This study focuses on the development of thermally sprayed coatings for magnetic data storage. In the con-text of Industry 4.0 and the associated digitization of production, there is more demand than ever for suitable data storage on components in order to be able to automatically identify and process products. The resistance of certain sprayed coatings to harsh environmental conditions, make them a promising alternative compared to other solutions for dynamic data storage such as the RFID chips already available on the market. This area of application results in the requirement for a high stability of the written data against external influences such as temperature, wear or interference fields. These requirements can be met by the tailored choice of material including a sufficient magnetic anisotropy of the sprayed coatings. The influence of the spraying process on the formation of the magnetic material properties in the applied coatings is discussed with the aim of being able to change and optimize them in a targeted manner. The characterization of the produced samples is done by structural and magnetic analysis methods

For the application of thermally sprayed titanium coatings, the high oxygen affinity and tendency to nitride formation in the presence of nitrogen represents a major challenge. Consequently, thermally sprayed titanium coatings are usually applied by cold gas spraying, vacuum plasma spraying and shrouded spraying processes. Nevertheless, the formation of oxides cannot be completely avoided with these methods. The pre-sent study demonstrates an alternative coating strategy for the application of oxide and nitride free thermally sprayed titanium coatings. Thereby, the previous limitations are overcome by transferring the coating process into a silane-doped argon gas environment to achieve an extremely low oxygen and nitrogen partial pressure. Thus, the created titanium coatings are oxide and nitride free and have an extremely low porosity. Moreover, by transferring of the corundum blasting process to this environment, the native oxide layer on the substrate surface can be removed and its reformation is suppressed. This results in full material bonding conditions with extremely high adhesive tensile strengths.

In addition to the proper functional properties, the adhesive strength represents one of the key criteria for industrial use of thermally sprayed coatings. Since conventional thermal spraying processes are almost carried out exclusively in air atmosphere, this leads to the oxidation of the particles and of interfaces within the coatings. As a result, conventional thermally sprayed metallic and metal-ceramic coatings are characterized by heterogeneous microstructures with interlamellar oxide fringes at the interfaces between individual splats and also between the coating and the substrate. This has a decisive influence on the bond strength and on the wear and corrosion protection properties of thermally sprayed coatings. The aim of this study is to present the potentials of thermal spraying processes carried out in a mixture of monosiliane and an inert gas at ambient pressure as an alternative to the known vacuum spraying process in order to prevent oxidation during the coating process. Using the example of arcsprayed coatings, it is demonstrated that the extremely low oxygen partial pressure in the silane-doped medium leads to coatings free of oxide seams with a reduced porosity and substantially enhanced properties.

In the semiconductor industry, plasma etching processes are widely used. Process chamber parts that are located in the plasma etching system are also exposed to the harsh environmental conditions. Thus, parts located close to the process area are typically coated with yttria to increase service life, and thus process performance. However, such yttria coatings are usually porous, and thus can be attacked by fluorine containing plasma. In order to increase the lifetime of the components in the plasma etching system, this research project aimed to improve the protective yttria layer by reducing the porosity of the protective layer. Specifically, a design of experiment was employed in which the porosity was the target value. The main effects of the coating parameters and their interactions including the surface treatment before the coating process were determined. Furthermore, the bonding of the protective coating to the component to be protected, as well as the element distribution and the coating morphology were investigated. The results and their ramifications with respect to the envisaged application will be discussed.

Osteoarthritis in the hip or knee is one of the most common diseases in industrialized countries. The implantation of an endoprosthesis as a joint replacement represents the most effective way to treat serious pathological changes in these joints. The lifetime of an endoprosthesis can be shortened by aseptic inflammation and osteolysis. The main cause for the aseptic inflammations, osteolysis, and thus, the failure of the endoprostheses are abrasion particles of the acetabular cup inlays that are caused by the tribological load of the prosthesis. This research project aims at developing coatings with enhanced tribological behaviour for endoprostheses by an active hydrodynamic lubrication of the joint with synovial fluid. In addition, biocompatibility, as well as the increase of the strength under static and cyclic loading need be realized. In the current approach, a deterministic fluid flow tube structure is formed in a thermally sprayed alumina layer by the introduction of a leachable placeholder. This tube structure allows the transverse transport of the synovial fluid through the alumina layer. Furthermore the synovial fluid can be transported into the lubricating gap of the sliding surfaces by leaving the alumina layer through the porous surface. First results will be presented and the ramifications in correlation to applications will be discussed.

