Connecting method of nickel-based single crystal alloy and nickel-based polycrystalline alloy and connecting piece of nickel-based single crystal alloy and nickel-based polycrystalline alloy

Abstract

The invention provides a nickel-based single crystal alloy and nickel-based polycrystalline alloy connecting method and a nickel-based polycrystalline alloy connecting piece, and the connecting method comprises the following steps: designing a hollow sheath connecting part with the same section shape and size as a connecting surface, and arranging a thermocouple outside the hollow sheath connecting part; assembling the processed nickel-based single / polycrystalline alloy and the hollow sheath connecting part in a clamp connecting tool, and applying a pre-tightening force to the clamp connecting tool so that two ends of the hollow sheath connecting part are respectively contacted with one end of a connecting surface of the nickel-based single crystal alloy and one end of a connecting surface of the nickel-based polycrystalline alloy; and electrifying the clamp connecting tool so as to heat the areas, in contact with the connecting surfaces, of the two ends of the hollow sheath connecting part to a first preset temperature, applying pressure and preserving heat, and then carrying out gradient cooling to a second preset temperature for preserving heat, so that the nickel-based single crystal alloy and nickel-based polycrystalline alloy connecting piece is obtained. According to the method, a smooth connection interface layer without holes, cracks and abnormal secondary phase growth can be obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of material processing, and in particular to a method for connecting a nickel-based single crystal alloy and a nickel-based polycrystalline alloy and a connecting piece thereof. Background Art

[0002] The integrated design of the blisk eliminates the airflow losses caused by airflow escaping between the tenon and the groove in traditional blisks. This not only reduces component weight by 20%-30%, lowering fuel consumption and emissions, but also effectively reduces heat transfer resistance and interfaces, thereby improving the thermal efficiency of the aero-engine, increasing engine efficiency and ultimately the thrust-to-weight ratio of the entire engine. With the increasing demand for aero-engine blisks, the blades and disks are joined together using high-quality single crystals produced by directional solidification and polycrystalline alloys produced by powder metallurgy, respectively. To achieve high-quality joining of nickel-based single / polycrystalline alloys, nickel-based superalloy single / polycrystalline joining technology has become a key area in urgent need of breakthroughs.

[0003] Currently, technologies used to join single crystals and polycrystals include electron beam welding, laser welding, brazing, linear friction welding, transient liquid phase welding, and hot isostatic pressing (HIP) diffusion welding. However, all of these technologies have shortcomings. Electron beam welding and laser welding produce joints with carbide segregation and crystallographic mismatch in the molten zone, as well as significant residual stress and deformation, which can easily lead to cracks in the weld zone. Brazing and transient liquid phase welding often form large amounts of brittle compounds and Si-B eutectics, which significantly degrade the mechanical properties of the joint. When joining single crystals to powdered superalloys via linear friction welding, the significant difference in high-temperature performance between single crystal and powdered superalloys makes it difficult for the single crystal side to deform during welding, preventing the formation of flash and resulting in numerous defects at the joint edge. While traditional HIP diffusion welding improves defects such as thermal cracking and porosity during fusion welding, the prolonged heating and holding times can lead to the risk of grain growth in the matrix on the polycrystal side, reducing material strength and increasing brittleness.

[0004] Based on this, there is an urgent need to provide a method for connecting nickel-based single crystal alloy and nickel-based polycrystalline alloy and a connecting piece thereof. Summary of the Invention

[0005] The embodiment of the present invention provides a method for connecting a nickel-based single crystal alloy and a nickel-based polycrystalline alloy and a connecting piece thereof, which can achieve stable connection between the nickel-based single crystal alloy and the nickel-based polycrystalline alloy without introducing brittle compounds and avoiding grain growth on one side of the polycrystalline alloy.

[0006] In a first aspect, the present invention provides a method for connecting a nickel-based single crystal alloy and a nickel-based polycrystalline alloy, the method comprising the following steps:

[0007] (1) processing the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively so that the shapes and sizes of the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are the same;

[0008] (2) designing a hollow sheathed connecting component having the same cross-sectional shape and size as the connecting surface, and arranging a thermocouple outside the hollow sheathed connecting component;

[0009] (3) assembling the processed nickel-based single crystal alloy and nickel-based polycrystalline alloy and the hollow sheath connection component in a fixture connection tool, and applying a pre-tightening force to the fixture connection tool so that both ends of the hollow sheath connection component are in contact with the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively;

[0010] (4) The fixture connection tool is energized to heat the areas where the two ends of the hollow sheath connection component contact the connection surface to a first preset temperature, and pressure is applied to the fixture connection tool and the temperature is kept at the first preset temperature. The fixture is then gradually cooled to a second preset temperature and kept warm to obtain a nickel-based single crystal alloy and nickel-based polycrystalline alloy connection piece.

