Arc Thermal Spray Research Articles

Enhanced cyclic oxidation resistance of Metcoloy II coated ASTM A53 Grade B steel by electric arc thermal spray

This study evaluates the enhanced cyclic oxidation resistance of Metcoloy II coatings applied to ASTM A53 Grade B steel substrates using electric arc thermal spray, across temperatures ranging from 500 °C to 700 °C. The research identifies distinct performance differences between coated and uncoated samples under cyclic oxidation conditions. Initially, both sample types exhibited mass increases due to oxide formation. However, uncoated samples developed non-protective iron oxides, while Metcoloy II coatings formed a protective layer of chromium and nickel oxides. During 500 oxidation cycles at 500 °C, uncoated samples showed a rapid mass increase, indicative of accelerated oxidation, whereas Metcoloy II coatings experienced a controlled mass gain, reflecting effective protection by chromium and aluminum oxides. At 700 °C, the mass variation trends were similar for both types initially; however, uncoated samples suffered significant mass loss due to iron oxide volatilization, emphasizing their susceptibility. Conversely, Metcoloy II coatings exhibited a reduced but steady mass increase, indicating their resilience under high-temperature conditions. Microstructural analysis confirmed the presence of a protective oxide layer in the coated samples, which is essential for reducing substrate oxidation. Although challenges such as coating detachment and thinning were observed, particularly at higher temperatures, Metcoloy II coatings maintained their protective role. This study highlights the coating's effectiveness in extending the lifespan of steel substrates subjected to cyclic oxidation, providing valuable insights for optimizing protective coatings in demanding industrial applications and advancing material science strategies for enhanced durability.

Investigating the corrosion resistance of Zn and Al coating deposited by arc thermal spraying process

Carbon steel is commonly used as a structural material in offshore windmill towers. The bases of these towers, which are located in tidal and submerged zones, often face corrosion challenges in marine environments. In this study, protective Zn and Al coatings were applied to S355J2 + N carbon steels by twin-wire arc spraying. The corrosion resistance of these coatings was evaluated by immersing them in various saline solutions, including NaCl solutions, sea salt solutions, and seawater. Corrosion tests were conducted for up to 1600 h. The results indicated that the corrosion rates of the Zn coatings and the accumulation of corrosion products on the Al coatings increased with higher concentrations of the testing solutions. The corrosion products of Zn coatings tested in sea salt solutions or seawater were mainly gordaite (NaZn4(SO4)(OH)6Cl(H2O)6), whereas those tested in NaCl solutions were mainly simonkolleite (Zn5(OH)8Cl2H2O). After testing in 5 wt% sea salt solutions for 1600 h, the Zn coatings exhibited interlayer decohesion owing to the formation of an oxide layer within the laminar structure. By contrast, the Al coatings displayed a well-mixed microstructure, ensuring strong adhesion and reducing susceptibility to interlayer decohesion in saline solutions. Consequently, in the current study, the Al-coated specimens demonstrated superior performance to that of the Zn-coated specimens in saline solutions.

Application of Arc Thermal Spray Process in Corrosion Protection of Steels and Electromagnetic Pulse Shielding

In the present work, an overview has been discussed on the application of arc thermal spray technology. This process used in erosion, corrosion and electromagnetic pulse (EMP) shielding. The Al coating exhibits excellent corrosion properties in simulated weathering i.e., Society of Automotive Engineers (SAE) J2334 as well as 3.5 wt.% NaCl solution at long run of application. However, weathering condition possesses Cl- and CO3-- ions, which simultaneously influence in the deterioration of Al coating. Once the Zn is alloyed with Al in coating, it enhances the corrosion attributed to the formation of severe defects and galvanic coupling between Al and Zn. The stainless steel and Ti coatings have been used on the concrete surface to reduce the corrosion of waste water reservoir where Ti is exhibited more corrosion resistance due to dense and uniform morphology as well as on the surface of Ti coating during exposure in acidic solution, it forms rutile and anatase, which further provide corrosion protection. Moreover, the Zn has beneficial properties in regards of EMP shielding rather than iron and Cu plate. Zn with copper has excellent EMP shielding compared to pure Cu. As the thickness is increased, the EMP shielding properties are increased. From this review article, it is suggested to reduce the porosity of arc thermal sprayed coating using some chemical post treatment.

