Plasma spray gun system and spraying method

Abstract

The invention discloses a plasma spray gun system and a spraying method, and the plasma spray gun system comprises a plasma spray gun main body which is used for generating plasma jet flow; the at least one cooling gas nozzle is arranged on the side of the outlet end of the plasma spray gun body, the outlet direction of the cooling gas nozzle is adjustable, and the cooling gas nozzle has the deflection freedom degree of + / -15 degrees to + / -60 degrees and is used for dynamically adjusting the spraying angle of cooling gas; the gas control module is used for dynamically adjusting the flow, pressure and pulse frequency of cooling gas according to the power or temperature signal of the plasma spray gun; the invention relates to a plasma spraying technology, in particular to a plasma spray gun system and a spraying method for improving the coating quality through double-layer gas cooling and dynamic regulation, different cooling gases are sprayed in stages through a double-layer nested nozzle, the gases are prevented from being mixed too early, progressive cooling is achieved, thermal shock is reduced, and the coating quality is improved. And the bonding strength of the high-melting-point material coating is improved.

Description

Technical Field

[0001] This invention relates to plasma spraying technology, and in particular to a plasma spray gun system and spraying method that improves coating quality through dual-layer gas cooling and dynamic control. Background Technology

[0002] Plasma spraying is a surface treatment technology that uses a plasma arc to heat powder materials to a molten or semi-molten state and then sprays them at high speed onto the substrate surface to form a coating. This technology has advantages such as high coating adhesion strength, low porosity, and a wide range of applicable materials, and is widely used in aerospace, machinery manufacturing, and electronics industries.

[0003] However, traditional plasma spraying cooling control has the following drawbacks:

[0004] 1) Cooling and melting conflict: Lateral cooling gas interferes with the plasma jet, resulting in powder unmelted rate >5%;

[0005] 2) Rigid process: Fixed cooling parameters cannot adapt to complex workpieces (such as curved surfaces and thin walls);

[0006] 3) High coating stress: Continuous cooling results in residual stress >400MPa;

[0007] Therefore, in order to solve at least some of the above problems, a plasma spray gun system and spraying method are proposed. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a plasma spray gun system and spraying method, which sprays different cooling gases in stages through double-layer nested nozzles to avoid premature gas mixing, achieve gradual cooling, reduce thermal shock, and improve the bonding strength of high melting point material coatings.

[0009] A plasma spray gun system includes: a plasma spray gun body for generating a plasma jet; and at least one cooling gas nozzle disposed on the side of the outlet end of the plasma spray gun body, wherein the outlet direction of the cooling gas nozzle is adjustable and has a deflection degree of freedom of ±15° to ±60° for dynamically adjusting the cooling gas injection angle.

[0010] It also includes a gas control module that dynamically adjusts the flow rate, pressure, and pulse frequency of the cooling gas based on the power or temperature signal of the plasma spray gun.

[0011] Furthermore, the cooling gas nozzle 2 includes an inner nozzle 21 and an outer nozzle 22 nested coaxially. The inner nozzle 21 sprays a first cooling gas, and the outer nozzle 22 sprays a second cooling gas. The two gases mix at a distance of 1 to 10 mm outside the nozzle outlet.

[0012] Furthermore, the flow channel cross-section of the inner nozzle 21 is a tapered-expanding Laval structure, with a throat diameter to outlet diameter ratio of 1:1.5 to 1:3, used to accelerate the cooling gas to supersonic speeds, Mach numbers of 1.2-2.5.

[0013] Furthermore, the outlet end face of the cooling gas nozzle 2 is provided with an adjustable guide ring 23, which is axially displaced by a piezoelectric actuator to adjust the outlet cross-sectional area change rate by ±30%.

[0014] Furthermore, the jet stream from the cooling gas nozzle 2 contains an adjustable pulse frequency (10-500Hz), which avoids stress concentration in the coating caused by excessive cooling through intermittent jetting.

[0015] Furthermore, the distance between the cooling gas nozzle 2 and the workpiece surface can be dynamically adjusted (5-50mm), and it is equipped with an infrared temperature feedback system to adjust the cooling gas flow rate in real time to match the cooling rate requirements of the molten coating.

