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The integrity and properties of ceramic coatings produced by atmospheric plasma spraying are highly controlled by the splat morphology and splat interconnection. In this study, the influence of selected parameters (spray angle, surface velocity of the spray gun, and substrate temperature) on splat morphology and coating microstructure was investigated. A favorite set of spray gun parameters, of which their effects on splat morphology and coating microstructure have been verified by previous experiments, were used to conduct the experiments for the present work. It was found that depositing fully molten particles on a hot substrate increases the fraction of disk-like splats by about 60% at the expense of the fraction of irregular splats. Preheating the substrate also increases the pore count and level of coating porosity, while it does not influence the density of segmentation cracks. In contrast, the surface velocity of the spray gun does not affect the splat morphology while a slow speed decreases the coating porosity and plays a significant role in generating segmentation cracks. Shifting the spray angle by 15�� distorts up to 20% of disk-like splats and slightly decreases the porosity level. However, changing the spray angle does not affect the generation of segmentation cracks., Journal of thermal spray technology;Vol. 30. 2021, pp 1015���1027

In dieser Arbeit wurde das Potenzial von Suspensionsplasmaspritzbeschichtungen (SPS) als Wärmedämmschichten untersucht. Im Allgemeinen kann diese Arbeit in vier Teile unterteilt werden. Im ersten Teil wurden die Auswirkungen von Spritzparametern auf die Mikrostruktur der Beschichtung untersucht. Darüber hinaus wurde ein vereinfachtes Modell erstellt, um die Beziehung zwischen mechanischen Eigenschaften und Lebensdauer zu beschreiben. Im zweiten Teil wurde ein Versagensmechanismus der säulenförmigen Beschichtung vorgeschlagen. Im dritten Teil wurde der Sintereffekt auf Beschichtungen untersucht. Im letzten Teil wurde die Temperaturwechselbeständigkeit von zweischichtigen GZO/YSZ-Beschichtungen untersucht. Zusammenfassend kann gesagt werden, dass SPS-Beschichtungen ein großes Potenzial als Wärmedämmschichten aufweisen. Weitere Untersuchungen sind erforderlich, um diese Art von Beschichtungen zu verstehen., Energie & Umwelt, 456

A solution-hardening of AISI 316L stainless-steel powder was conducted. The expansion of the crystal lattice and a strong increase in the nanoindentation hardness confirm the successful diffusion of carbon and nitrogen in the interstices. A multiphase state of the powder feedstock with phase fractions of the metastable S-phase (expanded austenite) mainly at the particle’s edge, and the initial austenitic phase within the core was found. Thermal spraying using high velocity oxy-fuel (HVOF) and atmospheric plasma spraying (APS) prove the sufficient thermal stability of the Sphase. Microstructural investigations of the HVOF coating reveal the ductility of the S-phase layer, while the higher heat load within the APS cause diffusion processes with the initial austenitic phase. The lattice expansion and the nanoindentation hardness decrease during thermal spraying. However, the absence of precipitates ensures the sufficient heat stability of the metastable S-phase. Even though further efforts are required for the thermochemical treatment of powder feedstock, the results confirm the feasibility of the novel powder treatment approach.

