Sprayed Layer Research Articles

НАПРЯЖЕННОЕ СОСТОЯНИЕ ПЛОСКИХ ОБРАЗЦОВ С НАПЫЛЕННЫМСЛОЕМ ПРИ ИСПЫТАНИЯХ НА ИЗГИБ

The subject of study is the analysis of the stress state during bending, both in the elastic and elastic-plastic stages, of a flat sample with a sprayed layer having different mechanical properties (elastic modulus and yield strength) than the substrate material. The goal is to select options for coatings of small (soft layer), neutral and large (hard layer) stiffness concerning the base metal, which has a lower yield strength, with different ratios of their thicknesses (0.2, 0.4 and 0.6). Tasks: to analyze the distribution of normal stresses, to determine the most loaded points on the surface of the sprayed layer and on the lower surface of the substrate, to determine the conditions and causes of the appearance of cracks in the sprayed layer and plastic deformations in the substrate. The methods used are computer simulations and analytical calculations. The following results were obtained. The nature of the distribution of normal stresses substantially depends on the ratio of the thicknesses of the sprayed layer and the substrate and does not change with their proportional increase or decrease. The most loaded points in the section where the normal stresses reach maximum values are the points on the surface of the sprayed layer and on the bottom surface of the substrate. The level of maximum normal stresses both in the sprayed layer and the substrate significantly exceeds (by 2 orders of magnitude) the tangents. That is, they are the main cause of the appearance of cracks in the sprayed layer and plastic deformations in the substrate. At the same time, the results of calculations using analytical formulas based on the laws of solid mechanics and computer simulations are the same, which confirms the adequacy of the modeling. The level of stresses at a constant thickness of the substrate is affected by both the relative thickness of the sprayed layer and its rigidity. The maximum stresses in the sprayed layer decrease with an increase in its relative thickness and increase with an increase in its relative rigidity. Соnclusion. The results obtained by various methods of theoretical studies allow us to determine the directions of improvement of equipment, technological methods of selecting modes, active materials for producing sprayed layers with high quality for assemblies and parts of various configurations and different materials of products and sprayed with the material. The findings of the work can be used in practice in the development of technological maps of the processes of deposition. The scientific novelty of the obtained results consists of the following: methods for studying the stress state of flat samples with a sprayed layer during bending tests have been improved; for the first time, the results of the influence of a set of characteristics of the deposition conditions on the strength characteristics of the sprayed layer on the substrate were obtained.

Surface modification of ramie fibers with silanized CNTs through a simple spray-coating method

Preliminary studies performed have indicated that carbon nanotube (CNT) coating is an effective method to enhance the bonding between a natural fiber and a resin matrix. However, the reported coating process is complex, and the improvement of the bonding strength is limited owing to obvious CNT aggregation. This paper reports a simple spray-coating method with uniform distribution of CNTs coated on ramie fiber surfaces. The dispersion of CNTs in a suspension for spray-coating was found to play a key role in CNTs distribution on the fiber surface. Silylated CNTs can be stably and uniformly suspended in a water and alcohol solution with a polyvinylpyrrolidone dispersant. The suspension was sprayed onto ramie fabric by using a hand-spraying pot, and CNTs were distributed on the fiber surface uniformly, as indicated by scanning electron microscopy results. The agglomeration of CNTs on the fiber surface became increasingly evident with an increase in the number of spray layers (from one to six). The effects of CNT coating on the flexural properties of the related composite and bonding properties were studied. The CNT-coated ramie fiber reinforced epoxy plate was prepared by a vacuum assistant resin transfer molding method. The CNT coating increased the flexural strength and modulus of the composite by 38.4% and 36.8%, respectively. A microdebonding test showed that the CNT coating increased the interfacial shear strength between a single ramie fiber and the epoxy resin by 25.7%, which is believed to result from stronger mechanical interlocking and chemical bonding.

