Plasma Spraying Method Research Articles

Microstructure and properties of Ni-Al coatings obtained by conventional and high-velocity atmospheric plasma spraying

In this paper, we report on the microstructure and properties study of the Ni-Al system (75/25 at. %) coatings obtained by atmospheric plasma spraying (APS) and high-velocity plasma spraying (HV-APS) methods which differ in the speed of the sprayed particles. The structure and phase composition were investigated using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray phase analysis (XRD). The paper presents the measurements results of porosity and microhardness, as well as the resistance of coatings to high-temperature oxidation. Additionally, we propose a phase transformations model that explains the difference in structure formation. For HV-APS and APS coatings, the difference in structure is shown to be due to different residence conditions of the sprayed particles in the plasma jet. Particles in the HV-APS coatings were completely melted, while a significant proportion of unmelted particles was observed in the APS coatings. HV-APS coatings have better high-temperature oxidation resistance compared to APS coatings, which is explained by a decrease in their porosity to ∼2 %.

Дослідження механічних властивостей і зносостійкості плазмових покриттів на основі інтерметаліду Fe-Al

Studies of the mechanical characteristics and abrasive resistance of FeAl-based plasma sprayed coatings are presented. Coatings were obtained by plasma spraying method using iron aluminide powders of Fe3Al, Fe-AlMg and Fe-TiAl systems. The powders were prepared by mechanochemical synthesis. The mechanical characteristics (hardness and elastic modulus) of the coatings were determined by microindentation method. It has been found that the hardness of the coatings is in the range of 2.9…5.4 GPa, the elastic modulus is in the range of 80…100 GPa. It is shown that the gas-abrasive resistance of all tested coatings at room temperature exceeds the wear resistance of St3 steel 1.4…4.3 times; when dry abrasive/rubber wheel testing the resistance of the coatings exceeds the resistance of St3 2.1…3.8 times. The resistance of Fe3Al, Fe-AlMg and Fe-TiAl coatings is higher 2.2…3.1 times than resistance of St3 steel under conditions of gas-abrasive wear at a temperature of 550 °C; the resistance of Fe3Al and Fe-TiAl coatings under the same conditions exceeds the resistance of heat-resistant steels 1.2…1.5 times. In all cases Fe3Al coating has the highest wear resistance because of low porosity and low content of brittle phases in the coating. An assessment of the relationship between the mechanical properties of coatings and wear resistance showed that the wear resistance of coatings increases with an increasing of their elastic modulus. Based on the results of studies the possibility of using FeAl-based coatings for the protection and hardening of parts and constructions operating under conditions of abrasive wear at temperatures range from 20 to 550 °C is shown.

Effect of microstructure on thermal cycle fatigue resistance in a SPS-TBC

The turbine blades of gas turbine engines used in thermal power plants are coated with a thermal barrier coating (TBC) made of ceramics to provide heat resistance. In recent years, gas turbines for power generation have been utilized as a regulating power source for engines, which are subject to frequent start-up and shutdown and output fluctuations. In this context, the suspension plasma spraying (SPS) method, which has been developed recently, has been studied intensively because it has a porous columnar structure and superior thermal cycle properties compared with the conventional atmospheric plasma spraying method. In this study, we evaluated the thermal cycle properties of TBCs with different microstructures prepared by varying the deposition conditions of the SPS method, and investigated the effect of microstructures on the thermal cycle properties. The experimental results indicated that the thermal cycle fatigue life of SPS-TBC increased with decreasing column diameter. The effect of microstructure on the thermal cycle fatigue life was discussed based on the thermal stress in top-coating evaluated by the FE analysis.

Biodegradable polymer properties through ceramic coatings

Coating of bio-based polymers with ceramic layer has attracted interest recently, the research topic raising difficulties regarding the technology of obtaining layers that involve very high working temperatures. The study aims to analyses the mechanical, tribological and structural characteristics of the Arboblend V2 Nature biodegradable polymer after the deposition of ceramic microlayers. The micro powders used were Amdry 6420 (Cr2O3), Metco 143 (ZrO2 18TiO2 10Y2O3) and Metco 136F (Cr2O3-xSiO2-yTiO2). The coated samples were obtained by injection molding and the deposition was achieved by using Atmospheric Plasma Spray (APS) method. The results of the related analyses showed that, in general, the deposits of ceramic micro particles increased the material surface characteristics (hardness, scratch resistance, apparent friction coefficient), due to the uniformity of the ceramic coating on the polymeric substrate. Based on these, it was possible to recommend the use of coated bio-based polymer - Arboblend V2 Nature in harsh operating conditions, such as the automotive industry.

