Preparation and performance of CNTs-enhanced PEEK-based porous composites based on FDM

Abstract:With its unique pore structure, porous composites can effectively store and release lubricating media, providing a functional basis for continuous lubrication for self-lubricating bearing cages. For high-performance bearing cage materials, it is necessary to solve the mechanical strength that meets the service requirements and have excellent tribological properties. Carbon nanotubes (CNTs)/polyether ether ketone (PEEK) porous self-lubricating bearing cage composites are prepared based on fused deposition molding (FDM) technology, and the preparation process, microstructure, mechanical properties and friction properties of CNTs/PEEK porous composites are explored. The results show that CNTs-enhanced PEEK-based porous composites by FDM molding process are feasible. The introduction of CNTs can effectively regulate the structure of PEEK-based porous materials, increasing the average pore size from 0.08 μm to 11.62 μm, and optimizing the porosity. With the increase of CNTs, the mechanical properties of porous materials increase first and then decrease. CNTs effectively improve the frictional properties of PEEK-based porous materials and ensure their excellent mechanical properties, providing a theoretical basis and process optimization guidance for the controllable preparation of high-performance self-lubricating bearing cages.

Key words: FDM; CNTs/PEEK； bearing cage; porous composites; mechanical properties; Frictional properties

introduction

The rapid development of high-speed rail, aviation, aerospace and other fields has made the service performance of high-end sports equipment develop to a worse and more extreme status quo [1]. As the supporting part of high-end moving parts, the performance of bearings and bearing units directly determines the service life of equipment. Studies have shown that bearing lubrication failure is an important cause of equipment failure, such as dozens of satellite failure cases caused by lubrication failure of bearing components [2]. In 2005, a flight accident occurred on a certain type of aircraft, and the cause of the accident was the wear of the raceway of the spindle bearing and the fracture of the cage, resulting in the failure of the shaft [3]. These cases highlight the limitations of traditional lubrication technology in high-end sports equipment applications.

Scholars generally believe that the preparation of cages based on porous self-lubricating materials can provide an opportunity to solve the above questions. When the bearing is running, the self-lubricating effect of the friction pair can be achieved under the synergistic action of centrifugal force, temperature rise and other factors, so as to achieve the purpose of reducing friction and anti-wear [4-6], and common types of self-lubricating materials such as polymers (polyether ether ketone PEEK, polytetrafluoroethylene PTFE, polyimide PI, etc.), metal-based (such as copper-based composites, iron-based composites, etc.), and ceramic-based (silicon carbide, silicon nitride, etc.) [7]. As a semi-crystalline high-performance thermoplastic polymer, polyether ether ketone (PEEK) is widely used in aerospace, medical devices, and energy fields due to its excellent mechanical properties, high temperature resistance, and chemical stability.

For the performance study of PEEK matrix composites, carbon nanotubes (CNTs) are often used as reinforcing fillers due to their high length-to-diameter ratio and excellent mechanical properties [12]. Studies have shown that the comprehensive performance of composites can be effectively improved by filling them into a polyether ether ketone (PEEK) matrix through reasonable surface treatment [13-14]. ATA et al. [15] studied the mechanical properties of CNT-enhanced PEEK and found that when the CNT content was 5 wt%, the tensile strength of the composite reached 112 MPa, which was about 24% higher than that of pure PEEK (~90 MPa). Hou et al. [16] compared the performance of carbon nanotubes (CNTs) to enhance PEEK under different molding processes. Under the condition of compression molding, when the CNTs content was 4 wt%, the flexural strength of the composite reached 338.5 MPa, which was significantly higher than that of pure PEEK (230.4 MPa) by 46.9%. ）。 Under injection molding conditions, when the CNTs content was 4 wt%, the tensile strength (101.09 MPa) was 23% higher than that of pure PEEK (82.19 MPa), and the flexural strength (280.65 MPa) was 37.7% higher than that of pure PEEK (203.88 MPa). Ye et al. [17] used 3D printing technology to prepare CNTs/PEEK composites, and their tensile strength reached 107.7 MPa, which was 27.4% higher than that of pure PEEK materials. The above studies confirm that CNTs can effectively improve the mechanical properties of PEEK matrix composites as reinforcing phases. However, none of these studies addressed the performance of porous CNTs/PEEK composites.

