High-temperature alloy plastic connection method for optimizing joint shape
By designing the boss-grooved joint shape on the connecting surface of the nickel-based high-temperature alloy, controlling plastic flow and stress concentration, the problem of low welding rate in the prior art is solved, and high-quality connections and higher welding rate are achieved.
Patent Information
- Application Number
- CN202510606098.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-12
- Publication Date
- 2025-06-27
AI Technical Summary
In the existing plastic connection technology of nickel-based high-temperature alloys, the planar joint causes the center of the connection surface to be completely welded, while the near edge gradually becomes the interface grain boundary, and there is a clear unwelded area in the outermost edge, resulting in a low welding rate.
The optimized boss-grooved joint shape is adopted. By setting boss and groove structure on the connection surface, and mechanical processing and ultrasonic cleaning, the plastic flow of metal at the joint during the plastic connection is controlled, so as to achieve equivalent stress concentration in a wider area and promote dynamic recrystallization and grain boundary migration.
By optimizing the joint shape, the connection quality of nickel-based high-temperature alloy is improved, the welding rate and mechanical properties of the joint are enhanced, and a higher level of equivalent stress concentration is ensured, forming a high-quality metallurgical combination.
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Figure CN120206087A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of high-temperature alloy solid-state connection. Background Art
[0002] Plastic joining is a new solid-state joining process. Compared with the traditional fusion welding process, there is no melting zone in the joint, so no cast structure is formed. The essence of the plastic joining process of nickel-based high-temperature alloys can be summarized as independent free surfaces achieving close contact at the atomic scale under the action of force or thermal coupling, and then forming a solid metallurgical bond through element diffusion across the interface. The key to achieving plastic joining is macro / micro plastic deformation. If the plastic flow of the connection interface is insufficient, the joint will not be completely welded, affecting the quality of the connection. Generally, the plastic flow and atomic diffusion of the connection interface can be enhanced by improving relevant process parameters, such as connection pressure, connection time, connection temperature, etc. However, excessive connection pressure will cause severe plastic deformation of the joint and affect the dimensional accuracy, while long-term heat preservation limits production efficiency and may cause coarsening of grains and precipitation phases, damaging the strength of the parent alloy. Studies have shown that the surface state of the connection has an important influence on the metal flow direction, rate and stress-strain state during plastic joining. Therefore, by optimizing the joint shape, the stress-strain state and plastic deformation degree of the metal on both sides of the connection surface can be controlled to improve the joint quality.
[0003] Currently, most nickel-based high-temperature alloy connection joints are planar joints. In plastic connection experiments and simulations, it was found that when the connection surfaces are two smooth planes, their stress state will be similar to that during isothermal compression: at the initial stage of deformation, the equivalent stress is evenly distributed in the center of the joint, so the interface bonding will start from the center of the joint, while the stress on the edge of the joint is smaller, and the metal will flow in the radial direction to form a bulge. The metal flow rate and direction on both sides of the interface are difficult to synchronize, so the effective welding area is small and the welding rate is low. Summary of the invention
[0004] The object of the present invention is to avoid the shortcomings of the prior art and provide a high-temperature alloy plastic connection method with an optimized joint shape for high-quality connection of nickel-based high-temperature alloys by optimizing the design of the boss-groove type joint geometry and controlling the plastic flow of the metal at the joint during the plastic connection process to achieve a higher level of equivalent stress concentration in a wider area of the connection surface to promote dynamic recrystallization and grain boundary migration.
[0005] To achieve the above object, the technical solution adopted by the present invention is: a high-temperature alloy plastic connection method for optimizing the joint shape, comprising the following steps: Step 1: Processing matching boss and groove structures on the surfaces to be connected of a pair of high-temperature alloy workpieces, and performing mechanical processing for cleaning and shaping on the surfaces to be connected; Step 2: After assembling and connecting the surfaces to be joined through the boss and groove structures, perform plastic connection to achieve complete microscopic metallurgical bonding within the macroscopic deformation of the superalloy workpiece. Step 3: Successively perform recrystallization annealing and stress relief annealing on a pair of superalloy workpieces after plastic connection, which is used for the recrystallization of the deformed grains remaining after plastic connection and promotes the migration of grain boundaries across the interface grain boundaries to heal the interface grain boundaries, thereby improving the connection quality.
