Today, the efficiency of turbines is limited by different losses. Minimizing these losses is a main goal to reduce fuel consumption and produce more environmentally friendly machines. Observations on the scales of fast swimming sharks display a riblet structure. These riblets provide a significant reduction of drag losses, but are quite sensitive on pollution. Therefore, for a good performance, it is essential to combine these structures with self-cleaning properties. A lateral- and depth-selective distribution of particles with a negative thermal expansion coefficient (NTE) in a binder with positive thermal expansion coefficient can be used to deform the surfaces depending on the temperature. At high temperatures a riblet structure will be formed by local expansion or shrinkage and at cooling down the surface will be cleaned by the reversal of the deformation. Beside the production of a coating with a lateral- and depth-selective distribution of the NTE-ceramics within the binder the thermodynamical stability of the ceramics inside the binder is part of the investigations to provide a sufficient long-time stability of the coating.

The heat produced by incinerator plants can be used to produce electricity and district heating. Metallic components, e. g. heat exchangers, are exposed to a highly corrosive atmosphere. Gases with particularly high chlorine contents lead to the very quick wear of the base material and define the service time and are the main reason for high maintenance costs. Spraying a corrosion-protective coating on conventional steel gives the possibility to improve the performance of the surface significantly. Due to its easy handling and low operating costs, wire arc spraying has become one of the most established processes. The thermal spray Ni- and Co-based coating alloys are state of the art. The substitution of these materials by Fe-based alloys will lead to a noticeable economic benefit. The latest research activities proved that the addition of silicon raises the corrosion resistance in comparison to FeCr- and NiCr-based alloys. In order to verify the potential of these materials, flux-cored wires with different compositions were manufactured and were applied by means of arc spraying. Subsequently, corrosion investigations were conducted on the specimens in an atmosphere containing chlorine.

Molten metals are extremely corrosive against steel-made molds. In addition to alternating thermal loads and erosion by hard particles the lifetime of molds in the permanent-mold casting industry is rather short. Tungsten-based pseudoalloys are able to increase the lifetime of these molds significantly, but, by now, their use is limited to sintered inlays at the mostly stressed parts of the mold. Coating the whole mold with these materials offers an increase of the lifetime and at the same time a reduction of the amount of deployed feedstock. Within this research project it was possible to increase the lifetime of a kernel in used in casting brass by a factor of 20 by cladding it with tungsten-based pseudoalloys. The metallurgical behaviour of the tungsten-based pseudoalloys is quite complex. By modifying the coating process different shapes and amounts of tungsten precipitations in the nickel-iron-binder can be realized. The different microstructure within the coating does strongly affect the mechanical and anti-corrosion properties of the coating.

Conventional processes of gas shielded metal arc welding (GMAW) do not offer directly the possibility for cladding heat sensitive materials such as aluminum with iron-based materials due to intermetallic Al/Fe phases form. This paper deals with the first evaluated cladding results of aluminum components with iron-based nanocrystalline solidifying materials by controlled shielded metal arc welding processes to improve wear resistance. In the present work, the design of experiments and data evaluations are systematically applied to get the first results about the dependence between controlled arc welding process parameters and the iron-based coatings of aluminum substrate. In particular, the effect of the chosen parameters such as wire feed speed, welding speed, frequency and further factors on the heat input, welding penetration, micro hardness, rate of welding penetration and width of intermetallic phases in the interface zone are investigated. Optical and scanning electron spectroscopy provide input for further statistical evaluation. The experiments were carried out using various controlled arc technologies which offer different control over the heat input to the substrates. Different power supplies were used.

The lifetime of casting molds in the aluminum industry is strongly limited by the corrosiveness of aluminum melts and alternating thermal and mechanical loads. With the added protection of sintered tungsten pseudoalloy inlays, casting molds have been known to last as much as 1000 times longer, and the work presented here indicates that it may be possible to replace the massive liners with a twin wire arc or plasma sprayed coating that can be tailored by varying spraying parameters.

The aim of this investigation is to show that it is possible to inject powder into a wire arc spray process as an alternative to using cored wire to produce particle-reinforced coatings. The equipment, materials, and procedures used are described in the paper along with the microstructure and properties of the coatings obtained. By changing the feedrate of CrC particles injected into a stream of chromium steel droplets, particle-reinforced graded layers were produced by wire arc spraying on the fly without having to stop the process.

Due to its easy handling and low operating costs, wire arc spraying has become one of the most established processes for applying protective coatings to components used in waste incineration plants. This paper discusses the development of relatively low-cost Fe-Cr-Si coating materials for incinerator applications and the corrosion and wear properties that have been achieved using conventional arc spraying methods.