At present, the mainstream preparation processes of porous self-lubricating bearing materials are cold-pressed sintering and template-filtration methods. FDM technology is one of the most commonly used printing technologies in additive manufacturing (also known as 3D printing) technology, which constructs three-dimensional objects by depositing molten materials layer by layer, which allows for flexible adjustment of material components and printing parameters during the manufacturing process, providing the possibility of customization and optimization of high-performance composites [18-20] 。

In this study, carbon nanotubes (CNTs) reinforced polyether ether ketone (PEEK)-based porous self-lubricating bearing cages were prepared by melt deposition-washing method. On this basis, the porous self-lubricating bearing cage material is prepared by FDM. Based on the previous study of the sample combination with excellent comprehensive performance (50% NACL pore-forming agent + 50% PEEK) [21-23], the microstructural evolution of porous self-lubricating materials under different preparation parameters and their influence on mechanical and frictional properties were systematically studied It provides a theoretical basis for the integrated design and preparation of structure-performance of porous self-lubricating bearing cage materials.

Preparation of CNTs-enhanced PEEK-based porous materials

2.1 Preparation of composite wire

Compound powder pretreatment

In order to enhance the interface bonding performance between CNTs and matrix materials and avoid the agglomeration of CNTs in porous parts affecting the porous effect, the powder was pretreated with surface modification, particle size control, dispersion optimization and other pretreatments.

PEEK powder is produced by Jilin Warnert Polymer Co., Ltd., with a particle size of 200 mesh, a density of 1.3g/cm3, and a melting point of 334°C. CNTs (TNMC7 type) are produced by Chengdu Zhongke Times Nanneng Technology Co., Ltd., and the main parameters are listed in Table 1. Sodium chloride powder is produced by Shanghai Maclean's Biochemical Co., Ltd., with a density of 2.1g/cm3, a melting point of 804°C, and sodium chloride through a 325-mesh sieve.

Table 1 Main parameters of CNTs

The pretreatment steps for CNTs are as follows: the CNTs are cleaned with acetone reflux, rinsed with ethanol and dried at 120°C to reduce the interference of sizing agents and dust on the surface. Then the CNTs were dispersed ultrasonically for 5h to improve the dispersion of the CNTs, and they were placed in an oven to dry for later use.

The nano calcium carbonate was modified for later use, the water bath was heated to 90°C after 30 minutes of ultrasonic dispersion of nano calcium carbonate with deionized water, the heated and melted sodium stearate was added to the slurry, the reaction was maintained at 90 °C for 2h and filtered, the filter cake was washed with hot anhydrous ethanol solution, and dried, ground and sifted.

Table 2The main components of porous materials are ratios and sample numbers

The specific PEEK/NaCl mass ratio and CNTs addition are listed in Table 2, according to which the appropriate amount of NaCl and PEEK powder (both were pre-dried at 120°C for 12h). The pretreated CNTs were weighed and dried in an oven at 80°C for 6h. Weigh cyclohexane 1,2-dicarboxylate diisononyl ester and modified nano calcium carbonate at 0.5wt% and 1wt% of the total mass of the composite powder PEEK/NaC. PEEK/CNTs/NaCl were mixed with additive powder (cyclohexane 1,2-dicarboxylate, modified nano calcium carbonate), mixed well in a ball mill for 8 hours, and the mixed powder was placed in an oven and dried at 120°C for 10 hours.

Preparation of composite filaments

The temperature of each section of the twin screw extruder is adjusted by the melt blend extrusion process, taking the preparation of the CN3#-1 sample corresponding to the composite wire as an example, and the temperature of each section of the twin screw extruder is shown in Table 3. The prepared wire is stored at 60°C.

Table 3 Temperature settings of each heating zone of twin screw extruder

Preparation of porous samples

The FDM process parameters using FDM rapid prototyping machine (ENGINEER Q300, Shaanxi Jugao Additive Intelligent Manufacturing Technology Development Co., Ltd., Weinan, China) are as follows: nozzle diameter is 1.0mm, nozzle temperature is 420°C, printing speed is 30mm/s, printing layer thickness is 0.2mm, and the sample prepared is shown in Fig. 1.

