Ti2AlNb alloy with high room temperature and high temperature fracture toughness and preparation method thereof

Abstract

The application relates to a Ti2AlNb alloy with high room-temperature and high-temperature fracture toughness and a preparation method thereof. Through cyclic forging, gradual heat preservation and slow cooling in each fire and multi-scale structure synergistic control of grading solid solution aging, a coarse lamellar O phase and a serrated grain boundary composite structure can be stably prepared, and dual high fracture toughness at room temperature and high temperature is simultaneously realized. The alloy is suitable for various high-temperature load forgings serving at 650 DEG C for a long time, and is especially suitable for application scenes of high-temperature components with strict requirements for material damage tolerance and comprehensive mechanical properties at high and low temperatures. The room-temperature intrinsic toughness of the alloy is greatly improved, the whole process is replicable, and the recognition degree is high. The short board that the traditional alloy can only single-optimize the toughness at a certain temperature is solved. The heat treatment process interval is wide, the optimal system performance is prominent, the strength and toughness are considered, the production adaptability is strong, and the alloy has good scale manufacturing and popularization value; meanwhile, the technical route has obvious organizational recognizability, and it is convenient to prove the distinguishing characteristics during the application scheme examination.

Description

Technical Field

[0001] This invention relates to the field of high-temperature intermetallic compound materials technology, specifically to a Ti2AlNb alloy possessing both high room-temperature and high-temperature fracture toughness and its preparation method. This method, through low-high-low-high cyclic forging, sequential heat treatment and slow cooling, and graded solution aging, achieves multi-scale microstructure synergistic control, stably preparing a composite microstructure of coarse lamellar O phase and serrated grain boundaries. It simultaneously achieves high fracture toughness at both room-temperature and high-temperature temperatures, making it suitable for various high-temperature load-bearing forgings with long-term service at 650 ℃, and particularly suitable for high-temperature component applications with stringent requirements for material damage tolerance and comprehensive high- and low-temperature mechanical properties. Background Technology

[0002] Ti2AlNb-based intermetallic alloys, with their low density, excellent high-temperature strength, and high-temperature oxidation resistance, possess enormous application potential in high-temperature load-bearing structures with long-term service at 650 ℃, making them a key intermetallic compound material to replace traditional high-temperature alloys. As high-end high-temperature components develop towards long-life and high-damage-tolerance design standards, materials need to simultaneously consider room-temperature and high-temperature crack propagation resistance, placing stringent requirements on the alloy's comprehensive fracture toughness at both high and low temperatures.

[0003] However, Ti2AlNb dual-phase alloys prepared by conventional processes have significant performance limitations, achieving only a limited balance between strength and plasticity. Room temperature fracture toughness is generally low, and damage tolerance at 650 °C is insufficient. Cracks tend to propagate rapidly during component service, posing safety hazards. Furthermore, traditional industry approaches to microstructure control generally believe that coarse lamellar O phases impair plasticity and toughness, and optimization methods have focused on refining grains and O phases, failing to tap the toughening potential of coarse lamellar O phases.

[0004] Current mature processing methods for Ti2AlNb-based alloys still suffer from numerous technical shortcomings. Forging within a single temperature range only produces straight B2 grain boundaries, failing to leverage the tortuous grain boundary structure to extend crack propagation paths and improve fracture resistance. Under conventional heat treatment regimes, a large number of fine needle-like O phases precipitate within the material. These precipitates readily become microcrack initiation sites, accelerating crack instability and propagation. Existing research lacks a compatible integrated process combining high- and low-temperature cyclic deformation with heat treatment and slow cooling. It is difficult to simultaneously prepare a composite microstructure of coarse lamellar O phases and serrated grain boundaries, and it is also impossible to simultaneously improve high- and low-temperature fracture toughness through two differentiated toughening paths: room-temperature O phase multi-system slip and high-temperature interface crack deflection. Therefore, the existing material properties are ill-suited to the usage standards of high-damage-tolerance high-temperature components.

