Method for improving the performance of a metal vacuum hot compression joint by surface nanocrystallization

Abstract

The application discloses a method for improving the performance of a metal vacuum hot compression connecting joint by surface self-nanocrystallization and relates to the technical field of metal hot pressing. The method comprises the following steps: machining a homogeneous CoCrFeMnNi high-entropy alloy into a round rod sample; grinding the connecting end contact surface of the round rod sample by using sandpaper; performing surface self-nanocrystallization treatment on the contact surface by using a high-energy shot blasting technology; cleaning the surface of the sample after the shot blasting treatment by using an organic solvent; firstly, welding a thermocouple at the center of the butt joint metal component and close to the connecting interface, then placing the round rod sample after the surface cleaning on a thermal simulation machine to make the contact surfaces completely align; under vacuum conditions, heating the sample to a set temperature and keeping the temperature for a period of time, then applying axial plastic deformation to the two contacting samples to connect them together, and cooling to room temperature, and the method is completed. Compared with a traditional vacuum hot compression process, the connecting temperature of the CoCrFeMnNi high-entropy alloy is reduced by 100 DEG C, and the compression strain is reduced by 50%.

Description

Technical Field

[0001] This invention relates to the field of metal hot pressing technology, and in particular to a method for improving the performance of metal vacuum hot compression joints by surface self-nano-machining. Background Technology

[0002] To expand the application of metallic materials in engineering practice, developing suitable joining technologies is crucial. Currently, various welding techniques have been used to join metallic materials, including tungsten inert gas welding (TIG), electron beam welding, and laser welding. Although these fusion welding processes can join similar or dissimilar metallic materials, the fusion zone and heat-affected zone in the joint are often accompanied by defects such as grain coarsening, residual stress, and elemental segregation, and are therefore considered weak points in mechanical properties.

[0003] To avoid the aforementioned problems, various solid-state joining technologies have become a research hotspot in recent years, such as ultrasonic welding, friction welding, and diffusion welding. However, these processes still have some shortcomings. For example, ultrasonic welding is difficult to achieve metallurgical bonding. Although friction welding has been shown to achieve a strong connection through the dynamic recrystallization process in the joint area, the inhomogeneity of the joint's microstructure weakens the overall mechanical properties of the joint. Diffusion joining is considered an ideal method for joining similar or dissimilar metal materials. However, obtaining defect-free diffusion joints requires high joining temperatures and long joining times, resulting in low welding efficiency.

[0004] Vacuum thermocompression joining offers a novel approach for achieving efficient and high-quality joining of metallic materials. It promotes fusion and atomic diffusion at the interface by inducing significant plastic deformation in the interface region, ultimately achieving a metallurgical bond. Therefore, compared with other solid-state joining technologies, vacuum thermocompression joining demonstrates irreplaceable advantages and broad applicability. Currently, this method has been successfully applied to the manufacture of engineering components such as nickel-based alloy turbine disks and large stainless steel nuclear power plant support rings.

[0005] The connection quality of vacuum heat compression joints is closely related to the evolution of the interface microstructure. However, conventional vacuum heat compression joints are prone to interface defects, resulting in insufficient connection strength. Furthermore, conventional vacuum heat compression processes typically require high connection temperatures and large deformations, leading to significant energy waste.

[0006] Therefore, those skilled in the art are dedicated to developing a new technology to optimize the metal vacuum thermal compression joining process. Summary of the Invention

[0007] In view of the above-mentioned deficiencies of the prior art, the technical problem to be solved by the present invention is a new technology that optimizes the metal vacuum thermal compression connection process.

[0008] To achieve the above objectives, the present invention provides a method for improving the performance of metal vacuum thermocompression joints through surface self-nano-machining, comprising the following steps:

[0009] Step 1: Machining the homogeneous CoCrFeMnNi high-entropy alloy into a round bar-shaped sample;

[0010] Step 2: Use sandpaper to grind the contact surface of the connecting end of the cylindrical sample to remove oxides, oil stains and other impurities on the contact surface and obtain a smooth surface.

