Method for regulating and controlling TiAl lamella direction and optimizing performance based on beta-phase sequential solidification

Abstract

The invention discloses a method for regulating and controlling TiAl lamellar direction and optimizing performance based on beta-phase sequential solidification, and relates to the technical field of alloy preparation. The problems that an existing TiAl alloy is poor in high-temperature performance, inconsistent in structure and serious in element segregation are solved. According to the method, the TiAl alloy is prepared by using electromagnetic cold crucible directional solidification equipment, and the lamellar direction in crystal grains in the TiAl alloy is regulated and controlled. The method specifically comprises the following steps: preparing an alloy ingot by using an electromagnetic cold crucible directional solidification process, and forming a beta phase between crystal grains by reducing the drawing speed, so as to optimize the lamellar direction; in the regulated and controlled directionally solidified TiAl alloy, the proportion of grains in the 0-45-degree lamellar direction is increased to 70-80%, the tensile strength at 900 DEG C is 450-600 MPa, and the ductility is 2-4%. And the large-size directionally solidified TiAl alloy with pollution-free interfaces and few transverse grain boundaries is prepared. The method is used for preparing the TiAl alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of TiAl alloy preparation and relates to a method for controlling the orientation of TiAl lamellae and optimizing their performance. Specifically, it relates to a method for controlling the orientation of TiAl lamellae and optimizing their performance based on sequential solidification of the β phase. This method is used to prepare lightweight, high-temperature-resistant materials for aircraft engine blades, using directional solidification of TiAl alloy lamellae to control their performance at temperatures up to 900°C. Background Art

[0002] With the rapid development of aero-engines and the increasing requirements for material performance in high-temperature service environments, TiAl alloy, as an important lightweight and high-strength structural material, is considered to be an important candidate material for low-pressure turbine blades, and its microstructure and mechanical properties have received widespread attention.

[0003] The TiAl alloys that are currently widely used usually need to undergo complex heat treatment processes to optimize their mechanical properties. The TiAl alloys prepared in this way have a large number of grain boundaries. When used as rotating parts of aircraft engines, the grain boundaries are prone to produce holes and cracks, making it difficult to meet the stability requirements in high-temperature environments. Directional solidification can eliminate a large number of transverse grain boundaries and prepare large-sized columnar crystals. And through one-step casting, it is more suitable for the molding of complex structure castings. During the high-speed rotation of aircraft engine turbine blades, each blade is mainly subjected to unidirectional centrifugal force. The performance of TiAl alloy is closely related to the direction of its lamellar arrangement. The smaller the angle between the force direction and the lamellar direction, the better the comprehensive performance of the TiAl alloy. However, due to the complexity of the phase transformation process, regulating the lamellar direction through directional solidification is a difficult problem that needs to be solved urgently.

[0004] For example: (1) The invention patent with publication number CN116334426A eliminates the interface contamination of TiAl alloy by using niobium crucible in the directional solidification preparation process and improves the mechanical properties of the alloy. However, niobium is expensive and difficult to process, and its use in preparing water-cooled crucibles is not conducive to its promotion and application. (2) The invention patent with publication number CN109280809A uses a water-cooled copper crucible and increases the pulling speed of directional solidification to prepare a large-sized TiAl alloy with finer interlamellar spacing. However, this method cannot take into account the control of the interlamellar direction. (3) The invention patent with publication number CN114703436A adds W, Cr, and B to the directionally solidified TiAl alloy, thereby refining the columnar crystal structure and the spacing of the banded B2 phase, and using the precipitation phase to achieve the improvement of the high-temperature mechanical properties of the titanium aluminum alloy in the axial direction. However, this method will refine the columnar crystals and increase the lateral grain boundaries. (4) Invention patent CN105821470A prepared a TiAl alloy with uniform lamellar orientation by optical floating zone directional solidification. However, the TiAl alloy prepared in this way is small in size and difficult to promote to industrial applications. Summary of the Invention

[0005] The present invention aims to address the problems of poor high-temperature performance, inconsistent microstructure, and severe element segregation in existing TiAl alloys, and further provides a method for controlling TiAl lamella orientation and optimizing performance based on sequential solidification of the β phase.

