) before and after heating. The substantial impact of the Cu excess on the recrystallization was also indicated by an in-situ heating experiment of a Cu-poor CIS film without a Cu2-xSe layer on top, in which neither grain growth nor defect annihilation was detected. Monitoring of the recrystallization within the CIS absorber layers was performed for the first time by means of STEM and provided direct evidence for the currently accepted theory of the grain growth mechanism. In the second part, a CIGS absorber grown via co-evaporation was analyzed. During the growth, one piece of the sample was removed before the recrystallization at the second stage. For the remaining piece, the three-stage process was completed. The defect concentrations as well as the in-depth elemental analysis were performed by STEM-LAADF imaging and EDXS, respectively. Similar to the in-situ heating results, much larger grains with reduced linear/planar defect concentrations were detected in the absorber layer for which the growth had been completed. Although most of the structural defects were annihilated after the recrystallization, few structural defects were detected by LAADF imaging after the recrystallization, and even after the completion of the three-stage growth process. Further analyses were performed via aberration-corrected, high-resolution STEM (HR-STEM) in combination with electron energy-loss spectroscopy (EELS) to elucidate the nature of individual microstructural defects from various stages of the growth. HR-STEM and EELS results revealed the structure and chemistry of defects that were present in both growth-interrupted and growth-finished samples: Σ3-twin boundaries and stacking faults with stoichiometric elemental distribution; grain boundaries, tilt boundaries and dislocations with cation redistribution, i.e. Cu enrichment and In depletion. Stoichiometric inversion boundaries, Cu enriched ‘complex’ PDs and an extrinsic Frank partial dislocation were detected only in the growth-interrupted Cu-poor samples, whereas a ‘Cu2-xSe secondary phase’ was detected only in the growth-finished absorber layer. The present work provided direct insight into the recrystallization of CIGS absorbers and evolution of structural defects, as well as a thorough investigation of individual defects in CIGS absorbers.

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32

Purmová, Jindra. "Effect of the modification of the polymer-rich phase composition on the formation of structural defects in radical suspension PVC." [S.l. : [Groningen : s.n.] ; University Library Groningen] [Host], 2007. http://irs.ub.rug.nl/ppn/.

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33

Jin, Xin. "Combining RBS/Channeling, X-ray diffraction and atomic-scale modelling to study irradiation-induced defects and microstructural changes." Thesis, Limoges, 2021. http://www.theses.fr/2021LIMO0017.

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Les particules énergétiques sont souvent impliquées dans les activités de la société moderne. Ils ont contribué à l'essor de l'industrie des semi-conducteurs et pourront à l'avenir jouer un rôle important dans la mise en forme des matériaux de manière contrôlée. Cependant, leur nature énergétique pose de grands défis. Ainsi, il est essentiel d'avoir une compréhension globale des mécanismes sous-jacents des défauts induits par l'irradiation et des changements microstructuraux associés. Expérimentalement, les effets induits par l'irradiation peuvent être suivis par des techniques de caractérisation telles que la rétrodiffusion de Rutherford en mode canalisé (RBS/C) et la diffraction des rayons X (XRD), pour ne citer que ces deux car elles sont extrêmement sensibles aux perturbations au sein des cristaux. Cependant, il n'est pas aisé d'établir un lien clair entre le résultat de la mesure et la quantité et la nature des défauts, et ce lien est généralement fait à partir de modèles phénoménologiques. Dans ce travail de thèse, afin de faire face à ce problème, nous avons couplé modélisations à l'échelle atomique et simulations de signaux de RBS/C et XRD. La première étape a consisté à améliorer un code de simulation RBS/C récemment développé qui peut générer des signaux à partir de structures atomiques. En modifiant les algorithmes décrivant les interactions ion-solide et en ajoutant de nouvelles fonctionnalités, nous avons amélioré la flexibilité du code et son applicabilité à différents types de matériaux. Par la suite, nous avons utilisé le code RBS/C amélioré avec un code pour la DRX, lui aussi utilisant les données de structures atomiques. Avec ces signaux, nous avons extraits des paramètres de désordre et de déformation élastique et nous avons déterminé les cinétiques d'évolution associées et ce, pour un matériau modèle, à savoir UO2. Les défauts d'irradiation ont été générés par dynamique moléculaire (MD) avec la technique de l'accumulation de paires de Frenkel. Les cinétiques issues des modélisations présentent un accord qualitativement étroit avec celles déterminées expérimentalement, indiquant la validité de la méthodologie utilisée. La décomposition des cinétiques modélisées a permis de décrire de façon quantitative l'évolution des différents de types de défauts. Enfin, nous avons calculé les signaux RBS/C et XRD à partir de cellules modèles de Fe produites par MD et contenant chacune un type de défauts à une concentration donnée, les deux informations étant connues. Une comparaison claire du désordre et de la déformation élastique induits par les différents types de défauts dans Fe a été faite. La relation entre le rendement RBS/C et l'énergie des ions sonde a également été étudiée et la dépendance en énergie, fonction de la nature des défauts, a été établie. L'approche globale utilisée dans ce travail doit désormais être étendue et testée dans d'autres matériaux
Energetic particles are involved in many activities of modern society. They constitute a significant aspect of the semiconductor industry and may play important role in shaping materials in a controllable way in the future. However, their energetic nature also poses grand challenges, especially in the nuclear industry. Thus, it is crucial to have a comprehensive understanding of the underlying mechanisms of irradiation-induced defects and the associated microstructural changes. Experimentally, irradiation-induced effects can be monitored by characterization techniques including, but not limited to, Rutherford backscattering spectrometry in channeling mode (RBS/C) and X-ray diffraction (XRD), because they are extremely sensitive to changes in the crystalline structure. However, it is not straightforward to establish a clear link between the characterization results and the defect quantity and nature, and this connection is usually made according to simple phenomenological models. In this thesis work, in order to cope with this problem, we performed RBS/C and XRD atomic-scale modelling. The first step was to improve a recently developed RBS/C simulation code that can generate RBS/C signals from arbitrary atomic structures. By modifying the algorithms describing ion-solid interactions and adding new features, we enhanced the flexibility of the code and its applicability to different types of materials. Subsequently, we employed the improved RBS/C code with a XRD program to compute disordering and elastic strain kinetics of a model material, namely UO2, as a function of irradiation fluence. Radiation defects in UO2 were simulated by molecular dynamics (MD) calculations. Both the strain and disordering kinetics exhibit qualitatively close agreement with those determined experimentally, indicating the validity of the used methodology. The decomposition of the kinetics was performed in order to study the effect of each defect separately, which enables a quantitative description of the disordering and strain build-up processes. Finally, we computed RBS/C and XRD signals from Fe MD cells, each of which contains one single type of defects. A clear comparison of disorder and elastic strain induced by different types of defects in Fe was made. The relation between RBS/C yield and He energy was also studied using the Fe MD cells, which shows dependency with defect types. The global approach used in this work has the hope to be extended and tested in more materials

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34

Thieme, Manuel. "Résistance visqueuse et frictionnelle du manteau lithosphérique : caractérisation microstructurale de l'olivine polycristalline déformée expérimentalement." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTG061/document.

