TiAl alloy low-temperature diffusion bonding method based on synergistic effect of surface hydrogenation treatment and Zr intermediate layer

Abstract

The invention discloses a TiAl alloy low-temperature diffusion bonding method based on the synergistic effect of hydrogenation treatment and a Zr intermediate layer, and aims to solve the technical problems that traditional TiAl alloy diffusion bonding is high in temperature and insufficient in joint strength. According to the method, a certain content of hydrogen element is introduced to the surface of the TiAl alloy through a hydrogenation treatment technology, meanwhile, Zr foil serves as a middle layer, and low-temperature efficient connection of the TiAl alloy is achieved through the synergistic effect of the hydrogen element and the Zr foil, specifically, hydrogenation treatment induces the TiAl alloy to generate a beta phase, the hardness of base metal is reduced, and the atomic diffusion rate is increased; the Zr intermediate layer and the Ti element in the TiAl alloy form a continuous solid solution, atomic diffusion is further accelerated, and the interface structure is optimized. And compared with a traditional process, the connection temperature is greatly reduced, and the method is suitable for batch manufacturing of TiAl alloy complex components. The method is suitable for manufacturing lightweight high-temperature-resistant components such as aircraft airfoils and engine hot ends. The method is suitable for manufacturing lightweight high-temperature-resistant components such as aircraft airfoils and engine hot ends.

Description

TECHNICAL FIELD

[0001] The application relates to a TiAl alloy low-temperature diffusion connection method. BACKGROUND

[0002] TiAl alloy is an ideal material for key components of a hypersonic aircraft due to low density (3.7-3.9 g / cm3), high melting point, high specific strength, and similar use temperature to a nickel-based high-temperature alloy. However, TiAl alloy has high brittleness and poor processing and forming capacity, and traditional diffusion connection needs to be performed at a high temperature of 1000-1200 DEG C, which not only leads to a decrease in the anti-oxidation capacity, but also puts strict requirements on the heating capacity of equipment, and increases production cost and energy consumption.

[0003] In the prior art, although the hydrogen placement technology alone can induce the generation of a beta phase of TiAl alloy and improve plasticity, the hydrogen placement in a solid phase or in a liquid phase is performed on the whole base material, and has a great influence on the performance of the base material. Direct diffusion connection of the hydrogen-placed TiAl alloy still needs a high temperature of 1050 DEG C, and the shear strength of the joint is low, which cannot meet the use requirement; although the Zr interlayer alone can form a solid solution with Ti, atomic diffusion is insufficient, pores are prone to occur in the joint, and the mechanical performance of the joint is limitedly improved. Therefore, it is urgent to develop a process for high-strength connection with less influence on the performance of the base material and low welding temperature. SUMMARY

[0004] In order to solve the problems of high connection temperature and high-strength joint of the existing TiAl alloy, the application provides a TiAl alloy low-temperature diffusion connection method based on the synergistic effect of hydrogen placement treatment and a Zr interlayer.

[0005] The TiAl alloy low-temperature diffusion connection method based on the synergistic effect of surface hydrogen placement treatment and a Zr interlayer is performed according to the following steps:

[0006] A Zr interlayer is placed between two TiAl alloy welding surfaces to obtain an assembly, and the assembly is placed in a vacuum diffusion welding furnace for vacuum diffusion connection; the two TiAl alloy welding surfaces each have a hydrogen permeation layer;

[0007] The preparation method of the hydrogen permeation layer is as follows: electrolytic hydrogen placement process is adopted, the TiAl alloy welding surface is first polished, and then is placed in a water bath for electrolytic hydrogen placement, the water bath temperature is 45-80 DEG C, the current is 0.1-1.0 A / cm 2 , the time is 40-100 h, the electrolyte concentration is 0.4-1.0 mol / L, and the thiourea concentration in the electrolyte is 1-5 g / L; a hydrogen permeation layer with a thickness of 20-50 microns is obtained on the surface of the TiAl alloy;

[0008] The process of the vacuum diffusion connection is as follows: the assembly is placed in a vacuum plasma diffusion welding furnace, heated to 900-950 DEG C at 10 DEG C / min under vacuum, and held for 60-120 min under a pressure of 20-30 MPa, and then cooled to room temperature to complete the connection.