Comparative Study on the Friction Property of Bearing Steel Modified Bygraphite/MoS2 Composite Coating and Manganese Phosphate Coating

Surface modification is an important method to improve the contact fatigue life of transmission parts. The preparation of high performance coating with good tribological properties on the gears and bearings has become the research trends. This paper presents graphite/MoS2 composite spray and manganese phosphate conversion coating prepared on the AISI52100 steel surface and investigates their anti-fatigue mechanism. The tribological properties of the modified layers were studied using a SRV-IV multifunctional friction and wear tester. The microstructure and interfacial components of the coating and wear surfaces were analyzed by SEM and EDS, respectively. The surface morphology and phase composition of the coating were evaluated through laser 3D microscopy and XRD analyses, respectively. Both modified layers showed good anti-friction and anti-wear properties. The friction coefficients of the surfaces modified by manganese phosphate coating and graphite/MoS2 decreased by 7 % and 14 %, respectively, and the corresponding extreme pressure properties increased by 11 % and 55 %, respectively. But the mechanism of anti-fatigue wear and the corresponding interfacial phenomena of the surface modification of the graphite/MoS2 composite spraying layer is different from those of manganese phosphate coating. The hard-ceramic particles with graphite and MoS2 are sprayed on the substrate to obtain the surface hardening layer, resulting in higher wear resistance. The graphite and MoS2 modified layer can greatly reduce the friction coefficient and improve the lubrication performance on the surface. Manganese phosphate coating serves as a chemical soft coating and is filled with rough corrugated caused by surface processing, which induces an ideal meshing surface after initial friction phase. The obtained hole-shaped structure and "infiltration" role contribute to the storage of lubricants and thus improves the lubrication performance.

Modeling L-Band Reflection and Emission From Seawater, Foam, and Whitecaps Using the Finite-Difference Time-Domain Method

Reflection and emission from flat and rough seas with embedded whitecaps (WCs) are investigated at L-band using a custom finite-difference time-domain electromagnetic model. The model is applied to multiple layers, with vertically inhomogeneous dielectric profiles representing foam and spray overlying a homogeneous seawater layer. The foam and spray layers are adapted from an L-band radiative transfer model, and the rough sea surface is a statistical realization of the Kudryavtsev wave spectrum model. The 1-D and 2-D model versions are validated for a flat sea with optional foam cover, and the emissivity effects of WCs embedded in flat and rough seas are investigated. An overlying spray layer is found to markedly reduce WC detectability. Possible applications are the stochastic simulation of WC cover and its effect on emissivity at various wind speeds, and the effects of wave and WC shape on emissivity.

Investigation on the relationship between slurry droplet entrainment and fine particle emission in the limestone-gypsum WFGD system

ABSTRACTThe entrainment of desulfurization slurry droplets out of the scrubber had a significant influence on the properties of fine particle emissions in the limestone-gypsum desulfurization system. Investigations on the relationship between entrainment of slurry droplets and generation of fine particles during the desulfurization process were carried out with an experimental system. The results showed that a large number of fine droplets and submicron particles existed in the flue gas out of the scrubber, which was attributed to the entrainment of slurry droplets during the desulfurization process. The entrained droplet sizes were closely connected with the slurry atomization characteristics, and majority of them were with sizes less than 20 μm. The mass ratio of solid contents in entrained and sprayed droplets ranged from 15% to 40%, and particles in the entrained droplets were much smaller. With the increase of superficial gas velocity, liquid–gas ratio, and desulfurization slurry concentration, the proportion of entrained micron droplets was significantly higher. Correspondingly, more fine particles were emitted with increased rates of number concentrations ranging from 20% to 50%. The optimizations of spray scrubber were beneficial for the reduction of entrained droplets and fine particles such as the adjustment of nozzle arrangement and the addition of spray layer. The decrease rate of emitted fine particle concentrations ranged from 10% to 30%.

