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1
López, Gabriel Alejandro. "Segregation and phase transformations at interfaces". [S.l. : s.n.], 2004. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11380449.
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Jedrecy, Alexandre. "Study of phase transformation of matter through topological coordinates". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS386.
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Au cours de cette thèse deux problèmes majeurs pour l’eau ont été étudiés : la transition liquide-liquide et la nucléation homogène de la glace. Pour cela nous avons utilisé l'état de l'art des méthodes d’échantillonnage amélioré, couplé avec une nouvelle variable qui contient les informations topologiques pertinentes des systèmes étudiés, le PIV. En calculant des profils d'énergie libre pour différentes conditions de pression et de température, nous avons pu montrer rigoureusement l’absence de barrière d’énergie libre et de second point critique pour la transition liquide-liquide avec le modèle TIP4P/2005. En échantillonnant l'ensemble des chemins de transition grâce à un nouvel algorithme TPS, nous avons aussi pu étudier précisément le mécanisme de nucléation homogène de l’eau avec le modèle TIP4P/Ice, montrant que la structure optimale des noyaux critiques est un empilement désordonné, les noyaux critiques purement cubique ou hexagonaux évoluant spontanément vers cette structure. De plus, nous avons pu montrer que la glace hexagonale s’agrégeait majoritairement en deux étapes, là où la glace cubique s’agrégeait en une étape. Finalement nous avons quantifié rigoureusement la qualité de notre métrique topologique PIV comme coordonnée de réaction pour étudier la nucléation : une analyse réalisée avec la méthode d'optimisation de la vraisemblance maximale basée sur la fonction de réalisation, indique que cette coordonnée surpasse un large éventail de coordonnées utilisées précédemment pour étudier ce problèmeDuring this thesis two major problems were studied : the liquid-liquid transition and the homogeneous nucleation of ice in water. To achieve this, we used state-of-the-art enhanced sampling methods, coupled with a new collective variable which store the relevant topological information of a system, the PIV. By rigorous calculation of free energy profile for various conditions of pressure and temperature, we have been able to show the lack of free energy barrier and thereof a second critical point for the liquid-liquid transition, with the TIP4P/2005 model of water. By sampling the transition path ensemble with a new TPS algorithm, we have been able to precisely study the homogeneous nucleation of ice in water with the TIP4P/Ice model, showing that critical nuclei arrange themselves optimaly in stacking disorder ice, with purely hexagonal or cubic nuclei spontaneously evolving toward this structure. The insight we obtained includes a two-step mechanism for the aggregation of new hexagonal ice molecules to the critical nucleus, compared to a one-step process for the addition of cubic ice molecules. Finally we performed a quantitative assessment of the quality of the PIV topological metric as reaction coordinate for nucleation : analysis by means of a rigorous likelihood optimization technique based on committor information, indicates that this coordinate outperforms a large set of previously considered coordinates
3
Abdedou, Nazim. "Non-equilibrium conditions at solid/liquid interfaces". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0346.
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Notre travail porte sur la fusion dite solutale survenant lorsque l'on met deux métaux en contact à une température comprise entre leurs températures de fusion respectives. L'interface solide/liquide se retrouve initialement fortement hors-équilibre et la cinétique propre à son retour à l'équilibre semble mettre en défaut les modèles généralement employés pour décrire la solidification et la fusion. Pour progresser dans la compréhension du processus, nous avons abordé le problème sous trois angles complémentaires. Dans un premier temps, nous avons réalisé des expériences in-situ de fusion solutale du système Au-Ag en utilisant la tomographie par rayons X. L'analyse critique des résultats semble montrer que l'interface solide-liquide reste hors équilibre pendant la fusion solutale, avec la persistance inattendue de gradients de concentration à la fin des expériences. Dans un deuxième temps, dans le but de mieux comprendre les expériences, nous avons mis en œuvre un modèle reposant sur la thermodynamique des processus irréversibles appliquée aux échanges d'espèces chimiques à travers une interface solide/liquide abrupte. Une paramétrisation des coefficients de transfert interfaciaux permet au modèle de reproduire qualitativement les comportements observés dans les expériences. Enfin, nous avons cherché à justifier les paramètres cinétiques du modèle thermodynamique en utilisant la dynamique moléculaire (DM) dans le système Cu-Ni. Nous avons ainsi démontré que les coefficients interfaciaux dépendent des concentrations à l'interface, en accord avec la paramétrisation du modèle thermodynamiqueOur work focuses on solutal melting, which occurs when two metals are brought into contact at a temperature between their respective melting temperatures. The solid/liquid interface is initially far from equilibrium, and the kinetics governing its return to equilibrium appear to challenge the models commonly used to describe solidification and melting. To advance our understanding of the process, we approached the problem from three complementary angles. First, we conducted in-situ experiments on the solutal melting of the Au-Ag system using X-ray tomography. Critical analysis of the results appears to indicate that the solid-liquid interface remains out of equilibrium during solutal melting, with the unexpected persistence of concentration gradients at the end of the experiments. Second, in an effort to better understand the experiments, we developed a model based on the thermodynamics of irreversible processes applied to the exchange of chemical species across a sharp solid/liquid interface. Parametrization of interfacial transfer coefficients enables the model to qualitatively reproduce the behaviors observed in the experiments. Finally, we sought to justify the kinetic parameters of the thermodynamic model using molecular dynamics (MD) in the Cu-Ni system. We thus demonstrated that the interfacial coefficients depend on the concentrations at the interface, consistent with the parametrization of the thermodynamic model
4
Houchmandzadeh, Bahram. "Contribution à l'étude des transitions de phase dans les lignes et interfaces". Grenoble 1, 1992. http://www.theses.fr/1992GRE10042.
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Dans ce travail, nous etudions certaines transitions de phase dans les lignes et interfaces. Le texte est concu en trois chapitres assez distincts. Dans le premier chapitre, les transitions de phase entre parois de bloch et ising dans un modele xy anisotrope sont etudiees. Nous generalisons la notion de parois de domaines aux systemes dynamiques ou une excitation parametrique joue le role de l'anisotropie. Le phenomene nouveau qui apparait alors est le mouvement des parois de bloch, avec une vitesse proportionnelle a leurs chiralites. Au deuxieme chapitre, nous etudions le role de la surface d'un cristal lors d'une transition de phase structurale, et nous comparons cette derniere a une transition de mouillage classique. Dans le cadre de notre modele, nous mettons en evidence une transition de phase de surface, comparable a une transition de premouillage, qui survient avant la transition de phase structurale du volume. Le troisieme chapitre etudie l'interaction entre deux chaines de polymeres, et la transition de localisation qui peut survenir dans ce systeme. Nous etudions plus particulierement la relation qui existe entre cette transition et l'enroulement mutuel des deux chaines. L'interaction entre les deux chaines qui a courte portee, peut comporter dans notre modele des termes qui favorisent l'enroulement
5
Roland, Christopher. "Phase transitions of phospholipid monolayers on air-water interfaces". Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66032.
