A device and method for coating the inner wall of a tubular workpiece

Abstract

The application discloses a kind of inner wall coating device for tubular workpiece, coating method, including vacuum chamber;Cylindrical cathode arc source is placed in tubular workpiece inside, with tubular workpiece together fixed connection is in the top of vacuum chamber;Heating system is assembled in vacuum chamber, for heating tubular workpiece;Cathode arc power supply is connected to cylindrical cathode arc source to form loop;Reactor is connected in series in the loop formed by cylindrical cathode arc source and cathode arc power supply, vacuum chamber;Asymmetric bipolar pulse bias power supply, as workpiece bias has output electrode A and output electrode B, output electrode A, B is connected tubular workpiece, vacuum chamber respectively.Combined with the positive and negative pulse periodic output characteristics of asymmetric bipolar pulse bias power supply, the problem of "anode disappearance" of cathode arc source discharge in semi-closed environment is solved by the arc-stabilizing effect of reactor, long-term stable operation of built-in cylindrical cathode arc source is realized, process is simple and stable, equipment structure is simple, and coating efficiency is high.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of surface science and engineering technology, and particularly relates to an inner wall coating device for tubular workpieces and a coating method. BACKGROUND

[0002] Tubular workpieces are the most common workpieces in production and life fields, and the inner wall coating treatment of tubular workpieces is the key to improving the performance of tubular workpieces. By depositing functional coatings such as wear-resistant coatings or corrosion-resistant coatings on the surface, the actual service performance of tubular workpieces can be improved, the service life of the workpieces can be increased, resources can be saved, and energy waste can be reduced. For example, depositing DLC coating on the inner wall of oil pipelines or chemical pipelines can improve their corrosion resistance; preparing ablation-resistant coatings on the inner walls of various gun barrels and cannon barrels can improve the ablation resistance of the inner walls, enhance the service stability, and prolong the service life. However, because of the special shape of tubular workpieces, the surface coating strengthening treatment methods and equipment that can be used need to be specially designed.

[0003] The existing inner wall coating technologies for elongated tubular workpieces mainly include the following: the first is a chemical vapor deposition method, the second is a spraying method, the third is a vacuum evaporation method, the fourth is a sputtering coating method, and the fifth is an arc ion plating method. Among them, the chemical vapor deposition method uses gas as the medium, and the spraying method is also limited by the technical characteristics. The types of film layers that can be prepared by the two methods are limited, and the technology is not suitable for many application scenarios; the vacuum evaporation method is only suitable for low-melting-point materials, and the coating distribution is uneven; the sputtering technology has a low ionization rate, and the grown coating has poor adhesion and is not easy to form a reaction product film layer. The method of using the arc ion plating technology to realize the inner wall coating of the tube through the focusing and constraining of the plasma by the electromagnetic field is the most. The arc ion plating technology has a wide range of target material compositions, a high ionization rate, and is suitable for reaction plating. The prepared film layer has high quality, good adhesion, uniform film formation, and high deposition efficiency, and is widely used in the fields of cutters, molds, and decorative plating.

[0004] But the existing arc ion plating process and device structure for the inner wall of the tubular workpiece are relatively complex, and the process stability and repeatability are insufficient. For example, in order to realize the discharge of the built-in columnar cathode target, one method is to install a movable permanent magnet on the outer wall of the columnar target to realize the arc discharge of the columnar cathode in the tubular workpiece, and further deposit inside. During the implementation of this method, the columnar target is in a partial discharge state, and the efficiency is difficult to improve, and the device structure is complex. Another method is to place the arc ion plating source outside the opening of the tubular workpiece in the vacuum chamber, and set two sets of magnetic field generating devices in the arc ion plating deposition device, one set is placed on the plasma transmission channel outside the vacuum chamber, and the other set is placed outside the tubular workpiece in the vacuum chamber. The magnetic field is used to focus the plasma beam, constrain the cross-sectional diameter and transmission efficiency of the plasma beam during transmission, and guide the plasma beam to diffuse along the central axis direction of the tubular workpiece. The pulse electric field is arranged inside the workpiece to accelerate the directional flow of the plasma by using the electric field, and the plasma beam is constrained and controlled by using the magnetic field and the electric field, so as to realize the deposition of the plasma on the inner wall of the tube. This method is a long-distance transport of plasma under the action of a specific electromagnetic field, which will cause the loss of the number and energy of the film-forming ions, reduce the film-forming efficiency and film-forming quality, and the film-forming process is unstable. This method is especially not suitable for the preparation of functional films with large thickness and the inner wall plating of tubular workpieces with large length.

[0005] Therefore, it is urgent to develop a plating device and a plating method suitable for the tubular workpiece, simplify the existing device and process for the inner wall plating of the tubular workpiece, and improve the plating stability and plating efficiency. SUMMARY

[0006] In order to solve the above problems, the purpose of the present application is to provide a stable and efficient inner wall plating device and plating method for a tubular workpiece, which uses the arc stabilizing effect of the electric reactor, and combines the positive and negative pulse periodic output characteristics of the asymmetric bipolar pulse bias power supply to solve the "anode disappearance" problem of the cathode arc source discharge in the semi-closed environment, realize the long-term stable work of the built-in columnar cathode arc source, and prepare functional coatings of different types and thickness requirements. At the same time, the present application completely follows the conventional arc ion plating process and film-forming principle, does not need to add auxiliary facilities such as electromagnetic field or turnover system, the process is simple and stable, the repeatability is high, the device structure is simple, the film quality and plating efficiency are high, the functional films with large thickness can be prepared, and the present application is suitable for large-scale batch production.

