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.

One of the most effecting parameters for the wire arc spraying with the regard to the properties of the sprayed coatings is the flow characteristic of the atomizing gas. Depending on the nozzle inner contour at the entrance of the torch, the atomizing gas is emanating the nozzle as a non-adjusted supersonic gas jet, either under- or over expanded. Thus, a convergent-divergent nozzle with a bell-shaped divergent exit is designed in order to generate a completely expanded atomizing gas flow inside the nozzle without any shock nodes in the emanating gas jet. The influence of the flow characteristic of the atomizing gas (air) on the droplet velocity is investigated by Laser- Doppler-Anemometry measurements. The coating quality is characterised with regard to the surface roughness and porosity.

In the last years laser beam cladding was recognised as a high quality coating process. Low thermal influence, high cooling rates, metallic bonding, minimal surface roughness are only some of the positive aspects. On the other hand the process efficiency is very low and the running costs in comparison to PTA or Thermal Spraying are high. Attempts to improve the productivity aim to enhance the efficiency of the beam source itself or to optimize the energy management. This is for example possible through a higher coating speed or through hybrid setups, which allow the use of an additional preheat source (e. g. plasma-assisted laser cladding). Regarding flexibility, defined as the capability of a process to answer in a short time to application requests, the effectiveness of laser cladding can be widely increased through free forming (shaping) of coatings without additional clamping devices. The geometric shape of the coating seam is mainly defined by gravity and surface tension of the melt. An additional force, as for example Lorentz force, can optimize the geometry and improve the process conditions. Wide seams allow for example a low number of overlapping layers when coating large areas and rise the specific area deposition rate. Slim coatings on the contrary are advantageous when generating 3-dimensional structures. The induced force depends from the applied magnetic field and the flow of an electric current. The presented investigations clarify the physical background, the interaction of the magnetic force and the geometric shape of the coating and the possibility to apply them for technical coatings. The application of an external force made it possible to increase the efficiency of the laser cladding process and to gain more interest of the industry.

Laser cladding offers several advantages as low dilution, low thermal influence and distortion of the components and a fine microstructure due to the high cooling rate. Nevertheless the set of laser cladding in the industrial production is nowadays limited to few applications, as the efficiency of laser sources is still too low and the running costs are too high. The absorption behaviour of metal surfaces, as for example steel, towards diode laser (up to approx. 42%) is very high compared to Nd:YAG (approx. 35%) and CO 2 -Laser sources (approx. 11%), so that some benefits can be expected. One of the disadvantages of diode laser was the low intensity and the difficulty to couple it in a fibre. The development of the last years reached to overcome these boundaries. High power diode lasers are nowadays available till 6 kW and can be coupled in fibres, allowing an easier processing. Investigations regarding laser alloying with high power diode laser confirm the appreciable reliability of this laser class. In order to improve efficiency of laser surface processing the hybrid process plasma-augmented-laser-cladding (PALC) with an Nd:YAG laser source was presented and confirmed that due to the pre-heating of the powder through the plasma transferred arc and the activation of the metallic surface a higher processing velocity (factor three) and efficiency could be reached by summing only one third of the energy with a PTA-equipment. Further more when processing with higher velocity the energy loss due to conductivity decreases so that a further positive increase of efficiency can be depicted. The suitability of fibre coupled high power diode laser for PALC hasn’t yet been investigated, even if the set of this laser type would be very advantageous. In this paper investigations regarding the process design and the necessary set up of the hybrid PALC-process with a 3 kW fibre coupled high power diode laser and wire coating metal are reported.

