A method for preparing a high-strength and high-plasticity TiAl alloy with an in-situ gamma phase cladding sheet layer structure

Abstract

The application relates to a preparation method of a high-strength and high-plasticity TiAl alloy with an in-situ gamma phase cladding sheet layer structure, and relates to the alloy preparation field. The application solves the problem that, in the prior art, the alpha to gamma phase change cannot be triggered accurately, the gamma phase can only be island-shaped precipitated, cannot be continuously cladded to sheet layer groups in-situ, and the hot plasticity and high-temperature strength and toughness coordination fail. The application is prepared by vacuum induction suspension melting technology for 4 to 5 times, and the compensation amount of Al element is set to 2% of the added mass when raw materials are configured; the alpha to gamma phase change interval of the alloy is determined by combined high-temperature in-situ laser confocal technology and differential scanning calorimetry analysis technology; the molten TiAl alloy is cut into a plurality of block-shaped samples, the block-shaped samples are placed in an argon protection atmosphere, and the samples are respectively kept at 1240 DEG C, 1280 DEG C and 1320 DEG C for 3 hours, and then air-cooled to room temperature; and the optimal heat treatment parameters are obtained as follows: 1320 DEG C, keeping for 3 hours, and air-cooling to room temperature. The application is used for TiAl alloy preparation.

Description

Technical Field

[0001] This invention relates to the field of high-temperature lightweight alloy hot working preparation technology, specifically to a design and preparation method for forming an in-situ γ-phase coated lamellar structure through heat treatment, and more particularly to a preparation method for a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure. Background Technology

[0002] TiAl alloys, as lightweight high-temperature structural materials, are promising candidates for high-end applications such as turbine blades in aerospace engines due to their low density, excellent high-temperature strength, and oxidation resistance. However, traditional TiAl alloys are prone to cracking during hot working due to stress concentration, significantly increasing the difficulty of forming and reducing the mechanical stability of components, thus hindering their industrial application. Current methods to improve the hot deformation capability of TiAl alloys mainly focus on three aspects: composition optimization, microstructure control, and preparation processes. Studies have shown that adding alloying elements such as Nb, Cr, and V can refine grains and improve room-temperature plasticity to some extent, but this often leads to a decrease in high-temperature strength, and the precise control of the amount of added elements is difficult, easily inducing new segregation defects. In terms of preparation processes, while techniques such as hot isostatic pressing and powder metallurgy can reduce the internal porosity of the alloy and increase density, they are limited by long production cycles and high costs, making large-scale production difficult. The effect of microstructure control on improving the mechanical properties of TiAl alloys has become a core research direction in recent years.

[0003] The room-temperature microstructure of TiAl alloys consists of γ-TiAl phase (face-centered cubic structure) and α2-Ti3Al phase (close-packed hexagonal structure). The ratio, morphology, and distribution of these two phases directly affect the alloy's deformability. Studies have found that introducing a γ-phase coating around the lamellar structure can significantly improve this situation. When the γ-phase surrounds the lamellar structure, it can coordinate deformation during alloy stress, effectively preventing crack initiation and propagation, thereby improving the alloy's plasticity. Simultaneously, the γ-phase can optimize the stress distribution within the microstructure, enhancing the alloy's load-bearing capacity under complex stress conditions and maintaining excellent mechanical properties at high temperatures. In TiAl alloys after traditional heat treatment, the γ-phase is often distributed in isolated island-like or irregular morphologies, easily becoming a stress concentration source during hot deformation, leading to increased deformation resistance and limited plastic deformation capacity, failing to fundamentally solve the problem of difficult hot deformation. Although a coating structure can be constructed by adding heterogeneous phases, the introduction of exogenous phases easily leads to problems such as poor interfacial compatibility and impurity segregation.

[0004] Based on the above analysis, it is clear that there is currently no effective means to stably achieve an "in-situ phase coating" structure. Therefore, it is necessary to develop a method that can form a uniform and continuous γ-phase coated lamellar structure in situ through a simple heat treatment process, without the need for exogenous additives, with strong process versatility, and can improve the synergy of thermal deformation from the root of the microstructure. Summary of the Invention

[0005] The purpose of this invention is to solve the problem in existing technologies where the α→γ phase transformation cannot be precisely triggered, resulting in the γ phase precipitating only in isolated islands and failing to continuously coat lamellar clusters in situ, leading to thermoplasticity and high-temperature strength failure. Therefore, this invention provides a method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ phase-coated lamellar structure.

[0006] The technical solution of this invention is:

[0007] A method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure includes the following steps:

[0008] Step 1: Melt the material 4-5 times using vacuum induction levitation melting technology. Considering the loss of Al, the compensation amount of Al is set to 2% of the added mass when preparing the raw materials.

[0009] Step 2: The α→γ phase transformation range of the alloy was determined to be 1220℃~1335℃ using a combination of high-temperature in-situ laser confocal technology and differential scanning calorimetry.

[0010] Step 3: Cut several block samples from the cast TiAl alloy using wire cutting technology. Place these block samples in an argon protective atmosphere and keep them at 1240℃, 1280℃ and 1320℃ for 3 hours respectively, and then air cool them to room temperature.

