SiC with a reticulated metal fiber interlayer f Method of sealing the end plugs of SiC clad tubes

Abstract

The application discloses a SiC f / SiC cladding tube end plug packaging method, belongs to nuclear reactor fuel element packaging and silicon carbide fiber reinforced silicon carbide composite material connecting technical field.The method is with reticular metal fiber material as reinforcing framework and is coated on its surface with solder coating, makes end plug;Then the outer surface of end plug and the inner surface of SiC f / SiC cladding tube are coated with solder coating again, realize SiC f / SiC cladding tube end plug packaging through sintering.The application is by introducing three-dimensional continuous network structure metal fiber framework and solder to form composite intermediate layer, utilizes its capillary constraint and space support, actively guides molten solder flow, ensures vertical deep cavity slit uniform and dense filling, eliminates the defect caused by loss.Soldering solid state fiber net will liquid solder be segmented and limited in grid unit, inhibits macro flow and loss, cooperates with appropriate mesh size, guarantees filling and prevents overflow, ensures that the weld is uniform and complete.

Description

Technical Field

[0001] This invention relates to nuclear reactor fuel element encapsulation and silicon carbide fiber-reinforced silicon carbide (SiC). f This invention relates to the field of SiC composite material bonding technology, specifically to a SiC composite material containing a mesh metal fiber interlayer. f / SiC cladding tube end plug encapsulation method. This invention is applicable to fourth-generation nuclear reactors and nuclear propulsion systems, and is a SiC solution for advanced nuclear energy systems. f The engineering application of SiC clad components provides a completely new technical path. Background Technology

[0002] Fourth-generation advanced nuclear reactors (such as sodium-cooled fast reactors and ultra-high temperature gas-cooled reactors) impose stringent requirements on fuel cladding materials that surpass those of traditional water reactors in order to achieve higher thermal efficiency and inherent safety, particularly regarding the urgent need for Accident Tolerant Fuel (ATF). Traditional zirconium alloy cladding is prone to violent oxidation and hydrogen production reactions in high-temperature steam environments (i.e., the zirconium-water reaction, whose significant risk has been demonstrated by the Fukushima nuclear accident), making it difficult to meet the loss-of-coolant accident requirements of next-generation reactors. In contrast, SiC... f / SiC composites are widely recognized as the most promising next-generation cladding candidate materials due to their excellent high-temperature stability, extremely low neutron absorption cross section, outstanding resistance to radiation swelling, and non-reactivity with water vapor at high temperatures.

[0003] However, due to the inherent strong covalent bond structure, high melting point, and extremely low self-diffusion coefficient of SiC ceramics, high-performance SiC... f The near-net-shape integral forming of SiC cladding tubes is difficult to achieve, making reliable connection with end plugs a core bottleneck restricting their engineering applications. Current mainstream joining technologies include diffusion welding, glass brazing, and metal brazing. While metal brazing is a mature technology, active brazing filler metals, such as Ag-Cu-Ti, have significant drawbacks: Ag has a high neutron absorption cross-section, severely impacting core physical performance and economics; simultaneously, the large mismatch in thermal expansion coefficients between the filler metal and the SiC matrix induces extremely high residual stress in the joint area. Furthermore, the insufficient radiation resistance of the metallic phase makes it difficult to ensure the long-term structural integrity of the joint under the harsh reactor environment.

[0004] To address the aforementioned issues, researchers have recently developed glass and glass-ceramic solder systems for SiC. fThe connection between SiC clad tubes and end plugs involves a basic technical approach: specific oxide powders (such as SiO2, Al2O3, Y2O3, CaO, etc.) are melted at high temperatures and then water-quenched to obtain glass frit, which is then ball-milled into glass solder powder. This glass solder is then coated onto the surfaces to be welded and sintered at high temperatures under a protective atmosphere, causing the glass to melt and fill the connection gap. After cooling, a glass or glass-ceramic weld is formed. Furthermore, NITE (Nano-Immersed Transient Eutectic) phase bonding technology has been developed, which involves adding sintering aids to SiC powder and achieving dense bonding through spark plasma sintering (SPS).

[0005] However, existing glass / glass-ceramic solder joining technologies still have the following common drawbacks: Firstly, there is a lack of effective constraints and guidance on the flow behavior of molten solder. Existing solutions rely on the natural flow of molten glass / solder to fill the axial annular gap under both pressureless and pressurized conditions. Due to the geometric characteristics of the joint as a vertical annular deep cavity slit, the molten solder is prone to uncontrollable loss and component segregation under gravity, making it difficult to fill the entire target gap uniformly and stably based on its own properties. This results in defects such as localized incomplete welding, voids, and uneven filling inside the joint, severely compromising the joint's tightness and initial sealing integrity.

[0006] Secondly, the weld microstructure is inherently brittle. Existing weld microstructures (glassy phase, microcrystalline phase, or NITE phase) lack ductile phases or fibrous networks to redistribute and dissipate residual stress caused by the mismatch in thermal expansion coefficients. During cooling, SiC… f The significant difference in thermal expansion coefficients between the SiC composite material and the brazing filler metal can generate high residual stress in the interface region. Defects caused by insufficient filling become dangerous stress concentration points, easily inducing the initiation and propagation of microcracks. Under the extreme service environment of high temperature and irradiation in nuclear reactors, porosity and microcracks can accelerate the evolution of irradiation damage, seriously threatening the long-term structural reliability and sealing performance of the joint.