[0007] The first purpose of the present application is to provide an inner wall plating device for a tubular workpiece, which comprises:

[0008] a vacuum chamber;

[0009] a columnar cathode arc source arranged inside the tubular workpiece and fixedly connected to the top of the vacuum chamber together with the tubular workpiece;

[0010] A heating system is arranged on the vacuum chamber for heating the tubular workpiece;

[0011] A cathode arc power source is connected to the columnar cathode arc source to form a loop;

[0012] An electric reactor is connected in series to the loop formed by the columnar cathode arc source, the cathode arc power source and the vacuum chamber;

[0013] An asymmetric bipolar pulse bias power source has output electrodes A and B for workpiece biasing, and the output electrodes A and B are connected to the tubular workpiece and the vacuum chamber respectively.

[0014] In an optional embodiment, the top of the vacuum chamber is provided with a top vacuum flange, and the tubular workpiece is fixed to the top of the vacuum chamber through the top vacuum flange.

[0015] The heating system is arranged on the top vacuum flange.

[0016] In an optional embodiment, the columnar cathode arc source has a rotating magnetic field structure, and a rotating motor of the columnar cathode arc source is fixed to the top vacuum flange.

[0017] In an optional embodiment, the heating system is composed of four straight tube heaters.

[0018] In an optional embodiment, the length-diameter ratio of the tubular workpiece is greater than or equal to 20:1, the inner diameter of the tubular workpiece is greater than or equal to 69 mm, and the discharge spacing of the columnar cathode arc source is greater than or equal to 15 mm.

[0019] The second object of the present application is to provide a method for coating the inner wall of a tubular workpiece, comprising the following steps:

[0020] S1: Workpiece assembly:

[0021] Assembly of the columnar cathode arc source and the tubular workpiece, loop connection of the columnar cathode arc source and the cathode arc power source, and connection of the workpiece biasing to the tubular workpiece and the vacuum chamber;

[0022] S2: Preheating and glow cleaning of the tubular workpiece:

[0023] Preheating the tubular workpiece with the heating system;

[0024] Self-glow discharge in the vacuum chamber is performed with the asymmetric bipolar pulse bias power source to form a low-temperature plasma region of low-pressure gas discharge between the tubular workpiece and the vacuum chamber, and the inner wall of the workpiece is sputter cleaned;

[0025] S3: Depositing functional film:

[0026] Working gas is introduced into the vacuum chamber, the columnar cathode arc source is turned on, and the target core magnetic field is rotated.

[0027] S4: cooling and taking out.

[0028] In an optional embodiment, the preheating temperature of the tubular workpiece in step S2 is 100-400 DEG C, the workpiece is baked to remove gas and improve film purity, and the workpiece inner wall film layer growth is provided with a basic temperature to improve film density; the negative pulse output amplitude of the asymmetric bipolar pulse bias power supply is 600-1100 V, the frequency is 40-60 KHz, and the sum of the positive and negative pulse duty cycles is less than or equal to 80%; the self-glow discharge sputtering cleaning process parameter requirements in the vacuum coating process are met.

[0029] The sputtering cleaning time is 10-30 min, and the specific time is determined by the workpiece surface state and the discharge parameters.

[0030] In an optional embodiment, the working gas pressure in step S3 is 0.5-5.0 Pa.

[0031] The target material composition selected during deposition of the functional film is Ti, Cr, Al, Ni, Cu, any one or a mixture of two or more, or a non-metal.

[0032] In an optional embodiment, the negative pulse of the asymmetric bipolar pulse bias power supply in step S3 is set as: voltage 300-800 V, frequency 40-60 KHz, and duty cycle 30-80%;

[0033] The positive pulse is set as: voltage 0-50 V, frequency 40-60 KHz, and duty cycle 20-50%;

[0034] The sum of the positive and negative pulse duty cycles is less than or equal to 80%;

[0035] The working time is 30 min-120 min.

[0036] The asymmetric bipolar pulse bias power supply is used to debug the plasma discharge state of the semi-closed space, combined with the theoretical analysis of the plasma transport process, to achieve the best positive and negative pulse bias amplitude, duty cycle and frequency, realize the deposition and growth of the inner surface film layer of the workpiece, and solve the problem of anode disappearance, realize the long-term stable work of the columnar cathode arc in the semi-closed space. In addition, when the bias power supply outputs a positive pulse, the electron bombardment effect improves the inner wall temperature and promotes the high-quality growth of the film layer, and a high-consistency functional layer is deposited on the inner wall of the tubular workpiece.

[0037] In an optional embodiment, the film layer thickness in step S3 is 1-20 mu m.

[0038] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0039] (1) In series between the target and the vacuum chamber, the electric reactance and the workpiece bias are connected, and the asymmetric bipolar pulse bias power supply is adopted to maintain the stable discharge of the built-in columnar cathode arc source. Also, the movable permanent magnet outside the tubular workpiece is avoided, and the problem of difficult improvement of deposition efficiency caused by local discharge of the built-in columnar cathode arc of the tubular workpiece is solved. The device structure is simple, the workpiece is convenient to load and unload, the process is stable and highly repeatable, the deposition efficiency is high, the functional film with large thickness can be prepared, and it is suitable for large-scale batch production of the inner wall coating of the tubular workpiece with a length of more than 500 mm.

[0040] (2) The asymmetric bipolar pulse bias power supply simultaneously realizes the periodical alternation of electron bombardment heating and coating, improves the film forming quality, has high ionization rate, can realize the deposition of metal film, alloy film and nitride, carbide and oxide reaction film, can prepare film layers with rich types, and is suitable for ion coating surface modification of the inner wall of the tubular workpiece.

