High-strength titanium alloy weldment and micro-deformation diffusion welding method thereof based on surface gradient nano activation

Abstract

The invention relates to the technical field of solid-phase welding and connection of metal materials, in particular to a high-strength titanium alloy weldment and a micro-deformation diffusion welding method based on surface gradient nano activation of the high-strength titanium alloy weldment. The surface gradient layer sequentially comprises a nanocrystalline layer, an ultra-fine crystal layer and a micron crystal layer from outside to inside, the thickness of the nanocrystalline layer is 5-10 micrometers, the grain size of the nanocrystalline layer is smaller than 100 nm, the micron crystal layer makes contact with an original structure of base metal, and a unique layered gradient recrystallization microstructure is formed in situ at a joint of a welding workpiece obtained through the method. The structure synergistically improves the strength and plasticity of the joint, and the comprehensive performance of the joint can reach the base metal level.

Description

Technical Field

[0001] This invention belongs to the field of solid-state welding and joining technology of metallic materials, specifically relating to a high-strength titanium alloy weldment and its micro-deformation diffusion welding method based on surface gradient nano-activation. Background Technology

[0002] Titanium alloys, as one of the most strategically valuable lightweight and high-strength materials, directly reflect a nation's high-end equipment manufacturing capabilities. Due to their excellent specific strength and stiffness, corrosion resistance, and damage tolerance, they have become key structural materials in high-end manufacturing fields such as aviation, aerospace, and shipbuilding. For example, TC4 titanium alloy (Ti-6Al-4V) has become the preferred material for key components such as hollow blades for aero-engines, layered injectors for aerospace engines, and microchannel heat exchangers for marine and shipborne applications. However, these components typically have complex internal cavity or microchannel structures to meet stringent requirements such as lightweight construction, high overall performance, and high service efficiency. Traditional hot working and subtractive manufacturing technologies struggle to simultaneously address the precision shaping and high-performance demands of complex internal cavity structures, necessitating the development of new manufacturing technologies that combine high precision and high reliability. Diffusion welding additive manufacturing technology, with its unique advantages of "layered discretization-solid-phase integration," provides a new manufacturing paradigm for the intensive and near-net-shape forming of complex internal cavities, microchannels, and multilayer composite structures.

[0003] Currently, researchers mainly employ electric field-assisted diffusion welding, surface hydrogen treatment, and surface mechanical grinding nano-sizing methods to reduce process parameters such as temperature and pressure in titanium alloy diffusion welding and promote interfacial bonding. Under current assistance, technologies such as spark plasma sintering can achieve low-temperature rapid diffusion welding of titanium alloys at relatively low welding temperatures. The current can generate localized high temperatures on the surface to be welded and promote interfacial adhesion. This process characteristic of localized high temperatures at the interface while the substrate of the sample to be welded remains effective in reducing overall creep deformation of the joint while achieving interfacial bonding. However, it faces technical challenges such as limited suitable surface shapes and areas, difficulties in current distribution and welding quality control, and is still difficult to apply to large and complex surface components. Surface hydrogen treatment can reduce the welding temperature of materials such as titanium alloys, reduce macroscopic plastic deformation and creep of the welded sample, and facilitate interfacial bonding under micro-deformation conditions. Hydrogen treatment provides a useful approach and experience for the chemical activation of diffusion welding surfaces, which can effectively improve the process difficulty of diffusion welding of materials such as titanium alloys. However, it also has problems such as hydrogen embrittlement risk, complex process and high cost. Surface mechanical grinding can promote the nano-sizing of the surface to be welded, reduce the activation energy required for interfacial atomic diffusion, enhance interfacial atomic diffusion at low temperature, and improve the interfacial welding rate and joint strength. However, this method also has problems such as long grinding time, low efficiency and limited applicable surface shape and size.

[0004] In summary, there is an urgent need for a process that is safe and efficient to operate, applicable to a wide range of shapes and sizes of surfaces to be welded, and can simultaneously improve the strength and plasticity of the joint, so as to achieve high-performance diffusion welding of titanium alloys under micro-deformation conditions. Summary of the Invention

[0005] The present invention aims to address the problem of how to provide a method for diffusion bonding of titanium alloys that can significantly reduce diffusion welding temperature and pressure, avoid macroscopic deformation of the workpiece, and simultaneously improve the joint strength and plasticity, as well as the high-performance joints made therefrom.

