High-performance Composite Coatings Research Articles

Optimized wear behaviors and related wear mechanisms of medium entropy alloy-based composite coatings

In this work, the (10 wt%, 30 wt%, 50 wt%) TiC reinforced AlFeCrCo medium entropy alloy (MEA) lightweight composite coatings with the extremely low porosity were successfully fabricated on Mg alloy substrate by resistance seam processing. The results showed that the microstructure of composite coating was consisting of a BCC-based MEA matrix and TiC particles, and a good metallurgical bonding with a semi-coherent relationship was formed between the coating and Mg alloy. Furthermore, the lightweight composite coatings (5.6–6.5 g cm−3) showed improved corrosion resistance over Mg alloy substrate. Specifically, the composite coatings exhibited optimized wear performance in the dry, deionized water and 3.5 wt% NaCl solution conditions with the increasing TiC content, surpassing related high/medium entropy alloy coatings, which is attributed to the formation of a coherent interface between the MEA matrix and the TiC particles. The first-principles calculations were performed to elucidate the nature for the higher bonding strength of TiC/MEA interface. In these wear conditions, the main wear mechanisms of composite coatings were discussed in terms of adhesive wear, oxidative wear and/or corrosive wear, in connection with their microstructure features and electrochemical behaviors. Based on the elevated anti-corrosion ability, this work has provided a strategy to fabricate advanced coatings on Mg alloys endowing with lower density, interfacial metallurgical bonding and optimized wear resistance, substantially contributing to the development of high-performance composite coatings.

Preparation and Characterization of High-Performance Composite Coatings Compatible with Near-Infrared Low Reflectivity and Low Infrared Emissivity

Polyurethane (PU)/Al-graphene composite coating with low infrared emissivity, a low near-infrared reflectivity of 1.06 μm, and satisfactory mechanical properties was prepared by using Al powder and graphene as composite pigments and PU as a binder, respectively. The study investigated the impact of the mass ratio of graphene to Al powder, as well as the total addition of functional fillers (Al powder and graphene), on infrared emissivity and near-infrared reflectivity, and the mechanical properties of the coating were studied. The results show that a large number of conjugated systems in the molecular structure of graphene can produce strong absorption of near-infrared radiation, allowing for the coating to exhibit low reflectivity at 1.06 μm in near-infrared radiation. The flake Al powder, with good electrical conductivity, can create a strong reflection in the 8–14 μm far-infrared radiation range, resulting in low emissivity and providing the coating with good infrared and laser-compatible stealth performance. By adjusting the mass ratio of graphene to Al powder, the infrared emissivity at 8–14 μm can be tuned from 0.371 to 0.644, and the reflectivity at 1.06 μm can be adjusted from 22.9% to 61.6%. Additionally, the coatings demonstrate satisfactory mechanical properties, with adhesion strength, flexibility, and impact strength reaching grade 1, 2 mm, and 50 kg · cm, respectively, for coatings with different mass ratios of graphene to Al powder. The PU/Al-graphene composite coating can be regarded as a new type of infrared and laser compatible stealth coating with good functional and mechanical properties.

Acid Radical Tolerance of Silane Coatings on Calcium Silicate Hydrate Surfaces in Aggressive Environments: The Role of Nitrate/Sulfate Ratio.

Silane is known as an effective coating for enhancing the resistance of concrete to harmful acids and radicals that are usually produced by the metabolism of microorganisms. However, the mechanism of silane protection is still unclear due to its nanoscale attributes. Here, the protective behavior of silane on the calcium silicate hydrate (C-S-H) surface is examined under the attack environment of nitrate/sulfate ions using molecular dynamics simulations. The findings revealed that silane coating improved the resistance of C-S-H to nitrate/sulfate ions. This resistance is considered the origin of silane protection against harmful ion attacks. Further research on the details of molecular structures suggests that the interaction between the oxygen in the silane molecule and the calcium in C-S-H, which can prevent the coordination of sulfate and nitrate to calcium on the C-S-H surface, is the cause of the silane molecules' strong adsorption. These results are also proved in terms of free energy, which found that the adsorption free energy on the C-S-H surface followed the order silane > sulfate > nitrate. This research confirms the excellent protection performance of silane on the nanoscale. The revealed mechanism can be further used to help the development of high-performance composite coatings.

