This study assesses the effect of injector geometry on particle injection in plasma spraying. Numerical simulations show that high particle velocities can be realized with an injector that is significantly longer than the norm. In order to verify the prediction, injectors with different diameters and lengths were used to spray Al 2 O 3 powders while measuring particle velocity at the injector outlet. Based on velocity, coating thickness, and XRD measurements, it is shown that small changes in injector geometry can have a significant influence on particle behavior without affecting phase composition. The unaltered state of the phase composition indicates that the particles did not possess enough momentum to penetrate the comparatively fast plasma jet.

A low thermal conductivity in feedstock material and high plasma temperatures generally lead to inhomogeneous heating of particles in plasma spraying. Existing modeling methods can determine heat transfer within idealized spherical particles with homogenous morphology, but in many cases, particles have an agglomerated morphology, consisting of multiple smaller particles that are packed together. The reduced contact area between the individual smaller particles results in a drastic reduction of the effective thermal conductivity of the agglomerate. On the other hand, it enhances heat transfer from the plasma gas due to the increased particle surface area and penetration of the hot plasma into the agglomerate. Moreover, the momentum transfer from the plasma to the agglomerate differs from that of a homogenous spherical particle, which can significantly affect heating dynamics. This paper presents a novel particle modeling approach that accounts for all such phenomena. Differences in kinematics and heating dynamics of the agglomerates are analyzed with regard to their packing densities.

The current study investigates the influence of the grain size fraction D of a FeCrB/WC-Co feedstock material on the coating properties. In previous studies, novel FeCrB/WC-Co wear and corrosion protection coatings applied by means of high velocity air-fuel (HVAF) spraying were developed by the authors. It was observed that coatings, which were produced with a slightly decreased powder grain size fraction and identical chemical composition showed improved coating properties, i.e. reduced crack formation in the coating at high powder feed rates . and lower current densities at high overpotentials. The goal of this study is to investigate the influence of the powder grain size fraction on the coating properties in more detail. Furthermore, the underlying mechanism for the improved coating properties, with regard to their corrosion behaviour, is investigated. Therefore, the FeCrB/WC-Co feedstock material with the grain size fractions of -20 +3 μm and -32 +11 μm and identical chemical composition was applied by means of HVAF-spraying and the coatings were subsequently analysed. Light microscopy was used to investigate the microstructure of the coatings. The wear and corrosion properties were analysed using pin-on-disc (POD) and electrochemical polarization tests respectively. XRD-measurements were used to investigate the phase composition and to develop a hypothesis for the different corrosion behaviours of the investigated coatings. The results show that HVAF-sprayed FeCrB/WC-Co coatings produced with a powder grain size fraction of -20 +3 μm exhibit lower current densities at high overpotentials, compared to the coatings produced with a powder grain size fraction of -32 +11 μm.

Hydrodynamic bearings have to fulfill different requirements, depending on the operating conditions. Yet, conventional hydrodynamic bearings could not be used in critical operating conditions such as permanent start / stop operations. This is the reason why rolling bearings are currently used for frequent starting operations and low circumferential velocities, as they occur in wind turbines. In order to operate hydrodynamic bearings in a fail-safe manner even under these increased requirements, new bearing materials are needed. Within this study two new bearing material concepts are developed and deposited by thermal spraying as coatings to interact in this tribological system. On the one hand, matrix materials containing friction-reducing solid lubricants and on the other hand, multilayer systems, which can be used in as-sprayed condition, are investigated. The aim of both concepts is to improve the operation properties under critical conditions. The coating concepts are therefore tested on a modified high-load ring-on-disc tribometer and are compared to a reference plain bearing material produced by conventional casting. In this way, it is shown whether these new concepts can meet the requirements of slow-moving and highly loaded hydrodynamic bearings.

