The lifetime of the high temperature ceramic coating 7 wt.% yttria-stabilized zirconia (7YSZ) is reduced when calcium-magnesium-alumino-silicate (CMAS) particulates enters aero-engines during operation in a sandy or dusty environment, melts, and infiltrates into the coating. 7YSZ undergo both chemical and mechanical degradation from CMAS infiltration during cycling. Characterization methods with synchrotron X-ray diffraction (XRD) provides a non-destructive means to measure the impact of time and temperature on coating degradation with high spatial resolution of 7YSZ coatings infiltrated and annealed by CMAS for 1 hour and 10 hours as well as at 1225 °C and 1250 °C. Additionally, qualitative results of cross-sectional scanning electron microscopy (SEM) allows for the additional observation and validation of the extent of degradation the coatings experience from CMAS infiltration. The XRD measurements show the extent of degradation is more sensitive to temperature around the melting range of CMAS with an increase of approximately 42.8% in the concentration of the monoclinic phases present in the coating at the surface when increasing the annealing temperature from 1225 °C to 1250 °C. It was also found that the degradation was more significant in the first hour of infiltration. There was an increase of 21.5% in the concentration of the monoclinic phases present within the coating at the surface when increasing the annealing time from 1 hour to 10 hours. The results presented within this thesis resolve the impact of time and temperature on the infiltration kinetics of CMAS in coatings which are important considerations in mitigating CMAS infiltration.

The use of plasma sprayed ceramic coats as thermal barrier coatings (TBCs) for the protection of metallic structures and equipment from severe thermal, abrasive and corrosive conditions has been documented extensively in the last two decades. The state-of-the-art TBCs consist of a double layer coat. a top ceramic layer and an intermediate bond coat (MCrAIY, M=Ni, Co, Fe) deposited on the alloy substrate. Zirconia, both stabilized and partially stabilized with different oxides has been used as the ceramic top coat due to its low thermal conductivity and low thermal expansion coefficient. Studies of the microstructure of the TBCs have shown aspects that can help the understanding of the properties of the coating. The ternary system ZrOz-Y203-TiCz is believed to offer improved properties when it is compared to Zr02-Y203. However, the use of &02-Y203-Ti02 as TBCs, a major part of this work, is not widely reported in the literature. The purpose of this thesis was to study the microstructure of a plasma sprayed ZrOrY203-TiO2 TBC using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Transmission Electron Microscopy (TEM). The evolution of the Zr41_phase distribution in the ceramic coat was followed by XRD after different heat treatments, with the finding that the cooling rate plays a decisive role in the final Zr42 phase composition. SEM studies allowed a description of the lamellae structure of the Zr02-Y203-TiOz coating. The evolution of the morphology, porosity and crack distribution in the coat after different thermal treatments were followed by SEM. Evidence of incipient sintering is observed in Zr02-Y203-Ti02 coats heated at temperatures higher than 1200 °C. This should lead to poor coating performance. EDS analysis revealed an heterogeneous distribution of titanium through the oating. A detailed microstructural characterization of the as-sprayed coating was done using TEM. Microstructural features such as micro-twins, antiphase-boundaries and mottled morphology associated with "non-transformable" tetragonal ZrO2 phase were identified. It is believed that these microstructural elements promote toughening and thermal stress relief mechanisms that provide the coating with the erosion and thermal shock resistance required for a TBC. The presence of TiO2 is linked to a higher proportion of tetragonal ZrO2 in the Zr02-Y203-Ti02 coating, therefore improved properties of the coating are expected. The addition of TiO2 promotes grain growth and decreases the final density in pressed and sintered Zr02-Y203-TiO2 powders. The results obtained are a contribution to the understanding of the microstructure of TBCs and to the sparse knowledge base of the ZrOrY2O3-TiO2 coatings. Further work should be done in the characterization of the ZrO2-Y2O3-Ti42 coatings and the study of its stability under different conditions in order to determine the real potential of this material offers as an alternative to the better known ZrOrY203 TBC.