For most HVOF sprayed tungsten carbide coatings powders with identical particle-size distributions and compositions are interchangeable, within the meaning that as long as the manufacturing process is identical other properties are nearly irrelevant. In plastic foil industry often complex strains occur on the surfaces of the used tools. These strains comprises from a chemical attack by means of released process gases due to the thermal conditions and from an abrasive component caused by additives of the plastic. Shaping calender rolls with a high gloss mirror finished surface may show only a minimal wear in such complex strains because otherwise the quality of the foil is affected in a negative way. In this range of applications the practical experience shows that with commercial characterization values such as microhardness and porosity HVOF sprayed tungsten carbide coatings are not sufficiently described. The article describes the effects of different microstructures on the application behaviour of a coating. For that purpose analytical methods such as quantitative phase analysis due to X-ray diffraction by means of Topas-Rietveld-Method were used. Preliminary results of the use of a novel high frequency eddy current test method suggest the potential to allow a local correlation of specific properties of the coatings with their microstructure.

Depending on the size and type defects of nickel-based alloy turbine blades two procedures are used mainly: cladding and high temperature brazing. The repair brazing of turbine blades is used to regenerate cracks and surface defects and is the focus of this work. In this contribution a two stage hybrid repair brazing process is presented which allows reducing the current process chain for repair brazing turbine blades. In the first stage of this process the filler metal (NiCrSi) then the hot gas corrosion protective coating (NiCoCrAlY) and finally the aluminium are applied in this order by atmospheric plasma spraying. In the second stage of this hybrid technology the applied coating system undergoes a heat treatment in which brazing and aluminising are combined. The temperature-time regime has an influence on the microstructure of the coating which is investigated in this work.

Despite their excellent specific mechanical properties magnesium-based alloys are not widely used in the industry due to their high affinity to oxygen. Given the need for lightweight design, there are increasing efforts to replace high density materials by magnesium. One way to cope with the high oxygen affinity of magnesium is the use of thermally sprayed anti-corrosion coatings. However, conventional thermal coating processes have various process-related limitations. A case in point is coating of complex geometries and internal coatings with small diameters that often cannot be realized by conventional processes. Due to the changed process order some of the limitations of conventional coating methods can be resolved by the transplantation of thermally sprayed coatings. This method is a composite casting process for the coating of die cast components, where the thermally sprayed coating is applied to the corresponding area of the mold prior to the casting process. The aim of this study is to compare the effectiveness of transplanted thermally sprayed coatings with corrosion protection properties to conventional coatings deposited by thermal spraying and to discuss the ramifications with respect to industrial applications.

In this research project a hybrid technology is developed to repair turbine blades. This technology incorporates procedural and manufacturing aspects like raising the degree of automation or lowering the effort of machining and includes materials mechanisms (e.g. diffusion processes) as well. Taking into account these aspects it is possible to shorten the process chain for regenerating turbine blades. In this study the turbine blades of the high pressure turbine are considered and therefore nickel-based alloys are regarded. To repair or regenerate turbine blades the following methods are employed: welding and brazing and a subsequent aluminizing CVD-process. The focus in this work lies on the brazing method and the required filler-metal is applied together with the hot-gas corrosion protective coating by means of thermal spraying and represents the first stage of this hybrid technology. In the second stage of this hybrid technology the brazing process is integrated into the aluminizing CVD-process and a first effort is presented here.

Be it to save the environment or to save money, engineers everywhere attempt to use materials which can’t normally withstand the surface stress they will be exposed to on their own. This is one of the reasons for the constant interest in new and innovative coating technologies. One such innovation is the transplantation of thermal sprayed coatings. In the transplantation process the coating is integrated into a high-pressure die casting process. In contrast to the conventional process chain, the coating is not directly applied to the work piece, but to a mold insert. During the pressure casting the melt infiltrates the coating and thus creates a join. This way the coating is indirectly applied to the die-cast work piece after removal from the mold. Additionally, depending on the materials involved, a material bonding connection similar to brazing is possible and results in an increased adhesion of the coating. A potentially very interesting trait of the transplantation process is, turning an internal coating process into an external coating process. This allows the coating of inside diameters well below the usual limit of an internal spray gun. Due to the high geometric accuracy of the process this can be potentially done without any need for additional finishing steps.

