Sprayed Coatings Research Articles

A novel cement-based flexible spray coating for flame retardant

With the increase in the depth of coal mining, the problem of coal spontaneous combustion due to air leakage in the coal mine roadways is becoming increasingly serious. However, traditional cement mortar spray coatings are prone to cracking and poor flexibility, and polyurethane type spray coatings are not flame retardant, they are unable to meet the spraying needs. This paper proposes the preparation of a cement-based flexible spray coating for flame retardant (CFSCF) by modifying the cement-based material with the addition of fly ash, cellulose and emulsion material. The initial dosage ranges of fly ash, cellulose and emulsion material were studied. The effects of different dosages of fly ash, cellulose and emulsion material on the 7-day tensile strength, 14-day tensile strength and 28-day tensile strength were studied, and the optimum ratio of CFSCF was determined by the response surface methodology. The tensile mechanical properties, micromorphology and flame retardant properties of CFSCF with the optimum ratio were studied. The results showed that: the tensile strength of CFSCF reached the maximum at 28 days of maintenance period, 2.55 MPa; the maximum elongation at break was 52.62% at 14 days; the tensile toughness was up to 833.05KJ m−3; when the material was pulled, the two walls of the crack would bond to each other, reflecting the excellent flexibility; the alcohol lamp burning test results showed that there is flame burning time of 0 s, the material leaves the flame extinguished, has good flame retardant properties.

Investigating the Fabrication of Perovskite Solar Cells by Ultrasonic Spray Coating: A Design of Experiments Approach

Investigating the Fabrication of Perovskite Solar Cells by Ultrasonic Spray Coating: A Design of Experiments Approach

Waste Biomass Originated Biocompatible Fluorescent Graphene Nano-Sheets for Latent Fingerprints Detection in Versatile Surfaces

In recent years, the application of biocompatible and non-toxic nanomaterials for the detection of fingerprints has become the major interest in the forensic sector and crime investigation. In this study, waste chickpea seeds, as a natural resource, were bioprocessed and utilized for the synthesis of non-toxic graphene nano-sheets (GNSs) with high fluorescence. The graphene GNS were synthesized via pyrolysis at high temperatures and were characterized by TEM, XPS, fluorescence and UV-Vis spectroscopy, and FTIR analysis. The GNS exhibited excitation-independent emission at about 620 nm with a quantum yield of over 10% and showed more distinct blue light under a UV lamp. Biocompatibility of the synthesized GNS in terms of cell viability (88.28% and 74.19%) was observed even at high concentrations (50 and 100 mg/mL), respectively. In addition, the antimicrobial properties of the synthesized GNS-based coatings were tested with the pathogenic strain of Bacillus cereus via live/dead cell counts and a plate counting method confirming their biocompatible and antimicrobial nature for their potential use in safe fingerprint detection. The developed chickpea-originated fluorescent GNS-based spray coatings were tested on different surfaces, including plastic, glass, silicon, steel, and soft plastic for the detection of crime scene fingerprints. Results confirmed that GNS can be used for the detection of latent fingerprints on multiple non-porous surfaces and were easy to detect under a UV lamp at 395 nm. These findings reinforce the suggestion that the developed fluorescent GNS spray coating has a high potential to increase sensitive and stable crime traces for forensic latent fingerprint detection on nonporous surface material. Capitalizing on their color-tunable behavior, the developed chickpea-originated fluorescent GNS-based spray coating is ideal for the visual enhancement of latent fingerprints.