[0041] (3) The columnar cathode arc source is built into the tubular workpiece, the discharge is uniform in the rotating target core structure, and the uniformity of film layer deposition is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical scheme of the exemplary embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor. In the drawings:

[0043] Figure 1 A structural schematic diagram of a device for coating the inner wall of a tubular workpiece is provided for the embodiments of the present application.

[0044] Figure 2 A cross-sectional view of the DLC film layer deposited on the inner wall of the oil pipeline prepared in Example 3.

[0045] Figure 3 A cross-sectional view of the CrN film layer deposited on the inner wall of the gun barrel prepared in Example 4.

[0046] Figure 4 Surface photos of the gun barrel after different shots when the inner wall of the gun barrel has no coating and has CrN coating in Example 4;

[0047] 4a is a surface photo of the gun barrel after 5 shots without coating, and 4b is a surface photo of the gun barrel after 110 shots with CrN coating.

[0048] Figure 5 A cross-sectional view of the TiN film layer deposited on the inner wall of the stainless steel pipe prepared in Example 5.

[0049] Figure 1 The various components and corresponding reference numerals are as follows:

[0050] 1 - target core magnetic field rotating motor, 2 - cathode arc power terminal, 3 - workpiece bias terminal, 4 - top vacuum flange, 5 - workpiece mounting bracket, 6 - cylindrical cathode arc source, 7 - tubular workpiece, 8 - heater, 9 - vacuum chamber, 10 - asymmetric bipolar pulse bias power supply, 11 - reactor, 12 - cathode arc power supply. DETAILED DESCRIPTION

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the following will be combined with the accompanying drawings for the embodiments of the present application to make a clear and complete description of the technical solutions in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various different configurations.

[0052] It should be noted that similar reference numerals and letters indicate similar items in the following drawings, and therefore, once an item is defined in one drawing, it need not be further defined and explained in subsequent drawings. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0053] In the description of the embodiments of the present application, the terms "center", "upper", "lower", "left", "right", "vertical", "longitudinal", "lateral", "horizontal", "inner", "outer", "front", "back", "top", "bottom", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly understood by those skilled in the art, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0054] In the description of the present application, unless otherwise explicitly specified and limited, the terms "set", "open", "mount", "connected", and "connected" should be understood broadly, for example, can be fixedly connected, can be detachably connected, or integrally connected; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or can be the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0055] Example 1:

[0056] As Figure 1As shown in the figure, a device for coating the inner wall of a tubular workpiece 7 comprises a vacuum chamber, a cylindrical cathode arc source 6 and a heating system, an asymmetric bipolar pulsed bias power supply 10, a reactor 11 and a cathode arc power supply 12.

[0057] The cylindrical cathode arc source 6 is placed inside the tubular workpiece 7 which is fixedly installed on a workpiece mounting support 5, and a top vacuum flange 4 is arranged on the top of the vacuum chamber, and the cylindrical cathode arc source 6 is fixedly installed on the top of the vacuum chamber together with the tubular workpiece 7 through the top vacuum flange 4. The cylindrical cathode arc source 6 is a gyromagnetic field structure, and a target central magnetic field rotating motor 1 of the cylindrical cathode arc source 6 is fixedly installed on the top vacuum flange 4 of the vacuum chamber, and a cathode arc power supply terminal 2 is arranged on the cylindrical cathode arc source 6 to form a loop with the cathode arc power supply 12. A tubular heater 8 with four straight pipes is uniformly arranged on the top vacuum flange 4 to form a heating system for heating the tubular workpiece 7. The reactor 11 is connected in series in the loop formed by the cylindrical cathode arc source 6, the cathode arc power supply 12 and the vacuum chamber 9, and a workpiece bias terminal 3 is arranged on the cylindrical cathode arc source 6 to connect the workpiece bias, and the workpiece bias uses the asymmetric bipolar pulsed bias power supply 10, and the asymmetric bipolar pulsed bias power supply has two output electrodes A and B which can periodically output positive and negative pulses with different amplitudes, and the output electrode A is connected to the tubular workpiece 7, and the output electrode B is connected to the vacuum chamber.

[0058] In a conventional arc ion plating process, the surface of the cylindrical cathode arc source 6 is composed of positively charged ions and negatively charged electrons, wherein the positively charged ions reach the workpiece surface under the guidance of negative bias to deposit into a film, and most of the negatively charged electrons need to pass through the vacuum chamber with the cathode target as an anode to reach the ground, thereby forming an electric circuit to maintain stable discharge on the target surface and continuously depositing a film on the workpiece surface. However, in the process of coating the tubular workpiece 7, the cylindrical cathode arc source 6 is placed inside the workpiece in a semi-closed environment, and the channel of the electrons in the plasma to the vacuum chamber wall is blocked, the "anode disappears", the target discharge cannot be maintained, and the arc current begins to decrease.

[0059] In the coating device provided by the application, the reactor connected in series in the loop composed of the cathode target and the vacuum chamber will induce a voltage U L in the same direction as the voltage U0 of the cathode target power supply when the target current decreases, and the two voltages are superimposed and applied to the cathode target, and the voltage Ue applied to the cathode target is Ue=U0+U LThe enhanced electric field on the cathode target surface facilitates breakdown and maintains discharge, improving the discharge stability of the built-in cathode target. At this time, the reactor is in a releasing state, slowing the rate of current decrease in the cathode target, thus buying time for the arc power supply to self-regulate and maintain stable discharge. Simultaneously, the A-pole of the asymmetric bipolar pulse bias power supply can output positive and negative pulses. By adjusting the amplitude, frequency, and duty cycle of the positive and negative pulses at the A-pole, the "anode disappearance" problem is eliminated, achieving synergy with the reactor to prevent the cathode arc source 6 from extinguishing and maintain a continuous and stable discharge on the cathode target surface inside the tube.

