Preparation method of inner and outer wall assembly of liquid engine jet pipe

Abstract

The invention discloses a preparation method of an inner and outer wall assembly of a liquid engine nozzle, which comprises the following steps: carrying out laser printing on copper alloy powder to obtain a copper alloy nozzle inner wall blank; the copper alloy spray pipe inner wall blank is machined, and a semi-finished spray pipe inner wall with a channel in the surface is obtained; the inner wall of the semi-finished spray pipe is subjected to surface modification treatment, and the inner wall of the semi-finished spray pipe subjected to surface modification is obtained; assembling and welding the surface-modified inner wall of the semi-finished spray pipe and a cooling ring to obtain the inner wall of the spray pipe with the cooling ring; and the inner wall of the spray pipe with the cooling ring is subjected to cladding treatment, and the inner and outer wall composite spray pipe assembly is obtained. Various performances of the inner wall of the jet pipe of the liquid rocket engine can be improved, and the reliability of the jet pipe in an extreme working environment is improved.

Description

Technical Field

[0001] This application belongs to the field of additive manufacturing technology, specifically relating to a method for preparing an inner and outer wall assembly of a liquid engine nozzle. Background Technology

[0002] Existing methods for fabricating the inner wall of liquid rocket engine nozzles are mainly divided into two categories: traditional fabrication techniques and additive manufacturing techniques. Traditional fabrication techniques primarily include processes such as smelting, forging, machining, and welding. These techniques are the mainstream manufacturing methods for liquid rocket engine nozzle components due to their high maturity and reliability. However, the main drawbacks of traditional methods are low material utilization and a significant weakening of the inner and outer wall performance after welding. Furthermore, welding technology is highly complex, and only a few companies possess this skill, leading to a supply shortage in the rocket engine market. In recent years, additive manufacturing technology has gradually gained attention due to its advantages such as high design freedom, high material utilization, rapid prototyping, customized production, and improved performance. Additive manufacturing technology shows significant advantages, especially in fabricating nozzles with complex structures such as internal cooling channels and variable cross-sections. The process of additively manufacturing nozzle inner and outer wall components typically includes steps such as model design, powder preparation, inner wall printing, post-processing, and outer wall deposition. However, despite the theoretical and experimental successes demonstrated by additive manufacturing technology, there are currently no successful cases, either domestically or internationally, of using additive manufacturing to fabricate inner and outer walls and launch rockets. This is primarily due to technical challenges such as high surface roughness of the rib grooves and nozzle deformation caused by excessive energy input. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the purpose of this application is to provide a method for manufacturing the inner and outer wall components of a liquid engine nozzle. This application aims to improve the various properties of the inner wall of a liquid rocket engine nozzle and enhance its reliability under extreme working environments.

[0004] To achieve the above objectives, this application provides the following technical solution: A method for preparing an inner and outer wall assembly of a liquid engine nozzle, the method comprising: laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank; machining the copper alloy nozzle inner wall blank to obtain a semi-finished nozzle inner wall with grooves on the surface; performing surface modification treatment on the semi-finished nozzle inner wall to obtain a surface-modified semi-finished nozzle inner wall; assembling and welding the surface-modified semi-finished nozzle inner wall with a cooling ring to obtain a nozzle inner wall with a cooling ring; and performing cladding treatment on the nozzle inner wall with the cooling ring to obtain a nozzle assembly with composite inner and outer walls.

[0005] Optionally, the step of laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank includes: constructing a three-dimensional model of the inner wall of the copper alloy nozzle to be formed and importing it into an SLM printer; printing copper alloy powder based on the three-dimensional model; and obtaining the copper alloy nozzle inner wall blank after printing is completed.

[0006] Optionally, the step of laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank further includes: performing differentiated cooling on each region of the copper alloy nozzle inner wall blank.

[0007] Optionally, before laser printing the copper alloy powder, the copper alloy powder is pretreated, the pretreatment including: drying and cooling the copper alloy powder; cleaning the cooled copper alloy powder; sieving the cleaned copper alloy powder; and storing the sieved copper alloy powder.

[0008] Optionally, the step of laser printing based on copper alloy powder to obtain a copper alloy nozzle inner wall blank further includes: heat treating the copper alloy nozzle inner wall blank.

[0009] Optionally, the copper alloy nozzle inner wall blank is machined to obtain a semi-finished nozzle inner wall with grooves on the surface, including: rough machining of the copper alloy nozzle inner wall blank; fine machining of the rough-machined copper alloy inner wall blank; and grooving and finishing of the inner wall surface of the fine-machined copper alloy blank.

[0010] Optionally, the copper alloy nozzle inner wall blank is machined to obtain a semi-finished nozzle inner wall with grooves on the surface, and the process further includes cooling the semi-finished nozzle inner wall obtained after machining.

