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Review

A Review of the Preparation, Modification, and Applications of Polyetheretherketone Coating

by
Yufei Chen
1,2,
Hongjun Ni
1,3,*,
Jae-Jun Park
2 and
Shuaishuai Lv
3,*
1
School of Mechanical Engineering, Nantong Institute of Technology, Nantong 226000, China
2
Department of Electrical and Electronic Engineering, Joongbu University, Goyang 10279, Gyeonggi-do, Republic of Korea
3
School of Mechanical Engineering, Nantong University, Nantong 226019, China
*
Authors to whom correspondence should be addressed.
Coatings 2024, 14(11), 1451; https://doi.org/10.3390/coatings14111451
Submission received: 13 October 2024 / Revised: 5 November 2024 / Accepted: 12 November 2024 / Published: 14 November 2024
Browse Figures
Versions Notes

Abstract

:
The progress of research on the preparation of polyetheretherketone (PEEK) coatings is systematically described with emphasis on the three coating preparation methods of thermal spraying, electrophoretic deposition, and melt extrusion coating, and the advantages and disadvantages of these methods and their main applications are reviewed. At the same time, research into the modification of PEEK coatings is also introduced, including modification using inorganic materials and chemical modification. Finally, the application of PEEK coatings is introduced, and its future development directions are prospected.

1. Introduction

Polyetheretherketone (PEEK) is a semi-crystalline high-performance engineering thermoplastic [1]. It was first developed by British Imperial Chemical Industries (ICI) in 1978 [2]. The first industrial applications of PEEK were mainly in the aerospace and automotive industries. With its excellent mechanical properties, high temperature resistance, chemical corrosion resistance, and wear resistance, it has been widely used in various industrial fields [3]. The unique properties of PEEK are due to its stable molecular structure. The chemical structure is shown in Figure 1; the aromatic ring provides rigidity, and the ether bond and ketone group provide good chemical and thermal stability [4].
Thanks to PEEK’s high glass transition temperature (143 °C) and melting temperature (343 °C), PEEK can still maintain excellent physical properties at extreme temperatures [5]. PEEK exhibits excellent electrical insulation and dielectric properties under different temperatures and harsh environments, especially maintaining a low dielectric constant and loss factor at high temperature and under humid conditions [6,7]. In addition, PEEK has good biocompatibility and is widely used in medical implants because it does not cause rejection or toxic reactions [8,9].
Although PEEK has become a high-performance coating that has attracted much attention due to its own advantages, a single PEEK coating can no longer meet the needs of modern industry for multifunctional coatings, such as higher thermal conductivity, wear resistance, and insulation. This paper systematically reviews the preparation technologies, modification methods, and typical applications of PEEK coatings.
Figure 2 shows the annual publication of papers on PEEK-related topics. Since 2000, the number of papers published on PEEK-related topics has generally shown a significant growth trend, especially after 2015, which shows that research in this field has gradually received more attention. Among the subjects discussed, chemical modification has been the main research direction. From 2010–2020, research on various topics in this stage increased significantly, especially regarding plasma spraying, chemical modification, and aerospace. The growth during this period may be due to the gradual recognition of PEEK’s characteristics in industrial applications. After 2020, the number of publications in this stage reached a peak, especially in the fields of automotive and aerospace applications, and the application of PEEK has been more widely explored and studied in these industries.

2. Preparation Methods for PEEK Coatings

There are three main methods for preparing PEEK coatings: thermal spraying, electrophoretic deposition, and melt extrusion. In the thermal spraying process, PEEK particles are sprayed onto the substrate at high speed through plasma spraying and other technologies to form a dense, high-temperature resistant coating. For electrophoretic deposition, under the action of an electric field, PEEK particles are evenly dispersed in water and deposited on the surface of the substrate, which is suitable for uniform coatings of complex shapes. During melt extrusion coating, PEEK is coated on the substrate through a heated extrusion process to form a continuous, flat, high-strength protective layer, which is suitable for long strips or linear substrates.

2.1. Thermal Spraying

Three methods have been introduced involving thermal spraying, including plasma spraying, flame spraying, and high-pressure high-speed oxygen—fuel spraying. In these methods, PEEK powder is melted and sprayed onto the surface of the substrate to form a uniform coating. The advantage of thermal spraying is that the coating thickness is controllable, and it is suitable for large or complex-shaped workpieces [10].

2.1.1. Plasma Spraying

Plasma spraying uses high-temperature plasma to heat PEEK powder to a molten or semi-molten state. The high temperature is used to melt the PEEK and spray it onto the surface of the substrate, depositing a PEEK coating with a thickness of about 50–500 µm on the surface of the substrate, thereby improving the wear resistance, corrosion resistance, and temperature resistance of the substrate [11].
Wu et al. [12] prepared PEEK coatings on aluminum substrates with various surface treatments by plasma spraying. PEEK fine powder with an average size of 50 μm was selected as the spraying material. A PT800 plasma spray system was used. The powder feeding rate was set to 10~20 g/min, and the powder feeding direction was 30° counterclockwise in the jet direction. Spraying was performed at a spraying distance of 80 mm. Four different surface treatments were selected. They included boiling (BT), etching (ET), polishing (PT), and unheat-treated surfaces (E). The three substrates (BT, ET, and PT) were heat-treated at 350 °C for 90 min to remove physically and chemically adsorbed water from the substrate surfaces. After plasma spraying, the spatter diameters of the four substrates were found to be 60 ± 5 μm, as shown in Figure 3. It was found that the PEEK coatings on the heat-treated ET and PT substrates had good adhesion and low porosity. The boiled (BT) substrate showed a large number of small pores (<1 µm) at the sputtered substrate interface. The untreated (E) substrate showed elongated pores (<2 µm) with nearly continuous cracks along the interface. The etched (ET) and polished (PT) substrates had fewer and smaller pores, while PT showed some fine pores (<100 nm).
Jiang et al. [13] prepared TiN/PEEK composite coating by injecting TiN and PEEK powder into double tunnels using plasma spraying technology. Carbon steel was used as the substrate, and 0–45 μm Ti powder and 60–80 μm PEEK powder were selected as raw materials. Before coating, the substrate surface was sandblasted. A Ni-10 wt.% aluminum alloy bonding layer was sprayed on the substrate to improve the bonding strength between the steel substrate and the composite coating. After spraying, the thickness of the TiN/PEEK composite coating was about 300 μm. The schematic diagram of double tunnel powder feeding is shown in Figure 4. It was found that the average friction coefficients of the TiN/PEEK composite coating were 0.59, 0.56, 0.51, 0.50, and 0.49 under loads of 100–500 N, respectively. The corrosion current density of the TiN/PEEK composite coating was about half of that of the TiN coating, and the corrosion potential was 53 mV higher than that of the TiN coating, indicating that the composite coating had better corrosion resistance.
Cui et al. [14] prepared a composite coating on the surface of TC4 titanium alloy by mixing ZrO2 and PEEK powder and using plasma spraying. The porosity of the ZrO2-15% PEEK coating reached 20.6% after heat treatment. The porous nanostructured ZrO2 and PEEK composite coating improved the thermal insulation performance of the material.
Research by Wu et al. focused on the interface bonding between the PEEK coating and the aluminum substrate, with the advantages of the corrosion resistance and lightweight properties of PEEK. Jiang et al.’s research improved the wear resistance and corrosion resistance of the TiN/PEEK composite coating, making it particularly suitable for protective coatings in harsh environments. Cui et al.’s research developed a porous nanostructured ZrO2/PEEK coating with excellent thermal insulation and biocompatibility, suitable for high-temperature or biomedical applications.
Plasma spraying is a new type of precision spraying process that is suitable for spraying materials with a high melting point, making the coating higher in quality and providing better coating uniformity and higher spraying efficiency. However, it requires higher process precision and quality control to ensure the uniformity and performance stability of the coating. In addition, high-temperature spraying may lead to coating degradation and a low interfacial bonding force. At the same time, thermal shock and the subsequent rapid cooling process may have a certain impact on the mechanical properties of the substrate.

