Polyimide composite coating reinforced by MXene-coated ZrO2 hybrid filler as well as preparation method and application of polyimide composite coating

Abstract

The invention discloses an MXene-coated ZrOhybrid filler reinforced polyimide composite coating as well as a preparation method and application thereof, and belongs to the technical field of functional coating materials. The method comprises the following steps: firstly, respectively carrying out surface modification on MXene and nano ZrO by virtue of dopamine and a silane coupling agent KH550, and then synthesizing an MXene-coated ZrO hybrid filler with a particle-plane structure by virtue of electrostatic and chemical effects; then introducing the hybrid filler into a polyamide acid precursor through an in-situ polymerization method, and forming a composite coating on the surface of a metal substrate through coating and gradient thermal imidization. According to the hybrid filler, the dispersity and interface combination of the hybrid filler in a matrix are remarkably improved, so that the coating has high hardness, strong adhesive force and excellent antifriction and wear-resisting properties. Experiments show that the friction coefficient of the coating is reduced by about 48% compared with that of a tin bronze matrix, the wear rate is reduced by about 91%, the coating is suitable for wear-resistant protection of surfaces of harsh friction pairs such as a hydraulic pump bearing bush pair, and the service life of parts can be remarkably prolonged.

Description

Technical Field

[0001] This invention relates to the field of functional coating materials technology, specifically to a wear-resistant and friction-reducing composite coating for surface protection of metal parts and its preparation method, and more particularly to a method for synergistically enhancing the comprehensive performance of polyimide-based coatings by constructing "particle-planar" hybrid fillers, as well as the resulting coatings and their applications. Background Technology

[0002] In high-end equipment manufacturing, such as hydraulic systems in aerospace and heavy machinery, core friction pairs (e.g., the swashplate and bearings in an axial piston pump) operate under extreme conditions of high pressure, high speed, and frequent load changes. These conditions lead to severe adhesive wear, abrasive wear, and fatigue wear on the friction pair surfaces, which are key bottlenecks restricting system reliability, efficiency, and service life. To address this problem, preparing high-performance protective coatings on the friction pair surfaces is an effective technical approach. Among these, polyimide (PI) resin is widely regarded as an ideal substrate material for wear-resistant coatings due to its excellent high-temperature resistance, outstanding mechanical properties, good film-forming properties, and self-lubricating characteristics.

[0003] However, the hardness and load-bearing capacity of pure polyimide coatings are limited, making it difficult to meet the extremely high requirements for wear resistance under the aforementioned harsh working conditions. Therefore, the industry commonly uses the method of adding functional fillers to the PI matrix for reinforcement and modification. In recent years, two-dimensional materials such as MXene (e.g., Ti3C2T) have been increasingly used. x Due to its unique layered structure, low shear strength, and good mechanical properties, zirconia (ZrO2) has attracted widespread attention as a solid lubricant filler. Meanwhile, due to its extremely high hardness, nano-zirconia (ZrO2) particles are often used as a hard reinforcing phase to improve the compressive strength and ploughing resistance of coatings. Existing technologies include studies on adding MXene alone to improve the friction reduction properties of PI coatings, or adding nano-ZrO2 alone to increase its hardness; there are also attempts to physically blend MXene with ZrO2 or other micro / nano particles (such as Al2O3, MoS2) before incorporating them into the PI matrix.

[0004] Although the aforementioned existing technologies have made some progress, they all have inherent defects and have failed to fundamentally solve the core contradictions faced by high-performance PI composite coatings: 1. Dispersion and interfacial compatibility issues of fillers: MXene nanosheets exhibit strong interlayer van der Waals forces, making them prone to re-stacking and agglomeration. This hinders their uniform dispersion in the polymer matrix, preventing them from fully utilizing their large specific surface area and lubrication potential. Simultaneously, their surface chemical inertness results in weak interfacial bonding with the PI matrix. Nano-ZrO2 particles have high surface energy and poor compatibility with organic polymers, easily forming defects at the interface, becoming stress concentration points, thus impairing the overall toughness of the coating and its adhesion to the substrate.

