A graphite and TZM high-temperature brazing method based on in-situ reinforcement of brazing seam

Abstract

The present disclosure provides a graphite and TZM high-temperature brazing method based on a brazing seam in-situ strengthening, comprising the following steps: assembling pretreated graphite base material and TZM alloy base material, and pretreated composite interlayer material to form a to-be-welded assembly; heating the to-be-welded assembly to a brazing temperature under the conditions of a protective atmosphere and applied pressure for heat preservation connection, so that the composite interlayer material melts and undergoes a metallurgical reaction, and the connection of graphite and TZM alloy is realized. By adopting Hastelloy C-276 / Ni / Nb as the composite interlayer material, the present disclosure utilizes the dissolution of Nb element to introduce strong carbide forming elements, and at the same time, with the help of the dissolution of Ni to graphite, liquid carbon atoms are obtained, so that high-quality metallurgical bonding of graphite and TZM is realized. The welding joint obtained by the method has a room temperature shear strength of up to 44.19 MPa, effectively solving the problems of large residual stress and low strength of traditional brazing.

Description

Technical Field

[0001] This disclosure relates to the field of brazing technology, and in particular to a high-temperature brazing method for graphite and TZM based on in-situ brazing seam strengthening. Background Technology

[0002] Modern CT scanners require X-ray tubes to generate enormous power in a very short time to shorten scan time and improve image resolution. The core component that generates X-rays is the rotating anode target disk. When the electron beam bombards the surface of the target disk, most of its kinetic energy is converted into heat, with only a small portion being converted into X-rays. Therefore, the target disk needs to have extremely high resistance to thermal shock and thermal fatigue, as well as high heat capacity and excellent thermal conductivity. TZM alloy is used to make target disks because of its extremely high high-temperature strength and hardness, excellent creep resistance, and good thermal and electrical conductivity. However, relying solely on TZM will result in a relatively short lifespan for the target disk.

[0003] Graphite possesses extremely high heat capacity, low density, and excellent thermal conductivity, making it widely used in nuclear industry and aerospace. In CT scanners, graphite is used in conjunction with TZM (thermoplastic zeolite) to reduce target disk weight and help distribute heat more evenly from the TZM target surface to the entire target disk and surrounding environment, thus extending the lifespan of the TZM. The connection between graphite and TZM includes mechanical bonding, adhesive bonding, diffusion welding, and brazing. Brazing, due to its advantages of low requirements for base material surface finish, minimal changes in the base material's microstructure, and high joint strength, is widely used for joining metals and non-metals, as well as for joining different materials.

[0004] Currently, most scholars use Ti-based brazing filler metals. However, using Ti-based brazing filler metals can easily lead to the formation of a thicker carbide layer on the graphite side of the weld, resulting in greater residual stress in the weld and lower strength of the welded joint. Therefore, developing a high-temperature brazing method for graphite and TZM is of great significance for obtaining graphite-TZM joints with higher room temperature strength and stronger heat resistance, thereby increasing the service life of TZM and graphite in CT scanners.

[0005] The information disclosed in the Background section is only intended to enhance the understanding of the background of this disclosure, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] To address the problems of difficulty in joining graphite and TZM and achieving high-temperature service in existing technologies, this disclosure provides a high-temperature brazing method for graphite and TZM based on in-situ brazing seam reinforcement.

[0007] This disclosure provides the following technical solutions:

[0008] A high-temperature brazing method for graphite and TZM based on in-situ brazing seam strengthening includes the following steps:

[0009] Step S100: Assemble the pretreated graphite base material, TZM alloy base material, and pretreated composite intermediate layer material to form the component to be welded.

[0010] Step S200: The components to be welded are heated to the brazing temperature under a protective atmosphere and pressure for heat preservation and connection, so that the composite intermediate layer material melts and undergoes a metallurgical reaction, thereby realizing the connection between graphite and TZM alloy.

[0011] In the method described, in step S100, the assembly process is as follows: pretreated graphite and TZM alloy base material, as well as pretreated composite intermediate layer material, are stacked from top to bottom in the order of TZM base material / composite intermediate layer material / graphite base material.

[0012] In the method described, the composite intermediate layer material is a multilayer composite structure composed of nickel-based alloy layer / metallic nickel layer / nickel-based alloy layer / metallic niobium layer stacked in that order.

[0013] In the method described, the nickel-based alloy layer is a Hastelloy C-276 foil with a single layer thickness of 0.05 mm.