Interfacial reaction induced synergetic strengthening effects on the plasma sprayed Ni3Al composite coating reinforced with hexagonal boron nitride nanoplatelets

Ni3Al has shown great potential in high-performance wear-resistant coating material for lots of tribological machinery components working in extremely aggressive environments owing to its anomalous strength-temperature dependence and coexistent atomic bonds (covalent and metallic bonds) in nature. In this research, hexagonal boron nitride nanoplatelet (BNNP) reinforced Ni3Al composite coatings are fabricated on Ti6Al4V substrate using plasma spray. The added BNNP can survive the harsh high-temperature conditions and are homogeneously distributed in the composite coatings. Trace amounts of in-situ synthesized AlN and AlB2 and local diffusion layer are found to form a stronger BNNP-Ni3Al interface in such a way that BNNPs act as anchors bonding Ni3Al matrix during rapid solidification. These BNNPs either locating within a splat or being sandwiched by the adjacent splats exert synergetic strengthening effects on individual splats and splat boundaries, imparting the lamellar structural composite coatings with noticeably improved mechanical and tribological properties. As compared with Ni3Al coating, BNNP/Ni3Al composite coatings showed an improvement in tensile strength, elongation, toughness, and wear resistance by 24.6 %, 21.4 %, 52.5 %, and 77 %, respectively. This research is expected to shed some light on BNNP potentials for designing and producing high-performance composite coatings using plasma spray.

Nano-modified functional composite coatings for metallic structures: Part I-Electrochemical and barrier behavior

Despite great efforts in polymeric coatings, premature failures of these coatings often cause structural corrosion. High-performance composite coatings by incorporation of nanomaterials are recently emerging multifunctional materials. Along this vein, this study aimed to evaluate the protective properties of nano-modified composite coatings. This work provided new insights into developing new high-performance nanocomposite coatings for strengthening the corrosion resistance of metallic structures. Three nanoparticles: carbon nanotubes (CNT), graphene nanoplatelets (GNP) and nano-silica (NS), were used as nanofillers for synthesizing epoxy-based nanocomposites. The new nano-modified composite coatings were systematically quantified to understand the link of tribological, mechanical, and electrical properties of the nanocomposites. The first part of this work focused on the electrochemical and barrier behavior of nanocomposites via electrochemical impedance spectroscopy (EIS) techniques and damage index. Results suggested that the 0.5–1.5 wt% NS and GNP based composites exhibited superior performance in corrosion inhibition, without damage recorded at the fresh stage. The corrosion resistance of 0.5 wt% NS composites still maintained intact after 100-hour accelerated exposure and remained as high as 92% capacity after 500-hour exposure. GNP composites also stayed with high corrosion resistance by 76% corrosion resistance after 500-hour exposure. As compared, CNT based composites exhibited a relatively lower corrosion resistance, with 85% at onset and 60% remaining capacity after long-term exposure. Water absorption results also confirmed a similar observation. The results from scanning electron microscopy revealed the coatings demonstrated good distribution of nanoparticles in the matrix. Integration of high-speed disk and ultrasonication has overcome nanoparticle agglomeration. However, large agglomeration was observed at higher concentrations. The results suggest the 0.5–1.5 wt% of nanofiller led to the most significant improvement in both mechanical and electrochemical properties.

Mechanical, electrochemical, and durability behavior of graphene nano-platelet loaded epoxy-resin composite coatings

Even though commercially coating systems, such as epoxy resin, have been used as structural coatings, the challenges are the defeats or voids experienced in these coatings during curing stages that hinder their long-term barriers performance. Also, low damage tolerance often leads to premature coating degradation. In this study, the new high-performance composite coatings were developed by incorporating graphene nanoplatelets in the epoxy resin. a comprehensive characterization of the new graphene-loaded composite coatings, including electrochemical behavior, tensile strength, ultimate strain, abrasion properties, and long-term durability performance, was investigated. The results demonstrated that the graphene-loaded composite coatings exhibited a significant improvement in resistance to abrasion and corrosion inhibition property. Improvement of mechanical properties of the graphene-loaded coatings in terms of tensile strength, failure strain and abrasion resistance allowed high damage tolerance for more broader engineering applications. Moreover, long-term durability tests further confirmed the coating loaded with a small amount of a graphene nano-reinforcement, such as 1.0% of graphene by weight, could display the high corrosion resistance by 75% of remaining capacity after 500-h exposure, as compared to the neat epoxy with a low value of 40% or less.

Graphene Reinforced Composites as Protective Coatings for Oil and Gas Pipelines.

