A brazing method for controlling the welding cracks of TiAl alloy

Abstract

The application discloses a brazing method for controlling welding cracks of TiAl alloy, and belongs to the field of brazing. The application aims at solving the problem that existing TiAl brazing joints are prone to micro cracks, thereby reducing the strength of the joints. The preparation method comprises the following steps: 1, mixing filler metal powder and beta phase stabilizing element powder; 2, adding pressure to obtain filler metal foil; and 3, brazing. The application is used for controlling welding cracks of TiAl alloy.

Description

Technical Field

[0001] This invention belongs to the field of brazing. Background Technology

[0002] TiAl intermetallic compounds have a density only half that of nickel-based superalloys and possess excellent mechanical properties, making them promising for applications in the aerospace field. However, they are brittle at room temperature, making them difficult to process and form, and difficult to manufacture integral components. The processing of composite components inevitably involves the problem of joining TiAl alloys.

[0003] Currently, TiAl alloy joining methods include fusion welding, brazing, and friction welding. Fusion welding, due to the inherent brittleness of TiAl alloy and the thermal stress caused by rapid cooling after welding, is prone to microcracks, affecting performance. Friction welding has significant limitations on the joining method and specimen size, making it unsuitable for complex joints. Brazing, with increasing brazing time, leads to coarser microstructures on both sides of the joint, easily resulting in microcrack formation. Therefore, there is an urgent need to develop welding methods that can effectively suppress microcracks in TiAl brazed joints and thereby improve joint strength. Summary of the Invention

[0004] The present invention aims to solve the problem that existing TiAl brazed joints are prone to microcracks, which leads to a decrease in joint strength, and provides a brazing method for controlling TiAl alloy welding cracks.

[0005] A brazing method for controlling welding cracks in TiAl alloys, comprising the following steps:

[0006] 1. Mix the brazing filler metal powder and β-phase stabilizing element powder evenly to obtain a mixed brazing filler metal;

[0007] The mass percentage of β-phase stabilizing element powder in the mixed solder is 10% to 20%.

[0008] 2. Press the mixed solder to obtain solder foil;

[0009] 3. Stack TiAl base material, brazing foil, and TiAl base material in sequence to obtain the component to be welded. Place the component to be welded in a vacuum brazing furnace and evacuate it. Then, preheat it at a temperature of 300℃~500℃ for 0.5h~1.5h. Then, hold it at the brazing temperature. After holding, first cool it down to 800℃~900℃ at a rate of 5℃ / min~10℃ / min, then cool it down to 200℃~400℃ at a rate of 3℃ / min~5℃ / min. Finally, cool it down to room temperature with the furnace and take out the sample. This completes the brazing method for controlling welding cracks in TiAl alloy.

[0010] The beneficial effects of this invention are:

[0011] I. This invention employs a combination of three methods—preheating before welding, brazing filler metal composition design, and controlled cooling rate—to control the generation of microcracks during the welding of TiAl intermetallic compounds. Preheating before welding can effectively release residual stress during the forming process of the TiAl alloy, and also helps to reduce the cooling rate after welding.

[0012] 2. During the brazing process, the present invention utilizes β-phase stabilizing elements to expand the β-phase region and shrink the α+γ region during the cooling process. Then, by cooling at a relatively fast rate to the eutectoid reaction temperature, the β-phase cannot be completely transformed. Since the high-temperature β-phase undergoes an ordered transformation into the B2 phase during the cooling process, the remaining β-phase will eventually result in the presence of some B2 phase in the brazing seam.

[0013] Third, after the brazing and heat preservation process is completed, at the eutectoid reaction temperature, the present invention reduces the cooling rate to form an ideal lamellar γ phase structure; finally, a suitable amount of hard B2 phase and γ phase eutectoid structure with network distribution is formed at the joint. The pinning effect of the B2 phase is used to improve the joint strength. The TiAl alloy parts connected by this method have an average shear strength ≥350MPa.

[0014] Instruction manual illustrations

[0015] Figure 1 The brazing process curve for step three of Example 1;

[0016] Figure 2 The image shows a scanning electron microscope (SEM) image of the joint interface microstructure of the TiAl alloy weldment prepared in Example 1. Detailed Implementation

[0017] Specific Implementation Method 1: This implementation method provides a brazing method for controlling welding cracks in TiAl alloys, which is carried out according to the following steps:

[0018] 1. Mix the brazing filler metal powder and β-phase stabilizing element powder evenly to obtain a mixed brazing filler metal;

[0019] The mass percentage of β-phase stabilizing element powder in the mixed solder is 10% to 20%.