Correlation of Tensile Properties of Arc-Sprayed Coatings and Easy Testing Methods

Different techniques are usually employed to evaluate the mechanical properties of arc-sprayed coatings. In many situations, comparing properties is complex, and values extracted from tensile tests are required for structural projects. X6CrNi18-8 stainless steel and molybdenum were sprayed onto a mild steel substrate using the electric arc thermal spray technique to discuss this issue. After a detailed microstructure characterization, tensile tests were performed on both coatings to determine the yield strength and total elongation. Easy techniques were also applied: Vickers hardness and Charpy impact test. Tensile tests have shown that applying coatings increased the steel substrate’s total elongation. Molybdenum coating presented a higher impact resistance than the X6CrNi18-8 one, resulting in no correlation between elongation and Charpy values. On the other hand, correlations between hardness and yield strength were identified, opening a discussion on the effects of the microstructure and type of test used.

Role of 5 wt.% Mg Alloying in Al on Corrosion Characteristics of Al-Mg Coating Deposited by Plasma Arc Thermal Spray Process.

The corrosion of steel structures in coastal areas is a major issue. Therefore, in the present study, the protection against the corrosion of structural steel is carried out by depositing 100 μm thick Al and Al-5 Mg coatings using a plasma arc thermal spray process, immersing them in 3.5 wt.% NaCl solution for 41 days (d). To deposit such metals, one of the best known processes, arc thermal spray, is frequently used, but this process has severe defects and porosity. Thus, to minimize the porosity and defects of arc thermal spray, a plasma arc thermal spray process is developed. In this process, we used normal gas to create plasma instead of argon (Ar) and nitrogen (N2) with hydrogen (H) and helium (He). Al-5 Mg alloy coating exhibited uniform and dense morphology, where it reduced more than four times the porosity compared to Al, where Mg fills the voids of the coating, resulting in greater bond adhesion and hydrophobicity. The open circuit potential (OCP) of both coatings exhibited electropositive values due to the formation of native oxide in Al, while in the case of Al-5 Mg, the coating is dense and uniform. However, after 1 d of immersion, both coatings showed activation in OCP, owing to the dissolution of splat particles from the corner where the sharp edges are present in the Al coating, while Mg preferentially dissolved in the Al-5 Mg coating and made galvanic cells. Mg is galvanically more active than Al in the Al-5 Mg coating. Due to the capacity of the corrosion products to cover the pores and defects, both coatings stabilized the OCP after 13 d of immersion. The total impedance of the Al-5 Mg coating is gradually increased and is higher than the Al, which can be attributed to the uniform and dense coating morphology where Mg dissolves and agglomerates to form globular corrosion products and deposit over the surface, thereby causing barrier protection. The defect bearing corrosion products on Al coating led to the cause having a higher corrosion rate than the Al-5 Mg coating. A total of 5 wt.% mg in the Al coating improved the corrosion rate by a rate of 1.6 times compared to the pure Al in the 3.5 wt.% NaCl solution after 41 d of immersion.