[0005] Therefore, developing a Ti2AlNb-based alloy preparation process that can directionally control the coarse lamellar O phase and serrated grain boundaries, and simultaneously achieve high room temperature and high temperature fracture toughness, would break through the dual bottlenecks of existing microstructure control ideas and processing technology, and have important practical value for the engineering promotion of high-temperature load-bearing forgings. Summary of the Invention

[0006] Existing Ti2AlNb-based alloys generally suffer from the inability to simultaneously achieve room-temperature and high-temperature fracture toughness. The industry has long considered coarse lamellar O phases as an unfavorable microstructure that degrades plasticity and toughness. Conventional single-temperature forging can only form straight B2 grain boundaries, and when combined with ordinary heat treatment, it easily generates a large number of fine needle-like O phases, which readily induce rapid crack propagation, failing to meet the long-term service requirements of high-damage-tolerance high-temperature components. This invention addresses these technical deficiencies by proposing a four-stage high- and low-temperature cyclic forging combined with sequential heat treatment and slow cooling, and a staged solution treatment and aging synergistic control scheme. Breaking away from the traditional approach of refining and toughening, this invention directionally prepares a composite microstructure of coarse lamellar O phases and serrated grain boundaries. Relying on the differentiated mechanism of room-temperature O phase slip intrinsic toughening and high-temperature interface deflection synergistic toughening, it simultaneously improves the material's room-temperature and high-temperature fracture resistance, adapting to the usage requirements of various high-temperature load-bearing forgings for long-term service.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: S1. Ingot blanking and homogenization treatment: Take Ti2AlNb-based alloy ingot, remove the surface oxide layer, complete the homogenization heat treatment, and carry out multi-fire upsetting and drawing to eliminate as-cast composition segregation and internal porosity defects, and obtain homogeneous forging blank. S2, First stage of low temperature deformation: Heat the temperature to 30-60 ℃ below the phase transformation point of alloy B2, carry out multi-fire upsetting and drawing deformation, and control the deformation amount of a single fire to 20%-50%, which can stably retain the nucleation core of the primary O phase. S3, First stage of high temperature deformation: Heat the temperature to 20-60 ℃ above the B2 phase transformation point of the alloy, and carry out 1-3 upsetting and drawing deformations to promote B2 grain deformation, grain boundary migration and subsequent O phase lamellar layer formation; S4. Second stage of low-temperature deformation: Cooling to 20-50 ℃ below the B2 phase transformation point of the alloy and performing multiple upsetting and drawing processes to retain and regulate the primary O phase in the microstructure; S5. Second stage of high-temperature final forging: The temperature is raised to 20-60 ℃ above the B2 phase transformation point of the alloy to complete the final forging. The high-temperature strain promotes the formation of serrated morphology of B2 grain boundaries, which provides a favorable microstructure for the precipitation of coarse lamellar O phase. S6. Slow cooling control: After each forging in steps S2, S3, S4, and S5, the surface of the billet is covered with heat-insulating material, such as quartz wool, ceramic fiber felt, or high-temperature heat-resistant insulation layer, to reduce the cooling rate of the billet, inhibit the large-scale precipitation of fine needle-like O phase, and directionally generate coarse primary lamellar O phase. S7. Staged solution aging heat treatment: The final forged billet is first held at 900-960 ℃ for 1-3 h and then oil-cooled or air-cooled, and then held at 740-820 ℃ for 12-36 h and then oil-cooled or air-cooled. The size and volume ratio of the dual-scale O phase are precisely controlled. The optimal heat treatment process is to hold at 940 ℃ for 2 h and then oil-cooled, followed by holding at 780 ℃ for 24 h and then oil-cooled.

[0008] Step S1, homogenization combined with multiple upsetting and drawing, aims to eliminate as-cast composition segregation and internal void defects, resulting in a uniformly structured forged billet.

[0009] The first stage of low-temperature deformation in step S2 can stably preserve the nascent O-phase nucleus.

[0010] The first stage of high-temperature deformation in step S3 can fully promote the deformation of B2 grains, facilitate grain boundary migration, and promote the formation of subsequent O phase layers.

