Connecting method and connector of Ni3Al-based single-crystal high-temperature alloy

Abstract

The invention relates to the technical field of material processing, and particularly provides a Ni3Al-based single-crystal high-temperature alloy connecting method and a connecting joint, and the Ni3Al-based single-crystal high-temperature alloy connecting method comprises the following steps: carrying out nanocrystallization treatment on the surface of a Ni3Al-based single-crystal high-temperature alloy by adopting a laser pulse shot peening method; the surfaces, subjected to nanocrystallization treatment, of at least two Ni3Al-based single crystal high-temperature alloys are attached to each other to obtain a connector to be welded, or a Ni middle layer is placed between the surfaces, subjected to nanocrystallization treatment, of the two Ni3Al-based single crystal high-temperature alloys to form the connector to be welded; and pulse current and pressure are applied to the connecting body to be welded so as to carry out diffusion welding. The problem that the Ni3Al-based single crystal high-temperature alloy is poor in connection performance during high-temperature solid-phase diffusion welding can be solved.

Description

Technical Field

[0001] The present invention relates to the technical field of material processing, and in particular, to a connection method and a connection joint for a Ni3Al-based single crystal superalloy. Background Art

[0002] Ni3Al metal compound has good microstructural and thermodynamic properties at high temperatures and is an ideal metal material for key components in aero-engines. It is mainly used in the production of blades at the most critical parts of the engine. Among them, Ni3Al-based single crystal superalloys have the characteristics of high creep resistance, high yield strength, good oxidation resistance, etc., and are mainly used to manufacture high thrust-to-weight ratio engine components. Studying the advanced welding technology of Ni3Al single crystal superalloys (IC10) and realizing their reliable connection and repair are of great significance for the production and manufacturing of aero-engines and for promoting the development of China's aviation industry.

[0003] When welding nickel-based single crystal superalloys, when the content of (Al + Ti) in the base metal exceeds 6 wt.%, brittle phases such as eutectic structure, carbides, and borides are likely to be generated in the weld, and induced polycrystals are caused, resulting in cracks in the heat affected zone. The appearance of these defects destroys the consistency of the single crystal structure and leads to a decrease in the overall performance of the material. Solid phase diffusion welding can effectively avoid the appearance of joint cracks and improve the mechanical properties of the joint. However, it is difficult for superalloys to deform, and ordinary solid phase diffusion welding requires a high temperature, a large pressure, and a long time, which will cause the coarsening of material grains and generate large residual stresses in the joint after pressurization, seriously damaging the performance of the material. Summary of the Invention

[0004] The present invention aims to solve the problem of poor connection performance of Ni3Al-based single crystal superalloys during high-temperature solid phase diffusion welding.

[0005] To solve the above problems, as a first aspect, the present invention provides a connection method for a Ni3Al-based single crystal superalloy, including:

[0006] Performing surface nanocrystallization treatment on the Ni3Al-based single crystal superalloy by using a laser pulse shot peening method;

[0007] Mutually attaching the nanocrystallization-treated surfaces of at least two Ni3Al-based single crystal superalloys to obtain a connection body to be welded; or, placing a Ni intermediate layer between the nanocrystallization-treated surfaces of two Ni3Al-based single crystal superalloys to form a connection body to be welded;

[0008] Applying a pulsed current and a pressure to the connection body to be welded for diffusion welding.

[0009] Optionally, the surface nanocrystallization treatment of the Ni3Al-based single crystal superalloy by laser shock peening includes:

[0010] An absorption layer and a constraint layer are sequentially arranged on the surface of the Ni3Al-based single crystal superalloy;

[0011] Laser shock peening is performed on the constraint layer.

[0012] Optionally, the absorption layer is aluminum foil or black paint.

[0013] Optionally, the constraint layer is a deionized water layer, and the thickness of the deionized water layer is 0.5 to 3 mm.

[0014] Optionally, the thickness of the Ni intermediate layer is 5 to 50 μm.