[0009] The principles and benefits of the present application are as follows:

[0010] The present application can significantly reduce the connection temperature of TiAl alloy diffusion welding by combining the advantages of hydrogen treatment and Zr interlayer, and can complete diffusion connection at a low temperature of 900-950 DEG C under the synergistic effect of hydrogen treatment and Zr interlayer, and obtain a high-strength welded joint. The electrolytic hydrogenation treatment can generate a hydrogen permeation layer of more than 20 μm on the surface of the TiAl alloy without affecting the performance of the TiAl alloy substrate. The content of β phase in the hydrogen permeation layer increases, and the β phase is a body-centered cubic (BCC) structure, and the atomic space utilization rate is about 68%, which is lower than the 74% of the face-centered cubic (FCC) structure γ-TiAl in the substrate, and the β phase has a larger atomic spacing and is more conducive to accommodating diffusion atoms. At the same time, the nano-hardness of the β phase is about 2.83 GPa, which is lower than the 3.3 GPa of the base material, which can reduce the overall hardness of the base material and improve its plastic deformation ability, ensuring that the Zr interlayer and the base material can realize close physical contact at a lower pressure, thereby eliminating the initial pores at the interface and creating the necessary conditions for the mutual solubility and diffusion of Zr and Ti. Zr and Ti belong to the same ⅣB group element, and they can be infinitely soluble and form a continuous Ti-Zr solid solution; and Zr will undergo a polymorphic transformation from α-Zr to β-Zr at 862 DEG C; the β-Zr phase has a larger atomic spacing than the α-Zr, which can further improve the diffusion rate of Ti and Al elements in the base material based on the hydrogen treatment. At the same time, the diffusion rate of Zr atoms to the TiAl base material and the diffusion rate of Ti atoms to the Zr interlayer are significantly improved, and a uniform (Ti, Zr) solid solution reaction layer is finally formed, effectively avoiding the generation of hard and brittle compounds.

[0011] In the vacuum diffusion connection process of the present application, the high-temperature and high-vacuum environment can promote the hydrogen elements in the base material to fully escape, so that the hydrogen content of the joint after welding is very low, thereby avoiding the adverse effects of hydrogen embrittlement on the performance.

[0012] The connection temperature of the present application is significantly lower than that of the traditional process, and is suitable for batch manufacturing of TiAl alloy complex components. It is suitable for the manufacturing of lightweight high-temperature resistant components such as aircraft wings and engine hot ends. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1A schematic diagram of the structure of the assembly obtained in Example 1, wherein 1 is a TiAl alloy base material, 2 is a TiAl alloy surface hydrogen permeation layer, and 3 is a Zr intermediate layer. DETAILED DESCRIPTION

[0014] The technical solution of the present application is not limited to the following specific embodiments, and also includes any reasonable combination of the specific embodiments.

[0015] Specific embodiment one: the TiAl alloy low-temperature diffusion bonding method based on the synergistic effect of surface hydrogenation treatment and Zr intermediate layer is carried out according to the following steps: placing a Zr intermediate layer between the two TiAl alloy welding surfaces to obtain an assembly, and placing the assembly in a vacuum diffusion bonding furnace for vacuum diffusion bonding; the two TiAl alloy welding surfaces each have a hydrogen permeation layer;

[0016] The preparation method of the hydrogen permeation layer is: using an electrolytic hydrogenation process.

[0017] The process of the vacuum diffusion bonding is: placing the assembly in a vacuum plasma diffusion bonding furnace, heating to 900-950℃ at 10℃ / min under vacuum, applying a pressure of 20-30MPa for 60-120min, and then cooling to room temperature to complete the bonding.

[0018] The specific embodiment has the following beneficial effects:

[0019] The present embodiment can significantly reduce the connection temperature of TiAl alloy diffusion welding by combining the hydrogenation treatment of TiAl alloy and the advantages of Zr interlayer. The diffusion connection can be completed at a low temperature of 900-950℃ under the synergistic effect of hydrogenation treatment and Zr interlayer, and a high-strength welded joint is obtained. The electrolytic hydrogenation treatment can generate a hydrogen permeation layer with a thickness of more than 20 μm on the surface of the TiAl alloy without affecting the performance of the TiAl alloy substrate. The content of β phase in the hydrogen permeation layer increases, and the β phase has a body-centered cubic (BCC) structure with an atomic space utilization rate of about 68%, which is lower than 74% of the face-centered cubic (FCC) structure γ-TiAl in the substrate. The interatomic gap of the β phase is larger and more conducive to accommodating diffusing atoms. At the same time, the nano-hardness of the β phase is about 2.83 GPa, which is lower than 3.3 GPa of the base material, which can reduce the overall hardness of the base material and improve its plastic deformation ability, ensuring that the Zr interlayer and the base material can realize close physical contact at a lower pressure, thereby eliminating the initial pores at the interface and creating the necessary conditions for the inter-diffusion of Zr and Ti. Zr and Ti belong to the same ⅣB group element, and they can be infinitely inter-diffused to form a continuous Ti-Zr solid solution. Zr will undergo a polymorphic transformation from α-Zr to β-Zr at 862℃. The β-Zr phase has a larger interatomic gap than the α-Zr, which can further improve the diffusion rate of Ti and Al elements in the base material based on the hydrogenation treatment. At the same time, the diffusion rate of Zr atoms to the TiAl base material and the diffusion rate of Ti atoms to the Zr interlayer are significantly improved, and a uniform (Ti, Zr) solid solution reaction layer is finally formed, effectively avoiding the generation of hard and brittle compounds.

[0020] In the process of vacuum diffusion connection, the high-temperature and high-vacuum environment can promote the hydrogen elements in the base material to fully escape, so that the hydrogen content of the joint after welding is extremely low, thereby avoiding the adverse effects of hydrogen embrittlement on the performance.

[0021] Specific implementation method two: The electrolytic hydrogenation process is different from that of the specific implementation method one. First, the welding surface of the TiAl alloy is polished, and then placed in a water bath for electrolytic hydrogenation. The water bath temperature is 45-80℃, the current is 0.1-1.0 A / cm 2 , the time is 40-100 h, the electrolyte concentration is 0.4-1.0 mol / L, and the thiourea concentration in the electrolyte is 1-5 g / L. A hydrogen permeation layer with a thickness of 20-50 μm is obtained on the surface of the TiAl alloy.

[0022] Specific implementation method three: The electrolytic hydrogenation process is different from that of the specific implementation method two. First, the welding surface of the TiAl alloy is polished with 400-3000# sandpaper, ultrasonically cleaned with acetone for 5 min, and then dried at 60℃. Then, the TiAl alloy is placed in a water bath for electrolytic hydrogenation. The water bath temperature is 70℃, the current is 0.5 A / cm 2, the time is 70h, the electrolyte concentration is 0.7mol / L, and the thiourea concentration in the electrolyte is 3g / L; a hydrogen permeation layer with a thickness of 25μm is obtained on the surface of the TiAl alloy.

[0023] Specific embodiment four: different from one of the specific embodiments one to three is that the process of the vacuum diffusion connection is as follows: the assembly is placed in a vacuum plasma diffusion welding furnace, the vacuum degree is 1×10 -3 Pa, the temperature is increased to 950℃ at a rate of 10℃ / min under a pressure of 25MPa, the temperature is kept for 90min, then the cooling is performed to room temperature at a cooling rate of 5℃ / min, and the connection is completed.

[0024] Specific embodiment five: different from one of the specific embodiments one to four is that the process of the vacuum diffusion connection is as follows: the assembly is placed in a vacuum plasma diffusion welding furnace, the vacuum degree is 1×10 -3 Pa, the temperature is increased to 950℃ at a rate of 10℃ / min under a pressure of 30MPa, the temperature is kept for 90min, then the cooling is performed to room temperature at a cooling rate of 5℃ / min, and the connection is completed.

[0025] Specific embodiment six: different from one of the specific embodiments one to five is that the Zr intermediate layer is a Zr foil with a thickness of 20-100μm.

[0026] Specific embodiment seven: different from the specific embodiment six is that the purity of the Zr foil is above 99.9%.

[0027] Specific embodiment eight: different from one of the specific embodiments one to seven is that the polishing process of the welding surface of the TiAl alloy is as follows: the 400-3000# sandpaper is used for step-by-step polishing, then the ultrasonic cleaning in acetone is performed for 5min, and finally the drying is performed at 60℃.

[0028] Specific embodiment nine: different from one of the specific embodiments one to eight is that the Zr intermediate layer is polished and cleaned before assembly, specifically, the 800# sandpaper is used for polishing, then the acetone cleaning is performed, and finally the drying is performed.