Металлографическая экспертиза как обратная связь между качеством и производством продукции

Despite the increasing automation of the process of designing and manufacturing metal products, their failure remains a common phenomenon. The metallographic examination is appointed, which can only be carried out at a proper level by the specialized accredited organizations to identify the causes of such incidents. A metallographic examination is a tool that acts as feedback between the output quality of products and the entire chain of numerous operations during production. The purpose of this work is, using a practical example, to demonstrate the possibility and special significance of the conclusions of the metallographic examination for the development of the product manufacturing technology. Using the high-speed plasma spraying method, the authors applied the NiCrBSi coating to the surface of the locomotive wheel pair axle to increase its wear resistance. The life bench tests of the axle revealed the main fatigue crack, the tests were stopped, and the axle was artificially broken completely. The analysis of metal quality, including chemical composition, mechanical properties (strength, ductility, and impact hardness), microstructure, metal purity according to the non-metallic inclusions, and parameters of a surface layer hardened by rolling, showed its full compliance with the regulatory documentation. The thickness and hardness parameters of the NiCrBSi coating also corresponded to the declared ones. According to the fractographic analysis, the fatigue fracture was initiated at multiple points, which was a characteristic sign of a common objective reason for the insufficient strength of a product not associated with some random factor. The metallographic examination identified that the main reason for the failure of a wheelset axle is the coating's insufficient fatigue strength. The numerous fatigue microcracks that originated in the coating grew into the base metal and led to the fatigue macrocracks formation at different height levels. The merging of these cracks led to widespread fatigue fracture surface formation.

The investigation of coated layers on the surface of ferritic stainless steel by using atmospheric plasma spray method

The investigation of coated layers on the surface of ferritic stainless steel by using atmospheric plasma spray method

Comprehensive study on corrosion protection properties of Al2O3, Cr2O3 and Al2O3–Cr2O3 ceramic coatings deposited by plasma spraying on carbon steel

In this study, individual Al 2 O 3 and Cr 2 O 3 coatings and Cr 2 O 3 -25, 50, 75 wt% Al 2 O 3 composite coatings were applied on carbon steel by atmospheric plasma spraying method. Corrosion experiments were performed on as-sprayed and epoxy resin sealed coatings including potentiodynamic polarization, electrochemical impedance spectroscopy and long-term immersion in 3.5 wt% NaCl solution. Phase composition and microstructure of the coatings were investigated by x-ray diffraction, optical microscopy and scanning electron microscopy, before and after the corrosion experiment. The results showed that the Cr 2 O 3 coating exhibited the best corrosion resistance, due to the densest microstructure and highest adhesion strength. The Cr 2 O 3 -25 wt% Al 2 O 3 coating had the highest interconnected porosities and thus had the least corrosion resistance compared to other coatings. In general, the as-sprayed coatings induced a maximum increase of 3.93 times the polarization resistance (R p ) in the polarization experiment and a 3.5 times increase in the charge transfer resistance (R ct ) in the EIS experiment, which was not significant. Stresses caused by increased volume of corrosion products in the coating-substrate interface resulted in the spallation of Cr 2 O 3 -25, 50 wt% Al 2 O 3 coatings from the substrate over long-term of immersion. The adhesion strength of the coatings was a determining criterion for the long-term durability of the coatings. The sealing treatment resulted in a significant increase in R p and R ct .

