A self-lubricating graphite-based friction-reducing composite material and its preparation method

Abstract

This invention discloses a self-lubricating graphite-based friction-reducing composite material and its preparation method, belonging to the field of solid lubricating composite material technology. The composite material consists of a metal matrix, graphite solid lubricating blocks, and an adhesive interface layer. The metal matrix surface has embedded holes / grooves into which the graphite blocks are embedded. The interface layer is formed by in-situ hot-pressing condensation of the o-phenylenediamine functional group layer on the metal side and the carboxyl functional group layer on the graphite side to generate a benzimidazole ring cross-linked structure. The metal matrix is ​​made of steel, copper alloy, etc., with an inner wall roughness Ra of 3.2–12.5 μm; the interface layer thickness is 5–100 μm, and the nitrogen atoms of the benzimidazole ring form coordination bonds with the metal, resulting in strong bonding and high-temperature resistance. During preparation, the metal and graphite are first functionalized pretreated, and then composited in a three-stage hot-pressing process to construct a covalent cross-linked network in situ. This invention exhibits strong interfacial bonding, excellent thermal stability, maintains high shear strength even at 300℃, has a low coefficient of friction, and good resistance to various media, making it suitable for high-temperature, heavy-load, and oil-free lubrication conditions.

Description

Technical Field

[0001] This invention relates to the field of solid lubricating composite materials technology, and in particular to a self-lubricating graphite-based friction-reducing composite material and its preparation method. Background Technology

[0002] In the field of mechanical engineering, conventional lubricating greases are prone to thermal decomposition or loss when friction pairs such as sliding bearings, guide rails, and seals operate under high temperature and high load conditions, leading to lubrication failure. Solid self-lubricating composite materials, due to their elimination of the need for external oil supply and ease of maintenance, have become an ideal solution to these problems.

[0003] Graphite, as a typical layered solid lubricant, possesses excellent friction-reducing properties and chemical stability. In existing technologies, embedding graphite blocks into a metal matrix to form composite materials is a common technical approach. However, the interfacial bonding between graphite and the metal matrix has always been a technical challenge: graphite has a highly inert surface, making it difficult to form effective chemical bonds with metals. Traditional adhesives mainly rely on physical adsorption or simple mechanical interlocking, which leads to a sharp decrease in bond strength under high-temperature conditions, causing the graphite blocks to loosen and detach, severely affecting the service life and reliability of components.

[0004] In the prior art, Chinese patent CN102145556A discloses a high-temperature resistant metal-fabric / resin self-lubricating bearing composite material, which adopts a multi-layer composite structure. The middle layer is a porous sintered tin bronze powder layer, and the surface layer is a composite of a mixed woven fabric and a self-lubricating wear-resistant resin. However, its essence is still a pre-formed resin system, and the interfacial bonding between the resin and the metal is mainly physical interlocking. At high temperatures, the interfacial strength decreases significantly after the resin softens. Polybenzimidazole (PBI) has good thermal stability and self-lubricating properties, but in the prior art, PBI is mostly used directly in the form of prepolymer, or composited with reinforcements through solution impregnation, coating, etc., making it difficult to form a directional chemical bond structure at the metal-graphite heterostructure interface.

[0005] Therefore, there is an urgent need to develop an adhesive technology that can form stable chemical bonds at the metal-graphite interface to improve the interfacial bonding strength and service reliability of embedded graphite self-lubricating composite materials under high-temperature conditions. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing a self-lubricating graphite-based friction-reducing composite material and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes a self-lubricating graphite-based friction-reducing composite material, comprising: Metal substrate with inlay holes or inlay grooves on its surface; A graphite solid lubricant block is embedded in the mounting hole or mounting groove of the metal substrate; And the adhesive interface layer located between the metal substrate and the graphite solid lubricant block; The adhesive interface layer is composed of a benzimidazole ring cross-linked structure formed by the in-situ condensation reaction of a metal surface treatment layer containing o-phenylenediamine functional groups and a graphite surface treatment layer containing carboxyl functional groups under hot-pressing conditions.

[0008] Preferably, the metal substrate is made of steel, copper, copper alloy or aluminum; the surface roughness Ra of the inner wall of the inlay hole or inlay groove is 3.2 to 12.5 μm.