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Perevoshchikova, Nataliya. "Modeling of austenite to ferrite transformation in steels". Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0342/document.
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La thèse porte sur la modélisation de la transformation de l'austénite en ferrite dans les aciers en mettant l'accent sur les conditions thermodynamiques et cinétiques aux interfaces alpha/gamma en cours de croissance de la ferrite. Dans une première partie, la thèse se concentre sur la description des équilibres thermodynamiques entre alpha et gamma à l'aide de la méthode CalPhad. Nous avons développé un nouvel algorithme hybride combinant la construction d'une enveloppe convexe avec la méthode classique de Newton-Raphson. Nous montrons ses possibilités pour des aciers ternaire Fe-C-Cr et quaternaire Fe-C-Cr-Mo dans des cas particulièrement difficiles. Dans un second chapitre, un modèle à interface épaisse a été développé. Il permet de prédire l'ensemble du spectre des conditions à l'interface alpha/gamma au cours de la croissance de la ferrite, de l'équilibre complet au paraéquilibre avec des cas intermédiaires des plus intéressants. Nous montrons que de nombreux régimes cinétiques particuliers dans les systèmes Fe-C-X peuvent être prévus avec un minimum de paramètres d'ajustement, principalement le rapport entre les diffusivités de l'élément substitutionnel dans l'interface épaisse et dans le volume d'austénite. Le troisième chapitre porte sur l'étude d'un modèle de champ de phase. Une analyse approfondie des conditions à l'interface données par le modèle est réalisée en utilisant la technique des développements asymptotiques. En utilisant les connaissances fournies par cette analyse, le rôle de la mobilité intrinsèque d'interface sur la cinétique et les régimes de croissance est étudié, à la fois dans le cas simple d'alliages binaires Fe-C et dans le cas plus complexe d'alliages Fe-C-MnTransformation in steels focusing on the thermodynamic and kinetics conditions at the alpha/gamma interfaces during the ferrite growth. The first chapter deals with the determination of thermodynamic equilibria between alpha and gamma with CalPhad thermodynamic description. We have developed a new hybrid algorithm combining the construction of a convex hull to the more classical Newton-Raphson method to compute two phase equilibria in multicomponent alloys with two sublattices. Its capabilities are demonstrated on ternary Fe-C-Cr and quaternary Fe-C-Cr-Mo steels. In the second chapter, we present a thick interface model aiming to predict the whole spectrum of conditions at an alpha/gamma interface during ferrite growth, from full equilibrium to paraequilibrium with intermediate cases as the most interesting feature. The model, despite its numerous simplifying assumptions to facilitate its numerical implementation, allows to predict some peculiar kinetics in Fe-C-X systems with a minimum of fitting parameters, mainly the ratio between the diffusivities of the substitutional element inside the thick interface and in bulk austenite. The third chapter deals with the phase field model of austenite to ferrite transformation in steels. A thorough analysis on the conditions at the interface has been performed using the technique of matched asymptotic expansions. Special attention is given to clarify the role of the interface mobility on the growth regimes both in simple Fe-C alloys and in more complex Fe-C-Mn alloys
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Borges, Gomes Lima Yuri. "Μοdélisatiοn atοmistique de la transfοrmatiοn de phase austénite-ferrite dans les aciers". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMR086.
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Cette thèse applique l'approche des Quasiparticles (QA) pour étudier les mécanismes à l'échelle atomique qui conduisent à la transformation de phase CFC à CC dans le fer. Dans un premier temps, cette étude se concentre sur le fer pur, fournissant des résulats détaillés sur la nature et le rôle des dislocations à l'interface CFC-CC. Il a été montré que l'interface CFC-CC est semi-cohérente, avec des marches, et contient deux réseaux de dislocations de transformations. L'approche des Quasiparticles a permis de révéler l'influence de la relation d'orientation sur les caractéristiques de l'interface. Bien que les relations d'orientation étudiées ont montré diférentes structures d'interface, il a été démontré que toutes suivent le même chemin de transformation atomique, dû au glissement des dislocations de transformation à l'interface. Il a été conclu que la transformation complète de CFC à CC implique le mécanisme de transformation de Kurdjumov-Sachs (KS) en deux variantes le long des lignes de dislocations, avec le mécanisme de transformation de Kurdjumov-Sachs-Nishiyama (KSN) qui émerge comme la moyenne de l'action des deux mécanismes KS. Cette description détaillée a servi de base pour l'étude des systèmes Fe-C, où la ségrégation du carbone à l'interface a été observée. De plus, il a été montré que les profils de concentration de carbone sont cohérents avec des conditions d'équilibre local à l'interfaceThis thesis applies the Quasiparticle Approach (QA) to investigate the atomic scale mechanisms driving the phase transformation from FCC to BCC structures in iron. Initially, the study focuses on pure iron, providing detailed results into the nature and role of dislocations, at the FCC-BCC interface. It was shown that the FCC-BCC interface is semi-coherent and stepped, with two sets of transformations dislocations at the interface. The QA framework reveals how each orientation relationship (OR) influences the interface characteristics. Although the ORs displayed different interface structures, all were ultimately found to follow the same atomic transformation path, driven by the glide of transformation dislocations at the interface. It was concluded that the complete FCC to BCC phase transformation involves the action of the Kurdjumov-Sachs (KS) transformation mechanism in two variants along the two sets of dislocations, with the Kurdjumov-Sachs-Nishiyama (KSN) mechanism emerging as the average of the two KS mechanisms. This detailed description served as a basis for the study of Fe-C systems, where carbon segregation at the interface was observed. Moreover, it was shown that the carbon concentration profiles were consistent with local equilibrium conditions at the interface
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Muehlemann, Anton. "Variational models in martensitic phase transformations with applications to steels". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:bb7f4ff4-0911-4dad-bb23-ada904839d73.
