Method for realizing ultra-low temperature connection by surface structure regulation of Ti2AlNb-based alloy

Abstract

The application discloses a method for realizing ultralow-temperature connection by surface structure regulation of Ti2AlNb-based alloy, and belongs to the field of diffusion connection.The application aims to solve the problem that cavities will become crack propagation positions and seriously affect the reliability of engineering components.The method comprises the following steps: step 1, after Ti2AlNb-based alloy is cut into a required size, a connecting surface is polished, polished, protected by a protective gas or vacuum induction quenched; step 2, then the connecting surface is ultrasonically rolled; step 3, after the connecting surface is butted, the connecting surface is diffusion welded under pulse current in a vacuum or a protective atmosphere, and then furnace-cooled to room temperature.The method realizes high-quality connection under low-temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of diffusion bonding, and more specifically, relates to a method for achieving ultra-low temperature bonding by controlling the surface microstructure of Ti2AlNb-based alloys. Background Technology

[0002] Currently, the mainstream methods for reducing diffusion bonding temperature are mainly achieved through surface nano-sizing or adding an intermediate layer. There are various ways to achieve surface nano-sizing. A smooth nanocrystalline layer can be deposited by electroplating, or a surface processing method can be used to generate dislocations and nanocrystals or nano-subgrains through severe plastic deformation. Such a surface rich in grain boundaries and dislocations can provide channels for atomic diffusion, greatly improving the ability of atomic diffusion. Current research has shown that surface mechanical attrition treatment (SMAT) can achieve surface nano-sizing of TA2 industrial pure titanium and has demonstrated its promoting effect on diffusion bonding. However, this nano-sizing behavior has a major drawback. SMAT bombards the entire sample to achieve plastic deformation, making it difficult to control the surface roughness of the treated surface, and the plastic deformation is not uniform. This invention plans to use ultrasonic rolling method (USRP), which is a novel technology for preparing surface gradient nanocrystalline layers. Its advantage is that the method of manufacturing surface nanocrystalline layers is not through overall bombardment, but through a combination of ultrasonic impact energy and static rolling on a single point. Therefore, the nanocrystalline plane prepared by ultrasonic rolling is more regular and has a lower surface roughness than that prepared by SMAT. For diffusion bonding, surface roughness has a significant impact on the joint. Higher surface roughness requires higher pressure or even higher temperatures to induce greater plastic deformation and achieve complete bonding, which is detrimental to precision diffusion bonding. However, if diffusion bonding is performed under relatively low temperature and low pressure welding parameters, the surface unevenness caused by SMAT (Surface Texture Atmosphere Adhesion) may remain during the diffusion bonding process, forming unclosed voids. In practical engineering applications, these voids can become locations for crack propagation, severely affecting the reliability of the engineered components. Summary of the Invention

[0003] The vacuum induction hardening technology used in this invention aims to form an extremely thin β / B2 single-phase layer at the interface. This single-phase layer has a body-centered cubic crystal structure. Compared with the α2 phase with a close-packed hexagonal crystal structure and the O phase with an orthorhombic crystal system, the body-centered cubic structure has more slip systems at high temperatures, making it easier to undergo plastic deformation. This is beneficial for sufficient contact and bonding of the surfaces to be welded during diffusion bonding. Furthermore, many studies have shown that the β / B2 single phase has a lower diffusion activation energy and a higher diffusion coefficient, and its vacancy formation energy within the crystal lattice is also relatively low. It is a more suitable phase for diffusion bonding in Ti2AlNb-based alloys. Numerous studies have shown that controlling the generation of β / B2 at the interface can effectively reduce the welding temperature. For example, for some near-α phase-dominant titanium alloys such as TC4, TC17, and Ti64, a commonly used method is to perform hot hydrogen treatment on the near-α phase titanium alloy. H, as a β / B2 phase stabilizing element, can segregate at the interface during diffusion bonding and form an effective bond. For the Ti2AlNb-based alloy to be joined in this invention, this alloy can achieve the characteristic of microstructure control only through heat treatment, without the need for complex and dangerous hot hydrogen treatment tests. It is only necessary to adjust the workpiece temperature to above 1050℃, and then suppress the equilibrium transformation through processes such as quenching to obtain the β / B2 single-phase microstructure. Therefore, this invention adopts the vacuum induction quenching process to prepare a layer of β / B2 single-phase microstructure on the surface without destroying the original α2 phase, O phase and β / B2 phase microstructure of Ti2AlNb inside, so as to achieve the purpose of surface microstructure modification.

[0004] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a method for achieving ultra-low temperature bonding by controlling the surface microstructure of Ti2AlNb-based alloys, comprising the following steps: Step 1: After cutting the Ti2AlNb-based alloy to the required size, the surfaces to be joined are ground, polished, and hardened by protective gas or vacuum induction. Step 2: Then, ultrasonically roll the surfaces to be joined. Step 3: After the surfaces to be joined are butted together, pulsed current diffusion welding is performed in a vacuum or protective atmosphere. After welding, the furnace is cooled to room temperature to complete the process.