[0005] 2. Limited Synergistic Effect of Simple Blending: Physical blending of unmodified MXene with nano-ZrO2, while intended to combine their lubrication and load-bearing advantages, fails to achieve ideal distribution and strong bonding of the fillers in the matrix due to the poor dispersibility of the two fillers and the lack of strong chemical bonds or stable interactions between them and the polymer matrix. As a result, the coating microstructure contains numerous interfacial defects. The friction-reducing effect of MXene and the hardening and load-bearing effects of ZrO2 fail to form an effective synergy. Often, the improvement of one property (such as hardness) comes at the expense of another property (such as adhesion or coefficient of friction), resulting in limited overall performance improvement, and may even lead to performance below expectations due to interfacial deterioration.

[0006] In summary, existing methods for modifying polyimide coatings with single fillers or through physical blending are limited by fundamental problems such as uneven filler dispersion, weak filler-matrix interfacial bonding, and a lack of functional synergy among different fillers. Therefore, there is an urgent need in this field to develop an innovative filler construction and composite technology. The core of this technology lies in how to construct a hybrid filler system with stable structure, excellent dispersibility, and strong interfacial bonding with the polymer matrix through materials design and surface chemical engineering. This system would synergistically improve the hardness, adhesion, friction reduction, and wear resistance of the polyimide coating, addressing the comprehensive and demanding requirements of key friction pairs on protective coatings under extreme operating conditions. This invention is proposed precisely to address this technological challenge.

[0007] It should be noted that the information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] The primary objective of this invention is to provide a novel material design and composite strategy to address the key technical bottlenecks commonly found in existing single or simple physical blend filler-reinforced polyimide (PI) coatings, such as poor filler dispersion, poor filler-matrix interface compatibility, and difficulty in synergistic function of different fillers.

[0009] A further objective of this invention is to provide a specific method for preparing an MXene@ZrO2 hybrid filler-reinforced polyimide composite coating based on the above-mentioned strategy. This method aims to construct a structurally stable and highly dispersible hybrid filler through chemical modification and controlled assembly, and to efficiently and uniformly introduce it into the PI matrix, ultimately forming a high-performance composite coating on a metal substrate.

[0010] Another objective of this invention is to provide an MXene@ZrO2 hybrid filler-reinforced polyimide composite coating prepared by the above method. This coating is expected to simultaneously possess high hardness, strong adhesion, and excellent friction reduction and wear resistance, achieving a synergistic improvement and optimal balance in overall tribological properties.

[0011] The ultimate objective of this invention is to provide the application of the above-mentioned composite coating in the wear-resistant and friction-reducing protection of the surface of critical friction pair components of mechanical equipment (especially the bearing pairs of axial piston pumps in hydraulic systems) under harsh working conditions, so as to significantly extend the service life of the components and improve the reliability of the equipment.

[0012] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, this invention provides a method for preparing an MXene@ZrO2 hybrid filler-reinforced polyimide composite coating. The core concept of this method is to first construct a hybrid filler with a stable "particle-planar" structure through surface chemical engineering, and then uniformly composite it into a PI matrix through in-situ polymerization. Specifically, it includes the following steps: S1: Preparation of MXene@ZrO2 hybrid filler. This step is fundamental to ensuring a synergistic improvement in the final coating performance. First, MXene nanosheets and nano-zirconia (ZrO2) particles are surface functionalized. A polydopamine (PDA) coating rich in phenolic hydroxyl and amino functional groups is introduced onto the MXene surface, and an aminosilane coupling agent (such as KH550) molecular chain is grafted onto the nano-ZrO2 surface. Subsequently, the two are mixed in a liquid medium (such as deionized water). Through electrostatic attraction, hydrogen bonding, and possible chemical bonding between the functional groups on the modified layer, the nano-ZrO2 particles are stably and firmly loaded on the surface and between the layers of the MXene nanosheets, thereby forming a unique hybrid structure that effectively prevents MXene stacking and promotes ZrO2 dispersion.