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This thesis concerns the mathematical modelling of phase transformations with a special emphasis on martensitic phase transformations and their application to the modelling of steels. In Chapter 1, we develop a framework that determines the optimal transformation strain between any two Bravais lattices and use it to give a rigorous proof of a conjecture by E.C. Bain in 1924 on the optimality of the so-called Bain strain. In Chapter 2, we review the Ball-James model and related concepts. We present some simplification of existing results. In Chapter 3, we pose a conjecture for the explicit form of the quasiconvex hull of the three tetragonal wells, known as the three-well problem. We present a new approach to finding inner and outer bounds. In Chapter 4, we focus on highly compatible, so called self-accommodating, martensitic structures and present new results on their fine properties such as estimates on their minimum complexity and bounds on the relative proportion of each martensitic variant in them. In Chapter 5, we investigate the contrary situation when self-accommodating microstructures do not exist. We determine, whether in this situation, it is still energetically favourable to nucleate martensite within austenite. By constructing different types of inclusions, we find that the optimal shape of an inclusion is flat and thin which is in agreement with experimental observation. In Chapter 6, we introduce a mechanism that identifies transformation strains with orientation relationships. This mechanism allows us to develop a simpler, strain-based approach to phase transformation models in steels. One novelty of this approach is the derivation of an explicit dependence of the orientation relationships on the ratio of tetragonality of the product phase. In Chapter 7, we establish a correspondence between common phenomenological models for steels and the Ball-James model. This correspondence is then used to develop a new theory for the (5 5 7) lath transformation in low-carbon steels. Compared to existing theories, this new approach requires a significantly smaller number of input parameters. Furthermore, it predicts a microstructure morphology which differs from what is conventionally believed.
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Ruck, Johannes [Verfasser] y Thomas [Akademischer Betreuer] Böhlke. "Modeling martensitic phase transformation in dual phase steels based on a sharp interface theory / Johannes Ruck ; Betreuer: Thomas Böhlke". Karlsruhe : KIT Scientific Publishing, 2021. http://d-nb.info/1233429361/34.
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Proult, Anne. "Microstructure des phases de frank et kasper : interfaces, defauts et transformation vers un ordre quasiperiodique". Paris 11, 1996. http://www.theses.fr/1996PA112433.
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Ce travail concerne la microstructure des phases de frank-kasper, en particulier, les interfaces. Les proprietes de ces phases cristallines et leurs liens avec les quasicristaux sont rappeles dans le premier chapitre, ces deux types de structures possedant le meme ordre local icosaedrique ou derive de l'icosaedre. Le deuxieme chapitre est consacre aux interfaces entre phases de frank-kasper et cristal simple. Ce travail est preliminaire a l'etude des interfaces entre quasicristal et cristal simple. Il est montre que les approches traditionnelles des interfaces basees sur la comparaison de deux cristaux simples ne sont pas adaptees aux phases de frank-kasper. Une nouvelle approche geometrique est alors proposee. Sa validite est testee sur des interfaces entre precipites de phases de frank-kasper et des matrices simples etudiees par microscopie electronique. L'approche proposee rend bien compte des plans d'interfaces et des relations d'orientation observes. Le troisieme chapitre est consacre aux transformations des phases de frank-kasper (ici une isostructure de alpha-manganese) vers un ordre quasiperiodique et au role des defauts dans ces transformations. Une sequence continue de phases quasiperiodiques du systeme mgal dont l'originalite est de posseder une symetrie cubique est presentee. La derniere etape de cette sequence possede en outre la symetrie d'inflation en 2+3. La decouverte des phases cubiques quasiperiodiques est issue d'un travail preliminaire sur des particules d'une isostructure de alpha-manganese du systeme fecrmo dont les diagrammes de diffraction etaient globalement aperiodiques et cristallins a petite echelle. L'analyse de cette microstructure montre que la structure alpha-manganese peut generer une frustration geometrique pouvant conduire a l'apparition d'un ordre quasiperiodique dans un systeme de symetrie cubique. Ceci est en accord avec l'observation des phases quasiperiodiques dans le systeme mgal
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Dong, Liang. "Interface morphology and its stability in martensitic phase transformation of NiTi shape memory alloy /". View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?MECH%202008%20DONG.
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López, Gabriel Alejandro [Verfasser]. "Segregation and phase transformations at interfaces / Institut für Metallkunde der Universität Stuttgart ... Vorgelegt von Gabriel Alejandro López". Stuttgart : Max-Planck-Inst. für Metallforschung, 2004. http://d-nb.info/972137238/34.
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Bai, Xianming. "Thermodynamics and Kinetics of Phase Transitions during Supercooling and Superheating: A Theoretical and Computational Investigation in Model Lennard-Jones Systems". Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-11132006-110828/.
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Thesis (Ph. D.)--Materials Science and Engineering, Georgia Institute of Technology, 2007.Martha A. Gallivan, Committee Member ; Andrei G. Fedorov, Committee Member ; Christopher Summers, Committee Member ; Thomas H. Sanders, Jr., Committee Member ; Mo Li, Committee Chair.
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Quidort, David. "Mécanismes et modélisation des cinétiques de la transformation bainitique dans les aciers". Grenoble INPG, 1999. http://www.theses.fr/1999INPG0182.
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Avec les progres de la modelisation informatique, les siderurgistes ont commence a developper des modeles mathematiques dont l'objectif est de predire l'evolution microstructurale et les proprietes mecaniques finales des aciers en fonction du traitement thermomecanique. Le travail de cette these s'inscrit dans cet effort en ayant pour objet l'etude des cinetiques de la transformation bainitique qui reste a ce jour l'une des plus mal comprises des nombreuses transformations microstructurales dans les aciers. L'approche suivie est avant tout experimentale et laisse une large place a la technique de thermodilatometrie couplee a des analyses microstructurales a differentes echelles. Notre etude s'appuie principalement sur trois nuances d'aciers a 0,5%c dont une nuance au silicium qui permet d'obtenir une bainite sans cementite. L'etude de l'etape de croissance montre que, quel que soit le caractere diffusif ou displacif de la transformation austenite-ferrite, c'est la diffusion du carbone dans l'austenite qui est le facteur limitant. Le modele propose permet decrire convenablement l'effet de la temperature et de la teneur en carbone de l'alliage sur les cinetiques. Nous montrons que le silicium ralentit la croissance en inhibant la precipitation de cementite qui accompagne generalement la transformation. L'effet propre du nickel est mis en evidence et est discute sur la base des modeles de solute-drag que nous avons adapte aux transformations allotropiques. Les vitesses de germination sont deduites pour l'acier industriel xc50 des cinetiques globales et du modele de croissance. Il apparait que c'est la diffusion du carbone dans les joints de grains austenitiques qui controle la dependance en temperature du taux de germination. A partir des equations obtenues pour la croissance et la germination, nous proposons un modele des cinetiques globales en conditions isothermes et en refroidissement continu, ainsi qu'un critere de declenchement de la transformation.
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Platt, Philip Michael. "Mechanical degradation in oxides formed on zirconium alloys". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/mechanical-degradation-in-oxides-formed-on-zirconium-alloys(290e5b3b-a07b-404f-9eca-a5301c472dab).html.
