Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph.D.)--Duquesne University, 2006. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references and abstracts.

The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment.  In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions. The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties.  Through the deposition of well designed bonding and template layer structures the above problems may be eliminated. Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts. Finally, the CVD-Al2O3 coating topography influences the contact conditions in sliding as well as in metal cutting. In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.

Resumo: Este trabalho está basicamente dividido em duas partes. A primeira está relacionada à limpeza da superfície da liga de alumínio AA6063T5 e sua influência na proteção contra a corrosão. A segunda parte se refere à preparação de revestimentos híbridos orgânicoinorgânico pelo processo sol-gel e deposição sobre a superfície da liga de alumínio por dipcoating. Três amostras de liga AA6063T5 foram investigadas: como recebida, debastada e polida mecanicamente e tratada quimicamente. O tratamento mecânico foi realizado utilizando lixas SiC de granulometria 320 a 4000 e o químico foi realizado utilizando uma solução aquosa contendo uma mistura de hidróxido, sulfato e cloreto de sódio. Todas as amostras foram caracterizadas fisicamente por difratometria de raios X (XRD), medidas de dureza, microscopia eletrônica de varredura (SEM) e microscopia óptica (MO), e por medidas de potencial de circuito aberto (OCP) e espectroscopia de impedância eletroquímica (EIS) em solução 3,5% NaCl. As imagens SEM mostraram que a presença de partícula intermetálicas na superfície da liga diminui após o tratamento químico comparado ao tratamento mecânico. Os resultados de EIS mostraram que o tratamento químico oferece maior resistência à corrosão do que as submetidas aos outros tratamentos, porque o ataque alcalino utilizado dissolveu a maioria dos precipitados contendo Fe ou Cu, elementos responsáveis por sítios catódicos. A lavagem com HNO3 pela qual passou a amostra tratada quimicamente provavelmente reforçou a camada de óxido, tornando a superfície da liga mais resistente ao ataque por cloreto. Os revestimentos híbridos foram somente depositados na liga que recebeu tratamento químico. Esses filmes híbridos foram preparados com tetraetoxi-silano (TEOS) e 3-metacriloxipropril trimetoxi silano (MPTS), pela hidrólise e policondensação em meio ácido seguido por... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This work is basically divided in two parts: the first one is related to the surface treatment of AA6063T5 aluminum alloy and its influence on the protection against corrosion. The second concerns to the preparation of organic-inorganic hybrid coatings by the sol-gel process that were deposited on the aluminum alloys by dip-coating. Three samples of AA6063T5 aluminum alloys were investigated, the as-received one, after mechanical and chemical treatment, respectively. The mechanical treatment was realized using SiC paper grades 320 to 4000 and the chemical one was done by an aqueous solution containing a mixture of sodium hydroxide, chloride and sulfate. All samples were physically characterized by X-ray diffractometry (XRD), hardness measurements, scanning electron microscopy (SEM) and optical microscopy (OM), and electrochemically by open circuit measurements (OCP) and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. The SEM images depicted that the presence of intermetallic particles on the alloy surface decreased after the chemical treatment compared to the mechanical one. The EIS results showed that the sample chemically treated possesses a higher corrosion resistance than those obtained using other procedures. EIS results showed that the chemically treated sample presented higher corrosion resistance than the ones submitted to other procedures. The alkaline treatment dissolves the great part of precipitates containing iron or copper, which are responsible by the cathodic sites formation. The washing of the sample with nitric acid solution after the alkaline treatment removes impurities from the surface and can give to the oxide layer higher resistance against the action of the chloride ion. The hybrid coatings were only deposited on the alloy that received the chemical treatment. Hybrid films containing tetraethoxysilane (TEOS) and 3-methacryloxypropyltrimetho... (Complete abstract click electronic access below) / Orientador: Assis Vicente Benedetti / Coorientador: Cecílio Sadao Fugivara / Banca: Celso Valentim Santilli / Banca: Patrícia Hatsue Suegama / Banca: Roberto Garcia / Banca: Adalgisa Rodrigues de Andrade / Doutor