[0020] 2. Press the mixed solder to obtain solder foil;

[0021] 3. Stack TiAl base material, brazing foil, and TiAl base material in sequence to obtain the component to be welded. Place the component to be welded in a vacuum brazing furnace and evacuate it. Then, preheat it at a temperature of 300℃~500℃ for 0.5h~1.5h. Then, hold it at the brazing temperature. After holding, first cool it down to 800℃~900℃ at a rate of 5℃ / min~10℃ / min, then cool it down to 200℃~400℃ at a rate of 3℃ / min~5℃ / min. Finally, cool it down to room temperature with the furnace and take out the sample. This completes the brazing method for controlling welding cracks in TiAl alloy.

[0022] The beneficial effects of this embodiment are:

[0023] I. This embodiment employs a combination of three methods—preheating before welding, brazing filler metal composition design, and cooling rate control—to control the generation of microcracks during the welding of TiAl intermetallic compounds. Preheating before welding can effectively release residual stress during the forming process of the TiAl alloy, and also helps to reduce the cooling rate after welding.

[0024] 2. In the brazing process, this embodiment utilizes β-phase stabilizing elements to expand the β-phase region and shrink the α+γ region during the cooling process. Then, by cooling at a relatively fast rate to the eutectoid reaction temperature, the β-phase cannot be completely transformed. Since the high-temperature β-phase undergoes an ordered transformation into the B2 phase during the cooling process, the remaining β-phase will eventually result in the presence of some B2 phase in the brazing seam.

[0025] 3. After the brazing and heat preservation process is completed, at the eutectoid reaction temperature, this embodiment reduces the cooling rate to form an ideal lamellar γ phase structure; finally, a suitable amount of hard B2 phase and γ phase eutectoid structure with network distribution is formed at the joint. The pinning effect of the B2 phase improves the joint strength. The TiAl alloy parts connected by this method have an average shear strength ≥350MPa.

[0026] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the solder powder mentioned in step one is AgCuTi powder, AgCuInTi powder, TiZrNiCu powder, TiNi powder, BNi2 powder, or BNi5 powder. Everything else is the same as in Specific Implementation Method One.

[0027] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the β-phase stabilizing element powder mentioned in step one is Mo powder, Nb powder, W powder, V powder, or Cr powder. Everything else is the same as in Specific Implementation Method One or Two.

[0028] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step two, the mixed brazing filler metal is pressurized under a pressure of 0.5t to 2t. Everything else is the same as in Specific Implementation Methods One to Three.

[0029] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the thickness of the solder foil mentioned in step two is 0.5mm to 2mm. Everything else is the same as in Specific Implementation Methods One to Four.

[0030] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the TiAl base material mentioned in step three is Ti-48Al, Ti-42Al-5V, Ti-45Al-8.5Nb-0.2W-0.03Y, or Ti-48Al-2Cr-2Nb. Everything else is the same as in Specific Implementation Methods One to Five.

[0031] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One through Six in that: in step three, the component to be welded is placed in a vacuum brazing furnace, and a vacuum of 5×10⁻⁶ is drawn. -3 Pa or below. Other aspects are the same as in embodiments one through six.

[0032] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in step three, the temperature is heated to 300℃ to 500℃ at a rate of 2℃ / min to 10℃ / min, and preheated for 0.5h to 1.5h at the temperature of 300℃ to 500℃. Everything else is the same as in Specific Implementation Methods One to Seven.

[0033] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step three, the temperature is raised to the brazing temperature at a rate of 5°C / min to 10°C / min, and held at the brazing temperature for 10 to 20 minutes. Everything else is the same as in Specific Implementation Methods One to Eight.

[0034] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that: in step three, the temperature is first heated to 400℃ to 500℃ at a rate of 5℃ / min to 10℃ / min, and then preheated for 1 hour to 1.5 hours at the same temperature; in step three, the temperature is first cooled to 850℃ to 900℃ at a rate of 8℃ / min to 10℃ / min, and then cooled to 200℃ to 300℃ at a rate of 4℃ / min to 5℃ / min. Everything else is the same as in Specific Implementation Methods One to Nine.

[0035] The beneficial effects of the present invention are verified using the following embodiments:

[0036] Example 1, combined with Figure 1 Detailed explanation:

[0037] A brazing method for controlling welding cracks in TiAl alloys, comprising the following steps:

[0038] 1. Mix the brazing filler metal powder and β-phase stabilizing element powder evenly to obtain a mixed brazing filler metal;

[0039] The mass percentage of β-phase stabilizing element powder in the mixed solder is 20%.