[0011] Optionally, assembling and welding the surface-modified semi-finished nozzle inner wall with the cooling ring to obtain a nozzle inner wall with a cooling ring includes: butt-jointing the cooling ring with the surface-modified semi-finished nozzle inner wall; setting welding parameters and performing welding; inspecting and cleaning the weld; and performing post-processing on the welded nozzle and cooling ring.

[0012] Optionally, the post-processing of the welded nozzle and cooling ring includes: annealing the welded nozzle and cooling ring; stress-relieving heat treatment of the annealed nozzle and cooling ring; and homogenization cooling treatment of the stress-relieving heat-treated nozzle and cooling ring.

[0013] Optionally, the process of cladding the inner wall of the nozzle with a cooling ring to obtain a nozzle assembly with composite inner and outer walls includes: preheating the inner wall of the nozzle with a cooling ring; uniformly coating the inner wall surface of the nozzle with cladding material and cladding the cladding material with a laser, while cooling the inner wall of the nozzle during the cladding process.

[0014] Compared with the prior art, the beneficial effects of this application are as follows: This application utilizes laser printing technology to precisely manufacture copper alloy nozzle inner wall blanks, and then machines them into semi-finished nozzle inner walls with grooves, effectively improving the geometric accuracy of the nozzle inner wall and the feasibility of complex structural designs. Surface modification treatment enhances the nozzle's wear resistance and corrosion resistance, improving its operational stability under high temperature and pressure environments. Cladding treatment improves the surface quality and durability of the nozzle inner wall, ensuring a tight bond between the nozzle and the cooling ring. This application overcomes the limitations of traditional manufacturing technologies, improving the functionality, reliability, and production efficiency of nozzles, and providing a novel technological path for the efficient manufacturing of liquid rocket engine nozzles. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of a method for preparing an inner and outer wall assembly of a liquid engine nozzle according to an embodiment of this application; Figure 2 This is a cross-sectional view of the copper alloy nozzle inner wall blank provided in another embodiment of this application; Figure 3 This is a cross-sectional view of the inner wall of a semi-finished nozzle provided in another embodiment of this application; Figure 4 This is a schematic diagram of the upper cooling ring provided in another embodiment of this application; Figure 5 This is a schematic diagram of the lower cooling ring provided in another embodiment of this application; Figure 6 This is a front view of the nozzle inner wall after surface modification, provided in another embodiment of this application; Figure 7 This is a top view of the inner wall of the nozzle after surface modification, provided in another embodiment of this application; Figure 8 This is a schematic diagram of an inner and outer wall assembly of a nozzle with an upper cooling ring and a lower cooling ring, provided in another embodiment of this application. Detailed Implementation

[0016] Specific embodiments of this application will now be described in detail with reference to the accompanying drawings. While specific embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.

[0017] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0018] To facilitate understanding of the embodiments of this application, the following will provide further explanation and description with reference to the accompanying drawings and specific embodiments, and the accompanying drawings do not constitute a limitation on the embodiments of this application.

[0019] Figure 1 This is a schematic flowchart illustrating a method for preparing an inner and outer wall assembly of a liquid engine nozzle according to an embodiment of this application. Figure 1 As shown, the method includes the following steps: S100: Laser printing is performed on copper alloy powder to obtain a copper alloy nozzle inner wall blank, wherein the copper alloy atomized powder includes any one of CuCr, CuCrZr or CuCrNb; S200: The copper alloy nozzle inner wall blank is machined to obtain a semi-finished nozzle inner wall with grooves on the surface; S300: Perform surface modification treatment on the inner wall of the semi-finished nozzle to obtain a surface-modified inner wall of the semi-finished nozzle; S400: The surface-modified semi-finished nozzle inner wall is assembled and welded with the cooling ring to obtain a nozzle inner wall with a cooling ring; S500: The inner wall of the nozzle with a cooling ring is clad to obtain a nozzle assembly with composite inner and outer walls.

[0020] In another exemplary embodiment, step S100, which involves laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank, includes the following steps: S101: A three-dimensional model of the inner wall of the copper alloy nozzle to be formed is constructed using computer-aided design software (such as CAD) and imported into an SLM printer; In this step, after placing the substrate plate for printing on the inner wall of the nozzle, the printing chamber of the SLM printer is evacuated to a vacuum level between 0.01 Pa and 5 Pa. Then, argon gas is introduced into the printing chamber as a protective gas. Subsequently, copper alloy powder is loaded into the powder hopper of the SLM printer, and printing parameters are set (e.g., laser power of 400W, scanning speed of 1000mm / s, and powder thickness of 30μm).

[0021] S102: Printing copper alloy powder based on a 3D model; In this step, copper alloy powder is printed layer by layer using laser to gradually build the shape of the nozzle inner wall that conforms to the three-dimensional model. After printing is completed, a nozzle inner wall shape is obtained. Figure 2 The copper alloy nozzle inner wall blank shown.