[0006] Furthermore, in the connection cross-section of the boss and groove structures, the height H of the boss is greater than the depth W of the groove, and the size of the boss embedded in the groove is in interference fit with the groove size to prevent the reduction of the connection rate caused by assembly looseness. Meanwhile, the boss is a boss with a circular, square or rectangular cross-section, and the cross-sectional shape of the groove is set to match the cross-sectional shape of the boss. After the boss and groove structures are fitted and connected, the thickness T of the groove is evenly distributed in the circumferential direction of the boss, and the thickness T of the groove is greater than 1 mm to prevent the problem that it is difficult to effectively provide radial compressive stress in plastic connection due to the fact that the degree of the outer bulge of the groove wall is greater than that of the boss.
[0007] Furthermore, before plastic connection, it also includes the treatment of the connection end faces of the boss and groove structures, specifically: First, use turning and milling to make the surface roughness Ra of the effective connection surface when the boss and groove are matched and connected ≤ 0.4; Then, polish the effective connection surface. The connection surface at the concave part is processed with a handheld grinder and a wool grinding head until the surface roughness Ra of the effective connection surface ≤ 0.05, and then perform ultrasonic cleaning, drying, and sealing for storage for later use; After the treatment is completed, if the plastic connection cannot be completed within 12 hours, it is necessary to re-treat the effective connection surface and then perform plastic connection.
[0008] Furthermore, the ultrasonic cleaning is ultrasonic cleaning with an ultrasonic frequency of 80 - 120 kHz, a power density of 0.3 - 0.8 W / cm2, a time of 5 - 10 min, a cleaning temperature of 50 - 70 °C, and a water-based cleaning agent, and finally dry and seal for storage.
[0009] Furthermore, during the processing of the superalloy workpiece, fillets with R0.1 - 0.25 are added to the outer edge of the boss top and the inner edge of the groove bottom to ensure that the interface grain boundaries can surely be generated at the rounded part of the groove, thereby enhancing the stability of the plastic connection process.
[0010] Further, before the first step, solution treatment and aging treatment are also included for the superalloy workpiece to improve the strength and toughness of the plastic connection of the superalloy workpiece. Specifically: Solution treatment: Heat-treat the superalloy workpiece at a temperature of 1170°C to 1200°C for 2h to 6h, and then air-cool; Aging treatment: The superalloy workpiece obtained by solution treatment is heat-treated at a temperature of 720°C to 730°C for 4h to 20h, and then air-cooled.
[0011] Further, in the second step, before the plastic connection, it also includes: Use a fixture to axially butt-join the superalloy workpieces using a boss and groove structure, and use energy storage spot welding to fix the superalloy sheet on a pair of superalloy workpieces for positioning; Then, with the axis of the boss as the reference, make the coaxiality of the boss and groove structure within 0.025mm, and apply an axial pressure of 50 - 100MPa to a pair of superalloy workpieces to make the connection surfaces in close contact.
[0012] Further, the plastic connection process of the superalloy workpiece is: Under the condition of evacuating to a furnace vacuum degree of more than 10 -3 Pa, at a strain rate of 0.001~10s -1 , a heating rate of 0.1~10°C / s, after the superalloy workpiece reaches a temperature of 900°C - 1200°C, hold for 3~10min, and perform plastic connection with a deformation amount of 30%~70%; The vacuum degree is used to ensure that no oxides or other contaminants are formed on the material surface of the superalloy workpiece during the plastic connection process, so as to improve the performance and reliability of the boss and groove structure; The process parameters of plastic connection are used to ensure the expected connection effect of the superalloy workpiece during the plastic connection process. The increase in temperature and the decrease in strain rate during plastic connection are both beneficial to grain recrystallization at the connection interface, but too high a temperature will cause the strengthening phase to dissolve back, leading to tissue coarsening and damaging the performance of the superalloy workpiece; when the strain rate is too low, the newly nucleated grains at the connection interface have sufficient time to significantly coarsen through the grain growth mechanism, resulting in out-of-control grain size and severely reducing the mechanical properties at the joint; The greater the deformation amount, the better the connection effect. Under the same other conditions, the greater the deformation amount, the longer the duration of the plastic connection process, the more sufficient the interfacial atom diffusion, and at the same time, a large deformation amount can provide sufficient distortion energy to ensure multiple rounds of recrystallization of the interfacial grains, which is beneficial to improving the connection effect; However, after the amount of deformation exceeds the limited range, the boss and groove structures are significantly upset, and the metal flow becomes more complex. If the metal flows on both sides of the interface cannot be synchronized, the atomic diffusion and microstructure evolution at the joint cannot cross the interface, which has no effect on plastic connection. After the plastic connection is completed, the superalloy workpiece is taken out and air-cooled to room temperature. This is used to prevent the superalloy workpiece from deforming and cracking, and during the air-cooling process, a slower cooling rate helps control the grain growth of the workpiece and better achieve microstructural metallurgical bonding.