Corrosion and corrosion-induced damage have resulted mostly in malfunctions and sometimes even in failures of metallic structures, including oil and gas pipelines. In this study, new high-performance composite coatings were developed by incorporating nanoparticles in the polymer resins with applications to oil and gas pipelines. The graphene nanoplatelets under different concentrations were used to prepare the epoxy-based nanocomposites and were then evaluated through mechanical and electrical tests. The integration of high-speed disk and ultrasonication were adopted as the dispersion technique to overcome nanoparticle agglomeration. Electron microscopy techniques were used to investigate the agglomeration. The new composites were qualitatively and quantitatively evaluated in terms of contact angle, surface roughness, adhesion to the substrate, corrosion resistance, and abrasion resistance. The results suggested that the composite with 0.5~1.0 wt.% of the graphene nanofillers led to the largest improvement in both mechanical and electrochemical properties. Distribution of nanoparticles in the matrix was observed using scanning electron microscopy and surface roughness using atomic force microscopy. Large agglomeration that was observed at the higher concentrations mainly resulted in the reduction of corrosion resistance and abrasion resistance.

Phase and structure formation mechanisms of SHS synthesized composite coatings

High performance composite coatings were synthesized by self-propagation high-temperature synthesis followed by gravitational-separation process based on thermite reaction. The phase, structure and composition of generated composite coatings were investigated, and formation mechanism was studied by thermodynamic analysis. Results showed that phase composition of Al-Fe2O3 reaction system consisted of Al2O3, Fe and FeAl2O4. In Al-Fe2O3/Al-Cr2O3 composite reaction system, Fe-Cr alloy was formed and FeAl2O4 phase disappeared, which could improve the corrosion resistance of composite coatings. Furthermore, the addition of SiO2 in SHS reaction favored the formation of low-melting point phase Al2O3·SiO2, which filled into voids of Al2O3 dendrites and reduced the porosity of composite coatings, thus improving their strength and densification level. Moreover, the generated transition structure in different reaction systems could buffer the residual stress to promote the binding between the composite coating and steel pipe.

Protective property of epoxy coatings containing polyaniline and laminar basalt in neutral, alkaline, and acidic media

It is very important to develop high performance composite coatings for efficient protection of metals from corrosion. In this work, high performance protection coatings on mild steel using epoxy as matrix containing polyaniline (PANI) and a newly developed laminar basalt (LB) were prepared and characterized. The contact angle, water absorption, adhesion strength, and passive property of the coating were also evaluated. The protection ability of these coatings on mild steel, exposed to 12 wt% sodium chloride (NaCl), 10 wt% sodium hydroxide (NaOH), and 10 wt% hydrochloric acid (HCl) solutions were monitored using electrochemical impedance spectroscopy (EIS), respectively. In neutral solution, the coating containing both PANI and LB (C‐PANI‐LB) offered very high corrosion protection performance and its impedance at 0.01 Hz was higher than 4.1 × 1010 Ω · cm2 after immersed for 60 days. However, in alkaline or acidic solution, C‐PANI‐LB behaved poorer than pure epoxy coating or PANI contained coatings, which were ascribed to the hydrolysis of LB and deterioration of the epoxy binder in these media.

Preparation and characterisation of TIG-alloyed hybrid composite coatings for high-temperature tribological applications

There is an increasing interest in the tribology community for developing high-performance composite coatings to meet severe tribological conditions in advanced mechanical systems which require high operating temperature and long life. In the present work, powder preplacement and tungsten inert gas (TIG) torch melting techniques have been employed to generate titanium carbide (TiC)-based composite coatings containing hexagonal boron nitride (hBN) or Ni–P coated hBN (Ni–P-hBN) lubricant additive. The effects of preplaced powder composition on the cross-sectional microstructures and surface hardnesses of the developed coatings were analysed. Furthermore, the friction and wear behaviours of the composite coatings at 600°C were evaluated using a Ducom ball-on-disc wear test rig. The results indicate that the TIG-melted surface containing TiC and Ni–P-hBN powder mixtures exhibits optimum properties combining good control of microstructures and uniformly distributed hardness as well as excellent tribological properties due to the enhanced wettability action of Ni–P encapsulated hBN particles.