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La convection dans le manteau terrestre est la principale force motrice du mouvement des plaques tectoniques. Alors que les parties inférieures du manteau supérieur se déforment de manière ductile, les plaques tectoniques sont rhéologiquement plus rigides que l'asthénosphère sous-jacente. Pour comprendre le couplage entre la convection profonde et les plaques tectoniques à la surface de la Terre, il est essentiel de comprendre les mécanismes de déformation visqueuse et frictionnelle du manteau lithosphérique. Mais à ce jour, la rhéologie du manteau supérieur juste au-dessous de la discontinuité de Mohorovicic est encore mal comprise. De plus, les premiers stades de la déformation viscoplastique à des températures intermédiaires (600-1000 ° C) pertinentes pour le manteau lithosphérique, ne sont ni bien documentés ni quantifiés. Dans le passé, la plupart des expériences de déformation étaient effectuées à des températures très élevées (> 1200 ° C). Pour fournir des valeurs mécaniques précises pour le manteau lithosphérique, nous avons besoin de données mécaniques mais aussi de la caractérisation de la microstructure associée pour comprendre la physique des mécanismes en jeu lors de la déformation permanente des roches riches en olivine. Dans cette thèse, nous avons réalisé des expériences de déformation en compression axiale à l'aide d'une presse Paterson (Géosciences Montpellier, Université de Montpellier, France) à haute pression et température (300 MPa, 1000-12000 ° C) et en torsion (‘rotary shear frictional testing machine’ au laboratoire de mécanique des roches, université de Durham, Royaume-Uni) à pression et température ambiantes. Les échantillons ont été caractérisés par microscopie électronique à balayage, diffraction d’ d'électrons rétrodiffusés et microscopie électronique en transmission. Après un chapitre d'introduction où l'état de l'art est détaillé et un chapitre consacré aux méthodes expérimentales et analytiques utilisées dans les projets scientifiques, la thèse s'organise en trois chapitres, chacun correspondant à trois articles scientifiques: le premier est publié (1) Évolution de la contrainte et des microstructures associées au fluage transitoire de l'olivine à 1000-1200 °C (Phys. Earth Planet. Int., doi: 10.1016/ j.pepi.2018.03.002. (https: //hal.archives- ouvertes.fr/hal-01746122) et les deux autres sont en préparation, (2) Densité de disclinaisons dans l'olivine polycristalline déformée expérimentalement à 1000 ° C et 1200 ° C (3) Déformation par cisaillement de l'olivine nano- et micro-cristalline. Le premier projet du chapitre III a montré que le durcissement mécanique observé ne peut pas provenir d'une simple augmentation de la densité de dislocations (e.g., la forêt) et que d'autres mécanismes doivent être mis en œuvre pour compenser les limites de glissements des dislocations. Dans le chapitre IV, les densités de dislocation géométriquement nécessaires (GND, défauts de translation) et les disclinaisons (défauts de rotation) sont quantifiées sur une série de roches déformées à différentes températures, déformations finies et niveaux de contrainte, mais aucune corrélation n'a été identifiée entre la densité de disclinaisons, et la contrainte, la déformation finie, ou la densité de GND. Le rôle des disclinaisons serait donc limité à la migration aux joints de grains, ce qui peut être suffisant pour débloquer les dislocations dans l'agrégat d'olivine polycristalline. Au chapitre V, les expériences de torsion ont confirmé l'effet négligeable de la taille du grain (olivine de 0,7 à 70 µm) sur la diminution drastique du coefficient de frottement, mais la caractérisation des échantillons n’a pas permis d'élucider le mécanisme principal de déformation. Cette thèse a permis de mieux caractériser la transition fragile-ductile d'une roche de type dunite à grains fins soumise à une déformation permanente aux températures du manteau sommitale
Convection in Earth’s mantle is the major driving force behind the movement of tectonic plates. While the lower parts of the upper mantle deform in a ductile way, the plates themselves are rheologically more rigid than the asthenosphere beneath. To understand how convection yields tectonic plates, it is vital to quantify the viscous and frictional strength of the lithospheric mantle. Yet to date, the rheology of the uppermost mantle just below the Mohorovicic discontinuity is still poorly understood. Furthermore, the early stages of visco-plastic deformation at intermediate temperatures (600 – 1000 °C) relevant of the lithospheric mantle are not well documented or quantified. In the past, most deformation experiments were performed at high temperatures (> 1200 °C). To provide accurate mechanical values for the lithospheric mantle, we need mechanical data but also a characterization of the associated microstructure to understand the deformation mechanisms at play during permanent deformation of olivine-rich rocks. In this thesis, I have performed deformation experiments in axial compression using a Paterson press (at Géosciences Montpellier, University of Montpellier, France) at high pressure and temperature (300 MPa, 1000 -12000 °C) and in torsion using a low to high velocity rotary shear frictional testing machine (Rock Mechanics Laboratory, Durham University, UK) at room pressure and temperatures. The recovered samples were characterized using scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. After an introduction chapter where the state-of-the-art is detailed, and a chapter focusing on experimental and analytical methods used during scientific projects, the thesis is organized as three subsequent chapters, each of them corresponding to three scientific articles: one is published (1) Stress evolution and associated microstructure during transient creep of olivine at 1000-1200 °C (Phys. Earth Planet. Int., doi: 10.1016/j.pepi.2018.03.002.); and the two others are in preparation, (2) Disclination density in polycrystalline olivine experimentally deformed at 1000 °C and 1200 °C; and (3) Shear deformation of nano- and micro-crystalline olivine at seismic slip rates. Chapter III has shown that the observed mechanical hardening can not come from a simple increase in dislocation density (e.g., entanglement) and that other mechanisms must be at play to compensate for the limitations of dislocation slip. For the first time, in chapter IV the densities of geometrically necessary dislocations (GND, translational defects) and disclinations (rotational defects) are quantified on a series of rocks deformed at different temperatures, finite strains and stress levels. No correlation has been identified between disclination density and stress, strain or GND. The role of the disclinations will therefore be limited to migration at grain boundaries, which may be sufficient to unblock dislocations in the polycrystalline olivine aggregate. In chapter V, torsion experiments confirmed the negligible effect of grain size (olivine from 0.07 to 70 μm) on the drastic decrease of the coefficient of friction, but the characterization of the samples did permit to shed light on the main mechanism of deformation. Thanks to an experimental approach and up-to-date material characterization, this thesis permitted better characterization of the brittle-ductile transition of a fine-grained dunite-type rock subjected to permanent deformation at uppermost mantle temperatures

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35

Moneghan, Matthew John. "Microstructural Deformation Mechanisms and Optimization of Selectively Laser Melted 316L Steel." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/104170.

