A coated nut and a method of making the same

Abstract

The application discloses a nut with a coating and a preparation method thereof, and technical scheme points are as follows: a nut base body, the surface of the nut base body is sequentially compounded from inside to outside with a metal bonding bottom layer, a metal ceramic wear-resistant and corrosion-resistant intermediate layer and an organic-inorganic hybrid self-lubricating hole sealing surface layer, the metal bonding bottom layer is a NiCrAlY alloy layer with a thickness of 50-100 microns, the metal ceramic wear-resistant and corrosion-resistant intermediate layer is a WC-Co-Cr composite layer with a thickness of 150-300 microns, and the organic-inorganic hybrid self-lubricating hole sealing surface layer is a modified polyimide-nano silicon dioxide-polytetrafluoroethylene composite layer with a thickness of 20-50 microns. Through gradient coating structure design, the application effectively alleviates the difference in thermal expansion coefficients between layers, the bonding force between the coating and the base body is greater than or equal to 60 MPa, which is higher than the bonding force level of existing fasteners, and the problems of easy cracking and easy falling of the coating are solved.

Description

Technical Field

[0001] This invention relates to the technical field of nuts and their manufacturing methods, and more specifically, to a coated nut and its manufacturing method. Background Technology

[0002] Nuts, as core basic fasteners, are widely used in the fastening connections of various industrial equipment, and their service performance directly determines the operational safety and service life of the equipment. In the harsh service conditions of high-end equipment such as wind turbine towers, offshore platforms, high-speed rail bogies, and chemical reactors, nuts are subjected to multiple effects such as alternating loads, salt spray corrosion, acid and alkali media erosion, and repeated disassembly and assembly friction and wear. They are prone to problems such as coating failure, substrate corrosion, and thread wear and slippage, which ultimately lead to preload reduction, connection failure, and even major safety accidents.

[0003] Existing surface protection technologies for nuts mainly include electro-galvanizing, hot-dip galvanizing, Dacromet coating, and ordinary phosphating. These processes are difficult to meet the dual requirements of wear resistance and corrosion resistance. Electro-galvanizing and hot-dip galvanizing coatings have limited corrosion resistance and low coating hardness, making them prone to wear and peeling after repeated disassembly and assembly. Although Dacromet coating has improved corrosion resistance, its wear resistance is extremely poor and it cannot withstand the high-frequency friction conditions of threaded pairs.

[0004] Therefore, a solution is needed to address the problem that the existing nuts cannot meet the required wear and corrosion resistance. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a coated nut and its preparation method. Through the gradient coating structure design, the difference in thermal expansion coefficient between the layers is effectively alleviated, which is much higher than the bonding strength level of existing fastener coatings, and the problem of easy cracking and peeling of the coating is solved.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a coated nut, comprising a nut substrate, wherein the surface of the nut substrate is sequentially coated from the inside to the outside with a metal bonding underlayer, a metal-ceramic wear-resistant and corrosion-resistant intermediate layer, and an organic-inorganic hybrid self-lubricating sealing surface layer; the metal bonding underlayer is a NiCrAlY alloy layer with a thickness of 50-100μm; the metal-ceramic wear-resistant and corrosion-resistant intermediate layer is a WC-Co-Cr composite layer with a thickness of 150-300μm; and the organic-inorganic hybrid self-lubricating sealing surface layer is a modified polyimide-nano silica-polytetrafluoroethylene composite layer with a thickness of 20-50μm.

[0007] The present invention is further configured such that the mass percentage of each element in the metal bonding underlayer is: Ni 60%-70%, Cr 20%-25%, Al 5%-8%, Y 0.5%-2%.

[0008] The present invention is further configured such that: in the metal-ceramic wear-resistant and corrosion-resistant intermediate layer, the mass percentage of each component is: WC 80%-88%, Co 8%-12%, Cr 4%-8%; the particle size of WC is 15-45μm, and the particle size of Co and Cr is 5-15μm.

