Search Results for thermal spraying

A new laser thermal spraying method has been developed and experimentally realized. The new method makes possible independent energy input to the powder stream and workpiece using conical laser beams and thus is more efficient than other methods. The new method offers environmental benefits in comparison to other techniques.

In many empirical studies on the structure and properties of thermally sprayed coatings, a set of two predefined parameters (e.g. porosity and elastic modulus) is correlated over a narrow range of structural variation assuming a continuous correlation function. Such a data evaluation assumes the existence of physical correlation’s between material behavior and microstructure. The experimental approach, undertaken in this study, comprises a maximum range of morphologies for starting materials with nearly identical chemical compositions to reveal the influence of microstructural changes of diverse defect species on different coating properties. The large matrix of structural and physical data is statistically correlated without any preconceived assumptions concerning the mathematical functions or the physicochemical nature of the property-microstructure-correlation’s. The divergent morphologies are realized by using different coating processes such as vacuum (VPS) and atmospheric (APS) plasma spraying, water stabilized plasma spraying (WSP), wire arc (WAS)- and flame spraying (FS), including variation of process specific parameters. The microstructure is systematically analyzed along length scales starting from defects in the micrometer down to the nanometer range. The microstructure and its anisotropy is quantified by small angle neutron scattering (SANS). The phenomenological coating behavior is successively investigated starting from basic properties such as electrical and thermal conductivity, elastic constants, residual stresses up to application oriented properties such as wear resistance. Property combinations presuming high sensitivity to microstructural changes are preferentially characterized and statistically correlated.

This article gives an overview of thermal spraying of polymers with respect to the different spraying processes, the polymer materials in use for thermal spraying and new trends of using polymers as separate spraying material and in combination with plastic and non-plastic materials. Flame spraying is by far the most common process used for thermal spraying of plastic materials. In addition in the past years two other processes have been used to produce thermal sprayed plastic coatings: plasma spraying and high-velocity oxy fuel spraying (HVOF). The areas where the different processes are used as well as the modifications to conventional plasma and HVOF devices and the advantages and disadvantages using these two processes to produce plastic coatings will be described. In addition to the common materials used for flame spraying (e.g., PA 11, PA 12 or EVAL), other materials giving new opportunities of application of thermal sprayed coatings have been used like PEEK and LCPs. The areas where these materials are used are described as well as the special features of these materials. Furthermore there are new trends in using plastic materials for thermal spraying. Thermal sprayed polymer materials are for example combined with plastic as well as non-plastic materials or pigments giving special effects to the coatings, e.g, reflective or anti-skidding coatings. It is described how coatings with the mentioned effects can be produced.

This study employs an XAI framework to gain insights into Residual Network and Artificial Neural Network models trained on both simulations and experimental data to predict deposition efficiency (DE) in atmospheric plasma spraying (APS). SHapley Additive exPlanations (SHAP), an interpretability framework, was then applied to help identify which process parameters have the most significant influence on the DE and to reveal how changes in specific parameters affect the DE by elucidating their impact on the model predictions.

Despite their light weight, 2.3 times lighter than Al, polymers are limited to application with low thermal, wear, and abrasion demands. The enhancement of the functional surfaces of the polymers using thermal spraying techniques is a challenging task due to the thermal degradation of polymers, the low wettability, and the disparate atomic properties. The twin-wire arc spraying (TWAS) process comprises two contradictory features. Almost all spraying particles are in a molten state on the one hand, and on the other hand, the spray plume has the lowest heat output among the different thermal spraying techniques. Therefore, it is a promising spraying technique for the required surface improvement. The surface of the 3D-printed parts was metalized using two successive layers. The first layer is a TWAS coating made of low-melting ZnAl 4 to avoid thermal degradation and provide a bond coat. The topcoat is also applied using a TWAS process and was made out of Ni-WC-Co as cored wires. The top hard coating has improved the wear resistance of the polymers by 14.6 times. The erosion of the coated and uncoated specimens was determined using a low-pressure cold gas spray gun. Ni-WC-Co coating led to more than five times higher erosion resistance.

