Increased understanding of plasma-polymer interactions is required to further the technological use of such processes, and elucidates heterogeneous physico-chemical reactions which occur under bombardment by complex combinations of energetic species. This thesis presents a systematic investigation into the effect of exposing organic and inorganic polymeric surfaces to controlled non-isothermal plasmas. Concurrently, a novel process is presented by which metal oxide gas barrier coatings are synthesized on polymer substrates by non- isothermal plasma treatment. Organic polymers exhibiting a range of structures were modified using non-isothermal plasmas at atmospheric and low pressure. The extent of atmospheric discharge oxygenation, measured by X-ray photoelectron spectroscopy (XPS), correlated with the polymers' ozonolysis rate constants. Surface physical disruption, studied using atomic force microscopy (AFM), after atmospheric discharge treatment was more pronounced than after low pressure plasma treatment. During low pressure oxygen plasma treatment, polymers containing phenyl groups were oxygenated to an extent which varied with the strength of π-π* valence band excitation in XPS C(1s) spectra of the untreated polymers, suggesting a dominance of reaction of plasma atomic oxygen at polymer radical sites excited by plasma vacuum ultraviolet radiation. The size of globules, observed by AFM, on the plasma modified surfaces correlated with the extent of surface chemical modification, inkeeping with a mechanism of chemically driven agglomeration of plasma oxidized low molecular weight polymer material. Oxygen plasma was more effective than water plasma in chemically modifying the surface of films of zirconium-normal-butoxide spin coated on polyester substrates, and the resulting optimized treatment produced a significant reduction in gas permeation of the substrate. XPS studies showed that oxygen plasma treatment of a polyphenylsilsesquioxane film on polyester film created a SiO(_2) layer less than 8 nm thin, which reduced O(_2) and Ar permeation of the coated film by 37.5 % and 31.6% respectively.

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New methods in the fabrication of top coat and bond coat have been introduced to improve the efficiency and performance of advanced thermal barrier coatings (TBCs).i. Top coat. Thick yttria-stabilized-zirconia (YSZ) coatings (300-400 μm) have been fabricated by using electrophoretic deposition (EPD) method. The EPD coatings have more favorable microstructures with uniformly distributed porosity and stronger bonding, in comparison with conventional air-plasma spray (APS) coatings. ii. Bond coat. Pt-diffused single γ’-phase bond coat has been fabricated by applying selective etching prior to the electroplating of Pt on CMSX-4 single crystal superalloys. The concern on the compromised scale adhesion caused by the depletion of Pt is effectively avoided, as Pt remains stable in a coherent γ’-phase layer after long-term diffusion and oxidation. Considerable cost of Pt could also be reduced. Commercial TBCs, comprising an electron beam physical vapour deposition (EBPVD) top coat, a Pt-enriched intermetallic bond coat and a CMSX-4 single crystal superalloy, have also been investigated focusing on the failures that typically occurred at the scale/alloy interface. Advanced characterization techniques have been used to study the chemical factors (Al, Pt, S, Hf, etc.) that determine the durability of TBCs. Mechanisms have been discussed that control the TBCs behaviours of diffusion, oxidation, and adhesion. i. Diffusion. A depletion of Pt near the scale/alloy interface inevitably occurs at high temperatures, which significantly weakens the scale adhesion. Mechanisms controlling the diffusion of Pt in Ni-based single crystal superalloys at high temperatures have been investigated focusing on the evolution of phase, microstructure, and composition. It was found that Pt has negative chemical interactions with Al, Ti and Ta, all of which could stabilize Pt in β- and γ’-phases, and therefore avoid the depletion of Pt. ii. Oxidation. Selective oxidation behaviour of Ni-based superalloys has been studied by using thermodynamic calculations, which is mainly affected by alloy compositions, oxygen partial pressures and temperatures. It was found that the formation of a protective α-Al2O3 scale is more favoured under lower oxygen partial pressures and higher temperatures. The additions of Al and Pt in Ni-based superalloys could also promote the formation of Al2O3 and the exclusion of NiO and spinel. The additions of reactive elements (RE), however, are less effective and may even cause severe internal oxidations due to a competitive oxidation between Al and RE.iii. Adhesion. Sulphur effect in TBCs mainly refers to a segregation of sulphur at the scale/alloy interface, which significantly deteriorates the scale adhesion to alloys. High resolution secondary ion mass spectrometry (Nano-SIMS) was employed to trace sulphur in commercial TBCs. The undesired “sulphur effect” on scale adhesion was suggested to be caused by the formation of residual sulphides beneath the scale with weaker ionic bonding to alloy cations, rather than a segregation of sulphur atoms. Possible solutions have been suggested to alleviate the sulphur effect in TBCs.