A Brief Review of Current Trends in the Additive Manufacturing of Orthopedic Implants with Thermal Plasma-Sprayed Coatings to Improve the Implant Surface Biocompatibility

The demand for orthopedic implants is increasing, driven by a rising number of young patients seeking an active lifestyle post-surgery. This has led to changes in manufacturing requirements. Joint arthroplasty operations are on the rise globally, and recovery times are being reduced by customized endoprostheses that promote better integration. Implants are primarily made from metals and ceramics such as titanium, hydroxyapatite, zirconium, and tantalum. Manufacturing processes, including additive manufacturing and thermal plasma spraying, continue to evolve. These advancements enable the production of tailored porous implants with uniform surface coatings. Coatings made of biocompatible materials are crucial to prevent degradation and enhance biocompatibility, and their composition, porosity, and roughness are actively explored through biocompatibility testing. This review article focuses on the additive manufacturing of orthopedic implants and thermal plasma spraying of biocompatible coatings, discussing their challenges and benefits based on the authors’ experience with selective laser melting and microplasma spraying of metal-ceramic coatings.

Evaluation of Hot Corrosion Behavior of WC-Co-Cr Coatings Coated by the HVOF Method

Thermal spray coating techniques have wide-ranging applications in various fields, including marine, automotive, biomedical, and aerospace industries. These methods are popularly used because materials coated with thermal spray coatings exhibit excellent resistance to oxidation, erosion, corrosion, and abrasive environments, particularly at high temperatures. The present study utilized the high-speed oxy-fuel (HVOF) technique, a state-of-the-art thermal spray coating method, to apply a hard cermet ceramic coating material consisting of WC-Co-Cr onto a 316L stainless steel substrate. Isothermal hot corrosion tests were also conducted at 750°C in the presence of 45% Na2SO4 and 55% V2O5 hot corrosion salts for 1, 3, and 5 hours. Advanced characterization techniques such as X-Ray Diffractometry (XRD), Energy Dispersive Spectrum (EDS), scanning electron microscopy (SEM), and elemental mapping analysis devices were used to characterize the samples coated with the HVOF technique before and after hot corrosion tests. The findings indicate that WC-Co-Cr hard coatings, which are known for their high resistance to abrasion, sustain severe damage at high temperatures. The coating was damaged after 5 hours in the hot corrosion tests performed in the presence of V2O5 and Na2SO4 molten salt at 750°C.

Deposition of ultra-thin coatings by a nature-inspired Spray-on-Screen technology

Nanometre-thick, ultrathin coatings applied over a large area are of paramount importance for various application fields such as biomedicine, space and automotive, organic electronics, memory devices, or energy storage devices. So far wet chemical deposition as a cost-effective, scalable, and versatile method can only be used for thicker deposits. Here the formation of uniform ultra-thin coatings with thicknesses below 15 nm using a nature-inspired, roll-to-roll compatible Spray-on-Screen (SoS) technology is reported. For this, the finite micro-droplet generation of Ultrasonic Spray Coating (USSC) is combined with the coating formation from a screen printing mesh. Hydrophobic micro-threads of the mesh, resembling the micro-hair on the legs of water striders, produce millidroplets from micro droplets, and when applying an external pressure to the mesh, dynamic wetting is enforced. The proposed technology is applicable for a wide variety of substrates and applications. It is shown by theory and experiment that ultra-thin coatings below 5 nm homogeneous over a large area can be deposited without the use of extended ink formulation or high substrate temperatures during or after deposition. This simple yet effective technique enables the deposition of ultra-thin films on any substrates, and is very promising to fabricate the organic, inorganic electronics devices and batteries cost effectively.

Study on the Performance of Polyurea Anti-Seepage Spray Coating for Hydraulic Structures

The surfaces of hydraulic structures are vulnerable to damage and cracking, which can result in high-pressure reservoir water entering cracks and endangering the safety of the structures. Therefore, it is necessary to strengthen the anti-seepage treatment and protection on the surfaces of the structures. In this paper, we explore the tensile and high-water-pressure breakdown resistance properties of polyurea coating material. To do so, we independently designed and manufactured a high-water-pressure breakdown test device for coating. Our experimental results indicated that the thickness of the polyurea coating decreased with an increase in elongation. Furthermore, we found that the breakdown resistance of the polyurea coating was related to the coating thickness and the bottom free section width. We then fitted the stress–strain curve obtained from the experimental test using the Ogden constitutive model. Based on this, we numerically simulated the high-water-pressure breakdown performance of the polyurea coating using the finite element software ABAQUS 2022. We obtained the relationships among maximum displacement, free section width, and coating thickness under high water pressure. Our numerical findings indicated that the vertical displacement of the midpoint increased linearly with width in the case of the same coating thickness under water pressure load. Conversely, for the same free section width, the vertical displacement decreased with increasing coating thickness.

