Preparation method of large-size titanium-aluminum alloy low-pressure turbine blade

Abstract

The invention relates to the technical field of Ti-Al intermetallic compound investment casting forming, in particular to a preparation method of a large-size titanium-aluminum alloy low-pressure turbine blade. The method comprises the following steps: preparing a blade profiling ceramic mold shell by lost-wax investment casting, roasting the mold shell, placing the roasted mold shell on a centrifugal turntable of vacuum induction furnace casting equipment, melting a titanium-aluminum alloy by induction heating, pouring titanium-aluminum liquid, injecting the titanium-aluminum liquid into the blade ceramic mold shell which rotates centrifugally, and solidifying and forming; and after the blade is naturally cooled to the temperature lower than 800 DEG C in a vacuum environment, opening a vacuum furnace door to take out the blade mold shell, and removing an outer ceramic mold shell layer of the blade through mechanical vibration to obtain a blade casting blank. After a titanium-aluminum blade casting blank is subjected to hot isostatic pressing treatment and heat treatment, the casting allowance of 1-3 mm of a blade body is removed through numerical control machining, the precise requirement for the dimensional tolerance of blade body parts is met, then a tenon and a sealing tooth part of the blade are subjected to precise grinding machining through the positioning reference of the blade body, and therefore the purpose of overall precise forming of the titanium-aluminum blade is achieved.

Description

Technical Field

[0001] This invention relates to the field of Ti-Al intermetallic compound investment casting technology, specifically a method for preparing large-size titanium-aluminum alloy low-pressure turbine blades, applicable to the preparation of low-pressure turbine blades for high-bypass turbofan aero-engines. Background Technology

[0002] TiAl alloys have a density only half that of nickel-based superalloys and can be used at temperatures of 600℃ to 700℃. Replacing nickel-based superalloys with TiAl alloys in the last two stages of the low-pressure turbine blades for high-thrust turbofan aero-engines can significantly reduce the static and dynamic loads of the engine, making a substantial contribution to improving the engine's thrust-to-weight ratio and fuel efficiency. This patent focuses on the application requirements of lightweight TiAl alloy low-pressure turbine blades in high-bypass turbofan aero-engines (bypass ratio greater than 4). It will conduct research and development on high-quality TiAl alloy blade manufacturing technology, effectively control the metallurgical quality and dimensional accuracy of cast TiAl alloy low-pressure turbine blades, further improve the technological maturity and product qualification rate of blade manufacturing, and develop new manufacturing processes for TiAl alloy low-pressure turbine blades. This will meet the technical requirements of reducing structural weight for achieving high thrust-to-weight ratios in my country's advanced high-thrust turbofan aero-engines.

[0003] Patent CN119457746A discloses a high-precision CNC machining method for large-size, high-curvature TiAl alloy turbine blades. The method involves casting a rectangular block from a metal mold and then machining the blade, falling under the category of mechanical forming. While this method improves the dimensional accuracy and surface quality of the blades to some extent, it still has some drawbacks. For example, the metal mold manufacturing cost is high, the cycle time is long, and the requirements for mold precision and durability are stringent. Furthermore, manual polishing during processing can still affect the consistency and quality stability of the product, making it impossible to completely avoid quality fluctuations caused by human factors.

[0004] Patent CN115740494A discloses a TiAl alloy blade and its manufacturing method, which uses powder additive printing to prepare the blade, differing significantly from investment casting. While electron beam selective melting (EBM) in additive manufacturing can produce TiAl alloy blades with high dimensional accuracy and surface finish, additive manufacturing equipment is expensive, has stringent operating environment requirements, and relatively low production efficiency, making it difficult to meet the needs of large-scale production.