[0009] Preferably, the metal surface treatment layer containing o-phenylenediamine functional groups is formed by coating and pre-curing a treatment solution containing N-(2-aminoethyl)-3-aminopropyltrialkoxysilane and 3,4-diaminobenzoic acid. The mass ratio of N-(2-aminoethyl)-3-aminopropyltrialkoxysilane to 3,4-diaminobenzoic acid is 1:0.3 to 1:1.5.

[0010] Preferably, the graphite surface treatment layer containing carboxyl functional groups is formed by vacuum impregnation and pre-baking of an impregnation solution containing polyamic acid and aromatic hydroxycarboxylic acid; The aromatic hydroxycarboxylic acid is one or more of p-hydroxybenzoic acid, m-hydroxybenzoic acid, or 3,4-dihydroxybenzoic acid, and the amount added is 2% to 15% of the solid mass of polyamic acid.

[0011] Preferably, the benzimidazole ring forms a coordination bond with the surface of the metal matrix through its nitrogen atom; the thickness of the adhesive interface layer is 5–100 μm.

[0012] This invention also proposes a method for preparing the aforementioned self-lubricating graphite-based friction-reducing composite material, comprising the following steps: S1. Metal substrate pretreatment: The inner wall of the mounting hole or mounting groove of the metal substrate is roughened and cleaned by sandblasting, and then coated with a treatment liquid containing o-phenylenediamine functional groups. It is pre-cured at 70-90℃ for 20-40 minutes to form a metal surface treatment layer. Sandblasting roughens the metal surface through plastic deformation, forming an uneven, rough structure (Ra 3.2–12.5 μm), which significantly increases the interfacial contact area. The treatment solution consists of N-(2-aminoethyl)-3-aminopropyltrialkoxysilane (KH792) and 3,4-diaminobenzoic acid. The silane undergoes a dehydration reaction with the M-OH (M=Fe / Cu / Al) on the metal surface to generate stable Si-OM covalent bonds. The carboxyl groups of the 3,4-diaminobenzoic acid molecules form hydrogen bonds and some amide bonds with the amino groups in the silane molecules, thereby stably anchoring the o-phenylenediamine active sites on the metal surface and preventing its volatilization and loss.

[0013] S2. Pretreatment of graphite solid lubricating blocks: Immerse the graphite solid lubricating blocks in an impregnation solution containing carboxyl functional groups and keep them under a vacuum of ≤200Pa for 10 to 30 minutes. After taking them out, pre-bake them at 80 to 120℃ in a stepwise manner for 30 to 60 minutes to form a graphite surface treatment layer. Under vacuum conditions (≤200Pa), the air in the graphite pores is extracted, and the carboxyl-containing impregnation solution penetrates into the graphite pores under the action of pressure difference. During the pre-drying process, the polar aprotic solvent gradually evaporates, and the resin forms a uniform semi-cured film on the graphite surface and in the pores, while generating a mechanical anchoring effect.

[0014] The impregnation solution is composed of polyamic acid (PAA) and aromatic hydroxycarboxylic acid. During the pre-curing stage, the adjacent carboxyl and amide groups within the polyamic acid molecule undergo a preliminary dehydration reaction to generate an imide ring, but retain a large number of free carboxyl groups for subsequent benzimidazole synthesis. p-hydroxybenzoic acid / 3,4-dihydroxybenzoic acid molecules bind to the carboxyl / amide groups of polyamic acid through hydrogen bonds, while its hydroxyl groups form hydrogen bonds with the oxygen-containing functional groups (-OH, -COOH) on the graphite surface, further enhancing the interfacial bonding force between the resin and graphite. S3. Hot-press composite: The treated graphite solid lubricant block is embedded in the inlay hole or inlay groove of the treated metal matrix, and in-situ condensation reaction and curing are carried out under hot-press conditions. After cooling, the self-lubricating graphite-based friction-reducing composite material is obtained.

[0015] 3,4-Diaminobenzoic acid (containing an o-phenylenediamine structure) on the metal surface undergoes a nucleophilic addition-elimination reaction with the free carboxyl groups of polyamic acid and aromatic hydroxycarboxylic acids on the graphite surface, forming amide bonds.