[0016] A plasma spray gun system spraying method includes the following steps:

[0017] Step 1: Start the plasma spray gun and introduce working gas (Ar / H2 or Ar / He mixture) into the plasma spray gun. A high-temperature plasma jet is generated at an arc power of 30-200kW, which feeds the spray powder (particle size 10-100μm) from the axial or lateral direction of the spray gun into the center of the plasma jet, so that it is fully melted.

[0018] Step 2: Simultaneously open cooling gas nozzle 2 and spray at a flow rate of 10–200 m / s to form an enveloping or partially mixed air curtain at a distance of 5–50 mm from the nozzle outlet; monitor the temperature of the molten coating in real time using an infrared thermometer, and dynamically adjust the cooling gas flow rate, pulse frequency, or nozzle distance to control the cooling rate of the molten coating at 10 m / s. 4 ~10 6 K / s.

[0019] Furthermore, when spraying high melting point materials (melting point > 2000℃), a double-layer nested nozzle is simultaneously activated. The inner nozzle 21 is filled with argon gas at a flow rate of 40% to 60%, while the outer nozzle 22 is filled with nitrogen gas at a flow rate of 60% to 40%. The two gases mix at a distance of 10 to 30 mm above the molten pool.

[0020] Furthermore, the ratio of the flow rate of the cooling gas to the flow rate of the plasma gas is 0.2:1 to 1:1.

[0021] 10. A coating method for a plasma spray gun system according to claim 7, characterized in that: when spraying a thin coating with a thickness <100μm, a pulse cooling mode is activated, and the pulse frequency is matched with the spray gun scanning speed, satisfying the following relationship:

[0022]

[0023] Where v is the spray gun scanning speed (5-50 mm / s); d is the width of the cooling air curtain (3-10 mm); and k is the correction factor (0.5-2).

[0024] Compared with the prior art, the advantages and positive effects of the present invention are:

[0025] By using double-layer nested nozzles to spray different cooling gases in stages, premature gas mixing is avoided, gradual cooling is achieved, thermal shock is reduced, and the bonding strength of high-melting-point material coatings is improved.

[0026] The cooling gas is accelerated to supersonic speed through the Laval flow channel, which enhances the penetration power and is suitable for high-power plasma spraying.

[0027] The outlet cross-sectional area can be adjusted in real time by means of an adjustable guide ring to meet the cooling requirements of different spraying materials (such as metal / ceramic).

[0028] By using pulse cooling and real-time feedback from infrared temperature measurement systems, the sudden cooling stress caused by continuous cooling is avoided, thus reducing the residual stress of the coating. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without creative effort. In the drawings:

[0030] Figure 1 This is a schematic diagram of the structure of the present invention;

[0031] Figure 2 This is a schematic diagram of the cooling gas nozzle structure of the present invention.

[0032] In the diagram: 1. Plasma spray gun body; 2. Cooling gas nozzle; 21. Inner nozzle; 22. Outer nozzle; 23. Guide ring. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] A plasma spray gun system includes: a plasma spray gun body 1 for generating a plasma jet; at least one cooling gas nozzle 2 disposed on the side of the outlet end of the plasma spray gun body 1, wherein the outlet direction of the cooling gas nozzle 2 is adjustable and has a deflection degree of freedom of ±15° to ±60° for dynamically adjusting the cooling gas injection angle.

[0035] It also includes a gas control module that dynamically adjusts the flow rate, pressure, and pulse frequency of the cooling gas based on the power or temperature signal of the plasma spray gun.

