A microtextured regenerated cooling channel, its preparation method and application

Abstract

This invention belongs to the field of regenerative cooling technology, specifically relating to a microtextured regenerative cooling channel, its preparation method, and its application. This invention employs selective laser melting (SLM) additive manufacturing to integrally generate longitudinally oriented rectangular microgrooves on the inner wall of the regenerative cooling channel. Then, under ultrasonic conditions, the channel is acid-washed with a mixed acid solution, wherein the mixed acid solution is a mixture of hydrofluoric acid and nitric acid. This invention uses SLM to integrally form the microtextured regenerative cooling channel, achieving precise control over the cross-sectional shape of the processed rectangular microgrooves. The resulting microtextured regenerative cooling channel, while maintaining a constant total coolant flow rate, can improve the coolant flow rate and temperature uniformity at the same cross-section within the regenerative cooling combustion chamber cooling channel. This prevents coolant overheating and vaporization in certain areas, thus avoiding localized damage to the combustion chamber and ensuring uniform and effective cooling of the regenerative cooling combustion chamber.

Description

Technical Field

[0001] This invention belongs to the field of regenerative cooling technology, specifically relating to a microtextured regenerative cooling channel, its preparation method, and its application. Background Technology

[0002] Space engines have become a hot research topic in the aerospace field in recent years. A space engine is an engine that uses liquid fuel and oxidizer as its energy source, and its components include a combustion chamber, a propellant supply system, and an engine control system. The combustion chamber is the component that converts the chemical energy of the propellant into jet kinetic energy; the nozzle expands and accelerates the high-temperature combustion gases, generating a high-speed jet. During operation, the extremely high Mach numbers and temperatures generated by the combustion of hydrocarbon propellants exceed the load-bearing capacity of existing materials. To address this issue, one of the key aspects of space engine design is solving the thermal protection problem of the spacecraft, particularly the cooling of the space engine's combustion chamber. Current methods cool the thrust chamber using a coolant, typically employing the engine's own liquid fuel as the cooling medium. The liquid fuel flows counter-currently to the high-temperature gases in the cooling channels inside the high-temperature component walls, absorbing heat through forced convection heat transfer, thereby reducing the wall temperature. When the liquid fuel leaves the high-temperature component, the component is cooled, and the liquid fuel re-enters the combustion chamber at a higher temperature, achieving energy regeneration. Therefore, this external convective cooling method is called regenerative cooling.

[0003] Modern engine combustion chambers widely use three types of cooling channel structures: corrugated plate cooling channels, milled groove cooling channels, and tube bundle cooling channels. Corrugated plate cooling channels, due to their structural characteristics, prevent half of the coolant from directly contacting the inner wall, hindering the reduction of the inner wall temperature. Tube bundle cooling channels, while lightweight and fast in heat dissipation, are often used in large-area, low-heat-flux, high-speed nozzle extensions. Milled groove cooling channels involve milling cooling grooves into the inner wall surface and welding the outer and inner walls together to form the cooling channel. Traditional cooling channel manufacturing methods, such as corrugated plate structures, suffer from low coolant-to-interface contact rates, leading to low heat exchange efficiency. Tube bundle structures are limited by poor structural rigidity and have high development costs. Milled groove structures, on the one hand, are problematic due to the risk of fuel coking, making it unsuitable for excessively flat internal channels in traditional regenerative cooling structures, resulting in poor space utilization in the wall thickness direction and significant room for weight reduction. On the other hand, the high thermal conductivity of metal materials in the thickness direction results in a lower equivalent thermal resistance in this direction, requiring improvement in insulation capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide a microtextured regenerative cooling channel, its preparation method, and its application. The microtextured regenerative cooling channel provided by this invention can significantly improve the product quality of the microgroove structure on the inner wall of the regenerative cooling pipe, improve the processing accuracy, and reduce the manufacturing cost. The obtained microgroove structure can increase the flow rate of the coolant in the regenerative cooling channel, increase the heat transfer coefficient between the wall and the coolant, effectively reduce the temperature of the inner wall, and have a better cooling effect.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a microtextured regenerated cooling channel, comprising the following steps:

[0007] A flow-oriented rectangular microgroove is integrally formed on the inner wall of the regeneration cooling channel using a selective laser melting additive manufacturing method, thus obtaining an initial microgroove structure on the inner wall of the regeneration cooling channel.

[0008] The initial microgroove structure is acid-washed with a mixed acid solution under ultrasonic conditions to obtain the microtexture regenerated cooling channel. The mixed acid solution is a mixture of hydrofluoric acid and nitric acid.

[0009] Preferably, the cross-section of the downstream rectangular microgroove is rectangular, and the groove width and depth are independently 200-500 μm; the groove spacing is 400-1000 μm.

[0010] Preferably, the particle size of the forming powder used in the selective laser melting is 15-53 μm; the forming powder used in the selective laser melting is TA15 titanium alloy powder.

[0011] Preferably, the selective laser melting is performed using a method of horizontal placement of the regenerative cooling channel and vertical processing;

[0012] The conditions for selective laser melting include: the laser type is continuous laser, the scanning path is a zigzag path, the powder layer thickness is 0.02-0.08 mm, the laser spot diameter is 80 μm, and the processing angle is 90°.

[0013] Preferably, the power of the continuous laser is 150-300W, the scanning speed is 800-1400mm / s, and the scanning interval is 0.06-0.16mm.

[0014] Preferably, the mixed acid solution of hydrofluoric acid and nitric acid includes HF, HNO3 and water; in the mixed acid solution of hydrofluoric acid and nitric acid: the mass percentage of HF is 1-10% and the mass percentage of HNO3 is 10-20%.