Enhanced surface quality and properties of cold spray Al coating by high current pulsed electron beam treatment

In this paper, high current pulsed electron beam (HCPEB) irradiation was employed to improve the surface density and properties of cold spray Al coating. The effects of the energy density on the microstructure, phase composition, stress, microhardness, wear, and corrosion behavior of coatings as-fabricated were investigated. HCPEB remelting treatment has improved the surface defects of cold spray coatings. The microhardness of treated coatings is higher than that of untreated coating, and the highest microhardness of the treated coatings occurs in the subsurface layer of the coatings. The wear track width and depth of the treated coating were lower than those of the untreated sample. The corrosion potential of the treated samples increases from −1.12 v to −0.95 v, and the corrosion current density reduces from 15.64 µA/cm2 to 3.31 µA/cm2. Our results demonstrated the wear and corrosion resistance of the cold spraying Al coating were dramatically improved by HCPEB irradiation.

Aspects of Creating Multilayer Coatings by Plasma Spraying

In the work, taking into account the state of the issue in the field of applying multilayer heat-shielding and wear-resistant coatings, directions of research are substantiated. The objectives of the development are: improvement of powder materials containing zirconium dioxide partially stabilized with yttrium oxide for plasma deposition of heat-shielding coa-tings; improvement of powder materials containing oxide ceramics and nickel-based alloys for plasma deposition of wear-resistant coatings; development of technological parameters of plasma spraying and subsequent processing by the effects of compression plasma on the coating; analysis of the quality of protective coatings obtained using the optimal technology by studying their structure and physical and mechanical properties. The ZrO 2 – 7 % Y 2 O 3 particles contain the predominant tetragonal Y 0.15 Zr 0.85 O 0.93 phase, monoclinic and cubic ZrO 2 phases, and the Al 2 O 3 –TiO 2 –Ni–Cr–Al–Y–Ta composition contains the Cr 1.12 Ni 2.88 phase of the nickel-based solid solution, the a-Al 2 O 3 , g-Al 2 O 3 phases, and the orthorhombic phase of titanium oxide TiO 2 that contribute to its wear resistance. subsequent optimization of technological parameters for the process of plasma spraying of multilayer heat-shielding and wear-resistant coatings. Technological parameters for the process of plasma spraying of multi-layer heat-shielding and wear-resistant coatings are investigated with subsequent optimization. The optimization criteria were the utilization factor of the sprayed powder material and the structure of the coatings. The influence of the spraying distance on the values of operational characteristics of the formed plasma coatings on Al 2 O 3 –TiO 2 –Ni–Cr–Al–Y–Ta has been studied. The obtained results of controlling the phase composition of coatings by varying the chemical composition of powder materials are presented. In the process of deposition, the differences in the phase composition of the formed material are the more significant, the more inhomogeneous the distribution of elements in the initial powder material. Tests have been carried out for cyclic testing in an oven at a maximum temperature within 1300 °C of heat-shielding coatings to determine their heat resistance. They proved the influence of the phase composition of the formed coatings on their ability to withstand high-temperature oxidation.

