A double-tapered anode structure of a special spray gun for laminar flow plasma spraying yttria coating

Abstract

This application provides a double-tapered anode structure for a special spray gun for laminar plasma spraying of yttrium oxide coatings. The anode structure includes: a channel for injecting laminar plasma jets, the channel being a through hole extending parallel to the central axis of the anode structure; the through hole includes, sequentially connected: an inlet channel for injecting the laminar plasma jet; a compression channel for compressing the laminar plasma jet; and an outlet channel for ejecting the laminar plasma jet; wherein the inlet channel includes a first tapered cavity and a second tapered cavity, the second tapered cavity being closer to the compression channel than the first tapered cavity; wherein the axial cross-section of both the first and second tapered cavities is tapered, and the taper of the first tapered cavity is smaller than that of the second tapered cavity. The double-tapered anode structure provided by this invention solves the problem of high-temperature oxygen loss that easily occurs in the current high-temperature laminar plasma spraying preparation of Y2O3 coatings.

Description

Technical Field

[0001] This application relates to the field of plasma spraying Y2O3 coating technology, and in particular to a double-tapered anode structure for a special spray gun for laminar plasma spraying of yttrium oxide coating. Background Technology

[0002] Plasma-sprayed yttrium oxide (Y2O3) coatings have been engineered and applied in semiconductor manufacturing equipment, high-temperature protective components, and the electronics industry in recent years. Among these applications, Y2O3 is most maturely used as a key protective coating for the inner wall of the etching chamber in semiconductor etching equipment. During etching, corrosive plasmas containing fluorine (F) and chlorine (Cl) can cause significant chemical erosion and sputtering wear. Traditionally used Al2O3 coatings have a high reaction rate in F-based plasma environments, easily generating detachable byproduct particles that affect wafer yield. In contrast, Y2O3 coatings have lower chemical reactivity and better plasma resistance. They exhibit a lower corrosion rate and release fewer harmful particles in F-based plasmas, significantly reducing the risk of microcontamination. Therefore, Y2O3 coatings have become the mainstream alternative to Al2O3 coatings in 8-inch and larger wafer etching equipment. In terms of fabrication processes, by controlling the plasma spraying process parameters, dense Y2O3 coatings with a porosity ≤0.3% and a hardness as high as 630–640 HV can be obtained, improving their corrosion resistance by approximately three times. Besides semiconductor etching equipment, Y2O3 coatings can be used as high-purity ceramic coatings in the electronics industry for packaging electronic components, providing insulation protection for high-frequency, high-power devices. In the field of optical windows, due to its transparency in the visible light band, it can be used as a window material for plasma etching equipment.

[0003] However, during the preparation of Y2O3 coatings using high-temperature laminar plasma spraying, the Y2O3 material is prone to irreversible oxygen loss reaction in a high-temperature plasma environment (>1500℃). This problem leads to: 1. Deterioration of coating performance: After Y2O3 particles lose oxygen, their color changes from white to gray or even black, and they lose optical transparency; 2. Stoichiometric deviation: The material changes from stoichiometric yttrium oxide to non-stoichiometric oxide, altering the phase composition and causing a significant decrease in corrosion resistance and insulation performance; 3. Increased wear and tear on spraying equipment: Under high output power, anode ablation is significant, and anode life is shortened to <10h, making it difficult to meet the needs of continuous and stable production.

[0004] Therefore, in the plasma spraying technology of Y2O3, although high-power spraying can improve the degree of particle melting and deposition efficiency, it will seriously induce the high-temperature oxygen loss phenomenon of Y2O3, making it difficult for the optical, structural, chemical and corrosion resistance properties of the coating to meet the application requirements, especially failing to meet the stringent requirements of the semiconductor industry for high purity, high insulation and low defects.

[0005] How to suppress high-temperature oxygen loss while maintaining high power density spraying is the core problem that current plasma spraying Y2O3 coating technology urgently needs to solve. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a double-tapered anode structure for a special spray gun for laminar plasma spraying of yttrium oxide coatings, in order to solve the problem of high-temperature oxygen loss that easily occurs when preparing Y2O3 coatings using current high-temperature laminar plasma spraying.

[0007] This invention provides a double-tapered anode structure for a special spray gun for laminar plasma spraying of yttrium oxide coatings. The technical solution adopted is as follows: A double-tapered anode structure for a laminar plasma spray gun for applying yttrium oxide coatings, the anode structure comprising: a channel for supplying laminar plasma jets, the channel being a through hole extending parallel to the central axis of the anode structure; the through hole comprising sequentially connected: An inlet channel for injecting the laminar plasma jet; Compression channels are used to compress the laminar plasma jet; An outlet channel for ejecting the laminar plasma jet; The inlet channel includes a first tapered cavity and a second tapered cavity, wherein the second tapered cavity is closer to the compression channel than the first tapered cavity; The axial cross-sections of the first and second tapered cavities are both tapered, and the taper of the first tapered cavity is smaller than that of the second tapered cavity.