This work investigates some of the unique properties that can be achieved by combining materials with positive and negative thermal expansion coefficients. In the experiments, different mixtures of MCrAlY, WO 3 , and Y 2 O 3 powders are deposited on stainless steel substrates by laser cladding and HVOF spraying. To facilitate the formation of negative expansion coefficient particles in a positive expansion coefficient matrix, nucleation centers are created by ion implantation followed by heat treating. SEM examination and XRD analysis of the coatings obtained confirm the viability of the processing approach.

The introduction of new wire arc spraying equipment with chopped power supplies offers many possibilities to improve the wire arc spraying process. These power sources provide higher process stability even at reduced voltages. On the one hand conventional applications can be enhanced and on the other hand new processes can be developed. Due to the high process stability the introduction of additional particles into the atomizing gas stream is possible. This can be applied to produce coatings with a high wear resistance as well as a high surface roughness. A combined technology of particle injection and the productive wire arc spraying process enables the economic production of innovative functional surfaces. In the last years ITSC, the injection of corundum particles had been presented. In this paper further strategies for inserting particles into the gas stream and experimental results are shown for iron based coatings. For the reinforcement different carbides were injected into the atomizing gas stream.

Casting molds in the aluminium industry show a short lifespan due to the high corrosiveness of aluminium melts and alternating thermal and mechanical loads. By using new materials, in example pseudoalloys containing tungsten, the lifetime of casting molds can be elongated up to hundredfold. Today, casting molds made of steel are state of the art. In spite of the advantages of pseudoalloys, high manufacturing cost and the increasing commodity price of tungsten prohibit the use of molds consisting of these progressive materials. By coating the standard steel molds with a FeNiW-layer, the excellent thermal and corrosive resistance of the pseudoalloy surface can be combined with minimal manufacturing costs. For present work steel substrates had been coated with FeNiW-pseudoalloys. Therefore, arc spraying and different deposit-welding methods (Laser, Plasma, TIG) had been compared. By modifying the machine parameter set, a smooth transition between substrate and coating was realized. Thermal and chemical resistance of the samples will be tested. In this paper first results are presented.

Thermal Spray processes are widely used to fabricate corrosion and wear resistant coatings respectively. However, these coatings have to be finished generally in subsequent steps, for example by turning, milling or grinding, to adjust the the required properties, e.g., surface roughness and accuracy. Up to now grinding is the most common post processing for wire arc sprayed coatings, but in recent years the hard turning technology gained high interest for coating treatment due to high machining efficiency. The aim of the present work is to enhance the machinability of different thermal sprayed coatings. DoE-based experiments regarding surface roughness, cutting forces and temperatures in the cutting zone had been carried out. Within the investigations a significant increase of hardness due to the hard turning process at Fe-Mn coatings had been verified. This effect, the force induced martensitic transformation, could improve the mechanical properties of the coating considerably. Based on the investigations presented in this paper, a deeper understanding of post processing of thermal sprayed coatings is given.

Increasing requirements on technical components for high-temperature-applications (e.g., turbine blades) demand for new developments in surface engineering. The selective combination of materials with positive and negative thermal expansion coefficients (NTE) will lead to a reversible activation of the surface depending on surface temperature: The generation of a riblet structure (“shark skin”) in operation condition by thermal expansion of the matrix and shrinkage of the NTE-ceramic and self-cleaning of the surface at cool down as a result of the reversal of the process. Due to its hygroscopicity the chosen NTE-ceramic Y 2 W 3 O 12 needs to be embedded into a binder matrix. Therefore a feedstock powder consisting of MCrAlY, WO 3 and Y 2 O 3 is mechanically alloyed in a high-energy ball mill. The powder is deposited on substrates by thermal spraying (VPS and HVOF) and laser cladding as well. After coating process a lateral- and depth-selective ion implantation of tungsten, yttrium and oxygen will force nucleation in predefined areas. A following heat treatment of the specimens supports the in-situ-formation of Y 2 W 3 O 12 .

Since many years, aluminum alloys are established as lightweight construction materials. To reach a partial wear protection for aluminum components in conjunction with seal faces, inlays, made of wear resistant materials, are commonly used. Problems concerning this approach are the necessary space and the endurance strength of the inlay - part joint. New process equipment offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases in the aluminum-steel interface as well as the thermal stresses. The usage of new nano crystalline solidifying wear resistant iron-based feedstock materials with advantageous physical and mechanical properties enables further applications beside the wear protection of surfaces, for example as metallic heat insulation layer with a low heat conductivity, close to the values of ceramics.