[0015] Preferably, the ultrasonic conditions include: ultrasonic power of 400-500W and frequency of 40-60kHz; and pickling temperature of 20-60℃ and time of 3-5min.

[0016] Preferably, after obtaining the initial microgroove structure and before performing the pickling, the method further includes: rinsing the initial microgroove structure using high-pressure gas, wherein the pressure of the high-pressure gas is 0.3 to 0.6 MPa.

[0017] The present invention provides a microtextured regenerated cooling channel prepared by the preparation method described above, wherein the inner wall surface of the microtextured regenerated cooling channel has an integrally formed longitudinal rectangular microgroove.

[0018] This invention provides the application of the microtextured regenerative cooling channel described above in the thermal protection of the engine combustion chamber.

[0019] This invention provides a method for fabricating a microtextured regenerated cooling channel, comprising the following steps: integrally forming a flow-oriented rectangular microgroove on the inner wall of the regenerated cooling channel using selective laser melting (SLM) additive manufacturing, thus obtaining an initial microgroove structure on the inner wall of the regenerated cooling channel; and acid-washing the initial microgroove structure under ultrasonic conditions with a mixed acid solution, wherein the mixed acid solution is a mixture of hydrofluoric acid and nitric acid, to obtain the microtextured regenerated cooling channel. This invention achieves precise control over the cross-sectional shape of the processed microgroove, including its contour, microtexture width, and microtexture depth, through integrated SLM processing of the microtexture within the regenerated cooling channel; and fabricates a surface feature with a precisely controllable cross-sectional shape and a smooth bottom morphology on the inner wall of the regenerated cooling channel. Compared to traditional methods of fabricating microtextures in microchannels (such as laser etching, which mainly achieves microtexture fabrication in the Z-axis direction), the microtextures of the regenerated cooling channels obtained by integrated SLM processing in this invention can be arranged in both the X and Y axes, breaking the limitations of traditional methods. The fabrication method for the microtextured regenerated cooling channels provided by this invention significantly improves product quality, processing accuracy, and reduces manufacturing costs. The microtextures fabricated by this invention can increase the coolant flow rate, increase the heat transfer coefficient between the wall and the coolant, and effectively reduce the inner wall temperature, resulting in better cooling performance compared to existing structures. Experimental results from the embodiments show that the microtextured regenerated cooling channels obtained by integrated SLM processing in this invention, due to the presence of microgrooves, reduce the average velocity at the boundary, thin the velocity boundary layer, and disrupt the original boundary layer flow structure, making the momentum and energy exchange between fluids at the boundary more intense. This confirms the flow resistance regulation and heat transfer enhancement effects of the microgrooves. The microtextured regenerative cooling channel prepared by this invention can improve the uniformity of coolant flow and temperature at the same cross-section within the cooling channel of the regenerative cooling combustion chamber while maintaining a constant total coolant flow rate. This prevents localized damage to the combustion chamber caused by coolant overheating and vaporization in certain areas, ensuring uniform and effective cooling of the regenerative cooling combustion chamber. This invention can be quickly adapted to actual engine structures, offering advantages such as wide applicability, cost-effectiveness, and significant results. It solves the problems of insufficient drag reduction and poor adaptability in existing technologies. Attached Figure Description

[0020] Figure 1 This is a zigzag scanning path diagram in an embodiment of the present invention;

[0021] Figure 2 The microstructure of different regions on the surface of sample No. 10 in Example 1 of this invention is shown below: Figure 2 (a) in the figure represents the morphology of region A. Figure 2 (b) in the image represents the morphology of region B. Figure 2(c) in the figure represents the morphology of region C. Figure 2 (d) in the figure represents the morphology of region D. Figure 2 (e) in the figure represents the morphology of region E;

[0022] Figure 3 The microstructure of region B in samples 4, 7, 10, and 13 of Example 1 of this invention is as follows: Figure 3 (a) in the text refers to sample number 4. Figure 3 (b) in the image represents sample number 7. Figure 3 (c) in the text refers to sample number 10. Figure 3 (d) in the text refers to sample number 13;

[0023] Figure 4 The microstructure of region B in samples 10, 12, and 11 of Example 1 of this invention is as follows: Figure 4 (a) in the text refers to sample number 10. Figure 4 (b) in the image is sample number 12. Figure 4 (c) in the text refers to sample number 11;

[0024] Figure 5 This is a diagram illustrating a specific implementation method of pickling during pickling in an embodiment of the present invention;

[0025] Figure 6 The surface morphology of 200 μm microgroove structures under different pickling times;

[0026] Figure 7 This is an EDS layered image of a sample that has not undergone acid washing in an embodiment of the present invention;

[0027] Figure 8 This is an EDS layered image of the sample after pickling with nitric acid + nitric acid in an embodiment of the present invention.