Pack cemented silicon carbide interlayer for plasma sprayed yttria over graphite

ABSTRACTThermodynamically stable and non-reactive yttrium oxide is proposed to be the coating material on high-density graphite (HDG) crucible for melting and consolidating uranium in the pyrochemical reprocessing of spent metallic nuclear fuels. Yttria deposited over HDG by atmospheric plasma spray (APS) process without interlayer cannot withstand temperatures above 1400°C because of large thermal expansion mismatch and high-temperature partial oxidation of underlying graphite substrate through pores and openings in the plasma sprayed yttria layer. To overcome this limitation, a stable oxidation-protective intermediate layer of SiC was developed over graphite by conventional pack cementation process using two different precursor powders. The coated samples were characterized with respect to coating thickness, microstructure, and phase composition. Experimental results revealed that the optimum pack composition for obtaining thick and diffused coating was 70 wt. % Si – 20 wt. % C – 10 wt. % Al2O3. Subsequently, yttria top coat was deposited over pack cemented HDG coupons by APS process with optimized process parameters. The interlayer of SiC developed by pack cementation for yttria top coat facilitated to extend the thermal cycling life of the coating in inert argon environment significantly. The onset of micro-cracking in the top coat with SiC interlayer occurred after 45, 25 and 13 thermal cycles at 1400°C, 1450°C and 1500°C, respectively.

Feasibility Study on Application of Seawater Flue Gas Desulfurization (SWFGD) in Ultra-low Emission (ULE)

As an economical and energy-saving environmental protection technology, seawater desulfurization technology is widely used in environmental protection facilities of coal-fired power plants. With the introduction of the ULE management, the traditional seawater desulfurization technology can no longer meet the increasingly stringent environmental requirements. Based on the theory of gas-liquid mass transfer and nozzle atomization size distribution analysis, this paper investigates the effect and limitation of desulfurization performance enhancement by adding spray layer. The research results show that the design efficiency of the fifth layer spray is only 31.94%, and the export SO2 is only reduced to 98mg/m3. The concentration level is far from the ULE standard (35mg/m3), and the spray layer does not fully meet the requirements of ULE standards. Therefore, further considerations need to be taken from other ways of increasing efficiency.

Study of the impact of the method of drawing the quality of restorative coatings

An integrated method of application of gas-flame coatings has been developed, which allows to improve the technological process of restoration of cylindrical surfaces of parts with simultaneous increase of their resource due to the improvement of quality indicators of spray coatings. Brush treatment is used to process the surface of the part under the application of coating and treatment of the spraying layers during the formation process, which ensures their microplastic deformation. It is established that the technological factors that influence the strength of grip and porosity, hardness of the spray coating are the structural and technological parameters of the brush. To obtain a generalized integrated quality assessment, it is proposed to use the average harmonic quality estimation of factors: bond strength, porosity and wear resistance. Comparative laboratory research performed on two technologies: traditional and integrated, showed that the quality of coverage of the latter is higher by 26%. The method of forming a wear-resistant surface by gas-flame spraying, integrated with brush treatment has been developed. It was established that the technological factors influence the adhesion and cohesive bonding strength of the coating coating with the basis are structural and technological parameters of the brush. It is proposed to use a generalized integral assessment of the quality of the coating coating as an average harmonious quality assessment of the factors: bond strength, porosity and wear resistance. In order to provide indicators that characterize the quality of the coating, a method of forming a wear-resistant surface by gas-flame spraying, an integrated-bath with a brush treatment is developed. On the basis of the study of kinetics and the mechanism of coating formation, as well as theoretical and experimental evaluation of the processes occurring when brushing the treated spray layers, it has been established that the technological factors affect the adhesion and cohesive bonding strength of the coating coating with the base are structural and technological parameters brushes The obtained results of dosage-recommend to recommend an integrated technology of gas-fired coatings for the recovery and strengthening of parts of vehicles such as shaft.

Fabrication of a kinetically sprayed CuO ultra-thin film to evaluate CO gas sensing parameters

We have introduced a new fabrication process for a CO gas sensor using a kinetically sprayed Cu thin layer, followed by oxidation at 250 °C.

