Cemented carbides (WC-Co) are powder metallurgical products produced by liquid phase sintering. WC-Co is widely used for making a large variety of cutting tools, such as drills and inserts turning applications, due to its great mechanical properties, where the hardness of the WC grains is combined with the toughness of the of the Co binder. WC grain size and grain size distribution are the two most important factors to control the mechanical properties of the products. This study examined the grain growth dependence of different milling and sintering times. The resulting grain size and grain size distribution were measured using image analysis on scanning electron microscopy images (SEM) and by using electron backscatter diffraction (EBSD). In addition, the correlation between hardness and coercivity, the most common indirect measures of grain size, and different methods of calculating average grain radius were investigated. An attempt was also made to study the contribution of defects to grain growth. This work also includes an overview of various grain growth equations and a numerical implementation of these. Experimental results show that for shorter sintering times, powders milled for short times (15 min and 1 h) have larger average grain radii. There is a crossover after 6 to 8 h of sintering, where the powders milled for a long time (40 h and 200 h), have larger average radii. The measured hardness values correlate well with the average grain radius calculated from the grain surface area and the coercivity correlates with the established equations. EBSD measurements detected boundaries that could not be detected by image analysis, and that were not Sigma 2 boundaries. It is likely that these boundaries are either low energy boundaries or boundaries between grains that are very closely oriented. Comparing heat-treated powder with the untreated resulted in a lower average grain size after sintering for the heat-treated powder. None of the growth equations investigated in this work could fully describe the experimental grain growth. Through increased understanding of the grain growth, the growth can be controlled and the end product can have the desired tool properties. The occurrence of abnormal grains in cutting tool applications can cause breakage, which is especially important to avoid in applications such as PCB drills. A correlation between hardness and grain size provides further means for cheap and fast indirect measures of the grain size in production. / Hårdmetall är ett pulvermetallurgiskt material som tillverkas genom smältfassintring och som kännetecknas av hårdhet, styvhet och god slitstyrka. Volframkarbidens (WC) kornstorlek och kornstorleksfördelning är två viktiga faktorer för att kontrollera de mekaniska egenskaperna i hårdmetall. I den här studien har korntillväxtens beroende på malning och sintring undersökts. WC-Co maldes och sintrades fyra olika tider och kornstorleksfördelningen mättes med bildanalys på svepelektronmikroskopbilder samt med ``electron backscatter diffraction'' (EBSD). I arbetet har även korrelationen mellan hårdhet, koercivitet och olika sätt att beräkna medelkornstorleken undersökts. Ett försök har också genomförts för att studera hur defekterna i det malda pulvret påverkar korntillväxten. I arbetet har även ett flertal olika tillväxtekvationer modellerats numeriskt och för och nackdelar med de olika tillväxtekvationerna har vägts mot varandra. En lång maltid (40 h och 200 h) visade sig ge liten kornstorlek för sintring kortare än 6 h, men för sintringar längre än 8 h gav istället kort malning (15 min och 1 h) den mindre kornstorleken. Det visade sig att uppmätt hårdhet korrelerar bäst med den medelkornstorleksradie som räknats fram från kornytan. I EBSD mätningarna kunde man observera ett flertal korngränser, utöver Sigma 2 korngränser, som inte hade detekterats med bildanalys. Värmebehandlingen av det malda pulvret minskade korntillväxten under efterföljande sintring. Ingen av de undersökta tillväxtekvationerna kunde beskriva de experimentella resultaten fullt ut. Genom ökad förståelse för korntillväxt kan man kontrollera tillväxten och slutprodukten kan få önskade egenskaper. Förekomsten av abnorm korntillväxt i skärverktyg i hårdmetall är en av de vanligaste kritiska defekterna och det är speciellt viktigt är undvika korntillväxt i tillverkning av små verktyg, som till exempel kretskortsborrar. Hårdhet och koercivitet är de vanligaste indirekta mätmetoderna för att mäta kornstorlek i produktion. En bra korrelation mellan kornstorlek och indirekta mätmetoder ger utökade verktyg för snabba och billiga mätningar.

