A decarburization resistant low pressure plasma spray apparatus

Abstract

The application discloses a kind of anti-decarburization type low pressure plasma spraying equipment, including vacuum spraying cavity, plasma torch, gas supply system, powder feeding device, vacuum pump set and control system, also including carbon potential atmosphere control module, the carbon potential atmosphere control module includes carbon-containing gas supply unit, gas mixing unit, cavity atmosphere detection unit and multi-point carbon potential injection subunit.The application injects trace carbon-containing reducing gas into vacuum spraying cavity by carbon potential atmosphere control module, in the high-temperature environment of plasma jet, carbon-containing gas pyrolysis produces active carbon atom, forms high-carbon active microenvironment around powder particle, ensures that carbon activity is always maintained in the best decarburization inhibition range, avoids decarburization inhibition deficiency caused by too low carbon potential or free carbon deposition in coating caused by too high carbon potential.

Description

Technical Field

[0001] This invention belongs to the field of thermal spraying technology, specifically, it relates to a decarburization-resistant low-pressure plasma spraying device. Background Technology

[0002] Low-pressure plasma spraying (LPPS) is a thermal spraying technology that uses a plasma jet to heat powder to a molten or semi-molten state and spray it at high speed onto the workpiece surface to form a coating in a low-pressure atmosphere (typically tens to hundreds of Pascals). Compared to atmospheric pressure plasma spraying, the plasma jet in a low-pressure environment is longer, the particle velocity is higher, and the degree of oxidation is lower, thus resulting in coatings with higher density and better adhesion.

[0003] In the low-pressure plasma spraying process of carbide coating materials (such as WC-Co, Cr3C2-NiCr, etc.), decarburization has been a long-standing critical quality issue. Taking WC-Co as an example, in the high-temperature environment of the plasma jet, WC undergoes thermal decomposition (…). The free carbon released from the decomposition is further oxidized and consumed by the residual oxygen. This causes the hard phase in the coating to change from WC to W2C or even metallic W, resulting in a significant decrease in the coating's hardness and wear resistance.

[0004] In existing technologies, conventional methods for suppressing decarbonization mainly include: (1) Optimize the spraying process parameters, such as reducing plasma power, shortening the spraying distance, and increasing the powder feeding rate, in order to reduce the residence time of powder particles in the high temperature zone. However, these measures often come at the cost of sacrificing coating deposition efficiency and bonding strength. (2) An inert gas protective curtain is set in the spraying area to reduce oxidation by isolating the outside air. However, this method can only control the atmosphere outside the spraying jet and has limited ability to regulate the atmosphere inside the plasma jet and the microenvironment around the powder particles. (3) The more advanced HVOF (high-speed flame spraying) is used to replace plasma spraying, but HVOF has limitations in preparing large-size, complex surface coatings and cannot achieve the same level of coating density as LPPS.

[0005] The aforementioned existing technologies all address decarburization from the perspective of "reducing heat input" or "isolating oxygen," which are passive protection approaches. Currently, there is no low-pressure plasma spraying equipment that actively regulates the carbon potential of the atmosphere inside the spraying chamber from a thermodynamic perspective to suppress decarburization by maintaining the carbide decomposition balance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is that existing low-pressure plasma spraying equipment lacks an effective means to actively inhibit decarburization from a thermodynamic perspective when spraying carbide coating materials. Existing passive protection methods have limited effectiveness and often sacrifice the overall performance of the coating. The present invention provides a decarburization-resistant low-pressure plasma spraying equipment.

[0007] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: The system includes a vacuum spraying chamber, a plasma spray gun, a gas supply system, a powder feeding device, a vacuum pump assembly, and a control system. It also includes a carbon potential atmosphere control module, which comprises a carbon-containing gas supply unit, a gas mixing unit, a chamber atmosphere detection unit, and a multi-point carbon potential injection subunit. The multi-point carbon potential injection subunit includes at least two injection nozzles spaced apart along the axial direction of the vacuum spraying chamber. Each injection nozzle is connected to the outlet of the gas mixing unit via an independent pipeline, and each independent pipeline is equipped with an independent flow control valve. The control system is configured to receive detection signals from the chamber atmosphere detection unit and output control signals to each precision mass flow controller and each independent flow control valve based on the detection signals, thereby adjusting the total amount of carbon potential control mixture entering the vacuum spraying chamber and the flow distribution ratio between the injection nozzles.

[0008] Compared with the prior art, the advantages of the present invention include: (1) This invention injects a trace amount of carbon-containing reducing gas (such as methane) into the vacuum spraying chamber through a carbon potential atmosphere control module. In the high-temperature environment of the plasma jet, the carbon-containing gas undergoes pyrolysis to produce activated carbon atoms, forming a high-carbon-activity microenvironment around the powder particles. According to the principle of thermodynamic equilibrium, when the carbon activity in the environment increases, the equilibrium of the decomposition reaction of carbides such as WC shifts to the left, thereby actively inhibiting decarburization at the molecular level. The chamber atmosphere detection unit in the carbon potential atmosphere control module monitors the oxygen partial pressure and carbon-containing gas concentration in real time. The control system uses a PID closed-loop control algorithm to dynamically adjust the amount of carbon-containing gas injected, ensuring that the carbon activity is always maintained within the optimal range for inhibiting decarburization, avoiding insufficient decarburization inhibition due to excessively low carbon potential or free carbon deposition in the coating due to excessively high carbon potential.

[0009] (2) The multi-point carbon potential injection subunit of the present invention, through multiple injection nozzles arranged at intervals along the cavity axis, and in conjunction with the independent flow control valve of each injection nozzle, can differentiate the injection flow rate of each injection nozzle according to the real-time detection results of the oxygen content sensor at each position, so as to achieve uniform distribution of carbon activity in the cavity and avoid the problem of uneven carbon activity distribution caused by single-point injection. The temperature-correlated carbon potential adaptive submodule dynamically adjusts the target concentration of the carbon potential control mixture according to the real-time temperature signal of the high temperature zone of the plasma jet and according to the preset temperature-carbon activity correlation model, so that the carbon potential control matches the actual temperature field. The pulse carbon potential modulation submodule periodically adjusts the injection flow rate of carbon-containing reducing gas according to the preset modulation frequency and duty cycle, and promotes the diffusion and penetration of carbon-containing gas in the plasma jet through periodic carbon activity fluctuations, while avoiding free carbon deposition caused by continuous high-concentration injection.

