Preparation method of high-hardness nanocrystalline coating for preventing storage welding of high-strength bolt

Abstract

The invention discloses a preparation method of a high-hardness nanocrystalline coating for preventing high-strength bolt storage welding, and belongs to the field of high-strength bolt surface treatment. The problems that in the long-term storage process of an existing high-strength bolt, the thread welding failure phenomenon occurs, and the storage life of the bolt is short are solved. The method comprises the following steps: 1, placing the high-strength bolt in a vacuum coating chamber of multi-arc ion plating equipment, adjusting the air pressure in a furnace, preheating and vacuumizing; 2, argon ion cleaning; 3, depositing a metal transition layer; 4, depositing a ceramic coating; and 5, turning off the power supply, introducing argon, and cooling to room temperature. The method is used for preparing the high-hardness nanocrystalline coating for preventing the high-strength bolt from being stored and welded.

Description

Technical Field

[0001] The present invention belongs to the field of surface treatment of high-strength bolts. Background Art

[0002] In the connection process of key structural components in the aerospace cutting-edge field and various civilian fields, welding and bolt connection are mainly used. Among them, bolt connection transmits loads through pre-tightening force and friction between thread surfaces, which can well meet the service performance requirements such as anti-shear and anti-tensile in the service environment, and is convenient for installation and disassembly, so it is widely used. In order to ensure the stable technical state of bolt connection products made of pure metals and steel products during long-term storage, such as long-term reliable connection and long-term sealing, etc., various specimens must be applied with a specified assembly torque during the assembly process. Compared with the microscopic plastic slip and local metallurgical bonding mechanism in the assembly welding process, storage welding is more concealed, which is mainly driven by the continuous diffusion of interface elements under the combined action of high temperature and high stress. As the storage time prolongs, metal atoms such as Fe and Cr gradually cross-border migrate to form a metallurgical diffusion connection. When the thickness of the diffusion layer exceeds the critical threshold, a firm welded interface will be formed even without experiencing macroscopic shear slip, resulting in the "jamming" failure of the threaded connection in the early stage of service. Therefore, constructing a barrier system from the diffusion source becomes the key path to solve the problem of storage welding.

[0003] At present, there are mainly three types of technical measures at home and abroad to prevent the seizure failure of specimens during storage: First, based on new tightening methods, advanced tightening devices are developed to improve the control accuracy of assembly torque loading and bolt rotation angle. However, due to factors such as different operators or construction environments, there is a large randomness, and essentially the seizure failure mode during specimen storage has not been changed. Therefore, simply relying on improving the bolt assembly tightening process, methods such as adding gaskets to improve the tightening device, and measures such as improving thread parameters cannot effectively and reliably prevent the seizure failure of specimens during storage; Second, anti-seizure aids are used. For example, adding porous zinc-plated or copper-plated coatings on the thread surface and using them in combination with lubricating grease can improve the anti-seizure performance of bolts. However, the introduction of lubricating grease will reduce the friction coefficient between the thread surfaces. A small friction coefficient is prone to loosening. Therefore, the introduction of lubricating grease reduces the anti-loosening performance of the specimen, and will seriously reduce the service reliability under the conditions that the connecting components bear vibration or tangential shear stress. In addition, there is also an environmentally friendly anti-seizure aid composed of a buffer, an adhesive, a diluent, and metal flakes coated on the thread surface. This anti-seizure aid can improve the anti-seizure ability of the specimen and no longer requires a lubricant. However, when the coated anti-seizure aid coating is damaged, the seizure phenomenon during storage will reappear, and the bonding strength between the aid and the thread substrate is low, the durability is poor, and the service life is short. In addition, the coating thickness is uneven, which is prone to cause specimen jamming. Most anti-seizure aids are liquid or paste, which are not applicable in complex service environments. Therefore, coating anti-seizure aids cannot effectively solve the problem of seizure failure of specimens during long-term storage. For the above situation, in order to effectively prevent the seizure failure of bolts during storage and improve the service life of bolts, it is urgent to develop a new type of anti-welding process for the thread surface. Summary of the Invention

[0004] The present invention aims to solve the problem of thread welding failure of existing high-strength bolts during long-term storage and the low storage life of bolts, and further provides a method for preparing a high-hard nanocrystalline coating to prevent the storage welding of high-strength bolts.