[0011] Performance testing revealed that the optimal heat treatment parameters for obtaining in-situ γ-phase coated lamellar structures are: 1320°C, holding for 3 hours, and air cooling to room temperature.

[0012] Furthermore, the raw material preparation process in step one is as follows: based on the target composition of the TiAl alloy, calculate the theoretical addition amount of each raw material, and add an additional 2% by mass of Al element as a compensation amount.

[0013] Furthermore, the operation of the vacuum induction suspension melting technology in step one includes the following steps:

[0014] Step 11: Put the proportioned raw materials into the crucible of the vacuum induction suspension melting equipment;

[0015] Steps 1 and 2: Close the equipment cavity and evacuate it to a vacuum level of 10. -3 To prevent the alloy from coming into contact with air and generating oxidation inclusions during the smelting process, the Pa level should be kept below 1.

[0016] Step 13: Start the induction heating system to heat the raw materials to a completely molten state, and use the electromagnetic stirring effect of suspension melting to achieve uniform mixing of the components in the melt;

[0017] Step 14: Repeat the above melting process 4 to 5 times, ensuring that the melt is completely solidified after each melting, and finally obtain a TiAl alloy ingot with uniform composition and no obvious defects.

[0018] Step 15: Sample the prepared ingot and detect its actual composition by inductively coupled plasma atomic emission spectrometry to confirm that the content of Ti, Al and other elements deviates from the design value within ±0.5%, ensuring that subsequent processes have a stable compositional basis.

[0019] Furthermore, step two, in determining the α→γ phase transformation range of the alloy, includes the following steps:

[0020] Step 21: Two types of samples are cut from the TiAl alloy ingot obtained in Step 1. One type is used for high-temperature in-situ laser confocal analysis, and the other type is used for differential scanning calorimetry analysis.

[0021] Step 22: By observing the microstructure evolution temperature through high-temperature in-situ laser confocal microscopy and recording the heat flow change curve during the heating process, the α→γ phase transformation range of the alloy was determined to be 1220℃~1335℃.

[0022] Furthermore, the method for obtaining the block samples in step three is as follows: several block samples of the same size are cut from the TiAl alloy ingot in step one using wire cutting technology, and the cleaned samples are placed into the heat treatment furnace respectively.

[0023] Furthermore, the preparation work for heat treatment of the block sample in step three is as follows: high-purity argon gas is introduced into the heat treatment furnace at a flow rate of 50 mL / min to ensure that the oxygen content in the furnace is ≤100 ppm to prevent oxidation of the sample during heat treatment.

[0024] Furthermore, the heat treatment step for the block sample in step three is as follows:

[0025] Step 31: Set three different heat preservation temperatures, namely 1240℃, 1280℃ and 1320℃, and keep the samples at each temperature for 3 hours.

[0026] Step 32: After the heat treatment is completed, immediately remove the block sample from the heat treatment furnace and allow it to cool naturally to room temperature in the air to complete the heat treatment process.

[0027] Furthermore, the process for determining the optimal heat treatment parameters in step three is as follows:

[0028] First, the microstructure of the samples after heat treatment at different temperatures was characterized to analyze the phase composition, phase ratio and microstructure morphology of each sample.

[0029] Then, the analysis results showed that the sample held at 1320℃ for 3 hours and air-cooled formed an equiaxed γ phase, uniformly coating the refined lamellar clusters, and the volume fraction of the brittle B2 phase was reduced to 2%. Therefore, this process was determined to be the optimal heat treatment process for preparing in-situ γ phase coated lamellar clusters.

[0030] Preferably, the sampling method in step one five and the method for obtaining the block sample in step three are both:

[0031] Cylindrical specimens for hot deformation and dog-bone-shaped specimens for high-temperature tensile testing of the same size were cut from the same location of the TiAl alloy sample after holding at 1320℃ for 3 hours and air cooling. The hot deformation temperature range was 1050℃~1250℃, the deformation amount was 60%~85%, and the strain rate was 0.001~0.1s. -1 The high-temperature tensile test was conducted at temperatures of 850℃ and 900℃, with a tensile rate of 0.3 mm / min.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. This invention proposes a method for preparing a high-strength and ductile TiAl alloy with an in-situ γ-phase-coated lamellar structure. This method involves timely heat treatment within the α→γ phase transformation range to induce non-uniform nucleation of the γ phase at the α phase boundary, forming an in-situ equiaxed γ-phase-coated lamellar structure. This structure readily generates high-density nanotwins and dislocation defects, which is beneficial for improving the hot deformation capability and high-temperature strength and ductility of the γ-TiAl alloy. This provides an important research idea and experimental basis for preparing large-size, high-quality TiAl alloy forgings and rolled plates.

[0034] 2. This invention employs α→γ phase transformation heat treatment to achieve in-situ γ-phase coating structure formation, completely avoiding problems such as poor interfacial compatibility and impurity segregation caused by exogenous substances, thus enabling the equiaxed γ-phase and lamellar clusters to form a naturally strong bonding interface. The core process of the preparation is "vacuum induction levitation melting + precise phase transformation heat treatment," and the heat treatment parameters are designed based on the alloy's own phase transformation law, adaptable to the microstructure control requirements of TiAl alloys with different compositions. Simultaneously, the process steps are simple, the operation is easy, and the production cycle is significantly shortened.