[0010] (3) The multi-level atmosphere management system of the present invention reduces the residual oxygen content in the cavity to an extremely low level by combining graded vacuuming with inert gas replacement, thereby reducing the oxidizing atmosphere that causes decarburization from the source. The local atmosphere protection device on the workpiece side forms a local carbon potential protection atmosphere curtain around the spraying area through an annular gas distributor, maintaining a high carbon activity environment in the final stage when the plasma jet reaches the workpiece surface, effectively suppressing interface decarburization during the coating deposition process. (4) This invention systematically solves the problem of decarburization in plasma spraying through multiple technological innovations: it pioneers a TaC / HfC inner liner layer, which takes into account both structural protection and precise carbon source compensation, and uses the high-temperature evaporation characteristics to fill the carbon potential blind zone in the core area of ​​the jet; it constructs a full-scale protection system of "cavity-jet-workpiece-powder", and each level achieves dynamic balance of carbon potential through a collaborative mechanism; it innovatively designs an interface decarburization that can be effectively suppressed without sacrificing process parameters, and significantly improves the overall performance of the coating. This solution breaks through the bottleneck of traditional technology and provides an efficient and reliable new path for the preparation of high-performance coatings, which is both practical and technologically advanced. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is an overall schematic diagram of a decarburization-resistant low-pressure plasma spraying device according to the present invention; Figure 2 This is a partial schematic diagram of a decarburization-resistant low-pressure plasma spraying device according to the present invention; Figure 3This is a schematic diagram of the powder pretreatment unit in a decarburization-resistant low-pressure plasma spraying device of the present invention; Figure 4 This is a schematic diagram of the control system in a decarburization-resistant low-pressure plasma spraying device of the present invention.

[0013] Figure label: 1. Vacuum spraying chamber; 2. Plasma spray gun; 3. Carbon potential atmosphere control module; 31. Carbon-containing gas supply unit; 311. Methane storage tank; 312. Precision mass flow controller; 313. Pressure reducing valve; 32. Gas mixing unit; 321. Premixing chamber; 322. Static mixer; 33. Chamber atmosphere detection unit; 331. Oxygen content sensor; 332. Mass spectrometer; 333. High-temperature zone temperature sensor; 34. Multi-point carbon potential injection subunit; 341. Injection nozzle; 342. Independent flow control valve; 4. Workpiece-side local atmosphere protection device; 41. Annular gas distributor ; 411. Flow guide hole; 42. Gas supply pipeline; 421. Independent flow regulating valve; 5. Powder pretreatment unit; 51. Sealed mixing tank; 52. Carbon source material supply device; 53. Powder feeding device; 6. Control system; 61. Main control module; 62. Carbon potential regulation submodule; 63. Atmosphere management submodule; 65. Temperature-correlated carbon potential adaptive submodule; 66. Pulse carbon potential modulation submodule; 7. Gas supply system; 8. Multi-stage atmosphere management system; 81. First-stage vacuuming subsystem; 82. Inert gas replacement subsystem; 822. Flow control valve group; 83. Second-stage vacuuming subsystem. Detailed Implementation

[0014] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The technical solution, its implementation process, and principles will be further explained below with reference to the accompanying drawings and specific implementation examples in the embodiments of this application.

[0015] It should be noted that the embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, the present invention covers any substitutions, modifications, equivalent methods and solutions made on the spirit, principles and scope of the present invention as defined by the claims. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] In the description of this application, the terms "first," "second," "third," and similar words do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms "a" or "one," and similar words, do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms "comprising" or "including," and similar words, mean that the elements or objects preceding "comprising" or "including" encompass the elements or objects listed following "comprising" or "including," and their equivalents, but do not exclude other elements or objects. The terms "connected" or "linked," and similar words, are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect.

[0017] In the description of this application, the terms "center," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used solely for the convenience of describing this application and for simplification, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, when using positional terms such as "both sides," "outer side," and "upper and lower," it should be understood that they are used only for ease of understanding and description, taking into account that the structure may be oriented to other positions.

[0018] In the description of this application, unless otherwise expressly specified and limited, the technical or scientific terms used shall have the ordinary meaning understood by a person with ordinary skills in the art to which this application pertains. Terms such as “installation,” “connection,” and “joining” shall be interpreted broadly, for example, as fixed connection, detachable connection, mating connection, or integral connection. For a person skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0019] The present invention aims to introduce and explain the structural composition of a decarburization-resistant low-pressure plasma spraying device and the cooperation relationship between the various components. Unless otherwise specified, the dimensions, materials, and manufacturing processes of the various components in the decarburization-resistant low-pressure plasma spraying device in the present invention can be selected according to specific circumstances, and no special limitations or explanations are made here.

[0020] Furthermore, to provide the public with a better understanding of the present invention, certain specific details are described in detail in the following description of the invention. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0021] Example 1

[0022] Please see Figures 1-4A decarburization-resistant low-pressure plasma spraying device includes a vacuum spraying chamber, a workpiece turntable, and a workpiece. The vacuum spraying chamber 1 is the main load-bearing structure of the device, and is a sealed 304 stainless steel welded structure. The inner cavity size is determined according to the workpiece size, and the design ultimate vacuum degree is 0.1 Pa. The side wall of the chamber is equipped with an observation window (tempered glass, for observing the spraying process inside the chamber), a process interface (for installing sensors, air inlet pipes, etc.), and a maintenance door (quick-opening door structure, for loading and unloading workpieces). The outer wall of the chamber is equipped with a cooling water jacket, and cooling water flows from... The water enters through the rear inlet and exits through the front outlet of the cavity, with a flow rate of 20L / min. During the spraying process, the cavity wall is continuously cooled. The side wall of the vacuum spraying cavity 1 is equipped with at least two atmosphere detection interfaces (flange sealing structure), located on the side near the plasma spray gun (front end) and the side near the workpiece clamping (rear end), respectively, for installing detection equipment such as oxygen content sensor 331. The bottom center of the vacuum spraying cavity 1 is equipped with an air extraction interface (DN100 flange), which is connected to the air inlet pipe of the vacuum pump group through a pressure-resistant pipe.

[0023] The vacuum spraying chamber 1 is equipped with a workpiece turntable 11 and a spray gun translation guide rail 12, which are located in the lower half and upper half of the chamber, respectively, forming a workpiece bearing and spray gun movement system for spraying operations.

[0024] The workpiece turntable 11 is the core mechanism in the equipment that carries and rotates the workpiece. It is located above the base plate inside the vacuum spraying chamber 1. Specifically, the workpiece turntable 11 includes a rotating platform, a spindle, bearing housings, a magnetic transmission assembly, and a drive motor. The rotating platform is a circular 304 stainless steel plate with three concentric annular T-slots on its upper surface for fixing the workpiece or workpiece clamp to the platform surface using T-bolts and pressure plates. A flange is located at the center of the lower surface of the rotating platform, connected to the upper flange of the spindle by high-strength bolts. The spindle is a 40Cr tempered steel shaft that vertically passes through the bearing housing on the base plate of the vacuum spraying chamber 1. The bearing housing is fixed to the opening in the base plate of the chamber via flanges. The bearing housing contains two sets of angular contact ball bearings (model 7212C, face-to-face installation) to bear the axial and radial loads of the spindle. A metal bellows sealing structure (welded bellows, material 316L) is used between the bearing housing and the base plate of the chamber to ensure the vacuum transmission of the chamber during spindle rotation. For airtight sealing, the magnetic drive assembly is located between the lower end of the main shaft and the drive motor. It includes an inner magnetic rotor fixed to the lower end of the main shaft and an outer magnetic rotor fixed to the output shaft of the drive motor. The two are separated by a stainless steel isolation sleeve (1.5mm thick, 316L material). The torque is transmitted without contact by using magnetic field coupling. The purpose of using magnetic drive is to avoid the leakage problems that may occur in traditional mechanical seal structures under low pressure environment and to ensure the long-term vacuum sealing reliability of the cavity. The drive motor is an AC variable frequency motor (power 0.75kW, rated speed 1500rpm), which is installed on the motor base below the bottom plate of the vacuum spraying cavity 1. The speed is controlled by the frequency converter. The rotation speed of the workpiece turntable 11 can be steplessly adjusted within the range of 5 to 30rpm. In this embodiment, the speed is set to 15rpm during spraying operation. The maximum load capacity of the workpiece turntable 11 is 50kg. Other workpiece turntables 11 can also be used. It is a relatively mature technology and will not be described in detail here.