[0008] As one of the preferred embodiments, the taper of the first tapered cavity is 80°, and the taper of the second tapered cavity is 120°.

[0009] As one preferred embodiment, the wall surface surrounding the cavity wall forming the first tapered cavity extends in a straight line inclined away from the central axis; the wall surface surrounding the cavity wall forming the second tapered cavity protrudes in an arc shape towards the central axis.

[0010] As one of the preferred embodiments, both the compression channel and the outlet channel are cylindrical, and the diameter of the outlet channel is larger than the diameter of the compression channel.

[0011] As one preferred embodiment, the anode structure includes an anode shell surrounding the through hole, the anode shell comprising a copper-tungsten composite material.

[0012] As one preferred embodiment, the anode shell includes an inner shell and an outer shell, the outer shell being sleeved on the outer periphery of the inner shell, and the inner wall surface of the inner shell forming the through hole; The inner shell is made of tungsten material, and the outer shell is made of a composite of copper, zirconium and copper materials.

[0013] As one preferred embodiment, the outer wall surface of the inner shell extends vertically in the axial direction and is press-fitted or brazed to the inner wall surface of the outer shell; the outer shell includes an integrally formed conical section and a straight cylindrical section, the outer wall surface of the conical section gradually extends outward from the inlet channel to the outlet channel, and then joins the straight cylindrical section, the straight cylindrical section surrounding a part of the compression channel and the outlet channel.

[0014] As one preferred embodiment, the diameter of the first tapered cavity is 9 mm and the axial extension length is 1.5 mm; the diameter of the compression channel is 4 mm-5 mm; the axial extension length of the outer shell, the inner shell, and the through hole is 40 mm; the diameter of the inclined beginning of the tapered section of the outer shell is 12 mm, the diameter of the inclined end is 14 mm, and the axial extension length is 32.7 mm; the diameter of the straight section of the outer shell is 16 mm.

[0015] As one of the preferred embodiments, the anode structure further includes a cooling water distribution ring, in which a spiral water groove is formed for circulating cooling water; wherein, the cooling water distribution ring is embedded in the anode shell and is integrally formed with the anode shell.

[0016] As one preferred embodiment, the anode structure further includes: A gas distribution ring is provided at the inlet channel of the anode shell to uniformly distribute the working gas before sending it into the arc zone.

[0017] Compared with the prior art, this application has the following advantages: The double-tapered anode structure provided in this application forms a stable, slender arc column through gradient geometric compression, thermal compression, and magnetic compression of the anode channel, suppressing turbulent disturbances. External disturbances are reduced, and the arc length is controllable; in laminar flow mode, the arc length can reach 500 mm, far exceeding the plasma jet length (30-50 mm) in turbulent flow mode. The long laminar plasma jet extends the flight path of the sprayed powder (such as Y2O3 particles) in the plasma arc, increasing particle residence time by 5 times, resulting in more complete energy absorption by the particles. Simultaneously, the arc compresses and expands significantly with changing current, concentrating the plasma power density. Under the same power, the sprayed powder melts more fully, thus achieving deep melting of the sprayed powder without increasing the total power, avoiding excessively high overall temperatures caused by increased power. Furthermore, the exit temperature can be reduced without jet instability, significantly reducing the oxygen loss of Y2O3 particles caused by excessively high temperatures during high-power spraying. This solves problems such as performance degradation, stoichiometric deviation, and anode ablation of the Y2O3 coating. Attached Figure Description

[0018] To more clearly illustrate the technical solution of this application, the drawings used in the description of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is an external outline diagram of the double-tapered anode structure of the laminar flow plasma spray gun for yttrium oxide coating according to an embodiment of this application; Figure 2 It is along Figure 1 A cross-sectional view along the AA direction.

[0020] Explanation of reference numerals in the attached figures: 1. Anode shell; 11. Inner shell; 12. Outer shell; 2. Inlet channel; 21. First tapered cavity; 22. Second tapered cavity; 3. Compression channel; 4. Outlet channel; 5. Cooling water distribution ring. Detailed Implementation

[0021] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0022] To better understand the technical solution of this application, the principle of oxygen loss during the preparation of Y2O3 coatings by high-temperature laminar plasma spraying will now be explained: At high temperatures, Y₂O₃ undergoes irreversible oxygen loss, causing the coating material to turn gray or black after plasma spraying, severely affecting its application. The oxygen loss behavior of Y₂O₃ materials at high temperatures has been studied in considerable detail. It mainly occurs in reducing atmospheres (such as vacuum or hydrogen) or during high-temperature activation processes, manifesting as the escape of lattice oxygen to form the non-stoichiometric compound Y₂O. 3-X This is accompanied by n-type semiconductorization. Under high temperature conditions, Y₂O₃ can undergo the following reaction:

[0023] It is known that in a vacuum or high-temperature activated environment, lattice oxygen escapes in the form of O2, leaving oxygen vacancies and forming an oxygen-deficient n-type semiconductor Y2O. 3-X The crystal structure remains cubic C-type, but the lattice expands slightly. Its properties increase with increasing oxygen loss, exhibiting n-type semiconductor behavior. This is particularly relevant at temperatures above 1500℃, in vacuum, and with an oxygen partial pressure <10. -10 Significant oxygen loss occurs under ATM or reducing atmospheres, the core of which is the detachment of lattice oxygen and the formation of oxygen vacancies.

[0024] Then, the current high-temperature laminar flow plasma spraying technology for preparing Y2O3 coatings is explained: Laminar flow plasma spraying is a novel plasma spraying process that operates in an atmospheric environment and is characterized by low Reynolds numbers and long, straight laminar jets. Compared to traditional turbulent plasma spraying (APS), it exhibits significant advantages in energy utilization, coating quality, and oxidation control. Specifically, it results in: ultra-long heating paths and low oxidation of particles; significantly extended residence time, with particles having a flight time in the jet that is 5–10 times longer than in traditional APS, leading to complete melting and even overheating and evaporation. Due to minimal air entrainment in the jet, metal or carbide powders are less prone to oxidation or decomposition, resulting in low oxidation levels; and evaporation-induced physical vapor deposition (PVD) can be achieved. Under high-power conditions, the powder material evaporates, forming a gas-liquid-solid co-deposition structure, improving coating density and bonding strength. It also results in minimal substrate thermal damage, low heat input, and suitability for high-temperature spraying of thin-walled parts and heat-sensitive substrates. The operating environment is quiet, with noise levels below 80 dB, significantly improving working conditions.

[0025] Therefore, laminar flow plasma spraying possesses the advantages of "three highs and two lows": high energy utilization (long jet, low attenuation), high coating quality (low porosity, high adhesion, low oxidation), high process flexibility (controllable gas-liquid-solid deposition), low heat input (low power, low substrate temperature rise), and low environmental interference (low noise, low air entrainment). This technology is particularly suitable for applications requiring extremely high density and purity, such as high-melting-point metals, carbide ceramics, and functionally graded coatings.

[0026] In the process of preparing Y₂O₃ coatings using laminar plasma spraying, the plasma spray gun is the core component that determines the plasma temperature field, flow field structure, particle heating behavior, and the final quality of the coating. The structural characteristics of the laminar plasma spray gun are mainly reflected in jet stability, nozzle design, gas flow control, and cooling systems. Its core objective is to form a long-distance, low-disturbance, high-temperature concentrated laminar plasma jet at the nozzle exit. Therefore, the anode structure of the spray gun directly affects arc stability, power density, thermal efficiency, and anode life, and is crucial for achieving high-quality Y₂O₃ coatings. However, existing laminar plasma spray gun anode structures generally exhibit the following structural features and the resulting technical problems: Characteristics of Single-Tapered Straight-Cylinder Anodes: Existing spray gun anode structures generally employ a single-tapered straight-cylinder structure. This results in a large plasma compression angle, making it difficult for the arc to be fully contracted, increasing the arc column diameter, and consequently significantly reducing the plasma power density. When the power density is insufficient, to ensure sufficient melting and deposition efficiency for Y2O3 particles, the only compensation is to increase the total power of the spray gun. However, with increased power, the plasma temperature rises, and the residence time in the high-temperature zone is prolonged, directly exacerbating the high-temperature oxygen loss reaction of Y2O3. This leads to problems such as coating performance degradation, increased wear and tear on spraying equipment, as mentioned in the background section.

[0027] External water-cooling structure characteristics: Existing spray guns generally place the cooling water channels outside the anode, separating the cooling water channels from the nozzle, which fails to achieve effective near-end cooling, resulting in low anode cooling efficiency. Under high-power spraying, this directly leads to anode temperatures often exceeding 500℃, far exceeding the optimal temperature range for copper materials under high-current discharge conditions. Prolonged exposure of the copper anode to high temperatures significantly accelerates thermal fatigue and ablation of the copper material, drastically reducing anode life (typically <10h). Simultaneously, the generated copper vapor and particles also contaminate the Y2O3 coating.

[0028] Characteristics of pure copper anode materials: Most existing spray guns use pure copper as the anode material. While it has good conductivity, it has a low melting point and weak resistance to ablation. Especially under high-power plasma spraying, the surface of the pure copper anode is prone to rapid erosion, forming copper vapor and particles that are injected into the plasma stream. These metallic contaminants eventually deposit inside the Y2O3 coating, reducing coating purity and insulation performance, failing to meet the stringent requirements of semiconductor equipment for high-purity ceramic coatings.