[0015] Optionally, the parameters of the laser shock peening are: pulse energy is 500 to 1500 mJ, spot diameter is 0.5 to 3 mm, laser intensity is 3 to 10 GW / cm 2 , repetition frequency is 1 to 3 Hz, pulse duration is 10 to 100 ns, and the number of laser pulses is 5 to 50 times.

[0016] Optionally, when the nanocrystallized surfaces of at least two Ni3Al-based single crystal superalloys are mutually adhered to obtain a joint to be welded, a pulsed current is applied to the joint to be welded, and after the joint to be welded is heated to 700 to 1150 °C, it is held for 15 to 60 min.

[0017] Optionally, when the Ni intermediate layer is placed between the nanocrystallized surfaces of two Ni3Al-based single crystal superalloys to form a joint to be welded, a pulsed current is applied to the joint to be welded, and after the joint to be welded is heated to 650 to 1000 °C, it is held for 15 to 30 min.

[0018] Optionally, the heating rate of the joint to be welded is 90 to 110 °C / min.

[0019] Optionally, during the heating stage of the joint to be welded, a gradually increasing pressure is applied to the joint to be welded, where the pressure increase rate is 8 to 10 MPa / min; during the holding stage of the joint to be welded, the pressure applied to the joint to be welded is maintained at 50 to 80 MPa.

[0020] As a second aspect, the present invention also provides a connection joint of a Ni3Al-based single crystal superalloy, and the connection joint is prepared by using the connection method of the Ni3Al-based single crystal superalloy as described above.

[0021] The beneficial effects of the present invention compared with the prior art are:

[0022] The present invention uses a diffusion welding method coupling surface nanocrystallization and pulsed current to join Ni3Al-based single crystal superalloys. Specifically, laser shock peening technology is used to introduce a gradient nanocrystalline structure on the surface of Ni3Al-based single crystal superalloys, realizing surface activation modification of Ni3Al-based single crystal superalloys before diffusion welding, increasing the near-surface defect concentration of superalloys, reducing the activation energy of surface atom diffusion of superalloys, facilitating the reduction of the diffusion welding temperature, and reducing joint deformation. Furthermore, an external electric field is introduced during the diffusion welding process, combining the advantage of the fast heating rate of pulsed current to achieve the effect of suppressing the growth of nanocrystals during the heating stage. The synergy between the surface nanocrystallization treatment of superalloys and pulsed current is conducive to significantly increasing the interfacial energy of the bonding interface of Ni3Al-based single crystal superalloys, increasing the rapid atomic diffusion channels, thereby effectively enhancing the diffusion coefficient, and then rapidly achieving reliable joining of Ni3Al-based single crystal superalloys at low temperatures. For the joint obtained by the present invention, the welding time is less than 30 min, the joint welding rate is above 99%, the tensile strength at room temperature is above 1000 MPa, and the shear strength reaches above 800 MPa; when the service temperature is 1100 °C, its shear strength reaches above 300 MPa, and the tensile strength is above 400 MPa. Description of the Drawings

[0023] Figure 1 is a flowchart of the joining method of Ni3Al-based single crystal superalloys in an exemplary embodiment of the present invention;

[0024] Figure 2 is a schematic diagram of the connection body to be welded in an exemplary embodiment of the present invention;

[0025] Figure 3 is a schematic diagram of the surface nanocrystallization treatment of Ni3Al-based single crystal superalloys in an exemplary embodiment of the present invention;

[0026] Figure 4 is a schematic structural diagram of the device for pulsed current-assisted diffusion joining of Ni3Al-based single crystal superalloys in an exemplary embodiment of the present invention;

[0027] Figure 5 is a schematic diagram of the changes in temperature and pressure during the pulsed current-assisted diffusion joining process of Ni3Al-based single crystal superalloys in an exemplary embodiment of the present invention.