[0007] Third, existing solutions all focus on optimizing solder composition or adjusting overall process parameters, failing to introduce a three-dimensional continuous reinforcing skeleton with capillary constraint and stress regulation functions separately in specific weak areas of the joint interface (such as axial annular gaps). Therefore, existing technologies cannot achieve an effective balance between overcoming gravity filling, alleviating residual stress, and maintaining process feasibility.

[0008] In summary, existing SiC fThe fundamental drawback of SiC composite core cladding tube and end plug connection technology is that traditional homogeneous solders or simple composite intermediate layers cannot simultaneously achieve active constraint on the microscopic flow behavior of molten solder and effective control of residual stress under harsh nuclear service conditions, leading to severe challenges to the long-term reliability of the joint. Therefore, there is an urgent need to develop a SiC composite solder that can overcome gravity-induced solder loss and segregation, and possess stress dissipation and toughening functions. f A new solution for connecting SiC-clad tubes to end plugs. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide a SiC containing a mesh metal fiber interlayer. f The SiC-clad tube end-plug encapsulation method solves the technical problems in the prior art, such as uncontrollable loss of molten glass / brazing filler metal due to gravity during vertical circumferential brazing, uneven axial segregation and filling, residual stress in brittle glass-ceramic welds due to thermal expansion coefficient mismatch and easy initiation and propagation of microcracks at defects, and the lack of a partitioned functional composite structure that can simultaneously achieve active constraint of melt flow and effective dissipation of residual stress.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A SiC containing a mesh metal fiber interlayer f The SiC-clad tube end-plug packaging method is characterized by the following steps: Step 1, Pretreatment and activation of the reinforcing skeleton: The pure metal reinforcing skeleton is polished, followed by ultrasonic cleaning and drying; or the pure metal reinforcing skeleton is polished, followed by ultrasonic cleaning and drying, and then a modified layer is prepared on the surface of the pure metal reinforcing skeleton.

[0011] Step 2, SiC f / Surface cleaning of SiC cladding tubes and end plugs: for SiC f The inner wall of the SiC clad tube and the side of the end plug are polished, followed by ultrasonic cleaning.

[0012] Step 3, Reinforcing skeleton cutting and pre-forming: Precisely cut the reinforcing skeleton according to the end plug geometry, ensuring clean cuts without damaging the mesh structure; wind the cut reinforcing skeleton around the outer circumference of the end plug, and pre-form it into a cylindrical shape using a temporary jig or hand pressure, ensuring its compatibility with SiC. f A uniform annular gap is formed on the inner wall of the SiC-clad tube.

[0013] Step 4, Preparation and loading of brazing filler metal slurry: Mix brazing filler metal powder and terpineol in a certain mass ratio to prepare a high solid phase slurry; use spraying or impregnation-centrifugation method to uniformly load the slurry onto the surface of the preformed fiber mesh to form a brazing filler metal coating; after coating, air dry and bake dry in sequence to obtain the brazing metal mesh preform.

[0014] Step 5, Component Assembly and Gap Filling: First, in SiC... f The inner wall of the SiC cladding tube and the side of the end plug are coated with a solder coating. Then, an axial preload is applied to attach the solder-carrying metal mesh preform to the side of the end plug and press it into the cladding tube as a whole.

[0015] Step 6, Vacuum Brazing Sintering and Densification: Step-by-step sintering is performed in a vacuum environment to promote full melting and wetting of the brazing filler metal, and to induce capillary action and interfacial reactions within the pores of the metal fiber skeleton; after sintering, the temperature is lowered, and then cooled in the furnace to obtain dense SiC. f / SiC packaged connection sample.

[0016] The present invention also has the following technical features: Specifically, in step one, the pure metal reinforced skeleton is a pure tungsten fiber mesh with a porosity of 75% to 85% or a pure molybdenum fiber mesh with a porosity of 75%.

[0017] Specifically, in step one, the modified layer is a nickel layer or a Y2O3 coating.

[0018] Specifically, in step one, the preparation process of the nickel layer is as follows: metallic Ni is continuously deposited on the surface of the pure metal reinforced skeleton by electroplating, with air completely isolated to prevent secondary oxidation of the tungsten fiber, thus obtaining a nickel-plated tungsten fiber mesh.

[0019] Specifically, in step one, the preparation process of the Y2O3 coating is as follows: a continuous Y2O3 interface-modified coating is prepared on the surface of a pure metal-reinforced skeleton using the sol-gel method, with air completely isolated to prevent secondary oxidation of the tungsten fiber, thus obtaining a Y2O3-modified tungsten fiber mesh.

[0020] Specifically, in step one, 1200-grit metallographic sandpaper is used for polishing.

[0021] Specifically, in step one, deionized water and anhydrous ethanol are used sequentially during ultrasonic cleaning, and the cleaning time is 10-15 minutes.

[0022] Specifically, in step one, the drying conditions are: drying in a vacuum environment at 60-80°C for more than 30 minutes.

[0023] Specifically, in step two, 1000# fine sandpaper is used for sanding.

[0024] Specifically, in step two, acetone and deionized water are used sequentially during ultrasonic cleaning, and the cleaning time is 15-20 minutes.

[0025] Specifically, in step four, the solder powder is selected from TiZrCuNi solder powder with a particle size of 10-30 μm.

[0026] Specifically, in step four, the thickness of the solder coating is 100–300 μm.

[0027] Specifically, in step four, the drying conditions are: drying under vacuum at 60–80°C.

[0028] Specifically, in step five, the thickness of the brazing filler coating is 0.2 to 0.5 mm.

