Properties Of Coatings Research Articles

Preparation of self-healing MXene/chitosan/benzaldehyde-polyurethane flexible conductive coating for dual-mode sensing applications

Flexible conductive coatings have the potential to imbue traditional textiles with a range of functional or intelligent properties, including sensing, light emission, heat generation, etc. However, these flexible coatings are prone to damage from external forces in real-world applications. This study focuses on developing a chemically modified flexible coating with MXene as a conductive ligand, aiming to strike the characteristics of mechanical, conductive, and self-healing harmoniously. The process involves synthesizing modified 4-vinyl benzaldehyde into polyurethane (VPU), which is then cross-linked with chitosan to enhance the self-healing efficiency. The conductive ligand, MXene, was modified with tannic acid to strengthen hydrogen bonding with the VPUs. The resulting self-healing waterborne polyurethane conductive coating exhibits an impressive self-healing efficiency of 96 %, along with a high tensile strength at a break of 5.58 MPa and an elongation at a break of 340 %. It also demonstrates antimicrobial effects against Escherichia coli and Staphylococcus aureus of up to 86.8 % and 90.1 %, respectively. Importantly, this study also explores the wearable applications of flexible electronic devices. They can detect pressures up to 100 kPa in a maximum sensitivity of 0.204 kPa−1 in the initial pressure range from 1 to 15 kPa. They can also monitor the pressure response of the foot in different motion states, suggesting potential integration with insoles or socks. This work offers a practical method for combining the key properties of polymer conductive coatings with the design of carbon nanomaterial-based stress-strain sensors. They are potentially applied to this approach including smart robots, e-skins, wearable health management systems, and artificial intelligence, among others.

The Effect of Spray Distance on the Hot Corrosion Behavior of HVOF‐Sprayed NiCrAlY Coatings in a Simulated Gas Turbine Environment

ABSTRACTTo utilize the unique properties of coatings produced using the high‐velocity oxy‐fuel (HVOF) method, this study examined the effect of spray distance on the hot corrosion behavior of NiCrAlY coatings deposited on a steel substrate. The coating samples were obtained at spray distances of 20, 25, and 30 cm. The flow rates of oxygen and propane were maintained constant at 300 and 60 lit/min, respectively. Additionally, the powder feeding rate was 32 g/min. The samples were then subjected to the hot corrosion test in a salt mixture of Na2SO4−60% V2O5 at 900°C in an ambient atmosphere. The surface and the cross section of the samples were observed using a scanning electron microscope (SEM) and the chemical composition of different sections was determined by energy‐dispersive spectroscopy (EDS). The phases were also characterized using X‐ray diffraction analysis (XRD). The best corrosion resistance was found in the sample coating formed at a spraying distance of 20 cm, as the results showed that increasing the spraying distance led to a reduction in the thermal and kinetic energy of the flame, resulting in increased porosity in the coating. This behavior can be attributed to the low oxide content of the coating, the higher aluminum content, and the richer NiAl phase, which serves as a reservoir for aluminum.

Effect of H<sub>3</sub>PO<sub>4</sub> and Phenol Additives on Gel Formation in Silica Fire Retardant Coatings for Building Materials

Increasing the fire resistance of wooden building structures is quite effectively ensured thanks to the development of fire-fighting compositions with aromatic components that contribute to the formation of a carbonized layer on the surface of the material during combustion. It is also known about the mutual positive influence of benzene fragments and phosphate-containing compounds on the fire-resistant characteristics of wood. The paper considers the possibility of complex use of phenol and orthophosphate acid to improve the flame retardant properties of SiO2-based coatings. The effect of modifying additives on the rheological properties of silicic acid sols was determined. Based on the results of IR spectroscopy, the influence of components on the nature of polycondensation in experimental SiO2 sols was evaluated. It is shown that the use of orthophosphate acid as a modifier leads to the initiation of predominantly linear polycondensation in experimental sols. It was established that small additions of phenol practically do not affect the course of polycondensation in experimental sols. Increasing the phenol content to 0.5% showed an effect on gel formation due to the possible addition of phenol to the skeletal silanol groups by the donor-acceptor mechanism, which makes it possible to have a synergistic effect of the complex additive of orthophosphate acid and phenol on the properties of the silica-containing flame retardant composition.

