No description available.

No description available.

No description available.

Inspired by Poirier¡¦s mechanism of self-assembled monolayers (SAMs) formation, we realized that observation of the change of molecular orientation relative to the surface using a suitable spectroscopic method might be able to reveal the self ¡V assemblied processes. We mimicked the SAMs formation under UHV conditions, the Reflection Absorption Infrared Spectroscopy (RAIRS) and Temperature-Programmed Desorption / Reaction Spectrometry (TPD/R) were utilized to understand the adsorption, self-assembling and thermal stability after vapor desorption of 1H, 1H, 2H, 2H-perfluorodecanethiol on Cu(111). At 100K, the adsorption of 1H, 1H, 2H, 2H-perfluorodecanethiol was entirely molecular. As the surface was annealed above 220K, the cleavage of the S ¡V H bonds occurred to afford chemisorbed thiolates. By comparisons of spectra to the SAMs / Au(111) and the bulk compound, forming of an orderly and densely packed monolayer on Cu(111) was inferred. Focusing on room temperature deposition experiments, We found that the increase in ratios of I£h(CF2 ¡ü chain) (bands in 1300cm-1 ~ 1400 cm-1) to I£h(CF2 ¡æ chain) (bands in 1100cm-1 ~ 1300 cm-1) as a function of exposure implicates a transition from that the lying ¡V down geometry to the more upright orientation relative to the surface as we anticipated, the phase transformation concomitant with the SAMs formation could be identified by RAIRS. By TPD/R measurements, the molecular desorption occurred at 220K and 290K, corresponding to the condensed multilayer and a physisorbed layer on top of the chemisorbed monolayer, respectively. Furthermore, the monolayer would undergo the S ¡V C bond dissociation to sender surface ¡V bound semifluorinated alkyl groups and sulfur atoms. The semifluorinated decene and decane were evolved above 360K as results of £] ¡V hydride elimination and hydrogen addition.

The effects of intermetallic compound (IMC) formation on reliability of Pb-free Sn-based solders for flip chip and three-dimensional (3D) interconnects were studied. The dissertation is organized into four parts. In the first part, the effect of Sn grain orientation on electromigration (EM) reliability of Pb-free Sn-based flip chip solder joints was studied. The Sn grain microstructure in flip chip solder joints was characterized using the electron backscatter diffraction (EBSD) technique, and wa found to be closely related to the EM failure mechanims. The approach to grain structure optimization for improved EM reliability was also explored. In addition to the experimental work, a kinetic analysis was formulated to investigate the early EM degradation mechanism in Sn-based solder joints with Ni under-bump metallization (UMB). The aforementioned kinetic analysis, the intrinsic diffusion coefficients were not readily available in the literature. In the second part of the work, a Monte Carlo method known as simulated annealing was applied to estimate the unknown diffusion coefficients using a multi-parameter optimization method by fitting to experimental measurements. The intrinsic diffusion coefficients of Ni and Sn in Ni₃Sn₄ between 150 and 200°C, and those of Cu and Sn in Cu₃Sn and Cu₆Sn₅ between 120 and 200°C were estimatd. The activation energies for these diffusion coefficients were also determined. Together, this provides the diffusivity parameters to predict the intermetallic growth as a function of temperature. The third objective focused on the EM reliability of Sn-based microbump joints in 3D interconnects with through-silicon vias (TSVs). No EM-induced bump failure was observed, showing a robust EM reliability in microbumps. High temperature thermal annealing test was also performed on microbumps with three different metallizations in an effort to explore structural and process optimization. Finally, interfacial reaction induced stress in IMC microbumps was investigated. A numerial analysis was formulated to study the concurrent diffusion, phase transformation, and deformation in the process of IMC formation. Stress generation due to unbalanced diffusion rates and volumetric change upon phase transformation was considered. The coupled analysis was applied to investigate Ni₃Sn₄ growth in the Ni-Sn microbumping system. A simulation approach based on finite difference method with moving boundaries was employed to numerically solve stress evolution in Ni₃Sn₄. The equilibrium stress was also investigated using a modified model with a finite thickness of solder. Simulation predictions were found to be in good qualitative agreement with experimental observations. / text