[0029] Specifically, in step five, the axial preload is 0.1 to 0.5 MPa.

[0030] Specifically, in step six, the vacuum level of the vacuum environment is ≤5×10⁻⁶. -3 Pa.

[0031] Specifically, in step six, the stepped sintering conditions are as follows: first, the temperature is increased to 450–550℃ at a rate of 8–12℃ / min and held for 25–35 min; then, the temperature is increased to 1100–1300℃ at a rate of 8–12℃ / min and held for 30–60 min. Preferably, the stepped sintering conditions are as follows: first, the temperature is increased to 500℃ at a rate of 10℃ / min and held for 30 min; then, the temperature is increased to 1200℃ at a rate of 10℃ / min and held for 30–60 min.

[0032] Specifically, in step six, the cooling conditions are: cooling to 450-550℃ at a rate of 4-6℃ / min. Preferably, the cooling conditions are: cooling to 500℃ at a rate of 5℃ / min.

[0033] Compared with the prior art, the present invention has the following technical effects: (I) This invention introduces a reinforcement with a three-dimensional continuous network structure (such as a tungsten fiber skeleton) to form a functionalized composite intermediate layer with the solder. Utilizing the capillary constraint effect and spatial support of the reinforcement network, it actively guides and confines the flow and distribution of the molten solder, ensuring uniform, dense, and complete filling within the vertical deep cavity slit, thereby fundamentally eliminating various defects caused by solder loss. The melting point of the metal fiber mesh (taking tungsten mesh as an example) is much higher than that of the solder (e.g., tungsten's melting point is approximately 3422℃, while TiZrCuNi solder's melting point is approximately 800-900℃). During brazing, when the solder melts and forms a liquid state, the metal mesh remains solid, thus forming a stable, rigid three-dimensional skeleton. This skeleton divides and confines the originally continuous liquid solder within countless independent grid units (i.e., "small molten pools"), equivalent to constructing a regular solid-phase barrier within the molten solder. This structure greatly suppresses the macroscopic flow and loss of the solder driven by capillary forces, temperature gradients, or gravity. In the annular joint of SiC clad tubes, the mesh size of a specific size (such as 100-200 μm) can ensure that the brazing filler metal fills the gap fully, and can also effectively prevent the brazing filler metal from overflowing into the non-connection area due to the physical barrier of the fiber network, thus ensuring the uniformity and integrity of the weld filling.

[0034] (II) This invention utilizes the high stiffness and high melting point of the reinforcing network to redistribute and dissipate heat stress during solidification and cooling, alleviating stress concentration caused by thermal mismatch of dissimilar materials and optimizing the stress state of the joint. This metal fiber mesh also functions as a high-melting-point, high-stiffness micro-structural unit. Through segmentation of the solder pool, mechanical interlocking, and its own deformation, it can redistribute and dissipate residual stress caused by the mismatch in thermal expansion coefficients of dissimilar materials, thereby alleviating interface stress concentration. In traditional brazed joints, the overall solidification shrinkage of the liquid solder often generates significant concentrated stress, which, coupled with the large difference in thermal expansion coefficients between SiC and the metal, easily induces interface cracks. With the introduction of the metal fiber mesh, the solidification process of the solder is divided into numerous independent microscopic "small molten pools." Due to the geometric constraints of the solid fibers on adjacent mesh units, their solidification shrinkage directions exhibit multidirectional and localized characteristics, and may even be opposite to each other. These shrinkage stresses, which occur at the microscale and are oriented differently, can interfere with each other and partially cancel each other out, thereby significantly reducing the overall residual stress level of the joint on a macroscopic scale and alleviating the stress concentration problem caused by thermal mismatch.

[0035] (III) This invention achieves an integrated "structure-function" connection solution, significantly improving the mechanical integrity, interface stability, and long-term sealing reliability of the joint under harsh environments while ensuring excellent filling quality. The high strength and toughness of the metal fiber mesh itself provide an additional load-bearing skeleton for the joint. During high-temperature service, the fiber mesh can share external loads and suppress plastic deformation of the brazing filler metal caused by creep. For example, in the long-term thermal cycling of a nuclear reactor, the brazing filler metal layer may gradually soften due to creep, while the metal mesh maintains the integrity of the joint structure through its rigid skeleton, suppressing cracking or deformation of the joint due to creep accumulation. At the same time, the interfacial bonding between the fiber mesh and the brazing filler metal (such as the metallurgical bonding formed by the brazing filler metal wetting the fiber surface) further enhances the joint's shear resistance and peel resistance.

[0036] (IV) In the high-energy neutron irradiation environment of nuclear reactors, metal fiber meshes (especially tungsten) exhibit excellent resistance to radiation swelling and transmutation stability. Tungsten has a low high neutron capture cross section, and the transmutation products (such as Re and Os) generated after irradiation have little impact on its mechanical properties. In contrast, some common brazing filler metals (such as Ag-based filler metals) are prone to atomic dislocation damage and elemental segregation under irradiation. The addition of fiber meshes not only improves the radiation resistance of the joint but also reduces the connectivity of irradiation defects in the filler metal through physical separation, thus inhibiting crack propagation. For example, neutron irradiation may generate voids in the filler metal, but the presence of metal meshes can prevent these voids from accumulating in a single direction, thereby delaying the irradiation embrittlement process of the joint.