[0040] 2. Under a pressure of 1t, the mixed brazing filler metal is pressurized to obtain brazing filler metal foil;

[0041] The thickness of the solder foil is 1 mm;

[0042] 3. Stack the TiAl base material, brazing foil, and TiAl base material in that order to obtain the component to be welded. Place the component to be welded in a vacuum brazing furnace and evacuate to 5×10⁻⁶. -3 The sample is heated to 400°C at a rate of 10°C / min and preheated for 1 hour at 400°C. Then, it is heated to 1200°C at a rate of 10°C / min and held for 10 minutes at a brazing temperature of 1200°C. After holding, it is cooled to 900°C at a rate of 10°C / min and then to 200°C at a rate of 5°C / min. Finally, it is cooled to room temperature in the furnace, and the sample is removed to obtain the TiAl alloy welded part.

[0043] The solder powder mentioned in step one is Ti-28Ni powder.

[0044] The β-phase stabilizing element powder mentioned in step one is Nb powder.

[0045] The TiAl base material mentioned in step three is Ti-42Al-5V.

[0046] Figure 2 The image shows a scanning electron microscope (SEM) image of the joint interface microstructure of the TiAl alloy welded component prepared in Example 1. As can be seen from the image, the TiAl alloy welded component has a good joint with no obvious microcracks or other defects. The grains are fine, with a grain size of approximately 5 μm. The joint microstructure is a two-phase structure consisting of lamellar γ-phase and lamellar B2-phase, which are interwoven and form a network of appropriate amounts of hard B2-phase and γ-phase eutectoid microstructure. Through grain boundary strengthening and second-phase strengthening, and utilizing the pinning effect of the B2-phase, the joint strength is improved.

[0047] The room temperature shear strength of TiAl alloy welded parts was tested using the national standard GB / T 11363-2008, and the room temperature shear strength was found to be 350 MPa.

Claims

1. A brazing method for controlling welding cracks in TiAl alloys, characterized in that... It is done in the following steps:

1. Mix the brazing filler metal powder and β-phase stabilizing element powder evenly to obtain a mixed brazing filler metal; The solder powder is Ti-28Ni powder; the mass percentage of β-phase stabilizing element powder in the mixed solder is 20%; the β-phase stabilizing element powder is Nb powder; 2. Press the mixed solder to obtain solder foil; 3. Stack TiAl base material, brazing foil, and TiAl base material in sequence to obtain the component to be welded. Place the component to be welded in a vacuum brazing furnace and evacuate it. Then heat it to 300℃~500℃ at a rate of 2℃ / min~10℃ / min. Preheat it at 300℃~500℃ for 0.5h~1.5h. Then heat it to the brazing temperature at a rate of 5℃ / min~10℃ / min. Hold it at the brazing temperature for 10min~20min. After holding, cool it down to 800℃~900℃ at a rate of 5℃ / min~10℃ / min. Then cool it down to 200℃~400℃ at a rate of 3℃ / min~5℃ / min. Finally, cool it down to room temperature with the furnace and take out the sample. This completes the brazing method for controlling welding cracks in TiAl alloy.

2. The brazing method for controlling welding cracks in TiAl alloys according to claim 1, characterized in that... In step two, the mixed brazing filler metal is pressurized under a pressure of 0.5t to 2t.

3. The brazing method for controlling welding cracks in TiAl alloys according to claim 1, characterized in that... The thickness of the brazing foil mentioned in step two is 0.5mm to 2mm.

4. The brazing method for controlling welding cracks in TiAl alloys according to claim 1, characterized in that... The TiAl base material mentioned in step three is Ti-48Al, Ti-42Al-5V, Ti-45Al-8.5Nb-0.2W-0.03Y or Ti-48Al-2Cr-2Nb.

5. The brazing method for controlling welding cracks in TiAl alloys according to claim 1, characterized in that... In step three, the components to be welded are placed in a vacuum brazing furnace, and a vacuum of 5×10⁻⁶ is drawn. -3 Below Pa.

6. The brazing method for controlling welding cracks in TiAl alloys according to claim 1, characterized in that... In step three, the temperature is first heated to 400℃~500℃ at a rate of 5℃ / min~10℃ / min, and then preheated for 1h~1.5h at the temperature of 400℃~500℃. In step three, the temperature is first cooled to 850℃~900℃ at a rate of 8℃ / min~10℃ / min, and then cooled to 200℃~300℃ at a rate of 4℃ / min~5℃ / min.

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