[0013] Further, the specific steps of step three are as follows: Recrystallization annealing is carried out at a temperature of 1050 - 1080 °C for 30 - 60 minutes of heat treatment and then furnace-cooled. Stress relief annealing is carried out at a temperature of 600 - 900 °C for 1 - 4 hours of heat treatment and then furnace-cooled.
[0014] Further, the superalloy is a nickel-based superalloy. At this time, the plastic connection process is as follows: Under the condition of evacuating to a furnace vacuum degree of more than 10 -3 Pa, with a strain rate of 0.001 - 1 s -1 , a heating rate of 1 - 10 °C / s, after the workpiece reaches a temperature of 1100 °C - 1200 °C, hold for 3 - 10 minutes, and perform plastic connection with a deformation amount of 30% - 70%. This is for adjustment in view of the difficult-to-deform materials, narrow hot working window, large deformation resistance, and poor weldability of nickel-based superalloys.
[0015] The beneficial effects of the present invention are as follows: To limit the direction of metal plastic flow and enable the metals on both sides of the joint surface to change synergistically, the present invention optimally designs the joint shape as a boss and groove type, and through finite element simulation and connection experiments, optimizes the matching relationship between the boss diameter, boss height, and groove depth. The results prove that the method of the present invention can achieve high-quality connection of nickel-based superalloys.
[0016] 1. When performing planar connection, the central part of the joint surface is completely welded, while the part near the edge gradually becomes the interface grain boundary, and there is an obvious unwelded area at the outermost edge. When the joint shape is changed, the constraint effect generated by the groove wall promotes the formation and welding of the interface grain boundary, and under optimal parameters, the starting welding zone of the interface grain boundary can reach the fillet of the groove wall.
[0017] 2. Due to the fillet matching relationship, the deformation amount at the fillet of the boss is larger, the metal flow is more complex, the number of dynamic recrystallization cycles is more, and the effect on grain refinement is more obvious. Therefore, a fine grain zone will be formed at the interface fillet and more deformed grains will appear on the boss side of the interface.
[0018] 3. The maximum tensile load that the boss-groove type joint can withstand is higher than that of the flat joint, which strongly proves the feasibility of the idea that "the change in joint shape leads to the change in stress state, thus affecting the interface bonding". Through the fracture analysis, in the fracture of the flat joint, some areas show a black and flat surface due to oxidation after non-welding when the joint is taken out, while no black and flat surface is found on the fracture surface of the boss-groove type joint. Brief Description of the Drawings
[0019] Figure 1 is a schematic diagram of the boss and groove structure of the present invention; Figure 2 is a schematic diagram of the boss and groove structure provided by a specific example of the present invention; Among them, (a) the boss and groove structure of Specific Example 1; (b) the boss and groove structure of Specific Example 2; Figure 3 is a micrograph of the connection at the rounded corner of the groove wall of the present invention; Figure 4 is a micrograph of the connection of the flat type joint in the prior art; Figure 5 is a micrograph of the connection of the boss and groove structure joint provided by Specific Example 1 of the present invention; Figure 6 is a micrograph of the connection of the boss and groove structure joint provided by Specific Example 2 of the present invention; Figure 7 is the displacement-load curve corresponding to different joint shapes; Figure 8 is a fracture morphology diagram of the flat joint in the prior art; Figure 9 is a fracture morphology diagram of the boss and groove structure joint provided by Specific Example 1 of the present invention; Figure 10 is a fracture morphology diagram of the boss and groove structure joint provided by Specific Example 2 of the present invention. Detailed Description of the Invention
[0020] The principles and features of the present invention will be described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.
[0021] To achieve the above object, the present invention provides the following specific embodiments: Example 1: A method for plastic connection of superalloy with optimized joint shape, comprising the following steps: Step 1: Subject a pair of superalloy workpieces to solution treatment and aging treatment in sequence to improve the strength and toughness of the plastic connection of the superalloy workpieces. Specifically: Solution treatment: Subject a pair of superalloy workpieces to heat treatment at a temperature of 1170°C to 1200°C for 2h to 6h, and then air-cool. Aging treatment: The superalloy workpiece obtained by solution treatment is air-cooled after heat treatment at a temperature of 720°C to 730°C for 4h to 20h.