[0037] (V) This invention pre-coats the surface of the tungsten fiber mesh to regulate the physicochemical behavior of the key interface of "tungsten fiber / molten brazing filler metal". It provides two typical coating schemes according to the target performance requirements, each achieving targeted technical effects: First, the metal coating (such as Ni) can significantly improve the wettability of molten brazing filler metal to tungsten fiber, forming a strong metallurgical bonding interface. At the same time, the plastic deformation of the metal coating can buffer thermal stress and prevent the occurrence of harmful interface reactions. It is a key process step to ensure the formation of a dense and strong bonding interface in the composite intermediate layer. Second, the rare earth oxide coating (such as Y2O3) utilizes the chemical inertness and poor wettability of Y2O3 to high-entropy alloy brazing filler metal to achieve diffusion blocking (inhibiting excessive dissolution of tungsten fiber), weak interface bonding (inducing crack deflection and releasing residual stress), and functions such as radiation resistance and high-temperature oxidation resistance. It is suitable for working conditions where joint toughness, thermal shock resistance and long-term service stability in nuclear environments are given priority.

[0038] (VI) This invention embodies the concept of "zonal design," employing this composite intermediate layer only in the weakest axial gap, while using mature processes in other areas, achieving a balance between performance improvement and process feasibility. The introduction of a metal fiber mesh as a brazing reinforcement skeleton proposed in this invention, through the synergistic mechanism of four aspects—the constraint and confinement of brazing filler metal flow by the solid-phase skeleton, the dispersion and offsetting mechanism of solidification shrinkage stress, the enhancement of joint mechanical properties, and special stability under irradiation—combines to comprehensively optimize filling quality, stress state, mechanical properties, and service life, thereby enhancing SiC… f The high-quality connection of SiC composite clad components provides a practical technical approach. Attached Figure Description

[0039] Figure 1 This is the technical approach of the present invention.

[0040] Figure 2 Comparison of the microstructure of the joint before and after the addition of tungsten fiber mesh.

[0041] Figure 3 Physical image of the component to be packaged and the finished product connected by brazing: (a) SiC f / SiC clad tube and end plug; (b) packaged physical sample.

[0042] Figure 4 Microstructure characterization of W fibers modified with Y2O3 interface.

[0043] Figure 5 CT scan 3D reconstruction and defect analysis of the joint cross-section before and after the addition of tungsten fiber mesh.

[0044] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0045] It should be noted that all raw materials used in this invention, unless otherwise specified, are those known in the art. For example: The paste-like solder used was a TiZrCuNi active solder produced by Beijing Huawirui Chemical Co., Ltd., and its composition is Ti 35 Zr 35 Cu 15 Ni 10 (wt%).

[0046] The terpineol used (purity ≥98%) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0047] SiC fThe preparation process of the SiC composite clad tube is as follows: it is directly woven on a mandrel from a ±45° layup two-dimensional braided preform to ensure accurate fiber orientation and uniform wall thickness (0.85–0.95 mm), and to reduce handling damage. The preform density is controlled at 1.15–1.45 g / cm³. 3 (Fiber volume fraction approximately 40%), followed by sequential interfacial coating and substrate densification treatments, ultimately yielding SiC. f / SiC clad tube.

[0048] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0049] Example 1 This embodiment provides a SiC containing a mesh metal fiber interlayer. f The SiC-clad tube end-plug encapsulation method uses a 75% porosity pure tungsten fiber mesh as a reinforcing skeleton and a TiZrCuNi active solder system, specifically including the following steps: Step 1: Pretreatment and activation of the reinforcing skeleton: A tungsten fiber mesh with a porosity of 75% was selected as the reinforcing skeleton. The surface of the fiber mesh was lightly and uniformly polished with 1200-grit metallographic sandpaper to remove the original oxide layer while strictly controlling the polishing intensity to protect the three-dimensional interconnected network structure of the fibers. Subsequently, it was ultrasonically cleaned in deionized water and anhydrous ethanol for 10 minutes each, and then dried in a vacuum environment at 60–80°C for at least 30 minutes to remove any residual liquid from the surface.

[0050] Step 2, SiC f / Surface cleaning of SiC cladding tube and end plug: The inner wall of the SiCf / SiC cladding tube and the sides of the end plug were lightly polished with 1000# fine sandpaper to remove surface dust and impurities. Then, the tube was ultrasonically cleaned with acetone and deionized water (15-20 min) to remove organic residues.

[0051] Step 3, Enhanced skeleton cutting and pre-forming: Precisely cut the fiber mesh according to the end plug geometry, ensuring clean cuts without damaging the mesh structure. Wrap the cut rectangular mesh around the outer circumference of the end plug, and pre-form it into a cylindrical shape using temporary clamps or hand pressure, ensuring a uniform annular gap between it and the inner wall of the casing tube.

[0052] Step 4, Preparation and Loading of Brazing Filler Slurry: TiZrCuNi brazing filler powder with a particle size of 10–30 μm is mixed with terpineol at a mass ratio of 2:0.3 to prepare a high-solids slurry. The slurry is uniformly loaded onto the surface of the pre-formed fiber mesh using a spraying or dip-and-centrifuge method, precisely controlling the coating thickness to 100–300 μm. The capillary effect of the mesh pores is utilized to adsorb the slurry, preventing clogging of the pores. After coating, the material is air-dried at room temperature, then dried under vacuum at 60–80℃ to completely remove volatile components, yielding the brazing filler metal mesh preform.

[0053] Step 5, Component Assembly and Gap Filling: Implement a double coating and assembly strategy. First, apply a 0.2–0.5 mm thick brazing filler metal coating to the inner wall of the cladding tube and the side of the end plug. Then, attach the preform to the side of the end plug and press it into the cladding tube as a whole. During assembly, apply an axial preload of 0.1–0.5 MPa. Utilize the elastic deformation of the metal mesh to compensate for assembly tolerances, ensuring tight contact between the preform and the base materials on both sides. A brazing filler metal filling channel is reserved to eliminate residual gaps.