[0013] S2: Preparation of polyimide composite coating. This step employs in-situ polymerization to ensure uniform nanoscale dispersion of the hybrid filler in the polymer precursor. The hybrid filler obtained in S1 is ultrasonically dispersed in a polar organic solvent (such as DMAc), followed by the sequential addition of diamine monomers and dianhydride monomers (such as ODA and PMDA), and a polycondensation reaction is carried out under an inert atmosphere and at a suitable temperature. The active functional groups on the surface of the hybrid filler can interact with the polyamic acid (PAA) chains, thereby generating a PAA composite slurry with uniform filler dispersion and good stability.

[0014] S3: Coating Forming and Curing. The composite slurry obtained in S2 is applied to the surface of a pretreated metal substrate by spraying, dipping, or spin coating, followed by a programmed gradient temperature heat treatment. This heat treatment process first slowly removes most of the solvent at a lower temperature (e.g., 60-80℃) to prevent coating cracking; then, the temperature is gradually increased to a higher temperature (e.g., 200-350℃) to induce a thermal imidization ring-closure reaction of PAA, converting it into polyimide, and achieving final curing of the coating, thereby obtaining a dense MXene@ZrO2 / PI composite coating with strong interfacial bonding on the substrate.

[0015] Secondly, this invention provides an MXene@ZrO2 hybrid filler-reinforced polyimide composite coating prepared by the above method. The coating is characterized in that the MXene@ZrO2 hybrid filler is uniformly dispersed in the continuous phase of the polyimide matrix with a unique "particle-planar" structure. Due to the construction of the hybrid filler and its good interfacial bonding with the matrix, this coating exhibits excellent comprehensive performance, with a Vickers hardness of not less than 20 HV, and under standard reciprocating dry friction test conditions (e.g., load 5 N, grinding against GCr15 steel balls), its average coefficient of friction is not higher than 0.36, and its wear rate is not higher than 1.0 × 10⁻⁻⁻⁶. 4 mm³ / (N·m).

[0016] Thirdly, this invention provides the application of the aforementioned MXene@ZrO2 hybrid filler-reinforced polyimide composite coating. This coating is particularly suitable for protecting the surfaces of metal friction pairs in mechanical equipment operating under extreme friction conditions. For example, it can be used on the tin bronze bearings or steel swashplate surfaces of hydraulic axial piston pumps, forming a robust, wear-resistant, and friction-reducing protective layer, thereby significantly reducing the coefficient of friction and wear rate of the friction pair and extending the pump's service life.

[0017] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages: 1. Innovative Filler Structure with Significant Synergistic Effect: This invention abandons simple physical blending and creatively constructs a stable hybrid filler with MXene as a two-dimensional carrier and nano-ZrO2 as hard particles through stepwise surface modification and liquid-phase self-assembly. This structure achieves a functional synergy of "1+1>2": the nano-ZrO2 particles effectively prevent the MXene sheets from re-stacking, fully utilizing their lubrication potential; simultaneously, the MXene sheets, as a flexible substrate, ensure the uniform dispersion of the hard particles. During friction, the two respectively assume the roles of load-bearing and anti-wear, and friction-reducing and lubricating, working synergistically at the friction interface.

[0018] 2. Fundamentally improved dispersibility and interfacial compatibility: The abundant polar functional groups (-OH, -NH2) on the surface of the hybrid filler greatly enhance its affinity and dispersion stability in polar solvents and PAA / PI matrices. More importantly, these functional groups can form strong physical or chemical interactions with polymer chains, significantly strengthening the filler-matrix interfacial bonding, reducing interfacial defects and stress concentration, thereby improving the overall density and mechanical integrity of the coating.

[0019] 3. A breakthrough balance in overall coating performance is achieved: Thanks to the optimization of the structure and interface described above, the coating of this invention successfully resolves the performance contradictions that are difficult to achieve simultaneously with traditional modified PI coatings. As shown in the example data, it not only maintains high hardness (>21 HV) but also achieves excellent substrate adhesion (critical load >20 N), while simultaneously reducing the coefficient of friction (~0.345) and wear rate (~0.9×10⁻⁻⁻⁶). 4 The ratio of mm³ / (N·m) has both dropped to extremely low levels. This integrated performance of "high hardness, strong adhesion, low friction, and wear resistance" is something that coatings with single fillers or physical blend fillers in the proportion cannot achieve.

