Diffusion connection matching structure, diffusion connection system and diffusion connection method

Abstract

The invention provides a diffusion connection matching structure, a diffusion connection system and a diffusion connection method.The matching structure comprises a first connector and a second connector, the first connector is arranged in the second connector in a sleeved mode, threads are correspondingly arranged on the outer wall of the first connector and the inner wall of the second connector, and the lead angle theta of the threads meets the condition that arctan mu1 < = theta < = arctan mu2, mu1 is the friction coefficient between the first joint and the second joint at the temperature of T1-T2; mu2 is lower than the friction coefficient between the first connector and the second connector at the temperature T1, the temperature T1 is 50% of the lowest melting point temperature of the materials of the first connector and the second connector, the temperature T2 is 75% of the lowest melting point temperature of the materials of the first connector and the second connector, and the threads are arranged to be in the mode that when axial stress is applied to the first connector at the temperatures T1 to T2, the temperature T1 is 50% of the temperature T2; the second connector and the first connector rotate relatively, and the first connector and the second connector form self-locking at the temperature lower than T1. Sliding diffusion bonding is adopted, growth of brittle intermetallic compounds is inhibited by means of interface friction force, and the joint bonding strength is improved.

Description

Technical Field

[0001] The present invention relates to the field of metal processing, and in particular to a diffusion bonding matching structure diffusion bonding system and a diffusion bonding method. Background Art

[0002] Pressure pipes and pipe joints in nuclear chemical industry need to withstand the corrosion of semi-boiling / boiling concentrated nitric acid. The service environment is harsh. Some processes in the key process flow also face factors such as high temperature, strong acid and complex ion composition, which further aggravates the corrosion effect of radioactive waste liquid on equipment materials. Zirconium alloy has a very low thermal neutron absorption cross section, good compatibility with uranium fuel, high hardness and good ductility, and is the core material of nuclear chemical industry. Zirconium alloy materials are expensive, which limits their use in all scenarios. In scenarios with relatively low safety level requirements, stainless steel and other materials are often selected to replace zirconium alloys. The connection of zirconium alloys with dissimilar metals such as stainless steel through composite pipe joints is a complex problem. It is necessary to develop reliable connection technology for zirconium alloy and stainless steel pipe joints to ensure the safety of equipment operation.

[0003] At present, the preparation methods for zirconium alloy and stainless steel composite pipe joints include fusion welding, electron beam welding, friction welding, explosion welding and diffusion welding. Among them, the diffusion welding technology has no strict requirements on the wall thickness of the pipe joint, and can achieve reliable connection between zirconium alloy and stainless steel, effectively avoid air intrusion and element burning, and ensure the service performance of the material, but diffusion welding is easy to form intermetallic compounds.

[0004] The paper Microstructure and mechanical properties of Zr-4 alloy and 316 stainless steel diffusion bonding joining Nb / Ni composite interlayer published in Advanced Engineering Materials proposed that there is a certain thickness of intermetallic compound reaction layer in the interface structure of the zirconium alloy and stainless steel joint. The thicker the intermetallic compound layer, the more unfavorable it is to the mechanical properties and corrosion resistance of the joint. The thickness of the intermetallic compound layer is determined by the diffusion welding temperature and the holding time. The longer the holding time at high temperature, the thicker the intermetallic compound layer. However, if the diffusion welding temperature is too low and the diffusion time is too short, the diffusion distance of atoms will be limited, resulting in an increase in the unwelded joint rate. Therefore, for the diffusion connection of zirconium alloy and stainless steel, it is impossible to suppress the formation of the intermetallic compound layer while satisfying the sufficient distance for atomic diffusion.

[0005] Patent CN114043065A proposes a method for hot isostatic pressing diffusion welding of an aluminum rotating target, which includes the following steps: (1) machining threads on the surface of a stainless steel tube, assembling a high-purity aluminum tube with a stainless steel tube and a low-carbon steel tube to obtain a sleeve, wherein the sleeve is a stainless steel tube, a high-purity aluminum tube and a low-carbon steel tube from the inside to the outside, respectively, and gaps are reserved between the stainless steel tube, the high-purity aluminum tube and the low-carbon steel tube; (2) the sleeve is sealed at both ends by stainless steel ring welding; (3) the sleeve after welding and sealing is degassed; (4) the sleeve after degassed is hot isostatic pressing to obtain a welded aluminum rotating target and a stainless steel tube; the method obtains an aluminum rotating target with no obvious weld and good bonding strength by machining threads, degassing and hot isostatic pressing diffusion process. The patent proposes setting threads on the surface of the stainless steel tube, but does not design the specific structure of the threads.