[0035] 3. The in-situ equiaxed γ-phase-coated lamellar structure formed by this invention is a novel microstructure not found in traditional cast TiAl alloys (coarse lamellar clusters). This structure can induce multiple microscopic defect behaviors during hot deformation. The easily deformable equiaxed γ-phase can activate more dislocation slip, and the fine lamellar interfaces can form high-density nanotwins and dislocations. These nanodefects can disperse and transfer stress, avoiding microstructural failure caused by stress concentration, and providing microstructural support for the alloy to possess high strength and high plasticity.

[0036] 4. Relying on the interfacial strengthening and defect control effects of the coating structure, the alloy prepared by this invention exhibits an excellent balance of strength and plasticity at high temperatures. At 850℃, the tensile strength reaches over 620 MPa with an elongation of 4.3%, and at 900℃, it still maintains over 520 MPa with an elongation of 12.5%, which is an improvement over traditional cast TiAl alloys (whose strength at 900℃ is generally below 450 MPa), achieving a synergistic balance of "high strength and high plasticity".

[0037] 5. Compared to traditional cast TiAl alloys, which are prone to localized cracking due to uneven microstructure during hot deformation, the alloy of this invention, thanks to the deformation synergy of its coating structure, can achieve uniform deformation without cracking under the same hot deformation conditions. Even under large deformation amounts with strain reaching 85%, it can still deform stably and maintain microstructural integrity. This improvement helps to overcome the deformation limit of TiAl alloys, reduce their forming difficulty, lower the difficulty of debugging hot working equipment and energy consumption in actual production, and expand the application scenarios of TiAl alloys in high-end manufacturing fields. Attached Figure Description

[0038] Table 1 shows the elemental content of the original TiAl alloy ingot prepared in this invention;

[0039] Figure 1 This describes the microstructure of the original TiAl ingot prepared according to the present invention;

[0040] Figure 2 This describes the microstructure of the heat-treated TiAl sample prepared according to the present invention.

[0041] Figure 3 The original TiAl sample was tested at 1150℃ for 0.01 s. -1 The microstructure with 60% deformation at a strain rate;

[0042] Figure 4 The TiAl sample after heat treatment was subjected to 1150℃ and 0.01s. -1 The microstructure with 60% deformation at a strain rate;

[0043] Figure 5 The TiAl sample after heat treatment was subjected to 1150℃ and 0.01s. -1The microstructure with 85% deformation at the strain rate;

[0044] Figure 6 These are the high-temperature tensile properties of the original TiAl sample and the heat-treated TiAl sample at 850℃ and 900℃. Detailed Implementation

[0045] Specific Implementation Method 1: A method for preparing a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure according to this embodiment includes the following steps:

[0046] Step 1: Melt the material 4-5 times using vacuum induction levitation melting technology. Considering the loss of Al, the compensation amount of Al is set to 2% of the added mass when preparing the raw materials.

[0047] Step 2: The α→γ phase transformation range of the alloy was determined to be 1220℃~1335℃ using a combination of high-temperature in-situ laser confocal technology and differential scanning calorimetry.

[0048] Step 3: Cut several block samples from the cast TiAl alloy using wire cutting technology. Place these block samples in an argon protective atmosphere and keep them at 1240℃, 1280℃ and 1320℃ for 3 hours respectively, and then air cool them to room temperature.

[0049] Performance testing revealed that the optimal heat treatment parameters for obtaining in-situ γ-phase coated lamellar structures are: 1320°C, holding for 3 hours, and air cooling to room temperature.

[0050] The method used in this invention transforms coarse lamellar clusters in the as-cast microstructure into an in-situ formed continuous, equiaxed γ-phase encapsulating fine lamellar clusters through phase transformation heat treatment. This microstructure possesses abundant phase interfaces and excellent interfacial bonding strength. During hot deformation, the easily deformable γ-phase can activate more dislocation slip, and the fine lamellar interfaces can form high-density nanotwins and dislocations. These activated nanodefects act as rapid channels for dispersing stress and strain at high temperatures and are also important barriers hindering crack propagation and connection. TiAl alloys with this in-situ encapsulated structure are less prone to cracking during hot deformation and exhibit better plastic deformation capacity. The close interfacial interaction and coordinated deformation behavior generated by the soft equiaxed γ-phase surrounding the hard lamellar clusters during high-temperature tensile testing introduce various plastic deformation and strengthening mechanisms, significantly improving the high-temperature strength and plasticity of TiAl alloys.

[0051] Compared with the hot deformation and high-temperature mechanical properties of cast TiAl alloys, the TiAl alloy prepared by heat treatment in the α→γ phase transformation range according to this invention can undergo uniform deformation without cracking under the same deformation conditions, and even maintains the integrity of the deformation under greater strain (85%). At temperatures above 850℃, the tensile strength can reach over 620 MPa, and the elongation reaches 4.3%. At 900℃, the tensile strength remains above 520 MPa, and the elongation reaches 12.5%, exhibiting more stable mechanical properties. The preparation method provided by this invention forms a uniform and continuous γ-phase coated lamellar structure in situ, avoiding the adverse effects of exogenous additives on the interface. It also boasts strong process versatility and can improve the synergistic enhancement of hot deformation and mechanical properties from the microstructure perspective.