In this work, gas-atomized FeCr powders were deposited on aluminum substrates by HVOF spraying, forming dispersion strengthened coatings with a dense layered structure and low porosity. SEM, TEM, and XRD analyses show that the coatings primarily consist of amorphous matrix (40%) with precipitated nanocrystals and hard boride phases. A number of coating properties, including microhardness, bonding strength, and thermal conductivity, were measured and are correlated with spraying conditions.

A high speed thermoanalytical method has been developed to determine the thermophysical properties of the powders used in thermal spraying. This method is based on heating the powder by means of an electron- or photon-beam in vessels made of materials with excellent heat conductivity. By comparing heating and melting behavior of powders with similar composition but different particle sizes and shapes, their properties can be determined. The suggested high speed thermoanalytical method makes it possible to investigate the heating and melting behavior of spray powders under high speed heating conditions. The results of the experiments, elaborated by this method can be used for further modeling work. Paper text in German.

Nanocrystalline Inconel 718 and Ni powders were prepared using two approaches: methanol and cryogenic attritor milling. High velocity oxy-fuel (HVOF) spraying of milled Inconel 718 powders was then utilized to produce Inconel 718 coatings with a nanocrystalline grain size. Isothermal heat treatments were carried out to study the thermal stability of the methanol milled and cryomilled Inconel 718 powders, as well as the HVOF Inconel 718 coatings. All nanocrystalline Inconel 718 powders and coatings studied herein exhibited significant thermal stability against grain growth as evidenced by a grain size around 100 nm following annealing at 1273 K for 60 min. In the case of the cryomilled nanocrystalline Ni powders, isothermal grain growth behavior was studied, from which the parameters required for the prediction of the microstructural evolution during a non-isothermal annealing were acquired. The theoretical simulation of grain growth behavior of nanocrystalline Ni during non-isothermal annealing conditions yields results that are in good correspondence with the experimental results.

There have been recent efforts to expand the thermal spraying capabilities for novel corrosion resistant coatings for metal bipolar plates were produced by thermal spraying for proton exchange membrane (PEM) fuel cell applications. Recently, substrate heated by plasma gun or by external laser beam has been proposed to enhance the mechanical and thermal properties of the coatings. Studies were found that with sufficient substrate heating, substrate melting may happen. When droplets solidified on a thin liquid layer on the top of the substrate, conditions will be similar to crystal growth and Epitaxy film growth will be possible. It is therefore possible that using substrate melting as tool to promote epi-layer growth using plasma spraying. Difficulty is how to control the substrate temperature to cause substrate melting during droplet solidification. In this study we will propose a new idea for better temperature control on the substrate. The capability of epitaxy growth using thermal spraying will be investigated. Molybdenum droplets impact on an Aluminum substrate will be studied. A splat formation model including undercooling, nucleation, and non-equilibrium solidification will be used to study the possibility of the substrate melting and grain size distribution.

The objective of the present work is to produce Mg-PSZ (magnesia partially stabilized zirconia) powders that were used to coat oxygen sensor tubes by plasma spraying. It is well known fact that zirconia based oxide thin films are the most widely used material as ionic conductors of oxygen. In this study, MgO stabilized ZrO 2 powders were produced by the sintering and crushing method. Starting powders were a high grade ZrO 2 , and a natural hydromagnesite (Mg-HC) as MgO source. ZrO 2 , and MgO were mixed in the compositions of ZrO 2 - 9mol % MgO. The mixtures were ball milled by using ZrO 2 balls. The fine powders were stabilized via thermal treatment in air at 1540°C for 24 hours. The powders were calibrated to the correct particle size distribution for plasma spraying. All powder samples were characterised by a well-defined techniques with an exhibited an average particle size of 10 µm. The powders consisted of monoclinic, tetragonal and cubic phases. They were sprayed by plasma spray to produce high temperature Mg-PSZ coatings on oxygen sensor tubes. It is worthwhile to point out that high temperatures were generated in the plasma spray jet, and the rapid quenching of the molten Mg-PSZ droplets deposited on the cold substrate subsequently occurred. After this process, thermal treatments were carried out to improve the film density and microstructural stability.