[0011] The second stage of low-temperature deformation in step S4 can preserve the nascent O-phase precursor structure and prevent the O-phase from re-dissolving at high temperatures.

[0012] The second stage of high-temperature final forging in step S5 can promote the formation of serrated morphology of B2 grain boundaries, providing a microstructure basis for the precipitation of coarse lamellar O phase.

[0013] Step S6 slow cooling control reduces the cooling rate by thermal insulation coating, promoting the formation of coarse primary lamellar O phase.

[0014] The optimal process for step S7, staged solution aging, is to hold at 940 ℃ for 2 h and then cool with oil, followed by holding at 780 ℃ for 24 h and then cooling with oil, to precisely control the size and volume ratio of the O phase in both scales.

[0015] The alloy microstructure has O phase as the matrix dominant phase, and the total integral of O phase is preferably greater than 70%, more preferably greater than 80%.

[0016] The alloy contains two scales of O phase structure: primary coarse lamellar O phase with a length of 5–13 μm and secondary acicular O phase with a length of 0.5–1.0 μm; the preferred size of the primary coarse lamellar O phase is 8.5–12.5 μm and the preferred size of the secondary acicular O phase is 0.8–1.0 μm.

[0017] The grain boundaries of the B2 phase in the alloy exhibit a serrated morphology, with a higher degree of tortuosity than that of conventional equiaxed / biphase structures.

[0018] The room temperature fracture toughness of the alloy is 30–40 MPa·m 1 / 2 The high-temperature fracture toughness at 650 ℃ is 50–65 MPa·m. 1 / 2 The preferred alloy has a room temperature fracture toughness ≥35 MPa·m 1 / 2 High-temperature fracture toughness at 650 ℃ ≥ 60 MPa·m1 / 2 .

[0019] The design concept of this invention is: To address the stringent requirements of high-temperature load-bearing components for high-temperature fracture toughness at both room temperature and high temperature, stable microstructure, and long service life, this study leverages the inherent material properties of Ti2AlNb-based alloys. Focusing on three key objectives—lamellar phase control, grain boundary modification, and full-temperature-range toughening matching—a complete process logic is established, encompassing ingot homogenization, four-stage alternating high and low temperature forging, gradual cooling to control microstructure, and graded solution aging. Through homogenization to eliminate ingot defects, cyclic forging to pre-form characteristic microstructures, slow cooling after forging to promote the formation of coarse lamellar O phases, and two-stage heat treatment to precisely control the two-phase scale, a stable two-phase microstructure dominated by the O phase and featuring serrated grain boundaries is formed. This addresses the shortcomings of existing similar alloys, such as low room-temperature toughness, insufficient high-temperature damage tolerance, and reliance solely on fine-grain toughening. Ultimately, a Ti2AlNb-based alloy exhibiting both high room-temperature fracture toughness and excellent high-temperature crack propagation resistance is obtained.

[0020] Its specific design concept is as follows: The design concept of lamellar phase toughening reverses the traditional understanding: abandoning the industry's inherent idea that "coarse lamellar O phase weakens plasticity and toughness", it actively uses large-size primary lamellar O phase as the core toughening carrier. By utilizing the characteristic that coarse lamellar O phase can activate multiple slip systems at the same time, it relies on internal plastic deformation to passivate crack tips and improve the intrinsic room temperature toughness of the alloy from the root.

[0021] The design concept of serrated grain boundary prefabrication with four alternating deformation stages: In response to the problem that conventional forging can only form straight grain boundaries and cannot prevent crack propagation, a four-stage alternating upsetting and drawing deformation of "low temperature-high temperature-low temperature-high temperature" is adopted. First, the O phase nucleation core is retained at low temperature. Then, plastic strain is introduced at high temperature to drive grain boundary migration. The primary lamellar precursor structure is locked at low temperature for the second time. Finally, the serrated grain boundary is shaped by the cumulative strain at high temperature, which provides a structural basis for crack deflection under high temperature conditions.

