A method for connecting foamed materials based on a hollow metal sphere configuration

Abstract

This invention relates to a method for joining foam materials based on a hollow metal sphere configuration, belonging to the field of porous metal material processing technology. It solves the problems of decreased porosity and performance degradation caused by high-energy joining in existing technologies, insufficient low-temperature bonding strength, and uneven current distribution and low bonding strength in porous structures due to pulsed current joining. The method of this invention includes the following steps: S1. Preparing hollow TiAl metal spheres; S2. Preparing and activating the microtexture of the sphere surface; S3. Mixing the spheres with aluminum powder, and then cold isostatically pressing them into foam material preforms; S4. Pre-placed an aluminum foil interlayer at the joining interface of the foam material, and then applying pulsed current and a gradient thermal field for joining. This method achieves efficient, low-temperature joining of metal foams while maintaining high porosity and interfacial strength, making it suitable for lightweight, high-reliability structures.

Description

Technical Field

[0001] This invention relates to the field of porous metal material processing and joining technology, and in particular to a method for joining foam materials based on a hollow metal sphere configuration. Background Technology

[0002] In the processing and application of metal foam materials, joining technology is a key aspect for achieving their structured applications. Joining metal foam materials refers to connecting metal foam units or prefabricated blocks into an integral structure using specific processes to meet particular engineering requirements.

[0003] However, in existing technologies, the joining of metal foam materials mainly employs high-energy joining methods (such as laser welding and diffusion welding) and low-temperature adhesive bonding techniques. However, existing metal foam joining technologies face the following contradictions: while high-energy joining methods (such as laser welding and diffusion welding) can provide high joint strength, they require high heat input, leading to decreased porosity and problems such as grain coarsening and expansion of the heat-affected zone, severely weakening the material's lightweight advantages and functional characteristics; while low-temperature adhesive bonding techniques, although avoiding thermal damage, suffer from low adhesive strength, poor weather resistance, and easy aging, making it difficult to meet the long-term service requirements of highly reliable structures (such as aerospace and automotive load-bearing components).

[0004] In recent years, pulsed current bonding has demonstrated advantages in metal matrix composites (such as fiber / particle reinforced systems) due to its "low-temperature and high-efficiency" characteristics. However, current research on pulsed current bonding mainly focuses on dense materials or continuous reinforcing phases, with limited research on its applicability to special porous structures such as hollow metal sphere reinforced foams. The presence of hollow spheres leads to uneven current conduction at the interface, resulting in insufficient local heat input and weakened bonding strength, thus limiting the application of pulsed current bonding in lightweight, high-reliability structures. Summary of the Invention

[0005] In view of the above analysis, the present invention aims to provide a foam material joining method based on a hollow metal sphere configuration, in order to solve at least one of the following problems in the joining process of existing metal foam materials: collapse of porous structure due to high heat input, low interface bonding strength, coarsening of grains in heat-affected zone, and insufficient strength, low efficiency and high energy consumption of low temperature joining technology.

[0006] On one hand, embodiments of the present invention provide a method for joining foam materials based on a hollow metal sphere configuration, comprising the following steps:

[0007] S1. Preparation of hollow TiAl metal spheres;

[0008] S2. Microtexture preparation and activation are performed on the surface of the hollow TiAl metal sphere to obtain the activated sphere;

[0009] S3. The activated spheres are mixed with aluminum powder and then cold isostatically pressed to form a precast foam material block;

[0010] S4. An aluminum foil intermediate layer is set at the connection interface of the two foam material prefabricated blocks to be connected, and a pulsed current and a gradient thermal field are applied to connect them.

[0011] Furthermore, in S1, the preparation of the hollow TiAl metal spheres includes:

[0012] S11. Titanium powder and aluminum powder in a mass ratio of 3:7 to 7:3 are mixed in anhydrous ethanol to form a mixed slurry;

[0013] S12. The mixed slurry is sprayed into a spherical mold preheated to 1200℃~1400℃ to form a hollow TiAl metal sphere structure;

[0014] S13. The hollow TiAl metal sphere structure is sieved to obtain the hollow TiAl metal sphere.

[0015] Furthermore, in S2, the preparation and activation of the surface microtexture includes the following steps:

[0016] S21. An array of grooves is formed on the surface of the hollow TiAl metal sphere using an ultrafast laser;

[0017] S22. A nanocrystalline layer is generated within the groove array;

[0018] S23. An Al2O3-ZrO2 composite nanocoating is deposited on the surface of the nanocrystalline layer to obtain the activated sphere.

[0019] Furthermore, the diameter of the hollow TiAl metal sphere is 100μm to 500μm.

[0020] Furthermore, in the groove array, the ratio of the width of the groove to the diameter of the hollow TiAl metal sphere satisfies 0.01 to 0.05; the ratio of the depth of the groove to the width of the groove satisfies 0.1 to 0.3.

[0021] Furthermore, the grain size of the nanocrystalline layer is ≤50nm.

[0022] Furthermore, the thickness of the composite nanocoating is 40 nm to 60 nm.

[0023] Furthermore, in S4, the aluminum foil intermediate layer is pure aluminum or aluminum alloy, and the thickness of the aluminum foil intermediate layer is 15μm-100μm.

[0024] Furthermore, in S4, the pulse current parameters are: pulse width 50μs~500μs, frequency 50kHz~200kHz, and pressure 5MPa~10MPa.

[0025] Furthermore, in S4, the temperature gradient ΔT of the gradient thermodynamic field satisfies the formula: ΔT=K×D n Where K = 60℃ / mm~90℃ / mm, n = 0.8~1.1.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1) This invention innovatively integrates hollow TiAl metal sphere reinforcement, surface micro / nano activation treatment, cold isostatic pressing, and pulsed current-gradient thermodynamic field synergistic connection technology. The hollow TiAl spheres possess lightweight, high strength, and excellent thermo-electrical matching; surface microtexture and nano-coating enhance interfacial activity and bonding strength; pulsed current and gradient thermodynamic field achieve precise localized energy input and efficient utilization. This invention effectively solves industry challenges such as structural collapse, weak interfacial bonding, and thermal damage in porous material connections, providing a new approach for lightweight, highly reliable structural connections in aerospace, automotive manufacturing, and other fields.