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In this paper, a novel approach is utilized to investigate the deformation mechanisms at the microstructural level in 3D printed alloys. The complex in-situ heat treatments during 3D printing leaves a unique and complicated microstructure in the as-built 3D printed metals, particularly alloys. The microstructure is made of a hierarchical stacking of some interconnected geometrical shapes, namely meltpools, grains, and cells. These are connected to each other by boundaries that might have different element compositions, and consequently, material properties, compared to the interior region of each geometrical unit. Deformation mechanisms in this microstructure are still highly unexplored, mainly because of the challenges on the way of performing experiments at the micrometer length scale. In this work, we establish an image processing framework that directly converts the SEM images taken from the microstructure of 3D printed 316L stainless steel alloys into CAD models. The model of the complicated microstructure is then scaled up, and the scaled model is 3D printed using polymeric materials. For 3D printing these samples, two polymers with contrasting mechanical properties are used. Distribution of these two polymers mimics the arrangement of soft and stiff regions in the microstructure of 3D printed alloys. These representative samples are subjected to mechanical loads and digital image correlation is utilized to investigate the deformation mechanisms, particularly the delocalization of stress concentration and also the crack propagation, at the microstructural level of 3D printed metals. Besides experiments, computational modeling using finite element method is also performed to study the same deformation mechanisms at the microstructure of 3D printed 316L stainless steel. Our results show that the hierarchical arrangement of stiff and soft phases in 3D printed alloys delocalizes the stress concentration and has the potential to make microstructures with significantly improved damage tolerance capabilities.
Master of Science
Many researchers have studied the impacts of laser parameters on the bulk material properties of SLM printed parts; few if any have studied how these parts break at a microstructural level. In this work we show how SLM printed parts with complex microstructures including grains, meltpools, and cells, deform and break. The cellular network that occurs in some SLM printed parts leads to a multi-material hierarchical structure, with a stiff network of thin boundaries, and a bulk "matrix" of soft cell material. This leads to similar properties as some composites, whereby the stiff network of cell boundaries leads to increased damage tolerance. We show both computationally through finite element analysis, and experimentally through multi-material 3D fabrication, that the microstructure leads to increased crack length in failure, as well as lower toughness loss and strength loss in the event of a crack. Essentially, the complex nature of the formation of these parts (high heating and cooling rates from laser melting) leads to a beneficial microstructure for damage tolerance that has not been studied from this perspective before.

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Wiezorek, J. M. K. "A TEM study of defect microstructures in the intermetallic titanium aluminides γ-TiAl and α2-Ti-3Al". Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309707.

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37

Yan, Miaolei. "Defect Analysis and Microstructural Effects on the Surface Exchange Properties of La0.7Sr0.3MnO3(LSM) Epitaxial Thin Films." Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/650.

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La0.7Sr0.3MnO3 (LSM) is a perovskite oxide material that possesses many interesting electromagnetic and electrochemical properties, making it desirable as magnetic tunnel junction (MTJ) and solid oxide fuel cell (SOFC) electrodes.

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Bracquart, Benoît. "Etude des interactions défaut géométrique / microstructure dans les mécanismes d’endommagement en fatigue à grand nombre de cycles d’alliages métalliques." Thesis, Angers, 2018. http://www.theses.fr/2018ANGE0009.

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L'objectif de ces travaux est d'étudier l'influence de la microstructure et de défauts géométriques de surface sur le comportement en fatigue à grand nombre de cycles (FGNC) d'un aluminium polycristallin de pureté commerciale. Ils s'appuient sur une campagne expérimentale de fatigue et des simulations numériques par la Méthode des Éléments Finis (MEF), afin de mieux appréhender les paramètres microstructuraux gouvernant l'amorçage de fissure aux défauts. Pour cela, les deux dimensions caractéristiques (grains et défaut) sont faites varier. Des traitements thermomécaniques sont mis ainsi en place pour contrôler la taille de grains, avant une caractérisation du comportement monotone et cyclique. Par la suite, des essais de FGNC uni-axiaux en traction-compression alternée sur éprouvettes avec défauts sont effectués, soit avec suivi de fissure de surface in-situ, soit avec étude de l'amorçage de fissure en fond de défaut après cyclage. Les résultats sont par la suite analysés afin de déterminer l'influence des différentes dimensions caractéristiques, ainsi que de l'orientation cristalline, via une campagne EBSD. Des simulations cycliques utilisant la MEF sont ensuite réalisées pour déterminer finement les champs mécaniques locaux. Ainsi, des maillages d'agrégats polycristallins 3D représentatifs des configurations expérimentales sont mis en place. Une loi de comportement de plasticité cristalline à gradient est utilisée afin de traduire le glissement plastique à l'échelle des systèmes de glissement et des effets de taille de grains. La répartition d'un indicateur de fatigue dans les différentes configurations est étudiée, afin de compléter les résultats expérimentaux
The aim of this study is to analyze the influence of microstructure and geometrical surface defects on the high cycle fatigue (HCF) behavior of acommercial purity polycrystalline aluminium. This work relies on an experimental test programme and numerical Finite Element (FE) simulations, in order to better understand microstructural parameters governing crack initiation at defects. To this end, both caracteristic dimensions (grains and defect) are varied. Thermomechanical treatments are set up to control the grain size, and obtained microstructures are caracterized monotonically and cyclically. Then, uniaxial fully reversed tension-compression HCF tests are carried out on specimens with defects, either with an in-situ surface crack monitoring, or a study of the crack initiation at the defect root after cycling. Results are then analyzed in order to determine the influence of different characteristic lengths, as well as crystalline orientation, via EBSD maps. Numerical FE simulations are then carried out to detetermine precisely local mechanical fields. To this end, polycrystalline aggregates 3D meshes representative of experimental configurations are set up. A crystal plasticity constitutive model with gradient is used in order to reproduce the plastic slip at the glide system scale, and the grain size effect. The distribution of afatigue indicator parameter in the different configurations is studied, in order to complement experimental results

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Müller, Julian [Verfasser], and Erdmann [Gutachter] Spiecker. "A Study on Microstructures and Extended Defects in Ni- and Co-Base Superalloys - Development and Application of Advanced TEM Techniques / Julian Müller. Gutachter: Erdmann Spiecker." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2016. http://d-nb.info/1111102503/34.

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40

Degeiter, Matthieu. "Étude numérique de la dynamique des défauts d’alignement des précipités γ’ dans les superalliages monocristallins à base de nickel". Thesis, Université de Lorraine, 2019. http://www.theses.fr/2019LORR0038/document.