Alkyd emulsions are currently being developed for coating applications. These paints combine the technical advantages of alkyd polymers, which give coatings of a high gloss finish, with the environmental and health benefits of solvent-free systems. Nonetheless, the drying and film formation of these systems involve several steps, none of which is well understood yet. These include creaming or sedimentation, evaporation of the continuous water phase, coalescence of the alkyd droplets, a possible phase-inversion, and the oxidative cross-linking of the alkyd polymer to form a hard coating. In this thesis. Magnetic Resonance Microscopy is used to investigate the film formation of alkyd emulsion coatings. As the process is complex, studies on a different range of emulsions and related systems are performed to gain further insight into the different steps involved. A combination of Liquid State Microscopy, diffusometry and broad line imaging (Stray Field Magnetic Resonance Imaging) is employed, and it is shown that this combination provides results extremely rich in information. First, a study of the cream layer and the creaming dynamics of model bulk oil-in-water emulsions containing different concentrations of thickener is presented. The experimental data are compared to the predictions of a numerical model, and evidence is gained that the presence of the thickener induces flocculation according to a depletion mechanism. Then, the water evaporation from alkyd emulsion droplets is investigated and the water concentration across the droplet is modelled according to an original model based on lateral diffusion of water. There is no evidence from spectroscopy and diffusometry for phase-inversion during the drying of alkyd emulsion coatings. Finally the cross-linking of alkyds containing driers is found to be non-uniform across the film thickness.

Thermal barrier coatings have been widely used to provide thermal protection to components in the hot section of gas turbines. This research focuses on two influencing factors on coating behavior: thermal gradient and cyclic oxidation. The delamination mechanics under thermal gradient is analyzed, taking thermally grown oxide into consideration. Coatings experience thermal gradients at different stages during actual service flight. One is due to engine power shut down when landing and the other due to internal cooling of the substrate. Thermally grown oxide (TGO) also acts as a critical factor in delamination mechanics. The induced stress gradient and corresponding energy release rate for interface delamination and shallower delamination are presented. Mechanism maps that explain the criteria for preventing delamination from developing and propagating are established. Three cooling trajectories are envisaged to analyze the variation in the possibility of delamination. Multilayer coatings used in components of the hot section of aero turbine engines also experience cyclic temperature variation during flight cycles. As experiment conditions vary and coating performance is improved, the time required to run through the test of coating failure can be both time-consuming and prohibitive. Therefore, protocols providing prediction of quantified coating behavior are in demand to shorten life-time tests. Curves of mass change are obtained from quantifying scale growth and loss by different models such as Cyclic Oxidation Spall Program (COSP). A modification is made by combining COSP and a mechanic based model to obtain critical parameters for lifetime prediction from short time experiment. The time for coatings to reach peak temperature during cycling is discovered to influence prominently on modeling results. Predictions for several coating compositions and cycling conditions are consistent with the data from the existing experiments of the coating system.

Organically modified sol-gel coatings have been investigated as potential replacements for chromate conversion coating of AA1050 and AA2024 aluminium alloys. The coatings were prepared by a combination of a completely hydrolysable precursor of tetra-n-propoxyzirconium (TPOZ), with a partially hydrolysable precursor of glycidoxypropyltrimethoxysilane (GPTMS). GPTMS contains organic functional groups, which are retained in the sol-gel coatings after the hydrolysis-condensation process. Different process parameters, e.g. GPTMS/TPOZ ratios, withdrawal speeds, solvent water concentrations, and curing temperatures were studied. Coatings produced using a low GPTMS/TPOZ ratio and a high withdrawal speed generated significant cracks due to the shrinkage of the coatings. It was found that increase of organic moieties reduced the shrinkage of the coatings and the tendency for crack formation. By controlling process parameters and ratios of organic and inorganic moieties, crack-free sol-gel coatings from 0.1 μm to 9 μm thick can be achieved. The sol-gel coatings formed are amorphous and contain organic epoxy-ether retained silicon oxide, silicon hydroxide, zirconium oxide, zirconium hydroxide, and zirconium acetate. The Si/Zr ratios of resultant sol-gel coatings are proportional to the initial GPTMS/TPOZ ratio. Cerium oxide nanoparticles were successfully incorporated into sol-gel coatings with a single layer and double layer sol-gel process. Through the dip coating process, crack-free sol-gel coatings, of varied thickness, were developed on different aluminium substrate, including electropolished superpure aluminium, magnetron sputtered aluminium with varied copper contents from 0 to 30 wt.%, and commercial AA1050 and 2024 aluminium alloys. Sol-gel coatings formed on commercial AA1050 and 2024 aluminium alloys revealed a significant passivation in 3.5 wt.% sodium chloride solution during anodic polarisation when the sol-gel coating is more than 1 µm thick and proper surface pretreatments of the alloys were used. Corrosion tests by immersion in 3.5 wt% sodium chloride solution and by salt spray in 5 wt.% sodium chloride solution revealed that sol-gel coatings successfully protected AA2024 aluminium alloy against the aggressive environment and have the potential to replace chromate containing coating systems.