[0022] S103: Differentiated cooling strategies are applied to different areas of the copper alloy nozzle inner wall blank.

[0023] In this step, after printing is completed, the blank on the inner wall of the nozzle needs to be cooled. Specifically, this application introduces a multi-strategy cooling method to ensure that the temperature of each area of ​​the blank on the inner wall of the nozzle can be uniformly and precisely controlled during the cooling process. The cooling method includes the following steps: Step 1: Install multiple temperature sensors on the inner wall blank of the copper alloy nozzle, especially in critical high-temperature areas (such as nozzle outlet, rib groove, etc.). Step 2: By collecting sensor data, the optimal cooling rate for each region is automatically calculated. For example, the nozzle inlet temperature is 800°C, and the target cooling rate is set to 5°C / min. To quickly reduce the inlet temperature, the airflow rate can be increased to 4 m / s (e.g., adjusting the fan or nozzle) to remove heat more quickly. The main wall region temperature is 1200°C, and the target cooling rate is 10°C / min. Due to the relatively high temperature in the main wall region, the system needs to increase the cooling rate, so the airflow rate is increased to 12 m / s. At this point, strong airflow accelerates cooling, ensuring a rapid drop in surface temperature and preventing deformation due to excessive heat. The rib region temperature is 1500°C, and the target cooling rate is 2°C / min. Due to the complexity of its shape, the rib region requires a very slow cooling rate. To avoid excessive thermal stress, the system reduces the airflow rate to 1.5 m / s to slowly remove heat. The nozzle outlet temperature is 1000°C, and the target cooling rate is 8°C / min. To cool the nozzle exit without causing deformation, the system increases the airflow rate to 6 m / s to dissipate heat more quickly and ensure nozzle stability.

[0024] It should be noted that different cooling rates are used for different regions of the nozzle to optimize performance based on the temperature requirements, material properties, and structural complexity of each region. Different parts of the nozzle face varying heat loads during operation; excessively rapid or slow cooling can lead to thermal stress, deformation, or cracking. Differentiated cooling rates effectively control temperature distribution, preventing localized overheating or undercooling, thereby improving the nozzle's thermal management efficiency, extending its service life, and ensuring its stability and reliability under high-temperature and high-pressure environments.

[0025] In another exemplary embodiment, in step S100, before laser printing the copper alloy powder, the copper alloy powder is pretreated, and the pretreatment includes the following steps: S1001: Drying and cooling copper alloy powder; In this step, the copper alloy powder is first placed in a vacuum drying oven and dried at 80°C to 120°C for 4 to 8 hours to fully remove residual moisture and trace amounts of volatile organic compounds from the powder surface and pores. After drying, the powder is slowly cooled in the furnace to prevent microcracks caused by particle size stress due to rapid cooling.

[0026] S1002: Plasma cleaning of cooled copper alloy powder; In this step, the dried and cooled copper alloy powder is introduced into a plasma chamber. A low-temperature argon plasma stream is used to physically etch and activate the surface of the cleaned copper alloy powder. (High-purity argon gas is introduced into the plasma chamber, and a high-frequency voltage is applied to generate low-temperature plasma. Argon ions (Ar+) collide with the copper alloy powder surface, physically etching away the oxide film and surface impurities, exposing a clean metal surface. During this process, the impact of plasma particles also causes micro-roughening of the copper alloy powder surface, thereby increasing surface activity and providing better bonding for powder melting in subsequent laser printing.) This removes the oxide film and adsorbed impurities from the powder surface, improves its melting uniformity and bonding activity under laser irradiation, and enhances the forming density.

[0027] S1003: Loosening treatment of copper alloy powder after plasma cleaning; In this step, the plasma-cleaned copper alloy powder is first placed in a dedicated loosening treatment tank filled with an appropriate amount of solvent (such as deionized water or alcohol solvent) to reduce the electrostatic attraction between the powder particles and to facilitate the propagation of ultrasonic waves. Next, the ultrasonic cleaning equipment is turned on. The ultrasonic waves (with a frequency set to 20kHz to 40kHz and an amplitude set to 15μm to 25μm) propagate through the solvent, generating high-frequency pressure waves and bubble oscillations between the powder particles, creating strong micro-vibrations. These micro-vibrations cause the powder particles to collide and separate, breaking up the aggregated powder particles and restoring them to a single particle state.

[0028] Simultaneously, resonance improves the sphericity consistency of the powder, thereby enhancing powder spreading and powder feeding uniformity.

[0029] It is important to note that the loosening treatment time is generally 20 to 40 minutes. If the ultrasonic treatment time is too short, the powder particles may not be sufficiently deagglomerated, while if the time is too long, the powder particles may break or be excessively deagglomerated, affecting their morphology and quality.