[0028] 2) This invention achieves a dense metallurgical bond at the joint interface through the synergistic effect of a fractal groove array (increasing the contact area), a nanocrystalline layer (grain size ≤50nm, promoting atomic diffusion), and an Al2O3-ZrO2 composite nanocoating (regulating stress and preventing cracks). The joint strength can reach more than 85% of the substrate strength, which is 40% higher than traditional brazing technology. The material porosity collapse rate is controlled below 5% (far superior to the 25%-40% of traditional methods), and the specific strength of the final product can reach 1.15-1.4, perfectly unifying high strength and lightweight.

[0029] 3) Utilizing the instantaneous heating characteristics of high-frequency pulsed current (50kHz~200kHz) (pulse width 50μs~500μs), combined with gradient thermal field control, rapid and efficient connection is achieved, with an efficiency of 1-2 min / m, approximately 1 / 3 of traditional laser welding methods. The process heat input of this invention is highly concentrated and controllable, strictly controlling the depth of the heat-affected zone (HAZ) to within 100μm, only 1 / 5 of that in laser welding, maximizing the protection of the porous structure of the foam matrix. Rapid pulsed thermal cycling effectively suppresses grain growth, refining the grain size in the connection zone to ≤5μm, avoiding the grain coarsening problem of ≥15μm in traditional welding. By optimizing pulse parameters (e.g., on / off ratio 1:2), energy consumption is significantly reduced to 8-12kJ / cm². 3 Compared to traditional constant current heating (25-40kJ / cm²), 3It saves more than 60% of energy.

[0030] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0031] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0032] Figure 1 A schematic diagram of the thermal explosion reaction forming of multiple TiAl metal spheres inside a spherical mold;

[0033] Figure 2 A schematic diagram illustrating the preparation and activation of microtextures on the surface of a single hollow TiAl metal sphere;

[0034] Figure 3 A schematic diagram of the interface structure connecting the TiAl foam material prefabricated block and the aluminum foil intermediate layer;

[0035] Figure 4 This is a schematic diagram illustrating the technical principle of the foam material bonding method of the present invention.

[0036] Figure 5 This is a schematic diagram of the fractal groove array of the present invention.

[0037] Figure label:

[0038] 1-Spherical mold; 2-Hollow TiAl metal sphere; 3-Al2O3-ZrO2 composite nano-coating; 4-Aluminum foil; 5-Hollow TiAl metal sphere with deposited Al2O3-ZrO2 composite nano-coating; 6-Aluminum powder; 7-Precast block. Detailed Implementation

[0039] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0040] In existing technologies, the joining of metal foam materials mainly employs high-energy joining methods (such as laser welding and diffusion welding) and low-temperature adhesive bonding techniques. However, these methods present significant contradictory problems. While high-energy joining methods can provide high joint strength, they require high heat input, leading to a significant decrease in the overall porosity of the material (relative decrease ≥25%), accompanied by problems such as grain coarsening (grain size ≥15μm) and expansion of the heat-affected zone (300-500μm), severely weakening the material's lightweight advantages and functional properties. On the other hand, while low-temperature adhesive bonding techniques avoid heat damage, the low strength of the adhesive layer, poor weather resistance, or insufficient brazed joint strength (only 45%-65% of the substrate strength) makes it difficult to meet the long-term service requirements of highly reliable structures (such as aerospace and automotive load-bearing components).

[0041] To address the above problems, this invention proposes a method for connecting foam materials based on a hollow metal sphere configuration, comprising the following steps:

[0042] S1. Preparation of hollow TiAl metal spheres;

[0043] S2. Microtexturing and activation of the sphere surface;

[0044] S3. Mix the sphere with aluminum powder, and then cold isostatically press it into a precast foam material block;

[0045] S4. Set an aluminum foil intermediate layer at the connection interface of the two precast foam material blocks to be connected, and apply pulse current and gradient thermal field to connect them.

[0046] Specifically, this invention achieves efficient bonding of hollow metal sphere foam materials through the following innovative methods, improving the joint strength and weather resistance, maintaining the material's lightweight advantage, and effectively solving the problems of decreased porosity and insufficient bonding strength caused by excessive heat input:

[0047] (1) Selection of hollow TiAl metal spheres: Hollow TiAl metal spheres were selected as the reinforcing phase. These spheres possess lightweight, high conductivity, high strength, and excellent thermal matching properties, effectively solving the performance limitations of traditional reinforcing materials. At the same time, the hollow structure provides a path for current conduction, improving the mechanical properties and electrical conductivity of the material.

[0048] (2) Surface micro-texture preparation and activation: The surface micro-nano structure preparation and activation treatment of the present invention enhances the metallurgical bonding performance of porous interfaces, achieves excellent interface bonding strength, and provides a stronger metallurgical bonding basis for material connection.

[0049] (3) Application of cold isostatic pressing technology: The cold isostatic pressing technology can effectively densify the material while maintaining its integrity, reduce the damage to the pore structure caused by traditional hot processing, maintain the material's lightweight advantage, and avoid the degradation of material properties caused by high-temperature processing.

[0050] (4) Synergistic connection process of pulsed current and gradient thermal field: The synergistic connection process of pulsed current and gradient thermal field is adopted. By selectively heating the interfacial aluminum foil intermediate layer (utilizing the low-temperature melting characteristics of aluminum, temperature <600℃), local low-temperature connection is achieved, which effectively controls the range of heat-affected zone and avoids damage to the overall structure of the material.

[0051] In terms of performance, this invention exhibits the following technical advantages:

[0052] (a) The connection strength is improved, reaching more than 85% of the strength of the substrate.

[0053] (b) The heat-affected zone (HAZ) is extremely shallow, less than 100 μm, only 1 / 5 the depth of traditional laser welding, significantly reducing thermal damage. At the same time, the grain size within the HAZ is controlled to ≤5 μm, effectively avoiding the grain coarsening problem (grain size ≥15 μm) commonly found in traditional welding.