[0028] Figure 9 The circulating water tunnel platform used in the embodiments of the present invention;

[0029] Figure 9 In the middle section: 1-Test section, 2-Water tank, 3-Insulation layer, 4-Heating element, 5-Wall to be heated, 6-Thermocouple, 7-Temperature transmitter, 8-Wall to be insulated, 9-Differential pressure transmitter, 10-Electromagnetic flowmeter, 11-Centrifugal pump, 12-Motor frequency converter, 13-Inlet contraction section; 14-Outlet expansion section;

[0030] Figure 10 This is a temperature change diagram of the heat-insulating wall surface of the regenerative cooling channel in an embodiment of the present invention;

[0031] Figure 11 This is a schematic diagram of a microgroove structure;

[0032] Figure 12 For process parameter sample models;

[0033] Figure 13 This is an actual effect diagram of the SLM forming process parameters sample in the embodiment;

[0034] Figure 14 Surface morphology of samples after pickling with different pickling solutions: Figure 14 (a) in the text represents pickling solution 1. Figure 14 (b) in the text is pickling solution 2. Figure 14 (c) in the text represents pickling solution 3. Figure 14 (d) in the text refers to pickling solution 4. Figure 14 (e) in the text refers to pickling solution 5;

[0035] Figure 15 Microgroove structure morphology: Figure 15 (a) in the image shows a cooling channel with a microgroove structure. Figure 15 (b) shows the optimized 3D morphology of the 200μm microgroove. Figure 15 (c) in the figure represents the optimized cross-sectional profile curve. Detailed Implementation

[0036] This invention provides a method for preparing a microtextured regenerated cooling channel, comprising the following steps:

[0037] A flow-oriented rectangular microgroove is integrally formed on the inner wall of the regeneration cooling channel using a selective laser melting additive manufacturing method, thus obtaining an initial microgroove structure on the inner wall of the regeneration cooling channel.

[0038] The initial microgroove structure is acid-washed with a mixed acid solution under ultrasonic conditions to obtain the microtexture regenerated cooling channel. The mixed acid solution is a mixture of hydrofluoric acid and nitric acid.

[0039] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0040] While surface-mount metal additive manufacturing (SLM) technology shows great promise in the aerospace field, the inherent step effect, spheroidization effect, and powder adhesion during the additive manufacturing process result in generally poor surface quality and high surface roughness in commercially available SLM-formed parts. For regenerable cooling channels in aerospace engines, the inner surface of the channel plays a crucial role in efficiently transferring the cooling medium. The morphology of the inner surface significantly impacts the flow state and heat transfer efficiency of the cooling medium within the channel, severely affecting the performance characteristics of the regenerable cooling channel. This invention achieves precise control over the forming quality of SLM, reduces surface roughness, and improves the accuracy and consistency between microgroove design and the actual formed contour.

[0041] This invention employs a selective laser melting additive manufacturing method to integrally form a flow-oriented rectangular microgroove on the inner wall of a regenerating cooling channel, thus obtaining an initial microgroove structure on the inner wall of the regenerating cooling channel. This invention selects a groove texture as the rough element for the inner wall of the flow channel. On the one hand, the groove texture is relatively simple, has few variables, and is easy to control; on the other hand, the groove texture has a relatively complete drag reduction and heat transfer enhancement mechanism. In this invention, the particle size of the forming powder used in the selective laser melting is preferably 15–53 μm. In a specific embodiment of this invention, the forming powder used in the selective laser melting is preferably TA15 titanium alloy powder. The TA15 titanium alloy powder is spherical. In a specific embodiment of this invention, the TA15 titanium alloy powder contains 5.5% Al, 1.5% Zr, 0.5% Mo, and 0.8% V, with the balance being Ti.

[0042] In a specific embodiment of the present invention, the additive manufacturing equipment used for selective laser melting is the M290 metal 3D printer manufactured by EOS GmbH, Germany. This equipment can achieve layer-by-layer sintering of metal powder by a laser beam. The equipment adopts a bottom-feed, unidirectional powder spreading method, and the protective gas is compatible with both argon (Ar) and nitrogen (N2) to keep the oxygen content in the chamber below 0.02% to prevent workpiece oxidation. Furthermore, this equipment has the advantages of being able to quickly, flexibly, and economically produce metal parts by directly utilizing CAD data.

[0043] In this invention, the integrated molding of "longitudinal rectangular microgrooves" provides superior heat transfer performance compared to transverse microgrooves without significantly increasing flow resistance within the channel. Furthermore, considering the step effect during SLM molding, this invention abandons triangular grooves and selects rectangular grooves, which offer higher molding quality, as the texture for modifying the inner wall of the flow channel. The microgroove morphology in this invention is as follows: Figure 11 As shown in the figure. Where p, s, and h represent the microgroove spacing, groove width, and groove depth, respectively, and α = 90°.

[0044] In a specific embodiment of the present invention, the width and depth of the microgrooves are preferably equal, and the groove width s = groove depth h is preferably 200-500 μm, specifically 200 μm, 300 μm, 400 μm or 500 μm. The groove spacing p is preferably 400-1000 μm, specifically 400 μm, 600 μm, 800 μm or 1000 μm.

[0045] In this invention, the selective laser melting is preferably performed using a method of horizontal placement of the regenerative cooling channel and vertical processing. The preferred conditions for selective laser melting include: the laser type is preferably a continuous laser; the scanning path is preferably a zigzag path; the powder layer thickness is preferably 0.02–0.08 mm, specifically 0.03 mm. The laser spot diameter is preferably 80 μm, and the processing angle is preferably 90°. The power of the continuous laser is preferably 150–300 W, more preferably 150 W, 200 W, 250 W, 275 W, or 300 W, and the power gradient of the continuous laser is preferably 50 W. The scanning speed is preferably 800–1400 mm / s, more preferably 800 mm / s, 1000 mm / s, 1200 mm / s, 1250 mm / s, or 1400 mm / s. The scanning interval is preferably 0.06 to 0.16 mm, more preferably 0.06 to 0.12 mm, and specifically preferably 0.1 mm, 0.12 mm, 0.14 mm or 0.16 mm. The gradient of the scanning interval is preferably 20 μm.

