A Method for Improving the Strength and Radial Uniformity of Inertia Friction Welded Joints of Superalloys

Abstract

The present invention provides a method for improving the strength and radial uniformity of inertia friction welding joints of high-temperature alloys, and belongs to the field of solid phase welding technology. The present invention uses inertia friction welding technology to perform high-quality connection of rotating workpieces of high-temperature alloys. Due to the uneven distribution of heat generation and pressure at the joint interface, the growth of recrystallized grains is affected, resulting in uneven distribution of radial structure and performance of the joint, which in turn induces the formation of a weak performance zone in the joint, resulting in uncoordinated deformation of the joint, which significantly affects the strength of the joint. The present invention improves the strength of the joint and significantly improves the uniformity of the radial structure and performance of the joint through the synergistic effect of solid solution strengthening and two-stage aging strengthening, promotes the dynamic recovery and dynamic recrystallization process of the joint, improves the structure morphology and distribution of the joint strengthening phase γ′, reduces the precipitation phases such as carbides, and realizes precise regulation of the joint structure and performance.

Description

Technical Field

[0001] The invention belongs to the technical field of solid phase welding, and in particular relates to a method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint. Background Art

[0002] With the urgent need for the development of high thrust-to-weight ratio of aero-engines, high-temperature alloys have excellent creep resistance, high temperature resistance and corrosion resistance, and have become the preferred material for hot-end components such as rotors of high-performance aero-engines. Inertia friction welding, as a typical solid-phase welding technology, can effectively avoid defects such as pores, cracks and slag inclusions that are prone to occur in traditional fusion welding. However, the complex and changeable service environment places extremely stringent requirements on joint strength. In addition, due to the uneven distribution of heat and pressure at the welding interface, the joint structure and performance show radial non-uniformity, which in turn affects the joint forming quality. Therefore, improving the strength and radial uniformity of high-temperature alloy inertia friction welding joints is of great significance to improving the performance and reliability of hot-end components of aero-engines.

[0003] The literature "Effect of heat treatment process on the microstructure and microhardness of inertia friction welding of FGH96 alloy, Zhang Chunbo, Liang Wu, Zhou Jun, et al., Journal of Welding, 2023, 44(8): 57-62" reported the effect of aging heat treatment on the microstructure and microhardness of inertia friction welding joints of FGH96 alloy. The study found that the content and morphology of the secondary γ′ phase in the weld area after aging treatment were similar to those in the weld state, and the secondary γ′ phase in the center of the weld was completely dissolved; from the center of the weld along the axis, the content of the secondary γ′ phase gradually increased and then tended to be stable; due to the small amount of precipitation of the tertiary γ′ phase, the overall microhardness of the weld area and the thermally affected zone was significantly improved. The secondary γ′ phase can improve the comprehensive performance of the joint through precipitation strengthening and dislocation interaction, but in the prior art, after post-weld aging treatment, the content and distribution of the secondary γ′ phase did not change significantly, especially no obvious strengthening phase precipitation in the weld core area, so the strengthening effect on the joint performance needs to be enhanced.

[0004] The literature "Effect of Aging Treatment on Room Temperature Tensile Behavior of Powder Superalloy Inertia Friction Welded Joints, Zhou Xiaoming, Feng Yefei, Zeng Weihu, et al., Powder Metallurgy Technology, 2021, 39(1): 41-48" reported that the room temperature tensile strength of the weld zone and heat-affected zone after post-weld aging treatment was significantly improved compared with the welded specimen, but the fracture position of the tensile specimen after aging treatment was still located in the weld zone and showed brittle fracture characteristics. The above technology improves the joint strength through post-weld aging treatment, but the tensile fracture position of the joint is still located in the weld, affecting the service behavior of the joint. This is mainly because the post-weld aging treatment has no significant effect on the overall grain change of the joint. The radial inhomogeneity of the joint will induce the formation of a weak performance zone in the joint, resulting in inconsistent joint deformation, which can easily cause joint fracture failure, limiting its application in key components in the equipment manufacturing field.

