Duplex smelting method for preparing large-size high-quality TiAl alloy cast ingot with fine and uniform dispersion distribution and strong interface bonding TiB2 reinforced phase

Abstract

The invention discloses a duplex smelting method for preparing a large-size and high-quality TiAl alloy cast ingot with fine and uniform dispersion distribution and a strong interface bonding TiB2 reinforced phase, and relates to the technical field of TiAl alloys. The technical problems that an alloy cast ingot prepared at present has the solidification defect, and a large cast ingot is difficult to form are solved. The method comprises the following steps: weighing raw materials; a large-size TiAl alloy cast ingot is prepared by adopting a duplex process combining vacuum consumable electrode arc melting and vacuum induction melting. The large-size and high-quality TiAl alloy cast ingot is successfully prepared based on the duplex smelting process, the TiB2 reinforced phase in the cast ingot is fine and evenly distributed in a dispersed mode and achieves strong interface bonding with the base body, and the forming process can provide reliable design basis for preparation of the high-performance TiAl alloy. The method is used for preparing the large-size high-quality TiAl alloy cast ingot.

Description

Technical Field

[0001] This invention relates to the field of TiAl alloy technology, specifically a duplex melting process for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed TiB2 reinforcing phases and strong interfacial bonding. Background Technology

[0002] With the rapid development of aerospace technology, the demand for high thrust-to-weight ratio structural materials is becoming increasingly urgent. Currently, nickel-based superalloys are the main structural materials widely used in the hot-section components of aero-engines. While possessing excellent high-temperature performance, their high density has become a key bottleneck limiting the improvement of engine thrust-to-weight ratio, significantly negatively impacting aircraft agility and fuel efficiency. Against this backdrop, developing a new generation of lightweight, high-strength, and high-temperature resistant structural materials has become crucial to breaking through the current thrust-to-weight ratio bottleneck of aero-engines. TiAl alloys not only exhibit superior high-temperature performance comparable to nickel-based superalloys, but their density is also only half that of superalloys. Furthermore, they possess excellent specific strength and superior corrosion resistance and creep resistance in the critical temperature range of 650–850°C. These characteristics make them highly promising lightweight high-temperature materials. Therefore, using TiAl alloys to replace nickel-based superalloys in the manufacture of engine blades is a feasible and effective way to achieve weight reduction and efficiency improvement.

[0003] Melting and casting is one of the more mature preparation and forming processes for TiAl alloys. Commonly used melting techniques mainly include vacuum consumable electrode arc melting and vacuum induction melting. Vacuum consumable electrode arc melting has the main advantages of stable processability, high production rate, low cost, and ease of large-scale industrial production; however, it is prone to macro / micro segregation and solidification defects (such as shrinkage cavities and porosity) during solidification, and poses a potential risk of crucible contamination, posing a challenge to the purity of the final ingot. Vacuum induction melting, as a high-purity melting process, produces alloy ingots with low impurity content, highly uniform composition, and less segregation due to strong electromagnetic stirring; however, its industrial application is severely limited by the complexity of the equipment, high cost, and difficulty in forming large ingots. Summary of the Invention

[0004] This invention aims to solve the technical problems of solidification defects in currently prepared alloy ingots and the difficulty in forming large ingots.

[0005] To balance the requirements of mass production and high quality for large ingots, this invention employs a dual-process combining vacuum consumable electrode arc melting and vacuum induction melting as an effective approach. This solution ensures the feasibility of large-scale ingot production while significantly improving the compositional uniformity and overall purity of the ingots, making it a key technical solution for simultaneously achieving high-quality products and large-scale production.

[0006] A duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases is carried out according to the following steps:

[0007] I. Raw Material Preparation: Weigh the raw materials according to the elemental percentages: Al 41~48 at.%, Nb 1.0~5.0 at.%, Mn 0.5~4.0 at.%, B 0.5~5.0 vol.%, with the balance being Ti. The raw materials include sponge Ti, Al pellets, Nb-containing intermediate alloy particles, Mn source, and nano boron powder; where "at.%" represents atomic percentage and "vol.%" represents volume percentage.

