Reducing the heat losses in heavy-duty diesel engines is of importance for improving engine efficiency and reducing CO2 emissions. Depositing thermal barrier coatings (TBCs) onto engine components has been demonstrated to have great potential to reduce heat loss from the combustion chamber as well as from exhaust components. The overall aim of this thesis is to evaluate the thermal cycling lifetime and thermal insulation properties of TBCs for the purpose of reducing heat losses and thermal fatigue in heavy-duty diesel engines. In the thermal cycling test inside exhaust manifolds, nanostructured yttria-stabilized zirconia (YSZ) performed best, followed by YSZ with conventional microstructure and then La2Zr2O7. Forsterite and mullite could not withstand the thermal cycling conditions and displayed large cracks or spallation. Two sol-gel composite coatings displayed promising thermal cycling performance results in a furnace test under similar conditions. Thermal cycling testing of YSZ coatings having different types of microstructure, in a furnace at temperatures up to 800°C, indicated that the type of microstructure exerted a great influence. For the atmospheric plasma sprayed coatings, a segmented microstructure resulted in the longest thermal cycling lifetime. An even longer lifetime was seen for a plasma spray–physical vapour deposition (PS-PVD) coating. In situ heat flux measurements inside the combustion chamber indicated that plasma-sprayed Gd2Zr2O7 was the TBC material providing the largest heat flux reduction. This is explained by a combination of low thermal conductivity and high reflectance. The plasma-sprayed YSZ and La2Zr2O7 coatings provided very small heat flux reductions. Long-term testing indicated a running-in behaviour of YSZ and Gd2Zr2O7, with a reduction in heat flux due to the growth of microcracks in YSZ and the growth of macrocracks in Gd2Zr2O7. / <p>QC 20170821</p>

No description available.

Polycrystalline NiTi shape memory alloys have the ability to recover their original, pre-deformed shape in the presence of external loads when heated through a solid-solid phase transformation from a lower-symmetry B19' martensite phase to a higher-symmetry B2 austenite phase. The strain associated with a shape memory alloy in an actuator application typically has thermal, elastic and inelastic contributions. The objective of this work was to investigate the aforementioned strains by recourse to in situ neutron diffraction experiments during selected combinations of heating, cooling and/or mechanical loading. The primary studies were conducted on polycrystalline Ni49.9Ti50.1 specimens on the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos National Laboratory. Quantitative information on the phase-specific strain, texture and phase fraction evolution was obtained from the neutron data using Rietveld refinement and single-peak analyses, and compared with macroscopic data from extensometry. First, the lattice strain evolution during heating and cooling in an unloaded sample (i.e., free-recovery experiment) was studied. The lattice strain evolution remained linear with temperature and was not influenced by intergranular stresses, enabling the determination of a thermal expansion tensor that quantified the associated anisotropy due to the symmetry of B19' NiTi. The tensor thus determined was subsequently used to obtain an average coefficient of thermal expansion that was consistent with macroscopic dilatometric measurements and a 30,000 grain polycrystalline self-consistent model. The accommodative nature of B19' NiTi was found to account for macroscopic shape changes lagging (with temperature) the start and finish of the transformation. Second, the elastic response of B19' martensitic NiTi variants during monotonic loading was studied. Emphasis was placed on capturing and quantifying the strain anisotropy which arises from the symmetry of monoclinic martensite and internal stresses resulting from intergranular constraints between individual variants and load re-distribution among variants as the texture evolved during variant reorientation and detwinning. The methodology adopted took into account both tensile and compressive loading given the asymmetric response in the texture evolution. Plane specific elastic moduli were determined from neutron measurements and compared with those determined using a self-consistent polycrystalline deformation model and from recently reported elastic stiffness constants determined via ab initio calculations. The comparison among the three approaches further helped understand the influence of elastic anisotropy, intergranular constraint, and texture evolution on the deformation behavior of polycrystalline B19' NiTi. Connections were additionally made between the assessed elastic properties of martensitic NiTi single crystals (i.e., the single crystal stiffness tensor) and the overall macroscopic response in bulk polycrystalline form. Lastly, the role of upper-cycle temperature, i.e., the maximum temperature reached during thermal cycling, was investigated during load-biased thermal cycling of NiTi shape memory alloys at selected combinations of stress and temperature. Results showed that the upper-cycle temperature, under isobaric conditions, significantly affected the amount of transformation strain and thus the work output available for actuation. With the objective of investigating the underlying microstructural and micromechanical changes due to the influence of the upper-cycle