[0052] The TiAl alloy prepared by this invention possesses an equiaxed γ phase (volume fraction of equiaxed γ phase is approximately 41%), refined lamellar clusters (volume fraction of lamellar clusters is approximately 57%), and a very small amount of B2 phase at room temperature (volume fraction of B2 phase is approximately 8% in cast TiAl alloys, while the volume fraction of B2 phase in the TiAl alloy prepared by this invention is reduced to 2%). The interlamellar spacing within the lamellar clusters is reduced from the original 433 nm to 69 nm. Compared with the cast TiAl alloy, the heat-treated TiAl alloy can be uniformly compressed by 60% at 1150℃~1250℃, and even compressed by 85%, without cracking; furthermore, at 850℃, the tensile strength of this alloy reaches 624 MPa, and the elongation reaches 4.3%; at 900℃, the tensile strength of this alloy still remains at 527 MPa, and the elongation is 12.5%, approximately twice that of the cast TiAl alloy. The TiAl alloy prepared by this invention possesses both good hot deformability and high-temperature ductility.

[0053] The TiAl alloy prepared by this invention forms an in-situ continuous equiaxed γ phase covering fine lamellar clusters. The equiaxed γ phase can improve the plasticity of the microstructure, while the refined lamellar clusters can maintain high-temperature strength. The precise matching of the two ratios achieves a microscopic synergy between plasticity and strength. In addition, the content of the hard and brittle B2 phase is significantly reduced, which helps to eliminate stress concentration and microstructure segregation defects caused by crack initiation.

[0054] Specific Implementation Method Two: This implementation method provides a method for preparing a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure. Step one involves the following raw material preparation process: Based on the target composition of the TiAl alloy, the theoretical addition amount of each raw material is calculated, and an additional 2% by mass of Al element is added as a compensation. This ensures that the Al element content in the final alloy meets the design requirements.

[0055] Specific Implementation Method 3: This implementation method provides a method for preparing a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure. The operation of the vacuum induction suspension melting technology in step one includes the following steps:

[0056] Step 11: Put the proportioned raw materials into the crucible of the vacuum induction suspension melting equipment;

[0057] Steps 1 and 2: Close the equipment cavity and evacuate it to a vacuum level of 10. -3 To prevent the alloy from coming into contact with air and generating oxidation inclusions during the smelting process, the Pa level should be kept below 1.

[0058] Step 13: Start the induction heating system to heat the raw materials to a completely molten state, and use the electromagnetic stirring effect of suspension melting to achieve uniform mixing of the components in the melt;

[0059] Step 14: Repeat the above melting process 4 to 5 times, ensuring that the melt is completely solidified after each melting, and finally obtain a TiAl alloy ingot with uniform composition and no obvious defects.

[0060] Step 15: Sample the prepared ingot and detect its actual composition by inductively coupled plasma atomic emission spectrometry to confirm that the content of Ti, Al and other elements deviates from the design value within ±0.5%, ensuring that subsequent processes have a stable compositional basis.

[0061] The solidified alloy ingot in step one of steps has dimensions of Ø120×90mm. Several cuboid blocks are cut from the ingot using digital electrical discharge machining (EDM) technology to serve as samples for testing hot deformation and high-temperature tensile properties.

[0062] Specific Implementation Method 4: A method for preparing a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure according to this embodiment includes the following steps in step two when determining the α→γ phase transformation range of the alloy:

[0063] Step 21: Two types of samples are cut from the TiAl alloy ingot obtained in Step 1. One type is used for high-temperature in-situ laser confocal analysis, and the other type is used for differential scanning calorimetry analysis.

[0064] Step 22: By observing the microstructure evolution temperature through high-temperature in-situ laser confocal microscopy and recording the heat flow change curve during the heating process, the α→γ phase transformation range of the alloy was determined to be 1220℃~1335℃.

[0065] The proposed preparation method innovatively combines high-temperature in-situ laser confocal microscopy with differential scanning calorimetry (DSC). The former allows real-time observation of the microstructure evolution of the alloy during the holding process, while the latter accurately captures the phase transformation heat effect. The combination of these two techniques precisely pinpoints the α→γ phase transformation range of the TiAl alloy, providing a scientific basis for selecting subsequent heat treatment temperatures and avoiding the problems of "insufficient phase transformation" or "overheating" caused by traditional temperature settings based on experience. Based on the precise phase transformation range, by comparing the heat treatment effects at three temperature nodes—1240℃, 1280℃, and 1320℃—the "1320℃ holding for 3 hours + air cooling" heat treatment process was identified. This process can precisely induce the formation of an in-situ γ-phase coating structure without requiring complex equipment or multiple steps, solving the problems of "poor process versatility and high control difficulty" in traditional heat treatment and achieving efficient and stable preparation of the target microstructure.

[0066] The TiAl alloy prepared by this invention can be stably deformed within a wide temperature range of 1050℃ to 1250℃, even achieving a large deformation of 85%. This avoids the problems of traditional TiAl alloys, which have a narrow hot deformation temperature range (mostly concentrated at 1250℃ and above) and are sensitive to temperature fluctuations, easily cracking due to temperature deviations (hot deformation is generally less than 60%). This patent improves the synergistic deformability of the microstructure and its adaptability to temperature changes by constructing an in-situ γ-phase coating structure, achieving stable forming with "large deformation - no cracking," thus solving the difficulties of "limited hot deformation and high forming difficulty" of traditional alloys.

