Aerospace bearing wear-resistant coating based on polysilazane and preparation method thereof

Abstract

The invention belongs to the technical field of coating preparation, and provides a polysilazane-based aerospace bearing wear-resistant coating and a preparation method thereof. Silicon carbide is subjected to surface hydroxylation and silane coupling agent modification, and is compounded with a zirconium-based metal organic framework; meanwhile, graphite phase carbon nitride and calcium fluoride are compounded to prepare a composite material to form bottom layer slurry; the preparation method comprises the following steps: modifying the surface of MoS2 through ascorbic acid to form a compound, mixing g-C3N4 and CaF2, and dispersing in a polysilazane solution to form intermediate layer slurry; preparing surface layer slurry from a MoS2 compound which is the same as that of the middle layer and g-C3N4atCaF2; through the multi-layer design of the bottom layer, the middle layer and the surface layer, the high hardness and thermal stability of SiC, the porous structure of MOF and the low friction performance of MoS2 are fully utilized, polysilazane serves as a base material and has a synergistic effect with all functional materials, and excellent wear resistance and lubricity are provided.

Description

Technical Field

[0001] The present invention belongs to the technical field of coating preparation, and relates to an anti-wear coating for aerospace bearings based on polysilazane and a preparation method thereof. Background Art

[0002] With the rapid development of modern aerospace technology, spacecraft are continuously moving towards higher performance, longer lifespan, and higher reliability. As one of the key components in spacecraft, aerospace bearings are subjected to harsh conditions such as extreme temperature variations, high-speed rotation, high vacuum, and strong radiation in complex working environments. To improve the service life and operational stability of aerospace bearings, the application of anti-wear coating technology is particularly important. However, traditional anti-wear coatings often have problems such as insufficient wear resistance and limited adhesion in high-temperature, high-vacuum, and strong friction environments, and can no longer fully meet the requirements of the aerospace field.

[0003] As an advanced inorganic polymer material, polysilazane has attracted much attention in the coating field in recent years due to its excellent high-temperature stability, oxidation resistance, chemical inertness, and mechanical strength. Polysilazane can be converted into ceramic silicon nitride materials at high temperatures, exhibiting extremely high hardness and excellent wear resistance. At the same time, the active functional groups in its molecular structure can react chemically with the substrate material, significantly improving the adhesion between the coating and the substrate. These characteristics make polysilazane an ideal coating precursor material for surface protection of aerospace bearings in extreme environments. Therefore, developing an anti-wear coating for aerospace bearings based on polysilazane to further improve the wear resistance of the coating and meet the higher requirements for material properties. Summary of the Invention

[0004] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide an anti-wear coating for aerospace bearings based on polysilazane and a preparation method thereof. By using multifunctional materials such as molybdenum disulfide, graphitic carbon nitride, silicon carbide, metal-organic frameworks, and calcium fluoride, combined with ascorbic acid modification, silane coupling agent modification, and calcination process, the surface functionalization and interface enhancement of the materials are achieved. The coating adopts a multi-layer design of a bottom layer, an intermediate layer, and a surface layer, thus meeting the needs of actual production.

[0005] To achieve this purpose, the present invention adopts the following technical solutions:

[0006] In the first aspect, the present invention provides a preparation method for an anti-wear coating for aerospace bearings based on polysilazane, and the preparation method is as follows:

[0007] A1, Add molybdenum disulfide powder into an ethanol aqueous solution, stir and disperse it, then perform ultrasonic oscillation under the condition of an ice-water bath. After centrifuging the ultrasonicated dispersion liquid, collect the upper liquid and wash it with ethanol, and disperse the washed molybdenum disulfide in deionized water to form a molybdenum disulfide dispersion liquid;

[0008] A2. Disperse ascorbic acid in a sodium phosphate solution. After stirring evenly, add the molybdenum disulfide dispersion to the sodium phosphate solution. Under a nitrogen atmosphere, heat to the first temperature and react fully. After the reaction is completed, wash, filter, and vacuum dry to obtain MoS2@P particles. Then disperse the MoS2@P particles in anhydrous ethanol, add a silane coupling agent, heat to the second temperature and stir to react. After the reaction is completed, wash and filter to obtain the surface-modified MoS2@P composite;

[0009] A3. Mix a calcium nitrate tetrahydrate solution and an ammonium fluoride solution, then add the g-C3N4 powder. After ultrasonic oscillation, heat to the first temperature to react. After the reaction is completed, centrifuge, wash, and vacuum dry. Place the dried product under a nitrogen atmosphere and heat to the third temperature for calcination to obtain the g-C3N4@CaF2 composite;

[0010] S1. Disperse silicon carbide in a sodium hydroxide solution, heat to the first temperature to react. After the reaction is completed, centrifuge and wash to obtain hydroxylated SiC. Disperse the hydroxylated SiC in an ethanol aqueous solution, add a silane coupling agent and heat to the fourth temperature to react. After the reaction is completed, centrifuge and wash to obtain the surface-modified SiC;

[0011] S2. Disperse a zirconium salt and terephthalic acid in N,N-dimethylformamide. After stirring evenly, add the surface-modified SiC. After ultrasonic dispersion, transfer it to a stainless steel reaction kettle with a polytetrafluoroethylene liner, heat to the fifth temperature to react. After the reaction is completed, wash and filter to obtain SiC@MOF. Under a nitrogen atmosphere, heat SiC@MOF to the third temperature for calcination to obtain the SiC@MOF composite;

[0012] S3. Disperse the SiC@MOF composite and the g-C3N4@CaF2 composite in solvent A. After ultrasonic oscillation, add polysilazane, PVP, and tetraethoxysilane, and stir evenly to form a bottom layer slurry. Disperse the MoS2@P composite and the g-C3N4@CaF2 composite in solvent B. After ultrasonic oscillation, add polysilazane and phenyltriethoxysilane, and stir evenly to obtain an intermediate layer slurry. Disperse the MoS2@P composite and the g-C3N4@CaF2 composite in solvent C. After ultrasonic oscillation, add polysilazane and hexamethyldisiloxane, and stir evenly to obtain a surface layer slurry. At room temperature, spray the bottom layer slurry, the intermediate layer slurry, and the surface layer slurry on the surface of the aerospace bearing matrix in sequence. The intermediate layer slurry and the surface layer slurry need to wait for the previous layer slurry to cure before spraying. After room temperature curing is completed, a polysilazane-based aerospace bearing wear-resistant coating is obtained.