High performance composite coatings on plastics: UV-curable cycloaliphatic epoxy resins reinforced by graphene or graphene derivatives

In this work, the design and manufacture of functional composite coatings on plastic substrates were investigated. In particular, graphene nano-platelets and graphene derivatives, that is, graphene reduced oxide modified by amino organo-silane compounds, were used to reinforce a radiation curable cycloaliphatic epoxy resin. The resulting composite materials were deposited on polycarbonate. The chemical structure of the coatings was characterized by FT-IR. Physical properties of the coatings, especially thermal stability, were evaluated by differential scanning calorimetry. Chemical endurance of the coatings was tested by dipping in acidic, saline and basic environments. Special protocols were, then, developed to evaluate the friction of the coatings as well as their potential to prevent the adhesion of contaminants on their surface (i.e., anti-soiling properties). Mechanical performance of the coatings was evaluated by pencil test (pencil hardness) and progressive load scratch test (scratch hardness). Graphene-reinforced cycloaliphatic epoxy resins were found to ensure good combination of physical, chemical and mechanical properties. Therefore, they can be considered attractive functional materials to deposit on advanced plastic substrates.

CO<sub>2</sub> Permeability Characterization of High Performance Composite Coating

In this work, the permeability of high performance composite coating (HPCC) and its containing layers fusion bonded epoxy (FBE) and middle density polyethylene (MDPE) to dissolved CO2 was investigated. The obtained results showed that the permeability to dissolved CO2 of HPCC, FBE, and MDPE are in order of HPCC<FBE<MDPE, the corresponding values of three coatings are 1.27 × 10-11 mol/atm⋅m⋅s, 1.54 × 10-11, and 3.51×10-10 mol/atm⋅m⋅s, respectively. The measurement methodology of dissolved CO2 permeability on organic coatings is feasible based on the present work.

Characterization of the permeability of a high performance composite coating to cathodic protection and its implications on pipeline integrity

In this work, the permeability of a high performance composite coating (HPCC) and its component layers, fusion bonded epoxy (FBE) and medium-density polyethylene (MDPE), to cathodic protection (CP) was investigated by various electrochemical measurements. Results demonstrate that the permeability of the coatings to water is ranked as FBE > MDPE > HPCC. Compared to FBE, MDPE, as a highly non-polar coating, plays a key role in protecting the HPCC from the water permeation. HPCC is impermeable to CP, and shows a pure capacitive behavior, with ultra-high low-frequency impedance at the order of 10 10 Ω cm 2 during the test period. Both FBE and MDPE coatings are permeable to CP, which will make up the degradation of the coatings due to the water-uptaking. Therefore, under an appropriate CP application, the two coatings are capable of maintaining the pipeline integrity. HPCC provides an excellent alternative to maintain the pipeline integrity in the soil environment.

Characterization of high performance composite coating for the northern pipeline application

High performance composite coating (HPCC) provides a potential, excellent coating alternative for integrity maintenance of pipelines in the northern area. In this work, the physical, chemical and mechanical properties of HPCC were investigated to determine the microstructure, water permeability, cathodic disbondment resistance, electrochemical impedance, adhesion and impact resistance of the coating. It is shown that the addition of polyethylene layer significantly improves the compactness of the coating and enhances its resistance to water and chemical penetration, resulting in a small water vapor transmission rate and permeance. There is a quite small cathodic disbondment of HPCC under the standard test. The impedance characteristic measured on HPCC-coated steel shows a capillary behavior, indicating an effective protection over the underlying steel from corrosion. The adhesion of HPCC to the substrate ranks top one according to both ASTM and CSA standards. The impact energy of HPCC is 9.7 J at 22 °C, and about 10.2 J around 0 °C.

Electrodeposition of composite Ni-based coatings with the addition of Ti or/and Al particles

Composite Ni+Ti, Ni+Al and Ni+Ti+Al coatings were prepared by codeposition of Ti or/and Al particles in a Ni matrix on a carbon steel substrate from the bath in which metallic powders were held in suspension. Deposits exhibited a presence of Ti and Al microsize particles embedded into the nanocrystalline nickel matrix. The influence of metal powder amount in the bath, as well as deposition current density on chemical composition of obtained coatings, has been investigated. It was stated that Ti and Al content in coatings rose with an increase in metal powder amount in the bath and reaches the maximum value of 68 and 44 wt.% for Ti and Al in Ni+Ti and Ni+Al coatings, respectively. The chemical composition of Ni+Ti+Al coatings was dependent on the mass ratio of Ti/Al powders in the bath and varied from 12 to 60 wt.% for Ti and from 4 to 25 wt.% for Al. By varying the parameters of deposition process, the optimum conditions for the production of composite Ni-based coatings containing Ti or/and Al microsize particles were obtained. The proposed electrodeposition method permits a new generation of high-performance composite coatings to be produced inexpensively and efficiently.