[0020] 4. Reliable preparation process and broad application prospects: The preparation method of this invention is based on mature solution polymerization and coating technology, with a clear process flow, controllable parameters, and easy large-scale implementation. The resulting coating can be applied in various ways and is suitable for metal parts with complex shapes. Bench tests on key friction pairs such as hydraulic pump bearings show that it can extend the wear life of components by more than 3 times, demonstrating great engineering application value and market potential. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the synthesis process of the MXene@ZrO2 hybrid filler of the present invention. It intuitively shows the process of modifying MXene and nano ZrO2 with dopamine and silane coupling agent respectively, and forming a "particle-planar" structure hybrid filler through electrostatic and chemical reactions.

[0022] Figure 2 The bar chart comparing the average friction coefficient and wear rate of various coatings obtained in the comparative examples and embodiments of the present invention clearly demonstrates the comprehensive advantages of the coating (MXene@ZrO2 / PI) of the present invention in terms of friction reduction and wear resistance.

[0023] Figure 3 The image shows the SEM morphology of the worn surface of the MXene@ZrO2 / PI composite coating prepared in Example 1 of this invention after a friction test, used to observe the wear mechanism and surface condition of the coating.

[0024] Figure 4The SEM morphology and corresponding EDS elemental distribution diagram of the transfer film formed on the surface of the GCr15 steel ball after friction with the coating of Example 1 are used to analyze the formation and chemical composition of the lubrication transfer film during the friction process.

[0025] Figure 5 Comparative photographs of the dispersion states of different fillers (including unmodified ZrO2, unmodified MXene, physical blends, and the hybrid filler of this invention) after standing in polyamic acid solution for different times visually demonstrate the excellent dispersion stability of the hybrid filler of this invention.

[0026] Figure 6 The images show the microstructure and elemental analysis of the MXene@ZrO2 hybrid filler prepared in Example 1 of this invention. (a)-(c) are scanning electron microscope (SEM) images at different magnifications, (d)-(e) are transmission electron microscope (TEM) images, and the rest are corresponding energy dispersive X-ray spectroscopy (EDS) surface scan elemental distribution maps. Together, they confirm the uniform loading of nano ZrO2 particles on the MXene sheets and the successful construction of the "particle-plane" hybrid structure.

[0027] Figure 7 The Fourier transform infrared (FTIR) spectra of the MXene@ZrO2 hybrid filler, dopamine-modified MXene (MXene-PDA), and aminated ZrO2 (ZrO2-NH2) prepared in Example 1 of this invention are compared to analyze the changes in surface functional groups and the formation of chemical bonds.

[0028] Figure 8 The X-ray photoelectron spectroscopy (XPS) analysis diagrams of the MXene@ZrO2 hybrid filler prepared in Example 1 of the present invention are shown. (a) is the full spectrum, and (b)-(d) are high-resolution fine spectra of C1s, O1s and N1s, respectively, which are used to analyze the surface chemical state and elemental bonding mode of the hybrid filler in depth. Detailed Implementation

[0029] To enable those skilled in the art to fully understand and implement the present invention, the technical solutions of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions in the art or under conditions recommended by the manufacturer. Unless otherwise specified, the reagents and materials used are all commercially available conventional products.

[0030] Example 1: Preparation and performance testing of MXene@ZrO2 / PI composite coating S1: Preparation and characterization of MXene@ZrO2 hybrid filler This embodiment details the preparation process of the core reinforcing phase of the present invention—MXene@ZrO2 hybrid filler—and its process principle is as follows: Figure 1 As shown.