Superalloys have performed well as blade and disc materials in turbine engines due to their exceptional elevated temperature strength, high resistance to creep, oxidation and corrosion as well as good fracture toughness. This study explores the use of a relatively new technique of strain measurement, high resolution electron backscatter diffraction (HR-EBSD) to measure local deformation fields. The heart of the HR-EBSD technique lies in comparing regions in EBSD patterns from a strained region of a sample to those in a pattern from an unstrained region. This method was applied to study the elastic strain fields and geometrically necessary dislocation density (GND density) distribution near hard carbide particles in a nickel-based superalloy MAR-M-002. Significant thermal strains were initially induced by thermal treatment, which included a final cooling from the ageing temperature of 870°C. Elastic strains were consistent with a compressive radial strain and tensile hoop strain that was expected as the matrix contracts around the carbide. The mismatch in thermal expansion coefficient of the carbide particles compared to that of the matrix was sufficient to have induced localized plastic deformation in the matrix leading to a GND density of 3 x 10¹³ m^–2 in regions around the carbide. These measured elastic strain and GND densities have been used to help develop a crystal plasticity finite element model in another research group and some comparisons under thermal loading have also been examined. Three-point bending was then used to impose strain levels within the range ±12% across the height of a bend bar sample. GND measurements were then made at both carbide-containing and carbide-free regions at different heights across the bar. The average GND density increases with the magnitude of the imposed strain (both in tension and compression), and is markedly higher near the carbide particles. The higher GND densities near the carbides (order of 10¹⁴ per m²) are generated by the large strain gradients produced around the plastically rigid inclusion during monotonic mechanical deformation with some minor contribution from the pre-existing residual deformation from thermal loading. A method was developed of combining the local EBSD measurements with FE modelling to set the average residual strains within the mapped region even when a good strain free reference point was unavailable. Cyclic loading was then performed under four point loading to impose strain levels of about ±8% across the height of bend bar samples. Similar measurements as in the case of monotonic deformation were made at several interruptions to fatigue loading. Observations from the cyclic loading such as slip features, carbide cracking, GND density accumulation have been explored around carbide particles, at regions away from them and near a grain boundary.

Deformační interakce mezi horninami na významném rozhraní k·ra - litosférický pláš' je jedním z hlavních proces·, jejichž pochopení umožní lépe popsat termomechanické procesy probíhající hluboko v rozsáhlých pohořích a především chování kontinentálního pláště během kolize kontinentálních desek. Tato disertační práce obsahuje tři hlavní kapitoly, představující výsledky r·zných geologických metod, využitých při zkoumání p·vodu a deformačního chování peridotitových těles ve spodní k·ře Variského orogenu. První kapitola prezentuje závěry ze strukturní studie Mohelenského peridotitu a okolních granulit· z Náměštského granulitového masívu. Jako jedinou efektivní metodou pro studium vnitřní stavby peridotitu se kv·li rozsáhlé serpentinizaci ukázalo měření přednostní mřížkové orientace (EBSD). V serpentinizovaném peridotitu byly zjištěny dva odlišné olivínové skluzné systémy, jejichž distribuce společně s detailním strukturním mapováním v okolním Náměš'ském granulitovém masívu umožnily vysvětlit reologické chování peridotitového tělesa v prostředí kořene orogenu. V této kapiole jsme se pokusili vytvořit geotektonický model, který popisuje historii peridotitového tělesa v rámci mnoha fází tektonické historie orogenního kořenu. Ve druhé kapitole představujeme výsledky z analýzy serpentinizačních proces· v...