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Dans les alliages multiphasés, la cohérence des interfaces entre des phases en désaccord paramétrique génère des champs élastiques internes à longue distance et généralement anisotropes. L'interaction de ces champs affecte fortement la cinétique des transformations de phase diffusives, et influence la forme et l'arrangement spatial des précipités. Dans la microstructure des superalliages monocristallins à base de nickel, obtenue par précipitation de la phase γ’ ordonnée L12 dans la matrice CFC γ, l'élasticité conduit à la formation d'alignements quasi-périodiques des précipités γ’ cuboïdaux. La microstructure γ/ γ’ possède cependant des défauts systématiques d'alignement des précipités: des branches, des macro-dislocations et des motifs en chevrons. Nous nous intéressons à l'origine de ces défauts d'alignement. Nous conduisons des analyses de stabilité de l'arrangement périodique de précipités en interactions élastiques. Contrairement à la stabilité attendue, les calculs semi-analytiques ont révélé l'instabilité de la distribution périodique de précipités γ’ cubiques, vis-à-vis de certains modes de perturbation. Les principales instabilités sont le mode longitudinal [100] et le mode transverse [110], et leur domaine d'instabilité est analysé vis-à-vis de l'anisotropie élastique. Le développement de ces modes instables est étudié par une méthode de champ de phase classique, en simulant l'évolution de microstructures périodiques soumises à des légères perturbations initiales. Nous montrons que l'expression des instabilités d'arrangement procède essentiellement par l'évolution de la forme des précipités, et conduit à la formation de motifs qui ont pu être reliés à des microstructures expérimentales. En particulier, le mode transverse [110] conduit à la formation de motifs en chevrons. Nous étudions l'influence du taux de phase γ’ et de l'inhomogénéité du module élastique C’, et nous montrons le rôle qu'ils jouent dans la stabilisation de l'arrangement périodique. Dans des simulations réalisées dans des études antérieures, la dynamique des défauts est analysée au moyen de paramètres topologiques issus de la phénoménologie des structures hors-équilibre. Au cours d'un recuit isotherme, nous observons que les branches et les macro-dislocations migrent dans la microstructure selon des mécanismes de montée et de glissement. Nous utilisons ensuite une nouvelle formulation des modèles de champ de phase, intrinsèquement discrète, dans laquelle les interfaces sont résolues essentiellement avec un pas de grille sans friction de réseau et avec une invariance par rotation précise. Cette approche, appelée Sharp Phase Field Method (S-PFM), est implémentée sur une grille CFC, et avec une description des quatre variants de translation des précipités γ’. Nous montrons que la S-PFM permet la modélisation de microstructures à grande échelle, avec plusieurs milliers de précipités à deux et trois dimensions, et donne ainsi accès à des informations statistiques sur l'évolution de la microstructure et sur la dynamique des défauts d'alignement. Nous discutons finalement la perspective de modéliser l'évolution de la microstructure γ/γ’ à une échelle supérieure par une description de la dynamique des défauts d'alignement des précipités
In multiphase alloys, internal elastic fields often arise as a result of a coherently adjusted misfit between the lattices of coexisting phases. Given their long-range and usually anisotropic nature, the interaction of these fields is known to significantly alter the kinetics of diffusion-controlled phase transformations, as well as influence the shapes and spatial arrangement of the misfitting precipitates. In the microstructure of single-crystal nickel-base superalloys, obtained by precipitation of the L12-ordered γ’ phase in the FCC γ matrix, elasticity leads to the formation of nearly periodic alignments of the cuboidal γ’ precipitates. However, the γ/γ’ microstructure systematically displays defects in the precipitate alignment: branches, macro-dislocations and chevron patterns. We first address the question of the origin of these alignment defects. Stability analyses of the periodic arrangement of elastically interacting precipitates are carried out. Contrary to the expected stability, the semi-analytical calculations revealed the periodic distribution of cubic γ‘ precipitates to be unstable against specific perturbation modes. The main instabilities are the [100] longitudinal mode and the [110] transverse mode, and their instability range is analyzed with respect to the elastic anisotropy. The consequences of these unstable modes are investigated using a classic phase field method, by modeling the evolution of periodic microstructures undergoing small initial perturbations. We show the expression of the instabilities mainly proceeds by the evolution of the precipitate shapes, and leads to the formation of patterns which were related to experimental microstructures. Specifically, the [110] transverse instability is responsible for the formation of chevron patterns. The effects of the volume fraction and of an inhomogeneity on the C’ shear modulus on the stability of the arrangement are studied, and we show the role they play in the partial stabilization of the periodic distribution, though the [100] longitudinal mode always remains unstable. In phase field calculations carried out in previous studies, the dynamics of alignment defects are analyzed by means of topological parameters derived from pattern formation theory. During annealing, branches and macro-dislocations were observed to migrate in the microstructure according to climbing and gliding mechanisms. We then use a new formulation of phase field models, intrinsically discrete, in which the interfaces are resolved with essentially one grid point with no pinning on the grid and an accurate rotational invariance. This approach, known as the Sharp Phase Field Method (S-PFM), is implemented on a FCC grid and accounts for the four translational variants of the γ’ precipitates. We show that the S-PFM allows for the modeling of large-scale microstructures, with several thousand precipitates both in two and three dimensions, and provides access to statistical information on the microstructure evolution and on the the dynamics of alignment defects. We finally discuss the perspective of modeling the evolution of the γ/γ’ microstructure at the macroscale by means of a description of the defect dynamics in the precipitate alignments

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Severs, John. "Microstructural characterisation of novel nitride nanostructures using electron microscopy." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:6229b51e-70e7-4431-985e-6bcb63bd99d1.

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Novel semiconductor nanostructures possess a range of notable properties that have the potential to be harnessed in the next generation of optical devices. Electron microscopy is uniquely suited to characterising the complex microstructure, the results of which may be related to the growth conditions and optical properties. This thesis investigates three such novel materials: (1) GaN/InGaN core/shell nanowires, (2) n-GaN/InGaN/p-GaN core/multi-shell microrods and (3) Zn₃N₂ nanoparticles, all of which were grown at Sharp Laboratories of Europe. GaN nanowires were grown by a Ni-catalysed VLS process and were characterised by various techniques before and after InGaN shells were deposited by MOCVD. The majority of the core wires were found to have the expected wurtzite structure and completely defect free – reflected in the strong strain-free photoluminescence peak –with a- and m- axis orientations identified with shadow imaging. A small component, <5%, were found to have the cubic zinc-blende phase and a high density of planar faults running the length of the wires. The deposited shells were highly polycrystalline, partially attributed to a layer of silicon at the core shell interface identified through FIB lift-out of cross section samples, and accordingly the PL was very broad likely due to recombination at defects and grain boundaries. A high throughput method of identifying the core size indirectly via the catalyst particle EDX signal is described which may be used to link the shell microstructure to core size in further studies. An n-GaN/InGaN/p-GaN shell structure was deposited by MOCVD on the side walls of microrods etched from c-axis GaN film on sapphire, which offers the possibility of achieving non-polar junctions without the issues due to non-uniformity found in nanowires. Threading dislocations within the core related to the initial growth on sapphire were shown to be confined to this region, therefore avoiding any harmful effect on the junction microstructure. The shell defect density showed a surprising relationship to core size with the smaller diameter rods having a high density of unusual 'flag' defects in the junction region whereas the larger diameter sample shells appeared largely defect free, suggesting the geometry of the etched core has an impact on the strain in the shell layers. The structure of unusual 'flag' defects in the m-plane junctions was characterised via diffraction contrast TEM, weak beam and atomic resolution ADF STEM and were shown to consist of a basal plane stacking faults meeting a perfect or partial dislocation loop on a pyramidal plane, the latter likely gliding in to resolve residual strain due to the fault formed during growth. Zn₃N₂ has the required bandgap energy to be utilised as a phosphor with the additional advantage over conventional materials of its constituent elements not being toxic or scarce. The first successful synthesis of Zn₃N₂ nanoparticles appropriate to this application was confirmed via SAD, EDX and HRTEM, with software developed to fit experimental polycrystalline diffraction patterns to simulated components suggesting a maximum Zn₃N₂ composition of ~30%. There was an apparent decrease in crystallinity with decreasing particle size evidenced in radial distribution function studies with the smallest particles appearing completely amorphous in 80kV HRTEM images. A rapid change in the particles under the electron beam was observed, characterised by growth of large grains of Zn₃N₂ and ZnO which increased with increasing acceleration voltage suggesting knock-on effects driving the change. PL data was consistent with the bandgap of Zn₃N₂ blue shifted from 1.1eV to around 1.8eV, confirming the potential of the material for application as a phosphor.

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Pélosin, Véronique. "Dynamique de l'évolution structurale et spectroscopie mécanique de multicouches AgNi." Grenoble 1, 1993. http://www.theses.fr/1993GRE10121.