[0054] Step 6, Vacuum brazing sintering and densification: The assembly is vertically fixed in a vacuum furnace (vacuum degree ≤ 5 × 10⁻⁶). - 3 Pa). A stepped sintering process is implemented: first, the temperature is increased to 500℃ at 10℃ / min and held for 30 min for degreasing; then, the temperature is increased to the brazing temperature (preferably 1200℃) at 10℃ / min and held for 30–60 min to promote full melting and wetting of the brazing filler metal, and to induce capillary action and interfacial reactions in the pores of the tungsten fiber skeleton; finally, the temperature is slowly cooled to 500℃ at 5℃ / min and then cooled with the furnace. By suppressing thermal stress and preventing joint cracking, dense SiC is ultimately obtained. f / SiC packaged connection sample.

[0055] Example 2 This embodiment provides a SiC containing a mesh metal fiber interlayer. f The SiC-clad tube end-plug encapsulation method uses a 75% porosity pure molybdenum (Mo) fiber mesh as a reinforcing skeleton and a TiZrCuNi active solder system, specifically including the following steps: Step 1: Pretreatment and activation of the reinforcing skeleton: For encapsulation requirements, a Mo fiber mesh with a porosity of 75% was selected as the reinforcing skeleton. The surface was lightly and uniformly polished using 1200# metallographic sandpaper. While removing the native oxide layer, the polishing intensity was strictly controlled to protect the three-dimensional interconnected network structure of the fibers. Subsequently, it was ultrasonically cleaned sequentially in deionized water and anhydrous ethanol (10 min each), and dried in a vacuum environment at 60–80℃ for at least 30 min.

[0056] Step 2, SiC f / Surface cleaning of SiC cladding tube and end plug: The inner wall of the SiCf / SiC cladding tube and the sides of the end plug were lightly polished with 1000# fine sandpaper to remove surface dust and impurities. Then, the tube was ultrasonically cleaned with acetone and deionized water (15-20 min) to remove organic residues.

[0057] Step 3, Enhance the cutting and pre-forming of the skeleton: Precisely cut the fiber mesh according to the geometry of the end plug, ensuring neat cuts without damaging the mesh structure. Wrap the cut rectangular mesh around the side of the end plug, and pre-form it using a temporary positioning jig or by hand, ensuring the accuracy of its annular gap fit with the tube wall.

[0058] Step 3, Enhanced skeleton cutting and pre-forming: Precisely cut the fiber mesh according to the end plug geometry, ensuring clean cuts without damaging the mesh structure. Wrap the cut rectangular mesh around the outer circumference of the end plug, and pre-form it into a cylindrical shape using temporary clamps or hand pressure, ensuring a uniform annular gap between it and the inner wall of the casing tube.

[0059] Step 4, Preparation and Loading of Brazing Filler Slurry: TiZrCuNi brazing filler powder with a particle size of 10–30 μm is mixed with terpineol at a mass ratio of 2:0.3 to prepare a high-solids slurry. The slurry is uniformly loaded onto the surface of the pre-formed fiber mesh using a spraying or dip-and-centrifuge method, precisely controlling the coating thickness to 100–300 μm. The capillary effect of the mesh pores is utilized to adsorb the slurry, preventing clogging of the pores. After coating, the material is air-dried at room temperature, then dried under vacuum at 60–80℃ to completely remove volatile components, yielding the brazing filler metal mesh preform.

[0060] Step 5, Component Assembly and Gap Filling: Implement a double coating and assembly strategy. First, apply a 0.2–0.5 mm thick brazing filler metal coating to the inner wall of the cladding tube and the side of the end plug. Then, attach the preform to the side of the end plug and press it into the cladding tube as a whole. During assembly, apply an axial preload of 0.1–0.5 MPa. Utilize the elastic deformation of the metal mesh to compensate for assembly tolerances, ensuring tight contact between the preform and the base materials on both sides. A brazing filler metal filling channel is reserved to eliminate residual gaps.

[0061] Step 6, Vacuum brazing sintering and densification: The assembly is vertically fixed in a vacuum furnace (vacuum degree ≤ 5 × 10⁻⁶). - 3 Pa). A stepped sintering process is implemented: first, the temperature is increased to 500℃ at 10℃ / min and held for 30 min for degreasing; then, the temperature is increased to the brazing temperature (preferably 1200℃) at 10℃ / min and held for 30–60 min to promote full melting and wetting of the brazing filler metal, and to induce capillary action and interfacial reactions in the pores of the tungsten fiber skeleton; finally, the temperature is slowly cooled to 500℃ at 5℃ / min and then cooled with the furnace. By suppressing thermal stress and preventing joint cracking, dense SiC is ultimately obtained. f / SiC packaged connection sample.

[0062] Example 3 This embodiment provides a SiC containing a mesh metal fiber interlayer. f The SiC clad tube end-plug encapsulation method specifically includes the following steps: Using a high-density pure tungsten fiber mesh with 85% porosity as a reinforcing skeleton, and a TiZrCuNi active solder system, specifically including the following steps: Step 1: Pretreatment and activation of the reinforcing skeleton: For encapsulation requirements, a tungsten fiber mesh with a porosity of 85% was selected as the reinforcing skeleton. The surface was lightly and uniformly polished using 1200# metallographic sandpaper. While removing the original oxide layer, the polishing intensity was strictly controlled to protect the three-dimensional interconnected network structure of the fibers. Subsequently, it was ultrasonically cleaned sequentially in deionized water and anhydrous ethanol (10 min each), and dried in a vacuum environment at 60–80℃ for at least 30 min.