Figure 1Print molded specimens

NACL pore-forming agent removal

The samples were placed in the ultrasonic cleaner for 48 h, during which they were electrically stirred to remove the internal porogenic Nacl, and the samples were removed from the oven for 5 h to dry at low temperature.

2.2 Performance testing

Structural features

The filamentation and printing properties of CNTs/PEEK composite powders were observed, the macroscopic morphology of the filaments was observed by optical microscope, and the micromorphology of CNTs-enhanced PEEK matrix composites was observed by laser scanning confocal microscope (LSCM, Zeiss-LSM800, Chernenko, Germany). The internal Nacl removal effect of the sample was tested using field emission scanning electron microscopy (EDS, Tokyo Electron JSM-IT800 type). The pore size and porosity distribution of CNTs-enhanced PEEK porous samples were tested using a mercury pore size meter (Mike, Autopore IV 950).

High temperature tribological performance test

The friction and wear properties of the material under dry friction conditions were tested using a high-temperature friction and wear testing machine (Lanzhou Zhongke Kaihua Technology Development Co., Ltd., HT-1000 type, Lanzhou, China). The test conditions were set as follows: the diameter of the grinding ball was 5 mm, the steel ball material was 9Cr18, the application load was 5 N, the friction radius was 5 mm, the rotation speed was set to 392 r/min, and the test time was 30 min.

Mechanical Properties Test

To study the mechanical properties of CNTs-enhanced PEEK porous samples, the Shore hardness tester (type TIME5410) was used. The flexural strength and tensile strength of porous PEEK materials were tested by electronic universal testing machine (Sansi vertical and horizontal UTM5305 type). The mechanical property test standards of the samples are shown in Table 4.

Table 4. Mechanical property test standards

outcome

3.1 Preparation performance of composite wire

Composite preparation properties

The preparation of composite powder melt blend extrusion and FDM printing were observed (Table 4 and Table 5).

Table 4 shows that the extrusion performance of composite wire shows a decreasing trend with the increase of CNTs content. This is due to the higher the proportion of CNTs, the higher the viscosity of the composite melt, and the worse its extrusion fluidity. In addition, the addition of CNTs changes the rheological properties of the composites, making their non-Newtonian fluid properties more pronounced, resulting in poor fluidity.

Table 4Composite wire extrusion performance with different CNTs content

Table 5 shows that the increase of CNTs content will affect the printing process and the surface quality of the printed parts, which is manifested as follows: the smoothness of wire feed and output is decreasing, and the surface of the printed part is rough. The addition of CNTs changes the thermal expansion coefficient, shrinkage rate and other properties of the material, so that the material cannot shrink or expand uniformly during the molding process, resulting in warping. In this regard, the substrate modification technology is used to use the glass base plate and lay stickers to improve the adhesion between the printing layer and the base plate to avoid warping.

Table 5 Printing performance of composites with different CNTs content

3.2 Macroscopic and microscopic morphology of composite filaments

Macroscopic morphology of composite wire

The surface morphology and fracture morphology of the composite filament were observed by optical microscope (Fig. 2 and Fig. 3).

It can be seen from Fig. 2 that when the content of NACL and PEEK is 1:1, the roughness of the surface of the filament increases significantly and affects the FDM printing performance. In addition, the winding performance of the wire and the controllability of wire diameter also deteriorate with the introduction of CNTs. The reasons for the above phenomenon are roughly as follows: the introduction of CNTs makes the flow performance of composites worse, and the agglomeration phenomenon is more serious when the mass fraction of CNTs is 3%, which also makes itThe roughness of the wire increases, and the flexibility becomes poor.

The mass fraction of CNTs was 0.5%	The mass fraction of CNTs is 1%	The mass fraction of CNTs is 3%

Figure 2Surface morphology of composite wires under different CNTs mass fractions

The mass fraction of CNTs was 0.5%	The mass fraction of CNTs is 1%	The mass fraction of CNTs is 3%

Figure 3Fracture morphology of the wire under different CNTs mass fractions

It can be seen from Fig. 3 that the bulge, hole size and distribution of the wire fracture morphology under different CNTs mass fractions are relatively uniform.