Ti-Ni phase transformation behaviour is very sensitive to the thermal and mechanical history of the alloy. Thermomechanical cycling through the full transformation range may degrade the Ti-Ni functional properties (functional fatigue). These repeated transformation cycles cause changes in the SMA phase transformation behaviour due to the formation and accumulation of defects in the alloy microstructure. The main objective of this thesis is to establish the relationships between the changes in Ti-Ni phase transformation behaviour caused by thermomechanical processes, especially in the R-phase range, and the functional properties of the Ti-Ni shape memory alloys (SMAs). Establishing these relationships should allow us to find appropriate thermomechanical processes to substantially improve the Ti-Ni one-way and two-way shape memory effects. To achieve this objective, several experimental techniques are used including measuring variations of the electrical resistivity with temperature, X-ray diffraction, isothermal tension testing, thermal cycling under constant stress, and thermal cycling under zero stress. This study of the phase transformation changes caused by thermomechanical processes has led to a new way of interpreting resistivity curves for calculating the transformation temperatures. Moreover, we have determined how the R-phase influences the functional properties of SMA and, finally, we have substantially improved the properties of one-way and two-way shape memory effects by using thermal processes that avoid permanent deformation of the alloy. / Las transformaciones de fase en aleaciones de NiTi son altamente dependientes de la composición de la aleación, así como de la historia térmica y mecánica previa al uso de la SMA. El objetivo principal de esta tesis es establecer los vínculos existentes entre los cambios producidos en las transformaciones de fase por procesos termomecánicos y las propiedades funcionales en aleaciones con memoria de forma de Ti-Ni, tal que nos permita hallar los procesos termomecánicos más adecuados que proporcionen una mejora substancial en las propiedades funcionales de estas aleaciones. La determinación de estas relaciones, prestando especial atención a la fase-R, nos debe proporcionar las claves para incrementar las propiedades de memoria de forma y doble memoria de forma. Para la consecución de este objetivo se han usado diferentes técnicas de caracterización experimental: variación de la resistividad eléctrica con la temperatura (ER), difractometría de rayos X (DRX), ensayos de tracción isotérmicos, ciclados térmicos a tensión constante y ciclados térmicos a tensión nula. A través del estudio exhaustivo de las transformaciones de fase, se ha aportado una nueva interpretación de las curvas de resistividad para el cálculo de las temperaturas de transformación, se ha determinado la influencia de la fase-R en las propiedades funcionales de las SMA y se han mejorado substancialmente las propiedades de memoria simple y doble memoria de forma mediante procesos térmicos que evitan deformaciones permanentes antes del uso de la aleación. / Les transformacions de fase en aliatges de NiTi són altament dependents de la composició de l'aliatge, així com de la història tèrmica i mecànica prèvia a l'ús de la SMA. L'objectiu principal d'aquesta tesi és establir els vincles existents entre els canvis produïts en les transformacions de fase per processos termomecànics i les propietats funcionals en aliatges amb memòria de forma de Ti-Ni, tal que ens permeti trobar els processos termomecànics més adequats que proporcionin una millora substancial en les propietats funcionals d'aquests aliatges. La determinació d'aquestes relacions, prestant especial atenció a la fase-R, ens ha de proporcionar les claus per incrementar les propietats de memòria de forma i doble memòria de forma. Per a la consecució d'aquest objectiu s'han usat diferents tècniques de caracterització experimental: variació de la resistivitat elèctrica amb la temperatura (ER), difractometria de raigs X (DRX), assaigs de tracció isotèrmics, ciclats tèrmics a tensió constant i ciclats tèrmics a tensió nula. A través de l'estudi exhaustiu de les transformacions de fase, s'ha aportat una nova interpretació de les corbes de resistivitat per al càlcul de les temperatures de transformació, s'ha determinat la influència de la fase-R en les propietats funcionals de les SMA i s'han millorat substancialment les propietats de memòria simple i doble memòria de forma mitjançant processos tèrmics que eviten deformacions permanents abans de l'ús de l'aliatge.

The primary focus of this research is to investigate the non-linear behavior of single crystal and polycrystalline relaxor ferroelectric PMN-xPT and PZN-xPT through experimentation and modeling. Characterization of single crystal and polycrystalline specimens with similar compositions was performed. These data give experimental insight into the differences that may arise in a polycrystal due to local interaction with inhomogeneities. Single crystal specimens were characterized with a novel experimental technique that reduced clamping effects at the boundary and gave repeatable results. The measured experimental data was used in conjunction with electromechanical characterizations of other compositions of single crystal specimens with the same crystallographic orientation to study the compositional effects on material properties and phase transition behavior. Experimental characterization provided the basis for the development of a model of the continuous phase transformation behavior seen in PMN-xPT single crystals. In the modeling it is assumed that a spatial chemical and structural heterogeneity is primarily responsible for the gradual phase transformation behavior observed in relaxor ferroelectric materials. The results are used to simulate the effects of combined electrical and mechanical loading. An improved rate-independent micromechanical constitutive model based on the experimental observations of single crystal and polycrystalline specimens under large field loading is also presented. This model accounts for the non-linear evolution of variant volume fractions. The micromechanical model was calibrated using single crystal data. Simulations of the electromechanical behavior of polycrystalline ferroelectric materials are presented. These results illustrate the effects of non-linear single crystal behavior on the macroscopic constitutive behavior of polycrystals.