[0005] Patent CN114687811A discloses a titanium-aluminum alloy turbine and its manufacturing method. By ultrasonically treating the molten material at the turbine core after centrifugal casting, the turbine blades develop a fully columnar crystalline structure, while the core exhibits a fine equiaxed crystalline structure, thereby improving the reliability of the titanium-aluminum alloy turbine. However, this method focuses on the microstructure control of the turbine core and blades, with insufficient consideration given to the overall dimensional accuracy control and surface quality improvement of the blades. Furthermore, its process is relatively complex, requiring additional ultrasonic treatment equipment and steps, increasing production costs and operational difficulty. Summary of the Invention

[0006] The purpose of this invention is to provide a method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades. The technical problem to be solved is to replace the current manufacturing method of near-net-shape casting (casting allowance < 0.7 mm) + manual grinding. By combining a larger casting allowance design (1-3 mm) with CNC machining, the method avoids the inability to remove surface porosity defects and the dimensional deviation of blade twisting caused by stress release, thereby obtaining large-size TiAl alloy low-pressure turbine blades with good metallurgical quality and high precision, which can significantly improve product quality and yield.

[0007] The technical solution of this invention is:

[0008] A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades includes the following steps:

[0009] Step 1: Use special wax material for blades to make blade wax molding. The blade wax pattern should be free of defects and flow line defects. Compare the design wax pattern with the blade part. The contour should have a machining allowance of 1-3mm. Set feeding strips in key parts of the blade body. After the wax pattern is corrected, a three-coordinate measurement should be performed to determine the precise control of the blade wax pattern size.

[0010] Step 2: The blade wax model is combined and welded with the sprue and pouring cup wax models. The joints are filled with liquid wax to create a smooth transition. Preparation of the blade ceramic mold shell: 6 to 8 layers of Y2O3 surface layer, transition layer and Al2O3 back layer are applied, with each layer drying for 8 to 48 hours.

[0011] Step 3: After dewaxing and firing, the blade mold shell is placed in an insulated sand box and filled with sand. The preheating regime for the mold shell is: temperature 400-600℃, time >10h.

[0012] Step 4: The TiAl alloy master alloy is heated in a vacuum water-cooled copper crucible induction furnace. The molten liquid is poured into a centrifugally rotating blade mold shell and solidified. After cooling, the mold shell is removed from the sand box and mechanically vibrated to remove the mold shell, thus obtaining the TiAl alloy blade billet.

[0013] Step 5: The TiAl alloy blade billet undergoes hot isostatic pressing at 1260℃ / 140MPa / 3~4h and heat treatment at 1010℃ / 12h.

[0014] Step 6: CNC machining removes the 1-3mm casting allowance from the blade body to meet the precise requirements of the blade body dimensional tolerance. Then, using the positioning datum of the blade body, the tenons and sealing teeth at both ends of the blade are precisely ground to achieve the overall precision forming goal of the TiAl alloy blade.

[0015] The method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades, by weight percentage, comprises the following TiAl alloy composition: Al: 29.3%–30.7%, Nb: 4.3%–5.3%, Mn: 2.3%–3.3%, B: 0.23%–0.28%, with the balance being Ti and unavoidable impurity elements; wherein the unavoidable impurity elements are Fe, Si, O, N, and H, with Fe ≤ 0.07%, Si ≤ 0.07%, O ≤ 0.085%, N ≤ 0.02%, and H ≤ 0.01%.

[0016] The method for preparing large-size titanium-aluminum alloy low-pressure turbine blades, wherein the smelting process of the TiAl alloy master alloy is as follows: the raw material is 0-1 grade sponge titanium, and the alloying elements Mn and Nb are added in the form of intermediate alloy; the alloying element Al is partially introduced by the intermediate alloy, and the insufficient part is added with pure Al; after the intermediate alloy and sponge titanium are batched and mixed, they are pressed into electrodes by a press; the electrodes are welded together, melted once in a vacuum arc furnace, and then melted and cast into a master alloy ingot by a vacuum arc solidification furnace.

[0017] The method for preparing large-size titanium-aluminum alloy low-pressure turbine blades involves using a lost-wax investment casting process to prepare the blade mold shell, followed by casting under vacuum centrifugal conditions. The number of blades cast in one batch is 8 to 12, and the formed blade blank has a machining allowance of 1 to 3 mm.

[0018] In the method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades, step 5 of the hot isostatic pressing and heat treatment process does not require tooling to prevent blade twisting and deformation due to the ample casting allowance.