[0031] First, aminated nano-zirconia (ZrO2-NH2) was prepared: 50 mg of nano-ZrO2 powder with an average particle size of approximately 60 nm was dispersed in 100 mL of anhydrous ethanol and sonicated for 1 hour. The pH of the dispersion was adjusted to 4-5 with oxalic acid solution, and 200 mg of silane coupling agent KH550 (γ-aminopropyltriethoxysilane) was added. The mixture was refluxed and stirred at 75 °C for 4 hours. After the reaction was completed, the product was centrifuged and washed (3500 rpm, 5 min) three times each with deionized water and anhydrous ethanol, and finally vacuum dried at 80 °C for 24 hours to obtain ZrO2-NH2 powder.

[0032] Secondly, dopamine-modified MXene (MXene-PDA) was prepared: 50 mg of multilayer Ti3C2T x MXene powder and 50 mg of dopamine hydrochloride were added to 100 mL of Tris-HCl buffer at pH 8.5, sonicated for 1 hour, and then magnetically stirred at room temperature for 24 hours. After the reaction was complete, the powder was obtained by centrifugation, washing, and freeze-drying.

[0033] Finally, hybrid assembly was performed: all the ZrO2-NH2 and MXene-PDA powders prepared above were added to deionized water and ultrasonically dispersed for 1 hour, followed by continuous stirring at room temperature for 24 hours. During this process, the nano-ZrO2 particles were stably loaded onto the surface and interlayer of MXene nanosheets by electrostatic attraction and chemical interaction between the amino groups on the ZrO2-NH2 surface and the phenolic hydroxyl and amino groups on the MXene-PDA surface. The product was collected by centrifugation and freeze-dried to obtain the final MXene@ZrO2 hybrid filler.

[0034] To confirm the successful construction and structural properties of the hybrid filler, a series of characterizations were performed. For example... Figure 6 As shown, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images clearly show that nano-ZrO2 particles (bright white dots) are uniformly and densely attached to the MXene sheets (gray substrate), successfully constructing a unique "particle-plane" hybrid structure that effectively prevents MXene stacking. The corresponding energy-dispersive X-ray spectroscopy (EDS) surface scanning results (…) Figure 6 The distribution maps of Ti, C, Zr, and O elements in the image confirm that the Zr element signal highly overlaps with the Ti and C element regions, demonstrating their close binding from a spatial distribution perspective. Fourier transform infrared spectroscopy (FTIR) analysis... Figure 7The results showed that the hybrid filler simultaneously possessed characteristic absorption peaks of both MXene-PDA and ZrO2-NH2, and that peak positions shifted, indicating interactions between surface functional groups. X-ray photoelectron spectroscopy (XPS) analysis... Figure 8 This further provides evidence for the surface chemical state; the new binding energy peak appearing in the N1s high-resolution spectrum indicates the possible presence of chemical bonds such as C=N, providing support for the stability of the hybrid structure. Furthermore, dispersion stability experiments (such as...) Figure 5 As shown in the figure, the MXene@ZrO2 hybrid filler prepared in this embodiment still maintains excellent dispersion after standing in polyamic acid (PAA) solution for 36 hours, which is far superior to unmodified filler and its physical blends. This lays a key foundation for achieving uniform dispersion in subsequent composite coatings.