[0011] Step 3: The sample with the contact surface ground flat is subjected to surface self-nanoization treatment by high-energy shot peening technology.

[0012] Step 4: Clean the surface of the shot-peened sample with an organic solvent;

[0013] Step 5: First, weld the thermocouple to the center of the mating metal components and close to the connection interface. Then, place the cleaned cylindrical sample in the center on the thermal simulator to make the contact surfaces completely aligned.

[0014] Step 6: Heat the sample to the set temperature under vacuum conditions and hold it for a period of time. After eliminating the temperature gradient, apply axial plastic deformation to the two contacting samples to connect them together. Then cool them to room temperature.

[0015] In a preferred embodiment of the present invention, in step 1, the homogeneous CoCrFeMnNi high-entropy alloy is prepared by the following method:

[0016] Step 11: Using alloying elements with a purity >99.9% as raw materials, prepare equiatomic CoCrFeMnNi high-entropy alloy ingots by vacuum induction melting.

[0017] Step 12: Homogenize the ingot under an inert atmosphere and high temperature, and then cool it to room temperature to obtain a homogenized CoCrFeMnNi high-entropy alloy.

[0018] Step 13: The homogenized CoCrFeMnNi high-entropy alloy is mechanically cut into cylinders of a set length, then hot-forged and recrystallized and annealed at a set temperature to obtain a homogenized CoCrFeMnNi high-entropy alloy.

[0019] Furthermore, in step 12, the inert atmosphere is argon, and the ingot homogenization temperature is 1100℃.

[0020] Furthermore, in step 13, the set temperature is 1000℃ and the annealing time is 2 hours.

[0021] In a preferred embodiment of the present invention, in step 2, the contact surface of the connecting end of the cylindrical sample is ground sequentially using sandpaper of 120#, 400#, 800#, and 2000#.

[0022] In another preferred embodiment of the present invention, in step 3, the conditions for high-energy shot peening are: shot peening pressure of 0.6 MPa, shot diameter of 0.3 mm, shot peening time of 30 s, and distance between the nozzle and the contact surface of the metal component of 5 cm.

[0023] In another preferred embodiment of the present invention, in step 6, at 1×10 -1 The sample was heated to 950°C at a rate of 10°C / s under a vacuum of Pa and held for 5 minutes to eliminate the temperature gradient.

[0024] In another preferred embodiment of the invention, in step 6, the two contacting samples are subjected to a 0.01s... -1 An axial plastic deformation with a strain rate of 0.4 is applied to connect them together.

[0025] In another preferred embodiment of the present invention, the percentage content of each atom in the homogeneous CoCrFeMnNi high-entropy alloy is as follows: Co 21.2%, Cr 19.7%, Fe 20.4%, Mn 19.1%, and Ni 19.6%.

[0026] The present invention also discloses the application of the method described above in metal vacuum thermocompression bonding.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention significantly reduces interfacial defects such as micropores and oxides in the joint through surface self-nanoification technology. At the same time, the joint also obtains a fine interfacial microstructure, forming a fine grain layer and a strain layer on the joint surface. By promoting the diffusion of interfacial atoms and the migration of interfacial grain boundaries, the interfacial connection quality is improved, and mechanical properties exceeding those of the base material are ultimately achieved, realizing the activation modification of the joint surface of the vacuum thermocompression joint.

[0029] This invention accelerates the closure of interfacial micropores and the decomposition of interfacial oxide particles during the bonding process through surface self-nano-treatment, thereby improving the rate of interface defect elimination. Furthermore, surface self-nano-treatment also increases the driving force for interfacial grain boundary migration, forming an interfacial grain boundary migration mechanism dominated by static recrystallized grain secondary growth, discontinuous dynamic recrystallization, and twin-induced interfacial grain boundary migration. This achieves rapid interfacial grain boundary migration and promotes the healing process of the bonding interface.

[0030] For CoCrFeMnNi high-entropy alloys, high-quality vacuum hot compression joints can be obtained at 950℃ and 0.4 strain by self-nano-processing the joining surface. Compared with the traditional vacuum hot compression process, the joining temperature is reduced by 100℃ and the compressive strain is reduced by 50%.