Micromorphology of CNTs-enhanced PEEK-based porous materials

CNTs-enhanced PEEK porous structures were analyzed using a laser confocal scanning analyzer and scanning electron microscopy (Figure 4), followed by EDS analysis of the elemental content of porous samples removed from Nacl preparation (Figure 5). Finally, the microstructural parameters (pore size, porosity) of porous PEEK materials were tested using mercury intrusion assay (Fig. 6).

The microscopic pore distribution and pore size inside the porous material are the key factors affecting its macroscopic properties, and the results from Fig. 4 show that NACL is originally a CNTs-enhanced PEEK porous structure with uniform pore distribution and good connectivity between pores, which indicates that the excellent pore formation ability of NaCl as a pore-forming agent is not affected by the introduction of CNTs. This is due to the excellent pore formation ability of NACL and the uniform size of NACL particles after screening, which can be used to prepare composites with rich pores and controllable pore size.

(a) The mass fraction of CNTs was 0.5%
(b) CNTs mass fraction of 1%
(c) The mass fraction of CNTs is 3%

Figure 4Microscopic morphology of porous materials

0.5wt%	1wt%	3wt%

Figure 5. EDS analysis results of samples with different CNTs mass fractions

After EDS analysis, as shown in Fig. 5, the pore forming agent NaCl was basically completely removed by the water solubility method under laboratory conditions, indicating that the introduction of CNTs did not affect the removal of NaCl inside the porous PEEK material, and the CNTs-enhanced PEEK porous composites could effectively avoid the residual effect of the porous agent, ensuring the good applicability of the CNTs-enhanced PEEK porous materials.

Figure 6. Characterization of microscopic pore parameters of porous specimens

As shown in Fig. 6(a), the introduction of CNTs significantly increases the average pore size of porous PEEK materials. When the mass fraction of CNTs reached 3%, the mean pore size increased significantly from 0.08 μm (without CNTs added) to 11.62 μm. This phenomenon can be attributed to the following mechanism: the addition of CNTs reduces the flow properties of the composite melt and promotes the agglomeration behavior of NaCl particles, resulting in a significant increase in pore size after NACL removal.

The test results in Fig. 6(b) show that the introduction of an appropriate amount of CNTs can significantly improve the porosity of the material. When the mass fraction of CNTs was 1%, the porosity increased from 12.92% to 28.50%, an increase of 120%. This change is mainly due to two synergistic effects: (1) the micron-scale pore structure formed by NaCl particles in the PEEK matrix; (2) The unique hollow tubular structure of CNTs acts as a "nanobridge", which effectively connects adjacent pores and constructs a three-dimensional network structure.

However, it should be noted that when the mass fraction of CNTs increased to 3wt%, the porosity of porous materials decreased to 18.14%. This phenomenon is caused by the fact that when the content of CNTs in porous materials increases to a certain extent, the fluidity of the composite material becomes seriously deteriorating, which affects the dispersion uniformity of NaCl and CNTs, aggravates the agglomeration effect of NaCl and CNTs, and leads to poor connectivity of pores, resulting in a decrease in the porosity of porous materials. It can be seen that the addition of CNTs has a significant impact on the microstructure of porous PEEK materials, but the porosity of porous materials does not increase with the increase of CNTs content, but there is an optimal addition range.

3.3 Properties of CNTs-enhanced PEEK-based porous composites

(1) Flexural strength

Figure 7Flexural strength of reinforced PEEK-based porous composites

The flexural strength test results (Figure 7) show that the introduction of CNTs makes the flexural strength of the reinforced PEEK-based porous material slightly lower than that of the unenhanced specimen. The reason for this phenomenon is that the introduction of CNTs significantly increases the porosity of porous PEEK specimens, while the existence of porous structure destroys the density of the material, and the flexural strength of porous specimens decreases with the increase of porosity. Compared with CN3#-1 (0.5%) and CN3#-2 (1%), the bending strength of CN3#-3 specimen (3%) with higher CNTs content decreased by 4MPa and 8.6Mpa. This is due to the high addition of CNTs and poor fluidity, resulting in uneven dispersion of CNTs and NACL in the composites, and the agglomeration between CNTs, resulting in local differences in the properties of porous materials and reducing the flexural strength of porous composites.

