This study shows that thermal spraying is a viable technique for the deposition of barium hexaferrite layers suitable for microwave absorption applications. More specifically, the study shows that impact quenching of molten BaCoTiFe 10 O 19 hinders the crystallization of the hexaferrite phase. Consequently, when spraying conditions induce near-full melting of the feedstock, the coating mostly consists of spinel and a glassy phase, a state with poor magnetic properties. These phases can be converted to hexaferrite by annealing, but in order to obtain enough crystalline hexaferrite in as-deposited layers, a controlled amount of unmelted material must be preserved. Atmospheric plasma spraying proved to be well suited for this purpose, producing layers with excellent magnetic properties, close to those of pure crystalline BaCoTiFe 10 O 19 . In these coatings, dense regions entrain many unmelted agglomerates of micron-sized particles, effectively preserving the hexaferrite phase.

This paper reports on the development of NiZn-ferrite powders and their deposition by air plasma and high-velocity oxyfuel spraying. The microstructure and phase composition of the powders and coatings are analyzed and the influence of process parameters on coating development is assessed for sprayed layers up to 500 μm thick. Particular attention is paid to the degradation of the spinel crystal structure, the formation of iron oxide phases, and elemental loss during spraying. The results show that a degree of ferrite decomposition occurs with the loss of zinc and formation of wüstite and that zinc loss is very dependent on the surface-to-volume ratio of the powder.

This work demonstrates the capabilities of oxide dispersion strengthened MCrAlY coatings and the process used to produce the feedstock powders. Mechanically alloyed powder mixtures were prepared in a high-energy ball mill using commercial NiCoCrAlY and YPSZ powders combined in different amounts. A high-velocity oxyfuel torch was used to deposit the powders on Inconel substrates that were then heat treated for 6 h at 1050 °C. Samples were also produced from unaltered NiCoCrAlY powder to serve as a reference. In high-temperature erosion tests, the strengthened coatings had a mass loss of 47 mg/cm 2 after 30 sec compared to 38 mg/cm 2 for the unstrengthened sample. High-temperature corrosion tests showed that the strengthened coatings were not dense enough to protect the substrate from oxidation. The hard phases inhibited sintering and diffusion effects during heat treatment. As a result, dislocations, defects, and voids could not move and were used by oxygen for diffusion. In further investigations, the strengthened coatings will be treated at a higher temperature to achieve a better sintering effect.

The objective of this work is the development and application of Fe-based wear- and corrosion-resistant coatings with uniform density and even coating surfaces. The coatings obtained were analyzed with respect to microstructure, hardness, and surface roughness.

Hypoeutectic AlSi engine blocks of modern passenger cars are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. A very promising alternative to the use of cylinder liners lies within the application of thermally sprayed coatings onto the walls of cylinder bores as friction partners for the piston rings. This work describes the development of a novel iron based wire feedstock as well as its application by the Plasma Transferred Wire Arc internal diameter coating system. The material developed within the frame of this work leads to partially amorphous coatings with embedded nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of Aluminium EN AW 6060 and onto cylinder bore walls of in-line 4 cylinder engines. All substrates were mechanically roughened in order to obtain high bond strengths of the sprayed coatings. The coatings microstructure was analysed by light optical microscopy, hardness measuring by transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.

MCrAlY materials are widely used as bond coats for thermal barrier coatings on turbine blades. The aim of this work is to improve mechanical properties and wear resistance of thermal sprayed NiCoCrAlY-coatings by strengthening the coating with hard phase particles. In order to retain the effect of the dispersion reinforcement at high temperatures, the use of temperature-stable oxide hard phases such as ZrO 2 is necessary. To realise this new material structure, the high energy ball milling process is applied and analysed. With this process it is possible to achieve a homogeneous distribution of the oxide hard phases in the NiCoCrAlY matrix. The mixture ratio between NiCoCrAlY and ZrO 2 was varied between 5 wt-% and 10 wt-% ZrO 2 . The influences of the milling time of the high energy ball milling process on the distribution of the hard phases in the metal matrix were analysed. After spraying with a HVOF system the mechanical properties of the coatings are measured and compared with conventional NiCoCrAlY coatings.