[0029] Simple tangential air intake characteristics: Existing spray guns typically employ a simple tangential air intake method, lacking a uniformly distributed ring structure to balance airflow distribution, resulting in a significant asymmetry in the gas flow field. Under uneven airflow conditions, the electric arc is prone to eccentric operation, forming localized high-temperature zones. Arc eccentricity not only exacerbates localized anode ablation but also causes uneven overheating of Y2O3 particles during spraying, leading to the formation of oxygen-depleted spots and ablation spots in the coating, thus compromising the coating's consistency and chemical properties.

[0030] It is known that existing laminar flow plasma spraying equipment suffers from inherent defects in the anode geometry, material selection, air intake organization, and cooling methods of the spray gun, leading to uncontrollable high-temperature oxygen loss in Y2O3. This makes it difficult to simultaneously achieve deposition efficiency, coating quality, and equipment lifespan under high-power spraying conditions. Therefore, it is necessary to redesign the anode nozzle geometry, material system, airflow distribution structure, and cooling path, focusing on the core objectives of "suppressing disturbances, extending the jet, and stabilizing the arc," to meet the requirements of "high power density, low oxygen loss, and long lifespan," ensuring the production of high-quality Y2O3 coatings that meet the stringent requirements of semiconductor applications even under low-to-medium power conditions.

[0031] Based on the above description, the technical solution of this invention application will be described as follows: Figure 1 This is a schematic diagram of the external outline of the double-tapered anode structure of the spray gun for laminar plasma spraying of yttrium oxide coating as shown in this invention. Figure 2 It is along Figure 1 A cross-sectional view along the AA direction. (See attached image.) Figure 1 and Figure 2 As shown, this invention provides a double-tapered anode structure for a special spray gun for laminar plasma spraying of yttrium oxide coating. The anode structure includes: a channel for injecting laminar plasma jet, the channel being a through hole extending parallel to the central axis of the anode structure; the through hole includes, sequentially connected: an inlet channel 2 for injecting the laminar plasma jet; a compression channel 3 for compressing the laminar plasma jet; and an outlet channel 4 for ejecting the laminar plasma jet; wherein, the inlet channel 2 includes a first tapered cavity 21 and a second tapered cavity 22, the second tapered cavity 22 being closer to the compression channel 3 than the first tapered cavity 21; wherein, the axial cross-section of both the first tapered cavity 21 and the second tapered cavity 22 is tapered, and the taper of the first tapered cavity 21 is smaller than the taper of the second tapered cavity 22.

[0032] Specifically, in a laminar flow plasma spray gun, the anode structure, which also serves as the nozzle, is located at the rear end of the spray gun. An arc zone exists between the cathode tip and the nozzle inlet. During operation, a high voltage is applied between the cathode and the nozzle (which acts as the anode), igniting the arc with a high-frequency spark. A working gas (such as argon, nitrogen, or a mixture thereof) is introduced into this zone to contact the arc, ionizing gas molecules or atoms to form a plasma composed of ions, electrons, and neutral particles. The inlet channel 2 serves as the inlet to the anode nozzle, located downstream of and connected to the arc zone. It receives the plasma arc formed between the cathode tip and the nozzle inlet and guides the high-temperature plasma arc into the channel within the anode structure. This channel, through the double-tapered inlet channel 2, compression channel 3, and outlet channel 4, achieves stable plasma flow and progressive compression, ultimately forming a high-energy-density laminar plasma jet, which is then ejected onto the workpiece from the outlet channel 4.

[0033] Specifically, the channel is a through-hole, used to allow the laminar plasma jet to be sprayed from the cathode end through the anode structure towards the workpiece. The through-hole is coaxial with the central axis of the anode structure, which reduces plasma arc eccentricity and ensures that the plasma jet is ejected directionally, at high speed, and stably along the axis. Based on the jet direction of the laminar plasma jet, the through-hole is divided into three sections from front to back, with each section corresponding to a different stage of plasma formation. The inlet channel 2 guides the initial accumulation of the plasma arc, the compression channel 3 compresses the plasma arc to increase the jet energy density, and the outlet channel 4 controls the stability and ejection shape of the jet. The three channels can be precision milled into a single piece using a CNC machine tool.