[0006] In view of the above technical problems, the present invention is specially introduced. Summary of the invention

[0007] The main purpose of the present invention is to provide a diffusion bonding matching structure diffusion bonding system and a diffusion bonding method to inhibit the generation of intermetallic compounds and improve the bonding strength between dissimilar metals.

[0008] In order to achieve the above object, the present invention provides a diffusion connection matching structure, including a first joint and a second joint, the first joint is sleeved inside the second joint, the outer wall of the first joint and the inner wall of the second joint are correspondingly provided with threads, and the thread lead angle θ of the thread satisfies the formula:

[0009] arctanμ1≤θ≤arctanμ2

[0010] Where μ1 is T 1 ~T 2 The friction coefficient between the first joint and the second joint at temperature; μ2 is lower than T 1 Friction coefficient between the first joint and the second joint at temperature, T 1 The temperature is 50% of the lowest melting point temperature of the materials of the first joint and the second joint, T 2 The temperature is 75% of the lowest melting point temperature of the materials of the first joint and the second joint.

[0011] The thread is set at T 1 ~T 2 When axial stress is applied to the first joint at different temperatures, the second joint rotates relative to the first joint, which is less than T 1 The first joint and the second joint form a self-locking state at the temperature.

[0012] Preferably, the thread profile is trapezoidal.

[0013] Preferably, the first joint is a stainless steel joint, and the second joint is a zirconium alloy joint.

[0014] Preferably, T 1 ~T 2 The friction coefficient between the stainless steel joint and the zirconium alloy joint is 0.3-0.6 at room temperature.

[0015] Preferably, less than T 1 The friction coefficient between the stainless steel joint and the zirconium alloy joint is 0.7 to 1.26 at room temperature.

[0016] Preferably, the thread lead angle θ is in the range of 20 to 50°.

[0017] Preferably, the maximum radial clearance between the first joint and the second joint in the initial assembly stage is 0.03-0.06 mm.

[0018] Preferably, the height of the trapezoid is 3 to 5 mm.

[0019] Preferably, the pitch of the thread is 30 to 40 mm.

[0020] In another aspect of the present application, a diffusion bonding system is proposed for performing diffusion bonding on a diffusion bonding fitting structure, wherein the system comprises a thrust bearing connected to the bottom of the second joint.

[0021] Preferably, a clamp is included, and the clamp is sleeved on the outside of the second joint and the thrust bearing.

[0022] Preferably, it also includes a chassis, which supports the thrust bearing and the clamp.

[0023] The diffusion bonding matching structure and diffusion bonding system proposed in the present invention achieve the following technical effects:

[0024] 1. The first joint and the second joint adopt a threaded matching structure, so that relative movement occurs between the first joint and the second joint at the diffusion connection temperature, and the growth of brittle intermetallic compounds is suppressed by the friction between the two; the surface roughness of the interface is reduced, close contact of the connection interface is achieved, and the diffusion channel of atoms is increased; the connection area, tensile strength and sealing of the joint are increased;

[0025] 2. The thread lead angle is designed based on the change of the friction coefficient between the first joint and the second joint during the diffusion connection heating process, so that the relative movement between the first joint and the second joint can be achieved at the diffusion connection temperature, and the first joint and the second joint remain in a self-locking state below the diffusion temperature;

[0026] 3. The pressure head is moved at a constant rate so that the atoms at the interface diffuse over a certain distance and relative sliding of the interface occurs before the formation of intermetallic compounds.

[0027] In another aspect of the present application, a diffusion bonding method is also proposed, comprising the following steps:

[0028] Step S1, determining the thread shapes of the first joint and the second joint, and processing the first joint and the second joint;

[0029] Step S2: Heat the vacuum furnace to 600-800°C and set the vacuum degree to 1.0-2×10 -3 Pa;

[0030] Step S3, applying axial pressure to one end of the first joint, under the action of the axial pressure, the second joint rotates and the first joint moves downward to perform diffusion welding.