[0013] Molybdenum disulfide is a typical two-dimensional layered material. Its crystal structure is composed of three atomic layers of sulfur-molybdenum-sulfur stacked together. Different layers are combined by weak van der Waals forces. During the friction process, the shear force applied externally can promote the interlayer slip of MoS2. This slip releases the stress caused by friction and reduces the friction coefficient. This slip mechanism enables MoS2 to exhibit excellent self-lubricating properties, especially in vacuum, ultra-high temperature or high-load environments. The crystal structure of MoS2 is formed by sulfur atoms and molybdenum atoms through strong covalent bonds to form a three-layer structure, which is stacked by weaker van der Waals forces to form a layered material. Under the action of external shear force, the interlayer van der Waals force of MoS2 is weak, enabling slip between layers. This slip releases the frictional stress and reduces the friction coefficient. In a vacuum environment, the interlayer slip mechanism of MoS2 completely depends on its inherent physical properties and has nothing to do with the atmosphere in the environment; the interlayer van der Waals force of MoS2 is weak, but the sulfur-molybdenum covalent bond within the layer is strong and has a high bond energy, enabling it to maintain a stable structure under high-temperature conditions. In a high-temperature environment, the sulfur atom layer on the surface of MoS2 can prevent oxygen from directly reacting with molybdenum atoms, thereby reducing the risk of oxidation or structural disintegration. Under high-temperature conditions, nano-scale cracks or defects may appear on the material surface. The interlayer slip characteristics of MoS2 can relieve the expansion of these defects through a dynamic stress release mechanism; the internal structure of MoS2 has high mechanical strength and hardness, which ensures that it will not easily undergo plastic deformation or fracture under high-load environments. Under high-load conditions, a large compressive stress will be generated at the friction interface. This pressure can promote the destruction of the interlayer van der Waals force of MoS2, making slip more likely to occur. The occurrence of slip not only reduces the shear force but also buffers the direct impact of the load on the coating substrate.

[0014] Ascorbic acid is a reducing agent. Its molecular structure contains multiple hydroxyl groups and enol structures, which can provide electrons to reduce substances in an oxidized state. In the reaction, ascorbic acid itself is oxidized to dehydroascorbic acid, and its role is to reduce the phosphorus element in sodium phosphate from a higher oxidation state to the elemental state. There are various allotropes of elemental phosphorus, including white phosphorus, red phosphorus, and black phosphorus. Black phosphorus is the most thermodynamically stable form among the allotropes of phosphorus. Under normal temperature and pressure conditions, black phosphorus has a layered structure similar to graphite. Each phosphorus atom is covalently bonded to three other phosphorus atoms, forming a two-dimensional structure. In contrast, white phosphorus has a tetrahedral structure with relatively high strain, so it is thermodynamically unstable; red phosphorus is an intermediate state, but its formation requires relatively high temperatures or special polymerization conditions. Therefore, under mild reduction conditions, the reaction tends to produce the most stable black phosphorus. When using ascorbic acid as a mild reducing agent, the stepwise reduction of sodium phosphate is slow and controlled, avoiding the possible formation of white phosphorus or red phosphorus under high-temperature conditions. Black phosphorus is a two-dimensional layered material, and its layers are also bonded by van der Waals forces. When a shear force is applied to the friction interface, the interlayer van der Waals forces of black phosphorus are easily broken, resulting in slip between the layers, which can participate in the lubrication of the friction interface. Microcracks or surface defects usually occur in the friction interface due to mechanical action, and these defects will further lead to local stress concentration and accelerate wear. Elemental phosphorus can be embedded in these cracks or defects through physical filling, reducing stress concentration and inhibiting crack propagation, thus achieving a self-repair effect. Due to the two-dimensional structure of the flakes, its spreading property is good, and it can effectively cover the surface of microcracks. And during high-temperature friction, the phosphorus flakes may react with oxygen or other chemical substances at the friction interface to form phosphorus oxides (such as phosphates) or phosphides. These reaction products form a stable protective film at the friction interface, which can inhibit further chemical oxidation or wear. The released phosphide or phosphorus oxide species can react chemically with the defects or active sites at the friction interface, and achieve interface repair by forming new chemical bonds (such as M-P or M-O-P bonds, where M refers to the metal element in the matrix material), further enhancing the integrity of the friction interface. The interlayer slip of MoS2 provides dynamic low-friction lubrication, while the two-dimensional structure of elemental phosphorus brings self-repair ability to the friction interface. During the friction process, MoS2 provides a basic low-friction environment. When there is local stress concentration or material wear, elemental phosphorus can be embedded in these cracks or defects through physical filling, reducing stress concentration and inhibiting crack propagation, thereby maintaining the integrity of the overall friction interface. At the same time, the presence of phosphides can passivate the active sites at the friction interface, inhibiting interface oxidation and wear. MoS2 reduces the generation of frictional heat through lubrication, while elemental phosphorus protects the interface at high temperatures through its physical properties and the released phosphides, forming a multiple protection mechanism.

[0015] g-C3N4 is a two-dimensional layered material. Each layer of its structure is a conjugated six-membered ring network based on triazine or cyanuric acid units. Within the layer, it is bonded by C=N and C-N covalent bonds, and between the layers, it is maintained by weak van der Waals forces. This weak interlayer binding force endows it with excellent mechanical flexibility and lubricity. The surface of g-C3N4 is rich in active sites such as amino groups, carbonyl groups, and π-electron clouds. These sites enable it to perform surface modification or composite with other materials (such as CaF2) through electrostatic interaction, hydrogen bonding, and π-π interaction. At the same time, g-C3N4 has a relatively high thermal decomposition temperature and exhibits good chemical stability and antioxidant properties at high temperatures. The two-dimensional layered structure of g-C3N4 enables it to reduce the friction coefficient through interlayer slip. During the friction process, the interlayer van der Waals forces are overcome by the shear force, resulting in interlayer slip and the release of frictional stress simultaneously. The surface active sites of g-C3N4 provide chemical binding sites for the growth and deposition of CaF2 nanoparticles. Through these sites, CaF2 nanoparticles can be evenly distributed and form a stable interface with g-C3N4. Calcium fluoride is an ionic compound with a cubic crystal structure, in which Ca 2+ and F - ions are bonded by strong ionic bonds. At high temperatures, ion migration may occur on the surface of CaF2 (redistribution of F - and Ca 2+ ), leading to a certain degree of relaxation and rearrangement of the surface structure. This rearrangement may reduce the binding force of surface atoms, thereby forming a slip layer with low shear strength on the surface. F- ions have strong chemical inertness and low surface energy, and can form a stable ionic film at the friction interface. This film can reduce the friction force between the interfaces; Ca 2+ is a positively charged ion. The electron cloud on the surface of the metal or oxide at the friction interface may be partially exposed, resulting in relative electronegativity. In a high-temperature environment, oxides and the like that may be generated on the surface of the interface material also have strong electronegativity and can attract Ca 2+ , Ca 2+ ions are adsorbed onto the surface of the friction interface material through electrostatic force, forming a positively charged ion adsorption layer. The electrostatically adsorbed Ca 2+ ions form an "electrochemical barrier" at the crack tip, reducing the diffusion of reactive oxygen species (such as O2 - , OH·), and inhibiting the chemical degradation of cracks. Disperse g-C3N4 into an aqueous solution, break the sheet agglomeration through ultrasonic treatment to form a stable two-dimensional sheet dispersion system. In the CaF2 generation reaction, add g-C3N4 to the solution and utilize its surface active sites to react with Ca 2+Adsorption occurs, and CaF2 particles gradually deposit on the surface of g-C3N4 to form a g-C3N4@CaF2 composite structure. Under the condition of nitrogen atmosphere calcination, a tighter bond is formed at the interface between CaF2 particles and g-C3N4 lamellae. g-C3N4 provides physical lubrication with low shear strength relying on its layered structure. Under the action of friction force, slip occurs between the layers of g-C3N4 to release stress and reduce the friction coefficient. CaF2 releases F - and Ca 2+ ions to form a lubricating ionic film at the interface. F- ions form a low-friction lubricating layer on the interface to further reduce the shear force. The formation of the lubricating film and the slip of g-C3N4 act synergistically to improve the lubrication performance of the wear-resistant coating.