[0030] It is important to note that if the copper alloy powder is not loosened after plasma cleaning, it is prone to agglomeration during laser printing, where multiple copper alloy powder particles stick together to form large clumps. This affects the flowability and uniformity of the copper alloy powder, resulting in uneven powder distribution on the print bed and causing printing defects such as porosity, incomplete fusion, or localized overheating. Simultaneously, agglomerated powder may affect the laser melting effect, leading to uneven surface quality on the nozzle inner wall and even affecting the strength and bonding performance of the cladding layer. Furthermore, poor powder sphericity will also affect the efficiency of the powder feeding system, causing unstable powder feeding and further reducing printing accuracy and quality. Therefore, loosening treatment is a crucial step in ensuring powder uniformity and printing accuracy; neglecting this step will severely impact the final nozzle quality.

[0031] S1004: Screening of copper alloy powder after loosening treatment; In this step, the loosened copper alloy powder can be sieved sequentially through 400-mesh and 800-mesh high-precision screens, and an adjustable vibration amplitude sieve machine can be used to remove excessively coarse and ultrafine powders, retaining only the main distribution powder of about 40μm to 50μm, so as to form a narrow particle size distribution that is more suitable for SLM melting and cold spray deposition, thereby improving the forming accuracy and strength of the copper alloy nozzle inner wall blank.

[0032] S1005: The sieved copper alloy powder is stored in an inert gas atmosphere.

[0033] In this step, the sieved copper alloy powder is immediately packed into a highly airtight aluminum foil bag and placed in a sealed container filled with argon gas for static storage, controlling the residual oxygen concentration to be <0.5%, so as to ensure that the copper powder is always in a low-oxygen, high-purity environment before use and to inhibit surface re-oxidation.

[0034] In summary, pretreatment removes moisture, oxides, and organic matter from the surface of copper alloy powder, thereby improving its flowability and melting uniformity. This ensures that the copper alloy powder melts uniformly and forms a good bond with the substrate during laser printing. Specifically, plasma cleaning removes oxide layers and surface impurities, increasing the surface activity of the copper alloy powder and providing better adhesion for laser melting. Furthermore, powder loosening treatment eliminates copper alloy agglomeration, making it more suitable for uniform powder spreading and spraying. Without pretreatment, copper alloy powder may experience uneven melting during laser printing due to surface oxidation or excessive impurities, leading to defects such as porosity, incomplete fusion, or poor bonding. This affects the quality and performance of the final nozzle inner wall, and may even weaken the structure, reducing the nozzle's lifespan and reliability.

[0035] In another embodiment, step S100, which involves laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank, further includes: heat-treating the copper alloy nozzle inner wall blank.

[0036] In this embodiment, the heat treatment of the copper alloy nozzle inner wall blank specifically includes the following steps: Step 1: Preheat the copper alloy nozzle inner wall blank; In this step, during the preheating stage, the blank is slowly heated to 320°C at a heating rate of 5°C / min and held at this temperature for 30 minutes. This process aims to release residual thermal stress and processing stress caused by rapid cooling and localized remelting of the molten pool during printing. This process effectively prevents stress concentration cracking during subsequent high-temperature processing and helps maintain fine grain size, creating basic conditions for uniform precipitation of the precipitate.

[0037] Step 2: Perform medium-temperature homogeneous diffusion treatment on the preheated copper alloy nozzle inner wall blank; In this step, the billet is heated from 320°C to a medium temperature range of 370°C to 390°C, and a temperature oscillation heat preservation treatment is performed within this range. The specific method of the temperature oscillation heat preservation treatment is to perform periodic temperature fluctuation adjustment within a range of ±5°C, with each thermal cycle lasting about 30 minutes, and the entire stage lasting about 2 hours.

[0038] Temperature disturbance can accelerate the migration and dispersion of alloying elements in the crystal lattice, while promoting the uniform precipitation of fine strengthening phases. This can effectively avoid segregation and agglomeration of coarse particles in the billet under static isothermal conditions, thereby improving the consistency of the billet structure and the basic mechanical properties.

[0039] Step 3: Aging treatment is performed on the copper alloy nozzle inner wall blank after medium-temperature homogeneous diffusion treatment; In this step, the copper alloy nozzle inner wall blank, after medium-temperature homogeneous diffusion treatment, is further heated to 520℃ and maintained at a constant temperature for 3 hours to enter the main aging strengthening stage. At this temperature, strengthening elements such as Cr and Zr in the copper alloy precipitate in nanoscale form as dispersed phases, effectively pinning dislocations and improving the high-temperature strength and creep resistance of the blank.

[0040] Step 4: Anneal and cool the copper alloy nozzle inner wall blank after aging treatment.