Influence of Different Metal Types on the Bonding Strength of Concrete Using the Arc Thermal Metal Spraying Method

Exterior finishes protect reinforced concrete buildings against environmental factors, improve their durability, and enhance their exterior design. In this study, the influence of different metal types used in arc thermal metal spraying on the adhesion between concrete and metal coatings was analyzed. Five metals with different melting points were tested, and the differences between their melting points and surface temperatures immediately after thermal spraying were measured. The bonding strength of each metal was evaluated. Additionally, the interface between the concrete surface and metal coating was analyzed using image analysis and optical microscopy. The results demonstrated that Zn achieved the highest bonding strength (1.84 MPa), which had the lowest melting point and surface temperature immediately after spraying, while Cu/Sn achieved the lowest strength (1.38 MPa), which had the highest temperatures. The bonding strength had a closer relationship (R2 = 0.9946) with the difference between the melting point and surface temperature immediately after spraying than that (R2 = 0.9589) with the surface temperature immediately after spraying. The bonding strength increased as the ratio of the non-interfacial failure area to the total area increased, ensuring a stronger attachment to the concrete surface. Overall, the results showed that the bonding strength was significantly affected by the metal type.

Effects of Surface Treatment Conditions on the Bonding Strength and Electromagnetic Pulse Shielding of Concrete Using the 85Zn-15Al Arc Thermal Metal Spraying Method.

The surface treatment of concrete enhances the bonding of its metal coatings. Therefore, in the present study, on the concrete surface, prior to the deposit of an 85Zn-15Al coating via an arc thermal spraying process, different surface treatments were considered for the effective electromagnetic pulse (EMP) shielding properties of the concrete. However, the direct coating on a concrete surface possesses lower bond adhesion, therefore it is of the utmost importance to treat the concrete surface prior to the deposition of the metal coating. Moreover, to obtain better bond adhesion and fill the defects of the coating, the concrete surface is treated by applying a surface hardener (SH), as well as a surface roughening agent (SRA) and a sealing agent (SA), respectively. The metal spraying efficiency, adhesion performance, and bonding strength under different concrete surface treatment conditions were evaluated. The EMP shielding effect was evaluated under the optimal surface treatment condition. The proposed method for EMP shielding exhibited over 60% of spraying efficiency on the treated surface and a bonding strength of up to 3.9 MPa for the SH-SRA-SA (combining surface roughening and pores/defects filling agents) specimen compared to the control one, i.e., 0.8 MPa. The EMP shielding values of the surface-treated concrete with surface hardener, surface roughening agent, and sealing agent, i.e., SH-SRA-SA specimens, exhibited 96.6 dB at 1000 MHz. This was about 12 times higher than without coated concrete.

Simulation assisted design and manufacturing of anode for the hard chrome plating of components with complex geometry

Hard chrome plating is a widespread coating technique for applying a protective coating layer to the surface of components. Due to the simplicity of industry-applied lead anodes, components with complex geometry are often plated with a non-uniform layer of chrome. In this work, a cost-effective process based on thermal arc spraying and additive manufacturing for fabricating anode with complex geometry is presented. A simulation-based approach was employed to design the anode geometry. The influence of anode-cathode distance and shielding on coating thickness was examined using a developed simulation model. The designed anode structure was additively manufactured using Multi-Jet-Fusion (MJF) process and subsequently arc sprayed with an electrically conductive coating system. The test samples were both plated with conventional lead anodes and the developed anode under the same industrial conditions to validate the simulation model. The coating thickness of the plated samples was characterized using an optical microscope. The results concluded that the developed simulation model can give a precise prediction of the thickness of the deposited coating. The strategy of varying anode-cathode distance is able to optimize small thickness inhomogeneity. To eliminate the edge effect, the shielding strategy is more effective. Chrome-plated samples using the developed anode show more homogenous coating distribution compared to those chrome-plated samples using conventional lead anodes.

Deposition of Different Metallic Coatings as Repair Materials for Concrete by Using a Twin-Wire Arc Thermal Spray Process