[0005] It can be seen that in order to solve the bottleneck problems in the above-mentioned existing technologies, it is urgent to develop a simple and efficient process method to simultaneously promote the improvement of joint strength and radial uniformity, and achieve precise control of the microstructure and properties of inertia friction welded joints of superalloys. Summary of the Invention

[0006] In view of the common problems such as poor joint strength and uneven distribution of radial microstructure and properties in the existing technologies mentioned above, the present invention provides a method for improving the strength and radial uniformity of inertia friction welded joints of superalloys. Through the synergistic effect of post-weld solution treatment + two-step aging treatment, significant improvement in the strength and radial uniformity of welded joints is achieved.

[0007] The present invention adopts the following technical solutions:

[0008] A method for improving the strength and radial uniformity of inertia friction welded joints of superalloys, comprising the following steps:

[0009] Step 1: Gradually grind the surface to be welded of the rotating workpiece of superalloy, immerse the ground workpiece in an anhydrous ethanol solution for ultrasonic cleaning, and then dry it for standby;

[0010] Step 2: Clamp the workpieces to be welded on the rotating end and the sliding end of the machine tool respectively, and correct and adjust the concentricity of the workpieces; weld the workpieces to be welded, and the welding interface realizes metallurgical bonding through processes such as plastic deformation, recrystallization, and diffusion;

[0011] Step 3: Remove the flash on the inner and outer sides of the inertia friction welded joint of the rotating workpiece of superalloy to meet the process design standard;

[0012] Step 4: Conduct solution strengthening treatment on the welded joint: heat it to the solution temperature at a constant heating rate, hold for a certain time, and then cool naturally to room temperature;

[0013] Step 5: Conduct two-step aging strengthening treatment on the joint after solution strengthening: heat it to the first-step aging temperature at a constant heating rate, hold, then cool to the second-step aging temperature at a constant cooling rate, hold, and then cool naturally to room temperature.

[0014] As a supplement to the technical solution of the present invention, in Step 4, the process parameters of the solution strengthening treatment are: the solution temperature is 1020 - 1140 °C, the preferred value is 1080 °C, the solution holding time is 1 - 6 h, and the heating rate is 300 - 600 °C / h.

[0015] As a supplement to the technical solution of the present invention, in step 5, the process parameters of the double-stage aging strengthening treatment are as follows: the first-stage aging temperature is 700-800°C, preferably 760°C, and the first-stage aging holding time is 4-10 h; the second-stage aging temperature is 600-700°C, preferably 650°C, and the second-stage aging holding time is 1-6 h; the heating rate is 300-600°C / h, and the cooling rate is 10-200°C / h.

[0016] As a supplement to the technical solution of the present invention, the superalloy is a nickel-based superalloy; the nickel-based superalloy includes FGH98, FGH101, GH4065, GH4169, etc.

[0017] As a supplement to the technical solution of the present invention, in step 2, the process parameters of the inertia friction welding are as follows: the initial rotation speed is 300-1000 r / min, the welding pressure is 20-500 MPa, and the moment of inertia is 30-500 kg·m 2 .

[0018] As a supplement to the technical solution of the present invention, in step 3, the surface roughness Ra after processing is <1.6 μm.

[0019] As a supplement to the technical solution of the present invention, in step 1, the rotating superalloy workpiece is a tubular structure with an inner diameter of 20-100 mm and an outer diameter of 30-180 mm.

[0020] Compared with the prior art, the present invention has the following advantages:

[0021] 1) The high-quality connection of the rotating superalloy workpiece is realized by using the inertia friction welding technology, breaking through the problems of defects such as pores, cracks and inclusions easily formed in the traditional fusion welding process, improving the interface bonding state, and providing a new solution for the precision connection of superalloy components.

[0022] 2) The solution strengthening treatment effectively promotes the uniform distribution of alloy strengthening elements such as Cr and Mo, eliminates element segregation, and realizes the fine control of the grain size of the joint, thereby improving the radial non-uniformity of the joint. In addition, almost all the primary γ' phases are dissolved after the solution treatment. During the subsequent cooling process, the secondary γ' phases are evenly precipitated and distributed in the γ matrix, significantly improving the joint strength.

