<p>  </p> <p>Stress corrosion cracking (SCC) is a longstanding critical materials challenge in austenitic stainless steels (AuSS). Recently, there has been mounting concern regarding the potential for Chloride-induced stress corrosion cracking (CISCC) along arc weld seams on austenitic stainless-steel canisters used as spent nuclear fuel (SNF) dry storage containers, due to the residual stress from the welding process and exposure to chloride-rich coastal air at storage sites. To ensure the safety of the SNF storage, fundamental understanding and mitigation methods of CISCC are critical in both engineering design and maintenance of the storage canisters before and after their deployment. With the recent development of high-resolution characterization and analysis techniques, a more robust and comprehensive understanding of the fundamental TGCISCC mechanism starts to be more accessible. In this thesis, comprehensive state-of-the-art techniques, including SEM, EBSD, HREBSD, FIB, ATEM, TKD, potential dynamic measurement, XRD, and nanoindentation will be used to further understand the mechanistic mechanism of TGCISCC in AuSS from macroscopic scale down to atomistic scale. </p>

Thermal spray coatings applied with high velocity techniques produce dense, industrial quality coatings with strong adhesion and minimal decomposition. This thesis reports on investigations of splat-substrate interactions for both solid and molten splats. Specifically, individual particles were studied to see how the particle is altered during the spray coating process, how they bond to the substrate and the role of surface oxides. Investigations of NiCr particles high velocity air fuel (HVAF) thermally sprayed onto different materials found that soft substrates predominantly had deeply penetrating solid particles, whereas harder substrates resisted particle penetration and had a higher percentage of molten splats. This effect is caused by particle kinetic energy converted into heat during plastic deformation. The percentage of particle kinetic energy converted into heat is proportional to substrate hardness. It was also discovered that during the coating process the oxide is not removed or altered in composition, but becomes redistributed over a larger surface area due to the plastic deformation of the substrate. During this process, small scale redistribution and penetration of the oxide material by the incoming particle occurs. These results support the idea that successful bonding can occur only when the surface oxide on the substrate and on the coating material has been disturbed (for solid splats) or disrupted (for molten splats). To date, our knowledge of solid splat bonding processes within thermal spray coatings has been very subjective where mechanical and chemical bonding has been expected to contribute. In this thesis, the splat-substrate interface was investigated with focused ion beam (FIB) microscopy, cross-sectional SEM and cross-sectional TEM. For solid NiCr splat HVAF coatings, the discovery of interfacial formations, together with no evidence of chemical bonding across the particle-substrate interface suggest that mechanical bonding is the dominant bonding mechanism for solid splat coatings; where as chemical bonding only plays a role when splats and/or substrate become molten. / GNS Science

Thermal spray coatings applied with high velocity techniques produce dense, industrial quality coatings with strong adhesion and minimal decomposition. This thesis reports on investigations of splat-substrate interactions for both solid and molten splats. Specifically, individual particles were studied to see how the particle is altered during the spray coating process, how they bond to the substrate and the role of surface oxides. Investigations of NiCr particles high velocity air fuel (HVAF) thermally sprayed onto different materials found that soft substrates predominantly had deeply penetrating solid particles, whereas harder substrates resisted particle penetration and had a higher percentage of molten splats. This effect is caused by particle kinetic energy converted into heat during plastic deformation. The percentage of particle kinetic energy converted into heat is proportional to substrate hardness. It was also discovered that during the coating process the oxide is not removed or altered in composition, but becomes redistributed over a larger surface area due to the plastic deformation of the substrate. During this process, small scale redistribution and penetration of the oxide material by the incoming particle occurs. These results support the idea that successful bonding can occur only when the surface oxide on the substrate and on the coating material has been disturbed (for solid splats) or disrupted (for molten splats). To date, our knowledge of solid splat bonding processes within thermal spray coatings has been very subjective where mechanical and chemical bonding has been expected to contribute. In this thesis, the splat-substrate interface was investigated with focused ion beam (FIB) microscopy, cross-sectional SEM and cross-sectional TEM. For solid NiCr splat HVAF coatings, the discovery of interfacial formations, together with no evidence of chemical bonding across the particle-substrate interface suggest that mechanical bonding is the dominant bonding mechanism for solid splat coatings; where as chemical bonding only plays a role when splats and/or substrate become molten. / GNS Science