[0008] 2. Raw material mixing: The sponge Ti, Al beads, Nb-containing intermediate alloy particles and Mn source weighed in step one are put into a mixer and mixed. The mixer speed is 30~55r / min, the mixing temperature is controlled at 25~45℃, and the mixing time is 0.5~2h to obtain the mixture.

[0009] 3. Layered paving: The high-purity nano boron powder weighed in step one is wrapped in aluminum foil and paved with the mixture obtained in step two in an alternating layered manner.

[0010] IV. Electrode Block Pressing: After the layered installation in step three is completed, multiple mixed electrode blocks are pressed using a hydraulic press.

[0011] 5. Assemble the electrodes: Weld the mixed electrode blocks pressed in step 4 in a vacuum welding box. The vacuum degree in the vacuum welding box is less than 1.0 Pa, the welding current is 1.0~3.5 kA, and the electrodes are cooled after welding.

[0012] VI. Vacuum Consumable Electrode Arc Melting: ① Place the electrode block welded in step five into the vacuum consumable electrode arc melting furnace and close the furnace door; ② Perform vacuum treatment, reducing the vacuum level to below 1 Pa, and repeat the vacuum operation three times to isolate air; ③ Perform the first melting with an arc starting current of 1~3 kA, a melting current of 3~5 kA, a melting voltage of 20~30 V, and a stabilizing current of 2~5 A. After melting, cool for 1~3 hours and remove the ingot; ④ Perform the second melting. After the first melting, clean the crucible and the upper furnace chamber, and flatten and turn the ingot. Then, weld the ingot to the consumable electrode system in the furnace, and remelt it using the same process parameters as the first melting. After cooling, remove the ingot; ⑤ Repeat the second melting operation ④ 2~3 times to obtain an alloy ingot with uniform composition and dense structure;

[0013] VII. Vacuum Induction Melting: ① Preheating: Preheat the mold at 100-150℃ for 20-50 minutes; ② Transfer the alloy ingot prepared in step VI to the vacuum induction furnace; ③ Vacuuming: Remove air from the equipment until the vacuum level reaches below 1 Pa, repeating the vacuuming operation three times; ④ Heating and Melting: Increase the power to 40-100 kW at a rate of 50-70 kW / min. After observing the initial melting of the alloy ingot and the formation of a stable molten pool, increase the power to 350-450 kW and maintain stability; after the alloy ingot is completely melted, maintain a constant power level for 1 minute. ⑤ Reduce the power at a rate of 20-50 kW / min and allow the melt to stand. When the melt shows signs of solidification, immediately increase the power to 350-450 kW at a rate of 50-70 kW / min and maintain it for 10-20 minutes while simultaneously performing high-frequency electromagnetic stirring. ⑥ Repeat step ⑤ 2-4 times. ⑦ Cool the melt to room temperature with the furnace, open the furnace and remove the melt to obtain a TiAl alloy ingot, which is a large-size, high-quality TiAl alloy ingot with fine, uniformly dispersed TiB2 reinforcing phase and strong interfacial bonding.

[0014] Furthermore, the Nb-containing master alloy particles mentioned in step one are Ti-Nb master alloy particles or Al-Nb master alloy particles; the Mn source is Al-Mn master alloy particles or pure Mn.

[0015] Furthermore, the purity of the sponge Ti in step one is >99.9 wt.%, the purity of the Al bean is >99.9 wt.%, and the purity of the nano boron powder is >99.9 wt.%.

[0016] Furthermore, to ensure a uniform distribution of boron, the number of alternating layers is appropriately increased.

[0017] Furthermore, in step three, the mass of each layer of mixture is controlled to be 1.5~3kg, and the mass of each layer of high-purity nano boron powder is 5~15g.

[0018] Furthermore, in step four, the pressing process involves holding a pressure of 500-800 MPa for 30-60 seconds.

[0019] Furthermore, the frequency of the low-frequency electromagnetic stirring described in step seven is 50~200 Hz.

[0020] Furthermore, the frequency of the high-frequency electromagnetic stirring described in step seven is 1000~3000Hz.