High temperature erosion performance of NiCrAlY/Cr2O3/YSZ plasma spray coatings

ABSTRACT The current investigation's objective was to assess the air jet erosion tester's ability to measure the erosive behaviour of plasma sprayed coatings on titanium-15 alloy. 65% NiCrAlY, 30% Cr2O3, and 5% YSZ make up the coating's chemical composition. A study of microstructure and phases was carried out. Microhardness and adhesive strength have both been measured in this work. With impact angles of 30° and 90° at 300°C, 500°C, and 700°C, Al2O3 erodent was utilised in a solid particle erosion test. An optical profilometer was used to calculate the erosion volume loss. The coating erosion resistance was found to be higher than the substrate sample for the test temperature that was employed, and this was more obvious at higher impact angles and higher temperatures The ductile character of the coating is seen in the contour of the deteriorated coating surface.

Effect of Laser Remelting of Fe-Based Thermally Sprayed Coating on AZ91 Magnesium Alloy on Its Structural and Tribological Properties

An Fe-based coating was thermally sprayed onto the surface of AZ91 magnesium alloy via the High-Velocity-Oxygen-Fuel (HVOF) method. The thermally sprayed coating with a thickness of 530 ± 25 µm and a porosity of 0.7 ± 0.1% did not show any macrostructural defects and did not cause any degradation of the AZ91 alloy. Laser remelting of the surface layer of the sprayed coating resulted in the recrystallization of the structure and the disappearance of presented pores, splat boundaries, and other defects. This led to an increase in the hardness of the remelted layer from the original 535 ± 20 HV0.3 up to 625 ± 5 HV0.3. However, during the laser remelting at a laser power of 1000 W, stress cracking in the coating occurred. The tribological properties were evaluated by the ball-on-plate method under dry conditions. Compared to the uncoated AZ91 magnesium alloy, a higher value of friction coefficient (COF) was measured for the as-sprayed coating. However, there was a decrease in wear rate and weight loss. The remelting of the surface layer of the as-sprayed coating led to a further decrease in the wear rate and weight loss. Based on the obtained data, it has been shown that the application of laser-remelted thermally sprayed Fe-based coatings on AZ91 Mg alloy improves hardness and tribological properties compared to bare Mg alloy and as-sprayed Fe-based coatings.

Chemical Solution Deposition of Protective Er2O3 and Y2O3 Coatings onto Stainless Steel for Molten Metal Casting using Metal-Nitrate Precursors.

Chemical solution deposition (CSD) methods involving the thermal decomposition of 5.0 M Er(NO3)3·5H2O and Y(NO3)3·6H2O precursor solutions were employed to fabricate protective erbia and yttria coatings onto stainless steel (SS304/SS316) coupons. The two techniques tested were dip and spray coating, which were then compared to a commercial yttria spray (ZYP Coatings). It was determined that solution concentration, solvent choice, injection of Er2O3 and Y2O3 micropowder, and the annealing temperature/ramp profile were critical to the coatings' physical properties. For dip coatings, thicknesses were 1-20 μm after two dipping/annealing cycles, and adhesion strength was ∼1000 psi, increasing up to ∼1300 psi if the SS coupons had preliminary sandblasting. Spray coatings from precursor solutions were reported to have thicknesses of 20-80 μm and adhesion strength less than 500 psi (regardless of the coupon surface finish). Cross-sectional views of the coatings confirmed subsurface porosity, and XRD results indicated that the coatings were polycrystalline, with patterns typical to that of cubic Er2O3 and Y2O3.

Comparative Study on the Organic Solvent of IrO2–Ionomer Inks used for Spray Coating of Anode for Proton Exchange Membrane Water Electrolysis

Currently, spray coating has attracted interest in the mass production of anode catalyst layers for proton exchange membrane water electrolysis (PEMWE). The solvent in the spray ink is a critical factor for the catalyst dispersion in ink, the microstructure of the catalyst layer, and the PEMWE performance. Herein, various pure organic solvents were examined as a substitute for conventional isopropanol-deionized water (IPA-DIW) mixture for ink solvent. Among the polar solvents that exhibited better IrO2 dispersion over nonpolar solvents, 2-butanol (2-BuOH) was selected as a suitable candidate. The PEMWE single cells were fabricated using 2-BuOH at various ionomer contents, spray nozzle types, and drying temperatures, and their performance was compared to the cells fabricated using a conventional IPA-DIW mixture. The PEMWE single cells with 2-BuOH solvent showed good performances comparable to the conventional IPA-DIW mixture case and highly durable performances under accelerated degradation tests.