[0005] A method for preparing a high-hard nanocrystalline coating to prevent the storage welding of high-strength bolts is carried out according to the following steps:

[0006] 1. Place the high-strength bolt in the vacuum coating chamber of a multi-arc ion plating equipment, turn on the roughing pump to adjust the air pressure in the furnace, then turn on the heating power supply for preheating, and finally turn on the Roots pump to evacuate the furnace.

[0007] 2. Carry out argon ion cleaning on the surface of the high-strength bolt.

[0008] 3. Turn on the Roots pump again to evacuate the furnace, turn on the metal target, and deposit a metal transition layer on the surface of the high-strength bolt for 5 min to 20 min under the conditions of a temperature of 200°C to 500°C and an arc current of 10 A to 150 A.

[0009] IV. Keep the metal target open, introduce the gas for forming the ceramic coating until the furnace pressure reaches 0.1 Pa - 0.9 Pa, turn on the bias power supply, and deposit the ceramic coating on the metal transition layer of the high-strength bolt surface for 10 min - 120 min under the conditions of a temperature of 200°C - 500°C, an arc current of 10 A - 150 A, a bias voltage of -250 V - -50 V, and a duty cycle of 10% - 90%;

[0010] V. After the coating is completed, turn off the arc power supply, heating power supply, and bias power supply, and finally introduce argon gas to cool to room temperature, thus completing the preparation method of the high-hardness nanocrystalline coating for preventing the storage welding of high-strength bolts.

[0011] The beneficial effects of the present invention are as follows:

[0012] The present invention adopts an improved multi-arc ion plating technology to prepare a highly dense and high-hardness TiN nanocrystalline ceramic coating on the surface of complex structures such as threads within a thickness range of no more than 5 μm, significantly improving its hardness, wear resistance, and anti-diffusion ability without affecting the thread fitting accuracy. This process forms a high-hard ceramic structure with a firmly bonded interface and a stable and uniform coating layer by systematically controlling key steps such as pre-treatment of the coating, ion bombardment cleaning, deposition of the metal transition layer, and deposition of the ceramic film layer.

[0013] 1. Aiming at the problem of storage welding of high-strength bolts, the present invention adopts a special multi-arc ion plating process to form a high-hardness nanocrystalline ceramic coating on the thread surface, effectively inhibiting the atomic diffusion on the thread surface. This ceramic coating effectively inhibits the interface migration of metal atoms such as Fe and Cr in the storage simulation experiment, and the welding failure rate is significantly reduced. The thickness of the diffusion layer is reduced by 87.5% compared with the uncoated bolts. Compared with the existing lubricant or coating additive solutions, this method has better durability and engineering feasibility in complex storage environments such as high strength and high temperature, and completely solves the welding failure problem of high-strength bolts during long-term storage. It can be widely applied to the anti-welding protection of threaded connection components with extremely high requirements for long-term storage reliability in fields such as aerospace, nuclear power, and high-end equipment.

[0014] 2. The nanocrystalline ceramic coating has extremely high hardness and excellent wear resistance, and can stably exist on the thread surface for a long time, ensuring the reliability of the bolt in the long-term storage state.

[0015] 3. The process is mature and stable, the thickness of the prepared coating is accurately controllable, and it does not affect the fit tolerance of the bolt, making it suitable for mass production and practical engineering applications. Description of the Drawings

[0016] Figure 1 It is the microscopic morphology observation result of the nanocrystalline TiN coating obtained on the bolt surface in Example 1;

[0017] Figure 2SEM image of the combination of the nanocrystalline TiN coating and the bolt surface thread in Example 1;

[0018] Figure 3 EDS analysis of the nanocrystalline TiN coating prepared on the bolt surface in Example 1, a) sampling position, b) corresponding elemental content map;

[0019] Figure 4 Hardness test of the nanocrystalline TiN coating prepared on the bolt surface in Example 1;