[0025] The spray gun translation guide rail can be a linear guide rail structure, fixed inside the vacuum spraying chamber 1 at the top (about 800mm from the bottom plate of the chamber). The guide rail is arranged along the axial direction of the chamber, with an effective stroke of 400mm. The plasma spray gun 2 is mounted on the spray gun translation guide rail via a slider. The slider is driven by a servo motor outside the chamber through a synchronous belt transmission mechanism to reciprocate along the guide rail. The reciprocating speed can be adjusted within the range of 50 to 300mm / s. In this embodiment, the reciprocating speed during the spraying operation is set to 200mm / s. The reciprocating motion of the spray gun translation guide rail is coordinated with the rotational motion of the workpiece turntable 11, so that the plasma jet can cover the entire area of ​​the workpiece to be sprayed, achieving uniform deposition of the coating.

[0026] The plasma spray gun 2 adopts an internal powder feeding structure and is suspended and installed inside the vacuum spraying chamber 1 via a spray gun translation guide rail. The plasma spray gun 2 includes a cathode, an anode nozzle, an insulator, and a gas channel. The cathode is a tungsten-cerium alloy rod (6mm in diameter and 80mm in length), installed in the cathode seat at the rear of the spray gun, and connected to the negative terminal of a DC power supply outside the chamber via a high-temperature resistant cable (passing through the chamber wall sealing flange), capable of withstanding a maximum current of 600A. The anode nozzle 14 is made of copper (oxygen-free copper, thermal conductivity 398W / (m·K)), and its inner wall has a spiral cooling water channel (channel cross-section 2mm×2mm, spiral angle 30°), which is connected to the external cooling water circulation system through a pressure-resistant water pipe (passing through the chamber wall sealing flange). The cooling water inlet temperature is 20°C, and the flow rate is 15. The flow rate is L / min. The cathode and anode nozzles are separated by an insulator (99.5% alumina ceramic, 5mm thick). The gas channel is located between the cathode and anode nozzles. The inner diameter of the channel gradually narrows from 12mm at the inlet end to 6mm at the outlet end (scaling nozzle structure). The working gas (Ar+H2 mixture) enters the gas channel through the pipeline from the gas supply system 3. The arc area formed between the cathode and anode nozzles is heated to a high temperature (>10000K) to form a plasma jet that is ejected from the outlet end of the anode nozzle. The powder feeding pipeline is introduced from the center of the cathode seat at the rear end of the plasma spray gun 2 (high temperature resistant stainless steel pipe with an inner diameter of 4mm) to feed the powder delivered by the powder feeding device 53 into the gas channel. The powder is heated to a molten or semi-molten state in the plasma jet and then ejected.

[0027] A tantalum carbide (TaC) liner, 0.5–1.0 mm thick, is installed on the inner wall of the gas channel. It is fixed to the gas channel wall via an interference fit. At room temperature, the TaC liner is pressed into the inner wall of the copper anode. During operation, the thermal expansion of copper exceeds that of TaC, achieving self-tightening. At the high-temperature operating state, a small amount of diffusion occurs at the interface, forming a Cu-Ta solid solution bonding layer, enhancing connection reliability. The tantalum carbide liner covers an area from the gas channel inlet to the anode nozzle outlet, with a total length of approximately 120 mm. The tantalum carbide liner is prepared by hot-pressing and sintering high-purity TaC material (purity ≥ 99.5%), with a particle size ≤ 5 μm, and a density ≥ 14.0 g / cm³. 3 (Theoretical density 14.5 g / cm³) 3 (Over 96%).

[0028] The carbon dissolution mechanism and carbon atom diffusion pathway of the tantalum carbide liner are described below: (1) Temperature distribution on the surface of the inner lining: When the plasma spray gun is working, the inner wall of the anode nozzle is kept at a low temperature by water cooling, but the local wall temperature of the arc attachment area (anode arc root spot area) can reach 1500-2500°C. This area is the main area where carbon dissolution occurs in the tantalum carbide inner lining. The surface temperature of the other areas of the inner lining (non-arc root attachment area) is about 500-1000°C due to the thermal conductivity of the copper substrate water cooling. The structure of tantalum carbide is completely stable within this temperature range. The arc attachment area rotates and moves circumferentially on the inner wall of the anode (driven by gas swirl), so that the carbon dissolution area sweeps circumferentially, realizing uniform micro carbon dissolution in the inner lining.

[0029] (2) Carbon dissolution process on the surface of tantalum carbide: Under the high temperature of the arc adhesion zone (local wall temperature 1500-2500°C), non-congruent evaporation (inconsistent evaporation) occurs on the surface of the tantalum carbide inner liner. Since the vapor pressure of carbon in TaC is much higher than that of tantalum, carbon atoms preferentially escape from the surface of the TaC lattice. At 2000°C, the vapor pressure of carbon on the TaC surface is about 10. -6 The Pa level is approximately 10 at 2500°C. -4 At the Pa level, H2 (15%–50% by volume) in the working gas undergoes a reduction reaction with carbon on the TaC surface at high temperature, generating CH4. x (x=1~4) Carbon-containing gas fragments enter the jet, and the hydrogen reduction reaction provides an additional driving force for carbon dissolution. The two mechanisms mentioned above work together to continuously output carbon in an active form into the plasma jet. This carbon dissolution process only occurs in the extremely thin layer (submicron level) on the outermost surface of the inner liner. The dissolution rate is extremely low and controllable. The TaC main structure is completely stable under normal working conditions (TaC melting point 3880°C is much higher than the actual working temperature of up to about 2500°C).

[0030] (3) Subsequent transformation pathway of carbon atoms: Activated carbon atoms escaping from the TaC surface enter the core region of the plasma jet with the working gas and are ionized into carbon ions (C) under high temperature. + It may react with hydrogen to generate carbon-containing intermediates such as CH4 and CH3. These carbon-containing substances diffuse in the high-temperature boundary layer on the surface of the powder particles, providing an activated carbon source for the carbide powder particles and compensating for the carbon lost due to decomposition in the high-temperature environment. The concentration of tantalum atoms generated by sublimation is extremely low (about 0.01 ppm in the jet), and has no significant effect on the plasma arc characteristics and coating composition.