[0031] Wherein step S1 includes determining the thread lead angle θ based on the following formula:

[0032] arctanμ1≤θ≤arctanμ2

[0033] Where μ1 is T 1 ~T 2 The friction coefficient between the first joint and the second joint at temperature; μ2 is lower than T 1 Temperature Friction coefficient between the first joint and the second joint, T 1 The temperature is 50% of the lowest melting point temperature of the materials of the first joint and the second joint, T 2 The temperature is 75% of the lowest melting point temperature of the materials of the first joint and the second joint.

[0034] Preferably, the pressure head applying the axial pressure in step S3 moves at a constant speed.

[0035] Preferably, the axial pressure in step S3 ranges from 10 to 50 KN.

[0036] Preferably, step S2 includes S21, heating to 400°C at a rate of 10°C / min, keeping the temperature for 10 minutes,

[0037] Step S22, heating to 600-800°C at a rate of 10°C / min, and keeping the temperature for 15-60 minutes.

[0038] Preferably, the method further comprises step S4, wherein after the diffusion welding is completed, the temperature is cooled to 750° C., the axial pressure is removed, the temperature is cooled to 150° C. in the furnace, and the vacuum system is closed.

[0039] The diffusion connection method proposed in the present invention achieves the following technical effects:

[0040] 1. Make the first joint and the second joint move relative to each other at the diffusion connection temperature, and use the friction between the two to inhibit the growth of brittle intermetallic compounds; reduce the surface roughness of the interface, achieve close contact of the connection interface, increase the diffusion channel of atoms; increase the connection area, tensile strength and sealing of the joint;

[0041] 2. The indenter moves at a constant rate, so that there is a certain distance for the atoms to diffuse between the interfaces, and relative sliding of the interfaces is ensured before the formation of intermetallic compounds.

[0042] 3. Use scanning electron microscopy to observe the microscopic interface structure of the intermetallic compound layer to adjust the relevant parameters of the constant displacement mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 A schematic diagram of the diffusion connection system of the present application is shown;

[0045] Figure 2 The stress conditions at the interface between the first joint and the second joint of the present application are shown;

[0046] Figure 3 Shown are the interface metallographic images of diffusion bonding (a) and sliding diffusion bonding (b);

[0047] Figure 4 SEM images of the interfaces of diffusion bonding (a) and sliding diffusion bonding (b) are shown;

[0048] Figure 5 The diffusion connection method process of this application is shown Figure 1 ;

[0049] Figure 6 The diffusion connection method process of this application is shown Figure 2 ;

[0050] Figure 7 A schematic diagram of the thread structure of the present application is shown;

[0051] Figure 8 The Zr-Fe binary equilibrium phase diagram is shown;

[0052] The above drawings include the following reference numerals:

[0053] 100, first joint; 200, second joint; 300, thrust bearing; 400, fixture; 500, chassis. DETAILED DESCRIPTION

[0054] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0055] The present invention is further described in detail below in conjunction with specific embodiments, and these embodiments cannot be understood as limiting the scope of protection claimed by the present invention. The term "including" when used indicates the existence of a feature, but does not exclude the existence or addition of one or more other features; the orientation or position relationship indicated by the terms "lateral", "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inside", "outside", etc. is based on the orientation or position relationship shown in the drawings, which is only for the convenience of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention; in addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance.

[0056] In the description, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0057] Embodiment 1:

[0058] Usually, the process temperature of diffusion bonding is high. In order to ensure that the atoms at the interface of dissimilar metals are fully diffused, it is often necessary to maintain high temperature conditions for a long time. When dissimilar metals are kept at high temperature for a long time, the atoms at the interface are prone to generate intermetallic compounds, resulting in a decrease in the joint connection performance. For example, when zirconium alloy and stainless steel are diffused, Zr(Fe,Cr) will be generated. 2 and Zr 2 (Fe, Ni) intermetallic compounds, the formation of which will significantly reduce the interface strength between zirconium alloy and stainless steel, thus failing to meet the requirements of spent fuel dissolvers for joints. Based on this problem, the present application makes the joints move relative to each other during the diffusion connection process, utilizes the friction between the interfaces to destroy the intermetallic compounds, continuously forms new interfaces, and improves the joint bonding strength.