[0028] Description of the Reference Numerals:

[0029] 1. Connection body to be welded; 2. Absorbing layer; 3. Constraint layer; 4. Pulsed current system; 5. Pressure system; 6. Vacuum pumping system; 7. Control system. Detailed Embodiments

[0030] To make the above objects, features, and advantages of the present invention more apparent and understandable, the following provides a detailed description of specific embodiments of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0032] The term "including" and its variations used herein are open-ended, that is, "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; the term "optionally" means "optional embodiment". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are used to distinguish different objects and are not used to describe a specific order or primary-secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0033] Currently, the welding methods for Ni3Al-based single-crystal superalloys include fusion welding, brazing, liquid-phase diffusion welding, and solid-phase diffusion welding, etc.

[0034] Fusion welding of nickel-based superalloys mainly includes laser welding, electron beam welding, and arc welding. When using the fusion welding method to weld nickel-based single-crystal superalloys, excessive heat input causes a large temperature gradient in the joint. Seriously, there are large residual stresses. At the same time, due to the large variety of elements contained in nickel-based alloys, various metallurgical reactions are likely to occur at high temperatures. There are Laves phases between the heterocrystals and dendrites near the weld centerline and weld toe, which are all favorable conditions for the formation and propagation of cracks in the joint. Therefore, when using the fusion welding method to weld single-crystal alloys, the joint performance is poor.

[0035] Brazing can achieve the joining of base materials at temperatures below the melting point of the base materials, which can, to a certain extent, avoid problems such as excessive heat input, excessive residual stress, and cracks in the heat-affected zone existing in fusion welding. Moreover, the brazing method is economical and simple, and can avoid crack problems caused by the melting and crystallization of base materials. However, there are significant differences in the composition between the joint and the base material after brazing, and low-melting-point compounds are likely to form in the joint, weakening the performance of the joint. When using the brazing method to join nickel-based single-crystal superalloys, low-melting eutectic structures or compounds containing B, C, or Si are likely to appear in the joint, and their continuous distribution in the joint will deteriorate the mechanical properties of the joint. For example, in the Chinese published literature - "Vacuum Brazing of Directionally Solidified Ni3Al-Based Superalloy IC6A", this literature uses three brazing fillers with different compositions to perform vacuum brazing on the Ni3Al-based superalloy IC6A. The test results show that under certain conditions, all three brazing fillers can obtain complete and dense joints, but a large number of compound phases appear in the joints, and these compounds are mainly boride and carbide phases.

[0036] Transient liquid-phase diffusion bonding has a good effect in reducing the bonding temperature, but the residual metal interlayer greatly reduces the heat resistance and oxidation resistance of the joint. Using methods such as an ultra-thin interlayer to promote element diffusion and interfacial reaction, the initial conditions are relatively harsh, and there are low-melting eutectic structures or compounds of B and C in the diffusion heat-affected zone of the joint, affecting the joint performance.

[0037] Ordinary solid-phase diffusion bonding can effectively avoid the appearance of joint cracks and improve the mechanical properties of the joint. However, ordinary solid-phase diffusion bonding requires high temperature, high pressure, and a relatively long time, which will lead to the coarsening of material grains and generate large residual stresses in the joint after pressurization, seriously damaging the material properties.

[0038] Pulsed current sintering is an efficient, low-cost, and low-energy-consuming powder metallurgy technology. Pulsed current sintering technology has been widely applied in material systems such as ultra-high temperature ceramics, refractory metals, cemented carbides, and high-entropy alloys. As a multi-energy-field-assisted sintering technology, pulsed current sintering directly heats the sample and induces phenomena such as discharge plasma and local Joule heat through a direct current pulsed current flowing through the interior of the sample while applying pressure to the sintered powder, thereby achieving low-temperature and rapid sintering of the material. Pulsed current-assisted diffusion bonding is a new bonding method proposed based on pulsed current sintering technology. Compared with traditional diffusion bonding, pulsed current-assisted diffusion bonding has outstanding advantages such as low bonding temperature, short time, and high precision.