[0020] Figure 5 Wear resistance test diagrams of the bolt coated with nanocrystalline TiN coating prepared in Example 1, the bolt coated with ordinary TiN coating in the comparative experiment, and the bolt without coating;

[0021] Figure 6 Friction coefficient test of the bolt coated with nanocrystalline TiN coating prepared in Example 1 and the bolt without coating, a) bolt without coating, b) bolt coated with nanocrystalline TiN coating prepared in Example 1;

[0022] Figure 7 Macroeconomic states of the bolt coated with nanocrystalline TiN coating prepared in Example 1 and the bolt without coating after 90 days of heating and pressurization test, a) assembly diagram of the bolt without coating and the nut, b) cross-sectional view of the bolt without coating and the nut, c) assembly diagram of the bolt coated with nanocrystalline TiN coating and the nut, d) bolt coated with nanocrystalline TiN coating after successful disassembly;

[0023] Figure 8 EDS diagrams of the threaded connection surface of the bolt coated with nanocrystalline TiN coating prepared in Example 1 and the nut after 90 days of heating and pressurization test, a) Ti element distribution diagram, b) N element distribution diagram, c) Fe element distribution diagram, d) Cr element distribution diagram;

[0024] Figure 9 Diffusion layer thickness of the bolt coated with nanocrystalline TiN coating prepared in Example 1 and the bolt without coating and the nut after 90 days of heating and pressurization test, a) and b) are the sampling positions of the bolt without coating when just assembled and the measured diffusion layer thickness at this position, c) and d) are the sampling positions of the bolt without coating after acceleration and the measured diffusion layer thickness at this position; e) and f) are the sampling positions of the bolt with coating after acceleration and the measured diffusion layer thickness at this position. Specific implementation method

[0025] Specific implementation method 1: A method for preparing a high-hard nanocrystalline coating to prevent the storage welding of high-strength bolts, which is carried out according to the following steps:

[0026] 1. Place the high-strength bolts in the vacuum coating chamber of the multi-arc ion plating equipment. Turn on the roughing pump to adjust the air pressure in the furnace, then turn on the heating power supply for preheating, and finally turn on the Roots pump to evacuate the furnace to vacuum;

[0027] 2. Conduct argon ion cleaning on the surface of the high-strength bolts;

[0028] 3. Turn on the Roots pump again to evacuate the furnace to vacuum. Turn on the metal target and deposit a metal transition layer on the surface of the high-strength bolts for 5 min to 20 min under the conditions of a temperature of 200°C to 500°C and an arc current of 10 A to 150 A;

[0029] 4. Keep the metal target on, introduce the gas for forming the ceramic coating until the air pressure in the furnace reaches 0.1 Pa to 0.9 Pa, turn on the bias power supply, and deposit a ceramic coating on the metal transition layer on the surface of the high-strength bolts for 10 min to 120 min under the conditions of a temperature of 200°C to 500°C, an arc current of 10 A to 150 A, a bias voltage of -250 V to -50 V, and a duty cycle of 10% to 90%;

[0030] 5. After the coating is completed, turn off the arc power supply, heating power supply, and bias power supply. Finally, introduce argon gas and cool to room temperature, and the preparation method of the high-hard nanocrystalline coating for preventing the storage welding of high-strength bolts is completed.

[0031] The purpose of argon ion bombardment cleaning in step 2 of this embodiment is to eliminate the gases and contaminants attached to the surface of the workpiece, expose the fresh surface of the substrate, and improve the bonding force between the deposited ions and the substrate.

[0032] The cleaning power supply used in step 2 and the bias power supply used in step 4 of this embodiment are both HIPIMS pulse power supplies.

[0033] The thickness of the ceramic coating in this embodiment can be adjusted within a size range not exceeding 5 μm according to the working conditions requirements of the sample and the thread tolerance fit.