[0011] Preferably, the cross-sections of the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are both circular, and the hollow sheath connection component is cylindrical.

[0012] Preferably, the hollow sheath connecting component is made of nickel-based polycrystalline alloy material.

[0013] More preferably, the hollow sheath connecting component has a thickness of 0.5-1.5 mm and a length of 2.5-7.5 mm.

[0014] Preferably, the thermocouple is located in a central area outside the hollow sheath connection component; wherein the thermocouple is connected to a temperature sensor for monitoring the temperature of the hollow sheath connection component area.

[0015] Preferably, in step (3), the preload force applied is 80-120 kgf.

[0016] Preferably, the first preset temperature is 1200-1250° C., the holding time at the first preset temperature is 5-10 s, and the heating rate is 4-10° C. / s.

[0017] More preferably, the second preset temperature is 1130-1180° C., and the holding time at the second preset temperature is 55-95 minutes.

[0018] Preferably, the gradient cooling process is as follows: the cooling temperature in the first stage is 1170-1180°C, and the holding time is 20-30s; the cooling temperature in the second stage is 1150-1160°C, and the holding time is 50-60s; the cooling temperature in the third stage is 1130-1180°C, and the holding time is 55-95min.

[0019] Preferably, the power is turned on and the pressure is applied in a vacuum environment, and the pressure applied at the first preset temperature and the second preset temperature are both 12-20 MPa.

[0020] Preferably, in step (4), after keeping the temperature at the second preset temperature, the step further includes the steps of sequentially depressurizing the fixture connection fixture and cooling the temperature to room temperature.

[0021] More preferably, the pressure of the decompression is 75-85 kgf, and the temperature is lowered to room temperature at a cooling rate of 5-10° C. / s.

[0022] Preferably, before step (3), the method further includes the steps of grinding, polishing, ultrasonically cleaning and pickling the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy and the two ends of the hollow sheath connection component in sequence.

[0023] In a second aspect, the present invention provides a nickel-based single crystal alloy and nickel-based polycrystalline alloy connecting piece prepared by the connection method described in any one of the first aspects above.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] In the present invention, the cross-sectional shape and size of the hollow sheath connection component are first designed to connect with the nickel-based single crystal alloy and the nickel-based polycrystalline alloy; then, the nickel-based single / polycrystalline alloy and the hollow sheath connection component are assembled in a fixture connection tooling, so that the hollow sheath connection component is located in the middle of the nickel-based single / polycrystalline alloy, and the two ends of the hollow sheath connection component are respectively in contact with the connection surface; finally, by electrically heating the contact area of ​​the connection surface, the Joule heating effect principle is applied, and when the current passes through the nickel-based single / polycrystalline alloy, it is regarded as a resistor. The resistance at the component is greater than that of the nickel-based single / polycrystalline alloy on both sides of it. Therefore, the introduction of the hollow sheath connection component changes the heat distribution, and thus generates more heat in the contact area of ​​the connection surface than the nickel-based single / polycrystalline alloy, avoiding the risk of grain growth in the matrix on the polycrystalline side; in addition, the introduction of the hollow sheath connection component changes the stress state of the connection surface. Since the rigid constraint of the hollow sheath connection component limits the lateral plastic flow in the connection surface area, the material produces a three-dimensional compressive stress state under axial pressure, thereby effectively reducing the porosity of the connection interface and reducing crack initiation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a schematic diagram of the overall structure of the nickel-based single crystal alloy, nickel-based polycrystalline alloy, hollow sheath connection component and fixture connection tooling provided by an embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the connection structure of a nickel-based single crystal alloy, a nickel-based polycrystalline alloy and a hollow sheath connection component provided in Example 1 of the present invention;

[0029] Figure 3 This is a scanning electron microscope image of the microstructure of the connection area between a nickel-based single crystal alloy and a nickel-based polycrystalline alloy provided in Example 1 of the present invention;

