In the TRISO (tristructural isotropic) coated fuel particle used in the High Temperature Reactor, the most important layer is a silicon carbide layer which acts as a pressure vessel. In this study, we have focused our study on the investigation of the Young’s modulus, hardness, residual stress, and fracture toughness of the SiC layer. Moreover, microstructures and impurities in silicon carbide were characterised and then related to both Young’s modulus and hardness of the SiC layer. Both nanoindentation and micro-indentation were used to determine Young’s modulus and hardness of the SiC. Raman spectroscopy, X-ray diffraction, and scanning electron microscopy techniques were used to examine impurities, phases and microstructure of silicon carbide layers, respectively. Young’s modulus was measured at different positions of a polished surface of the SiC with different CVD growth and crystal orientations. With help from the finite element modelling, it has been found that Young’s modulus of the SiC is dependent on the grain orientation of the SiC. Mechanical properties of silicon carbide are affected by the presence of excess silicon, excess carbon, stacking faults, texture, grain size, property of grain boundary. The effect of these factors on Young’s modulus and hardness, are investigated with the orthogonal analysis. The analysis concludes that the most important factor on Young’s modulus is texture while the most significant factor on hardness is grain boundary. Grain size is secondarily important factor to affect hardness. Stacking faults and impurities almost have no influence on Young’s modulus and hardness. The residual stress in the silicon carbide layer was measured based on the peak shift in Raman spectra of the SiC and is in a range of 150-300 MPa. Fracture resistance in the radial direction of the SiC layer is larger than those in the circumferential direction. The difference is controlled by the layer-like structure of the SiC coating.

Práce je zaměřena na výzkum a vývoj technologie přípravy tvrdých anodických vrstev na třech různých typech neželezných materiálů a to (i) hliníkové slitině (AA1050), (ii) čistém hořčíku (99.9% Mg) a (iii) zinkové slitině (ZnTi2). Vhodnou kombinací anodizačních podmínek (napětí, proudová hustota, teplota a složení elektrolytu atd.) lze vytvářet anodické vrstvy s rozdílnými vlastnostmi. V rámci předložené práce byl prokázán vliv předúpravy a anodizačních podmínek na vzhled, morfologii, tloušťku a tvrdost vytvořených anodických vrstev. Pro zvýšení tribologických vlastností a tvrdosti byly anodické vrstvy přímo dopovány Al2O3 částicemi nebo kombinací Al2O3 a PTFE částic během anodizačního procesu. Teoretická část práce popisuje základní principy anodizace, metody používané v průmyslové praxi a v práci je také popsán technologický proces. Experimentální část je rozdělena na tři základní části. První část se věnuje anodické oxidaci hliníkové slitiny AA1050. Druhá část je zaměřena na anodizaci čistého hořčíku a poslední část je zaměřena na anodizaci zinkové slitiny ZnTi2, která není tak známá jako anodizace hliníku.

Print quality demands for coated papers are steadily growing, and achieving coating uniformity is crucial for high image sharpness, colour fidelity, and print uniformity. Coating uniformity may be divided into two scales: coating thickness uniformity and coating microstructure uniformity, the latter of which includes pigment, pore and binder distributions within the coating layer. This thesis concerns the investigation of both types of coating uniformity by using an approach of quantitative microscopy.First, coating thickness uniformity was analysed by using scanning electron microscope (SEM) images of paper cross sections, and the relationships between local coating thickness variations and the variations of underlying base sheet structures were determined. Special attention was given to the effect of length scales on the coating thickness vs. base sheet structure relationships.The experimental results showed that coating thickness had a strong correlation with surface height (profile) of base sheet at a small length scale. However, at a large length scale, it was mass density of base sheet (formation) that had the strongest correlation with coating thickness. This result explains well the discrepancies found in the literature for the relationship between coating thickness variation and base sheet structure variations. The total variance of coating thickness, however, was dominated by the surface height variation in the small scale, which explained around 50% of the variation. Autocorrelation analyses were further performed for the same data set. The autocorrelation functions showed a close resemblance of the one for a random shot process with a correlation length in the order of fibre width. All these results suggest that coating thickness variations are the result of random deposition of particles with the correlation length determined by the base sheet surface textures, such as fibre width.In order to obtain fundamental understandings of the random deposition processes on a rough surface, such as in paper, a generic particle deposition model was developed, and systematic analyses were performed for the effects of particle size, coat weight (average number of particles), levelling, and system size on coating thickness variation. The results showed that coating thickness variation3grows with coat weight, but beyond a certain coat weight, it reaches a plateau value. A scaling analysis yielded a universal relationship between coating thickness variation and the above mentioned variables. The correlation length of coating thickness was found to be determined by average coat weight and the state of underlying surfaces. For a rough surface at relatively low coat weight, the correlation length was typically in the range of fibre width, as was also observed experimentally.Non-uniformities within the coating layer, such as porosity variations and binder distributions, are investigated by using a newly developed method: field emission scanning electron microscopy (FESEM) in combination with argon ion beam milling technique. The combination of these two techniques produced extremely high quality images with very few artefacts, which are particularly suited for quantitative analyses of coating structures. A new evaluation method was also developed by using marker-controlled watershed segmentation (MCWS) of the secondary electron images (SEI).The high resolution imaging revealed that binder enrichment, a long disputed subject in the area, is present in a thin layer of a 500 nm thickness both at the coating surface and at the base sheet/coating interface. It was also found that the binders almost exclusively fill up the small pores, whereas the larger pores are mainly empty or depleted of binder.