The Influence of Particle Size and Calcium Content on Performance Characteristics of Metakaolin- and Fly-Ash-Based Geopolymer Gels.

This research systematically investigates the influence of raw material particle size and calcium content on the geopolymerization process to gain insight into the physical and mechanical properties of geopolymer gels, including setting time, fluidity, pore structure, compressive strength, and leaching characteristics of encapsulated Cr3+ heavy metal ions. Utilizing a diverse range of particle sizes of metakaolin (MK; 3.75, 7.5, and 12 µm) and fly ash (FA; 18, 45, and 75 µm), along with varied calcium levels, this study assesses the dual impact of these factors on the final properties of both metakaolin- and fly-ash-based geopolymers. Employing sophisticated analytical techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Nuclear Magnetic Resonance (NMR), the research meticulously documents alterations in chemical bonding, micro-morphology, and pore structures. Key findings reveal that reducing the size of MK and FA particles to 3.75 and 18 µm, respectively, enhances the compressive strength of their matrices by 128.37 and 297.58%, respectively, compared to their original values (63.59 and 33.87 MPa, respectively) at larger particle sizes. While smaller particle sizes significantly bolster compressive strength, they adversely affect slurry flow and reduce the leaching rates of Cr3+ from MK- and FA-based matrices, reaching 0.42 and 0.75 mg/L at 3.75 and 18 µm, respectively. Conversely, increased calcium content markedly enhances setting times and contributes to the formation of dense microstructures through the production of calcium aluminate silicate hydrate (C-A-S-H) gels, thus improving the overall curing performance and durability of the materials. These insights underline the importance of fine-tuning particle size and calcium content to optimize geopolymer formulations, offering substantial benefits for varied engineering applications and promoting more sustainable construction practices.

Enhancing the Wear Performance of 316L Stainless Steel with Nb2O5 Coatings Deposited via DC Sputtering at Room Temperature under Varied Environmental Conditions

Niobium-based oxides have garnered increased attention in recent years for their remarkable enhancement of corrosion resistance, as well as biofunctional properties of various metallic materials, including 316L SS. However, the mechanical properties of these promising coatings have not been fully elucidated. This study investigated how much the environmental conditions (air, artificial saliva, and NaCl solution) impact the wear performance of 316L SS without and with Nb2O5 coatings deposited via the reactive sputtering technique. The results exhibited a notable decrease in friction coefficient (55% in air, 18% in artificial saliva, 10% in 0.9 wt% NaCl solution), wear area (46% in air, 36% in AS, 17.5% in 0.9 wt% NaCl solution), and wear rate (44.0% in air, 19.5% in AS, 12.0% in 0.9 wt% NaCl solution). Ultimately, the results obtained in the present study elucidate the synergistic mechanisms of corrosion and wear in 316L SS containing Nb2O5 coatings, highlighting its significant potential for applications in the biomedical sector.

Research on the laser melting coating process of an AlCoCrFeNi high‐entropy alloy

AbstractLaser cladding technology is an advanced surface modification technique that has gained significant attention in various fields due to its energy savings, efficiency, and environmental friendliness. This paper discusses the preparation of AlCoCrFeNi high‐entropy alloy (HEA) coatings on the surface of a 5083 aluminum alloy using laser cladding technology under the Ar gas conditions. An orthogonal test system was used to optimize the laser cladding process parameters. The microstructure, as well as the mechanical, frictional, and electrochemical properties of the HEA coatings, were comparatively analyzed under the two process conditions S4 and S10. The results indicate that, under S10, the HEA coatings exhibit optimal surface quality. The coatings contained a mixture of Face‐centered cubic (FCC) and Body‐centered cubic (BCC) phases. Microscopic examination revealed three distinct areas: dark, gray, and off‐white. The coatings can significantly improve the wear and corrosion resistance of the alloy substrate. For the best results, it is set the laser power to 200 W, the laser scanning distance to .05 mm, and the laser scanning rate to 1250 mm/s. This present study offers a novel technical foundation for the fabrication of HEA coatings.