Manufacturing a die-cast workpiece with a thermal spray coating usually requires multiple steps. An alternative approach demonstrated in this study integrates the spray process into a high-pressure die casting step, eliminating the need for surface preparation and post processing of the coating. To achieve this, the coating is applied to a mold insert rather than the workpiece. During pressure casting, the melt infiltrates the coating and thus creates a joint. Depending on the coating and substrate, a bonding connection similar to brazing is possible. The ability to manufacture coatings this way makes it possible to coat inside diameters well below the limit of an internal spray gun.

The aim of the research project is to combine repair brazing with protective coating against hot-gas corrosion into a common integrated process. Both the braze-metal as well as the hot-gas corrosion protection coating is applied by means of thermal spraying. The material layout is to be realized as far as possible to the near net shape by using thermal spraying. The processes are to be performed in such a way that the brazing is integrated into the CVD diffusion annealing process as a transient liquid phase bonding (TLP bonding) process which, as a consequence, can then be eliminated as a separate processing step. The thermal spraying processes of atmospheric plasma spraying (APS), high velocity oxygen fuel spraying (HVOF) and cold gas spraying (CGS) are to be qualified for this purpose. Thus the project working hypothesis is to be able to transform thermal coating and joining processes into a common integrated hybrid process and, in doing so, obtain both high-quality and economic advantages. The importance of combining these processes lies in reducing the effort of grinding as well as economizing on the vacuum brazing, which is currently a separate process step, and consequently lowering the production costs.

The main goal of this work is to improve the coating properties of three-cathode atmospheric plasma sprayed coatings with respect to porosity and residual stresses. This was done by use of numerical simulation coupled with advanced diagnostic methods. A numerical model for the triple injection of alumina feedstock, as well as acceleration and heating of the powder particles in the characteristic threefold symmetrical plasma jet cross section produced by a three-cathode-plasma torch was developed. The modeling results for the standard injector’s position “0” were calculated and experimentally verified by Laser Doppler Anemometry (LDA). Based on the criteria defined for concentrated feedstock transport and homogeneous thermal treatment of powder particles in the plasma jet, the optimal injection position was found. In the next step a previously developed, coupled CFD-FEM-simulation model was used for simulations of the coating build-up, describing flattening, solidification and deformation due to shrinkage for alumina particles on a rough substrate surface.

When plasma spraying operations require high throughput, three-cathode guns may be specified due to their stationary plasma jet and elevated power characteristics, higher feeding rates, and adequate deposition efficiencies compared to one-cathode guns. A new three-anode gun system has been introduced to the market that offers a combination of high power inputs into the plasma as well as stable process conditions. These new guns feature a narrower nozzle outlet diameter compared to multi-cathode designs and they can be used with hydrogen as secondary plasma gas. Both of these characteristics result in higher plasma velocities and net powers. The conceptional designs for two such guns are discussed as well as their suitability for suspension and shrouded plasma spraying.

Up to now no coating systems are marketable in the field of direct hot extrusion, which provide both surface protection of the parts being in contact to the billet (i.e. container and die), and a significant reduction of the frictional losses being induced by the billet passing along the container walls. To dispense the use of lubricants and to enhance the usable forming capacity of the process, different oxide ceramics were given in one suspension and plasma sprayed. The aim is to reach a mixing of the feedstock to obtain deterministic solid solutions of the oxide phases which show a reduction of their coefficient of friction under dry sliding conditions. To reach this goal the high surface-to-volume ratio of feedstock with primary particle sizes below 100 nm was used. By means of X-ray diffraction it could be proven, that the desired phases could be synthesized. The coatings showed a considerable lowering of their frictional coefficient in tribological testings against 100Cr6 in the region of the operation temperatures for the hot extrusion of aluminium alloys. Besides the experimental work the fundamentals of the mixing process of different oxides regarding crystallographic aspects are discussed.

