Papers by Keyword: Thermal Spraying

Abstract: This study investigates the indentation fracture toughness (IFT) of six HVOF-applied cermet coatings. The materials tested were WC-42CrC-16Ni and Cr₃C₂-37WC-18NiCoCr. For each material, three coatings were produced using varying deposition parameters. IFT was measured under a 100 N load, and the K_iC values were calculated using the method proposed by Chicot. For the Cr₃C₂-37WC-18M coating, the K_iC value increased with higher oxygen and kerosene flow rates. Conversely, for the WC-42CrC-16Ni coating, higher K_iC values were observed at lower oxygen and kerosene flow rates.

Abstract: This paper focuses on the deposition and characterization of tungsten carbide (WC) hard thin films using the plasma jet deposition technique, with special emphasis on their hydroabrasive wear behavior. Tungsten carbide coatings are recognized for their exceptional properties such as high hardness, excellent wear and corrosion resistance, and chemical and thermal stability. The plasma jet deposition technology allows the formation of dense layers, well adhered to the substrate, with precise control over the thickness and microstructure of the deposited layer. The study analyzed process parameters, such as spray distance and particle velocity, which influence the microstructure and performance of the deposited layers. The characterization of the layers was carried out by methods such as scanning electron microscopy (SEM) and the composition was determined with the help of the EDX probe. The tribological properties of the WC layer were also investigated.

Abstract: The present research aimed to evaluate the effect of nickel-based electrochemical metallization (EMNi) on the quality and performance of electric motor components, compared to high-velocity oxy-fuel (HVOF) thermal spray coating, the most widely used coating in the mining industry. The experiment was conducted using motor components comprised of 4340 VCN steel, 4140 VCL steel, 1045 steel, and stainless steel, which underwent both treatments. The surface temperature of the components was monitored during the processing stage, followed by evaluations of their Rockwell hardness (HRC) and surface characteristics (taper, ovality, parallelism, finish, wear) at the onset (day 0) and after 2 years of use the results indicate that EMNi delivers electric motor components with superior finishes and extended warranty and service life in comparison to HVOF.

Abstract: Various industrial parts and equipment made of steel need to withstand demanding conditions. In order to increase performance and lifetime, surface processing and functional coatings can be applied. In this study we report on the evaluation of coated carbon steel with commercial corrosion-resistant powders Diamalloy 4276 and Woka 7502 by Oerlikon Metco, using thermal spraying. Further functionalization is performed by rendering thermal sprayed surfaces syperhydrophobic via gas phase deposition of trichloro-1H,1H,2H,2H-perfluorooctyl silane, (PFOTS). Electrochemical impedance spectroscopy, contact angle and water condensation studies reveal the protective properties of coatings prepared by both materials as well as the superiority of Diamalloy 4276 based coatings. Corrosion was evaluated under a harsh 20% w/w H₂SO₄ environment. Rendering the coating superhydrophobic improves water condensation under the tested conditions of high (80%) relative humidity.

Abstract: Coatings obtained by spraying materials with a high-temperature gas jet onto a substrate followed by thermal treatment of the deposited materials (thermal gas coatings) are increasingly being used. The practical experience of using thermal spray coatings, accumulated over the past 20–30 years in industries, shows that in this way it is possible, as a rule, to reduce the wear of machine parts operating under various conditions by a factor of 2–5. The effectiveness of the technology has also been proven in the protection of products from corrosion and thermal damage. The efficiency of the applied materials is determined by their structure, which largely depends on the choice of the composition of the material, the method, and modes of application. A comprehensive solution to these issues with the study of the mechanism of the processes of formation of thermal gas coatings will create a scientific basis for the technology for its successful implementation in production. At the same time, the importance of studying the processes and optimizing the technological parameters of spraying and subsequent coating treatment increases. Optimization is carried out, as a rule, according to the results of experiments. Let us consider the study on the example of the development of wear-resistant composite coatings with solid lubricant inclusions with the substantiation of the technique and criteria for optimizing technological parameters taking into account the most important properties of sprayed protective coatings.