[0021] This invention aims to further improve the overall performance of TiAl alloys by introducing boron (B), which allows the alloy to precipitate a TiB2 phase during solidification. This precipitated phase significantly enhances the alloy's strength and creep resistance through a second-phase strengthening mechanism. Furthermore, the morphology, size, and distribution of the TiB2 precipitate are key factors affecting alloy performance. Ideally, a fine, uniform, and dispersed TiB2 phase can significantly optimize alloy performance: on the one hand, a uniformly dispersed TiB2 phase can effectively hinder dislocation movement, alleviate stress concentration at grain boundaries, and delay the nucleation of interfacial cracks and voids, thereby significantly extending the alloy's service life; on the other hand, the small size of the TiB2 phase can also prevent it from becoming a crack initiation point due to interfacial stress concentration. The interfacial bonding strength between the TiB2 phase and the matrix is ​​another crucial factor affecting alloy performance. If the bonding strength is insufficient, the TiB2 phase is prone to detachment during service. The resulting voids will first induce stress concentration, then promote void aggregation and crack initiation and propagation, ultimately leading to premature fracture failure and significantly shortening the alloy's actual service life. Therefore, achieving a fine and dispersed distribution of the TiB2 phase and its strong interfacial bonding with the matrix is ​​an effective strategy to significantly improve the overall performance of the alloy.

[0022] This invention provides a duplex melting process for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases. Large-size TiAl alloy ingots are prepared through a rational duplex melting process. Compositional analysis and microstructure characterization are performed at different heights of the ingots to evaluate the compositional distribution, impurity content, and the morphology, size, and distribution characteristics of the TiB2 phase. Tensile specimens are cut from the alloy ingots and subjected to room temperature tensile tests. The microstructure after tensile deformation is characterized to reveal the interfacial bonding strength between the TiB2 phase and the matrix.

[0023] Based on the above analysis, this invention first employs a dual-process method combining vacuum consumable electrode arc melting and vacuum induction melting to prepare TiAl alloy ingots. Then, based on compositional analysis and microstructure characterization at different locations on the ingot, the forming quality of the ingot and the morphology, size, and distribution characteristics of the TiB2 phase are systematically evaluated. Finally, a large-size TiAl alloy ingot was successfully prepared. This ingot exhibits uniform compositional distribution, extremely low impurity content, and its microstructure displays an ideally fine, uniformly dispersed TiB2 phase with strong interfacial bonding to the matrix, effectively meeting the key material quality requirements for high-performance applications.

[0024] Beneficial effects of this invention:

[0025] Based on a dual-melting process, this invention successfully prepared large-size, high-quality TiAl alloy ingots. The TiB2 reinforcing phase inside the ingots is fine, uniformly dispersed, and achieves strong interfacial bonding with the matrix. This forming process can provide a reliable design basis for the preparation of high-performance TiAl alloys.

[0026] (1) This invention employs a dual process combining vacuum consumable electrode arc melting and vacuum induction melting to successfully produce high-quality, large-size TiAl alloy ingots. The mechanism for achieving high quality lies in the following: the vacuum consumable electrode arc melting process, which involves multiple ingot flipping, initially promotes uniform distribution of raw materials and removes some impurity elements; the variable frequency electromagnetic stirring during the subsequent vacuum induction melting further promotes the homogenization of the melt composition and effectively avoids element volatilization; at the same time, the high vacuum environment inside the furnace also promotes the deep removal of residual gaseous impurities, ultimately significantly improving the forming quality of the ingot.

[0027] (2) The TiAl alloy ingot prepared by this invention has a uniform and dense internal structure, exhibiting a fine, fully lamellar structure. This fully lamellar structure significantly enhances the high-temperature performance of the alloy. Furthermore, the microstructure is free of obvious defects such as segregation, voids, and cracks, demonstrating excellent forming integrity and high forming quality. Simultaneously, the TiB2 reinforcing phase exhibits a fine, uniform, and dispersed ideal morphology in the matrix, and this microstructure provides a crucial guarantee for the alloy's excellent comprehensive mechanical properties.

[0028] (3) The alloy ingot prepared by this invention exhibits high interfacial bonding strength between the TiB2 reinforcing phase and the matrix, and no significant interfacial debonding or reinforcing phase detachment occurs under tensile or other external loads. This high interfacial bonding strength is attributed to the high-quality forming achieved by the duplex melting process. This process effectively solves two major technical challenges in TiAl alloys: achieving uniform distribution of the reinforcing phase and improving interfacial bonding strength. It provides a theoretical basis for the preparation of high-performance TiAl alloys and significantly promotes their application in high-temperature components such as engine blades.