[0022] Step 2: Process the mating boss and groove structures on the surfaces to be joined of a pair of superalloy workpieces, and perform machining for cleaning and shaping on the surfaces to be joined. Among them, as Figure 1 shown, in the connection section of the boss and groove structures, the height H of the boss is greater than the depth W of the groove, and the size of the boss embedded in the groove is in interference fit with the groove size to prevent the connection rate from decreasing due to assembly looseness. Meanwhile, the boss is a boss with a circular, square or rectangular cross-section, and the cross-sectional shape of the groove is set to match the cross-sectional shape of the boss. After the boss and groove structures are fitted and connected, the thickness T of the groove is evenly distributed in the circumferential direction of the boss, and the thickness T of the groove is greater than 1mm to prevent the problem that in plastic connection, it is difficult to effectively provide radial compressive stress because the degree of the groove wall bulging outwards is greater than that of the boss.
[0023] As Figure 3 shown, during the processing of the superalloy workpiece, fillets with R0.1 to 0.25 are added to the outer edge of the top of the boss and the inner edge of the bottom of the groove to ensure that the interface grain boundaries can surely be generated at the fillet of the groove, thereby enhancing the stability of the plastic connection process. It can be seen from Figure 3 that the boss first contacts the fillet of the groove under the action of the upsetting force, and the fillet of the groove provides a reaction force. Under the combined action of the two forces, local metal will undergo severe plastic deformation until the boss surface and the groove bottom surface are in large-area contact. This process promotes the formation of the interface grain boundaries. At the same time, the amount of metal deformation at the fillet is significantly greater than that at the plane surface layer, and multiple rounds of dynamic recrystallization can occur at the fillet, thereby promoting the healing of the interface grain boundaries.
[0024] Step 3: Process the connecting end faces of the boss and groove structures, specifically: First, use turning and milling to make the surface roughness Ra of the effective connection surface when the boss and groove are fitted and connected ≤ 0.4; Then, polish the effective connection surface. The connecting surface of the concave part is processed with a handheld grinder and a wool grinding head until the surface roughness Ra of the effective connection surface ≤ 0.05, and then ultrasonic cleaning, drying and sealing are carried out for storage for later use; After the processing is completed, if the plastic connection cannot be completed within 12 hours, it is necessary to reprocess the effective connection surface and then perform the plastic connection.
[0025] Among them, the ultrasonic cleaning is ultrasonic cleaning with an ultrasonic frequency of 80 - 120 kHz, a power density of 0.3 - 0.8 W / cm², a time of 5 - 10 min, a cleaning temperature of 50 - 70 °C, and a water-based cleaning agent. Finally, it is dried and stored in a sealed manner.
[0026] Step Four: Use a fixture to axially butt-join the superalloy workpieces using the boss and groove structures, and use energy storage spot welding to fix the superalloy sheet on a pair of superalloy workpieces for positioning; Next, with the axis of the boss as the reference, the coaxiality of the boss and groove structures is within 0.025 mm. Apply an axial pressure of 50 - 100 MPa to a pair of superalloy workpieces to make the connection surfaces in close contact, and assemble and connect the surfaces to be joined through the boss and groove structures; Step Five: Perform plastic connection to achieve complete microscopic metallurgical bonding within the macroscopic deformation of the superalloy workpieces; Under the condition of evacuating to a furnace vacuum of more than 10 -3 Pa, with a strain rate of 0.001 - 10 s -1 , a heating rate of 0.1 - 10 °C / s, after the superalloy workpieces reach a temperature of 900 °C - 1200 °C, hold for 3 - 10 min, and perform plastic connection with a deformation amount of 30% - 70%; The vacuum degree is used to ensure that no oxides or other contaminants are formed on the material surface of the superalloy workpieces during the plastic connection process, so as to improve the performance and reliability of the boss and groove structures; The process parameters of plastic connection are used to ensure the expected connection effect of the superalloy workpieces during the plastic connection process. The increase in temperature and the decrease in strain rate during plastic connection are both beneficial to grain recrystallization at the connection interface, but too high a temperature will cause the strengthening phase to dissolve back, leading to tissue coarsening and damaging the performance of the superalloy workpieces; when the strain rate is too low, the newly nucleated grains at the connection interface have sufficient time to significantly coarsen through the grain growth mechanism, resulting in out-of-control grain size and severely reducing the mechanical properties at the joint; The greater the deformation amount, the better the connection effect. Under the same other conditions, the greater the deformation amount, the longer the duration of the plastic connection process, the more sufficient the atomic diffusion at the interface, and at the same time, a large deformation amount can provide sufficient distortion energy to ensure multiple rounds of recrystallization of the interface grains, which is beneficial to improving the connection effect; However, after the deformation amount exceeds the limited range, the boss and groove structures are significantly upset, and the metal flow situation will be more complex. If the metal flow on both sides of the interface cannot be synchronized, the atomic diffusion effect and tissue evolution at the joint cannot cross the interface, which has no effect on plastic connection; After the plastic connection is completed, the superalloy workpiece is taken out and air-cooled to room temperature; this is used to prevent the superalloy workpiece from deforming and cracking, and during the air-cooling process, a slower cooling rate helps control the grain growth of the workpiece and better achieve microstructural metallurgical bonding.