[0031] (4) Quantitative effect of carbon source compensation: Under the spraying parameters of this embodiment (plasma power 60kW, total working gas flow rate 52L / min), the total mass loss rate of the tantalum carbide liner is about 0.005g / h, which translates to a carbon concentration in the plasma jet of about 0.1ppm. The amount of carbon source compensation accounts for a very low proportion of the carbon flow rate of the sprayed powder (about 1% to 3%), and will not change the coating composition. However, since carbon atoms are released directly in the core area of ​​the jet - an area that is difficult for externally injected carbon-containing gas to reach due to jet dynamics - even at extremely low concentrations, the carbon partial pressure in the core area of ​​the jet can be effectively maintained, suppressing the carbon loss of carbide powder particles during flight. After continuous spraying for 200 hours, the thickness reduction of the liner does not exceed 0.05mm, and the performance of the spray gun does not change significantly. The liner is designed as a replaceable cylindrical bushing structure, which can be disassembled and replaced through the flange at the end of the spray gun. The designed service life is not less than 500 hours.

[0032] Please see Figures 1-4 The gas supply system 3 provides working gas for the plasma spray gun 2. It is mounted on a gas cylinder rack outside the vacuum spraying chamber 1. The gas supply system 3 includes a high-purity argon cylinder (99.999% purity, 40L volume, 15MPa working pressure), a high-purity hydrogen cylinder (99.999% purity, 40L volume, 15MPa working pressure), a two-stage pressure reducing valve (reducing the high pressure inside the cylinder to 0.3MPa working pressure), a mass flow controller (range 0-50L / min, accuracy ±1%FS, used for Ar and H2 flow measurement respectively), and a static mixer. Argon and hydrogen are respectively reduced in pressure by their respective two-stage pressure reducing valves and measured by the mass flow controller, and then mixed in the static mixer according to a set ratio (in this embodiment, Ar:H2 = ...). The working gas is mixed evenly at a volume ratio of 75:25. The mixed working gas passes through a pressure-resistant stainless steel pipe (inner diameter 8mm, pressure resistance 1MPa) and enters the gas channel of the plasma spray gun 2 through the sealing flange on the wall of the vacuum spraying chamber 1. In this embodiment, the Ar flow rate is 40L / min, the H2 flow rate is 12L / min, and the total flow rate is 52L / min. The Ar:H2 ratio can be adjusted within the range of 50:50 to 85:15.

[0033] The powder feeding device 53 continuously and uniformly supplies coating powder to the plasma spray gun 2. It is installed on an equipment platform outside the vacuum spraying chamber 1. The powder feeding device 53 is a scraper-type powder feeder, including a powder storage hopper (5L capacity, 304 stainless steel), a powder feeding disc (100mm diameter, with evenly distributed hemispherical grooves on the disc surface), and a stepper motor drive mechanism. The top of the powder storage hopper is equipped with a sealing cover for loading the coating powder that has undergone carbon coating treatment by the powder pretreatment unit. During operation, the stepper motor drives the powder feeding disc to rotate, and the grooves on the powder feeding disc scoop powder from the bottom of the powder storage hopper. When rotating to the discharge port, the powder is subjected to gravity and... The powder falls into the discharge pipe under the action of the scraper, and is fed into the plasma spray gun 2 through the powder feeding pipeline. The powder feeding rate is controlled by the speed of the stepper motor. In this embodiment, the powder feeding rate is 30g / min. The powder feeding pipeline is a high-temperature resistant stainless steel pipe (316L material) with an inner diameter of 4mm. It starts from the discharge port of the powder feeding device 53, passes through the sealing flange on the wall of the vacuum spraying chamber 1, and extends along the inside of the chamber to the rear end of the plasma spray gun 2. It is inserted into the gas channel inside the gun body from the center of the cathode seat. The powder feeding pipeline is equipped with a carrier gas (argon) interface, and 0.5L / min of argon gas is used as the carrier gas to continuously transport the powder into the spray gun.

[0034] The vacuum pump unit provides the required low-pressure environment for the vacuum spraying chamber 1. It is installed on a pump platform below the vacuum spraying chamber 1 and connected to the evacuation port at the bottom of the chamber via a pressure-resistant pipe. The vacuum pump unit includes a rotary vane mechanical pump (pumping speed 200 L / s, ultimate vacuum 0.5 Pa) and a Roots pump (pumping speed 500 L / s) for primary vacuuming, and a turbomolecular pump (pumping speed 500 L / s, ultimate vacuum 10 Pa) for secondary vacuuming. -3 The system consists of a pump (Pa) and a matching backing pump (rotary vane pump, pumping speed 60L / s). Each pump is connected to the cavity evacuation port via a butterfly valve, a high vacuum valve, and pipelines. The atmosphere management submodule 63 of the control system 6 controls the start and stop of each pump and the switching of valves.

[0035] Please see Figures 1-4 The carbon potential atmosphere control module 3 is installed on the equipment rack outside the vacuum spraying chamber 1. It is connected to the inside of the chamber through multiple pipelines passing through the sealing flange of the chamber wall. The carbon potential atmosphere control module 3 includes a carbon gas source supply unit 31, a gas mixing unit 32, a chamber atmosphere detection unit 33, and a multi-point carbon potential injection subunit 34. The carbon-containing gas supply unit 31 includes a methane storage tank 311 (a standard 40L high-pressure gas cylinder containing methane gas with a purity ≥99.9%), an acetylene storage tank (for backup), a two-stage pressure reducing valve 313 (which reduces the high pressure inside the cylinder to a working pressure of 0.2MPa), and a precision mass flow controller 312 (range 0~500sccm, control accuracy ±0.5%FS, response time <100ms, remotely controlled by the control system 6 via a 4~20mA analog signal). Methane, as the preferred carbon-containing reducing gas, undergoes pyrolysis in the high-temperature region (>2000K) of the plasma jet. The activated carbon atoms and hydrogen produced have reducing properties, which can simultaneously inhibit the decomposition and oxidation of carbides.

[0036] The gas mixing unit 32 includes a premixing chamber 321 (stainless steel cylindrical structure, volume 500mL) and a static mixer 322 (spiral blade structure, pipe diameter DN15, containing 8 mixing units, mixing efficiency >95%). Methane enters one inlet of the premixing chamber 321 after the flow rate is regulated by a precision mass flow controller 312. At the same time, a branch is drawn from the Ar pipeline of the gas supply system 3 and enters the other inlet of the premixing chamber 321. The two gases are uniformly mixed by the static mixer 322 to obtain a carbon potential controlled mixture. The carbon potential controlled mixture flows out from the outlet of the static mixer 322 and is divided into two paths: one path enters each injection nozzle 341 of the multi-point carbon potential injection subunit 34; the other path enters the annular gas distributor 41 of the workpiece-side local atmosphere protection device 4. The volume concentration of methane in the carbon potential controlled mixture is controlled within the range of 0.3% to 5%, preferably 1% to 3%.

[0037] The cavity atmosphere detection unit 33 includes two zirconia oxygen sensors 331 and a mass spectrometer 332 installed on the side wall of the vacuum spraying cavity 1. The zirconia oxygen sensors 331 are fast-response zirconia probes (detection limit 10ppm, response time <50ms, operating temperature 600°C, with built-in heater), respectively installed at the front end (near the plasma spray gun side) and the rear end (near the workpiece clamping side) of the cavity 1. The mass spectrometer 332 (quadrupole mass spectrometer, mass range 1~300amu, detection limit 0.1ppm) is connected to the inside of the cavity through a sampling pipeline, and can simultaneously detect the partial pressure of components such as O2, CO2, CO, CH4, H2, and N2. In addition, a high-temperature zone temperature sensor 333 (K-type thermocouple, range 0~1400°C, accuracy ±2°C) is installed on the plasma jet path, with the temperature measuring end extending into the edge region of the plasma jet (about 20mm from the central axis of the jet).