[0030] Figure 4 This is a scanning electron microscope image of a precipitated phase in the connection region of a nickel-based single crystal alloy and a nickel-based polycrystalline alloy provided in Example 1 of the present invention;

[0031] Figure 5 This is a tensile property test diagram of the connection area of ​​a nickel-based single crystal alloy and a nickel-based polycrystalline alloy at room temperature provided in Example 1 of the present invention;

[0032] Figure 6 This is a scanning electron microscope image of the microstructure of the connection area between a nickel-based single crystal alloy and a nickel-based polycrystalline alloy provided in Comparative Example 1 of the present invention;

[0033] Figure 7 This is a scanning electron microscope image of the microstructure of the connection area between a nickel-based single crystal alloy and a nickel-based polycrystalline alloy provided in Comparative Example 2 of the present invention;

[0034] In the figure, 100-hydraulic device, 200-fixture connection tooling, 300-nickel-based polycrystalline alloy, 400-hollow sheath connection component, 500-nickel-based single crystal alloy, 600-vacuum protection box, 700-temperature sensor, 800-cooling device, 900-current direction. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0036] like Figure 1 As shown, an embodiment of the present invention provides a method for connecting a nickel-based single crystal alloy and a nickel-based polycrystalline alloy, the connecting method comprising the following steps:

[0037] (1) processing the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively so that the shapes and sizes of the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are the same;

[0038] (2) Designing a hollow sheathed connecting component 400 having the same cross-sectional shape and size as the connecting surface, and arranging a thermocouple outside the hollow sheathed connecting component 400;

[0039] (3) Assembling the processed nickel-based single crystal alloy 500 and nickel-based polycrystalline alloy 300 and the hollow sheath connection component 400 in the fixture connection tool 200, and applying a pre-tightening force to the fixture connection tool 200 so that the two ends of the hollow sheath connection component are tightly fitted with the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively;

[0040] (4) The fixture connection tooling 200 is energized to heat the areas where the two ends of the hollow sheath connection component 400 contact the connection surface to a first preset temperature, and pressure is applied to the fixture connection tooling 200 and the temperature is kept at the first preset temperature. The temperature is then gradually lowered to a second preset temperature and kept at the second preset temperature to obtain a nickel-based single crystal alloy and nickel-based polycrystalline alloy connection piece.

[0041] In the embodiment of the present invention, the cross-sectional shape and size of the connection surface with the nickel-based single crystal alloy and the nickel-based polycrystalline alloy (hereinafter referred to as nickel-based single / polycrystalline alloy) are first designed to design the hollow sheath connection component; then, the nickel-based single / polycrystalline alloy and the hollow sheath connection component are assembled in a fixture connection tooling, so that the hollow sheath connection component is located in the middle of the nickel-based single / polycrystalline alloy, and the two ends of the hollow sheath connection component are respectively in contact with the connection surface; finally, by electrically heating the contact area of ​​the connection surface, the Joule heating effect principle is applied, and when the current passes through the nickel-based single / polycrystalline alloy, it acts as a resistor. Since the resistance of the hollow sheath connection component is greater than that of the nickel-based single / polycrystalline alloy on both sides of it, the introduction of the hollow sheath connection component changes the heat distribution, so the heat generated in the contact area of ​​the connection surface is greater than that of the nickel-based single / polycrystalline alloy, avoiding the risk of grain growth in the matrix on the polycrystalline side; and the introduction of the hollow sheath connection component changes the stress state of the connection surface. Since the rigid constraint of the hollow sheath connection component limits the lateral plastic flow in the connection surface area, the material produces a three-dimensional compressive stress state under axial pressure, thereby effectively reducing the porosity of the connection interface and reducing crack initiation.

[0042] like Figure 1 and Figure 2 As shown, according to some preferred embodiments, the cross-sections of the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are both circular, and the hollow sheath connection component is cylindrical.

[0043] Taking into account that stress concentration problems may occur during the heating process when the cross-section of the connecting surface and the hollow sheath component are processed into other shapes such as squares, rectangles, etc., in an embodiment of the present invention, the connecting surface of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy is processed into a circular cross-section, and a cylindrical hollow sheath connecting component with the same diameter as the circular cross-section is designed and processed accordingly. This is not only conducive to a close fit between the connecting surface and the hollow sheath connecting component, but also helps to ensure that the stress distribution at the contact connection interface between the hollow sheath connecting component and the connecting surface during heating and pressurization is uniform, thereby avoiding cracks or unevenness at the connection interface.