In modern jet engines, the efficiency of the compressor stages is highly dependent on the clearance between blade tip and casing. In order to improve efficiency of gas turbines (i.e. areo engines as well as land based gas turbines), the gap between the rotating turbine blades and casing has to be minimized. Any increase in the gap results in power loss. Abradable coatings permit a minimization of the clearance and control of the over-tip leakage by allowing the blade tips to cut into the coating. Thermal sprayed abradable coatings aim at a well balanced profile of properties relevant for the application as abradable seals. Amongst others these include: abradability, ageing resistance, corrosion and oxidation resistance, surface finish and bond strength to substrate materials. In this work, abradable coatings consisting of a multiphase material, comprising a metal matrix in addition to a solid lubricant as well as a defined level of porosity, were developed using the Triplex Pro 200 (Sulzer Metco, Wohlen, Switzerland) in order to increase the reproducibility and deposition efficiency. Additionally the influence of the process parameters on coating characteristics such as porosity, hardness and, resulting from this, coating erosion properties and abradability was investigated.

HVOF-sprayed carbide based coatings such as WC/Co or Cr 3 C 2 /NiCr are industrially well established for wear and corrosion protection applications. Due to their high carbide content of typically 75 wt.-% and more, they are providing a very high hardness and excellent wear resistance. Unfortunately costs for matrix materials like Ni or Co underlie strong fluctuations and are significant higher compared to iron. Therefore an alternative concept to the conventional carbides is based on TiC-strengthened low cost Fe-base materials, which are already in use for sintering processes. Depending on the carbon content the Fe-base material can additionally offer a temperable matrix for enhanced wear behaviour. Within this study the sprayability of TiC-strengthened Fe-powders with a gaseous and a liquid fuel driven HVOF-system has been investigated. The resulting coatings have been analysed with respect to microstructure, hardness and phase composition and compared to galvanic hard chrome, HVOF-sprayed and remelted NiCrBSi and HVOF-sprayed Cr 3 C 2 /NiCr (80/20) coatings as well as sintered Fe/TiC reference materials. Furthermore the Fe/TiC coatings have been heat treated to proof the retained temperability of the Fe-matrix after thermal spray processing. For determination of wear properties tribometer tests have been conducted. Currently the corrosion resistance of the sprayed Fe/TiC coatings is investigated as well the wear behaviour in a practical hydraulic test bench.

Saving energy is a major concern in every aspect of the economy, especially in the automotive and aerospace industry. The use of lightweight materials is one way to reduce weight of moving parts and thus energy consumption. Research activities to improve the porosity on the one hand, and the coating properties like wear and corrosion resistance on the other hand, show the potential of a hybrid coating process. The creation of thermal-sprayed coatings and a laser post-treatment enable a minimization of porosity and an improvement of wear properties. Different coating materials (e.g. Al-Si alloy) have been investigated regarding microstructure, hardness, wear- and corrosion protection.

Carbon fibre reinforced carbon (CFC) composites have been more and more used in different industrial areas as high temperature materials. Some application examples are CFC components in modern furnaces for heat-treatment and brazing. Because CFC components can react with metallic materials when they contact each other, diffusion barrier coatings are essentially important for such CFC components. The aim of the project IGF 14.880 N “Thermally sprayed diffusion barrier coatings for CFC components in high temperature applications” is to develop diffusion barrier coatings by thermal spraying technology. In the project, different coating systems have been developed and investigated regarding the coating build-up, coating microstructure, bonding, thermal shock resistance and diffusion barrier function. The research results reveal that some developed coating systems are suitable for applications in furnaces. In the present paper, some research results of this project are reported.