[0027] Step Six: Perform recrystallization annealing and stress relief annealing on a pair of superalloy workpieces after plastic connection in sequence, which is used for the recrystallization of the deformed grains remaining after plastic connection, and promote the migration of grain boundaries across the interface grain boundaries to make the interface grain boundaries close, thereby improving the connection quality.
[0028] Specifically: The recrystallization annealing is a heat treatment carried out at a temperature of 1050 - 1080 °C for 30 - 60 min and cooled in the furnace; The stress relief annealing is a heat treatment carried out at a temperature of 600 - 900 °C for 1 - 4 h and cooled in the furnace.
[0029] Example 2: The same as Example 1, except that the superalloy is a nickel-based superalloy, and the plastic connection process at this time is: Under the condition of evacuating to a furnace vacuum of more than 10 -3 Pa, with a strain rate of 0.001 - 1 s -1 , a heating rate of 1 - 10 °C / s, after the workpiece reaches a temperature of 1100 °C - 1200 °C, hold for 3 - 10 min, and perform plastic connection with a deformation amount of 30% - 70%; This is for adjustment in view of the difficult-to-deform material, narrow hot working window, large deformation resistance, and poor weldability of nickel-based superalloys.
[0030] As Figures 2 to 6 shown, in order to further illustrate the technical solution and technical effect of the present invention, the following specific examples are provided, and the materials of the superalloy workpieces used are all nickel-based superalloys: Specific Example 1: For the plastic connection of nickel-based superalloys, the plastic connection is carried out using a 1.5 - 2 - 7 type boss and groove structure, and the boss is cylindrical, and the groove is a cylindrical groove matching the cylindrical shape of the boss; Among them, as Figure 2 shown in (a) of , the 1.5 - 2 - 6 type means that the groove depth is 1.5 mm - the boss height is 2 mm - the diameters of the boss and groove are 6 mm; Step One: Pretreatment of nickel-based superalloy The pretreatment process of the superalloy workpiece before connection mainly includes solution treatment (1170 °C - 1200 °C / 2 h - 6 h / air cooling) and aging treatment (720 °C - 730 °C / 4 h - 20 h / air cooling).
[0031] Step 2: Surface treatment of the connector before connection The surfaces of the workpieces to be connected are designed with matching shapes to control the macroscopic distribution and microscopic distribution of the connection process. The boss and groove structures of the workpieces to be connected are processed by turning and milling, and the surface roughness of the workpieces to be connected is Ra≤0.4. Then, the surface to be connected is polished, and the surface roughness of the end face to be connected is required to be Ra≤0.05. Then, ultrasonic cleaning, drying, sealing and storage are carried out for standby use. If the connection cannot be completed within 12 hours, the joint surface needs to be re-treated to prevent surface oxidation and contamination.
[0032] Step 3: Assembly positioning of the workpieces to be connected On the fixture, axially butt the groove and boss ends of the sample together, and use energy storage spot welding to fix the high-temperature alloy sheet on the base on both sides of the joint to implement assembly positioning. Taking the boss axis as the reference, the coaxiality is required to be within 0.025mm. Apply an initial pressure to the workpiece to make the connected workpieces in close contact.
[0033] Step 4: Workpiece into the furnace Place the workpiece to be connected at the center of the furnace platform of the plastic connection equipment, place graphite limit blocks on both sides, and require the graphite limit blocks to be 0.15±0.05mm lower than the workpiece to be connected, and close the furnace door.
[0034] Step 5: Plastic connection of workpieces Vacuum treatment is performed before plastic connection, and the vacuum degree is maintained for 10 -3 Pa or more. During the connection process, parameters such as temperature, time, strain rate, and deformation have a key influence on the flow of metal at the joint interface, organizational evolution, atomic diffusion, and interface micro-metallurgical bonding. The connection parameters selected in this embodiment are obtained through in-depth theoretical research and repeated experiments, and are the preferred choice. Specifically, the strain rate is 0.001s -1 , heating rate 10℃ / s, keep warm for 5min after reaching 1110°, and the deformation is 30%.