temperature, the texture evolution was systematically analyzed. While the changes in transformation strain were closely related to the evolution in texture of the room temperature martensite, retained martensite in the austenite state could additionally affect the transformation strain. Additionally, multiple thermal cycles were performed under load-biased conditions in both NiTi and NiTiPd alloys, to further assess and understand the role of retained martensite. Dimensional and thermal stabilities of these alloys were correlated with the volume fraction and texture of retained martensite, and the internal strain evolution in these alloys. The role of symmetry, i.e., B19' monoclinic martensite vs. B19 orthorhombic martensite in these alloys was also assessed. This work not only established a methodology to study the thermal and elastic properties of the low symmetry B19' monoclinic martensite, but also provided valuable insight into quantitative micromechanical and microstructural changes responsible for the thermomechanical response of NiTi shape memory alloys. It has immediate implications for optimizing shape memory behavior in the alloys investigated, with extension to high temperature shape memory alloys with ternary and quaternary elemental additions, such as Pd, Pt and Hf. This work was supported by funding from NASAÂ s Fundamental Aeronautics Program, Supersonics Project (NNX08AB51A) and NSF (CAREER DMR-0239512). It benefited additionally from the use of the Lujan Neutron Scattering Center at Los Alamos National Laboratory, which is funded by the Office of Basic Energy Sciences (Department of Energy) and is operated by Los Alamos National Security LLC under DOE Contract DE-AC52-06NA25396.

Les composants d’électronique de puissance ont (et vont encore avoir !) eu une grande influence sur les secteurs de l'énergie et des transports. Ces pièces sont notamment constitués d’assemblages céramique –cuivre pour lesquels la tenue mécanique doit être maîtrisée afin de garantir dans le future une durabilité d’environ 30 ans sous l’action de cycles thermiques plus en plus grande. Une analyse des mécanismes de défaillance des assemblages DBC (Direct Bonding Copper) utilisés en électronique de puissance est étudiée (le délaminage le long de l’interface cuivre -céramique et/ou la rupture fragile de la céramique). Pour identifier le comportement élastoplastique du cuivre, nous avons montré qu’il est nécessaire d’utiliser une plaque de cuivre ayant subi l’ensemble des traitements thermiques liés au processus d’assemblage. Le comportement élastique fragile de la céramique est décrite dans le cadre d’une statistique de Weibull. Dès lors, une caractérisation du délaminage cuivre-céramique sous flexion quatre points a permis d’identifier un modèle cohésif pour l’interface. La calibration des paramètres cohésifs est menée en utilisant les données à deux échelles : i) macroscopique de force-déplacement ii) locale de suivi optique de la fissuration avec le déplacement imposé. L’intégrité mécanique des assemblages DBC pour différentes épaisseurs des couches de cuivre et de céramique a été étudié. Nous avons montré que les configurations avec un rapport proche de l’unité sont les plus dangereuses en engendrant un délaminage, qui se poursuit sous cyclage thermique. Ce dernier peut être notablement réduit en structurant le pourtour de la surface de cuivre avec des trous cylindriques répartis périodiquement. Ainsi, un modèle éléments finis permettant d’évaluer les assemblages les plus prometteurs en terme de durabilité a été établie. En l’absence de défauts géométrique, la couche de cuivre reste intègre, même dans le cas d’un délaminage dont le front induit une concentration de contrainte. / The power electronics components (and still will have!) have a great influence on the energy and transport sectors. These parts are made of ceramic-copper assemblies for which the mechanical strength must be controlled to ensure durability about 30 years under the thermal cycles increasingly larger. A failure mechanisms analysis in DBC (Direct Copper Bonding) assemblies used in power electronics is studied (the delamination along the interface copper - ceramic and/or the brittle ceramic fracture). To identify the elastoplastic behavior of copper, we showed that it’s necessary to use a copper plate having undergone the heat hole treatments related to the assembly process. The ceramic gragile elastic behavior is descrobed within the Weibull statictics framework. Consequently, a copper-ceramic delamination characterization under four points bending made it possible to identify a cohesive model for the interface. The cohesive calibration parameters is carried out by using the data in two scales: i) strentgh-displacement macroscopic ii) local cracking optical follow-up with imposed displacement. The mechanical integrity of DBC assemblies of different thickness of copper and ceramic has been studied. We showed that the configurations with a ratio close to the unit are most dangerous by generating a delamination, which continues under thermal cycling. This risk of delamination can be notably reduced by structuring the copper circumference surface with cylindrical holes distributed periodically. Thus, a finite elements model allowing us to evaluate the most promising assemblies in term of durability, was estabilshed. In the absence of geometrical defects, the copper layer must remains, even in the delamination case whose face induces a concentration stress.