[0046] In this invention, the laser volumetric energy density of the continuous laser is as shown in Equation 1:

[0047] Ev = P L / (V S ×H S ×D S Formula 1,

[0048] In Equation 1: P L V represents the power of a continuous laser. S For scanning speed, H S D is the scan spacing. S For thicker powder layer.

[0049] After obtaining an initial microgroove structure on the inner wall of the regeneration cooling channel, the present invention performs acid washing on the initial microgroove structure under ultrasonic conditions using a mixed acid solution to obtain microchannels on the inner wall of the regeneration cooling channel. The mixed acid solution is a mixed acid solution of hydrofluoric acid and nitric acid.

[0050] In this invention, after obtaining the initial microgroove structure and before performing the pickling, the invention preferably further includes: rinsing the initial microgroove structure using high-pressure gas, preferably at a pressure of 0.3–0.6 MPa. The invention preferably uses high-pressure gas to preliminarily rinse the SLM-formed metal part (containing the initial microgroove structure) to remove metal powder and dust from the surface of the SLM-formed metal part. After rinsing, a rinsed sample is obtained. The invention preferably further includes: using a steel brush to preliminarily clean the loose powder and dust from the surface of the initial microgroove structure of the rinsed sample.

[0051] In this invention, the purpose of acid washing is to remove powder adhering to the sample surface and prevent excessive corrosion of the microtexture.

[0052] In this invention, the mixed acid solution of hydrofluoric acid and nitric acid preferably includes HF, HNO3, and water. The water is preferably deionized water. In the mixed acid solution of hydrofluoric acid and nitric acid: the mass percentage of HF is preferably 1-10%, specifically 1%, 3%, 5%, or 10%, most preferably 3%; the mass percentage of HNO3 is preferably 10-20%, specifically 20%.

[0053] In this invention, the ultrasonic conditions include: the ultrasonic power is preferably 400-500W, and the frequency is preferably 40-60kHz. The acid washing is specifically preferably performed by immersing the sample containing the initial microgroove structure in a mixed acid solution. The acid washing temperature is preferably 35°C. The acid washing time is preferably 3-5 minutes. The acid washing is preferably performed under water bath heating conditions.

[0054] In this invention, the pickling time should not be too short, as this will lead to incomplete pickling, leaving powder residue on the microtexture surface and affecting drag reduction. Furthermore, with prolonged pickling time, the pickling solution, while removing adhering powder and surface microburrs, will also cause severe corrosion to the microtexture structure. However, this invention uses a "dual-acid solution" for pickling (i.e., dual-acid pickling). Due to the addition of nitric acid, a layer of oxide film is formed on the sample surface during dual-acid pickling, effectively protecting the main body of the texture and preventing damage to the texture caused by pickling while removing surface microburrs.

[0055] In this invention, after pickling, the pickled sample is preferably dried to obtain a microtextured regenerated cooling channel. In this invention, the drying is preferably oven drying.

[0056] The present invention provides a microtextured regenerated cooling channel prepared by the preparation method described above, wherein the inner wall surface of the microtextured regenerated cooling channel has an integrally formed longitudinal rectangular microgroove.

[0057] This invention provides the application of the microtextured regenerative cooling channel described above in the thermal protection of the engine combustion chamber.

[0058] In this invention, the engine combustion chamber is specifically a space engine combustion chamber.

[0059] In summary, the technical effects of this invention are as follows:

[0060] 1. Compared with other microtexturing technologies, this invention utilizes laser surface microtexturing technology, which can be performed in an atmospheric environment without causing pollution. It is simple to fabricate without requiring other auxiliary processes, has low equipment costs, a wide range of processing objects, and allows for control over appropriate dimensions and morphology. Therefore, selective laser melting (SLM) technology is considered one of the most promising processing technologies in the field of drag-reducing surface microtexturing. It offers advantages such as wide material adaptability, minimal heat-affected zone, and virtually no recasting.

[0061] 2. This invention uses ultrasonic-assisted pickling. The bubbles generated by the high-frequency ultrasonic waves grow at the junction of the particles and the surface. Under the repeated impact of the bubbles, the unmelted particles on the sample surface can be completely removed. This can effectively remove most of the unmelted particles and powder adsorbed on the SLM surface and further accelerate the pickling process. At the same time, the pickling uniformity is better, which effectively reduces the pitting corrosion problem caused by local over-pickling.

[0062] 3. This invention uses dual acids for pickling. Compared with single acid pickling, single acid pickling is more vigorous and requires less pickling time. Heating helps to improve the surface quality of the pickled surface and significantly shortens the pickling time (too high a pickling temperature will cause the acid to evaporate and affect the concentration, and the evaporated acid vapor is harmful to the human body, so this experiment uses a heating temperature of 35°C).

[0063] 4. The method provided by this invention is simple to operate, has low equipment requirements, and effectively meets the heat exchange needs of the combustion chamber wall, ensuring the reliability of the regenerative cooling channel layout. This method is flexible, can shorten the product processing cycle and cost, effectively reduce product defects, and meet the practical application requirements of aerospace combustion chambers.

[0064] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0065] Example 1

[0066] This embodiment provides a method for manufacturing microtextures for the inner wall of a regenerating cooling channel based on integrated SLM processing, including the following steps:

[0067] In this embodiment, a rectangular groove texture is selected as the roughness element of the inner wall of the flow channel. On the one hand, the groove texture is relatively simple, has few variables and is easy to control; on the other hand, the groove texture has a relatively complete drag reduction and heat transfer enhancement mechanism.