In recent years there has been a growing demand to produce lightweight high pressure die cast (HPDC) parts for structural applications to decrease vehicle mass and to reduce manufacturing costs. Due to the coupled rapid heat flow and complex flow/deformation that occur in the process, the formation of microstructure and defects in HPDC are still not fully understood. Developing a better understanding of microstructure formation is essential to enable advances in die design and process optimisation, as well as alloy development, to improve the quality and productivity of HPDC components. Therefore, this thesis aims to enhance this understanding by conducting detailed microstructural analysis of samples produced in controlled HPDC experiments. In the first series of experiments, various microstructure characterisation techniques were used to study salient HPDC microstructural features. The microstructures of castings were characterised at different length scales, from the scale of the casting to the scale of the eutectic interlamellar spacing. The results show that the salient as-cast microstructural features, e.g. externally solidified crystals (ESCs), defect bands, surface layer, grain size distribution, porosity and hot tears were similar for both two HPDC-specific Al alloys used, AlSi4MgMn and AlMg5Si2Mn. The formation of these features has been explained by considering the influence of flow and solidification during each stage of the HPDC process. The formation of defect bands is further studied by investigating the ratio between band thickness ( ) and average grain size in the band ( ). Suitable methods for measuring w and dsb in HPDC have been developed. The w/dsb relationship of defect bands has been investigated in HPDC specimens from a range of alloys, casting geometries and band locations within castings. The bands were measured to be 7-18 mean grains wide. This is substantial evidence that defect bands form due to strain localisation in partially solidified alloys during cold-chamber and hot-chamber HPDC. At the end of solidification, dilatant shear bands contain a higher eutectic volume fraction and/or porosity content than adjacent material. In the cross-section of the AM50 Mg alloy, the centrally-located band contains a much higher volume fraction of concentrated porosity than the second-outermost band and insignificant porosity was found in the outermost band. The level of porosity in bands was attributed to the relative difficulty of feeding shrinkage for each band location. As the feeding of material during the intensification stage is important for the reduction of porosity, the influence of intensification pressure (IP) and gate thickness on the transport of material through the gate during the latter stages of HPDC were investigated. Microstructural characterisation of the gate region indicated a marked change in feeding mechanism with increasing IP and gate size. Castings produced with a high IP and/or thick gate contained a relatively low fraction of total porosity and shear band-like features existed through the gate, suggesting that semi-solid strain localisation in the gate is involved in feeding during the pressure intensification stage. When a low IP is combined with a thin gate, no shear band was observed in the gate and feeding was less effective, resulting in a higher level of porosity in the HPDC component. As equiaxed primary crystals are subjected to intense shear during HPDC, their agglomeration and bending behaviour were investigated in the last series of experiment. Samples produced by near-static cooling, HPDC and Thixomoulding®, where the solidifying crystals experience different levels of mechanical stresses, were characterised. The electron backscatter diffraction (EBSD) technique was used to acquire grain misorientation data which is linked to the crystal agglomeration and bending behaviour during solidification. The number fraction of low-energy grain boundaries in HPDC and Thixomoulded samples was substantially higher than in ‘statically cooled’ samples. This is attributed to the much higher shear stresses and pressure applied on the solidifying alloy in HPDC and Thixomoulding, which promote crystal collisions and agglomeration. In-grain misorientations were found to be significant only in branched dendritic crystals which were subjected to significant shear stresses. This is related to the increased bending moment acting on long protruding dendrite arms compared to more compact crystal morphologies.

Dans le cadre du développement des réacteurs de génération IV, de nouvelles études sont menées dans le domaine des matériaux. L'objectif de ce travail est d'améliorer la compréhension du comportement mécanique et de l'endommagement de composites à matrice métallique Mo(TiC)x% contenant une forte fraction volumique de particules, et cela, dans le domaine de températures [25 – 700 °C].<br /><br />La caractérisation microstructurale a permis de comprendre l'histoire du matériau et d'identifier la nature d'une troisième phase (Mo,Ti)C fomée par diffusion du molybdène dans le carbure de titane. L'étude expérimentale a aussi révélé la percolation des particules céramiques au sein de la structure.<br />Les essais mécaniques ont mis en évidence les principales caractéristiques du matériau : le comportement macroscopique dépend à la fois de la vitesse de déformation et de la température. Ces mécanismes sont attribués au comportement thermiquement activé du molybdène.<br /><br />Nous proposons alors diverses simulations de microstructures comprenant des inclusions élastiques-fragiles dans une matrice viscoélastique. L'évolution du comportement mécanique du composite a été modélisée à l'aide d'une approche cristalline sur un agrégat 3D réel. L'agrégat numérique utilisé pour modéliser le comportement mécanique fait appel à une technique de reconstruction 3D via une acquisition par FIB/SEM/EBSD.<br /><br />Ainsi, la réponse du modèle est en bon accord avec les résultats expérimentaux et permet de décrire en fonction de la température :<br />- les mécanismes de plasticité du molybdène, en tenant compte de la transition basse/haute température ;<br />- l'endommagement du carbure de titane et les effets de la percolation.