[0038] The multi-point carbon potential injection subunit 34 includes four injection nozzles 341 (illustrated as 341a, 341b, 341c, and 341d) arranged axially along the vacuum spraying chamber 1. Each injection nozzle 341 is a straight pipe nozzle made of 316L stainless steel (inner diameter 2mm, outer diameter 4mm), and the outlet end is provided with a conical flare (flare angle 30°, inner diameter 6mm after flare). The front ends of the four injection nozzles 341 extend into the chamber at different axial positions: 341a is located near the plasma spray gun outlet (about 100mm from the spray gun outlet), and 341b is located in the middle section of the jet (about 300mm from the spray gun outlet). 341c is located approximately 100mm in front of the workpiece, and 341d is located approximately 100mm behind the workpiece, with a spacing of 200mm. The rear end of each injection nozzle 341 is connected to the outlet end of the gas mixing unit 32 through an independent pipeline (3mm inner diameter). Each independent pipeline is equipped with an independent electromagnetic flow control valve 342 (response time <80ms), which is independently controlled by the control system 6. The initial injection flow rate of each injection nozzle 341 is distributed in a gradient decreasing from the front end to the rear end: 341a is 80sccm, 341b is 60sccm, 341c is 40sccm, and 341d is 20sccm.

[0039] During the spraying process, the temperature of the plasma jet gradually decreases along its path from the spray gun outlet to the workpiece surface (approximately 3000K at the spray gun outlet and approximately 1500K at the workpiece surface). The thermodynamic equilibrium constants of carbide decomposition are different at different locations, thus requiring different carbon activities. By using the independent flow control valves 342 of each injection nozzle 341 to differentiate and adjust the carbon potential at each location, the amount of mixed gas injected is controlled, thereby achieving a gradient distribution of carbon activity along the cavity axis. This ensures that the carbon activity at each location matches the temperature conditions and decarburization requirements at that location.

[0040] Please see Figures 1-4 The control system 6 is an integrated control system based on a PLC (Siemens S7-1500 series). It is installed in an independent control cabinet outside the vacuum spraying chamber 1 and is connected to various components of the equipment via cables and communication lines. The control system 6 includes the following sub-modules: Main control module 61: Used to coordinate the running sequence and process parameters of each subsystem. The touch screen human-machine interface (12-inch color touch screen) is installed on the control cabinet panel.

[0041] Carbon potential control submodule 62: Used to receive the detection signal from the cavity atmosphere detection unit 33, calculate the carbon activity value at each position, execute the PID closed-loop control algorithm, and output control signals to the precision mass flow controller 312 and each independent flow control valve 342.

[0042] Carbon activity (aC) is indirectly calculated using data from oxygen content sensor 331 and mass spectrometer 332.

[0043] Where K1 is the reaction The equilibrium constant, taken as an average cavity temperature of 1500K, is K1≈ 1.2×10⁻⁶. 5 With a Pa value of 0.5, the optimal carbon activity range is 0.3–0.8.

[0044] The carbon activity distribution deviation is calculated using the following formula:

[0045] The control system 6 compares the deviation with a set threshold (15%). If the deviation exceeds 15%, the flow rate of the injection nozzle corresponding to the side with lower carbon activity is increased (by 5 sccm each time), while the flow rate of the injection nozzle corresponding to the side with higher carbon activity is decreased (by 5 sccm each time) until the deviation converges to within 15%.

[0046] The mapping relationship between the flow rate of each injection nozzle and carbon activity was established through a pre-calibration experiment: for every 10 sccm increase in flow rate of 341a, the carbon activity at the corresponding position increases by approximately 0.08; for 341b, it increases by approximately 0.06; for 341c, it increases by approximately 0.05; and for 341d, it increases by approximately 0.04.

[0047] PID closed-loop control algorithm: The carbon potential regulation submodule 62 adopts an incremental PID control algorithm.

[0048] Where Δu(k) is the control increment, e(k) is the deviation value, and Kp, Ki, and Kd are PID parameters, tuned by the critical proportional gain method. In this embodiment, Kp=2.5, Ti=3.0s, and Td=0.5s. An integral separation strategy is set: when the deviation |e(k)| is greater than 30% of the carbon activity setpoint, the integral action is canceled. The control response cycle is determined by the oxygen content sensor response time (about 50ms), the PLC calculation cycle (about 10ms), and the electromagnetic flow control valve response time (about 80ms), with a total response time of about 140ms, which meets the requirement of not exceeding 200ms.

[0049] Temperature-correlated carbon potential adaptive submodule 65: Establishes a temperature-carbon activity correlation model based on the thermodynamic equilibrium principle of WC decomposition reaction. The thermal decomposition reaction of WC is as follows:

[0050] The relationship between the standard Gibbs free energy change of this reaction and temperature is:

[0051] The relationship between the reaction equilibrium constant K and ΔG° is as follows:

[0052] Where R is the gas constant (8.314 J / (mol·K)) and T is the absolute temperature (K), the minimum carbon activity required to prevent WC from decomposing is:

[0053] Considering a safety margin factor of n=1.3, and setting the upper limit of carbon activity to 0.8, the carbon activity setting value is:

[0054] Temperature-carbon activity correspondence

[0055] For the Cr3C2-NiCr system, the carbide decomposition reaction is as follows:

[0056] Mapping from carbon activity target value to methane injection flow rate: The linear relationship established through calibration experiments is as follows:

[0057] Therefore, the total methane injection flow rate is set to:

[0058] Pulse carbon potential modulation submodule 66: Outputs a square wave signal with adjustable frequency (0.5~5Hz) and adjustable duty cycle (40%~70%), which is superimposed on the PID control output. During the high level period, the PID output is multiplied by a gain coefficient of 1.5, and during the low level period, it is multiplied by 0.5. In this embodiment, the modulation frequency is 2Hz and the duty cycle is 60%.

[0059] The submodules communicate with each other via PROFINET industrial Ethernet. The control system 6 is equipped with safety interlock functions: it automatically alarms and suspends spraying when the oxygen partial pressure suddenly rises (>100ppm); it automatically switches to the backup gas source when the pressure of the methane storage tank is lower than 0.5MPa.

[0060] Please see Figures 1-4 The multi-stage atmosphere management system 8 is installed on the pump platform outside the vacuum spraying chamber 1; The primary vacuum subsystem 81 includes a rotary vane mechanical pump 811 (pumping speed 200 L / s) and a Roots pump 812 (pumping speed 500 L / s), used in series to pre-pump the cavity from atmospheric pressure to 100 Pa.

[0061] Inert gas replacement subsystem 82 includes a high-purity argon gas source 821, a solenoid valve group 822, and a mass flow meter 823. After evacuating to 100Pa in the first stage, high-purity argon gas is introduced into the cavity to 5000Pa. After maintaining the pressure for 30 seconds, it is extracted to 100Pa. The replacement is repeated 4 times. After the replacement is completed, the residual oxygen content can be reduced to below 50ppm.