[0059] This application proposes a diffusion connection matching structure, such as Figure 1As shown, it includes a first joint 100 and a second joint 200, the first joint 100 is sleeved inside the second joint 200, and the outer wall of the first joint 100 and the inner wall of the second joint 200 are correspondingly provided with threads. When axial stress is applied to one of the joints, the two joints rotate relative to each other along the threads. By adopting a thread rotation structure, rotational diffusion welding is realized. During the rotation process, friction contact is formed between the contact surfaces of the two joints, which inhibits the formation of a brittle intermetallic compound layer. The diffusion of atoms between new interfaces is continuously carried out under high temperature environment. Since some diffused atoms already exist on both sides of the new interface, it is beneficial to further diffuse the atoms between interfaces after slipping, which satisfies the mutual diffusion distance of atoms between interfaces and controls the formation of intermetallic compound layers.

[0060] The material types of the first joint and the second joint of the present application are not specifically limited. As long as the material is suitable for diffusion welding processing, it is applicable to the solution proposed in the present application.

[0061] In order to destroy the intermetallic compounds formed during the diffusion bonding process, it is necessary to ensure that the two joints slide relative to each other at the diffusion bonding temperature. In addition, it is also necessary to ensure that the two joints cannot move relative to each other at the non-diffusion temperature no matter how much pressure is applied.

[0062] This application analyzes the stress condition of the first joint, such as Figure 2 As shown, F is the axial pressure applied to the first joint, F 1 and F 2 They are the force component F parallel to the thread lead angle and the force component F perpendicular to the thread lead angle. N is the support force of the second joint thread on the first joint thread, which is equal to F 2 , μF N is the contact friction force at the interface between the first joint and the second joint. 2 When μF is less than F1, the interface between the first joint and the second joint will move relative to each other. 2 When it is less than F1, the interface between the first joint and the second joint will move relative to each other.

[0063] When the axial pressure remains unchanged, the friction coefficient and the thread lead angle are the key factors affecting the friction force, and are also the key to determining whether the first joint and the second joint can move relative to each other. The present application found that the friction coefficient between the first joint and the second joint changes significantly at the diffusion connection temperature. Assuming that at the diffusion temperature T 1 ~T 2 The friction coefficient between the first joint and the second joint in the range is μ 1 , less than T 1 The friction coefficient between the two is μ 2 . F 1 and F2 The relationship between the lead angle θ and the thread angle is shown in equations (1) and (2). In order to ensure that the relative sliding between the first joint and the second joint only occurs during the diffusion insulation stage, the F 1 Should be greater than the friction force μ between the two at this temperature 1 F 2 , less than T 1 Within range F 1 Should be less than the friction force μ between the two within this temperature range 2 F 2 , see formula (3), substitute expressions (1) and (2) into formula (3), and finally obtain the relationship between the thread lead angle θ and the friction coefficient μ as shown in formula (4). Therefore, by setting the thread lead angle within a reasonable range, it can be ensured that the first joint and the second joint rotate relative to each other under the axial pressure at the diffusion temperature; and when it is lower than the diffusion temperature, the self-locking state of the first joint and the second joint is maintained regardless of the pressure.

[0064] F 1 =F sinθ formula (1)

[0065] F N =F 2 =F cosθ formula (2)

[0066] μ 1 F 2 ≤F 1 ≤μ 2 F 2 Formula (3)

[0067] arctanμ1≤θ≤arctanμ2 Formula (4)

[0068] Among them, μ 1 T 1 ~T 2 The friction coefficient between the first joint 100 and the second joint 200 at the temperature; μ 2 For less than T 1 The friction coefficient between the first joint 100 and the second joint 200 at temperature, T 1 The temperature is 50% of the lowest melting point temperature of the materials of the first joint 100 and the second joint 200, T 2 The temperature is 75% of the lowest melting point temperature of the materials of the first joint 100 and the second joint 200. The formula is derived by force and is not limited by materials. Therefore, the thread lead angle of joints suitable for the diffusion bonding process can be designed by the formula to achieve relative movement between the two joints during diffusion bonding.

[0069] The thread profile of the present application adopts a trapezoidal structure, which has a more stable thread root during transmission and is beneficial to the performance of the joint. Preferably, the height of the trapezoid in the present application is 3 to 5 mm. The pitch of the thread is 30 to 40 mm.