[0029] Specific embodiment ten: different from one of the specific embodiments one to nine is that the vacuum condition is that the vacuum degree is not more than 1×10 -2 Pa.

[0030] Example 1:

[0031] The TiAl alloy low-temperature diffusion connection method based on the surface hydrogenation treatment and the Zr intermediate layer synergistic effect in this embodiment is performed according to the following steps:

[0032] Placing a Zr interlayer between two TiAl alloy surfaces to be welded to obtain an assembly, and placing the assembly in a vacuum diffusion welding furnace to perform vacuum diffusion connection; the two TiAl alloy surfaces to be welded each have a hydrogen permeation layer; the TiAl alloy is a Ti-44Al-6Nb alloy with a size of 5*5*3mm; the Zr interlayer is 50μm thick, has a size of 5*5mm, and has a purity of more than 99.9%; the Zr interlayer is polished and cleaned before assembly, specifically, 800# sandpaper is used for polishing, then acetone is used for cleaning, and finally drying is performed;

[0033] The preparation method of the hydrogen permeation layer is as follows: first, the surface to be welded of the TiAl alloy is polished with 400-3000# sandpaper, ultrasonic cleaned with acetone for 5min, and then dried at 60℃, and then placed in a water bath for electrolytic hydrogenation, with a water bath temperature of 70℃, an electric current of 0.5A / cm 2 , a time of 70h, an electrolyte concentration of 0.7mol / L, and a thiourea concentration in the electrolyte of 3g / L; a hydrogen permeation layer with a thickness of 25μm is obtained on the surface of the TiAl alloy;

[0034] The process of the vacuum diffusion connection is as follows: placing the assembly in a vacuum plasma diffusion welding furnace, heating to 950℃ at a rate of 10℃ / min under a vacuum degree of 1*10 -3 Pa, applying a pressure of 25MPa for 90min, and then cooling to room temperature at a cooling rate of 5℃ / min to complete the connection.

[0035] The welded joint obtained by the diffusion connection in this embodiment forms a (Ti,Zr) solid solution layer at the interface, and the bonding rate is 100%; the shear strength reaches 162MPa.

[0036] Example 2:

[0037] The TiAl alloy low-temperature diffusion connection method based on the synergistic effect of surface hydrogenation treatment and a Zr interlayer in this embodiment is performed according to the following steps:

[0038] Placing a Zr interlayer between two TiAl alloy surfaces to be welded to obtain an assembly, and placing the assembly in a vacuum diffusion welding furnace to perform vacuum diffusion connection; the two TiAl alloy surfaces to be welded each have a hydrogen permeation layer; the TiAl alloy is a Ti-44Al-6Nb alloy with a size of 5*5*3mm; the Zr interlayer is 50μm thick, has a size of 5*5mm, and has a purity of more than 99.9%; the Zr interlayer is polished and cleaned before assembly, specifically, 800# sandpaper is used for polishing, then acetone is used for cleaning, and finally drying is performed;

[0039] The preparation method of the hydrogen permeation layer is: using electrolytic hydrogenation process, first polishing the welding surface of the TiAl alloy by 400-3000# sandpaper, ultrasonic cleaning with acetone for 5 min, drying at 60°C, then placing in a water bath kettle for electrolytic hydrogenation, water bath temperature is 70°C, current is 0.5A / cm 2 , time is 70h, electrolyte concentration is 0.7mol / L, and thiourea concentration in the electrolyte is 3g / L; a hydrogen permeation layer with a thickness of 25μm is obtained on the surface of the TiAl alloy;

[0040] The process of the vacuum diffusion connection is: placing the assembly in a vacuum plasma diffusion welding furnace, under the condition of vacuum degree of 1×10 -3 Pa, heating to 950°C at a rate of 10°C / min, applying a pressure of 30MPa for 90min, and then cooling to room temperature at a cooling rate of 5°C / min, to complete the connection.

[0041] The welded joint obtained by the diffusion connection in this example forms a (Ti, Zr) solid solution layer at the interface, the bonding rate is 100%, and the shear strength reaches 189MPa.