[0054] (c) The pore collapse rate is reduced to less than 5%, which is far lower than the 25%-40% of traditional laser welding, effectively maintaining the lightweight characteristics of the material and preserving the integrity of the pore structure.

[0055] (d) The connection efficiency is 1-2 min / m, which significantly improves production efficiency.

[0056] (e) The specific strength reaches 1.15-1.4, which enhances the structural properties of the material.

[0057] These technological advantages make this invention have significant application potential and development prospects in the field of lightweight and highly reliable metal foam material connection, providing an efficient and reliable connection solution for fields with extremely high material performance requirements such as aerospace and automotive manufacturing.

[0058] Furthermore, in step S1, the preparation of the hollow TiAl metal spheres includes the following steps:

[0059] S11. Titanium powder and aluminum powder are placed in an ultrasonic vacuum jar containing anhydrous ethanol at a mass ratio of 3:7 to 7:3 (e.g., 3:7, 4:6, 5:5, 6:4, 7:3, 5:5). The mixture is thoroughly mixed by ultrasonic action to form a uniform slurry.

[0060] S12. The mixed slurry is sprayed into a spherical mold preheated to 1200℃~1400℃ (e.g. 1200℃, 1240℃, 1280℃, 1320℃, 1360℃, 1400℃), the mold being in a vacuum environment to avoid interference from oxidation and other impurities.

[0061] S13. Under high-temperature conditions, anhydrous ethanol rapidly evaporates, while titanium and aluminum powders undergo a thermal explosion reaction, accompanied by intense exothermic reaction and gas release. This process causes the mixture to rapidly expand within the mold and form multiple hollow TiAl metal spheres, such as... Figure 1 As shown, the spherical mold 1 contains multiple hollow TiAl metal spheres 2 of different sizes.

[0062] S14. The formed hollow TiAl metal spheres are screened by a sieving device to collect hollow TiAl metal spheres with a particle size range of 100μm to 500μm (e.g., 100μm, 200μm, 300μm, 400μm, 500μm) to meet the requirements of subsequent processing and application.

[0063] It should be noted that, through analysis of the thermal explosion reaction process (the combined effects of localized melting of titanium-aluminum powder, gas escape, and melt surface tension), and combined with the measured properties of the prepared spheres, such as low density and high specific surface area, it is inferred that the hollow structure of the TiAl metal spheres is not a simple closed cavity, but rather an internally formed honeycomb-like porous cavity, resulting in a lightweight configuration. This specific configuration is the key reason why the material possesses both low density (lightweight), high specific surface area, and good mechanical properties.

[0064] Hollow spheres used in traditional metal foams are primarily made of materials such as stainless steel, nickel-based alloys, or titanium alloys. These materials are typically prepared using processes such as powder metallurgy, electrodeposition, or vapor deposition. However, these methods have several drawbacks: stainless steel spheres have a high density, which is not conducive to weight reduction; nickel-based alloy spheres are expensive and complex to process; and traditional titanium alloy spheres require high-temperature treatment, which can easily lead to uneven wall thickness or deformation. Furthermore, while aluminum alloy hollow spheres can reduce weight, their lower strength makes them prone to interface problems during connection, thus affecting joint performance.

[0065] This invention utilizes hollow TiAl metal spheres, which offer significant advantages over traditional materials. TiAl metal spheres combine lightweight and thermal stability with high strength, making them more suitable for subsequent pulsed current connection processes. Due to TiAl's excellent electrical conductivity, it ensures uniform current distribution during connection, while its low coefficient of thermal expansion reduces thermal stress, thereby improving joint reliability.

[0066] Specifically, in step S11, titanium powder with a purity ≥99.9% and a particle size of 10μm–50μm and aluminum powder with a purity ≥99.9% and a particle size of 10μm–50μm are mixed in a mass ratio of 3:7 to 7:3 and placed in an ultrasonic vacuum container filled with anhydrous ethanol. The amount of anhydrous ethanol is sufficient to completely submerge the powder. Under vacuum conditions, ultrasonic-assisted dispersion is used, with ultrasonic dispersion parameters of frequency 20kHz–60kHz and time 5min–30min, to ensure uniform mixing of the powder. In this step, the role of anhydrous ethanol is to prevent the powder from sticking together before the high-temperature reaction and to rapidly volatilize during the thermal explosion reaction, avoiding any impact on the product composition.

[0067] Specifically, in step S12, the uniformly mixed titanium-aluminum powder slurry is sprayed through a nozzle into a preheated spherical mold.

[0068] The mold is made of high-purity graphite and is a hollow sphere with a diameter of 500μm to 1000μm. The preheating temperature of the mold is 1200℃ to 1400℃ (within the range of the titanium-aluminum thermal explosion reaction temperature). The main function of the mold is to control the sphericity of the product and ensure that the formed hollow TiAl metal spheres have a uniform spherical structure.

[0069] This invention innovatively employs an ultrasonic-assisted dispersion and thermal explosion reaction spray forming process to prepare TiAl hollow spheres, which has significant advantages over traditional methods:

[0070] First, ultrasonic-assisted dispersion is used to achieve uniform mixing of titanium and aluminum powders, ensuring the homogeneity of the slurry. Then, utilizing the characteristics of a thermal explosion reaction, the titanium and aluminum powders undergo a vigorous reaction at high temperatures, with the volatility of aluminum promoting the formation of hollow structures. This process not only avoids the contamination problems associated with traditional pore-forming agents but also achieves in-situ generation of hollow structures, ensuring the purity and structural integrity of the material.

[0071] Secondly, the thermal explosion reaction is completed within seconds, and its instantaneous high temperature ensures that the material reacts fully while effectively suppressing grain coarsening. This rapid reaction mechanism avoids the grain growth problems commonly encountered in traditional high-temperature sintering processes, thus ensuring the uniformity of the material's microstructure and its high strength properties.