2.1.2. Flame Spraying

Flame spraying is a thermal spraying process that uses the high temperature generated by combustion gas to melt powder materials and spray them onto the surface of the substrate to form a protective coating. Research on flame spraying mainly involves parameter control, coating uniformity, and coating adhesion, and it is often used in anti-corrosion and repair applications [15].
Tharajak et al. [16] incorporated hexagonal boron nitride (h-BN) powders of different particle sizes and contents into PEEK by ultrasonic treatment. They selected PEEK powder with an average size of 60 μm and h-BN powders of three particle sizes (0.1, 0.5, and 1.5 μm). The 0.1 and 0.5 μm particles were round plate-like aggregates, while the 1.5 μm size consisted of a mixture of fine and coarse h-BN particles. The substrate used was low carbon steel. PEEK powders with h-BN contents of 2, 4, 6, and 8 wt.% were added to an ethanol solvent in an ultrasonic bath and mixed and dried in an oven. A h-BN/PEEK coating with a thickness of 250~300 μm was prepared by flame-spraying technology, as shown in the SEM images in Figure 5. It was found that the h-BN/PEEK coating with an h-BN particle size of 0.1 μm exhibited the lowest specific wear rate. The specific wear rate of the h-BN/PEEK composite coating increased with the increase in h-BN content and particle size. The PEEK composite material filled with 8 wt.% h-BN and with a particle size of 0.1 μm had a relatively low specific wear rate, and the friction coefficient was also significantly reduced. The specific wear rate and friction coefficient were 13 × 10−6 mm3/Nm and 0.2, respectively.
Li et al. [17] added 300 mesh and 600 mesh carbon fiber-reinforced composites (CF) as fillers into PEEK. The diameter of CF powder with a particle size of 300 mesh was about 5 μm and the length was between 10 μm and 50 μm. The length of CFs in the 600 mesh powder was 10~25 μm. PEEK and CF mixed powders with CF contents of 10 and 30 wt.%, respectively, were prepared by ultrasonic dispersion. The coating was prepared by flame spraying. Pure PEEK powder and CF/PEEK mixed powder were sprayed onto 17-4PH substrate using a CP-3000 flame sprayer. The thickness of the flame-sprayed coating was 150~200 μm. With the increase in CF content, the porosity of CF/PEEK composite coatings with CF of 300 and 600 mesh increased. Compared with the composite coating with the same content of 600 mesh CF, the CF/PEEK composite coating with 300 mesh CF showed greater porosity. The performance parameters of PEEK powder, flame-sprayed pure PEEK coating and flame-sprayed CF/PEEK composite coating are shown in Table 1. The study found that the surface hardness of pure PEEK coating was 0.28 GPa. The hardness of CF/PEEK composite coating containing 10 wt.% 300 mesh CF decreased slightly, while the hardness of coating containing 30 wt.% 300 mesh CF increased to 1.31 times that of pure PEEK coating. The elastic modulus of CF/PEEK composite coating containing 10 wt.% 300 mesh CF was 1.45 times that of pure PEEK coating. Table 1 shows the FTIR peak intensity ratio (IC=O/IC=C), glass transition temperature (Tg), melting temperature (Tm), crystallinity (Xc), and grain size (dp) of PEEK powder, flame-sprayed pure PEEK coating and flame-sprayed CF/PEEK composite coating at 1707 to 1598 cm−1.
Li et al. [18] also used flame spraying to prepare carbon nanotube (CNT)/PEEK nanocomposite coatings. The PEEK powder had a particle size of about 20 μm, the outer diameter of multilayer carbon nanotubes was 40–60 nm, the length was >5 μm, and the purity was greater than 97 wt.%. PEEK and CNT mixed powders were prepared by mechanical blending (MB) and ultrasonic dispersion (UD) methods. The CNT contents in the (CNT)/PEEK nanocomposite coatings were 0.1, 0.5, 1.0, and 2.0 wt.%. The thickness of the flame-sprayed coating was 150–200 μm. The friction coefficient and specific wear rate of the flame-sprayed CNT/PEEK nanocomposite coating are shown in Figure 6. It was found that good CNT dispersion effectively inhibited the thermal degradation of PEEK, reduced hole defects, and improved the mechanical strength of the coating.
Soveja et al. [19] prepared PEEK coatings on stainless steel and aluminum alloy substrates by flame spraying and used different types of lasers (CO2, Nd, diode laser) to remelt the coatings. PEEK powder with an average particle size of 25 µm was selected, and a PEEK coating was prepared through flame-spraying technology. The thickness of the coating was 100–150 µm. Laser remelting of the coating is used on the basis of flame spraying. The study found that the adhesion of the coating was significantly improved after flame spraying and CO2 laser remelting. The friction coefficient of the treated coating was about 0.325, and the wear rate of the PEEK coating was reduced by about 50% to 10.5 × 10−6 mm3/N·m.
The h-BN-filled PEEK composite coating studied by Tharajak has excellent wear resistance and lubricity. Li et al. [17,18] studied carbon fiber-reinforced PEEK coating and carbon nanotube-reinforced PEEK coating. The carbon fiber-reinforced PEEK coating showed enhanced mechanical properties and wear resistance, and the carbon nanotube-reinforced PEEK coating showed excellent wear resistance. Based on flame spraying, Soveja used laser remelting to improve the density, adhesion, friction coefficient, and wear resistance of PEEK coating.
Flame-spraying technology can form functional coatings on the surface of PEEK and other substrates. By incorporating modified materials such as h-BN, CF, or CNTs, the microhardness of the coating can be significantly improved, and the friction coefficient and wear rate can be reduced, thereby improving the overall performance of the coating. However, there are high process requirements and problems such as thermal stress and matrix degradation that need to be solved.

2.1.3. High-Pressure and High-Velocity Oxy–Fuel Spraying

High-pressure and high-speed oxy–fuel spraying generates high-speed airflow through the combustion of oxygen and fuel under high pressure, which melts and sprays powder materials onto the surface of the substrate to form a dense and wear-resistant coating [20].
Krishal et al. [21] used high-velocity oxygen–fuel (HVOF) and auxiliary combustion high-velocity air–fuel (AC-HVAF) thermal spraying technology to prepare PEEK coating. The PEEK powder size was selected as 45 μm, the spray gun nozzle length parameters were 150 mm, the spraying distance was 280 mm, and the lateral speed was 300 mm/s. The influence of PEEK coating quality and performance on ANSI304 stainless-steel substrates with different surface roughness was studied. The stainless-steel substrate was subjected to degreasing, etching, and steel grit blasting surface treatments. The surface roughness of the substrate was found to have a significant impact on the properties of the PEEK coating. Higher surface roughness helps to improve the adhesion of the coating, but appropriately increasing the roughness can improve the adhesion. However, the surface treatment increases the process difficulty and may lead to more pores and unevenness on the coating surface, affecting the overall performance of the coating. The surface profile is shown in Figure 7 and Figure 8.
The HVOF coating process has the advantages of high density and low porosity, and it is suitable for coatings that require high wear resistance and corrosion resistance, but the equipment cost is high and the process is complex.
In summary, the process parameters of the above three thermal spraying methods are summarized as shown in Table 2. Current, gas flow, spraying distance, powder feed rate, substrate preheating temperature, and spraying speed are all key process parameters for thermal spraying preparation of PEEK coatings. The advantages and disadvantages of the three thermal spraying methods and their application scenarios are summarized in Table 3.

2.2. Electrophoretic Deposition

In this method, the coating is formed by depositing PEEK nanoparticles onto a conductive substrate under the action of an electric field. It is suitable for coating workpieces with complex geometric shapes, and the coating uniformity is good [22].
Cao et al. [23] introduced tantalum nitride (TaN) nanoparticles into PEEK coatings by electrophoretic deposition. PEEK powder with a particle size of 25 μm and TaN powder with a particle size of 260 nm were selected as raw materials for preparing composite coatings. The suspension consisted of 100 mL of electrophoretic deposition solution (50 mL of ethanol and 50 mL of chitosan solution (containing 5 mL of acetic acid and 0.1 wt.% chitosan)). Chitosan was used as a dispersant to modify the surface potential of PEEK and TaN particles. These particles were modified to be positively charged and improve the deposition efficiency. Finally, the solution was mixed with different mass fractions of TaN nanoparticles (0, 1.31, 3.23, and 6.25 wt.%) and stirred until fully mixed into four electrolytes. A Pt sheet was used as the anode and the titanium substrate was used as the cathode. The distance between the cathode and the anode was fixed at 1 cm, and electrophoresis was performed at 15~25 V for 30~180 s. It was found that the introduction of TaN nanoparticles into PEEK coatings improved deposition efficiency, enhanced deformation resistance, and improved the hardness, elastic modulus, and bonding strength of the coatings. Compared with pure PEEK coatings, the friction coefficient of P-TN-3 was greatly reduced by 31.25%. The wear resistance of P-TN-3 was also greatly improved, and its specific wear rate was reduced from 9.42 × 10−5 to 1.62 × 10−5 mm3·N−1·m−1. The uniform composite TaN/PEEK coating prepared by electrophoretic deposition adhered well to the titanium alloy substrate. The cross-sectional SEM images of the coatings (Figure 9a,c) showed that under the same deposition conditions, the coating thickness was increased from 56.8 μm to 86.8 μm by introducing TaN nanoparticles, and the Ta element’s distribution in the coatings was relatively uniform (Figure 9c–e). Both PEEK and P-TN-3 coatings were well bonded to the titanium substrate. Heat treatment resulted in a uniform and dense coating. The coating was well bonded to the substrate, and no obvious cracks were found at the interface.
Kusmierczyk et al. [24] adopted a multilayer design concept. The coating used Cu, HA, and ZnS as the base layer, and the outer layer was a PEEK coating. The Cu/HA/ZnS+PEEK coating was prepared by electrophoretic deposition and heat treatment technology. The scheme is shown in Figure 10. The complementary advantages of different materials are achieved through the multilayer structure. The coating system has conductivity, mechanical strength, wear resistance and biocompatibility. The particle size of PEEK powder is 2–15 μm, the size of ZnS nanoparticles is 100 nm, and the average size of HA nanoparticles is 10 nm. The chemical treatment used 45 mL HNO3, 5 mL HF, and a maximum of 100 mL distilled water. After etching for 5 min and soaking in distilled water, it was heated at 550 °C for 2 h and then furnace cooled. Zirconium alloy was used as the working electrode and austenitic stainless-steel plate was used as the counter electrode. The distance between the electrodes was 10 mm. The EPD of the ZnS+PEEK and HA layers was constant voltage (varied by 20 V) with stable deposition times of 15 s and 30 s, respectively. The hardness of the ZnS/PEEK base layer was slightly higher than that of the unfilled amorphous PEEK coating, and the Young’s modulus was slightly lower, at 0.21 ± 0.02 and 3.7 ± 0.2 GPa, respectively.
Clavijo et al. [25] used PEEK powder with a particle size less than 25 mm and a co-solvent suspension containing 5% isopropyl alcohol and 95% ethanol. The distance between the electrodes was 2 cm. After EPD, the samples were slowly dried in the air for 24 h. After the electrophoretically deposited samples were sintered in the air at 350 °C for 30 min, a uniform PEEK coating was obtained on the stainless steel substrate. The rheological behavior and suspension structure of PEEK particles dispersed in co-solvents were studied under different pH values and shear rates, with pH = 8 being the optimal value.
Similarly, Fatih E et al. [26] also analyzed suspension composition and process parameters and prepared a PEEK-HA composite coating on a titanium substrate using electrophoretic deposition. HA was 4 wt.% in the optimal ratio, and 75 V was the optimal voltage. It was found that the addition of HA significantly improved the biocompatibility of the coating while maintaining the excellent mechanical properties of PEEK. The schematic diagram of EPD and deposition mechanism of PEEK-HA composite coating is shown in Figure 11.
PEEK coatings prepared by electrophoretic deposition have the advantages of smoothness, uniformity, and improved mechanical properties, but the stability of the suspension is key to the process, otherwise problems such as unevenness or particle aggregation occur, affecting the coating’s performance. The stability of the suspension mainly depends on the optimization and control of process parameters.