[0034] During the storage process of threads, the essence of the welding failure phenomenon lies in the fact that under the actual working conditions of strong coupling of temperature and pre-tightening force, after a long time, the atoms on the surface of the threaded connection fully interdiffuse, forming a metallurgical bond, resulting in an increasing unloading torque of the threaded structure during long-term storage until the bolt cannot be disassembled. Therefore, reducing the atomic interdiffusion ability of the thread surface can effectively improve the long-term storage life of the bolt. In this specific embodiment, by preparing a high-hardness nanocrystalline coating on the surface of the specimen thread substrate, the hardness and wear resistance of the thread substrate can be effectively improved, and the nanocrystalline coating has good compactness. Moreover, the activation energy of atomic diffusion in the ceramic material is higher than that in the threaded substrate made of metal material. Therefore, it can effectively reduce the interdiffusion migration ability of atoms between the thread surfaces under the strong coupling condition of temperature-stress during long-term storage, thereby effectively preventing the thread welding failure phenomenon that occurs during the long-term storage and use of the specimen and improving the storage life of the bolt.

[0035] The beneficial effects of this embodiment are as follows:

[0036] In this embodiment, an improved multi-arc ion plating technology is adopted to prepare a high-density and high-hardness TiN nanocrystalline ceramic coating on the surface of complex structures such as threads within a thickness range of no more than 5 μm, significantly improving its hardness, wear resistance, and anti-diffusion ability without affecting the thread fitting accuracy. This process forms a high-hard ceramic structure with a firmly bonded interface and a stable and uniform coating layer by systematically controlling key steps such as coating pretreatment, ion bombardment cleaning, deposition of metal transition layer, and deposition of ceramic film layer.

[0037] 1. Aiming at the problem of storage welding of high-strength bolts, this embodiment adopts a special multi-arc ion plating process to form a high-hardness nanocrystalline ceramic coating on the thread surface, effectively inhibiting the atomic diffusion on the thread surface. This ceramic coating effectively inhibits the interfacial migration of metal atoms such as Fe and Cr in the storage simulation experiment, and the welding failure rate is significantly reduced. The thickness of the diffusion layer is reduced by 87.5% compared with the uncoated bolt. Compared with the existing lubricant or coating additive solutions, this method has better durability and engineering feasibility in complex storage environments such as high strength and high temperature, and completely solves the problem of welding failure during the long-term storage of high-strength bolts. It can be widely applied to the anti-welding protection of threaded connection components with extremely high requirements for long-term storage reliability in fields such as aerospace, nuclear power, and high-end equipment.

[0038] 2. The nanocrystalline ceramic coating has extremely high hardness and excellent wear resistance, and can stably exist on the thread surface for a long time, ensuring the reliability of the bolt in the long-term storage state.

[0039] 3. The process is mature and stable, the thickness of the prepared coating is accurately controllable, and it does not affect the fitting tolerance of the bolt, making it suitable for batch production and practical engineering applications.

[0040] Embodiment 2: The difference between this embodiment and Embodiment 1 is that: the material of the high-strength bolt described in Step 1 is high-chromium alloy steel. Others are the same as in Embodiment 1.

[0041] Embodiment 3: The difference between this embodiment and either Embodiment 1 or Embodiment 2 is that: the high-strength bolt described in Step 1 is a pre-treated high-strength bolt, and the pretreatment is specifically carried out according to the following steps: the surface of the high-strength bolt is successively sanded, sandblasted, and pickled, then ultrasonically cleaned with a solvent, then washed with water, and finally dried. Others are the same as in Embodiment 1 or Embodiment 2.

[0042] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that: the sanding is specifically carried out using silicon carbide sandpaper with a mesh number of 60 to 3500; the sandblasting is specifically carried out using sand grains with a mesh number of 80 to 180 for sandblasting, and the sand grains are quartz sand, silica sand, glass sand, pearlescent sand, or special sand; the pickling treatment is specifically carried out under the condition that the temperature is lower than 80°C, and the pickling solution is used for 1 min to 20 min, and the pickling solution is hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, chromic anhydride, hydrofluoric acid, or organic acid. Others are the same as in Embodiment 3.

[0043] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that: the solvent is acetone or absolute ethanol, and the ultrasonic cleaning is specifically carried out under the condition that the power is 30 W / L to 60 W / L, and the ultrasonic cleaning is carried out for 20 min to 60 min. Others are the same as in Embodiments 1 to 4.