Surface temperature and heat flux measurements were made in a single cylinder SI engine piston when uncoated and with two different surface coatings: a metal TBC and YSZ. A new thermocouple was developed to accurately measure surface temperatures. The engine was operated in a standard full load mode and a knock promoting mode featuring heated intake air and advanced spark timing. Cylinder pressures were measured to quantify knock. It was found that average heat flux into the piston substrate was 33 % higher with the metal TBC and unchanged with the YSZ relative to the uncoated surface. The increase with the metal TBC was attributed to its surface roughness. However, the metal TBC and YSZ reduced peak heat flux by 69 and 77 %, respectively. Both the metal TBC and YSZ reduced knock compared to the uncoated surface. After testing, the metal TBC was undamaged and the YSZ was slightly chipped.

Surface temperature and heat flux measurements were made in a single cylinder SI engine piston when uncoated and with two different surface coatings: a metal TBC and YSZ. A new thermocouple was developed to accurately measure surface temperatures. The engine was operated in a standard full load mode and a knock promoting mode featuring heated intake air and advanced spark timing. Cylinder pressures were measured to quantify knock. It was found that average heat flux into the piston substrate was 33 % higher with the metal TBC and unchanged with the YSZ relative to the uncoated surface. The increase with the metal TBC was attributed to its surface roughness. However, the metal TBC and YSZ reduced peak heat flux by 69 and 77 %, respectively. Both the metal TBC and YSZ reduced knock compared to the uncoated surface. After testing, the metal TBC was undamaged and the YSZ was slightly chipped.

Thermal barrier coatings (TBCs) have become an important part of turbine technology by providing thermal protection to the underlying metallic components. These coatings are typically made from a zirconia-based ceramics which have a low thermal conductivity and thermal expansion coefficients similar to those of the superalloys. Early failure in these coatings is most often due to foreign object damage and erosion resulting in delamination and spallation. To protect against these types of failure, new materials with increased toughness are needed. There are two main toughening mechanisms in ceramics: transformation toughening, which is limited to low temperature applications and ferroelastic toughening which is accessible at all temperatures. Ferroelastic toughening occurs when the c-axis of the tetragonal grain undergoes reorientation under the application of an external stress. In this study, ferroelastic toughening is examined by Raman spectroscopy. It is shown that by using polarized confocal Raman spectroscopy one can not only observed the ferroelastic process, but also measure the parameters that control the increase in toughness observed. Ferroelastic toughening was observed in two ways in the 18mol% ceria stabilized zirconia (18CSZ) samples studied here. Samples were either exposed to indentation damage or uniaxial loading. In both of these cases maps of the ceramic surface were taken using Raman spectroscopy following loading and the relative intensities of the tetragonal peaks were analyzed. The resulting intensity profiles were used to monitor the reorientation of domains corresponding to ferroelastic toughening. Changes in domain orientation were observed that corresponded to the reorientation of domains along cracks as well as on a larger scale along those cracks. Domain reorientation was also observed under uniaxial loading and the stresses required for domain formation and movement were measured.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Deposition rate; zirconia; TBC; texture; microstructure; EB-PVD. Includes bibliographical references (p. 78-79).

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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.

Dissertation Master of Technology Mechanical Engineering Faculty of Engineering Cape Peninsula University of Technology 2014 / Thermal Barrier Coatings (TBC’s) created by Electron Beam Physical Vapour Deposition (EB-PVD) are widely used in the aerospace industry. Advancements in the field however are hindered by the cost and time required for research and development. Hence, there exists a need for a more comprehensive understanding of coating parameter interactions to better predict response values without the need for extensive pre-production testing. This thesis seeks to provide a response surface for EB-PVD coatings, by investigating the following EB- PVD independent input variables: electron beam emission current, gas ratio, vacuum pressure, substrate temperature, roughness and process time in order to generate a predictive statistical model. Output variables were numerous, however emphasis was placed on: TBC coating thickness and density of columns generated during the process. It is impossible to select an “optimum process recipe”; rather, there exists many optimal combinations suited to specific coating structure and its application. Therein lies the need for this model, able to predict TBC properties according to input variables. Using ALD’s Smart Coater (ALD Vacuum Technologies GmbH), a ceramic top coat (Yttria partially stabilized zirconia, YPSZ, ZrO2-7%Y2O3) was deposited onto 40x30x5mm Inconel 617 samples with NiAl bond coat. These samples were subsequently tested to determine coating properties. The research will show that the complex nature of EB-PVD TBCs may be simplified, at least to a certain degree through a statistical analysis of the interactions between process variables.