[0014] In the method described, the nickel layer is a pure nickel foil with a thickness of 0.1 mm.

[0015] In the method described, the niobium layer is a pure niobium foil with a thickness of 0.03 to 0.05 mm.

[0016] In the method described, the applied pressure is 0.05 to 0.2 MPa.

[0017] In the method, the heating rate is 80-100°C / min, and the cooling rate is 20-30°C / min.

[0018] In the method described, the brazing temperature is 1350–1450°C, and the holding time is 5–15 minutes.

[0019] In the method described, the pretreatment of the graphite base material and the TZM alloy base material includes cutting, grinding and ultrasonic cleaning of the surfaces to be welded; the pretreatment of the composite intermediate layer material includes cutting, grinding and ultrasonic cleaning.

[0020] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0021] This disclosure provides a high-temperature brazing method for graphite and TZM based on in-situ brazing seam strengthening. It employs Hastelloy C-276 / Ni / Nb as a composite intermediate layer material, utilizing the dissolution of Nb to introduce strong carbide-forming elements. Simultaneously, it leverages the dissolution of graphite by Ni to obtain liquid carbon atoms, improving wetting and generating (Mo,Nb)C and (Mo,Ni)C carbides in situ to strengthen the brazing seam, achieving a high-quality metallurgical bond between graphite and TZM. Furthermore, the welded joint obtained using this method exhibits a room temperature shear strength as high as 44.19 MPa, effectively solving the problems of high residual stress and low strength in traditional brazing.

[0022] The description provided is merely an overview of the technical solution disclosed herein. In order to make the technical means of this disclosure clearer and more understandable, to the point that those skilled in the art can implement it according to the contents of the specification, and in order to make the described and other objects, features and advantages of this disclosure more obvious and understandable, specific embodiments of this disclosure are illustrated below. Attached Figure Description

[0023] Various other advantages and benefits of this disclosure will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0024] Figure 1 This is a schematic diagram of a high-temperature brazing method for graphite and TZM based on in-situ brazing seam strengthening provided in this disclosure;

[0025] Figure 2 A schematic diagram of the brazing assembly of the graphite base material, TZM alloy base material and composite intermediate layer material provided in this disclosure;

[0026] Figure 3 SEM morphology image of the graphite-TZM welded joint obtained in Embodiment 1 of this disclosure;

[0027] Figure 4 The shear strength-displacement curve of the graphite-TZM welded joint obtained in Embodiment 1 of this disclosure;

[0028] Figure 5 SEM morphology image of the graphite-TZM welded joint obtained in Comparative Example 1 provided in this disclosure;

[0029] Figure 6 SEM shear strength-displacement curve of the graphite-TZM welded joint obtained in Comparative Example 1 provided in this disclosure;

[0030] Figure 7 SEM morphology image of the graphite-TZM welded joint obtained in Comparative Example 2 provided in this disclosure;

[0031] Figure 8 Shear strength-displacement curve of the graphite-TZM welded joint obtained in Comparative Example 2 provided in this disclosure. Detailed Implementation

[0032] The following will be combined with the appendix Figures 1 to 8 The embodiments described herein are provided in detail and are intended to explain, rather than limit, this disclosure. While specific embodiments of this disclosure are shown in the accompanying drawings, it should be understood that this disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0033] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions of preferred embodiments of this disclosure are for the purpose of implementing the general principles of the specification and are not intended to limit the scope of this disclosure. The scope of protection of this disclosure is determined by the appended claims.

[0034] To facilitate understanding of the embodiments of this disclosure, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments, and the accompanying drawings do not constitute a limitation on the embodiments of this disclosure.

[0035] A high-temperature brazing method for graphite and TZM based on in-situ brazing seam strengthening, see [link to relevant documentation]. Figure 1 It includes the following steps:

[0036] Step S100: Assemble the pretreated graphite base material, TZM alloy base material, and pretreated composite intermediate layer material to form the component to be welded.

[0037] Step S200: The components to be welded are heated to the brazing temperature under a protective atmosphere and pressure for heat preservation and connection, so that the composite intermediate layer material melts and undergoes a metallurgical reaction, thereby realizing the connection between graphite and TZM alloy.