Applying dense chromium protective layers between interconnector and cathode can efficientlydiminish chromium related degradation of solid oxide fuel cells (SOFCs). Especiallyatmospherically plasma sprayed (APS) Mn$_{1.0}$Co$_{1.9}$Fe$_{0.1}$O$_{4}$ (MCF) coatings demonstrated their effectiveness concerning Cr retention within stacks tested in Jülich. Nevertheless, strong microstructural and phase changes of these coatings during operation were reported in literature, but not fully understood yet. This thesis was part of a collaborative project called “SOFC-Degradation” (grant no.03SF0494A), which was focused on different degradation phenomena emerging during SOFC operation. The goal of the present work was to investigate the basic mechanisms leading to the observed changes of APS-MCF coatings during operation. The results should enable long-term prediction and facilitate accelerated test-procedures. Additionally, wet powder spraying (WPS) was investigated as a cost efficient alternate coating technique. APS-MCF coatings were heat treated in air in combination with common steel substrates and cathode contact layers to simulate SOFC operation conditions. During the APS-process MCF is reduced and deposited in a rock salt configuration ((Mn,Co,Fe)$_{1}$O$_{1}$), which is metastable at room temperature. By annealing these coatings in air, the material transforms to the low temperature (T < 1100 °C) stable spinel phase ((Mn,Co,Fe)$_{3}$O$_{4}$). This phase transformation is connected to an oxygen uptake and is accompanied by a volume expansion of the material. Inside the crack-network that can be found in as-sprayed coatings, this volume expansion leads to a densification and crack-healing. Subsequently, the phase transformation, which is also anoxidation process, is dominated by solid state diffusion of cations as soon as the cracks areclosed. Thereby cobalt is enriched at the layer’s surface as its diffusion coefficient is higher than that of manganese or iron within the layer formed. The outward diffusion of cations generates a counterflow of vacancies into the bulk, where they accumulate to form small pores. A two-phase-system composed of a cobalt-rich rock salt phase and a manganese- and iron-rich spinel phase can be observed in the coating’s bulk. Extending the annealing time results in a decrease of rock salt phase and an increase of spinel phase. When the transformation to the spinel phase is completed, solid state diffusion strives for a homogeneous distribution of elements on the long term. An increase of the annealing temperature accelerates the observed phenomena. [...]

Die Kernfusion besitzt großes Potenzial eine CO$_{2}$-neutrale Energieversorgung zukünftiger Generationen zu ermöglichen. Dabei stellt die technische Nutzbarmachung dieser Energiequelle bislang eine Herausforderung dar. Insbesondere führen hohe thermische Lasten und Neutronen-induzierte Schädigung zu extremen Anforderungen an die Materialauswahl für Plasma-zugewandte Komponenten (PFCs). Diese sind daher nach derzeitigem Verständnis aus einer Wolfram-Schutzschicht, welche an eine Struktur aus niedrig aktivierbarem ferritisch-martensitischen (RAFM) Stahl gefügt wird, zu fertigen. Aufgrund des diskreten Übergangs von Materialeigenschaften an der RAFM-W-Fügezone sowie thermischer Lasten, entstehen hier makroskopische Spannungen und plastische Dehnungen. Ein gangbarer Weg, diese zu reduzieren, stellt die Implementierung einer Zwischenschicht mit gradiertem RAFM/W-Verhältnis, einem s.g. funktional gradiertem Material (FGM), in der Fügezone dar. In der vorliegenden Arbeit werden Makrospannungen und -dehnungen in der ersten Wand des Fusionsreaktors DEMO mittels einer Finite Elemente Simulation untersucht und bewertet. In diesem Rahmen werden Modell-Komponenten mit und ohne gradierter Zwischenschicht berücksichtigt und der Vorzug eines FGM herausgestellt. Parameterstudien dienen einer konstruktiven Richtlinie für die strukturelle Umsetzung von FGMs und Komponenten der ersten Wand. Es wird außerdem die Machbarkeit von vier Methoden (Magnetron Sputtering, Flüssigphaseninfiltration, modifiziertes atmosphärisches Plasmaspritzen und Electro Discharge Sintering) hinsichtlich der Herstellung von FGMs studiert. Die entstehenden Schichten werden mikrostrukturell, thermo-physikalisch und mechanisch detailliert untersucht. Auf Grundlage dieser Charakterisierung und der Finite Elemente Simulation wird ihre Eignung als gradierte Schicht in der ersten Wand von DEMO evaluiert und schließlich mit alternativen Fügesystemen, die derzeit im Forschungsumfeld erprobt werden, verglichen.

IOP conference series / Materials science and engineering 181, 012013(2017). doi:10.1088/1757-899X/181/1/012013, Published by Institute of Physics, London [u.a.]