[0041] In this step, after the heat treatment holding stage is completed, the billet is cooled in the furnace to approximately 300°C and then subjected to zoned controlled cooling. During this stage, controlled-flow slow-cooling air is introduced into the rib area (cooling rate controlled within 0.5°C / min), while the main wall area continues to be cooled naturally in the furnace (approximately 1.5°C / min). This differential cooling method maintains the ductility of the rib area, avoiding brittleness or structural warping caused by heat input during subsequent cold spraying or laser cladding. Simultaneously, it allows the strengthening microstructure of the main wall area to fully emerge, achieving a gradient distribution of strength and toughness, which contributes to the stable improvement of the overall structural performance in the future.

[0042] In summary, the heat treatment method employed in this application, through a phased, multi-parameter precisely controlled process path, enables comprehensive optimization of the microstructure and properties of the copper alloy nozzle inner wall blank after SLM printing. Specifically, the initial low-temperature holding helps release residual printing stress and prevents microcracks from forming during subsequent heat treatment; the temperature oscillation-based holding in the mid-temperature zone breaks the limitations of traditional isothermal aging, promoting uniform diffusion of alloying elements and dispersed precipitation of fine precipitates, thus improving microstructure consistency and deposition stability; the high-temperature aging stage allows for sufficient precipitation of strengthening phases, significantly enhancing the high-temperature mechanical properties and thermal fatigue resistance of the blank; and the introduction of a zoned differentiated temperature control strategy during cooling not only preserves the flexibility of the rib groove area and avoids cladding deformation, but also ensures sufficient deposition of strengthening phases in the main wall area, achieving optimal structural differentiation and synergistic performance.

[0043] In another exemplary embodiment, step S200 involves machining the copper alloy nozzle inner wall blank to obtain a semi-finished nozzle inner wall with grooves on its surface, including the following steps: S201: Fix the copper alloy nozzle inner wall blank on the machining table of the CNC machine tool to ensure the precise positioning of the blank, and use a roughing tool to perform preliminary cutting on the blank to remove most of the excess material.

[0044] During rough machining, it is crucial to carefully control the depth of cut and feed rate to minimize heat buildup and prevent deformation caused by thermal stress in the workpiece. Rough machining creates the necessary conditions for subsequent finish machining, ensuring the basic shape and dimensions of the inner wall surface.

[0045] S202: After rough machining, use a finishing tool to perform fine cutting on the inner wall of the nozzle.

[0046] This step optimizes cutting parameters (such as a lower feed rate and appropriate cutting depth) to ensure that the inner wall surface of the nozzle is smooth, uniform, and free of obvious scratches or surface defects.

[0047] S203: After the inner wall is finished, grooves are made on the inner wall surface of the nozzle according to the design requirements by using a special milling tool or wire cutting technology.

[0048] In this step, the depth, width, and shape of the channel need to be customized according to specific cooling requirements or hydrodynamic requirements. Furthermore, during the grooving process, cutting parameters (such as milling cutter speed, tool angle, and cutting fluid usage) must be set appropriately to ensure the accuracy of the channel shape and surface quality.

[0049] S204: After the channel is machined, use precision tools or grinding tools to finish the channel edges to ensure smoothness and dimensional accuracy, avoiding sharp edges or burrs. Deburring not only improves the mechanical properties of the nozzle's inner wall but also prevents cracks or wear during subsequent use.

[0050] S205: Cooling the inner wall of the semi-finished nozzle obtained after machining.

[0051] In this step, during the machining process, internal stress often occurs on the inner wall surface of the nozzle due to the accumulation of cutting heat. Therefore, it is necessary to cool and relieve the stress on the machined inner wall of the nozzle. For example, it can be cooled slowly by natural cooling or by using coolant to cool it evenly, so as to ensure the dimensional stability of the inner wall and avoid deformation.

[0052] Based on the above steps, the following can be obtained: Figure 3 The image shows the inner wall of a semi-finished nozzle with grooves on its surface.

[0053] In another exemplary embodiment, step S300 involves performing a surface modification treatment on the inner wall of the semi-finished nozzle to obtain a surface-modified inner wall of the semi-finished nozzle, including the following steps: S301: Clean the inner wall of the semi-finished nozzle; In this step, a laser is used to clean the inner wall of the semi-finished nozzle, which has grooves on its surface, to remove oxides, residual metal shavings, and other impurities. Simultaneously, the high energy of the laser beam creates a microstructure on the inner wall surface, increasing surface roughness and providing a foundation for subsequent coating adhesion.

[0054] S302: Surface modification is achieved by spraying copper alloy interlayer and nickel interlayer onto the inner wall surface of the cleaned semi-finished nozzle; In this step, the surface modification is specifically performed as follows: the channel is sealed with filler to ensure that it is level with the rib height, and copper alloy powder is cold-sprayed to 3mm to 8mm. In addition, a nickel layer is sprayed using an air blower with a thickness of about 3mm to 5mm, and then the channel filler is removed.