[0019] In the method for preparing large-size titanium-aluminum alloy low-pressure turbine blades, steps 4 to 6 combine investment casting and machining processes to achieve a good match of complete mold filling, high metallurgical quality qualification rate, and stable dimensional accuracy.

[0020] The method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades, wherein the performance index range of the TiAl alloy blades is as follows: tensile strength σ at room temperature. b=600~700MPa, plasticity δ=0.6~1.5%, fatigue strength σ=400~550MPa; tensile strength σ at 650℃ b =550~700MPa, plasticity δ=0.8~2%, fatigue strength σ=380~500MPa, endurance strength σ=350~450MPa after 100h.

[0021] The method described above describes a method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades. The TiAl alloy blades are used to manufacture lightweight, high-temperature resistant, and low-pressure turbine blade components for large aero-engines, and can replace traditional nickel-based high-temperature alloys for long-term use in the range of 600-700℃.

[0022] The design concept of this invention is:

[0023] This invention addresses the urgent need for lightweight, high-strength TiAl alloy low-pressure turbine blades in my country's key high-thrust turbofan aero-engine development. It develops a high-efficiency manufacturing process for large-size TiAl alloy low-pressure turbine blades, solving the problems of low metallurgical quality and large dimensional dispersion in precision-cast TiAl alloy blades. This improves the overall performance margin of precision-cast low-pressure turbine blades and addresses technical challenges such as casting, metallurgical defect control, and dimensional accuracy control of thin-walled TiAl alloy low-pressure turbine blades with lengths exceeding 200mm. Furthermore, it establishes methods for metallurgical quality and dimensional control, ultimately achieving stable control of metallurgical quality and dimensional accuracy.

[0024] This invention utilizes the combined effects of lost-wax investment casting and CNC precision machining to provide relatively relaxed manufacturing conditions for large-size low-pressure turbine blades made of TiAl alloy with a narrow forming process window. This avoids the costly investment in precision molds and the lengthy process of repeated iterations of dimensional deformation caused by blade twisting. Under appropriate allowance design conditions, TiAl alloy low-pressure turbine blades can be successfully centrifugally filled using conventional titanium alloy casting methods. The thickened blade design offers advantages such as good fluidity during casting, good tip filling, high blade strength after casting, and easy vibration-based shell removal. Most importantly, under these conditions, the loose reaction layer (0.3–1.5 mm) on the surface of the TiAl alloy low-pressure turbine blade can be completely removed through machining, resulting in a high blade yield, strong dimensional controllability, and reduced billet input. The overall effect is significantly superior to the net-form precision casting design with no allowance, and it also offers advantages such as lower cost, higher yield, and ease of operation.

[0025] This invention utilizes lost-wax investment casting to prepare a ceramic mold shell for blade conforming. After firing, the mold shell is placed on a centrifugal turntable in a vacuum induction furnace casting equipment. Induction heating is used to heat the titanium-aluminum alloy to its melting temperature of 1450–1550℃ for 2–3 minutes. The molten titanium-aluminum is then poured into the centrifugally rotating ceramic mold shell to solidify. Under vacuum, the blade is allowed to cool naturally to below 800℃ before the vacuum furnace door is opened and the mold shell is removed. Mechanical vibration is used to remove the outer ceramic mold shell layer, resulting in a blade casting blank. The titanium-aluminum blade casting blank undergoes hot isostatic pressing at 1260℃ / 140MPa / 3–4h and heat treatment at 1010℃ / 12h. CNC machining is then used to remove a 1–3mm casting allowance from the blade body to meet precise dimensional tolerances. Finally, using the blade's positioning reference, the tenons and sealing teeth are precisely ground, achieving the overall precision forming of the titanium-aluminum blade.