[0022] The design concept of phase size control after slow cooling after each forging pass: In response to the defects of natural cooling that easily leads to the precipitation of a large amount of fine needle-like O phase and induces microcracks, the billet is uniformly coated with heat insulation material after each round of forging to control the cooling rate, reduce the cooling rate of the billet, inhibit the rapid precipitation of fine O phase, and directionally cultivate coarse primary lamellar O phase of appropriate size.

[0023] The design concept of precise microstructure control through graded solution aging is as follows: a two-stage heat treatment process is adopted. First, high-temperature solution treatment optimizes the uniformity of matrix composition, and then low-temperature aging precipitates secondary needle-like O phases to assist in strengthening. The size and volume fraction of primary lamellar phases and fine precipitates are precisely matched to balance the alloy strength and high and low temperature fracture resistance.

[0024] The differentiated toughening matching design concept for temperature zones: It distinguishes between room temperature and 650 ℃ high temperature service conditions and matches exclusive toughening mechanisms. At room temperature, it achieves internal toughening by relying on the plastic slip of coarse lamellar O phase; at high temperature, it superimposes external shielding toughening by O / B2 interface hindrance and crack deflection induced by O phase with different orientations. The two mechanisms work together to simultaneously improve fracture toughness across the entire temperature range.

[0025] The advantages and beneficial effects of this invention are: This invention departs from traditional approaches to microstructure control, achieving highly efficient toughening with coarse lamellar O phases. Existing research generally considers coarse lamellar O phases to degrade alloy plasticity and toughness, leading to a long-standing focus on refining the O phase as an optimization direction. This invention fully utilizes the characteristic of coarse lamellar O phases to simultaneously activate multiple slip systems, relying on the plastic deformation of the lamellars themselves to blunt crack tips, significantly improving the alloy's intrinsic room-temperature toughness. This breaks with industry norms and opens up entirely new pathways for toughening control.

[0026] The four-stage alternating high and low temperature forging process, combined with gradual cooling, simultaneously obtains the target microstructure. Employing a segmented forging process of low temperature-high temperature-low temperature-high temperature, coupled with slow cooling after each forging pass by covering with insulating material, this method not only shapes serrated B2 grain boundaries through accumulated strain but also reduces the cooling rate to suppress the precipitation of fine needle-like O phases, directionally generating large-sized primary lamellar O phases. This achieves the synergistic preparation of a dual-scale O phase composite microstructure and tortuous grain boundaries in one step. The process is highly reproducible and easily identifiable.

[0027] A dual toughening mechanism adaptable to different service temperatures simultaneously improves fracture toughness at room temperature and high temperature. At room temperature, fracture energy is dissipated by the slippage of coarse lamellar O phase. At high temperature, in addition to retaining the plastic toughening effect of O phase, the serrated grain boundaries and O phases with different orientations can promote repeated crack deflection. The superimposed interface retardation effect forms a synergistic effect of internal and external toughening, effectively improving the damage tolerance at 650 ℃ and solving the shortcoming of traditional alloys that can only optimize toughness at a single temperature.

[0028] It has a wide range of heat treatment processes, outstanding optimal performance, and balances strength and toughness.

[0029] This invention features a wide adjustable range of solution treatment and aging temperatures, suitable for the production of forgings of different specifications. The preferred heat treatment regime is 940 ℃ / 2h oil cooling + 780 ℃ / 24h oil cooling, which allows for precise control of the size and volume fraction of the two types of O phases. Under optimal microstructure, the alloy's room temperature fracture toughness can reach 35 MPa·m. 1 / 2 The high-temperature fracture toughness at 650 ℃ reaches 55–65 MPa·m. 1 / 2 While retaining the inherent high-temperature strength and oxidation resistance of Ti2AlNb alloy, it significantly improves the ability to resist crack propagation.

[0030] The process is complete and coherent, applicable to a variety of high-temperature components, and has a wide range of engineering applications. The entire process forms a complete closed loop, from homogeneous ingot casting, segmented forging, controlled cooling after forging to graded heat treatment. The parameters of each process are clear and controllable, and it can process various blanks such as discs and ring forgings. It is suitable for compressor discs, casings, rings, and high-temperature load-bearing structural components for aero-engines. It has strong production adaptability and good value for large-scale manufacturing and promotion. At the same time, the technical route has obvious organizational identifiability, which facilitates the demonstration of distinguishing features during patent examination.