[0016] Wherein, R1 is the structure of the benzene ring of 3,4-diaminobenzoic acid and its connection with the metal surface; R2 is the structure of the connection between the free carboxyl group, the aromatic carboxylic acid and the graphite surface; Preferably, in step S3, the hot pressing is performed under an inert gas protective atmosphere, and the conditions are as follows: The preheating section is kept at 100–130℃ for 15–30 minutes at a pressure of 0.1–0.3 MPa; In the first reaction section, the temperature is increased to 160-190℃ at a rate of 2-5℃ / min, and held for 45-90 minutes, while the pressure is increased to 0.4-0.8MPa.

[0017] Under high temperature and nano-ZnO catalysis, another amino group in the monoamide molecule undergoes a dehydration and ring-closure reaction with the amide carbonyl group to generate a benzimidazole ring with a rigid conjugated structure, which covalently links the metal and graphite through the benzimidazole ring.

[0018] The second reaction section is heated to 200-240℃ at a rate of 1-3℃ / min, held at that temperature for 60-120 minutes, and the pressure is increased to 0.8-1.5MPa. The remaining carboxyl and amide groups on the polyamic acid molecular chain are all dehydrated to form polyimide, which forms a high-temperature resistant PI matrix network.

[0019] After the cooling section cools down to below 80℃ at a rate of ≤3℃ / min, it is depressurized and removed.

[0020] Preferably, the preparation method of the treatment solution containing the o-phenylenediamine functional group is as follows: N-(2-aminoethyl)-3-aminopropyltrialkoxysilane is added to an alcohol-water mixed solvent with a pH of 4.0-5.5 and hydrolyzed at room temperature for 15-30 minutes; 3,4-diaminobenzoic acid is dissolved in anhydrous alcohol, heated to 40-50°C to dissolve, and then slowly added to the above hydrolysate, and stirred at room temperature for 10-20 minutes to obtain the solution.

[0021] Preferably, the impregnation solution containing carboxyl functional groups is prepared by: diluting a polyamic acid solution with a polar aprotic solvent to a viscosity of 100-300 mPa·s, adding an aromatic hydroxycarboxylic acid, stirring to dissolve, optionally adding a nano-metal oxide catalyst, and ultrasonically dispersing for 5-15 minutes to obtain the solution; the nano-metal oxide catalyst is ZnO.

[0022] Compared with the prior art, the beneficial effects of the present invention are: 1. In existing technologies, the adhesion between graphite and metal largely relies on the physical adsorption, mechanical intercalation, or weak hydrogen bonding of traditional adhesives such as epoxy resins and phenolic resins. These forces have low bond energies (typically below 50 kJ / mol), and under high-temperature conditions, intensified molecular thermal motion leads to desorption of the interfacial adsorption layer, macroscopically manifesting as a sharp decrease in adhesive strength. This invention utilizes an in-situ interfacial condensation reaction to directionally construct a benzimidazole heterocyclic cross-linked structure between the metal and graphite. The reaction mechanism is as follows: the o-phenylenediamine functional group in the metal surface treatment layer undergoes dehydration condensation and ring closure with the carboxyl group in the graphite surface treatment layer under thermal drive, generating a stable CN covalent bond. The bond energy of this covalent bond exceeds 305 kJ / mol, far higher than the physical adsorption energy. Therefore, even at 300°C, a strong chemical bond can be maintained at the interface, overcoming the inherent defect of high-temperature debonding in traditional adhesives.

[0023] 2. In addition to covalent bonding, this invention introduces a second interfacial strengthening mechanism. The in-situ generated benzimidazole ring framework contains a highly electronegative imine nitrogen atom (-N=). The lone pair electrons on this nitrogen atom can coordinate with the empty d orbitals on the surface of transition metal matrices such as iron and copper, forming stable coordinate bonds. This synergistic anchoring structure of "covalent bond + coordinate bond" is not found in existing single polymer coatings or adhesives. Under high-temperature frictional shear stress, the coordinate bond, as a dynamically reversible chemical interaction, can effectively dissipate stress concentration at the interface, inhibit the initiation and propagation of microcracks, thereby significantly improving the interfacial shear fatigue resistance of the composite material under thermo-mechanical coupling conditions.