[0026] The advantages and beneficial effects of this invention are:

[0027] 1. The manufacturing process of large-size titanium-aluminum alloy low-pressure turbine blades of the present invention is based on the precision casting of small-size titanium-aluminum alloy blades (length L<200mm). While maintaining the blade profile, the casting allowance is appropriately expanded to solve the problem of insufficient filling of large-size titanium-aluminum blades. The increased profile allowance provides sufficient reference adjustment space for subsequent machining, and solves the drawbacks of inconsistent dimensions and many surface defects caused by manual grinding. It can significantly improve the production qualification rate of blades and reduce the manufacturing cost. It is applicable to the forming process of high-thrust turbofan aero-engine blades.

[0028] 2. In the process of casting and manufacturing TiAl alloy low-pressure turbine blades using this invention, there is no need to consider the dimensional consistency constraints caused by stress torsion deformation during the blade process. High-precision blades are obtained by machining the final allowance. The appropriate allowance results in good casting and filling effect, strong forming consistency under centrifugal force, and the blade surface after machining is smooth without metallurgical defects. The TiAl alloy blade body has fine and uniform grain size and no internal defects such as cold shuts and shrinkage cavities.

[0029] 3. The length of the large-size low-pressure turbine blades made of TiAl alloy of the present invention can reach 250-400mm, which breaks through the size of precision casting blades without margin, and is suitable for the preparation of low-pressure turbine blades for high-bypass and high-thrust turbofan aero engines.

[0030] 4. This invention raises the technological maturity level of TiAl alloy low-pressure turbine blades from the current level 5 to level 7, laying a solid foundation for their application in my country's advanced medium-bypass turbofan aero-engines.

[0031] 5. Compared with patent CN119457746A, this invention, in the casting process of TiAl alloy low-pressure turbine blades, utilizes a larger casting allowance (1-3 mm) combined with hot isostatic pressing and heat treatment processes to achieve a fine and uniform grain size in the TiAl alloy blade body, eliminating internal defects such as cold shuts and shrinkage cavities. In contrast, while metal mold casting in CN119457746A can reduce the probability of inclusion defects, its effectiveness in controlling metallurgical defects easily generated by large deformation during casting, hot pressing, and heat treatment of large-sized blades is limited, and it cannot fundamentally guarantee the metallurgical quality of the blades.

[0032] 6. Compared with patent CN115740494A, this invention employs investment casting technology. By optimizing process parameters such as coating and sintering of the ceramic mold shell, it effectively avoids defects such as inclusions and porosity, thus improving the metallurgical quality of the blade. Simultaneously, a reasonable heat treatment process further improves the blade's microstructure, resulting in fine and uniform grain size, free from internal defects such as cold shuts and shrinkage cavities, thereby enhancing the blade's mechanical properties and reliability. In contrast, the additive manufacturing process in CN115740494A, due to the special properties of the TiAl alloy material, is prone to defects such as cracks and porosity during printing. Although electromagnetic field-assisted treatment can improve these defects, they are still difficult to completely avoid. Attached Figure Description

[0033] Figure 1 The wax pattern of TiAl alloy low-pressure turbine blade prepared for an embodiment of the present invention.

[0034] Figure 2 The TiAl alloy low-pressure turbine blade casting prepared for an embodiment of the present invention.

[0035] Figure 3 The TiAl alloy low-pressure turbine blade part prepared according to an embodiment of the present invention is a machined part.

[0036] Figure 4 High-magnification micrograph of the cross-section of a TiAl alloy turbine blade prepared for an embodiment of the present invention. Detailed Implementation

[0037] In its specific implementation, this invention provides a method for preparing large-size titanium-aluminum alloy low-pressure turbine blades. It eliminates the need to consider the disordered dimensional changes during blade preparation. Instead, a certain casting allowance is added to the blade wax pattern, exceeding the dimensional fluctuation range of the blade. The blade and gating system are combined to form a mold shell. The blade blank is then cast under vacuum centrifugal conditions. After hot isostatic pressing and heat treatment, it is machined to the precise dimensional tolerances specified in the drawings using a dedicated CNC machining center. The machined blade is then measured using a coordinate measuring machine. Qualified blades are finally ground to the required roughness level (Ra < 0.8 μm) using a vibratory finishing machine. The processed blades also undergo batch sampling for dissection, microstructure analysis, and mechanical testing. Only blades that pass all tests are delivered.