[0063] Step 2, SiC f / Surface cleaning of SiC cladding tube and end plug: The inner wall of the SiCf / SiC cladding tube and the sides of the end plug were lightly polished with 1000# fine sandpaper to remove surface dust and impurities. Then, the tube was ultrasonically cleaned with acetone and deionized water (15-20 min) to remove organic residues.

[0064] Step 3, Enhanced skeleton cutting and pre-forming: Precisely cut the fiber mesh according to the end plug geometry, ensuring clean cuts without damaging the mesh structure. Wrap the cut rectangular mesh around the outer circumference of the end plug, and pre-form it into a cylindrical shape using temporary clamps or hand pressure, ensuring a uniform annular gap between it and the inner wall of the casing tube.

[0065] Step 4, Preparation and Loading of Brazing Filler Slurry: TiZrCuNi brazing filler powder with a particle size of 10–30 μm is mixed with terpineol at a mass ratio of 2:0.3 to prepare a high-solids slurry. The slurry is uniformly loaded onto the surface of the pre-formed fiber mesh using a spraying or dip-and-centrifuge method, precisely controlling the coating thickness to 100–300 μm. The capillary effect of the mesh pores is utilized to adsorb the slurry, preventing clogging of the pores. After coating, the material is air-dried at room temperature, then dried under vacuum at 60–80℃ to completely remove volatile components, yielding the brazing filler metal mesh preform.

[0066] Step 5, Component Assembly and Gap Filling: Implement a double coating and assembly strategy. First, apply a 0.2–0.5 mm thick brazing filler metal coating to the inner wall of the cladding tube and the side of the end plug. Then, attach the preform to the side of the end plug and press it into the cladding tube as a whole. During assembly, apply an axial preload of 0.1–0.5 MPa. Utilize the elastic deformation of the metal mesh to compensate for assembly tolerances, ensuring tight contact between the preform and the base materials on both sides. A brazing filler metal filling channel is reserved to eliminate residual gaps.

[0067] Step 6, Vacuum brazing sintering and densification: The assembly is vertically fixed in a vacuum furnace (vacuum degree ≤ 5 × 10⁻⁶). - 3 Pa). A stepped sintering process is implemented: first, the temperature is increased to 500℃ at 10℃ / min and held for 30 min for degreasing; then, the temperature is increased to the brazing temperature (preferably 1200℃) at 10℃ / min and held for 30–60 min to promote full melting and wetting of the brazing filler metal, and to induce capillary action and interfacial reactions in the pores of the tungsten fiber skeleton; finally, the temperature is slowly cooled to 500℃ at 5℃ / min and then cooled with the furnace. By suppressing thermal stress and preventing joint cracking, dense SiC is ultimately obtained. f / SiC packaged connection sample.

[0068] Example 4 This embodiment provides a SiC containing a mesh metal fiber interlayer. f The SiC-clad tube end-plug encapsulation method uses a 75% porosity nickel-plated modified tungsten fiber mesh as a reinforcing skeleton and a TiZrCuNi active solder system, specifically including the following steps: Step 1: Pretreatment and activation of the reinforcing skeleton: A tungsten (W) fiber mesh substrate with a porosity of 75% was selected. The surface was lightly and uniformly polished using 800# metallographic sandpaper, strictly controlling the polishing intensity to protect the three-dimensional interconnected network structure of the fibers while removing the original oxide layer. Subsequently, it was ultrasonically cleaned sequentially in deionized water and anhydrous ethanol (10 min each), and dried in a vacuum environment at 70℃ for 35 min. Immediately after drying, electroplating was performed to continuously deposit a Ni-modified metal layer on the surface of the tungsten fibers. Air was completely isolated throughout the process to prevent secondary oxidation of the tungsten fibers, resulting in a nickel-plated tungsten fiber mesh.

[0069] Step 2, SiC f / Surface cleaning of SiC cladding tubes and end plugs: for SiC f The inner wall and side of the SiC cladding tube undergo a fine surface treatment: Light sanding with 1500# fine sandpaper removes surface dust and weakly adhering phases, taking care not to damage the SiC fibers or induce microcracks. Subsequently, ultrasonic cleaning with acetone and deionized water for 18 minutes is performed sequentially to thoroughly remove organic residues.

[0070] Step 3, Enhanced skeleton cutting and pre-forming: Precisely cut the fiber mesh according to the end plug geometry, ensuring clean cuts without damaging the mesh structure. Wrap the cut rectangular mesh around the outer circumference of the end plug, and pre-form it into a cylindrical shape using temporary clamps or hand pressure, ensuring a uniform annular gap between it and the inner wall of the casing tube.

[0071] Step 4, Preparation and Loading of Brazing Filler Slurry: TiZrCuNi brazing filler powder with a particle size of 10–30 μm is mixed with terpineol at a mass ratio of 2:0.3 to prepare a high-solids slurry. The slurry is uniformly loaded onto the surface of the pre-formed fiber mesh using a spraying or dip-and-centrifuge method, precisely controlling the coating thickness to 100–300 μm. The capillary effect of the mesh pores is utilized to adsorb the slurry, preventing clogging of the pores. After coating, the material is air-dried at room temperature, then dried under vacuum at 60–80℃ to completely remove volatile components, yielding the brazing filler metal mesh preform.