[0035] Step 6: Remove the connected workpiece After plastic connection, the workpiece is taken out and air-cooled to room temperature.
[0036] Step 7: Heat treatment of the connected workpiece The workpiece after plastic connection is subjected to recrystallization annealing, and the process parameters are: 1080℃ / 30min / furnace cooling.
[0037] Step 8: Connector quality inspection The workpiece was cut along the axis by wire cutting, and its structure was characterized after grinding, polishing and corrosion. In order to evaluate the interface bonding strength of the workpiece after plastic connection, the mechanical properties of the workpiece were checked by a tensile testing machine, and then the tensile fracture morphology of the workpiece was analyzed.
[0038] Specific Example 2: Plastic connection of nickel-based superalloys is carried out by using a 1.5-2-7 type boss and groove structure. The boss is cylindrical, and the groove is a cylindrical groove matching the cylindrical shape of the boss. Among them, as Figure 2 shown in (b) below, the 1.5-2-7 type means that the groove depth is 1.5 mm - the boss height is 2 mm - the diameters of the boss and the groove are 7 mm. The specific steps are as follows: Step 1: Pretreatment of nickel-based superalloys The pretreatment process of the superalloy workpiece before connection mainly includes solution treatment (1170 °C - 1200 °C / 2 h - 6 h / air cooling) and aging treatment (720 °C - 730 °C / 4 h - 20 h / air cooling).
[0039] Step 2: Machining of the boss and groove of the workpiece to be connected The surfaces of the workpieces to be connected are designed with matching shapes to control the macroscopic distribution and microscopic distribution during the connection process. Different matching shapes of the boss and groove of the workpieces to be connected are as Figure 2 shown in (a) below. The parameters are as follows: the groove depth is 1.5 mm, the boss height is 2 mm, and the diameters of the boss and the groove are 7 mm. The end faces of the workpieces to be connected are processed by turning and milling, and the surface roughness Ra of the workpieces to be connected is ≤ 0.4. To ensure the connection effect, the boss and groove need to be in interference fit to prevent assembly loosening and reduce the connection rate.
[0040] Step 3: Surface treatment of the joint before connection The surface to be connected is polished, and the surface roughness Ra of the end face to be connected is required to be ≤ 0.05. Subsequently, ultrasonic cleaning, drying, and sealing preservation are carried out for use. If the connection cannot be completed within 12 hours, the surface treatment of the joint needs to be carried out again to prevent surface oxidation and contamination.
[0041] Step 4: Assembly and positioning of the workpieces to be connected On the fixture, the groove and boss ends of the specimens are axially butt-jointed and combined, and energy storage spot welding is used to fix the nickel-based alloy sheets on the matrixes on both sides of the joint to implement component positioning. Based on the axis of the boss, the coaxiality is required to be within 0.025 mm. An initial pressure is applied to the workpiece to make the connecting workpieces in close contact.
[0042] Step 5: Loading the workpiece into the furnace The assembled workpieces to be connected are placed at the center of the furnace platform of the connecting equipment, and graphite limit blocks are placed on both sides of the workpieces to be connected. The graphite limit blocks are 0.15 ± 0.05 mm lower than the workpieces to be connected, and the furnace door is closed.
[0043] Step 6: Connection of the workpiece Vacuum pumping is carried out before connection, and the vacuum degree is maintained at 10 during the connection process-3 Above Pa. During the connection process, parameters such as temperature, time, strain rate, and deformation amount have a key impact on the metal flow situation, microstructure evolution, atomic diffusion, and interfacial micro-metallurgical bonding at the joint interface. The selection of connection parameters in this embodiment is obtained through in-depth theoretical research and repeated experiments, and is an optimal choice, specifically as follows: the strain rate is 0.001 s -1 , the heating rate is 10 °C / s, after reaching 1110 °C, it is held for 5 min, and the deformation amount is 30%.
[0044] Step Seven: Remove the connected workpiece After plastic connection, take out the workpiece and air-cool it to room temperature.
[0045] Step Eight: Heat treatment of the connector Perform recrystallization annealing on the workpiece after plastic connection, and the process parameters are: 1080 °C / 30 min / furnace cooling.