Thermal barrier coatings (TBCs) have been used widely in aerospace and land-based gas turbines. The TBC system consists of a top coat layer, a thermally grown oxide (TGO), a bond coat layer and a substrate. The growth kinetics of the TGO significantly affects the durability of TBCs. At a critical TGO thickness, the growth stresses exceed the ceramic-bond coat interface strength, resulting in TBC system failure. Regardless of the deposition method used, it is vitally important to accurately predict the TBC lifetime by investigating the determinants of the failure. The main objective of this study was to investigate the effect of oxidation stress induced by TGO layer in high temperature cycling environment through a series of reliable numerical simulations. Indeed, this oxidation stress is a known factor of interface degradation, and may result in failure of the ceramic-metal interface. A 2-D finite element model of the TBC was built via ANSYS APDL software, to conduct parametric studies of increasing complexity. The model accounted for elasticity first, before creep was integrated. Then, the model included swelling induced by phase transformation associated with oxidation, incorporating the effect of volumetric expansion of the newly grown TGO. This coupled oxidation constitutive approach was implemented for a typical air plasma spray deposited TBC coating. The interfacial radial stresses induced by the gradual oxidation were investigated. Different morphologies of the TBC interface were also considered to analyze the roughness effect on interface stresses. A complete model including swelling, creep, aging effects on the TBC layers at a given roughness was finally investigated.

Published Article / The abattoir Hygiene Management System (HMS) was regulated in South Africa under the Meat Safety Act 40 of 2000. Presently, there is no national regulated microbiological standard to compare against meat tested at abattoirs as an indicator of good hygiene practices. The aim of the study was to establish a provincial guideline for a microbiological baseline. This may be used to verify the performance of the implemented HMS. Thirty red meat and twenty-two poultry abattoirs were sampled to determine baseline Total Bacterial Counts (TBCs). The results of this study were compared to standards presently used in the United Kingdom (UK). The results compared favourably.

Multiple dielectric crossing waveguides are indispensable in building a complex optical integrated circuit. Since each input/output waveguide will have many crossings, it is important to design a low-loss waveguide crossing to ensure the overall radiation loss is kept at a minimum. The beam propagation method (BPM) is usually the method of choice for modeling large but low-index-contrast waveguide devices. BPM assumes one-way propagation and adopts the paraxial approximation. It is neither able to consider reflection of electromagnetic (EM) fields nor to perform wide angle propagation of forward fields. Therefore, it can not be used to analyze perpendicular dielectric crossing waveguides. At a maximum 0.5 dB power loss per crossing, the difficulty of simulation a waveguide crossing is how to compute the complex coupling waves with high enough precision. In this thesis, two-dimensional planar integrated optical waveguide crossing is studied in detail for the through and cross power coupling coefficients with the finite-difference frequency-domain (FD-FD) method. By exploiting the dual symmetries: the ¡§+¡¨ symmetry and the ¡§X¡¨ symmetry in the perpendicular crossing waveguide, we are able to compute the EM fields and their power coefficients without using artificial absorbing boundary conditions (ABC) nor using the perfectly matching layer (PML). We develop the layer-mode based transparent boundary condition (LM-TBC) [1] for launching the fundamental incident mode as well as transmitting the reflected and scattered wave fields off the crossing area. Numerical results including the field distribution, power coefficients are carefully verified and the convergent comparisons are also studied in the thesis.

The strive to increase the engine efficiency in terms of fuel consumption and lower emissions have lead to higher demands on materials. In this thesis five different thermal barrier coatings applied using air plasma spraying to three materials commonly used for exhaust application are evaluated. This thesis work was done at Scania CV in Södertälje with main focus on evaluation during thermal cycling. The goal of this thesis is to evaluate the coatings and correlate their behaviour to their characteristic microstructure. The coatings were evaluated through their stability in thermal conductivity, fracture toughness, hardness, porosity and failure modes. The parameters where obtained using laser flash, Vickers indentation, Vickers indentation fracture toughness and microscopic evaluation methods. The evaluation shows that conventionally used zirconia based materials exhibits low thermal conductivity, high hardness, and stable fracture toughness compared to other evaluated materials. One material that can be applicable in diesel exhaust application is mullite, which showed similar performance to zirconia based materials. For the use of TBC together with SiMo51 a different bondcoat than conventional NiCrAlY needs to be evaluated. / Strävan efter att konstruera effektivare motorer för att generera minskade utsläpp och bättre bränsleekonomi har genererat högre krav på konstruktionsmaterialen som används idag. I detta examensarbete som utförts på Scania CV i Södertälje utvärderas fem olika termiska barriärsskikt som belagts med plasma sprayning på tre vanligt förekommande konstruktionsmaterial för grenrör. Målet med detta examensarbete är att utvärdera beläggningarnas beteende under termisk cykling och koppla deras beteende till karakteristiska mikrostrukturer. Beläggningarna utvärderades genom att jämföra deras värmeledningsförmåga, hårdhet, brottseghet och porositet. Materialparametrarna utvärderades genom laser flash, Vickers hårdhetsmätning, Vickers brottseghet samt mikroskopiska bildanalyser. Resultaten visar att kommersiellt använda zirkonium baserade material uppvisar låg värmeledningsförmåga, hög hårdhet och hög brottseghet i förhållande till övriga material. Ett annat material som analyserats, mullit, visar på liknande beteenden som zirkonium baserade material men behöver utvärderas ytterligare. Om SiMo51 används som substratmaterial finns behovet att utvärdera användningen av andra typer av bindskikt än det austenitiska NiCrAlY nu använt.