[0039] Pulse current assisted diffusion bonding uses the joule heat generated by pulse current as the heat source, introduces an electric field on the basis of solid-phase diffusion bonding, and can promote interface healing through effects such as electromigration and plasticity. At the same time, pulse current diffusion welding has the characteristics of low connection temperature and short time, which greatly inhibits the formation of brittle compounds. During the pulse current diffusion welding process, the welding interface has a large impedance, which can significantly increase the deformation resistance of the workpieces to be welded, achieve high-precision and reliable welding, and avoid problems such as parent material phase transformation, grain growth, and composition segregation caused by long-term exposure to high-temperature environments. In addition, pulse current assisted diffusion bonding can shorten the process flow, reduce costs, and improve the overall performance of the connection joint. Therefore, applying the characteristics of pulse current to promote interfacial mass transfer and reaction to the diffusion bonding of Ni3Al-based single-crystal superalloys is expected to quickly achieve reliable bonding of Ni3Al-based single-crystal superalloys at low temperatures.

[0040] An embodiment of the present invention provides a method for bonding Ni3Al-based single-crystal superalloys. Referring to Figure 1 and Figure 2 shown, it includes:

[0041] Step S1: Nanostructure the surface of the Ni3Al-based single-crystal superalloy by laser shock peening.

[0042] Step S2: Bond the nanostructured surfaces of at least two Ni3Al-based single-crystal superalloys together to obtain the workpiece to be welded 1.

[0043] Or, place an Ni interlayer between the nanostructured surfaces of the two Ni3Al-based single-crystal superalloys to form the workpiece to be welded 1.

[0044] Step S3: Apply pulse current and pressure to the workpiece to be welded 1 for diffusion welding.

[0045] It should be understood that in step S2, the nanostructured surfaces of the Ni3Al-based single-crystal superalloys can be directly bonded together to form the workpiece to be welded 1, or an Ni interlayer can be placed between the nanostructured surfaces of the two Ni3Al-based single-crystal superalloys to form the workpiece to be welded 1.

[0046] The present invention uses a diffusion welding method coupling surface nanocrystallization with pulsed current to join Ni3Al-based single crystal superalloys. That is, a laser shock peening technique is used to introduce a gradient nanocrystalline structure on the surface of the Ni3Al-based single crystal superalloy, realizing the surface activation modification of the Ni3Al-based single crystal superalloy before diffusion welding, so as to increase the near-surface defect concentration of the superalloy, reduce the surface atomic diffusion activation energy of the superalloy, which is beneficial to reducing the temperature of diffusion welding and minimizing joint deformation. Further, an external electric field is introduced during the diffusion welding process, combined with the advantage of the fast heating rate of pulsed current, to achieve the effect of suppressing the growth of nanocrystals during the heating stage. The synergy between the surface nanocrystallization treatment of the superalloy and pulsed current is conducive to significantly increasing the interfacial energy of the Ni3Al-based single crystal superalloy, increasing the rapid atomic diffusion channels, thereby effectively enhancing the diffusion coefficient, and then rapidly achieving reliable joining of the Ni3Al-based single crystal superalloy at low temperature. For the joined joint obtained by the present invention, the welding time is less than 30 min, the joint welding rate is above 99%, the tensile strength at room temperature is above 1000 MPa, and the shear strength reaches above 800 MPa; when the service temperature is 1100 °C, its shear strength reaches above 300 MPa, and the tensile strength is above 400 MPa.

[0047] In some embodiments, an Ni interlayer is selected and placed between the base materials to be welded. First, Ni has a low hardness and good plasticity, and can fill the interfacial pores during the diffusion welding process, forming a contact interface, increasing the contact interface area and providing sufficient diffusion paths for diffusion welding. Second, Ni and the Ni3Al-based single crystal superalloy do not produce brittle intermetallic compounds, but can introduce a chemical potential gradient, thus promoting atomic diffusion during the diffusion welding process; finally, the melting point of Ni is as high as 1455 °C, having certain high-temperature properties. Therefore, the Ni interlayer can improve the strength of the diffusion welded joint and reduce the welding temperature.