[0060] The coating apparatus provided by this invention avoids the need for a movable permanent magnet outside the tubular workpiece 7, thus solving the problem of poor deposition efficiency due to partial discharge of the internal cylindrical cathode arc in the tubular workpiece 7. It also avoids the problem of sacrificing deposition efficiency, reducing film quality, and decreasing deposition uniformity by setting an electromagnetic field to extend the plasma transport distance at the cathode arc source in order to achieve film deposition on the inner wall of slender tubular workpieces. Furthermore, this invention eliminates the need for auxiliary facilities such as a plasma confinement electromagnetic field or a workpiece flipping system in addition to the magnetic field used for arc discharge. The equipment has a simple structure, the tubular workpiece 7 is easy to load and unload, the process is stable and highly repeatable, and the deposition efficiency is high. It can prepare thick functional films and is suitable for large-scale, stable, and mass production of coatings on the inner walls of long tubular workpieces (greater than 500 mm) or short tubular workpieces (less than 500 mm).

[0061] The coating device provided by this invention achieves stable and uniform coating on the inner wall of the slender tubular workpiece 7, which is suitable for the actual needs of uniform coating on the inner wall of tubular workpieces 7 with different length-to-diameter ratios. The length-to-diameter ratio of the tubular workpiece 7 can be greater than 20:1, the minimum inner diameter of the tubular workpiece 7 is 69mm, the minimum discharge spacing of the columnar cathode arc source 6 is 15mm, and the uniformity of the film thickness is better than ±90%.

[0062] Example 2:

[0063] A method for coating the inner wall of a tubular workpiece 7, using the coating apparatus described in Example 1, includes the following steps:

[0064] S1: Workpiece assembly.

[0065] The cylindrical cathode arc source 6 is placed inside the tubular workpiece 7, which is then hoisted onto the workpiece mounting bracket 5 and together they are installed into the vacuum chamber 9 and fixed to the top of the chamber. A reactor 11 (100A / 1mH) is connected in series between the cylindrical cathode arc source 6 and the cathode arc power supply 12. The tubular workpiece 7 is connected to the A terminal of the asymmetric bipolar pulse bias power supply 10, and the vacuum chamber is connected to the B terminal. The bias power supply has an output power of 30KW.

[0066] The tubular workpiece 7 in S1 can be a tubular workpiece 7 with different length-diameter ratios, which can be greater than or equal to 20:1, the minimum inner diameter of the workpiece is 69 mm, and the minimum discharge spacing of the cathode arc source 6 is 15 mm. The workpiece material can be steel and its alloy, titanium and its alloy, and other different metal materials.

[0067] S2: Preheating and glow cleaning of the tubular workpiece 7.

[0068] The tubular workpiece 7 is preheated by using a straight tube heater 8, and the preheating temperature is up to 400℃, preferably between 100-300℃, according to the composition of the workpiece and the composition of the film layer; then argon is introduced to clean the inner wall of the workpiece by argon ion glow sputtering. Asymmetric bipolar pulse bias power supply is used to realize self-glow discharge in the chamber, and the vacuum degree in the chamber is maintained at 1.0 Pa-2.0 Pa. During the argon ion sputtering cleaning process, the bias power supply works in the negative pulse conventional bias mode, the tubular workpiece 7 is connected to the bias power supply A pole, and the vacuum chamber is connected to the bias power supply B pole. The glow cleaning bias working parameters are determined according to the composition of the workpiece and the composition of the film layer, the negative pulse voltage amplitude is set to be up to 1100V, preferably 600V-800V, the frequency is 40-60KHz, the sum of the positive and negative pulse duty cycles is less than or equal to 80%, preferably 60-80%, a low-pressure gas discharge low-temperature plasma zone is formed between the tubular workpiece 7 and the vacuum chamber 9, the workpiece inner wall is sputter cleaned, and the time is 10-30 min.

[0069] S3: Depositing functional film.

[0070] The required working gas is sent into the vacuum chamber, the columnar cathode arc source 6 is turned on, and the target core magnetic field is rotated to improve the uniformity of film formation. The target core magnetic field rotating motor 1 is fixed on the vacuum flange 4 at the top of the vacuum chamber. The discharge voltage of the column target before the installation of the tubular workpiece 7 is 18V-28V, and after the installation of the tubular workpiece 7, the impedance characteristics of the plasma become larger, and the discharge voltage of the cathode arc power supply increases to 45V-50V.

[0071] The working gas and target material composition are selected according to the process requirement. When depositing a metal film layer, Ar gas is selected as the working gas, when depositing a nitride coating, N2 and Ar mixed gas is selected as the working gas, the mixed gas is in a volume ratio of 5:1-10:1; when depositing a carbide coating, C2H2 and H2 mixed gas is selected as the working gas, the mixed gas is in a volume ratio of 10:1-15:1; the working gas pressure is maintained at 0.5-5.0 Pa. The target material composition can be Ti, Cr, Al, Ni, Cu and the like metal or non-metal, or a composite of two or three or more than three metals. The target current is 40-120 A, the working bias negative pulse is set as: voltage 300-800 V, frequency 40-60 KHz, duty cycle 30-80%; the positive pulse is set as: voltage 0-50 V, frequency 40-60 KHz, duty cycle 20-50%; and the sum of the positive and negative pulse duty cycles cannot be higher than 80%; the working time is 30 min-130 min, and the deposited film layer thickness is in the range of 1-20 μm. Pure metal film, nitride film and carbide film and the like various film systems can be prepared, the same film systems as those prepared by the cathodic arc ion plating can be prepared, the film layer thickness is controlled by controlling the plating time, and the film layer thickness from 1 μm to 20 μm can be realized.

