Papers by Keyword: Plasma Spraying

Abstract: Abradable coatings are used in modern gas turbine engines to minimise clearances and reduce gas leakage through the blade tips. The development of wear-resistant coatings for turbine casings is challenging due to the high-temperature operating conditions and aggressive fuel combustion products. The balance between erosion and abrasion resistance of coatings necessitates the search for new optimal solutions. This article discusses the properties of two new abradable coatings based on composite powders. The composite powders were synthesised by mechanochemical alloying of aluminium, silicon (8%) and boron nitride (20%). The main component were industrial aluminium powders of two types, obtained by spraying primary aluminium melt, with a rounded and elongated shape, which affected the porosity of the sprayed coatings, which was 2.8% and 9.5%, respectively. The prepared powder was coated by Atmospheric Plasma Spraying (APS) with generating a laminar plasma jet. As a result, abradable coatings with the required set of performance properties were obtained. Emphasis is placed to the structure, chemical composition, and microhardness of coatings made of round and elongated powders. The resulting coatings can be recommended for use as abradable coatings. Among the considered coatings, elongated powder coatings have higher hardness and potentially higher abrasive and erosion resistance for high-temperature turbines.

Abstract: The paper presents a new concept of a thermally sprayed composite coating obtained by mixing NiCrAl powder with chromium carbide Cr₃C₂ in an amount of approximately 30 wt.%. The aim of the research was to obtain a material combining the advantages of a metallic matrix and a ceramic phase, with increased resistance to wear and erosion. The plasma spraying (APS) process was carried out on a carbon steel substrate with variable technological parameters: arc current intensity (300/500/700 A) and hydrogen flow (4/8/12 NLPM), while maintaining the other conditions constant.The thickness, porosity, microstructure, chemical composition (using the EDS method), hardness, erosion resistance, and tribological wear of the coatings were evaluated. The results showed that the greatest thickness (approx. 150 µm) and lowest porosity (below 3 vol. %) were obtained at the maximum process parameters – 700 A and 12 NLPM. In turn, the thinnest and most irregular coating (approx. 70 µm) was obtained at the lowest hydrogen flow (4 NLPM), which was due to insufficient melting of the powder particles.Increasing the current intensity and hydrogen flow had a beneficial effect on all analyzed coating properties – especially hardness (up to 273.7 HV0.2), erosion resistance (the smallest mass loss of 0.007 g), and tribological wear resistance (the smallest volume loss of 2.925 mm³). A decrease in any of the parameters resulted in a deterioration of the layer properties. The optimal mechanical and structural properties of the NiCrAl + Cr₃C₂ composite coating were achieved at the maximum plasma spraying parameters: a power current of 700 A and a hydrogen flow rate of 12 NLPM.

Abstract: In this paper, the surface modification for Al alloy cylinder block (AACB) was investigated in order to improve the surface properties of AACB inner wall. It is found that the laser roughing process can increase the contact area, thereby modifying the morphology of the interface between layer and matrix and improving obviously the bonding force. The properties, including strength, hardness, heat resistance and wear resistance, were improved mainly due to the Fe-based powder plasma spraying process. Owing to the combination of laser roughing and plasma spraying, low porosity of the layer was obtained, enabling the surface to hold a certain amount of lubricating oil, leading to the improvement in engine performance. Via the analysis of microstructure, hardness, mechanical properties and machining dimension, it is suggested that the combination of laser roughing and plasma spraying can act as a feasible way to tailor the properties of surface layer and provide great potential to improve the practical applications of AACB in the field of automotive industry.

Abstract: The influence of various design and technological parameters of the process of plasma deposition of coatings on their quality is considered. In the process of research, regularities were revealed and relationships were established between the factors and criteria of technological processes, which make it possible to solve optimization problems when developing technological recommendations and improving the methods of applying plasma coatings. The results of the research are the obtained mathematical models that can be applied to analyze the influence of individual factors, as well as their combination on the quality indicators of the process of forming coatings with given physical and mechanical properties.

Abstract: The paper presents the results of studies of the plasma spraying modes effect on the level of residual stresses in coatings. The analysis of experimental data has shown that the sign of residual stresses is not changed in the spraying process. The magnitude of the tensile stresses mainly depends on the temperature of samples heating, the biggest influence being that of plasma torch current arc. An increase in the current leads to an increase in the substrate temperature, which is explained by the increase in the thermal power of the plasma jet. An increase in the flow rate of the plasma-forming gas leads to a decrease in the temperature of the samples, since the heat content of the plasma decreases. An increase in the spraying distance has a similar effect, and its increase leads to a decrease in the substrate temperature. We obtained the functional dependence of the residual stress level on the plasma spraying modes.

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: A Ni60/Ni-WC composite coating was fabricated by the plasma spraying technology and microstructure of the coating was analyzed. Moreover, erosion resistance of the coating under different erosion angles was tested. Results demonstrated that the coating has lamellar structures and contain some pores. WC particles distribute evenly in the coating and bond well with the parent phase. When the erosion angle increase, the weight loss of the erosion-induced coating increases firstly and then decreases, showing plastic-brittle composite erosion characteristics.

Abstract: Thermal barrier coatings are widely used for protection of gas turbine parts against high temperature oxidation and hot corrosion. In present work the microstructural assessment of TBCs produced by atmospheric plasma spray (APS) method was conducted. Three types of ceramic powders were used: magnesia- stabilized zirconia oxide (Metco 210), yttria stabilized zirconia oxide (YSZ -Metco 204) and fine-grained YSZ – Metco 6700. As a base material the Inconel 713 was used as well and CoNiCrAlY was plasma sprayed (APS) as a bond coat. The thickness of all ceramic layers was in range 80 – 110 μm. The elemental mapping of cross-section of magnesia-stabilized zirconia showed the presence of Mg, Zr and O in outer layer. In the YSZ ceramic layer the Y, Zr and O were observed during elemental mapping. The isothermal oxidation test was conducted at 1100 °C for 500 h in static laboratory air. On all samples the delamination and spallation of ceramic layers was observed. Chemical composition analysis of coatings showed the presence of two areas: the first one contained elements from bond coats: Ni, Cr, Al, Co and second area contained O, Cr Co and O that suggest the scale formation. The obtained results showed the total degradation of all ceramic layers as a result of internal stresses in bond-coat. Microscopic analysis showed the areas with complete degradation of bond coats and formation of thick oxides layer.

Abstract: Composite mold samples used in squeeze casting was fabricated by plasma spraying with 5CrMnMo and 3YSZ, which was shown high bonding strength and good thermal shock resistance. The best parameters with transition coat were explored by mechanical analyses. As results, the transition layer structure made of 75 percent NiCoCrAlY powders showed bonding strength was higher to 34.35MPa and that thermal cycles were up to 46.8 times. The effect of the transition layer was analyzed by microstructures and the failure mechanism of the coating material with a transition layer was discussed. The conclusion was that the physical mismatch and thermodynamic mismatch between the matrix and ceramic layers were the main cause of the failure.

Abstract: The article is devoted to the analysis of the internal structure and properties of a copper-graphite coating applied to a copper electrode. The article provides a calculation of the transient contact resistance of electrodes with a coating obtained using plasma spraying technology. Copper-graphite powder with high arc resistance was used as a spraying substance. Coated electrodes were tested for erosion resistance by an arc at currents of several kiloamperes. The aim of the work is to determine the effect of the composition and internal structure of the coating on the transient processes in the contact gap.