[0044] Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is that: in Step 1, the roughing pump is turned on to adjust the furnace pressure to below 1 Pa, then the heating power supply is turned on, and under the condition that the temperature is 200°C to 500°C, preheat for 0.5 h to 2 h, and finally the Roots pump is turned on to evacuate the furnace to less than 1×10 -2 Pa. Others are the same as in Embodiments 1 to 5.

[0045] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that: in Step 2, argon is introduced until the furnace pressure is 1×10 -1 Pa to 2×10 -1 Pa, the bias power supply is turned on, and under the condition that the temperature is 200°C to 500°C and the bias voltage is -300 V to -2000 V, the high-strength bolt is subjected to argon ion cleaning for 5 min to 60 min. After the argon ion cleaning, the bias power supply is turned off. Others are the same as in Embodiments 1 to 6.

[0046] Embodiment VIII: The difference between this embodiment and any one of Embodiments I - VII is that in Step 3, the Roots pump is turned on again to evacuate the furnace to a vacuum lower than 1×10 -2 Pa. Others are the same as those in Embodiments I - VII.

[0047] Embodiment IX: The difference between this embodiment and any one of Embodiments I - VIII is that in Step 3, the metal target is a high - purity Ti target with a purity of 99.999%; the metal transition layer in Step 3 is a high - purity Ti transition layer with a purity of 99.999%. Others are the same as those in Embodiments I - VIII.

[0048] Embodiment X: The difference between this embodiment and any one of Embodiments I - IX is that in Step 4, the gas for forming the ceramic coating is one or a combination of two of nitrogen and methane gases, and the purity of the gas for forming the ceramic coating is 99.999%; the ceramic coating in Step 4 is TiN or TiCN. Others are the same as those in Embodiments I - IX.

[0049] The following examples are used to verify the beneficial effects of the present invention:

[0050] Example 1:

[0051] A method for preparing a high - hardness nanocrystalline coating to prevent the storage welding of high - strength bolts is carried out according to the following steps:

[0052] I. Place the high - strength bolts in the vacuum coating chamber of a multi - arc ion plating equipment. Turn on the roughing pump to adjust the furnace pressure to 1×10 -1 Pa, then turn on the heating power supply, preheat for 2 h at a temperature of 400 °C, and finally turn on the Roots pump to evacuate the furnace to 1×10 -3 Pa;

[0053] II. Introduce argon gas until the furnace pressure is 2×10 -1 Pa. Turn on the bias power supply and perform argon ion cleaning on the high - strength bolts for 60 min at a temperature of 400 °C and a bias voltage of - 1000 V. After argon ion cleaning, turn off the bias power supply;

[0054] III. Turn on the Roots pump again to evacuate the furnace to 1×10 -3 Pa. Turn on the metal target and deposit a metal transition layer on the surface of the high - strength bolts for 5 min at a temperature of 400 °C and an arc current of 80 A;

[0055] IV. Keep the metal target open, introduce the gas for forming the ceramic coating until the furnace pressure reaches 0.9 Pa, turn on the bias power supply, and deposit the ceramic coating on the metal transition layer of the high-strength bolt surface for 60 min under the conditions of a temperature of 400 °C, an arc current of 80 A, a bias voltage of -80 V, and a duty cycle of 70%.

[0056] V. After the coating is completed, turn off the arc power supply, heating power supply, and bias power supply. Finally, introduce argon gas and cool to room temperature to obtain the bolt coated with the nanocrystalline TiN coating, that is, the preparation of the nanocrystalline TiN coating on the bolt surface is completed.

[0057] The material of the high-strength bolt described in Step I is 1Cr18Ni11Si4AlTi high-chromium alloy steel.

[0058] The high-strength bolt described in Step I is a pre-treated high-strength bolt. The pretreatment is specifically carried out according to the following steps: The surface of the high-strength bolt is successively polished with sandpaper, sandblasted, and pickled, then ultrasonically cleaned with a solvent, washed with water, and finally dried.