[0067] Specific Implementation Method 5: The preparation method of a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure in this embodiment is as follows: the block sample in step 3 is obtained by cutting several block samples of the same size from the TiAl alloy ingot in step 1 using wire cutting technology, and then placing the cleaned samples into a heat treatment furnace.

[0068] This facilitates the acquisition of heat-treated blanks of uniform specifications, ensuring that the microstructure differences in subsequent comparative experiments at different temperatures are caused solely by heat treatment parameters, thus eliminating interference from sample size and surface condition.

[0069] Specific Implementation Method Six: The preparation method of a high-strength and ductile TiAl alloy with an in-situ γ-phase coated lamellar structure in this embodiment includes the following steps in step three: high-purity argon gas is introduced into the heat treatment furnace at a flow rate of 50 mL / min to ensure that the oxygen content in the furnace is ≤100 ppm to prevent oxidation of the sample during the heat treatment process.

[0070] Creating a low-oxygen environment avoids surface oxidation / internal oxygen contamination of samples at high temperatures, ensuring that the phase composition and interface structure after heat treatment truly reflect the process effect.

[0071] Specific Implementation Method Seven: This implementation method describes a method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure. The heat treatment step for the bulk sample in step three is as follows:

[0072] Step 31: Set three different heat preservation temperatures, namely 1240℃, 1280℃ and 1320℃, and keep the samples at each temperature for 3 hours.

[0073] Step 32: After the heat treatment is completed, immediately remove the block sample from the heat treatment furnace and allow it to cool naturally to room temperature in the air to complete the heat treatment process.

[0074] By comparing three temperatures simultaneously over time, the temperature at which the γ-coated structure can be generated in situ was determined; air cooling utilizes a moderate cooling rate to simultaneously complete the precipitation of the γ phase and suppress the B2 phase, thereby establishing the optimal heat treatment regime.

[0075] Specific Implementation Method Eight: The preparation method of a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to this implementation method, wherein the determination process of the optimal heat treatment parameters in step three is as follows:

[0076] First, the microstructure of the samples after heat treatment at different temperatures was characterized to analyze the phase composition, phase ratio and microstructure morphology of each sample.

[0077] Then, the analysis results showed that the sample held at 1320℃ for 3 hours and air-cooled formed an equiaxed γ phase, uniformly coating the refined lamellar clusters, and the volume fraction of the brittle B2 phase was reduced to 2%. Therefore, this process was determined to be the optimal heat treatment process for preparing in-situ γ phase coated lamellar clusters.

[0078] Microscopic data were used to verify and confirm that "1320℃-3h-air cooling" is the only process that can generate the target γ-coated structure in situ with the least amount of brittle B2, thus establishing the optimal heat treatment parameters.

[0079] Specific Implementation Method Nine: This implementation method provides a method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure. The sampling method in step one-five and the method for obtaining the block sample in step three are both:

[0080] Cylindrical specimens for hot deformation and dog-bone-shaped specimens for high-temperature tensile testing of the same size were cut from the same location of the TiAl alloy sample after holding at 1320℃ for 3 hours and air cooling. The hot deformation temperature range was 1050℃~1250℃, the deformation amount was 60%~85%, and the strain rate was 0.001~0.1s. -1The high-temperature tensile tests were conducted at temperatures of 850℃ and 900℃, with a tensile rate of 0.3 mm / min. The microstructure of the hot-deformed samples was characterized, and the changes in the hot deformation properties and high-temperature mechanical properties of the TiAl alloy in the as-cast and heat-treated states were summarized.

[0081] At a high temperature of 850℃, the TiAl alloy prepared by this invention achieves a tensile strength of 624 MPa. At 900℃, the tensile strength of the alloy remains at 527 MPa, and the elongation increases from 4.3% to 12.5%. Compared with the problem of "rapid strength decay at high temperatures" in traditional TiAl alloys, this patent effectively improves the microstructure stability at high temperatures by modifying the phase composition and ratio and refining the lamellar clusters. This ensures that the alloy can still withstand high loads in high-temperature service scenarios, and is expected to meet the high-temperature load-bearing requirements of aerospace, automotive engines and other fields.

[0082] Combined with Table 1, Figures 1 to 6 Description of embodiments of the present invention:

[0083] Step 1: Based on the target composition of the TiAl alloy (containing Ti, Al, and other necessary alloying elements), calculate the theoretical addition amount of each raw material. Considering the tendency of Al to volatilize and burn off during vacuum induction levitation melting, add an additional 2% by mass of Al as compensation during the raw material preparation stage to ensure that the Al content in the final alloy meets the design requirements. Vacuum induction levitation melting operation: Add the proportioned raw materials (including the compensated Al raw materials) into the crucible of the vacuum induction levitation melting equipment; close the equipment cavity and evacuate to a vacuum level of 10. -3 To prevent oxidation inclusions caused by the alloy coming into contact with air during melting, the Pa level was kept below a certain value. The induction heating system was activated to heat the raw materials to a completely molten state, and the electromagnetic stirring effect of suspension melting was used to achieve uniform mixing of the components within the melt. To further improve the homogeneity of the composition, the melting process was repeated 4-5 times, ensuring complete solidification of the melt after each melting, ultimately obtaining a TiAl alloy ingot with uniform composition and no obvious defects. Samples of the prepared ingots were taken, and the actual composition was detected by inductively coupled plasma optical emission spectrometry (ICP-OES). It was confirmed that the content of Ti, Al, and other elements deviated from the design values ​​within ±0.5%, ensuring a stable compositional basis for subsequent processes. The corresponding elemental contents are shown in Table 1.