[0072] Furthermore, the thermal explosion reaction utilizes the material's own exothermic properties to promote efficient element synthesis, not only avoiding the deformation problems caused by traditional high-temperature sintering but also improving preparation efficiency. This process can rapidly generate TiAl hollow spheres with honeycomb-like porous cavities, providing an ideal lightweight and high-strength interface structure for subsequent high-strength bonding processes.

[0073] In summary, the process of this invention not only improves the purity and structural stability of TiAl hollow spheres, but also enhances the preparation efficiency, providing a new technical approach for lightweighting and high-performance applications in aerospace, automotive manufacturing, and other fields.

[0074] Furthermore, in step S2, as Figure 2 As shown, the preparation and activation of microtextures on the surface of the sphere includes the following steps:

[0075] S21. Using ultrafast lasers to process fractal groove arrays on the contact surface of hollow TiAl metal spheres;

[0076] S22. The surface of the fractal groove is subjected to laser shock strengthening treatment to generate a nanocrystalline layer on its surface;

[0077] S23. Deposit an Al2O3-ZrO2 composite nanocoating on the surface of the nanocrystalline layer.

[0078] Furthermore, in step S21, an ultrafast laser processing system with a femtosecond or picosecond pulse width is selected. This laser system can release high energy in an extremely short time, thereby ensuring processing accuracy and efficiency. A three-dimensional fractal processing path covering the sphere's contact surface is planned using computer-aided design (CAD) software. During processing, through the coordinated control of the laser scanning motion and the three-dimensional fractal processing path, a consistent array of fractal grooves is formed on the sphere's contact surface.

[0079] Appendix Figure 5 An array of fractal grooves on the surface of a hollow TiAl metal sphere is shown. The grooves are arranged in an ordered and repeating pattern, forming a continuous microtexture with self-similar characteristics, which functionally optimizes the surface of the sphere.

[0080] Specifically, the arrangement of the grooves ensures a uniform distribution on the surface of the sphere, thereby effectively increasing the contact area without sacrificing the overall structural strength of the sphere. This invention controls the ratio of the groove width to the sphere diameter to be between 0.01 and 0.05, and the ratio of the groove depth to the width to be between 0.1 and 0.3, thus ensuring an effective increase in contact area while avoiding an excessive reduction in the structural strength of the sphere, increasing the contact area by approximately 300%.

[0081] Furthermore, the fractal groove design features geometric fractal characteristics, with its fractal dimension optimized to be controlled between 1.2 and 1.6. Through mechanical interlocking, it effectively increases the contact area by up to 300%. Simultaneously, the fractal groove's structural design guides stress dispersion along the normal direction, reducing the stress concentration factor to 1.2–1.5, a reduction of 50%–70% compared to traditional designs. This contributes to improving the overall connection strength from a structural perspective.

[0082] Furthermore, in stage S22, a nanocrystalline layer is generated on the surface of the fractal groove using laser shock peening via the following steps:

[0083] S221. Pretreatment: First, the groove surface is ultrasonically cleaned with anhydrous ethanol at a frequency of 20kHz to 60kHz for 5 to 15 minutes to remove processing residues. Then, a coating is sprayed. The coating consists of graphite and acrylate in a mass ratio of 1:1 to 3:1, with a thickness of 20±5μm. This serves as a laser energy absorption layer, which can improve the laser energy absorption rate.

[0084] S222. Laser Shock Enhancement: A nanosecond pulsed laser (Nd:YAG) with a wavelength set at 1064 nm is used to match the spectral characteristics of the absorption layer. The pulse energy is controlled at 5-15 J to regulate the plasma pressure peak; the spot diameter is 1-3 mm to ensure coverage of the groove width; the pulse width is 10-30 ns to control the depth of the heat-affected zone; the overlap rate is 50%-70% to avoid unimpacted areas.

[0085] S223. Dynamic confinement: A flowing water layer with a thickness of 1.5-2 mm and a flow velocity of 0.3-0.7 m / s is used as the confinement medium. This can extend the plasma pressure action time to the microsecond level, thereby enhancing the effect of laser shock.

[0086] S224. Process quality control: Utilizing a high-speed camera (frame rate 10) 7 The plasma morphology is captured online (fps), and the laser energy is adjusted via feedback to ensure process stability. Simultaneously, electron backscatter diffraction (EBSD) analysis is used to ensure that the grain size does not exceed 50 nm, and the proportion of grain boundaries with an orientation difference greater than 15° is not less than 80%. The grain size of the nanocrystalline layer of this invention is controlled within 50 nm (e.g., 10 nm, 20 nm, 30 nm, 40 nm, 50 nm), and its ultra-high density grain boundaries (≥10... 16 m -2 It can provide a short-circuit diffusion path, generate a high concentration of non-equilibrium vacancies, reduce the diffusion activation energy by 65%, thereby improving the interfacial diffusion activity and providing a fast diffusion channel for subsequent bonding, thus improving the metallurgical bonding efficiency by 370 times.

[0087] Furthermore, in stage S23, an Al2O3-ZrO2 composite nanocoating is deposited on the surface of the nanocrystalline layer through the following steps:

[0088] S231. Surface Plasma Activation: Using a gas mixture consisting of Ar (80% vol) and O2 (20% vol), at a power of 300 W, a processing time of 5 min, and a vacuum degree of 10... -2Plasma activation treatment is performed under Pa conditions. Plasma activation treatment can effectively remove surface organic matter and hydroxylate it, thereby reducing the contact angle to below 5° (superhydrophilic state) and avoiding secondary pollution.

[0089] S232. Magnetron sputtering deposition of Al2O3 layer: High-purity Al2O3 target material (purity 99.99%, diameter 100mm) is used for deposition using a DC magnetron sputtering system with a substrate rotation speed of 10rpm to ensure coating uniformity.

[0090] S233. Pulsed laser interface enhancement: using a wavelength of 355nm (ultraviolet) and an energy density of 0.5J / cm². 2 Laser parameters with a pulse width of 10 ns. The mechanism of laser action is to induce amorphization of the Al2O3 layer, thereby forming micropores with a diameter of 5-10 nm, which enhances the mechanical intercalation with the ZrO2 layer.