[0070] This application focuses on the case where the first joint 100 is a stainless steel joint and the second joint 200 is a zirconium alloy joint. 1 ~T 2 The friction coefficient between the stainless steel joint and the zirconium alloy joint is 0.3 to 0.6. 1 The friction coefficient between the stainless steel joint and the zirconium alloy joint at the temperature is 0.7 to 1.26. In the present application, in order to realize that the matching structure formed by the zirconium alloy and the stainless steel thread can rotate relative to each other under pressure at the diffusion temperature and form self-locking in the range less than the diffusion temperature, the thread lead angle θ of the two joints of the zirconium alloy and the stainless steel is preferably in the range of 20 to 50°.

[0071] The present application characterizes the interface between the first joint and the second joint based on diffusion connection and sliding diffusion connection. Figure 3 (a) is a metallographic image of the diffusion bonding interface with only pressure but no sliding. It can be seen that there is a continuous intermetallic compound layer, which is a brittle phase and is not conducive to the mechanical properties and corrosion resistance of the joint; Figure 3 (b) is the metallographic image of the sliding diffusion bonding interface. It can be seen that there is no intermetallic compound layer on the interface and the interface connection is good. To further explore the two diffusion bonding interfaces, the backscatter mode of the scanning electron microscope was used to magnify the interface to 5000 times. Figure 4 (a) is the SEM image of the diffusion bonding interface with only pressure but no sliding, showing the presence of a continuous intermetallic compound layer; Figure 4 (b) SEM image of the sliding diffusion bonding interface. There is no intermetallic compound layer at the sliding friction diffusion bonding interface, which further confirms that the formation of intermetallic compounds can be inhibited by sliding friction.

[0072] In addition, the present application tests the tensile strength of the joints obtained by diffusion bonding and sliding diffusion bonding, and it can be seen that the tensile strength of the joints can be greatly improved by complete sliding diffusion bonding.

[0073] Table 1. Tensile strength of different connection methods

[0074] Connection tensile strength No-slip diffusion connection 98MPa Micro sliding diffusion connection 150MPa Completely sliding diffusion connection 350MPa

[0075] In addition, at the diffusion temperature, the first joint and the second joint will expand in the radial direction. To ensure that the first joint and the second joint can rotate relative to each other at the diffusion temperature, a certain radial gap should be formed between the first joint 100 and the second joint 200 during the initial assembly stage. The preferred maximum radial gap is 0.03 to 0.06 mm.

[0076] Another aspect of the present application proposes a diffusion connection system, referring to the attached Figure 2 As shown, it is used to perform diffusion bonding on the diffusion bonding matching structure, and the diffusion bonding system is a vacuum furnace (not shown in the figure), and includes a thrust bearing 300 located in the vacuum furnace, and the thrust bearing 300 is connected to the bottom of the second joint 200. When axial pressure is applied to the first joint and the temperature of diffusion bonding is reached, the second joint rotates.

[0077] In addition, a fixture 400 is also provided in the vacuum furnace, and the fixture 400 is sleeved on the outside of the second joint 200 and the thrust bearing 300, and the fixture 400 limits the axial movement of the second joint 200. The diffusion connection matching structure, the fixture and the thrust bearing are all located on the upper part of the chassis 500 in the vacuum furnace, and the chassis 500 supports the thrust bearing 300 and the fixture 400.

[0078] In summary, the diffusion bonding coordination structure and diffusion bonding system proposed in this embodiment achieve the following technical effects:

[0079] 1. The first joint and the second joint adopt a threaded matching structure, so that relative movement occurs between the first joint and the second joint at the diffusion connection temperature, and the growth of brittle intermetallic compounds is suppressed by the friction between the two; the surface roughness of the interface is reduced, close contact of the connection interface is achieved, and the diffusion channel of atoms is increased; the connection area, tensile strength and sealing of the joint are increased;

[0080] 2. The thread lead angle is designed based on the change of the friction coefficient between the first joint and the second joint during the diffusion connection heating process, so that the relative movement between the first joint and the second joint can be achieved at the diffusion connection temperature, and the first joint and the second joint remain in a self-locking state below the diffusion temperature.

[0081] 3. Optimize the thread structure and size to promote the rotational diffusion connection between the first joint and the second joint.

[0082] Another aspect of the present application provides a diffusion connection method for a matching structure, as shown in the attached Figure 5 As shown, the following steps are included:

[0083] Step S1, determining the thread shapes of the first joint and the first joint, and processing the first joint and the first joint.