[0006] The technical solution of the present invention is: a method for regulating the direction of TiAl lamellae and optimizing performance based on β-phase sequential solidification, comprising the following steps: preparing TiAl alloy using an electromagnetic cold crucible directional solidification device, and regulating the direction of lamellae in the grains of the TiAl alloy: Step 1: preparing a directionally solidified master alloy ingot; Step 2: Prepare the feeding rod; Cut a round rod from the master alloy ingot in step 1 to serve as a feed rod; Step 3: Prepare the pull rod; Step 4: Prepare electromagnetic cold crucible for directional solidification; Step 41: After installing the water-cooled copper crucible, close the furnace door and evacuate. When the pressure drops to 3 Pa, close the vacuum valve and fill the furnace with argon to 500 Pa. Step 42: Repeat the above steps at least 4-8 times; finally, fill the furnace with argon until the pressure inside the furnace reaches 350 MPa; Step 5: Start the cooling water circulation system: Start the power cabinet heating, adjust the voltage to 100V, increase 10V every 40-60s, and when the power reaches 40-50kW, keep warm for 5-10 minutes. Then open the upper and lower pulling systems at the same time to conduct directional solidification experiments. During this period, keep the crystallizer temperature at 25°C; the pulling speed of the lower pulling system is 0.05-1mm / min; Step 6: After the directionally solidified sample rod reaches the predetermined growth length, close the upper and lower pulling systems, reduce the power supply voltage by a gradient of 50V per minute, and finally reduce it to 0, turn off the power, open the furnace body, and take out the sample rod. At this point, the preparation of TiAl alloy is completed.

[0007] Furthermore, in step 1, a 20 kg grade directionally solidified master alloy ingot is obtained by induction melting mold solidification.

[0008] Furthermore, the composition of the alloy ingot in step 1 is: 40-48% Al, 5-10% Nb, 0.1-1% C, 0.8-2.4% Ta, 0.4-1.6% Hf, and the balance Ti, in atomic percentage.

[0009] Furthermore, the specific preparation process of the feeding rod in step 2 is as follows: Round bars of φ18-24mm×130mm are cut from the master alloy ingot, and the surface wire cutting marks are removed after grinding. Dovetails and dovetail grooves are processed at the head and tail of the round bars respectively. Four round bars are selected and connected to each other at the head and tail to form feeding rods.

[0010] Preferably, the diameter of the feeding rod in step 2 is 20-22 mm.

[0011] Furthermore, the preparation method of the pulling rod in step 2 is as follows: A 30 mm × 30 mm × 55 mm base is cut from the master alloy ingot, polished to remove surface wire cutting marks, and fitted onto the lower pull rod through a dovetail structure to form a lower pull rod.

[0012] Preferably, the pulling speed of the lower pulling system in step five is 0.1-0.3 mm / min.

[0013] Preferably, the pulling speed of the lower pulling system in step five is 0.2 mm / min.

[0014] Preferably, the pulling speed of the lower pulling system in step five is 0.7 mm / min.

[0015] Preferably, the pulling speed of the lower pulling system in step five is 0.9 mm / min.

[0016] Compared with the prior art, the present invention has the following effects: 1. This invention is a method for controlling the orientation and optimizing the properties of TiAl lamellae through sequential solidification of the β phase, using a preparation process based on electromagnetic cold crucible directional solidification technology. By controlling the pulling speed, the lamella orientation distribution of the TiAl alloy is optimized, improving the high-temperature performance of the cast TiAl alloy at 900°C, and preparing large-scale directionally solidified TiAl alloys with no contamination from interfaces and few lateral grain boundaries.