[0055] S303: Annealing treatment is performed on the inner wall of the semi-finished nozzle coated with copper alloy interlayer and nickel interlayer.

[0056] In this step, annealing is performed, heating the nozzle to an appropriate temperature (300°C to 500°C) to eliminate residual stress in each layer, including the copper alloy interlayer and the nickel interlayer, and to improve the density of each layer, thereby enhancing the high-temperature resistance of the nozzle.

[0057] In summary, after surface modification treatment, the following can be obtained: Figure 6 and Figure 7 The surface-modified inner wall of the semi-finished nozzle is shown. Figure 7 In the image, it can be clearly seen that the inner wall of the nozzle includes the main wall 2-1 and the inner wall rib groove 2-2, as well as the copper alloy interlayer 3 and the nickel interlayer 4.

[0058] In another exemplary embodiment, step S400, assembling and welding the surface-modified semi-finished nozzle inner wall with the cooling ring to obtain a nozzle inner wall with a cooling ring, includes the following steps: S401: As follows Figure 4 The upper cooling ring 1-1 shown and Figure 5 The lower cooling ring 1-2 shown is connected to the inner wall of the surface-modified semi-finished nozzle; In this step, both the upper cooling ring 1-1 and the lower cooling ring 1-2 are made of special metal materials or alloys, requiring accurate positioning on the inner wall of the nozzle. Specifically, positioning clamps can be used to firmly fix the upper cooling ring 1-1 and the lower cooling ring 1-2 to the inner wall of the semi-finished nozzle, ensuring that the cooling rings do not shift or misalign during welding. Furthermore, when fixing, the difference in thermal expansion coefficients between the cooling rings and the nozzle should be considered to ensure that the cooling rings and the nozzle maintain a good bond at high temperatures after welding.

[0059] S402: Set the welding parameters and perform welding; In this step, welding parameters need to be set and equipment needs to be debugged before the actual welding. Specifically, depending on factors such as the material and thickness of the nozzle and cooling ring, a suitable welding process is selected, such as TIG welding (tungsten inert gas welding) or laser welding.

[0060] During welding, it is essential to ensure the stability of parameters such as welding current, welding speed, and gas shielding flow rate, and to maintain appropriate welding temperature and weld pool size. Furthermore, special attention should be paid to the welding sequence to avoid excessive heating at once, which could lead to excessive thermal stress or deformation. After welding, the desired result can be obtained as follows: Figure 8 The nozzle inner wall shown is surface-modified with upper cooling ring 1-1 and lower cooling ring 1-2.

[0061] S403: Inspect and clean the welds; In this step, after welding is completed, the weld needs to be inspected for quality. This can be done through visual inspection, ultrasonic testing, or X-ray flaw detection to ensure that the weld is free of defects such as porosity, cracks, and lack of fusion. Afterward, the weld surface is cleaned to remove excess weld slag and oxides.

[0062] S404: Post-processing of the welded nozzle, upper cooling ring, and lower cooling ring.

[0063] In this step, the welded nozzle and cooling ring assembly may deform due to the thermal stress generated during welding, thus requiring post-treatment. The post-treatment includes sequential annealing, stress-relieving heat treatment, and homogenization cooling. Specifically, the annealing process involves heating the nozzle to an appropriate temperature (typically 300°C to 500°C) and holding it for a period to eliminate residual stress from the welding process. Subsequently, stress-relieving heat treatment is performed, heating the nozzle to a specific temperature (approximately 500°C to 700°C) and holding it for a period to release internal stresses in the material. Finally, the nozzle undergoes homogenization cooling using a slow cooling method, controlling the cooling rate to avoid temperature differences, thereby ensuring that the nozzle does not deform or crack during cooling, improving its overall stability and durability.

[0064] In another exemplary embodiment, step S500, which involves cladding the inner wall of the nozzle with the cooling ring to obtain a nozzle assembly with composite inner and outer walls, includes the following steps: S501: Preheat the inner wall of the nozzle with a cooling ring; In this step, the preheating temperature is set between 200℃ and 400℃, and the specific temperature needs to be adjusted according to the processing requirements. Preheating allows the inner wall of the nozzle to reach a certain temperature, which helps to reduce thermal stress during the cladding process, thereby ensuring that the cladding layer melts uniformly and bonds firmly to the inner wall surface of the nozzle.

[0065] S502: A high-temperature resistant and wear-resistant alloy is selected as the cladding material. The cladding material is uniformly deposited on the inner wall surface of the nozzle, achieving results such as... Figure 8The nozzle inner and outer wall assembly shown has upper and lower cooling rings. During the cladding process, the excessively high temperature is reduced by the cooling circulation channel formed by the inner wall surface rib groove, the cold spray coating interlayer, and the cooling rings at both ends.