[0068] In this embodiment, to more efficiently investigate the influence of different process parameters on the forming quality of microgrooves of different sizes, four surface structures were designed on a cuboid model with geometric dimensions of 50mm × 10mm and a height of 2mm: smooth walls, microgroove walls with s = h = 200, 300, 400, and 500μm, respectively. Figure 12 As shown in Table 1, the dimensions of the microgrooves in different zones are the microgrooves dimension parameters.

[0069] Table 1. Microgroove dimensions in different regions

[0070]

[0071] In this embodiment, the same sample is prepared using the same process parameters. The number of samples is determined according to the set parameter range. In order to ensure the forming quality of the microgroove, all samples are printed vertically in the same direction as the microgroove. The samples are arranged sparsely and staggeredly to avoid mutual interference between the samples.

[0072] In this embodiment, the metal 3D printer used has an SLM forming powder particle size of 15-53 micrometers, a continuous laser type, and a zigzag scanning path (e.g., Figure 1 As shown in Table 2, the fixed parameters were determined as follows: powder thickness of 0.03 mm, spot size of 0.08 mm, and processing angle of 90° (horizontal placement, vertical processing). The orthogonal variables were laser power (150-300 W), scanning speed (800-1400 mm / s), and scanning spacing (0.06-0.12 mm). A three-factor, four-level orthogonal experiment was designed, as shown in Table 2.

[0073] Table 2. Orthogonal experimental parameter settings for SLM process parameters

[0074]

[0075] Figure 13 This is a diagram showing the actual effect of the SLM forming process parameters on the sample in this embodiment. From... Figure 13 As can be seen, all 16 selected combinations of process parameters can completely print the designed sample structure and microgroove structures of different scales at the macroscopic level, indicating that the range of process parameters obtained in the preliminary experiment is relatively reasonable. This eliminates a large number of invalid parameter combinations in order to further analyze the influence of process parameters on the microgroove forming quality and find the optimal process parameters.

[0076] Figure 2 Microscopic morphology of different areas on the surface of sample No. 10: Figure 2 (a) in the figure represents the morphology of region A. Figure 2 (b) in the image represents the morphology of region B. Figure 2 (c) in the figure represents the morphology of region C. Figure 2 (d) in the figure represents the morphology of region D. Figure 2 (e) in the figure represents the morphology of region E.

[0077] from Figure 2 As can be seen, under the same process parameters, compared to a smooth surface, such as Figure 2 In (a), SLM additive manufacturing shows a microgroove structure surface as... Figure 2 In cases (b), (c), (d), and (e), powder adhesion is significantly increased, resulting in much poorer forming quality. This is because the microgroove structure has many detailed dimensions, requiring frequent start-stop cycles during laser scanning. The forming quality at the beginning and end of the molten pool is lower compared to continuous scanning, making it difficult to guarantee the quality of the formed microgroove structure. Furthermore, the limited laser spot diameter results in insufficient resolution when fabricating fine structures. Additionally, the microgroove structure itself is prone to gas backflow at the bottom, further increasing powder adhesion and accumulation. However, as the microgroove size increases, these problems will be significantly improved. This means that process parameters that enable high-quality fabrication of small-scale microgroove structures often result in better forming quality when fabricating large-scale microgroove structures.

[0078] Figure 3 The microstructure of a 200 μm microgroove is shown under different combinations of laser power and scanning speed process parameters with a scanning spacing of 0.16 mm. Figure 3 As seen in (a) and (b), when the laser power and scanning speed are low, insufficient laser volumetric energy density input causes a large amount of metal powder to enter the molten pool before it is fully melted. As the molten pool cools, this powder solidifies within it, resulting in a significant increase in the roughness of the solidified molten pool. With the accumulation of errors, the continuity and integrity of the formed microgroove structure are poor. Sample No. 10, for example... Figure 3 In sample (c), compared to samples 4 and 7, increasing both laser power and scanning speed resulted in a significant improvement in the microgroove forming quality. This is because simply increasing laser power would lead to an excessively long laser spot focusing time, resulting in excessive energy input to the molten pool per unit time. This would make the molten pool highly unstable, exacerbate the spheroidizing effect, and cause spattering droplets to degrade the microgroove surface quality. However, this does not mean that higher laser power and faster scanning speed will necessarily lead to better microgroove forming quality, as seen in sample 13. Figure 3 The surface quality of sample (d) was actually worse than that of sample 10. This is because higher laser power means excessive instantaneous energy input and an active molten pool. However, the excessively fast scanning speed causes the molten pool to cool rapidly. It is precisely in this rapid energy input and rapid energy withdrawal that the metal powder becomes more active, resulting in a decrease in the microgroove forming quality instead of an increase. Therefore, matching the laser power and scanning speed is necessary to obtain a high-quality microgroove structure.

[0079] Figure 4The images show the micromorphology of the microgrooves at different scanning intervals. Figure 4 As can be seen in (a) of sample 10, the large scanning interval resulted in insufficient liquid metal to completely fill the remelted expansion zone, causing a depression in the remelted expansion zone in both scanning paths. This made the area prone to inclusions, resulting in poor microgroove quality. Figure 4 In (c), the scanning interval of sample 11 was too small, causing the liquid metal in the middle remelting expansion zone to overflow to both sides, resulting in poor microgroove quality.