[0017] 2. The present invention designs the elements so that the primary phase during the solidification of the alloy is the β phase. The C element is designed to be added to strengthen the alloy by solid solution. The selected Al element content is less than 48%, and high melting point β stabilizing elements such as Ta, Hf, and Nb are designed to be added to improve the high temperature performance and make the primary phase during the solidification of the alloy the β phase. The preferred growth orientation of the β phase is <001> The direction of the direction solidified TiAl alloy prepared by the present invention is parallel to the direction of heat flow, which provides a prerequisite for controlling the direction of the layer. After rapid cooling of the liquid phase, the structure of the directionally solidified TiAl alloy is dendritic β grains, and the primary phase is β phase.

[0018] 3. The present invention achieves the directional formation of low-angle lamellar structures by precisely controlling the pulling speed to 0.1-0.3 mm / min. By controlling the pulling speed parameter of the lower drawbar, the present invention achieves sequential solidification of the alloy, with the β phase growing on the first-solidified lamellae, and the later-solidified lamellae continuing to grow on the β phase. The lamellar orientation is inherited, resulting in ingots with a low-angle lamellar orientation ratio of up to 70-80%. This provides quantifiable process parameters and a reliable theoretical basis for controlling the lamellar orientation of directionally solidified TiAl alloys.

[0019] 4. The TiAl alloy ingots produced by the present invention exhibit a tensile strength of 450-600 MPa at 900°C and an elongation of 2-4%. By optimizing the directional solidification pulling speed parameters of the TiAl alloy, the present invention successfully achieves a uniform grain structure with a controllable lamellar orientation distribution, achieving a good match between high-temperature strength and ductility. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a macroscopic photograph of the directionally solidified TiAl alloy prepared by the present invention; Figure 2 It is the statistical result of the lamellar direction ratio of the directionally solidified TiAl alloy prepared by the present invention; Figure 3 This is a microstructure photograph of a directionally solidified TiAl alloy prepared by the present invention; Figure 4 This is a 900°C high-temperature tensile curve of the directionally solidified TiAl alloy prepared by the present invention. DETAILED DESCRIPTION

[0021] Specific embodiment 1: This embodiment includes the following steps of preparing TiAl alloy using electromagnetic cold crucible directional solidification equipment and regulating the direction of the lamellae in the TiAl alloy grains: Step 1: preparing a directionally solidified master alloy ingot; Step 2: Prepare the feeding rod; Cut a round rod from the master alloy ingot in step 1 to serve as a feed rod; Step 3: Prepare the pull rod; Step 4: Prepare electromagnetic cold crucible for directional solidification; Step 41: After installing the water-cooled copper crucible, close the furnace door and evacuate. When the pressure drops to 3 Pa, close the vacuum valve and fill the furnace with argon to 500 Pa. Step 42: Repeat the above steps at least 4-8 times; finally, fill the furnace with argon until the pressure inside the furnace reaches 350 MPa; Step 5: Start the cooling water circulation system: Start the power cabinet heating, adjust the voltage to 100V, increase 10V every 40-60s, and when the power reaches 40-50kW, keep warm for 5-10 minutes. Then open the upper and lower pulling systems at the same time to conduct directional solidification experiments. During this period, keep the crystallizer temperature at 25°C; the pulling speed of the lower pulling system is 0.05-1mm / min; Step 6: After the directionally solidified sample rod reaches the predetermined growth length, close the upper and lower pulling systems, reduce the power supply voltage by a gradient of 50V per minute, and finally reduce it to 0, turn off the power, open the furnace body, and take out the sample rod. At this point, the preparation of TiAl alloy is completed.

[0022] The fixed, elevated power supply voltage in step five of this embodiment ensures uniform and sufficient heating of the alloy, preventing cracks caused by uneven heating of the upper feed rod. Holding the temperature for a period of time stabilizes the magnetic field distribution and the shape of the molten pool, facilitating the growth of the directionally solidified ingot.

[0023] The slower pulling speed of this embodiment reduces lateral heat dissipation and prevents the lamellae from growing laterally.