[0044] According to some preferred embodiments, the hollow sheath connecting component is made of nickel-based polycrystalline alloy material; the thickness of the hollow sheath connecting component is 0.5-1.5 mm (for example, it can be 0.5 mm, 0.8 mm, 1 mm, 1.2 mm or 1.5 mm), and the length is 2.5-7.5 mm (for example, it can be 2.5 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm or 7.5 mm).

[0045] In an embodiment of the present invention, the hollow sheath connection component is made of a nickel-based polycrystalline alloy material and is placed between the connection surfaces of the nickel-based single / polycrystalline alloy. Its rigidity constrains the plastic flow of the connection surfaces, which is beneficial to reducing thermal stress mismatch and crack initiation; and by controlling the wall thickness and length of the hollow sheath connection component, it is beneficial to accurately monitor and control the temperature during the power-on heating process, which is beneficial to achieve stable connection of the nickel-based single / polycrystalline alloy and ensure the smoothness and flatness of the connection interface.

[0046] According to some preferred embodiments, the thermocouple is located in a central area outside the hollow sheath connection component; wherein the thermocouple is connected to a temperature sensor for monitoring the temperature of the hollow sheath connection component area.

[0047] In an embodiment of the present invention, a thermocouple is arranged outside the hollow area of ​​the hollow sheath connecting component (for example, by welding), preferably in the central area of ​​the hollow sheath connecting component, and the thermocouple is connected to the temperature sensor 700, so that the actual temperature of the connection interface between the hollow sheath connecting component and the nickel-based single / polycrystalline alloy can be monitored in real time, and the subsequent power-on heating temperature can be accurately controlled according to the monitored temperature.

[0048] According to some preferred embodiments, in step (3), the preload force applied is 80-120 kgf (for example, 80 kgf, 90 kgf, 100 kgf, 110 kgf or 120 kgf).

[0049] In the embodiment of the present invention, continue to refer to Figure 1 , respectively assemble the nickel-based single / polycrystalline alloy materials in the fixture connection tooling, respectively make one end of the connection surface of the nickel-based single / polycrystalline alloy materials be in relative positions, and place the hollow sheath connection component between the nickel-based single / polycrystalline alloy materials, and apply a certain pre-tightening force to the fixture connection tooling through the hydraulic device 100, so that the two ends of the hollow sheath connection component are tightly fitted with one end of the connection surface of the nickel-based single / polycrystalline alloy, thereby avoiding defects in the connection interface during the subsequent power connection process.

[0050] It should be noted that the specific structure of the clamp connection tooling in the embodiment of the present invention is not specifically limited, as long as it can achieve the fixing and power-on functions in the embodiment of the present invention.

[0051] According to some preferred embodiments, the first preset temperature is 1200-1250°C (for example, it can be 1200°C, 1210°C, 1220°C, 1230°C, 1240°C or 1250°C), the holding time at the first preset temperature is 5-10s (for example, it can be 5s, 6s, 7s, 8s, 9s or 10s), and the heating rate is 4-10°C / s (for example, it can be 4°C / s, 6°C / s, 8°C / s or 10°C / s); the second preset temperature is 1130-1180°C (for example, it can be 1130°C, 1140°C, 1150°C, 1160°C, 1170°C or 1180°C), and the holding time at the second preset temperature is 55-95min (for example, it can be 55min, 60min, 70min, 70min, 90min or 95min).

[0052] According to some preferred embodiments, the gradient cooling process is as follows: the cooling temperature in the first stage is 1170-1180°C (for example, 1170°C, 1175°C or 1180°C), and the holding time is 20-30s (for example, 20s, 22s, 25s, 28s or 30s); the cooling temperature in the second stage is 1150-1160°C (for example, 1150°C, 1155°C or 1160°C), and the holding time is 50-60s (for example, 50s, 55s or 60s); the cooling temperature in the third stage is 1130-1180°C (for example, 1170°C, 1175°C or 1180°C), and the holding time is 20-30s (for example, 20s, 22s, 25s, 28s or 30s). ℃ (for example, it can be 1130℃, 1140℃, 1150℃, 1160℃, 1170℃ or 1180℃), and the insulation time is 55-95min (for example, it can be 55min, 60min, 70min, 70min, 90min or 95min); power is turned on and pressure is applied under a vacuum environment, and the pressure applied at the first preset temperature and the second preset temperature is 12-20MPa (for example, it can be 12MPa, 13MPa, 14MPa, 15MPa, 16MPa, 17MPa, 18MPa, 19MPa or 20MPa).