[0005] Further specifying, the Ti2AlNb-based alloy is Ti-22Al-25Nb.

[0006] Further specifying, in step 1, the polishing is performed by sequentially using 45# diamond sandpaper, 60# SiC sandpaper, 240# SiC sandpaper, 400# SiC sandpaper, 800# SiC sandpaper, 1500# SiC sandpaper, 2000# SiC sandpaper and 3000# SiC sandpaper to polish the surfaces to be joined.

[0007] Further specifying, in step 1, a SiO2 polishing slurry is used for polishing; the SiO2 polishing slurry may be a SiO2 suspension with a particle size of 50nm.

[0008] Further specifying, in step 1, the surface to be connected is placed under an ultra-high frequency planar induction coil and heated in a protective atmosphere, with a heating frequency of 800~1100kHz, a heating power of 1.9kW~2.9kW, and a heating current of 26.8A~36.8A, followed by water quenching.

[0009] Further specifying, in step 1, the protective atmosphere can be argon, high-purity nitrogen, or reducing argon-hydrogen.

[0010] Furthermore, the argon-hydrogen gas is composed of 95% nitrogen and 5% hydrogen by volume percentage. Further specifying the process parameters for ultrasonic rolling in step 2: ultrasonic power of 600W~1000W, linear speed of 600mm~1500mm, feed rate of 0.03~0.08mm, static pressure of 500N~1000N, frequency of 25~38KHz, and amplitude of 6μm~14μm.

[0011] To further specify, in step 3, the inert atmosphere is either nitrogen or argon.

[0012] Further specifying, in step 3, the vacuum level shall not exceed 1×10⁻⁶. - 2 Pa.

[0013] Further specifying, in step 3, the temperature is increased to 850℃ at a heating rate of 2-5℃ / min and held for 30min.

[0014] Another object of the present invention is to provide a Ti2AlNb-based alloy component, which is produced by any of the methods described above.

[0015] Compared with the prior art, the present invention has the following beneficial effects: When using pulsed current for diffusion bonding at 850℃, the untreated Ti-22Al-25Nb joint exhibits low bonding strength. However, Ti-22Al-25Nb samples treated with surface induction hardening and ultrasonic roll forming for grain refinement achieve reliable diffusion bonding. Compared to Ti-22Al-25Nb joints directly bonded at 950℃, the bonding strength of this invention is increased by 100 MPa. EBSD analysis results indicate that the work hardening effect of ultrasonic roll forming slightly reduces the joint toughness, but the diffusion bonding process effectively controls the phase structure of the joint, allowing the O phase to re-precipitate as a reinforcing phase at the joint location, thus achieving high-quality bonding under low-temperature conditions. Under diffusion bonding conditions at 850℃, the axial deformation during welding is almost negligible, thereby achieving deformation-free precision diffusion bonding.

[0016] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0017] Figure 1 It is the X-ray diffraction pattern of the original hot-rolled base material; Figure 2 The X-ray diffraction pattern of single-phase Ti-22Al-25Nb obtained after induction hardening heat treatment is shown. Figure 3 It is the grain structure morphology of the joint after the microstructure of the surface to be welded has been controlled and then diffused by pulsed current. Figure 4 This is a comparison of the joint strength obtained by direct connection at 950℃ and connection after surface treatment at 850℃. Detailed Implementation

[0018] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0019] Example 1: The method for achieving ultra-low temperature bonding by controlling the surface microstructure of Ti2AlNb-based alloys in this example is carried out through the following steps: Step 1: Cut the Ti-22Al-25Nb alloy into small test blocks of 30mm×20mm×10mm using wire electrical discharge machining. The rolling plane (ultrasonic rolling) is a 30mm×20mm plane, with the 30mm edge pointing in the rolling direction and the 20mm edge perpendicular to the rolling direction. The 30×20mm rectangular surface will be selected as the diffusion bonding plane, so this plane is briefly referred to as the welding surface.

[0020] First, the surfaces to be welded are induction hardened. The surfaces are then ground with sandpaper (using 45# diamond sandpaper, 60# SiC sandpaper, 240# SiC sandpaper, 400# SiC sandpaper, 800# SiC sandpaper, 1500# SiC sandpaper, 2000# SiC sandpaper, and 3000# SiC sandpaper in sequence). After that, they are finely polished with SiO2 polishing slurry (SiO2 suspension with a particle size of 50nm). Then, the surfaces to be welded are placed under an ultra-high frequency planar induction coil. A protective atmosphere hood is added to the induction heating position of the induction device. The protective atmosphere is argon, the heating frequency is 1000kHz, the heating power is 2.0kW, and the heating current is 30A. After that, the surfaces are water-quenched to prepare a β / B2 single-phase structure of appropriate thickness.