Onnanoscale phenomena inthe electroacoustic sputtering process

Introduction. The effect of variable parameters of the electroacoustic sputtering (ELAS) process on the characteristics of the crystalline structure of hardening coatings is studied. The ELAS parameter values providing nanostructured cover coatings for machine parts and cutting tools are determined. Hardening through using such coatings allows achieving a significant (5-10 times) increase in the life of hardenable machine parts and various tools designed for mechanical processing. To obtain coatings with the desired properties of the surface layer, nanocrystalline materials should be selected. In this case, a certain content of the amorphous phase is permissible.Materials and Methods. To carry out the X-ray structural analysis, the X-ray diffraction Russian-made device DRON-3M was used. The Scherrer-Wilson method was applied to determine the granularity of particle blocks from the value of the intrinsic broadening of the diffractogram peaks. The conclusions obtained in this paper are based on the method of separation of the affecting factor contributions into broadening the diffraction reflection peaks (the Warren-Averbach method).Research Results. Depending on the process conditions and the technique for obtaining nanostructured materials, a nonuniquely interpretable change in the indices of the diffraction peaks broadening occurs, which is generally characteristic of nanocrystalline metals. One of the possible explanations for this phenomenon is the presence of a nanosized effect in the hardened layer. The occurrence of the nanocrystalline structure in the sputtered layer verifies the calculated values of the dimensions of the coherent scattering regions (CSR). The occurrence of affecting values of the misorientation angle of the crystal structure is verified by the CSR value for the investigated 110 and 220 reflexes, which is supported by a high percentage of the amorphous phase.Discussion and Conclusions. The electroacoustic scattering method is promising for obtaining nanocrystalline structures in the surface and subsurface layers of the sprayed samples. The ELAS process variables variation leads to the parameter spread of the crystal lattice and coherent scattering areas. In this case, there is no definite trend. In the future it is expected to solve the given problem. First, experiments will be conducted to determine the optimal sputtering regimes that could stimulate the formation of nanocrystalline structures. Secondly, visual observation and evaluation of the sprayed layer structure using electron microscopy is planned.

Evaluation of cavitation erosion resistance of arc-sprayed Fe-based amorphous/nanocrystalline coatings in NaCl solution

Abstract The cavitation erosion behavior of Fe-based amorphous/nanocrystalline coatings has been investigated in specimens prepared by arc spraying process. The cavitation erosion test was performed in a vibratory cavitation apparatus using 3.5 wt% NaCl solution. The results showed that the FeNiCrBSiNbW coating with an amorphous/nanocrystalline structure exhibited higher cavitation erosion resistance compared to the 316L coating in 3.5 wt% NaCl solution. The spray formed defects such as pores, micro-cracks, intersplat regions and oxides in the FeNiCrBSiNbW coating had a negative effect on the cavitation erosion and corrosion behavior. The cavitation erosion failure of the FeNiCrBSiNbW coating was attributed to a brittle fracture mode. The primary cavitation erosion mechanism involved erosion of the intersplats regions, formation of pitting corrosion products and brittle detachment of sprayed layers.

Determination of the strength of polymer-metal interfaces under mixed mode loading using butt-bonded hollow cylinders

This contribution deals with the investigation of a novel testing approach for identifying the strength of polymer-metal interfaces under shear, tensile and combined shear-tensile load. To this end, a specimen geometry, being deployable independent on the material pairing, is determined by a simulative parameter study. Within the according finite element simulations, the cohesive zone approach is applied for the interface and a user-defined material model for the polymer. The simulation results are validated from an aluminum/polyamide 6 hybrid manufactured by hot pressing. Here, a NiAl5 thermal spray layer is utilized as mechanical adhesion promoter. The numerical as well as the experimental results prove that the identified geometry is well suited to determine the strength of polymer-metal interfaces. Furthermore, the experimental results reveal that the quadratic stress damage initiation criterion for the cohesive zone model is not appropriate for the investigated interface. Consequently, an alternative damage initiation criterion is proposed.

Influence of Al2O3-13TiO2 powder on a C45 steel using atmospheric plasma spray process

In automotive industry, we encounter conventional treatments for the protection of crankshaft journals, such as induction, nitridization, carburization or chrome plating. This study aims to analyze the sprayed layers using an atmospheric spray plasma coating method on the surface of C45 steel specimens used in crankshaft construction, with the Spraywizard 9MCE installation. The Al2O3-13TiO2 powder was used for the coating. The sprayed layers were analyzed microstructured and morphologically by means of optical and electronic microscopy as well as X-ray diffraction. Indentation and microscratch tests were performed to study the adhesion of sprayed layers on the base material. It has been observed from the analyzed samples that the layers obtained by spraying with Al2O3-13TiO2 are superior in terms of hardness compared to the base material. The layers have a morphological appearance of compact nature and have a good adhesion to the base material. The study reveals that spraying of appropriate powders into the plasma jet can be an alternative to classical thermal treatments on the crankshaft journals.