2.3. Melt Extrusion Coating

Melt extrusion coating is a method of heating a polymer material to a molten state and then coating it onto the surface of a substrate through an extruder. This technology can form a uniform and dense coating and is often used in anti-corrosion and insulation applications [27].
Yaragalla et al. [28] used melt extrusion technology to prepare graphene-reinforced PEEK composite wires. The prepared PEEK powder (particle size of about 1 mm) with or without deposited GnP filler was melt-mixed and extruded in a co-rotating twin-screw extruder. The temperature along the profile of the barrel was from 380 °C to 400 °C. The screw rotated at a speed of about 100 rpm and the outlet channel size was 3.30 mm. The extruded PEEK and PEEK-GnP nanocomposites, with a diameter of about 1.05 ± 0.04 mm, formed a strong interface between the filler and the matrix through hydrogen bonding and π–π* interactions. The mechanical properties of PEEK/GnP (GnP reached 1.0 wt.%) were significantly improved, with Young’s modulus and ultimate tensile strength reaching 2676 ± 166 MPa and 139 ± 11 MPa, respectively, which were increased by about 25% and about 34% (compared with pure PEEK), and the maximum elongation at the break reached 253 ± 8% (pure PEEK was 192 ± 13%).
Similarly, Tewatia et al. [29] added graphene to PEEK and prepared graphene-reinforced polymer matrix composites using high-shear melt processing. The content of double-layer/tri-layer graphene in polyetheretherketone (2Gn-PEEK and 5Gn-PEEK) was 2 wt.% and 5 wt.%, respectively, with good distribution and particle–matrix interaction. Adding graphene to PEEK induced surface crystallization and increased crystallinity. The flexural modulus of PEEK, 2Gn-PEEK, and 5Gn-PEEK remained constant at 3.8 GPa. For PEEK and 2Gn-PEEK, the stress at 5% strain remained constant at 129 MPa, but for 5Gn-PEEK, it dropped to 117 MPa. The storage modulus of PEEK and 5Gn-PEEK at room temperature (25 °C) increased from 1.36 GPa to 1.76 GPa, respectively, and the Tg of PEEK and 5Gn-PEEK increased from 152 °C to 166 °C, respectively.
Li et al. [30] compared the effects of carbon nanotubes (CNTs) and whiskers on the electrical and thermal conductivity of PEEK composites, and compared the effects of different mixing methods (i.e., dry mixing, wet mixing, and melt mixing). Among the three methods, it was found that melt mixing using twin-screw extrusion most easily obtained excellent mechanical, thermal stability, and electrical properties. Because the Wh-CNTs composite had high crystallinity, for a loading of 1 wt.% and above, the volume resistivity of the PEEK/Wh-CNTs composite was lower than that of the PEEK/c-MWCNTs composite. Pure PEEK has a higher volume resistivity of 1016 Ω·cm; however, at a higher CNT loading, the PEEK/Wh-CNTs composite had lower volume resistivity values at 3, 5, and 10 wt.%, which were approximately 1.42 × 107, 5.89 × 103, and 10.96 Ω·cm, respectively. The thermal conductivity of pure PEEK sheet is relatively low, at 0.232 W/(m·K). The thermal conductivity of the composite increased with the increase in CNT content. The thermal conductivity of the composite filled with Wh-CNTs was 0.44 and 0.741 W/(m·K) at 5 and 10 wt.% loading, respectively.
Li et al. [31] studied the effect of melt extrusion process parameters on the preparation of carbon fiber (CF)-PEEK composites. Based on PEEK and T800 carbon fibers with different melt flow rates (MFR), they prepared strong plastic synergistic CF/PEEK composites by adjusting melt fluidity and crystallization behavior. Physical blending was carried out in a twin-screw extruder at 380 °C to obtain a series of CF/PEEK composites with CF mass fractions of 0%, 10%, 20%, and 30%. The tensile strength of PEEK is about 100 MPa, while the tensile modulus is about 4 GPa. With the addition of CF, the tensile properties were significantly enhanced. At the same CF content, CF/PEEK composites with higher MFR values showed better tensile properties due to their high crystallinity. The tensile strength of CF/PEEK103-30% was as high as 303 MPa, and the tensile modulus as high as 40 GPa. PEEK103-30% had excellent flexural strength and modulus, reaching 453 MPa and 30 GPa, respectively.
Laser can also be used as a melting tool. Dahmen et al. [32] used laser melting of granular PEEK materials to study the influence of the surface morphology and preheating temperature of the substrate on the adhesion properties of the PEEK layer after laser melting, as well as the loss of base material hardness during the process. Curmi et al. [33] targeted PEEK viscosity factors and used screw extrusion technology to prepare PEEK materials of different viscosity grades by adjusting the viscosity of PEEK. They tested the interlayer shear strength and found that lower viscosity helped to improve the melting state. Lower material fluidity and interlayer fusion improved the interlayer shear strength. At lower MVR, the crystallinity decreased from 33% to 30% as the extruder temperature increased and the melt temperature increased.
Controlling temperature stability during the extrusion process is critical for the melting characteristics of the PEEK material and the performance of the final product. Comelli et al. [34] compared the effects of isothermal and non-isothermal processes on the melting behavior of PEEK. They measured the melting peak of PEEK under different extrusion conditions and analyzed its thermal behavior. They found that the melting peak of PEEK under isothermal conditions was different from under non-isothermal conditions. There were significant differences, with the former showing a more stable melting temperature and smaller changes in thermal behavior while the latter may lead to fluctuations in melting temperature and changes in material properties.
The melt extrusion process is a common method for preparing PEEK coatings. First, by heating PEEK to a molten state, the process can precisely control the thickness and shape of the coating to ensure a uniform coating effect. In addition, the melt extrusion process is suitable for large-scale industrial production, with high production efficiency and relatively low cost. By adding fillers such as graphene and carbon nanotubes, the thermal and mechanical properties of PEEK coatings prepared by the melt extrusion process can be significantly enhanced, making them suitable for application in high-temperature and high-strength environments. In addition, the viscosity control of PEEK has a direct impact on the interlayer shear strength, which is beneficial to improving the overall performance of the coating material.
However, the melt extrusion process also has some shortcomings. First of all, PEEK has a high melting temperature, strict equipment requirements, and high energy consumption. In addition, surface pretreatment is crucial for the adhesion of the coating; otherwise, it will easily lead to poor adhesion of the coating to the substrate. In summary, although the melt extrusion process is suitable for preparing high-performance PEEK coatings, it still needs further optimization to solve problems such as adhesion and energy consumption.
In summary, the advantage of thermal spraying methods (such as plasma spraying, flame spraying and high-pressure and high-speed oxygen–fuel spraying) is that they can prepare coatings with controllable thickness, which are suitable for large or complex workpieces and have good wear resistance and corrosion resistance. However, high temperatures may cause degradation of PEEK coatings and have adverse effects on the performance of the substrate. Plasma spraying is suitable for coatings that need to withstand high temperatures, while flame spraying optimizes the coating quality by adjusting the preheating temperature and the spray gun speed. High-pressure and high-speed oxygen–fuel spraying provides higher bonding strength and lower porosity, making it suitable for high-demand fields such as aerospace. The electrophoretic deposition method is suitable for processing workpieces with complex geometries. The coating is uniform and has strong adhesion. It is often combined with additives such as HA or TaN to improve biocompatibility and wear resistance. However, electrophoretic deposition has strict requirements in terms of pH and the solvent type in the suspension, affecting the flexibility of operation. The melt extrusion coating method has a wide range of applications. The interface bonding of the PEEK coating can be improved by adjusting the melt flow rate to improve the performance of the composite material. The disadvantage is that the temperature needs to be strictly controlled to prevent the coating’s performance from fluctuating.
In summary, various methods for preparing PEEK coatings have different advantages, disadvantages, and application scenarios. With the development of science and technology, new and efficient preparation processes are also being continuously studied, such as electrospinning and ultrasonic spraying.