Investigation of the Influence of the Oxygen Flow Rate on the Mechanical, Structural and Operational Properties of 86WC-10Co-4Cr Coatings, as Determined Using the High-Velocity Oxyfuel Spraying Method

The structural-phase composition and tribological and performance properties of coatings based on an 86WC-10Co-4Cr composition obtained by the HVOF method at varying (150 L/min, 170 L/min, 190 L/min) oxygen flow rates were studied. The results showed that the coefficient of friction of coatings in gear oil remained almost unchanged with the variation in oxygen flow rate. However, microhardness increased significantly with an increasing oxygen flow rate, reaching a maximum at 190 L/min. An increasing oxygen flow rate was also accompanied by an increase in roughness and coating thickness, with a decrease in porosity, particularly notable at 190 L/min. Adhesion strength reached the maximum values for the A2 and A3 coatings under high loads. The phase composition of the coatings included WC, W2C and CoO phases irrespective of the oxygen flow rate, and their microstructure was characterized by a more homogeneous and dense structure. Thus, this study confirmed that the optimal oxygen flow rate for achieving an improved performance and tribological characteristics of 86WC-10Co-4Cr coatings is 190 L/min.

Phase quantification in a duplex stainless steel welds using NDT techniques

ABSTRACT Duplex stainless steels are composed of ferrite and austenite in equal volume fractions of these phases, which provides an excellent combination of mechanical properties and corrosion resistance, especially when compared with conventional stainless steel grades. When these steels are welded, there are significant changes in the austenite-to-ferrite ratio therefore in their final properties. Nowadays, the ferritoscope is the unique non-destructive technique used to quantify these two phases content in situ. This tester instrument is limited to the evaluation of large areas, is not suitable for the heat affected zone and is also very sensitive to the surface finish, being considered an intermediate precision technique. So, it is necessary to develop more reliable field techniques. In this research, thermoelectric power measurements and induced current techniques are proposed to evaluate the phase quantification in S32205 welds. According to the results, both techniques are reliable and highly sensitive to phase changes in the weld bead, heat affected zone and base metal. For the thermoelectric power technique, a probe with nickel tip should be used to obtain the highest sensitivity and for the induced current technique, a probe type-pencil with a central frequency of 6 MHz should be used.

Tribological properties of a smart Ti3C2Tx-based epoxy coating: Providing an idea to solve the weak tribological properties of traditional smart coatings

Friction damage is always a major threat to the wide application of smart anticorrosion coatings. Here, the tribological properties of a smart Ti3C2Tx-based epoxy coating (MLT@EP) is adjusted by the reasonable collocation of mesoporous silica nanocapsules loading onto Ti3C2Tx-based plane (MLT). MLT@EP not only maintains good smart anticorrosion, but also has remarkable anti-friction and anti-wear properties. Its friction coefficient exhibits a low and steady trend, and the wear rate arrived at 1.14 × 10−5 mm3/N·m, which is decreased by 58.3 ∼ 93.3 % compared to control groups. The excellent tribological properties are mainly attributed to the synergistic effect of MXene-based lubrication film, high resistance to plastic deformation, and strong internal interaction.

Effect of coated graphene on friction and wear properties of nickel-based self-lubricating coatings prepared by laser cladding

Graphene is an ideal material for improving the self-lubricating properties of coatings, but the high-energy laser beam can damage graphene during the laser cladding process. Therefore, in this paper, amorphous silicon dioxide (SiO2) is used to surface coat graphene particles to obtain silica-coated graphene with core-shell structure (G@SiO2). By adding niobium carbide (NbC) as the ceramic reinforcing phase and G@SiO2 nanoparticles as the solid lubricant in Ni60, a self-lubricating composite coating was prepared on the surface of 45 steel matrix by laser cladding technology. It is shown that G@SiO2 can promote the grain refinement of NbC in the coating. On the other hand, the addition of G@SiO2 promotes the generation of hard phase of chromium carbide, which together with NbC improves the hardness of the material. The maximum microhardness of the composite coating was 946 HV, which was 302.7% higher than that of the 45 steel base material. The lowest coefficient of friction value of the coated material was 0.25, and the lowest wear amount was 2.45 × 106 μm3. Compared with the composite coating without added G@SiO2, the coefficient of friction of the coated material with the addition of G@SiO2 was reduced by 50% and wear amount was reduced by 62%.