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The present work has been produced as part of an on-going collaboration between the University of Manchester and Amec, with the primary aim of furthering mechanistic understanding of corrosion processes in zirconium alloys out-of-reactor. Zirconium alloys are used as cladding material for nuclear fuel pellets, and correct understanding of the corrosion process in autoclave is essential to predicting material behaviour in-reactor. This EngD thesis is composed of five proposed papers that investigate observations and hypotheses under the theme of mechanical degradation in oxides formed on zirconium alloys in autoclave. First investigations concern observed stress relaxation in zirconium oxide. Finite element analysis is used to capture mechanical aspects of the corrosion process and apply this to stress behaviour determined previously using synchrotron x-ray diffraction. The results indicate that a mechanism other than creep or hydrogen induced lattice strain must be present to account for the observed stress relaxation. One such potential mechanism is crack formation; statistical analysis of scanning electron microscopy images has been used to identify a link between the development of roughness at the metal-oxide interface, crack formation in the oxide and transition points or acceleration in the corrosion kinetics. Parameters such as the median radius of curvature and profile slope (Rdq) have been applied, as these parameters do not require the definition of a periodic wavelength or amplitude. These and other parameters are related to information in literature to indicate that for samples of Zircaloy-4 and ZIRLOTM, which go through transition, the interface roughness changes in a way that would increase localised stress concentrations. The third material is an experimental low tin alloy, which under the same oxidation conditions, and during the same time period, does not appear to go through transition and does not develop an interface roughness in the same way. A critical assessment of finite element analysis applied to oxidising non-planar interfaces shows the significant limitations in the existing mechanism for representing oxidation expansion and stress formation. Autoclave oxidation experiments of artificially roughened samples of Zircaloy-4 were carried out to further understand the impact of out-of-plane stress generation. The results indicate a divergence based on surface roughness after ~86 days oxidation. SEM examination of images in cross section highlighted accelerated oxidation above surface roughness peaks, and an increased crack area in rougher samples. Finally, finite element analysis of the tetragonal to monoclinic phase transformation showed that biaxial compressive stress relaxation, or the tri-axial tensile stress associated with an advancing crack tip, could reduce the transformation strain energy and destabilise the tetragonal phase. The volumetric expansion and shear strain associated with the phase transformation produces stress in the surrounding oxide sufficient to generate nano-scale cracks perpendicular to the metal-oxide interface. This would allow fast ingress routes for oxygen containing species, and therefore acceleration in the corrosion kinetics.
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Liu, Jing. "Mechanisms of lifetime improvement in Thermal Barrier Coatings with Hf and/or Y modification of CMSX-4 superalloy substrates". Doctoral diss., University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3423.
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In modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime of TBCs was measured using a furnace thermal cycle test that consisted of 10-minute heat-up, 50-minute dwell at 1135C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over 3200 cycles with appropriated Hf- and/or Y alloying of CMSX-4 superalloys. This significant improvement in TBC lifetime is the highest reported lifetime in literature with similar testing parameters. Beneficial role of reactive element (RE) on the durability of TBCS were systematically investigated in this study. Photostimulated luminescence spectroscopy (PL) was employed to non-destructively measure the residual stress within the TGO scale as a function of thermal cycling. Extensive microstructural analysis with emphasis on the YSZ/TGO interface, TGO scale, TGO/bond coat interface was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning electron microscopy (STEM) as a funcion of thermal cycling including after the spallation failure. Focused ion beam in-situ lift-out (FIB-INLO) technique was employed to prepare site-specific TEM specimens. X-ray diffraction (XRD) and secondary ion mass spectroscopy (SIMS) were also employed for phase identification and interfacial chemical analysis. While undulation of TGO/bond coat interface (e.g., rumpling and ratcheting) was observed to be the main mechanism of degradation for the TBCs on baseline CMSX-4, the same interface remained relatively flat (e.g., suppressed rumpling and ratcheting) for durable TBCs on Hf- and/or Y-modified CMSX-4. The fracture paths changed from the YSZ/TGO interface to the TGO/bond coat interface when rumpling was suppressed. The geometrical incompatibility between the undulated TGO and EB-PVD YSZ lead to the failure at the YSZ/TGO interface for TBCs with baseline CMSX-4. The magnitude of copressive residual stress within the TGO scale measured by PL gradually decreased as a function of thermal cycling for TBCs with baseline CMSX-4 superalloy substrates. This gradual decrease corrsponds well to the undulation of the TGO scale that may lead to relaxation of the compressive residual stress within the TGO scale. For TBCs with Hf- and/or Y-modified CMSX-4 superalloy substrates, the magnitude of compressive residual stress within the TGO scale remained relatively constant throughout the thermal cycling, although PL corresponding to the stress-relief caused by localized cracks at the TGO/bond coat interface and within the TGO scale was observed frequently starting 50% of lifetime. A slightly smaller parabolic growth constant and grain size of the TGO scale was observed for TBCs with Hf- and/or Y- modified CMSX-4. Small monoclinic HfO2 precipitates were observed to decorate grain boundaries and the triple pointes within the alpha-Al2O3 scale for TBCs with Hf- and/or Y-modified CMSX-4 substrates. Segregation of Hf/Hf4+ at the TGO/bond coat interfaces was also observed for TBCs with Hf- and/or Y-modified CMSX-4 superalloys substrates. Adherent and pore-free YSZ/TGO interface was observed for TBCs with Hf- and/or Y-modified CMSX-4, while a significant amount of decohesion at the YSZ/TGO interface was observed for TBCs with baseline CMSX-4. The beta-NiAl(B2) phase in the (Ni,Pt)Al bond coat was observed to partially transform into gama prime-Ni3Al (L12) phase due to depletion of Al in the bond coat during oxidation. More importantly, the remaining beta-NiAl phase transformed into L10 martensitic phase upon cooling even though there was no significant difference in these phase transformations for all TBCs. Results from these microstructural observations are documented to elucidate mechanisms that suppress the rumpling of the TGO/bond coat interface, which is responsible for superior performance of EB-PVD TBCs with (Ni,Pt)Al bond coat and Hf- and/or Y-modified CMXS-4 superalloy.Ph.D.
Department of Mechanical, Materials and Aerospace Engineering
Engineering and Computer Science
Materials Science & Engr PhD
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Restrepo, Lopez Ricardo. "Topics in spatial and dynamical phase transitions of interacting particle systems". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/42729.