Thermal spray coatings applied with high velocity techniques produce dense, industrial quality coatings with strong adhesion and minimal decomposition. This thesis reports on investigations of splat-substrate interactions for both solid and molten splats. Specifically, individual particles were studied to see how the particle is altered during the spray coating process, how they bond to the substrate and the role of surface oxides. Investigations of NiCr particles high velocity air fuel (HVAF) thermally sprayed onto different materials found that soft substrates predominantly had deeply penetrating solid particles, whereas harder substrates resisted particle penetration and had a higher percentage of molten splats. This effect is caused by particle kinetic energy converted into heat during plastic deformation. The percentage of particle kinetic energy converted into heat is proportional to substrate hardness. It was also discovered that during the coating process the oxide is not removed or altered in composition, but becomes redistributed over a larger surface area due to the plastic deformation of the substrate. During this process, small scale redistribution and penetration of the oxide material by the incoming particle occurs. These results support the idea that successful bonding can occur only when the surface oxide on the substrate and on the coating material has been disturbed (for solid splats) or disrupted (for molten splats). To date, our knowledge of solid splat bonding processes within thermal spray coatings has been very subjective where mechanical and chemical bonding has been expected to contribute. In this thesis, the splat-substrate interface was investigated with focused ion beam (FIB) microscopy, cross-sectional SEM and cross-sectional TEM. For solid NiCr splat HVAF coatings, the discovery of interfacial formations, together with no evidence of chemical bonding across the particle-substrate interface suggest that mechanical bonding is the dominant bonding mechanism for solid splat coatings; where as chemical bonding only plays a role when splats and/or substrate become molten. / GNS Science

Thermal spray coatings applied with high velocity techniques produce dense, industrial quality coatings with strong adhesion and minimal decomposition. This thesis reports on investigations of splat-substrate interactions for both solid and molten splats. Specifically, individual particles were studied to see how the particle is altered during the spray coating process, how they bond to the substrate and the role of surface oxides. Investigations of NiCr particles high velocity air fuel (HVAF) thermally sprayed onto different materials found that soft substrates predominantly had deeply penetrating solid particles, whereas harder substrates resisted particle penetration and had a higher percentage of molten splats. This effect is caused by particle kinetic energy converted into heat during plastic deformation. The percentage of particle kinetic energy converted into heat is proportional to substrate hardness. It was also discovered that during the coating process the oxide is not removed or altered in composition, but becomes redistributed over a larger surface area due to the plastic deformation of the substrate. During this process, small scale redistribution and penetration of the oxide material by the incoming particle occurs. These results support the idea that successful bonding can occur only when the surface oxide on the substrate and on the coating material has been disturbed (for solid splats) or disrupted (for molten splats). To date, our knowledge of solid splat bonding processes within thermal spray coatings has been very subjective where mechanical and chemical bonding has been expected to contribute. In this thesis, the splat-substrate interface was investigated with focused ion beam (FIB) microscopy, cross-sectional SEM and cross-sectional TEM. For solid NiCr splat HVAF coatings, the discovery of interfacial formations, together with no evidence of chemical bonding across the particle-substrate interface suggest that mechanical bonding is the dominant bonding mechanism for solid splat coatings; where as chemical bonding only plays a role when splats and/or substrate become molten. / GNS Science

In dieser Arbeit wird die Beschichtung von Substraten mit Hilfe einer Ultraschallsprühanlage beschrieben. Es wurden Dispersionen aus Siliziumnanopartikeln und Organosiliziumpräkursoren genutzt, um Beschichtungen mit verschiedenen Dicken im Bereich von einigen hundert Nanometern bis zu mehreren Mikrometern auf verschiedenen metallischen Substraten zu erzeugen. Anschließend wurden diese der Blitzlampentemperung (FLA) unterzogen. Bei dünnen Beschichtungen mit Dicken von ca. 19 µm wurden nach der Blitzlampentemperung Filme auf dem Substrat erzeugt. Es wurden unterschiedliche Objektgrößen nach der Blitzlampentemperung in Abhängigkeit von dem Umgebungsdruck und der Pulslänge beobachtet. Bei dickeren Beschichtungen mit Dicken von ca. 38 µm bzw. 57 µm wurden selbstablösende Folien aus Silizium bei moderaten Pulsenergien von 4 J/cm² und durch das Anlegen von 5∙10-3 mbar Unterdruck während der Blitzlampentemperung hergestellt. Durch die Verwendung von Pulslängen mit 17,5 ms und Energien von bis zu 60 J/cm² wurden aus den ca. 38 µm dicken Beschichtungen nach der Blitzlampentemperung durch Übertragung auf ein Molybdänsubstrat ultradünne Siliziumschichten mit 280 nm Schichtdicke erzeugt. Mit Hilfe von Siliziumpresslingen wurde die maximale Eindringtiefe der Energie bei der Blitzlampentemperung ermittelt. Diese wurden bei verschiedenen Pulslängen und Energien mit der Blitzlampe getempert. Durch das Brechungsvermögen der Presslinge wurde an diesen sowohl die Oberfläche als auch durch Querschnittsaufnahmen die Sinterung bzw. das Schmelzen in der Tiefe nach der Blitzlampentemperung untersucht. Der Einfluss der Blitzlampentemperung auf die Polymorphie und die Kristallinität von Bis-mut(III)oxiden wurde untersucht. Die Charakterisierung der Siliziumfolien, Siliziumschichten und Siliziumpresslinge als auch der Bismut(III)oxide erfolgte unter anderem mittels Röntgenpulverdiffraktometrie, Rasterelektronenmikroskopie sowie Röntgenphotoelektronenspektroskopie.