[0084]

[0085] Step Two: Two types of samples are cut from the TiAl alloy ingot obtained in Step One: one type is a cylindrical sample with dimensions of φ6mm×2mm (for high-temperature in-situ laser confocal analysis), and the other type is a block sample with a mass of 10~15mg (for differential scanning calorimetry analysis). The surfaces of both types of samples are ground and polished to avoid surface defects affecting microstructure observation. The block sample is placed on the heating stage of the high-temperature in-situ laser confocal microscope, and high-purity argon gas (purity ≥99.999%) is introduced as a protective gas to prevent high-temperature oxidation of the sample.

[0086] The sample was heated from room temperature to 1240℃ / 1280℃ / 1320℃ at a heating rate of 10℃ / min. During the heating process, the evolution of the internal microstructure was observed in real time using a laser confocal system. When the γ phase (face-centered cubic structure) was observed to nucleate and grow at the lamellar boundaries, the phase transition temperature was recorded, and the phase transition range was determined to be 1210℃~1339℃. The block sample was placed in an alumina crucible of a differential scanning calorimeter and protected with high-purity argon gas. It was heated from room temperature to 1400℃ at a heating rate of 10℃ / min. The heat flow curve during the heating process was recorded by the instrument. When a significant endothermic peak appeared on the curve, the corresponding temperature was the characteristic temperature of the α→γ phase transition. Combined with the microstructure evolution temperature observed by high-temperature in-situ laser confocal microscopy, the α→γ phase transition range of the TiAl alloy was finally accurately determined to be 1220℃~1335℃.

[0087] Step 3: From the TiAl alloy ingot from Step 1, several block samples with dimensions of 30mm (length) × 10mm (width) × 15mm (height) were cut using wire cutting technology. The cleaned samples were placed in a heat treatment furnace, and high-purity argon gas was introduced into the furnace to ensure the oxygen content was below 100ppm, preventing oxidation during heat treatment. Three different holding temperatures were set (1240℃, 1280℃, and 1320℃), and the samples were held at each temperature for 3 hours. After the holding time, the samples were immediately removed from the furnace and allowed to cool naturally to room temperature in air, completing the heat treatment process. The microstructure of the samples after heat treatment at different temperatures was characterized, and the phase composition, phase ratio, and microstructure of each sample were analyzed. The results showed that the γ phase in the 1240℃ heat-treated sample was mainly composed of isolated large particles and did not form a coating structure; the γ phase coating in the 1280℃ heat-treated sample was discontinuous; while the sample that was held at 1320℃ for 3 hours and then air-cooled formed the target structure of "uniform coating of refined lamellar clusters (volume fraction of about 57%) with equiaxed γ phase (volume fraction of about 41%)", and the volume fraction of brittle B2 phase was reduced to 2%. Therefore, this process was determined to be the optimal heat treatment process for preparing in-situ γ phase coated lamellar cluster structures.

[0088] In addition, cylindrical specimens for hot deformation and dog-bone-shaped specimens for high-temperature tensile testing of the same size were cut from the same location on the TiAl alloy samples that underwent heat treatment at 1320℃ for 3 hours followed by air cooling in steps one and three. The hot deformation temperature range was 1050℃~1250℃, the deformation was 60% (or even 85%), and the strain rate was 0.05 s⁻¹. -1 The high-temperature tensile tests were conducted at temperatures of 850℃ and 900℃, with a tensile rate of 0.3 mm / min. The microstructure of the hot-deformed samples was characterized, and the changes in the hot deformation properties and high-temperature mechanical properties of the TiAl alloy in the as-cast and heat-treated states were summarized.

[0089] Figure 1 (a) shows the microstructure of the original cast TiAl alloy sample, where the bright white B2 phase is clearly visible in a network distribution. Figure 1 (b) is Figure 1 (a) is an enlarged view within the blue dashed box. The microstructure is dominated by coarse lamellar clusters, with bright white B2 phase and dark gray blocky γ phase coupled and distributed at the boundaries of the lamellar clusters. The enrichment and segregation of β-phase stable solutes such as Nb and Cr in the TiAl alloy promotes the stability of the β-phase at high temperatures at room temperature, thus forming the B2 phase. Statistical calculations show that the average size of the lamellar clusters is approximately 100 μm, and the lamellar clusters exhibit a single orientation.