3. Modification Technology for PEEK Coatings

Modification is usually used to improve the wear resistance and insulation properties of coatings. In PEEK coating modification technology, on the one hand, filler reinforcement can be used to improve the mechanical strength and wear resistance of PEEK coatings by adding fillers such as nanoparticles or glass fibers; on the other hand, chemical modification can be used to improve the surface adhesion, chemical resistance, and other properties of PEEK by introducing active groups or chemical treatment, so as to adapt to different application requirements [35].

3.1. Filler Reinforcement

Adding inorganic fillers such as silica (SiO2), alumina (Al2O3), or carbon nanotubes can improve the hardness, wear resistance, and thermal stability of coatings. This type of modification is usually used to improve the wear resistance and insulation properties of coatings [36].
Saeed et al. [37] mixed SiO2 particles with PEEK. The size of the nano-silica powder was 20–30 nm and the average size of the PEEK powder was 68.35 μm. The nano-silica powder was first modified with KH570 silane coupling agent, and PEEK-SiO2 composite materials were then prepared. It was found that adding 3% SiO2 to PEEK was the best choice. The PEEK/SiO2 composite material improved the hardness and compressive strength of PEEK while improving the thermal stability and wear resistance of the material. The average lateral strength reached 3503.02 MPa, which was a significant improvement compared with 2694.61 MPa for pure PEEK material.
Li et al. [38] prepared PEEK-based composites using PI as organic filler and h-BN and nano-SiO2 particles as inorganic fillers. Under conditions above the glass transition temperature, the tribological properties of PEEK were significantly improved; the friction coefficient of the composite material with a PI content of 20%, an h-BN content of 4%, and a nano-SiO2 content of 4% was stable at 0.06 at 200 °C, and the wear rate was 60% lower than that of PEEK. The infrared thermal images of the surface friction of peek and composite materials are shown in Figure 12.
Gu et al. [39] used a cold sintering process to prepare a silicon nitride (Si3N4)@SiO2/PEEK core–shell composite material with a SiO2 shell layer. The preparation process of the Si3N4@SiO2/PEEK composite material is shown in Figure 13. It was found that with the increase in the SiO2 shell thickness, the density of the composite material continued to increase, and the hardness first increased and then did not change much. The friction coefficient and wear rate of the Si3N4@SiO2/PEEK composite material with a SiO2 shell thickness of 50 nm were reduced by 15% and 80%, respectively, compared with the friction coefficient and wear rate of the SiO2 shell thickness of 12.5 nm.
Ahmed et al. [40] studied the addition of different types and contents of nano-SiO2 to PEEK and prepared PEEK/SiO2 composites. The introduction of 10 wt.% hydrophobic nano-SiO2 into the PEEK matrix improved the elastic modulus, flexural strength, and microhardness. The addition of a high content of nano-SiO2 filler (more than 10%) weakened the mechanical properties of the nanocomposite.
Chen et al. [41] introduced GO nanosheets as an interface enhancer to address the interface bonding problem between SiO2 and PEEK. Tests showed that the addition of SiO2 and GO greatly optimized the modulus, strength, and fracture toughness of the composite. The tensile strength and Young’s modulus of the PEEK/SiO2 composite increased with the increase in SiO2 content. When the SiO2 content was 30 wt.%, the maximum tensile strength and Young’s modulus of the PEEK/SiO2 composite were about 95.9 ± 0.6 MPa and 4.007 ± 0.005 GPa, respectively, 6.4% and 21.2% higher than those of pure PEEK. When the GO content was 1.5% wt, the maximum tensile strength and Young’s modulus of the PEEK/SiO2/GO composite further increased to about 101.5 ± 0.7 MPa and 4.62 ± 0.08 GPa, which were 12.6% and 39.4% higher than those of pure PEEK.
PEEK filler reinforcement is a technology that improves the performance of PEEK by adding different fillers (such as silica, hexagonal boron nitride, carbon nanotubes, etc.). Through the addition of these fillers, the mechanical properties, wear resistance, thermal stability, and biocompatibility of coatings have been significantly improved. For example, SiO2-reinforced PEEK composites have excellent mechanical properties and biocompatibility. The addition of h-BN and nano-SiO2 fillers can effectively improve the high-temperature friction performance of PEEK/PI-based composites. The mechanical properties of PEEK can also be enhanced by adding graphene oxide and SiO2, and the surface bioactivity is improved.
The mechanical properties, wear resistance, thermal stability and biocompatibility of PEEK coatings can be significantly improved through filler reinforcement. The addition of fillers such as nano-SiO2 and h-BN can effectively improve the high-temperature friction performance of the coating and extend its service life. In addition, fillers can also improve the surface wettability and adhesion of the coating, making it adaptable to a wider range of application environments. However, filler-reinforced PEEK coatings may have poor dispersibility, especially as the uniform dispersion of nano-scale fillers in the matrix is difficult to achieve, which may lead to uneven local performance. Secondly, the addition of fillers sometimes increases the brittleness of the material and reduces its toughness. In addition, the high cost of some fillers may limit their large-scale promotion in industrial applications.

3.2. Chemical Modification

The surface energy and adhesion properties of PEEK coatings can be improved by chemical methods such as graft copolymerization or surface functionalization. This method is often used to improve the adhesion between the coating and the substrate or improve the surface wettability [42].
Zimmerer et al. [43] used carboxylic acid and diamine for wet chemical modification of the PEEK surface. The synthesis route is shown in Figure 14. Different chemical groups were introduced into the PEEK surface through chemical reactions, which increased the surface energy and wettability and improved the bonding properties of PEEK with other materials.
Zhu et al. [44] addressed the problem of relatively weak interfacial strength between glass fiber (GF) and the polyetheretherketone (PEEK) matrix. By introducing dual compatibilizers of aminated PEEK and acylated carbon nanotubes (CNTs), they established an effective method to enhance the interfacial interaction between GF and the PEEK matrix. The preparation scheme is shown in Figure 15. This method helps to enhance the compatibility, multiple interactions, and mechanical interlocking between the fiber and the matrix. It was found that the interlaminar shear strength (ILSS), tensile strength, and modulus of the modified GF/PEEK composite material were significantly improved by 75% (~35 MPa), 23% (~338 MPa), and 12% (~18 GPa), respectively.
Xu et al. [45] chemically modified the PEEK surface by ultraviolet laser ablation and introduced different chemical functional groups. They found that the C=O and O–C=O bonds and the newly generated polar carboxylic acid groups changed significantly, changing the material’s surface wettability and enhancing its adhesion and interfacial properties. Lyu et al. [46] modified the PEEK surface by Friedel–Crafts acylation reaction and introduced carboxyl functional groups to enhance adhesion and biocompatibility. Elwathig et al. [47] and Bai et al. [48] both modified PEEK surfaces by grafting amino groups (NH2). The former focused on enhancing the interfacial adhesion between carbon fiber and PEEK, while the latter focused on improving the hydrophilicity and cell compatibility of PEEK. Bai et al. introduced -NH2 into the PEEK surface by sulfonation and halogenation reactions to achieve the purpose of PEEK amination. After EDA chemical grafting, the wettability of PEEK was significantly improved, and the water contact angle of SPEEK36-EDA was 44.97 ± 1.44°.
Chemical modification significantly improves the surface properties of PEEK, especially wettability and adhesion, and can effectively enhance the interfacial bonding with other materials. These modification methods are flexible and diverse, and the performance of the material can be customized by selecting appropriate chemical groups according to different application requirements. In addition, some methods such as amino grafting also improve the hydrophilicity and biocompatibility of PEEK, expanding its application in the biomedical field. Although chemical modification has obvious advantages, its processes are relatively complex and costly, especially when applied on a large scale in industry. Some chemical modification processes may introduce side reactions, affecting the performance of PEEK, such as reducing its heat resistance or mechanical strength. In addition, some wet chemical treatment processes may be environmentally unfriendly, the treatment agent must be carefully selected, and the reaction conditions must be controlled.
In summary, the modification technologies for PEEK coatings include filler reinforcement and chemical modification. These technologies each have their own unique advantages and scope of application. Selecting the appropriate modification method can optimize the performance of PEEK coatings according to different application requirements and meet the requirements of different fields.