[0053] Unlike traditional heating methods such as muffle furnace heating, in the embodiment of the present invention, by respectively energizing the two ends of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy in the fixture connection tooling, due to the Joule heating effect, when the current passes through the nickel-based single crystal alloy → hollow sheath connection component → nickel-based polycrystalline alloy in sequence, the sample itself is used as a resistor to generate heat. Moreover, since the resistance at the hollow sheath connection component is greater than the resistance at the nickel-based single / polycrystalline alloys on both sides, the distribution of heat in the three areas changes. Therefore, the heat generated in the hollow sheath connection component area is greater than the heat at the nickel-based single / polycrystalline alloys on both sides, thereby effectively avoiding the risk of grain growth in the alloy matrix on the polycrystalline side.

[0054] Furthermore, considering that traditional heating methods are slow and can lead to secondary γ' phase agglomeration, hindering subsequent γ' phase dissolution, the present invention employs an electrical heating method to rapidly raise the temperature to a first preset temperature and then maintain it under pressure. This method rapidly breaks down the oxide layer at the interface, reducing contact resistance and promoting effective metal-metal contact. It also achieves a semi-solid state at the interface between the hollow sheathed connection component and the nickel-based single- or polycrystalline alloy, enhancing the molecular diffusion rate at the interface. Furthermore, precise control of the holding time and pressure allows for rapid atomic diffusion at the interface, achieving a good metallurgical bond. This ensures accurate heating temperature. Subsequently, the temperature is precisely controlled from the first preset temperature to the second preset temperature through a stepwise cooling method, effectively controlling heat accumulation and preventing excessive material deformation. Furthermore, a temperature sensor monitors the temperature within the hollow sheathed connection component in real time during the heating and cooling processes, and a PID controller is employed to accurately and stably control the temperature in complex thermal-mechanical coupling scenarios, effectively suppressing the thermal hysteresis effect of traditional heating methods. By adjusting the Kp (proportional coefficient) value of the PID controller, current overshoot or delayed response can be prevented. In this embodiment, the Kp value range is preferably 0.0002-0.0005.

[0055] At the same time, before power is applied, in the embodiment of the present invention, the entire fixture connection tooling is first vacuumed (<10 -3 The hollow sheathed connection component isolates the nickel-based single / polycrystalline alloy connection surface area from the outside world and, in conjunction with the vacuum environment, blocks the diffusion of oxygen in the connection surface area, reducing the formation of oxides such as Al2O3 and TiO2. Furthermore, the heating process is preferably performed in a vacuum protective chamber 600, which not only ensures a constant vacuum environment but also prevents heat diffusion during the heating process.

[0056] According to some preferred embodiments, in step (4), after keeping warm at the second preset temperature, the step also includes the steps of successively decompressing the fixture connection tooling and cooling it to room temperature; the decompression pressure is 75-85kgf (for example, it can be 75kgf, 80kgf or 85kgf), and the temperature is cooled to room temperature (25-30℃) at a cooling rate of 5-10℃ / s (for example, it can be 5℃ / s, 6℃ / s, 7℃ / s, 8℃ / s, 9℃ / s or 10℃ / s).

[0057] In an embodiment of the present invention, after the insulation is completed and the external load is removed from the fixture connection tooling, the equipment is cooled at a controllable rate using a rapid cooling system equipped therein. By precisely adjusting the cooling rate, the precipitation size and distribution of the second phase (such as the γ' phase) in the connection area can be effectively controlled, thereby obtaining a connection interface with excellent mechanical properties.

[0058] According to some preferred embodiments, before step (3), the method further includes the steps of grinding, polishing, ultrasonically cleaning and pickling the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy and the hollow sheath connection parts in sequence.