[0009] The present invention is further configured such that the raw materials of the organic-inorganic hybrid self-lubricating sealing surface layer, by mass parts, include: 30-50 parts of amino-terminated modified polyimide resin, 10-20 parts of nano-silica sol, 5-15 parts of polytetrafluoroethylene micro powder, 1-3 parts of coupling agent, 2-5 parts of curing agent, and 20-40 parts of organic solvent.

[0010] The present invention is further configured such that: the particle size of the nano-silica sol is 10-30 nm and the solid content is 30%; the particle size of the polytetrafluoroethylene micro powder is 1-5 μm; the coupling agent is silane coupling agent KH550; the curing agent is aromatic diamine curing agent; and the organic solvent is a mixed solvent of N,N-dimethylacetamide and anhydrous ethanol at a volume ratio of 2:1.

[0011] The above-mentioned technical objective of the present invention is also achieved through the following technical solution: a method for preparing a coated nut, comprising the following steps: S1 Substrate Pretreatment: The nut substrate is subjected to degreasing, derusting, and sandblasting roughening treatment in sequence to obtain the pretreated nut substrate; S2 Metal Bonding Underlayer Preparation: NiCrAlY alloy powder was sprayed onto the pretreated nut substrate surface using a supersonic flame spraying process to form a metal bonding underlayer. Preparation of S3 metal-ceramic wear-resistant and corrosion-resistant intermediate layer: WC-Co-Cr composite powder is sprayed onto the surface of the metal bonding substrate using a supersonic flame spraying process to form a metal-ceramic wear-resistant and corrosion-resistant intermediate layer; Preparation of S4 surface layer precursor: Weigh the raw materials of organic-inorganic hybrid self-lubricating sealing surface layer according to the formula, mix and stir evenly to obtain surface layer precursor coating. S5 surface layer preparation and curing: The surface layer precursor coating is uniformly sprayed onto the surface of the metal-ceramic wear-resistant and corrosion-resistant intermediate layer using a high-pressure air spraying process. After leveling at room temperature, it is cured by gradient temperature increase to obtain an organic-inorganic hybrid self-lubricating sealing surface layer, and finally a nut with coating is obtained.

[0012] The present invention is further configured such that: in step S1, the sandblasting roughening treatment uses white corundum sand with a mesh size of 46-60, the sandblasting pressure is 0.5-0.7MPa, the sandblasting distance is 100-150mm, the surface roughness of the substrate after sandblasting is Ra≥6.3μm, and the spraying operation is completed within 4 hours after sandblasting.

[0013] The present invention is further configured such that: in step S2, the process parameters for supersonic flame spraying are: oxygen flow rate 1800-2200 L / h, kerosene flow rate 18-22 L / h, powder feed rate 30-40 g / min, spraying distance 300-350 mm, spray gun moving speed 200-300 mm / s, and substrate temperature ≤150℃; in step S3, the process parameters for supersonic flame spraying are: oxygen flow rate 2000-2400 L / h, kerosene flow rate 20-24 L / h, powder feed rate 35-45 g / min, spraying distance 350-400 mm, spray gun moving speed 150-250 mm / s, and substrate temperature ≤120℃.

[0014] In summary, the present invention has the following beneficial effects: 1. Gradient coating structure design achieves synergistic optimization of multiple performance aspects, solving the core pain points of existing technologies. This invention adopts a three-layer gradient structure of "metal bonding base layer - metal-ceramic wear-resistant and corrosion-resistant intermediate layer - organic-inorganic hybrid self-lubricating sealing surface layer", achieving functional gradient matching of "high bonding strength - high wear resistance and strong corrosion resistance - self-lubricating sealing" from the inside out. This effectively alleviates the difference in thermal expansion coefficients between layers, and the bonding strength between the coating and the substrate is ≥60MPa, which is far higher than the bonding strength level of existing fastener coatings, completely solving the problems of easy cracking and peeling of the coating.