Aim of this project is to produce anti-corrosion coatings for high temperature applications by wire arc spraying. It is necessary to adjust the feedstock material as well as the spray equipment in order to control the coating composition and the coating morphology. The substitution of expensive Ni- and Co-based feedstock by Fe-based alloys leads to an economic benefit. In combination with wire arc spraying, the total coating costs can be reduced significantly. There is also an enomous potential for reduction of service costs in waste incineration plants due to an enhanced coating service life and shorter downtime for the anti-corrosion coating repair.

Nowadays wire arc spraying of chromium steel has gained an important market share for corrosion and wear protection applications. In order to optimize the process parameters and to evaluate the effect of the spray parameters DoE based experiments have been carried out as well. In this paper, the effects of the process parameters of spray current, voltage and atomizing gas pressure on the particle jet properties of mean particle velocity and mean particle temperature as well as plume width are presented. To monitor these values the AccuraSpray system was used. The properties of the coatings with regard to morphology, composition and phase formation are included as well. These investigations are part of the development of new power supplies and the enhancement of spray parameter range. As a result of these experiments the spray parameters can be adjusted according to the requirements of the chromium steel coatings.

A method for the production of particle reinforced coatings by wire arc spraying will be presented in this paper. This technology is based on twin-wire electric arc spraying (TWEA) process. Here, additional particles were injected into the atomizing gas stream and sprayed in a non molten state along with wire feedstock material onto the substrate. According to the reinforcing particles, the process can be applied to produce coatings with a high wear resistance as well as a high surface roughness. In a wide range of applications, these coating characteristics are required. Due to economic constraints, coatings of large surfaces have to be done in short times at low costs. Based on wire arc spraying, the thermal spray process with the highest deposition performance, the mentioned industry requirements can be fulfilled.

Since many years, aluminum alloys are established as lightweight construction materials. To reach a partial wear protection for aluminum components in conjunction with seal faces, inlays, made of wear resistant materials, are commonly used. Problems concerning this approach are the necessary space and the endurance strength of the inlay - part joint. In the following paper an alternative for the replacement of the inlays by cladding with an innovative and easy to handle short arc technology will be discussed. This technology offers the potential to control the energy input into the substrate and so the formation of brittle intermetallic phases in the aluminum-steel interface as well as the thermal stresses. The usage of new nano crystalline solidifying wear resistant iron-based feedstock materials with advantageous physical and mechanical properties enables further applications beside the wear protection of surfaces, for example as metallic heat insulation layer with a low heat conductivity, close to the values of ceramics.

Plasma Transferred Arc (PTA) welded coatings are used to improve surface properties of mechanical parts. Advantages are the high reliability of the process and the low dilution of substrate and coating material. Processing of surfaces by PTA welding is restricted at the time to flat horizontal position. Furthermore industry is interested in the development of strategies for coating with PTA in constraint position as complex 3-D parts could be then easily processed as well. Under commercial aspects, the process design can be optimized in order to increase process efficiency and to reduce heat input during the welding process. Process optimization involves the determination of guidelines for PTA welding in constraint positions as well. Modelling the process gives an alternative to reduce the experimental effort to optimize the welding process. Results of simulation studies of the PTA welding process will be given in the present work. It will be shown, that coating conditions can be optimized by varying plasma gas flow, heat input and heat flow, process speed or powder injection with regard to welding in constraint positions. The defined controlling of the PTA welding allows to modify process management with less experimental effort and to develop coating strategies for processing in different positions. In experimental investigations the developed coating strategies will be confirmed by producing PTA coatings in constraint position as well as complex 3-D parts.

In this paper the principle of “Thermal Spray Molding” and some application are presented. Micro technology is a very fast growing market nowadays. Metallic micro devices can be produced for example by means of stereo lithography and selective etching. Unfortunately the material range for these processes is limited. The new manufacturing concept of thermal spray molding uses powder or wire as base material, so that an extended material choice for micro parts, for example micro components made of super hard or corrosion resistant steel is possible.

Innovative short arc technology is gaining high interest for low temperature joining strategies exemplified by the soldering of zinc coated steels and the joining of steel/aluminum hybrid joints. Controlled short arc allows on one hand a very low heat input in the component, so that melting of the base material can be limited. On the other hand it is possible to use low temperature melting filler wires, as for example zinc wire. New development in controlling short arc have been performed in the last year and reached its maturity for welding production (e.g. Cold Metal Transfer (CMT) of Fronius or Cold Arc in EWM). In both cases the short arc is controlled after drop transfer. One way to perform control is a high dynamic wire feed, which allows high dynamic retracting wire end. Another possibility represents a new type of highly dynamic inverter switching, combined with very fast digital current control, to reduce drastically the peak power in the arc when the short arc is reignited. The consequence of this is a no-sputter, low heat processing procedure. The arc is considerably colder due to the power reduction on re-ignition, which means that a lower heat input is possible.