The crushed and rounded ferroboron (FeB) powders of Fe-18.8B-0.2C-0.5Si-0.8Al (wt %) were deposited onto an aluminum substrate by thermal spraying methods to improve its tribological properties. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties like graphite were incorporated to the iron boride powders as solid lubricant by sintering process and high energy ball milling technique which allows homogeneous distribution of solid lubricants in a hard metallic matrix to obtain protective coatings with low friction coefficient. As-sprayed coatings are composed of mainly h-BN and FeB, iron matrix supersaturated with boron owing to the rapid solidification of molten droplets flattened on a substrate. The friction and wear behaviors of each coating were evaluated using ring-on-disk type wear tester under paraffin base oil condition in air atmosphere. Preliminary results revealed that iron boride powder with h-BN powder (5 wt.%) is an applicable method to produce a protective composite coating against friction and wear.

In the thermal spraying technology a lot of things have been and still are happening in education and training of personnel and in quality management. The QM-system that was established by the GTS e.V.– the Association of Thermal Sprayers – was pioneer and does an excellent job concerning its requirements. These GTS QM-requirements are meanwhile completed by newly created and internationally accepted EWF-education and training guidelines of supervising personnel and thermal spray workers. These guidelines involve also the new ISO standards of the Thermal Spraying Coordinator and the Approval Testing of Thermal Sprayers. Meanwhile the ETS (European Thermal Sprayer) and the ETSS (European Thermal Spraying Specialist) education and training courses are very much in demand. For the QM-System the standard ISO 14922 Part 2-4 (Quality requirements of thermally sprayed structures) is established, which includes the standard ISO 14918 (Approval Testing of Thermal Sprayers). Here, different destructive testing procedures are required depending on the spray process, which provide useful statements concerning the quality of sprayed coatings. With the GTS-Certification, the EWF-Qualifications and the ISO Standards a System is installed, which meets the increased Demands of Trade and Industry for High Quality Sprayed Coatings.

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.

The adaptation of medium-entropy alloys (MEAs) by minor alloying constituents allows a targeted modification of the property profile of this material class for surface protection applications. In the present work, the potential of BSiC additions in the MEA system CrFeNi as base for adapted feedstock materials for thermal spraying is investigated. The alloy development was carried out in an electric arc furnace. Compared with the initial alloy, a significant increase in the wear resistance of the castings was demonstrated for the adapted alloy composition. Subsequently, powder was produced and characterized by inert gas atomization, followed by processing via high velocity oxy-fuel (HVOF) spraying. The tribological behavior was evaluated comparatively for all manufacturing variants considered. A good agreement in the property profile was determined, confirming the basic alloy development approach based on metallurgical processes. The evaluation of the process-structure property relationships confirms the great potential of adapted alloy systems for complex alloys in the field of surface engineering.

Stainless austenitic steels like the 316L (1.4404) are widely applied in various applications and were also used for surface protection using thermal spraying. The reason for this is the easy processability and the high corrosion resistance. Stainless austenitic steels typically contain the following alloying elements: The formation of an austenitic microstructure is achieved by nickel (Ni). The addition of chromium (Cr) lead to good corrosion resistance due to formation of an oxide layer. For resistance against pitting corrosion, molybdenum (Mo) can be added. Also, stainless austenites usually exhibit very low carbon and nitrogen contents to prevent chromium carbides and nitrides which reduces the corrosion resistance. However, both alloying elements cannot be classified as being detrimental in stainless austenites in general. In contrast high nitrogen contents can also be used to improve the chemical properties, especially the resistance against pitting corrosion. Finally, carbon and nitrogen lead to an increase in hardness of the thermal sprayed layer. Based on this knowledge, a high-strength austenite for thermal spraying was developed. The new high strength austenite was processed by HVAF spraying with different particle distributions and parameter variations. Resulting coatings were investigated regarding the microstructure, elemental composition, hardness and corrosion properties in comparison to the standard coating material 316L.