Using a concrete surface, the ingress of aggressive ions and the initiation of the corrosion reaction of an embedded steel rebar were studied. To reduce the corrosion reaction of the embedded steel rebar, either a coating on the steel rebar or a repair material was used on the concrete surface. Therefore, in the present study, 200 µm thick Cu, Ti, and 85Zn-15Al were used as repair materials, and their coatings were deposited on the concrete surface using a twin-wire arc thermal spray process. Different experiments such as bond adhesion, water permeability, immersion in a 5 wt.% NaCl solution, and accelerated carbonation were performed to assess the durability of the coatings, and the characterization of the coatings was performed by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The Cu and 85Zn-15Al coatings exhibited severe defects and porosity; therefore, these coatings exhibited very low bond adhesion, whereas the Ti coating showed a dense and compact morphology, and its bond adhesion value was 11 times greater than that of the Cu coating. The NaCl immersion results can be used to determine the extent of the deterioration of different coatings in coastal areas; based on these results, the Cu coating exhibited delamination, while 85Zn-15Al showed white rust deposition. By contrast, there was no detrimental effect of NaCl immersion on the Ti coating during the 28 days under study, and the coating exhibited characteristics identical to those observed after deposition. The Ti coating reduced the carbonation depth by 1.5–2 times that of the Cu and 85Zn-15Al coatings after four and eight weeks of exposure. The present study suggests that Ti can be the potential metal used as a repair material for concrete to enhance the durability of buildings and infrastructure.

Gas Shielding and Stand-off–distance Effects in Ti-6Al-4V Protective Coatings Deposited by Electric Arc Thermal Spraying for Aluminum Die Casting Molds

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Numerical Calculation of the Arc-Sprayed Particles’ Temperature in Transient Thermal Field

The physical and mechanical properties of the coatings produced by electric arc thermal spraying are closely related to the velocity and temperature of the particles that interact with the substrate surface. Knowing the temperature variation of the sprayed particles allows establishing their aggregation state, respectively determining the spraying distance, so that the state of aggregation of the particles at the impact moment is predominantly liquid. Obviously, when the sprayed particle passes through the spray cone, it cools continuously due to the low and variable temperature of the entrainment gas. This paper aims to determine analytically the thermal behavior of the particles entrained by the gas jet formed at the thermal spraying in an electric arc, depending on the variable temperature, existing along the spraying cone. In this sense, by modeling with finite elements, using the ANSYS program, the temperature inside the spray jet was determined, and by a mathematical model carried out based on the thermal balance equations, the thermal profile of the sprayed particles was determined. The thermal profile demonstrates that their temperature suddenly increases to the solidification temperature, then increases to the melting temperature—due to the latent heat of solidification, after which it decreases to 300 K.

Performance Evaluation in a Boiler Environment of a Metallic Coating Obtained by Electric Arc Thermal Spraying Using Iron-based Alloy

Resumo A Aspersão Térmica (ASP) é um processo para fabricação de revestimentos metálicos de baixo custo e alta produtividade. Esses revestimentos são usados em tubos de trocadores de calor para promover boa resistência a corrosão e ao desgaste. Este trabalho avaliou um revestimento metálico Fe-Cr-Nb-Ni-B depositado por ASP, nas condições sem selante e com selante à base de resina de silicone e alumínio, na proteção de tubos de aço quanto à corrosão e desgaste por atrito de partículas no ambiente de uma caldeira para geração de vapor d`água. Selantes ou esquemas de pintura, são soluções comumente usadas para melhorar a resistência à corrosão. As situações testadas expuseram o revestimento e substrato de amostras com e sem selante, em uma caldeira durante sete e doze meses. Utilizou-se técnicas de metalografia, microscopia eletrônica de varredura, análise química por espectroscopia de energia dispersiva e análise e processamento digital de imagens. Os resultados mostraram que embora o selante tenha sido removido do revestimento pelo atrito do fluxo de partículas presentes na água em operação na caldeira, o revestimento metálico manteve-se integro em relação à sua aderência ao substrato e camada de espessura depositada, sendo considerado uma solução promissora para a proteção de tubulações de caldeiras.

Role of Coating Processes on the Corrosion Kinetics and Mechanism of Zinc in Artificial Seawater.