The effect of substrate surface treatment (substrate sputter cleaning) in a cathodic arc plasma prior to unbalanced magnetron deposition of transition metal nitride coatings on the performance of the coated components has been investigated. In particular the influence of parameters such as ion species, ion energy and exposure time on the changes in substrate surface topography, microstructure and micro-chemistry were studied employing transmission electron microscopy, energy dispersive X-ray analysis, electron energy loss spectroscopy, X-ray diffraction, atomic force microscopy and optical microscopy. The consequences for both the microstructure of subsequently grown transition metal nitride coatings and their adhesion were elucidated. The relevance for practical applications was demonstrated using the example of dry high-speed milling tests, which showed that an appropriate choice of substrate surface pre-treatment parameters can double the life time of the coated tools. This was found to be due to an improved adhesion as a result of a combina-tion of reduced oxygen incorporation at the interface between coating and substrate and local epitaxial growth of the coating. The latter is promoted by certain sub-strate surface pre-treatment procedures, which provide clean surfaces with preserved crystallographic order.

Phase transformation behavior, micro structural development, mechanical and tribological properties of electroless Ni-B coating was characterized using different characterization techniques. As deposited electroless Ni-B coating containing 94 wt. % of NI and 6 wt. % of B is amorphous. It crystallizes via two exothermic reactions one at 3000C and another at 430˚C. It has been observed that there is also slow evolution of the heat in between this two exothermic reactions. XRD studies display that as deposited coating undergoes multi-stage crystallization events. At the first exothermic peak NI3B phases crystallizes, in between two a phase mixture of Ni and Ni3B and at the second exothermic peak NI2B + Ni3B crystallizes. Evolution of the free Ni in the complete crystalline coating is not predicted by the equilibrium phase diagram of the Ni-B system. Microscopic observation of the as deposited coating displays a novel compositionally modulated microstructure comprises of different length scales ranging from micrometer to nanometer level. In situ TEM study along with composition analysis were carried out in order to track the crystallization pathway and microstructural development. This kind of composition fluctuation of the coating is intrinsic to the deposition process. In best of our knowledge this kind of microstructure is the first time reported example of phase separation in a binary metal-metalloid system without spinoidal decomposition. Effect of this kind of microstructure and phase evolution on the mechanical and tribological properties of the coating is very profound. Increase in the nanocrystalline borides content of the coating increases the hardness value of the coating as well as improved tribological properties of the coating. In the low load regime (5 N and less) wear resistance of the coating is provided by the oxide layer formed on the wear track by preventing the direct contact between the coating and counterface. Local temperature rise due to friction and nancrystalline nature of the coating enhances the tendency of oxide layer formation. Characterization of the oxide layer was carried out using SEM, EPMA, Nanoindenation and Raman Spectroscopy. Whereas in case high load regime (above 5 N) this oxide layer breaks off and direct contact between the coating and counterface is established. This increases the wear rate of the coating. Material is removed from the coating through subsurface crack formation and propagation by low cycle fatigue mechanism. Effect of amorphous phase and free Ni on the tribological properties of the coating is detrimental by promoting a strong adhesion between the coating and steel counter face, whereas nanocrystalline borides shows opposite effect. A nano tribological studies using lateral force microscopy shows that nanocrystalline borides decreases the coefficient of friction of the coating. Phase evolution and microstructural characterization also shows that above 450˚C there is a significant diffusion of the boron from the coating to the steel substrate. This restrict the high temperature tribological studies of the coating up to a temperature range of 450˚C. Wear data along with worn track characterization demonstrate the fact that above 100˚C even in low load regime wear rate is very high. Wear of the coating is mainly governed by the plastic deformation of the coating and breakage of the protective oxide layer. Analytical calculation as well experimental observation shows that during the time of wear the temperature at the local contact region reaches a very high value even up to 1100˚C. This may soften the coating and causes the wear though plastic deformation of the coating.