[0084] In step S1, the thread lead angle θ is determined based on the following formula:

[0085] arctanμ1≤θ≤arctanμ2

[0086] Where μ1 is T 1 ~T 2 The friction coefficient between the first joint 100 and the second joint 200 at the temperature; μ2 is lower than T 1 Temperature Friction coefficient between the first joint 100 and the second joint 200, T 1 The temperature is 50% of the lowest melting point temperature of the materials of the first joint 100 and the second joint 200, T 2 The temperature is 75°C, which is the lowest melting point of the materials of the first joint 100 and the second joint 200.

[0087] Step S2: Heat the vacuum furnace to 600-800°C and set the vacuum degree to 1.0-2×10 -3 Pa. To ensure uniform temperature rise in the vacuum furnace, the temperature was raised at a rate of 10°C / min to above 400°C and kept at that temperature for 10 minutes, and then continued to be raised at a rate of 10°C / min to the set diffusion bonding temperature and kept at that temperature for 15-60 minutes.

[0088] Step S3, applying axial pressure to one end of the first joint 100, under the action of the axial pressure, the second joint 200 rotates and the first joint 100 moves downward to perform diffusion welding.

[0089] In step S3, the pressure head applying axial pressure moves at a constant rate, so that the atoms between the interfaces diffuse over a certain distance and relative sliding of the interfaces occurs before the intermetallic compound is generated, and the atoms between the new interfaces are continuously diffused under high temperature. Since some diffused atoms already exist on both sides of the new interface, it is beneficial to further diffuse the atoms between the interfaces after sliding. In the present application, the preferred range of axial pressure is 10 to 50 KN to ensure sufficient diffusion of atoms between the interfaces.

[0090] The specific process of constant rate is as follows: a. Set the maximum displacement and maximum force; b. The indenter moves in displacement mode. If the set maximum displacement can be reached, displacement control is mainly used; if the set maximum displacement is not reached, force control mode is enabled; c. If the indenter has not reached the set displacement value under the maximum set force, the indenter stops moving and the set target displacement is not reached.

[0091] Step S4: After the diffusion welding is completed, cool to 750°C, remove the axial pressure, cool to 150°C in the furnace, and close the vacuum system. Figure 8 As shown, zirconium alloy and stainless steel are not easy to react to form intermetallic compounds below 750°C, so there is no need to continue the rotation motion after lowering the temperature to this level.

[0092] The following will describe the zirconium alloy and stainless steel diffusion bonding structure and method with specific embodiments.

[0093] like Figure 7 As shown, preferably, the major diameter of the external thread of the stainless steel component and the major diameter d1 of the internal thread of the zirconium alloy component are 20 mm, the height of the trapezoidal tooth profile is 4 mm, and the minor diameter of the external thread of the stainless steel component and the minor diameter of the internal thread of the zirconium alloy component are d 1 -2h = 12 mm. The thread lead angle θ is set to 30°, and the thread pitch P is calculated to be 36.3 mm based on formula (5).

[0094] P=Πd1 tanθ formula (5)

[0095] P=a+b+4h tanβ Formula (6)

[0096] The height h of the trapezoidal tooth profile is 4mm, a+b=34.1mm, a and b are 16mm and 18.1mm respectively, c=18.14mm, d=20.24mm; the major diameter d1 of the zirconium alloy internal thread is 20mm, and the minor diameter d2 is 12mm.

[0097] The stainless steel component has an external thread with a major diameter d1 of 20 mm, a minor diameter d2 of 12 mm, a thread lead angle θ of 15°, a trapezoidal tooth profile height of 4 mm, a pitch P of 16.8 mm, a+b=14.7 mm, a and b are 6 mm and 8.7 mm respectively, c=8.14 mm, and d=10.84 mm; the internal thread of the zirconium alloy component has a major diameter d1 of 20 mm, and a minor diameter d2 of 12 mm.