[0034] The improvement in this embodiment lies in the double-tapered design of the inlet channel 2. From front to back, there are a first tapered cavity 21 and a second tapered cavity 22, with the taper of the first tapered cavity 21 being smaller than that of the second tapered cavity 22. In this embodiment, the taper can be understood as the size of the cone angle of the tapered inlet channel 2, that is, the angle of inclination of the tangent of the inner wall of the inlet channel 2 relative to the central axis. The taper of the first tapered cavity 21 is smaller than that of the second tapered cavity 22. The plasma arc entering the inlet channel 2 is gradually accelerated through the double-tapered inlet. The first tapered cavity 21 first compresses the plasma arc to form a high-energy-density plasma jet, while the second tapered cavity 22 expands the plasma arc, reduces disturbance at the arc root, forms a slender arc column, and promotes stable adhesion of the arc within the compression channel 3. Within the compression channel 3, which is cylindrical with the smallest diameter, the plasma arc is mechanically compressed and thermally compressed by the cooling wall, significantly increasing the plasma energy density and forming a high-power-density laminar plasma jet. Therefore, when the plasma arc is introduced into the channel inside the anode structure, it is first compressed and then expanded, which can increase the power density while reducing the outlet temperature.

[0035] Preferably, the taper of the first tapered cavity 21 is 80°, and the taper of the second tapered cavity 22 is 120°. By accurately calculating the taper of the dual-tapered channels, a smooth transition of the plasma arc can be achieved, suppressing the generation of turbulence.

[0036] Therefore, compared to the numerous problems existing in traditional single-tapered straight cylindrical anode structures, the double-tapered straight cylindrical anode structure of this application forms a stable and slender arc column through gradient geometric compression, thermal compression, and magnetic compression of the anode channel, suppressing turbulent disturbances. Furthermore, external disturbances are reduced, and the arc length is controllable; in laminar flow mode, the arc length can reach 500 mm, far exceeding the plasma jet length (30-50 mm) in turbulent flow mode. The long laminar plasma jet extends the flight path of the sprayed powder (such as Y2O3 particles) in the plasma arc, increasing the particle residence time by 5 times, and allowing for more complete energy absorption by the particles. Simultaneously, the arc compresses and expands significantly with the change in current, resulting in concentrated plasma power density. Under the same power, the powder is melted more fully, thus achieving deep melting of the powder without increasing the total power. This avoids excessively high overall temperature caused by increasing power and reduces the exit temperature without jet instability. Consequently, it significantly reduces the oxygen loss of Y2O3 particles caused by excessively high temperature during high-power spraying, thereby solving problems such as performance degradation, stoichiometric deviation, and anodic ablation of the Y2O3 coating.

[0037] Thus, the anode structure of the laminar plasma spray gun for Y2O3 coating provided in this embodiment can maintain high power density spraying while suppressing high-temperature oxygen loss. Using this technology, a high-quality Y2O3 coating with an oxygen loss area of ​​no more than 2% can be prepared in a single pass at a power of 14-16kW, meeting the technical requirements of continuous production. This technology is particularly suitable for spraying critical protective coatings on semiconductor etching cavities, meeting the stringent requirements of the semiconductor industry for high purity, high insulation, and low defects. Of course, this design also has universal reference value for the spraying process of high-melting-point, easily decomposed materials.

[0038] Furthermore, the wall surface surrounding the cavity wall forming the first tapered cavity 21 extends in a straight line inclined away from the central axial direction; the wall surface surrounding the cavity wall forming the second tapered cavity 22 protrudes arc-shaped towards the central axis. In this embodiment, the cavity wall surface of the first tapered cavity 21 opens outward in a straight line along the axial direction. The cavity wall surface of the second tapered cavity 22 protrudes inward in an arc shape along the axial direction, having an arc angle, as marked R1 in the figure. Therefore, the second tapered cavity 22 adopts an arc-shaped transition wall structure, with its wall curvature continuously changing. Based on fluid dynamics optimization design considerations, it achieves smooth expansion, high energy concentration, and low turbulence growth, thereby ensuring the formation of a stable slender electric arc column.

[0039] Furthermore, both the compression channel 3 and the outlet channel 4 are cylindrical, with the outlet channel 4 having a larger diameter than the compression channel 3. The compression channel 3 and the outlet channel 4 are cylindrical channels (i.e., cylindrical straight holes) of equal diameter in the axial direction, with their axes coaxial with the central axis of the anode. The walls surrounding the compression channel 3 and the outlet channel 4 are parallel to the central axis. The compression channel 3 causes the plasma arc to be contracted in this section, significantly increasing the energy density and central velocity. Simultaneously, the outlet channel 4 has a larger cylindrical diameter than the compression channel 3, thus increasing the power density and reducing the outlet temperature as the plasma jet, efficiently compressed within the compression channel 3, exits and enters the outlet channel 4 before being ejected.