[0015] 2. Core performance achieves a leap forward, meeting the long-term service requirements of high-end equipment under harsh operating conditions. The metal-ceramic intermediate layer of this invention has a hardness ≥1200HV, and its wear resistance is more than 10 times that of traditional galvanized layers. After repeated disassembly and assembly of the threaded pair 500 times, the coating shows no significant wear; it shows no red rust after ≥3000 hours of neutral salt spray testing, and its corrosion resistance is more than 3 times that of Dacromet coating; the surface friction coefficient is ≤0.15, possessing excellent self-lubricating properties, significantly reducing the risk of threaded pair seizing. Under highly corrosive and high-wear conditions such as marine, chemical, and wind power environments, its service life can reach more than 10 years, significantly reducing equipment maintenance costs and resource consumption, and meeting the requirements of energy-saving and environmentally friendly industrial development.

[0016] 3. The preparation process is green and environmentally friendly, with no heavy metal pollution, and is suitable for industrial mass production. The supersonic flame spraying and high-pressure air spraying processes used in this invention produce no toxic or harmful substances such as cyanide and hexavalent chromium throughout the entire process, and generate very little wastewater and exhaust gas, which meets the national requirements for green manufacturing. The process parameters are stable and controllable, the spraying process can be automated, the coating thickness is uniform, and the pass rate is high, making it suitable for the large-scale industrial production of fasteners. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other.

[0018] In the description of this invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom", etc., indicating the orientation or positional relationship are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0019] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installed," "equipped with," "set up / connected," "connected," etc., should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0020] The present invention will now be described in detail.

[0021] Example 1: This example provides a coated nut. The nut base is a 35CrMoA high-strength alloy steel M24 hexagonal nut. The base surface is coated with a metal bonding underlayer, a metal-ceramic wear-resistant and corrosion-resistant intermediate layer, and an organic-inorganic hybrid self-lubricating sealing surface layer from the inside to the outside.

[0022] The metal bonding underlayer is a NiCrAlY alloy layer with a thickness of 80μm and the mass percentages of each element are: Ni 65%, Cr 22%, Al 10%, Y 1%; the metal-ceramic wear-resistant and corrosion-resistant intermediate layer is a WC-Co-Cr composite layer with a thickness of 200μm and the mass percentages of each component are: WC 85%, Co 10%, Cr 5%, with WC particle size of 20-30μm and Co and Cr particle size of 5-10μm; the organic-inorganic hybrid self-lubricating sealing surface layer is a modified polyimide-nanodi The silica-polytetrafluoroethylene composite layer has a thickness of 30 μm. The raw materials, by mass parts, are: 40 parts of amino-terminated modified polyimide resin, 15 parts of nano silica sol, 10 parts of polytetrafluoroethylene micro powder, 2 parts of silane coupling agent KH550, 3 parts of aromatic diamine curing agent, and 30 parts of mixed organic solvent. Among them, the nano silica sol has a particle size of 20 nm and a solid content of 30%, the polytetrafluoroethylene micro powder has a particle size of 2-3 μm, and the mixed organic solvent is N,N-dimethylacetamide and anhydrous ethanol mixed at a volume ratio of 2:1.

