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Reactive Plasma Spraying (RPS) with a hydrocarbon gas has been studied as a method to improve the mechanical properties of a commercially available 80:20 nickel-chromium alloy, and subsequently as a method to reduce the oxygen content of sprayed MCrAlY coatings. A conventional d.c. plasma torch has been modified by attaching a conical graphite tube (reactor) onto the end of the gun. The powder is then sprayed through the reactor with injected reactive hydrocarbon gas. The reactor shrouds the plasma flame from the external atmosphere and contains the desirable inner atmosphere necessary for RPS. When spraying using a reactor and reactive gas the plasma environment is changed significantly. Work has been carried out to establish the effect various spray parameters have on the final coating such that new parameters can be selected which maximise the coatings quality and performance Reactively sprayed 80: 20 Ni/Cr coatings have been produced with an in- stiu carbide reinforcing phase, leading to greatly improved wear properties compared with conventionally sprayed coatings. Reactively sprayed MCrAlY coatings have been deposited with an order of magnitude reduction in oxide levels, leading to considerably fewer line defects such as oxide stringers and delarninations. An attempt has been made with the aid of computational fluid dynamics software, to model phenomenon occurring inside the reactor section as a method to appraise reactor design and suggest further design improvements.

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The friction surfacing process is a derivative of friction welding and retains all the benefits of that welding process - solid phase, forged microstructures and excellent metallurgical bonds. This work is aimed at the development of mathematical and statistical models for the optimisation of the significant process parameters in order to allow rapid development of new applications using standard CNC equipment. Also the possibility of implementing real-time control systems have been investigated and developed. A friction surfacing database has been configured to allow continuos recording and storage of the useful machine outputs. Later, an infrared pyrometer and thermocouples have also been connected to the data acquisition set-up establishing fully automated information flow from the process. A conversion procedure has been developed to ensure that the experimental results are applicable in industrial environments. Response surface map and the method of visual optimisation have been developed. They are an essential part of the methodology for experimental optimisation of the friction surfacing process. The problem of modelling and optimisation has also been approached using accurate statistical methods. Artificial intelligence in the form of neural networks has been used to improve the accuracy of the derived friction surfacing analytical relationships. For the first time dynamic study of the process has been carried out and CARIMA models have been derived using a modified version of the recursive least squares, to ensure high sensitivity and stability of the identification procedure. New conversion technique has been developed, allowing the use of existing models for materials that have not been used for friction surfacing before, reducing significantly the number of experiments. The idea of using indicator parameters has been introduced for the first time in this research. Such parameters are the force, the torque and the interface temperature and they can be measured on-line. It has been shown that variations of these parameters reflect in the quality of the coating characteristics that cannot be measured on-line. Real-time control has also been considered. An algorithm involving fuzzy logic and self-tuning extremum controller has been developed to continuously monitor and compensate in real-time against the variations in the coating characteristics, and respectively in the indicator parameters. The proposed methodology has been used to design a control system that is capable of maintaining optimal process characteristics. The value of this work is also in reducing the lead-time and hence the cost for determining the optimum parameters for a given coating material on a given substrate geometry. This is an important feature when developing new applications for the friction surfacing process. On the basis of this research a range of new commercial applications have emerged including the manufacture of machine knives for the food, pharmaceutical and packaging industries, repair of car engine valve seats, turbine blades, reclamation of shafts, etc.