[0024] 3. In this invention, the polyamic acid used in the graphite surface treatment layer not only serves as a carrier for carboxyl functional groups, but also undergoes a simultaneous thermal imidization reaction during the hot-pressing curing stage, transforming into a polyimide (PI) backbone with extremely high heat resistance. Simultaneously, the benzimidazole rings generated at the interface and the imide rings in the polyimide both belong to aromatic heterocyclic structures, exhibiting a good match in their coefficients of thermal expansion, forming a rigid three-dimensional interpenetrating network structure at high temperatures. This network structure endows the adhesive interface layer with excellent high-temperature creep resistance and oxidation resistance, avoiding the softening, thermal decomposition, and volume shrinkage problems that easily occur in traditional organic adhesive layers above 200°C. This ensures that the graphite lubricant block maintains a tight bond with the metal substrate under wide temperature range conditions, maintaining stable friction-reducing and lubrication functions. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0026] Example 1

[0027] (1) Pretreatment of metal substrate: 45# steel is selected as the metal substrate, and cylindrical inlay holes with a diameter of 20mm and a depth of 15mm are machined on its surface. The inner wall of the inlay hole is roughened by sandblasting (brown corundum sand, particle size 80 mesh, air pressure 0.5MPa), then ultrasonically cleaned with acetone for 10 minutes, and dried at 80℃ for 30 minutes.

[0028] Preparation of a treatment solution containing o-phenylenediamine functional groups: Mix 90 parts by weight of deionized water and 10 parts by weight of anhydrous ethanol, and adjust the pH to 4.8 with glacial acetic acid to obtain an alcohol-water mixed solvent. Add 6 parts by weight of KH-792 silane coupling agent to the above solvent and hydrolyze at room temperature for 25 minutes. Separately, dissolve 4 parts by weight of 3,4-diaminobenzoic acid in 30 parts by weight of anhydrous ethanol, heat to 45°C and stir to dissolve. Slowly add this solution dropwise to the above hydrolysate, and continue stirring at room temperature for 15 minutes to obtain a homogeneous and transparent treatment solution.

[0029] The above-mentioned treatment solution is evenly sprayed onto the inner wall of the mounting hole and placed in an oven at 80°C for 30 minutes to pre-cur it, forming a metal surface treatment layer.

[0030] (2) Pretreatment of graphite solid lubricant block: Select high-purity graphite (purity ≥99%) and process it into cylindrical graphite blocks with a diameter slightly smaller than the inlay hole (gap 0.05~0.10mm). Wipe the surface of the graphite block with anhydrous ethanol and dry it at 110℃ for 1 hour.

[0031] Preparation of impregnation solution containing carboxyl functional groups: Take 100 parts by weight of polyamic acid solution (solid content 18%, solvent NMP), add 30 parts by weight of NMP to dilute to a viscosity of about 180 mPa·s. Add 3 parts by weight of p-hydroxybenzoic acid and stir to dissolve. Add 0.8 parts by weight of nano ZnO (average particle size 50 nm) and ultrasonically disperse for 10 minutes.

[0032] Place the graphite block in a vacuum impregnation tank, pour in the impregnation liquid until completely submerged, and evacuate to a vacuum degree ≤100Pa, maintaining this for 20 minutes until no obvious bubbles escape. After restoring to normal pressure, remove the graphite block and drain excess liquid from the surface. Place it in an oven for pre-drying with a stepped temperature increase: hold at 80℃ for 30 minutes, then hold at 120℃ for 20 minutes.

[0033] (3) Hot pressing composite: The pretreated graphite block is embedded in the mounting hole of the metal matrix and placed in a hot press, with nitrogen gas introduced for protection. Hot pressing process: The temperature is increased from room temperature to 120℃ at 3℃ / min, held for 20 minutes, and the pressure is 0.2MPa; the temperature is increased to 180℃ at 3℃ / min, held for 60 minutes, and the pressure is increased to 0.5MPa; the temperature is increased to 220℃ at 2℃ / min, held for 90 minutes, and the pressure is increased to 1.0MPa; the temperature is decreased to below 80℃ at 2℃ / min, the pressure is released and the material is removed, thus obtaining the self-lubricating graphite-based friction-reducing composite material.