[0024] The power cabinet in this embodiment heats the alloy by adjusting the voltage to 100V and increasing it by 10V every 40-60 seconds. This voltage regulation method ensures continuous and stable heat input during the heating process, ensuring uniform heating of the material while effectively preventing cracking caused by localized overheating of the upper feed rod.

[0025] In this embodiment, after installing a water-cooled copper crucible, the furnace door is closed and vacuum is applied. When the pressure drops to 3 Pa, the vacuum valve is closed and argon is filled into the furnace to 500 Pa. This process is repeated at least 4 to 8 times. By repeatedly vacuuming and filling with argon, oxygen is removed from the furnace, reducing the oxygen content in the directionally solidified ingot and improving the alloy's performance.

[0026] In this embodiment, after the power source reaches the specified power, the temperature is maintained for 5-10 minutes. Then, the upper and lower pull systems are simultaneously opened to conduct the directional solidification experiment. By setting the holding time, the electromagnetic field distribution reaches a steady state and forms a stable molten pool morphology, thus providing a flat and stable solid-liquid interface for the directional solidification process, ensuring that β preferentially grows along the

[001] crystal direction and perpendicular to the solid-liquid interface.

[0027] Specific embodiment 2: In step 1 of this embodiment, a 20 kg grade directionally solidified master alloy ingot is obtained by induction melting mold shell solidification.

[0028] This setup utilizes electromagnetic induction heating and a water-cooled copper mold to form a metal shell, achieving high-purity melting. This prevents crucible contamination for active materials like TiAl. Its precise temperature control and electromagnetic stirring ensure uniform composition and minimize segregation, while the vacuum or inert gas environment effectively reduces porosity and impurities. Due to the high room-temperature brittleness of TiAl alloys, a 20 kg ingot can be prepared to avoid cracks while producing a large ingot, facilitating subsequent processing.

[0029] Other components and connection relationships are the same as those in the first embodiment.

[0030] Specific embodiment three: The composition of the alloy ingot in step one of this embodiment is: 40-48% Al, 5-10% Nb, 0.1-1% C, 0.8-2.4% Ta, 0.4-1.6% Hf, and the balance Ti in atomic percentage.

[0031] With this configuration, the Ta, Hf, and Nb elements in this composition are high-melting-point elements, which help improve the high-temperature performance of the TiAl alloy. A trace amount of C, as an interstitial element, solid-solution-enhances the alloy, producing a significant solid-solution strengthening effect. The remaining composition and connections are the same as in Specific Embodiments 1 or 2.

[0032] In this embodiment, the Ta in the composition acts as a β-stabilizing element, and together with the relatively low Al content, ensures that the primary phase during alloy solidification is the β phase. This facilitates the regulation of the β-to-α phase transformation dynamics during directional solidification, thereby enabling active control of the orientation of the TiAl alloy lamellae.

[0033] The solidification mode corresponding to the alloy composition of the present invention is β solidification, and the preferred growth direction of β is <001> The crystal direction is parallel to the temperature gradient direction. This is beneficial for the crystal to grow along the heat flow direction during directional solidification, thereby regulating the direction of the lamellae.

[0034] Specific embodiment 4: The specific preparation process of the feed rod in step 2 of this embodiment is as follows: Round rods measuring 18-24mm x 130mm are cut from the master alloy ingot and polished to remove surface wire-cutting marks. Dovetails and dovetail grooves are machined at the ends of the rods. Four rods are then connected end to end to form feed rods. This arrangement creates a significant skin effect when a feed rod of this size is subjected to the magnetic induction force of the coil, resulting in high heating efficiency. This facilitates the production of high-quality directionally solidified ingots. Other components and connections are the same as those in Specific Embodiments 1, 2, or 3.

[0035] Specific implementation method 5: The diameter of the feeding rod in step 2 of this implementation method is 20-22 mm.