Production of Re doped La2Zr2O7 based TBCs and numerical analysis of their use on IC engine piston surface

In this study, first of all, a metallic bond layer was coated on the metal substrate using the HVOF method. Then, Gd and Yb doped La2Zr2O7 powders, which were specially produced to obtain a low thermal conductivity value, were coated on the metallic bond layer by atmospheric plasma spraying method. The coatings were produced in single-layer and double-layer designs using YSZ as the buffer layer. In the microstructure analysis, it was observed that the coatings exhibited the characteristic microstructure properties of the materials produced by atmospheric plasma spraying method. In the phase analysis, it was found that the Gd and Yb doped La2Zr2O7 was in the form of defect fluorite type structure after plasma spraying. The thermal conductivity of the YSZ coating ranged from 0.88 to 1.00 W/mK, while the thermal conductivity of the doped La2Zr2O7 coatings was measured between 0.38 and 0.68 W/mK. Especially, the lowest thermal conductivity values were obtained in the double-layer Gd doped coating. As a result of modeling these coatings on the piston surface of a diesel engine using the finite element method, it was found that the maximum and minimum surface temperatures of the pistons increased by 69% and 60%, respectively. There was also a reduction of up to 6.5% in the temperature of the piston substrate surface.

The effect of the SiC content on the high duration erosion behavior of SiC/ZrB2– SiC/ZrB2 functionally gradient coating produced by shielding shrouded plasma spray method

In this research, the effect of the ZrB 2 middle layer and SiC Weight percentage on the erosion behavior of SiC/ZrB 2 – SiC/ZrB 2 functionally gradient coating were investigated. For this purpose, SiC gradient coating was prepared via the reactive melt infiltration method (RMI). Afterwards ZrB 2 –SiC layers containing 10, 20 and 30 wt% SiC and, ZrB 2 as the outer layer were applied on SiC coated graphite via solid shielding shrouded plasma spraying (SSPS). To investigate the erosion resistance of the coating, the specimens were subjected to oxy-acetylene and propane flame. The results showed that by applying the ZrB 2 –SiC layer between SiC and ZrB 2 coating, due to the gradual change of the coefficient of thermal expansion mismatch and reduction of thermal stresses, erosion resistance improves, so that the coating with 20 wt% SiC with mass and linear erosion rate, −0.072 × 10 −4 g.cm −2 .s −1 , 0.0166 μm s −1 respectively had the best erosion resistance under oxy propane flame. In the oxyacetylene flame test, a similar result was obtained to the oxy propane test and the SiC/ZrB 2 -20% wt. SiC/ZrB 2 coating had the lowest erosion rate.

Effect of graphite addition on tribological behaviour of plasma sprayed Cr2O3-TiO2 coating

In this investigation, Cr2O3-TiO2 + Ni Graphite ceramic coating was deposited using plasma spray method. Abrasive wear tests were conducted for determining the tribological behavior of coating. Wear and friction tests were performed at different loads and at a fixed sliding velocity. Structural and mechanical characterization of as deposited and worn out coatings was done. X-Ray Photoelectron Spectroscopy (XPS) was also used to confirm the formation of various oxides. Results showed that there is 18–44% reduction in friction coefficients and 1.3–2 times reduction in wear rates by the graphite addition in Cr2O3-TiO2 coating. Improvement in fracture toughness was also obtained which led to the better wear resistance of Cr2O3-TiO2-Ni Graphite coating. Consequences of tribo film formation and responsible wear mechanisms are also pointed out. Results of the present study can lead the way to study the effects of heat treatment and coating thickness on tribological behavior of the coating.

Assessment of tribotechnical properties and resistance to wear of plasma coatings

In order to determine the operating conditions of parts for which restoration of worn surfaces is acceptable by the method of plasma spraying of various powder alloys, contact fatigue tests were carried out under cyclic contact impulse loading. In addition, tribotechnical tests were carried out with various wear-resistant coatings under conditions of liquid sliding friction.
 Bench and operational tests showed the use of coatings obtained using modern plasma technologies, the feasibility of protecting parts operating in conditions of corrosion, waterjet and cavitation wear, as well as in sliding friction.
 The coating sprayed with Ni-Al intermetallic alloy powder provides the most reliable protection against shock cyclic impact and abrasion during liquid friction than other materials studied.
 Coating with wear-resistant self-fluxing powder Ni-Cr-B-Si-C alloy, hardened by solid carboboride phases, without its additional heat treatment for restoration of surfaces working in sliding friction pairs, is not recommended.