The objective of this thesis project was to compare the stress behaviour in thermal barrier coatings (TBCs) with FE analyses in both 2D and 3D. The main focus was to analyse the vertical stresses in the topcoat (TC) and how they varied in relation to different thicknesses of the thermally grown oxide (TGO), spraying methods of the bondcoat (BC) and the topography of the BC. For the 2D simulations six samples were used; three with BCs sprayed with high-velocity oxy-fuel spraying and three sprayed with atmospheric plasma spraying. The samples had been exposed to isothermal heat treatment at 1150 °C for 0, 100 and 200 hours. Five images of each sample were taken with a scanning electron microscope, resulting in a total of 30 images. FE simulations based on these 30 images were done simulating a cooling from 1100 °C to 100 °C. The 3D simulations were based on surfaces created from coordinates measured with stripe projection technique on three samples consisting of only substrate and BC. Three domains of each sample had been measured and three CAD models based on randomly selected surfaces of each domain were made, resulting in 27 CAD models. The CAD models were used in the 3D FE simulations also simulating a cooling from 1100 °C to 100 °C. The results showed that the 2D simulations corresponds to published assertions about a stress inversion after TGO growth and that cracking will propagate from one peak to another, presuming the roughness of the TGO can be expressed as a wave. No conclusions of differences between spraying methods of the BC could be drawn. The stress inversion phenomenon was also found in the 3D simulations. By inspecting the TGO/TC-interface profile in different sections of a 3D model, difficulties in predicting the stress behaviour in a TBC with 2D were explained. No differences in stresses in relation to the BC roughness could be stated.

Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-08-14T12:53:45Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE_Versão_depósito na central.pdf: 5398168 bytes, checksum: 86dabd444bb2e345c6039ecb024634b1 (MD5) / Made available in DSpace on 2017-08-14T12:53:45Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) TESE_Versão_depósito na central.pdf: 5398168 bytes, checksum: 86dabd444bb2e345c6039ecb024634b1 (MD5) Previous issue date: 2016-05-24 / CNPQ / Ao considerar o contexto dos estudos sobre Turismo de Base Comunitária (TBC) e a evidência da governança como um dos fatores limitantes à consolidação de experiências turísticas de base comunitária, esta tese defende que a governança condiciona a reprodução dos princípios de participação e protagonismo comunitário, centrais às discussões do TBC. Dessa maneira, o objetivo geral desta tese é propor um modelo de análise da governança do TBC (MAG do TBC). Considerando uma perspectiva metodológica qualitativa baseada na teoria adaptativa de Layder (1993; 1998), o caminho metodológico compreendeu quatro fases distintas, nas quais fazem parte: uma pesquisa bibliográfica, duas consultas a especialistas por meio de grupo de discussões e verificação empírica do modelo em uma experiência de turismo consolidada, a Associação Acolhida na Colônia, sediada no município de Santa Rosa de Lima -SC. Ademais, a verificação empírica do MAG do TBC no campo possibilitou a emergência de novos critérios que foram incorporados à versão final do modelo. Os dados oriundos destas fases do estudo foram examinados e discutidos a partir da análise do conteúdo categorial. Desse modo, propõese que a análise da governança em experiências turística de TBC consolidadas seja analisada com base em três dimensões da governança, a saber: participação, transparência e eficácia. A operacionalização da análise destas dimensões se dá por meio da sistematização de elementos constituintes e seus critérios de análise, inerentes a cada dimensão supracitada. / Considering the context of the studies about Communitarian Based Tourism (CBT) and the evidence of governance as one of the limiting factors to the consolidation of the CBT experiences, this thesis defends that the governance influences the reproducing of the principles of participation and communitarian protagonism, central to CBT discussions. This way, the general aim of this research is propose a model of governance analysis of the CBT (MAG of TCB). Considering a qualitative methodology perspective based on adaptive theory of Layder (2993; 1998), the methodological way comprehended four different phases, which are composed by: bibliographical research, two queries to specialists through discussing groups and empiric verification of the model in an experience of consolidated tourism, the Association Acolhida na Colônia, placed in the city Santa Rosa de Lima-SC. Moreover, the empiric verification of the MAG of TBC in the field enabled the emergency of new criteria that were incorporated to final version of the model. The data from these phases of the study were examined and discussed from the analysis of categorical subject. This way, it is proposed that the analysis of governance in consolidated TBC touristic experience is analyzed based in three governance dimensions: participation, transparency and efficiency. The operationalization of these dimensions analysis is given through systematization of constituting elements and its criteria of analysis, inherent to each dimension mentioned above.