[0023] The method for preparing a coated nut in this embodiment includes the following steps: S1 Substrate pretreatment: Degreasing: Place the nut base in an alkaline degreasing solution, ultrasonically clean for 20 minutes to remove surface oil, rinse with deionized water, and dry at 100℃. Rust removal: Immerse the degreased nut base in pickling and passivation solution for 8 minutes to remove surface oxide scale and rust, rinse with deionized water until neutral, and dry at 100℃; Sandblasting roughening: 46-mesh white corundum abrasive was used, with a sandblasting pressure of 0.6 MPa and a sandblasting distance of 120 mm. The surface roughness of the substrate after sandblasting was Ra = 7.2 μm. The coating operation was completed within 2 hours after sandblasting. S2 metal bonding underlayer preparation: Supersonic flame spraying was used to spray NiCrAlY alloy powder onto the pretreated nut substrate surface. The process parameters were: oxygen flow rate 2000 L / h, kerosene flow rate 20 L / h, powder feed rate 35 g / min, spraying distance 320 mm, spray gun moving speed 250 mm / s, and substrate temperature... A metal bonding underlayer with a thickness of 80 μm was prepared by controlling the temperature below 120℃; Preparation of the S3 metal-ceramic wear-resistant and corrosion-resistant intermediate layer: WC-Co-Cr composite powder was sprayed onto the surface of the metal bonding underlayer using a supersonic flame spraying process. The process parameters were: oxygen flow rate 2200 L / h, kerosene flow rate 22 L / h, powder feed rate 40 g / min, spraying distance 380 mm, spray gun moving speed 200 mm / s, and substrate temperature controlled below 100℃, resulting in a metal-ceramic wear-resistant and corrosion-resistant intermediate layer with a thickness of 200 μm; S 4. Preparation of the surface layer precursor: Weigh the raw materials according to the formula. First, add the amino-terminated polyimide resin to the mixed organic solvent and stir until completely dissolved. Then, add the silane coupling agent KH550 and stir for 30 minutes. Next, add the nano-silica sol and polytetrafluoroethylene micro powder in sequence and stir at high speed for 60 minutes. Finally, add the aromatic diamine curing agent, stir evenly, and then degas under vacuum for 15 minutes to obtain the surface layer precursor coating. S5. Surface layer preparation and curing: Use a high-pressure air spraying process to uniformly spray the surface layer precursor coating onto the metal ceramic wear-resistant and corrosion-resistant coating. The intermediate layer surface was etched with a spraying pressure of 0.4 MPa, a spraying distance of 220 mm, a spray gun moving speed of 350 mm / s, and two spraying passes with an 8-minute interval between each pass. After spraying, the surface was allowed to stand at room temperature for 15 minutes to level, and then a gradient temperature curing process was performed: first, the surface was kept at 80℃ for 30 minutes, then at 120℃ for 60 minutes, and finally at 180℃ for 90 minutes, with a heating rate of 3℃ / min. After curing, the surface was cooled to room temperature in the oven to obtain an organic-inorganic hybrid self-lubricating sealing surface layer, which ultimately produced a nut with a coating.

[0024] Example 2: This example provides a coated nut. The nut base is a 42CrMoA high-strength alloy steel M30 hexagonal nut. The base surface is coated from the inside out with a metal bonding underlayer, a metal-ceramic wear-resistant and corrosion-resistant intermediate layer, and an organic-inorganic hybrid self-lubricating sealing surface layer.

[0025] The metal bonding underlayer is a NiCrAlY alloy layer with a thickness of 50 μm and the mass percentages of each element are: Ni 70%, Cr 20%, Al 8%, Y 2%; the metal-ceramic wear-resistant and corrosion-resistant intermediate layer is a WC-Co-Cr composite layer with a thickness of 150 μm and the mass percentages of each component are: WC 88%, Co 8%, Cr 4%, with WC particle size of 15-25 μm and Co and Cr particle size of 5-10 μm; the organic-inorganic hybrid self-lubricating sealing surface layer is a modified polyimide-nanodioxide layer. The silicon-polytetrafluoroethylene composite layer has a thickness of 20 μm. The raw materials, by mass parts, are: 30 parts of amino-terminated modified polyimide resin, 10 parts of nano-silica sol, 5 parts of polytetrafluoroethylene micro powder, 1 part of silane coupling agent KH550, 2 parts of aromatic diamine curing agent, and 40 parts of mixed organic solvent. Among them, the nano-silica sol has a particle size of 10 nm and a solid content of 30%, the polytetrafluoroethylene micro powder has a particle size of 1-2 μm, and the mixed organic solvent is N,N-dimethylacetamide and anhydrous ethanol mixed at a volume ratio of 2:1.