[0066] In this step, during the laser cladding process, the cladding material is heated and melted by a laser beam. The melted cladding layer quickly bonds with the substrate to form a strong metallurgical bond. Metallurgical bond means that the cladding layer and the substrate are tightly bonded in the microstructure to form an integral metal structure, thereby improving the adhesion of the cladding layer. It should be noted that this process requires precise control of laser power, scanning speed, scanning distance and angle, as well as the feeding rate of the cladding material. The specific cladding process is as follows: A three-dimensional solid model of the sample to be formed is created. The inner wall of the surface-modified nozzle with upper and lower cooling rings is assembled with the tooling and mounted together on the worktable. Cooling water is pre-circulated through the lower cooling ring to ensure the inlet pressure is between 0.5 MPa and 2 MPa, preventing deformation of the rib grooves during laser cladding. The distance and angle between the laser head and the outer surface of the inner wall are adjusted, with the distance set to 10 mm to -50 mm and the angle varying between 45° and 90°. Simultaneously, printing parameters are set: power from 800W to 2000W, speed from 4 mm / s to 10 mm / s, and powder feed rate from 5 g / min to 10 g / min. After cladding, the desired nozzle inner and outer wall assembly is obtained. The laser cladding powder is 316L, Inconel 625, or Inconel 718 alloy powder.

[0067] Furthermore, it's important to note that if the laser power is too low (e.g., set to 200W), it may not achieve a good bond with the inner wall; if the power is too high (e.g., set to 2500W), it may cause excessive heat buildup, leading to substrate deformation or cracks in the cladding layer on the outer wall. Therefore, setting the power to 1500W ensures reliable bonding and appropriate strength between the cladding layer and the inner wall.

[0068] If the scanning speed is too fast (e.g., set to more than 10 mm / s), the cladding material will not have enough time to fully fuse with the substrate, which may lead to inconsistent thickness of the cladding layer or even unfused areas. Conversely, if the speed is too slow (e.g., below 2 mm / s), the cladding area may overheat, resulting in over-melted areas and increasing the risk of cracking. Therefore, setting it to 6 mm / s can ensure uniform melting of the cladding material while avoiding overheating, thus obtaining a stable cladding layer.

[0069] If the powder feed rate is too high (e.g., set to 15 g / min), too much cladding material will be supplied, which may cause some powder to fail to melt in time, resulting in pores or unfused areas. If the powder feed rate is too low (e.g., set to 1 g / min), the cladding layer may be uneven and insufficient in thickness, failing to meet the required performance standards. Setting it to 6 g / min ensures that the cladding material is properly matched with the laser power and scanning speed, guaranteeing the uniformity and density of the cladding layer.

[0070] S503: Cool the inner wall of the nozzle after cladding.

[0071] In this step, this application adopts a zoned temperature control cooling method, setting different cooling rates for different areas of the nozzle inner wall (because the material thickness and structural complexity of different parts of the nozzle inner wall are different, using a uniform cooling rate may lead to stress concentration, thereby causing cracks or deformation), specifically including: Step 1: Divide the cooling zones according to the geometry and structural features of the nozzle's inner wall; In this step, the nozzle can be divided into sections, such as the inner wall, outer wall, ribs, and main wall. Temperature sensors (such as infrared thermometers) are then used to monitor the temperature of each area of ​​the nozzle in real time.

[0072] Step 2: Perform initial overall cooling of the nozzle. This stage can be achieved using airflow cooling or cryogenic liquid spray at a relatively slow cooling rate to ensure the nozzle temperature drops to a certain range.

[0073] Step 3: Set different cooling parameters for each cooling area of ​​the nozzle after overall cooling. For example, the rib area of ​​the nozzle can be set to a slower cooling rate (0.5℃ / min), the main wall area can be set to a faster cooling rate (1.5℃ / min), and the joint and support areas can be cooled at a medium rate (1℃ / min).

[0074] Step 4: After the zoned cooling is completed, the homogenization cooling stage begins to ensure that the temperature of all areas gradually approaches the same level, thereby avoiding stress concentration caused by temperature differences between different areas.

[0075] In summary, this application effectively controls the thermal stress distribution of the nozzle after the cladding process by setting different cooling rates for different areas, thus avoiding cracks, deformation, and material failure caused by excessive temperature differences. Furthermore, by precisely adjusting the cooling rates of the main wall, ribs, and connecting areas, each area is treated under appropriate cooling conditions, thereby optimizing the material's microstructure and improving its strength, toughness, and wear resistance.