[0080] In summary, this embodiment investigated the effects of the core SLM parameters—laser power, scanning speed, and scanning spacing—on the fabrication of high-quality microgroove structures through orthogonal experiments on the fabrication process parameters of microgroove SLM. The optimal process parameters for fabricating microgroove structures with a minimum diameter of 200 μm were obtained as follows: laser power of 275 W, scanning speed of 1250 mm / s, scanning spacing of 100 μm, powder thickness of 30 μm, and the printing direction being 90° to the horizontal direction.

[0081] In this embodiment, high-pressure gas is used to perform preliminary rinsing on the SLM-formed metal parts to remove metal powder and dust from the surface of the SLM-formed metal parts;

[0082] Use a steel brush to initially clean the loose powder and dust from the surface of the etched workpiece;

[0083] The purpose of pickling in this embodiment is to remove powder adhering to the sample surface and prevent excessive corrosion of the microtexture. Although optimizing the SLM process parameters in this embodiment can yield a microgroove structure with good continuity and a relatively complete structure, the problems of powder adhering and spheroidization on the surface cannot be solved by optimizing the SLM process parameters alone. In actual production, SLM formed workpieces often require post-processing to improve their surface quality.

[0084] This embodiment employs a method that combines dual acid etching (DAE) with ultrasonic surface treatment simultaneously. Specific instruments and conditions used in the operation are as follows: Figure 5 As shown.

[0085] In this embodiment, the pickling solutions used in the pickling process are: a single-acid pickling solution of hydrofluoric acid (HF) and a dual-acid pickling solution of hydrofluoric acid (HF) + nitric acid (HNO3). The different types and compositions of the pickling solutions are shown in Table 3. Pickling solution 1 serves as a control group, which is cleaned using only deionized water. Pickling solutions 2 to 5 are single-acid pickling systems, and pickling solution 6 is a dual-acid pickling system.

[0086] Table 3 Types of pickling solutions and their component ratios

[0087]

[0088] This embodiment explores the effects of core pickling parameters, such as acid concentration ratio and pickling time, on the fabrication of microgroove structures using SLM. Through analysis, the optimal pickling parameters most suitable for the microgroove structures in this project are obtained.

[0089] (1) Effect of pickling solution concentration ratio on microgroove structure

[0090] Currently, commonly used pickling solutions for solid titanium in factories are divided into single-acid and dual-acid systems. The core component of both is hydrofluoric acid. Hydrofluoric acid is used to chemically react with the titanium alloy surface, achieving the purpose of efficiently removing burrs and adhering unmelted or semi-melted particles. The main difference lies in whether nitric acid is added. The reaction between titanium and hydrofluoric acid promotes hydrogen embrittlement of the parts, which has a significant impact on microgroove structures. When nitric acid reacts with titanium, it forms a dense oxide film on the titanium surface, passivating the sample surface, reducing hydrogen embrittlement, and also helping to prevent excessive corrosion of the microgroove structure. Therefore, this embodiment will use a dual-acid pickling solution to pickle the microgroove cooling channels.

[0091] In this embodiment, hydrofluoric acid concentrations of 1%, 3%, 5%, and 10% were selected for testing. Since the above reaction is endothermic, to increase the reaction rate and ensure more uniform pickling of the microgroove surface, a polytetrafluoroethylene beaker containing the pickling solution was first placed in an ultrasonic cleaner. Ultrasonic vibration was started, and the water bath heating temperature was set to 35°C. After the pickling solution reached the set temperature, the samples were immersed in pickling solutions 1-5 for ultrasonic cleaning for 3 minutes each. Then, the samples were removed from the pickling solution and placed in deionized water for ultrasonic cleaning to remove any remaining pickling solution before observation. Figure 14 Macroscopic morphology of 200μm microgrooves after pickling with different pickling solutions. Figure 14 Surface morphology of samples after pickling with different pickling solutions: Figure 14 (a) in the text represents pickling solution 1. Figure 14 (b) in the text is pickling solution 2. Figure 14 (c) in the text represents pickling solution 3. Figure 14 (d) in the text refers to pickling solution 4. Figure 14 (e) in the text refers to pickling solution 5. From Figure 14 As shown in (a), deionized water is ineffective in removing the adhering powder and spherical particles from the sample surface. Therefore, the surface quality of the sample prepared by SLM is extremely poor, and only the designed microgroove structure can be faintly seen. With increasing hydrofluoric acid concentration... Figure 14 In (b) and (c), the amount of surface-adhering powder and spheroidized particles is significantly reduced, and the outline of the designed microgroove structure gradually becomes clearer. When the hydrofluoric acid concentration increases to 5%, Figure 14 In (d), it is clearly visible that the designed microgroove structure begins to deteriorate, and the microgroove structure is no longer continuous and complete. Furthermore, when the hydrofluoric acid concentration is directly increased to 10%, Figure 14 The surface color of sample (e) changed, turning yellowish-white, indicating that the microgroove structure was excessively corroded and severely oxidized. Based on the above discussion, this embodiment selected a 5% hydrofluoric acid concentration as the hydrofluoric acid concentration for the post-pickling treatment of the microgroove cooling channel.