[0023] 3) Through the step-by-step aging strengthening treatment, the precipitation of the tertiary γ' phases is promoted during the cooling process. By using the pinning effect of the precipitated phases, the abnormal growth trend of grains in the high-temperature environment is effectively inhibited. Compared with single-stage aging, step-by-step aging can increase the precipitation density of the tertiary γ' phases and control the morphology of the precipitated phases, further improving the joint strength and radial uniformity. Description of the Drawings

[0024] Figure 1 The solution aging treatment process curve adopted in the embodiment of the present invention;

[0025] Figure 2 The grain distribution of the joint in the as-welded state in the embodiment of the present invention;

[0026] Figure 3 The grain distribution of the joint in the heat-treated state in the embodiment of the present invention;

[0027] Figure 4 The distribution and morphology of strengthening phases in different regions of the joint in the embodiment of the present invention: (a) as-welded state; (b) heat-treated state;

[0028] Figure 5 The tensile strength of the joint in the as-welded state and heat-treated state in the embodiment of the present invention;

[0029] Figure 6 The tensile fracture positions of the joint in the as-welded state and heat-treated state in the embodiment of the present invention: (a) as-welded state; (b) heat-treated state. Detailed implementation manners

[0030] For the convenience of understanding the technical solution, the present invention provides the following embodiments. Specifically, the FGH96 superalloy is selected for welding, but it is not limited to the superalloys of the above grades. The method disclosed in the present invention is also applicable to the regulation of the strength and radial uniformity of inertia friction welded joints of other grades of superalloys.

[0031] Embodiment 1:

[0032] Step 1: Before welding, the surface to be welded of the rotating superalloy workpiece with an inner diameter of 28 mm and an outer diameter of 62 mm is gradually polished with sandpapers of different particle sizes, and the polished workpiece is immersed in an anhydrous ethanol solution for ultrasonic cleaning for 15 min, and then dried with a hair dryer and kept for use.

[0033] Step 2: The workpieces to be welded are respectively clamped on the rotating end and the sliding end of the machine tool, and at the same time, it is ensured that their axes coincide, and the concentricity of the workpieces is corrected and adjusted. Set the inertia friction welding process parameters: the initial rotational speed is 645 r / min, the welding pressure is 320 MPa, and the moment of inertia is 388 kg·m 2 , after the flywheel drives the workpiece at the rotating end to reach the initial rotational speed, the driving motor of the main shaft is separated from the rotating end, and it starts to enter the free parking state. At the same time, the workpiece at the sliding end is driven by a hydraulic servo to move towards the rotating end. Under the action of the axial pressure, the surfaces to be welded rub against each other to generate heat until they reach the high-temperature plastic state. The high-temperature plastic metal at the welding interface is extruded from the interface to form a flash. Under the continuous action of the friction torque, the rotational speed of the workpiece at the rotating end gradually decreases until it stops. After maintaining the pressure for 4 s, the sliding end is withdrawn. The friction interface realizes metallurgical bonding through processes such as plastic deformation, recrystallization, and diffusion, and the welding process ends.

[0034] Step 3: Adopt the turning process, and utilize the rotational movement of the welded part and the linear movement of the tool to remove the flash on the inner and outer sides of the inertia friction welded joint of the superalloy rotating workpiece, so that the surface roughness Ra of the machined surface is less than 1.6 μm.

[0035] Step 4: Perform solution strengthening treatment on the welded joint: Heat it to 1080 °C at a heating rate of 500 °C / h and hold for 2 h, and then cool it naturally to room temperature.

[0036] Step 5: Heat the solution-strengthened joint to the first-stage aging temperature of 760 °C at a heating rate of 500 °C / h, hold for 6 h, then cool it to the second-stage aging temperature of 650 °C at a rate of 55 °C / h, hold for 1 h, and then cool it naturally to room temperature.