In conclusion, it is not advisable to simply improve the mechanical properties of porous materials by increasing the content of CNTs. However, the value is concerned that although the introduction of CNTs reduces the flexural strength of the sample to a certain extent, the introduction of CNTs can greatly improve the porosity of porous materials while still showing good flexural strength, and the porosity of CN3#-1 specimen with a mass fraction of 0.5% CNTs is twice that of the 3# specimen without CNTs, but the bending strength is only reduced by 27.8%.

(2) Hardness

Figure 8 Hardness of reinforced PEEK-based porous composites

The hardness performance test results (Fig. 8) show that the hardness of the CNTs-enhanced porous PEEK specimen is lower than that of the PEEK specimen without CNTs-enhanced phase, and the hardness value increases first and then decreases with the increase of CNTs content, which is consistent with the change of bending strength of the porous specimens before. The reason for this phenomenon is also the introduction of CNTs, which significantly improves the porosity of porous PEEK specimens, and porous materials with high porosity are more prone to plastic deformation when subjected to external stress, so the hardness of porous materials after adding CNTs is generally lower than that of uncoated nanotube materials. However, due to the high strength and hardness of CNTs, the introduction of reinforced porous materials by CNTs can still effectively improve the hardness of porous composites. Compared with the 4# specimen without CNTs added in Zhang Hui's paper, its strength was the lowest among porous samples of 73HD due to its porosity (23.65%), while the porosity (28.5%) of CN3#-2 porous specimen with CNTs mass fraction of 1% was higher than that of 4#, but the strength of the porous specimen increased to 79.6HD.

The addition of CNTs is too high, which will make it disperse unevenly in the PEEK-based porous material, resulting in uneven internal stress of the material, resulting in a decrease in the hardness of the porous material, and the hardness of the CN3#-2 porous sample with 3% CNTs mass is reduced to 73.4HD. This also proves that it is not advisable to improve the mechanical and tribological properties of porous materials while blindly increasing the content of CNTs.

Tensile strength

Fig. 9. Tensile strength of a specimen of reinforced PEEK-based porous material

The tensile performance test results (Fig. 9) show that the tensile strength of the PEEK material filled with CNTs is improved. From a microscopic perspective, the introduction of concentrated acid by CNTs through carboxylation treatment leads to the formation of five-membered rings, seven-membered rings or other types of "defects" during the process of PEEK/NaCl melting blending, resulting in a curved structure of the CNTs themselves, which promotes the cross-linking of CNTs/PEEK and CNTs/CNTs to form a strong interfacial bond. In the tensile test, when subjected to the stress transmitted by the CNTs/PEEK interface, the interfacial bonding force can effectively resist the stress deformation trend of the material, and there is a chemical bond between the composites, which shows that the PEEK matrix composites filled with CNTs have high tensile strength.

In addition, the mechanical properties of CNTs on composites are affected by their orientation and dispersion effects in the matrix material. Good dispersion effect and reasonable orientation can effectively improve the mechanical properties of the material, otherwise it may reduce the mechanical properties of the material. It is undeniable that the dispersion effect and orientation of CNTs in the composites prepared in this study are random, so there is a possibility of adverse effects on the mechanical properties of the composites.

(4) Friction performance

Under special working conditions such as ultra-high vacuum, alternating high and low temperatures, and multiple starts and stops, aerospace bearings have increased oil consumption between friction pairs and are facing dry friction. Therefore, this paper studies the tribological properties of porous materials under dry friction.

The friction coefficient curve and average friction coefficient are shown in Fig. 10 under dry friction conditions, and the friction coefficient curve and average friction coefficient under high temperature dry friction are shown in Fig. 11.