[0034] Example 2

[0035] (1) Pretreatment of metal substrate: Brass (H62) was selected as the metal substrate, and the size of the mounting hole was the same as in Example 1. The substrate was roughened by sandblasting (brown corundum sand, 100 mesh, air pressure 0.4MPa), ultrasonically cleaned with acetone, and dried at 80℃.

[0036] The formulation of the treatment solution was adjusted to: 5 parts by weight of KH-792 silane coupling agent and 5 parts by weight of 3,4-diaminobenzoic acid. The remaining steps were the same as in Example 1. The pre-curing conditions were 85°C for 25 minutes.

[0037] (2) Pretreatment of graphite solid lubricant blocks: The graphite blocks were treated in the same way as in Example 1. The impregnation solution formula was adjusted to: 100 parts by weight of polyamic acid solution (solid content 15%), 4 parts by weight of m-hydroxybenzoic acid, and 1.0 part by weight of nano ZnO. Pre-baking conditions: 80℃ for 30 minutes and 110℃ for 25 minutes.

[0038] (3) Hot pressing composite: The hot pressing process was adjusted as follows: the temperature of the second reaction section was 230°C, the temperature was kept for 120 minutes, and the pressure was increased to 1.2 MPa. The other conditions were the same as in Example 1.

[0039] Example 3

[0040] (1) Pretreatment of metal substrate: 6061 aluminum alloy was selected as the metal substrate. The formulation of the treatment solution was the same as in Example 1. The pre-curing conditions were 70℃ for 40 minutes.

[0041] (2) Pretreatment of graphite solid lubricant block: 5 parts by weight of 3,4-dihydroxybenzoic acid were added to the impregnation solution, and 1.0 part by weight of nano ZnO was added. The rest is the same as in Example 1.

[0042] (3) Hot pressing composite: The temperature of the second reaction section is 210℃, and the temperature is maintained for 100 minutes. The rest is the same as in Example 1.

[0043] The following comparison model was also set: Comparative Example 1: Based on Example 2, the difference is that the in-situ condensation reaction system is not used, and a commercially available traditional high-temperature adhesive (traditional phenolic resin adhesive) is used instead. Otherwise, it is the same as Example 2.

[0044] Comparative Example 2: Based on Example 2, the difference is that the metal matrix is ​​treated with only a common silane coupling agent and does not contain 3,4-diaminobenzoic acid, so it cannot provide o-phenylenediamine functional groups to participate in condensation and ring closure. Otherwise, it is the same as Example 2.

[0045] Comparative Example 3: Based on Example 2, the difference is that the graphite block was only impregnated with pure polyamic acid solution, without the addition of aromatic hydroxycarboxylic acid, and the carboxyl content came only from the terminal carboxyl groups of polyamic acid itself. The rest was the same as in Example 2.

[0046] Comparative Example 4: Based on Example 2, the difference is that the graphite block is not vacuum impregnated, but only the impregnation liquid is brushed on the surface, and the carboxyl functional groups exist only in the very shallow layer of the graphite surface. The rest is the same as Example 2.

[0047] Comparative Example 5: Based on Example 2, the difference is that the highest hot-pressing temperature is only 160°C, which is lower than the temperature required for effective ring closure of the benzimidazole ring. The rest is the same as Example 2.

[0048] Comparative Example 6: Based on Example 2, the difference is that the aromatic hydroxycarboxylic acid in the graphite impregnation solution is replaced with an aliphatic carboxylic acid (acetic acid), and the rest is the same as in Example 2.