[0038] In this embodiment, Hastelloy C-276 / Ni / Nb is used as the composite intermediate layer material. The dissolution of Nb introduces strong carbide-forming elements, while Ni dissolves graphite to obtain liquid carbon atoms, improving wetting and generating (Mo,Nb)C and (Mo,Ni)C carbides in situ to strengthen the brazing joint, achieving a high-quality metallurgical bond between graphite and TZM. Furthermore, the joint obtained using this method exhibits a room temperature shear strength as high as 44.19 MPa, effectively solving the problems of high residual stress and low strength in traditional brazing.

[0039] In a preferred embodiment of the method, in step S100, the assembly process is as follows: pretreated graphite and TZM alloy base material, as well as pretreated composite intermediate layer material, are stacked from top to bottom in the order of TZM base material / composite intermediate layer material / graphite base material.

[0040] For this embodiment, see Figure 2 The reason for stacking the TZM base material on top, the composite intermediate layer material in the middle, and the graphite base material at the bottom is that graphite has low surface energy and is difficult to wet by liquid metal. Placing it at the bottom allows the molten intermediate layer to spread naturally downward under gravity, fully covering the graphite surface, thereby improving interfacial wettability and promoting the diffusion of carbon atoms from graphite to the molten pool, providing sufficient carbon source for the in-situ generation of carbide reinforcing phases such as (Mo,Nb)C and (Mo,Ni)C. At the same time, TZM, as a base material with a relatively high density, is placed on top, which can apply a certain pressure to the intermediate layer, preventing the liquid phase from being squeezed out of the weld and ensuring a full weld formation. If the layers are not stacked in this order (e.g., graphite is placed on top), the liquid metal will preferentially flow downwards to the TZM, causing large-area unbonded defects at the graphite / intermediate layer interface due to lack of liquid. Carbon atoms will also have difficulty diffusing upwards into the weld center, which not only fails to form a sufficient strengthening phase, but also easily leads to the formation of a continuous brittle carbide layer in some areas due to excessively rapid reaction. Ultimately, this results in a sharp decrease in joint strength and makes it impossible to achieve a reliable metallurgical bond.

[0041] In a preferred embodiment of the method, the composite intermediate layer material is a multilayer composite structure composed of nickel-based alloy layer / metallic nickel layer / nickel-based alloy layer / metallic niobium layer stacked in that order.

[0042] The sequential stacking of nickel-based alloy layers / metallic nickel layers / nickel-based alloy layers / metallic niobium layers (e.g., C-276 / Ni / C-276 / Nb) is a functional structural design based on the physicochemical properties of the base materials on both sides: The C-276 layer near the TZM side is rich in elements such as Mo, Cr, and W, and can form a continuous solid solution with Mo in the TZM at high temperatures, achieving good metallurgical bonding. At the same time, it provides the Mo source required for the formation of (Mo,Ni)C by dissolving part of the TZM. The metallic nickel layer, as the main liquid phase source, can both dissolve graphite to provide carbon atoms and improve wettability to refractory metals, promoting element diffusion. The metallic niobium layer near the graphite side, as a strong carbide-forming element source, reacts with carbon atoms diffused from graphite after dissolving in the liquid phase, generating a dispersed (Mo,Nb)C reinforcing phase in situ at the graphite interface, avoiding the continuous brittle carbide layer that is easily formed by traditional solders.

[0043] If the layers are not stacked in this order, for example, if the Nb layer is placed on the TZM side or the C-276 and Ni layers are interchanged, the following will occur: the Nb layer will directly contact the TZM. Since the carbon content in the TZM is extremely low, Nb cannot exert its strong carbide-forming ability and will instead easily form brittle intermetallic compounds; if all of the C-276 is placed on the graphite side and the Nb layer is in the middle, the graphite interface will lack sufficient strong carbide-forming elements, making it difficult to generate the (Mo,Nb)C strengthening phase; if the symmetry of the multilayer structure is disrupted, it will easily lead to uneven liquid phase distribution and disordered element diffusion paths, making it impossible to form gradient composite structures on both sides at the same time, ultimately increasing the residual stress and reducing the strength of the joint, making it impossible to achieve a high-quality connection.

[0044] In a preferred embodiment of the method, the nickel-based alloy layer is a Hastelloy C-276 foil with a single layer thickness of 0.05 mm.

[0045] In a preferred embodiment of the method, the nickel layer is a pure nickel foil with a thickness of 0.1 mm.

[0046] In a preferred embodiment of the method, the niobium layer is a pure niobium foil with a thickness of 0.03 to 0.05 mm.