[0091] S234. Reactive sputtering deposition of ZrO2 layer: Ar (95% vol) and O2 (5% vol) were used as reactive gases, and the target material was a metallic Zr target (99.95% purity). A pulsed DC sputtering mode was used with a frequency of 50 kHz and a duty cycle of 70% to achieve high-quality deposition of ZrO2 layer.

[0092] S235. Alternating Deposition and Annealing: Alternating deposition was performed according to a [Al2O3 (5nm) / ZrO2 (5nm)]×5 stacked structure, with a total thickness of 50nm. Subsequently, vacuum annealing was carried out in a high-purity N2 atmosphere (dew point less than -70℃) at a temperature of 450℃ (below the recrystallization temperature of the nanocrystalline layer) for 30 minutes. The annealing process transformed ZrO2 from an amorphous state to the tetragonal phase (t-ZrO2), thereby endowing the coating with phase transformation toughening capabilities.

[0093] Furthermore, the thickness of the composite nanocoating is 40nm to 60nm (e.g., 40nm, 44nm, 48nm, 52nm, 56nm, 60nm).

[0094] Preferably, the thickness of the composite nanocoating is 50 nm ± 10 nm. This invention achieves excellent performance through a gradient design of the coefficient of thermal expansion. Specifically, it involves a TiAl substrate (23.6 × 10⁻⁶ nm thicker than a standard layer). -6 / K) to the ZrO2 intermediate layer (10.5×10 -6 / K) then to the Al2O3 surface layer (8.1×10 -6The coefficient of thermal expansion (COP) varies gradually across the substrate ( / K). The ZrO2 intermediate layer acts as a transition layer, bridging the thermal expansion difference between the substrate and the surface Al2O3 layer, thus reducing interfacial stress. Simultaneously, the ZrO2 layer absorbs crack propagation energy through the phase transformation toughening effect (t→m) of its tetragonal-to-monoclinic phase, reducing residual stress in the coating by up to 66%. Furthermore, the surface Al2O3 layer inhibits interfacial oxidation, and combined with surface smoothing treatment, reduces the high-temperature friction coefficient to below 0.15, thereby comprehensively optimizing the performance of the interface.

[0095] Through the synergistic effect of the above processes (such as...) Figure 4 As shown, the fractal groove array achieves initial high-strength bonding through mechanical interlocking, significantly increasing the contact area by 300%. Its unique geometric constraint structure guides atoms to accumulate in the nanocrystalline layer along a predetermined path. The nanocrystalline layer, with its ultra-high density of grain boundaries, constructs atomic-level rapid diffusion channels, increasing the diffusion rate by several orders of magnitude. It is estimated that the metallurgical bonding efficiency can be improved by up to 370 times. Simultaneously, it accelerates atomic migration, ultimately forming a defect-free transition layer with a thickness of not less than 5 μm. Furthermore, the Al2O3-ZrO2 composite nanocoating, through its gradient design of thermal expansion coefficients, effectively absorbs and releases interfacial thermal stress, reducing residual stress by 66%, thereby effectively suppressing the generation of thermal stress cracks and ensuring the integrity of the diffusion layer.

[0096] Through the synergistic effect of these three factors, not only is the interfacial bonding quality of porous materials significantly improved, but the final product also possesses excellent mechanical properties and connection reliability. The interfacial bonding strength surpasses the intrinsic limits of traditional materials, reaching over 85% of the substrate strength, while the pore collapse rate is controlled below 5%, greatly maintaining the material's lightweight advantage. The specific strength of the final product can reach 1.15-1.4, achieving a high level of unity between lightweight design and high reliability—a first in the industry.

[0097] Specifically, in stage S3, prefabricated foam material blocks are prepared using a cold isostatic pressing process. The specific steps are as follows:

[0098] S31. The hollow Ti-Al metal spheres processed in step S2 are thoroughly mixed with high-purity aluminum powder (purity ≥99.9%) with a particle size of 10μm to 50μm at a mass ratio of 1:1 under vacuum drying. This mixing ratio ensures that the aluminum powder fully fills the gaps between the spheres while maintaining the overall fluidity of the material, thus providing a good foundation for subsequent molding.

[0099] S32. The uniformly mixed powder is loaded into a flexible mold and prefabricated into porous preforms of a specific shape using a cold isostatic pressing (CIP) process. The parameters of the CIP process are controlled within the range of pressure 200-300 MPa and holding time 5-10 min. These pressure and holding time settings ensure that the preforms have good structural strength and molding quality, while avoiding damage to the material's microstructure due to excessive pressure or holding time.

[0100] Through the above process, the resulting foam material prefabricated block possesses an optimized pore structure and excellent mechanical properties, achieving a balance between lightweight and structural strength. This provides an ideal matrix material for the subsequent pulsed current-gradient thermal field bonding process, ensuring the overall efficiency and reliability of the process.

[0101] Furthermore, in stage S4, the connection of the precast foam blocks is achieved through an optimized pulsed current-gradient thermal field process, the specific steps of which are as follows:

[0102] S41. Place an aluminum foil interlayer with a thickness of 15μm to 100μm (e.g., 15μm, 30μm, 45μm, 60μm, 75μm, 90μm, 100μm) at the interface between the two precast foam material blocks to be connected. Figure 3 As shown, the aluminum foil can be pure aluminum or an aluminum alloy. Aluminum foil was chosen based on its low melting point (pure aluminum melts at 660℃, while some aluminum alloys can melt as low as 577℃) and high thermal conductivity. Under the action of a pulsed current, the aluminum foil can rapidly heat up and form a low-temperature bonding interface below 600℃. This process ensures good metallurgical bonding while avoiding damage to the porous structure of the foam material from high temperatures, thus maintaining the connection strength while preserving the material's lightweight properties.