[0038] The following section uses cast TiAl-4522XD alloy (Ti-30Al-4.8Nb-2.8Mn-0.24B, wt%) billet to illustrate the process steps of this invention.

[0039] Example

[0040] In this embodiment, the TiAl alloy billet composition by weight percentage is: Al 30.0%, Nb 4.8%, Mn 2.8%, B 0.24%, with the balance being Ti and unavoidable impurity elements; wherein, the unavoidable impurity elements are Fe, Si, O, N, and H, with Fe 0.06%, Si 0.05%, O 0.06%, N 0.02%, and H 0.007%.

[0041] The existing TiAl alloy low-pressure turbine blade has a length L300mm and a chord width of 53mm. Based on this process route, the following steps are defined:

[0042] The first step is to prepare the wax material. The blades use F28-1 type wax material (precision casting wax material for aviation blades, such as that produced by Jiangsu Zhuhua New Materials Co., Ltd.), and the pouring cup and runner use R838 type wax material (wax material for the gating system, such as that produced by Jiangsu Zhuhua New Materials Co., Ltd.). Select the mold for wax molding according to the identification number. The pressure of the wax injection machine should be controlled at 1.5-2.0MPa, and the mold closing pressure should be controlled at 4-6MPa to perform blade wax molding.

[0043] The blade wax pattern is free of defects such as flaws and streamlines. The casting allowance for the blade wax pattern is designed based on the dimensional characteristics of the blade. The contour of the wax pattern compared to the blade part has a machining allowance of 2mm. The allowance design principle ensures that the blade blank can be successfully machined into a complete blade even if the blade body undergoes random twisting during the wax pattern-mold-casting-heat treatment process, without black skin or undercasting. It also aims to minimize the allowance as much as possible to ensure that the microstructure of the blade meets the standard requirements. Feeding strips can be set in key local parts of the blade body. After the wax pattern is corrected, a coordinate measuring machine is performed to determine the precise control of the blade wax pattern dimensions.

[0044] The second step involves assembling and welding the blade wax model with the sprue and pouring cup wax models. The joints are filled with liquid wax for a smooth transition. Once the blade wax models are pressed and assembled, they are coated and shelled. The shelling environment is maintained at 22±2℃ and 70%±10% humidity. The Y2O3 surface layer dries for 24 hours, and the sand used for the surface layer is controlled within 80-60 mesh. The transition layer coating slurry is prepared by mixing -320 mesh corundum powder and silica sol at a mass ratio of 3:1. The sand used for the transition layer and Al2O3 back layer is controlled within 60-30 mesh, and each layer of sand is sieved before use. Module drying time: 16 hours for the second layer (transition layer), and 8 hours for layers 3-7 (Al2O3 back layer).

[0045] The third step is to place the mold shell into an insulated sand box after dewaxing and firing. Then, fill the sand box with sand and compact it. The preheating temperature of the sand box is set to 600℃ and the preheating time is 12 hours.

[0046] The smelting process of TiAl alloy master alloy is as follows: the raw material is 0-1 grade sponge titanium, and the alloying elements Mn and Nb are added in the form of intermediate alloy; the alloying element Al is partially introduced by the intermediate alloy, and the insufficient part is added with pure Al; after the intermediate alloy and sponge titanium are batched and mixed, they are pressed into electrodes by a press; the electrodes are welded together, melted once in a vacuum arc furnace, and then melted and cast into master alloy ingots in a vacuum arc solidification furnace.

[0047] The TiAl alloy master alloy is heated in a vacuum water-cooled copper crucible induction furnace. The molten liquid is poured into a centrifugally rotating blade mold shell and solidified. After cooling to 700°C, the mold shell is removed from the sand box and mechanically vibrated to remove the mold shell, thus obtaining the blade casting blank. The master alloy loading weight is (20±1) kg. Before induction furnace melting, the leakage rate should be checked, the pre-vacuum degree should be controlled within 0.2 mbar, and the total melting power should be controlled at 700 kW. The titanium-aluminum alloy is heated to the melting temperature of 1500°C and held for 3 minutes using induction heating. The centrifugal speed is set to 400 rpm. After the cast blade mold shell cools, the hammer is used to strike the pouring cup and the horizontal runner to obtain the blade casting blank. The serial number of the blade is marked.