4. Application of PEEK Coatings

PEEK coatings are widely used in the aerospace field, automotive industry, and electrical and electronic fields. In the aerospace field, where spacecraft operate in extreme environments, PEEK coatings can withstand high temperatures and corrosion, and PEEK’s electrical insulation properties make it suitable for insulation coating of various electronic equipment and cables to ensure safe and reliable operation [49]. In the automotive industry, PEEK coatings are widely used in high-performance components such as engine components, fuel systems, and electrical connectors. PEEK’s wear resistance and chemical stability ensure a long service life and can maintain performance under harsh working conditions [50]. In the electronic and electrical fields, PEEK coatings are often used due to their excellent electrical insulation properties and heat resistance. They are used for cable insulation, connectors, and circuit boards to prevent electrical short circuits and provide reliable protection in high-temperature environments. At the same time, PEEK’s chemical resistance makes it suitable for use in humid or corrosive environments, further improving its reliability in electronic equipment [51,52].

4.1. Aerospace

Due to its high heat resistance and chemical resistance, PEEK is widely used in insulation protection of aircraft engine components, fuselage structural parts, and avionics equipment.
PEEK materials can be used in aerospace for composite joints. Quan et al. [53] studied the fracture behavior of aerospace-grade PEEK composites and aluminum alloy bonded joints, pointing out that the PEEK coating played a key interface strengthening role between the composite materials and aluminum alloys. effect. The PEEK coating not only provided excellent durability, but also improved the crack resistance of the joints and was effectively able to resist interface separation due to stress concentration. In another study, Quan et al. explored the strong interaction between PEEK and thermoset resin composites. By forming a strong interface between thermoplastic materials and thermoset materials, high-performance composite connectors can be manufactured [54]. The development of this strong interaction is particularly important for complex structural parts in aerospace. PEEK coating plays a vital role in the bonding of composite materials, significantly improving the structural strength and thermal stability of joints, ensuring they maintain stable performance under harsh flight conditions. Kalra et al. [55] discussed the applicability of PEEK materials in the space environment, especially for application in spacecraft and antenna structures. They found that the PEEK coating performed very well in the space environment and could resist cosmic radiation, extreme temperature fluctuations, and material degradation under vacuum conditions.
PEEK material has an extremely high strength-to-weight ratio and is suitable for lightweight structural parts, which can reduce the overall weight of spacecraft and aircraft, thus improving fuel efficiency. In composite materials and metal joints, PEEK coating can significantly enhance the interface bonding force, provide excellent crack resistance, and ensure structural integrity and durability. PEEK materials can withstand the extreme environments in space, including strong radiation and vacuum environments, and are especially suitable for spacecraft and satellite structural parts.

4.2. Auto Industry

PEEK coatings have important applications in automotive engine components, fuel systems and electronic control systems because they provide excellent wear resistance and insulation.
Hastie et al. [56] studied the performance of carbon fiber-reinforced PEEK (CFRP/PEEK) drive shafts in high-temperature environments and found that the PEEK coating was effectively able to maintain its mechanical properties at high temperatures with significantly reduced weight, especially suitable for applications in high-temperature environments such as automotive components operating in extreme temperatures. Andrade et al. [57] studied the effect of PEEK surface treatment on friction and wear properties and found that the surface-treated PEEK coating could significantly reduce the friction coefficient and wear rate under lubricating conditions and extend the service life of components.
The application advantages of PEEK coating in the automotive industry are mainly due to its lightweight nature, high temperature resistance, and self-lubricating properties. Compared with traditional metal materials, PEEK can not only reduce the weight of cars but also improve the durability and reliability of components. In addition, PEEK’s excellent chemical resistance enables it to maintain stability in corrosive environments, such as high-temperature components in automotive engines and exhaust systems.

4.3. Electronics and Electrical

As an insulating material, PEEK coating is widely used in the protection of electronic components, especially in high-temperature and corrosive environments, such as motor insulation, circuit board protection, etc. As electronic equipment develops towards greater efficiency and lighter weight, PEEK coating has become the preferred material for applications in high-temperature and high-voltage environments.
Sun et al. [58] prepared a composite material with high thermal conductivity and electrical conductivity on a 3D PEEK/CF (carbon fiber) felt skeleton by electroplating a copper network. This technology significantly improved the thermal conductivity of the composite material and expanded the application of PEEK in heat dissipation and conductivity in electrical equipment. Niu et al. [59] studied the use of self-crosslinking polyetherimide and nanoparticles to adjust the high-temperature dielectric properties of PEEK. By synthesizing different PEEK composite materials, the dielectric strength can be improved without sacrificing mechanical strength, thereby enhancing application performance in high-temperature environments. Alimohammadi et al. [60] introduced a new piezoelectric bioactive nanocomposite in a sulfonated PEEK (SPEEK) matrix composed of dispersed polyvinylidene fluoride (PVDF) and containing nanohydroxyapatite (nHA) and carbon nanofiber (CNF) fillers for the preparation of coatings.
In the electronic and electrical industries, PEEK coating provides excellent insulation protection and heat dissipation performance by optimizing the thermal conductivity, electrical conductivity, and dielectric properties of materials. With the modification and development of composite materials such as copper-coated PEEK/CF composites, high-temperature dielectric materials, and bioactive coatings, PEEK coatings have been widely used. PEEK coating can effectively isolate current, protect electrical components, and improve heat dissipation capabilities by combining with conductive materials.

5. Conclusions

Through different modification technologies such as physical modification, chemical modification and composite material technology, the performance of PEEK has been significantly improved. These modification methods include adding fillers and surface modifications that significantly improve the heat resistance, corrosion resistance, mechanical properties, and biocompatibility of PEEK. PEEK coatings have been widely used in aerospace, medical equipment, the automotive industry, and electronic and electrical applications.
With the continuous advancement of materials science and engineering technologies, modification methods for PEEK will be further developed. For example, the application of nanotechnology, smart materials, and self-healing materials may further improve the performance of PEEK and make it stable under more extreme conditions. It is necessary to explore more environmentally friendly PEEK modification methods to reduce the impact on the environment during production and processing. At the same time, developing PEEK materials that are degradable or easier to recycle will be an important direction in future materials science. Future research is likely to focus on developing PEEK composites with multiple functions. For example, integrated sensing functions, adaptive functions that respond to environmental changes, etc., will bring higher-performance materials and more application possibilities to multiple industries.
The continuous improvement and application expansion of PEEK coating technology will promote technological progress and innovation in many fields. With the continuous development of science and technology, PEEK and its modified materials will play an important role in a wider range of fields.