[0059] The sandpaper polishing is specifically carried out using silicon carbide sandpaper with a mesh number of 3000; the sandblasting treatment is specifically carried out using sand grains with a mesh number of 180 for sandblasting, and the sand grains are quartz sand; the pickling treatment is specifically carried out at a temperature of 60 °C for 10 min using a pickling solution, and the pickling solution is hydrochloric acid with a mass percentage of 12%.

[0060] The solvent is acetone, and the ultrasonic cleaning is specifically carried out under the condition of a power of 60 W / L for 30 min.

[0061] The metal target described in Step III is a high-purity Ti target (99.999%); the metal transition layer described in Step III is a high-purity Ti transition layer (99.999%).

[0062] The gas for forming the ceramic coating described in Step IV is high-purity nitrogen (99.999%); the ceramic coating described in Step IV is TiN.

[0063] The cleaning power supply used in Step II and the bias power supply used in Step IV are both HIPIMS pulse power supplies.

[0064] Comparative Experiment: This comparative experiment differs from Example 1 in that the metal target in Step 3 is a common industrial titanium target with a purity of 95%; the gas used to form the ceramic coating in Step 4 is common industrial nitrogen with a purity of 99.99%; the bias power supply in Step 4 is changed to a DC power supply; in Step 4, a ceramic coating is deposited on the metal transition layer on the surface of a high-strength bolt for 60 minutes at a temperature of 400°C, an arc current of 80A, a voltage of -50V, and a duty cycle of 70%; and in Step 5, a bolt coated with a common TiN coating is obtained, thus completing the formation of a common TiN coating on the bolt surface. All other procedures are the same as in Example 1.

[0065] Figure 1 The microscopic morphology of the nanocrystalline TiN coating prepared on the bolt surface in Example 1 is shown in FIG. It can be seen that the coating has a smooth morphology, is composed of a large number of ultrafine grains, has a dense structure, and has no large particles enriched on the coating surface.

[0066] Figure 2 This is a scanning electron microscope image of the bonding between the nanocrystalline TiN coating and the bolt thread in Example 1. It shows that the coating completely covers the substrate and is of good quality with a uniform thickness of approximately 2.4 μm.

[0067] Figure 3 EDS analysis of the nanocrystalline TiN coating produced on the bolt surface in Example 1 (a) Sampling location, b) corresponding element content. It can be seen that the coating surface contains only two elements: N (13.11 at%) and Ti (86.89 at%).

[0068] Figure 4 The hardness test of the nanocrystalline TiN coating prepared on the surface of the bolt in Example 1 was carried out; the average hardness of the four sampling points reached 3174HV, which is about 20% higher than the hardness of the currently common TiN coating and 10 times higher than the hardness of the uncoated bolt.

[0069] Wear resistance test: A pressure load of 30N is applied between the sample and the test plate. The test plate is reciprocated by the motor. The distance between the sample and the test plate is 1cm each time. The reciprocating motion period of the test plate is 2s. The motor frequency is 0.5Hz, and the total number of wear cycles is 300. Figure 5 The wear resistance test diagram of the bolt coated with nanocrystalline TiN coating prepared in Example 1, the bolt coated with ordinary TiN coating and the bolt without coating in the comparative experiment; it can be seen that the volume wear rate of the uncoated sample is 5.9×10 - 3 mm 3 ·N -1 ·m -1 The volume wear rate of the ordinary TiN coating sample is 4.08×10 -3 mm 3 ·N-1 ·m -1 , the volumetric wear rate of the nanocrystalline TiN coating specimen is 1.86×10 -4 mm 3 ·N -1 ·m -1 . The volumetric wear rate of the nanocrystalline TiN coating is reduced by 68.5% compared to the uncoated specimen and by 54.4% compared to the conventional TiN coating.