[0049] Performance testing: Room temperature interfacial shear strength and high temperature interfacial shear strength were tested according to GB / T 7124-2008; tribological properties were tested according to GB / T 3960-2016; thermal stability was tested according to GB / T 27761-2011. The results are shown below: Table 1. Performance test results of self-lubricating graphite-based friction-reducing composite materials

[0050] Data Analysis: Test data shows that Examples 1-3, using the in-situ condensation process, maintained a shear strength of 7.1–8.9 MPa at 300°C, and the strength retention rate remained stable at 46.5%–47.6% from room temperature to 300°C. In contrast, Comparative Example 1, using traditional phenolic resin bonding, only achieved 8.7%, and Comparative Examples 2, 4, and 5 experienced overall interface detachment at 300°C. This difference stems from the unique rigid conjugated structure of the benzimidazole ring, whose thermal decomposition temperature exceeds 500°C. This structure forms a synergistic heat-resistant system with the polyimide matrix, resulting in a 5% thermal weight loss temperature of 481–492°C at the interface layer, an increase of over 135°C compared to traditional phenolic resin. Further comparative verification showed that the benzimidazole ring contributed 94% of the high-temperature interfacial strength: Comparative Example 2, which lacked the o-phenylenediamine functional group, could not form covalent crosslinks, and its strength at 300℃ was only 0.5 MPa; Comparative Example 5, which had insufficient ring-closing temperature, also experienced a significant performance degradation due to the low benzimidazole formation rate; while the aliphatic benzimidazole generated by Comparative Example 6, which used aliphatic carboxylic acids, had poor thermal stability, and its strength at 300℃ was only 33.7% of that of aromatic benzimidazole.

[0051] Synergistic optimization of surface treatment processes is a key guarantee for improving interface performance. The combination of vacuum impregnation and metal surface functionalization achieves multi-level interface bonding. The vacuum impregnation process allows the carboxyl-containing polyamic acid solution to penetrate 50-100 μm into the internal pores of graphite. After curing, it forms a resin nail mechanical anchoring structure, contributing approximately 40% of the interface bonding force. Comparative Example 4 only uses surface brushing, and the resin cannot penetrate the pores. Its room temperature shear strength is only 40.6% of that of Example 2, and it fails rapidly at high temperatures due to interface peeling. The functionalization treatment of the metal surface achieves a strong organic-inorganic interface bond through chemical bonding: after hydrolysis, KH-792 silane forms Si-OM covalent bonds with the hydroxyl groups on the metal surface, while anchoring 3,4-diaminobenzoic acid to provide o-phenylenediamine active sites, upgrading the interface bonding from simple mechanical interlocking to chemical bonding. In addition, the addition of nano-ZnO catalyst reduced the benzimidazole cyclization reaction temperature from 250℃ to 220℃, shortened the reaction time by 50%, and increased the ring-closure rate to over 95%, effectively avoiding excessive degradation of the resin at high temperatures.

[0052] The compatibility differences and performance regulation rules of different metal matrices provide a clear direction for the industrial application of composite materials. Test results show that the 45# steel matrix has the best overall performance, with a shear strength of 8.9 MPa at 300℃, suitable for heavy-duty, high-temperature general applications; the H62 brass matrix has a shear strength of 8.3 MPa at 300℃, and due to its excellent electrical and thermal conductivity, it is suitable for use in applications requiring heat dissipation and electrical conductivity, such as motors and bearings; the 6061 aluminum alloy matrix has a shear strength of 7.1 MPa at 300℃, meeting the lightweight requirements of aerospace, automotive parts, and other fields. The performance differences mainly stem from the different coordination abilities of metal ions with the nitrogen atoms of the benzimidazole ring, Fe... 3+ Its coordination ability is stronger than Cu 2+ And Al 3+ Therefore, the interfacial bonding with the steel substrate is stronger. In the future, the interfacial bonding strength can be further improved by performing micro-arc oxidation treatment on the aluminum alloy surface to increase the surface hydroxyl content and roughness; at the same time, the hot pressing process parameters can be optimized, and the heating rate and pressure curve can be adjusted for different metal substrates to achieve the best balance between performance and cost.

[0053] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A self-lubricating graphite-based friction-reducing composite material, characterized in that, include: Metal substrate with inlay holes or inlay grooves on its surface; A graphite solid lubricant block is embedded in the mounting hole or mounting groove of the metal substrate; And the adhesive interface layer located between the metal substrate and the graphite solid lubricant block; The adhesive interface layer is composed of a benzimidazole ring cross-linked structure formed by the in-situ condensation reaction of a metal surface treatment layer containing o-phenylenediamine functional groups and a graphite surface treatment layer containing carboxyl functional groups under hot-pressing conditions.