Author Contributions

Conceptualization, Y.C. and J.-J.P.; writing—original draft preparation, Y.C. and S.L.; writing—review and editing, Y.C. and H.N. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD), Key R&D Projects of Jiangsu Province (BE2023765), Jiangsu Province Innovation Support Program (International Science and Technology Cooperation) Project (BZ2023002), Jiangsu Province Science and Technology Plan Special Fund (International Science and Technology Cooperation) Project (BZ2024048).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Pedroso, J.M.; Enger, M.; Bandeira, P.; Magalhães, F.D. Comparative Study of Friction and Wear Performance of PEK, PEEK and PEKK Binders in Tribological Coatings. Polymers 2022, 14, 4008. [Google Scholar] [CrossRef] [PubMed]
  2. Alam, F.; Varadarajan, K.M.; Koo, J.H.; Wardle, B.L.; Kumar, S. Additively Manufactured Polyetheretherketone (PEEK) with Carbon Nanostructure Reinforcement for Biomedical Structural Applications. Adv. Eng. Mater. 2020, 22, 2000483. [Google Scholar] [CrossRef]
  3. Wang, C.; Luan, J.; Xu, Z.; Zhao, W.; Zhang, M. Preparation and Properties of a Novel, High-Performance Polyether Ether Ketone Fabric. High Perform. Polym. 2018, 30, 794–802. [Google Scholar] [CrossRef]
  4. Jin, L.; Ball, J.; Bremner, T.; Sue, H.-J. Crystallization Behavior and Morphological Characterization of Poly(Ether Ether Ketone). Polymer 2014, 55, 5255–5265. [Google Scholar] [CrossRef]
  5. Goyal, R.K.; Tiwari, A.N.; Mulik, U.P.; Negi, Y.S. Thermal, Mechanical, and Dielectric Properties of High Performance PEEK/AIN Nanocomposites. J. Nanosci. Nanotechnol. 2009, 9, 6902–6909. [Google Scholar] [CrossRef]
  6. Liu, Z.; Wang, L.; Hou, X.; Wu, J. Investigation on Dielectrical and Space Charge Characteristics of Peek Insulation Used in Aerospace High-Voltage System. IEEJ Trans. Electr. Electron. Eng. 2020, 15, 172–178. [Google Scholar] [CrossRef]
  7. Ve, T.A.; Hestad, O.L.; Hvidsten, S. The Effect of Water Content on Time Domain Dielectric Response in Polyetheretherketone. IEEE Trans. Dielectr. Electr. Insul. 2023, 30, 501–508. [Google Scholar] [CrossRef]
  8. Chan, K.W.; Liao, C.Z.; Wong, H.M.; Yeung, K.W.K.; Tjong, S.C. Preparation of Polyetheretherketone Composites with Nanohydroxyapatite Rods and Carbon Nanofibers Having High Strength, Good Biocompatibility and Excellent Thermal Stability. RSC Adv. 2016, 6, 19417–19429. [Google Scholar] [CrossRef]
  9. Zhu, Y.; Cao, Z.; Peng, Y.; Hu, L.; Guney, T.; Tang, B. Facile Surface Modification Method for Synergistically Enhancing the Biocompatibility and Bioactivity of Poly(Ether Ether Ketone) That Induced Osteodifferentiation. ACS Appl. Mater. Interfaces 2019, 11, 27503–27511. [Google Scholar] [CrossRef]
  10. Zhang, Y.X.; Chen, X.H.; Li, J.; Li, C.M.; Li, X.; Gao, T.; Li, H.; Jing, T.T.; Liu, W. Tribological Properties of PEEK-Based Composite Coating Prepared by Thermal Spraying. Phys. Scr. 2023, 98, 055923. [Google Scholar] [CrossRef]
  11. Dupuis, A.; Ho, T.H.; Fahs, A.; Lafabrier, A.; Louarn, G.; Bacharouche, J.; Airoudj, A.; Aragon, E.; Chailan, J.-F. Improving Adhesion of Powder Coating on PEEK Composite: Influence of Atmospheric Plasma Parameters. Appl. Surf. Sci. 2015, 357, 1196–1204. [Google Scholar] [CrossRef]
  12. Wu, J.; Munroe, P.R.; Withy, B.; Hyland, M.M. Study of the Splat-Substrate Interface for a PEEK Coating Plasma-Sprayed onto Aluminum Substrates. J. Therm. Spray Technol. 2010, 19, 42–48. [Google Scholar] [CrossRef]
  13. Jiang, J.; Wang, Y.; Chi, Y.; Mao, X.; Dong, Y.; Yang, Y.; He, J.; Lu, X. Wear and Corrosion Resistance of TiN/PEEK Composite Coatings Fabricated by Gas Twin-Tunnel Plasma Spraying. J. Therm. Spray. Technol. 2023, 32, 1273–1285. [Google Scholar] [CrossRef]
  14. Cui, Y.; Hu, Z.; Ma, Y.; Yang, Y.; Zhao, C.; Ran, Y.; Gao, P.; Wang, L.; Dong, Y.; Yan, D. Porous Nanostructured ZrO2 Coatings Prepared by Plasma Spraying. Surf. Coat. Technol. 2019, 363, 112–119. [Google Scholar] [CrossRef]
  15. Tailor, S.; Vashistha, N.; Modi, A.; Modi, S.C. One-Step Fabrication of Thermal Sprayed Polymer Coating on Metals. Mater. Res. Express 2020, 7, 016425. [Google Scholar] [CrossRef]
  16. Tharajak, J.; Palathai, T.; Sombatsompop, N. Morphological and Physical Properties and Friction/Wear Behavior of h-BN Filled PEEK Composite Coatings. Surf. Coat. Technol. 2015, 273, 20–29. [Google Scholar] [CrossRef]
  17. Li, Y.; Wei, L.; Man, Z.; Liu, S.; Wang, S.; Lei, M. Mechanical and Tribological Properties of Carbon Fiber-reinforced Polyetheretherketone Composite Coatings by Flame-spraying Method. Polym. Compos. 2022, 43, 8443–8457. [Google Scholar] [CrossRef]
  18. Li, Y.; Man, Z.; Lin, X.; Wei, L.; Wang, H.; Lei, M. Role of Well-Dispersed Carbon Nanotubes and Limited Matrix Degradation on Tribological Properties of Flame-Sprayed PEEK Nanocomposite Coatings. J. Tribol. 2022, 144, 012101. [Google Scholar] [CrossRef]
  19. Soveja, A.; Sallamand, P.; Liao, H.; Costil, S. Improvement of Flame Spraying PEEK Coating Characteristics Using Lasers. J. Mater. Process. Technol. 2011, 211, 12–23. [Google Scholar] [CrossRef]
  20. Yu, J.; Liu, X.; Yu, Y.; Li, H.; Liu, P.; Huang, K.; Sun, R. Research and Application of High-Velocity Oxygen Fuel Coatings. Coatings 2022, 12, 828. [Google Scholar] [CrossRef]
  21. Patel, K.; Doyle, C.S.; Yonekura, D.; James, B.J. Effect of Surface Roughness Parameters on Thermally Sprayed PEEK Coatings. Surf. Coat. Technol. 2010, 204, 3567–3572. [Google Scholar] [CrossRef]
  22. Abdulkareem, M.H.; Abdalsalam, A.H.; Bohan, A.J. Influence of Chitosan on the Antibacterial Activity of Composite Coating (PEEK /HAp) Fabricated by Electrophoretic Deposition. Prog. Org. Coat. 2019, 130, 251–259. [Google Scholar] [CrossRef]
  23. Cao, L.; Zhang, P.; Li, S.; Wang, Q.; Zeng, D.; Yu, C.; Li, Q.; Liao, Y.; Lin, Z.; Li, W. Effects of TaN Nanoparticles on Microstructure, Mechanical Properties and Tribological Performance of PEEK Coating Prepared by Electrophoretic Deposition. Trans. Nonferrous Met. Soc. China 2022, 32, 3334–3348. [Google Scholar] [CrossRef]
  24. Kuśmierczyk, F.; Cieniek, Ł.; Kopia, A.; Zimowski, S.; Moskalewicz, T. Development and Characterization of Multilayered Cu/HA/ZnS + PEEK Coating System by Hybrid Technology. Met. Mater. Trans. A 2023, 54, 2803–2818. [Google Scholar] [CrossRef]
  25. Clavijo, S.; Membrives, F.; Boccaccini, A.R.; Santillán, M.J. Characterization of Polyetheretherketone Particle Suspensions for Electrophoretic Deposition. J. Appl. Polym. Sci. 2014, 131, 40953. [Google Scholar] [CrossRef]
  26. Baştan, F.E.; Atiq Ur Rehman, M.; Avcu, Y.Y.; Avcu, E.; Üstel, F.; Boccaccini, A.R. Electrophoretic Co-Deposition of PEEK-Hydroxyapatite Composite Coatings for Biomedical Applications. Colloids Surf. B Biointerfaces 2018, 169, 176–182. [Google Scholar] [CrossRef]
  27. Tseng, J.-W.; Liu, C.-Y.; Yen, Y.-K.; Belkner, J.; Bremicker, T.; Liu, B.H.; Sun, T.-J.; Wang, A.-B. Screw Extrusion-Based Additive Manufacturing of PEEK. Mater. Des. 2018, 140, 209–221. [Google Scholar] [CrossRef]
  28. Yaragalla, S.; Zahid, M.; Panda, J.K.; Tsagarakis, N.; Cingolani, R.; Athanassiou, A. Comprehensive Enhancement in Thermomechanical Performance of Melt-Extruded PEEK Filaments by Graphene Incorporation. Polymers 2021, 13, 1425. [Google Scholar] [CrossRef]
  29. Tewatia, A.; Hendrix, J.; Dong, Z.; Taghon, M.; Tse, S.; Chiu, G.; Mayo, W.E.; Kear, B.; Nosker, T.; Lynch, J. Characterization of Melt-Blended Graphene—Poly(Ether Ether Ketone) Nanocomposite. Mater. Sci. Eng. B 2017, 216, 41–49. [Google Scholar] [CrossRef]
  30. Li, S.; Wen, F.; Sun, C.; Wang, Z.; Chen, R.; He, Q.; Mu, J. A Comparative Study on the Influences of Whisker and Conventional Carbon Nanotubes on the Electrical and Thermal Conductivity of Polyether Ether Ketone Composites. J. Appl. Polym. Sci. 2021, 138, 50720. [Google Scholar] [CrossRef]
  31. Li, J.; Liu, H.; Wang, Y.; Wang, L.; Liu, G.; Chen, C.; Wei, L.; Li, H. Strength-Plasticity Synergetic CF/PEEK Composites Obtained by Adjusting Melt Flow Rate. Polymer 2024, 305, 127186. [Google Scholar] [CrossRef]