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Differents appareils ont ete adaptes a la spectroscopie mecanique de films minces autoportants ou adherents a un substrat. Les deux principaux dispositifs mis au point, tres performants et plurifonctionnels, sont un tensiodilatometre et une lame vibrante. Nous nous somme interesses a des multicouches agni a mailles deformees fabriquees par pulverisation cathodique. Les deux elements sont immiscibles et presentent un fort desaccord parametrique, 15%. La taille des grains est nanometrique. Nous avons etudie les differents stades de l'evolution microstructurale de ces materiaux, relaxation interfaciale et destratification, grace a des mesures de resistivite et de dilatometrie effectuees en continu au cours de cycles de temperature. Le comportement mecanique des echantillons a ete analyse pour une large gamme de periodes, dans l'etat brut de fabrication mais aussi lors de traitements thermiques. Des courbes effort-deformation tracees en tension uniaxiale montrent que les lois de l'elasticite lineaire demeurent verifiees. Le module d'young ne presente aucune singularite, quelle que soit la periode etudiee. Les constantes de cisaillement determinees par diffusion brillouin sont abaissees substantiellement aux faibles periodes. Les mesures ont aussi revele une limite d'ecoulement plastique geante. En regime dynamique, les mouvements des defauts internes, joints de grains et interfaces, sont inhibes par ancrage reciproque. En utilisant des films adherents a un substrat de silicium, nous avons suivi les variations des contraintes internes generees thermiquement ou induites par les reorganisations structurales. Il apparait que le relachement de ces contraintes lors du stade de relaxation interfaciale est a mettre en relation avec la densification qui accompagne cette relaxation. Enfin, nous avons mis en evidence des effets de module et d'amortissement d'origine magnetoelastique. Ils renseignent sur la mobilite des parois de domaines magnetiques. Le niveau de contrainte a une incidence tres forte sur l'amplitude de ces effets

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43

Simsek, Sanli Ekin [Verfasser], Hans-Joachim [Akademischer Betreuer] Kleebe, and Peter A. van [Akademischer Betreuer] Aken. "Investigation of Microstructural Defects in Cu(In,Ga)Se2 Thin Films by Scanning Transmission Electron Microscopy / Ekin Simsek Sanli ; Hans-Joachim Kleebe, Peter A. van Aken." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2019. http://d-nb.info/1191369854/34.

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Gomes, Affonseca Netto Nelson. "The Effect of Friction Stir Processing on The Microstructure and Tensile Behavior of Aluminum Alloys." UNF Digital Commons, 2018. https://digitalcommons.unf.edu/etd/790.

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Friction Stir Processing (FSP) is a promising thermomechanical technique that is used to modify the microstructure of metals locally, and thereby locally improve mechanical properties of the material. FSP uses a simple and inexpensive tool, and has been shown to eliminate pores and also reduce the sizes of intermetallics in aluminum alloys. This is of great interest for research on solidification, production and performance of aluminum alloy castings because FSP can enhance the structural quality of aluminum casting significantly by minimizing the effect of those structural defects. In the literature, there is evidence that the effectiveness of FSP can change with tool wear of the tool used. Therefore, a study was first conducted to determine the effect of FSP time on the tool life and wear in 6061-T6 extrusions. Results showed the presence of two distinct phases in the tool life and wear. Metallographic analyses confirmed that wear in Phase I was due to fracture of the threads of the tool and Phase II was due to regular wear, mostly without fracture. Moreover, built-up layers of aluminum were observed between threads. The microhardness profile was found to be different from those reported in the literature for 6061-T6, with Vickers hardness increasing continuously from the the stir zone to the base material. To investigate the degree of effectiveness of FSP in improving the structural quality of cast A356 alloys, ingots with different quality (high and low) were friction strir processed with single and multiple passes. Analysis of tensile test results and work hardening characteristics showed that for the high quality ingot, a single pass was sufficient to eliminate the structural defects. Subsequent FSP passes had no effect on the work hardening characteristics. In contrast, tensile results and work hardening characteristics improved with every pass for the low quality ingot, indicating that the effectiveness of FSP was dependent on the initial quality of the metal. The evolution of microstructure, specifically the size and spacing of Silicon (Si) eutectic particles, was investigated after friction stir processing of high quality A356 castings with single and multiple passes. Si particles were found to coarsen with each pass, which was in contrast with previous findings in the literature. The nearest neighbor distance of Si particles also increased with each FSP pass, indicating that microstructure became progressively more homogeneous after each pass. In the literature, the improvement observed after FSP of Al-Si cast alloys was attributed to the refinement of Si particles. Tensile data from high quality A356 ingot showed that there was no correlation between the size of Si particles and ductility. To the author’s knowledge, this is the first time that the absence of a correlation between Si particle size and ductility has been found.

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Lombard, Hannalie. "Optimized fatigue and fracture performance of friction stir welded aluminium plate : a study of the inter-relationship between process parameters, TMAZ, microstructure, defect population and performance." Thesis, University of Plymouth, 2007. http://hdl.handle.net/10026.1/2389.

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Friction stir welding (FSW) is an exciting new solid-state welding process with the potential to advantageously impact many fabrication industries. Current take-up of the process by industry is hindered by lack of knowledge of suitable welding parameters for any particular alloy and sheet thickness. The FSW process parameters are usually chosen empirically and their success is evaluated via simple mechanical property testing. There are severe drawbacks with such methods of determining manufacturing conditions. These include indirect relationships between tensile and fatigue properties, particularly for welds, and a high probability of totally missing real optimized conditions. This research is therefore undertaken as a first step in providing information that will assist manufacturing industry to make sound decisions with respect to selecting FSW parameters for weldable structural alloys. Some of the key issues driving material selection for manufacturing are weld quality in terms of defects, fatigue strength and crack growth, and fracture toughness. Currently a very limited amount of data exists regarding these mechanical properties of FSW welds, and even less information exists regarding process parameter optimization. This is due to the mechanical microstructural complexity of the process and the relatively large number of process parameters (feed, speed, force and temperature) that could influence weld properties. In order to advance predictive understanding and modeling for FS welds, it is necessary to develop force and energy based models that reflect the underlying nature of the thermo-mechanical processes that the material experiences during welding. This project aims at determining the influence and effect of Friction Stir Welding process control parameters on the microstructure of the thermo-mechanically affected zone, the defect population in the weld nugget, hardness, residual stresses, tensile and fatigue performance of 6 mm plate of 5083-H321 aluminium alloy, which is known to be susceptible to planar defect formation. Welds were made with a variety of process parameters (that is feed rate and rotational speed) to create different rates of heat input. Forces on the FSW tool (horizontal and vertical), torque and tool temperature were measured continuously during welding from an instrumented FSW tool. Detailed information on fatigue performance, residual stress states, microstructure, defect occurrence, energy input and weld process conditions, were investigated using regression models and contour maps which offer a unique opportunity to gain fundamental insight into the process-structure-property relationships for FS welds. Weld residual strains have been extensively measured using synchrotron X-ray diffraction strain scanning to relate peak residual stresses and the widths of the peak profiles, taken from a single line scan from the mid depth of the FS welds, with the weld process conditions and energy input into the welds. Several residual stress maps were also investigated. The optical and scanning electron microscope were used to determine the type of intrinsic defects present in the FSW fatigue and tensile specimens. Vickers hardness measurements were taken from the mid depth of the welds and were compared with the weld input parameters. The main contribution of this thesis is as follow: (i) the relationship between input parameters and process parameters; (ii) the relationship between input weld parameters (that is feed rate and rotational speed) and process parameters (that is vertical downwards force Fz, tool temperature, tool torque and the force footprint data), energy input and tensile strength, fatigue life and residual stresses to obtain regions of optimum weld conditions; (iii) identification of the defects present in FSW, their relationship with process parameters and their effect on tensile strength and fatigue life; and (iv) the usefulness of the real time process parameter monitoring automated instrumented FSW tool to predict the mechanical properties of the welds.