[0059] In an embodiment of the present invention, before assembly, the above-mentioned pretreatment is first performed on one end of the connection surface of the nickel-based single / polycrystalline alloy and the surfaces of both ends of the hollow sheath connection component to make their surface roughness less than 0.8 μm, thereby making the surfaces of the connection surface and the hollow sheath connection component smooth, ensuring that both ends of the hollow sheath connection component are in close contact with the connection surface of the nickel-based single / polycrystalline alloy, and avoiding poor contact between the connection surface and the end surface during subsequent power-on.

[0060] At the same time, it should be noted that in order to avoid poor electrical contact, one end of the nickel-based single / polycrystalline alloy and the fixture connection tooling needs to be polished to ensure that both ends are flat; further, the inside and outside of the hollow sheath component also need to be polished to prevent short contact of the thermocouple on the ring side during the welding process of the thermocouple.

[0061] According to some preferred embodiments, during the grinding process, silicon carbide sandpaper of different mesh sizes (for example, 400#, 800#, 1200#, 2000#) is used to grind the connection surfaces of the nickel-based single / polycrystalline alloy in sequence to keep the surface of the material flat; during the polishing process, 3um and 1um diamond polishing liquids are first used for rough polishing for 2-5 minutes, and then a 20nm silica suspension is used for fine polishing for 5 minutes to further reduce the roughness of the connection surface to 0.8μm; then acetone or alcohol is used for ultrasonic cleaning for 10-15 minutes to remove oil stains on the surface of the connection surface; finally, 10-15% nitric acid solution is used for pickling for 3-5 minutes to remove the oxide film on the surface of the connection surface, and then the surface is placed in a drying oven for drying.

[0062] The present invention also provides a nickel-based single crystal alloy and nickel-based polycrystalline alloy connecting piece prepared by any of the above-mentioned connecting methods.

[0063] In summary, in the embodiments of the present invention, by designing a hollow sheathed connection component and employing precise temperature-controlled heating and stepped, controlled-rate cooling, efficient connection of nickel-based single- and polycrystalline alloys is achieved. Heat distribution at the connection interface is optimized, preventing degradation of the nickel-based single- and polycrystalline alloy substrates. Furthermore, by adjusting the stress state at the connection interface, the formation of holes and cracks at the connection interface is reduced. Furthermore, the addition of additional brazing filler metal is eliminated, avoiding the introduction of Si and B eutectic structures and a large amount of brittle compounds, thereby improving the strength of the connection interface. This achieves excellent joint performance for nickel-based high-temperature single- and polycrystalline alloy connections, resulting in a smooth, flat, hole- and crack-free connection transition layer with no abnormal growth of secondary phases.

[0064] In the embodiment of the present invention, the above method has excellent process universality and is applicable to the connection of various types of nickel-based single crystal alloys (for example, DD5 alloy prepared by directional solidification) and nickel-based polycrystalline alloys (for example, FGH96 alloy prepared by powder metallurgy method). It can also be extended to the precision connection of typical nickel-based high-temperature alloys such as Inconel 718 and Hastelloy X. At the same time, this method can also be extended to the connection of other types of heterogeneous alloys.

[0065] In order to more clearly illustrate the technical solutions and advantages of the present invention, a method for connecting a nickel-based single crystal alloy and a nickel-based polycrystalline alloy and a connecting piece thereof are described in detail through the following embodiments.

[0066] Example 1:

[0067] (1) One end of the connection surface of the nickel-based single crystal alloy (DD5) and the nickel-based polycrystalline alloy (FGH96) is processed respectively so that the cross-sections of the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are both circular and of the same size (diameter of 12 mm);

[0068] First, the connection surface was polished and leveled with 400#, 800#, 1200#, and 2000# silicon carbide sandpaper in sequence; then, 3um and 1um diamond polishing liquids were used for rough polishing for 5 minutes each, and 20nm silicon dioxide suspension was used for fine polishing for 5 minutes; then, acetone and alcohol were used for ultrasonic cleaning for 10 minutes in sequence to remove oil stains; then, 10% HNO3 solution was used for pickling for 5 minutes to remove the oxide film, and then the connection surface was dried in a drying oven to achieve a surface quality of Ra < 0.8μm; and the end of the nickel-based single crystal alloy and nickel-based polycrystalline alloy connected to the fixture connection tooling was polished and leveled with 400#, 800#, 1200#, and 2000# silicon carbide sandpaper;