Effects of process parameters on deposition behavior and mechanical properties of alumina coatings by aerosol deposition

Effects of process parameters on deposition behavior and mechanical properties of alumina coatings by aerosol deposition

Physical and microstructural properties of YSZ + Cr2O3 thermal barrier coatings developed using HVOF technique

A composite coating material of Yttria-Stabilized Zirconia (YSZ) and Chromium Oxide (Cr2O3) was developed on the surface of Al-6061 substrates. The coating consisting of equal measures of the composite material of YSZ and Cr2O3 was successfully obtained using the High-Velocity Oxy Fuel (HVOF) technique. The surface roughness and coating thickness of the composite coatings are evaluated. The surface roughness (Ra) was evaluated showing an average of 6.0848 µm using the Surface Roughness Tester (SRT). The coating thickness was evaluated showing an average of 220.8 µm using the Coating Thickness Tester (CTT). The surface roughness and the coating thickness obtained are comparable to typical physical properties of Thermal Barrier Coatings (TBC’s). The microstructural evaluation of the coated specimens was performed through the Scanning Electron Microscope (SEM), showing the clear unification of materials The determination of the elemental composition of surface coatings was performed through the EDAX tests, which clearly established the elements in the coatings. This article is indicative of the achievement of TBC’s consisting of composite materials though HVOF technique as an alternative to TBC’s obtained through surface coats and bond coats.

Multiscale textured solar absorber coatings for next-generation concentrating solar power

A high-temperature stable solar absorber is crucial for next-generation (Gen3) concentrating solar power (CSP) plants, to enable high temperature operation, maximize power generation efficiency, and thereby reduce the levelized cost of energy. This study presents novel, fractal-textured solar absorber coatings whose multiscale feature scales effectively match the visible region of the solar spectrum, leading to superb absorptive properties. Single and bimetallic oxide coatings of copper, cobalt and manganese were prepared on Inconel 625 substrates using electrodeposition. The effect of electrodeposition parameters and annealing temperature are systematically studied to optimize the morphology and properties of the oxide coatings. Multiscale textured bimetallic coatings of copper manganese oxide and copper cobalt oxide demonstrate a superior absorptance of 0.985, a remarkably low emittance <0.45 and an exceptional optical efficiency of ∼96 % under Gen3 CSP operating conditions, surpassing previously reported values in the literature by about 5 %. Durability tests confirmed the coatings’ steadfast endurance of mechanical and environmental stress, making them suitable for long-term application in harsh CSP environments.

Fresh and Hardened Properties of Alkali-Activated POFA-GGBFS Pastes Cured in Ambient Temperature – An Initial Mix Design

Weak soils are characterised by their high compressibility and low shear strength, which requires stabilisation to improve their compaction and strength characteristics before being used for construction projects. Recent trends in soil stabilisation show an increased interest in the application of waste-derived geopolymers as low-carbon materials to address the carbon emission problem related to cement production. This paper presents the preliminary findings of using Palm Oil Fuel Ash (POFA) and Ground Granulated Blast Furnace Slag (GGBFS) binary blends as geopolymer precursor materials. These binary waste material blends were activated using alkaline solutions, namely Sodium Hydroxide (NH) and Sodium Silicate (NS), to synthesise geopolymers at ambient temperatures. Three main factors were considered for the optimisation of the geopolymer mix design, as recommended by past research: alkali equivalent (8-11.5%), activator modulus (0-0.7), and slag replacement (fixed at 30%). Alkali equivalent and activator modulus parameters were varied and tested to establish its initial and final setting times, workability and strength properties, while the slag replacement percentage was set at 30%. This study aimed to determine the most influential parameters to produce the geopolymer material with the highest compressive strength and satisfactory setting times and workability. Single-source alkali activators (NH only) used on POFA-GGBFS produced specimens with smaller flow diameters, longer initial and final setting times, and lower compressive strength than specimens activated with NH and NS. Geopolymer specimens synthesised with NH and NS produce stiffer compounds possessing higher compressive strength values and explosive-type failure modes due to their higher silica content. At ambient temperatures, TM-Mix 2 (7% alkali equivalent and 0.7 activator modulus) produced the highest compressive strength value of 67.3 MPa at 28 days curing, flow diameter of 227 mm, with the initial and final setting time of 25 minutes and 45 minutes, respectively. Consequently, the results show that the preliminary POFA-GGBFS geopolymer mix design could produce sustainably sourced geopolymer compounds with adequate strength and acceptable setting time and workability. This study is part of a current investigation to further optimise the POFA-GGBFS mix design for the purpose of weak soil stabilisation.