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Pereira, Daniel. "Avaliação do método de correntes parasitas para caracterização microestrutural e inspeção de defeitos em superligas à base de níquel." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/97238.

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Superligas à base de níquel vêm sendo extensivamente utilizadas em diversas aplicações nas indústrias devido ao excelente comportamento mecânico e anticorrosivo. No entanto, essas ligas possuem certas particularidades que levam à necessidade de desenvolvimento de técnicas de inspeção e caracterização metalúrgica, como forma de garantir a integridade estrutural dos componentes fabricados com essas ligas. Neste trabalho, a técnica de correntes parasitas foi aplicada à superligas à base de níquel com duas propostas distintas: 1) Em um primeiro momento foi realizado o estudo da evolução microestrutural da liga Inconel 718 durante o processo de envelhecimento através da combinação do ensaio por correntes parasitas, análise de difração de raios-X, análise metalográfica, medidas de dureza e tamanho de grão. As medidas foram realizadas em amostras submetidas a diferentes ciclos de tratamentos térmicos variando entre 620-1035°C. Os resultados mostraram que as diferentes microestruturas do Inconel 718 têm efeitos distintos na condutividade elétrica quando medidos através da técnica de correntes parasitas. A influência da microestrutura na condutividade pode ser mostrada sendo devido à competição de dois efeitos sobre o espalhamento de elétrons: a purificação da matriz e a morfologia, distribuição e tamanho dos precipitados. A combinação dos valores de dureza e condutividade elétrica provou ser uma forma rápida e prática de determinar o nível de envelhecimento da liga; 2) Em um segundo momento foi desenvolvido um processo de otimização de sensores através de modelagem por elementos finitos (MEF). Através de uma metodologia de otimização, os parâmetros de construção e operação de um sensor foram otimizados para inspeção de defeitos superficiais e subsuperficiais esperados em materiais cladeados com Inconel 625. O sensor com a geometria ótima foi construído e testado a fim de verificar a eficiência do processo de otimização. Uma ótima correlação entre os resultados numéricos e experimentais foi encontrada e o sensor ótimo se mostrou eficiente na inspeção de pequenos defeitos superficiais e subsuperficiais na liga Inconel 625 quando operado nas frequências apropriadas.
Nickel-based superalloys have been extensively used in various industries due to its unique mechanical and corrosion behavior. However, these alloys show particular characteristics which lead to the need for specific inspection and metallurgical characterization techniques in order to ensure the structural integrity of components manufactured from these alloys. In this work , the eddy current technique was applied to nickel-base superalloys with two aims: 1 ) Firstly, the microstructural evolution of Inconel 718 during aging processes has been studied through a combination of eddy current testing, X-ray diffraction analysis, metallography, hardness and grain size measurements. Measurements were carried out in samples subjected to different heat treatment cycles between 620-1035°C. Results show that different microstructures of Inconel 718 have a distinguishable effect on electrical conductivity when this is measured through an appropriately sensitive technique (i.e. eddy current testing). The influence of microstructure on conductivity could be shown to be due to the competition between two effects on the scattering of electrons: matrix purification and precipitate size, distribution and morphology. A combination of hardness values and electrical properties proved to be a fast and practical way of determining the stage of aging of the alloy; 2) An optimization method of eddy current sensor design was developed through finite element modeling (FEM). Through a methodology of optimization, the construction and operation parameters of the sensor were optimized for inspection of superficial and subsuperficial defect, commonly found in weld overlay Inconel 625 claddings. A prototype of this sensor with the optimum geometry was built and tested on blocks identical to those considered in the models in order to verify the efficiency of the optimization process. A very good agreement between numerical and experimental results was found. Moreover, the optimal sensor was efficient to detect small surface and subsurface defects in Inconel 625 when operated at appropriate frequencies.

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Jouanny, Emilie. "Étude de l'évolution microstructurale sous irradiation aux ions Ti2+ de deux alliages de titane : lien avec les propriétés mécaniques." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0071/document.

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Ce travail de thèse s’intéresse à l’évolution de la microstructure sous irradiation d’alliages de titane, en vue de leur potentielle utilisation dans le domaine du nucléaire. Une étude paramétrique (température, dose et flux d’irradiation) a donc été menée, à l’aide de simulations d’irradiations neutroniques par des irradiations aux ions (plateforme JANNuS – Saclay), sur les alliages T40 et TA6V, et de caractérisations microstructurales qualitatives et quantitatives post irradiation (MET, analyse d’image, SAT). Ainsi, différents défauts d’irradiation ont été identifiés. En particulier, la présence de boucles à composante dans l’alliage T40 et de précipités riches en vanadium dans l’alliage TA6V a clairement pu être mise en évidence dès la température de 300°C. La microstructure résultante est fortement dépendante des paramètres d’irradiation et de l’alliage de titane considéré. Un effet important de la température (entre 300°C et 430°C) a été noté sur les boucles de dislocations de type pour l’alliage T40 et sur les précipités pour l’alliage TA6V. Les doses et les flux considérés à 300°C ne modifient pas la distribution des défauts des deux alliages. A 430°C, l’augmentation de la dose modifie peu le paysage des boucles de dislocations de type pour l’alliage TA6V contrairement à l’alliage T40. Les précipités, quant à eux ne semblent pas affectés par l’augmentation de la dose. Une analyse des mécanismes mis en jeu est proposée. Enfin, des essais de nano-indentation ont permis une première description du lien microstructure / propriétés mécaniques. A 430°C, l'alliage T40 ne semble pas être impacté mécaniquement par l’évolution de la microstructure avec la dose d’irradiation contrairement à l'alliage TA6V
This PhD work deals with microstructural evolution of titanium alloys under irradiation, due to their potential use in the nuclear field. Parametric study (temperature, dose and irradiation flux) was conducted, using ion irradiations (JANNuS – Saclay platform) to simulate neutron irradiation damage. Two titanium alloys (CP Ti grade 2 and Ti-6Al-4V) were considered and qualitative and quantitative post irradiation microstructural characterizations were done (TEM, image analysis, APT). Thus, various irradiation defects were identified. In particular, presence of -component loops was highlighted in CP Ti grade 2 and vanadium-rich precipitates in Ti-6Al-4V from the temperature of 300°C. Resulting microstructure is hardly depending on irradiation parameters and considered titanium alloys. Important effect of temperature (between 300°C and 430°C) was noted on -type dislocation loops in CP Ti grade 2 and precipitates in Ti-6Al-4V. At 300°C, dose and flux have no effect on the defect distribution of the two titanium alloys. At 430°C, the increase of dose has a little consequence on the -type dislocation loops in Ti-6Al-4V, contrary to the ones observed in CP Ti grade 2. Precipitates, observed in Ti-6Al-4V, do not seem to be affected by the increase of the dose. Analysis of involved mechanisms is proposed. Finally, nano-indentation tests have allowed to get first description of the link between microstructure and mechanical properties. At 430°C, CP Ti grade 2 do not seem to be affected mechanically by the microstructural evolution with the irradiation dose, contrary to Ti-6Al-4V

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ARNAUD, JEAN-CLAUDE. "Etude de l'endommagement par fluage des aciers inoxydables austenitiques entre 550 degre c et 650 degre c." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0083.