[0069] (2) Design and process hollow sheathed connecting parts with the same cross-sectional shape and equal diameter (12mm) as the connecting surface (such as Figure 2 As shown, the shape is hollow cylinder, wall thickness 1mm, length 5mm);

[0070] First, the two ends of the hollow sheath connection component were polished flat with 400#, 800#, 1200#, and 2000# silicon carbide sandpaper in sequence; then, 3um and 1um diamond polishing liquids were used for rough polishing for 5 minutes each, and 20nm silica suspension was used for fine polishing for 5 minutes; then, acetone and alcohol were used for ultrasonic cleaning for 10 minutes in sequence to remove oil stains; then, 10% HNO3 solution was used for pickling for 5 minutes to remove the oxide film, and then the components were placed in a drying oven for drying to achieve a surface quality of Ra < 0.8μm at both ends of the hollow sheath connection component;

[0071] After grinding the inside and outside of the hollow sheath connection component with 400#, 800#, 1200#, and 2000# silicon carbide sandpaper, a thermocouple is welded to the center area outside the hollow sheath connection component.

[0072] (3) Assembling one end of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy on the fixture connection tooling respectively, and setting the hollow sheath connection component between the nickel-based single crystal alloy and the nickel-based polycrystalline alloy, and applying a 100 kgf pre-tightening force to the fixture connection tooling by a hydraulic device so that the two ends of the hollow sheath connection component are tightly fitted with one end of the connection surface of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively;

[0073] (4) The assembled nickel-based single crystal alloy and nickel-based polycrystalline alloy are placed in a vacuum oven for evacuation, and then the fixture is powered on to rapidly heat the areas where the two ends of the hollow sheath connection component contact the connection surface to a first preset temperature (1200°C) at a heating rate of 5°C / s. The temperature is monitored in real time by a temperature sensor and the heating temperature is precisely controlled by a PID controller. A pressure of 12 MPa is applied to the fixture and the temperature is kept at the first preset temperature for 5 seconds. The pressure is then maintained. The temperature was gradually cooled to the second preset temperature (1130°C) while the force remained unchanged and kept warm for 60 minutes. First, the temperature was reduced from 1200°C to 1170°C and kept warm for 30 seconds. Then, the temperature was reduced from 1170°C to 1150°C and kept warm for 60 seconds. Finally, the temperature was reduced from 1150°C to 1130°C and kept warm for 60 minutes. After the insulation, the pressure was unloaded to a preload force of 80 kgf. The temperature was cooled to room temperature (25°C) at a cooling rate of 5°C / s. After being taken out, a connecting piece of DD5 nickel-based single crystal alloy and FGH96 nickel-based polycrystalline alloy was obtained.

[0074] In order to observe the microstructure of the connection interface in Example 1, the connection area of ​​the connector obtained above was polished and leveled with 400#, 800#, 1200#, and 2000# sandpaper in sequence. Then, it was coarsely polished with 3um and 1um diamond polishing liquids for 5 minutes each. Finally, the ground surface was finely polished with a 20nm SiO2 suspension for 5 minutes. It was then etched with 50gCuCl2, 250mLHCl, and 250mLC2H5OH in sequence to reveal the grain size at the connection interface. It was then etched with a 1:10 H2O2 and HCL etching solution for 30 seconds to reveal the γ' phase precipitation. Figure 3 and Figure 4 As shown, the connection interface in Example 1 presents a dense and uniform microstructure, and the grain size at the connection interface does not show obvious growth compared with the original grain size (nickel-based single / polycrystalline alloy), and the precipitated phase at the connection interface layer and the precipitated phase in the matrix (nickel-based single / polycrystalline alloy) do not grow abnormally.

[0075] Furthermore, the prepared connector (hereinafter referred to as the connector sample) was cut along the axial direction of the cylinder, and a standard tensile test sample was cut out according to the design drawing using a wire cutting process. The tensile test was carried out at room temperature. Figure 5 It can be seen that the curve of the connection sample is between the DD5 nickel-based single crystal alloy and the FGH96 nickel-based polycrystalline alloy, with a yield strength of 834 MPa, a tensile strength of 1073 MPa, and an elongation of 8.4%. It can be seen that a high-reliability connection of nickel-based single crystal / polycrystalline alloy is achieved in this embodiment 1.