[0036] The plasma spray gun body utilizes an electric arc to ionize the working gas, generating a high-temperature plasma jet to melt the powder. The cooling gas nozzle, with its adjustable angle design, can flexibly change the direction of the cooling gas spray according to the spraying scenario. The gas control module dynamically adjusts the cooling parameters based on the spray gun power or temperature signal using feedback control principles. The plasma spray gun body provides the energy source for spraying. The angle adjustment of the cooling gas nozzle ensures that the cooling gas can accurately act on the molten coating area. The gas control module realizes intelligent control of the cooling process, ensuring that the coating forms under suitable cooling conditions, improving coating quality. When spraying complex curved workpieces, the adjustable angle nozzle can deflect in real time by ±15° to ±60° to ensure that the cooling gas curtain is always perpendicular to the normal direction of the workpiece surface, with a deviation angle ≤5°.

[0037] The cooling gas nozzle 2 includes an inner nozzle 21 and an outer nozzle 22 nested coaxially. The inner nozzle 21 sprays a first cooling gas, and the outer nozzle 22 sprays a second cooling gas. The two gases mix at a distance of 1 to 10 mm outside the nozzle outlet.

[0038] The coaxial nested double-layer nozzles spray different cooling gases respectively. Utilizing the principle of gas diffusion, the two gases are mixed at a specific distance outside the nozzle outlet, avoiding premature mixing that would affect their respective properties. The inner and outer layer gases retain their respective properties before mixing, and after mixing, they can exert a synergistic cooling effect, which not only enhances cooling efficiency, but also allows for the selection of appropriate gas combinations according to the needs of different coating materials, reducing adverse effects on the coating, such as preventing coating oxidation or nitriding.

[0039] The inner nozzle 21 has a flow channel cross-section of a tapered-expanding Laval structure, with a throat diameter to outlet diameter ratio of 1:1.5 to 1:3, used to accelerate the cooling gas to supersonic speeds, with Mach numbers of 1.2-2.5.

[0040] The tapered-expanding Laval structure utilizes gas dynamics principles. When the gas flows through the throat, its speed reaches the speed of sound, and it continues to accelerate to supersonic speeds in the expanding section. The specific ratio between the throat and the outlet diameter ensures that the gas can be stably accelerated to the target Mach number. The supersonic cooling gas can rapidly penetrate the high-temperature atmosphere surrounding the plasma jet, reaching the surface of the molten coating directly, improving the cooling rate and uniformity, and meeting the rapid cooling requirements of high-power plasma spraying.

[0041] The outlet end face of the cooling gas nozzle 2 is provided with an adjustable guide ring 23. The guide ring 23 is axially displaced by a piezoelectric actuator, and the outlet cross-sectional area change rate is adjusted by ±30%.

[0042] With this configuration, the adjustable guide ring achieves axial displacement through a piezoelectric actuator, changing the nozzle outlet cross-sectional area. Based on the relationship between flow rate and cross-sectional area in fluid mechanics, the flow rate and flow distribution of the cooling gas are adjusted. By adjusting the rate of change of the outlet cross-sectional area, the cooling intensity requirements of different coating materials can be adapted to achieve precise control of the cooling effect and avoid defects such as stress concentration and cracks in the coating caused by improper cooling.

[0043] The jet stream from the cooling gas nozzle 2 contains an adjustable pulse frequency (10-500Hz), which avoids stress concentration in the coating caused by excessive cooling through intermittent jetting.

[0044] With this setup, the pulse cooling mode uses intermittent injection to make the cooling process periodic. By controlling the pulse frequency, the cooling intensity and the heat dissipation requirements of the coating are balanced, avoiding excessive cooling caused by continuous cooling. Intermittent injection reduces the continuous contact between the cooling gas and the coating, reducing the residual stress generated by rapid and continuous cooling of the coating. At the same time, the pulse frequency can be adjusted according to the coating thickness, material properties, etc., to improve the mechanical properties of the coating.

[0045] The distance between the cooling gas nozzle 2 and the workpiece surface can be dynamically adjusted (5-50mm), and it is equipped with an infrared temperature feedback system to adjust the cooling gas flow rate in real time to match the cooling rate requirements of the molten coating.

[0046] The cooling gas is an inert gas, nitrogen, or compressed air, with a temperature below -20°C, or is pre-cooled by an external refrigeration device such as a vortex tube cooler.