[0031] Instruction manual illustrations Figure 1 Microstructure of Ti2AlNb-based alloy after forging process in Example 1; Figure 2 The image shows the microstructure of the Ti2AlNb-based alloy after the heat treatment process described in Example 1. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the embodiments, but the present invention is not limited to these embodiments.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods or product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0034] The present invention will be further described in detail below through embodiments.

[0035] Example 1 In this embodiment, a method for preparing an O-phase-dominant Ti2AlNb-based alloy exhibiting both high room temperature and high temperature fracture toughness includes the following steps: S1. Ingot blanking and homogenization treatment: Remove the oxide layer on the surface of Ti2AlNb-based alloy ingot, complete the homogenization heat treatment, and then carry out multi-fire upsetting and drawing to eliminate as-cast segregation and porosity, and obtain a homogeneous forging blank. S2, First stage of low-temperature deformation: The temperature is raised to 45 ℃ (1010 ℃) below the B2 phase transformation point, and three upsetting and drawing processes are carried out, with a single upsetting deformation of 30%; S3, First stage of high-temperature deformation: The temperature is raised to 40℃ above the B2 phase transformation point (1095℃), and two-stage upsetting deformation is carried out, with a single-stage deformation of 30%; S4, Second stage low-temperature deformation: Cool down to 35 ℃ (1020 ℃) ​​below the B2 phase transformation point, and perform three upsetting and drawing operations, with a single-fire deformation amount of 30%; S5, Second stage high-temperature final forging: The final forging is completed by heating to 40℃ above the B2 phase transformation point (1095℃), with a single-fire deformation of 30%; S6. Unified Slow Cooling Control: After each forging cycle in steps S2-S5, the material is used to cover the area for natural slow cooling, without exposure to air cooling throughout the process. This inhibits the precipitation of fine O phases and promotes the directional formation of coarse primary lamellar O phases. Figure 1 As shown; S7. Staged solution treatment and aging heat treatment: Forging billet held at 940 ℃ for 2 h and then oil-cooled, followed by holding at 780 ℃ for 24 h and then oil-cooled. Figure 2 As shown.

[0036] Example 2 In this embodiment, a method for preparing an O-phase-dominant Ti2AlNb-based alloy exhibiting both high room temperature and high temperature fracture toughness includes the following steps: S1. Ingot blanking and homogenization treatment: Remove the oxide layer on the surface of Ti2AlNb-based alloy ingot, complete the homogenization heat treatment, and then carry out multi-fire upsetting and drawing to eliminate as-cast segregation and porosity, and obtain a homogeneous forging blank. S2, First stage of low-temperature deformation: The temperature is raised to 30 ℃ (1025 ℃) below the B2 phase transformation point, and three upsetting and drawing processes are carried out, with a single upsetting deformation of 30%; S3, First stage of high-temperature deformation: The temperature is raised to 20℃ above the B2 phase transformation point (1075℃), and two-stage upsetting deformation is carried out, with a single-stage deformation of 30%; S4, Second stage low-temperature deformation: Cool down to 20 ℃ below the B2 phase transformation point (1035 ℃), and perform three upsetting and drawing operations, with a single-fire deformation amount of 30%; S5, Second stage high-temperature final forging: The final forging is completed by heating to 20℃ above the B2 phase transformation point (1075℃), with a single-fire deformation of 30%; S6. Unified slow cooling control: After each forging fire in steps S2 to S5, the material is wrapped with heat insulation and naturally slow-cooled, without being exposed to air cooling throughout the process, which inhibits the precipitation of fine O phase and directionally generates coarse primary lamellar O phase. S7. Graded solution aging heat treatment: Forging billet held at 940 ℃ for 2 h and then oil cooled, followed by holding at 780 ℃ for 24 h and then oil cooled.