[0016] Silicon carbide (SiC) is a thermodynamically stable compound with excellent mechanical strength, high-temperature resistance, and chemical inertness. However, its surface is usually rather inert and difficult to bind with other materials or molecules. Through chemical treatment under alkaline conditions, hydroxyl groups can be introduced onto the SiC surface to enhance its surface chemical activity. OH- ions in the alkaline solution react with silicon atoms on the SiC surface to form Si-OH. In the reaction, silicon atoms on the SiC surface combine with hydroxide ions in the solution to generate a hydroxylated silicon surface. Silane coupling agents are a class of molecules containing siloxane groups and organic functional groups. They can bind to the surface of inorganic materials through Si-O bonds and introduce organic functional groups onto the material surface. The siloxane groups in the silane coupling agent solution hydrolyze to form silanols, and the silanols generated by hydrolysis undergo a condensation reaction with the Si-OH groups on the hydroxylated SiC surface to form strong Si-O-Si bonds. The surface of the surface-modified SiC particles is bound with silane coupling agent molecules through Si-O-Si bonds. This modification not only improves the surface chemical activity of SiC but also introduces more organic functional groups, enhancing the binding ability with the MOF precursor; in the present invention, Zr 4+ reacts with terephthalic acid in the solvent N,N-dimethylformamide to form a Zr-based MOF. The silane-modified SiC surface provides attachment sites to promote the growth of MOF on the surface of SiC particles to form a composite structure. In the subsequent calcination stage, the organic part in the MOF is decomposed or carbonized to enhance the stability and mechanical properties of the composite material and form a porous structure at the same time. A large number of Si-OH groups are introduced onto the SiC surface through surface hydroxylation, and these groups provide chemical binding sites for further silane modification. The silane coupling agent binds to the SiC surface through Si-O-Si bonds and introduces reactive groups (such as amino groups and carboxyl groups) at the other end of the molecule. These groups can chemically interact with the MOF precursor to promote the growth of MOF on the SiC surface. During the growth process of MOF, Zr 4+Chemical coordination occurs with the functional groups modified on the SiC surface to form a strong interface bond. The strong interface bond ensures the uniform distribution of MOF on the SiC surface and avoids the interface delamination or cracking problems that may occur in traditional composite materials. The chemical bonding at the interface not only significantly improves the bonding strength between SiC and MOF, but also improves the composite material's resistance to crack extension through the effective transfer of interface energy. After calcination in a nitrogen atmosphere, the MOF shell is partially converted into metal oxides or carbides, further enhancing the high temperature resistance and oxidation resistance of the composite material. The porous structure is retained during the calcination process, providing excellent lubrication properties and mechanical structural properties. The porosity and flexibility of MOF can absorb part of the stress under friction and mechanical load, thereby delaying the formation and extension of cracks. The high strength of SiC provides a physical barrier for cracks, further improving the crack resistance. Secondly, the chemical inertness of SiC enables it to resist high-temperature oxidation, and MOF further forms a dense protective film after calcination to prevent the penetration of oxygen or water molecules.

[0017] In complex working environments (such as high temperature, friction, oxidation, etc.), single-function coatings often cannot meet multiple performance requirements. Therefore, gradient coatings gradually optimize the lubrication and wear resistance of coatings by combining functional materials at different levels. Polysilazane is a precursor material that is converted into a ceramic material by heating and curing. It has high hardness, chemical stability and high temperature resistance. It is the main support framework of the bottom layer. At the same time, polysilazane also provides a good dispersion and bonding interface for functional additives. In the bottom slurry, the porous structure of Zr-MOF absorbs mechanical impact and relieves stress concentration, thereby improving crack resistance. SiC is a superhard material with excellent wear resistance and high-temperature strength. The hydroxylated SiC undergoes a condensation reaction with the polysilazane matrix to form a stable Si-O-Si bond to enhance the interfacial bonding force. The two-dimensional layered structure of g-C3N4 has high chemical stability and heat resistance, which can prevent oxygen from penetrating into the substrate at high temperatures. The bottom slurry enhances the adhesion, wear resistance and crack resistance of the coating. In the middle and surface slurries, the layered structure of MoS2 provides lubrication through interlayer slip. Phosphorus can be embedded in these cracks or defects through physical filling, reducing stress concentration and inhibiting crack propagation, thereby maintaining the integrity of the overall friction interface. At the same time, the presence of phosphides can passivate the active sites of the friction interface, inhibiting interface oxidation and wear. The two-dimensional structure of g-C3N4 cooperates with MoS2 in the middle layer to provide lubrication.

[0018] As a preferred technical solution of the present invention, in A1, the mass volume ratio of the molybdenum disulfide powder to the ethanol aqueous solution is 1g:120mL.

[0019] In some alternative examples, the frequency of the ultrasonic oscillation is 60 - 80 KHz. For example, it can be 60.0 KHz, 62.0 KHz, 64.0 KHz, 66.0 KHz, 68.0 KHz, 70.0 KHz, 72.0 KHz, 74.0 KHz, 76.0 KHz, 78.0 KHz or 80.0 KHz. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0020] In some alternative examples, the ultrasonic oscillation time is 4 - 5 h. For example, it can be 4.0 h, 4.1 h, 4.2 h, 4.3 h, 4.4 h, 4.5 h, 4.6 h, 4.7 h, 4.8 h, 4.9 h or 5.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0021] In some alternative examples, the concentration of the molybdenum disulfide dispersion is 1 mg / mL.

[0022] As a preferred technical solution of the present invention, in A2, the mass - volume ratio of ascorbic acid to sodium phosphate solution is 1 g:50 mL.

[0023] The mass fraction of the sodium phosphate solution is 2 - 3 wt.%.

[0024] In some alternative examples, the volume ratio of the molybdenum disulfide dispersion to the sodium phosphate solution is 2:5.