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In this work we provide several improvements in the study of phase transitions
of interacting particle systems:
- We determine a quantitative relation between non-extremality of the limiting Gibbs measure of a tree-based spin system, and the temporal mixing of
the Glauber Dynamics over its finite projections. We define the concept of 'sensitivity' of a reconstruction scheme to establish such a relation. In particular, we focus on the independent sets model, determining a phase
transition for the mixing time of the Glauber dynamics at the same location of
the extremality threshold of the simple invariant Gibbs version of the model.
- We develop the technical analysis of the so-called spatial mixing conditions for interacting particle systems to account for the connectivity structure of the underlying graph. This analysis leads to improvements regarding the location of the uniqueness/non-uniqueness phase transition for the independent sets model over amenable graphs; among them, the elusive hard-square model in lattice statistics, which has received attention since Baxter's solution of the analogous hard-hexagon in 1980.
- We build on the work of Montanari and Gerschenfeld to determine the existence of correlations for the coloring model in sparse random graphs. In particular, we prove that correlations exist above the 'clustering' threshold of such a model; thus providing further evidence for the conjectural algorithmic 'hardness' occurring at such a point.
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Jaouen, Christiane. "Etude des mécanismes des transformations de phase induites par irradiation aux ions dans les systèmes métalliques". Poitiers, 1987. http://www.theses.fr/1987POIT2019.
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Etude par mesure de conductivite electrique, par retrodiffusion rutherford et par microscopie ionique en transmission des differents aspects du melange ionique dans le systeme mt/al (mt=fe, co, ni) et fe-mg. Analyse des differents facteurs controlant la formation d'une phase et celle d'une phase amorphe. Analyse des mecanismes de transformation cristal-amorphe de l'alliage ni::(50)al::(50) en couche mince. Influence des parametres d'irradation sur cette transformation
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Pugh, Peter Rupert Thomas. "Brillouin Light Scattering studies of magnetic thin films and multilayers". Thesis, University of Salford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365952.
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Bos, Cornelis. "Atomistic simulation of interface controlled solid state phase transformations". [S.l. : s.n.], 2005. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-25279.
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Bo, Arixin. "Investigation of the mechanical and electron interaction properties of layered titanate nanowires". Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/105649/4/Arixin_Bo_Thesis.pdf.
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This project reports first-hand knowledge on the mechanical and electron interaction properties of titanate nanowires which possess a broad range of applications. Using experimental techniques, the mechanical bending and tensile behaviours of individual nanowires are analysed from which a time-dependant recovery and an atypical reversible defect motion of the nanowires are observed. Applying electron beam irradiation, joint formation between two titanate nanostructures is demonstrated with the underlying mechanisms explained. The electron-titanate interaction phenomenon is also shown to be a practical tool for tailoring structures at nanoscale.
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Hennessy, Matthew Gregory. "Mathematical problems relating to the fabrication of organic photovoltaic devices". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:7753abec-bb6e-4d8a-aa5b-b527c5beb49b.
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The photoactive component of a polymeric organic solar cell can be produced by drying a mixture consisting of a volatile solvent and non-volatile polymers. As the solvent evaporates, the polymers demix and self-assemble into microscale structures, the morphology of which plays a pivotal role in determining the efficiency of the resulting device. Thus, a detailed understanding of the physical mechanisms that drive and influence structure formation in evaporating solvent-polymer mixtures is of high scientific and industrial value. This thesis explores several problems that aim to produce novel insights into the dynamics of evaporating solvent-polymer mixtures. First, the role of compositional Marangoni instabilities in slowly evaporating binary mixtures is studied using the framework of linear stability theory. The analysis is non-trivial because evaporative mass loss naturally leads to a time-dependent base state. In the limit of slow evaporation compared to diffusion, a separation of time scales emerges in the linear stability problem, allowing asymptotic methods to be applied. In particular, an asymptotic solution to linear stability problems that have slowly evolving base states is derived. Using this solution, regions of parameter space where an oscillatory instability occurs are identified and used to formulate appropriate conditions for observing this phenomenon in future experiments. The second topic of this thesis is the use of multiphase fluid models to study the dynamics of evaporating solvent-polymer mixtures. A two-phase model is used to assess the role of compositional buoyancy and to examine the formation of a polymer-rich skin at the free surface. Then, a three-phase model is used to conduct a preliminary investigation of the link between evaporation and phase separation. Finally, this thesis explores the dynamics of a binary mixture that is confined between two horizontal walls using a diffusive phase-field model and its sharp-interface and thin-film approximations. We first determine the conditions under which a homogeneous mixture undergoes phase separation to form a metastable bilayer. We then present a novel mechanism for generating a repeating lateral sequence of alternating A-rich and B-rich domains from this bilayer.
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Nikas, Yvonne Jiang. "Topics in phase transitions at interfaces". Connect to resource, 1989. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1232732921.
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Squarcini, Alessio. "Phase Separation and Interfaces. Exact Results". Doctoral thesis, SISSA, 2015. http://hdl.handle.net/20.500.11767/4900.
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We will devote Chapter 1 to a short review of traditional approaches to interfacial phenomena. This starts with an overview on phenomenological descriptions and terminates with a discussion on mean field theories of interfaces. In Chapter 2 we recall some essential notions of scattering theory in two dimensions on which we will rely in the rest of the thesis. In Chapter 3 we will pose the basis of the exact field-theoretic approach to phase separation in two dimensions. In particular, we will develop the formalism for the study of interfaces in a strip geometry. Drops on a flat substrate and the corresponding wetting transition will be discussed in Chapter 4. In Chapter 5 we will analyze phase separation in presence of a wedge-shaped substrate and its field-theoretical implications.
The exposition will cover phase separation both with and without the occurrence of intermediate phases. These two regimes will be discussed in detail for the strip, half-plane and wedge geometries. Our study is based on universal properties of the scaling limit and accounts exactly for the properties of the different universality classes.
The field-theoretical approach to near-critical behavior does not exhaust its applications to interfacial phenomena. We will conclude in Chapter 6 with a further application in which we will consider the thermal Casimir e↵ect, i.e. the analogue of the quantum Casimir e↵ect for statistical systems near criticality. We will show how bulk and boundary e↵ects, jointly with the symmetry of boundary conditions, play a role in the determination of the long-distance decay of the Casimir force.
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Kempen, Antoine. "Solid state phase transformation kinetics". [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=964251191.
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Kempen, Antonius Theodorus Wilhelmus. "Solid state phase transformation kinetics". Stuttgart : Max-Planck-Institut für Metallforschung, 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9795832.
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Dolby, Paul. "Phase coherent transport at normal-superconductor interfaces". Thesis, Lancaster University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414944.
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Agrawal, Vaibhav. "Multiscale Phase-field Model for Phase Transformation and Fracture". Research Showcase @ CMU, 2016. http://repository.cmu.edu/dissertations/850.