[0098] Step 1: Select materials: use a zirconium alloy tube with an outer diameter of D1 and an inner diameter of D2 and a stainless steel bar with a diameter of D3;

[0099] Step 2: Determine the lead angle and thread shape of the rotating thread;

[0100] Step 3: Turning the internal and external threads, and requiring the thread surface roughness to be less than 0.05 μm to meet the surface requirements for diffusion bonding;

[0101] Step 4: Assembling the thrust bearing and the zirconium alloy component: turning an external thread on one end of the zirconium alloy component, and turning an internal thread corresponding to the internal thread on the inner wall of the thrust bearing for assembling the two components;

[0102] Step 5: Assemble the components assembled in step 4 with the stainless steel components, with a maximum radial assembly gap of 0.05 mm to ensure that there is room for rotational movement between the zirconium alloy and the stainless steel during the diffusion bonding process;

[0103] Step 6: Place the components assembled in step 5 on the graphite disk in the vacuum high-temperature furnace and fix them with a clamp for rotational diffusion connection:

[0104] A diffusion bonding process flow is set up. When the temperature is raised to the diffusion bonding temperature, pressure is applied to the upper end of the stainless steel component in a constant displacement mode. With the help of thrust bearings, the movement direction of the zirconium alloy component is changed from vertical to rotational to achieve slip between interfaces. After the temperature is lowered to below the diffusion temperature, the pressure is removed and finally cooled with the furnace.

[0105] The present application uses a scanning electron microscope to analyze the intermetallic compound layer of the interface microstructure. First, a 6mm×6mm×6mm sample block containing the interface portion is cut out using electric spark wire cutting, and then SiC sandpaper is used to grind from 150# to 7000# in sequence, and then the surface is polished on a polishing machine with a 0.25μm diamond polisher until it is bright and has no obvious scratches. The sample is placed in a mixed solution of 10mL hydrofluoric acid, 45mL concentrated nitric acid, and 45mL deionized water and corroded by immersion for 10s, and then the corrosive liquid on the surface of the sample is rinsed off with water and alcohol in turn, and dried with a hair dryer for standby use. Finally, a thermal field emission scanning electron microscope is used to observe the intermetallic compound layer of the microscopic interface structure, and the relevant parameters of the constant displacement mode are adjusted according to the microscopic interface structure.

[0106] Step 7: After the diffusion bonding is completed, the rod-shaped material of the diffusion bonding is processed into a tube using a lathe to obtain a diffusion bonding pipe joint.

[0107] The diffusion bonding process refers to placing the assembled sample on a graphite plate coated with solder resist and fixing it with a clamp, and then placing it in the furnace of a high-temperature diffusion furnace. The vacuum degree in the vacuum diffusion furnace can reach a minimum of 5×10 -4 Pa, the vacuum furnace equipment uses hydraulic devices to provide pressure and positioning movement. Then the pressure head is lowered to a position about 5mm away from the component to facilitate subsequent pressurization at a specific temperature. After closing the furnace door, the entire furnace chamber is evacuated by a mechanical pump and a molecular pump. When the vacuum degree reaches 1.0-1.5×10 -3 Pa, the heating system can be started.

[0108] To ensure uniform temperature rise in the furnace, heat at a rate of 10℃ / min to above 400℃ and keep warm for 10 minutes, then continue to heat at a rate of 10℃ / min to the set diffusion bonding temperature and keep warm for 15-60 minutes. At this time, start the constant displacement mode of the pressure head to apply pressure to the stainless steel component. After the insulation stage, slowly cool at a rate of 5℃ / min to prevent the joint from generating large thermal stress due to excessive cooling. The pressure head can be removed when it cools to below 750℃. Finally, the vacuum system can be closed when the furnace cools to 150℃, and the diffusion bonding test is completed.

[0109] In summary, the diffusion bonding method proposed in this embodiment achieves the following technical effects:

[0110] 1. Make the first joint and the second joint move relative to each other at the diffusion connection temperature, and use the friction between the two to inhibit the growth of brittle intermetallic compounds; reduce the surface roughness of the interface, achieve close contact of the connection interface, increase the diffusion channel of atoms; increase the connection area, tensile strength and sealing of the joint;

[0111] 2. The indenter moves at a constant rate, so that there is a certain distance for the atoms to diffuse between the interfaces, and relative sliding of the interfaces is ensured before the formation of intermetallic compounds.

[0112] 3. Use scanning electron microscopy to observe the microscopic interface structure of the intermetallic compound layer to adjust the relevant parameters of the constant displacement mode.

