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.

Due to the low running costs, high spray rates and efficiency wire arc spraying has become one of the most important thermal spray technology, especially as a tool for coating large areas with high deposition rates. The main applications are corrosion and wear protection of large structures, such as coating with zinc for anodic corrosion protection or with high-alloyed chromium steel for longer surface service time. Disadvantages of the arc spraying process are on the one hand that only electrically conductive materials can be processed and on the other hand the higher oxygen content within the coating compared to other thermal spray processes such as HVOF or APS. Innovative and flexible power supply systems were developed for arc welding technologies in the last decade. Today power supply devices with new features for arc wire spraying technologies are present at the market, too. Particle flow conditions as well as coating properties such as morphology and oxide content can be optimized by changing the current generator characteristic and modulating the energy input for example by pulsing the spray voltage up to 500 Hz. As a consequence of the power modulation the oxidation of the particles can be reduced by a lower heat input based on lower average spray voltage. Investigations in order to influence the droplet behaviour and the coating microstructure using dynamic current generators were performed for zinc, aluminium and copper. The effect of different modulation frequencies, pulse lengths and pulse voltages are presented.

Low running costs, high spray rates and efficiency make electric arc spraying a good tool for coating large areas with high production rates. The main applications are in the field of corrosion and wear protection of large structures, e. g. parts for bridges or offshore industry. New applications are expected for high quality coatings produced by cored wires. Disadvantages of the arc spraying process are that only electrically conductive wires can be processed and the lower particle velocity in comparison to other thermal spray processes like HVOF or APS. Depending on the process parameters the oxidation of particles has a negative effect on the mechanical and the electrochemical properties of the coating, too. In this paper some investigations with new and flexible power supply systems for arc spraying are presented. The particle size and the morphology of the coating can be optimised, due to the possibility of changing the current generator characteristic and modulating the power by pulsing up to 500 Hz. The oxidation of particles can be reduced by a lower heat input based on lower spray voltage. For a higher quality of the coating microstructure investigations with dynamic generators were performed for Zn, Al, ZnAl, 110MnCrTi8 and Al. An enhancement of the process stability was achieved, too.

HVOF-sprayed coatings have become increasingly important for many different industries. Because of this, the ability to adjust coating process parameters according to a customer’s demands becomes a necessity. Several studies have been done on various powders, spray parameters, and the resulting coating properties such as coating hardness, wear resistance, and internal stress. On the other hand few studies have been published regarding post-treatment and finishing processes. This study is intended to investigate the entire production process, from thermal spraying to the ready-to-use finished layer; the primary points of consideration were hardness, surface quality (roughness), and resulting microstructure. The scope of this study is to present initial results of cylindrical grinding as a finishing process. Several different tungsten-carbide-based coatings of various compositions and particles sizes were produced by thermal spraying under varying kerosene-oxygen flow, spray distance, and powder feed rates. Machining parameters such as speed of workpiece rotation and longitudinal feed rate were tested as well.