[0072] S4: cooling and taking out the workpiece.

[0073] After the deposition of the functional film layer is completed, the tubular workpiece 7 is taken out after the temperature is reduced to room temperature.

[0074] The application is described in more detail below with specific examples.

[0075] Example 3: depositing a diamond-like coating on the inner wall of an oil pipeline to improve corrosion resistance.

[0076] Step (1):

[0077] The cleaned and dried stainless steel oil pipeline workpiece is installed on the special workpiece mounting bracket 5 and integrated with the vacuum flange 4 at the top of the vacuum chamber, then the columnar cathode arc source 6 is installed into the tubular workpiece 7, the tubular workpiece 7, the columnar cathode arc source 6 and the vacuum chamber flange are integrated as a whole, hoisted to the top of the vacuum chamber, and then connected and fixed with the vacuum chamber 9.

[0078] The tubular stainless steel pipe has a length of 2800 mm, an inner diameter of 140 mm, and a length-diameter ratio of 20:1; the columnar cathode arc Cr target has a length of 2900 mm and an outer diameter of 80 mm; the discharge distance between the target and the workpiece is 30 mm. After the workpiece is installed, the reactor 11 is connected in series in the loop formed by the columnar cathode arc source 6, the cathode arc power supply 12 and the vacuum chamber 9, the workpiece 7 bias connection end is connected to the A pole of the asymmetric bipolar pulse bias power supply 10, and the vacuum chamber is connected to the B pole of the bias power supply. The vacuum pumping system is started to begin vacuumizing.

[0079] Step (2):

[0080] The vacuum degree is better than 10 -2 After the pressure is stabilized at 1.0 Pa, the direct tube heater 8 is turned on to preheat the tubular workpiece 7 to 100°C. After the temperature is maintained at 100°C, argon gas is introduced to start the argon ion glow sputtering cleaning. The vacuum degree in the chamber is maintained at 1.0 Pa, the bias power supply is set to a unipolar negative pulse working mode, the negative pulse voltage is set to 800 V, the frequency is 60 KHz, and the duty cycle is 80%. A low-pressure gas discharge low-temperature plasma zone is formed between the workpiece and the vacuum chamber to sputter clean the inner wall of the workpiece, and the time is 30 min.

[0081] Step (3):

[0082] The argon gas flow rate and the vacuum degree remain unchanged, the columnar cathode arc Cr target power supply is turned on, the current is set to 100 A, and a Cr bottom layer is deposited. The bias power supply is set to an asymmetric bipolar pulse bias working mode, the negative pulse voltage is set to 600 V, the frequency is 60 KHz, the duty cycle is 60%, the positive pulse voltage is set to 10 V, the frequency is 60 KHz, and the duty cycle is 20%. The time is 5 min, and the thickness of the Cr layer is 100-150 nm. Then, C2H2 is gradually added to deposit a CrC transition layer. Finally, the ratio of C2H2 to Ar gas is 10:1, the vacuum degree is maintained at 3.0 Pa, the negative pulse voltage is set to 300 V, the frequency is 60 KHz, the duty cycle is 30%, the positive pulse voltage is set to 10 V, the frequency is 60 KHz, and the duty cycle is 20%. The deposition time is 60 min, and the thickness is 4 μm. Subsequently, the Cr target power supply is turned off, H2 reaction gas is added, the ratio of C2H2:H2:Ar is 15:7:1, the vacuum degree is maintained at 5.0 Pa, the negative pulse voltage is set to 800 V, the frequency is 60 KHz, the duty cycle is 60%, the positive pulse voltage is set to 50 V, the frequency is 60 KHz, and the duty cycle is 20%. The deposition time is 60 min, and the thickness of the DLC layer is 3 μm. The thickness of the entire functional layer is 7-7.5 μm.

[0083] Step (4):

[0084] After the deposition of the functional film layer is completed, the workpiece is taken out after the temperature decreases to room temperature.

[0085] As Figure 2The DLC film layer is deposited on the inner wall of the oil pipeline by the above steps, the film layer is amorphous and dense structure, the overall thickness is 7 pm, and the uniformity of the film layer thickness in the range of the total length 2800 mm of the tubular workpiece 7 is 91%. The Vickers microhardness of the inner surface of the workpiece is increased from 350HV to 1200HV according to the test method for metal microhardness in GBT 4342-1991. The neutral salt spray corrosion resistance of the pipeline coated with the DLC coating is tested according to GB / T 10125-2012, and the prepared DLC coating pipeline is rated according to GB / T 6461-2002 after 360h of neutral salt spray corrosion. The corrosion resistance of the pipeline coated with the DLC coating reaches R A 8, and the corrosion resistance of the pipeline without coating is R A 8 after 96h of neutral salt spray corrosion. The DLC film layer greatly improves the hardness and corrosion resistance of the inner wall of the pipeline.

[0086] Example 4: Depositing CrN on the inner wall of the barrel to improve the ablation resistance.