In a variety of engineering applications, components are subjected to corrosive environment. Protective coatings are essential to improve the functional performances and/or extend the lifetime of the components. Thermal sprayingas a cost-effective coating deposition technique offers high flexibility in coatings' chemistry/morphology/microstructure design. However, the inherent pores formed during spraying limit the use of coatings for corrosion protection. The recently developed supersonic spray method, High-Velocity-Air-Fuel (HVAF), brings significant advantages in terms of cost and coating properties. Although severely reduced, the pores are not completely eliminated even with the HVAF process. In view of the above gap to have a high quality coating, bi-layer coatings have been developed to improve the corrosion resistance of the coatings. In a bi-layer coating, an intermediate layer is deposited on the substrate before spraying the coating. The electrochemical behavior of each layer is important to ensure a good corrosion protection. The corrosion behavior of the layers strongly depends on coating composition and microstructure, which are affected by feedstock material and spraying process. Therefore, the objective of the researchis to explore the relationships between feedstock material, spraying process, microstructure and corrosion behavior of bi-layer coatings. A specific motivationis to understand the corrosion mechanisms of the intermediate layer which forms the basis for developing superior protective coatings. Cr3C2-NiCr top layer and intermediate layers (Fe-, Co- and Ni-based) were sprayed by different thermal spraying processes. Microstructure analysis, as well as various corrosion tests, e.g., electrochemical, salt spray and immersion tests were performed. The results showed a direct link between the corrosion potential (Ecorr) of the intermediate layer and the corrosion mechanisms. It was found that the higher corrosion resistance of Ni-based coatings than Fe- and Co-based coatings was due to higher Ecorr of the coating in the galvanic couple with top layers. Inter-lamellar boundaries and interconnected pores reduced the corrosion resistance of intermediate layers, however a sufficient reservoir of protective scale-forming elements (such as Cr or Al) improved the corrosion behavior.

Kolfiber CF kan användas som positiv elektrod i strukturella batterier om de beläggs med ett aktivt material, såsom litiumjärnfosfat LFP. Fördelen med att använda kolfibrer som elektroder är att de samtidigt kan bära mekanisk belastning och lagra elektrisk energi. Det finns flera tekniker för att belägga kolfibrerna. I denna rapport kommer en jämförelse att göras av fibrer som belagts med elektroforetisk deponering, sprutbeläggning och pulverimpregnering. Elektrokemisk karakterisering kommer att avgöra och utvärdera prestandan hos dessa tre tekniker. Cellerna som monterades med sprutbeläggda och pulverimpregnerade prover visade de högsta kapaciteterna, 141 mAh/g vid C/10 respektive 139 mAh/g vid C/14. Vidare testning utfördes på de pulverimpregnerade proverna för att studera elektriska egenskaper och beteende, såsom elektrokemisk impedansspektroskopi EIS, cyklisk voltammetri CV och långtids-cykling. Svepelektronmikroskop SEM analys genomfördes för att observera ytmorfologin och förstå hur de elektrokemiska testerna kan påverka fibrernas yta. / Carbon Fibres (CF) can be used as the positive electrode in structural batteries if they are coated with an active material such as Lithium Iron Phosphate Oxide (LFP). The advantage of using carbon fibres as electrodes is that they simultaneously can carry the mechanical load and store electrical energy. There are several techniques to coat the carbon fibres. In this report, a comparison will be made on fibres coated using electrophoretic deposition, spray coating and powder impregnation. Electrochemical characterisation will determine and evaluate the performance of these three techniques. Cells assembled with spray-coated and powder-impregnated samples delivered the highest capacities, 141 mAh/g at C/10 and 139 mAh/g at C/14, respectively. Further testing was conducted on the powder-impregnated samples to study the electrical properties and behaviour, such as Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV) and long-term cycling. Scanning Electron Microscopy (SEM) analysis was performed to see the surface morphology and understand how electrochemical testing can affect the surface of the fibres.