Cette étude constitue une contribution dans un grand projet européen dénommé : 3DICE (3D Integration of Chips using Embedding technologies). La fiabilité mécanique et thermomécanique des composants 3D a été étudiée par des essais normalisés et des simulations numériques. L’essai de chute et le cyclage thermique ont été sélectionnés pour la présente étude. Des analyses de défaillance sont menées pour compléter les approches expérimentales. Les propriétés mécaniques des éléments constituant les composants ont fait l’objet d’une compagne de caractérisation complétée par des recherches bibliographiques. Les simulations numériques, dynamiques transitoires pour l’essai de chute et thermomécanique pour l’essai de cyclage thermique, ont été réalisées pour une estimation numérique de la tenue mécanique des composants. Les modèles numériques sont utilisés pour optimiser le design des composants et prédire les durées de vie en utilisant un modèle de fatigue. / This work establishes a contribution in an important European project mentioned 3DICE (3D Integration of Chips using Embedding technologies). The mechanical and thermomechanical reliability of 3D microelectronic components are studied by employing standardized tests and numerical modeling. The board level drop test and thermal cycling reliability tests are selected for this study. Failures analysis has been used to complete the experimental study. The mechanical properties of elements constituting the microelectronic components were characterized using DMA, tensile test and nanoindentation. Bibliographical researches have been done in order to complete the materials properties data. Numerical simulations using submodeling technique were carried out using a transient dynamic model to simulate the drop test and a thermomechanical model for the thermal cycling test. Numerical results were employing in the design optimization of 3D components and the life prediction using a fatigue model.

Made available in DSpace on 2015-05-08T14:59:43Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3419531 bytes, checksum: 47a7d7cdb7277fb0c7f884e30a96df42 (MD5) Previous issue date: 2012-09-14 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work was evaluated the influence of multiple quenching in the peak temperatures of phase transformation (PTPT) in the alloy Cu-11.8Al-0.6Be-0.5Nb-0.27Ni (%wt), as well as the influence that deformation applied in temperatures above Ms, at nominal composition Cu-11.8Al-0.6Be-0.5Nb-0.27Ni, Cu-11.8Al-0.55Be-0.5Nb-0.27Ni and Cu-11.8Al-4Nb-2.16Ni-0.5Be, would have on the residual deformation. The alloys were melted, homogenized during 12h by 850ºC and machined using wire electroerosion. Then, the samples were quenched in water at room temperature and subsequently analyzed by optical microscopy, scanning electron microscopy, using energy dispersive x-ray, differential scanning calorimetric analysis and x-ray diffractometry. For samples quenched successively, it was found a large change in PTPT after 22 quenching, there is no reverse transformation in this range. From the 34th quenching, the PTPT remained constant around 420ºC and severe changes in your micrographs were detected. Nevertheless, there was no change in Cu/Al able to change the PTPT. Alloys with containing nominal composition 0.4% and 0.2%Be indicated strong influence of the Be in the PTPT. When analyzed by x-ray diffractometry, the sample with 0.2Be indicated the presence of &#946;' and &#947;' phases, when aged by 530ºC. For quantifying the residual deformations, the samples were subjected to static tensile and loading/unloading tests. When subjected large deformation and temperature near Ms, the results showed a great residual deformation, whereas small deformations with temperatures above Af showed not to be viable. The alloy Cu-11.8Al-4Nb-2.16Ni-0.5Be when tractioned, showed excessive weakness even after treatment of solubilization. / Neste trabalho