Regulation and control method of TiAl alloy double-peak lamellar structure

Abstract

The invention discloses a regulation and control method for a TiAl alloy double-peak lamellar structure, and belongs to the technical field of TiAl alloy heat treatment. A TiAl alloy sample is firstly subjected to heat treatment to prepare a conventional lamellar structure composed of coarse gamma lamellas, then the conventional lamellar structure is heated to 5-50 DEG C below a T alpha / (alpha + gamma) or T (alpha + beta) / (alpha + beta + gamma) phase transformation point, heat preservation is conducted for 5-120 min, rapid cooling is conducted, and a metastable lamellar structure containing a small amount of gamma coarse lamellas is obtained; and finally, low-temperature tempering treatment is conducted, heat preservation is conducted for 5 min to 300 min at the temperature of 700 DEG C to 1000 DEG C, furnace cooling is conducted to the room temperature, and the TiAl alloy with the double-peak lamellar structure is obtained. Through the regulation and control method, the formation of a discontinuous precipitation zone and a non-equilibrium structure is effectively inhibited while the gamma lamellas of the TiAl alloy are refined, and compared with a conventional lamellar structure composed of coarse gamma lamellas, the yield strength of the TiAl alloy can be improved by at least 50 MPa through the prepared double-peak lamellar structure, and the steady-state creep rate of the alloy is reduced by more than 5 times.

Description

Technical Field

[0001] This invention relates to the field of TiAl alloy heat treatment technology, and specifically to a method for controlling the bimodal lamellar structure of TiAl alloy. Background Technology

[0002] TiAl alloys, due to their low density, excellent high-temperature strength, and good oxidation resistance, are considered ideal lightweight high-temperature structural materials for aerospace and automotive industries. However, the microstructure of these alloys typically consists of coarse lamellar clusters and their internal coarse γ-lamellae. This structural feature often makes it difficult for their yield strength and high-temperature creep resistance to meet the stringent requirements of advanced equipment. Currently, techniques such as thermomechanical processing or cyclic heat treatment have effectively refined the lamellar cluster size of TiAl alloys, thereby significantly improving the alloy's yield strength. However, a stable and reliable process for refining the γ-lamellae within the lamellar clusters still lacks a reliable method. Existing γ-lamellae refinement methods are prone to inducing discontinuous precipitation zones or forming non-equilibrium structures such as blocky or feathery structures at the lamellar cluster interfaces during implementation. The presence of these harmful structures not only fails to guarantee performance improvement but also severely deteriorates the alloy's high-temperature creep resistance. Therefore, developing a process that can effectively refine γ-lamellae while avoiding the formation of harmful discontinuous precipitation zones or non-equilibrium structures has become a pressing technical challenge in this field. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies by providing a method for controlling the bimodal lamellar structure of TiAl alloys. This method refines the γ-lamellae while effectively suppressing the formation of harmful structures such as discontinuous precipitation zones and non-equilibrium structures. Currently, no research or patents with the same technical approach have been found domestically or internationally.

[0004] To achieve the above objectives, this invention proposes a method for controlling the bimodal lamellar structure of TiAl alloys, comprising the following steps: S1. Prepare TiAl alloy and heat it to T α / (α+γ) or T (α+β) / (α+β+γ) Hold at 5℃~50℃ above the phase transition point for 5min~60min, then slowly cool to room temperature to obtain a conventional lamellar tissue composed of coarse γ-lamellae. S2. Heat the TiAl alloy with a conventional lamellar structure to T. α / (α+γ) or T (α+β) / (α+β+γ) The temperature was set at 5°C to 50°C below the phase transition point, held for 5 to 120 minutes, and then rapidly cooled to obtain a metastable lamellar structure containing a small amount of coarse γ lamellae; the T α / (α+γ) The phase transition temperature between the α single-phase region and the (α+γ) two-phase region; T (α+β) / (α+β+γ) The phase transition temperatures are those of the (α+β) two-phase region and the (α+β+γ) three-phase region. S3. The TiAl alloy with metastable lamellar structure is subjected to low-temperature tempering treatment, held at 700°C~1000°C for 5min~300min, and then cooled to room temperature in the furnace to obtain a TiAl alloy with bimodal lamellar structure.

[0005] Preferably, in step S1, the TiAl alloy is composed of elements with the following atomic percentages: 40 at.%~50 at.% Al and 0~10 at.% alloying elements; the alloying elements are one or more of Nb, Mo, V, Cr, Zr, Mn, Ni, Fe, Hf, Ta, W, Re, C, Si, B, Y and O.

[0006] Preferably, in step S1, the TiAl alloy prepared includes small TiAl alloy samples, component blanks, or components prepared by plastic deformation, powder metallurgy, or additive manufacturing processes.