Nowadays combustion engines are the most common way to impel vehicles. Thereby losses occur, due to cooling, exhaust gas and friction. Modern engines roughly dissipate 8% of the chemical energy stored in the fuel because of friction in different tribological systems. The highest potentials for optimisation can be found in the tribological system of inner surface of combustion chamber and piston ring. Besides friction, corrosive stress of inner surface of combustion chamber increases e.g. due to the utilization of auxiliary systems such as Exhaust-Gas-Recovery. In order to save energy, reduce emissions and enhance the lifetime of combustion engines innovative coating material systems need to be developed, especially for inner surface of combustion chamber. This study focuses on the development of innovative iron based materials for combustion chamber application using Plasma Transferred Wire Arc (PTWA) and Rotating Single Wire Arc (RSW) technologies. In order to improve the wear and corrosion resistance boron and chromium are added into the feedstock material. After deposition, different honing topographies are manufactured in order to evaluate their influence on the tribological behavior. Furthermore, electro-chemical corrosion tests are conducted by using an electrolyte simulating the exhaust gas concentrate. In conclusion an optimised coating material deposited by PTWA and RSW and improved surface topographies can be combined.

Air plasma spraying is a variation of thermal spraying that is used, among others, for the production of thermal barrier and wear resistant coatings. High plasma temperatures enable the processing of ceramic powder particles which have a high melting point and cannot be processed otherwise. Due to their low heat conductance, the ceramic particles are not necessarily fully melted during their flight in the free jet and prior to the impact on the substrate surface. Experimental particle temperature measurements by means of particle diagnostics systems deliver merely the surface temperature of the particles while the melting degree of the ceramic particles remains unknown. Therefore, the temperature field within spherical Al 2 O 3 particles is numerically investigated for a commonly used particle size distribution by considering different particle sizes. The model includes a two-way coupled particle-laden free jet model and takes the latent heat of melting and evaporation into account. The effect of the particles size as well as the stand-off distance on the melting degrees of the particles in the given powder size distribution is determined.

One important trend in thermal spraying is the application of novel Fe-based corrosion/wear protection coating systems. A typical field of application for such corrosion and abrasive wear protection coatings are rotary dryers of paper machines. At the moment, these cylinders are coated by wire arc spraying. A disadvantage of the wire arc sprayed coatings is their high thickness, which has a heat-insulation effect, and their high roughness. Therefore, an expensive post production grinding process is necessary in order to achieve the required surface quality. The goal is to develop a HVAF process that enables the production of thin, dense and near net shape corrosion/wear protection coating systems, which significantly reduce the post-production time and costs. In this study, the HVAF coating process and a novel Fe-based feedstock material are investigated. In the first step the Fe-based powder is analysed thermally using differential scanning calorimetry, to investigate the solidification and melting temperature of the feedstock material. Furthermore, the influence of the spraying distance and the powder feed rate on the microstructure and porosity of the resulting coatings is investigated using light microscopy. Furthermore, the deposition efficiency of HVAF coatings is analysed regarding their economic efficiency.

At present, main bearings in wind turbines are equipped with rolling bearings without exception. Sliding bearings instead can offer a number of advantages, including easier maintenance and extended lifetime. While conventional manufacturing processes for large sliding bearings face their limits regarding processable materials, thermal spraying can provide an effective alternative to meet the requirements by applying coating systems on the bearing surfaces. Within this study a wide range of different feedstock materials based on standard bearing materials and common wear and friction reducing coating systems are investigated. The coatings are tested on tribometers based on the load distribution within the main bearing at critical operating conditions of the wind turbine gained from a validated simulation model. A tribological methodology is developed to investigate the application related properties of the thermally sprayed coatings. The effects of load and geometry of the counter body on the friction and wear behavior of the coatings are investigated using a pin-on-disc and a modified high-load ring-on-disc tribometer. The presented results provide a major contribution to the purpose of identifying an appropriate coating system to meet the requirements of slow-moving and highly loaded sliding bearings.

Sealants are widely used in order to enhance the performance of porous thermally sprayed coatings, e.g. for electrical insulation or corrosion protection. In order to accomplish required properties, a good infiltration is necessary. The methods to assess the success of a sealing often rely on determining the infiltration depth by SEM or adding colour pigments to the sealer. In this study, a new approach for assessing the success of a sealing operation is investigated. The underlying assumption is that porous coatings are not gas-tight and by sealing them, the measurable gas flow can be reduced. Therefore, the success of a sealing operation may be assessed by comparing gas flows at defined conditions prior and subsequent to sealing. This hypothesis is investigated by coating special highly porous substrates with a wide range of coating porosities and thicknesses, sealing these coatings, comparing nitrogen flows at a defined pressure prior and subsequent to the sealing operation and correlating the measured changes of nitrogen flow with traditionally assessed infiltration depth and filling degree.