[0006] To achieve the above objectives, the first aspect of the present invention provides a micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation, characterized by comprising the following steps:

[0007] S1. Grind the workpiece surface to remove surface contaminants and oxide scale, and make the surface roughness lower than Ra0.8μm; perform ultrasonic cleaning on the workpiece surface to remove surface oil; dry the surface with cold air at 20-25℃ and protect it with non-woven fabric to obtain a smooth surface to be activated.

[0008] S2. Process the surface to be activated to form a surface gradient layer on the workpiece surface. The surface gradient layer consists of a nanocrystalline layer, an ultrafine crystalline layer and a microcrystalline layer from the outside to the inside. The thickness of the nanocrystalline layer is 5-10 μm and the grain size of the nanocrystalline layer is less than 100 nm. The microcrystalline layer is in contact with the original structure of the parent material.

[0009] The surface of the workpiece obtained by S3 finishing and S2 polishing is made so that the surface roughness Ra is less than 0.4μm. The surface to be welded is pickled with Keller's reagent for 30-60s to remove the surface oxide film. The surface is then rinsed with deionized water to remove the residual Keller's reagent. The surface to be welded is then ultrasonically cleaned in acetone and / or anhydrous ethanol organic solvent. Finally, the surface is dried with cold air at 20-25℃ to obtain a smooth surface to be welded.

[0010] S4. Assemble the smooth surfaces to be welded obtained in S3. After assembly, close the diffusion welding furnace door, perform vacuuming, welding, and cooling to obtain a workpiece with micro-deformation diffusion welded connection.

[0011] The second aspect of the present invention provides a high-strength titanium alloy weldment prepared by a micro-deformation diffusion welding method based on surface gradient nano-activation of the above-mentioned high-strength titanium alloy weldment.

[0012] Beneficial effects:

[0013] (1) The diffusion welding method provided by the present invention significantly reduces the energy consumption and equipment requirements of the process, avoids thermal damage and macroscopic deformation of the workpiece, and is particularly suitable for diffusion welding of precision components.

[0014] (2) The welded parts prepared by the diffusion welding method provided by the present invention improve the strength and plasticity of the joint, and their comprehensive performance can reach or even exceed that of the base material.

[0015] (3) The diffusion welding method provided by the present invention is characterized by high efficiency, convenient operation and wide applicability to the shape and area of ​​the workpiece to be welded, which further enhances its engineering application potential.

[0016] Instruction manual illustrations

[0017] Figure 1 The figures show the microstructure of the joint interface of the welded workpieces in Embodiment 1 and Comparative Example 1 of the present invention. In the figures, (a) shows the microstructure of the joint of the welded workpiece in Embodiment 1; and (b) shows the microstructure of the joint of the welded workpiece in Comparative Example 1. Detailed Implementation

[0018] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0019] Currently, diffusion welding additive manufacturing mainly faces two technical challenges. First, the requirements for forming precision are being upgraded. For fine structures such as microchannels and thin-walled plates, the micro-deformation conditions cannot be met after welding, and the axial deformation after welding cannot be strictly controlled within 1%, leading to structural instability or functional failure. Second, the performance requirements for joints are being improved. Under extreme service environments (such as high-frequency vibration and alternating loads), joints cannot simultaneously possess excellent comprehensive mechanical properties of high strength and plasticity.

[0020] In traditional diffusion welding processes, high temperature and high pressure are often used to eliminate interfacial porosity, promote interfacial recrystallization or grain boundary migration, thereby ensuring the quality of interfacial bonding. Traditional diffusion welding of titanium alloys requires high temperatures close to the β phase transformation point and large welding pressures. For example, diffusion welding of TC4 titanium alloys typically uses high temperatures of 850~950 ℃, and at the same time, large welding pressures are required, which can easily lead to problems such as workpiece deformation and instability, grain coarsening, and performance damage. In addition, high temperature and high pressure conditions place stringent requirements on equipment, resulting in low production efficiency and high costs. If a low temperature and low pressure process is used, although structural accuracy can be guaranteed and thermal damage can be reduced, problems such as interfacial porosity and weak, flat interfaces become prominent, resulting in insufficient mechanical properties of the joint. This leads to problems such as high welding scrap rate and poor service reliability in actual production. It can be seen that the existing diffusion welding technology faces a core process contradiction of "high precision - high performance" inversion. It is difficult to achieve good metallurgical bonding of diffusion weld interfaces under micro-deformation conditions, and the joint often becomes a brittle fracture source due to weak interfacial properties, which limits the application of diffusion welding technology in high-end manufacturing fields such as aerospace.