[0025] In some alternative examples, the first temperature is 80 - 90 °C. For example, it can be 80.0 °C, 81.0 °C, 82.0 °C, 83.0 °C, 84.0 °C, 85.0 °C, 86.0 °C, 87.0 °C, 88.0 °C, 89.0 °C or 90.0 °C. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0026] In some alternative examples, the time for sufficient reaction at the first temperature is 6 - 7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h. However, it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0027] In some alternative examples, the mass - volume ratio of the MoS2@P particles to absolute ethanol is 1 mg:1 mL.

[0028] In some alternative examples, the silane coupling agent is 3-aminopropyltriethoxysilane, with a mass that is 10-20% of the mass of the MoS2@P particles. For example, it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0029] In some alternative examples, the second temperature is 40-50 °C. For example, it can be 40.0 °C, 41.0 °C, 42.0 °C, 43.0 °C, 44.0 °C, 45.0 °C, 46.0 °C, 47.0 °C, 48.0 °C, 49.0 °C, or 50.0 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0030] In some alternative examples, the reaction time under stirring at the second temperature is 5-6 h. For example, it can be 5.0 h, 5.1 h, 5.2 h, 5.3 h, 5.4 h, 5.5 h, 5.6 h, 5.7 h, 5.8 h, 5.9 h, or 6.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0031] As a preferred technical solution of the present invention, in A3, the molar ratio of calcium nitrate tetrahydrate to ammonium fluoride is 1:1.

[0032] In some alternative examples, the volume ratio of the calcium nitrate tetrahydrate solution to the ammonium fluoride solution is 1:1.

[0033] In some alternative examples, the concentration of the calcium nitrate tetrahydrate solution is 0.1 M.

[0034] In some alternative examples, the mass-volume ratio of the g-C3N4 powder to the calcium nitrate tetrahydrate solution is 1 g:100 mL.

[0035] In some alternative examples, the reaction time at the first temperature is 6-7 h. For example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h, or 7.0 h, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0036] In some alternative examples, the third temperature is 300-310 °C. For example, it can be 300.0 °C, 301.0 °C, 302.0 °C, 303.0 °C, 304.0 °C, 305.0 °C, 306.0 °C, 307.0 °C, 308.0 °C, 309.0 °C, or 310.0 °C, but is not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0037] In some alternative embodiments, the calcination time at the third temperature is 2 - 3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0038] As a preferred technical solution of the present invention, in S1, the mass - to - volume ratio of silicon carbide to sodium hydroxide solution is 1 g:50 mL.

[0039] In some alternative embodiments, the concentration of the sodium hydroxide solution is 1 M.

[0040] In some alternative embodiments, the reaction time at the first temperature is 2 - 3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0041] In some alternative embodiments, the silane coupling agent is 3 - aminopropyltriethoxysilane, and its mass is 40 - 50% of the mass of hydroxylated SiC, for example, it can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50%, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0042] In some alternative embodiments, the fourth temperature is 70 - 80 °C, for example, it can be 70.0 °C, 71.0 °C, 72.0 °C, 73.0 °C, 74.0 °C, 75.0 °C, 76.0 °C, 77.0 °C, 78.0 °C, 79.0 °C or 80.0 °C, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0043] In some alternative embodiments, the reaction time at the fourth temperature is 6 - 7 h, for example, it can be 6.0 h, 6.1 h, 6.2 h, 6.3 h, 6.4 h, 6.5 h, 6.6 h, 6.7 h, 6.8 h, 6.9 h or 7.0 h, but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0044] As a preferred technical solution of the present invention, in S2, the zirconium salt is Zr(NO3)4·5H2O, and the molar - to - volume ratio of the zirconium salt to N,N - dimethylformamide is 1 mmol:50 mL.

[0045] In some alternative examples, the molar ratio of the zirconium salt to terephthalic acid is 1:1.

[0046] In some alternative examples, the mass-to-volume ratio of the surface-modified SiC to N,N-dimethylformamide is 0.2 g:50 mL.

[0047] In some alternative examples, the fifth temperature is 130 - 140 °C, for example, it can be 130.0 °C, 131.0 °C, 132.0 °C, 133.0 °C, 134.0 °C, 135.0 °C, 136.0 °C, 137.0 °C, 138.0 °C, 139.0 °C or 140.0 °C, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0048] In some alternative examples, the reaction time at the fifth temperature is 14 - 16 h, for example, it can be 14.0 h, 14.2 h, 14.4 h, 14.6 h, 14.8 h, 15.0 h, 15.2 h, 15.4 h, 15.6 h, 15.8 h or 16.0 h, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0049] In some alternative examples, the calcination time at the third temperature is 2 - 3 h, for example, it can be 2.0 h, 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h or 3.0 h, but it is not limited to the listed values, and other unlisted values within this range are equally applicable.

[0050] As a preferred technical solution of the present invention, in S3, in the bottom layer slurry, the mass ratio of the SiC@MOF composite, g-C3N4@CaF2 composite, polysilazane, and PVP is 0.5:0.25:2:0.1.

[0051] In some alternative examples, the solvent A is a mixed solution of DMF and absolute ethanol, and the volume ratio is 3:1.

[0052] In some alternative examples, the mass-to-volume ratio of the polysilazane to the solvent A is 1 g:10 mL.

[0053] In some alternative examples, when preparing the intermediate layer slurry, the mass ratio of the MoS2@P composite, g-C3N4@CaF2 composite, polysilazane, and phenyltriethoxysilane is 0.5:0.25:2:0.2.

[0054] The solvent B is a mixed solution of DMF and absolute ethanol, and the volume ratio is 2:1.

[0055] The mass-volume ratio of the polysilazane to Solvent B is 1 g:10 mL.

[0056] In some alternative examples, in the surface slurry, the mass ratio of the MoS2@P composite, the g-C3N4@CaF2 composite, the polysilazane, and hexamethyldisiloxane is 0.5:0.25:2:0.2.

[0057] Solvent B is a mixed solution of DMF and absolute ethanol with a volume ratio of 1:1.

[0058] The mass-volume ratio of the polysilazane to Solvent B is 1 g:10 mL.