2. The self-lubricating graphite-based friction-reducing composite material according to claim 1, characterized in that: The metal substrate is made of steel, copper, copper alloy or aluminum; the surface roughness Ra of the inner wall of the inlay hole or inlay groove is 3.2 to 12.5 μm.

3. The self-lubricating graphite-based friction-reducing composite material according to claim 1, characterized in that: The metal surface treatment layer containing o-phenylenediamine functional groups is formed by coating and pre-curing a treatment solution containing N-(2-aminoethyl)-3-aminopropyltrialkoxysilane and 3,4-diaminobenzoic acid. The mass ratio of N-(2-aminoethyl)-3-aminopropyltrialkoxysilane to 3,4-diaminobenzoic acid is 1:0.3 to 1:1.

5.

4. The self-lubricating graphite-based friction-reducing composite material according to claim 1, characterized in that: The graphite surface treatment layer containing carboxyl functional groups is formed by vacuum impregnation and pre-baking of an impregnation solution containing polyamic acid and aromatic hydroxycarboxylic acid; The aromatic hydroxycarboxylic acid is one or more of p-hydroxybenzoic acid, m-hydroxybenzoic acid, or 3,4-dihydroxybenzoic acid, and the amount added is 2% to 15% of the solid mass of polyamic acid.

5. The self-lubricating graphite-based friction-reducing composite material according to claim 1, characterized in that: The benzimidazole ring forms a coordination bond with the surface of the metal matrix through its nitrogen atom; the thickness of the adhesive interface layer is 5-100 μm.

6. A method for preparing a self-lubricating graphite-based friction-reducing composite material as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Metal substrate pretreatment: The inner wall of the mounting hole or mounting groove of the metal substrate is roughened and cleaned by sandblasting, and then coated with a treatment liquid containing o-phenylenediamine functional groups. It is pre-cured at 70-90℃ for 20-40 minutes to form a metal surface treatment layer. S2. Pretreatment of graphite solid lubricating blocks: Immerse the graphite solid lubricating blocks in an impregnation solution containing carboxyl functional groups and keep them under a vacuum of ≤200Pa for 10 to 30 minutes. After taking them out, pre-bake them at 80 to 120℃ in a stepwise manner for 30 to 60 minutes to form a graphite surface treatment layer. S3. Hot-press composite: The treated graphite solid lubricant block is embedded in the inlay hole or inlay groove of the treated metal matrix, and in-situ condensation reaction and curing are carried out under hot-press conditions. After cooling, the self-lubricating graphite-based friction-reducing composite material is obtained.

7. The preparation method according to claim 6, characterized in that, In step S3, the hot pressing is carried out under an inert gas protective atmosphere, and the conditions are as follows: The preheating section is kept at 100–130℃ for 15–30 minutes at a pressure of 0.1–0.3 MPa; In the first reaction section, the temperature is increased to 160-190℃ at a rate of 2-5℃ / min, and held for 45-90 minutes, while the pressure is increased to 0.4-0.8MPa. The second reaction section is heated to 200-240℃ at a rate of 1-3℃ / min, held at that temperature for 60-120 minutes, and the pressure is increased to 0.8-1.5MPa. After the cooling section cools down to below 80℃ at a rate of ≤3℃ / min, it is depressurized and removed.

8. The preparation method according to claim 6, characterized in that, The preparation method of the treatment solution containing the o-phenylenediamine functional group is as follows: N-(2-aminoethyl)-3-aminopropyltrialkoxysilane is added to an alcohol-water mixed solvent with a pH of 4.0-5.5 and hydrolyzed at room temperature for 15-30 minutes; 3,4-diaminobenzoic acid is dissolved in anhydrous alcohol, heated to 40-50°C to dissolve, and then slowly added to the above hydrolysate and stirred at room temperature for 10-20 minutes to obtain the solution.

9. The preparation method according to claim 6, characterized in that, The impregnation solution containing carboxyl functional groups is prepared by diluting a polyamic acid solution with a polar aprotic solvent to a viscosity of 100-300 mPa·s, adding an aromatic hydroxycarboxylic acid, stirring and dissolving, optionally adding a nano-metal oxide catalyst, and ultrasonically dispersing for 5-15 minutes to obtain the solution; the nano-metal oxide catalyst is ZnO.

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