Enhanced model protein adsorption of nanoparticulate hydroxyapatite thin films on silk sericin and fibroin surfaces

Hydroxyapatite coated metallic implants favorably combine the required biocompatibility with the mechanical properties. As an alternative to the industrial coating method of plasma spraying with inherently potential deleterious effects, sol-gel methods have attracted much attention. In this study, the effects of intermediate silk fibroin and silk sericin layers on the protein adsorption capacity of hydroxyapatite films formed by a particulate sol-gel method were determined experimentally. The preparation of the layered silk protein/hydroxyapatite structures on glass substrates, and the effects of the underlying silk proteins on the topography of the hydroxyapatite coatings were described. The topography of the hydroxyapatite layer fabricated on the silk sericin was such that the hydroxyapatite particles were oriented forming an oriented crystalline surface. The model protein (bovine serum albumin) adsorption increased to 2.62 µg/cm2 on the latter surface as compared to 1.37 µg/cm2 of hydroxyapatite on glass without an intermediate silk sericin layer.The BSA adsorption on glass (blank), glass/c-HAp, glass/m-HAp, glass/sericin/c-HAp, and glass/sericin/m-HAp substrates, reported as decrease in BSA concentration versus contact time.

Phase transformation mechanism of the APS yttria partially stabilized hafnia coating undergoing thermal exposure

8 mol.% Y2O3 partially stabilized HfO2 (YSH8) free-standing coating was prepared by air plasma spraying (APS) method, and the crystal structure and phase transformation under 1300 °C were studied using Rietveld method of XRD, SEM and TEM. Results show that the as-sprayed YSH8 coating is mainly composed of tetragonal structure (T phase). The phase transformation of YSH8 coating is controlled by the diffusion of Y element. As the thermal exposure time prolongs, the weight fraction of monoclinic phase (M phase) quickly increases and reaches 68.1 % after 24 h. The Y content at the interface between the M phase and the original microstructure increases to 9 %–17 % after 24 h, and is in cubic phase. After exposure for 24, the T phase completely transforms to C + M phase.

An experimental study on emission of a diesel engine fuelled with SME (safflower methyl ester) and diesel fuel

In this study, safflower methyl ester (SME), which is an alternative fuel, was obtained from safflower seed oil (SO) for a CI engine by using transesterification method. The use of the produced fuel in an air-cooled single-cylinder diesel engine was investigated. The obtained SME was blended with diesel fuel at the rate of 20% and 50% (vol.) and also 100% SME was used. BSFC, NOX, CO, smoke density, HC, EGT, BTE, vibration and thermal image analyses were made in the test engines. In the first stage, diesel and SME fuel mixtures were used in the test engine volumetrically. In the second stage, the experiments were repeated by coating the combustion chamber elements of the same engine with chromium oxide by plasma spray method. It was determined that BSFC, CO, smoke and HC decreased but NOX, BTE, EGT and vibration increased in all test fuels in the coated engine compared to the standard engine. CO, HC, and smoke emission values of SME and its mixtures decreased except for BTE, BSFC, and NOX compared to diesel fuel. Safflower seeds can be grown easily in many parts of the world and can be considered as an alternative fuel for diesel engines.

Plasma sprayed thermal barrier coatings: Effects of polyamide additive on injection molding part quality

AbstractA simple and economic atmospheric plasma spraying method for thermal barrier coatings (TBCs) preparation on the mold cavity was developed to improve the injection parts properties. 7 wt% yttria stabilized zirconia was used as spray material with polyamide 11 (PA 11) as pore‐forming agents to improve the coating properties. The effect of PA 11 powder contents on the microstructure, thermal conductivity, bonding strength and hardness of TBCs were studied. The results show that the thermal conductivity of TBCs decreased with the addition of PA 11, and the bonding strength reached maximum of 21.38 MPa with 10% PA 11 addition. Further studies confirm that TBCs were able to maintain a high and stable temperature in the mold cavity due to its low thermal conductivity, validated by the elimination of the welding line. With TBCs, the average tensile strength and elongation at yield of the injection parts increased by 25.6% and 128%, respectively.