[0059] In a second aspect, the present invention provides a polysilazane-based aerospace bearing wear-resistant coating prepared by using the preparation method of a polysilazane-based aerospace bearing wear-resistant coating described in the first aspect.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The interlayer slip of MoS2 provides dynamic low-friction lubrication, and the two-dimensional structure of elemental phosphorus brings self-healing ability to the friction interface. When there is local stress concentration or material wear, elemental phosphorus can be embedded in these cracks or defects through physical filling, reducing stress concentration and inhibiting crack propagation, thereby maintaining the integrity of the overall friction interface. At the same time, the presence of phosphides can passivate the active sites of the friction interface. MoS2 reduces the generation of frictional heat through lubrication, and elemental phosphorus protects the interface at high temperatures by releasing phosphides, forming a multiple protection mechanism; (2) g-C3N4 provides physical lubrication with low shear strength relying on its layered structure. Under the action of frictional force, the interlayer of g-C3N4 slips to release stress and reduce the friction coefficient. CaF2 further reduces the shear force by releasing ions to form a low-friction lubricating layer on the interface. The formation of the lubricating film and the slip of g-C3N4 act synergistically to improve the lubrication performance of the wear-resistant coating; (3) SiC introduces a large number of Si-OH groups through surface hydroxylation, promoting the growth of MOF on the surface of SiC to form a strong interfacial bond. After calcination, the porosity and flexibility of MOF can absorb part of the stress under the action of friction and mechanical load, thereby delaying the formation and propagation of cracks. The high strength of SiC provides a physical barrier for cracks, further improving the crack resistance performance. Secondly, the chemical inertness of SiC enables it to resist high-temperature oxidation, and after calcination, MOF further forms a dense protective film to prevent the penetration of oxygen or water molecules; (4) The gradient coating gradually optimizes the lubrication performance and wear resistance of the coating through the combination of functional materials at different levels. The polysilazane provides good wear resistance and forms a synergistic effect with other materials, enhancing the coating adhesion and wear resistance. Description of the Drawings

[0061] Figure 1SEM image of the g-C3N4@CaF2 composite prepared in Example 1 of the present invention;

[0062] Figure 2 SEM image of the SiC@MOF composite prepared in Example 1 of the present invention;

[0063] Figure 3 TEM image of the SiC@MOF composite prepared in Example 1 of the present invention. Detailed implementation manners

[0064] The technical solution of the present invention will be described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific specific implementation manners of the present invention and are used to illustrate the concept of the present invention; these descriptions are all explanatory and exemplary, and should not be construed as limiting the implementation manners of the present invention and the protection scope of the present invention. Except for the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims of this application and its specification. These technical solutions include technical solutions that make any obvious substitutions and modifications to the embodiments described herein.

[0065] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products and have not been further purified.

[0066] Example 1

[0067] This example provides a wear-resistant coating for aerospace bearings based on polysilazane, and its preparation method specifically includes the following steps:

[0068] A1. Add 1 g of molybdenum disulfide powder to 120 mL of ethanol aqueous solution, stir and disperse, and then under the condition of an ice-water bath, perform ultrasonic oscillation at 60 KHz for 4.3 h. After centrifuging the ultrasonicated dispersion, collect the upper layer liquid and wash it with ethanol, and disperse the washed molybdenum disulfide in deionized water to form a 1 mg / mL molybdenum disulfide dispersion;

[0069] A2. Disperse 1 g of ascorbic acid in 50 mL of 2.4 wt.% sodium phosphate solution, stir evenly, then add 20 mL of molybdenum disulfide dispersion to the sodium phosphate solution. Under a nitrogen atmosphere, heat up to 81 °C and react fully for 6.1 h. After the reaction is completed, wash, filter, and vacuum dry to obtain MoS2@P particles. Then disperse 100 mg of MoS2@P particles in 100 mL of absolute ethanol, add 12 mg of 3-aminopropyltriethoxysilane, heat up to 44 °C and stir and react for 5.2 h. After the reaction is completed, wash and filter to obtain the surface-modified MoS2@P composite;

[0070] A3. Mix 50 mL of 0.1 M calcium nitrate tetrahydrate solution with 50 mL of 0.1 M ammonium fluoride solution, then add 0.5 g of g-C3N4 powder. After ultrasonic oscillation, heat the mixture to 81 °C and react for 6.4 h. After the reaction, centrifuge, wash, and dry in vacuo. Place the dried product in a nitrogen atmosphere, heat it to 308 °C and calcine for 2.4 h to obtain the g-C3N4@CaF2 composite;

[0071] S1. Disperse 1 g of silicon carbide in 50 mL of 1 M sodium hydroxide solution, heat to 88 °C and react for 2.8 h. After the reaction, centrifuge and wash to obtain hydroxylated SiC. Disperse 400 mg of hydroxylated SiC in 40 mL of ethanol aqueous solution, add 160 mg of 3-aminopropyltriethoxysilane and heat to 72 °C to react for 6.3 h. After the reaction, centrifuge and wash to obtain surface-modified SiC;

[0072] S2. Disperse 1 mmol of ZrNO 34 ·5H2O and 1 mmol of terephthalic acid in 50 mL of N,N-dimethylformamide. After stirring evenly, add 0.2 g of surface-modified SiC. After ultrasonic dispersion, transfer the mixture to a stainless steel autoclave lined with polytetrafluoroethylene, heat to 133 °C and react for 14.2 h. After the reaction, wash and filter to obtain SiC@MOF. Under a nitrogen atmosphere, heat SiC@MOF to 306 °C and calcine for 2.4 h to obtain the SiC@MOF composite;

[0073] S3. Disperse 0.5 g of the SiC@MOF composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent A. After ultrasonic oscillation, add 2 g of polysilazane and 0.1 g of PVP, and stir evenly to form the bottom layer slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent B. After ultrasonic oscillation, add 2 g of polysilazane and stir evenly to obtain the middle layer slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent C. After ultrasonic oscillation, add 2 g of polysilazane and stir evenly to obtain the surface layer slurry. At room temperature, spray the bottom layer slurry, the middle layer slurry, and the surface layer slurry on the surface of the aerospace bearing substrate in sequence. The middle layer slurry and the surface layer slurry need to wait for the previous layer slurry to solidify before spraying. After room temperature curing is completed, a polysilazane-based wear-resistant coating for aerospace bearings is obtained.

[0074] Figure 1 This is the SEM image of the g-C3N4@CaF2 composite prepared in this example. It can be clearly seen that CaF2 is evenly deposited on the surface of g-C3N4 without obvious agglomeration; Figure 2 This is the SEM image of the SiC@MOF composite prepared in this example;Figure 3 TEM image of the SiC@MOF composite prepared in this example.

[0075] Example 2

[0076] This example provides a wear-resistant coating for aerospace bearings based on polysilazane, and its preparation method specifically includes the following steps:

[0077] A1. Add 1 g of molybdenum disulfide powder to 120 mL of an ethanol aqueous solution, stir and disperse it, then under the condition of an ice-water bath, ultrasonically vibrate it at 70 KHz for 4.8 h. After centrifuging the ultrasonicated dispersion liquid, collect the upper liquid and wash it with ethanol, and disperse the washed molybdenum disulfide in deionized water to form a 1 mg / mL molybdenum disulfide dispersion liquid;

[0078] A2. Disperse 1 g of ascorbic acid in 50 mL of a 2.1 wt.% sodium phosphate solution, stir evenly, then add 20 mL of the molybdenum disulfide dispersion liquid to the sodium phosphate solution. Under a nitrogen atmosphere, heat it to 89 °C and react for 6.8 h. After the reaction is completed, wash, filter, and vacuum dry to obtain MoS2@P particles. Then disperse 100 mg of MoS2@P particles in 100 mL of absolute ethanol, add 19 mg of 3-aminopropyltriethoxysilane, heat it to 41 °C and stir and react for 5.7 h. After the reaction is completed, wash and filter to obtain the surface-modified MoS2@P composite;