[0092] Figure 6 Surface morphology of 200 μm microgroove structures under different pickling times: Figure 6 (a) in the image represents the un-pickled sample. Figure 6 (b) in the diagram represents pickling for 2 minutes. Figure 6 (c) in the text refers to pickling for 4 minutes. Figure 6 (d) in the figure represents pickling for 6 minutes. Figure 6 As shown in (b), a large amount of powder adhering to the sample surface was removed within the first 2 minutes of pickling, but a large amount of metal powder remained at the bottom of the groove. Simultaneously, the surface of the microgroove structure was covered with many pits due to the shedding of metal powder, and the edges of these pits were relatively sharp, resulting in a large overall surface roughness of the microgroove. With increasing pickling time, at 4 minutes, from... Figure 6 As shown in (c), the metal powder in the microgroove structure has been largely removed. Simultaneously, due to the corrosive effect of the pickling solution, the sharp edges remaining after the metal powder detached have also been passivated. Measurements of the microgroove structure dimensions show that the microgroove structure is basically consistent with the design dimensions, indicating that the microgroove structure has not been corroded or damaged at this point. However, when the pickling time is further increased to 6 minutes, [the following text appears to be incomplete and requires further context: "from..."] Figure 6 As can be seen in (d) at this point, the groove spacing of the microgroove structure has increased and the rib structure size has decreased, indicating that the microgroove structure has already been subjected to excessive corrosion.

[0093] In summary, based on the above experiments, the optimal process parameters for pickling the closed cooling channel of the minimum 200μm microgroove structure in this embodiment are determined as follows: the pickling solution adopts a dual-acid system with an HF-HNO3 concentration ratio of 5%:20%, heated in a water bath at 35℃ with ultrasonic assistance, and the pickling time is 5 minutes. Figure 15 The image shows the morphology of the 200μm microgroove structure after applying optimal pickling process parameters to complete the cooling channel structure. From... Figure 15 The pickling effect is good and meets the usage requirements.

[0094] In this embodiment, the pickling time should not be too short, as this will lead to incomplete pickling, leaving powder residue on the microtexture surface and affecting the drag reduction effect. Simultaneously, with prolonged pickling time, the pickling solution, while removing adhering powder and surface microburrs, will also cause severe corrosion to the microtexture structure. However, the addition of nitric acid in dual-acid pickling forms an oxide film on the sample surface, effectively protecting the main body of the texture and preventing damage to the texture caused by pickling while removing surface microburrs.

[0095] The sample was removed with tweezers and dried to obtain a microtextured regenerated cooling channel sample.

[0096] Energy dispersive spectroscopy (EDS) analysis was performed on the rectangular groove structure surfaces of the samples prepared before pickling in Example 1, the samples prepared after double pickling with pickling solution 6, and the samples after single pickling with pickling solution 4 in Example 1. The results of the EDS analysis are shown in Table 4. Figure 7 This is an EDS layered image of the un-washed sample from Example 1. Figure 8 The image shows the EDS layered image of the sample after being pickled with pickling solution 6 in Example 1. The results show that the common elements and contents of the un-pickled and pickled samples after EDS are Ti, Al, Zr, Mo, and V. The contents of these elements are largely consistent with the recommended contents in the technical standards, indicating a high degree of reliability in the EDS results. Furthermore, fluorine was detected on the surface of the pickled sample, which is due to the presence of hydrofluoric acid in the pickling solution. Compared with the surface elements of the un-pickled sample, the carbon and oxygen elements on the sample surface decreased significantly after pickling, indicating that pickling can effectively remove surface oxides generated during SLM processing.

[0097] Table 4. Energy dispersive spectroscopy (EDS) analysis results of the samples in Example 1 and Comparative Example 1.

[0098]

[0099] Example 2

[0100] This embodiment provides a method for manufacturing microtextures for the inner wall of a regenerating cooling channel based on integrated SLM processing, including the following steps:

[0101] In this embodiment, three samples with different microgroove sizes were prepared.

[0102] Sample 1: Microgroove dimensions: p = 400 μm, s = h = 250 μm;

[0103] Sample 2: Microgroove dimensions: p = 400 μm, s = h = 350 μm;

[0104] Sample 3: Microgroove dimensions: p = 400 μm, s = h = 450 μm;

[0105] Among them, blank sample: smooth wall surface.

[0106] The SLM process parameters are as follows: laser power of 275W, scanning speed of 1250mm / s, scanning spacing of 100μm, powder thickness of 30μm, and the printing direction is at 90° to the horizontal direction. Pickling operation: A dual-acid system is used for pickling, with an HF-HNO3 concentration ratio of 5%:20%. The pickling is performed in a 35°C water bath with ultrasonic assistance for 5 minutes. The remaining operations are the same as in Example 1.

[0107] The samples (samples 1-3 and a blank sample) with different trench wall surfaces prepared in Example 2 were subjected to circulating water tunnel experiments. The circulating water tunnel experiments were conducted using a circulating water tunnel platform, and the device diagram of the circulating water tunnel platform is shown in Figure 2. Figure 9 As shown. In the circulating water tunnel platform of the circulating water tunnel experiment: 1 is the test section; 2 is the water tank; 3 is the insulation layer; 4 is the heating element; 5 is the wall to be heated; 6 is the thermocouple; 7 is the temperature transmitter; 8 is the wall to be insulated; 9 is the differential pressure transmitter; 10 is the electromagnetic flowmeter; 11 is the centrifugal pump; 12 is the motor frequency converter; 13 is the inlet contraction section; 14 is the outlet expansion section.

[0108] Figure 9 This is a plan view of a multi-functional circulating water tunnel, which consists of test pipe section 1, pump 11, flow meter 10, differential pressure transmitter 9, temperature transmitter 7, contraction pipe section 13, expansion pipe section 14, and water tank 2. The test section in the middle has a 500mm spacing, allowing for the installation of single-cooling-channel or parallel multi-cooling-channel samples as needed for experiments. It can also be replaced with a PIV transparent test pipe section.