[0029] This invention is used to prepare large-size, high-quality TiAl alloy ingots. Attached Figure Description

[0030] Figure 1 A photograph of the large-size, high-quality TiAl alloy ingot prepared for this embodiment;

[0031] Figure 2 This is a schematic diagram showing the sampling and testing locations of the large-size, high-quality TiAl alloy ingot prepared for the example; the red-marked areas represent compositional analysis, and the green-marked areas represent microstructure characterization.

[0032] Figure 3SEM microstructure images of six locations (I-VI) of a large-size, high-quality TiAl alloy ingot prepared for the example;

[0033] Figure 4 The images show the microstructure of the deformed region of the large-size, high-quality TiAl alloy ingot prepared for the example after room temperature tensile testing. (a) is a SEM microstructure image, (b) is another SEM microstructure image, and (c) is a TEM image. Detailed Implementation

[0034] Specific Implementation Method 1: This implementation method describes a duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases. The method is carried out according to the following steps:

[0035] I. Raw material preparation: Weigh the raw materials according to the element percentages of Al 41~48 at.%, Nb 1.0~5.0 at.%, Mn 0.5~4.0 at.%, B 0.5~5.0 vol.%, and the balance Ti. The raw materials include sponge Ti, Al beads, Nb-containing intermediate alloy particles, Mn source and high-purity nano boron powder.

[0036] 2. Raw material mixing: The sponge Ti, Al beads, Nb-containing intermediate alloy particles and Mn source weighed in step one are put into a mixer and mixed. The mixer speed is 30~55r / min, the mixing temperature is controlled at 25~45℃, and the mixing time is 0.5~2h to obtain the mixture.

[0037] 3. Layered paving: The high-purity nano boron powder weighed in step one is wrapped in aluminum foil and paved with the mixture obtained in step two in an alternating layered manner.

[0038] IV. Electrode Block Pressing: After the layered installation in step three is completed, multiple mixed electrode blocks are pressed using a hydraulic press.

[0039] 5. Assemble the electrodes: Weld the mixed electrode blocks pressed in step 4 in a vacuum welding box. The vacuum degree in the vacuum welding box is less than 1.0 Pa, the welding current is 1.0~3.5 kA, and the electrodes are cooled after welding.

[0040] VI. Vacuum Consumable Electrode Arc Melting: ① Place the electrode block welded in step five into the vacuum consumable electrode arc melting furnace and close the furnace door; ② Perform vacuum treatment, reducing the vacuum level to below 1 Pa, and repeat the vacuum operation three times to isolate air; ③ Perform the first melting with an arc starting current of 1~3 kA, a melting current of 3~5 kA, a melting voltage of 20~30 V, and a stabilizing current of 2~5 A. After melting, cool for 1~3 hours and remove the ingot; ④ Perform the second melting. After the first melting, clean the crucible and the upper furnace chamber, and flatten and turn the ingot. Then, weld the ingot to the consumable electrode system in the furnace, and remelt it using the same process parameters as the first melting. After cooling, remove the ingot; ⑤ Repeat the second melting operation ④ 2~3 times to obtain an alloy ingot with uniform composition and dense structure;

[0041] VII. Vacuum Induction Melting: ① Preheating: Preheat the mold at 100-150℃ for 20-50 minutes; ② Transfer the alloy ingot prepared in step VI to the vacuum induction furnace; ③ Vacuuming: Remove air from the equipment until the vacuum level reaches below 1 Pa, repeating the vacuuming operation three times; ④ Heating and Melting: Increase the power to 40-100 kW at a rate of 50-70 kW / min. After observing the initial melting of the alloy ingot and the formation of a stable molten pool, increase the power to 350-450 kW and maintain stability; after the alloy ingot is completely melted, maintain a constant power level for 1 minute. ⑤ Reduce the power at a rate of 20-50 kW / min and allow the melt to stand. When the melt shows signs of solidification, immediately increase the power to 350-450 kW at a rate of 50-70 kW / min and maintain it for 10-20 minutes while simultaneously performing high-frequency electromagnetic stirring. ⑥ Repeat step ⑤ 2-4 times. ⑦ Cool the melt to room temperature with the furnace, open the furnace and remove the melt to obtain a TiAl alloy ingot, which is a large-size, high-quality TiAl alloy ingot with fine, uniformly dispersed TiB2 reinforcing phase and strong interfacial bonding.