[0079] A3. Mix 50 mL of a 0.1 M calcium nitrate tetrahydrate solution with 50 mL of a 0.1 M ammonium fluoride solution, then add 0.5 g of g-C3N4 powder, ultrasonically vibrate it, and then heat it to 89 °C and react for 6.9 h. After the reaction is completed, centrifuge, wash, and vacuum dry. Place the dried product under a nitrogen atmosphere, heat it to 301 °C and calcine it for 2.1 h to obtain the g-C3N4@CaF2 composite;

[0080] S1. Disperse 1 g of silicon carbide in 50 mL of a 1 M sodium hydroxide solution, heat it to 81 °C and react for 2.6 h. After the reaction is completed, centrifuge and wash to obtain hydroxylated SiC. Disperse 400 mg of hydroxylated SiC in 40 mL of an ethanol aqueous solution, add 180 mg of 3-aminopropyltriethoxysilane and heat it to 76 °C and react for 6.8 h. After the reaction is completed, centrifuge and wash to obtain the surface-modified SiC;

[0081] S2. 1 mmol of ZrNO 34Disperse 0.5H2O and 1 mmol of terephthalic acid in 50 mL of N,N-dimethylformamide. After stirring evenly, add 0.2 g of surface-modified SiC. After ultrasonic dispersion, transfer it to a stainless-steel reaction kettle lined with polytetrafluoroethylene. Heat it to 130 °C and react for 15.8 h. After the reaction, wash and filter to obtain SiC@MOF. Under a nitrogen atmosphere, heat SiC@MOF to 301 °C and calcine it for 2.9 h to obtain the SiC@MOF composite;

[0082] S3, Disperse 0.5 g of the SiC@MOF composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent A. After ultrasonic oscillation, add 2 g of polysilazane and 0.1 g of PVP, and stir evenly to form the bottom slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent B. After ultrasonic oscillation, add 2 g of polysilazane, and stir evenly to obtain the middle layer slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent C. After ultrasonic oscillation, add 2 g of polysilazane, and stir evenly to obtain the surface layer slurry. At room temperature, spray the bottom slurry, the middle layer slurry, and the surface layer slurry on the surface of the aerospace bearing substrate in sequence. The middle layer slurry and the surface layer slurry need to wait for the previous layer of slurry to cure before spraying. After room temperature curing, a polysilazane-based wear-resistant coating for aerospace bearings is obtained.

[0083] Example 3

[0084] This example provides a polysilazane-based wear-resistant coating for aerospace bearings, and its preparation method specifically includes the following steps:

[0085] A1, Add 1 g of molybdenum disulfide powder to 120 mL of an ethanol aqueous solution. After stirring and dispersing, under the condition of an ice-water bath, ultrasonic oscillate at 80 KHz for 4.1 h. Centrifuge the ultrasonicated dispersion liquid, collect the upper liquid, wash it with ethanol, and disperse the washed molybdenum disulfide in deionized water to form a 1 mg / mL molybdenum disulfide dispersion liquid;

[0086] A2, Disperse 1 g of ascorbic acid in 50 mL of a 2.9 wt.% sodium phosphate solution. After stirring evenly, add 20 mL of the molybdenum disulfide dispersion liquid to the sodium phosphate solution. Under a nitrogen atmosphere, heat it to 86 °C and react fully for 6.4 h. After the reaction, wash, filter, and vacuum dry to obtain MoS2@P particles. Then disperse 100 mg of MoS2@P particles in 100 mL of absolute ethanol, add 16 mg of 3-aminopropyltriethoxysilane, heat it to 49 °C and stir and react for 5.9 h. After the reaction, wash and filter to obtain the surface-modified MoS2@P composite;

[0087] A3. Mix 50 mL of 0.1 M calcium nitrate tetrahydrate solution with 50 mL of 0.1 M ammonium fluoride solution, then add 0.5 g of g-C3N4 powder. After ultrasonic oscillation, heat the mixture to 86 °C and react for 6.1 h. After the reaction, centrifuge, wash, and dry under vacuum. Place the dried product in a nitrogen atmosphere, heat it to 305 °C, and calcine for 2.9 h to obtain the g-C3N4@CaF2 composite;

[0088] S1. Disperse 1 g of silicon carbide in 50 mL of 1 M sodium hydroxide solution, heat it to 86 °C, and react for 2.1 h. After the reaction is completed, centrifuge and wash to obtain hydroxylated SiC. Disperse 400 mg of hydroxylated SiC in 40 mL of an ethanol-water solution, add 200 mg of 3-aminopropyltriethoxysilane, and heat it to 79 °C to react for 6.1 h. After the reaction, centrifuge and wash to obtain surface-modified SiC;

[0089] S2. Disperse 1 mmol of ZrNO 34 ·5H2O and 1 mmol of terephthalic acid in 50 mL of N,N-dimethylformamide. After stirring evenly, add 0.2 g of surface-modified SiC. After ultrasonic dispersion, transfer the mixture to a stainless-steel autoclave with a polytetrafluoroethylene liner, heat it to 139 °C, and react for 14.6 h. After the reaction, wash and filter to obtain SiC@MOF. Under a nitrogen atmosphere, heat SiC@MOF to 307 °C and calcine for 2.5 h to obtain the SiC@MOF composite;

[0090] S3. Disperse 0.5 g of the SiC@MOF composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent A. After ultrasonic oscillation, add 2 g of polysilazane and 0.1 g of PVP, and stir evenly to form the bottom slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent B. After ultrasonic oscillation, add 2 g of polysilazane, and stir evenly to obtain the intermediate slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent C. After ultrasonic oscillation, add 2 g of polysilazane, and stir evenly to obtain the surface slurry. At room temperature, spray the bottom slurry, the intermediate slurry, and the surface slurry onto the surface of the aerospace bearing matrix in sequence. The intermediate slurry and the surface slurry need to wait for the previous layer of slurry to solidify before spraying. After room-temperature curing is completed, a polysilazane-based wear-resistant coating for aerospace bearings is obtained.