avaliou-se a influência de têmperas múltiplas, nas temperaturas de pico da transformação de fase (TPTF) e na microestrutura da liga Cu-11,8Al-0,6Be-0,5Nb-0,27Ni (% em peso), bem como a influência que deformações aplicadas, em temperaturas a partir de Ms, às ligas de composição nominal Cu-11,8Al-0,6Be-0,5Nb-0,27Ni, Cu-11,8Al-0,55Be-0,5Nb-0,27Ni e Cu-11,8Al-4Nb-2,16Ni-0,5Be, teriam nas deformações residuais. As ligas foram fundidas, homogeneizadas durante 12h a 850ºC e usinadas via eletroerosão à fio. Em seguida, os corpos de prova foram temperados em água a temperatura ambiente sendo posteriormente analisadas via microscopia óptica, microscopia eletrônica de varredura, utilizando-se energia dispersiva de raios-x (EDS), análise calorimétrica diferencial de varredura (DSC) e difratometria de raios-X. Para as amostras cicladas termicamente, verificou-se que após 22 têmperas uma mudança significativa nas TPTF ocorre, não havendo a partir deste intervalo transformação reversa. A partir da 34ª têmpera, as TPTF permaneceram constantes em torno de 420ºC e as micrografias indicaram mudanças severas em suas microestruturas. Não obstante, não se verificou alteração na relação Cu/Al capaz de alterar as TPTF. As amostras contendo composição nominal de 0,4% e 0,2% de Be indicaram que as ligas estudadas são fortemente influenciadas pela presença do Be. Quando analisada por difratometria de raios-x, a amostra com 0,2Be indicou a presença das fases &#946; e &#947; , quando submetida a tratamento de envelhecimento a 530ºC. Para a quantificação das deformações residuais, os corpos de prova foram submetidos aos ensaios de tração estática e de carregamento/descarregamento. As amostras submetidas a deformações próximas as de ruptura e com temperatura de ensaio próximo a Ms mostraram resultar em deformações residuais de maiores intensidades, enquanto quedeformações de pequena magnitude, com temperaturas acima de Af, mostraram não serem viáveis. A liga de composição nominal Cu-11,8Al-4Nb-2,16Ni-0,5Be, quando ensaiada sob tração, mostrou fragilidade excessiva mesmo após tratamento térmico de solubilização.

Les environnements ont tendance à être plus sévères (plus chauds et quelquefois plus froids). À ce titre, l’électronique de puissance haute température est un enjeu majeur pour le futur. Concernant les technologies d’assemblage à haute température, les brasures haute température comme l'alliage 88Au/12Ge, 97Au/3Si et 5Sn/95Pb pourraient supporter ces niveaux de contraintes thermiques, qui sont actuellement développées pour répondre à ces exigences. Nous avons effectué les caractérisations électriques, mécaniques et thermomécaniques des matériaux d’assemblage. Une étude thermique a réalisée par des méthodes expérimentales et des simulations numériques, l’étude numérique est réalisée sous ANSYS dans le but d’estimer les influences des différents paramètres sur la performance thermique de l’assemblage. En plus, les cyclages thermiques passif de grande amplitude sont effectués pour analyser la fiabilité des modules de puissance dans ces conditions d’utilisation. / The environments tend to be more severe (hotter and sometimes colder). As such, the high temperature power electronics is a major challenge for the future. Concerning the technologies for high temperature assembly, high temperature brazing alloy as 88Au / 12Ge, 97Au / 3Si and 5Sn / 95Pb could support these levels of thermal stresses, which are being developed to answer these requirements. We performed the electric, mechanical and thermomechanical characterizations for the materials of assembly. A thermal study was realized by experimental methods and numerical simulations, the numerical study is carried out in ANSYS in order to estimate the influences of the various parameters on the thermal performance of the assembly. In addition, the passive thermal cycles of large amplitude are conducted to analyze the reliability of the power modules in these conditions.