[0042] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the Nb-containing master alloy particles mentioned in step one are Ti-Nb master alloy particles or Al-Nb master alloy particles; the Mn source is Al-Mn master alloy particles or pure Mn. Everything else is the same as in Specific Implementation Method One.

[0043] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the purity of the sponge Ti in step one is >99.9 wt.%, the purity of the Al bean is >99.9 wt.%, and the purity of the high-purity nano boron powder is >99.9 wt.%. Everything else is the same as in Specific Implementation Method One or Two.

[0044] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step three, the mass of each layer of mixture is controlled to be 1.5~3kg, and the mass of each layer of high-purity nano-boron powder is 5~15g. Everything else is the same as in Specific Implementation Methods One to Three.

[0045] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: in step four, the pressing process, the holding pressure is 500~800MPa, and the holding time is 30~60s. Everything else is the same as in Specific Implementation Methods One to Four.

[0046] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step five, the number of mixed electrode blocks welded in the vacuum welding box is 2 to 5. Everything else is the same as in Specific Implementation Methods One to Five.

[0047] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the air leakage rate during the welding process in step five is less than 1.0 Pa / min. Everything else is the same as in Specific Implementation Methods One to Six.

[0048] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the cooling time after welding in step five is greater than 15 minutes; and the state of the electrode block and weld joint after welding is simultaneously controlled. Everything else is the same as in Specific Implementation Methods One to Seven.

[0049] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the frequency of the low-frequency electromagnetic stirring in step seven is 50~200 Hz. Everything else is the same as in Specific Implementation Methods One to Eight.

[0050] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the frequency of the high-frequency electromagnetic stirring in step seven is 1000~3000Hz. Everything else is the same as in Specific Implementation Methods One to Nine.

[0051] The scope of this invention is not limited to the above-described embodiments; a combination of one or more specific embodiments can also achieve the purpose of the invention.

[0052] Example:

[0053] This embodiment discloses a duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases. The nominal design chemical composition of the TiAl alloy ingot is Ti-45Al-2Nb-2Mn-0.8 (vol.%)TiB2. The preparation method of this TiAl alloy ingot is carried out according to the following steps:

[0054] I. Raw Material Preparation: Based on the chemical composition of the TiAl alloy ingot (Ti-45Al-2Nb-2Mn-0.8 (vol.%)TiB2), where the percentage content of each element is Al 45 at.%, Nb 2 at.%, Mn 2 at.%, B 0.8 vol.%, and the balance is Ti), the raw materials are weighed. These raw materials include sponge Ti, Al pellets, Ti-Nb master alloy particles, Al-Mn master alloy particles, and high-purity nano-boron powder; the purity of the sponge Ti is >99.9 wt.%, the purity of the Al pellets is >99.9 wt.%, and the purity of the high-purity nano-boron powder is >99.9 wt.%.

[0055] II. Raw material mixing: The sponge Ti, Al beans, Ti-Nb master alloy particles and Al-Mn master alloy particles weighed in step one are put into a mixer and mixed. The mixer speed is 40r / min, the mixing temperature is controlled at 35℃, and the mixing time is 1h to obtain the mixture.

[0056] 3. Layered application: The high-purity nano boron powder weighed in step 1 is wrapped in aluminum foil and applied to the mixture obtained in step 2 in an alternating layered manner. The mass of each layer of mixture is 2.5 kg and the mass of each layer of high-purity nano boron powder is 10 g.

[0057] IV. Electrode Block Pressing: After the layered paving in step three is completed, a 2500T hydraulic press is used to press three mixed electrode blocks of the same specifications. The holding pressure is 750MPa and the holding time is 50s.

[0058] V. Electrode Assembly: The mixed electrode blocks pressed in step four are welded in a vacuum welding box. The vacuum degree in the vacuum welding box is less than 1.0 Pa, and the leakage rate is less than 1 Pa / min throughout the process. The welding current is 2 kA, and the welding is cooled for 30 minutes after welding. At the same time, the condition of the welded electrode blocks (which must be flat, firm, and oxidation-proof) and the weld points (which must be free of oxidation, otherwise they must be thoroughly ground) is strictly controlled.