[0035] S2: Preparation and Properties of MXene@ZrO2 / PI Composite Coating After obtaining the hybrid filler, a composite coating was prepared by in-situ polymerization. Under nitrogen protection, 38.4 mg (1 wt% of the total PI mass) of the above MXene@ZrO2 hybrid filler was added to 50 mL of N,N-dimethylacetamide (DMAc) solvent and ultrasonically dispersed for 1 hour. Subsequently, 2 g of 4,4′-diaminodiphenyl ether (ODA) monomer was added to the homogeneous dispersion and stirred until completely dissolved. The reaction system was cooled in an ice-water bath, and 2.18 g of pyromellitic dianhydride (PMDA) monomer (ODA:PMDA molar ratio of 1:1) was added in batches with continuous stirring, controlling the feeding rate to maintain the system temperature below 20°C. After the addition was complete, the reaction was continued at room temperature for 12 hours to carry out the polycondensation reaction, obtaining an MXene@ZrO2 / PAA composite slurry with a solid content of approximately 14.5% and a suitable viscosity. Tin bronze (grade QSN6.5-0.1Y) was selected as the substrate. It was first roughened by sandblasting, then ultrasonically cleaned with acetone and dried. A composite slurry was uniformly coated onto the pretreated tin bronze surface using a spraying process, controlling the wet film thickness to ensure a final dry film thickness of approximately 100-120 μm. The coated sample was then placed in an 80℃ vacuum oven for 10 hours to slowly and thoroughly remove most of the solvent. Subsequently, a programmed thermal imidization treatment was performed: under air atmosphere, the temperature was increased in steps at a rate of 2℃ / min, and held at 100℃, 200℃, and 300℃ for 1 hour each, ultimately completing the conversion of polyamic acid to polyimide and the complete curing of the coating. After furnace cooling, the MXene@ZrO2 / PI composite coating was obtained.

[0036] The obtained coating underwent comprehensive performance testing. Vickers hardness testing (load 1000 gf, holding pressure 15 s) showed a hardness of 21.74 HV. The adhesion strength between the coating and the substrate was evaluated by micro-scratch testing (loading rate 10 N / min, maximum load 30 N), and the critical adhesion load was determined to be 20.1 N. Tribological properties were evaluated on a ball-disc reciprocating friction testing machine. The grinding balls were 6 mm diameter GCr15 steel balls, and the test conditions were: load 5 N, frequency 2 Hz, stroke 10 mm, dry friction at room temperature, and test time 1800 s. The results showed that the coating had an average coefficient of friction of 0.345 and a wear rate of 0.9 × 10⁻⁻⁻⁶. 4 mm³ / (N·m). Figure 3 The SEM morphology of the coating after wear is shown. The worn surface is relatively smooth and flat, with only slight ploughing grooves and a small amount of wear debris, which is typical of slight abrasive wear. This indicates that the coating has excellent wear resistance. Figure 4 The study showed that a continuous and dense transfer film was formed on the surface of the grinding steel ball. EDS elemental analysis confirmed that the transfer film was rich in elements such as Ti and C from MXene, proving that MXene can effectively form a lubricating transfer film during the friction process, which is one of the key mechanisms for achieving a low coefficient of friction.

[0037] Examples 2 and 3: Preparation of MXene@ZrO2 / PI composite coatings with different filler contents This embodiment investigates the effect of filler content. Following the preparation method of Example 1, only the amount of MXene@ZrO2 hybrid filler added was changed to prepare composite coatings with filler contents of 0.5 wt% and 2 wt%, respectively. Performance tests showed that the coating achieved optimal overall tribological properties when the filler content was 1 wt% (Example 1). When the filler content was 0.5 wt% (Example 2), the reinforcing effect was limited; when the content increased to 2 wt% (Example 3), the slurry viscosity increased significantly, potentially affecting the coating process and filler dispersion uniformity, and the overall performance was not further improved.

[0038] Comparative Example 1: Preparation of Pure PI Coating Without adding any fillers, 2g of ODA and 2.18g of PMDA were polymerized, coated, and heat-treated in 50mL of DMAc using the same process as in Example 2 to prepare a pure PI coating. Its Vickers hardness was 17.96 HV, the critical adhesion load was 17.8 N, the average coefficient of friction was 0.391, and the wear rate was 11.5 × 10⁻⁻⁻⁶. 4 mm³ / (N·m).

[0039] Comparative Example 2: Preparation of ZrO2 / PI Composite Coating Referring to Example 2, a ZrO2 / PI coating was prepared using 38.4 mg of unmodified nano-ZrO2 powder (instead of MXene@ZrO2 hybrid filler). Its hardness increased to 21.68 HV, and its wear rate decreased to 0.9 × 10⁻⁻⁻⁶. 4 mm³ / (N·m), but the adhesion decreases to about 15 N, and the average coefficient of friction increases to 0.410.