[0031] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0032] Figure 1 This is the phase diagram obtained by electron backscatter diffraction of the initial material microstructure in this invention;

[0033] Figure 2 This is a schematic diagram of the dimensions of the cylindrical sample in this invention;

[0034] Figure 3 This is a schematic diagram of the surface self-nanoization of the contact surface of the cylindrical sample using high-energy shot peening process in this invention.

[0035] Figure 4 These are scanning electron microscope images of the surface of the metal component after surface self-nanoification in this invention;

[0036] Figure 5 This is a schematic diagram of the vacuum thermal compression connection process in this invention and a diagram of the welding position of the thermocouple;

[0037] Figure 6 This is a schematic diagram of the interface microstructure of the self-nano-structured joint before vacuum thermocompression connection in this invention;

[0038] Figure 7 These are correlation diagrams obtained by electron backscatter diffraction of the interface microstructure after vacuum thermocompression connection of the surface self-nanotype joint in this invention, where (a) is the inverse pole diagram obtained by electron backscatter diffraction, (b) is the orientation difference diagram obtained by electron backscatter diffraction, and (c) is a schematic diagram of the connection mechanism. Detailed Implementation

[0039] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0040] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0041] Example 1: Preparation of homogeneous CoCrFeMnNi high-entropy alloy

[0042] The initial experimental material was an asphalt-state equiatomic CoCrFeMnNi high-entropy alloy. Using high-purity (>99.9%) alloying elements as raw materials, equiatomic CoCrFeMnNi high-entropy alloy ingots were prepared by vacuum induction melting. To improve its chemical homogeneity, the ingots were homogenized in an argon atmosphere at 1100℃ for 24 hours, and then cooled to room temperature in the furnace to obtain a homogenized CoCrFeMnNi high-entropy alloy. The homogenized CoCrFeMnNi high-entropy alloy was cut into Φ80mm×80mm cylinders, then hot-forged to a diameter of 40mm, and recrystallized and annealed at 1000℃ for 2 hours to obtain a uniaxial grain structure without subgrains, i.e., a homogeneous CoCrFeMnNi high-entropy alloy, whose microstructure is as follows: Figure 1 As shown, this alloy consists solely of a single-phase face-centered cubic solid solution. The percentages of each atomic component in this alloy are shown in Table 1 below.

[0043] Table 1. Chemical composition (atomic percentage) of homogeneous CoCrFeMnNi high-entropy alloy materials.

[0044]

[0045] Example 2: Surface self-nano-machining improves the performance of metal vacuum thermocompression joints

[0046] A method for improving the performance of a metal vacuum thermocompression joint through surface self-nano-machining includes the following steps:

[0047] The first step is to machine the homogeneous CoCrFeMnNi high-entropy alloy prepared in Example 1 into the following form: Figure 2 The cylindrical sample shown;

[0048] The second step is to grind the contact surface of the connecting end of the cylindrical sample with sandpaper of 120#, 400#, 800# and 2000# in turn to remove impurities such as oxides and oil stains on the contact surface and obtain a smooth surface.

[0049] The third step involves grinding the contact surface of the sample until it is smooth, then performing a surface self-nanoization treatment on the contact surface using high-energy shot peening technology (e.g., Figure 3 As shown in the figure, the shot peening pressure was 0.6 MPa, the shot diameter was 0.3 mm, the shot peening time was 30 s, and the distance between the nozzle and the contact surface of the metal component was 5 cm. The microstructure of the contact surface after shot peening is as follows. Figure 4 As shown;

[0050] The fourth step is to clean the surface of the shot-peened sample with an organic solvent to remove impurities such as oil and oxide film.

[0051] Fifth, weld the thermocouple to the center of the mating metal components, close to the connection interface, such as... Figure 5 As shown;

[0052] Step 6: Place the cleaned cylindrical sample in the center of the thermodynamic simulator, ensuring the contact surfaces are perfectly aligned. Figure 5 As shown;

[0053] Step 7, in 1×10 -1 The sample was heated to 950°C at a rate of 10°C / s under a vacuum of Pa, and held for 5 minutes to eliminate the temperature gradient. Subsequently, the two contacting samples were heated at a rate of 0.01s. -1 An axial plastic deformation with a strain rate of 0.4 is applied to connect them together.