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Identification et analyse des mecanismes microscopiques de l'endommagement. Analyse statistique du glissement intergranulaire et de l'endommagement d'echelle micrometrique. Determination des mecanismes de deformation. Observation des differents stades de l'endommagement et determination des tailles "critiques" des defauts

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49

Liu, Meishuai. "Study on microstructural and crystallogarphic characteristics of phase transformation induced by ECP in annealed Cu-40%Zn alloy." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0210.

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Ce travail porte sur les caractéristiques microstructurales et cristallographiques des alliages Cu-40%Zn traités par Electric Current Pulse (ECP). La relation d'orientation (RO) de transformation de phase et sa corrélation avec les défauts cristallins ont été étudiés. Les mécanismes de formation des défauts cristallins dans la phase mère et des sous-structures dans les précipités β induit par L'ECP ont également été étudiés. La transformation de la phase α en β peut être induite par un traitement ECP avec formation de précipités fins β pouvant persister à température ambiante. Avec l'augmentation de la densité de courant électrique, la quantité de précipités et les sites de formation augmentent des joints de grains α à l'intérieur des grains. Les précipités β suivent différentes RO en fonction du site de formation. Les joints de grains β sont en RO Kurdjumov-Sachs (KS); tandis que les β intragranulaires sont en Nishiyama-Wasserman (NW). Dans les premiers sites, on observe des dislocations {111}α/<11̅0>α, alors que dans les seconds, les fautes d’empilements {111}α/<112̅>α sont présentes. Les analyses de déformation de transformation ont révélé que, en RO KS, la déformation maximale du réseau requise est un cisaillement sur le système {111}α/<112̅>α, tandis qu'en NW, la déformation maximale correspond à un cisaillement sur le système {111}α/<112̅>α. Ainsi, les dislocations {111}α/<11̅0>α existants le long des joints de grains α fournissent la précontrainte requise par la transformation KS, alors que les fautes d'empilement {111}α/<112̅>α entourées par les dislocations partielles {111}α/<112̅>α offrent une précontrainte facilitant la transformation NW. Différents types de défauts cristallins sont formés dans la matrice α par les traitements ECP en fonction de la densité de courant. À faible densité, une grande quantité de fautes d'empilement {111}α/<112̅>α, puis des nano-mâcles sont produites dans la matrice α. A haute densité, des réseaux de dislocations sont formés à proximité des précipités β composés de dislocations coins parfaites {111}α/<11̅0>α et des dislocations de Frank. La différence de volume entre le phases α et β analysée avec la déformation de transformation révèle que cette dernière nécessite une dilatation dans la direction [11̅0]α et une contraction dans la direction [111]α. La première entraîne l’apparition de dislocations coins {111}α/<11̅0>α devant les larges faces {31̅1}α et la dernière induit la formation des dislocations de Frank devant les larges faces {121}α. Ainsi, des réseaux de dislocations se forment le long des bords des grandes faces des précipités β où les deux types de dislocations se rencontrent. De plus, les précipités β contiennent deux types d’agrégats atomiques de taille nanométrique de structure n en RO Burgers et de structure ω en RO Blackburn avec la matrice β. Ils ont été formés par un déplacement atomique en deux étapes. Pour la structure n, la première étape est le brassage atomique de chaque second plan {110}β dans la direction <11̅0>β et la seconde consiste en un changement de structure principalement par un cisaillement selon {11̅2}β /<1̅11>β. Pour la structure ω, le premier est un mélange atomique sur chaque deuxième et troisième plan {112̅}β dans les directions ±[111]β, puis des déformations normales dans trois directions perpendiculaires (<111>β, <112̅>β et <11̅0>β). L’apparence concomitante des deux structures réside dans le fait que l’augmentation de volume accompagnant la formation de n peut être annulée par la diminution de volume accompagnant la distorsion ω, ce qui minimise l’énergie de déformation de transformation. Ce travail fournit des informations fondamentales sur les alliages Cu-40%Zn pour interpréter l’impact des défauts sur les relations d'orientation de transformations en phase solide, sur la formation de divers types de défauts induits par la transformation de phase ultra-rapide ainsi que sur les mécanismes de formation des sous-structures des phases produites
A thorough investigation has been conducted on the microstructural and crystallographic features of Electric Current Pulse (ECP) treated Cu-40%Zn alloys. The phase transformation orientation relationship (OR) and its correlation with crystal defects have been studied and the formation mechanisms of ECP induced crystal defects in the parent phase and the sub-structures in the β precipitates were also analyzed. The α to β heating phase transformation can be induced by ECP treatment with the formation of fine β precipitates that can be remained to the room temperature. With the increase of the electric current density, the amount of precipitates is increased and the formation sites increase from α grain boundaries to grain interiors. The β precipitates follow different ORs depending on the formation site. The grain boundary β phase obeys the Kurdjumov-Sachs (K-S) OR; whereas the intragranular β respects the Nishiyama-Wasserman (N-W) OR. In the former sites, the {111}α /<11̅0>α dislocations are observed, whereas in the latter, the {111}α/<112̅>α stacking faults are found. Transformation strain analyses revealed that under the K-S OR the maximum lattice deformation required is a shear on the {111}α /<11̅0>α slip system, whereas under the N-W OR the maximum deformation is a shear on the {111}α /<112̅>α system. Thus the existing {111}α /<11̅0>α dislocations along the α grain boundaries provide pre-strain required by the transformation via the K-S path, whereas the {111}α /<112̅>α stacking faultsboarded by {111}α /<112̅>α partial dislocations offer pre-strain facilitating the transformation via the N-W path. Different types of crystal defects are formed in the α matrix by the ECP treatments depending on the current density. At low density, large amount of {111}α /<112̅>α stacking faults and then nano twins are produced in the α matrix. At high density, dislocation nets are formed near the β precipitates that are composed of edge typed {111}α /< 11̅0 >α perfect dislocations and the Frank typed dislocations. The volume misfit between the α and the β phase analyzed with transformation deformation reveals that the transformation from α to β requires an expansion along [11̅0]α direction and a contraction along [111]α direction. The former results in the appearance of the {111}α /<11̅0>α edge typed dislocation arrays in front of the {31̅1}α broad faces and the latter induces the formation of the Frank typed dislocations in front of the {121}α broad faces. Thus, dislocation nets formed along the edges of the broad faces of the β precipitates where the two kinds of dislocations meet. Furthermore, the β precipitates contain two kinds of nano-sized and diffuse atomic clusters with the  structure obeying the Burgers OR and with the ω structure obeying the Blackburn OR with the β matrix. They were each formed through a two-stepped atomic displacement. For the  structure, the first step is the atomic shuffle of each second {110}β plane in the <11̅0>βdirection and the second is a structure change mainly by a shear on the {11̅2}β /<1̅11>β. For the ω structure, the first is an atomic shuffle on each second and third {112̅}β plane in the ±[111]β directions and then normal strains in three mutually perpendicular directions (<111>β, <112̅>β and <11̅0>β). The concomitant appearance of the two structures lies in the fact that the volume increase accompanying the  formation can be canceled by the volume decrease accompanying the ω distortion, which minimizing the transformation strain energy. The results of this work provide fundamental information on the Cu-40%Zn alloys for interpreting the impact of the crystal defects on the solid phase transformation ORs, on the formation of various types of crystal defects induced by the ultra-rapid phase transformation and on the formation mechanisms of sub structures in the product phase

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Silva, Francisco EstÃnio da. "Reconhecimento de PadrÃes AtravÃs de AnÃlises EstatÃsticas e Fractais Aplicadas a Dados de Ensaios NÃo-Destrutivos." Universidade Federal do CearÃ, 2011. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=7330.