[0109] Heating plates were installed on the lower wall (heated wall) of the test section to simulate the unilateral heating condition of the regenerative cooling channel (heating temperature of 200℃). Five thermocouples were arranged at equal intervals along the flow direction in the middle of the upper wall (insulated wall) of the cooling channel of the test section, and their average value was calculated to evaluate the thermal protection performance of the test pipe section. A layer of insulation cotton was wrapped around the outermost layer of the entire test pipe section to reduce heat loss and the interference of ambient temperature on the test results. Ordinary tap water was used as the coolant, and the inlet water temperature was controlled at 24±0.5℃.

[0110] The experimental Reynolds number is D h denoted as characteristic length, p as fluid density, U as fluid velocity, and v as fluid dynamic viscosity.

[0111] Where: D h The value is 4.

[0112] p is 1000 kg / m 3 .

[0113] U is 0.38, 0.99, 1.54, 1.96, 2.42m / s.

[0114] v is 0.001 Pa × s.

[0115] See by the temperature of the insulated wall surface Figure 10The analysis shows the thermal protection capability of the regenerated cooling channel. Under the condition of heating the outer wall at 200°C, the temperature of the insulating surface of the microgrooved cooling channel is consistently lower than that of the smooth wall cooling channel. Moreover, as the No. increases, the difference between the two initially increases gradually, and then tends to level off. This indicates that, under the manufacturing technology of this scheme, the enhanced heat transfer effect of the regenerated cooling flow is significantly improved compared to the smooth channel due to the effect of the microtexture.

[0116] As can be seen from the above embodiments:

[0117] 1. This invention, based on practical needs and applications, designs a method for manufacturing a microtextured regenerated cooling channel inner wall microtexture that can significantly improve product quality, increase processing accuracy, and reduce manufacturing costs.

[0118] 2. The microchannel microtexture processed by this invention can increase the flow rate of the coolant, increase the heat transfer coefficient between the wall and the coolant, and effectively reduce the temperature of the inner wall, thus having a better cooling effect than existing structures.

[0119] 3. This invention achieves precise control over the cross-sectional shape of the processed micro-grooves, including the contour, micro-texture width, and micro-texture depth, by using SLM integrated processing to form the micro-texture within the regenerated cooling channel; and processes a surface feature with a precisely controllable cross-sectional shape and a smooth bottom morphology on the surface of the micro-channel.

[0120] 4. Traditional methods for fabricating microtextures in microchannels, such as laser etching, mainly achieve the purpose of microtexture fabrication in the Z-axis direction. However, SLM integrated fabrication of microtextures and regeneration cooling channel microtextures can achieve the arrangement of microtextures in the X and Y axes, breaking the limitations of traditional methods.

[0121] 4. Under the condition that the total coolant flow rate remains unchanged, the present invention can improve the coolant flow rate and the uniformity of temperature at the same cross section in the cooling channel of the regenerative cooling combustion chamber, thereby preventing the coolant from overheating and vaporizing in a certain place, causing local damage to the combustion chamber, and ensuring uniform and effective cooling of the regenerative cooling combustion chamber.

[0122] 5. This invention can be quickly adapted to the actual engine structure, and has the advantages of wide applicability, economy and convenience, and significant effect, solving the problems of insufficient drag reduction effect and poor adaptability of existing technologies.

[0123] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a microtextured regenerated cooling channel, characterized in that, Includes the following steps: A flow-oriented rectangular microgroove is integrally formed on the inner wall of the regeneration cooling channel using a selective laser melting additive manufacturing method, thus obtaining an initial microgroove structure on the inner wall of the regeneration cooling channel. The cross-section of the downstream rectangular microgroove is rectangular, and the width and depth of the groove are independently 200~500μm; The groove spacing is 400~1000μm; The selective laser melting is performed using a method of horizontal placement of the regenerative cooling channel and vertical processing. The conditions for selective laser melting include: the laser type is a continuous laser, the scanning path is a zigzag path, the powder layer thickness is 30μm, the processing angle is 90°, the power of the continuous laser is 275W, the scanning speed is 1250mm / s, and the scanning interval is 100μm. The initial microgroove structure was acid-washed with a mixed acid solution under ultrasonic conditions to obtain the microtexture regenerated cooling channel. The mixed acid solution was a mixture of hydrofluoric acid and nitric acid, wherein the mass percentage of HF in the mixed acid solution was 1-5%, the mass percentage of HNO3 was 10-20%, the acid washing temperature was 35°C, and the acid washing time was 5 min.

2. The preparation method according to claim 1, characterized in that, The particle size of the forming powder used in the selective laser melting is 15~53μm; the forming powder used in the selective laser melting is TA15 titanium alloy powder.

3. The preparation method according to claim 1 or 2, characterized in that, The conditions for selective laser melting include: the diameter of the laser spot is 80 μm.

4. The preparation method according to claim 1, characterized in that, The mixed acid solution of hydrofluoric acid and nitric acid includes HF, HNO3 and water.

5. The preparation method according to claim 1 or 4, characterized in that, The conditions for the ultrasound include: the power of the ultrasound is 400~500W and the frequency is 40~60kHz.

6. The preparation method according to claim 1, characterized in that, After obtaining the initial microgroove structure, before performing the pickling, the process further includes rinsing the initial microgroove structure using high-pressure gas at a pressure of 0.3~0.6 MPa.

7. The microtextured regenerated cooling channel prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The inner wall of the microtextured regenerative cooling channel has integrally formed, flow-oriented rectangular microgrooves.

8. The application of the microtextured regenerative cooling channel as described in claim 7 in the thermal protection of the engine combustion chamber.

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