Mitigation of chloride driven stress corrosion cracking susceptibility of 316L austenitic stainless steel using plasma sprayed TiO2 coating

AbstractThe present study proposes a protective TiO2 coating against chloride driven stress corrosion cracking problem of 316L austenitic stainless steel. To test the performance of the proposed coating, the severe chloride‐based boiling magnesium chloride solution at 155 °C was chosen. For experimentation, the constant strain‐based U‐bend specimens were coated with TiO2 using atmospheric plasma spray method. The results indicated higher resistance by TiO2 coated specimens against stress corrosion cracking problem, while the bare specimens experienced severe damage in the boiling magnesium chloride solution under various strain loading configurations. The coating‐electrolyte system of TiO2 coated sample demonstrated over seven times higher resistance, eventually led to reduction in corrosion rate over fifteen times compared to the bare 316L stainless steel in the boiling magnesium chloride solution. This improved performance of the coated 316L stainless steel is attributed to inhibition of outward diffusion of iron‐chromium‐nickel in the corrosive environment and the high chemical stability of TiO2.

Improvements of Arboblend V2 Nature Characteristics through Depositing Thin Ceramic Layers.

The paper aims to investigate the behavior of Arboblend V2 Nature biopolymer samples covered with three ceramic powders, Amdry 6420 (Cr2O3), Metco 143 (ZrO2 18TiO2 10Y2O3) and Metco 136F (Cr2O3-xSiO2-yTiO2). The coated samples were obtained by injection molding, and the micropowder deposition was achieved by using the Atmospheric Plasma Spray (APS) method, with varied thickness layers. The present study will only describe the results for nine-layer deposition because, as the number of layers’ increases, the surface quality and mechanical/thermal characteristics such as wear, hardness and thermal resistance are also increased. The followed determinations were conducted: the adhesion strength, hardness on a microscopic scale by micro-indentation, thermal analysis and structural and morphological analysis. The structural analysis has highlighted a uniform deposition for the ZrO2 18TiO2 10Y2O3 layer, but for the layers that contained Cr2O3 ceramic microparticles, the deposition was not completely uniform. The thermal analysis revealed structural stability up to a temperature of 230 °C, the major degradation of the biopolymer matrix taking place at a temperature around 344 °C. The samples’ crystalline structure as well as the presence of the Cr2O3 compound significantly influenced the micro-indentation and scratch analysis responses. The novelty of this study is given by itself the coating of the Arboblend V2 Nature biopolymer (as base material), with ceramic microparticles as the micropowder coating material. Following the undertaken study, the increase in the mechanical, tribological and thermal characteristics of the samples recommend all three coated biopolymer samples as suitable for operating in harsh conditions, such as the automotive industry, in order to replace plastic materials.

Retraction Note to: Ablation Behavior of SiC/ZrB2 Multilayer Coating Prepared by Plasma Spray Method

Retraction Note to: Ablation Behavior of SiC/ZrB2 Multilayer Coating Prepared by Plasma Spray Method

Water pump shaft resource recovery technology

The article describes the technology of restoration of seats for bearings by plasma spraying based on the analysis of defects of the shaft of a centrifugal pump used in water industry. Based on the analysis of the wear of the shaft surfaces and the technological processes of restoration of the pump shafts, the method of plasma spraying of metal is selected. To achieve high adhesion, a multivariate experiment was conducted. The regression equation is described that describes the changes in the strength of the sprayed layer from the technological processing conditions. Recommended installation and technological conditions provide strength during plasma spraying.

High-Temperature Dielectric and Microwave Absorption Property of Atmospheric Plasma Sprayed Al2O3-MoSi2-Cu Composite Coating

Al2O3-MoSi2 coating has excellent high-temperature stability. On this basis, Al2O3-MoSi2-Cu composite high-temperature absorbing coating was prepared by atmospheric plasma spraying method. The phase transition characteristics of Al2O3-MoSi2-Cu spraying feedstock under high temperatures were analyzed by thermogravimetric test, the phase analysis of coating was performed by an in situ XRD test at different temperatures, and the microstructure of the coating was characterized by SEM. The test results of high-temperature microwave absorption performance show that, in high-temperature air atmosphere, the Cu in the coating is gradually transformed into Cu2O by oxygen atom diffusion, and the microwave absorption performance of the coating gradually increases with the increase in temperature. The 1.7 mm-thick coating at 500 °C has the best absorbing performance with a reflection loss (RL) value of −17.96 dB and an effective absorbing bandwidth (RL < −10 dB) in X-band of 2.42 GHz. The prepared Al2O3-MoSi2-Cu composite high-temperature absorbing coating takes into account the dual advantages of high-temperature stability and high-temperature absorbing properties.