[0062] The secondary vacuum subsystem 83 includes a turbomolecular pump 831 (pumping speed 500 L / s) and a backing pump 832 (rotary vane pump, pumping speed 60 L / s), used to pump the cavity from 5000 Pa to a working vacuum of 20 Pa.

[0063] The workpiece-side local atmosphere protection device 4 is installed inside the vacuum spraying chamber 1; Annular gas distributor 41: It is a 316L stainless steel annular structure (inner diameter 80mm, outer diameter 120mm, wall thickness 5mm), which is fixed to the front end of the plasma spray gun 2 by an L-shaped stainless steel bracket, about 80mm away from the workpiece surface. There are 16 guide holes 411 (diameter 2mm, at a 20° angle with the jet axis) on the inner ring surface, which makes the carbon potential control mixture converge in the axial direction to form a conical annular converging airflow of carbon potential control mixture.

[0064] Gas supply line 42: One end is connected to the annular gas chamber of the annular gas distributor 41, and the other end passes through the sealing flange of the cavity wall and is connected to the outlet end of the gas mixing unit 32. It is connected in parallel with the multi-point carbon potential injection subunit 34 to draw gas. The gas supply line 42 is equipped with an independent electromagnetic flow regulating valve 421 (response time <80ms), which is independently controlled by the control system 6. In this embodiment, the gas supply flow rate is set to 200sccm.

[0065] The powder pretreatment unit 5 is a pretreatment device that is set up independently of the vacuum spraying chamber 1 and is installed at an independent work station in the spraying workshop; Sealed mixing tank 51: It is a sealed 304 stainless steel tank with a volume of 50L. The design pressure is atmospheric pressure to slightly positive pressure. The top of the tank is equipped with a feed port (DN50 quick-connect clamp interface), an exhaust port (connected to the activated carbon tail gas treatment device) and an observation window. The inside of the tank is equipped with a double spiral belt mechanical agitator (300mm diameter, 800mm length), driven by a variable frequency motor (0.75kW power, 50~200rpm speed). The bottom of the tank is equipped with a conical contraction section and a discharge port (DN25 butterfly valve control).

[0066] Carbon source material supply device 52: It is an independently set screw metering feeder, which is connected to the feed port at the top of the sealed mixing tank 51 through a DN15 stainless steel feed pipe. It includes a hopper (5L capacity, storing nano-graphite powder, particle size 20-50nm, purity >99%) and a screw conveyor (screw diameter 20mm, screw pitch 15mm). The speed is controlled by a variable frequency motor to achieve precise metering and injection, with a metering accuracy of ±2%.

[0067] Fluidized bed structure: Integrated above the conical contraction section at the bottom of the sealed mixing tank 51, it includes a 316L stainless steel porous sintered plate (diameter 350mm, thickness 5mm, pore size 5~10μm, porosity 35%) and an inert gas (high-purity nitrogen) inlet pipeline. The inlet pipeline is equipped with a pressure reducing valve and a rotor flow meter, and the airflow velocity is controlled at 0.3~0.8m / s to keep the powder in a fluidized suspension state.

[0068] The working process of powder pretreatment unit 5 is as follows: (1) Add WC-Co powder (WC particle size 0.5~2μm, Co content 12wt%, 10kg) into the sealed mixing tank 51 through the feed port and close the sealing cover; (2) Start nitrogen flow (inlet pressure 0.03MPa, flow rate 100L / min); (3) Start the stirring paddle (speed 100 rpm), and at the same time inject nano-graphite powder (50g) at 0.5% of the powder mass through the carbon source material supply device 52. (4) Continue the coating process for approximately 30 minutes; (5) Turn off the nitrogen and the agitator, release the carbon-coated powder from the bottom outlet of the tank, and after passing it through an 80-mesh sieve, load it into the powder storage hopper of the powder feeding device 53.

[0069] Complete Workflow Step 1 (Preparation before spraying - powder pretreatment): The operator completes the carbon coating treatment of the carbide powder at the powder pretreatment station. After carbon coating, the powder is discharged, sieved and loaded into the powder storage hopper of the powder feeding device 53. At the same time, the pressure of each gas cylinder, the cooling water system and the status of the control system are checked.

[0070] Step 2 (Workpiece clamping and cavity sealing): Open the inspection door of the vacuum spraying cavity 1, clamp the workpiece (such as turbine blades) after sandblasting and cleaning pretreatment onto the rotating platform 111 of the workpiece turntable 11 using a special spraying fixture, fix it in the T-slot with T-bolts, adjust the position of the workpiece so that the surface to be sprayed is facing the spraying direction of the plasma spray gun 2, set the spraying distance to 300mm, close the inspection door and lock it.

[0071] Step 3 (vacuuming and atmosphere replacement): The atmosphere management submodule 63 of the control system 6 automatically executes: (1) first-stage vacuuming to 100Pa (about 15 minutes); (2) inert gas replacement 4 times (about 10 minutes); (3) second-stage vacuuming to working vacuum of 20Pa (about 10 minutes), the whole process takes about 35 minutes.

[0072] Step 4 (Carbon Potential Pre-establishment): The carbon potential atmosphere control module 3 is activated. First, in the first injection mode, carbon potential control mixture (methane concentration 2%) is injected into each injection nozzle 341 at the same flow rate (60 sccm each) to pre-establish the overall carbon potential of the cavity. After the oxygen partial pressure at both the front and rear ends is stabilized below 10 ppm, the module switches to the second injection mode. Based on the detection signals of each oxygen content sensor 331, the flow rate of each injection nozzle 341 is adjusted to form a gradient distribution. The flow rate distribution of each injection nozzle 341 is adjusted to the set gradient (set value 0.65, deviation controlled within ±10%).

[0073] Step 5 (Spraying Operation): Start the plasma spray gun 2 to preheat the workpiece at 60kW power (about 2 minutes to 150-200°C), start the pulse carbon potential modulation submodule 66 (2Hz, duty cycle 60%), after preheating, start the powder feeding device 53 to feed powder at a rate of 30g / min, at the same time start the workpiece side local atmosphere protection device 4 (200sccm), the workpiece turntable 11 rotates at 15rpm, the spray gun translation guide rail 12 reciprocates at 200mm / s, the temperature-correlated carbon potential adaptive submodule 65 dynamically adjusts the carbon activity setting value according to the temperature of the high temperature zone (about 2800K), spraying for about 15 minutes, the coating thickness is about 200μm.

[0074] Step Six (Cooling and Removal): After spraying, turn off the powder feeding device and spray gun in sequence, turn off the gas supply of the local atmosphere protection device, keep the carbon potential atmosphere control module running (methane flow rate reduced to 50%), let the workpiece cool naturally in the carbon potential protection atmosphere for about 15 to 20 minutes to below 200°C, turn off the carbon potential control, slowly fill the cavity with dry air (5L / min) to atmospheric pressure (about 6 minutes), and remove the workpiece.

[0075] Example 1: A WC-12Co coating was sprayed using the equipment of this invention. The plasma power was 60kW, Ar flow rate was 40L / min, H2 flow rate was 12L / min, spraying distance was 300mm, powder feeding rate was 30g / min, methane concentration was 2%, chamber pressure was 20Pa, four-point injection flow rate was 80 / 60 / 40 / 20sccm, annular distributor flow rate was 200sccm, pulse modulation was 2Hz / 60%, temperature adaptive setpoint was 0.80, coating WC phase content was 93.5%, decarburization rate was 6.5%, and microhardness was HV. 1280 .