[0047] The thickness of the niobium layer is controlled within the range of 0.03–0.05 mm to provide an appropriate amount of the strong carbide-forming element Nb, allowing it to fully dissolve and diffuse to the graphite side during brazing. There, it reacts with carbon atoms dissolved from the graphite to form a dispersed (Mo,Nb)C reinforcing phase in the weld. If the thickness of the niobium layer is too small (e.g., <0.03 mm), insufficient Nb supply will easily lead to an insufficient amount of carbide reinforcing phase generated, failing to effectively exert its dispersed strengthening effect. If the thickness of the niobium layer is too large (e.g., >0.05 mm), the excess Nb cannot be completely dissolved, or a continuous brittle carbide layer will form on the graphite side, easily leading to a decrease in the thermal expansion coefficient matching and an increase in residual stress.

[0048] In a preferred embodiment of the method, the applied pressure is 0.05 to 0.2 MPa.

[0049] The applied pressure is controlled within the range of 0.05–0.2 MPa to ensure close contact between the foils in the composite interlayer and between the foils and the base materials on both sides, promoting liquid phase spreading and element diffusion. If the applied pressure is too low (e.g., <0.05 MPa), the contact pressure is insufficient, and micro-voids are likely to exist at the interface, resulting in insufficient liquid phase filling, poor wetting, and the formation of incomplete welding defects. If the applied pressure is too high (e.g., >0.2 MPa), excessive pressure can easily cause compression deformation or damage to the graphite base material, squeezing the molten liquid phase out of the weld, resulting in weld thinning, compositional imbalance, and thus reducing joint quality.

[0050] In a preferred embodiment of the method, the heating rate is 80–100 °C / min, and the cooling rate is 20–30 °C / min.

[0051] The heating rate is controlled within the range of 80–100 °C / min to ensure that all components of the composite interlayer reach their melting points synchronously and rapidly and undergo the expected metallurgical reaction. If the heating rate is too low (e.g., <80 °C / min), the heating is too slow, which may cause premature solid-phase diffusion or local melting of the interlayer before reaching the target temperature, destroying the synergistic effect of the multilayer structure and affecting the subsequent formation of in-situ carbides. If the heating rate is too high (e.g., >100 °C / min), the heating is too fast, and thermal stress cracks may occur in the base material (especially graphite) due to thermal shock. At the same time, the melting of each layer is asynchronous, the reaction is incomplete, and the joint quality deteriorates.

[0052] Controlling the cooling rate within the range of 20–30 °C / min achieves a balance between alleviating residual welding stress and controlling microstructure. If the cooling rate is too low (e.g., <20 °C / min), the cooling is too slow. Although this is beneficial for stress release, it can easily lead to excessively long high-temperature dwell time, causing coarsening of existing carbides and growth of weld grains, thus reducing the mechanical properties of the joint. If the cooling rate is too high (e.g., >30 °C / min), the cooling is too fast, and the thermal stress generated in the weld cannot be released in time, which can easily lead to microcracks inside the joint, resulting in a significant decrease in joint strength or even cracking.

[0053] In a preferred embodiment of the method, the brazing temperature is 1350–1450°C, and the holding time is 5–15 min.

[0054] The brazing temperature should be controlled within the range of 1350–1450℃, and the holding time within the range of 5–15 minutes. This ensures that the composite interlayer melts fully, elements diffuse sufficiently, and in-situ carbide formation is completed, while preventing deterioration of the base material microstructure. If the brazing temperature is too low (e.g., <1350℃) or the holding time is too short (e.g., <5 minutes), the interlayer will not melt completely, elements will not diffuse sufficiently, and the amount of carbide formed will be insufficient, resulting in low joint bonding strength. If the brazing temperature is too high (e.g., >1450℃) or the holding time is too long (e.g., >15 minutes), it can easily cause coarse grains in the TZM alloy, excessive reaction between graphite and the weld to form an excessively thick carbide layer, and excessive liquid phase, leading to excessive weld flow, poor formation, and reduced joint performance.

[0055] In a preferred embodiment of the method, the pretreatment of the graphite base material and the TZM alloy base material includes cutting, grinding and ultrasonic cleaning of the surfaces to be welded; the pretreatment of the composite intermediate layer material includes cutting, grinding and ultrasonic cleaning.