Die Applikation von Wärmedämmschichten ermöglicht die Erhöhung der Eingangstemperatur und somit die Verbesserung der Effizienz von Gasturbinen. Solche Wärmedämmschichten werden entweder über atmosphärisches Plasmaspritzen (APS) oder über Gasphasenabscheidung mittels Elektronenstrahlverdampfung (EB-PVD) hergestellt. Die Plasma Spray-Physical Vapor Deposition-(PS-PVD)-Technologie vereint die Vorteile beider Technologien, wie z. B. hohe Abscheideraten und vergleichsweise geringe Prozesskosten (APS) sowie die Abscheidung von kolumnaren Schichten (EB-PVD) mit hoher Dehnungstoleranz. In der Arbeit wurden die anwendungsrelevanten Eigenschaften (Korrosion/Erosion) der Schichten untersucht und optimiert. Mittels einer Voroxidation der Bondcoatoberfläche wurde die Lebensdauer über das Niveau von APS-Schichten gesteigert. Durch die Beschichtung von Turbinenschaufelmodellen wurde die Realisierbarkeit der Beschichtung echter Bauteile nachgewiesen. Zusätzlich wurde das Prozessverständnis verbessert.

Es wird eine neuartige Werkzeug- und Formenbautechnologie zur kostengunstigen Herstellung standzeitoptimierter Formwerkzeuge vorgestellt. Mit dieser Technologie ist die wirtschaftliche Fertigung von Prototypen und Kleinserien auch im schwer verarbeitbaren Serienwerkstoff moglich. Das entwickelte innovative Herstellverfahren fur Giesformen und Spritzgieswerkzeuge basiert auf der Abformung eines Positivmodells durch Schichtverbunde. Diese, die Geometrie des Modells speichernden, grenzflachenoptimierten Schichtverbunde bilden mit einer Hinterfutterung nach Entfernen des Teiles und dem Anbringen der giestechnischen Einrichtung die Werkzeugstammform. Der Aufbau der Schichtverbunde erfolgt mit aktivierten Bogenbeschichtungsverfahren (PVD-Verfahren) fur die die spatere Werkzeugoberflache bildende Funktionsschicht und durch Plasmaspritzbeschichten (APS) fur die Stutzschicht. Mit einem derart hergestellten Spritzgieswerkzeug konnen mehr als 1000 Teile eines mit Glasfasern verstarkten Kunststoffes oder mehr als 1500 Teile eines unverstarkten Kunststoffes in hoher Qualitat gefertigt werden. Casting molds, produced by coating of prototypes A new method for the cost effective production of forming tools is introduced. These tools can be used for the production of prototypes and small series of products. The new method for the production of moulds and injection moulding tools consists of the following steps: •coating of a positive model with a hard coating by physical vapour deposition (PVD)-technologies •deposition of a support coating, consisting of a metal coating, applied by an atmospheric plasma spraying technology •embedding in a polymer removing of the positive model •completion of the tool by adding the moulding equipment By using such a tool it is possible to produce more than 1000 parts of a polymer (enforced by glass fibre) or more than 1500 parts of a regular polymer.

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In dieser Arbeit werden verschiedene Beschichtungsverfahren vorgestellt, mit deren Hilfe es möglich ist, aus nanoskaligen Pulvern Schichten herzustellen. Dabei war es das Ziel vor allem dicke Schichten im Bereich von 1 bis 10 µm herzustellen. Als Beschichtungsverfahren wurde das Dip-Coating mit Hilfe von wässrigen Suspensionen und anschließender Lasersinterung und das atmosphärische Plasmaspritzen eingesetzt. Darüber hinaus wurde untersucht, ob es möglich ist unter Zuhilfenahme eines CO2-Lasers Metalle, Gläser und Keramiken elektrozusprühen. Als Beschichtungswerkstoffe beim Dip-Coating und Plasmaspritzen wurden SiO2- und Al2O3- Nanopulver verwendet. Diese wurden auf Metall- und Glassubstraten aufgebracht. Durch das Dip-Coating konnten aus wässrigen Suspensionen Schichten auf Borosilikatglas mit Dicken im Bereich von ca. 11 µm hergestellt werden. Die chemischen und mechanischen Eigenschaften der Schichten wurden mit denen der unbeschichteten Gläser verglichen. Dabei konnte die chemische Beständigkeit und die mechanische Festigkeit der Gläser mit Hilfe der Beschichtung gesteigert werden. Mit Hilfe des atmosphärischen Plasmaspritzens konnten Al2O3-Schichten der Alpha-Phase mit Dicken im Bereich von ca. 100 µm hergestellt werden. Beim laserunterstützten Elektrosprühen konnte gezeigt werden, dass es möglich ist, Kupfer und Al2O3 in Normalatmosphäre zu sprühen. Dabei konnten Partikel im Nanometerbereich hergestellt werden. This thesis presents different coating techniques that make it possible to manufacture coatings out of nano-scaled powders. It was the main goal to produce coatings with depths from 1 to 10 µm. Dip-coating with the help of aqueous suspensions followed by laser sintering and atmospheric plasma spraying were used as coating techniques. In addition, a series of tests was conducted to find out whether it is possible to electro spray metal, glass and ceramic with the aid of CO2-laser. SiO2- and Al2O3 nano-scaled powders were used as coating materials during the dip-coating and plasma spraying. They were put on metal and glass substrates. The dip-coating made it possible to produce coatings with a depth of approximately 11 µm out of aqueous suspensions that were put on borosilicate glass. The chemical and mechanical properties of the coatings were compared to those of the uncoated glass. The tests showed that the coating improved the chemical resistance and the mechanical strength of the glass. Al2O3 coatings of the alpha-phase with a depth of approximately 100 µm were produced with the aid of atmospheric plasma spraying. During the laser-supported electro statical spraying it was shown that it is possible to spray copper and Al2O3 in standard atmosphere. Here, it was possible to produce nano-scaled particles.