[0047] With this setup, the infrared temperature feedback system monitors the temperature of the molten coating in real time and transmits the temperature signal to the control unit. The control unit adjusts the distance between the nozzle and the workpiece to change the intensity of the cooling gas according to the preset cooling rate requirements, while also adjusting the flow rate to form a closed-loop control. Dynamically adjusting the distance between the nozzle and the workpiece ensures that the cooling gas is working at the optimal distance. The infrared temperature feedback enables real-time correction of the cooling process, keeping the cooling rate of the molten coating within the ideal range, ensuring a uniform coating structure, and reducing defects.

[0048] A plasma spray gun system spraying method includes the following steps:

[0049] Start the plasma spray gun and introduce working gas (Ar / H2 or Ar / He mixture) into the plasma spray gun. A high-temperature plasma jet is generated at an arc power of 30 to 200 kW, which feeds the spray powder (particle size 10 to 100 μm) from the axial or lateral direction of the spray gun into the center of the plasma jet, so that it is fully melted.

[0050] 2) Simultaneously open cooling gas nozzle 2 and spray at a flow rate of 10–200 m / s to form an enveloping or partially mixed air curtain at a distance of 5–50 mm from the nozzle outlet; monitor the temperature of the molten coating in real time using an infrared thermometer, and dynamically adjust the cooling gas flow rate, pulse frequency, or nozzle distance to control the cooling rate of the molten coating at 10 m / s. 4 ~10 6 K / s.

[0051] First, the powder is heated to a molten state using a high-temperature plasma jet. Then, a cooling gas curtain is used to cool the molten coating. Combined with real-time feedback from infrared thermography, cooling parameters are adjusted according to temperature changes. Following the principles of heat transfer and material solidification, this ensures that the powder, after being fully melted, solidifies into a coating under suitable cooling conditions. By controlling the cooling rate within a specific range, the grain structure and mechanical properties of the coating can be effectively controlled, improving the coating quality stability.

[0052] When spraying high melting point materials (melting point > 2000℃), double-layer nested nozzles are used simultaneously. The inner nozzle 21 is filled with argon gas at a flow rate of 40% to 60%; the outer nozzle 22 is filled with nitrogen gas at a flow rate of 60% to 40%. The two gases are mixed 10 to 30 mm above the molten pool.

[0053] The ratio of the flow rate of the cooling gas to the flow rate of the plasma gas is 0.2:1 to 1:1.

[0054] The cooling gas flow rate and the plasma gas flow rate are kept in a specific ratio. Based on the matching relationship between the plasma jet energy and the cooling requirements, the cooling intensity is ensured to be sufficient for the coating to solidify quickly, without excessively interfering with the stability of the plasma jet. This ensures the coordinated work of the cooling system and the plasma jet system, avoids the plasma jet being damaged by excessive cooling gas flow rate, or the expected cooling effect not being achieved due to insufficient flow rate, and maintains the stability of the spraying process and the coating quality.

[0055] When spraying high-melting-point materials (melting point > 2000℃), double-layer nested nozzles 21 / 22 are simultaneously activated. The inner nozzle 21 is filled with argon gas at a flow rate of 40%–60%, while the outer nozzle 22 is filled with nitrogen gas at a flow rate of 60%–40%. The two gases mix at a distance of 10–30 mm above the molten pool.

[0056] When spraying a thin coating with a thickness of <100μm, the pulse cooling mode is activated, and the pulse frequency is matched with the spray gun scanning speed, satisfying the following relationship:

[0057]

[0058] Where f is the pulse frequency (Hz), v is the spray gun scanning speed (5-50 mm / s), d is the width of the cooling air curtain (3-10 mm), and k is the correction factor (0.5-2).

[0059] The pulse frequency is related to the spray gun scanning speed, the width of the cooling air curtain, and the correction coefficient to ensure that the spray gun movement distance does not exceed the width of the air curtain within each pulse cooling cycle, thus avoiding cooling blind spots.