[0103] S42. A high-frequency DC pulsed current and a gradient thermal field are applied to the aluminum foil interlayer using a pulsed current device. The pulsed current generates concentrated Joule heat through the aluminum foil, causing it to rapidly melt and wet the surfaces of the prefabricated blocks on both sides. Through liquid-phase mass transfer and subsequent cooling and solidification, a stable metallurgical bond is achieved. In this process, the aluminum foil interlayer effectively acts as a connecting interface, promoting a stable bond between the two foam materials while meeting the requirements of lightweight and high strength of the overall structure.

[0104] Furthermore, the pulsed current device consists of the following three main parts:

[0105] (1) Pulse current generator: It can output pulse signals with adjustable frequency between 50kHz and 200kHz (e.g., 50kHz, 75kHz, 100kHz, 125kHz, 150kHz, 175kHz, 200kHz) and adjustable pulse width between 50μs and 500μs (e.g., 50μs, 100μs, 150μs, 200μs, 250μs, 300μs, 350μs, 400μs, 450μs, 500μs). By comprehensively adjusting the frequency and pulse width, the device can achieve a duty cycle range of 10% to 90%, thereby utilizing the concentrated effect of Joule heating.

[0106] (2) Gradient electrode system: A copper / graphene composite multilayer heteroelectrode is used to establish an axial temperature gradient ΔT. The temperature gradient ΔT and the diameter D of the hollow Ti-Al metal sphere satisfy the relationship ΔT=K×Dn, where the value of K ranges from 60℃ / mm to 90℃ / mm, and the value of n ranges from 0.8 to 1.1.

[0107] (3) Pressure sensing module: used to monitor the interface contact resistance in real time, with a measurement accuracy of ±0.1mΩ. Within the pressure range of 5MPa-10MPa, the pressure sensing module can ensure tight contact at the connection interface.

[0108] Furthermore, to further improve connection efficiency and quality, this invention also optimizes the relevant parameters: by using high-frequency pulses (frequency ≥ 50 kHz) and short pulse widths (≤ 0.1 ms), the exposure time of materials at high temperatures can be effectively shortened, thereby suppressing the occurrence of interface oxidation; by combining low duty cycles (10%-30%) and high peak currents (≥ 500 A), the concentration effect of Joule heating is used to promote atomic diffusion; and by employing an intermittent pulse mode (on / off ratio of 1:2), the temperature field is maintained by means of heat conduction, thereby reducing energy consumption.

[0109] The technical advantages of this invention are mainly reflected in the following aspects: the heating rate of the pulsed current-gradient thermal field can reach 300-500℃ / s, significantly higher than the 20-50℃ / s of the traditional constant current heating method. This not only shortens the processing time but also greatly improves production efficiency. The interface temperature control accuracy reaches ±5℃, which is higher than the ±15℃ of the traditional method, helping to ensure the stability of the connection quality. The energy consumption is only 8-12kJ / cm². 3 It is far lower than the 25-40 kJ / cm of traditional methods. 3 This demonstrates higher energy efficiency. Furthermore, grain growth tendency is effectively controlled, with grain size in the heat-affected zone less than 5 μm, far smaller than the ≥15 μm of traditional methods, thus helping to maintain the material's microstructure and properties.

[0110] In summary, this invention, through the synergistic optimization of multiple parameters, including key parameters such as pulse frequency, duty cycle, and temperature gradient formula (ΔT), comprehensively surpasses traditional constant current heating methods in terms of energy consumption, efficiency, and accuracy. This invention achieves efficient and uniform bonding of hollow metal spherical foam materials while maintaining the material's lightweight and high-performance characteristics. This provides an innovative and effective solution for the application of lightweight, highly reliable structures.

[0111] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0112] Example 1

[0113] A method for bonding foam materials based on a hollow metal sphere configuration includes the following steps:

[0114] S1. Preparation of hollow TiAl metal spheres, including the following steps:

[0115] S11. Mix titanium powder (99.9% purity, 30μm particle size) and aluminum powder (99.9% purity, 30μm particle size) at a mass ratio of 3:7; place the mixture in an ultrasonic vacuum container filled with anhydrous ethanol. The ethanol should completely submerge the powder. Disperse the powder using ultrasound under vacuum to ensure uniform mixing.

[0116] S12. Inject the slurry into a graphite spherical mold (800 μm in diameter) that has been preheated to 1300°C; the mold is set in a vacuum environment.

[0117] S13. At high temperature, anhydrous ethanol evaporates rapidly, while titanium powder and aluminum powder undergo a thermal explosion reaction, forming multiple hollow TiAl metal spheres inside the mold;

[0118] S14. The formed hollow TiAl metal spheres are sieved to collect hollow TiAl metal spheres with a particle size of 300 μm.

[0119] S2. Microtexture preparation and activation of the sphere surface, including the following steps:

[0120] S21. Use an ultrafast laser to process a fractal groove array on the contact surface of a hollow TiAl metal sphere. Select an ultrafast laser processing system with a femtosecond or picosecond pulse width, a pulse width of 10-100 fs, and a repetition frequency of 1-10 kHz.

[0121] A three-dimensional fractal machining path covering the contact surface of the sphere is planned using computer-aided design (CAD) software. During the machining process, through the coordinated control of laser scanning motion and the three-dimensional fractal machining path, an array of fractal grooves with a depth of approximately 2 μm and a width of approximately 10 μm is formed on the contact surface of the sphere.

[0122] S22. A nanocrystalline layer with a grain size of 40 nm is generated on the surface of the fractal groove by laser shock strengthening. The specific steps are as follows:

[0123] S221. Pretreatment: First, the groove surface is ultrasonically cleaned with anhydrous ethanol at a frequency of 40 kHz for 10 min to remove processing residues. Then, a blackening coating is sprayed. The coating consists of graphite and acrylate in a mass ratio of 2:1 and has a thickness of 20±5 μm. This serves as a laser energy absorption layer, which can improve the laser energy absorption rate.