[0048] The fourth step involves hot isostatic pressing at 1260℃ / 140MPa / 4h and heat treatment at 1010℃ / 12h for the TiAl alloy blade billet.

[0049] The fifth step involves using CNC machining to remove the 2mm casting allowance from the blade body to meet the precise requirements of the blade body dimensional tolerance. Then, using the positioning datum of the blade body, the tenons and sealing teeth at both ends of the blade are precisely ground. After passing the three-coordinate inspection, the surface is vibrated and finished. Once the surface roughness meets the standard, the blade is delivered.

[0050] In this embodiment, the performance indicators of the large-size low-pressure turbine blade made of TiAl alloy are as follows:

[0051] All dimensional inspections meet the profile tolerance requirement (±0.15mm), remain within the positive tolerance range of 0 to +0.1, and surface roughness < Ra0.5;

[0052] The leaf blade has a smooth transition without any polishing or undulation. X-ray and surface fluorescence tests of the leaf interior show no defects exceeding the standard levels such as looseness, shrinkage, looseness, and inclusions.

[0053] Tensile strength σ of blade auxiliary rod at room temperature b =653MPa, plasticity (elongation) δ =1.2%, fatigue strength σ =535MPa (3×10 7 (repeated cycles);

[0054] Tensile strength σ at 650℃ b =610MPa, plasticity (elongation) δ =1.6%, fatigue strength σ =456MPa (3×10 7 (Cycles), 650℃ creep strength σ=410MPa (duration 100h).

[0055] This embodiment combines investment casting with machining to remove common surface porosity defects while ensuring the dimensional accuracy of the blade (<0.15mm). This avoids surface porosity defects and dimensional deviations caused by manual grinding, resulting in large-size TiAl alloy low-vortex blades with good metallurgical quality and consistent dimensional accuracy. This TiAl alloy is used to manufacture lightweight, high-temperature resistant components for advanced aero-engines, replacing traditional nickel-based high-temperature alloys for long-term use in the 650-700℃ range.

[0056] like Figure 1 As shown in the figure, the TiAl alloy blade wax model has a clear and flat outline, which makes it easy to place on the process table for precise assembly and welding. The casting allowance on the blade surface is designed to be 2mm.

[0057] like Figure 2As shown in the photograph of the TiAl alloy low-pressure turbine blade billet after hot isostatic pressing, it can be seen that the addition of casting allowance improves the fluidity of the thin-walled blade, the blade casting is fully filled, and the shrinkage head at the sealing tooth of the blade effectively collects the waste residue and gas overflowing from the mold shell at the end of the centrifugal casting.

[0058] like Figure 3 As shown, the TiAl alloy low-pressure turbine blade blanks are machined by CNC instead of manual grinding. By finely adjusting the machining datum and ensuring appropriate casting allowance, the integrity of the blade machining is guaranteed. There is no black skin or undercasting phenomenon. The blade surface has a smooth transition and consistent dimensional accuracy.

[0059] like Figure 4 As shown in the high-magnification micrograph of the TiAl alloy blade cross section, the 4522XD alloy blade has a uniform and fine as-cast microstructure with grains ranging from 50 to 100 μm, and the microstructure consists entirely of α2+γ lamellar grains.

[0060] The results of the examples show that the present invention significantly improves the efficiency of blade manufacturing through a method for preparing large-size titanium-aluminum alloy low-pressure turbine blades. Under cost-saving conditions, it can obtain large-size blades with precise dimensions and good metallurgical quality. The method of the present invention for preparing TiAl alloy low-pressure turbine blades overcomes the drawbacks of large dimensional fluctuations and substandard surface metallurgical quality in the near-net-shape forming process of TiAl alloy blades. It broadens the forming process window for TiAl alloy blades, ensures thorough centrifugal casting, and increases the yield rate from less than 10% to 55%. The average grain size of the as-cast microstructure of the prepared blades is <100μm, and the mechanical properties are highly consistent and have a high margin of error.