[0037] Step 6: Conduct microstructure analysis and mechanical property testing on the welded joint. As Figure 3 shown, it can be found that the overall grains show an increasing trend after solution aging treatment. The grains in the weld nugget zone are relatively uniform along the radial direction. Equiaxed grains are generated by dynamic recrystallization in the thermo-mechanically affected zones on both sides of the pipe wall, thus improving the radial non-uniformity of the grains in this area. Figure 4 In (b) is the distribution and morphology of the strengthening phases in different regions of the joint in the heat-treated state. Secondary and tertiary γ′ phases gradually precipitate during the cooling stage, and the distribution of the strengthening phases in different regions of the joint is relatively uniform. The morphology of the strengthening phases in the weld nugget zone and the thermo-mechanically affected zone is mainly spherical, while the morphology of the strengthening phases in the base material is mainly cubic. As Figure 5 shown, the radial distribution of the tensile strength of the joint at room temperature is relatively uniform after solution aging treatment, and the maximum difference is only 4.4 MPa. The tensile strength is the highest at the center of the pipe wall, with a maximum value of 1520.3 MPa. The tensile fracture position is mainly concentrated in the base material region, as shown in Figure 6 (b) in.

[0038] Example 2:

[0039] Step 1: Before welding, use sandpapers with different grits to gradually polish the surface to be welded of the superalloy rotating workpiece with an inner diameter of 28 mm and an outer diameter of 62 mm. Immerse the polished workpiece in an anhydrous ethanol solution for ultrasonic cleaning for 15 min, and then dry the surface with a hair dryer and keep it for use.

[0040] Step 2: Clamp the workpieces to be welded on the rotating end and the sliding end of the machine tool respectively, and at the same time ensure that their axes coincide, and correct and adjust the concentricity of the workpieces. Set the inertia friction welding process parameters, with an initial rotational speed of 645 r / min, a welding pressure of 320 MPa, and a moment of inertia of 388 kg·m 2, after the flywheel drives the rotating-end workpiece to reach the initial rotational speed, the driving motor of the main shaft separates from the rotating end and starts to enter the free-stop state. At the same time, the sliding-end workpiece is driven by a hydraulic servo to move towards the rotating end. Under the action of the axial pressure, the surfaces to be welded rub against each other to generate heat until they reach the high-temperature plastic state. The high-temperature plastic metal at the welding interface is extruded from the interface to form flash. Under the continuous action of the frictional torque, the rotational speed of the rotating-end workpiece gradually decreases until it stops. After maintaining the pressure for 4 s, the sliding end is withdrawn. The frictional interface undergoes processes such as plastic deformation, recrystallization, and diffusion to achieve metallurgical bonding, and the welding process ends.

[0041] Step 3: Adopt a turning machining process to remove the flash on the inner and outer sides of the inertia friction welding joint of the superalloy rotating component by using the rotational movement of the welded part and the linear movement of the tool, so that the surface roughness Ra of the machined surface is <1.6 μm.

[0042] Step 4: Perform solution strengthening treatment on the welded joint. Heat it to 1020 °C at a heating rate of 500 °C / h and hold for 2 h, and then cool it naturally to room temperature.

[0043] Step 5: Heat the joint after solution strengthening to the first-stage aging temperature of 700 °C at a heating rate of 500 °C / h, hold for 6 h, then cool it to the second-stage aging temperature of 600 °C at a rate of 55 °C / h, hold for 1 h, and then cool it naturally to room temperature.

[0044] Step 6: Conduct microstructure analysis and mechanical property testing on the welded joint. The obtained experimental laws are roughly the same as those in Example 1. The difference is that at room temperature, the maximum difference in the radial tensile strength of the joint is 8.1 MPa, and the maximum value of the tensile strength is 1514.3 MPa.

[0045] Example 3:

[0046] Step 1: Before welding, use sandpapers with different grit sizes to gradually polish the surfaces to be welded of the superalloy rotating component with an inner diameter of 28 mm and an outer diameter of 62 mm. Immerse the polished workpiece in an anhydrous ethanol solution for ultrasonic cleaning for 15 min, and then dry the surface with a hair dryer and keep it for use.