Figure 10The friction coefficient curve and average friction coefficient of each sample under dry friction conditions

(a) Friction factor curve (b) Average friction coefficient

Figure 11The friction coefficient curve and average friction coefficient of each sample under dry friction conditions

From Fig. 10, the friction coefficient of PEEK porous materials decreased significantly with the increase of CNTs content, with CN3#-3 decreasing by 63.4% and CN3#-2 by at least 30.9%. The amplitude and time of the friction coefficient of CNTs-reinforced PEEK composites tended to be much lower than that of the PEEK samples without CNTs-enhanced phases. This may be due to two reasons: on the one hand, CNTs have high strength and rigidity, which can effectively bear and disperse external pressure, increasing the actual contact area. On the other hand, CNTs have good thermal and electrical conductivity, and CNTs abrasives can also act as lubricants, which can effectively transfer and disperse the heat generated by friction and reduce thermal wear. In conclusion, the introduction of CNTs can effectively improve the frictional properties of PEEK-based porous materials.

From Fig. 11, the friction coefficient in the high-temperature dry friction experiment is generally higher than that at normal temperature, and the local temperature continues to rise due to severe friction, and the adhesion phenomenon is easy to occur during the friction process, resulting in the local friction coefficient becoming larger. With the addition of CNTs, the friction coefficient of PEEK-based porous composites showed a decreasing trend, with a maximum decrease of 31.71%, and the amplitude of the friction coefficient curve (a) became more and more stable, which was the same as the aboveThe introduction of CNTs effectively improves the frictional properties of PEEK-based porous materials. CNTs can improve the high-temperature frictional stability of PEEK-based porous materials.

Comprehensive performance

The mechanical properties (bending properties, hardness, tensile properties) and tribological properties of the samples under dry friction conditions were comprehensively analyzed and compared (Fig. 11).

Figure 12. Comprehensive analysis results of macro performance data

From the above figure, it can be seen that compared with PEEK-based porous materials, the introduction of CNTs improves the frictional properties of materials and ensures their sample mechanical properties.

For porous materials, their macroscopic friction properties are synergistic due to the synergy of material density, pore size and porosity, and it is difficult to independently analyze the influence of any analysis factor in specific analysis. The limitations of this study are that we studied the preparation method of CNTs-enhanced PEEK composites, the influence of sample porosity on their mechanical properties and the dry friction properties of the samples, but did not avoid the agglomeration phenomenon of CNTs with high quality specific content and the failure to obtain the optimal addition of CNTs. In addition, the self-lubricating performance of the bearing cage needs to be further studied on its oil content, oil retention rate and oil friction. Therefore, the frictional properties of the materials prepared in this study need to be further studied.

conclusion

In this paper, the feasible type of PEEK-based porous composites reinforced by FDM molding CNTs, the composite samples formed by powder to wire molding, and the effects of different CNTs content on the properties of PEEK-based porous samples were explored by water solubilization, and the conclusions were as follows:

The CNTs-reinforced PEEK-based porous composites with FDM molding process can form defect-free and high-porosity samples, and the feasibility of powder pretreatment-wire extrusion-FDM printing-water-soluble porosity removal process route is verified.

NACL has excellent pore formation performance in CNTs/PEEK composites, and can effectively prepare uniformly distributed micron-level holes.

The introduction of CNTs effectively optimized the porosity and pore size of the material, and the average pore size increased from 0.08 μm to 11.62 μm, but there was an optimal addition amount of porosity CNTs content in porous materials, and excessive CNTs led to poor pore connectivity, resulting in a decrease in porosity of porous materials.

The mechanical properties of CNTs-enhanced PEEK-based porous materials increase first and then decrease with the increase of CNTs, and the friction properties are improved. However, excessive CNTs will reduce the flexural strength, hardness and tensile strength of porous materials.