[0060] Based on the spray gun's moving speed and the cooling air curtain's coverage area, a suitable pulse frequency is calculated using a formula to ensure that each pulse can effectively cover the corresponding spraying area. For thin coatings, this formula ensures that pulse cooling is synchronized with the spray gun's movement, allowing the cooling process to uniformly cover the coating surface, avoiding cooling blind spots or over-cooled areas, reducing defects such as cracking and peeling caused by uneven cooling in thin coatings, and improving the quality of thin coatings.

[0061] The derivation process of the pulse frequency is as follows:

[0062] The formula for calculating the coverage area of ​​a single pulse is:

[0063] Spray gun travel distance It should be ≤ the width of the air curtain d, that is

[0064] Because actual overlapping coverage is required (to avoid edge effects), a value of k needs to be introduced, let's assume... Where k>1;

[0065] The k-value calibration process for spraying a 50μm yttrium-stabilized zirconia (YSZ) thermal barrier coating onto a nickel-based superalloy substrate using the plasma spray gun system (with pulse cooling module) of this invention is as follows:

[0066] First, set the parameters:

[0067] Spray gun moving speed v: 10mm / s (fixed), air curtain width d: 5mm (measured by high-speed camera), cooling gas: nitrogen (flow rate 20L / min, pulse duty cycle 50%), test k value range: 0.5~3.0 (step 0.5).

[0068] For each k value, a 10×10cm sample was sprayed, and the standard deviation (σ) of the coating thickness was measured using a coating thickness measuring instrument (such as an eddy current thickness gauge, an ultrasonic thickness gauge, or microscopy).

[0069] The surface stress of the coating was detected by X-ray diffraction (XRD).

[0070] Crack density was observed using SEM;

[0071] The experimental results are shown in Table 1:

[0072] Table 1

[0073]

[0074]

[0075] Referring to Table 1, after balancing cooling uniformity (σ<2μm) and stress control (<250MPa), the optimal k = 1.5;

[0076] For different coating materials, the k value needs to be adjusted: Metal coatings (such as NiCrAlY): k = 1.2~1.8 (high thermal conductivity, requiring lower overlap); Ceramic coatings (such as YSZ): k = 1.5~2.0 (high brittleness, requiring higher coverage).

[0077] To further verify whether the corrected k value is the optimal value, the following operating conditions were used for verification:

[0078] When the spray gun scanning speed is set to v = 20 mm / s, the air curtain width is set to d = 5 mm, and k = 1.5;

[0079] Calculate the frequency f = 20 / 5 * 1.5 = 6 (Hz)

[0080] The measured coating thickness deviation was ±1.9μm, and the residual stress was 215MPa. The values ​​were all within the range of balanced cooling uniformity (σ<2μm) and stress control (<250MPa), which was consistent with the prediction.

[0081] Compared with the thickness deviation of ±5μm and stress of 320MPa in traditional continuous cooling, the deviations are smaller than those in traditional continuous cooling, thus verifying the effectiveness of the formula.

[0082] The effectiveness of this spray gun is verified through specific examples below:

[0083] Example 1: In this example, the plasma spray gun body 1 adopts a common DC arc plasma spray gun structure. It has a cathode and an anode inside, and an electric arc is generated between the two electrodes by a DC power supply, which ionizes the incoming working gas (such as a mixture of argon and hydrogen) to form a high-temperature plasma jet. The outlet end of the plasma spray gun body 1 is circular with a diameter of 15mm to ensure stable output of the plasma jet.

[0084] The cooling gas nozzle 2 is a single-channel design, made of high-temperature and corrosion-resistant silicon nitride ceramic. It is mounted on the side of the outlet end of the plasma spray gun body 1 via an adjustable metal bracket (existing technology, not shown or described further). The distance between the nozzle and the outlet end of the plasma spray gun body 1 is 10mm. The initial outlet angle of the cooling gas nozzle 2 is set to a 30° angle with the plasma jet direction. It has an electric adjustment mechanism that can dynamically adjust the spray angle within a range of ±15° to adapt to different spraying requirements. The gas control module uses a programmable logic controller (PLC) as the core control unit, connected to a temperature sensor and a power sensor. The temperature sensor is mounted on the outer shell of the plasma spray gun body 1 to monitor the spray gun's operating temperature in real time; the power sensor is connected to the DC power supply output to monitor the arc power. Based on the temperature and power signals fed back from the sensors, the PLC controls the electromagnetic regulating valve on the cooling gas pipeline to dynamically adjust the cooling gas flow rate within the range of 5-20L / min, maintain the pressure at 0.2-0.5MPa, and set the pulse frequency range to 10-100Hz.