Actuellement le prix de l'énergie augmente continuellement. Ainsi, un des grands défis de la société est de limiter au maximum la consommation énergétique. La mise en oeuvre de matériaux pour l’énergie et le développement de leurs propriétés est au coeur de cette problématique.Dans cette optique, ce travail est dédié à l’évaluation d’un nouveau procédé de fabrication thermomagnétique dans le but de développer de nouvelles microstructures et/ou des propriétés améliorées inaccessibles par des traitements thermomécaniques classiques. L’objectif principal est d'étudier l'effet du champ magnétique sur deux principaux alliages, Fe-Co et Fe-Ni en vue d'améliorer leurs propriétés magnétiques douces.Dans les alliages Fe-Co, les températures de transformation de la ferrite vers l’austénite, mesurées jusqu’à16T, sont augmentées par l'application d'un champ magnétique intense. Ce décalage est modélisé en fonction du champ, en se basant sur une analyse thermodynamique. Dans les deux alliages, la phase ferritique eststabilisée par le champ intense à plus haute température ce qui permet le développement d’une microstructure àgros grains. Les propriétés magnétiques douces sont également améliorées par l'application d'un champ magnétique à la fois dans l’alliage Fe-Co27% et dans Fe-Co49%V2% en induisant respectivement le développement d’une texture Goss dans le premier alliage et une forte anisotropie induite dans le second.Dans les alliages Fe - Ni contenant 80% l'utilisation d’un champ magnétique intense pendant le traitement thermique (jusqu'à 7 T) permet d’améliorer le développement de l'anisotropie induite, permettant de« coucher » la forme du cycle d'hystérésis. Le comportement magnétique dynamique du matériau est ainsiamélioré par le champ magnétique.Ces résultats significatifs soutiennent l'idée que l'introduction du champ magnétique dans les techniques defabrication des matériaux conventionnels est une piste prometteuse pour améliorer d’avantage leurs propriétésfonctionnelles. / Energy is becoming increasingly expensive and a major challenge for the society is to minimize energyconsumption. One of the issues of this challenge focuses on the industrial processing of energy related materialand the development of their properties.The overall objective of this work is to evaluate thermo-magnetic processing as a new technology with thegoal of developing novel microstructures and/or improved properties unattainable through conventionalthermo-mechanical processing. This main target is addressed with the study of the effect of magnetic field ontwo main alloys, Fe-Co and Fe-Ni in view of improving their functional soft magnetic properties.In FeCo alloys the non – equilibrium ferrite to austenite phase transformation measured up to 16T is foundto be increased by the application of a high magnetic field. Its evolution with the field intensity is explainedusing a thermodynamic analysis. In both grades, the ferrite phase is found to be stabilized at higher temperaturetogether with a coarse grains microstructure during recrystallization and growth in high field. Soft magneticproperties are also improved by the application of a magnetic field both in the Fe-Co27% and Fe-Co49%-V2%alloys by a field induced Goss texture enhancement and an extended field induced anisotropy respectively.In the Fe – 80%Ni composition the use of high magnetic field during processing (up to 7T) is found toimprove the magnetic induced anisotropy and to tailor the hysteresis loop shape. The dynamic magneticbehavior is greatly improved by high field annealing.These significant results support the idea that introducing the magnetic field application into conventionalmaterials processing is a promising way to improve material properties.