References

Cai X C, Ma S H, Liang M G, et al. Lubrication Engineering, 2024, (2):1. (in Chinese)

Yadav, E.; Chawla, V.K. An explicit literature review on bearing materials and their defect detection techniques. Mater. Today Proc. 2022, 50, 1637–1643. [CrossRef]

Li S H, Wei C, Wu Y H, et al. Bearing, 2023 (9). (in Chinese)

Sun, J.; Yan, K.; Zhu, Y.; Hong, J. A High-Similarity Modeling Method for Low-Porosity Porous Material and Its Application in Bearing Cage Self-Lubrication Simulation. Materials 2021, 14, 5449. [CrossRef]

Marchetti, M.; Jones, W.R., Jr.; Pepper, S.V.; Jansen, M.J.; Predmore, R.E. In-situ, on-demand lubrication system for space mechanisms. Tribol. T. 2003, 46, 452–459. [CrossRef]

Friedrich, K. Polymer composites for tribological applications. Adv. Ind. Eng. Polym. Res. 2018, 1, 3–39. [CrossRef]

John M, Menezes P L. Self-Lubricating Materials for Extreme Condition Applications[J]. Materials, 2021,14(19):5588.

SUN Z,LIU Q X,LIU F,et al. Influences of cryo-thermal cycling on the tensile properties of short carbon fiber/polyetherimide composites[J]. Composite Structures,2024,344. DOI:10.1016/j.compstruct.2024.118336.

Li Peixi, Zhou Dezhi, Yang Changming, et al. Research Progress in Biological 3D Printing: Additive Fabrication of Animal, Plant and Microbiological Cells [J].Journal of Mechanical Engineering,2023,59 (19):237-252.

Wang, Q.; Zheng, F.; Wang, T. Tribological properties of polymers PI, PTFE and PEEK at cryogenic temperature in vacuum. Cryogenics 2016, 75, 19–25. [CrossRef]

Pei, X.; Friedrich, K. Sliding wear properties of PEEK, PBI and PPP. Wear 2012, 274, 452–455. [CrossRef]

ROBESON L M． Correlation of separation factor versus permeability for polymeric membranes［J］． Journal Membrane Science，1991， 62: 165 － 185

ROBESON L M． The upper bound revisited［J］． Journal Membrane Science，2008，320: 390 － 400．

WAIDAN R，GHANEM B，PINNAU I． Fine-tuned intrinsically ultra microporous polymers redefine the permeability /selectivity upper bounds of membrane-based air and hydrogen separations［J］． ACS Macro Letters，2015，4: 947 － 951．

Ata S, Hayashi Y, Nguyen Thi T B, et al. Improving thermal durability and mechanical properties of poly(ether ether ketone) with single-walled carbon nanotubes [J]. Polymer, 2019, 176: 60-5.

Hou Yuejiao. Preparation and Properties of Polyether Ether Ketone/Nanotube Composites[D]. Dalian University of Technology, 2017. DOI:10.26992/d.cnki.gdlqc.2017.000047.

Ye Xin. Study on Crystallization Properties and 3D Printing Properties of PEEK/CNTs Materials[D]. Zhejiang Normal University, 2022. DOI:10.27464/d.cnki.gzsfu.2022.000156.

WANG P，ZOU B，DING S L，et al. Preparation of short CF/GF reinforced PEEK composite filaments and their comprehensive properties evaluation for FDM-3D printing[J]. Composites Part B: Engineering，2020，198. DOI:10.1016/j.compositesb.2020.108175.

ZHANG Y N，XU F J，ZHANG C Y，et al. Tensile and interfacial properties of polyacrylonitrile-based carbon fiber after different cryogenic treated condition[J]. Composites Part B: Engineering， 2016，99:358‒365.

TIAN Guo qiang，WU Kai，GAO Sensen，et al. Effect of FDM process parameters on dimensional accuracy of CF/PETG parts[J]. Engineering Plastics Application，2024，52(8):104‒109，116.

ZHANG H, DUAN M, QIN S, et al. Preparation and modification of poropolyetheretherketone (PEEK) cage material based on fused deposition modeling (FDM) [J]. Polymers, 2022, D10.3390/ polym14245403.

FDM preparation and tribological properties of porous polyether ether ketone cage materials [J]. Bearings, 2023, (10): 57-62. DOI:10.19533/j.issn1000-3762.2023.10.009.

Zhang, Z., Zhang, H., Wang, J. et al  . Study on mechanics and high temperature tribological properties of porous bearing cage material [J].  Journal of Reinforced Plastics and Composites,2023, DOI:10.1177/07316844231201479.