[0070] Friction coefficient test: Load is 10 N; rotational speed is 260 r / min, linear velocity is 0.8 m / s; reciprocating friction mode, atmospheric conditions, normal temperature and pressure, GCr15 steel ball as the counterbody, unload once every 300 s, measure the wear amount, and the total friction time is 1500 s. Figure 6 Friction coefficient test for the bolt with nanocrystalline TiN coating prepared in Example 1 and the uncoated bolt. a) Uncoated bolt, b) Bolt with nanocrystalline TiN coating prepared in Example 1; The sliding friction coefficient of the bolt substrate before coating is about 0.15 at the initial stage of running-in. The friction coefficient fluctuates gently before 800 s and fluctuates greatly after 800 s. This is the result of the fatigue wear of the substrate surface leading to the fragmentation of the surface layer and a large change in the friction coefficient. The sliding friction coefficient of the high-strength bolt after coating is still about 0.15 at the initial stage of running-in, and the friction coefficient changes little within 1500 s. This indicates that the surface nanocrystalline TiN coating has good wear resistance and the coating is not significantly worn during the entire test period.

[0071] Heating and pressurizing simulation experiment: By increasing the pre-tightening force between the bolt and nut (nut material is 20Cr) to 170 N·m and raising the environmental temperature to 400 °C, an accelerated stress condition under typical storage environment is constructed to simulate the high-temperature and high-stress coupling state at the thread interface during long-term service and accelerate the evolution process of the welding process. The test results are as Figures 7 to 9 shown.

[0072] Figure 7 Macrostates of the bolt with nanocrystalline TiN coating prepared in Example 1 and the uncoated bolt after 90 days of heating and pressurizing test. a) Assembly drawing of uncoated bolt and nut, b) Cross-sectional view of uncoated bolt and nut, c) Assembly drawing of bolt with nanocrystalline TiN coating and nut, d) Bolt with nanocrystalline TiN coating after successful disassembly; After the above heating and pressurizing experiment, the uncoated bolt shows welding failure after the heating and pressurizing experiment with the same parameters, and the bolt cannot be disassembled and can only be analyzed by overall destruction, as shown in a) and b); while the coated bolt can be assembled and disassembled normally, and there is no obvious change in the thread surface of the coated bolt after disassembly macroscopically, as shown in c) and d). In comparison, the anti-welding failure ability of the coated bolt is greatly improved, which confirms that the hard ceramic coating can effectively improve the anti-seizure service life of the bolt.

[0073] Figure 8 EDS diagram of the threaded connection surface of the bolt and nut pair coated with nanocrystalline TiN coating prepared in Example 1 after 90 days of heating and pressurization test, a) Ti element distribution diagram, b) N element distribution diagram, c) Fe element distribution diagram, d) Cr element distribution diagram; it can be seen that there are clear enrichment zones of Ti and N elements in the ceramic coating area, as shown in a) and b), while the matrix Fe and Cr elements show a steep gradient distribution at the interface and cannot cross the ceramic coating for interdiffusion, as shown in c) and d), which proves that the metal atoms on the threaded connection surface are effectively blocked from migrating across the interface under the action of the titanium nitride ceramic coating, improving the anti-welding performance of the bolt.

[0074] Figure 9 Diffusion layer thickness of the bolt coated with nanocrystalline TiN coating prepared in Example 1 and the uncoated bolt and nut pair after 90 days of heating and pressurization test, a) and b) are the sampling positions of the uncoated bolt and the measured diffusion layer thickness at this position when just assembled, c) and d) are the sampling positions of the uncoated bolt and the measured diffusion layer thickness at this position after acceleration; e) and f) are the sampling positions of the coated bolt and the measured diffusion layer thickness at this position after acceleration. It can be seen from the figure that after subtracting the initial calibration value of 1 μm, the diffusion layer thickness of the bolt coated with nanocrystalline TiN coating prepared in Example 1 after being paired with the nut is 0.23 μm, and the diffusion layer thickness of the uncoated bolt after subtracting the calibration value and being paired with the nut is 1.84 μm under the same acceleration stress and acceleration time. In comparison, the diffusion layer thickness after coating is reduced by 87.5%, fully verifying the effectiveness of its anti-welding performance.