[0059] VI. Vacuum Consumable Electrode Arc Melting: ① Place the electrode block welded in step five into the vacuum consumable electrode arc melting furnace and close the furnace door; ② Perform vacuum treatment, reducing the vacuum level to below 1 Pa, repeating the vacuum operation three times to isolate air and prevent oxidative contamination of the melt; ③ Perform the first melting with an arc starting current of 1.5 kA, a melting current of 4 kA, a melting voltage of 27 V, and a stabilizing current of 4 A. After melting, cool for 2 hours and remove the ingot; ④ Perform the second melting, cleaning the crucible and upper furnace chamber after the first melting, reversing the ingot, and then welding the ingot to the consumable electrode system in the furnace. Then, remelt using the same process parameters as the first melting, and remove the ingot after cooling; ⑤ Repeat the second melting operation ④ twice to obtain an alloy ingot with uniform composition and dense structure;

[0060] VII. Vacuum Induction Melting: ① Preheating: Preheat the mold at 100℃ for 35 minutes; ② Transfer the alloy ingot prepared in step VI to the vacuum induction furnace; ③ Vacuuming: Remove air from the equipment until the vacuum level reaches below 1 Pa, repeating the vacuuming operation three times; ④ Heating and Melting: Increase the power to 70kW at a rate of 60kW / min. After observing the initial melting of the alloy ingot and the formation of a stable molten pool, increase the power to 400kW and maintain stability; after the alloy ingot is completely melted, maintain the power at 400kW for 15 minutes, while simultaneously applying a low-frequency 100Hz electric current. Magnetic stirring is used to ensure uniform distribution of the alloy composition, especially to ensure that the reinforcing phase is uniformly dispersed in the matrix and to avoid agglomeration; ⑤ The power is reduced at a rate of 30 kW / min and allowed to stand. When the melt shows signs of solidification, the power is immediately increased to 400 kW at a rate of 60 kW / min and held for 15 min while simultaneously performing electromagnetic stirring at a high frequency of 2000 Hz; ⑥ The process in step ⑤ is repeated 3 times; ⑦ The melt is cooled to room temperature in the furnace, and the furnace is opened to remove the ingot, which is a large-size, high-quality TiAl alloy ingot with fine, uniformly dispersed TiB2 reinforcing phase and strong interfacial bonding.

[0061] Compositional testing and tissue characterization:

[0062] (1) Sample cutting: A sample was cut from the top, bottom and middle of the large-sized high-quality TiAl alloy ingot prepared in this embodiment, and from the center and edge of each position for composition analysis. The sample size was 10mm×10mm×20mm (20mm is the height direction of the ingot). Subsequently, a sample of the same size was cut from the adjacent position of the sample for composition analysis and the microstructure was observed using an electron microscope.

[0063] (2) Composition determination: The overall purity of the alloy ingot is evaluated based on the content of impurity elements in the composition test results; the uniformity of the spatial distribution of the composition is analyzed by comparing the main element concentration deviations of samples at different heights and lateral positions.

[0064] (3) Microstructure characterization: The microstructure of samples at different locations was systematically characterized. First, the focus was on detecting whether there were micro-defects such as voids and cracks in the microstructure, and evaluating the microstructure uniformity and forming quality of the ingot. Then, the volume fraction, morphology, size and distribution characteristics of the TiB2 reinforcing phase were analyzed in depth.

[0065] Room temperature tensile test:

[0066] Tensile specimens with a gauge length of 18 mm, a width of 5 mm, and a thickness of 1.5 mm were cut from the large-size, high-quality TiAl alloy ingot prepared in this embodiment.

[0067] Room temperature tensile test: ① Fix the clamping ends of the tensile specimen on both sides of the electronic universal testing machine to ensure axial alignment and stable clamping; ② Install an extensometer in the gauge length of the specimen to accurately measure the actual deformation during the tensile process; ③ Apply a tensile load at a constant rate of 0.2~0.5 mm / min at room temperature until the specimen breaks; ④ After tensile fracture, unload and remove the fractured tensile specimen; ⑤ Characterize the microstructure after tensile deformation, and evaluate the interfacial bonding strength between the TiB2 phase and the matrix by analyzing whether there are phenomena such as the detachment of the TiB2 phase.