Performance of Thermally Sprayed Nickel and Tungsten-Based Coatings in Slurry Erosion Conditions: A Review

Abstract The energy needs of a country cannot be fulfilled by a single source of energy, so renewable energy sources like solar, wind, and hydro energy are widely used throughout the world. In countries where sufficient hydro energy resources are available, hydropower plants have been installed to produce electricity. But countries where the rivers originate from hilly areas (like India and Nepal) have to deal with the losses due to the wear caused by the silt particles presented in water. The silt content in water causes the erosion of material in different components of hydropower plants. To avoid these losses thermally sprayed hard surface coatings are widely used as a protective layer. This review focuses on the performance of composite coatings based on nickel and tungsten in slurry erosion conditions. A comprehensive investigation of studies conducted on thermally sprayed nickel- and tungsten-based coatings is discussed in this review paper. The review reveals that high velocity oxy-fuel is widely used by different researchers to develop composite coatings. Materials like Ni–20Cr2O3, Ni–Al2O3, Ni–Cr–Si–B, WC–10Co, WC–10Co–Cr, and Ni–Cr–B–Si–Fe–WC (Co) have been used in different studies to minimize the wear of material in slurry conditions.

Mo-alloyed stainless steel coating with improved cavitation erosion resistance by plasma spraying a specially designed core-shell-structured powder

Plasma spray coatings are widely used to protect materials from cavitation erosion. However, the limited interlamellar bonding and porous structure of plasma spray coatings limit the potential of utilization of the coating materials for cavitation protection. In the present study, to improve the resistance of cavitation erosion for plasma spray coatings, molybdenum (Mo)-alloyed stainless steel coating with enhanced interlamellar bonding was deposited by spraying a specially designed core-shell-structured Mo-clad-304SS powder through shrouded plasma spray. The post-spray diffusion heat treatment was then also performed to further enhance the lamellar interface bonding of the coating. Owing to the high susceptibility to cohesion of the coating, cavitation erosion test was performed on the surface of resultant coatings to evaluate the quality of the interlamellar bonding within the coating. Results show that the cavitation erosion resistance of the 304SS-17Mo alloy coating with enhanced interlamellar bonding was significantly improved by 100% compared with that of conventional 304SS coating. After diffusion heat treatment, the cavitation erosion resistance of 304SS-17Mo alloy coating was further improved to as high as that of 304SS bulk due to the newly formed hard phases.

Investigation of Novel Nano-carbide WC/CoCr Coatings Applied by HVAF

AbstractWear leads to high material and energy losses in various industries. The manufacturing of novel nano-carbide WC/CoCr powder feedstock materials promises a further increase in the performance of thermally sprayed wear protection coatings. A novel experimental powder and a commercial ultra-fine carbide WC/CoCr reference are thermally sprayed onto a 1.0038 substrate by High Velocity Air Fuel (HVAF) spraying. The specimens are metallographically prepared and analyzed by means of light microscopy (LM) and scanning electron microscopy (SEM). Vickers Hardness testing is conducted by micro-indentation, and the porosities are determined by optical image analysis. X-ray diffractometry (XRD) analysis is used to investigate the phase retention. Fine nanocrystalline WC structures are preserved in the dense coatings. A significant effect of powder type on the porosity of the coating was found. No systematic relationships could be identified between the coating structure and the two parameter settings. It was possible to influence decarburization via both the powder type and the selected parameters. The resulting experimental and commercial nanostructured WC/CoCr coatings exhibit high, narrow hardness values with medians of 1.400 < HV0.3 < 1.470. The novel nanostructured coating can contribute to reduced wear and therefore improve the efficient utilization of critical raw materials like tungsten.