  32. Dahmen, M.; Vedder, C.; Speckens, M.; Stollenwerk, J.; Loosen, P. Influence of Surface Preheating and Pretreatment on the Adhesion of Laser-Melted PEEK to Aluminum Substrates. Surf. Coat. Technol. 2022, 448, 128922. [Google Scholar] [CrossRef]
  33. Curmi, A.; Rochman, A.; Buhagiar, J. Influence of Polyether Ether Ketone (PEEK) Viscosity on Interlayer Shear Strength in Screw Extrusion Additive Manufacturing. Addit. Manuf. 2024, 84, 104086. [Google Scholar] [CrossRef]
  34. Comelli, C.A.; Yi, N.; Davies, R.; Van Der Pol, H.; Ghita, O. Observation of Peek Melting Peaks within the Additive Manufacturing Material Extrusion Process in Relation to Isothermal and Non-Isothermal Processes. Macro Mater. Amp. Eng. 2024, 309, 2300386. [Google Scholar] [CrossRef]
  35. Keul, C.; Liebermann, A.; Schmidlin, P.; Roos, M.; Sener, B.; Stawarczyk, B. Influence of PEEK Surface Modification on Surface Properties and Bond Strength to Veneering Resin Composites. J. Adhes. Dent. 2014, 16, 383–392. [Google Scholar] [CrossRef]
  36. Doumeng, M.; Berthet, F.; Delbé, K.; Marsan, O.; Denape, J.; Chabert, F. Effect of Size, Concentration, and Nature of Fillers on Crystallinity, Thermal, and Mechanical Properties of Polyetheretherketone Composites. J. Appl. Polym. Sci. 2022, 139, 51574. [Google Scholar] [CrossRef]
  37. Saeed, H.M.; Jassim, R.K. Characterization and Assessment of PEEK/Silicon Dioxide Composite. Int. J. Dent. 2023, 2023, 3343071. [Google Scholar] [CrossRef]
  38. Li, M.; Yang, J.; Ma, S.; Liu, G.; Yang, H.; Yao, J. Effect of h-BN and Nano-SiO2 Fillers on the High-Temperature Tribological Properties of PEEK/PI-Based Composites. Lubricants 2023, 11, 416. [Google Scholar] [CrossRef]
  39. Gu, D.; Wang, G.; Chen, X.; Liu, Z.; Chen, S.; Xie, H. SiO2 Shell Thickness Affects the Tribological Properties of Si3N4@SiO2/PEEK Core–Shell Composite Prepared by Cold Sintering. Mater. Lett. 2023, 345, 134488. [Google Scholar] [CrossRef]
  40. Abd El-Fattah, A.; Youssef, H.; Gepreel, M.A.H.; Abbas, R.; Kandil, S. Surface Morphology and Mechanical Properties of Polyether Ether Ketone (PEEK) Nanocomposites Reinforced by Nano-Sized Silica (SiO2) for Prosthodontics and Restorative Dentistry. Polymers 2021, 13, 3006. [Google Scholar] [CrossRef]
  41. Chen, C.; Meng, L.; Hu, Y.; Su, Z.; Zhang, T.; Ouyang, Z.; Li, W.; Wan, J.; Wu, Q. Graphene Oxide-Reinforced Poly (Ether-Ether-Ketone)/Silica Composites with Improved Mechanical Performance and Surface Bioactivity. J. Mech. Behav. Biomed. Mater. 2021, 124, 104811. [Google Scholar] [CrossRef]
  42. Almasi, D.; Izman, S.; Assadian, M.; Ghanbari, M.; Abdul Kadir, M.R. Crystalline Ha Coating on Peek via Chemical Deposition. Appl. Surf. Sci. 2014, 314, 1034–1040. [Google Scholar] [CrossRef]
  43. Zimmerer, C.; Schwind, M.; Putzke, S.; Frenzel, R.; Drechsler, A.; Simon, F. Surface Functionalization of Poly(Ether Ether Ketone) by Wet-Chemical Modification with Carboxylic Acids and Diamine. J. Adhes. Sci. Technol. 2024, 38, 139–162. [Google Scholar] [CrossRef]
  44. Zhu, S.; Qian, Y.; Hassan, E.A.M.; Shi, R.; Yang, L.; Cao, H.; Zhou, J.; Ge, D.; Yu, M. Enhanced Interfacial Interactions by PEEK-Grafting and Coupling of Acylated CNT for GF/PEEK Composites. Compos. Commun. 2020, 18, 43–48. [Google Scholar] [CrossRef]
  45. Xu, P.; Zhu, F.; Wang, X.; Zhang, J.; Sun, T. Roles of Chemistry Modification for Surface Wettability of Polyether-Ether-Ketone (PEEK) by Ultraviolet Laser Ablation. Mater. Res. Express 2023, 10, 065304. [Google Scholar] [CrossRef]
  46. Lyu, X.; Kanda, R.; Tsuda, S.; Hashimoto, Y.; Fujii, T.; Kashiwagi, K. Novel Carboxylation Method for Polyetheretherketone (PEEK) Surface Modification Using Friedel–Crafts Acylation. Int. J. Mol. Sci. 2023, 24, 15651. [Google Scholar] [CrossRef]
  47. Hassan, E.A.; Elagib, T.H.; Memon, H.; Yu, M.; Zhu, S. Surface Modification of Carbon Fibers by Grafting PEEK-NH2 for Improving Interfacial Adhesion with Polyetheretherketone. Materials 2019, 12, 778. [Google Scholar] [CrossRef]
  48. Bai, J.; Ding, R.; Wang, Y.; Chen, T.; Xu, Q.; Feng, B.; Duan, K.; Zhi, W.; Weng, J.; Wang, J. Surface Modification of Polyetheretherketone by Grafting Amino Groups to Improve Its Hydrophilicity and Cytocompatibility. Mater. Res. Express 2019, 6, 115413. [Google Scholar] [CrossRef]
  49. Gu, D.; Wang, Z.; Liu, K.; Xu, M.; Chen, S.; Li, Z.; Tang, Z.; Wang, S. Textured Surfaces Preparation and Tribological Properties of PTFE/PMMA and PEEK/PMMA Composites With Steel Spheres Embedded on Their Surfaces. Tribol. Trans. 2022, 65, 901–911. [Google Scholar] [CrossRef]
  50. Li, J.; Dong, H.; Tang, Z.; Li, P.; Wu, B.; Ma, Y.; Huang, L.; Zhang, L.; Li, C.; Xiong, J. Influence of Surface Pretreatment on the Bonding Mechanism and Mechanical Properties of AA5052/CFRP Friction Stir Spot Welded Joint. J. Manuf. Process. 2023, 105, 112–123. [Google Scholar] [CrossRef]
  51. Xu, Z.; Hui, J.; Lv, J.; Wei, D.; Yan, Z.; Zhang, H.; Wang, J. An Investigation of Methods to Enhance Adhesion of Conductive Layer and Dielectric Substrate for Additive Manufacturing of Electronics. Sci. Rep. 2024, 14, 10351. [Google Scholar] [CrossRef]
  52. Goyal, R.K.; Rokade, K.A.; Kapadia, A.S.; Selukar, B.S.; Garnaik, B. PEEK/SiO2 Composites with High Thermal Stability for Electronic Applications. Electron. Mater. Lett. 2013, 9, 95–100. [Google Scholar] [CrossRef]
  53. Quan, D.; Wang, G.; Zhao, G.; Alderliesten, R. On the Fracture Behaviour of Aerospace-Grade Polyether-Ether-Ketone Composite-to-Aluminium Adhesive Joints. Compos. Commun. 2022, 30, 101098. [Google Scholar] [CrossRef]
  54. Quan, D.; Ma, Y.; Yue, D.; Liu, J.; Xing, J.; Zhang, M.; Alderliesten, R.; Zhao, G. On the Application of Strong Thermoplastic–Thermoset Interactions for Developing Advanced Aerospace-Composite Joints. Thin-Walled Struct. 2023, 186, 110671. [Google Scholar] [CrossRef]
  55. Kalra, S.; Munjal, B.S.; Singh, V.R.; Mahajan, M.; Bhattacharya, B. Investigations on the Suitability of PEEK Material under Space Environment Conditions and Its Application in a Parabolic Space Antenna. Adv. Space Res. 2019, 63, 4039–4045. [Google Scholar] [CrossRef]
  56. Hastie, J.C.; Guz, I.A.; Kashtalyan, M. Response of Carbon/PEEK Automotive Driveshafts with/without an Inner Isotropic Layer at High Temperature Considering Temperature-Dependent Material Properties. Proc. Inst. Mech. Eng. Part. L J. Mater. Des. Appl. 2023, 237, 1406–1415. [Google Scholar] [CrossRef]
  57. Andrade, T.F.D.; Wiebeck, H.; Sinatora, A. Effect of Surface Finishing on Friction and Wear of Poly-Ether-Ether-Ketone (PEEK) under Oil Lubrication. Polímeros 2016, 26, 336–342. [Google Scholar] [CrossRef]
  58. Sun, Y.; Zhang, M.; Zhang, Y.; Luan, J.; Dang, H.; Jiang, D.; Yang, Y. Fabrication of High Thermal and Electrical Conductivity Composites via Electroplating Cu Network on 3D PEEK/CF Felt Skeletons. Compos. Commun. 2021, 28, 100909. [Google Scholar] [CrossRef]
  59. Niu, S.; Bai, X.; Cheng, Y.; Qin, H.; Zhang, Y.; Jiang, Z. Tuning High-Temperature Dielectric Properties of Poly Ether Ether Ketone by Using Self-Crosslinkable Polyetherimide and Nanoparticles. Polym. Test. 2023, 117, 107858. [Google Scholar] [CrossRef]
  60. Alimohammadi, M.; Ramazani, S.A. Surface Modification of Polyether Ether Ketone Implant with a Novel Nanocomposite Coating Containing Poly (Vinylidene Fluoride) toward Improving Piezoelectric and Bioactivity Performance. Colloids Surf. B Biointerfaces 2023, 222, 113098. [Google Scholar] [CrossRef]
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Figure 1. Chemical structure of PEEK.
Figure 1. Chemical structure of PEEK.
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Figure 2. Annual publications of papers on various PEEK-related topics.
Figure 2. Annual publications of papers on various PEEK-related topics.
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Figure 3. SEM images of plasma-sprayed splats from the BT (a), ET (b), and PT (c) substrate surface held at 23 °C [12].
Figure 3. SEM images of plasma-sprayed splats from the BT (a), ET (b), and PT (c) substrate surface held at 23 °C [12].