[0076] After obtaining the inner wall of the engine nozzle using the above method, this application conducts detailed performance tests, specifically including tests on its surface hardness, high-temperature resistance, corrosion resistance, oxidation resistance, wear resistance, weld joint strength, and fatigue life. Surface hardness is measured using a hardness tester; high-temperature and corrosion resistance are verified using a high-temperature furnace and corrosion test solution to simulate the working environment; oxidation resistance is tested using an oxidation test; wear resistance is tested using a friction and wear testing machine; weld joint strength is tested using tensile and shear tests; and fatigue life is verified using an alternating load testing machine to simulate actual working loads. All tests employ standardized testing methods to ensure the reliability and performance of the nozzle under high-temperature and high-pressure environments. Furthermore, this application compares the performance of the inner wall of the nozzle prepared using this method with that prepared using conventional methods. Specific test and comparison results are shown in Table 1. Table 1

[0077] Table 1 compares the test results of the method of this application with those of existing methods on multiple performance indicators. The modified nozzle inner wall of this application exhibits significant advantages in surface hardness, high-temperature resistance, corrosion resistance, oxidation resistance, wear resistance, weld joint strength, and fatigue life. Specifically, the nozzle hardness of this application is increased by approximately 20-30%, its high-temperature resistance and corrosion resistance are superior to those of existing methods, wear is reduced by approximately 20%, the tensile strength of the weld joint is increased by approximately 20%, and the fatigue life is improved by more than 25%. Overall, the method of this application significantly improves the comprehensive performance of the nozzle, especially its stability and reliability under high-temperature and high-pressure environments.

[0078] The above embodiments are only for illustrating the technical concept and features of this application, and are intended to enable those skilled in the art to understand the content of this application and implement it accordingly. They should not be construed as limiting the scope of protection of this application. All equivalent changes or modifications made in accordance with the spirit and essence of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing an inner and outer wall assembly of a liquid engine nozzle, characterized in that, The method includes: Laser printing was performed on copper alloy powder to obtain a copper alloy nozzle inner wall blank. The copper alloy nozzle inner wall blank is machined to obtain a semi-finished nozzle inner wall with grooves on the surface; The inner wall of the semi-finished nozzle is subjected to surface modification treatment to obtain a surface-modified inner wall of the semi-finished nozzle. The surface-modified semi-finished nozzle inner wall is assembled and welded with the cooling ring to obtain a nozzle inner wall with a cooling ring. The inner wall of the nozzle with a cooling ring is clad to obtain a nozzle assembly with composite inner and outer walls.

2. The method according to claim 1, characterized in that, The process of laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank includes: Create a 3D model of the inner wall of the copper alloy nozzle to be formed and import it into an SLM printer; Copper alloy powder is printed based on a 3D model. After printing, a copper alloy nozzle inner wall blank is obtained.

3. The method according to claim 2, characterized in that, The process of laser printing copper alloy powder to obtain a copper alloy nozzle inner wall blank also includes: The copper alloy nozzle inner wall blank is cooled in different regions according to different strategies.

4. The method according to claim 1, characterized in that, Before laser printing on copper alloy powder, the copper alloy powder is pretreated, and the pretreatment includes: The copper alloy powder is dried and cooled. Clean the cooled copper alloy powder; The cleaned copper alloy powder is sieved. The sieved copper alloy powder is stored.

5. The method according to claim 1, characterized in that, The method of obtaining a copper alloy nozzle inner wall blank by laser printing based on copper alloy powder also includes: The copper alloy nozzle inner wall blank is subjected to heat treatment.

6. The method according to claim 1, characterized in that, The copper alloy nozzle inner wall blank is machined to obtain a semi-finished nozzle inner wall with grooves on its surface, including: The copper alloy nozzle inner wall blank is rough machined; The copper alloy inner wall blank after rough machining is then precision machined. Grooves are cut into the inner wall surface of the finished copper alloy billet and then trimmed.

7. The method according to claim 6, characterized in that, The process of machining the copper alloy nozzle inner wall blank to obtain a semi-finished nozzle inner wall with grooves on the surface further includes: The inner wall of the semi-finished nozzle obtained after machining is cooled.

8. The method according to claim 1, characterized in that, The assembly and welding of the surface-modified semi-finished nozzle inner wall with the cooling ring to obtain a nozzle inner wall with a cooling ring includes: The cooling ring is then joined to the inner wall of the surface-modified semi-finished nozzle. Set the welding parameters and then perform the welding. Inspect and clean the welds; Post-processing is performed on the welded nozzle and cooling ring.

9. The method according to claim 8, characterized in that, The post-processing of the welded nozzle and cooling ring includes: Annealing is performed on the welded nozzle and cooling ring. The annealed nozzle and cooling ring are subjected to stress-relieving heat treatment. The nozzle and cooling ring after stress relief heat treatment are subjected to homogenization cooling treatment.

10. The method according to claim 1, characterized in that, The process of cladding the inner wall of the nozzle with a cooling ring to obtain a nozzle assembly with composite inner and outer walls includes: Preheat the inner wall of the nozzle with a cooling ring; The cladding material is uniformly coated onto the inner wall surface of the nozzle, and then clad with a laser. At the same time, the inner wall of the nozzle is cooled during the cladding process.

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