[0090] Figure 2 It is the fibrous structure morphology of the cast alloy after three heat treatment processes. Figure 2 Images (a)-(b) show the microstructures of the cast TiAl alloy obtained after holding at 1240℃ for 3 hours and then air-cooling to room temperature. The increased temperature enhances the atomic diffusion coefficient and thermal mobility, leading to accelerated diffusion of the β-phase stabilizing elements and consequently reducing the volume fraction of the B2 phase. At this heat treatment temperature, only slightly above the lower limit of the α→γ phase transformation temperature, the nucleation and growth of the γ phase are relatively slow, with only a few isolated γ phase islands observed forming at the lamellar boundaries. Therefore, under these heat treatment conditions, the microstructure of the TiAl alloy is still dominated by lamellar clusters, with a relatively low volume fraction of the γ phase, and it is not yet possible to form a microstructure with continuous equiaxed γ phase covering the lamellar clusters. Figure 2 (c)-(d) show the microstructures obtained after the cast TiAl alloy was held at 1280℃ for 3 hours and then air-cooled to room temperature. At this temperature, the volume fraction of the equiaxed γ phase increases. These γ phases not only nucleate and grow through compositional and energy fluctuations between lamellar clusters, but also migrate their own grain boundaries within the lamellar clusters through continuous coarsening dominated by Al element diffusion at the lamellar interfaces. However, the content of the γ phase is still insufficient to form a more complete shell to surround the lamellar clusters. When the heat treatment temperature is increased to 1320℃, the corresponding microstructure is as follows: Figure 2As shown in (e)-(f), the volume fraction of the equiaxed γ phase increases, while the volume fraction of the B2 phase decreases significantly. Statistical analysis shows that after heat treatment at three different temperatures, the volume fraction of the equiaxed γ phase increases from 0.31% to 39%. The discontinuous coarsening of the equiaxed γ phase leads to discontinuities in the lamellar clusters. During air cooling, the orientation of the precipitated lamellars increases, ultimately forming a microstructure of lamellar clusters coated with the equiaxed γ phase. The interlamellar spacing is refined from 433 nm to 69 nm, while the grain boundary extension of the γ phase at the lamellar boundaries is the reason hindering the coarsening of the lamellar clusters.

[0091] Figure 3 The sample is a cast TiAl alloy cylindrical specimen at 1150℃ and 0.01s. -1 The high-temperature microstructure retained after compressing by 60% at a strain rate. For example... Figure 3 As shown in (a), the compressed sample in the lower left corner exhibits a 45° shear fracture, which is the classic brittle fracture mode of TiAl alloys. It can be seen that during hot deformation, there is incompatibility between the coarse lamellar clusters and the surrounding γ phase and brittle B2 phase interfaces, leading to uncoordinated plastic deformation of the alloy. This is the main reason for cracking in cast TiAl alloys. Figure 3 (b) is Figure 3 (a) shows the magnified morphology within the blue dashed box. The results indicate that although the deformation of the TiAl alloy under casting conditions reached 60%, the volume fraction of the γ phase was low, resulting in minimal recrystallization. This recrystallization of the γ phase was limited to the lamellar boundaries. Furthermore, the network-distributed B2 phase also fractured and elongated along the twisting direction of the lamellar clusters. Therefore, the cast TiAl alloy sample exhibited poor hot formability.

[0092] Figure 4 The TiAl alloy cylindrical sample, after being held at 1320℃ for 3 hours and then air-cooled, was then subjected to further cooling at 1150℃ for 0.01 seconds. -1 The high-temperature microstructure retained after compressing by 60% at a strain rate. For example... Figure 4 As shown in (a), the lower left corner shows the macroscopic morphology of the compressed sample; no cracking is observed at the sample edges. Figure 3 (a) In comparison, the alloy is significantly refined. Figure 4 (b) is Figure 4(a) shows an enlarged microstructure within the blue dashed box. Unlike the hot-deformed microstructure of the cast TiAl alloy, the heat-treated deformed microstructure exhibits abundant recrystallized grains originating from the lamellar boundaries and the γ phase within the lamellar clusters. These equiaxed γ phases, while recrystallizing, also promote the high-temperature decomposition and degradation of the lamellar clusters, ultimately forming a fine equiaxed grain structure. Furthermore, the β-phase stabilizing elements have sufficient diffusion time at high temperatures, and the dissolution of these elements reduces the B2 phase content. Therefore, the high-temperature deformed microstructure transforms from the original coarse, twisted lamellar clusters, a small amount of recrystallized material, and the B2 phase into uniform, fine equiaxed γ-phase recrystallization and a very small amount of fine B2 phase. Figure 4 (c) is a transmission electron image of the compressed structure. It can be clearly seen that high-density dislocations are generated inside these equiaxed γ recrystallizations. Compared with heterogeneous phase interfaces, dislocations can pass through these grain boundaries smoothly, thereby reducing dislocation pile-up at the interface. The reduced content of lamellar clusters and B2 phase also reduces the barrier to dislocation migration at their own interfaces, which contributes to the uniform distribution of stress and strain in the deformation region.

[0093] Figure 5 The TiAl alloy cylindrical sample, after being held at 1320℃ for 3 hours and then air-cooled, was then subjected to further cooling at 1150℃ for 0.01 seconds. -1 The high-temperature microstructure retained after compressing 85% at a strain rate. For example... Figure 5 As shown in (a), the compressed sample still maintains its intact edges and has not cracked. Figure 5 (b) is Figure 5 (a) Enlarged view of the tissue within the blue box. (and) Figure 4 The microstructure in (b) is similar, still consisting of recrystallized equiaxed γ phase with an average grain size of approximately 5 μm. The larger deformation extended the compression time of the sample, leading to a further decrease in the content of the B2 phase. The decrease in the content of brittle phase and the increase in the recrystallized γ phase content contribute to improving the hot formability of the alloy.