Ceramics have been widely used for personnel and vehicle armour because of their desirable properties such as high hardness and low density. However the brittle nature associated with the ceramic materials, i.e. low toughness, reduces their ability to withstand multiple ballistic hits. The present work is focused on ceramic armour materials made from alumina and zirconia toughened alumina (ZTA). The effects of grain size and zirconia phase transformation toughening on the mechanical and high strain rate properties in both materials were investigated in detail. Alumina, 10%, 15% and 20% nano ZTA with 1.5 mol% yttria stabiliser were produced with various grain sizes. The processing of the materials started from suspension preparation, spray freeze drying of the suspension and die pressing to produce homogeneous green bodies with densities above 54%. Then, the green bodies were sintered using conventional single stage and/or two stage sintering to produce the samples with full density and a range of grain sizes (0.5 to 1.5 µm alumina grains and 60 to 300 nm zirconia grains). The effects of the processing conditions on the microstructures were studied and the optimum processing route for each sample was determined. The mechanical properties of the alumina and ZTA samples were investigated, including Vickers hardness, indentation toughness, 4-point bend strength and wear resistance. The results showed that, with an increasing amount of zirconia addition, evident increases of the toughness, strength and wear resistance properties were observed, whilst the hardness reduced slightly correspondingly. The effect of density and grain sizes on the hardness and toughness were studied as well: larger alumina grain size led to a higher hardness and negligible change in toughness, whilst the zirconia grain coarsening enhanced the phase transformation toughening effect and the samples displayed a higher toughness. In addition to the investigation of the mechanical properties, the alumina and nano ZTA samples were subjected to high strain rate testing, including split Hopkinson pressure bar (SHPB) (8-16 m/s) and gas gun impact testing (100-150 m/s). The high strain rate performances were compared in terms of their fracture behaviours, fragmentation process and fragment size distribution. Raman spectroscopy was used to measure the amount of zirconia phase transformation in ZTA samples after the high strain rate testing. The residual stress and dislocation density in alumina grains after testing were quantitatively measured using Cr3+ fluorescence spectroscopy. The results indicated that zirconia phase transformation can reduce the residual stress and dislocation densities in the ZTA samples, resulting in less damage, lower plastic deformation and less crack propagation. In addition, a nano zirconia material with 1.5 mol% yttria stabiliser (1.5YSZ) was subjected to a gas gun impact test with a very high impact speed (142 m/s); a deep projectile penetration was observed, due to the low hardness of the pure zirconia, whilst the sample stayed intact. The result further confirmed that the zirconia phase transformation toughening effect can improve the sample's high strain rate performance.

Des matériaux composites à matrice Al renforcée par des particules d'alliage ω-Al7Cu2Fe ont été synthétisés par frittage flash à partir de poudre icosaédrique i-Al-Cu-Fe et de poudre d'aluminium. La transformation de phase de i-Al-Cu-Fe en ω-Al-Cu-Fe est étudiée à partir d'analyses d'échantillons modèles à interface plane. Les résultats montrent que la transformation de phase s'accompagne de la formation d'une phase liquide et de l'apparition de composés AlCu et Al2Cu. Elle met en jeu la diffusion des trois éléments cuivre, aluminium et fer. Parallèlement, la matrice Al s'enrichit en cuivre. La microstructure complexe finale dépend de la porosité initiale. Les composites Al/ω-Al-Cu-Fe ont été déformés par compression à vitesse imposée, entre 273 et 823 K. L'évolution de la contrainte d'écoulement avec la température met en évidence deux régimes de déformation plastique. L'analyse microstructurale, par microscopie électronique en transmission, révèle la présence de précipités ϴ'-Al2Cu dans la matrice Al. L'évolution de cette microstructure avec la température est discutée conjointement à l'évolution de la contrainte d'écoulement. La déformation plastique du composite se situant essentiellement dans la matrice, une caractérisation locale des propriétés mécaniques de cette matrice a été réalisée par nano-indentation. Les courbes force-déplacement montrent des instabilités de déformation plastique. Les analyses chimiques locales mettent en évidence la corrélation entre hétérogénéités chimiques et instabilités mécaniques. Ces résultats sont analysés dans le cadre d'interactions entre dislocations et solutés mobiles. / Al/ω-Al7Cu2Fe composites were synthesized by spark plasma sintering from initial icosahedral Al-Cu-Fe and Al powders. The i- to ω-Al-Cu-Fe phase transformation is studied from model samples with planar Al/i-Al-Cu-Fe initial interface. The phase transformation occurs in solid and liquid states and reveals the presence of AlCu and Al2Cu intermediate phases. The phase transformation involves Cu, Fe and Al diffusion and the Al matrix is enriched in Cu. The initial porosities play a key role in the final complex microstructure.Compression tests were performed on Al/ω-Al7Cu2Fe composites at constant strain-rate in the temperature range 293-823 K. The evolution of the flow stress with temperature reveals two deformation regimes. The observations performed by transmission electron microscopy show that ϴ’-Al2Cu precipitation occurs in the Al matrix during the synthesis. The evolution of the matrix microstructure with temperature is analysed and discussed together with the evolution of the flow stress. As the plastic deformation takes place in the ductile Al matrix, local mechanical caracterisation is performed in the matrix using nano-indentation tests. The load-displacement curves show serrated behavior. Local chemical analyses demonstrate correlation between chemical heterogeneities and mechanical instabilities. These results are analysed in the frame of interactions between dislocations and mobile solutes.