Zinc (Zn) coating is being used to protect steel structures from corrosion. There are different processes to deposit the coating onto a steel substrate. Therefore, in the present study, a 100 µm thick Zn coating was deposited by arc and plasma arc thermal spray coating processes, and the corrosion resistance performance was evaluated in artificial seawater. Scanning electron microscopy (SEM) results showed that the arc thermal spray coating exhibited splats and inflight particles, whereas plasma arc spraying showed a uniform and dense morphology. When the exposure periods were extended up to 23 d, the corrosion resistance of the arc as well as the plasma arc thermal spray coating increased considerably. This is attributed to the blocking characteristics of the defects by the stable hydrozincite (Zn5(OH)6(CO3)2).

Microstructure and properties of arc sprayed Zn-Al alloy coatings

In this study, zinc-aluminum alloy coatings were deposited on low carbon steel substrates by arc thermal spraying with different current and spraying distances. Optical microscope (OM) was used to characterize the deposited coatings. From the experiment, it is found that the samples that use different electric currents and spraying distances result in the different microstructure of the coating surfaces and different mechanical properties. The sample that uses higher current tends to have a higher hardness than the sample with a lower electric current at the same spraying distance.

Morphological and corrosion studies of ammonium phosphate and caesium nitrate treated Al coating deposited by arc thermal spray process

In the present studies, the Al coating deposited by arc thermal spraying process was treated with different concentrations of ammonium phosphate mono basic ((NH4)H2PO4) and caesium nitrate (CsNO3) to improve the morphology and corrosion characteristics of the coating. As coated (AC) sample exhibits pores and defects onto the surface but once the treatment was carried out, the coating shows reduction in porosity as observed by scanning electron microscopy (SEM). The treated coatings contain caesium aluminum oxide (CAO: Cs2Al2O3) and ammonium aluminum hydrogen phosphate hydrate (AHP: (NH4)3Al5H6(PO4)8.18H2O) as composite oxides identified by X-ray diffraction (XRD). Electrochemical impedance spectroscopy (EIS) results reveal that as the exposure periods are increased, the resistance to coating/treatment (Rc/t) and charge transfer resistance (Rct) of AC and 0.5 M NH4H2PO4 and 0.0025 M CsNO3 (CN2) are increased with exposure periods in artificial ocean water solution. The improvement in total impedance values at 0.01 Hz of AC sample is attributed to formation of corrosion products which fill the pores/defects of coating while CN2 sample owing to the treatment film i.e. AHP and CAO and transformation of AHP into stable form. As the amount of NH4H2PO4 and CsNO3 is increased up to 1 M and 0.005 M i.e. CN3, the AHP film dissolved and enhances the corrosion reaction. Thus, cracking is observed in corrosion products. The enhancement in corrosion resistance of CN2 sample is attributed to the formation of α-Al(OH)3 (bayerite) and Al3(PO4)2(OH)3(H2O)5 (Aluminium hydroxide phosphate hydrate: AHPH) in greater amount as corrosion products. These corrosion products of CN2 sample are stable, sparingly soluble and protective.

Electromagnetic Shielding Performance of Different Metallic Coatings Deposited by Arc Thermal Spray Process.

Advancement in electronic and communication technologies bring us up to date, but it causes electromagnetic interference (EMI) resulting in failure of building and infrastructure, hospital, military base, nuclear plant, and sensitive electronics. Therefore, it is of the utmost importance to prevent the failure of structures and electronic components from EMI using conducting coating. In the present study, Cu, Cu-Zn, and Cu-Ni coating was deposited in different thicknesses and their morphology, composition, conductivity, and EMI shielding effectiveness are assessed. The scanning electron microscopy (SEM) results show that 100 µm coating possesses severe defects and porosity but once the thickness is increased to 500 µm, the porosity and electrical conductivity is gradually decreased and increased, respectively. Cu-Zn coating exhibited lowest in porosity, dense, and compact morphology. As the thickness of coating is increased, the EMI shielding effectiveness is increased. Moreover, 100 µm Cu-Zn coating shows 80 dB EMI shielding effectiveness at 1 GHz but Cu and Cu-Ni are found to be 68 and 12 dB, respectively. EMI shielding effectiveness results reveal that 100 µm Cu-Zn coating satisfy the minimum requirement for EMI shielding while Cu and Cu-Ni required higher thickness.