[0021] The inventors have discovered a method for diffusion bonding of titanium alloys that can significantly reduce diffusion welding temperature and pressure, avoid macroscopic deformation of the workpiece, and simultaneously improve joint strength and plasticity, as well as a high-performance joint and welding method made therefrom.

[0022] The first aspect of this invention provides a micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation, characterized by comprising the following steps:

[0023] S1. Grind the workpiece surface to remove surface contaminants and oxide scale, and make the surface roughness lower than Ra0.8 μm; perform ultrasonic cleaning on the workpiece surface to remove surface oil; dry the surface with cold air at 20-25 ℃ and protect it with non-woven fabric to obtain a smooth surface to be activated.

[0024] S2. Process the surface to be activated to form a surface gradient layer on the workpiece surface. The surface gradient layer consists of a nanocrystalline layer, an ultrafine crystalline layer and a microcrystalline layer from the outside to the inside. The thickness of the nanocrystalline layer is 5-10 μm and the grain size of the nanocrystalline layer is less than 100 nm. The microcrystalline layer is in contact with the original structure of the parent material.

[0025] The workpiece surface obtained by S3 finishing and S2 polishing has a surface roughness Ra of less than 0.4 μm. The surface to be welded is then pickled with Keller's reagent for 30-60 s to remove the surface oxide film. The surface is then rinsed with deionized water to remove the residual Keller's reagent. The surface to be welded is then ultrasonically cleaned in acetone and / or anhydrous ethanol organic solvent. Finally, the surface is dried with cold air at 20-25 ℃ to obtain a smooth surface to be welded.

[0026] S4. Assemble the smooth surfaces to be welded obtained in S3. After assembly, close the diffusion welding furnace door, perform vacuuming, welding, and cooling to obtain a workpiece with micro-deformation diffusion welded connection.

[0027] In this invention, the gradient nanostructure introduced by surface nanostructuring provides a high-density atomic diffusion short-circuit channel, significantly reducing the diffusion activation energy and enabling atoms to achieve long-range diffusion at low temperatures. On the other hand, the extremely high plastic rheological ability of the surface nanocrystalline layer allows the interface to achieve close contact and pore closure under low pressure.

[0028] The excess grain boundary energy and high deformation storage energy introduced by the surface gradient nano-activation treatment drive recrystallization in the interface region. The newly formed grain boundaries can easily cross and annihilate the original interface, completely eliminating crack sources such as interfacial micropores and weak, flat interfaces. Ultimately, a unique layered gradient recrystallized microstructure is formed in situ at the joint. This structure avoids stress and strain concentration through the coupling effect of "fine grain strengthening" and "coarse grain coordinated plasticity" and the gradient characteristics.

[0029] The specific nanocrystalline layer thickness and grain size of the nanocrystalline layer in this invention have abundant deformation energy storage, a large number of crystal defects such as grain boundaries and dislocations.

[0030] In this invention, activation can be achieved through intense plastic deformation techniques, such as high-pressure water jet impact, temperature-coordinated surface shot peening, and laser impact.

[0031] According to the present invention, in step S2, the thickness of the ultrafine crystal layer is 10-100 μm, and the grain size of the ultrafine crystal layer is 0.1-1.0 μm.

[0032] In this invention, the ultrafine crystalline layer mainly exhibits a highly plastic deformation structure.

[0033] According to the present invention, in step S2, the thickness of the micron-crystal layer is 10-200 μm, and the grain size of the micron-crystal layer is 1.0-10.0 μm.

[0034] According to the present invention, in step S3, the thickness removed by the finishing and polishing is less than 5 μm.

[0035] According to the present invention, in step S3, the ultrasonic cleaning time is 10-15 min.

[0036] According to the present invention, in step S3, the cleaned workpiece is stored under atmospheric conditions for no more than 8 hours.

[0037] According to the present invention, in step S4, the evacuation reduces the vacuum level of the vacuum chamber to 1.0 × 10⁻⁶. -3 ~9.0×10 -3 Pa.

[0038] According to the present invention, in step S4, the welding conditions include: heating the workpiece to be welded to the welding temperature at a heating rate of 10-20 °C / min, wherein the welding temperature is 0.4-0.6 T. m T m The melting point of the titanium alloy being welded should be such that the pressure at the weld interface does not exceed 0.1 R. p R p The value represents the yield strength of the titanium alloy being welded at the welding temperature, with a holding time of 30-90 minutes.