[0085] A WC-10Co ultrathin wear-resistant coating with a thickness of 80 μm was prepared on the surface of a precision mold made of H13 steel. The cooling gas was CO2, the pre-cooling temperature was -28℃ (cooled by a vortex tube), and the cooling gas temperature during spraying was -25℃. The airflow velocity was 180 m / s (Laval nozzle Mach number 1.8); a 7.5 Hz square wave pulse was used with a duty cycle of 40% and a pulse delay time of 2 ms (relative to the powder spray phase difference).

[0086] The plasma spray gun system is started by introducing working gas. After the plasma jet stabilizes, the cooling gas nozzle 2 is turned on. When the temperature of the plasma spray gun body 1 rises due to prolonged operation or the arc power increases, the gas control module automatically increases the cooling gas flow rate and adjusts the spray angle appropriately to ensure that the plasma spray gun body 1 operates within a suitable temperature range. At the same time, it ensures the cooling effect of the cooling gas on the plasma jet and the molten coating, thereby improving the coating quality. The coating test results are shown in Table 2.

[0087] Table 2

[0088] Detection parameters This invention Traditional methods Coating thickness deviation ±3μm ±12μm Transverse crack density 0.2 / mm 1.8 / mm Bond strength 68MPa 45MPa

[0089] Example 2:

[0090] This embodiment optimizes the structure of the cooling gas nozzle 2 based on Embodiment 1. The cooling gas nozzle 2 adopts a coaxial nested inner nozzle 21 and outer nozzle 22 design. The inner nozzle 21 is made of tungsten carbide, and the flow channel adopts a tapered-expanding Laval structure with a throat diameter of 2 mm and an outlet diameter of 3 mm. It can accelerate the cooling gas to supersonic speeds, achieving an outlet Mach number of 1.5. The outer nozzle 22 is made of alumina ceramic, with an outlet inner diameter of 8 mm and an outer diameter of 10 mm. The outlet end faces of the inner nozzle 21 and the outer nozzle 22 are flush, and the two cooling gases mix 15 mm outside the nozzle outlet.

[0091] Argon gas is introduced into the inner nozzle 21 as the main cooling gas, accounting for 55% of the flow rate; nitrogen gas is introduced into the outer nozzle 22 as the auxiliary cooling gas, accounting for 45% of the flow rate. A WC-10Co ultra-thin wear-resistant coating with a thickness of 80μm is prepared on the surface of a precision mold made of H13 steel.

[0092] In the actual spraying process, the double-nested cooling gas nozzle structure utilizes the supersonic argon gas accelerated by the inner nozzle 21 to quickly remove the heat from the plasma jet and the coating surface, while the outer nitrogen gas further expands the cooling range and plays a certain protective role, reducing coating oxidation and significantly improving the quality and performance of the coating. The measurable droplet superheat is reduced by about 200K, the carbon loss rate is reduced from 12% to 6.5%, and the coating hardness HV0.3 is increased by 18%.

[0093] Example 3:

[0094] To further verify the advantages of the plasma spray gun system (double-layer nested nozzle + pulse cooling) of this invention in improving the performance of thermal barrier coatings, a comparative study was conducted on aerospace turbine blades using both a conventional spray gun and the spray gun of this invention. Specific parameters are shown in Table 3.

[0095] Table 3

[0096]

[0097]

[0098] Table 4 shows a comparison of the coating performance produced using a conventional spray gun and the spray gun of this invention:

[0099] Table 4

[0100]

[0101] The above embodiments demonstrate that the dynamic adjustment capability of the present invention can improve coating performance indicators by 30%-150%, with significant advantages, especially in extreme conditions such as ultra-thin coatings and high-melting-point materials.