[0036] This configuration ensures a significant skin effect during induction heating, resulting in higher energy conversion efficiency. This design not only improves heating efficiency but also ensures the production of high-quality, directionally solidified ingots with uniform structure and low defect rates. Other components and connections are the same as those in Specific Embodiments 1, 2, 3, or 4.

[0037] Specific embodiment six: The preparation method of the pulling rod in step 2 of this embodiment is as follows: cut a 30 mm × 30 mm × 55 mm base from the mother alloy ingot, polish it to remove the surface wire cutting marks, and fit it to the lower pulling rod through a dovetail structure to form a lower pulling rod.

[0038] In this way, the size is selected to ensure that the gap between the base and the wall of the water-cooled copper crucible is small to prevent leakage. On the other hand, its high height allows it to be completely immersed in the coolant to form a stable temperature gradient. The other components and connection relationships are the same as those in specific embodiments one, two, three, four or five.

[0039] Specific embodiment seven: The pulling speed of the lower pulling system in step five of this embodiment is 0.1-0.3 mm / min.

[0040] With this arrangement, the degree of supercooling at the solid-liquid interface front is low, and the solidification mode is heterogeneous nucleation, so that the solidification sequence is a lamellar-β phase-lamellar pattern, achieving sequential solidification. The other components and connection relationships are the same as those of specific embodiments one, two, three, four, five or six.

[0041] In this embodiment, grains with a 0-45° lamellae orientation account for 70-80% of the total. The angle between the close-packed planes of the face-centered cubic crystals is 60°. The 0-45° oriented lamellae in the first-solidifying grains have a 75% probability of being inherited by the later-solidifying grains through face nucleation. This achieves localized control of lamellae orientation. At 900°C, the tensile strength is between 450 and 600 MPa, and the elongation is between 2 and 4%.

[0042] This embodiment reduces lateral heat dissipation and suppresses the lateral growth trend of the lamellar tissue by controlling the slower pulling speed.

[0043] Specific embodiment 8: The pulling speed of the lower pulling system in step 5 of this embodiment is 0.2 mm / min.

[0044] This configuration controls the pulling speed of the lower pull system between 0.1 and 0.3 mm / min, reducing the undercooling at the solid-liquid interface front, allowing the grains to solidify in a heterogeneous nucleation pattern and promoting sequential solidification of the lamellar structure. This process, by designing a lamellar-β-phase-lamellar solidification pattern, allows the direction of the post-solidified lamella to be controlled by crystal orientation.

[0045] Other components and connection relationships are the same as those in the first, second, third, fourth, fifth, sixth or seventh embodiment.

[0046] Specific embodiment 9: The pulling speed of the lower pulling system in step 5 of this embodiment is 0.7 mm / min.

[0047] Specific embodiment 10: The pulling speed of the lower pulling system in step 5 of this embodiment is 0.9 mm / min.

[0048] The ingot microstructure obtained using the present invention exhibits a 0-45° oriented lamellar grain ratio of 70-80%. This structural characteristic is attributed to the nucleation of newly formed lamellae within the β phase at the lamellar interface of solidified grains. This nucleation process follows a specific orientation relationship, whereby the phase transformation planes of the newly formed lamellae maintain an approximately 60° orientation with both the β phase close-packed plane and the solidified grain lamellae. This characteristic significantly increases the proportion of low-angle oriented lamellar grains to 70-80%. Tests at 900°C show tensile strength in the 450-550 MPa range, with elongation in the 2-4% range.

[0049] Combine Figures 1 to 4 Describe the embodiments of the present invention: Example 1: This example is based on a specific alloy composition: 47% Al, 6% Nb, 0.1% C, 1.6% Ta, 0.8% Hf, and the balance Ti. A directionally solidified ingot is prepared by the following steps: 1. Obtaining 20 kg grade directional solidification master alloy ingot by induction melting mold solidification 2. Cut φ20mm×130mm round bars from the master alloy ingot, polish to remove surface wire cutting marks, and connect them to each other through dovetail and dovetail groove structures to form feeding rods.