[0048] Specifically, during the surface nanocrystallization process of superalloys, on the one hand, compared with the coarse-grained structure, the nanocrystalline structure has a higher Gibbs free energy and grain boundary volume fraction, so it has a higher diffusion rate and a strong tendency for thermally-driven grain growth. On the other hand, the gradient nanocrystalline structure realizes the gradient structure change of Ni3Al-based single-crystal superalloys from nanocrystalline to coarse-grained from the surface to the interior. Since the specific surface area and surface energy of nanomaterials are much larger than those of bulk materials, they can be fused with each other at low temperatures (far lower than the melting point of the corresponding bulk materials), and the fused nanomaterials can work at high temperatures, that is, they have the characteristics of low-temperature sintering and high-temperature service, thus having great advantages in welding technology. However, the nanocrystalline structure has a high Gibbs free energy and a strong tendency for thermally-driven grain growth at lower temperatures. But once the grains grow, the advantages of the nanoscale will be lost, and the pulsed current has the advantage of a fast heating rate. Therefore, the pulsed current diffusion welding technology can be used to avoid the growth of nanocrystals during the heating stage and retain the advantages of high diffusion coefficient and high Gibbs free energy of nanocrystals.

[0049] Compared with fusion welding, the connection process adopted in the present invention can obtain a welded joint without welding defects such as cracks. Compared with brazing, there is no eutectic structure or compounds containing B, C, or Si in the connection joint. Compared with transient liquid phase diffusion bonding, the welding temperature of the present invention is low and the welding time is short, and no liquid phase is generated during the welding process. Compared with ordinary solid-phase diffusion welding, it can effectively avoid the appearance of joint cracks, improve the mechanical properties of the joint, reduce the welding temperature, time and pressure, effectively relieve the residual stress, reduce welding defects, and further improve the joint performance.

[0050] In some alternative embodiments, step S1 specifically includes:

[0051] S11: Sequentially arrange an absorption layer 2 and a constraint layer 3 on the surface of the Ni3Al-based single-crystal superalloy;

[0052] S12: Perform laser pulse shot peening on the constraint layer 3.

[0053] In the embodiments of the present invention, such as Figure 3As shown, the high-power laser pulse passes through the constraint layer 3 and acts on the absorption layer 2, instantaneously generating high-temperature and high-pressure plasma. The shock waves generated during the expansion of these plasmas can penetrate deep into the interior of the Ni3Al-based single-crystal superalloy material, thereby changing the microstructure of its surface or near-surface to form a gradient nanocrystalline structure. Among them, the constraint layer 3 is conducive to restricting the expansion of the plasma, enhancing the shock wave pressure, enabling it to accumulate energy in the narrow space between the material and the constraint layer 3, and also helping to evenly distribute the shock wave energy, reducing local stress concentration, thereby improving the uniformity of shot peening. The absorption layer 2 is used to prevent the laser from directly ablating the material, prevent ablation from occurring near the specimen surface, and helps to induce the formation of high-amplitude residual stress. It can also enhance the absorption of the laser beam energy by the specimen surface and increase the peak pressure of the laser shock wave.

[0054] In some alternative embodiments, the absorption layer 2 is an aluminum foil or black paint. Among them, the thickness of the absorption layer 2 can be 10 to 200 μm, and the constraint layer 3 can be a deionized water layer with a thickness range of 0.5 to 3 mm.

[0055] In some alternative embodiments, the Ni intermediate layer can specifically be a Ni foil with a thickness of 5 to 50 μm. By controlling the thickness of the Ni intermediate layer within the micron range, a joint with a relatively high connection strength can be obtained.

[0056] In some alternative embodiments, in the above step S12, the parameters of the laser pulse shot peening are as follows: the pulse energy is 500 to 1500 mJ, the spot diameter is 0.5 to 3 mm, the laser intensity is 3 to 10 GW / cm2, the repetition frequency is 1 to 3 Hz, the pulse duration is 10 to 100 ns, and the number of laser pulses is 5 to 50 times.