<p dir="ltr">Fretting wear occurs when two contacting bodies under load are subjected to small amplitude oscillatory motion. Depending on the applied normal load, displacement amplitude, coefficient of friction and resulting shear force, two types of fretting wear regimes exist – (i) partial slip and (ii) gross slip. At displacement amplitudes higher than gross slip condition, sliding wear regime prevails. Fretting wear becomes dominant in machine components subject to vibrations such as bearings, dovetail joints, etc. whereas sliding wear is observed in brakes, piston-ring applications, etc. The work in this dissertation primarily focuses on characterizing the material response of various machine components subjected to fretting and sliding wear regimes.</p><p dir="ltr">At first, the friction and fretting wear behavior of inlet ring and spring clip components used in land-based gas turbines was investigated at elevated (<a href="" target="_blank">500°C</a>) temperature. In order to achieve this objective, a novel high-temperature fretting wear apparatus was designed and developed to simulate the conditions existing in a gas turbine. The test apparatus was used to investigate fretting wear of atmospheric plasma sprayed (APS) Cr₃C₂-NiCr (25% wt.), high-velocity oxy-fuel (HVOF) sprayed Cr₃C₂-NiCr (25% wt.), HVOF sprayed T-800 and APS sprayed PS400 coated inlet rings against HVOF-sprayed Cr₃C₂-NiCr (25% wt.) coated spring clip. The PS400 coated inlet rings demonstrated a significant reduction in friction and wear. A finite element (FE) framework was also developed to simulate fretting wear in HVOF-sprayed Cr₃C₂-NiCr composite cermet coating. The material microstructure was modelled using Voronoi tessellations with a log-normal distribution of grain size. Moreover, the individual material phases in the coating were randomly assigned to resemble the microstructure from an actual SEM micrograph. A damage mechanics based cohesive zone model with grain deletion algorithm was used to simulate debonding of the ceramic carbide phase from the matrix and resulting degradation from repeated fretting cycles. The specific wear rate obtained from the model for the existing material microstructure was benchmarked against experiments. Novel material microstructures were also modeled and demonstrated to show less scatter in wear rate.</p><p dir="ltr">Following, a three-dimensional (3D) continuum damage mechanics (CDM) FE model was developed to investigate the effects of fretting wear on rolling contact fatigue (RCF) of bearing steels. In order to determine the fretting scar geometry, a 3D arbitrary Lagrangian-Eulerian (ALE) adaptive mesh (AM) FE model was developed to simulate fretting wear between two elastic bodies for different initially pristine fretting pressures (0.5, 0.75 and 1 GPa) and friction coefficients (0.15, 0.175 and 0.25) resulting in stick zone to contact width ratios, c/a = 0.35, 0.55 and 0.75. The resulting wear profiles were subjected to various initially pristine RCF pressures (1, 2.2 and 3.4 GPa). The pressure profiles for RCF were determined by moving the contact over the fretted wear profiles in 21 steps. These pressure profiles were then used in the CDM-FE model to predict the RCF life of fretted surfaces. The results indicate that increased fretting pressure leads to more wear on the surface, thereby reducing RCF life. As the RCF pressure increases (P_RCF ≥ 2.2 GPa), the effect of fretting on RCF life decreases for all fretting pressures and c/a values, indicating that life is primarily governed by the RCF pressure. The results from CDM-FE model were used to develop a life equation for evaluating the L₁₀ life of fretted M-50 bearing steel for the range of tested conditions.</p><p dir="ltr">Lastly, the sliding wear characteristics of pitch and poly-acrylonitrile based carbon-carbon (C/C) composites were investigated in air and nitrogen environment by designing and developing a disc brake test rig. It was found that the temperature of the disc, the surrounding environment, the supplied energy flux as well as the type of composite play a critical role in determining whether C/C composites operate in normal wear or dusting wear regime. Further analysis of wear mechanisms revealed interface and matrix cracking with fiber breakage from tests in air environment, whereas in nitrogen environment, particulate and layered debris played a prominent role.</p>

We present a novel top-electrode spray-coating process for the solution-based deposition of silver nanowires (AgNWs) onto vacuum-processed small molecule organic electronic solar cells. The process is compatible with organic light emitting diodes (OLEDs) and organic light emitting thin film transistors (OLETs) as well. By modifying commonly synthesized AgNWs with a perfluorinated methacrylate, we are able to disperse these wires in a highly fluorinated solvent. This solvent does not dissolve most organic materials, enabling a top spray-coating process for sensitive small molecule and polymer-based devices. The optimized preparation of the novel AgNW dispersion and spray-coating at only 30 °C leads to high performance electrodes directly after the deposition, exhibiting a sheet resistance of 10.0 Ω □−1 at 87.4% transparency (80.0% with substrate). By spraying our novel AgNW dispersion in air onto the vacuum-processed organic p-i-n type solar cells, we obtain working solar cells with a power conversion efficiency (PCE) of 1.23%, compared to the air exposed reference devices employing thermally evaporated thin metal layers as the top-electrode.