[0040] Through the above design, the plasma jet can maintain a longer accumulation state after leaving the nozzle, forming a laminar plasma jet. This jet length can reach 500 mm. The residence time of powder particles in this long and stable laminar plasma jet is extended several times, allowing more time to absorb heat and completely melt. The fully melted particles impact the workpiece, forming a denser coating with higher bonding strength. The aperture of the outlet channel 4 is larger than that of the compression channel 3, allowing the powder temperature to decrease and the flow rate to further increase at the outlet channel 4, thus reducing the exit temperature of the powder particles. Especially for Y2O3 powder, the controlled heating process effectively reduces oxygen loss due to overheating, lowering the peak surface temperature of the Y2O3 particles, reducing the oxygen escape rate, and minimizing irreversible oxygen loss reactions, thereby ensuring the chemical stability and protective performance of the Y2O3 coating.

[0041] In another technical solution, the anode structure includes an anode shell 1 surrounding the through hole, the anode shell 1 comprising a copper-tungsten composite material. Compared to traditional anode materials using pure copper, which only considers thermal conductivity but has a low melting point, high evaporation / ablation rate, insufficient mechanical strength, and copper vapor or particles being drawn into the plasma jet, contaminating the coating, the anode shell 1 in this embodiment is made of a copper-tungsten composite material, or includes a combination of copper-tungsten composite material or other metal materials. Tungsten has a high melting point and is almost not ablated. Copper, on the other hand, has high thermal conductivity, which can quickly remove the high heat generated by the anode. Therefore, this embodiment utilizes the high melting point and ablation resistance of tungsten and the high thermal conductivity of copper, balancing thermal conductivity and high-temperature ablation resistance, effectively reducing the anode surface temperature under high-power plasma spraying conditions, inhibiting anode ablation and metal evaporation, thereby reducing particulate contamination of the coating and significantly extending the anode's service life.

[0042] Preferably, the anode shell 1 includes an inner shell 11 and an outer shell 12. The outer shell 12 is fitted around the outer periphery of the inner shell 11, and the inner wall surface of the inner shell 11 forms the through hole. The inner shell 11 is made of tungsten, and the outer shell 12 is made of a composite of chromium, zirconium, and copper. In this embodiment, the inner shell 11 is made of pure tungsten, and the outer shell 12 is a composite material made of copper, zirconium, and copper, thus forming a copper-tungsten gradient composite structure from the inside out. Because the inner shell 11 forms the channel inside the anode structure, the pure tungsten inner shell 11 directly bears the arc heat load, resulting in higher resistance to ablation. The chromium-zirconium-copper outer shell 12 maintains high thermal conductivity, enabling the anode to dissipate heat quickly and forming a stable thermal compression effect. The inner and outer shells adopt a gradient composite structure from tungsten to copper. Compared with a simple copper-tungsten composite structure or a pure copper structure, the spray gun can form a stable laminar plasma jet with a length of up to 500mm. The particle residence time is increased by 3-5 times. Direct cooling is not required. Under high-power spraying conditions, Y2O3 particles are fully melted without oxygen loss. At the same time, the anode life is greater than 25 hours (currently 12 hours).

[0043] This structure can also be disassembled and assembled using a universal wrench, which also makes it easy to install.

[0044] It can be understood that the wall surface of each channel is the inner wall surface of the inner shell 11. Specifically, the outer wall surface of the inner shell 11 extends vertically in the axial direction and is press-fitted or brazed to the inner wall surface of the outer shell; the outer shell 12 includes an integrally formed conical section and a straight cylindrical section. The outer wall surface of the conical section gradually extends outward from the inlet channel 2 towards the outlet channel 4, and then joins the straight cylindrical section. The straight cylindrical section surrounds a part of the compression channel 3 and the outlet channel 4.

[0045] In this embodiment, the outer wall of the pure tungsten inner shell 11 is cylindrical for easy processing and installation, and the inner wall is machined to form the through hole mentioned above. The inner wall of the chromium-zirconium-copper outer shell 12 is also cylindrical and is directly attached to the outer wall of the pure tungsten inner shell 11. The two can be connected by press fitting or brazing to ensure that the high heat generated by the inner tungsten can be quickly transferred to the outer copper for heat dissipation. The inner and outer shells form a tight and stable whole with high structural strength and improved resistance to plasma thermal shock. Then, the outer shell 12 is integrally machined to form a conical section and a cylindrical section. The conical section can be used for hydrodynamic control to obtain a laminar plasma jet and stabilize the laminar plasma jet, avoiding turbulence ejected from the outlet channel 4. The cylindrical section corresponds to the outlet channel 4 and the rear section of the compression channel 3 above the outlet channel 4. The cylindrical section has better thermal conductivity, further protecting the nozzle life.