[0047] Step 2: Clamp the workpieces to be welded on the rotating end and the sliding end of the machine tool respectively, and at the same time ensure that their axes coincide, and correct and adjust the concentricity of the workpieces. Set the inertia friction welding process parameters, the initial rotational speed is 645 r / min, the welding pressure is 320 MPa, and the moment of inertia is 388 kg·m 2, after the flywheel drives the rotating end workpiece to reach the initial rotational speed, the driving motor of the main shaft is separated from the rotating end, and it starts to enter the free parking state. At the same time, the sliding end workpiece is driven by a hydraulic servo to move towards the rotating end. Under the action of the axial pressure, the surfaces to be welded rub against each other to generate heat until they reach the high-temperature plastic state. The high-temperature plastic metal at the welding interface is extruded from the interface to form a flash. Under the continuous action of the frictional torque, the rotational speed of the rotating end workpiece gradually decreases until it stops. After maintaining the pressure for 4 s, the sliding end is withdrawn. The friction interface undergoes processes such as plastic deformation, recrystallization, and diffusion to achieve metallurgical bonding, and the welding process ends.

[0048] Step 3: Adopt a turning processing technology to remove the flash on the inner and outer sides of the inertia friction welded joint of the superalloy rotating component by using the rotational movement of the welded part and the linear movement of the tool, so that the surface roughness Ra of the processed surface is <1.6 μm.

[0049] Step 4: Perform solution strengthening treatment on the welded joint. Heat it to 1140 °C at a heating rate of 500 °C / h and hold for 2 h, and then cool it naturally to room temperature.

[0050] Step 5: Heat the joint after solution strengthening to the first-stage aging temperature of 800 °C at a heating rate of 500 °C / h, hold for 6 h, then cool it to the second-stage aging temperature of 700 °C at a rate of 55 °C / h, hold for 1 h, and then cool it naturally to room temperature.

[0051] Step 6: Conduct microstructure analysis and mechanical property testing on the welded joint. The obtained experimental laws are roughly the same as those in Example 1. The difference is that the maximum difference in the radial tensile strength of the joint at room temperature is 10.2 MPa, and the maximum value of the tensile strength is 1510.7 MPa.

[0052] Comparative Example 1:

[0053] Step 1: Before welding, use sandpapers with different grits to gradually polish the surfaces to be welded of the superalloy rotating workpiece with an inner diameter of 28 mm and an outer diameter of 62 mm. Immerse the polished workpiece in an anhydrous ethanol solution for ultrasonic cleaning for 15 min, and then dry the surface with a hair dryer and keep it for use.

[0054] Step 2: Clamp the workpieces to be welded on the rotating end and the sliding end of the machine tool respectively, and ensure that their axes coincide, and correct and adjust the concentricity of the workpieces. Set the inertia friction welding process parameters: the initial rotational speed is 645 r / min, the welding pressure is 320 MPa, and the moment of inertia is 388 kg·m 2, after the flywheel drives the rotating-end workpiece to reach the initial rotational speed, the driving motor of the main shaft is separated from the rotating end, and it starts to enter the free parking state. At the same time, the sliding-end workpiece is driven by a hydraulic servo to move towards the rotating end. Under the action of the axial pressure, the surfaces to be welded rub against each other to generate heat until they reach the high-temperature plastic state. The high-temperature plastic metal at the welding interface is extruded from the interface to form flash. Under the continuous action of the frictional torque, the rotational speed of the rotating-end workpiece gradually decreases until it stops. After holding the pressure for 4 s, the sliding end is withdrawn. The frictional interface undergoes processes such as plastic deformation, recrystallization, and diffusion to achieve metallurgical bonding, and the welding process ends.

[0055] Step 3: Adopt the turning processing technology to remove the flash on the inner and outer sides of the inertia friction welding joint of the superalloy rotating workpiece by using the rotational movement of the welded part and the linear movement of the tool, so that the surface roughness Ra of the machined surface is <1.6 μm.

[0056] Step 4: Conduct a microstructure analysis and mechanical property test on the welded joint. As Figure 2 shown, due to dynamic recrystallization, fine equiaxed grains are generated in the weld nugget zone. From the center of the pipe wall to both sides, the width and average grain size of the weld nugget zone increase. In addition, obvious grain refinement phenomenon exists in the thermal-mechanical affected zones on both sides of the pipe wall. Figure 4 In (a), it is the distribution and morphology of the strengthening phases in different regions of the joint in the as-welded state. The strengthening phases in the weld nugget zone are almost completely dissolved. As the distance from the weld nugget zone increases, the secondary γ′ phases gradually increase and tend to be stable. Due to the increase in local strain energy, the morphology of the secondary γ′ phases gradually changes from spherical to cubic. As Figure 5 shown, at room temperature, there is a large gradient in the tensile strength of the joint along the radial direction, and the maximum difference is 41.2 MPa. The tensile strength is the highest at the center of the pipe wall, with a maximum value of 1491.98 MPa. The tensile fracture position is mainly concentrated in the heat-affected zone, as shown in Figure 6 (a).