[0056] For example, when pre-treating the graphite base material and the TZM alloy base material, the surfaces of the graphite and TZM to be welded are first polished step by step with 400-grit, 600-grit and 1000-grit sandpaper, and then placed in ethanol and ultrasonically cleaned at a frequency of 70-150kHz for 5-30 minutes.

[0057] When pre-treating the composite intermediate layer material, the upper and lower surfaces of C-276, Ni, and Nb foils are first polished step by step with 1000-grit and 1500-grit sandpaper. Then, the C-276, Ni, and Nb foils are placed in ethanol and ultrasonically cleaned at a frequency of 70-150kHz for 5-30 minutes.

[0058] To better understand this disclosure, the following more specific embodiments are provided to illustrate the technical effects of this disclosure.

[0059] Example 1

[0060] TZM was cut into 10mm×10mm×3mm pieces using molybdenum wire cutting. For each 10mm×10mm×3mm cube of TZM, any 10mm×10mm surface was selected as the surface to be soldered. Graphite was cut into 20mm×14mm×7mm pieces using diamond cutting. For each 20mm×14mm×7mm graphite piece, any 20mm×14mm surface was selected as the surface to be soldered. The surfaces of the graphite and TZM to be soldered were polished step by step using 400-grit, 600-grit, and 1000-grit sandpaper to remove surface impurities and ensure that the surfaces to be soldered were smooth and flat. After polishing, they were placed in ethanol and ultrasonically cleaned at a frequency of 100kHz for 5 minutes in an ultrasonic cleaner. The cleaned graphite and TZM were then placed in a vacuum bag for later use.

[0061] C-276, Ni, and Nb foils were cut with scissors to obtain 10mm × 10mm foils. The top and bottom surfaces of the foils were then sanded progressively with 1000-grit and 1500-grit sandpaper. After sanding, the foils were placed in ethanol and ultrasonically cleaned at 100kHz for 5 minutes. The cleaned foils were then placed separately into vacuum bags. The C-276, Ni, and Nb foils were bonded together in the order C-276 / Ni / C-276 / Nb using a spot welder. The foils were then held together with pressure using two flat surfaces to obtain a C-276 / Ni / Nb composite foil. This composite foil was flattened and sealed in a bag for later use. The thickness of C-276 was 0.05mm, Ni was 0.1mm, and Nb was 0.04mm.

[0062] The TZM, C-276 / Ni / Nb composite foil and graphite are stacked from bottom to top in the following order: 20mm×14mm×7mm graphite (soldering side up) / C-276 / Ni / Nb composite foil / 10mm×10mm×3mm TZM (soldering side down) to obtain the assembly.

[0063] The assembly is placed in the furnace, and a pressure of 0.1 MPa is pre-applied along the axial direction of the surface to be welded by the pressure head to ensure close contact between the base material and the C-276 / Ni / Nb composite foil. Then, argon gas is introduced into the furnace at a flow rate of 5 L / min to stabilize the atmosphere inside the furnace. Heating is started at a rate of 100 °C / min to 1400 °C, then held at that temperature for 10 min, and then cooled to below 200 °C at a rate of 20 °C / min. The sample is then removed to obtain the welded joint.

[0064] The SEM morphology image of the welded joint obtained in this embodiment can be found in [reference needed]. Figure 3As shown in the figure, the weld exhibits a gradient composite structure: a C+(Mo,Ni)C structure is formed near the TZM side, achieving good metallurgical bonding with the TZM base material; the weld center is a C+Ni(s,s) region; a C+(Mo,Nb)C structure is formed near the graphite side, and the carbides are dispersed and no continuous brittle layer is formed, verifying the effectiveness of the in-situ strengthening mechanism.

[0065] Shear tests were performed using an electronic universal testing machine with a loading speed of 0.5 mm / min. The results are shown in [reference needed]. Figure 4 .Depend on Figure 4 As can be seen, the room temperature shear strength of the welded joint obtained in this embodiment can reach up to 44.19 MPa, while the welded joint strength of traditional Ti-based brazing filler metals (such as Ti-35Ni and Ti-40Cr welded to TZM / graphite) is only up to 26.5 MPa. The joint strength obtained in this embodiment is 1.5 times that of the traditional joint, avoiding the formation of a layered carbide layer on the graphite side of the weld, and relying on the C-Ni eutectic reaction to form a strong connection.