Claims

1. A method for preparing a high-hardness nanocrystalline coating to prevent the welding of high-strength bolts, characterized in that It is carried out according to the following steps: First, place the high-strength bolt in the vacuum coating chamber of the multi-arc ion plating equipment, turn on the roughing pump to adjust the air pressure in the furnace, then turn on the heating power supply for preheating, and finally turn on the Roots pump to evacuate the furnace to vacuum; Second, perform argon ion cleaning on the surface of the high-strength bolt; Third, turn on the Roots pump again to evacuate the furnace to vacuum, turn on the metal target, and deposit a metal transition layer on the surface of the high-strength bolt for 5 min to 20 min under the conditions of a temperature of 200 °C to 500 °C and an arc current of 10 A to 150 A; Fourth, keep the metal target on, introduce the gas for forming the ceramic coating until the air pressure in the furnace reaches 0.1 Pa to 0.9 Pa, turn on the bias power supply, and deposit a ceramic coating on the metal transition layer on the surface of the high-strength bolt for 10 min to 120 min under the conditions of a temperature of 200 °C to 500 °C, an arc current of 10 A to 150 A, a bias voltage of -250 V to -50 V, and a duty cycle of 10% to 90%; Fifth, after the coating is completed, turn off the arc power supply, heating power supply, and bias power supply, and finally introduce argon gas and cool to room temperature, thus completing the preparation method of the high-hard nanocrystalline coating for preventing the storage welding of high-strength bolts.

2. The preparation method of a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts according to claim 1, wherein The material of the high-strength bolt described in Step 1 is high-chromium alloy steel.

3. A method for preparing a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts during storage according to claim 1, characterized in that The high-strength bolt described in Step 1 is a pre-treated high-strength bolt, and the pretreatment is specifically carried out according to the following steps: successively sand the surface of the high-strength bolt, perform sandblasting treatment and pickling treatment, then perform ultrasonic cleaning with a solvent, then perform water washing, and finally dry.

4. A method for preparing a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts during storage, characterized in that The sanding is specifically carried out by using silicon carbide sandpaper with a mesh number of 60 to 3500; the sandblasting treatment is specifically carried out by using sand grains with a mesh number of 80 to 180 for sandblasting, and the sand grains are quartz sand, silica sand, glass sand, pearlescent sand or special sand; the pickling treatment is specifically carried out by treating with a pickling solution for 1 min to 20 min under the condition that the temperature is lower than 80 °C, and the pickling solution is hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, chromic anhydride, hydrofluoric acid or organic acid.

5. A method for preparing a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts as claimed in claim 3, wherein The solvent is acetone or absolute ethanol, and the ultrasonic cleaning is specifically carried out under the condition of a power of 30 W / L to 60 W / L for 20 min to 60 min.

6. A method for preparing a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts during storage according to claim 1, characterized in that In Step 1, start the roughing pump to adjust the pressure in the furnace to below 1 Pa, then turn on the heating power supply, and preheat for 0.5 h to 2 h under the condition that the temperature is 200 °C to 500 °C. Finally, start the Roots pump to evacuate the furnace to below 1×10 -2 Pa.

7. A method for preparing a high-hardness nanocrystalline coating to prevent the welding of high-strength bolts during storage, characterized in that In Step 2, argon is introduced until the furnace pressure reaches 1×10 -1 Pa to 2×10 -1 Pa. The bias power supply is turned on, and under the conditions of a temperature of 200°C to 500°C and a bias voltage of -300V to -2000V, the high-strength bolts are subjected to argon ion cleaning for 5 minutes to 60 minutes. After the argon ion cleaning, the bias power supply is turned off.

8. A method for preparing a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts during storage according to claim 1, characterized in that In Step 3, the Roots pump is turned on again to evacuate the furnace to a vacuum level lower than 1×10 -2 Pa.

9. A method for preparing a high-hardness nanocrystalline coating to prevent the welding of high-strength bolts during storage according to claim 1, characterized in that The metal target described in Step 3 is a high-purity Ti target with a purity of 99.999%; the metal transition layer described in Step 3 is a high-purity Ti transition layer with a purity of 99.999%.

10. The preparation method of a high-hardness nanocrystalline coating for preventing the welding of high-strength bolts according to claim 1, characterized in that The gas for forming the ceramic coating described in Step 4 is a combination of one or two of nitrogen gas and methane gas, and the purity of the gas for forming the ceramic coating is 99.999%; the ceramic coating described in Step 4 is TiN or TiCN.

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