[0057] In some alternative embodiments, the above step S3 can specifically include: when the nano-treated surfaces of at least two Ni3Al-based single-crystal superalloys are mutually adhered to obtain the welded connection body 1, a pulsed current can be applied to the welded connection body 1. After heating the welded connection body 1 to 700 to 1150 °C, keep it warm for 15 to 60 min, and finally cool it in the furnace. Among them, the heating rate of the welded connection body 1 is 90 to 110 °C / min. Correspondingly, the maximum voltage of the pulsed current is 10 to 12 V, the maximum current is 10 to 12 kA, and the pulse frequency is 30 to 50 kHz.

[0058] In some other alternative embodiments, the above step S3 can also include: when the Ni intermediate layer is placed between the nano-treated surfaces of two Ni3Al-based single-crystal superalloys to form the welded connection body 1, a pulsed current can be applied to the welded connection body 1. After heating the welded connection body 1 to 650 to 1000 °C, keep it warm for 15 to 30 min. The heating rate of the welded connection body 1 is also 90 to 110 °C / min.

[0059] Figure 4 Schematic diagram of the pulsed current assisted diffusion bonding device for Ni3Al-based single crystal superalloy in an exemplary embodiment. Specifically, referring to Figure 4 as shown, the pulsed current assisted diffusion bonding device for Ni3Al-based single crystal superalloy includes a pulsed current system 4, a pressure system 5, a vacuum pumping system 6, and a control system 7. Among them, the pulsed current system 4 is used to apply current to the workpieces to be welded 1, the pressure system 5 is used to apply pressure to the workpieces to be welded 1, the vacuum system is used to maintain the vacuum environment in the furnace, and the control system 7 is used to control the bonding process. During the pulsed current assisted diffusion bonding process of Ni3Al-based single crystal superalloy, the workpieces to be welded 1 can be placed in a graphite mold, and graphite paper is placed between the graphite mold and the workpieces to be welded 1 to make the mold and the workpieces to be welded 1 in full contact and reduce the interfacial contact resistance. Then, close the furnace door and evacuate through the vacuum pumping system 6. When the vacuum degree reaches the requirement, turn on the pulsed current system 4 and the pressure system 5 to apply pulsed current and pressure to the workpieces to be welded 1, and use the Joule heat generated inside the workpieces for diffusion welding.

[0060] Figure 5 Schematic diagram of the temperature and pressure changes during the pulsed current assisted diffusion welding process of Ni3Al-based single crystal superalloy in an exemplary embodiment. Figure 5 In, the abscissa represents the time change, and the ordinate represents the change of welding parameters (temperature and pressure). Among them, the upper curve shows the temperature change trend of the workpieces to be welded 1 with time, and the lower curve shows the pressure change trend applied to the workpieces to be welded 1 with time. From Figure 5 it can be seen that during the heating stage of the workpieces to be welded 1, a gradually increasing pressure is applied to the workpieces to be welded 1, where the pressure increase rate is 8 to 10 MPa / min; during the holding stage of the workpieces to be welded 1, the pressure applied to the workpieces to be welded 1 is maintained at 50 to 80 MPa; the pressure is released when the workpieces to be welded 1 are cooled with the furnace. Generally speaking, the service temperature of Ni3Al-based single crystal superalloy is above 1100 °C. By adopting pulsed current assisted diffusion bonding, the present invention has the characteristics of low bonding temperature and pressure and short time, so as to realize the reliable bonding of Ni3Al-based single crystal superalloy at low temperature and its normal application at high temperature.

[0061] In some alternative embodiments, before step S1, the following steps are further included: using metallographic sandpaper to polish the surface to be welded of the Ni3Al-based single-crystal superalloy until it is clean, successively polishing the welding surface with 80#, 240#, 400#, 800#, 1000#, 1500#, 2000#, 3000# sandpaper, and polishing it with diamond polishing agent to make it show a bright metallic luster. The non-welding surface is polished with 80# and 240# sandpaper, and then put into absolute ethanol and cleaned with an ultrasonic cleaner for 30 minutes and dried. This is to ensure the smooth progress of the surface nanocrystallization process in step S1.