This study is focused in the process optimization and implementation of the liquid feedstock plasma spray process conducted at atmospheric pressure, in which the feedstock is injected into a free expanding plasma jet generated by industrial-type DC torches, in the form of a suspension or solution-precursor. In here, a liquid carrier is used to transport feedstock particles with sizes falling into the submicrometric and nanometric range, into the useful region of the plasma jets. This condition brings about a series of important changes in the microstructure of the deposited coatings, highlighted by a reduction in coating-building splats of up to 3 orders magnitude as compare to those observed in standard plasma spray process, and by a fine porosity with pore sizes in the nanometer range. A universal apparatus for the precise dosage of the liquid feedstock was developed considering the geometrical constraints of the different torches under consideration. Moreover, various injection port designs, mainly grouped as atomizers or mechanical injectors, were analyzed. A series of experiments, mostly based on the characterization of the sprayed feedstock and resulting coatings, were design to isolate the most relevant process parameters. The results from the splats analysis were used to spatially resolve the trajectories of the feedstock particles resulting from the interaction of the liquid carrier with the flow of the plasma jet. SEM analysis of the splats and sprayed bulk material morphologies collected at different standoff distances, was used to study the process of agglomeration and consolidation processes that follow the fragmentation and evaporation of the feedstock droplets. Image analysis tools were used to quantify and grouped into size classes the detected splats. These results were to establish the correlations between feedstock properties and the particle size distributions of the sprayed feedstock, which were positively correlated to spray and process efficiencies, which lay bellow 25% and are relatively low when comparing to the efficiency observed in conventional plasma spray. A model that describes the fragmentation of the liquid feedstock and its evaporation was formulated. The droplets size and time scales are proven to be in good agreement with the experimental results. Furthermore, the properties of the various coatings sprayed with the developed apparatus were correlated to results from the splat analysis. The study of the cross-section and fracture surfaces of the coatings served to establish the links between the coating microstructural features and interaction of the liquid feedstock with the plasma jet, providing useful information for the validation of the theoretical model. Macroscopic and microstructural properties of the sprayed coatings are in good agreement with the results previously reported in literature, which are characterized by a columnar growth between multi-lamellar structures reach in segmentation cracks and with density values of about 4 to 4.3 g·cm$^{-3}$. The resulting coatings are mainly porous, with porosity values in excess of 30%. Moreover, various areas of implementation in which the new microstructural features inherent to the LFPS process, have being explored. These areas were mainly the spraying of thermal barrier coatings and the deposition of the various functional layers of the solid-oxide fuel-cell systems, with an emphasis in the development of gas-tight electrolyte layer based on yttrium-stabilized zirconia. A process for the deposit of dense gas-tight layers with an average thickness of 50 $\mu$m resulted from the parametrical study, which resulted in a patent application. This method had the peculiarity of producing a bistratified layer system, in which the upper region of the coating remelts due to the high thermal flux between the plasma jet and the substrate. In here, the formation of the bistratified layer system during the uninterrupted spray process, is inherent to the set of torch and feedstock parameters.