[0087] Step (1):

[0088] The cleaned and dried titanium alloy barrel workpiece is installed on the special workpiece mounting bracket 5, the workpiece mounting bracket 5 and the vacuum chamber top vacuum flange 4 are an integral whole, then the columnar cathode arc source 6 is installed inside the tubular workpiece 7 from the top of the vacuum chamber flange, the workpiece, the columnar cathode arc source 6 and the vacuum chamber flange form an integral whole, and are hoisted to the top of the vacuum chamber and fixed with the vacuum chamber 9.

[0089] The tubular titanium alloy workpiece is 1400mm long, 82mm in inner diameter, and the length-diameter ratio is 17:1. The length of the columnar cathode arc Cr target is 800mm, the outer diameter is 39mm, and the discharge distance between the target and the workpiece is 21.5mm. Due to the service characteristics of the artillery, only the inner wall of 600mm length range where the gunpowder ablation is the most serious is surface strengthened, the long columnar cathode arc source 6 is completely enclosed inside the tubular workpiece 7, and effectively covers the required processing area. After the workpiece is installed, the reactor 11 is connected in series in the loop formed by the columnar cathode arc source 6 and the cathode arc power supply 12, the vacuum chamber 9, the tubular workpiece 7 bias connection end connects the A pole of the asymmetric bipolar pulse bias power supply, and the vacuum chamber connects the B pole of the bias power supply. Start the vacuum pumping system and start pumping.

[0090] Step (2):

[0091] The vacuum degree is better than 10 -2After the Pa, open straight tube heater 8, the workpiece is preheated to 200 ℃, temperature is maintained at 200 ℃, argon is introduced to start argon ion glow sputtering cleaning. The vacuum degree in the chamber is maintained at 1.0 Pa, the bias power supply is set to unipolar negative pulse working mode, the negative pulse voltage is set to 800 V, the frequency is 60 KHz, the duty cycle is 80%, a low pressure gas discharge low temperature plasma zone is formed between the workpiece and the vacuum chamber, the workpiece inner wall is sputtered and cleaned, and the time is 15 min.

[0092] Step (3):

[0093] The Ar gas flow is unchanged, the vacuum is unchanged, the columnar cathode arc Cr target power supply is turned on, the current is set to 80 A, the Cr bottom layer is deposited. The bias power supply is set to asymmetric bipolar pulse bias working mode, the negative pulse voltage is set to 600 V, the frequency is 40 KHz, the duty cycle is 60%, the positive pulse voltage is set to 10 V, the frequency is 40 KHz, the duty cycle is 20%, the time is 5 min, and the thickness of the Cr layer is 100-150 nm. Then gradually add N2 gas to deposit the CrN functional layer, the final N2 gas and Ar gas ratio is 5:1, the vacuum degree is maintained at 2.0 Pa, the negative pulse voltage is set to 300 V, the frequency is 40 KHz, the duty cycle is 30%, the positive pulse voltage is set to 10 V, the frequency is 40 KHz, the duty cycle is 20%, and the deposition time is 240 min. Then the Cr target power supply is turned off, and the thickness of the entire functional layer is about 15 μm.

[0094] Step (4):

[0095] After the deposition of the functional film layer, the workpiece is taken out after the temperature drops to room temperature.

[0096] As shown in Figure 3 , a CrN coating with a thickness of about 15 μm is successfully deposited on the inner surface of a long tube with a size of φ82mmx1400mm by the above steps, the columnar crystal structure of the film layer grows densely without defects, and the thickness uniformity of the film layer deposited on the inner wall of the tubular workpiece within a length of 7600mm is 95%. Referring to "GBT4342-1991 Metal Micro Vickers Hardness Test Method", the Vickers microhardness of the inner wall of the workpiece is increased from 600HV to 1500HV, and in the shooting experiment, the inner wall ablation is detected by an endoscope. After 5 shots of the uncoated workpiece, the inner wall of the barrel appears obvious oxide layer shedding and ablation pits, and after 110 shots of the CrN coated barrel, there is no ablation damage, and the CrN coating effectively improves the ablation resistance of the barrel. Figure 4 is a photograph of the inner wall surface of the barrel observed by an endoscope under 5 times magnification Figure 4 a is a surface photograph of the uncoated barrel after 5 shots, with obvious ablation pits and oxide layer shedding; Figure 4 b is a surface photograph of the CrN coated barrel after 110 shots, without ablation damage).

[0097] Example 5: Accelerator stainless steel inner wall deposition of TiN, reducing the outgassing of stainless steel pipes.

[0098] Step (1):

[0099] The cleaned and dried stainless steel tubular workpiece 7 is installed on a dedicated workpiece mounting bracket 5, and the workpiece clamp and the vacuum chamber top vacuum flange 4 are integrated as a whole. Then the cylindrical cathodic arc source 6 is installed inside the tubular workpiece 7 from the top of the vacuum chamber flange, and the tubular workpiece 7, cylindrical cathodic arc Ti target 6 and vacuum chamber flange form a whole, which is hoisted to the top of the vacuum chamber and fixed with the vacuum chamber 9.

[0100] The tubular stainless steel pipe is 800 mm long, with an inner diameter of 69 mm and a length-diameter ratio of 11:1. The cylindrical cathodic arc Ti target is 800 mm long and has an outer diameter of 39 mm. The discharge distance between the target and the workpiece is 15 mm. After the workpiece is installed, the cathodic arc 6 and the cathodic arc power supply 12, the vacuum chamber 9 form a loop in series with the reactor 11, the tubular workpiece 7 bias connection end connects the asymmetric bipolar pulse bias power supply 10A pole, and the vacuum chamber connects the bias power supply B pole. Start the vacuum pumping system and start vacuumizing.