[0066] Comparative Example 1

[0067] TZM was cut into 10mm×10mm×3mm cubes using molybdenum wire cutting. Any 10mm×10mm surface of the 10mm×10mm×3mm cube TZM was selected as the surface to be welded. Graphite was cut into 20mm×14mm×7mm cubes using diamond cutting. Any 20mm×14mm×7mm surface of the 20mm×14mm×7mm graphite was selected as the surface to be welded. The surfaces to be welded of graphite and TZM were polished step by step using 400-grit, 600-grit, and 1000-grit sandpaper to remove surface impurities and ensure that the surfaces to be welded were smooth and flat. After polishing, they were placed in ethanol and ultrasonically cleaned at a frequency of 100kHz for 5 minutes in an ultrasonic cleaner. The cleaned graphite and TZM were then placed in a vacuum bag for later use.

[0068] C-276, Ni, and Nb foils were cut with scissors to obtain 10mm × 10mm foils. The top and bottom surfaces of the foils were then sanded progressively with 1000-grit and 1500-grit sandpaper. After sanding, the foils were placed in ethanol and ultrasonically cleaned at 100kHz for 5 minutes. The cleaned foils were then placed separately into vacuum bags. The C-276, Ni, and Nb foils were bonded together in the order C-276 / Ni / C-276 / Nb using a spot welder. The foils were then held together with pressure using two flat surfaces to obtain a C-276 / Ni / Nb composite foil. This composite foil was flattened and sealed in a bag for later use. The thickness of C-276 was 0.05mm, Ni was 0.1mm, and Nb was 0.02mm.

[0069] The TZM, C-276 / Ni / Nb composite foil and graphite are stacked from bottom to top in the following order: 20mm×14mm×7mm graphite (soldering side up) / C-276 / Ni / Nb composite foil / 10mm×10mm×3mm TZM (soldering side down) to obtain the assembly.

[0070] The assembly is placed in the furnace, and a pressure of 0.1 MPa is pre-applied along the axial direction of the surface to be welded by the pressure head to ensure close contact between the base material and the C-276 / Ni / Nb composite foil. Then, argon gas is introduced into the furnace at a flow rate of 5 L / min to stabilize the atmosphere inside the furnace. Heating is started at a rate of 100℃ / min to 1400℃, then held at that temperature for 10 min, and then cooled to below 200℃ at a rate of 20℃ / min. The sample is then removed to obtain the welded joint.

[0071] The SEM morphology image of the welded joint obtained in this comparative example can be found in [reference needed]. Figure 5 As shown in the figure, compared with Example 1, due to insufficient Nb content, a significant C+(Mo,Nb)C strengthening region was not formed near the graphite side. The main body of the weld is dominated by C+Ni(s,s) microstructure, and the amount of carbide formation is significantly reduced. This microstructure means that the in-situ strengthening effect is weakened, the bonding strength between the weld and the graphite side is insufficient, and there is a lack of the moderating effect of carbides on the coefficient of thermal expansion, resulting in greater residual stress.

[0072] Shear tests were performed using an electronic universal testing machine, with a loading speed set to 0.5 mm / min. The results are shown in [reference needed]. Figure 6 .Depend on Figure 6 It can be seen that the room temperature shear strength of the welded joint obtained in this comparative example is the highest at 37.92 MPa, which is lower than the 44.19 MPa of Example 1.

[0073] Comparative Example 2

[0074] TZM was cut into 10mm×10mm×3mm pieces using molybdenum wire cutting. For each 10mm×10mm×3mm cube of TZM, any 10mm×10mm surface was selected as the surface to be soldered. Graphite was cut into 20mm×14mm×7mm pieces using diamond cutting. For each 20mm×14mm×7mm graphite piece, any 20mm×14mm surface was selected as the surface to be soldered. The surfaces of the graphite and TZM to be soldered were polished step by step using 400-grit, 600-grit, and 1000-grit sandpaper to remove surface impurities and ensure that the surfaces to be soldered were smooth and flat. After polishing, they were placed in ethanol and ultrasonically cleaned at a frequency of 100kHz for 5 minutes in an ultrasonic cleaner. The cleaned graphite and TZM were then placed in a vacuum bag for later use.