Ill., graph. Darst.

One of the most difficult topics in the design and development of future fusion devices, e.g. ITER (Latin for "the way") is the field of plasma facing components for the divertor. In steady-state mode these will be exposed to heat fluxes up to 20 MW/m2. The favored design-option is a component made out of tungsten and copper-alloys. Since these materials differ in their thermal expansion coefficient and their elastic modulus a temperature gradient within the component, caused by thermal loads, results in stresses at the interface. An alternative design-option for divertor-components deals with the insertion of a functionally graded material (FGM) between tungsten and copper. This establishes a continuous change of material properties and therefore minimize the stresses and optimize the thermal behavior of the component. Low pressure plasma-spraying and direct laser-sintering are introduced as possible production-methods of graded W/Cu-composites. Based on preliminary investigations both are used for fabricating W/Cu-composite materials with different mixing ratios. Thermo-mechanical and thermo-physical material properties will be determined on these composites and extrapolated to all mixing ratios. For laser-sintering these are limited to Cu-contents of ~20 to 100 Vol%. Therefore the plasma-spraying process is favored. In finite-element-analyses the graded material and its material properties will be implemented into a 2-D simulation-model of a divertor component. The composition and the design of the graded W/Cu-composite will be optimized. Best results are obtained by high contents of tungsten within the graded layer, which are still improved by a macro-brush design with dimensions of 4.5 x 4.5 mm2. This results in a transfer of critical stresses from the mechanical bonded interface between the plasma facing and the graded material to the diffusion bonded interface between the graded material and copper. The joining of tungsten, a plasma-sprayed graded W/Cu-interlayer, OFHC-Cu (Oxygen Free High Conductivity) and CuCrZr will be done by Hot Isostatic Pressing. Parameters are a temperature of 550øC an a pressure of 195 MPa. Electrochemical deposited copper and nickel are added. Copper is used as surface layer of the graded W/Cu-composite and nickel for the strengthening of the diffusion bonding. Ultra-sonic-testing revealed narrow areas with inhomogeneous bonding at the interface, mainly nearby the outer surface of the module. The module containing the macro-brush has been tested at the electron-beam test facility JUDITH. It survived power loads at steady state operation of 23.8 MW/m2 and 150 cycles at 20 MW/m2 during thermal fatigue experiments. These results verify, that the insertion of a graded W/Cu-interlayer increases the resistance against thermal loads. Especially in the combination with the castellated structure.

The application of gas turbines for the generation of electricity has significantly increased over the past decades. In order to reduce emissions and to conserve fossil fuels, the thermal efficiency of stationary gas turbines should be increased. This can be achieved mainly by higher turbine inlet temperatures and by reduction of the cooling air flow. The use of thermal barrier coatings (TBCs) has great potential for increasing the thermal efficiency, while at the same time limiting metal temperatures of the blades. The exploitation of the potential of TBCs has, however, been hampered by the lack of systematic data concerning the damage development, and of the material properties that affect it. In the present work, the damage development in a TBC system has been investigated under simulated service conditions. The system consisted of an atmospheric plasma sprayed, yttrium stabilized zirconium oxide; a bond coat (BC) layer of NiCoCrAlY (balance Ni, 21.1%Co, 17.1%Cr, 12.6%Al, 0.61%Y, 0.4%Hf) that also acts as a corrosion protection; and a substrate of the polycrystalline turbine blade alloy IN 792 CC or the single crystalline CMSX-4. For the isothermal low cycle fatigue (LCF) testing, additional means for the heating of coated specimens were developed and for the thermomechanical fatigue (TMF) tests, completely new test techniques were necessary. The manufacture of specimens of the isolated coating and compression testing of these specimen were successfully carried out. The results obtained show that there are significant differences in the damage development in TMF loading and in isothermal (LCF) loading. In TMF loading with maximum and minimum temperatures of 950 and 450°C, shorter fatigue lives than those in the LCF tests were measured. Investigations of the damage in the TBC using acoustic emission and calculation of the stress in the TBC have contributed to the understanding of the damage processes. To obtain data for the analysis of the mechanical behaviour, the time-dependent deformation behaviours of both TBC and BC and the elastic modulus of the TBC were determined. Based on these data, a deformation model was derived, which interpreted the deformation under compressive stress as a change in the defect structure of the TBC.