When compared with conventional thermal spraying processes, thermal spraying of suspensions allows to produce coatings with outstanding properties in terms of microstructure, surface topography, and phase compositions, as well as mechanical, electrical or tribological requirements. The use of suspensions as feedstock results in an almost unlimited flexibility in terms of chemical composition of the sprayed coatings. Moreover, thermal spraying of suspensions is a promising technique for processing expensive raw materials. Zn 2 TiO 4 coatings are only one example where the high costs of blended oxide powders as feedstock material hinders the market introduction, whereas outstanding electrical properties and photocatalytic activity of thermally sprayed Zn 2 TiO 4 coatings are of great interest for various industrial applications. In this work, single oxide ZnO and TiO 2 raw materials as well as a Zn 2 TiO 4 feedstock powder were used to develop tailored aqueous suspensions suitable for thermal spraying. To follow the formation of the compositions in the system ZnO-TiO 2 , differential thermal analysis (DTA) and thermal gravimetry (TG) measurements were performed. Preparation routes of stable suspensions with low sedimentation rates, low viscosity and good flowability are discussed. Exemplary microstructures and phase compositions of sprayed coatings are shown. In all sprayed coatings, the Zn 2 TiO 4 phase has been formed during Suspension High Velocity Oxygen Fuel Spraying (S-HVOF). This work demonstrates the potential to develop appropriate cost-efficient suspension feedstocks from single oxide raw materials to obtain Zn 2 TiO 4 coatings.

Machines and other equipment that are used in industry are generally long-term investments. Once invested, the machines usually run for several decades until a technical reinvestment is necessary. Nowadays, the 4th industrial revolution is taking place and digitalization is omnipresent. Big Data, Internet of Things (IoT) and Artificial Intelligence (AI) are just some of the technological innovations that are shaping the future right now. These innovations do not work with the manually driven equipment that has been invested some years ago because they are all based on data – and these (partly) manually operated equipment don´t produce data or they don´t collect it properly. In order to produce and collect data, the manually working machines have to be replaced – or retrofitted! voestalpine Stahl GmbH and its technical service and maintenance department (TSM, furthermore short voestalpine) decided to retrofit the existing equipment based on technological, economical as well as sustainability reasons. The approach, advantages and limitations are displayed here.

Abradable seal coatings are widely employed in the gas turbine of aero-engine, which not only strength enough to resist the impact of external particles and airflow, but also excellent wear resistance. In the current study, we concentrate on APS sprayed Aluminum Bronze Polyester abradable coating that can be used in turbo engines both for seals and clearance control. A composite thermal spray powder, substantially in the form of clad particles each of which has coarse polyester powders and sub-particles of Cu-Al alloy powders, was prepared using mechanically clad process. Abradable seal coating was prepared by atmospheric plasma spraying. The microstructure, hardness, bonding strength, thermal shock resistance and corrosion resistance of coatings were researched. Properties of the coating were able to meet the application requirements. The coating microstructures and phase compositions were evaluated via SEM. The corrosion mechanisms of the coating were compared by analyzing the cross-sectional and top surface microstructures of the as-sprayed and eroded coatings.

Because of their characteristic spray geometry, pressure-gas-atomizers can be used to create thick coatings from molten metal. Production rates of pressure-gas-atomizers are substantially higher compared to conventional Thermal Spraying (100 – 200 kg/h based on molten tin). The shape of the spray cone can be designed by the geometry of the atomizer. The mean particle sizes and velocities (molten tin and tin-copper alloys) are controlled by the gas flow. Powder products and coatings of several millimeters on steel substrates were investigated. The average density of the layer was higher than 99%.

Long-term experience in handling and using individual thermal spray processes has led to the development of gas supply systems which guarantee a smooth operation at the highest level. Concrete examples will help to demonstrate the benefits and advantages such systems can offer the thermal spray user.