[0050] 3. Cut a 30 mm × 30 mm × 55 mm base from the mother alloy ingot, polish it to remove the surface wire cutting marks, and fit it to the lower pull rod through a dovetail structure to form a lower pull rod.

[0051] 4. After installing the water-cooled copper crucible, close the furnace door and evacuate the furnace. When the pressure drops to 3 Pa, close the vacuum valve and fill the furnace with argon to 500 Pa. Repeat the above steps five times. Finally, fill the furnace with argon until the pressure reaches 350 MPa.

[0052] 5. Start the cooling water circulation system. Start the power cabinet heating and adjust the voltage to 100V. Increase the voltage by 10V every 60 seconds. When the power reaches 45kW, hold the temperature for 5 minutes. Then, open the upper and lower pull systems simultaneously and conduct the directional solidification experiment. During this period, maintain the mold temperature at 25°C. The pull speed of the lower pull system is 0.9mm / min.

[0053] 6. After the directional solidification specimen rod reaches the desired length, close the upper and lower pull systems, reduce the power supply voltage by 50V per minute, and finally reduce it to 0. Turn off the power supply. Open the furnace and remove the specimen rod.

[0054] Example 2: This example is based on a specific alloy composition: 47% Al, 6% Nb, 0.1% C, 1.6% Ta, 0.8% Hf, and the balance Ti. A directionally solidified ingot is prepared by the following steps: 1. Obtaining 20 kg grade directional solidification master alloy ingot by induction melting mold solidification 2. Cut φ20mm×130mm round bars from the master alloy ingot, polish to remove surface wire cutting marks, and connect them to each other through dovetail and dovetail groove structures to form feeding rods.

[0055] 3. Cut a 30 mm × 30 mm × 55 mm base from the mother alloy ingot, polish it to remove the surface wire cutting marks, and fit it to the lower pull rod through a dovetail structure to form a lower pull rod.

[0056] 4. After installing the water-cooled copper crucible, close the furnace door and evacuate the furnace. When the pressure drops to 3 Pa, close the vacuum valve and fill the furnace with argon to 500 Pa. Repeat the above steps five times. Finally, fill the furnace with argon until the pressure reaches 350 MPa.

[0057] 5. Start the cooling water circulation system. Start the power cabinet heating and adjust the voltage to 100V. Increase the voltage by 10V every 60 seconds. When the power reaches 45kW, hold the temperature for 5 minutes. Then, open the upper and lower pull systems simultaneously and conduct the directional solidification experiment. During this period, maintain the crystallizer temperature at 25°C. The pull speed of the lower pull system is 0.7mm / min.

[0058] 6. After the directional solidification specimen rod reaches the desired length, close the upper and lower pull systems, reduce the power supply voltage by 50V per minute, and finally reduce it to 0. Turn off the power supply. Open the furnace and remove the specimen rod.

[0059] Example 3: This example is based on a specific alloy composition: 47% Al, 6% Nb, 0.1% C, 1.6% Ta, 0.8% Hf, and the balance Ti. A directionally solidified ingot is prepared by the following steps: 1. Obtaining 20 kg grade directional solidification master alloy ingot by induction melting mold solidification 2. Cut φ20mm×130mm round bars from the master alloy ingot, polish to remove surface wire cutting marks, and connect them to each other through dovetail and dovetail groove structures to form feeding rods.

[0060] 3. Cut a 30 mm × 30 mm × 55 mm base from the mother alloy ingot, polish it to remove the surface wire cutting marks, and fit it to the lower pull rod through a dovetail structure to form a lower pull rod.

[0061] 4. After installing the water-cooled copper crucible, close the furnace door and evacuate the furnace. When the pressure drops to 3 Pa, close the vacuum valve and fill the furnace with argon to 500 Pa. Repeat the above steps five times. Finally, fill the furnace with argon until the pressure reaches 350 MPa.