[0039] In this invention, specific welding conditions can suppress creep deformation and improve production efficiency.

[0040] At a specific welding temperature, through thermal activation, the highly active gradient nanolayer at the interface undergoes intense recovery, recrystallization, and grain boundary migration processes.

[0041] The specific welding temperature, pressure, and holding time work together to promote the healing of the pores at the interface. Relying on the genetic evolution of the gradient nanostructure, a new recrystallized structure with a layered gradient distribution of grain size is formed that runs through the original interface, thereby eliminating the original interface and achieving complete metallurgical bonding of the workpieces to be welded.

[0042] According to the present invention, in step S4, the cooling conditions include cooling to 20-30°C with the furnace.

[0043] The second aspect of the present invention provides a high-strength titanium alloy weldment prepared by a micro-deformation diffusion welding method based on surface gradient nano-activation of the above-mentioned high-strength titanium alloy weldment.

[0044] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. All other embodiments implemented by those skilled in the art based on the embodiments of the present invention without creative improvements are within the protection scope of the present invention.

[0045] Example 1

[0046] S1. Select a TC4 titanium alloy rod with a diameter of 40 mm as the base material for diffusion welding. First, use wire EDM to cut the base material into cylinders with a height of 30 mm. Select one end face of the cylinder as the diffusion welding surface. Then, use sandpaper grinding discs of different grits (240#, 400#, 800#, 1500#, and 2000# in sequence) to grind the diffusion welding surface to remove surface contaminants and oxide scale, and make the surface roughness Ra 0.1 μm. Then, ultrasonically clean the surface of the workpiece to be welded in anhydrous ethanol for 10 min to remove surface oil. Finally, use cold air at 25 ℃ to dry the surface and protect it with non-woven fabric to obtain a smooth surface to be activated.

[0047] S2. The clean titanium alloy surface to be welded prepared in S1 is activated by high-pressure water jet impact at a pressure of 1800 MPa. Under high pressure, a nanostructure layer with a continuous gradient of grain size is formed from the surface to the interior of the surface to be welded. The thickness of the nanocrystalline layer is 8 μm and the grain size of the nanocrystalline layer is less than 100 nm. The thickness of the ultrafine crystalline layer is 10 μm and the grain size of the ultrafine crystalline layer is 0.1-1.0 μm. The thickness of the micron crystalline layer is 15 μm and the grain size of the micron crystalline layer is 1.0-10.0 μm.

[0048] S3. To address the increased roughness (approximately Ra 1.0 μm) caused by high-pressure water jet impact nano-activation treatment, and the potential introduction of fine contaminants, the activated surface was again polished using 1500# and 2000# grit sandpaper to restore the surface roughness to Ra 0.1 μm. The polishing time was strictly controlled to not exceed 10 minutes, and the thickness removed was less than 5 μm to preserve the effective nano-activation layer. Measurements showed that the total thickness of the surface gradient layer after polishing was 30 μm, and the grain size of the nanocrystal layer was 50 nm. Next, the surface to be welded was acid-washed with Keller's reagent for 40 seconds to remove the surface oxide film. Then, the surface was rinsed with deionized water to remove any remaining Keller's reagent, and the workpiece surface was ultrasonically cleaned in anhydrous ethanol for approximately 10 minutes. Finally, the surface was dried with cold air at 25 ℃ to obtain a smooth surface for welding. Subsequently, within 2 hours after cleaning, the workpiece should be assembled into the diffusion welding vacuum chamber.

[0049] S4. Welding Assembly and Micro-deformation Diffusion Welding Process Settings. The activated and cleaned surfaces to be welded are butt-assembled and placed in the vacuum chamber of the diffusion welding equipment. Graphite or ceramic clamps are used to assemble the workpieces, and slight pressure is applied to hold them in place. After assembly, the diffusion welding furnace door is closed, and the vacuum valve is opened to evacuate the chamber, reducing the vacuum level to 6 × 10⁻⁶. -3Pa. Simultaneously, the workpiece to be welded was heated to the welding temperature at a heating rate of 10 ℃ / min, and diffusion welding was performed at a diffusion welding temperature of 790 ℃, a welding pressure of 10 MPa, and a holding time of 40 min.

[0050] After the welding and heat preservation are completed, the workpiece is cooled to room temperature in the vacuum chamber. Then the vacuum chamber door is opened to obtain the welded workpiece A1.

[0051] Comparative Example 1

[0052] The diffusion welding method of Example 1 is different in that steps S2 and S3 are omitted, and the welded workpiece D1 is obtained.