L’amortisseur thermique étudié dans le cadre de cette thèse a pour objectif de limiter les pics de température des composants électroniques fonctionnant en régime transitoire au moyen d’une structure composite consistant en un réseau de nanotubes de carbone (NTC) rempli de matériau à changement de phase (MCP) solide-liquide, le tout étant contenu dans un boîtier en silicium (Si). Ce système passif vise à augmenter l’inertie thermique volumique du composant grâce à la chaleur latente du MCP tout en maintenant une bonne conductance thermique grâce aux NTC. Un dispositif expérimental polyvalent a été développé spécifiquement pour caractériser les différentes générations d’échantillons fabriqués par les partenaires du projet THERMA3D. L’excitation thermique de l’échantillon est réalisée au moyen d’un laser en face amont et la réponse thermique est mesurée par caméra infrarouge simultanément sur les faces amont et aval. L’application d’une peinture sélectionnée sur l’échantillon permet d’accéder à sa température après un étalonnage dédié. Des méthodes d’estimation de paramètres ont été développées pour quantifier les deux caractéristiques essentielles de l’amortisseur thermique que sont sa capacité de stockage thermique et sa résistance thermique. Les sensibilités de la résistance thermique aux caractéristiques de la connexion Si/NTC et à la longueur des NTC ont été étudiées et les résistances thermiques d’interface Si/NTC ont été identifiées comme dominantes au sein du système. Des essais de cyclage thermique ont permis d’évaluer la fiabilité de l’ensemble de manière accélérée. Le comportement du MCP et la qualité du matériau de scellement ont été analysés par voie optique. Par ailleurs, la plus élevée des deux résistances thermiques d’interface Si/NTC a été localisée grâce à la visualisation infrarouge du réseau de NTC à travers le silicium semi-transparent. Enfin, une méthode de contrôle non destructif de la qualité de l’interface Si/NTC a été développée pour les amortisseurs thermiques de dernière génération. / The purpose of the studied thermal damper is to smooth the temperature peaks of transient electronic components via a composite structure consisting of an array of carbon nanotubes (CNT) filled with solid-liquid phase change material (PCM), the whole being embedded in a silicon (Si) casing. This passive system is intended to increase the thermal inertia per unit of volume of the electronic component thanks to the latent heat of the PCM while maintaining a high thermal conductance thanks to the CNT. A versatile test bench was specifically developed in order to characterize the different generations of samples fabricated by the partners of the THERMA3D project. The thermal excitation of the front side of the sample is generated by a laser and the thermal response is measured simultaneously on the front and back sides by an infrared camera. A selected paint can be deposited on the sample in order to access its temperature by means of a dedicated calibration. Parameter estimation methods were developed in order to quantify both main characteristics of the thermal damper: its heat storage capacity and its thermal resistance. The sensitivities of the thermal resistance to the features of the Si/CNT connection and to the length of the CNT were studied and it was found out that the interfacial thermal resistances Si/CNT are dominant in the system. Thermal cycling tests enabled to assess the reliability of the thermal damper in an accelerated manner. The behavior of the PCM and the quality of the sealing material were optically analyzed. Besides, the infrared visualization of the CNT array through the semi-transparent silicon enabled to identify the highest of both Si/CNT interfacial thermal resistances. Finally, a non-destructive testing method for the evaluation of the quality of Si/CNT interfaces was developed for the latest generation of thermal dampers.