[0062] 5. Start the cooling water circulation system. Start the power cabinet heating and adjust the voltage to 100V. Increase the voltage by 10V every 60 seconds. When the power reaches 45kW, hold the temperature for 5 minutes. Then, open the upper and lower pull systems simultaneously and conduct the directional solidification experiment. During this period, maintain the mold temperature at 25°C. The pull speed of the lower pull system is 0.2mm / min.

[0063] 6. After the directional solidification specimen rod reaches the desired length, close the upper and lower pull systems, reduce the power supply voltage by 50V per minute, and finally reduce it to 0. Turn off the power supply. Open the furnace and remove the specimen rod.

[0064] Example 4: This example is based on Example 1, Example 2, Example 3 and Figure 1 Macrostructure diagram of a directionally solidified ingot. (a) shows the macrostructure of a directionally solidified specimen produced at a pulling speed of 0.9 mm / min, (b) shows the macrostructure of a directionally solidified specimen produced at a pulling speed of 0.7 mm / min, and (c) shows the macrostructure of a directionally solidified specimen produced at a pulling speed of 0.2 mm / min. Comparison shows that as the pulling speed decreases, the length and width of the columnar crystals increase simultaneously. Growth continuity gradually improves. This is because a slower pulling speed reduces lateral heat dissipation and suppresses the lateral growth trend of the grains, resulting in continuously growing large columnar crystals.

[0065] Example 5: This example is based on Example 1 to Example 4 and Figure 2Directional solidification lamellar orientation statistics. (a) shows the lamellar orientation statistics for a directionally solidified specimen prepared at a pulling rate of 0.9 mm / min, (b) shows the lamellar orientation statistics for a directionally solidified specimen prepared at a pulling rate of 0.7 mm / min, and (c) shows the lamellar orientation statistics for a directionally solidified specimen prepared at a pulling rate of 0.2 mm / min. Comparison shows that reducing the pulling rate significantly increases the proportion of grains with lamellar orientations of 0-45° in the alloy. This is because the lower solidification rate effectively reduces the undercooling at the solid-liquid interface, prompting the nucleation of new lamellae on the β phase at the lamellar interface of the solidified grains. This nucleation process follows a specific orientation relationship, where the phase transformation planes of the new lamellae maintain an angle of approximately 60° with the close-packed planes of the β phase, and the close-packed planes of the β phase maintain an angle of approximately 60° with the lamellar orientation of the solidified grains. This characteristic significantly increases the probability of forming low-angle oriented lamellar grains.

[0066] Example 6: This example is based on Example 1 to Example 5 and Figure 3 Microstructures in directionally solidified TiAl alloys. (a) shows the microstructure of a directionally solidified sample produced at a pulling speed of 0.9 mm / min, (b) shows the microstructure of a directionally solidified sample produced at a pulling speed of 0.7 mm / min, and (c) shows the microstructure of a directionally solidified sample produced at a pulling speed of 0.2 mm / min. Comparison reveals that as the pulling speed decreases, the angle between the lamellae and the pulling direction gradually decreases, and the B2 phase in the structure shifts from a network distribution to a directional arrangement. This indicates that reducing the pulling speed optimizes the directional effect. By controlling the pulling rate, the undercooling at the solid-liquid interface front is reduced, promoting sequential solidification of the lamellae. The high-temperature β phase solidifies sequentially and is retained until room temperature, forming a directional B2 phase.

[0067] Example 7: This example is based on Example 1 to Example 6 and Figure 4 900°C high-temperature tensile curves of a directionally solidified TiAl alloy. Figure 1 shows the microstructure of a directionally solidified specimen produced at a pulling speed of 0.9 mm / min, Figure 2 shows the microstructure of a directionally solidified specimen produced at a pulling speed of 0.7 mm / min, and Figure 3 shows the microstructure of a directionally solidified specimen produced at a pulling speed of 0.2 mm / min. It can be seen that when the pulling speed is reduced to 0.2 mm / min, the alloy achieves optimal high-temperature tensile properties, thanks to the large proportion of low-angle lamellar orientations, with a tensile strength of 506 MPa and an elongation of 3.4%.