Thermal Barrier Coatings (TBC) are used to shield hot sections of gas turbine engines, helping to prevent the melting of metallic surfaces. TBC is a sophisticated layered system that can be divided into top coat, bond coat, and the super-alloy substrate. The highly heterogeneous microstructure of the TBC consists of defects such as pores, voids, and cracks of different sizes, which determine the coating’s final thermal and mechanical properties. The service lives of the coatings are dependent on these parameters. These coatings act as a defensive shield to protect the substrate from oxidation and corrosion caused by elevated temperatures. Yttria Stabilized Zirconia (YSZ) is the preferred thermal barrier coating for gas turbine engine applications. There are a certain number of deposition techniques that are used to deposit the thermal coating layer on the substrate; commonly used techniques are Air Plasma Sprayed (APS) or Electron Beam Physical Vapour Deposition (EB-PVD). The objective of this thesis is to model an optimized TBC that can be used on next-generation turbine engines. Modelling is performed to calculate the effective thermal conductivity of the YSZ coating deposited by EB-PVD by considering the effect of defects, porosities, and cracks. Bruggeman’s asymmetrical model was chosen as it can be extended for various types of porosities present in the material. The model is used as an iterative approach of a two-phase model and is extended up to a five-phase model. The results offer important information about the influence of randomly oriented defects on the overall thermal conductivity. The modelled microstructure can be fabricated with similar composition to have an enhanced thermal insulation. The modelling results are subsequently compared with existing theories published in previous works and experiments. The modelling approach developed in this work could be used as a tool to design the porous microstructure of a coating.

<div>Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) provide thermal and environmental protection to superalloy components operating within the combustor and high pressure sections of a gas turbine. However, calcium-magnesium-aluminum silicate (CMAS) deposits originated from particulate matter ingested through the air intake degrade YSZ TBCs, ultimately decreasing the overall efficiency of the engines. With the introduction of biofuels into gas turbines, a new list of impurities with no precedent in jet engines may interact with TBCs, arising the possibility to form CMAS deposits without flying in a particular environment and to exacerbate CMAS negative effect through the addition of other contaminants.</div><div><br></div><div>In this work, a cyclic thermal gradient rig was developed to test TBCs in similar conditions as in a gas turbine. The heat flux and non-contact surface temperature measurements were validated with a thermal transient model. The effect of biofuel impurities on YSZ TBCs was evaluated by spraying the coatings with impurity cocktails, solutions containing the impurities of interest, and subsequently testing their lifetimes in the ablation rig.</div><div><br></div><div>Detailed microstructure analysis revealed that APS and EB-PVD TBCs fail in different ways when exposed to equal concentrations of CMAS. When contaminating APS TBCs with varying combinations of CMAS constituents (e.g., S, C-S, C-A, C-A-S, C-M-S, and C-M-A-S), it was possible to identify that coatings delaminated at different rates depending on the combination of CMAS constituents. Finally, the effect of CMAS in combination with contaminants exclusive of biofuels was analyzed on YSZ TBCs. X-ray diffraction (XRD) analysis and micrographs revealed that glass modifiers (e.g., K₂O and ZnO) accelerated the degradation of YSZ TBCs.</div>