Aspects regarding the influence of the processing regime on the surface quality of thermal sprayed coatings

Thermal spray coatings are increasingly gaining ground in their use for various applications: protecting the surfaces from stresses, temperatures, corrosive or abrasive environments at various temperatures, repairing surfaces and providing new features, etc. One of the important operations in defining the role that a thermal spray layer will have is finishing the surface after coating by mechanical machining. In this paper the surfaces of five thermal coated samples mechanically finished by two different methods were studied. Surface morphology was observed by electronic microscopy, the appearance being correlated with the micro-hardness and roughness of these surfaces before and after processing. It was observed that the choice of the method of processing depends on the hardness of the surface and its chemical composition.

Microstructural aspects at coating-substrate interface for some thermal sprayed layers on valve discs

One of the improvements that can be made to internal combustion engines, without significantly altering the structural elements, is increasing the temperature in the combustion chamber by coating its component elements with thermal barrier coatings (TBC). In this paper were analysed from the microstructure point of view the coating-substrate interfaces of three layers deposited by thermal spraying: S1 - Cr2C3 - NiCr, S2 - MgZrO - NiCr and S3 - ZrO - CaO. The investigations were performed by electronic microscopy on the cross sections taken from the samples after they were subjected to similar heating to the one produced during the operation. It has been observed that all three types of coatings have a much better density, are chemically stable and have good adhesion to the substrate, which recommends them for this type of use.

Hydrophobic/icephobic coatings based on thermal sprayed metallic layers with subsequent surface functionalization

Hydrophobic/icephobic coatings have been fabricated using a combination of thermal sprayed metallic MCrAlY (M = Ni, Co) coatings with a subsequent deposition process using 1H,1H,2H,2H-perfluorooctyltriethoxysilane (POTS). The MCrAlY coatings provide the desirable surface roughness feature for hydrophobicity, and water contact angle of 135° was directly obtained after aged in the atmosphere for 1 week. However, it was found that the hydrophobicity of MCrAlY was not stable under water impinging due to unstable hydrocarbon absorption. Better hydrophobicity with water contact angle of 154° and improved durability have been achieved by further modification using POTS vapour on the rough MCrAlY coatings. X-ray photoelectron spectroscopy results revealed that replacement of absorption of hydrocarbon by functional C-F groups played important role in the improvement of hydrophobicity and durability. The ice adhesion test confirmed that lower ice adhesion strength of MCrAlY based coatings have been obtained compared with the threshold for icephobicity which is desirable to be applied as icephobic coatings for aircraft. The electro-thermal heating de-icing test showed an energy saving of 28.6% for de-icing with the two-step MCrAlY based coatings. The combination of strong metallic MCrAlY rough layers and the subsequent functionalization enables a new approach for the fabrication of durable hydrophobic/icephobic coatings.

Development of a shear-tensile testing method to qualify metal spraying technologies

The metal spraying is widely used process to extend the resistance against to wearing, erosion or corrosion. The related standard defines these surface protective methods as special processes because these cannot be qualify by a non-destructive testing method which clearly states the fulfilment of the requirements of a given work. Therefore the quality of the given surface protective method can be determined only during the later use. The main goal of this work is to define a control method which can be used for qualify the given metal spraying method. In our work the used base material as carrier material was P235GH steel and we investigated 6 different metal sprayed layers. To avoid the stress concentrator areas (small cracks) on the surface before the test the surface was grinded and EDM was used to cut out the samples from the manufactured work pieces. To investigate the properties of the sprayed layers tensile tests were used. From the data the strength of the composites and the layers can be calculated. Based on the shear-tensile test we created a calculation method which can be used to qualify the metal spraying methods before its use.