[0068] The large-size, high-quality TiAl alloy ingot prepared in this embodiment is as follows: Figure 1 As shown, the ingot measures φ200mm × 400mm, weighs approximately 50kg, and has a smooth, flat surface without obvious protrusions, depressions, or other macroscopic defects, exhibiting good surface quality. Samples were cut from the top, bottom, and center and edge positions of the middle region of the obtained alloy ingot for compositional analysis. The sampling locations are shown in the figure. Figure 2 As shown in the red-marked area, each sample measures 10mm × 10mm × 20mm, and the specific composition at different locations is shown in Table 1. The composition test results show that the overall impurity content of the ingot is extremely low, indicating that the material has high purity; at the same time, the composition data at each sampling point are highly similar, indicating that the composition of the ingot is uniform on a macroscopic scale.

[0069] Table 1 (Unit: wt.%)

[0070]

[0071] In this embodiment, a dual-melting process combining vacuum consumable electrode arc melting and vacuum induction melting was used to prepare a large-size, high-quality TiAl alloy ingot. The microstructure of different locations was systematically characterized to evaluate the ingot's forming quality and analyze the volume fraction, morphology, size, and distribution characteristics of the TiB2 reinforcing phase. The sampling locations were closely adjacent to the composition analysis areas, specifically as follows: Figure 2 The area marked in green is shown in the middle.

[0072] Figure 3This paper presents SEM microstructure images of six locations (I-VI) of a large-size, high-quality TiAl alloy ingot prepared in this embodiment. Analysis shows that all locations exhibit a fully lamellar structure (composed of α2 / γ lamellar clusters), with no obvious segregation features (such as blocky B2 phase) at grain boundaries. Furthermore, no obvious defects such as voids or cracks were observed, and the microstructure morphology of each region is similar, indicating good ingot forming quality and uniform composition distribution. Further observation revealed that the TiB2 reinforcing phase exhibits fine size and uniformly dispersed spatial characteristics at different locations. Quantitative analysis using image analysis software showed that the volume fractions of the TiB2 phase at locations I-VI were 0.82%, 0.80%, 0.76%, 0.83%, 0.81%, and 0.78%, respectively, which are highly consistent with the nominal design value of 0.8%, with a small deviation range. This further reveals the significant advantages of this process in controlling the reinforcing phase content and ensuring consistent spatial distribution.

[0073] Tensile specimens were prepared by cutting the large-size, high-quality TiAl alloy ingots used in this embodiment, and tensile tests were conducted at a constant rate of 0.5 mm / min at room temperature. After the specimens fractured, the microstructure of the deformed areas was characterized, and the interfacial bonding strength between the TiB2 phase and the matrix was evaluated by analyzing whether interfacial failure behaviors such as TiB2 phase detachment occurred.

[0074] Figure 4 The image shows the SEM microstructure of the deformed region of the large-size, high-quality TiAl alloy ingot prepared in this embodiment after a room-temperature tensile test. Observation reveals that, under external load, although void nucleation and crack initiation occur in the alloy microstructure, the TiB2 reinforcing phase remains tightly bonded to the matrix without detachment or interfacial peeling. This phenomenon directly confirms the excellent interfacial bonding strength between the TiB2 phase and the matrix.

[0075] Based on the above tests, it is verified that the present invention successfully prepared large-size, high-quality TiAl alloy ingots. Furthermore, the TiB2 reinforcing phase in the microstructure exhibits an ideal morphology of fine, dispersed, and uniform distribution, forming a strong interfacial bond with the matrix. This dual-melting process can provide a theoretical basis for the preparation of high-performance TiAl alloys.

Claims

1. A duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases, characterized in that... This method is performed in the following steps: I. Raw material preparation: Weigh the raw materials according to the element percentages of Al 41~48 at.%, Nb 1.0~5.0 at.%, Mn 0.5~4.0 at.%, B 0.5~5.0 vol.%, and the balance Ti. The raw materials include sponge Ti, Al pellets, Nb-containing intermediate alloy particles, Mn source and nano boron powder.