[0076] Comparative Example 2:

[0077] Comparative Example 2 is substantially the same as Example 1, except that in step (4), the second preset temperature is 1150° C. and the applied pressure is 10 MPa.

[0078] The connecting piece was ground, polished and etched in the same manner as in Example 1 to obtain Figure 6 The microstructure shown in the figure is Figure 6 It can be seen that when the second preset temperature is 1150°C and the applied pressure is too low, obvious cracks appear in the connection interface area, and fracture occurs in the elastic section during the tensile test.

[0079] Comparative Example 3:

[0080] Comparative Example 3 is substantially the same as Example 1, except that, in step (4), the second preset temperature is 1130° C. and the applied pressure is 20 MPa.

[0081] The connecting piece was ground, polished and etched in the same manner as in Example 1 to obtain Figure 6 The microstructure shown in the figure is Figure 7 It can be seen that when the second preset temperature is 1130°C and the applied pressure is large, obvious interface bulges appear in the connection interface area, and obvious cracks appear, making it impossible to achieve effective connection between the two interfaces.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for connecting a nickel-based single crystal alloy and a nickel-based polycrystalline alloy, characterized in that: The connection method comprises the following steps: (1) processing the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively so that the shapes and sizes of the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are the same; (2) designing a hollow sheathed connecting component having the same cross-sectional shape and size as the connecting surface, and arranging a thermocouple outside the hollow sheathed connecting component; (3) assembling the processed nickel-based single crystal alloy and nickel-based polycrystalline alloy and the hollow sheath connection component in a fixture connection tool, and applying a pre-tightening force to the fixture connection tool so that both ends of the hollow sheath connection component are in contact with one end of the connection surface of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy respectively; (4) The fixture connection tool is energized to heat the areas where the two ends of the hollow sheath connection component contact the connection surface to a first preset temperature, and pressure is applied to the fixture connection tool and the temperature is kept at the first preset temperature. The fixture is then gradually cooled to a second preset temperature and kept warm to obtain a nickel-based single crystal alloy and nickel-based polycrystalline alloy connection piece.

2. The connection method according to claim 1, characterized in that: The cross-sections of the connecting surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy are both circular, and the hollow sheath connecting component is cylindrical.

3. The connection method according to claim 1 or 2, characterized in that: The hollow sheath connecting component is made of nickel-based polycrystalline alloy material; and / or The thickness of the hollow sheath connection component is 0.5-1.5 mm, and the length is 2.5-7.5 mm.

4. The connection method according to claim 1, characterized in that: The thermocouple is located in a central area outside the hollow sheath connecting component.

5. The connection method according to claim 1, characterized in that: In step (3), the preload force applied is 80-120 kgf.

6. The connection method according to claim 1, characterized in that: The first preset temperature is 1200-1250° C., the holding time at the first preset temperature is 5-10 seconds, and the heating rate is 4-10° C. / s; and / or The second preset temperature is 1130-1180° C., and the holding time at the second preset temperature is 55-95 minutes.

7. The connection method according to claim 1 or 6, characterized in that: The gradient cooling process is as follows: the cooling temperature of the first stage is 1170-1180°C, and the holding time is 20-30s; the cooling temperature of the second stage is 1150-1160°C, and the holding time is 50-60s; the cooling temperature of the third stage is 1130-1180°C, and the holding time is 55-95min; and / or Power is applied and pressure is applied under vacuum environment, and the pressure applied at the first preset temperature and the second preset temperature is both 12-20 MPa.

8. The connection method according to claim 1, characterized in that: In step (4), after the second preset temperature is maintained, the steps of sequentially depressurizing the fixture connection fixture and cooling the fixture to room temperature are also included; Preferably, the pressure of the decompression is 75-85 kgf, and the temperature is lowered to room temperature at a cooling rate of 5-10° C. / s.

9. The connection method according to claim 1, characterized in that: Before step (3), the method further includes the steps of grinding, polishing, ultrasonically cleaning and pickling the connection surfaces of the nickel-based single crystal alloy and the nickel-based polycrystalline alloy and the two ends of the hollow sheath connection component in sequence.

10. A nickel-based single crystal alloy and nickel-based polycrystalline alloy connector, characterized in that: The method is prepared by the connection method according to any one of claims 1 to 9.

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