[0091] Example 4

[0092] This example provides a polysilazane-based wear-resistant coating for aerospace bearings, and its preparation method specifically includes the following steps:

[0093] A1. Add 1 g of molybdenum disulfide powder to 120 mL of an ethanol aqueous solution. After stirring and dispersing, under the condition of an ice-water bath, ultrasonically vibrate at 60 KHz for 4.9 h. After centrifuging the ultrasonicated dispersion, collect the upper liquid and wash it with ethanol, and disperse the washed molybdenum disulfide in deionized water to form a 1 mg / mL molybdenum disulfide dispersion;

[0094] A2. Disperse 1 g of ascorbic acid in 50 mL of a 2.7 wt.% sodium phosphate solution. After stirring evenly, add 20 mL of the molybdenum disulfide dispersion to the sodium phosphate solution. Under a nitrogen atmosphere, heat to 83 °C and react fully for 6.7 h. After the reaction, wash, filter, and vacuum dry to obtain MoS2@P particles. Then disperse 100 mg of MoS2@P particles in 100 mL of absolute ethanol, add 13 mg of 3-aminopropyltriethoxysilane, heat to 46 °C and stir to react for 5.4 h. After the reaction, wash and filter to obtain a surface-modified MoS2@P composite;

[0095] A3. Mix 50 mL of a 0.1 M calcium nitrate tetrahydrate solution with 50 mL of a 0.1 M ammonium fluoride solution, then add 0.5 g of g-C3N4 powder. After ultrasonic vibration, heat to 83 °C and react for 6.7 h. After the reaction, centrifuge, wash, and vacuum dry. Place the dried product under a nitrogen atmosphere, heat to 303 °C and calcine for 2.7 h to obtain a g-C3N4@CaF2 composite;

[0096] S1. Disperse 1 g of silicon carbide in 50 mL of a 1 M sodium hydroxide solution, heat to 84 °C and react for 2.4 h. After the reaction is completed, centrifuge and wash to obtain hydroxylated SiC. Disperse 400 mg of hydroxylated SiC in 40 mL of an ethanol aqueous solution, add 170 mg of 3-aminopropyltriethoxysilane and heat to 74 °C to react for 6.5 h. After the reaction, centrifuge and wash to obtain a surface-modified SiC;

[0097] S2. Disperse 1 mmol of ZrNO 34 ·5H2O and 1 mmol of terephthalic acid in 50 mL of N,N-dimethylformamide. After stirring evenly, add 0.2 g of the surface-modified SiC. After ultrasonic dispersion, transfer it to a stainless steel reaction kettle with a polytetrafluoroethylene inner liner, heat to 136 °C and react for 15.3 h. After the reaction, wash and filter to obtain SiC@MOF. Under a nitrogen atmosphere, heat SiC@MOF to 310 °C and calcine for 2.2 h to obtain a SiC@MOF composite;

[0098] S3. Disperse 0.5 g of the SiC@MOF composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent A. After ultrasonic oscillation, add 2 g of polysilazane and 0.1 g of PVP, and stir evenly to form the bottom slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent B. After ultrasonic oscillation, add 2 g of polysilazane and stir evenly to obtain the intermediate slurry. Disperse 0.5 g of the MoS2@P composite and 0.25 g of the g-C3N4@CaF2 composite in 20 mL of solvent C. After ultrasonic oscillation, add 2 g of polysilazane and stir evenly to obtain the surface slurry. At room temperature, spray the bottom slurry, the intermediate slurry, and the surface slurry on the surface of the aerospace bearing matrix in sequence. The intermediate slurry and the surface slurry need to wait for the previous layer of slurry to solidify before spraying. After room temperature curing, a polysilazane-based wear-resistant coating for aerospace bearings is obtained.

[0099] Comparative Example 1

[0100] This comparative example provides a polysilazane-based wear-resistant coating for aerospace bearings. The difference from Example 1 is that the mass fraction of the sodium phosphate solution in A2 is adjusted to 4.7 wt.%, which is 2.3 wt.% higher than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0101] Comparative Example 2

[0102] This comparative example provides a polysilazane-based wear-resistant coating for aerospace bearings. The difference from Example 1 is that the mass fraction of the sodium phosphate solution in A2 is adjusted to 0.1 wt.%, which is 2.3 wt.% lower than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0103] Comparative Example 3

[0104] This comparative example provides a polysilazane-based wear-resistant coating for aerospace bearings. The difference from Example 1 is that the mass of 3-aminopropyltriethoxysilane in S1 is adjusted to 300 mg, which is 140 mg higher than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0105] Comparative Example 4

[0106] This comparative example provides a polysilazane-based wear-resistant coating for aerospace bearings. The difference from Example 1 is that the mass of 3-aminopropyltriethoxysilane in S1 is adjusted to 20 mg, which is 140 mg lower than that in Example 1. Other process parameters and operating conditions are exactly the same as those in Example 1.

[0107] The hardness test method of the aerospace bearing wear-resistant coating based on polysilazane prepared by the present invention is GB / T6739-2022; the wear resistance mass loss test method is GB / T 1768-2006; the adhesion test method is GB / T 9286-2021; and the thermal shock test method is GB / T 30873-2014 (400°C / 1h, water quenching method five times). The test results are shown in Table 1.

[0108] Table 1 Test results of wear-resistant coatings for aerospace bearings based on polysilazane in Examples 1-4 and Comparative Examples 1-4

[0109] Hardness Mass loss (%) Adhesion Thermal shock test Example 1 5H 0.33 Grade 0 No visible cracking Example 2 5H 0.38 Grade 0 No visible cracking Example 3 5H 0.34 Grade 0 No visible cracking Example 4 5H 0.31 Grade 0 No visible cracking Comparative example 1 3H 0.57 Grade 2 Visible cracking Comparative example 2 3H 0.59 Grade 1 Visible cracking Comparative example 3 2H 0.61 Grade 2 Visible cracking Comparative example 4 3H 0.54 Grade 2 Visible cracking

[0110] It can be seen from Table 1 that, compared with Example 1, the hardness, wear resistance and adhesion of Comparative Example 1 are all lower than those of Example 1, and the result of the thermal shock test is that there is visible cracking; the hardness, wear resistance and adhesion of Comparative Example 2 are all lower than those of Example 1, and the result of the thermal shock test is that there is visible cracking. This is because the main role of sodium phosphate in the reaction system is to provide phosphate ions, which introduce phosphorus elements into the MoS2 surface through chemical reactions to form a MoS2@P complex. Too high or too low a mass fraction of sodium phosphate will affect the uniformity of surface functionalization and the stability of the generated phosphorus-based coating. In Comparative Example 1, the mass fraction of the sodium phosphate solution is too high. Excessive concentration of phosphate ions may lead to the formation of a thick or non-uniform phosphorus modification layer on the surface, forming a fragile interface, resulting in a decrease in the hardness of the coating and hindering the effective reaction between the silane coupling agent and the MoS2 surface. The by-products in the phosphorus modification layer (such as phosphate deposits) may reduce the interfacial bonding force, resulting in a decrease in the adhesion of the coating. Excessive concentration of sodium phosphate may lead to the formation of a thicker phosphating layer on the MoS2 surface, which is easy to break or peel off during friction. At the same time, too many by-products may form a weak interface in the coating, reducing the overall wear resistance. Excessive phosphorus modification may lead to the formation of too many phosphate phases in the coating, which are unstable and easily decomposed or expanded at high temperatures, resulting in cracks in the coating during thermal shock. The mass fraction of the sodium phosphate solution in Comparative Example 2 is too low, the phosphorus modification layer on the MoS2 surface is thin and uneven, and there are fewer surface active sites. In the subsequent coating preparation, the chemical bonding effect between the silane coupling agent and MoS2 is weakened, the phosphorus modification on the MoS2 surface is insufficient, and a stable interface structure cannot be formed in the coating. The insufficiently modified MoS2 particles are easy to fall off during the friction process, resulting in reduced wear resistance of the coating. At the same time, the insufficiently phosphorus-modified MoS2 particles are unevenly distributed in the coating, resulting in mismatched thermal expansion coefficients, and the coating is prone to cracks due to stress concentration during high-temperature cycles.