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We address two problems in this thesis. First, a phase-field model for structural phase transformations in solids and second, a model for dynamic fracture. The existing approaches for both phase transformations and fracture can be grouped into two categories. Sharp-interface models, where interfaces are singular surfaces; and regularized-interface models, such as phase-field models, where interfaces are smeared out. The former are challenging for numerical solutions because the interfaces or crack needs to be explicitly tracked, but have the advantage that the kinetics of existing interfaces or cracks and the nucleation of new interfaces can be transparently and precisely prescribed. The diffused interface models such as phasefield models do not require explicit tracking of interfaces and makes them computationally attractive. However, the specification of kinetics and nucleation is both restrictive and extremely opaque in such models. This prevents straightforward calibration of phase-field models to experiment and/or molecular simulations, and breaks the multiscale hierarchy of passing information from atomic to continuum. Consequently, phase-field models cannot be confidently used in dynamic settings. We present a model which has all the advantages of existing phase-field models but also allows us to prescribe kinetics and nucleation criteria. We present a number of examples to characterize and demonstrate the features of the model. We also extend it to the case of multiple phases where preserving kinetics of each kind of interface is more complex. We use the phase transformation model with certain changes to model dynamic fracture. We achieve the advantage of prescribing nucleation and kinetics independent of each other. We demonstrate examples of anisotropic crack propagation and crack propagation on an interface in a composite material. We also report some limitations of phase-field models for fracture which have not been mentioned in the existing literature. These limitations include dependence of effective crack width and hence the effective surface energy on the crack speed, lack of a reasonable approximation for the mechanical response of cracked region and inability to model large deformations.
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Beck, Markus. "Boron in Palladium: interaction, phase formation and phase transformation". [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9556602.
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Coppari, Gian Marco. "Decomposizione spinodale: analisi del processo e simulazione numerica". Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21631/.
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Il seguente elaborato di tesi è rivolto a dare una descrizione del tutto generale al fenomeno della decomposizione spinodale sulla base dei meccanismi microscopici della diffusione. Attraverso una opportuna correzione della equazione di diffusione di Fick è stata ricavata l'equazione di Cahn-Hilliard, che permette la descrizione corretta del fenomeno diffusivo. Il processo di deduzione dell'equazione passa per la determinazione del profilo di concentrazione all'interfaccia di due fasi come strumento di minimizzazione dell'energia interna del sistema e quindi come procedimento per raggiungere una condizione di equilibrio termodinamico. La soluzione del problema bidimensionale è stata graficata numericamente con un codice in ambiente MATLAB, da cui sono stati ricavati dati a supporto dei risultati teorici dedotti.
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Lei, Siu Long. "Phase-field simulations of two-phase flows /". View abstract or full-text, 2009. http://library.ust.hk/cgi/db/thesis.pl?MATH%202009%20LEI.
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Graham, John Samuel. "Electrical phenomena at interfaces in liquid phase reprographics". Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261192.
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MELO, JOSE RONALDO CHAVES DE. "NUMERICAL SIMULATION OF TWO-PHASE FLOW WITH INTERFACES". PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1995. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=18967@1.
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Este trabalho apresenta um método numérico para solução de escoamentos bidimensionais de fluidos incompressíveis e imiscíveis com presença de interfaces. As equações de conservação são discretizadas através do método de volumes finitos. A modelagem de interface se baseia no método VOF, em que a quantidade relativa de um dos fluidos em cada volume de volume de controle é descrita por uma variável, aqui denominada saturação. Conhecida a distribuição desta variável, é possível a reconstrução da interface quando necessário.
A principal particularidade do presente trabalho é que a reconstrução da interface leva em conta seu ângulo de inclinação dentro de cada volume de controle. Isto permite que a advecção da interface se realize com maior precisão do que normalmente se encontra nos trabalhos desenvolvidos a partir do método VOF. Este ângulo de inclinação é obtido partir das saturações da célula analisada e das duas células vizinhas também cortadas pela interface. A determinação da curvatura da interface, importante para o cálculo da pressão capilar, também é facilitada a partir do presente esquema. Domínios axisimétricos, onde os volumes de controle apresentam geometrias mais complexas, também são bem resolvidos, utilizando-se um tratamento especial para os volumes de controle junto ao eixo. Prevê-se ainda a especificação do ângulo de contato da interface com uma parede sólida.
Foram testados com sucesso vários problemas, apresentando bons resultados e garantindo a validação do método.The present work presents a numerical method for the solution of two-dimensional flows of incompressible and immicible fluids in the presence of na interface. The conservation equations are discretized by the finite volume method. The interface modeling is based on the VOF method, in which the relative amount of the fluids in each control volume is described by a variable, denominated here as saturation. Once the distribution of this quantity is known, it is possible to construct the interface, when needed. The main contribution of this work is related to the reconstruction of the interface. For that purpose, it is taken into account the interface angle of inclination inside the control volume. This allows a more precise interface advection that it is usually found with the algorithms based on the VOF method. The interface angle inside a cell is obtained based on its saturation ando n the saturationof two adjacentcells crossed by the interface. By the presents scheme, the interface curvature needed to calculate the capillary pressure can then be easily obtained. Axi-symmetric domains were also considered. For these cases, an special treatment near the axis was necessary. Finally, the algorithm allows the specification of the interface contact angle with a solid surface. Several test problems were examined, presenting good results, validating the method.
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Fischer, Hélène. "Élaboration et propriétés physiques de supperréseaux à base de manganèse". Nancy 1, 1995. http://www.theses.fr/1995NAN10011.
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Des superréseaux Mn/Ir (111), Mn/Ir (100) et Fex Mn1-x/Ir (100) avec 0,3 0,8 ont été élaborés par e. J. M. La structure de Mn est cubique à faces centrées déformée trigonalement dans Mn/Ir (111), et tétragonalement dans Mn/Ir (100). Dans les deux cas, le comportement de Mn est soit paramagnétique de Pauli, soit antiferromagnétique de Tn supérieure à 400 k. Par ailleurs, l'épitaxie de l'alliage Fe-Mn est pseudomorphe avec une nucléation 2d sur 9 plans à 100°C. Cet alliage épitaxie est tétragonal centre ; il présente une transition magnéto-structurale pour X = 0,5. Son comportement est ferromagnétique lorsque le fer est majoritaire, alors que l'alliage massif correspondant est antiferromagnétique. Lorsque le manganèse est majoritaire, l'alliage épitaxie est antiferromagnétique. L’utilisation systématique du rayonnement synchrotron a permis de proposer une technique nouvelle d'étude des défauts dans les superréseaux métalliques par diffusion diffuse de rayons X. Cette méthode consiste en la mesure de l'intensité réfléchie par l'échantillon en dehors des pics de Bragg du cristal. Une analyse systématique permet alors de caractériser les interfaces par des longueurs de corrélation des défauts ou des interfaces dans le plan des interfaces et dans la direction de croissance. Ces longueurs sont reliées à la nature des défauts étudiés. Rugosité et interdiffusion d'interfaces peuvent alors être pleinement distinguées. Tous les résultats obtenus ont été confirmés par microscopie électronique à transmission en section transverse
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Gueu, Solagon. "Analyse expérimentale de la dynamique de l'interface d'un film annulaire vertical soumis ou non à un écoulement de gaz à contre courant". Vandoeuvre-les-Nancy, INPL, 1996. http://www.theses.fr/1996INPL081N.