[0072] Step 5, Component Assembly and Gap Filling: Implement a double coating and assembly strategy. First, apply a 0.2–0.5 mm thick brazing filler metal coating to the inner wall of the cladding tube and the side of the end plug. Then, attach the preform to the side of the end plug and press it into the cladding tube as a whole. During assembly, apply an axial preload of 0.1–0.5 MPa. Utilize the elastic deformation of the metal mesh to compensate for assembly tolerances, ensuring tight contact between the preform and the base materials on both sides. A brazing filler metal filling channel is reserved to eliminate residual gaps.

[0073] Step 6, Vacuum brazing sintering and densification: The assembly is vertically fixed in a vacuum furnace (vacuum degree ≤ 5 × 10⁻⁶). - 3 Pa). A stepped sintering process is implemented: first, the temperature is increased to 500℃ at 10℃ / min and held for 30 min for degreasing; then, the temperature is increased to the brazing temperature (preferably 1200℃) at 10℃ / min and held for 30–60 min to promote full melting and wetting of the brazing filler metal, and to induce capillary action and interfacial reactions in the pores of the tungsten fiber skeleton; finally, the temperature is slowly cooled to 500℃ at 5℃ / min and then cooled with the furnace. By suppressing thermal stress and preventing joint cracking, dense SiC is ultimately obtained. f / SiC packaged connection sample.

[0074] Example 5 This embodiment provides a SiC containing a mesh metal fiber interlayer. f The SiC-clad tube end-plug encapsulation method uses a 75% porosity Y2O3-coated modified tungsten fiber mesh as a reinforcing skeleton and a TiZrCuNi active solder system. The specific steps include: Step 1: Pretreatment and activation of the reinforcing framework: A tungsten (W) fiber mesh substrate with a porosity of 75% was selected. The surface was lightly and uniformly polished using 800# metallographic sandpaper, strictly controlling the polishing intensity to protect the three-dimensional interconnected network structure of the fibers while removing the original oxide layer. Subsequently, it was ultrasonically cleaned sequentially in deionized water and anhydrous ethanol (10 min each), and dried in a vacuum environment at 70℃ for 35 min. After drying, a continuous Y₂O₃ interface-modified coating was prepared on the surface of the tungsten fibers using a sol-gel method, isolating the fibers from air throughout the process to prevent secondary oxidation, thus obtaining a Y₂O₃-modified tungsten fiber mesh.

[0075] Step 2, SiC f / Surface cleaning of SiC cladding tubes and end plugs: for SiC f The inner wall and side of the SiC cladding tube undergo a fine surface treatment: Light sanding with 1500# fine sandpaper removes surface dust and weakly adhering phases, taking care not to damage the SiC fibers or induce microcracks. Subsequently, ultrasonic cleaning with acetone and deionized water for 18 minutes is performed sequentially to thoroughly remove organic residues.

[0076] Step 3, Enhanced skeleton cutting and pre-forming: Precisely cut the fiber mesh according to the end plug geometry, ensuring clean cuts without damaging the mesh structure. Wrap the cut rectangular mesh around the outer circumference of the end plug, and pre-form it into a cylindrical shape using temporary clamps or hand pressure, ensuring a uniform annular gap between it and the inner wall of the casing tube.

[0077] Step 4, Preparation and Loading of Brazing Filler Slurry: TiZrCuNi brazing filler powder with a particle size of 10–30 μm is mixed with terpineol at a mass ratio of 2:0.3 to prepare a high-solids slurry. The slurry is uniformly loaded onto the surface of the pre-formed fiber mesh using a spraying or dip-and-centrifuge method, precisely controlling the coating thickness to 100–300 μm. The capillary effect of the mesh pores is utilized to adsorb the slurry, preventing clogging of the pores. After coating, the material is air-dried at room temperature, then dried under vacuum at 60–80℃ to completely remove volatile components, yielding the brazing filler metal mesh preform.

[0078] Step 5, Component Assembly and Gap Filling: Implement a double coating and assembly strategy. First, apply a 0.2–0.5 mm thick brazing filler metal coating to the inner wall of the cladding tube and the side of the end plug. Then, attach the preform to the side of the end plug and press it into the cladding tube as a whole. During assembly, apply an axial preload of 0.1–0.5 MPa. Utilize the elastic deformation of the metal mesh to compensate for assembly tolerances, ensuring tight contact between the preform and the base materials on both sides. A brazing filler metal filling channel is reserved to eliminate residual gaps.

[0079] Step 6, Vacuum brazing sintering and densification: The assembly is vertically fixed in a vacuum furnace (vacuum degree ≤ 5 × 10⁻⁶). - 3 Pa). A stepped sintering process is implemented: first, the temperature is increased to 500℃ at 10℃ / min and held for 30 min for degreasing; then, the temperature is increased to the brazing temperature (preferably 1200℃) at 10℃ / min and held for 30–60 min to promote full melting and wetting of the brazing filler metal, and to induce capillary action and interfacial reactions in the pores of the tungsten fiber skeleton; finally, the temperature is slowly cooled to 500℃ at 5℃ / min and then cooled with the furnace. By suppressing thermal stress and preventing joint cracking, dense SiC is ultimately obtained. f / SiC packaged connection sample.

[0080] Comparative Example 1 Comparative Example 1 presents a SiC f The traditional encapsulation brazing method for SiC-clad tube end plugs is basically the same as the process in Example 1, except that no additional metal fiber mesh intermediate layer is added.