[0046] In some embodiments, a cooling water distribution ring 5 can be integrated into the straight section. Correspondingly, the anode structure also includes a cooling water distribution ring 5, within which a spiral water groove is formed for the flow of cooling water; wherein, the cooling water distribution ring 5 is embedded within the anode shell 1 and integrally formed with the anode shell 1. In this embodiment, the integrated design of the cooling water distribution ring 5 and the nozzle improves heat dissipation efficiency and extends service life. The integrated anode gun body design also reduces connection gaps, improving sealing and thermal stability. A powder feeding port can be provided near the nozzle inlet, with the angle of the powder feeding port controlled between 0° and ±5° to ensure precise injection of the sprayed powder into the core area of ​​the plasma jet.

[0047] In another embodiment, a gas distribution ring (not shown in the figure) can be installed at the nozzle inlet channel 2 to ensure that the airflow is evenly distributed before entering the arc zone, reduce disturbance to the plasma arc, and control the plasma arc to always be in a centered position, avoiding arc eccentricity. In this embodiment, it can also be used in conjunction with an adjustable swirl vane. With the adjustable swirl vane, tangential air intake can form a swirling flow, enhancing arc stability; axial direct current air intake is suitable for laminar flow mode, reducing lateral disturbance.

[0048] In conjunction with the above embodiments, the spiral water groove of the cooling water distribution ring 5 can be designed to extend spirally along the axial direction within the outer shell 12, reducing the wall temperature of the anode shell 1 to less than 350°C. The use of a gas distribution ring to uniformly deliver the working gas into the plasma arc allows a stable, slender arc column to enter the inlet channel 2 of the anode structure, thereby improving the uniformity of the coating thickness obtained by spraying.

[0049] In summary, this embodiment optimizes key parameters such as the flow field distribution, compression angle, expansion angle, channel length ratio, and the coupling relationship between aperture and flow velocity within the plasma jet. The goal is to achieve a stable laminar plasma jet with smooth airflow transition and suppression of turbulence. After precise fluid dynamics calculations and multiple rounds of simulation optimization, the characteristic parameters of the anode structure are determined as follows: The diameter of the first tapered cavity 21 is 9 mm, and its axial extension length is 1.5 mm; the diameter of the compression channel 3 is 4 mm-5 mm; the axial extension lengths of the outer shell 12, the inner shell 11, and the through hole are all 40 mm; the diameter of the inclined beginning of the tapered section of the outer shell 12 is 12 mm, the diameter of the inclined end is 14 mm, and the axial extension length is 32.7 mm; the diameter of the straight section of the outer shell 12 is 16 mm. Through the double-tapered anode structure provided in this embodiment of the invention, the channels within the anode structure formed by the double-tapered inlet channel 2, compression channel 3, and outlet channel 4 enable high-power-density spraying at low to medium power (14-16 kW), allowing particles to melt in a short time, while simultaneously reducing the exit temperature of the plasma jet and decreasing the oxygen escape rate, thereby effectively suppressing irreversible oxygen loss from Y2O3. Furthermore, laminar plasma jets exhibit low noise, with an operating noise level of only 69-83 dB, far lower than the 130 dB of turbulent jets. The jet boundaries are clear, airflow disturbances are minimal, and radial diffusion is low, resulting in a highly directional, long-distance laminar plasma beam.

[0050] The technical solution of the present invention will be described in more detail below with reference to the embodiments.

[0051] Correspondingly, in a second aspect, the present invention provides a method for preparing a Y2O3 coating by laminar plasma spraying using the double-tapered anode structure of the special spray gun for laminar plasma spraying of yttrium oxide coating provided in the first aspect of the present invention. This method includes six steps: (1) Powder preparation Spherical granulated powder with a particle size of 5-100µm, 99.95% Y2O3, single cubic phase, was vacuum dried at 120°C for 2 hours for later use.

[0052] (2) Substrate pretreatment Clean the substrate and dry it with hot air; The substrate is sandblasted using white corundum with a particle size of 50-100µm, at a pressure of 0.4-0.6MPa, and with a Ra of 3-5µm.

[0053] (3) Laminar flow plasma spraying system settings Coating powder: 99.95% Y₂O₃ spherical powder with a particle size of 5-100µm. Working gas: Main / auxiliary gas is Ar (4Lmin). -1 ) / N2 (5Lmin) -1 Voltage / Current: 100V / 120A. Power: 16kW. Powder Feeding Rate: 6gmin -1 Spraying distance: 220mm. Scanning speed: 500mm / s -1Substrate preheating: 220℃. Single pass thickness: ≈20µm. Total thickness: 200µm.

[0054] (4) Spraying implementation The invention employs a double-tapered anode structure, using a 30s Ar-based low-power arc-starting and slow-rise current to avoid instantaneous high-temperature oxygen entrapment. This ensures uniform thickness and prevents thermal stress cracking. The speed of the robotic arm or turntable is controlled at 300-800 mm / s. -1 Each coat is 10-30µm thick, with a total thickness of 100-300µm, and is applied in multiple layers.