Hydropower is the most important power balancing resource in the Swedish electrical power system, regulating the power supply to match the load. Consequently, several hydropower plants have periods of stand-by operation where the power production is absent but where several devices within a plant are still active. Such a device is the step-up power transformer, which during stand-by operation still generates no-load energy losses. These losses can accumulate to a considerable amount of energy and costs during the long technical lifetime of the apparatus. One option to minimize these no-load energy losses is by turning the transformer off when its generating unit is in stand-by operation. However, when this transformer operational change has been explained to experts in the field, the most common response has been that a more frequent reenergizing of a transformer leads to higher risks for errors or transformer breakdowns. This study aimed to analytically investigate three effects from this operational change. First, the potential of fatigue failure for the windings due to the increased sequences of inrush current. Secondly, the thermal cycling as a consequence of change in present losses. Lastly, the energy and economic saving potentials for hydropower plants where this operational adjustment is applied. The study used both established as well as analytical tools explicitly created for this study. These were then applied on currently active transformers in different plant categories in Fortum’s hydropower fleet.  The study primarily showed three things. Firstly, risk of fatigue failure due to the increased presence of inrush currents did not affect the transformer’s technical lifetime. Secondly, the thermal cycling changes were slightly larger with absent no-load losses during stand-by operation. The average temperature for the transformer decreased, which in general is seen as a positive indicator for a longer insulation lifetime and thus the transformer’s technical lifetime. Finally, the created frameworks showed the potential of saving energy and money for all plant categories, where the potential grew with the installed production capacity and the stand-by operation timeshare. Despite the simplifications made to describe the complex reality of a transformer operating in a hydropower plant, this thesis contributes to lay a foundation for future investigation of an easy adjustment to avoid unnecessary energy losses and costs for transformers in hydropower plants.

Advances in wide-bandgap semiconductor devices have increased the allowable operating temperature of power electronic systems. High-temperature devices can benefit applications such as renewable energy, electric vehicles, and space-based power electronics that currently require bulky cooling systems for silicon power devices. Cooling systems can typically be reduced in size or removed by adopting wide-bandgap semiconductor devices, such as silicon carbide. However, to do this, semiconductor device packaging with high reliability at high temperatures is necessary. Transient liquid phase (TLP) die-attach has shown in literature to be a promising bonding technique for this packaging need. In this work TLP has been comprehensively investigated and characterized to assess its viability for high-temperature power electronics applications. The reliability and durability of TLP die-attach was extensively investigated utilizing electrical resistivity measurement as an indicator of material diffusion in gold-indium TLP samples. Criteria of ensuring diffusive stability were also developed. Samples were fabricated by material deposition on glass substrates with variant Au–In compositions but identical barrier layers. They were stressed with thermal cycling to simulate their operating conditions then characterized and compared. Excess indium content in the die-attach was shown to have poor reliability due to material diffusion through barrier layers while samples containing suitable indium content proved reliable throughout the thermal cycling process. This was confirmed by electrical resistivity measurement, EDS, FIB, and SEM characterization. Thermal and mechanical characterization of TLP die-attached samples was also performed to gain a newfound understanding of the relationship between TLP design parameters and die-attach properties. Samples with a SiC diode chip TLP bonded to a copper metalized silicon nitride iv substrate were made using several different values of fabrication parameters such as gold and indium thickness, Au–In ratio, and bonding pressure. The TLP bonds were then characterized for die-attach voiding, shear strength, and thermal impedance. It was found that TLP die-attach offers high average shear force strength of 22.0 kgf and a low average thermal impedance of 0.35 K/W from the device junction to the substrate. The influence of various fabrication parameters on the bond characteristics were also compared, providing information necessary for implementing TLP die-attach into power electronic modules for high-temperature applications. The outcome of the investigation on TLP bonding techniques was incorporated into a new power module design utilizing TLP bonding. A full half-bridge inverter power module for low-power space applications has been designed and analyzed with extensive finite element thermomechanical modeling. In summary, TLP die-attach has investigated to confirm its reliability and to understand how to design effective TLP bonds, this information has been used to design a new high-temperature power electronic module.