Abstract: The subject of this work is to evaluate the influence and adhesion degree of different coating layers deposited on a ductile cast iron substrate by two different methods, thermal spraying and welding with and without use of an interlayer. Microstructures of different zones and interfaces of coated specimens are investigated using optical microscope and scanning electron microscope SEM. Also, the mechanical behavior was evaluated by tensile test. It is found that when stainless steel thermal spraying coating onto the ductile cast iron substrate, the use of the nickel-based interlayer Ni allowed us to mitigate the disadvantages of cracking at the interface. This is due to the mechanical effect of nickel plasticity. In the case of coating by welding, the use of nickel-based buttering ENi-CI allowed us to reduce the diffusion of graphite to stainless steel, resulting in a reduction in the formation of harder alloy carbides. Finally, the mechanicals tests in particular the tensile test shows that the coating by welding is effective but causes a structural hardening; on the other hand the coating realized by thermal spraying does not really present sufficient adhesion.

Abstract: The most popular spraying technologies include: flame spraying, arc spraying and plasma spraying. Spraying technologies allow for the formation of coatings with a desired chemical composition and thickness. However, such coatings characterize by numerous imperfections associated with the nature of the process itself. It is obvious that some of imperfections in thermal spraying coatings can be eliminated by choosing the right parameters of the process. However, in order to improve the properties and eliminate material discontinuous, it is necessary to conduct the remelting process. Research in most cases, showed that the reduction of porosity and simultaneous increase in hardness are possible only by remelting the coating using different heat sources. By adjusting the technological parameters and remelting speed, it is possible to precisely control the depth of the remelted material and thus the properties of final coatings. The paper presents the remelting processes of thermal spraying coatings in relation to technologies, properties and applications.

Abstract: Thermal spraying is one of the most promising methods for obtaining thermal barrier coatings for aerospace applications. Providing the necessary set of coating properties and their stable reproducibility are an actual task of the modern production. The purpose of this work was to determine the influence of the initial powders fractional composition on the structure and properties of the protective coating. The microstructure and the elemental composition features of the heat-resistant and ceramic layers of the thermal barrier coating are investigated. It is shown that the microstructure, porosity and microhardness of the coating ceramic layer depend on the ZrO₂+8%Y₂O₃ initial powder fractional composition. The porosity of the coating and the average pore size increase with increasing particle size of the powder. The maximum value of the ceramic layer microhardness is observed when using a powder fraction of 40-80 μm. The studies have found that microstructure and the necessary combination of coating physical and mechanical properties are achieved during the deposition of zirconia powder fractions 40-80 microns.

Abstract: This paper discusses the mathematical model of powder material particles heating in the gas flow when applying plasma gas and thermal coatings. It has been assumed that while moving in the plasma, the particle is heated by convective heat transfer and radiative heat transfer. To ensure accuracy and validity of calculation, two characteristic regions have been outlined: Core, where the temperature, density, and viscosity of plasma, as well as the other parameters are assumed as constant; and the region from the core to the coated surface (substrate), where these parameters are the functions of the plasma flow coordinates. One of the assumptions is that the shape of the particles is near-spherical, and the thermal flow’s action to the particles’ surface is uniform. Special attention has been paid to correct selection of criteria , which allowed to simplify the solution and reduce it to the ordinary first-order differential equation derived from the particle heat balance equation.

Abstract: In solid oxide fuel cells (SOFC) for operating temperatures of 800 °C or below, the use of ferritic stainless steel can lead to degradation in cell performance due to chromium migration into the cells at the cathode side [1]. Application of a coating on the ferritic stainless steel interconnect is one option to prevent Cr outward migration through the coating. MnCo_1.9Fe_0.1O₄ (in the following designated as MCF) spinels act as a diffusion barrier and retain high conductivity during operation [2]. Knowledge about the residual stress depth distribution throughout the complete APS coating system is important and can help to optimize the coating process. This implicitly requires reliable residual stress analysis in the coating, the interface region and in the substrate.For residual stress analysis on these specific layered systems diffraction based analysis methods (XRD) using laboratory X-ray sources can only by applied at the very surface. For larger depths sublayer removal is necessary to gain reliable residual stress data. The established method for sublayer removal is electrochemical etching, which fails, since the spinel layer is inert. However, a mechanical layer removal will affect the local residual stress distribution.As an alternative, mechanical residual stress analyses techniques can be applied. Recently, we established an approach to analyse residual stress depth distributions in thick film systems by means of the incremental hole drilling method [5, 6]. In this project, we refined our approach for the application on MCF coatings with a layer thickness between 60 – 125 μm.