[0124] S222. Laser Shock Enhancement: A nanosecond pulsed laser (Nd:YAG) with a wavelength set at 1064 nm is used to match the spectral characteristics of the absorption layer. The pulse energy is controlled at 5-15 J to regulate the peak plasma pressure; the spot diameter is 1-3 mm to ensure coverage of the groove width; the pulse width is 10-30 ns to control the depth of the heat-affected zone; and the overlap rate is 50-70% to avoid unimpacted areas.

[0125] S223. Dynamic confinement: A flowing water layer with a thickness of 1.5-2 mm and a flow velocity of 0.5 m / s is used as the confinement medium, which can extend the plasma pressure action time to the microsecond level.

[0126] S224. Process quality control: Utilizing a high-speed camera (10... 7 The plasma morphology is captured online at fps, and the laser energy is adjusted via feedback. Simultaneously, EBSD analysis is used to ensure that the grain size does not exceed 40 nm and that the proportion of grain boundaries with an orientation difference greater than 15° is not less than 80%.

[0127] S23. Deposit an Al2O3-ZrO2 composite nanocoating with a thickness of 50 nm on the surface of the nanocrystalline layer, the specific steps of which are as follows:

[0128] S231. Surface Plasma Activation: Using a gas mixture of Ar (80% vol) and O2 (20% vol), at a power of 300 W, a processing time of 5 min, and a vacuum degree of 10... -2 Plasma activation treatment is performed under Pa conditions to remove organic matter and hydroxylate the surface, thereby reducing the contact angle to less than 5°, achieving a superhydrophilic state, and avoiding secondary pollution.

[0129] S232. Magnetron sputtering deposition of Al2O3 layer: A high-purity Al2O3 target (99.99%, diameter 100mm) was used for deposition using a DC magnetron sputtering system with a substrate rotation rate of 10rpm.

[0130] S233. Pulsed laser interface enhancement: Laser parameters are wavelength 355nm (ultraviolet), energy density 0.5J / cm². 2 The pulse width is 10 ns. Its mechanism of action is that the laser induces the amorphization of the Al2O3 layer, thereby forming micropores with a diameter of 5-10 nm, which enhances the mechanical intercalation with the ZrO2 layer.

[0131] S234. Reactive sputtering deposition of ZrO2 layer: The reactive gases are Ar (95% vol) and O2 (5% vol), the target material is a metallic Zr target (99.95%), and the pulsed DC sputtering mode is used with a frequency of 50 kHz and a duty cycle of 70%.

[0132] S235. Alternating Deposition and Annealing: Alternating deposition was performed according to a [Al2O3 (5nm) / ZrO2 (5nm)]×5 stacked structure, with a total thickness of 50nm. Then, vacuum annealing was carried out in a high-purity N2 atmosphere (dew point less than -70℃) at a temperature of 450℃ (below the recrystallization temperature of the nanocrystalline layer) for 30 minutes. The annealing process transformed ZrO2 from an amorphous state to a tetragonal phase (t-ZrO2), acquiring phase transformation toughening capability.

[0133] S3. Cold isostatic pressing is used to form precast foam blocks, including the following steps:

[0134] S31. The hollow Ti-Al metal spheres processed in step S2 are thoroughly mixed with high-purity aluminum powder (purity ≥99.9%) with a particle size of 30μm at a mass ratio of 1:1 under vacuum drying environment;

[0135] S32. The uniformly mixed powder is cold isostatically pressed (pressure 250MPa, holding time 8min) to form a precast foam material block.

[0136] S4. The connection of the precast foam blocks is accomplished using optimized pulsed current-gradient thermal field technology. The specific implementation steps are as follows:

[0137] S41. Set an aluminum foil (pure aluminum or aluminum alloy) intermediate layer with a thickness of 60μm at the connection interface of the two foam material prefabricated blocks to be connected;

[0138] S42. A high-frequency DC pulse (frequency 100kHz, pulse width 300μs, duty cycle 20%) and a gradient thermal field are applied to the intermediate layer of the aluminum foil using a pulsed current device to achieve connection. The gradient thermal field ΔT is 2100℃, and the pressure is 8MPa. Under the action of the pulsed current, the aluminum foil rapidly forms a low-temperature connection interface of <600℃.

[0139] Example 2

[0140] A method for connecting foam materials based on a hollow metal sphere configuration differs from Example 1 only in the following parameters:

[0141] The pulse current frequency was increased to 150kHz, the pulse width was shortened to 200μs, the duty cycle was 15%, and an intermittent pulse mode (on / off ratio 1:2) was adopted to reduce energy consumption. The composite nano-coating thickness was 40nm, and the aluminum foil interlayer thickness was 15μm.

[0142] Example 3

[0143] A method for connecting foam materials based on a hollow metal sphere configuration. The only difference from Example 1 is that the diameter of the hollow Ti-Al metal sphere is 100 μm, the groove depth h = 0.6 μm, and the groove width is 3 μm. The pulse frequency is 50 kHz, the pulse width is 500 μs, and the duty cycle is 10%. The gradient thermal field ΔT is 1200℃, and the pressure is 5 MPa. The composite nano-coating thickness is 50 nm, and the aluminum foil interlayer thickness is 60 μm.

[0144] Example 4

[0145] A method for connecting foam materials based on a hollow metal sphere configuration differs from Example 1 only in that: the diameter of the hollow Ti-Al metal sphere is 500 μm, the groove depth h = 3 μm, and the groove width is 15 μm. The pulse frequency is 200 kHz, the pulse width is 100 μs, and the duty cycle is 30%. The gradient thermal field ΔT is 4500℃, and the pressure is 10 MPa. The composite nano-coating thickness is 60 nm, and the aluminum foil interlayer thickness is 100 μm.

[0146] Example 5

[0147] A method for connecting foam materials based on a hollow metal sphere configuration differs from Example 1 only in that: the diameter of the hollow Ti-Al metal sphere is 300 μm, the groove depth h = 3 μm, and the groove width is 15 μm. The pulse frequency is 125 kHz, the pulse width is 300 μs, and the duty cycle is 20%. The gradient thermal field ΔT is 2700℃, and the pressure is 7 MPa. The composite nano-coating thickness is 50 nm, and the aluminum foil interlayer thickness is 80 μm.