nÃo hà / O desenvolvimento de revestimentos metÃlicos cada vez mais resistentes à corrosÃo e ao desgaste mecÃnico tem originado inÃmeros estudos na Ãrea de eletrodeposiÃÃo. Com intuito de se obter ligas metÃlicas com boas propriedades mecÃnicas, associadas a uma elevada resistÃncia à corrosÃo, à que os revestimentos de Zn-Mn tÃm sido bastante abordados nos Ãltimos anos, tendo em vista que estes oferecem melhores caracterÃsticas anticorrosivas quando comparados com revestimentos de zinco metÃlico, usualmente utilizados na indÃstria convencional. Neste trabalho, objetivou-se a obtenÃÃo e caracterizaÃÃo das ligas de Zn-Mn eletrodepositadas sobre eletrodos de platina e cobre metÃlico a partir de soluÃÃes a base de sais de sulfato dos metais em questÃo. Estudou-se a liga de Zn-Mn com utilizaÃÃo de voltametria cÃclica e linear, como tambÃm de cronoamperometria, onde nesta etapa todas as amostras foram obtidas em banho sem agitaÃÃo, à temperatura ambiente, 25ÂC, em diferentes densidades de corrente. Analisou-se tambÃm a estrutura fÃsica e morfolÃgica das ligas obtidas com uso de tÃcnicas como Microscopia EletrÃnica de Varredura (MEV) e Energia Dispersiva de Raios-X (EDX), variando-se parÃmetros como: densidade de corrente aplicada, pH da soluÃÃo eletrolÃtica, temperatura de deposiÃÃo e concentraÃÃo dos reagentes presentes no eletrÃlito. Para anÃlise da estrutura quÃmica das espÃcies formadas na liga em questÃo, utilizou-se a tÃcnica de DifraÃÃo de Raios-X (DRX) nas amostras obtidas em eletrodo de cobre. A partir dos resultados obtidos por meio das anÃlises voltamÃtricas, pÃde-se determinar os potenciais de reduÃÃo e oxidaÃÃo para a liga Zn-Mn onde estes ocorreram isoladamente para o zinco e para o manganÃs. Para as anÃlises de MEV e EDX observou-se que o manganÃs na liga apresenta-se na forma de oxido e o zinco na forma de metal isolado. Para as anÃlises de DRX, pÃde-se determinar as fases em que as espÃcies de Zn-Mn apresentam-se na liga, assim como tambÃm espÃcies de zinco e manganÃs isoladas. Os melhores resultados foram obtidos quando se aplicou uma densidade de corrente de 10 mA.cm-2, pH 6,0, temperatura ambiente e proporÃÃo de 1:1 entre o zinco e o manganÃs no eletrÃlito. / The development of alloys that are resistant to corrosion and good wear resistance led to several studies on the electrodeposition field. With the intention of carry out alloys with good mechanic properties, associated to a high corrosion resistance, Zn-Mn alloys have been frequently studied in the last years, once they offer better anticorrosive characteristics when compared to metallic zinc films, usually used in the conventional industry. This work aimed obtain and characterize Zn-Mn alloy electrodeposited on platinum electrode and metallic cooper from solutions composed by sulfate salts from the metals previously mentioned. Zn-Mn alloys were studied by using of cyclic and linear voltammetry, and also chronoamperommetry, in which all samples were obtained in bath without agitation, room temperature, 25 C, on different current densities. The physical and morphological structure of the alloys that have been obtained were analyzed by using technique such as scanning electronic microscopy (SEM) and X-ray dispersive energy (XDE), varying parameters such as: current density applied, pH, deposition temperature and reagents concentration in the bath. In order to analyze the chemical structure of the species formed on the alloy mentioned, a x-ray diffraction (XRD) technique was used with the samples obtained in cooper electrode. From the results obtained through voltammetric analyses, it is possible to determine the potential of reduction and oxidation of Zn-Mn alloy, which occurred separately to zinc and manganese. It was possible to observe that the manganese in the alloy appears as the oxide and the zinc as an isolated metal. Through XRD analysis, it was possible to determine the phases in which the Zn-Mn species appears in the alloy, and also isolated zinc and manganese. The best results were obtained when was applied 10mA.cm-2 current density; pH 6,0; room temperature and 1:1 proportion of zinc and manganese in the electrolytic bath.

Atomic vapors condensed onto solid surfaces form a remarkable category of condensed matter materials, the so-called thin films, with a myriad of compositions, morphological structures, and properties. The dynamic process of atomic condensation exhibits self-assembled pattern formation, producing morphologies with atomic-scale three-dimensional structures of seemingly limitless variety. This study attempts to shed new light on the dynamical growth processes of thin film deposition by analyzing in detail a previously unreported specific distinct emergent structure, a crystalline triangular-shaped spike that grows within copper and silver thin films. I explored the deposition parameters that lead to the growth of these unique structures, referred to as ``nanospikes'', fabricating approximately 55 thin films and used scanning electron microscopy and x-ray diffraction analysis. The variation of parameters include: vapor incidence angle, film thickness, substrate temperature, deposition rate, deposition material, substrate, and source-to-substrate distance. Microscopy analysis reveals that the silver and copper films deposited at glancing vapor incidence angles, 80 degrees and greater, have a high degree of branching interconnectivity between adjacent inclined nanorods. Diffraction analysis reveals that the vapor incidence angle influences the sub-populations of crystallites in the films, producing two different [110] crystal texture orientations. I hypothesize that the growth of nanospikes from nanorods is initiated by the stochastic arrival of vapor atoms and photons emitted from the deposition source at small diameter nanorods, and then driven by localized heating from vapor condensation and photon absorption. Restricted heat flow due to nanoscale thermal conduction maintains an elevated local temperature at the nanorod, enhancing adatom diffusion and enabling fast epitaxial crystal growth, leading to the formation and growth of nanospikes. Electron microscopy and x-ray diffraction analysis, and comparisons to related scientific literature, support this hypothesis. I also designed a highly modular ultrahigh vacuum deposition chamber, capable of concurrently mounting several different pieces of deposition equipment, that allows for a high degree of control of the growth dynamics of deposited thin films. I used the newly designed chamber to fabricate tailor-made nanostructured tantalum films for use in ultracapacitors, for the Cabot Corporation. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2011-01-17 15:22:47.533