[0026] The method for preparing a coated nut in this embodiment includes the following steps: S1 Substrate pretreatment: Degreasing: Place the nut base in an alkaline degreasing solution, ultrasonically clean for 15 minutes to remove surface oil, rinse with deionized water, and dry at 100℃. Rust removal: Immerse the degreased nut base in pickling and passivation solution for 5 minutes to remove surface oxide scale and rust, rinse with deionized water until neutral, and dry at 100℃; Sandblasting roughening: 60-mesh white corundum abrasive was used, with a sandblasting pressure of 0.5 MPa and a sandblasting distance of 150 mm. The surface roughness of the substrate after sandblasting was Ra = 6.5 μm. The coating operation was completed within 3 hours after sandblasting. S2 Metal bonding underlayer preparation: Supersonic flame spraying was used to spray NiCrAlY alloy powder onto the pretreated nut substrate surface. The process parameters were: oxygen flow rate 1800 L / h, kerosene flow rate 18 L / h, powder feed rate 30 g / min, spraying distance 350 mm, spray gun moving speed 300 mm / s, and substrate temperature controlled below 150℃. A 50 μm thick metal bonding underlayer was obtained. S3 Metal-ceramic wear-resistant and corrosion-resistant intermediate layer preparation: Supersonic flame spraying was used to spray WC-Co-Cr composite powder onto the surface of the metal bonding underlayer. The process parameters were: oxygen flow rate 2... The spraying rate was 000L / h, kerosene flow rate was 20L / h, powder feed rate was 35g / min, spraying distance was 400mm, spray gun moving speed was 250mm / s, and substrate temperature was controlled below 120℃ to prepare a 150μm thick metal-ceramic wear-resistant and corrosion-resistant intermediate layer; S4 Preparation of surface layer precursor: the same preparation method as in Example 1, prepared according to the formula of this example; S5 Preparation and curing of surface layer: the surface layer precursor coating was uniformly sprayed onto the surface of the metal-ceramic wear-resistant and corrosion-resistant intermediate layer using a high-pressure air spraying process, with a spraying pressure of 0.3MPa, a spraying distance of 250mm, a spray gun moving speed of 400mm / s, and two spray passes with a 5min interval between each pass; after spraying, the layer was allowed to stand at room temperature for 10min to level, and then gradient temperature curing was performed, with the curing process the same as in Example 1, finally obtaining a nut with a coating.

[0027] Example 3: This example provides a coated nut. The nut base is a 25Cr2MoVA high-strength alloy steel M20 hexagonal nut. The base surface is coated with a metal bonding underlayer, a metal-ceramic wear-resistant and corrosion-resistant intermediate layer, and an organic-inorganic hybrid self-lubricating sealing surface layer from the inside to the outside.

[0028] The metal bonding underlayer is a NiCrAlY alloy layer with a thickness of 100μm and the mass percentages of each element are: Ni 60%, Cr 25%, Al 14.5%, Y 0.5%; the metal-ceramic wear-resistant and corrosion-resistant intermediate layer is a WC-Co-Cr composite layer with a thickness of 300μm and the mass percentages of each component are: WC 80%, Co 12%, Cr 8%, with WC particle size of 30-45μm and Co and Cr particle size of 10-15μm; the organic-inorganic hybrid self-lubricating sealing surface layer is a modified polyimide- The nano-silica-polytetrafluoroethylene composite layer has a thickness of 50μm. The raw materials, by mass parts, are: 50 parts of amino-terminated modified polyimide resin, 20 parts of nano-silica sol, 15 parts of polytetrafluoroethylene micro powder, 3 parts of silane coupling agent KH550, 5 parts of aromatic diamine curing agent, and 20 parts of mixed organic solvent. Among them, the nano-silica sol has a particle size of 30nm and a solid content of 30%, the polytetrafluoroethylene micro powder has a particle size of 3-5μm, and the mixed organic solvent is N,N-dimethylacetamide and anhydrous ethanol mixed at a volume ratio of 2:1.