[0037] Example 3 In this embodiment, a method for preparing an O-phase-dominant Ti2AlNb-based alloy exhibiting both high room temperature and high temperature fracture toughness includes the following steps: S1. Ingot blanking and homogenization treatment: Remove the oxide layer on the surface of Ti2AlNb-based alloy ingot, complete the homogenization heat treatment, and then carry out multi-fire upsetting and drawing to eliminate as-cast segregation and porosity, and obtain a homogeneous forging blank. S2, First stage of low-temperature deformation: The temperature is raised to 60 ℃ (995 ℃) below the B2 phase transformation point, and three upsetting and drawing processes are carried out, with a single upsetting deformation of 30%; S3, First stage of high-temperature deformation: The temperature is raised to 60 ℃ above the B2 phase transformation point (1115 ℃), and two-stage upsetting and drawing deformation is carried out, with a single-stage deformation of 30%; S4, Second stage low-temperature deformation: Cool down to 50 ℃ (1005 ℃) below the B2 phase transformation point, and perform three upsetting and drawing operations, with a single-fire deformation amount of 30%; S5, Second stage high-temperature final forging: The final forging is completed by heating to 60 ℃ above the B2 phase transformation point (1115 ℃), with a single-fire deformation of 30%; S6. Unified slow cooling control: After each forging fire in steps S2 to S5, the material is wrapped with heat insulation and naturally slow-cooled, without being exposed to air cooling throughout the process, which inhibits the precipitation of fine O phase and directionally generates coarse primary lamellar O phase. S7. Graded solution aging heat treatment: Forging billet held at 940 ℃ for 2 h and then oil cooled, followed by holding at 780 ℃ for 24 h and then oil cooled.

[0038] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the four-stage high and low temperature alternating forging in steps S2 to S5 is cancelled, and a one-time isothermal forging in the single-phase region at 1080℃ is adopted. The total cumulative deformation is equal to the total deformation of all forging in Example 1. After forging, there is no heat insulation coating and direct air cooling. The billet composition, homogenization, graded solution aging, heating and cooling rates, and sample preparation and testing standards are exactly the same as those in Example 1, and finally Ti2AlNb-based alloy forgings are obtained.

[0039] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the forging temperature, deformation amount and number of forging fires in steps (1) to S5 remain completely unchanged, the slow cooling process after forging in step S6 is deleted, and air cooling is performed directly after each forging fire is completed; the remaining raw materials, heat treatment and operation process are the same as in Example 1, and Ti2AlNb based alloy forgings are finally obtained.

[0040] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that all forging and slow cooling parameters in steps (1) to S6 are exactly the same, except that the solution treatment process in step S7 is adjusted to 960℃ for 2 hours and oil cooling, and the aging regime remains unchanged; the remaining billet, forging operation and cooling method are kept the same, and finally Ti2AlNb based alloy forgings are obtained.

[0041] Table 1. Comparison of microstructure and room temperature mechanical properties of Ti2AlNb-based alloys in Examples 1-3 and Comparative Examples 1-3

[0042] The experimental results above show that by using the four-stage high and low temperature alternating forging combined with heat insulation and slow cooling, and the integrated preparation process of staged solution aging of the present invention, a composite structure of coarse lamellar primary O phase + fine secondary acicular O phase and serrated B2 grain boundaries can be generated in a directional manner, and Ti2AlNb-based alloy forgings with excellent room temperature and high temperature fracture toughness can be prepared.