[0148] Comparative Example 1

[0149] The foam material is connected using a traditional constant current heating method, and the foam material prefabricated blocks are connected using a resistance furnace heating method. There is no gradient thermal field, the heating rate is 30℃ / s, the pressure is 10MPa, and the holding time is 10min.

[0150] Comparative Example 2

[0151] The only difference from Example 1 is that step S2 is omitted, and the hollow TiAl metal spheres have no fractal groove array, nanocrystalline layer and Al2O3-ZrO2 coating on their surface.

[0152] Comparative Example 3

[0153] The foam material was joined using a conventional diffusion welding process at a welding temperature of 900℃, a pressure of 15MPa, and a holding time of 30min.

[0154] Comparative Example 4

[0155] The foam material was joined using a conventional brazing process, employing Al-Si brazing filler metal (melting point 577℃). Heating method: induction heating, heating rate 50℃ / s. Filler metal thickness: 100μm, pressure: 5MPa, holding time: 5min.

[0156] Comparative Example 5

[0157] The only difference from Example 1 is that DC sintering is used instead of pulsed current, with a current density of 100 A / mm. 2 Heating rate: 80℃ / s, no gradient thermal field.

[0158] Comparative Example 6

[0159] Conventional TiAl metal spheres were used: The only difference from Example 1 was that solid TiAl metal spheres were used instead of hollow ones. All other steps and parameters were the same as in Example 1.

[0160] Comparative Example 7

[0161] The only difference from Example 1 is that the cold isostatic pressing process in step S3 is omitted. The hollow TiAl metal spheres processed in step S2 and the loosely mixed aluminum powder are directly filled into the mold and joined under the same pulsed current-gradient thermodynamic field process parameters (step S4). Other steps and parameters are the same as in Example 1.

[0162] The characterization results are summarized in Table 1.

[0163] Table 1

[0164]

[0165] Compared with Comparative Examples 1-7, Examples 1-5 of the present invention exhibit superior performance in terms of bonding strength (reaching 83%-88% of the substrate strength, significantly higher than the 5%-65% of the Comparative Examples), heat-affected zone control (≤100μm, only 1 / 10 to 1 / 3 of the 300-1000μm of the Comparative Examples), structural integrity (pore collapse rate <5.5%, significantly lower than the 25%-90% of the Comparative Examples), process efficiency (bonding efficiency 1-2 min / m, 2-5 times that of the 4-10 min / m of the Comparative Examples), and energy consumption (energy consumption 7-12 kJ / cm). 3 Only the comparative example is 25-70 kJ / cm. 3 It exhibits significant advantages in aspects such as 1 / 10 to 1 / 3 of the strength of the material, while effectively suppressing grain coarsening in the heat-affected zone (grain size ≤5μm, much finer than the ≥15μm of the comparative example), resulting in a specific strength of 1.15-1.4, which is much higher than the 0.4-0.9 of the comparative example. This fully demonstrates the comprehensive breakthrough of the method of the present invention in terms of high strength, low damage, and high-efficiency bonding.

[0166] In summary, this invention achieves high strength, low damage, and high-efficiency bonding of foam materials through hollow metal sphere configuration optimization, surface microtexture activation, and synergistic regulation of pulsed current-gradient thermodynamic field. All performance indicators surpass those of traditional methods, providing an innovative solution for the engineering application of lightweight structural materials.

[0167] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for connecting foam materials based on a hollow metal sphere configuration, characterized in that, Includes the following steps: S1. Preparation of hollow TiAl metal spheres; S2. Microtexture preparation and activation are performed on the surface of the hollow TiAl metal sphere to obtain the activated sphere; The microtexture preparation and activation includes the following steps: S21. An array of grooves is formed on the surface of the hollow TiAl metal sphere using an ultrafast laser; S22. A nanocrystalline layer is generated within the groove array; S23. An Al2O3-ZrO2 composite nanocoating is deposited on the surface of the nanocrystalline layer to obtain the activated spheres; S3. The activated spheres are mixed with aluminum powder and then cold isostatically pressed to form a precast foam material block; S4. An aluminum foil intermediate layer is set at the connection interface of the two precast foam material blocks to be connected, and pulsed current and gradient thermal field are applied to connect them. The temperature gradient ΔT of the gradient thermal field and the diameter D of the hollow TiAl metal sphere satisfy the formula: ΔT=K×D n Where K = 60℃ / mm ~ 90℃ / mm, n = 0.8 ~ 1.

1.

2. The method according to claim 1, characterized in that, In S1, the preparation of the hollow TiAl metal spheres includes: S11. Titanium powder and aluminum powder in a mass ratio of 3:7 to 7:3 are mixed in anhydrous ethanol to form a mixed slurry; S12. The mixed slurry is sprayed into a spherical mold preheated to 1200℃~1400℃ to form a hollow TiAl metal sphere structure; S13. The hollow TiAl metal sphere structure is sieved to obtain the hollow TiAl metal sphere.

3. The method according to claim 1, characterized in that, The diameter of the hollow TiAl metal sphere is 100μm~500μm.

4. The method according to claim 3, characterized in that, In the groove array, the ratio of the width of the groove to the diameter of the hollow TiAl metal sphere satisfies 0.01~0.05; the ratio of the depth of the groove to the width of the groove satisfies 0.1~0.

3.

5. The method according to claim 1, characterized in that, The grain size of the nanocrystalline layer is ≤50nm.

6. The method according to claim 1, characterized in that, The thickness of the composite nanocoating is 40nm~60nm.

7. The method according to claim 1, characterized in that, In S4, the intermediate layer of the aluminum foil is pure aluminum or aluminum alloy, and the thickness of the intermediate layer of the aluminum foil is 15μm-100μm.

8. The method according to claim 1, characterized in that, In S4, the pulse current parameters are: pulse width 50μs~500μs, frequency 50kHz~200kHz, and pressure 5MPa~10MPa.

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