[0040] Comparative Example 3: Preparation of MXene / PI Composite Coating Referring to Example 2, an MXene / PI coating was prepared using 38.4 mg of unmodified MXene powder (instead of the MXene@ZrO2 hybrid filler). It exhibited a hardness of 21.78 HV, an adhesion of 19.5 N, and an average coefficient of friction of 0.360, but also a high wear rate of 3.5 × 10⁻⁻⁻⁶. 4 mm³ / (N·m).

[0041] Comparative Example 4: Preparation of ZrO2+MXene blend / PI composite coating Referring to Example 2, 19.2 mg of unmodified ZrO2 and 19.2 mg of unmodified MXene were physically blended and then added to prepare a PI coating reinforced with blended filler. Its hardness was 20.14 HV, adhesion was 18.5 N, average coefficient of friction was 0.380, and wear rate was 2.6 × 10⁻⁻⁻⁶. 4 mm³ / (N·m).

[0042] Detailed performance data for the above embodiments and comparative examples are summarized in Table 1 below. The comparison clearly shows that Comparative Example 1 (pure PI) does not excel in any of its properties. Comparative Example 2 (ZrO2 only) significantly improved hardness and wear resistance, but severely compromised adhesion and increased the coefficient of friction. Comparative Example 3 (MXene only) performed well in terms of friction reduction and adhesion, but its wear resistance was insufficient. Comparative Example 4 (physical blend) had performance indicators between Comparative Example 2 and Comparative Example 3, failing to achieve a breakthrough in performance improvement. This demonstrates that simple mechanical mixing cannot produce a synergistic effect.

[0043] In contrast, the coating of Example 1 (MXene@ZrO2 / PI) exhibits comprehensive and excellent overall performance: while maintaining high hardness (21.74 HV), it achieves the highest adhesion (20.1 N), and realizes the lowest coefficient of friction (0.345) and extremely low wear rate (0.9 × 10⁻⁻⁶). 4 mm³ / (N·m)). Figure 2The bar chart visually compares the friction coefficient and wear rate data, highlighting the dual advantages of the coating of this invention. This simultaneous optimization of "high hardness, toughness, friction reduction, and wear resistance" is not a simple summation of the performance of a single filler, but rather stems from the unique structure of the "particle-planar" hybrid filler constructed in this invention and the synergistic effect generated by its excellent interfacial bonding with the matrix. Nano-ZrO2 particles, acting as hard support points, effectively enhance the coating's load-bearing capacity and anti-plowing ability; MXene sheets, as a lubricating phase, promote the formation of a low-friction transfer film; and the chemical hybrid structure of the two ensures their uniform dispersion and stable bonding in the matrix, avoiding performance shortcomings.

[0044] Finally, the coating prepared in Example 1 of this invention was applied to the tin bronze bearing surface of a certain type of axial piston pump for bench testing. Under the same extreme operating conditions, the wear life of the coated bearing pair was extended by more than three times compared with the uncoated bearing pair, and the operating friction power consumption and temperature rise were effectively reduced, fully verifying the excellent effect and application potential of the coating of this invention in solving the wear problem of key friction pairs in actual engineering.