One of the most popular test methods for the evaluation of thermally sprayed coatings and substrate pre-treatment is the bond strength test in accordance to the standard EN 582 (in Europe) or ASTM C633-79 (in the U.S.). An interlaboratory test, carried out in 2003, has shown that bond strength tests of samples that were joined by different institutions in accordance to DIN EN 582 lead to bond strength values that varied by the factor 2, even if the same adhesive was used. The test not only made clear that the adhesives used to join the loading block to the substrate block but also many other parameters have a tremendous influence on the results of the bond strength tests. It was also clarified that the DIN standard needs to be supplemented in order to improve the comparability and the reproducibility of the bond strength test results. The first aim of this work was to identify the influencing parameters by carrying out Failure Mode and Effect Analyses (FMEA) together with namable institutions. Based on these results, a work instruction based on the DIN standard will be composed in order to avoid its weak spots. Later, a second interlaboratory test will be carried out to evaluate the quality of the work instruction.

Process optimization and innovative material applications gain more and more interest under the aspect of continuously increasing functional and structural demands on thermal sprayed coatings. With the cascaded triple arc plasma gun generation, the atmospheric plasma spraying process was advanced by delivering enhanced plasma stability and, associated with this, higher deposition efficiency. The TriplexPro 200 is the latest version of a three cathode plasma spraying system on the market and offers distinctly higher particle velocities, due to its advanced nozzle design. As a result of the higher particle velocities, lower particle oxidation and higher coating density can be realized. In order to increase the corrosion protection of metallic coatings and the thermal properties of TBCs, the aim of the work performed is a parametric study to deposit advanced coating systems for high temperature applications.

After having established an offline process control based on the optical process diagnostic system PFI (Particle Flux Imaging) the process robustness has been increased by experimental identification of the impact of the noise factors „electrode wear“ and „injector wear“ in the APS process. Neural networks were used for implementing a process controller into a GTV APS process control center. In combination with the PFI system a tool was installed in the process center that is able to predict coating quality by analyzing some characteristics of the plasma and the particle plume. The neural network can be trained for all applications and all feedstock materials. An offline controller is instructing the operator through a desktop in order to train the network. The training, that means the monitoring of the process through different parameter setups and its reactions, is generated and executed automatically. Due to the fact that controlling the process parameters cannot influence every aspect of the coating quality, noise factors have to be regarded. For the APS process the electrode wear and the injector wear were identified as the most influencing noise factors. Both were analyzed by means of Design of Experiment (DOE) and long-term monitoring (200 hrs). The samples were characterized by light microscopy and different coating test methods that were chosen with respect to the coatings functions (e.g. wear resistance). The result of this work is a set of parameters that are as robust against both noise factors as possible and that are adapted to certain changes by a neural network process control.

The number of parameters influencing the plasma spraying process is very high. Only a part of these parameters can be controlled online; some of them such as gas flows, current, voltage and spraying distance can be controlled easily, others such as particle temperature and velocity can only be controlled with substantially higher effort. As differences from parameter values preinstalled or given at the start of the process, the noise factors affect the coating properties in different ways and show big effects on the coating quality. Nevertheless there is only little knowledge about the significance of several noise factors and about the influence of small process parameter fluctuations on the coating properties. Because some of these noise factors such as plasma torch degradation cannot be avoided, the aim of this work is to determine the sets of coating parameters, where the influence of noise factors is minimized. This should be achieved by using online diagnostic tools, that afford the observation of fast and easy controllable process characteristics. On the other hand process errors shall be identified in an early process stage using appropriate diagnostic methods.

Being the 7th most abundant element on the earth, magnesium and its alloys have become very promising in numerous industrial applications because of some of their distinguished properties, including high thermal conductivity, high strength/weight ratio, good machinability etc. However, some inferior properties especially the poor wear and corrosion resistance have obstructed a widespread use. As one of the most effective solutions, thermal spraying can deposit an adequate protective coating on the substrate, but the necessary grit-blasting operation before spraying leads to high grit-residues on the magnesium surface therefore degrading the deposit performance. The PROTAL® process, combining a laser surface preparation with the deposition stage, can avoid this kind of disadvantage. This paper presents the possibility of employing PROTAL® to prepare a resistant Ni-Cr coating on a magnesium substrate. The coating adhesion and interface microstructure were especially investigated.