[0043] Comparing the three sets of samples in Examples 1, 2, and 3, it can be seen that the forging deformation, forging passes, post-forging slow cooling regime, and solution aging heat treatment process are completely consistent across the three sets of samples. The only difference lies in the range of heating temperature settings for each stage of high and low temperature forging. Example 2 uses the lower limit of the forging temperature, resulting in the lowest average size of the primary lamellar O and the lowest overall O phase integral. The degree of B2 grain boundary serration is relatively weak, and the room temperature and 650 ℃ fracture toughness are the lowest among the three sets of samples. Example 3 uses the upper limit of the forging temperature, resulting in a slight increase in the size of the primary lamellar O. However, excessively high forging temperatures will cause a small amount of grains to grow slightly, and the proportion of O phase will decrease slightly. The high and low temperature toughness is slightly lower than that of Example 1. Example 1 selects the optimal forging temperature in the middle of the range, which has the best matching of strain accumulation effect. It can form high-amplitude serrated B2 grain boundaries and obtain coarse lamellar primary O phase with a volume fraction >85%. It fully utilizes the dual effects of room temperature multi-slip intrinsic toughening and high-temperature crack deflection extrinsic toughening. The room temperature and high-temperature fracture toughness are the best among the three sets of samples. Therefore, it can be seen that the forging temperature of the present invention has a wide process adaptability window. High toughness structure can be obtained by any temperature in the range combined with the complete forging-slow cooling-heat treatment process, and the intermediate preferred temperature can achieve the optimal match between microstructure and mechanical properties.

[0044] Comparing Examples 1-3 with Comparative Example 1, it can be seen that Examples 1-3 employ the four-stage high-low temperature alternating multi-fire forging process of the present invention, while Comparative Example 1 only uses single-phase region single-time isothermal forging, without multi-temperature region strain accumulation and direct air cooling after forging; the alloy of Comparative Example 1 lacks high-amplitude serrated grain boundaries, the size of the primary lamellar O phase is significantly reduced, the fracture toughness at room temperature and 650 ℃ is significantly reduced, the crack propagation path is straight, and the external shielding toughening effect brought about by interface deflection is lacking. Therefore, it can be seen that the segmented high-low temperature alternating forging of the present invention can accumulate multi-directional plastic strain, promoting the formation of serrated morphology of B2 grain boundaries, and simultaneously providing a reserve microstructure for the precipitation of coarse lamellar O phase. It is the core forging process for simultaneously improving the alloy chamber and high-temperature damage tolerance.

[0045] Comparing Examples 1-3 with Comparative Example 2, it can be seen that in Examples 1-3, each forging was followed by a heat-insulating material and slow cooling. In Comparative Example 2, the forging temperature and deformation parameters remained unchanged for the four stages, but the heat-insulating slow cooling process was omitted. Excessive cooling of the billet significantly inhibited the precipitation of coarse lamellar primary O phase, resulting in fine primary O phase. This significantly increased the number of microcrack initiation sites, greatly weakened the room-temperature intrinsic slip toughening mechanism, and caused simultaneous deterioration of both room-temperature and high-temperature fracture toughness. Therefore, heat-insulating slow cooling is an indispensable key supporting process for controlling the formation of coarse lamellar primary O phase and ensuring the alloy's room-temperature intrinsic toughness.

[0046] Comparing Examples 1-3 and Comparative Example 3, it can be seen that Examples 1-3 uniformly adopted a low-temperature solution treatment at 940 ℃ followed by an aging heat treatment at 780 ℃. Comparative Example 3's forging and slow cooling processes were completely consistent with the Examples, only the solution temperature was increased to 960 ℃. High-temperature solution treatment caused a large amount of primary lamellar O phase to dissolve back into the B2 matrix. After aging, the density of secondary acicular O phase increased sharply, exacerbating the stress concentration at the phase interface, making cracks easier to connect and propagate rapidly, and simultaneously significantly reducing the fracture toughness at room temperature and 650 ℃. Therefore, 940 ℃ low-temperature solution treatment is the optimal temperature range for this invention, which can reasonably balance the proportion of primary and secondary O phases and is a necessary heat treatment condition for achieving dual toughening at high and low temperatures.

[0047] The results show that this invention uses a dual mechanism of intrinsic toughening due to multi-system slip of the O phase at room temperature and extrinsic toughening due to deflection of grain boundaries / phase boundaries at high temperature as the core of its microstructure design. It is complemented by a four-stage alternating high and low temperature forging process, sequential heat treatment and slow cooling, and low-temperature staged solution aging. The forging temperature process window is wide, and the coarse lamellar primary O phase + fine secondary acicular O composite microstructure and serrated B2 grain boundaries can be precisely controlled within this range. This avoids various microstructural defects and toughness limitations caused by single-temperature forging, rapid air cooling after forging, and high-temperature solution treatment. The alloy obtained in Example 1 using the optimal process achieves a room temperature fracture toughness of 40 MPa·m. 1 / 2 The fracture strength at 650℃ can reach 65 MPa·m. 1 / 2 The room temperature and high temperature fracture toughness are significantly better than all comparative specimens, making it suitable for key components such as discs of long-term service aero-engines and ring-shaped load-bearing forgings, meeting the stringent requirements of long service life and high damage tolerance of equipment.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0049] The microstructure and mechanical properties of the Ti2AlNb-based alloy prepared by this invention are as follows: Figure 1 , Figure 2 The actual measured data is shown in the graph.