Hochfeste kupferhaltige Aluminiumlegierungen gelten gemeinhin als „schwer“ anodisierbar, deshalb werden in der vorliegenden Arbeit werkstoffseitige und prozessseitige Maßnahmen zur Verbesserung der Schichtqualität erforscht. Zur eindeutigen Abgrenzung des Einflusses der Cu-Verteilung vom Einfluss anderer Legierungselemente und Verunreinigungen wurde für die Anodisierexperimente zusätzlich zur kommerziellen Legierung EN AW-2024 die hochreine Modelllegierung AlCu4 als Untersuchungswerkstoff gewählt. Insbesondere für die Modelllegierung AlCu4 konnte erstmals eine systematische Veränderung des Schichtbildungsmechanismus beschrieben werden. Mit zunehmender Ausscheidungsbildung nimmt das Ausmaß der Sauerstoffentwicklung ab, woraus erhöhte Schichtdicken und -härten folgen. Die nach Anodisieren der warmausgelagerten Zustände erhaltenen Schichtmikrostrukturen wurden erstmals im Rahmen dieser Arbeit mittels Rasterelektronenmikroskopie beschrieben. Aufgrund reduzierter Schichtrücklösung sind auch auf der Legierung EN AW-2024 im warmaus-gelagerten und überalterten Zustand höhere Schichtdicken und -härten für eine Elektrolyttemperatur von 20 °C erzielbar. Bei einer Elektrolyttemperatur von 5 °C können die Schichtdicke und -härte vor allem durch Zugabe von Additiven zum schwefelsauren Grundelektrolyt gesteigert werden. Im Unterschied zu konventionellen organischen Additiven resultiert die Zugabe von Salpetersäure darüber hinaus in einer Absenkung der Anodisierspannung zu Prozessbeginn und damit in einer Reduzierung der erforderlichen elektrischen Energie. Mit steigender Additivkonzentration nimmt jedoch die Ritzbeständigkeit der Schichten infolge erhöhter Mikrorissigkeit ab. Es ist folglich ein Optimum aus Schichthärte und Mikrorissigkeit zu finden. / High-strength aluminum-copper alloys are generally recognized to be “hardly” anodizable. Hence, the influences of material and process parameters were investigated within this work in order to improve the coating properties. Apart from the commercial alloy EN AW-2024, the high purity model alloy AlCu4 was used for the anodizing experiments in order to distinguish between the influence of the copper distribution and the influence of other alloying elements and impurities. Regarding the model alloy AlCu4, a systematic change of the coating growth mechanism was described for the first time. The extent of oxygen evolution decreases with the intensification of the precipitation leading to increased coating thickness and hardness. In this work, the coating microstructures, resulting from the anodic oxidation of the artificially aged conditions, were described by scanning electron microscopy, for the first time. Due to reduced chemical dissolution of the coatings, higher coating thickness and hardness can also be achieved after room-temperature anodizing of the alloy EN AW-2024 in the artificially aged conditions. For hard-anodizing at an electrolyte temperature of 5 °C, the coating thickness and hardness can be particularly improved by using additives in combination with the sulfuric acid base electrolyte. Beyond that and in contrast to the effect of conventional organic additives, the addition of nitric acid enables the reduction of the anodizing voltage at the beginning of the process and therefore, the reduction of the required electrical energy. However, the scratch resistance of the coatings decreases with increasing additive concentration due to the occurrence of micro crack networks. Consequently, the coating hardness and the amount of microcracks have to be optimized in order to meet concrete application requirements.