2. Raw material mixing: The sponge Ti, Al beads, Nb-containing intermediate alloy particles and Mn source weighed in step one are put into a mixer and mixed. The mixer speed is 30~55r / min, the mixing temperature is controlled at 25~45℃, and the mixing time is 0.5~2h to obtain the mixture.

3. Layered paving: The high-purity nano boron powder weighed in step one is wrapped in aluminum foil and paved with the mixture obtained in step two in an alternating layered manner. IV. Electrode Block Pressing: After the layered installation in step three is completed, multiple mixed electrode blocks are pressed using a hydraulic press.

5. Assemble the electrodes: Weld the mixed electrode blocks pressed in step 4 in a vacuum welding box. The vacuum degree in the vacuum welding box is less than 1.0 Pa, the welding current is 1.0~3.5 kA, and the electrodes are cooled after welding. VI. Vacuum Consumable Electrode Arc Melting: ① Place the electrode block welded in step five into the vacuum consumable electrode arc melting furnace and close the furnace door; ② Perform vacuum treatment, reducing the vacuum level to below 1 Pa, and repeat the vacuum operation three times to isolate air; ③ Perform the first melting with an arc starting current of 1~3 kA, a melting current of 3~5 kA, a melting voltage of 20~30 V, and a stabilizing current of 2~5 A. After melting, cool for 1~3 hours and remove the ingot; ④ Perform the second melting. After the first melting, clean the crucible and the upper furnace chamber, and flatten and turn the ingot. Then, weld the ingot to the consumable electrode system in the furnace, and remelt it using the same process parameters as the first melting. After cooling, remove the ingot; ⑤ Repeat the second melting operation ④ 2~3 times to obtain an alloy ingot with uniform composition and dense structure; VII. Vacuum Induction Melting: ① Preheating: Preheat the mold at 100-150℃ for 20-50 minutes; ② Transfer the alloy ingot prepared in step VI to the vacuum induction furnace; ③ Vacuuming: Remove air from the equipment until the vacuum level reaches below 1 Pa, repeating the vacuuming operation three times; ④ Heating and Melting: Increase the power to 40-100 kW at a rate of 50-70 kW / min. After observing the initial melting of the alloy ingot and the formation of a stable molten pool, increase the power to 350-450 kW and maintain stability; after the alloy ingot is completely melted, maintain a constant power level for 1 minute. ⑤ Reduce the power at a rate of 20-50 kW / min and allow the melt to stand. When the melt shows signs of solidification, immediately increase the power to 350-450 kW at a rate of 50-70 kW / min and maintain it for 10-20 minutes while simultaneously performing high-frequency electromagnetic stirring. ⑥ Repeat step ⑤ 2-4 times. ⑦ Cool the melt to room temperature with the furnace, open the furnace and remove the melt to obtain a TiAl alloy ingot, which is a large-size, high-quality TiAl alloy ingot with fine, uniformly dispersed TiB2 reinforcing phase and strong interfacial bonding.

2. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... The Nb-containing master alloy particles mentioned in step one are Ti-Nb master alloy particles or Al-Nb master alloy particles; the Mn source is Al-Mn master alloy particles or pure Mn.

3. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... The purity of the sponge Ti mentioned in step one is >99.9 wt.%, the purity of Al bean is >99.9 wt.%, and the purity of the nano boron powder is >99.9 wt.%.

4. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... Step 3: Control the mass of each layer of mixture to be 1.5~3kg, and the mass of each layer of high-purity nano boron powder to be 5~15g.

5. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... Step four is the pressing process, with a holding pressure of 500~800MPa and a holding time of 30~60s.

6. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... Step 5 involves welding 2 to 5 mixed electrode blocks inside a vacuum welding box.

7. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... During the welding process in step five, the air leakage rate is less than 1.0 Pa / min.

8. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... Step 5: Cooling time after welding should be greater than 15 minutes; and the condition of the electrode block and weld points after welding should be monitored at the same time.

9. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... The frequency of the low-frequency electromagnetic stirring described in step seven is 50~200 Hz.

10. The duplex melting method for preparing large-size, high-quality TiAl alloy ingots with fine, uniformly dispersed, and strongly interfacially bonded TiB2 reinforcing phases according to claim 1, characterized in that... The frequency of the high-frequency electromagnetic stirring described in step seven is 1000~3000Hz.

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