[0050] Matters not covered in this invention are common knowledge.

[0051] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a Ti2AlNb alloy possessing both high room temperature and high temperature fracture toughness, characterized in that, Includes the following steps: S1. Ingot blanking and homogenization treatment: Take Ti2AlNb-based alloy ingots, remove the surface oxide layer, perform homogenization treatment, and then perform multi-fire upsetting and drawing blanking. S2, First stage low-temperature deformation: The temperature is raised to 30-60℃ below the B2 phase transformation point for multi-stage upsetting and drawing deformation, with the deformation amount per stage controlled at 20%-50%; S3, First stage of high temperature deformation: Heat to 20-60 ℃ above the B2 phase transformation point, and perform 1-3 upsetting and drawing deformations; S4, Second stage low temperature deformation: Cool down to 20-50 ℃ below the B2 phase transformation point, and perform multiple upsetting and drawing processes; S5, Second stage high-temperature final forging: The final forging is completed by heating to 20-60 ℃ above the B2 phase transformation point; S6. Slow cooling control: After each forging is completed in steps S2, S3, S4, and S5, the surface of the billet is covered with insulation materials such as quartz wool, ceramic fiber felt, or high-temperature heat-resistant insulation layer to keep it warm and slow cooling. S7. Graded solution aging heat treatment: The forging billet is first held at 900-960 ℃ for 1-3 h and then oil-cooled or air-cooled, and then held at 740-820 ℃ for 12-36 h and then oil-cooled or air-cooled.

2. The method for preparing the Ti2AlNb alloy with both high room temperature and high temperature fracture toughness according to claim 1, characterized in that, The optimal process for step S7, staged solution aging, is to hold at 940 ℃ for 2 h and then cool with oil, followed by holding at 780 ℃ for 24 h and then cooling with oil, to precisely control the size and volume ratio of the O phase in both scales.

3. A Ti2AlNb alloy as described in claim 1, possessing both high room temperature and high temperature fracture toughness, characterized in that, The alloy microstructure has O phase as the matrix dominant phase, and the total integral of O phase is preferably greater than 70%, more preferably greater than 80%.

4. The Ti2AlNb alloy with both high room temperature and high temperature fracture toughness according to claim 3, characterized in that, The alloy contains two scales of O phase structure: primary coarse lamellar O phase with a length of 5–13 μm and secondary acicular O phase with a length of 0.5–1.0 μm; the preferred size of the primary coarse lamellar O phase is 8.5–12.5 μm and the preferred size of the secondary acicular O phase is 0.8–1.0 μm.

5. The Ti2AlNb alloy with both high room temperature and high temperature fracture toughness according to claim 3, characterized in that, The grain boundaries of the B2 phase in the alloy exhibit a serrated morphology, with a higher degree of tortuosity than that of conventional equiaxed / biphase structures.

6. The Ti2AlNb alloy with both high room temperature and high temperature fracture toughness according to claim 3, characterized in that, The room temperature fracture toughness of the alloy is 30–40 MPa·m 1 / 2 The high-temperature fracture toughness at 650 ℃ is 50–65 MPa·m. 1 / 2 .

7. The Ti2AlNb alloy with both high room temperature and high temperature fracture toughness according to claim 3, characterized in that, The preferred alloy has a room temperature fracture toughness of 35–40 MPa·m. 1 / 2 High-temperature fracture toughness at 650 ℃ is 60~65 MPa·m 1 / 2 .

Images