Laser post treatment is a well known procedure in order to homogenize the geometry, the microstructure and aspect of the surface of thermal sprayed coatings. Furthermore the properties of coatings, as for example corrosion resistance can be improved, as a sealing layer is induced by remelting. High power laser sources as CO 2 -, Nd:YAG as well as diode laser are used for this aim. They allow a very deep remelting zone in a depth-range between 0,2-2 mm. Contemporarily the hard phases as well carbides in the coating degenerate due to the very high heat input and the wear resistance of the coating decreases. Short-pulse laser are very advantageous for processing surfaces in a very narrow band (under 50 µm). Applications are nowadays developed for the surface treatment of aluminium cylinder running surfaces and of titanium implants. The short-pulse laser post processing can be a very profitable methods to improve the behaviour of coatings without damaging hard phases. Investigations on remelting of PTA- and thermal sprayed coatings with a Nd:YAG-short-puls laser and with an excimer laser are reported in this paper. Surface quality as for example roughness of PTA-coatings with tungsten carbides (NiCrBSi+60%WSC) could be improved and a slight surface sealing layer was induced. Depending on the adopted laser system, different surface roughness profiles can be reached. In further investigations the suitability of the method was proven for thermally sprayed coatings of NiCrBSi

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.

The industrial set of PPAW-cladding has gained a higher importance in the last few years. The process is characterised by high quality layers of about 1-2 mm with a low dilution of about 5 % and without intermediate layers. The great amount of different alloys, which can be processed as powders, opens a wide range for industrial applications. Manually PTA-cladding can be performed in different working positions. Presently the full mechanised PTA-cladding process is carried out in horizontal position. Thus the components have to be moved relative to the plasma arc. In order to improve operating efficiency and flexibility when processing wear and corrosion resistant coatings it is necessary to enlarge the working area and to set strategies for cladding in constrain position. The effect of the gravitation force leads in this case to a very difficult governing of the pool, which flows downwards and affects the quality of the coating. Basic knowledge of the mechanised process depending on the cladding position, for example with industrial robots, is not available at the moment, even if this is necessary when cladding huge heavy components. The present work shows coating strategies as well as the influence of process parameters while cladding steel with corrosion and wear resistant powders in constrain position (bottom-up and top-down). Investigations with Ni- and Co-based alloys were examined and the suitability for constrain position was evaluated. Through an optimisation of the heat input it was possible to influence positively the melt flow and to carry out successfully coatings. Finally the transferability was successfully proven on a complex three dimensional component.

HVOF-, arc- and plasma sprayed coatings are widely used for wear protection. Today these type of layers are dominant if thin coatings from 50 up to 500 µm and low heat input into the work piece are required. The main disadvantage of thermally sprayed coatings is the adhesion to the substrate and the early failure when cyclic loaded. In both cases a metallurgical bonding to the substrate can improve the life cycle time. Plasma transferred arc (PTA) welded coatings show a metallurgical bonding to the substrate. The main disadvantages of this coating technology are the dilution of about 5%, the heat input into the substrate and that nowadays all welding positions seem to be impossible to carry out. In this paper the theoretical background for welding thin coatings (less than 500 µm) with a decreased dilution and in all welding positions is given and experimentally proved.

Laser cladding is a very promising technology from a metallurgical point of view. The benefits are low heat input into the substrate, high cooling rates resulting in a fine microstructure of the coating and an excellent metallurgical bonding to the substrate. The main disadvantage of laser cladding, however, is poor process efficiency, which causes high processing costs. In order to gain interest on the industrial level an optimisation of the energy management, for example reducing the energy loss through conduction, is necessary. Improved process efficiency and reduced processing time can be realized by a hybrid technology of coupling laser with a plasma arc. The feed can be coaxial to the plasma gun in form of powder. The main advantage of this process is that the processing area as well as the powder is preheated and activated by a transferred arc. The laser power is mainly used for heating up the feedstock material till melting temperature. The experimental results prove the theoretical considerations. Compared to laser cladding an increase in cladding speed and a lower energy input are reached. Further the efficiency towards material can be nearly doubled, reducing stock costs. At last the heat-affected zone is reduced, which offers the possibility to process crack sensitivity materials.

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.