Atmospheric Corrosion Behavior of Arc Thermal Spray Zn-Al Coatings Using Accelerated atmospheric Field Test for Ten-Years

Thermal spray such as Al, Zn-Al and Al-Mg is one of the surface treatments technologies that long-term high corrosion resistance can expect. Therefore, in recent years, these coatings technologies is widely used for infrastructures such as a large-scale bridges, wind-power generating tower and a intricately shaped pole transformer. However, there are few reports about the corrosion life investigations while a sprayed coating is applied in various environment.In this study, as a basic study on corrosion life of thermal spray coatings, accelerated field test with artificial sea water for 10 years were carried out for thermal spray Zn-Al coatings. By using artificial sea water, accelerated field test accelerates corrosion due to chloride in comparison with a general atmosphere field test. Thermal sprayed specimens were prepared using an arc thermal spraying method with compressed air on carbon steel subjected surface treatment. The dimensions of specimens for corrosion field tests are 70×150×2.3mm. The edges of each specimens were protected by a coating of epoxy resin. The chemical composition (mass%) of arc spraying Zn-Al layer is 70% Zn, 30% Al. The average thickness of arc spraying layer were 150, 120 and 90µm, respectively, which was obtained by measuring the thickness of arc spraying layer from confocal laser scanning microscope. After arc spraying, sealing was not performed to penetrate the inherent pores and void of arc spraying layer. Furthermore, the average thickness 90µm of hot dip galvanized was prepared as comparison specimens of arc spraying Al-Zn coating. The scratched were made straight on a lower part center of each specimen surface. The accelerated field test were performed with artificial sea water in conformity with ASTM D1141. The artificial sea water was applied to the surface of each specimens uniformly by a brush as 24 hour is set one cycle. In additions, a general atmospheric field test was carried out for the same periods. Atmospheric corrosion behavior of arc thermal spray coating were evaluated by surface observation, X-ray diffraction (XRD), coating thickness measurement, element analyses using electro probe micro-analyser (EPMA) and electrochemical measurement.In arc spray Zn-Al coating for 10 years under accelerated field test, the granular white corrosion product were observed uniformly on the whole surface of each coating thicknesses. In hot dip galvanized coating, the powdery white corrosion product of Zn were observed uniformly on the whole surface. Furthermore, red rust was slightly observed at the edge of specimen. As a results of XRD, the corrosion product of the arc sprayed coating formed by an accelerated field test using the artificial sea water formed the product which is the same as a general atmosphere field test. In the coating thickness of Zn-Al 150µm, there is no significant difference in the coating thickness in atmospheric field tests for 10 years. On the other hand, the coating thickness of Zn-Al coating 90µm decreased. In addition, the effects of artificial sea water cannot be recognized in each thickness of arc spray Zn-Al. In EPMA analysis, corrosion products of Zn6Al2(OH)16CO3・4H2O were preferentially formed in the scratched regions of the arc spray Zn-Al surface.Consequently, arc spray Zn-Al coating maintained the high corrosion resistance in an accelerated field test for 10 years.

Weatherability of arc Thermal Spray Al-Mg Coating in a Simulated Marine Environment