[0101] Step (2):

[0102] The vacuum degree is better than 10 -2 Pa, turn on the straight pipe heater 8, preheat the tubular workpiece 7 to 250°C, and maintain the temperature at 250°C. After the temperature is maintained at 250°C, argon gas is introduced to start argon ion glow sputtering cleaning. The vacuum degree in the chamber is maintained at 1.0 Pa, the bias power supply is set to single polarity negative pulse working mode, the negative pulse voltage is set to 800V, the frequency is 40KHz, the duty cycle is 80%, a low pressure gas discharge low temperature plasma zone is formed between the workpiece and the vacuum chamber, the workpiece inner wall is sputtered and cleaned, and the time is 30min.

[0103] Step (3):

[0104] The Ar gas flow is unchanged, the vacuum is unchanged, the cylindrical cathodic arc Ti target power supply is turned on, the current is set to 40A, and the Ti bottom layer is deposited. The bias power supply is set to asymmetric bipolar pulse bias working mode, the negative pulse voltage is set to 600V, the frequency is 40KHz, the duty cycle is 60%, the positive pulse voltage is set to 10V, the frequency is 40KHz, the duty cycle is 20%, the time is 10min, and the Ti layer thickness is 100-120nm. Then gradually add N2 gas, the final N2 and Ar gas ratio is 3:1, the vacuum degree is maintained at 3.0 Pa, the negative pulse voltage is set to 300V, the frequency is 40KHz, the duty cycle is 60%, the positive pulse voltage is set to 10V, the frequency is 40KHz, the duty cycle is 20%, the deposition time is 40min, the TiN thickness is 1μm, and then the Ti target power supply is turned off.

[0105] Step (4):

[0106] After the functional film deposition is completed, the workpiece is removed after the temperature drops to room temperature.

[0107] like Figure 5 As shown in the image, a TiN film was successfully deposited on the inner wall of the stainless steel pipe through the above steps. The cross-sectional photograph shows a thickness of 1 μm, and the columnar crystal structure of the film is densely grown without obvious defects. Within an 800 mm length region of the tubular workpiece 7, the uniformity of the film deposition thickness on the inner wall is 93%. The TiN film can effectively improve the gas adsorption performance of the inner wall of the stainless steel pipe.

[0108] In summary, the coating equipment and coating method of the present invention can achieve the following beneficial effects:

[0109] 1. An inductor is connected in series between the target and the vacuum chamber, and an asymmetric bipolar pulse bias power supply is used for workpiece bias to maintain stable discharge of the built-in cylindrical cathode arc source 6, thus solving the problem of arc extinction of the built-in cathode arc source 6.

[0110] By utilizing the arc-stabilizing effect of a reactor and combining it with the periodic positive and negative pulse output characteristics of an asymmetric bipolar pulse bias power supply, the "anode disappearance" problem of cathode arc source 6 discharge in a semi-enclosed environment is solved, enabling long-term stable operation of the built-in columnar cathode arc source 6 and the preparation of functional coatings with different types and thicknesses. Furthermore, this avoids the need for a movable permanent magnet outside the tubular workpiece 7, thus solving the problem of partial discharge in the built-in columnar cathode arc of the tubular workpiece 7 and the difficulty in improving deposition efficiency.

[0111] This also avoids the problems of low film formation efficiency and uneven deposition caused by the electromagnetic field that extends the plasma transport distance due to the cathode arc source 6. The equipment has a simple structure, convenient workpiece loading and unloading, stable process with high repeatability, and high deposition efficiency, capable of producing thick functional films. It is suitable for large-scale mass production of coatings on the inner walls of tubular workpieces 7. It is suitable for the actual needs of uniform coating on the inner walls of tubular workpieces 7 with different aspect ratios. The aspect ratio of the tubular workpiece 7 can be greater than 20:1, the minimum inner diameter of the workpiece is 69mm, the minimum discharge spacing of the cathode arc source 6 is 15mm, and the film thickness uniformity is better than ±90%.

[0112] 2. The asymmetric bipolar pulse bias power supply simultaneously achieves the alternating cycles of electron bombardment heating and coating, improving film quality. It boasts a high ionization rate, enabling the deposition of metal films, alloy films, and reactive films such as nitrides, carbides, and oxides. This allows for the preparation of a wide variety of film types, making it suitable for ion plating surface modification of the inner walls of tubular workpieces, improving service performance and extending service life.

[0113] The asymmetric bipolar pulse power supply is a high-frequency inverter switching power supply, has A and B two electrodes, A is connected with the workpiece and B is connected with the vacuum chamber. The output waveform is asymmetric bipolar pulse voltage, each pulse cycle contains bipolar pulse of negative pulse and positive pulse, and the voltage and duty cycle of positive / negative pulse are independently and continuously adjustable. The asymmetric bipolar pulse bias power supply (hereinafter referred to as bias power supply) has two electrodes as anode and cathode in the working process. When the power supply outputs negative pulse, the A electrode is cathode and the B electrode is anode; when the power supply outputs positive pulse, the A electrode is anode and the B electrode is cathode. When the workpiece is self-glowing sputter cleaned, the low vacuum degree high bias discharge mode is used to provide argon ions for sputter cleaning of the inner wall of the workpiece. During the argon ion sputter cleaning process, the workpiece is connected to the A electrode of the bias power supply, the vacuum chamber is connected to the B electrode of the power supply, and after the power supply is turned on, a low-pressure gas discharge low-temperature plasma zone is formed between the workpiece and the vacuum chamber, and the inner wall of the workpiece is sputtered to complete the glow cleaning process.