[0081] Step 1, SiC f / Surface cleaning of SiC cladding tubes and end plugs: for SiC f The inner wall and end plug sides of the SiC cladding tube undergo fine surface treatment: Lightly sand with 1500# fine sandpaper to remove surface dust and weakly adhering phases, taking care not to damage the SiC fibers or induce microcracks. Then, ultrasonically clean with acetone and deionized water for 18 minutes sequentially to thoroughly remove organic residues, and dry for later use.

[0082] Step 2, preparation of solder paste: Select TiZrCuNi active solder, select solder powder with a particle size of 10-30 μm, and use terpineol as an organic binder to prepare solder paste.

[0083] Step 3, component assembly: Apply a 0.3 mm thick brazing filler metal coating evenly to the inner wall of the cladding tube and the side of the end plug, press the end plug coaxially into the cladding tube, and apply an axial preload of 0.3 MPa during the assembly process.

[0084] Step 4, Vacuum Brazing Sintering and Densification: The assembly is placed vertically in a vacuum furnace, and the vacuum level inside the furnace is maintained at 4×10⁻⁶. -4 Pa. A stepped heating regime was implemented: the temperature was increased to 500℃ at 7℃ / min and held for 30 min for degreasing, then increased to 1200℃ at 12℃ / min and held for 45 min; finally, the temperature was slowly cooled to 500℃ at 5℃ / min and then cooled in the furnace to obtain a control sample without a metal interlayer.

[0085] Table 1. Product performance data of the examples and comparative examples

Claims

1. A SiC containing a mesh-like metal fiber interlayer f The SiC-clad tube end-plug encapsulation method is characterized by... The method includes: using a mesh metal fiber material as a reinforcing skeleton and coating its surface with a solder coating to form an end plug; then the outer surface of the end plug and SiC f The inner surface of the SiC clad tube is coated with a solder coating again, and the SiC is then sintered to achieve SiC cladding. f / SiC encapsulated tube end plug packaging.

2. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, The method includes the following steps: Step 1, Pretreatment and activation of the reinforcing skeleton: The pure metal reinforcing skeleton is polished, followed by ultrasonic cleaning and drying; or the pure metal reinforcing skeleton is polished, followed by ultrasonic cleaning and drying, and then a modified layer is prepared on the surface of the pure metal reinforcing skeleton. Step 2, SiC f / Surface cleaning of SiC cladding tubes and end plugs: for SiC f The inner wall of the SiC clad tube and the side of the end plug are polished, followed by ultrasonic cleaning. Step 3, Reinforcing skeleton cutting and pre-forming: Precisely cut the reinforcing skeleton according to the end plug geometry, and then wind the cut reinforcing skeleton around the outer periphery of the end plug to ensure its fit with SiC. f / A uniform annular gap is formed on the inner wall of the SiC-clad tube; Step 4, Preparation and loading of brazing filler metal slurry: Mix brazing filler metal powder and terpineol in a certain mass ratio to prepare a high solid phase slurry. Load the slurry evenly onto the surface of the pre-formed fiber mesh to form a brazing filler metal coating. After coating, the material is air-dried and then oven-dried to obtain a brazing metal mesh preform. Step 5, Component Assembly and Gap Filling: First, in SiC... f The inner wall of the SiC cladding tube and the side of the end plug are coated with a solder coating. Then, an axial preload is applied to attach the solder-carrying metal mesh preform to the side of the end plug and press it into the cladding tube as a whole. Step 6, Vacuum brazing sintering and densification: Step-by-step sintering is performed in a vacuum environment. After sintering, the temperature is lowered and then cooled in the furnace to obtain dense SiC. f / SiC packaged connection sample.

3. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step one, the pure metal reinforced skeleton is a pure tungsten fiber mesh with a porosity of 75% to 85% or a pure molybdenum fiber mesh with a porosity of 75%; the modified layer is a nickel layer or a Y2O3 coating.

4. The SiC containing a mesh metal fiber interlayer as described in claim 2 f The SiC-clad tube end-plug encapsulation method is characterized by... In step one, the preparation process of the nickel layer is as follows: metallic Ni is continuously deposited on the surface of a pure metal reinforced skeleton by electroplating, with air completely isolated, to obtain a nickel-plated tungsten fiber mesh; In step one, the preparation process of the Y2O3 coating is as follows: a continuous Y2O3 interface-modified coating is prepared on the surface of a pure metal-reinforced skeleton using the sol-gel method, with air completely isolated, to obtain a Y2O3-modified tungsten fiber mesh.

5. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step one, deionized water and anhydrous ethanol are used sequentially during ultrasonic cleaning, with a cleaning time of 10–15 minutes.

6. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step two, acetone and deionized water are used sequentially during ultrasonic cleaning, and the cleaning time is 15-20 minutes.

7. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step four, the solder powder is selected from TiZrCuNi solder powder with a particle size of 10-30 μm; the thickness of the solder coating is 100-300 μm.

8. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step five, the thickness of the brazing filler coating is 0.2 to 0.5 mm.

9. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step five, the axial preload is 0.1 to 0.5 MPa.

10. The SiCf / SiC cladding tube end-plug encapsulation method with a mesh metal fiber intermediate layer as described in claim 2, characterized in that, In step six, the conditions for the stepped sintering are as follows: first, the temperature is increased to 450-550℃ at a rate of 8-12℃ / min and held for 25-35 min; then, the temperature is increased to 1100-1300℃ at a rate of 8-12℃ / min and held for 30-60 min.

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