Three-cathode plasma spraying is characterized by high process robustness in terms of particle in-flight properties due to high stability of plasma jet. However, during coating parts with complex geometries, process parameters such as stand-off distance and spray angle usually cannot be kept at optimized conditions. In this study, the process robustness during three-cathode plasma spraying of a novel FeCrMnBC alloy was investigated by varying stand-off distance and spray angle to simulate spray conditions for complex geometries. A three-cathode plasma generator TriplexProTM-210 was used to spray FeCrMnBC powder with a fraction of -45 +20 µm onto substrates of cast iron EN-GJL-250. The stand-off distance and the spray angle were varied from d=90 mm to d=110 mm and between ø=90° and ø=60°, respectively, while the other process parameters were kept constant. The results revealed that the reduction of spray angle caused an about 15 % decrease of coating thickness, about 40 % porosity increase and about 15% increase of bond strength. In contrast, the variation of stand-off distance changed only insignificantly the coating thickness, porosity and bond strength. The variation of stand-off distance and spray angle did not result in significant changes in the coating microhardness. The reduction of spray angle resulted in significant worsening of the corrosion protection ability of the coating system.

Fe-based coatings, such as novel FeCrMnBC alloys, have both economic and ecological advantages compared to other coatings like Ni-based or Co-based coatings. In recent years, high performance Fe-based wear and corrosion resistant coating systems have been developed. Some of them have even been introduced into the market. However, the suitability of the FeCrMnBC alloy as coating for cast iron under complex erosive and corrosive stresses in particle-loaded fluids for pump parts has not been investigated yet. Especially the impact of the process robustness of three-cathode plasma spraying coatings applied with variable process parameters like stand-off distance and spray angle is in the focus of interest. The objective of the present work has been the characterization of novel FeCrMnBC alloys, for the first time deposited via Thermal Spray processes. The corrosion resistances as well as the cavitation and erosion properties were separately evaluated by current density-potential measurements and supersonic cavitation in artificial sea water. Erosion corrosion behavior has been investigated in a pump test rig with 10 wt.-% corundum (Al 2 O 3 ) particles. The results show that the reduction of spray angle and the variation of stand-off distance limit the corrosion and cavitation resistance in different ways. The erosion behavior shows only small variations for the tested parameters. The results reveal that the FeCrMnBC coatings exhibit high process robustness for the chosen parameter variations and a large potential to improve the protection of cast iron even for not optimized conditions.

By means of In-Mold-Metal-Spraying (IMMS), wire arc sprayed metal coatings are transferred onto plastic parts during the injection molding process for the efficient production of metallized plastic parts. One potential field of application of IMMS parts are electrical applications such as electrically conductive tracks or electromagnetic shielding. In the current study, the properties of the transferred coatings, especially the electrical resistivity, are determined. Different feedstock materials are used for the application of the coatings. In the first investigation, pressurized air is used as atomizing gas for wire arc spraying. In contrary to Zn coatings, Cu coatings applied with pressurized air have a significantly higher electrical resistivity in comparison to massive copper. One possible reason for this is the oxidation of the Cu particles during the spraying process. Therefore, N 2 and a mixture of N 2 and H 2 are used as atomizing gas to reduce the oxidation of particles. Consequently, the electrical resistivity of IMMS parts can be significantly reduced. Furthermore, spraying distance, current and pressure of the atomizing gas are varied to investigate the influence of these process parameters on the coating properties.

A new process called in-mold metal spraying (IMMS) shows good potential for producing metallized plastic parts quickly and inexpensively. A zinc layer is deposited on mold cavity inserts using wire arc spraying and subsequently transferred to a plastic carrier via injection molding. Finely adjusted bonding strength between the carrier body and coating is essential for successful coating transfer. To that end, this study evaluates the influence of carrier body surface pretreatments on the transferability and bonding strength of zinc coating. Carrier bodies made of different types of steel pretreated by glass bead blasting and EDM were tested and their surface topography examined. In the initial experiments, the hardness and surface topography of carrier bodies were identified as factors that can influence coating transferability. Further experiments focusing on the adhesion strength of zinc on hardened and annealed carrier bodies were conducted to verify the influence of hardness on bonding strength.