[0029] The method for preparing a coated nut in this embodiment includes the following steps: S1 Substrate pretreatment: Degreasing: Place the nut base in an alkaline degreasing solution, ultrasonically clean for 30 minutes to remove surface oil, rinse with deionized water, and dry at 100℃; Rust removal: Immerse the degreased nut base in pickling and passivation solution for 10 minutes to remove surface oxide scale and rust, rinse with deionized water until neutral, and dry at 100℃; Sandblasting roughening: 46-mesh white corundum abrasive was used, with a sandblasting pressure of 0.7 MPa and a sandblasting distance of 100 mm. The surface roughness of the substrate after sandblasting was Ra = 8.1 μm. The coating operation was completed within 1 hour after sandblasting. S2 Metal bonding underlayer preparation: Supersonic flame spraying was used to spray NiCrAlY alloy powder onto the pretreated nut substrate surface. The process parameters were: oxygen flow rate 2200 L / h, kerosene flow rate 22 L / h, powder feed rate 40 g / min, spraying distance 300 mm, spray gun moving speed 200 mm / s, and substrate temperature controlled below 150℃. A 100 μm thick metal bonding underlayer was obtained. S3 Metal-ceramic wear-resistant and corrosion-resistant intermediate layer preparation: Supersonic flame spraying was used to spray WC-Co-Cr composite powder onto the surface of the metal bonding underlayer. The process parameters were: oxygen flow rate 2... With a flow rate of 400 L / h, a kerosene flow rate of 24 L / h, a powder feeding rate of 45 g / min, a spraying distance of 350 mm, a spray gun moving speed of 150 mm / s, and a substrate temperature controlled below 120 °C, a 300 μm thick metal-ceramic wear-resistant and corrosion-resistant intermediate layer was prepared. S4: Preparation of the surface layer precursor: The preparation method was the same as in Example 1, prepared according to the formula of this example. S5: Surface layer preparation and curing: The surface layer precursor coating was uniformly sprayed onto the surface of the metal-ceramic wear-resistant and corrosion-resistant intermediate layer using a high-pressure air spraying process. The spraying pressure was 0.5 MPa, the spraying distance was 200 mm, the spray gun moving speed was 300 mm / s, and the spraying passes were 3, with a 10-min interval between each pass. After spraying, the layer was allowed to stand at room temperature for 20 min to level, and then cured with a gradient temperature increase. The curing process was the same as in Example 1, ultimately yielding a nut with a coating.

[0030] Comparative Example 1: This comparative example is a commercially available ordinary electroplated zinc nut. The base material is the same 35CrMoAM24 hexagonal nut as in Example 1, and the thickness of the electroplated zinc layer is 8μm.

[0031] Comparative Example 2: This comparative example is a commercially available Dacromet coated nut. The substrate is the same 35CrMoAM24 hexagonal nut as in Example 1, and the Dacromet coating thickness is 10μm.

[0032] Comparative Example 3: This comparative example is a single WC-Co-Cr coated nut. The substrate is the same 35CrMoAM24 hexagonal nut as in Example 1. Only the WC-Co-Cr coating is sprayed on the surface of the substrate, with a thickness of 280μm. The spraying process is the same as step S3 in Example 1, without metal bonding underlayer and top layer.

[0033] Performance testing: The nuts obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing according to the following standards: Coating adhesion test: The test was conducted in accordance with GB / T8642-2002 "Determination of tensile bond strength of thermal spray coatings"; Coating hardness test: The test was conducted in accordance with GB / T4340.1-2009 "Metallic materials - Vickers hardness test - Part 1: Test method", with a load of 300g; Friction coefficient test: The test shall be conducted in accordance with GB / T22893-2008 "Test Method for Friction Coefficient of Fasteners"; Corrosion resistance test: Conduct a neutral salt spray test according to GB / T10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test" and record the time when red rust appears; Wear resistance test: The wear rate of the coating was tested using an MMW-1 vertical universal friction and wear tester. Test conditions: load 200N, rotation speed 200r / min, wear time 30min, and the mating part was a 45# steel disc. Disassembly and assembly performance test: The nut was repeatedly disassembled and assembled using a torque wrench, and the number of disassembly and assembly steps that resulted in obvious wear and peeling of the coating was recorded.

[0034] The test results are shown in the table below: The test results show that the coated nuts obtained in Examples 1-3 of this invention are significantly superior to the existing technology products in terms of coating adhesion, hardness, corrosion resistance, wear resistance, self-lubricating properties, and disassembly and assembly performance. They achieve a synergistic improvement in wear resistance and corrosion resistance, fully meet the long-term service requirements of high-end equipment under harsh working conditions, and verify the advanced nature and reliability of the technical solution of this invention.