[0062] In another embodiment of the present invention, a connection joint of Ni3Al-based single-crystal superalloy is provided, and this connection joint is prepared by using the connection method of Ni3Al-based single-crystal superalloy as described above. Specifically, the connection joint of Ni3Al-based single-crystal superalloy is obtained by connecting two Ni3Al-based single-crystal superalloys by using the above connection method.

[0063] The present invention will be described in detail through specific examples and comparative examples as follows:

[0064] Example 1

[0065] The connection method of Ni3Al-based single-crystal superalloy in this example includes the following steps:

[0066] (1) Surface nanocrystallization treatment

[0067] IC10 is processed into a size with a diameter of 15 mm and a thickness of 6 mm. Use metallographic sandpaper to polish the surface to be welded of IC10 until it is clean. The welding surface is successively polished with metallographic sandpaper with mesh numbers of 80#, 240#, 400#, 800#, 1000#, 1500#, 2000#, 3000#, and polished with diamond polishing agent to make it show a bright metallic luster. The non-welding surface is polished with metallographic sandpaper with mesh numbers of 80# and 240#, and then put into absolute ethanol and cleaned with an ultrasonic cleaner for 30 minutes, and the sample is dried with a hair dryer.

[0068] A 50-μm-thick aluminum foil is pasted on the processed area of the polished IC10 surface as an absorption layer, and then a 2-mm-thick deionized water layer is formed on the material surface using a water pump and a spray gun as a constraint layer. The parameters of laser shock peening are: pulse energy 1000 mJ, spot diameter 1 mm, laser intensity 5 GW / cm 2 , repetition frequency 1 Hz, pulse duration 50 ns, number of laser pulses 20 times.

[0069] (2) Pulse current-assisted diffusion welding

[0070] The surfaces of IC10 after being nano-processed are mutually adhered to assemble the connection body to be welded. The connection body to be welded is placed in a graphite mold, and a graphite paper is placed between the graphite mold and the connection body to be welded, so that the mold and the connection body to be welded are in full contact and the interfacial contact resistance is reduced. Then, close the furnace door to evacuate, and then turn on the pulsed current system and the pressure system. Heat the connection body to be welded to 800 °C at a heating rate of 100 °C / min and keep it warm for 40 min. At the same time, apply pressure at a pressure increasing rate of 8 MPa / min, and the pressure during the heat preservation stage is maintained at 64 MPa. An infrared thermometer is used to monitor the temperature of the connection interface during the diffusion welding process. After welding, turn off the pulsed current system and the pressure system, and cool the connection body to be welded with the furnace to room temperature by water cooling. Then open the furnace door, take out the welded specimen, and finally obtain the IC10 connection joint. The maximum voltage of the pulsed power supply built in the pulsed current system is 10 V, the maximum current is 10 kA, the pulse frequency is 30 kHz, and the duty cycle is about 83.33%.

[0071] Example 2

[0072] The difference between this example and Example 1 is that in step (2), a 25-μm-thick Ni foil is placed between the surfaces of IC10 after being nano-processed to form a connection body to be welded with a sandwich structure. The connection body to be welded is placed in a graphite mold, and a graphite paper is placed between the graphite mold and the connection body to be welded, so that the mold and the connection body to be welded are in full contact and the interfacial contact resistance is reduced. Then, close the furnace door to evacuate, and then turn on the pulsed current system and the pressure system. Heat the connection body to be welded to 700 °C at a heating rate of 100 °C / min and keep it warm for 30 min. At the same time, apply pressure at a pressure increasing rate of 8 MPa / min, and the pressure during the heat preservation stage is maintained at 64 MPa. An infrared thermometer is used to monitor the temperature of the connection interface during the diffusion welding process. After welding, turn off the pulsed current system and the pressure system, and let the connection body to be welded cool to room temperature with the furnace. Then open the furnace door, take out the welded specimen, and finally obtain the IC10 connection joint.

[0073] Comparative Example 1

[0074] The difference between this comparative example and Example 1 is that the Ni3Al-based single-crystal superalloy is not subjected to surface nano-processing and is directly subjected to pulsed current-assisted diffusion welding.