[0021] Step 2: Due to the coarse grains and sparse grain boundaries of the generated β / B2 single-phase structure, the lack of grain boundary diffusion severely limits diffusion connectivity. Therefore, the grain size of the prepared structure control layer is nanoscaled. The method used is ultrasonic rolling. The sample is placed face up on an ultrasonic rolling machine with an ultrasonic power of 800W, a linear speed of 1200mm, a feed rate of 0.05mm, a static pressure of 800N, a frequency of 30KHz, and an amplitude of 10μm. After treatment, the grains of the sample are significantly refined, and the grain size can reach 110nm~220nm. The surface roughness decreases from Ra=0.0054μm after polishing to Ra=0.013~0.031. However, for diffusion connectivity, this deterioration in roughness can be compensated for by plastic deformation during the bonding process.

[0022] Step 3: Finally, a diffusion bonding process is performed. To reduce high-temperature creep, suppress macroscopic plastic deformation, and inhibit the recrystallization behavior of nanocrystals during the heating process, a pulsed current is used to rapidly heat the weld area. After the surfaces to be joined are butted together, they are placed in a vacuum diffusion welding furnace with a vacuum level of 1×10⁻⁶. - The furnace was heated to 850°C at a rate of 5°C / min, held for 30 minutes, and then cooled to room temperature.

[0023] Traditional hot-press diffusion bonding requires a lengthy process of 980℃-20MPa-3h, and it takes 50 minutes to rise from room temperature to the target welding temperature. Using the process flow scheme of this embodiment, the target welding temperature can be reached in 5 minutes, and a defect-free diffusion bond joint can be obtained by holding at 850℃ for only 30 minutes. The strength can reach 72%~85% of the original base material. If the temperature is increased to 880℃, the strength can reach 86%~91% of the base material. The welding temperature is reduced by more than 100℃, and the holding time is reduced by 83.3%. Furthermore, the crystallographic properties of the base material can be obtained through XRD analysis. Compared with hot-press diffusion welding, the sample after pulsed current diffusion bonding precipitated a large amount of brittle α2 phase, and the material toughness was severely deteriorated. However, the sample with surface structure control and low-temperature pulsed current bonding showed almost no changes in internal structure.

[0024] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A method for achieving ultra-low temperature bonding by controlling the surface microstructure of Ti2AlNb-based alloys, characterized in that, Includes the following steps: Step 1: After cutting the Ti2AlNb-based alloy to the required size, the surfaces to be joined are ground, polished, and hardened by protective gas or vacuum induction. Step 2: Then, ultrasonically roll the surfaces to be joined. Step 3: After the surfaces to be joined are butted together, pulsed current diffusion welding is performed in a vacuum or protective atmosphere. After welding, the furnace is cooled to room temperature to complete the process.

2. The method according to claim 1, characterized in that, The Ti2AlNb-based alloy is Ti-22Al-25Nb.

3. The method according to claim 1, characterized in that, The grinding process involves sequentially using 45# diamond sandpaper, 60# SiC sandpaper, 240# SiC sandpaper, 400# SiC sandpaper, 800# SiC sandpaper, 1500# SiC sandpaper, 2000# SiC sandpaper, and 3000# SiC sandpaper to grind the surfaces to be joined.

4. The method according to claim 1, characterized in that, Polishing was performed using SiO2 polishing slurry.

5. The method according to claim 1, characterized in that, The surfaces to be joined are placed under an ultra-high frequency planar induction coil and heated in a protective atmosphere with a heating frequency of 800~1100kHz, a heating power of 1.9kW~2.9kW, and a heating current of 26.8A~36.8A, followed by water quenching.

6. The method according to claim 1, characterized in that, The protective atmosphere can be selected from argon, high-purity nitrogen, or reducing argon-hydrogen, wherein the argon-hydrogen is composed of 95% nitrogen and 5% hydrogen by volume percentage.

7. The method according to claim 1, characterized in that, The process parameters for ultrasonic roller pressing are as follows: ultrasonic power is 600W~1000W, linear speed is 600mm~1500mm, feed rate is 0.03~0.08mm, static pressure is 500N~1000N, frequency is 25~38KHz, and amplitude is 6μm~14μm.

8. The method according to claim 1, characterized in that, The inert atmosphere is nitrogen or argon; the vacuum level is not higher than 1×10⁻⁶. - 2 Pa.

9. The method according to claim 1, characterized in that, Heat to 850℃ at a heating rate of 2-5℃ / min and hold for 30 minutes.

10. A Ti2AlNb-based alloy component, characterized in that, The Ti2AlNb-based alloy component is produced by the method described in any one of claims 1-9.

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