[0035] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A coated nut, characterized in that: The nut substrate comprises, from the inside out, a metal bonding underlayer, a metal-ceramic wear-resistant and corrosion-resistant intermediate layer, and an organic-inorganic hybrid self-lubricating sealing layer. The metal bonding underlayer is a NiCrAlY alloy layer with a thickness of 50-100 μm. The metal-ceramic wear-resistant and corrosion-resistant intermediate layer is a WC-Co-Cr composite layer with a thickness of 150-300 μm. The organic-inorganic hybrid self-lubricating sealing layer is a modified polyimide-nano silica-polytetrafluoroethylene composite layer with a thickness of 20-50 μm.

2. A coated nut according to claim 1, characterized in that: The mass percentage of each element in the metal bonding underlayer is: Ni 60%-70%, Cr 20%-25%, Al 5%-8%, Y 0.5%-2%.

3. A coated nut according to claim 1, characterized in that: In the metal-ceramic wear-resistant and corrosion-resistant intermediate layer, the mass percentage of each component is: WC 80%-88%, Co 8%-12%, Cr 4%-8%; the particle size of WC is 15-45μm, and the particle size of Co and Cr is 5-15μm.

4. A coated nut according to claim 1, characterized in that: The raw materials of the organic-inorganic hybrid self-lubricating sealing surface layer, by mass parts, include: 30-50 parts of amino-terminated modified polyimide resin, 10-20 parts of nano-silica sol, 5-15 parts of polytetrafluoroethylene micro powder, 1-3 parts of coupling agent, 2-5 parts of curing agent, and 20-40 parts of organic solvent.

5. A coated nut according to claim 1, characterized in that: The nano-silica sol has a particle size of 10-30 nm and a solid content of 30%; the polytetrafluoroethylene micro powder has a particle size of 1-5 μm; the coupling agent is silane coupling agent KH550; the curing agent is an aromatic diamine curing agent; and the organic solvent is a mixed solvent of N,N-dimethylacetamide and anhydrous ethanol at a volume ratio of 2:

1.

6. A method for preparing a coated nut according to any one of claims 1-5, characterized in that: Includes the following steps: S1 Substrate Pretreatment: The nut substrate is subjected to degreasing, derusting, and sandblasting roughening treatment in sequence to obtain the pretreated nut substrate; S2 Metal Bonding Underlayer Preparation: NiCrAlY alloy powder was sprayed onto the pretreated nut substrate surface using a supersonic flame spraying process to form a metal bonding underlayer. Preparation of S3 metal-ceramic wear-resistant and corrosion-resistant intermediate layer: WC-Co-Cr composite powder is sprayed onto the surface of the metal bonding substrate using a supersonic flame spraying process to form a metal-ceramic wear-resistant and corrosion-resistant intermediate layer; Preparation of S4 surface layer precursor: Weigh the raw materials of organic-inorganic hybrid self-lubricating sealing surface layer according to the formula, mix and stir evenly to obtain surface layer precursor coating. S5 surface layer preparation and curing: The surface layer precursor coating is uniformly sprayed onto the surface of the metal-ceramic wear-resistant and corrosion-resistant intermediate layer using a high-pressure air spraying process. After leveling at room temperature, it is cured by gradient temperature increase to obtain an organic-inorganic hybrid self-lubricating sealing surface layer, and finally a nut with coating is obtained.

7. A method for preparing a coated nut according to claim 6, characterized in that: In step S1, the sandblasting roughening treatment uses white corundum abrasive with a mesh size of 46-60, a sandblasting pressure of 0.5-0.7MPa, a sandblasting distance of 100-150mm, and a substrate surface roughness Ra≥6.3μm after sandblasting. The coating operation is completed within 4 hours after sandblasting.

8. A method for preparing a coated nut according to claim 6, characterized in that: In step S2, the process parameters for supersonic flame spraying are: oxygen flow rate 1800-2200 L / h, kerosene flow rate 18-22 L / h, powder feed rate 30-40 g / min, spraying distance 300-350 mm, spray gun moving speed 200-300 mm / s, and substrate temperature ≤150℃; In step S3, the process parameters for supersonic flame spraying are: oxygen flow rate 2000-2400 L / h, kerosene flow rate 20-24 L / h, powder feed rate 35-45 g / min, spraying distance 350-400 mm, spray gun moving speed 150-250 mm / s, and substrate temperature ≤120℃.

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