Claims

1. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades, characterized in that, Includes the following steps: Step 1: Use special wax material for blades to make blade wax molding. The blade wax pattern should be free of defects and flow line defects. Compare the design wax pattern with the blade part. The contour should have a machining allowance of 1-3mm. Set feeding strips in key parts of the blade body. After the wax pattern is corrected, a three-coordinate measurement should be performed to determine the precise control of the blade wax pattern size. Step 2: The blade wax model is combined and welded with the sprue and pouring cup wax models. The joints are filled with liquid wax to create a smooth transition. Preparation of the blade ceramic mold shell: 6 to 8 layers of Y2O3 surface layer, transition layer and Al2O3 back layer are applied, with each layer drying for 8 to 48 hours. Step 3: After dewaxing and firing, the blade mold shell is placed in an insulated sand box and filled with sand. The preheating regime for the mold shell is: temperature 400-600℃, time >10h. Step 4: The TiAl alloy master alloy is heated in a vacuum water-cooled copper crucible induction furnace. The molten liquid is poured into a centrifugally rotating blade mold shell and solidified. After cooling, the mold shell is removed from the sand box and mechanically vibrated to remove the mold shell, thus obtaining the TiAl alloy blade billet. Step 5: The TiAl alloy blade billet undergoes hot isostatic pressing at 1260℃ / 140MPa / 3~4h and heat treatment at 1010℃ / 12h. Step 6: CNC machining removes the 1-3mm casting allowance from the blade body to meet the precise requirements of the blade body dimensional tolerance. Then, using the positioning datum of the blade body, the tenons and sealing teeth at both ends of the blade are precisely ground to achieve the overall precision forming goal of the TiAl alloy blade.

2. The method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, The composition of TiAl alloy by weight percentage is as follows: Al: 29.3%–30.7%, Nb: 4.3%–5.3%, Mn: 2.3%–3.3%, B: 0.23%–0.28%, with the balance being Ti and unavoidable impurity elements; among which, the unavoidable impurity elements are Fe, Si, O, N, and H, with Fe ≤ 0.07%, Si ≤ 0.07%, O ≤ 0.085%, N ≤ 0.02%, and H ≤ 0.01%.

3. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, The smelting process of TiAl alloy master alloy is as follows: the raw material is 0-1 grade sponge titanium, and the alloying elements Mn and Nb are added in the form of intermediate alloy; the alloying element Al is partially introduced by the intermediate alloy, and the insufficient part is added with pure Al; after the intermediate alloy and sponge titanium are batched and mixed, they are pressed into electrodes by a press; the electrodes are welded together, melted once in a vacuum arc furnace, and then melted and cast into master alloy ingots in a vacuum arc solidification furnace.

4. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, The blade mold shell is prepared by lost-wax investment casting process and cast under vacuum centrifugal conditions. The number of blades cast in one batch is 8 to 12. The formed blade blank is reserved with a machining allowance of 1 to 3 mm.

5. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, In step 5, the entire hot isostatic pressing and heat treatment process does not require tooling to prevent the blades from twisting or deforming because of the ample casting allowance.

6. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, In steps 4 to 6, a good match is achieved by combining investment casting and machining processes, resulting in complete mold filling, high metallurgical quality qualification rate, and stable dimensional accuracy.

7. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, The performance range of TiAl alloy blades is as follows: Tensile strength σ at room temperature b =600~700MPa, plasticity δ=0.6~1.5%, fatigue strength σ=400~550MPa; tensile strength σ at 650℃ b =550~700MPa, plasticity δ=0.8~2%, fatigue strength σ=380~500MPa, endurance strength σ=350~450MPa after 100h.

8. A method for manufacturing large-size titanium-aluminum alloy low-pressure turbine blades according to claim 1, characterized in that, TiAl alloy blades are used to manufacture lightweight, high-temperature, low-pressure turbine blade components for large aero-engines, replacing traditional nickel-based high-temperature alloys for long-term use in the 600-700℃ range.

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