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FundaÃÃo de Amparo Ã Pesquisa do Estado do CearÃ
Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico
In this work a procedure is studied for pattern classification related to different types of data, namely: (1) signals obtained from ultrasonic testing ( pulse-echo technique) and magnetic signals obtained from BarkhÃusen noise in samples of ferritic-pearlitic carbon steel tubes which, due to temperature effects, have shown microstructural changes as consequence of the total or partial transformation of the pearlite into spherodite; (2) images built from TOFD ultrasonic testing and 8 bit digital radiographic images obtained from carbon steel 1020 sheets, with different welding defects. From the data obtained, images have been considered with the defects as lack of fusion, lack of penetration, porosity and images without defect. For this aim, non-conventional mathematical techniques have been used for the preprocessing of the data, namely, the statistical analyses, Hurst analysis (RSA) and detrended fluctuation analysis (DFA), and fractal analyses, box counting analysis (BCA) and minimal cover analysis (MCA). The curves obtained with the initial mathematical treatment, discrete functions of the temporal window width, have been handled with the supervised and non-supervised pattern recognition techniques known as principal component analysis and Karhunen-LoÃve (KL) transformation analysis respectively. With respect to the magnetic signals, the KL classifier has been shown to be very efficient when applied to DFA obtained from the magnetic flux, with a success rate around 94%. On the other hand, for the magnetic noise signals we have not obtained an acceptable success rate independently of the pre-processing used. However, when were considered the curves obtained by concatenating all curves of the pre-processing was obtained a consistent average success rate of 85%. As far as the rate of success of the PCA classifier is concerned, an excellent success of 96% has been reached for concatenated curves of selected data of magnetic noise only. As far as the analyses of the backscattered ultrasonic signals is concerned, it was not possible to classify the different stages of the microstructural degradation by using KL or PCA independently of the pre-processing used. As far as the analyses of the D-scan images are concerned, by applying PCA a rate of success of 81% has been obtained with MCA data, 73% has been obtained by concatenating all curves from the different fractal and statistical analyses and around 85% when concatenating the best individual results (DFA and MCA). On the other hand, considering the KL classifier, high success rates have been verified for the training stage, between 96% and 99%, and a maximum success rate (100%), when concatenating all analyses. With respect to the testing results, the best success rate which has been reached was approximately 77%, when concatenating all the curves obtained from the statistical and fractal pre-processing. For the digitalized radiographic images, relevant individual rates of success (between 70% and 90%) for the training set (consisting of all data) have been obtained for the classifier KL only, and a 100% success rate, when concatenating all the curves obtained from the pre-processing of the images.
Neste trabalho estudou-se uma metodologia de classificaÃÃo de padrÃes relacionados a dois tipos de dados: (1) sinais obtidos atravÃs dos ensaios ultrassÃnicos (tÃcnica pulso-eco) e sinais magnÃticos obtidos atravÃs de ruÃdo Barkhausen realizados em amostras de tubos de aÃo carbono ferrÃtico-perlÃtico que devido aos efeitos da temperatura de trabalho apresentaram mudanÃas microestruturais decorrentes da transformaÃÃo parcial ou total da perlita em esferoiditas; e (2) imagens construÃdas a partir de ensaios ultrassÃnicos (tÃcnica TOFD) e imagens radiogrÃficas digitais de chapas de aÃo carbono 1020 soldadas, obtidas com resoluÃÃo de 8bits, nas quais foram inseridos diversos tipos de defeitos de soldagem. Dos dados gerados, foram estudadas as imagens com os defeitos de falta de fusÃo (FF), falta de penetraÃÃo (FP), porosidade (PO) e uma classe designada como sem defeito (SD). Para tanto, utilizaram-se de tÃcnicas matemÃticas nÃo convencionais no prÃ-processamentos dos dados conhecidas como anÃlises estatÃsticas de Hurst (RSA) e flutuaÃÃo sem tendÃncia (DFA) e as anÃlises fractais de contagem de caixas (BCA) e de mÃnima cobertura (MCA). Em seguida as curvas obtidas desse tratamento matemÃtico inicial, funÃÃes discretas da largura da janela temporal, foram utilizadas na alimentaÃÃo das tÃcnicas de reconhecimento de padrÃes nÃo supervisionada e supervisionada conhecidas, respectivamente, como anÃlise de componentes principais (PCA) e anÃlise da transformaÃÃo de Karhunen-LoÃve (KL). Em relaÃÃo aos estudos dos sinais magnÃticos, o classificador KL mostrou-se eficiente quando aplicado Ãs DFA do fluxo magnÃtico, com uma taxa de sucesso em torno de 94%. JÃ para os sinais do ruÃdo magnÃtico nÃo se obteve uma taxa de sucesso aceitÃvel, independente do prÃ-processamento utilizado. Entretanto quando todas as curvas de todas as anÃlises, dos dois tipos de sinais magnÃticos (ruÃdo e fluxo), foram concatenadas, obteve-se uma taxa mÃdia de sucesso consistente de aproximadamente 85%. No tocante Ãs taxas de sucesso do classificador PCA, somente para o ruÃdo magnÃtico e considerando todas as curvas concatenadas para um grupo de dados selecionados, conseguiu-se uma taxa de sucesso de 96%. A respeito das anÃlises dos sinais ultrassÃnicos retroespalhados, tambÃm nÃo foi possÃvel classificar, nem com a KL e nem com a PCA, os diferentes estÃgios de degradaÃÃo microestrutural, independemente do prÃ-processamento utilizado. No tocante Ãs analises das imagens D-scan, obteve-se com a PCA, taxas de sucesso de 81% considerando apenas os dados das MCA, 73% quando as curvas de todas as anÃlises estatÃsticas e fractais foram concatenadas, e em torno de 85%, quando apenas as curvas das melhores anÃlises (DFA e MCA) foram concatenadas. JÃ considerando o classificador KL, verificaram-se taxas de sucesso na etapa de treinamento, entre 96% e 99%, e mÃxima taxa de sucesso (100%) no caso dos vetores de todas as anÃlises concatenados. Em relaÃÃo aos resultados dos testes, a melhor taxa de sucesso alcanÃada foi aproximadamente de 77% quando se concatenaram todas as curvas oriundas dos prÃ-processamentos estatÃsticos e fractais. Com respeito Ãs imagens radiogrÃficas digitalizadas somente com o classificador KL (na etapa de treinamento, com 100% dos vetores) obtiveram-se taxas de sucesso individuais entre 70 e 90% de acertos e 100% de sucesso na classificaÃÃo quando se concatenaram as curvas de todos os prÃ-processamentos das imagens.

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Дисертації з теми "Microstructure defects"

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