[0094] Figure 6(a) and (b) show the high-temperature tensile properties of a dog-bone-shaped sample of fused-cast TiAl alloy and a dog-bone-shaped sample of TiAl alloy after holding at 1320℃ for 3 hours and then air-cooling, respectively. As shown in the figure, at 850℃, the tensile strength of the fused-cast TiAl alloy is 499 MPa, and the elongation is 3.6%; after heat treatment, the tensile strength of the TiAl alloy is 624 MPa, and the elongation is 4.3%. At 900℃, the tensile strength of the fused-cast TiAl alloy decreases to 452 MPa, and the elongation is 6.8%; after heat treatment, the tensile strength of the TiAl alloy remains at 527 MPa, and the elongation is 12.5%, which is approximately twice that of the fused-cast TiAl alloy. This indicates that the TiAl alloy prepared by the method provided in this invention balances high-temperature strength and plasticity, and has superior hot deformation capability and high-temperature mechanical properties. This method broadens the hot deformation process ideas for TiAl alloys and is of great significance for the multi-directional application of TiAl alloys in aerospace engines, thermal protection systems, aircraft skins, panels, and other fields.

[0095] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure, characterized in that: Includes the following steps: Step 1: Melt the material 4-5 times using vacuum induction levitation melting technology. Considering the loss of Al, the compensation amount of Al is set to 2% of the added mass when preparing the raw materials. Step 2: The α→γ phase transformation range of the alloy was determined to be 1220℃~1335℃ using a combination of high-temperature in-situ laser confocal technology and differential scanning calorimetry. Step 3: Cut several block samples from the cast TiAl alloy using wire cutting technology. Place these block samples in an argon protective atmosphere. The heat treatment process parameters for obtaining the in-situ γ phase coated lamellar structure are: 1320°C, heat treatment for 3 hours, and air cooling to room temperature. The TiAl alloy is composed of the following components: 。 2. The method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 1, characterized in that: The raw material preparation process in step one is as follows: calculate the theoretical addition amount of each raw material based on the target composition of the TiAl alloy.

3. The method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 2, characterized in that: The operation of the vacuum induction suspension melting technology in step one includes the following steps: Step 11: Put the proportioned raw materials into the crucible of the vacuum induction suspension melting equipment; Steps 1 and 2: Close the equipment cavity and evacuate it to a vacuum level of 10. -3 To prevent the alloy from coming into contact with air and generating oxidation inclusions during the smelting process, the Pa level should be kept below 1. Step 13: Start the induction heating system to heat the raw materials to a completely molten state, and use the electromagnetic stirring effect of suspension melting to achieve uniform mixing of the components in the melt; Step 14: Repeat the above melting process 4 to 5 times, ensuring that the melt is completely solidified after each melting, and finally obtain a TiAl alloy ingot with uniform composition and no obvious defects. Step 15: Sample the prepared ingot and detect its actual composition by inductively coupled plasma atomic emission spectrometry. Confirm that the content of Ti, Al, Nb, Cr, Re, and C elements deviates from the design value within ±0.5%, ensuring a stable compositional basis for subsequent processes.

4. A method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 1 or 3, characterized in that: Step two, in determining the α→γ phase transformation range of the alloy, includes the following steps: Step 21: Two types of samples are cut from the TiAl alloy ingot obtained in Step 1. One type is used for high-temperature in-situ laser confocal analysis, and the other type is used for differential scanning calorimetry analysis. Step 22: By observing the microstructure evolution temperature through high-temperature in-situ laser confocal microscopy and recording the heat flow change curve during the heating process, the α→γ phase transformation range of the alloy was determined to be 1220℃~1335℃.

5. The method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 4, characterized in that: The method for obtaining the block samples in step three is as follows: several block samples of the same size are cut from the TiAl alloy ingot in step one using wire cutting technology, and the cleaned samples are placed into the heat treatment furnace respectively.

6. The method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 5, characterized in that: Step 3 involves preparing the block sample for heat treatment by introducing high-purity argon gas into the heat treatment furnace at a flow rate of 50 mL / min, ensuring that the oxygen content in the furnace is ≤100 ppm to prevent oxidation of the sample during the heat treatment process.

7. The method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 6, characterized in that: The heat treatment steps for the block sample in step three are as follows: Step 31: Set the insulation temperature to 1320℃ and maintain the temperature for 3 hours; Step 32: After the heat treatment is completed, immediately remove the block sample from the heat treatment furnace and allow it to cool naturally to room temperature in the air to complete the heat treatment process.

8. The method for preparing a high-strength, high-ductility TiAl alloy with an in-situ γ-phase coated lamellar structure according to claim 7, characterized in that: The process for determining the heat treatment parameters in step three is as follows: First, the microstructure of the samples after heat treatment at different temperatures was characterized to analyze the phase composition, phase ratio and microstructure morphology of each sample. Then, the analysis results show that the sample that was kept at 1320℃ for 3 hours and air-cooled formed an equiaxed γ phase, uniformly covering the target structure of refined lamellar clusters, and the volume fraction of brittle B2 phase decreased to 2%.

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