A presente pesquisa tem como finalidade o estudo de ensaio de aderência para revestimentos de argamassa, a partir de esforços de cisalhamentos. A ABNT NBR 13528:2010 trata do ensaio de aderência de revestimento, determinada por meio da aplicação de uma carga constante, normal, aplicada sobre um suporte metálico ligado diretamente a um corpo-de-prova do revestimento a ser ensaiado. Nessa pesquisa procurou-se verificar, em laboratório, a determinação da resistência de aderência ao cisalhamento como mais um parâmetro na avaliação dos revestimentos de argamassa. Esse estudo foi realizado através do ensaio de arrancamento oblíquo ao revestimento a ser analisado. A mesma norma recomenda que, para delimitação da superfície do corpo-de-prova, esses deverão ser de forma circular de 50 mm de diâmetro. No entanto, nesse trabalho foram utilizados corposde- prova de seção quadrada de 100 mm de lado com a finalidade de adaptar-se à forma e ao tipo de execução dos ensaios a serem realizados na pesquisa. Para realização da pesquisa foram confeccionados painéis de blocos cerâmicos revestidos com argamassa sobre os quais foram ensaiados corpos-de-prova sob os ângulos de 0, 45 e 90. Para tornar possível a realização dos ensaios sob os ângulos de 45 e 0 foi necessário elaborar dispositivos adaptadores para execução dos respectivos ensaios. O objetivo desse trabalho consistiu em determinar a resistência de aderência ao cisalhamento a partir da aplicação de uma carga de arrancamento aplicada obliquamente ao revestimento. Através de uma Análise de variância, verificou-se que os resultados obtidos apontam uma relação entre a carga de arrancamento oblíqua (45) e a resistência de aderência ao cisalhamento (0), objetivo dessa pesquisa / This research studies aims the determination of bond of rendering mortar, through shear efforts. The ABNT NBR 13528:2010 prescribes the test method of bond strength of mortar rendering, determined a constant load applied on a normal metallic device, connected directly to a specimen rendering mortar to be tested. This survey sought to verify, in the laboratory, the determination of resistance to shear adhesion as another parameter in the evaluation of rendering mortar. This study was carried out by testing pullout oblique to the rendering to be parsed. The same standard recommends that delimitation of the body surface-specimens these should be circular 50 mm in diameter. However, in this work were used specimens of squared form whose sides measure 100 mm having both surfaces in order to adapt the form and type of carrying out the tests to be carried out in the search. For the research achievement were made of ceramic bricks panels which were tested specimens under the angles from 0, 45 and 90. To make it possible to carry out the tests under the angles of 45 and 0 required adapter devices to run their tests. The goal of this work was to determine the resistance to shear adhesion from applying a load of pullout applied obliquely to finish. Through an analysis of variance, the results suggest a relationship between the workload pullout oblique (45) and the resistance to shear adhesion (0), goal of this research