Ill., graph. Darst.

Compositwerkstoffe mit Hartstoffverstärkung für das thermische Spritzen finden eine breite Anwendung als Beschichtungswerkstoffe, da sie einen sehr guten Verschleißschutz bieten. Die bislang zur Verfügung stehenden konventionellen karbidhaltigen Pulver für die Herstellung verschleißfester Schichten enthalten zum Teil höhere Mengen an Elementen, die sowohl als kostenintensiv als auch bedenklich im Hinblick auf die Umweltverträglichkeit (z.B. Ni, Cr und Co) einzustufen sind. Die Untersuchungen wurden im Rahmen der Zusammenarbeit des Lehrstuhls für Verbundwerkstoffe der TU Chemnitz mit dem Belorussischen Institut für Pulvermetallurgie Minsk durchgeführt. Die vorliegende Arbeit befaßt sich mit der Entwicklung neuartiger SHS-Verbundwerkstoffe auf der Basis von Eisen-Titankarbid, die als preiswerte und umweltfreundliche Spritzpulver zum thermischen Spritzen von verschleißbeständigen Schichten eingesetzt werden können. Als metallische Bindephasen für die Herstellung der Verbundpulver wurden kostengünstiges Eisen und unterschiedliche Eisenlegierungen verwendet. Es werden die Gesetzmäßigkeiten des Werkstoffverhaltens während der SH-Synthese, bei der spritztechnischen Verarbeitung durch die APS-, VPS- und HVOF sowohl bei der Schichtbildung als auch während der verschiedenen Verschleißuntersuchungen vorgestellt, die durch umfassende metallkundliche Betrachtungen begleitet werden. Die Ergebnisse aus den Verschleißuntersuchungen der synthetisierten TiC-haltigen Spritzschichten sowie der Spritzschichten aus den herkömmlichen Pulvern werden verglichen. Die gewonnenen Erkenntnisse schaffen Voraussetzungen für vielfältige Anwendungen von SHS-Verbundwerkstoffen des Fe/TiC-Systems für das thermische Spritzen hochverschleißfester Schichten.

Thermal barrier coatings are increasingly utilized to protect gas turbine components from high temperature exposure. Thus the use of TBCs allows an improvement of the system efficiency, since the coated components can support higher inlet temperatures. To predict the life duration of the TBC-system, the determination of the high temperature behavior of the protective coatings in composite geometry is indispensable. In the present study, experiments were selected to evaluate the thermoelastic properties of a plasma sprayed TBC in composite geometry. The curvature behavior of three-layer specimen strips was observed between room temperature and 1000°C, when submitted exclusively to temperature. Also isothermal 4-point bending tests were performed at room temperature, 600°C and 950°C. During curvature and bending experiments, shape and structure changes were monitored in-situ using a high resolution telescope in combination with a digital data acquisition system. The high temperature experiments on the TBC-specimen strips demonstrate that the bonded materials behave elastic up to 600°C. Depending on the specimens geometry, i.e. on the stress distribution, non-elastic effects can occur above 600°C. When all layers show an elastic behavior, the stress distribution can be calculated at room and at high temperatures by using a linear-elastic model developed for this purpose. Also the temperature dependent elastic modulus of the ceramic TBC in composite geometry can be derived.

Der Laserstrahl stößt in das Feld der Oberflächenbehandlung vor. In einzigartiger Weise lassen sich einsatzgerechte Funktionsoberflächen mit dem Laser erzeugen: Härten, Umschmelzen, Legieren und Beschichten sind einige der möglichen Verfahrensvarianten.

ZrO2 thermal barrier coatings have been plasma sprayed onto steel substrates with a FeCrAlY bond layer. During spraying the conditions have been varied by cooling the back side of the substrate in ice-water or heating it on a hot plate, and simultaneously cooling the sprayed surface with air at various pressures. The residual strain distributions have been measured in the as-sprayed couples using the incremental blind-hole method. The measurements show that residual strains can be controlled through temperature manipulation, and the method can be used to determine the optimum spraying conditions. The microstructure has been observed in a transmission electron microscope, and the effect of microstructural features on the microstrains are briefly discussed.