[0054] Step 8: After vacuum heat compression connection is completed, allow the connected sample to cool naturally to room temperature.

[0055] The interfacial microstructure before and after vacuum thermocompression bonding via surface self-nanotyped joints was investigated, and the results are as follows: Figure 6 , Figure 7 As shown.

[0056] As can be seen from the figure, surface self-nanotyping can refine the microstructure of the interface. Figure 6 This effectively improves the interfacial bonding performance of vacuum thermocompression connections. Figure 7 This promotes the metallurgical bonding of metal vacuum thermal compression joints.

[0057] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for improving the performance of a metal vacuum thermocompression joint through surface self-nano-machining, characterized in that, Includes the following steps: Step 1: Machining the homogeneous CoCrFeMnNi high-entropy alloy into a round bar-shaped sample; Step 2: Use sandpaper to grind the contact surface of the connecting end of the cylindrical sample to remove oxides, oil stains and other impurities on the contact surface and obtain a smooth surface. Step 3: The sample with the contact surface ground flat is subjected to surface self-nanoization treatment by high-energy shot peening technology. Step 4: Clean the surface of the shot-peened sample with an organic solvent; Step 5: First, weld the thermocouple to the center of the mating metal components and close to the connection interface. Then, place the cleaned cylindrical sample in the center on the thermal simulator to make the contact surfaces completely aligned. Step 6: Heat the sample to the set temperature under vacuum conditions and hold it for a period of time. After eliminating the temperature gradient, apply axial plastic deformation to the two contacting samples to connect them together, and then cool them to room temperature. In step 3, the conditions for high-energy shot peening are: shot peening pressure of 0.6 MPa, shot diameter of 0.3 mm, shot peening time of 30 s, and distance between the nozzle and the contact surface of the metal component of 5 cm. In step 6, at 1×10 -1 The sample was heated to 950°C at a rate of 10°C / s under a vacuum of Pa and held for 5 minutes to eliminate the temperature gradient. In step 6, the two contacting samples are subjected to a 0.01s interval. -1 An axial plastic deformation with a strain rate of 0.4 is applied to connect them together.

2. The method for improving the performance of metal vacuum thermocompression joints by surface self-nano-sizing as described in claim 1, characterized in that, In step 1, the homogeneous CoCrFeMnNi high-entropy alloy is prepared by the following method: Step 11: Using alloying elements with a purity >99.9% as raw materials, prepare equiatomic CoCrFeMnNi high-entropy alloy ingots by vacuum induction melting. Step 12: Homogenize the ingot under an inert atmosphere and high temperature, and then cool it to room temperature to obtain a homogenized CoCrFeMnNi high-entropy alloy. Step 13: The homogenized CoCrFeMnNi high-entropy alloy is mechanically cut into cylinders of a set length, then hot-forged and recrystallized and annealed at a set temperature to obtain a homogenized CoCrFeMnNi high-entropy alloy.

3. The method for improving the performance of metal vacuum thermocompression joints by surface self-nano-machining as described in claim 2, characterized in that, In step 12, the inert atmosphere is argon, and the ingot homogenization temperature is 1100℃.

4. The method for improving the performance of metal vacuum thermocompression joints by surface self-nano-machining as described in claim 2, characterized in that, In step 13, the set temperature is 1000℃ and the annealing time is 2 hours.

5. The method for improving the performance of a metal vacuum thermocompression joint by surface self-nano-machining as described in claim 1, characterized in that, In step 2, the contact surfaces of the connecting ends of the cylindrical sample are ground sequentially using sandpaper of 120#, 400#, 800#, and 2000#.

6. The method for improving the performance of a metal vacuum thermocompression joint by surface self-nano-machining as described in claim 1, characterized in that, The homogeneous CoCrFeMnNi high-entropy alloy has the following percentage contents of each atom: Co 21.2%, Cr 19.7%, Fe 20.4%, Mn 19.1%, and Ni 19.6%.

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