[0102] The above-disclosed embodiments are merely specific examples of the present invention. However, the present invention is not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A plasma spray gun system, characterized in that, include: Plasma spray gun body (1), used to generate plasma jet; At least one cooling gas nozzle (2) is provided on the side of the outlet end of the plasma spray gun body (1). The outlet direction of the cooling gas nozzle (2) is adjustable and has a deflection degree of ±15° to ±60°, which is used to dynamically adjust the cooling gas injection angle. It also includes a gas control module that dynamically adjusts the flow rate, pressure, and pulse frequency of the cooling gas based on the power or temperature signal of the plasma spray gun.

2. The plasma spray gun system according to claim 1, characterized in that: The cooling gas nozzle (2) includes an inner nozzle (21) and an outer nozzle (22) nested coaxially. The inner nozzle (21) sprays a first cooling gas, and the outer nozzle (22) sprays a second cooling gas. The two gases mix at a distance of 1 to 10 mm outside the nozzle outlet.

3. The plasma spray gun system according to claim 2, characterized in that: The inner nozzle (21) has a flow channel cross-section of a tapered-expanding Laval structure, with a throat diameter to outlet diameter ratio of 1:1.5 to 1:3, used to accelerate the cooling gas to supersonic speeds, with Mach numbers of 1.2-2.

5.

4. The plasma spray gun system according to claim 1, characterized in that: The outlet end face of the cooling gas nozzle (2) is provided with an adjustable guide ring (23). The guide ring (23) is axially displaced by a piezoelectric actuator, and the outlet cross-sectional area change rate is adjusted by ±30%.

5. The plasma spray gun system according to claim 1, characterized in that: The jet stream from the cooling gas nozzle (2) contains an adjustable pulse frequency (10-500Hz), which avoids stress concentration in the coating caused by excessive cooling through intermittent jetting.

6. The plasma spray gun system according to claim 1, characterized in that: The distance between the cooling gas nozzle (2) and the workpiece surface can be dynamically adjusted (5-50mm), and it is equipped with an infrared temperature feedback system to adjust the cooling gas flow rate in real time to match the cooling rate requirements of the molten coating.

7. A coating method for a plasma spray gun system according to any one of claims 1 to 6, characterized in that: Includes the following steps: Step 1: Start the plasma spray gun and introduce working gas (Ar / H2 or Ar / He mixture) into the plasma spray gun (1). A high-temperature plasma jet is generated at an arc power of 30 to 200 kW, and the spray powder (particle size 10 to 100 μm) is fed into the center of the plasma jet from the axial or lateral direction of the spray gun so that it is fully melted. Step 2: Simultaneously open the cooling gas nozzle (2) and spray at a flow rate of 10-200 m / s to form an enveloping or partially mixed air curtain at a distance of 5-50 mm from the nozzle outlet; monitor the temperature of the molten coating in real time using an infrared thermometer, and dynamically adjust the cooling gas flow rate, pulse frequency, or nozzle distance to control the cooling rate of the molten coating at 10 m / s. 4 ~10 6 K / s.

8. The spraying method of a plasma spray gun system according to claim 7, characterized in that: When spraying high melting point materials (melting point > 2000℃), double-layer nested nozzles are used simultaneously. The inner nozzle (21) is filled with argon gas at a flow rate of 40% to 60%; the outer nozzle (22) is filled with nitrogen gas at a flow rate of 60% to 40%. The two gases are mixed 10 to 30 mm above the molten pool.

9. The spraying method of a plasma spray gun system according to claim 7, characterized in that: The ratio of the flow rate of the cooling gas to the flow rate of the plasma gas is 0.2:1 to 1:

1.

10. A coating method for a plasma spray gun system according to claim 7, characterized in that: When spraying a thin coating with a thickness of <100μm, the pulse cooling mode is activated, and the pulse frequency is matched with the spray gun scanning speed, satisfying the following relationship: Where v is the spray gun scanning speed (5-50 mm / s); d is the width of the cooling air curtain (3-10 mm); and k is the correction factor (0.5-2).

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