[0053] The axial deformation of the joint of the welded workpiece in Example 1 and the joint of the welded workpiece in Comparative Example 1 were 0.68% and 0.65%, respectively, both meeting the requirement of micro-deformation of less than 1%, and the connection was achieved at a relatively low diffusion welding temperature of 790 ℃ (lower than the 850-950 ℃ used in conventional processes).

[0054] Instruction manual attached Figure 1 A comparison of the microstructure morphology of the joint interface is presented. It is evident that the joint obtained in Example 1 achieved a 100% interface weld rate, with fine recrystallized grains forming at the interface. The grain size gradient changed from the base material region to the interface, completely eliminating the original interface. In contrast, the joint in Comparative Example 1 had an interface weld rate of approximately 81%, still exhibiting significant unwelded or porous interfaces, thus reducing the quality of the interface bonding. Further tensile mechanical property tests on the two sets of joints revealed that the activated joint in Example 1 had a tensile strength and elongation at break of 971 MPa and 18.5%, respectively, while the joint in Comparative Example 1 had a tensile strength and elongation at break of 942 MPa and 2.6%, respectively, representing a strength increase of 29 MPa and a significant improvement in plasticity, reaching 7.1 times that of the joint in Comparative Example 1. In summary, the micro-deformation diffusion welding method provided by this invention significantly promotes high-quality interface bonding of titanium alloys under low-temperature micro-deformation constraint conditions, achieving a synergistic improvement in the strength and plasticity of the diffusion welded joint.

[0055] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation, characterized in that, Includes the following steps: S1. Grind the workpiece surface to remove surface contaminants and oxide scale, and reduce the surface roughness to below Ra0.8μm; perform ultrasonic cleaning on the workpiece surface to remove surface oil. The surface is dried with cold air at 20-25℃ and protected with non-woven fabric to obtain a smooth surface to be activated; S2. Process the surface to be activated to form a surface gradient layer on the workpiece surface. The surface gradient layer consists of a nanocrystalline layer, an ultrafine crystalline layer and a microcrystalline layer from the outside to the inside. The thickness of the nanocrystalline layer is 5-10 μm and the grain size of the nanocrystalline layer is less than 100 nm. The microcrystalline layer is in contact with the original structure of the parent material. The surface of the workpiece obtained by S3 finishing and S2 polishing is made so that the surface roughness Ra is less than 0.4μm. The surface to be welded is pickled with Keller's reagent for 30-60s to remove the surface oxide film. The surface is then rinsed with deionized water to remove the residual Keller's reagent. The surface to be welded is then ultrasonically cleaned in acetone and / or anhydrous ethanol organic solvent. Finally, the surface is dried with cold air at 20-25℃ to obtain a smooth surface to be welded. S4. Assemble the smooth surfaces to be welded obtained in S3. After assembly, close the diffusion welding furnace door, perform vacuuming, welding, and cooling to obtain a workpiece with micro-deformation diffusion welded connection.

2. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S2, the thickness of the ultrafine crystal layer is 10-100 μm, and the grain size of the ultrafine crystal layer is 0.1-1.0 μm.

3. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S2, the thickness of the micron-sized crystal layer is 10-200 μm, and the grain size of the micron-sized crystal layer is 1.0-10.0 μm.

4. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S3, the thickness removed by the finishing and polishing is less than 5 μm.

5. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S3, the ultrasonic cleaning time is 10-15 minutes.

6. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S3, the cleaned workpiece is stored under atmospheric conditions for no more than 8 hours.

7. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S4, the evacuation reduces the vacuum level of the vacuum chamber to 1.0 × 10⁻⁶. -3 ~9.0×10 - 3 Pa.

8. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S4, the welding conditions include: heating the workpiece to be welded to the welding temperature at a heating rate of 10-20℃ / min, where the welding temperature is 0.4-0.6T. m T m The melting point of the titanium alloy being welded should be such that the pressure at the weld interface does not exceed 0.1R. p R p The value represents the yield strength of the titanium alloy being welded at the welding temperature, with a holding time of 30-90 minutes.

9. The micro-deformation diffusion welding method for high-strength titanium alloy weldments based on surface gradient nano-activation according to claim 1, characterized in that, In step S4, the cooling conditions include cooling the furnace to 20-30°C.

10. The high-strength titanium alloy weldment obtained by the micro-deformation diffusion welding method based on surface gradient nano-activation as described in any one of claims 1-9.

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