[0045] Table 1 Comparison of Performance of Different Coatings Coated samples Vickers hardness (HV) Critical adhesion load (N) Average coefficient of friction (COF) <![CDATA[Wear rate (10⁻ 4 mm³ / (N·m))]]> Tin bronze matrix 202.47 0 0.660 10.0 Comparative Example 1: Pure PI 17.96 17.8 0.391 7.0 <![CDATA[Comparative Example 2: ZrO2 / PI]]> 21.68 15.0 0.410 0.9 Comparative Example 3: MXene / PI 21.78 19.5 0.360 3.5 Comparative Example 4: Blend / PI 20.14 18.5 0.380 2.6 <![CDATA[Example 1: 1 wt% MXene@ZrO2 / PI]]> 21.74 20.1 0.345 0.9 <![CDATA[Example 2: 0.5 wt% MXene@ZrO2 / PI]]> 20.78 18.9 0.365 1.3 <![CDATA[Example 3: 2wt% MXene@ZrO2 / PI]]> 21.15 19.6 0.352 1.1 The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made based on the content of this specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for preparing MXene@ZrO2 hybrid filler reinforced polyimide composite coating, characterized in that, The method comprises the following steps: S1: preparing MXene@ZrO2 hybrid filler: mixing MXene nanosheets surface-modified with first active functional groups with nano-zirconium oxide particles surface-modified with second active functional groups in a liquid medium, loading the nano-zirconium oxide particles on the surface and interlayer of the MXene nanosheets through the interaction between the first active functional groups and the second active functional groups to form a "particle-plane" hybrid structure, and obtaining the MXene@ZrO2 hybrid filler; S2: preparing polyimide composite coating: dispersing the MXene@ZrO2 hybrid filler prepared in step S1 in an organic solvent, adding a diamine monomer, stirring uniformly, then adding a dianhydride monomer, and performing polycondensation reaction to obtain a polyamic acid composite slurry containing uniformly dispersed hybrid filler; S3: coating forming and curing: coating the polyamic acid composite slurry obtained in step S2 on the surface of a pretreated metal substrate, performing gradient temperature heat treatment to remove the solvent and complete the thermal imidization process of the polyamic acid, and forming the MXene@ZrO2 hybrid filler reinforced polyimide composite coating on the surface of the metal substrate.

2. The production method according to claim 1, characterized by, In step S1, the first active functional groups are derived from polydopamine surface modification of the MXene nanosheets; and the second active functional groups are derived from amino silane coupling agent surface modification of the nano-zirconium oxide particles.

3. The production method according to claim 2, characterized by, The polydopamine surface modification is specifically obtained by stirring and reacting MXene and dopamine in a Tris-HCl buffer solution, and then washing and drying; and the amino silane coupling agent is γ-aminopropyl triethoxysilane.

4. The method of claim 1, wherein, In step S1, the MXene nanosheet is Ti3C2T x wherein T is a -OH, -O, or -F surface termination; and the zirconium oxide nanoparticles have a particle size of 20-100 nm.

5. The preparation method according to claim 1, characterized in that, In step S2, the addition amount of the MXene@ZrO2 hybrid filler is 0.1 wt% to 5 wt% of the total mass of the diamine monomer and the dianhydride monomer.

6. The method of claim 1, wherein, In step S2, the diamine monomer is 4,4'-diamino diphenyl ether, the dianhydride monomer is pyromellitic dianhydride, and the organic solvent is N,N-dimethylacetamide, N-methyl pyrrolidone or N,N-dimethylformamide.

7. The preparation method according to claim 1, characterized in that, In step S3, the gradient temperature heat treatment procedure comprises: first treating at 60-80°C for 1-10 hours, then increasing the temperature in a stepwise manner to 200-350°C and keeping the temperature for 0.5-3 hours to complete the thermal imidization reaction.

8. The method of claim 1, wherein, The metal substrate is tin bronze, copper alloy, aluminum alloy or steel.

9. A MXene@Zr02 hybrid filler-reinforced polyimide composite coating, characterized in that, Prepared by the method of any one of claims 1 to 8.

10. The MXene@ZrO2 hybrid filler enhanced polyimide composite coating according to claim 9, characterized in that, In the coating, the MXene@ZrO2 hybrid filler is dispersed in the polyimide matrix in a "particle-plane" structure, and the Vickers hardness of the coating is not less than 20 HV, and under the reciprocating dry friction condition of a load of 5 N, a frequency of 2 Hz and a stroke of 10 mm, when the counter friction pair is a GCr15 steel ball, the average friction coefficient is not higher than 0.36, and the wear rate is not higher than 1.0*10 4 mm³ / (N·m).

11. Use of the MXene@ZrO2 hybrid filler reinforced polyimide composite coating of claim 9 or 10 in the preparation of a surface protective coating for a mechanical equipment friction pair component.

12. Use according to claim 11, characterized in that, The mechanical equipment friction pair component is a bushing or swash plate of a hydraulic axial plunger pump.

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