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L’epaisseur instantanée d'un film annulaire soumis ou non à un écoulement de gaz est analysée grâce à des méthodes statistiques, à la théorie du chaos et à l'aide de la transformée en ondelettes. Ces méthodes appliquées aux mesures, réalisées à l'aide de sondes conductimétriques à fils parallèles en 5 positions de la section d'essai de 40,6 mm de diamètre et de 2,2 m de longueur, ont permis d'obtenir de nombreux résultats sur l'évolution longitudinale et la dynamique du film. Citons : * l'existence d'un nombre de Reynolds de liquide global critique, situé autour de 3000. Le comportement en moyenne et dynamique du film est bien distinct en deca et au delà de cette limite. Par exemple : - l'amplification des vagues et l'augmentation de l'épaisseur du film et de la célérité moyenne moins fortes dans la première zone. - l'épaisseur du substrat et la fréquence prépondérante qui sont quasi constantes quand le nombre de Reynolds global est supérieur à 3000. - la dimension de corrélation qui est quasi indépendante du débit de liquide quand l'écoulement est turbulent (Re_L > 3000) alors que dans la zone laminaire, son évolution est fonction de la distance. * la dépendance de la structure de l'interface du film en fonction de la distance. Par exemple, quand la distance augmente, l'amplitude et la célérité des vagues croissent alors que la fréquence prépondérante et la dimension fractale diminuent. * la célérité des vagues indépendante de la fréquence. * une relation linéaire entre la célérité moyenne et l'amplitude maximale des vagues. * l'influence de l'interaction liquide-gaz diminue quand le débit de liquide augmente. La célérité des vagues et la dimension fractale chutent à l'approche du point de flooding. * une possibilité de filtrage des signaux par la transformée en ondelettes.
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Alps, Mike. "The phase transformation friction angle of sand". abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1442864.
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Huan, C. H. A. "Phase transformation and nuclear resonance in acoustics". Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379905.
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Al, Yasari Ammar Azeez Mahdi. "Phase Transformation in the Aluminum/Tungsten System". Wright State University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=wright1628683858642303.
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Mohapatra, Goutam. "Phase transformation kinetics the role of stress /". [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-28837.
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Maeda, Nobuo y nobuo@engineering ucsb edu. "Phase Transitions of Long-Chain N-Alkanes at Interfaces". The Australian National University. Research School of Physical Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20011203.151921.
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An experimental study of phase transitions of long-chain n-alkanes induced by the effect of interfaces is described.
¶
The phase behaviour of long-chain n-alkanes (carbon number 14, 16, 17, 18) adsorbed at isolated mica surfaces and confined between two mica surfaces has been studied in the vicinity of and down to several degrees below the bulk melting points, Tm. Using the Surface Force Apparatus we have measured the thickness of alkane films adsorbed from vapour (0.97 [equal to or greater-than] p/p[subscript o] [equal to or greater-than] 0.997), studied capillary condensation transition, subsequent growth of capillary condensates between two surfaces, and phase transitions in both the adsorbed films and the condensates. By measuring the growth rate of the capillary condensates we have identified a transition in the lateral mobility of molecules in the adsorbed films on isolated mica surfaces. This transition to greater mobility occurs slightly above Tm for n-hexadecane, n-heptadecane and n-octadecane but several degrees below Tm for n-tetradecane, and is accompanied by a change in wetting behaviour and a measurable decrease in adsorbed film thickness for n-heptadecane and n-octadecane. Capillary condensates that form below Tm remain liquid, but may freeze if the degree of confinement is reduced by separation of the mica surfaces. An increase in the area of the liquid-vapour interface relative to that of the liquid-mica interface facilitates freezing in the case of the long-chain alkanes, which show surface freezing at the liquid-vapour interface.
¶
Although thermodynamic properties of the surface freezing transition have been rather well documented, the kinetics involved in formation of such ordered monolayers has so far received very little attention. We studied the surface tension of n-octadecane as a function of temperature in the vicinity of Tm, using the static Wilhelmy plate and the dynamic maximum bubble pressure methods. The two methods give different results on cooling paths, where nucleation of the surface ordered phase is involved, but agree on heating paths, where both methods measure properties of the equilibrium surface phase. On cooling paths, the surface of bubbles may supercool below the equilibrium surface freezing temperature. The onset of surface freezing is marked by a sharp drop in the surface tension. The transition is accompanied by an increased stability of the films resulting in longer bubble lifetimes at the liquid surface, which suggests that the mechanical properties of the surfaces change from liquid-like to solid-like. Our results suggest occurrence of supercooling of the monolayer itself.
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Osborn, William R. "Statics and dynamics of interfaces in multi-phase fluids". Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318759.
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Maeda, Nobuo. "Phase transitions of long-chain n-alkanes at interfaces". View thesis entry in Australian Digital Theses Program, 2001. http://thesis.anu.edu.au/public/adt-ANU20011203.151921/index.html.
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Ou, Jifei. "Material transformation designing shape changing interfaces enabled by programmable material anisotropy". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91304.
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Thesis: S.M., Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2014.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 91-93).
This thesis takes a material perspective on designing transformable interfaces. The structure of material and mechanical properties such as stiffness, can determine not only its static performances, but also, with the help of external forces, support dynamic shape change. By encoding structural or stiffness distribution in the actuated materials, we can partially offload the shape-changing control from actuators (digital) to the material itself (analogue), in order to achieve expressive transformations that current modularized actuation system cannot easily provide. The implementation of this thesis will be three series of material primitives and three application prototypes that demonstrate the real world potential of this research.
by Jifei Ou.
S.M.
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O'Hare, Kieran D. "Mass transfer at a two-phase interface". Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317126.
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Jamie, Elizabeth A. G. "Colloidal interfaces in confinement". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:26b47a79-7198-4983-9109-174ac2d3e01d.