[0055] (5) Post-processing Turn off the spraying system, keep purging with Ar for 2 minutes, and allow it to cool naturally to below 50°C to suppress cracking.

[0056] To seal the pores, vacuum annealing at 120℃ for 2 hours and saturated solution impregnation were performed to reduce the porosity of the coating.

[0057] (5) Quality inspection The porosity of the Y2O3 coating was determined by metallographic / SEM image analysis; the bond strength of the Y2O3 coating was determined by the ASTM C633 tensile test; the phase composition of the Y2O3 coating was determined by XRD analysis; and the surface roughness of the Y2O3 coating was determined by Ra analysis.

[0058] The above method embodiments are basically similar to the system embodiments, so the description is relatively simple. For relevant details, please refer to the description of the system embodiments.

[0059] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0060] It should also be noted that, in this document, the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations, nor should they be construed as indicating or implying relative importance. Moreover, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device.

[0061] The foregoing has provided a detailed description of the dual-tapered anode structure of a special spray gun for laminar plasma spraying of yttrium oxide coatings provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are merely for the purpose of helping to understand this application, and the content of this specification should not be construed as a limitation of this application. Furthermore, those skilled in the art will recognize that various modifications and variations in specific implementation methods and application scope may occur based on this application. It is neither necessary nor possible to exhaustively list all implementation methods here, but obvious variations or modifications derived therefrom are still within the protection scope of this application.

Claims

1. A double-tapered anode structure for a special spray gun for laminar plasma spraying of yttrium oxide coating, characterized in that, The anode structure includes: a channel for supplying laminar plasma jet injection, the channel being a through hole extending parallel to the central axis of the anode structure; the through hole includes sequentially connected: An inlet channel for injecting the laminar plasma jet; Compression channels are used to compress the laminar plasma jet; An outlet channel for ejecting the laminar plasma jet; The inlet channel includes a first tapered cavity and a second tapered cavity, wherein the second tapered cavity is closer to the compression channel than the first tapered cavity; The axial cross-sections of the first and second tapered cavities are both tapered, and the taper of the first tapered cavity is smaller than that of the second tapered cavity.

2. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating as described in claim 1, characterized in that, The first tapered cavity has a taper of 80°, and the second tapered cavity has a taper of 120°.

3. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating as described in claim 1, characterized in that, The wall surface surrounding the cavity wall forming the first tapered cavity extends in a straight line at an angle away from the central axis; the wall surface surrounding the cavity wall forming the second tapered cavity protrudes in an arc shape towards the central axis.

4. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating as described in claim 1, characterized in that, Both the compression channel and the outlet channel are cylindrical, and the diameter of the outlet channel is larger than that of the compression channel.

5. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating according to any one of claims 1-4, characterized in that, The anode structure includes an anode shell surrounding the through hole, the anode shell comprising a copper-tungsten composite material.

6. The double-tapered anode structure of a special spray gun for laminar plasma spraying of yttrium oxide coating according to claim 5, characterized in that, The anode shell includes an inner shell and an outer shell, the outer shell is sleeved on the outer periphery of the inner shell, and the inner wall surface of the inner shell forms the through hole. The inner shell is made of tungsten material, and the outer shell is made of a composite of copper, zirconium and copper materials.

7. The double-tapered anode structure of a special spray gun for laminar plasma spraying of yttrium oxide coating according to claim 6, characterized in that, The outer wall of the inner shell extends vertically in the axial direction and is press-fitted or brazed to the inner wall of the outer shell; the outer shell includes an integrally formed conical section and a straight cylindrical section, the outer wall of the conical section gradually extends outward from the inlet channel to the outlet channel and then joins the straight cylindrical section, the straight cylindrical section surrounds a part of the compression channel and the outlet channel.

8. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating according to claim 7, characterized in that, The first tapered cavity has a diameter of 9 mm and an axial extension length of 1.5 mm; the compression channel has a diameter of 4 mm-5 mm; the outer shell, the inner shell, and the through hole all have an axial extension length of 40 mm; the outer shell has a tapered section with an inclined starting end diameter of 12 mm, an inclined ending end diameter of 14 mm, and an axial extension length of 32.7 mm; and the outer shell has a straight section with a diameter of 16 mm.

9. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating according to claim 5, characterized in that, The anode structure further includes a cooling water distribution ring, in which a spiral water groove is formed for the flow of cooling water; wherein, the cooling water distribution ring is embedded in the anode shell and is integrally formed with the anode shell.

10. The double-tapered anode structure of a laminar flow plasma spray gun for yttrium oxide coating according to claim 5, characterized in that, The anode structure also includes: A gas distribution ring is provided at the inlet channel of the anode shell to uniformly distribute the working gas before sending it into the arc zone.

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