Anchoring mycelium on CNTs to make strong and smart self-regenerative composite materials

How to develop new recycled composite materials to meet the growing global demand for sustainable materials is of great interest. In this paper, by leveraging the growth of mycelium to anchor CNTs, the self-regenerative mycelium-CNTs composite materials (MCCs) are created. It demonstrates good strength (∼30 MPa), self-healing (restore ∼98 % original strength), and self-sensing properties. Finally, a human care-computer interaction device is developed to demonstrate the application of this technology. Our manufacturing process utilizes the autonomous growth of living cells grown in in vitro cultures to produce regenerable living composites that do not require harsh chemical processing and polluting exhaust emissions. The final mechanical properties are comparable to commercial polymer plastics, and their functional properties can be further tuned by introducing nanoparticles.

Microstructure and properties of plasma sprayed NbC-Al2O3 composite coatings

Niobium carbide has received widespread attention due to its high melting point, high strength, high chemical stability and high wear resistance, but the current preparation of niobium carbide coatings using plasma spraying technology suffers from low deposition efficiency, poor fusibility of the composite powders, high porosity, and high defects in the coating microstructure. Therefore, the microstructure and properties of NbC-Al2O3 composite coatings prepared by plasma spraying NbC-Al2O3-SiC composite powder and reactive plasma spraying Nb2O5-SiC-Al composite powder were comparatively investigated in this paper. The reaction mechanism of Nb2O5-SiC-Al composite powder during plasma spraying as well as the mechanism of the formation of coatings were analyzed in detail. The results showed that compared with the ex-situ NbC-Al2O3-SiC coating fabricated by plasma spraying, the in-situ Nb2O5-SiC-Al composite coating prepared by reactive plasma spraying had an obvious layer structure, low porosity (5.8%), high hardness (1141 HV0.1), high toughness (22.94 J/m2), and good scratch resistance properties.

Mathematical modelling and validation of the mechanical properties of HVOF-sprayed WC-12Co coatings considering the phase composition and defects generated at different process parameters

The thermal spraying process involves many machine-based parameters or independent variables (fuel flow rate, oxygen flow rate, powder feed rate, stand-off distance and many others in the HVOF process). Any combination of these parameters produces only two measurable responses, namely, particle temperature and particle velocity. In this current work, first, the machine-based spray parameters are varied in specific ways to produce different particle temperatures at near-constant velocities and vice-versa. This approach has reduced the number of independent variables to only two. These two factors further influence the in-flight particle reactions, thereby affecting the phase composition and the microstructural defects in the as-sprayed coatings. The X-ray diffraction patterns of the as-sprayed coatings revealed the presence of W2C, W, Co3W9C4, and amorphous Co-W-C phases apart from the WC phase. The W2C and W originated owing to the decarburization of the WC phase. On the other hand, the dissolution of the carbide in molten binder led to the formation of Co3W9C4 and the amorphous Co-W-C phase. The nano-hardness of both the carbide and binder phases increased with an increase in particle temperature owing to a higher degree of decarburization and carbide dissolution respectively. The porosity was the most significant micro-structural defect present in the as-sprayed coatings. An increase in either particle temperature or velocity reduced the porosity present in the as-sprayed coatings. The mechanical properties (microhardness, elastic modulus and indentation fracture toughness) tend to improve as porosity decreases. A comprehensive mathematical model was proposed to predict the mechanical properties of as-sprayed coatings as a function of composition and defects. Finally, the process maps of mechanical properties were plotted in temperature-velocity space.