Claims

1. A method for diffusion bonding of TiAl alloy at low temperature based on synergistic effect of surface hydrogenation treatment and Zr interlayer, characterized in that: The TiAl alloy low-temperature diffusion bonding method based on the synergistic effect of surface hydrogenation treatment and Zr interlayer is performed according to the following steps: placing a Zr interlayer between two TiAl alloy welding surfaces to obtain an assembly, and placing the assembly in a vacuum diffusion bonding furnace to perform vacuum diffusion bonding; the two TiAl alloy welding surfaces each have a hydrogen permeation layer; The hydrogen permeation layer is prepared by using an electrolytic hydrogenation process. The vacuum diffusion bonding process is as follows: placing the assembly in a vacuum plasma diffusion bonding furnace, heating at 10 ℃ / min to 900-950 ℃ under vacuum, applying a pressure of 20-30 MPa for 60-120 min, and then cooling to room temperature to complete the bonding.

2. The method for diffusion bonding of TiAl alloy at low temperature based on synergistic effect of surface hydrogenation treatment and Zr interlayer according to claim 1, characterized in that: The electrolytic hydrogenation process is that the welding surface of the TiAl alloy is polished first, and then is placed in a water bath pot for electrolytic hydrogenation, the water bath temperature is 45-80 DEG C, the current is 0.1-1.0 A / cm 2 , the time is 40-100 h, the electrolyte concentration is 0.4-1.0 mol / L, the thiourea concentration in the electrolyte is 1-5 g / L; a hydrogen permeation layer with a thickness of 20-50 μm is obtained on the surface of the TiAl alloy.

3. The method for diffusion bonding of TiAl alloy at low temperature based on synergistic effect of surface hydrogenation treatment and Zr interlayer according to claim 2, characterized in that: The electrolytic hydrogenation process is as follows: first, the welding surface of the TiAl alloy is polished by 400-3000# sandpaper, ultrasonic cleaned by acetone for 5 minutes, dried at 60 DEG C, and then placed in a water bath for electrolytic hydrogenation, wherein the water bath temperature is 70 DEG C, the current is 0.5 A / cm 2 , the time is 70 hours, the electrolyte concentration is 0.7 mol / L, and the thiourea concentration in the electrolyte is 3 g / L; a hydrogen permeation layer with a thickness of 25 μm is obtained on the surface of the TiAl alloy.

4. The method for diffusion bonding of TiAl alloy at low temperature based on synergistic effect of surface hydrogenation treatment and Zr interlayer according to claim 1, characterized in that: The process of the vacuum diffusion connection is: the assembly is placed in a vacuum plasma diffusion welding furnace, the vacuum degree is 1×10 -3 The connection is completed under the condition that the temperature is increased to 950℃ at 10℃ / min, a pressure of 25MPa is applied for 90min, and then the cooling speed is 5℃ / min to room temperature.

5. The method for TiAl alloy low temperature diffusion bonding based on surface hydrogenation treatment and Zr interlayer synergistic effect according to claim 1, characterized in that: The process of the vacuum diffusion connection is: the assembly is placed in a vacuum plasma diffusion welding furnace, the vacuum degree is 1×10 -3 The connection is completed under the condition that the temperature is increased to 950℃ at 10℃ / min, a pressure of 30MPa is applied for 90min, and then the cooling speed is 5℃ / min to room temperature.

6. The method for TiAl alloy low temperature diffusion bonding based on surface hydrogenation treatment and Zr interlayer synergistic effect according to claim 1, characterized in that: The Zr interlayer is a Zr foil with a thickness of 20-100 μm.

7. The method for TiAl alloy low temperature diffusion bonding based on synergistic effect of surface hydrogenation treatment and Zr interlayer according to claim 6, characterized in that: The purity of the Zr foil is greater than 99.9%.

8. The method for TiAl alloy low temperature diffusion bonding based on surface hydrogenation treatment and Zr interlayer synergistic effect according to claim 1, characterized in that: The polishing process of the TiAl alloy welding surface is as follows: polishing step by step using 400-3000# sandpaper, then ultrasonic cleaning in acetone for 5 min, and finally drying at 60 ℃.

9. The method for TiAl alloy low temperature diffusion bonding based on surface hydrogenation treatment and Zr interlayer synergistic effect according to claim 1, characterized in that: The Zr interlayer is polished and cleaned before assembly, specifically polished using 800# sandpaper, then cleaned using acetone, and finally dried.

10. The method for TiAl alloy low temperature diffusion bonding based on surface hydrogenation treatment and Zr interlayer synergistic effect according to claim 1, characterized in that: The vacuum condition is a vacuum degree of not more than 1 x 10 -2 Pa.

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