[0046] Step Nine: Quality inspection of the connector Cut along the axial direction of the workpiece by wire electrical discharge machining, and perform microstructure characterization after grinding, polishing, and etching. To evaluate the interfacial bonding strength of the workpiece after plastic connection, use a tensile testing machine to check the mechanical properties of the workpiece, and then analyze the tensile fracture morphology of the workpiece.
[0047] In summary, to evaluate the microscopic quality and interfacial bonding state of the plastic connection joint, through the observation of the microstructure of the connection interface after plastic connection, such as Figures 4 - 6 shown: When connecting in a plane, only the central part of the connection surface is completely welded, while the part near the edge gradually becomes the interfacial grain boundary, and there is an obvious unwelded area at the outermost edge, and the connection rate is low.
[0048] After the present invention adopts the boss and groove structure, the restraint effect generated by the groove wall promotes the formation and welding of the interfacial grain boundary. At the rounded corner of the groove wall under optimal parameters is the starting welding area of the interfacial grain boundary. And due to the rounding matching relationship, the deformation amount at the rounded corner of the boss will be larger, the metal flow will be more complex, the number of dynamic recrystallization rounds will be more, and the grain refinement effect will be more obvious. Therefore, a fine grain zone will be formed at the interfacial rounded corner and more deformed grains will appear on the boss side of the interface.
[0049] In order to more intuitively show the influence of the joint shape on plastic connection, tensile tests are carried out on different joint shapes. The results are as Figure 5 shown. The maximum tensile load that the boss-groove type joint can withstand is higher than that of the plane joint, which strongly proves the feasibility of the idea that "the change of joint shape leads to the change of stress state and thus affects the interfacial bonding".
[0050] Furthermore, observe the morphology of the tensile fracture of the plastic connection experiment of joints with different shapes, such asFigures 6 - 8 As shown, a black flat surface appears in a partial area of the fracture of the flat joint. This is because the non-welded area is rapidly oxidized under the action of the remaining temperature and air after the joint is taken out. However, no black flat surface is found on the fracture surface of the boss-groove joint, which proves that the welded area of the boss-groove joint is larger than that of the flat joint.
[0051] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A high-temperature alloy plastic connection method for optimizing joint shape, characterized in that: The following steps are involved: Step 1: Processing matching boss and groove structures on the surfaces to be connected of a pair of high-temperature alloy workpieces, and performing mechanical processing for cleaning and shaping on the surfaces to be connected; Step 2: After the surfaces to be connected are assembled and connected through the boss and groove structure, plastic connection is performed to achieve complete microscopic metallurgical bonding within the macroscopic deformation of the high-temperature alloy workpiece; Step 3: The pair of high-temperature alloy workpieces that have been plastically connected are subjected to recrystallization annealing and stress relief annealing in sequence to recrystallize the deformed grains remaining after plastic connection and promote the migration of grain boundaries across the interface grain boundaries to bridge the interface grain boundaries, thereby improving the connection quality.
2. The high-temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: In the connection section of the boss and groove structure, the height H of the boss is greater than the depth W of the groove, and the size of the boss embedded in the groove matches the size of the groove, and the connection is an interference fit to prevent loose assembly and reduce the connection rate; At the same time, the boss is a boss with a circular, square or rectangular cross-section, and the cross-sectional shape of the groove is matched with the cross-sectional shape of the boss, so that after the boss and groove structure are matched and connected, the thickness T of the groove is evenly distributed in the circumferential direction of the boss, and the thickness T of the groove is greater than 1 mm, which is used to prevent the problem of difficulty in effectively providing radial compressive stress in the plastic connection due to the fact that the degree of outward bulging of the groove wall is greater than the degree of bulging of the boss.
3. The high temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: Before plastic connection, the connection end faces of the boss and groove structures are also processed, specifically: Firstly, turning and milling are used to make the effective connection surface roughness Ra≤0.4 when the boss and the groove are matched and connected; Next, the effective connection surface is polished, and the connection surface of the concave part is processed with a handheld grinder and a wool grinding head until the roughness of the effective connection surface is Ra≤0.05, followed by ultrasonic cleaning, drying, sealing and storage for later use; After the treatment is completed, if the plastic connection cannot be completed within 12 hours, the effective connection surface needs to be re-treated before plastic connection.
4. The high temperature alloy plastic connection method for optimizing joint shape according to claim 3, characterized in that: The ultrasonic cleaning is carried out at an ultrasonic frequency of 80-120 kHz and a power density of 0.3-0.8 W / CM 2 , ultrasonic cleaning with a time of 5 to 10 minutes, a cleaning temperature of 50 to 70°C, and a water-based cleaning agent. Finally, blow dry and store in a sealed container.