Influence of Heat Treatment on Microstructure and Mechanical Properties of Laser Cladding Coatings

This study investigates the influence of various heat treatment processes on the microstructure and properties of laser cladding Fe314 coatings. The microstructure, phases, and impact fracture morphology of the cladding layer were observed using X-ray diffraction and scanning electron microscopy, among other methods. The hardness and impact performance of the cladding layer were also tested. The results indicated that there was compositional segregation and non-equilibrium microstructure in the untreated cladding layer, with an average microhardness of 368.67 HV and an impact toughness of 27 J, exhibiting quasi-cleavage fracture. The stress-relief annealing treatment resulted in a uniform distribution of M23C6 carbides inside the cladding layer. The pinning effect generated by M23C6 reduced the microhardness by 16.26% and increased the impact toughness to 54 J. The impact fracture surface exhibited ductile fracture. After secondary normalizing and annealing, the microstructure of the cladding layer transformed into a fine single-phase austenite structure, and fine M7C3 carbides precipitated at the grain boundaries. Under the effects of fine grain strengthening and dispersion strengthening, the microhardness of the cladding layer decreased by 38.14%, and the average impact absorbed energy of the specimen was 64 J, showing complete ductile fracture.

Bridging the gap between high-entropy alloys and metallic glasses: Control over disorder and mechanical properties of coatings

High-entropy alloys (HEAs) and high-entropy metallic glasses (HEMGs) represent two intensively researched classes of materials with high technological interest for applications as functional coatings with high strength, hardness, toughness, and corrosion resistance. The distinctive structural difference between single-phase crystalline solid solutions for HEAs and liquid-like disorder for HEMGs generates a seemingly insuperable contrast. In this work, we demonstrate that we can deliberately choose between crystalline or glassy properties by introducing structural disorder in HfMoNbTiZr thin films of identical composition. Using pulsed laser deposition (PLD) at different growth conditions, we reproducibly tune the structure of HfMoNbTiZr coatings from crystalline to fully amorphous. We show that the level of disorder has a profound impact on the mechanical properties of the coatings using the hardness derived from nanoindentation measurements as an example. While the hardness of polycrystalline HfMoNbTiZr layers already exceeds the single-phase bulk value, the amorphous HfMoNbTiZr is even clearly harder, demonstrating a distinctive improvement with introducing disorder. Our findings bridge the two seemingly different concepts of HEAs and HEMGs and demonstrate that structural disorder is not a given material property. Instead, disorder can serve as a useful design parameter for customizing the properties of functional coatings.

Effect of welding gas mixtures on weld material and bead geometry

Abstract Shielding gas is an essential parameter in welding processes, serves to shield the molten material from the atmosphere and external contaminations while providing a stable electric-arc pathway during the process, thus influencing the quality of the weld bead and several other aspects of the process. Therefore, any welding-based process, such as wire-arc additive manufacturing, could benefit from shielding gas mixture optimisation to selectively improve the processing and possibly the final mechanical properties of the welded material. In this study welding of EN AW 5183 aluminium (single weld bead and wire-arc additive manufacturing build-up) was conducted using several gas mixtures and their influence on final geometry defects, and microstructure measured. The gas mixtures used were a combination of varying amounts of carbon dioxide, nitrogen, and oxygen. These were added to commercially available argon gas. It was observed that: CO2 additions led to an unfavourable bonding defect and increased mean grain size; nitrogen additions caused a decrease in mean grain size, decreased pore count while maintaining a similar pore volume fraction to the reference argon mixture samples; oxygen additions showed slight reduction of mean grain size, decreased pore count and decreased pore volume fraction. These results further showcase that varying shielding gas mixtures influence the final material properties and should be considered as an additional improvement route for conventional welding and additive manufacturing.