[0114] During the coating process, when the workpiece receiving electrode A outputs positive pulse, the electrons in the plasma inside the tubular workpiece 7 bombard the inner wall of the workpiece under the action of the electric field, the bombardment of the tubular workpiece 7 is obvious, which helps the film layer growth, and improves the ionization rate of the film forming particles, further improves the film forming quality and deposition efficiency of the inner wall of the tubular workpiece 7. When the workpiece receiving electrode A outputs negative pulse, the tubular workpiece 7 is in a conventional bias working mode, and the thin film on the inner wall of the tubular workpiece 7 begins to deposit. The glow and film deposition processes adopt two working modes of the bias power supply respectively, which effectively improves the working efficiency and process flexibility. The film layer prepared by using the bias power supply is dense, resistant to ablation and corrosion, and has high hardness, and the performance of the film layer is better than that of the film layer prepared by the existing inner wall coating technology.

[0115] 3. The cylindrical cathode arc source 6 is built-in in the tubular workpiece 7, and the rotating target core structure discharges uniformly, which guarantees the uniformity of film layer deposition.

[0116] The built-in cylindrical cathode arc source 6 has a rotating target core structure, and the discharge is uniform, so that the uniformity of film layer deposition is greatly improved and is better than ± 90%.

[0117] The method and device solve the problem that the deposition efficiency and uniformity decrease with the increase of hole depth in the external electromagnetic field long-distance transport method, completely follow the conventional arc ion plating process and operation method, and effectively improve the uniformity and deposition quality of the inner wall coating of the tubular workpiece 7.

[0118] The components involved in the coating device of the patent application can be commercially available components without special instructions. The processes, methods, test methods, test equipment and reagents used in the coating method of the patent application are known technologies or commercially available without special instructions.

[0119] The above detailed description of the specific implementation is further detailed for the purpose, technical solution and beneficial effect of the present application, and it should be understood that the above is only a specific implementation of the present application and is not used to limit the protection scope of the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. An apparatus for coating the inner wall of a tubular workpiece, characterized by, include: Vacuum chamber; A columnar cathode arc source is placed inside a tubular workpiece and is fixedly connected to the top of the vacuum chamber together with the tubular workpiece; A heating system, assembled on the vacuum chamber, is used to heat the tubular workpiece; A cathode arc power supply is connected to the cylindrical cathode arc source to form a circuit; The reactor is connected in series in the circuit formed by the columnar cathode arc source, the cathode arc power supply and the vacuum chamber; An asymmetric bipolar pulse bias power supply, used as a workpiece bias voltage, has output electrode A and output electrode B, which are connected to the tubular workpiece and the vacuum chamber, respectively.

2. The apparatus for coating the inner wall of a tubular workpiece according to claim 1, wherein The top of the vacuum chamber is provided with a top vacuum flange, and the tubular workpiece is fixed to the top of the vacuum chamber through the top vacuum flange; The heating system is mounted on the top vacuum flange.

3. The apparatus for coating the inner wall of a tubular workpiece according to claim 2, wherein The columnar cathode arc source has a swirling magnetic field structure, and the rotating motor of the columnar cathode arc source is fixed on the top vacuum flange.

4. The apparatus for coating the inner wall of a tubular workpiece according to claim 2, wherein The heating system consists of four straight tube heaters.

5. The apparatus for coating the inner wall of a tubular workpiece according to claim 1, wherein The tubular workpiece has a length-to-diameter ratio greater than or equal to 20:1, an inner diameter greater than or equal to 69 mm, and a discharge spacing of the columnar cathode arc source greater than or equal to 15 mm.

6. The plating method for the inner wall plating apparatus for a tubular workpiece according to any one of claims 1 to 5, characterized by, Includes the following steps: S1: Workpiece assembly: Assembly of the columnar cathode arc source and the tubular workpiece; circuit connection of the columnar cathode arc source and the cathode arc power supply; connection of the workpiece bias voltage to the tubular workpiece and the vacuum chamber. S2: Preheating and glow discharge cleaning of tubular workpieces: The tubular workpiece is preheated using a heating system; A self-glow discharge is performed in the vacuum chamber using an asymmetric bipolar pulse bias power supply to form a low-pressure gas discharge low-temperature plasma zone between the tubular workpiece and the vacuum chamber, which is then used for sputter cleaning of the inner wall of the workpiece. S3: Deposited functional membrane: The working gas is introduced into the vacuum chamber to turn on the columnar cathode arc source, and the target magnetic field rotates at the same time. S4: Cool down and pick up the item.

7. The coating method according to claim 6, wherein In step S2, the preheating temperature of the tubular workpiece is 100~400℃, the negative pulse output amplitude of the asymmetric bipolar pulse bias power supply is 600V-1100V, the frequency is 40-60KHz, and the sum of the positive and negative pulse duty cycles is less than or equal to 80%. The sputtering cleaning time is 10~30 minutes.

8. The coating method according to claim 6, wherein In step S3, the working gas pressure is 0.5~5.0 Pa; The target material used for depositing functional films is any one or a mixture of two or more of Ti, Cr, Al, Ni, and Cu, or a non-metallic material.

9. The coating method according to claim 6, wherein In step S3, the negative pulse of the asymmetric bipolar pulse bias power supply is set as follows: voltage 300-800V, frequency 40-60KHz, duty cycle 30-80%; The positive pulse settings are: voltage 0-50V, frequency 40-60KHz, duty cycle 20-50%; The sum of the duty cycles of the positive and negative pulses is less than or equal to 80%; The working time is 30-130 minutes.

10. The coating method according to claim 6, wherein In step S3, the thickness of the deposited film ranges from 1 μm to 20 μm.

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