[0075] The performance parameters of the connection joints obtained in Examples 1 to 2 and Comparative Example 1 are shown in Table 1:

[0076]

[0077] As can be seen from Table 1, subjecting the Ni3Al-based single crystal superalloy to surface nanocrystallization treatment first and then performing SPS-assisted diffusion welding is beneficial to significantly reduce the joining temperature, while improving the tensile strength and shear strength of the joint at room temperature and high temperature, and realizing the reliable joining of the Ni3Al-based single crystal superalloy joint at low temperature and its service process at high temperature. Using Ni foil as the intermediate layer can further improve the tensile strength and shear strength of the joint at room temperature and high temperature compared with direct welding.

[0078] Although the present invention is disclosed as above, the scope of protection of the present invention is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A joining method for Ni3Al-based single crystal superalloy, characterized in that, Including: The surface of the Ni3Al-based single crystal superalloy is subjected to surface nanocrystallization treatment by laser pulse peening; The nanocrystallized surfaces of at least two of the Ni3Al-based single crystal superalloys are mutually adhered to obtain a connection body to be welded; or, an Ni intermediate layer is placed between the nanocrystallized surfaces of the two Ni3Al-based single crystal superalloys to form a connection body to be welded; A pulsed current and pressure are applied to the connection body to be welded for diffusion welding.

2. The joining method of the Ni3Al-based single crystal superalloy according to claim 1, wherein The surface of the Ni3Al-based single crystal superalloy is subjected to surface nanocrystallization treatment by laser pulse peening, including: An absorption layer and a constraint layer are sequentially arranged on the surface of the Ni3Al-based single crystal superalloy; Laser pulse peening is performed on the constraint layer.

3. The joining method of the Ni3Al-based single crystal superalloy according to claim 2, characterized in that, The absorption layer is aluminum foil or black paint, and / or, the constraint layer is a deionized water layer, and the thickness of the deionized water layer is 0.5 to 3 mm.

4. The joining method of the Ni3Al-based single crystal superalloy according to claim 2, characterized in that, The thickness of the Ni intermediate layer is 5 to 50 μm.

5. The joining method of the Ni3Al-based single crystal superalloy according to claim 2, characterized in that, The parameters of the laser shock peening are as follows: the pulse energy is 500 to 1500 mJ, the spot diameter is 0.5 to 3 mm, the laser intensity is 3 to 10 GW / cm 2 , the repetition frequency is 1 to 3 Hz, the pulse duration is 10 to 100 ns, and the number of laser pulses is 5 to 50 times.

6. The joining method of the Ni3Al-based single crystal superalloy according to claim 1, characterized in that, When the nanocrystallized surfaces of at least two of the Ni3Al-based single crystal superalloys are mutually adhered to obtain a connection body to be welded, a pulsed current is applied to the connection body to be welded, and after the connection body to be welded is heated to 700 to 1150 °C, it is kept warm for 15 to 60 min.

7. The joining method of the Ni3Al-based single crystal superalloy according to claim 1, characterized in that, When the Ni intermediate layer is placed between the nanocrystallized surfaces of the two Ni3Al-based single crystal superalloys to form a connection body to be welded, a pulsed current is applied to the connection body to be welded, and after the connection body to be welded is heated to 650 to 1000 °C, it is kept warm for 15 to 30 min.

8. The joining method of the Ni3Al-based single crystal superalloy according to claim 6 or 7, characterized in that, In the heating stage of the connection body to be welded, a gradually increasing pressure is applied to the connection body to be welded, wherein the pressure increasing rate is 8 to 10 MPa / min; In the heat preservation stage of the connection body to be welded, the pressure applied to the connection body to be welded is kept at 50 to 80 MPa.

9. The joining method of the Ni3Al-based single crystal superalloy according to claim 6 or 7, characterized in that, The heating rate of the connection body to be welded is 90 to 110 °C / min.

10. A joining joint of a Ni3Al-based single crystal superalloy, characterized in that, The connection joint is prepared by using the connection method of the Ni3Al-based single crystal superalloy according to any one of claims 1-9.

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