The goal of this research group is to homogenize properties of three-cathode plasma sprayed coatings on basis of numerical simulations and advanced diagnostics. Results of the first project phase as well as an outlook to future work are presented. A numerical model for investigation of plasma flow in the free jet, produced by three-cathode torch was developed. Modelling results are verified by plasma diagnostics (Computer Tomography). In order to include particle shrinking effects, coating formation simulation is accomplished by a newly developed model, based on Computational Fluid Dynamics coupled with the Finite Element method, whereat diagnostics carried out in the fields of particle diagnostics. During the next phase of the project, the investigation of the plasma free jet and particle injection by advanced diagnostics and simulation respectively is scheduled. In a subsequent stage the transition from conventional particles to suspensions will be considered. Coating formation simulations are scaled up to dimensions of macroscopic tensile tests. By combining these overarching investigations, appropriate process parameters for homogenized coatings will be obtained.

In the area of atmospheric plasma spraying, newly-developed triple-cathode technologies offer the potential to homogenize the coating properties with respect to porosity and residual stresses. Focused on numerical simulation, combined with advanced diagnostics, the goal of this research group is to adjust these properties systematically. A numerical model that couples fluid dynamic, electro-magnetic and thermal phenomena for a three-cathode torch was developed to investigate the plasma and the electric arc behaviour inside the torch. With help of self-developed computer tomography equipment, which is based on emission spectroscopy, combined with the solution of the Saha equation in thermodynamical equilibrium, it is now possible to reconstruct the 3- dimensional temperature distribution close to the torch outlet. This measurement allows us to confirm the torch numerical modelling. Coating formation is simulated by coupled computational fluid dynamics (CFD) and FEM simulation, so that fluid structure interaction is taken into account. This innovative approach has the advantage to predict residual stresses which occur during cooling and moreover the shrinking effects can be considered. By simulation of the individual regions, in combination with experimental results, which also include the particle velocity, diameter and surface temperature, the corresponding process parameters can be obtained for the desired coating properties.

In this study, suspension plasma spraying is used to produce self-lubricating titanium oxide coatings. Certain nonstoichiometric titanium oxide phases, called Magneli phases, exhibit a reduction in friction under dry sliding conditions at elevated temperatures. These phases, however, tend to undergo crystal changes during thermal spraying, resulting in the loss of their good friction behavior. In this work, the goal is to stabilize these phases with suitable lattice substitutions for Ti 4+ . The resulting phases are shown to be homologous to Ti n O 2 n -1 , but have the advantages of a three-component system, making them more thermally stable with a broader area of formation.

In order to homogenize the properties of APS sprayed coatings, the spray process was investigated using numerical simulations combined with innovative diagnostic techniques. The process was subdivided into three areas: the plasma torch, the free jet, and coating formation. By simulating these areas separately and combining the results, appropriate process parameters for homogenized coatings were obtained. For a comprehensive computation of coating formation which, besides the impact, flattening, and solidification of particles, includes the mechanical properties of the coating, a volume of fluid algorithm is coupled with a finite element model. In order to verify the modeling of the plasma jet and to provide input data for the coating formation, diagnostic efforts were concentrated on measuring the gas temperature of the plasma as well as particle shape, velocity, and temperature. The results of spatially resolved 3D analysis employing an innovative tomography system are presented and compared with the numerical results.

In this work several powder materials typically used for wear and corrosion protection (WCCoCr, Cr 3 C 2 NiCr, Cr 2 O 3 ) were considered for developing near net shape coatings. In contrast to grain sizes commonly used in thermal spray processes the grain sizes of all examined powders were specified with maximum 25 µm (-15+5 µm, -20+5 µm, -25+5 µm). During the coating experiments the HVOF process was used to apply carbide based powder materials (WCCoCr, Cr 3 C 2 NiCr) whereas the APS process was used to deposit Cr 2 O 3 coatings. Taguchi techniques were utilized in order to reduce the number of experiments and to evaluate and to adjust main process variables. The effectiveness of these techniques could be verified by spraying validation samples successfully. The coatings were examined in terms of deposition efficiency, surface roughness, hardness, porosity, wear and corrosion resistance. The results showed that improvements in terms of porosity, surface roughness and corrosion resistance could be reached by introducing fine powder materials in the spray process. Reducing the influence of effects like decarburization or oxidation caused by the overheating of small spray particles should be considered in future work.