Les piles à combustible Solid Oxide Fuel Cell sont des systèmes de production d'électricité. Une cellule élémentaire est un multicouche constitué de matériaux céramiques et de métal. Elles sont très sensibles aux contraintes mécaniques générées lors des cycles thermiques et d'oxydo-réduction, limitant leur durée de vie.Ce travail a porté sur la détermination expérimentale des contraintes résiduelles dans des cellules SOFC à anode support en fonction des sollicitations du système. Parallèlement à des mesures in-situ en température, une approche multi-échelles a été développée pour évaluer les hétérogénéités de contraintes dans l'électrolyte liées à la forte anisotropie élastique de la zircone yttriée qui le constitue. Différentes techniques ont été mise en œuvre afin de couvrir les 3 ordres de contraintes. Les mesures à l'échelle macroscopique ont été effectuées par diffraction de rayons X de laboratoire (méthode des sin²(Ψ)). La microdiffraction de rayonnement synchrotron en mode faisceau blanc et monochromatique a permis, après un important travail d'amélioration du protocole de mesure et d'analyse, de déterminer les tenseurs complets de contraintes et déformations grain à grain dans l'électrolyte. Les déformations intra-granulaires ont été évaluées par une technique d'EBSD.Les résultats obtenus ont permis d'analyser les mécanismes principaux qui régissent les évolutions de contraintes dans l'électrolyte. Des hétérogénéités de contraintes entre grains liées à leurs orientations cristallographiques ont été mises en évidence. Au-delà du problème des SOFC, les techniques mises en œuvre ouvrent la voie aux validations expérimentales des modèles mécaniques poly-cristallins.

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

In order to increase efficiency and lifetime of cutting tools it is typical to apply thin coatings by physical or chemical vapour deposition. Applying coatings on cutting tools has shown an increase in both efficiency and lifetime and are of large interest in further development. The study of coatings and their mechanical properties is a very active research area and produces tools extensively used in the industry.  The behaviour of materials on a macroscopic scale can typically be related to microscopic properties. Some coatings produced by Chemical Vapour Deposition (CVD) but especially Physical Vapour deposition (PVD) have crystal structures which are difficult to analyse by conventional methods due to crystal sizes in the nanometre scale. For nanocrystalline materials standard methods fall short due to a limited resolution of the methods.  Recently a method for electron diffraction of crystalline samples was suggested to be used differently in order to achieve a higher resolution. Unlike earlier when electrons were reflected from the sample, using Electron Backscattering Diffraction (EBSD), the electrons were transmitted through thin samples with thicknesses in the magnitude of 100 nm, which enabled the crystal structure to be determined. The new method is typically referred to as either Transmission Kikuchi Diffraction (TKD) or transmission EBSD (t-EBSD) with a resolution down to approximately 10 nm.  The goal with this master thesis has been to evaluate sample preparation methods and TKD studies on PVD samples. Each step has been divided into parameters which govern the sample preparation and analysis and optimized accordingly in order to achieve best possible results of the crystal structure of PVD coatings. From this it has been possible to show how TKD is optimally performed and which difficulties and limitations that are present.  In this thesis two coatings, TiN and (Ti,Al)N, have been studied with TKD and two different preparation methods have been attempted. These were precision mechanical polishing and in-situ lift out with a Dual Beam System. Mechanical polishing did not succeed in producing samples for TKD but was not ruled out as a possibility while the in-situ lift out method could both produce samples and achieve a crystallographic indexing around 80 %. The only areas which were difficult to index were crystal boundaries and crystal clusters where individual crystals were in the range of &lt;30 nm. In these areas overlapping Kikuchi patterns were observed due to the resolution limit of TKD.

No description available.

X-ray diffraction (XRD) profile fitting (Rietveld method) was used in this study to characterize the microstructure for seven microalloyed steels, which were produced through thermomechanical controlled processing (TMCP). Microstructure characterization was conducted through the strip thickness. The microstructural variables studied include subgrain size, dislocation density, texture index and weight percent of retained austenite. The subgrain size was also analyzed by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The effects of processing parameters, including coiling temperature, cooling rate and alloying elements, on the microstructure were also investigated. It was found that decreasing the coiling temperature resulted in a finer subgrain size and higher dislocation densities. The texture index was observed to increase with decreasing coiling temperature. The subgrain size decreased and dislocation density increased as the amount of alloying elements (Ni, Mo and Mn) were increased. The amount of retained austenite increased at the strip center with increasing coiling temperature and increasing C and Ni content. / Materials Engineering