Coating flows can be defined as a laminar free surface flows, whereby a liquid layer is applied onto a solid substrate. A typical industrial application consists of co-rotating cylindrical rollers, which are used to apply a liquid coating (paint) onto a moving substrate, and depending on the direction of the rollers, can be configured in either forward or reverse mode. These types of coating solution flows are industrially important applications, and convey viscoelastic aspects due to their polymeric content and unsteady polymeric behaviour. The process often possesses localized regions of high shear and extension rates (narrow nip and wetting-line zones), which may cause instabilities on the coated substrate (ribbing, leveling, striping). These non-Newtonian and viscoelastic studies for industrial reverse roll coating focus on the use of computational techniques to model these types of coating flows, alongside the analysis of the fluid flow behaviour and under varied rheological properties. Two flow problem configurations have been considered, a model benchmark problem of mixed combined-separating flow, and the industrial application of reverse roll coating flow. Predictions and corresponding solutions are reported for viscous, inelastic and complex viscoelastic fluid properties. The numerical formulation adopts a Taylor-Galerkin pressure-correction (TGPC) scheme, using a finite element method for viscous, inelastic flows and a hybrid finite element/finite volume method for their viscoelastic counterparts. The research plan is centered around computational fluid dynamics and rheological studies, with the main target focused on industrial roll-coating operations. From simple theory, Newtonian and non-Newtonian coating flows possess specific, yet disparate characteristics. This may lead to distinct and significant differences in their detailed flow behaviour, and in the stressing levels generated, dependent upon the nature of the flow configuration. The study is segmented into several stages: initially, solution was sought for a benchmark flow problem, where a semi- implicit time stepping finite element procedure was employed to simulate a mixed combined- separating flow. Here, both viscous and viscoplastic material approximations have been introduced. Secondly, the industrial application of reverse roll coating flow was addressed for viscous inelastic coating fluids. This incorporated scenarios of inclusion and not of a dynamic wetting line and consideration of the effects of a rubber elastomer-cover upon the applicator roll. Thirdly, viscoelastic paint coatings were addressed for the industrial reverse roll coating flow. Here, a hybrid finite element/finite volume sub-cell method was utilized, and with inclusion of a dynamic wetting line. Of the various viscoelastic material models available, use has been made of the Phan-Thien Taimer (PTT) network class of models, in both linear and exponential variety, and of the FENE class of models, with FENE-CR and FENE-P versions. This has offered a richness in capacity over variation of rheological properties. The choice of computational methods has been justified and the TGPC algorithm was deemed suitable for problem solution. The methodology tested on combined-separating flow provided high-quality numerical results, which compare favorably against experiments, literature and theory. When applied to the reverse roll coating problem, the TGPC algorithm has been coupled to a time-dependent free-surface update procedure, to determine the dynamic movement of the meniscus and the wetting line. Around the nip-region, the flow problem manifests strong flow features, which have been investigated for a range of rheological properties of varying shear and extensional response. The direct impact these have on localized peak nip-pressures and distributional lift levels has been observed, where several relief mechanisms have been successfully identified (important to optimize process control). The influence of solvent fraction, extensional viscosity and increasing elasticity, up to critical stress states have been analysed in considerable detail. In summary, the success of this work indicates optimal flow process settings and preferential Theological coating properties to employ, with respect to this industrial coating process. As such, it lays the foundation and guide towards achieving a stable and consistent coating application - specifically, as high-speed high-gain production is of current demanded.

Microorganisms attachment to the surfaces located in the marine water has become a significant problem. Historically, the antifouling properties of the coatings were achieved by using biocides, which had a negative consequence to the marine environment. Currently, alternative environmental friendly methods are required. This thesis aimed to investigate and produce the antifouling coatings that can be used as potential candidates in the marine industry. In this study, a range of novel polymer nanocomposite coatings was fabricated via the method of solvent and tested based on the strategy of microbial adhesion. The composition of the coatings mainly contains polidimethylsiloxane (PDMS) and different nanomaterials. The coatings applied on glass substrate were characterised using X-ray spectroscopy (XRD), scanning electron microscopy (SEM), contact angle measurements, inductively coupled plasma mass spectroscopy (ICP-MS) and atomic force microscopy (AFM). In biofouling assays, attachment of bacteria B. Subtilis and three marine microalgae (Skeletonema sp., Amphora sp., D. Salina) was investigated in laboratory scale. The obtained results suggested that small amount of nanoparticles in the polymer matrix can improve the antifouling settlement behaviour of the coatings. All microalgae attached more on PDMS/SiO2 and control surfaces (glass and PDMS) compared to the coatings containing multiwall carbon nanotubes (MWCNT) and sodium bismuth titanate (NBT). The influence of contact time, surface roughness and surface wettability was also studied. The microbial attachment varied significantly with respect to contact time and surface properties. There was no obvious evidence showing that the wetting properties and the roughness of the coatings have an effect on growth ... [cont.].