[0076] Example 2: Spraying a Cr3C2-NiCr coating, plasma power 55kW, methane concentration 1.5%, chamber pressure 15Pa, four-point injection 70 / 50 / 35 / 15sccm, coating Cr3C2 phase content 89.2%, decarburization rate 10.8%, microhardness HV 980 .

[0077] Example 3: A WC-12Co coating was sprayed without pulse modulation and temperature adaptation (fixed carbon activity 0.65). The coating had a WC phase content of 90.1%, a decarburization rate of 9.9%, and a microhardness of HV. 1200 .

[0078] Comparative Example 1 (Prior Technology): Conventional LPPS equipment, no carbon potential modulation, no powder carbon coating, coating WC phase content 76.8%, decarburization rate 23.2%, microhardness HV 1050 .

[0079] Comparative Example 2 (Reduced Power): With conventional LPPS equipment, the power was reduced to 40kW, the decarburization rate was 16.5%, but the deposition efficiency decreased from 65% to 42%, the porosity increased from 0.8% to 2.3%, and the bonding strength decreased from 72MPa to 55MPa.

[0080] Comparative Example 3 (Inert Gas Curtain): A conventional LPPS equipment with a pure argon gas curtain (excluding methane) achieved a decarbonization rate of 18.1%.

[0081] Comparative Example 4 (Single-point injection): The device of this invention uses only single-point injection (middle of the cavity, 200 sccm). The decarburization rate is 14.4%, and the WC content deviation at different locations of the coating is ±8.3%.

[0082] Comparison of coating performance between the examples and comparative examples

[0083] First, Example 1 was compared with Comparative Example 1. Both used the exact same spraying process parameters. The difference was that Example 1 used a carbon potential atmosphere control module (including a multi-point carbon potential injection sub-unit, a temperature-correlated carbon potential adaptive sub-module, and a pulsed carbon potential modulation sub-module) and performed powder carbon coating pretreatment, while Comparative Example 1 used conventional LPPS equipment. The results showed that the decarburization rate of the coating in Example 1 was only 6.5%, which was significantly reduced by about 72% compared to 23.2% in Comparative Example 1. The WC phase content increased from 76.8% to 93.5%, and the coating microhardness increased from HV. 1050 Upgrade to HV 1200 The deposition efficiency (65%), coating porosity (0.7%), and bonding strength (75 MPa) were comparable to or slightly improved compared to Comparative Example 1. This indicates that the carbon potential atmosphere control module can actively suppress carbide decomposition and decarbonization from the thermodynamic equilibrium level without affecting the deposition efficiency and density of the coating.

[0084] Secondly, Example 1 was compared with Comparative Example 2. Comparative Example 2 reduced decarburization by reducing the plasma power to 40kW. Although the decarburization rate decreased from 23.2% to 16.5%, the deposition efficiency plummeted from 65% to 42%, the coating porosity increased from 0.9% to 2.3%, and the bonding strength decreased from 72MPa to 55MPa. The overall performance of the coating was severely degraded. This shows that the traditional method of suppressing decarburization by reducing heat input inevitably comes at the cost of coating quality, while the carbon potential control method achieves a better decarburization suppression effect while maintaining normal spraying power.

[0085] Third, comparing Example 1 with Comparative Example 3, Comparative Example 3 added a common argon protective curtain (without methane) to a conventional LPPS equipment, and the decarbonization rate was 18.1%, which was better than Comparative Example 1 but far worse than Example 1. This shows that the passive protection method of simply relying on inert gas to isolate oxygen has limited effect on inhibiting decarbonization, because the high-temperature decomposition reaction inside the plasma jet is not affected by the external oxygen concentration, and the decomposition equilibrium must be inhibited by increasing carbon activity.

[0086] Fourth, Example 1 was compared with Comparative Example 4. Both used carbon potential atmosphere control modules and were treated with powder carbon coating. The difference was that Comparative Example 4 only used single-point injection. The results showed that the decarburization rate of Comparative Example 4 was 14.4%, which was far worse than the 6.5% of Example 1. Moreover, the WC phase content deviation at different positions of the coating was as high as ±8.3% (Example 1 was only ±2.1%). This indicates that multi-point carbon potential injection sub-unit is the key structural feature for achieving efficient and uniform decarburization suppression.

[0087] Fifth, comparing Example 1 with Example 3, the difference is that Example 3 did not enable pulse carbon potential modulation and temperature-correlated carbon potential adaptive functions. The decarbonization rate of Example 3 was 9.9%, which was worse than 6.5% of Example 1, indicating that pulse carbon potential modulation and temperature-correlated carbon potential adaptive functions have a significant contribution to further improving the decarbonization suppression effect.

[0088] Sixth, in Example 2, the Cr3C2-NiCr coating was sprayed using the equipment of the present invention, and the decarburization rate was 10.8%, indicating that the technical solution of the present invention is not only applicable to the WC-Co system, but also applicable to other carbide coating materials.

[0089] In summary, this invention, starting from the technical perspective of "carbon potential regulation," breaks through the passive protection approach of existing technologies that rely on "reducing heat input" and "isolating oxygen." It inhibits carbide decomposition by actively regulating the carbon activity of the spraying environment. Through the synergistic combination of four technologies—multi-point differentiated injection, temperature-correlated adaptive regulation, pulsed carbon potential modulation, and powder carbon coating pretreatment—it achieves a significant reduction in the decarburization rate from 23.2% to 6.5%, while also comprehensively improving the overall performance of the coating. This multi-level, multi-dimensional carbon potential regulation technology system, based on a systematic integration of the understanding of the thermodynamic mechanism of carbide decarburization, possesses outstanding substantive characteristics and significant progress.

[0090] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A decarburization-resistant low-pressure plasma spraying device, comprising a vacuum spraying chamber (1), a plasma spray gun (2), a gas supply system (7), a powder feeding device (53), a vacuum pump group, and a control system (6), characterized in that, It also includes a carbon potential atmosphere control module (3), which includes: A carbon-containing gas supply unit (31) includes at least one storage tank for carbon-containing reducing gas and a precision mass flow controller (312) connected thereto. Gas mixing unit (32), the gas mixing unit (32) includes a premixing chamber (321) and a static mixer (322) disposed on one side of the premixing chamber (321), used to uniformly mix the carbon-containing reducing gas and the inert gas according to a set ratio to obtain a carbon potential regulating mixed gas; The cavity atmosphere detection unit (33) includes an oxygen content sensor and / or a mass spectrometer (332) for real-time detection of the atmosphere composition inside the vacuum spraying cavity (1); The multi-point carbon potential injection subunit (34) includes at least two injection nozzles (341) arranged at intervals along the axial direction of the vacuum spraying chamber (1). Each injection nozzle (341) is connected to the outlet of the gas mixing unit (32) through an independent pipeline. Each independent pipeline is provided with an independent flow control valve (342). The control system (6) is configured to receive the detection signal from the cavity atmosphere detection unit (33) and output control signals to each of the precision mass flow controllers (312) and each of the independent flow control valves (342) according to the detection signal, so as to adjust the total amount of carbon potential control mixture entering the vacuum spraying cavity (1) and the flow distribution ratio between each injection nozzle (341).

2. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: The carbon-containing reducing gas is one or more of methane, acetylene, or propane, and the volume concentration of the carbon-containing reducing gas in the carbon potential regulating mixture is 0.3% to 5%; preferably, the carbon-containing reducing gas is methane, and the volume concentration of methane in the carbon potential regulating mixture is 1% to 3%.

3. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: The cavity atmosphere detection unit (33) includes at least two oxygen content sensors (331), which are respectively set on the side wall of the vacuum spraying cavity (1) near the plasma spray gun and near the workpiece clamping side; the oxygen content sensor (331) is a zirconia concentration cell type oxygen sensor, whose detection limit is not higher than 10ppm and whose response time is not greater than 100ms; the control system (6) adopts a PID closed-loop control algorithm, and the control response period is not greater than 200ms.

4. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: The control system (6) further includes a temperature-correlated carbon potential adaptive submodule (65), which includes at least one high-temperature zone temperature sensor (333) disposed on the plasma jet path inside the vacuum spraying cavity (1) for detecting the temperature of the high-temperature zone of the plasma jet; the control system (6) dynamically adjusts the target concentration of carbon-containing reducing gas in the carbon potential regulating mixture according to the temperature detection signal of the high-temperature zone temperature sensor (333) and a preset temperature-carbon activity correlation model.

5. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: It also includes a multi-level atmosphere management system (8), which includes: a first-level vacuum subsystem (81), including a mechanical pump and a Roots pump, for pre-evacuating the vacuum spraying chamber (1) from atmospheric pressure to a first preset vacuum degree; a second-level vacuum subsystem (83), including a turbomolecular pump or a diffusion pump, for evacuating the vacuum spraying chamber (1) from a preset intermediate pressure to a working vacuum degree; and an inert gas replacement subsystem (82), including a high-purity inert gas source and a flow control valve group (822), for performing multiple rounds of gas replacement on the vacuum spraying chamber (1) during the vacuuming process; the control system (6) controls the first-level vacuum subsystem (81), the inert gas replacement subsystem (82) and the second-level vacuum subsystem (83) to work alternately according to a preset program; the inert gas replacement subsystem (82) fills the vacuum spraying chamber (1) with inert gas to a first preset pressure in each replacement cycle, maintains the preset pressure holding time and then evacuates again, and the number of replacement cycles is not less than 3 times.

6. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: It also includes a workpiece-side local atmosphere protection device (4), which includes an annular gas distributor (41) and a gas supply line (42). The annular gas distributor (41) is located in the spraying direction of the plasma spray gun (2) and between the plasma spray gun (2) and the workpiece. The annular gas distributor (41) is provided with guide holes (411) evenly distributed in the circumferential direction, which are used to output annular converging airflow of carbon potential control mixture around the workpiece spraying area. One end of the gas supply line (42) is connected to the outlet of the gas mixing unit (32), and the other end is connected to the inlet of the annular gas distributor (41). The gas supply line (42) is provided with an independent flow regulating valve (421) independent of the multi-point carbon potential injection subunit (34).

7. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: The inner wall of the gas channel of the plasma spray gun (2) is provided with a tantalum carbide or hafnium carbide liner. The liner is a cylindrical bushing structure and is fixed to the inner wall of the gas channel by interference fit. The thickness of the liner is 0.3 to 1.5 mm. The liner covers the section of the gas channel from the arc column area between the cathode and the anode to the outlet end of the anode nozzle.

8. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: It also includes a powder pretreatment unit (5), which is a pretreatment device set independently of the vacuum spraying chamber (1), including a sealed stirring tank (51), a carbon source material supply device (52) and a fluidized bed structure; the sealed stirring tank (51) is a closed tank with a mechanical stirring paddle inside; the carbon source material supply device (52) is an independently set metering and feeding device, which is connected to the inlet of the sealed stirring tank (51) through a feed pipeline; the fluidized bed structure is set at the bottom of the sealed stirring tank (51), including a porous gas distribution plate and an inert gas inlet pipeline connected thereto; the carbon source material is nano-graphite powder or carbon black, and the coating amount is 0.1% to 2% of the mass of the carbide spraying powder.

9. The anti-decarburization type low-pressure plasma spraying equipment according to claim 1, characterized in that: The control system (6) further includes a pulse carbon potential modulation submodule (66), which is used to periodically increase and decrease the injection flow rate of the carbon-containing reducing gas according to a preset modulation frequency and duty cycle during the spraying process. The modulation frequency is 0.5 to 5 Hz, and the duty cycle is 40% to 70%.

10. A method of using the anti-decarburization type low-pressure plasma spraying equipment as described in any one of claims 1 to 9, characterized in that, Includes the following steps: Step 1: Powder pretreatment -- Add carbide spray powder to the sealed mixing tank (51) of the powder pretreatment unit (5), start the inert gas supply and mechanical stirring paddle of the fluidized bed structure, and inject carbon source material according to the set ratio through the carbon source material supply device (52). After coating treatment, take out the coated powder from the bottom outlet of the sealed mixing tank (51) and put it into the powder storage hopper of the powder feeding device (4). Step 2: Clamp the workpiece on the workpiece turntable (11) inside the vacuum spraying chamber (1) and close the inspection door. Step 3: The multi-level atmosphere management system (8) is started and the staged vacuuming and inert gas replacement procedure is executed to evacuate the vacuum spraying chamber (1) to the working vacuum level. Step 4: The carbon potential atmosphere control module (3) is started. The control system (6) first operates in the first injection mode, injecting carbon potential control mixed gas into each injection nozzle (341) at the same time to pre-establish the overall carbon potential of the cavity. When the residual oxygen partial pressure in the cavity stabilizes below the set value, it switches to the second injection mode. According to the detection signal of each oxygen content sensor (331), the injection flow rate of each injection nozzle (341) is adjusted respectively, and the flow rate of each injection nozzle (341) is adjusted to the set gradient. Step 5: Start the plasma spray gun (2) to preheat the workpiece. At the same time, the pulse carbon potential modulation submodule (66) is started and the carbon-containing reducing gas injection flow rate is periodically adjusted according to the preset modulation frequency and duty cycle. Start the powder feeding device (4) to send the carbon-coated powder into the plasma spray gun (2). At the same time, start the workpiece side local atmosphere protection device (4) to deliver the carbon potential regulation mixed gas to the annular gas distributor (41) through the gas supply pipeline (42) to form a local carbon potential protection atmosphere curtain around the workpiece spraying area. During the spraying process, the temperature-related carbon potential adaptive submodule (65) dynamically adjusts the target concentration of the carbon potential regulation mixed gas according to the temperature-carbon activity correlation model based on the real-time temperature signal of the high temperature zone temperature sensor (333). Step 6: After spraying, turn off the spray gun, powder feeding device and workpiece side local atmosphere protection device, keep the carbon potential control mixture injected until the workpiece cools down to below the set temperature, then fill with air to normal pressure and take out the workpiece.

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