Osseointegrative effect of rhBMP-2 covalently bound on a titan-plasma-spray-surface after modification with chromosulfuric acid in a large animal bone gap-healing model with the G\xf6ttingen minipig

BackgroundBone morphogenetic proteins play an important role as osseointegrative factors. It is used widely in orthopedic research and surgery to enhance the osseointegrative potential of implants, e.g., in spinal fusion or alveolar socket augmentation. The aim of the present study was to investigate the benefit of rhBMP-2 on a titan plasma spray (TPS) layer after a special modification with chromosulfuric acid (CSA) at different postoperative times, regarding osseoconduction and osseoinduction.MethodsWe allocated 27 Göttinger minipigs into three groups consisting of nine animals each. They received four dumbbell-shaped implants in the metaphyseal parts of the femora. The implants had a TPS surface with (CSA group) and without a CSA treatment (TPS group). The former received an additional layer of BMP-2 (BMP-2 group). For the assessment of osseointegration after healing periods of 4, 8, and 12 weeks, histomorphometry was applied to undecalcified specimens after staining according to Masson-Goldner. An intravital labeling with different fluorochromes was used in the gap model. A multivariable analysis with repeated measurement design was performed for statistical evaluation.ResultsWe observed several statistical differences in a three-way ANOVA. The comparison between the BMP-2 and the TPS group (two-way ANOVA) showed statistically significant differences in terms of the osseoinduction (osteoid volume), and pronounced for the osseoconduction (bone and osteoid ongrowth), in favor of the BMP-2 group. In the pairwise comparison between BMP-2 and CSA (two-way ANOVA), no statistical significance occurred. The intravital staining with tetracycline, calcein green, and xylenol orange revealed no considerable differences between the groups.ConclusionBMP-2, covalently bound on a CSA-treated TPS surface, has positive effects on the osseointegration in the large animal bone gap-healing model over the observation period of 12 weeks.

Influence of Cr-Content on the thermoelectric and mechanical properties of NiCr thin film thermocouples synthesized on thermally sprayed Al2O3

Ni/Ni-Cr thin film thermocouples were deposited by means of DC magnetron sputtering for the application in plastic extrusion dies. In order to ensure the application of the thermocouples on complex surfaces, a thermally sprayed Al2O3 layer was used between the substrate and the thin films for thermal insulation and electrical isolation. The study includes the deposition, characterization, calibration, and validation of thin film thermocouples. The influence of the composition (10 at.-%, 20 at.-% and 30 at.-% Cr) was analyzed concerning mechanical and electrical properties. It was found out that the electrical resistance increases with the temperature and the Cr-content due to a decreasing crystallite size. By means of a scratch-tester and nanoindentation, a higher scratch load and hardness were observed for larger Cr-contents on the thermally sprayed Al2O3 coating. Despite the composition, the influence of the size as well as the thickness of the thermocouples were analyzed regarding the Seebeck coefficient. Independent from the size and Cr-content, all thermocouples feature a comparable Seebeck coefficient of about 40 μV/K. This high coefficient is similar to that of wire thermocouples, showing a low number of defects in the thin films. The ceramic coating features a thermal insulation of about 20 °C at 200 °C, allowing a more accurate measurement of the ambient medium.

Nickel based coatings used for erosion-corrosion protection in a geothermal environment

Development of advanced coatings for corrosion protection for different technological application currently has a strong emphasis worldwide. Nickel alloy based coatings have for example been tested and studied for oil and gas industry application, but not so much for geothermal industry. This paper aims to reveal a study on the potential application of Nickel chromium-based coating, high-velocity oxygen fuel (HVOF) sprayed, for geothermal power plants components for corrosion-erosion and wear protection. Various tests and analysis were performed to assess the suitability of the coating for the geothermal environment. Microstructure and chemical composition of the coating was analyzed by optical and Secondary Electron Microscope (SEM) equipped Energy Dispersive X-Ray Spectroscopy (EDS). The mechanical properties of the coatings were evaluated through nano-indentation and adhesion tests. Hardness test of the coating was measured with a Vickers hardness tester, using 200 g load. The hardness value of the coating was high in comparison with the reference sample. Wear tests revealed that the sprayed layer had good adhesion and cohesion, and that the wear resistance improved by 12% compared to the reference sample. The samples were exposed to geothermal steam for thirty days to test the erosion-corrosion resistance. The coating was investigated before and after the corrosion test with visual, optical and electron microscopic analysis to investigate the corrosive effect of the geothermal steam. The results from the EDS analysis showed evidence of some minor erosion-corrosion damages at the surface of the coating as well as delamination and cracking of the coating.