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Figure 4. Schematic diagram of twin-tunnel powder feeding [13].
Figure 4. Schematic diagram of twin-tunnel powder feeding [13].
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Figure 5. SEM images of h-BN/PEEK composites: (a) 2 wt.% h-BN, particle size of 0.1 μm, (b) 2 wt.% h-BN, particle size of 1.5 μm, (c) 8 wt.% h-BN, particle size of 0.1 μm, and (d) 8 wt.% h-BN, particle size of 1.5 μm [16].
Figure 5. SEM images of h-BN/PEEK composites: (a) 2 wt.% h-BN, particle size of 0.1 μm, (b) 2 wt.% h-BN, particle size of 1.5 μm, (c) 8 wt.% h-BN, particle size of 0.1 μm, and (d) 8 wt.% h-BN, particle size of 1.5 μm [16].
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Figure 6. Friction coefficient and specific wear rate of flame-sprayed neat PEEK coatings and flame-sprayed CNT/PEEK nanocomposite composite coatings using MB and UD powders with different CNT contents [18]. (a,b) show the friction coefficient curves of flame-sprayed neat PEEK coatings and flame-sprayed CNTs/PEEK nanocomposite composite coatings using MB and UD powders with different CNT contents during the sliding time of 120 min. (c,d) show the friction coefficient and the specific wear rate of flame-sprayed neat PEEK coatings and flame-sprayed CNTs/PEEK nanocomposite composite coatings using MB and UD powders with different CNT contents.
Figure 6. Friction coefficient and specific wear rate of flame-sprayed neat PEEK coatings and flame-sprayed CNT/PEEK nanocomposite composite coatings using MB and UD powders with different CNT contents [18]. (a,b) show the friction coefficient curves of flame-sprayed neat PEEK coatings and flame-sprayed CNTs/PEEK nanocomposite composite coatings using MB and UD powders with different CNT contents during the sliding time of 120 min. (c,d) show the friction coefficient and the specific wear rate of flame-sprayed neat PEEK coatings and flame-sprayed CNTs/PEEK nanocomposite composite coatings using MB and UD powders with different CNT contents.
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Figure 7. AFM surface scan and surface profile of degreased substrate [21].
Figure 7. AFM surface scan and surface profile of degreased substrate [21].
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Figure 8. AFM surface scan and surface profile of etched substrate [21].
Figure 8. AFM surface scan and surface profile of etched substrate [21].
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Figure 9. Cross-section SEM images (a,c) and corresponding EDX elemental mappings (b,d,e) of PEEK (a,b) and P-TN-3 (c–e) coatings [23].
Figure 9. Cross-section SEM images (a,c) and corresponding EDX elemental mappings (b,d,e) of PEEK (a,b) and P-TN-3 (c–e) coatings [23].
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Figure 10. Scheme of particular stages of multilayer Cu/HA/ZnS+PEEK coating fabrication [24].
Figure 10. Scheme of particular stages of multilayer Cu/HA/ZnS+PEEK coating fabrication [24].
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Figure 11. Schematic diagram of EPD and deposition mechanism of PEEK-HA composite coating [26].
Figure 11. Schematic diagram of EPD and deposition mechanism of PEEK-HA composite coating [26].
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Figure 12. Infrared thermal image of peek and surface friction of composite materials at 0 min, 40 min, 80 min: (a–c) PEEK, (d–f) +20P (g–i) +20P/4B/2Si [38].
Figure 12. Infrared thermal image of peek and surface friction of composite materials at 0 min, 40 min, 80 min: (a–c) PEEK, (d–f) +20P (g–i) +20P/4B/2Si [38].
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Figure 13. Schematic of the preparation of Si3N4@SiO2/PEEK composites [39].
Figure 13. Schematic of the preparation of Si3N4@SiO2/PEEK composites [39].
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Figure 14. Synthetic routes to endow PEEK surfaces with aliphatic functionalization (PEEK-Ac) and carboxylic end groups (PEEK-COOH) or primary amino groups (PEEK–EDA) [43].
Figure 14. Synthetic routes to endow PEEK surfaces with aliphatic functionalization (PEEK-Ac) and carboxylic end groups (PEEK-COOH) or primary amino groups (PEEK–EDA) [43].
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Figure 15. Schemes for preparation of GF/PEEK based on interfacial modifications of GF [44].
Figure 15. Schemes for preparation of GF/PEEK based on interfacial modifications of GF [44].
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Table 1. Intensity ratios (IC=O/IC=C) of FTIR peaks at 1707–1598 cm−1, glass transition temperature (Tg), melting temperature (Tm), crystallinity degree (Xc), and crystallite size (dp) of PEEK powders, flame-sprayed pure PEEK coatings and flame-sprayed CF/PEEK composite coatings [17].
Table 1. Intensity ratios (IC=O/IC=C) of FTIR peaks at 1707–1598 cm−1, glass transition temperature (Tg), melting temperature (Tm), crystallinity degree (Xc), and crystallite size (dp) of PEEK powders, flame-sprayed pure PEEK coatings and flame-sprayed CF/PEEK composite coatings [17].
SampleCF Size (Mesh)CF Content (wt.%)IC=O/IC=CTg (°C)Tm (°C)Xc (%)dp (nm)
PEEK powder 0147.1343.444.217
Pure PEEK coating--0.2155.3334.645.3416
CF/PEEK coating300100.14151.4335.742.2411
CF/PEEK coating300300.1153.8335.426.9510
CF/PEEK coating600100.16150.7335.735.911
CF/PEEK coating600300.22157.3334.832.514
Table 2. Process parameters of three thermal spraying methods.
Table 2. Process parameters of three thermal spraying methods.
TypeData
ResearcherWuJiangSovejaTharajakLiPatel
Current/A150420----
Gas Flow RatesN2:40 SLPMArgon: 60–80 L/h, N2: 0.5 g/minAcetylene:6 L/min, Oxygen: 16 L/minOxygen: 47.34 L/min (60 psi), Propane: 27.70 L/min (65 psi), Nitrogen: 160 psi--
Spray Distance/mm80100140120-280
Powder Feed Rate10–20 g/minTi: 0.9 g/min, PEEK: 0.1 g/min35 L/min12 g/min--
Preheating Temperature/°C~23--200200-
Spray Gun Speed /mm s−1--15080300300
“-”: not mentioned in the researcher’s publication.
Table 3. Advantages, disadvantages, and application scenarios of thermal spraying.
Table 3. Advantages, disadvantages, and application scenarios of thermal spraying.
MethodAdvantagesApplicable ScenariosLimitations
Plasma sprayingCan reach extremely high temperatures, suitable for melting high-melting-point materials.Where uniform thickness and high-density coating are required.Complex equipment and high cost.
PEEK powder is deposited evenly, providing good bonding strength and wear resistance.Suitable for precision parts in aerospace and electronic equipment.Requires high technical level to operate.
Flame sprayingSimple equipment and low cost.Widely used in the automotive industry and general industrial equipment.The coating bonding strength and density are lower than other methods.
Suitable for coating requirements of large-area substrates.Suitable for wear-resistant and corrosion-resistant coatings with low requirements.Not suitable for extreme environment applications.
HVOF sprayingHigh particle velocity, resulting in dense, highly adhesive coatings.Parts requiring high wear resistance and low friction in mechanical engineering.High equipment costs.
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Chen, Y.; Ni, H.; Park, J.-J.; Lv, S. A Review of the Preparation, Modification, and Applications of Polyetheretherketone Coating. Coatings 2024, 14, 1451. https://doi.org/10.3390/coatings14111451

AMA Style

Chen Y, Ni H, Park J-J, Lv S. A Review of the Preparation, Modification, and Applications of Polyetheretherketone Coating. Coatings. 2024; 14(11):1451. https://doi.org/10.3390/coatings14111451

Chicago/Turabian Style

Chen, Yufei, Hongjun Ni, Jae-Jun Park, and Shuaishuai Lv. 2024. "A Review of the Preparation, Modification, and Applications of Polyetheretherketone Coating" Coatings 14, no. 11: 1451. https://doi.org/10.3390/coatings14111451

APA Style

Chen, Y., Ni, H., Park, J. -J., & Lv, S. (2024). A Review of the Preparation, Modification, and Applications of Polyetheretherketone Coating. Coatings, 14(11), 1451. https://doi.org/10.3390/coatings14111451

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