[0111] As can be seen from Table 1, compared with Example 1, the hardness, wear resistance, and adhesion of Comparative Example 3 are all lower than those of Example 1, and the thermal shock test result shows visible cracking; the hardness, wear resistance, and adhesion of Comparative Example 4 are all lower than those of Example 1, and the thermal shock test result shows visible cracking. As a silane coupling agent, 3-aminopropyltriethoxysilane can form chemical bonds between components through chemical reactions, thereby improving the interfacial bonding force and overall performance of the coating. In Comparative Example 3, there is too much 3-aminopropyltriethoxysilane, and the surface modification layer is too thick. Excessive condensation reactions may occur between silane molecules, generating excess siloxane polymerization by-products. The too-thick silane layer may form a weak bonding area at the interface, thus reducing adhesion and hardness. The mechanical strength of the silane layer itself is relatively low, and the silane layer is easily sheared or damaged during the friction process, resulting in reduced wear resistance. In Comparative Example 4, there is too little 3-aminopropyltriethoxysilane. When the dosage of 3-aminopropyltriethoxysilane is too low, the silane coupling agent is not sufficient to fully cover SiC, and the incompletely modified SiC or MoS2@P particles have a weak bonding force with the matrix (such as polysilazane) in the coating and are difficult to form a firm interfacial bond with the polysilazane matrix in the coating, reducing the wear resistance.

[0112] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of an anti-wear coating for aerospace bearings based on polysilazane, characterized in that, The preparation method includes: S1. Dispersing silicon carbide in a sodium hydroxide solution, reacting to obtain hydroxylated SiC, dispersing the hydroxylated SiC in an ethanol aqueous solution, adding a silane coupling agent, and reacting to obtain surface-modified SiC; S2. Dispersing a zirconium salt and terephthalic acid in N,N-dimethylformamide, adding the surface-modified SiC, reacting to obtain SiC@MOF, and calcining the SiC@MOF under a nitrogen atmosphere to obtain a SiC@MOF composite; S3. Dispersing the SiC@MOF composite and the g-C3N4@CaF2 composite in solvent A, adding polysilazane, PVP, and tetraethoxysilane to form a bottom layer slurry, dispersing the MoS2@P composite and the g-C3N4@CaF2 composite in solvent B, adding polysilazane and phenyltriethoxysilane to obtain an intermediate layer slurry, dispersing the MoS2@P composite and the g-C3N4@CaF2 composite in solvent C, adding polysilazane and hexamethyldisiloxane to obtain a surface layer slurry, and obtaining a polysilazane-based wear-resistant coating for aerospace bearings after curing at room temperature.

2. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 1, wherein, The preparation method of the MoS2@P composite includes: A1. Adding molybdenum disulfide powder to an ethanol aqueous solution, stirring and dispersing, performing ultrasonic oscillation under the condition of an ice-water bath, centrifuging the ultrasonicated dispersion, collecting the upper liquid, washing with ethanol, and dispersing the washed molybdenum disulfide in deionized water to form a molybdenum disulfide dispersion; A2. Dispersing ascorbic acid in a sodium phosphate solution, stirring evenly, adding the molybdenum disulfide dispersion to the sodium phosphate solution, heating to a first temperature under a nitrogen atmosphere for sufficient reaction, washing, filtering, and vacuum drying after the reaction to obtain MoS2@P particles, dispersing the MoS2@P particles in absolute ethanol, adding a silane coupling agent, heating to a second temperature and stirring for reaction, and washing and filtering after the reaction to obtain a surface-modified MoS2@P composite.

3. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 1, characterized in that, The preparation method of the g-C3N4@CaF2 composite includes: A3. Mixing a calcium nitrate tetrahydrate solution and an ammonium fluoride solution, adding g-C3N4 powder, performing ultrasonic oscillation, heating to a first temperature for reaction, centrifuging and washing and vacuum drying after the reaction, placing the dried product under a nitrogen atmosphere, and calcining at a third temperature to obtain a g-C3N4@CaF2 composite.

4. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 1, wherein, In S1: The concentration of the sodium hydroxide solution is 1M; The silane coupling agent is 3-aminopropyltriethoxysilane, and the mass is 40-50% of the mass of the hydroxylated SiC.

5. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 1, characterized in that, In S2: The zirconium salt is Zr(NO3)4·5H2O, and the molar volume ratio of the zirconium salt to N,N-dimethylformamide is 1 mmol:50 mL; The molar ratio of the zirconium salt to terephthalic acid is 1:

1.

6. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 1, wherein, In S3: When forming the bottom layer slurry: The mass ratio of the SiC@MOF composite, the g-C3N4@CaF2 composite, polysilazane, PVP, and tetraethoxysilane is 0.5:0.25:2:0.1:0.2; The solvent A is a mixed solution of DMF and absolute ethanol, and the volume ratio is 3:1; When obtaining the intermediate layer slurry: The mass ratio of the MoS2@P composite, g-C3N4@CaF2 composite, polysilazane, and phenyltriethoxysilane is 0.5:0.25:2:0.2; The solvent B is a mixed solution of DMF and absolute ethanol with a volume ratio of 2:1; When obtaining the surface slurry: The mass ratio of the MoS2@P composite, g-C3N4@CaF2 composite, polysilazane, and hexamethyldisiloxane is 0.5:0.25:2:0.2; The solvent C is a mixed solution of DMF and absolute ethanol with a volume ratio of 1:

1.

7. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 2, wherein, In A1: The concentration of the molybdenum disulfide dispersion is 1 mg / mL.

8. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 2, wherein, In A2: The mass fraction of the sodium phosphate solution is 2-3 wt.%; The silane coupling agent is 3-aminopropyltriethoxysilane with a mass of 10-20% of the mass of the MoS2@P particles.

9. The preparation method of an anti-wear coating for aerospace bearings based on polysilazane according to claim 3, characterized in that, In A3: The molar ratio of calcium nitrate tetrahydrate to ammonium fluoride is 1:1; The volume ratio of the calcium nitrate tetrahydrate solution to the ammonium fluoride solution is 1:1; The concentration of the calcium nitrate tetrahydrate solution is 0.1 M.

10. A polysilazane-based aerospace bearing wear-resistant coating is obtained by the preparation method of a polysilazane-based aerospace bearing wear-resistant coating according to any one of claims 1-9.

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