[0113] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A diffusion connection matching structure, comprising a first joint (100) and a second joint (200), wherein the first joint (100) is sleeved inside the second joint (200), It is characterized in that The outer wall of the first joint (100) and the inner wall of the second joint (200) are correspondingly provided with threads, and the thread lead angle θ of the threads satisfies the formula: arctanμ1≤θ≤arctanμ2 Wherein, μ1 is the friction coefficient between the first joint (100) and the second joint (200) at a temperature between T1 and T2; μ2 is the friction coefficient between the first joint (100) and the second joint (200) at a temperature lower than T1, the T1 temperature is 50% of the lowest melting point temperature of the materials of the first joint (100) and the second joint (200), and the T2 temperature is 75% of the lowest melting point temperature of the materials of the first joint (100) and the second joint (200), The thread is configured such that when an axial stress is applied to the first joint (100) at a temperature between T1 and T2, the second joint (200) and the first joint (100) rotate relative to each other, and the first joint (100) and the second joint (200) form a self-locking state at a temperature lower than T1.

2. The diffusion bonding matching structure according to claim 1, characterized in that: The thread profile of the thread is trapezoidal.

3. The diffusion bonding matching structure according to claim 1 or 2, characterized in that: The first joint (100) is a stainless steel joint, and the second joint (200) is a zirconium alloy joint.

4. The diffusion bonding matching structure according to claim 3, characterized in that: The friction coefficient between the stainless steel joint and the zirconium alloy joint at the temperature of T1 to T2 is 0.3 to 0.

6.

5. The diffusion bonding matching structure according to claim 3, characterized in that: The friction coefficient between the stainless steel joint and the zirconium alloy joint at a temperature less than T1 is 0.7 to 1.

26.

6. The diffusion bonding matching structure according to claim 3, characterized in that: The thread lead angle θ ranges from 20° to 50°.

7. The diffusion bonding matching structure according to claim 1 or 2, characterized in that: The maximum radial clearance between the first joint (100) and the second joint (200) in the initial assembly stage is 0.03-0.06 mm.

8. The diffusion bonding matching structure according to claim 2, characterized in that: The height of the trapezoid is 3-5 mm.

9. The diffusion bonding matching structure according to claim 2, characterized in that: The pitch of the thread is 30-40 mm.

10. A diffusion bonding system for performing diffusion bonding on the diffusion bonding matching structure according to claims 1 to 5, characterized in that: It comprises a thrust bearing (300), wherein the thrust bearing (300) is connected to the bottom of the second joint (200).

11. The diffusion bonding system according to claim 10, characterized in that: It comprises a clamp (400), wherein the clamp (400) is sleeved on the outside of the second joint (200) and the thrust bearing (300).

12. The diffusion bonding system according to claim 11, characterized in that: Also included is a chassis (500) which supports the thrust bearing (300) and the clamp (400).

13. A diffusion bonding method, the diffusion bonding matching structure according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step S1, determining the thread shapes of the first joint and the second joint, and processing the first joint and the first joint; Step S2: Heat the vacuum furnace to 600-800°C and set the vacuum degree to 1.0-2×10 -3 Pa; Step S3, applying axial pressure to one end of the first joint (100), under the action of the axial pressure, the second joint (200) rotates, and the first joint (100) moves downward, to perform diffusion welding, Wherein step S1 includes determining the thread lead angle θ based on the following formula: arctanμ1≤θ≤arctanμ2 Wherein, μ1 is the friction coefficient between the first joint (100) and the second joint (200) at a temperature between T1 and T2; μ2 is the friction coefficient between the first joint (100) and the second joint (200) at a temperature lower than T1, the T1 temperature is 50% of the lowest melting point temperature of the materials of the first joint (100) and the second joint (200), and the T2 temperature is 75% of the lowest melting point temperature of the materials of the first joint (100) and the second joint (200).

14. The diffusion bonding method according to claim 13, characterized in that: In step S3, the pressure head applying the axial pressure moves at a constant speed.

15. The diffusion bonding method according to claim 14, characterized in that: The axial pressure in step S3 ranges from 10 to 50 KN.

16. The diffusion bonding method according to claim 13, characterized in that: Step S2 includes S21, heating to 400°C at a rate of 10°C / min, keeping the temperature for 10 minutes, Step S22, heating to 600-800°C at a rate of 10°C / min, and keeping the temperature for 15-60 minutes.

17. The diffusion bonding method according to claim 13, characterized in that: The process also includes step S4, wherein after the diffusion welding is completed, the temperature is cooled to 750° C., the axial pressure is removed, the temperature is cooled to 150° C. in the furnace, and the vacuum system is closed.

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