[0068] Although the present invention has been disclosed above with reference to preferred embodiments, this is not intended to limit the present invention. Those skilled in the art may also make other changes within the spirit of the present invention, and apply the present invention to fields not mentioned herein. Of course, these changes made in accordance with the spirit of the present invention should be included in the scope of protection claimed by the present invention.

Claims

1. A method for controlling TiAl lamella orientation and optimizing performance based on sequential solidification of β phase, characterized by: The method includes the following steps of preparing TiAl alloy by using electromagnetic cold crucible directional solidification equipment and regulating the direction of lamellae in the grains of TiAl alloy: Step 1: preparing a directionally solidified master alloy ingot; Step 2: Prepare the feeding rod; Cut a round rod from the master alloy ingot in step 1 to serve as a feed rod; Step 3: Prepare the pull rod; Step 4: Prepare electromagnetic cold crucible for directional solidification; Step 41: After installing the water-cooled copper crucible, close the furnace door and evacuate. When the pressure drops to 3 Pa, close the vacuum valve and fill the furnace with argon gas to 500 Pa. Step 42: Repeat the above steps at least 4-8 times; finally, fill the furnace with argon until the pressure inside the furnace reaches 350 MPa; Step 5: Start the cooling water circulation system: Start the power cabinet heating, adjust the voltage to 100V, increase 10V every 40-60s, and when the power reaches 40-50kW, keep warm for 5-10 minutes. Then open the upper and lower pulling systems at the same time to conduct directional solidification experiments. During this period, keep the crystallizer temperature at 25°C; the pulling speed of the lower pulling system is 0.05-1mm / min; Step 6: After the directionally solidified sample rod reaches the predetermined growth length, close the upper and lower pulling systems, reduce the power supply voltage by a gradient of 50V per minute, and finally reduce it to 0, turn off the power, open the furnace body, and take out the sample rod. At this point, the preparation of TiAl alloy is completed.

2. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 1, characterized in that: In step 1, a 20 kg grade directionally solidified master alloy ingot is obtained by induction melting mold solidification.

3. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 2, characterized in that: The composition of the alloy ingot in step 1 is as follows: 40-48% Al, 5-10% Nb, 0.1-1% C, 0.8-2.4% Ta, 0.4-1.6% Hf, and the balance Ti, in atomic percentage.

4. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 1 or 3, characterized in that: The specific preparation process of the feeding rod in step 2 is as follows: Round bars of φ18-24mm×130mm are cut from the master alloy ingot, and the surface wire cutting marks are removed after grinding. Dovetails and dovetail grooves are processed at the head and tail of the round bars respectively. Four round bars are selected and connected to each other at the head and tail to form feeding rods.

5. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 3, characterized in that: The diameter of the feed rod in step 2 is 20~22mm.

6. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 1 or 5, characterized in that: The preparation method of the pulling rod in step 2 is as follows: A 30 mm × 30 mm × 55 mm base is cut from the master alloy ingot, polished to remove surface wire cutting marks, and fitted onto the lower pull rod through a dovetail structure to form a lower pull rod.

7. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 1, characterized in that: The pulling speed of the lower pulling system in step 5 is 0.1-0.3 mm / min.

8. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 1, characterized in that: The pulling speed of the lower pulling system in step 5 is 0.2 mm / min.

9. The high-frequency induction heating dual-coil coupled rotation controlled melting equipment for processing multi-component alloys according to claim 1, characterized in that: The pulling speed of the lower pulling system in step 5 is 0.7 mm / min.

10. The method for controlling TiAl lamella orientation and optimizing performance based on β-phase sequential solidification according to claim 1, characterized in that: The pulling speed of the lower pulling system in step 5 is 0.9 mm / min.

Images