In this investigation, different atomizing gases, arc wire spray guns, and wire sizes were used to deposit ZnAl coatings on high-strength steel substrates. Sample sets corresponding to different gas mixtures and pressures as well as other parameters were produced and the coatings obtained were evaluated based on morphology, porosity, composition, phase distribution, and oxide content. The results are presented and discussed, particularly with regard to corrosion lifetime and performance.

The objective of this work is the development of highly amorphous, iron based coatings for thermal barrier applications. Based on the results of previous work, a chemical composition of Fe 72 Si 4 B 20 Nb 4 was selected and modified in order to improve glass forming ability and corrosion resistance. Three metallic glass powder mixtures with different amounts of Cr and Fe were prepared, characterized, and deposited by air plasma and HVOF spraying. Different gas flow rates and standoff distances were used and particle temperatures and velocities were measured during spraying. The deposits were examined, tested, and compared and were found to have good potential for thermal barrier coating applications.

In this work, the aim is to develop a cost-effective coating to protect cast iron and carbon steel from corrosion and wear. An alloy with a composition of FeCr25Mn10BC was designed that could be readily converted to powder form by gas atomization. Different sized powders were produced, characterized, and subsequently sprayed using a three-cathode air plasma generator. It was found that fine powders with fractions of -25 +10 μm and -10 μm had a much higher affinity to oxidation than coarser ones. Nevertheless, using suitable parameters, dense coatings with low oxide content could be realized even with the finest powder. The results show that full utilization of the powder is achievable due to the wide parameter window of three-cathode plasma spraying and that the average deposition efficiency is more than 70%. In addition to savings in material and processing costs, the new alloy system provides greater wear resistance than stainless steel coatings and exhibits significantly higher corrosion resistance than unprotected cast iron and carbon steel.

Newly-developed multi electrode spraying systems have improved the process stability and coating properties in air plasma spraying (APS) significantly. The new generation three-cathode torches, i.e. TriplexProTM-200/210, can be operated without significant plasma fluctuations. In previous studies a numerical model, which couples fluid dynamic, electro-magnetic and thermal relationships to investigate the flow characteristics in the torch were introduced. In this study further development of the model with respect to meshing and turbulence model will be introduced. Furthermore, free jet simulations will be conducted which use temperature and pressure profile at the outlet of the torch as inletting boundary conditions. Advanced diagnostic methods will be implemented to verify the capability of the numerical models.

In thermal spraying uncoated substrates usually require roughening. As the most common roughening method, grit blasting increases the surface area and produces undercuts, which facilitate mechanical interlocking and thus promote the bonding between the substrate and coating. The effects of grit blasting parameters, i.e. the particle size, the blasting angle, the stand-off distance and the pressure, on the resulting surface topography are investigated. Furthermore the efficiency and wear behavior of the blasting media are analyzed. Influences of three different blasting media, corundum, alumina zirconia and steel shot, on the surface roughening are compared.

Thermally sprayed Fe-based coatings reinforced by TiC particles are a cost effective alternative to carbide coatings such as WC/CoCr, Cr 3 C 2 /NiCr and hard chrome coatings. They feature a good wear resistance and, with sufficient amount of alloying elements like Cr and Ni, also a high corrosion resistance. In hydraulic systems the piston is coated for protection against corrosion and wear. New water-based hydraulic fluids require an adaption of the coating system. In order to investigate the wear and corrosion resistance of Fe/TiC a novel powder consisting of a FeCr27Ni18Mo3 matrix and 34 wt.-% TiC was applied by HVOF and compared to reference samples made of WC/CoCr (HVAF) and hard chrome. Besides an in-depth coating characterization (metallographic analyses, EMPA), wear resistance was tested under reverse sliding in a water-based hydraulic fluid. Corrosion resistance was determined by polarization in application-oriented electrolytes (hydraulic fluid at 60 °C, artificial sea water at RT).

This study evaluates a new surface finishing process called laser-assisted turning. WC-CoCr coatings were produced by HVOF spraying and characterized based on surface morphology, microstructure, and friction and wear properties. The coatings were then treated using the new process and re-examined and tested. Surface roughness and hardness were significantly improved, although friction and wear properties were found to be inferior to those of WC-CoCr coatings finished by grinding and polishing.