Plasma thermal spray Al-Mg coating are extensively used in critical infrastructures such as a large-scale bridges, power transmission tower because of their high corrosion protection in corrosive environments. However, there are few reports about the corrosion life investigations while a sprayed coating is applied in various environment. In this study, as a basic study on corrosion life of plasma spray coatings, atmospheric field test in a simulated marine environment for 3 years were carried out for plasma spray Al-Mg coatings. By using artificial sea water, the atmospheric field test in a simulated marine environment accelerates corrosion due to chloride in comparison with a general atmosphere field test. Plasma sprayed specimens were prepared using a plasma spraying method with inert gas on carbon steel subjected surface treatment. The dimensions of specimens for corrosion field tests are 70×150×2.3mm. The edges of each specimens were protected by a coating of epoxy resin. The chemical composition (mass%) of plasma spraying Al-Mg layer is 95% Al, 5%Mg. The average thickness of plasma spraying layer were 175, 90, 60 and 30µm, respectively, which was obtained by measuring the thickness of plasma spraying layer from confocal laser scanning microscope. After plasma spraying, sealing was not performed to penetrate the inherent pores and void of plasma spraying layer. Furthermore, the average thickness 90µm of hot dip galvanized was prepared as comparison specimens of plasma spraying Al-Mg coating. The atmospheric field test in a simulated marine environment were performed with artificial sea water in conformity with ASTM D1141. The artificial sea water was applied to the surface of each specimens uniformly by a brush as 24 hour is set one cycle. Application quantity of artificial sea water is 2.3×10-3L per one specimen. In additions, a general atmospheric field test was carried out for the same periods. Atmospheric corrosion behavior of plasma thermal spray coating were evaluated by surface observation, X-ray diffraction (XRD), coating thickness measurement, element analyses using electro probe micro-analyser (EPMA) and electrochemical measurement. In plasma spray Al-Mg 30µm coating, red rust occurred on the whole surface of specimen in 3 months, and corrosion protection performance cannot be obtained. In surface observation of Al-Mg 175, 90 and 60, there is no significant changes in a simulated marine environment for 3 years. In XRD spectrum, Mg(OH)2 was identified as the corrosion products formed on Al-Mg coating. The coating thickness of Al-Mg 30µm decreased in a simulated marine environment for 3 years. In EPMA analysis, element Mg always coexisted with Al in the plasma spraying layer. Some voids and pored existed in the inner part of plasma spraying, and oxide which invaded in the inner part of plasm spraying coating occured around these voids and pored. Consequently, in the coating thickness smaller, plasma spray layer cannot be maintained the high corrosion resistance in a simulated marine environment for 3 years.

Evaluation of adhesion of epoxy resin sealant to improve the corrosion resistance of thermal sprayed coatings

The adhesion of coatings on a given substrate has fundamental importance on a coating/substrate system's functionality. The current paper presents the adhesion strength results of FeCr and CoCr-based deposits produced by the electric arc thermal spray process on carbon steel, with an intermediate layer of 95Ni5Al. Three chemical compositions were tested for coating deposition and were characterized using plate and tube specimens made of carbon steel UNS G10200 to result in a screening of performance. Microstructural evaluation by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were performed. Coating strength was measured using the standard pull-off test method. The corrosion resistance was analyzed with salt spray exposure, electrochemical polarization, and impedance spectroscopy (EIS) tests. The adhesion strength of FeCr and CoCr alloy coatings shows an overall average tensile strength of 27.2 MPa. All sealed conditions presented low corrosion and the samples with epoxy sealant exhibited a high resistance against corrosion. The X-ray diffraction results have revealed alpha and gamma FeCr alloys and chromite as deposited phases after the coating process.

Properties of Al2O3 coatings obtained by electric arc plasma method in “dynamic vacuum”

The results of studies of the influence of the electrophysical characteristics of a heterogeneous plasma flow on the properties of Al2O3 coatings (phase composition, adhesion, porosity) during plasma arc thermal spraying on a steel grade 20 in dynamic vacuum, in the pressure range from 7 to 50 kPa and at 100 kPa are presented. As well as the results for different plasma thermal spraying modes (power, consumption rate of plasma-forming gas and powder, pressure in the chamber). For the plasma torch design in this work, it was shown that Al2O3 particles are deposited most efficiently when their size is up to 100 μm, with an arc current of 300 A, flow rates for powder 0.1 g/s and for plasma-forming gas of up to 1 g/s in the pressure range (2.0-3.0) • 104 Pa.