[0057] By comparing Example 1 with Comparative Example 1, it can be seen that by adopting the solution aging heat treatment method proposed by the present invention, the strength and radial uniformity of the joint can be significantly improved. Specifically, the grains in the heat-treated state generally show an increasing trend and the grain distribution along the radial direction is more uniform. The cooling stage promotes the precipitation of secondary and tertiary γ′ phases, and the content of the strengthening phases in different regions of the joint is significantly increased and the distribution is more uniform. In addition, after heat treatment, the tensile strength of the joint at room temperature is significantly improved and the tensile strength gradient along the radial direction is significantly reduced. The tensile fracture position in the as-welded state is concentrated in the weld nugget zone, while the tensile fracture position in the heat-treated state is concentrated in the base metal region. Through the synergistic strengthening effect of solution + double-stage aging proposed by the present invention, the strength and radial uniformity of the inertia friction welding joint of superalloy can be significantly improved.

[0058] Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present invention and do not constitute any form of limitation to the present invention. Those skilled in the art should fully understand that it is entirely feasible to modify the technical solutions described in the foregoing embodiments or perform equivalent replacements on any part or all of the technical features therein. As long as these modifications or replacements do not deviate from the protection scope determined by the claims of the present invention, they should be regarded as reasonable extensions of the present invention.

Claims

1. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint, characterized in that: The following steps are involved: Step 1: Grind the surface of the high-temperature alloy rotating workpiece to be welded step by step, immerse the polished workpiece in anhydrous ethanol solution for ultrasonic cleaning, and then dry it for standby use; Step 2: Clamp the workpiece to be welded at the rotating end and sliding end of the machine tool respectively, and calibrate and adjust the concentricity of the workpiece; weld the workpiece to be welded; Step 3: Remove the flash inside and outside the inertia friction welding joint of the high-temperature alloy rotating workpiece to meet the process design standards; Step 4: The welded joint is heated to the solution temperature at a constant heating rate and then kept warm, and then naturally cooled to room temperature; wherein the solution temperature is 1020-1140 °C, the solution holding time is 1-6 h, and the heating rate is 300-600 °C / h; Step 5: Heat the solution-strengthened joint to the first-stage aging temperature at a constant heating rate, cool it to the second-stage aging temperature at a constant cooling rate after insulation, and naturally cool it to room temperature after insulation; the first-stage aging temperature is 700~760 ℃, the first-stage aging insulation time is 4~10 h, and the heating rate is 300~600 ℃ / h; the second-stage aging temperature is 600~650 ℃, the second-stage aging insulation time is 1~6 h; the cooling rate is 10~200 ℃ / h.

2. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint according to claim 1, characterized in that: The solution temperature is 1080°C.

3. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint according to claim 1 or 2, characterized in that: The first stage aging temperature is 760°C, and the second stage aging temperature is 650°C.

4. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint according to claim 1 or 2, characterized in that: The high temperature alloy is a nickel-based high temperature alloy; the nickel-based high temperature alloy includes FGH98, FGH101, GH4065 or GH4169.

5. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint according to claim 1 or 2, characterized in that: In step 2, the inertia friction welding process parameters are: initial speed of 300-1000 r / min, welding pressure of 20-500 MPa, moment of inertia of 30-500 kg•m 2 .

6. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint according to claim 5, characterized in that: In the step 3, the surface roughness Ra after processing is less than 1.6 μm.

7. A method for improving the strength and radial uniformity of a high-temperature alloy inertia friction welding joint according to claim 6, characterized in that: The high-temperature alloy rotating workpiece is a tubular structure with an inner diameter of 20-100 mm and an outer diameter of 30-180 mm.

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