5. The high-temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: During the processing of the high-temperature alloy workpiece, a fillet of R0.1-0.25 is added to the outer edge of the boss top and the inner edge of the groove bottom to ensure that the interface grain boundary can be generated at the groove fillet, thereby enhancing the stability of the plastic connection process.
6. The high-temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: Before the step 1, the method further includes sequentially performing solid solution treatment and aging treatment on the high temperature alloy workpiece to improve the strength and toughness of the plastic connection of the high temperature alloy workpiece, specifically: Solution treatment: heat treat the high temperature alloy workpiece at 1170℃~1200℃ for 2h~6h, and then air cool; Aging treatment: The high-temperature alloy workpiece obtained by solution treatment is heat treated at a temperature of 720℃~730℃ for 4h~20h and then air-cooled.
7. The high temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: In step 2, before the plastic connection, the method further includes: Using a fixture to axially butt-jointly assemble the high-temperature alloy workpieces using a boss and a groove structure, and using energy storage spot welding to fix the high-temperature alloy sheet on a pair of high-temperature alloy workpieces to achieve positioning; Next, taking the boss axis as a reference, the coaxiality of the boss and the groove structure is within 0.025 mm, and an axial pressure of 50-100 MPa is applied to a pair of high-temperature alloy workpieces to make the connection surfaces in close contact.
8. The high temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: The plastic connection process of the high temperature alloy workpiece is: Evacuate to a vacuum degree of 10 -3 Under conditions above Pa, at a strain rate of 0.001~10s -1 , the heating rate is 0.1~10℃ / s, the high-temperature alloy workpiece reaches the temperature of 900℃-1200℃ and is kept warm for 3~10min, and the deformation is 30%~70% for plastic connection; The vacuum degree is used to ensure that oxides or other contaminants are not formed on the material surface of the high-temperature alloy workpiece during the plastic connection process, so as to improve the performance and reliability of the boss and groove structure; The process parameters of plastic connection are used to ensure that the expected connection effect of the high-temperature alloy workpiece is achieved during the plastic connection process. The increase in temperature and the decrease in strain rate of plastic connection are both conducive to the recrystallization of grains at the connection interface. However, too high a temperature will cause the strengthening phase to dissolve back, causing the microstructure to coarsen and damage the performance of the high-temperature alloy workpiece. When the strain rate is too low, the new grains that have nucleated at the connection interface have sufficient time to significantly coarsen through the grain growth mechanism, resulting in uncontrolled grain size and serious reduction of the mechanical properties of the joint. The greater the deformation, the better the connection effect. Under the same other conditions, the greater the deformation, the longer the plastic connection process lasts, and the more sufficient the interface atoms diffuse. At the same time, the large deformation can provide sufficient distortion energy to ensure that the interface grains undergo multiple rounds of recrystallization, which is beneficial to improving the connection effect. However, when the deformation exceeds the specified range, the boss and groove structures are significantly upset, and the metal flow becomes more complicated. If the metal flow on both sides of the interface cannot be synchronized, the atomic diffusion and organizational evolution of the joint cannot cross the interface, which has no effect on plastic connection. After completing the plastic connection, the high-temperature alloy workpiece is taken out and air-cooled to room temperature; this is used to prevent the high-temperature alloy workpiece from deformation and cracking. During the air cooling process, the slower cooling rate helps to control the grain growth of the workpiece and better achieve micro-metallurgical bonding.
9. The high temperature alloy plastic connection method for optimizing joint shape according to claim 1, characterized in that: The step three is specifically as follows: Recrystallization annealing is a heat treatment at 1050-1080°C for 30-60 minutes, followed by furnace cooling; Stress relief annealing is a heat treatment at a temperature of 600-900°C for 1-4 hours, followed by furnace cooling.
10. The high temperature alloy plastic connection method for optimizing joint shape according to any one of claims 1 to 9, characterized in that: The high temperature alloy is a nickel-based high temperature alloy, and the plastic connection process is: Evacuate to a vacuum degree of 10 -3 Under conditions above Pa, at a strain rate of 0.001~1s -1 , heating rate 1~10℃ / s, when the workpiece reaches the temperature of 1100℃~1200℃, keep warm for 3~10min, and plastic connection is performed with deformation of 30%~70%; Used for adjustments to difficult-to-deform materials, such as nickel-based high-temperature alloys with narrow hot working windows, large deformation resistance and poor weldability.