Thermal Spray Coating Technology – A Review

Thermal spray coating involves heating of coating materials (ceramic, carbide, and metal alloys) to a semi-molten or molten state and propels to substrate. The flame temperature is in the range of 3,000 to 16,000OC but the surface temperature of the substrate rarely exceeds 500 OC depending on the thermal spray processes being used. The coating materials are feed into the spray gun in the form of powders, rods or wires. Thermal spray coating is use for the following purposes; (i) increase corrosion and wear resistance, (ii) protection against electromagnetic, or electrostatic, (iii) protection against radio frequency interference, (iv) metal buildup and, (iv) cosmetic. Thermal spray coating can be categorized into five most common processes; (i) Flame arc spraying, (ii) Electric Arc spraying, (iii) Plasma arc spraying, (iv) High-velocity Oxy/Fuel (HVOF) and (v) Detonation Gun. In this paper, thermal spraying processes will be explained, along with the advantages and disadvantages of one another.

7 Construction and Characterization of a Thermal Spray Coating Aerosol Generator

Abstract Thermal spray coating (TSC) is a surface treatment process whereby feedstock material is sprayed onto surfaces under pressure where it solidifies and forms a solid coating. In metal TSC processes, large quantities of aerosols, including fine and ultrafine metal particles are generated. However, exposure assessment for TSC is lacking. The goal of this study was to construct a TSC aerosol generation system and to characterize the physicochemical properties of aerosols generated during coating processes. A computer-controlled, automated electric arc wire-TSC aerosol generator system was built in an enclosed room, where a rotary motor rotates a metal feedstock pipe in circular and up-and-down directions to allow even deposition of coating material on the pipe surface. The characteristics of aerosolized particles during spray coating using a stainless-steel wire (PMET 720) showed that: 1) respirable mass concentrations ranged from 142–218 mg/m3 (3 spray shots with each shot of 1-sec during 20-min sampling), 2) diameter of peak particle number concentrations was between 360 nm and 400 nm, 3) mass median aerodynamic diameter determined by an impactor ranged from 290–370 nm, 4) particle morphology was observed to be diverse including chain-like agglomerates and spherical and cylinder-like shapes, and 5) metal composition was 80% iron, 17% chromium, and 3% manganese with trace amounts of nickel and copper. These findings are limited to one wire type and suggests the need for further investigations evaluating various parameters (e.g., wire/powder types, high/low energy, ventilation on/off) to obtain emission rates and recommend control measures.

Improving the flowability of fine WC-12Co powder using atmospheric pressure nitrogen microwave plasma torch treatment

WC-Co powders are mainly used in thermal spray coatings, which improve corrosion and wear resistance as well as the regeneration capacity of damaged components. The use of fine powders in the thermal spray coating process is essential to form a dense coating layer. However, fine powders possess poor flowability due to their morphology and van der Waals forces between particles. These characteristics limit their application in thermal spray coatings. In this study, a nitrogen microwave plasma torch was applied to WC-12Co powder (D50 = 20 μm) to improve the flowability of the powder. The rough surface of the particle was melted and changed to a smooth, spherical surface. As a result, the flowability of the plasma-treated powder improved significantly from 0 to 4.02 g/s. Thus, a microwave plasma torch improves the flowability of fine WC-12Co powders and is suitable for continuous treatment and mass production of plasma spray powders.

Calculation and investigation of the phase composition of a composite intermetallic layer synthesized on the surface of VT6 titanium alloy from Cu–SiC and Al–SiC powders

The physical and chemical foundations of the technology of cold gas-dynamic spraying of coatings on titanium for two types of charge are considered, in one of which chemically inactive copper is used as a ductile metal in combination with abrasive silicon carbide powder, in the other – chemically active aluminum in combined with silicon carbide. A thermodynamic modeling technique has been developed to select the composition of the coating charge and predict the change in its phase composition at high temperature.