[0075] C-276, Ni, and Nb foils were cut with scissors to obtain 10mm × 10mm foils. The top and bottom surfaces of the foils were then sanded progressively with 1000-grit and 1500-grit sandpaper. After sanding, the foils were placed in ethanol and ultrasonically cleaned at 100kHz for 5 minutes. The cleaned foils were then placed separately into vacuum bags. The C-276, Ni, and Nb foils were bonded together in the order C-276 / Ni / C-276 / Nb using a spot welder. The foils were then held together with pressure using two flat surfaces to obtain a C-276 / Ni / Nb composite foil. This composite foil was flattened and sealed in a bag for later use. The thickness of C-276 was 0.05mm, Ni was 0.1mm, and Nb was 0.06mm.

[0076] The TZM, C-276 / Ni / Nb composite foil and graphite are stacked from bottom to top in the following order: 20mm×14mm×7mm graphite (soldering side up) / C-276 / Ni / Nb composite foil / 10mm×10mm×3mm TZM (soldering side down) to obtain the assembly.

[0077] The assembly is placed in the furnace, and a pressure of 0.1 MPa is pre-applied along the axial direction of the surface to be welded by the pressure head to ensure close contact between the base material and the C-276 / Ni / Nb composite foil. Then, argon gas is introduced into the furnace at a flow rate of 5 L / min to stabilize the atmosphere inside the furnace. Heating is started at a rate of 100℃ / min to 1400℃, then held at that temperature for 10 min, and then cooled to below 200℃ at a rate of 20℃ / min. The sample is then removed to obtain the welded joint.

[0078] The SEM morphology image of the welded joint obtained in this comparative example can be found in [reference needed]. Figure 7 As shown in the figure, compared with Example 1, due to the excessive Nb content, the C+(Mo,Nb)C carbide layer formed near the graphite side is significantly thicker and tends to be continuous, with carbide aggregation occurring in some areas. This excessively thick carbide layer is brittle and easily becomes a channel for crack initiation and propagation. At the same time, the excessive Nb leads to incompletely dissolved residues or the formation of brittle intermetallic compounds, weakening the interfacial bonding strength.

[0079] Shear tests were performed using an electronic universal testing machine with a loading speed of 0.5 mm / min. See the results below. Figure 8 .Depend on Figure 8 It can be seen that the room temperature shear strength of the welded joint obtained in this comparative example is up to 40.09 MPa, which is lower than 44.19 MPa in Example 1.

[0080] Although the embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this disclosure is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the teachings of this specification and without departing from the scope of protection of the claims of this disclosure, and all of these are within the scope of protection of this disclosure.

Claims

1. A high-temperature brazing method for graphite and TZM based on in-situ brazing seam strengthening, characterized in that, Includes the following steps: Step S100: Assemble the pretreated graphite base material, TZM alloy base material, and pretreated composite intermediate layer material to form the component to be welded. Step S200: The components to be welded are heated to the brazing temperature under a protective atmosphere and pressure for heat preservation and connection, so that the composite intermediate layer material melts and undergoes a metallurgical reaction, thereby realizing the connection between graphite and TZM alloy.

2. The method according to claim 1, characterized in that, Preferably, in step S100, the assembly process is as follows: the pretreated graphite and TZM alloy base material, as well as the pretreated composite intermediate layer material are stacked from top to bottom in the order of TZM base material / composite intermediate layer material / graphite base material.

3. The method according to claim 1, characterized in that, The composite intermediate layer material is a multi-layer composite structure composed of nickel-based alloy layer / metallic nickel layer / nickel-based alloy layer / metallic niobium layer stacked in that order.

4. The method according to claim 3, characterized in that, The nickel-based alloy layer is a Hastelloy C-276 foil with a single layer thickness of 0.05 mm.

5. The method according to claim 3, characterized in that, The nickel layer is a pure nickel foil with a thickness of 0.1 mm.

6. The method according to claim 3, characterized in that, The niobium layer is a pure niobium foil with a thickness of 0.03–0.05 mm.

7. The method according to claim 1, characterized in that, The applied pressure is 0.05 to 0.2 MPa.

8. The method according to claim 1, characterized in that, The heating rate is 80–100 °C / min, and the cooling rate is 20–30 °C / min.

9. The method according to claim 1, characterized in that, The brazing temperature is 1350–1450℃, and the holding time is 5–15 minutes.

10. The method according to claim 1, characterized in that, The pretreatment of the graphite base material and the TZM alloy base material includes cutting, grinding and ultrasonic cleaning of the surfaces to be welded; the pretreatment of the composite intermediate layer material includes cutting, grinding and ultrasonic cleaning.

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