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A fluid-fluid demixing colloid-polymer system provides us with an opportunity to study interfacial phenomena that cannot be observed in molecular systems due to unfavourable length and timescales. We develop such a system compatible with cells of varying dimensions, allowing us to investigate confined interfacial behaviour in real space using Confocal Scanning Laser Microscopy. The degree to which a system is affected by the sedimentation-diffusion gradient is dependent on the ratio of the suspension height to the gravitational length of the colloids. We illustrate that we may control the distance of our interface to the critical point by altering the suspension height, determining the importance of the gravitational field. Furthermore, the timescale on which the sedimentation- diffusion gradient is established is considerably longer than that of initial fluid-fluid demixing. We show that after the formation of the macroscopic interface, the system passes through a series of local mechanical equilibria on the way to achieving full equilibrium. Should the system be of sufficient height, it will pass through the gas-liquid critical point opening up new ways to study critical phenomena. The time and length scales of the fluid-fluid demixing of our system may be manipulated by altering the density and viscosity of our solvent. We exploit a slowed phase separation process to study the interplay between demixing and wetting phenomena of systems in the vicinity of a single wetting surface, and confined between two parallel plates. We demonstrate that the presence of a surface strongly affects the morphology of phase separation. The growth of the wetting layer is determined by the demixing regime of the system, and may be accelerated by hydrodynamics. The additional restriction by a second surface limits the lengthscale of coarsening domains and may further alter the mechanism of wetting layer growth.
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Poter, Simon Christopher. "Fluid phase coexistence by molecular simulation". Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242790.
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Bittner, Florian. "Untersuchung der Wechselwirkung von Verarbeitung, Gefüge und Eigenschaften hartmagnetischer Mn-Al-Legierungen mit L1 0-Struktur". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2018. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-231582.
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Die vorliegende Arbeit behandelt die Wechselwirkung von Verarbeitung und Gefüge Mn-Al basierter hartmagnetischer Werkstoffe sowie die Auswirkung des Gefüges auf deren Eigenschaften. Dabei wurde das Gefüge der metastabilen tau-Phase im Anschluss an die Phasenbildung aus der Hochtemperaturphase epsilon-MnAl und die Auswirkung einer anschließenden Umformung untersucht. Der Schwerpunkt der Arbeit lag in der Analyse der Evolution verschiedener Gefügebestandteile, wie Grenzflächenverteilung, Versetzungen und Korngröße unter Verwendung von Rasterelektronenmikroskopie und Elektronenrückstreubeugung.
Die epsilon-tau Umwandlung kann auf 2 verschiedene Routen erfolgen. In beiden Fällen wird die Bildung von 3 kristallographisch unterschiedlichen zwillingsähnlichen Defekten beobachtet, die als wahre Zwillinge, Ordnungszwillinge und Pseudozwillinge bezeichnet werden. Sie lassen sich als Rotationen um einen kristallographischen {111}-Pol beschreiben. Der Anteil der Zwillingsdefekte nach der Umwandlung, aber auch die Korngröße und Versetzungsdichte sind von der gewählten Umwandlungsroute abhängig. Während die Sättigungspolarisation annähernd gleich ist, reagiert die Koerzitivfeldstärke sensitiv auf den Gefügezustand. Eine niedrige Korngröße und hohe Versetzungsdichte tragen zu ihrer Erhöhung bei.
Eine anschließende Kaltumformung erzeugt ein vielfach verzwillingtes Verformungsgefüge mit hoher Koerzitivfeldstärke. Wärmebehandlungen und die Analyse der Schärfe von Kikuchi-Beugungsbildern haben gezeigt, dass nicht die hohe Zwillingsdichte, sondern primär Versetzungen im Verformungsgefüge die Koerzitivfeldstärke steigern. Warmumformung von tau-MnAl führt zur dynamischen Rekristallisation. Die Kinetik der Gefügeneubildung und die resultierende Korngröße sind stark von der Umformtemperatur abhängig. Durch Umformung lässt sich eine kristallographische Texturierung von tau-MnAl erreichen. Die Orientierung der magnetisch leichten [001]-Richtung ist dabei vom gewählten Umformverfahren und gegebenenfalls von der Nachbehandlung abhängig. Statische und dynamische Rekristallisation reduzieren den Anteil der Zwillingsdefekte signifikant und besonders Pseudozwillinge und Ordnungszwillinge werden im Gefüge beseitigt. Das Rekristallisationsgefüge weist gegenüber dem Umwandlungsgefüge einen geringeren Widerstand gegen die mit der Zersetzungsreaktion verbundene Bildung von beta-Mn auf. Die Ursache liegt in einer selektiven beta-Mn-Bildung an allgemeinen Korngrenzen, während die Zwillingsdefekte einen erhöhten Widerstand gegen sie Zersetzung aufweisen.
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Devaraj, Arun. "Phase Separation and Second Phase Precipitation in Beta Titanium Alloys". Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc67975/.
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The current understanding of the atomic scale phenomenon associated with the influence of beta phase instabilities on the evolution of microstructure in titanium alloys is limited due to their complex nature. Such beta phase instabilities include phase separation and precipitation of nano-scale omega and alpha phases in the beta matrix. The initial part of the present study focuses on omega precipitation within the beta matrix of model binary titanium molybdenum (Ti-Mo) alloys. Direct atomic scale observation of pre-transition omega-like embryos in quenched alloys, using aberration-corrected high resolution scanning transmission electron microscopy and atom probe tomography (APT) was compared and contrasted with the results of first principles computations performed using the Vienna ab initio simulation package (VASP) to present a novel mechanism of these special class of phase transformation. Thereafter the beta phase separation and subsequent alpha phase nucleation in a Ti-Mo-Al ternary alloy was investigated by coupling in-situ high energy synchrotron x-ray diffraction with ex-situ characterization studies performed using aberration corrected transmission electron microscopy and APT to develop a deeper understanding of the mechanism of transformation. Subsequently the formation of the omega phase in the presence of simultaneous development of compositional phase separation within the beta matrix phase of a Ti-10V-6Cu (wt%) alloy during continuous cooling has been investigated using a combination of transmission electron microscopy and atom probe tomography. The results of these investigations provided novel insights into the mechanisms of solid-state transformations in metallic systems by capturing the earliest stages of nucleation at atomic to near atomic spatial and compositional resolution.
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Pederson, Robert. "Microstructure and phase transformation of Ti-6Al-4V". Licentiate thesis, Luleå, 2002. http://epubl.luth.se/1402-1757/2002/30.
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Hedström, Peter. "Deformation and martensitic phase transformation in stainless steels /". Luleå : Department of Applied Physics and Mechanical Engineering, Division of Engineeing Materials, Luleå University of Technology, 2007. http://epubl.ltu.se/1402-1544/2007/67/.
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