[0007] Preferably, in step S1, if the TiAl alloy has an α single-phase region, the TiAl alloy is heated to T. α / (α+γ) If the TiAl alloy does not have an α single-phase region, and is heated to T at a temperature 5°C to 50°C above the phase transformation point. (α+β) / (α+β+γ) 5℃~50℃ above the phase transition point.

[0008] Preferably, in step S1, the slow cooling rate is 5°C / min to 20°C / min.

[0009] Preferably, in step S1, the conventional lamellar tissue is a full lamellar tissue or a near-lamellar tissue.

[0010] Preferably, in step S2, if the TiAl alloy contains an α single-phase region, the TiAl alloy is heated to T. α / (α+γ) If the TiAl alloy does not have an α single-phase region, and is heated to T at 5℃~50℃ below the phase transformation point. (α+β) / (α+β+γ) 5℃~50℃ below the phase transition point.

[0011] Preferably, in step S2, the rapid cooling method is air cooling.

[0012] Preferably, in step S3, the coarse lamellar layers and fine lamellar layers are distributed alternately in the bimodal lamellar structure.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The bimodal lamellar structure prepared by this invention significantly reduces the overall size of the γ-lamellae due to the precipitation of a large number of nanoscale γ-lamellae between the coarse lamellar layers, while effectively suppressing discontinuous precipitation and the occurrence of non-equilibrium structures at the lamellar cluster interface.

[0014] Compared with conventional lamellar structures composed of coarse γ-lamellae, the bimodal lamellar structure prepared by this invention can increase the yield strength of TiAl alloy by at least 50 MPa and reduce the steady-state creep rate of the alloy by more than 5 times.

[0015] This invention provides a process for controlling the bimodal lamellar structure of TiAl alloys. By heat-treating the (α+γ) two-phase region or the (α+β+γ) three-phase region and then rapidly cooling and tempering at low temperature, the strength and creep resistance of TiAl alloys are synergistically improved. This process has the advantages of simple operation, good process stability, and high repeatability. Attached Figure Description

[0016] Figure 1 This is a conventional lamellar microstructure diagram of the TiAl alloy provided in Embodiment 1 of the present invention.

[0017] Figure 2 This is a diagram of the bimodal lamellar structure of the TiAl alloy provided in Embodiment 1 of the present invention.

[0018] Figure 3 This is a conventional lamellar microstructure diagram of the TiAl alloy provided in Embodiment 2 of the present invention.

[0019] Figure 4 This is a diagram of the bimodal lamellar structure of the TiAl alloy provided in Embodiment 2 of the present invention. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Existing technologies generally believe that the key to refining γ-lamellae lies in obtaining a supersaturated α2 phase through rapid cooling, followed by low-temperature tempering to induce the precipitation of fine γ-lamellae. However, while this method can achieve lamellar refinement, the instability of the α2 phase during rapid cooling inevitably leads to the formation of discontinuous precipitation zones or non-equilibrium structures such as blocky or feathery formations, severely impairing the high-temperature performance of the alloy. To resolve this contradiction, this invention abandons the traditional approach of "refining all coarse γ-lamellae" and proposes a novel microstructure control strategy: by intentionally retaining some coarse γ-lamellae to stabilize the α2 phase matrix, a large number of nanoscale fine γ-lamellae are induced to precipitate in the regions between the coarse lamellae using a low-temperature tempering process. This approach of "exchanging partial retention for overall refinement" successfully constructs a bimodal lamellar microstructure with alternating distributions of coarse and fine lamellae. Although some coarse γ-lamellae are still retained in the final microstructure, the average size of the γ-lamellae is significantly reduced overall. More importantly, this method fundamentally suppresses the formation of discontinuous precipitation zones and non-equilibrium microstructures, thus ensuring the excellent high-temperature mechanical properties of the TiAl alloy while achieving microstructure refinement. This innovative concept provides a practical new approach to achieving a synergistic improvement in the strength and creep properties of TiAl alloys.

[0022] Specifically, a method for controlling the bimodal lamellar structure of TiAl alloys is proposed, including the following steps: S1. Prepare conventional lamellar structures; prepare TiAl alloy and heat it to T. α / (α+γ) or T (α+β) / (α+β+γ) Hold at 5℃~50℃ above the phase transition point for 5min~60min, then cool to room temperature to obtain a conventional lamellar tissue composed of coarse γ-lamellae. Specifically, in step S1, the prepared TiAl alloy sample is composed of the following atomic percentages of elements: Al 40 at.%~50 at.% and alloying elements 0~10 at.%; the alloying elements are one or more of Nb, Mo, V, Cr, Zr, Mn, Ni, Fe, Hf, Ta, W, Re, C, Si, B, Y, and O; wherein, the TiAl alloy sample includes small TiAl alloy samples, component blanks, or components prepared by casting plastic deformation, powder metallurgy, or additive manufacturing processes; plastic deformation includes forging, extrusion, or rolling; powder metallurgy includes spark plasma sintering or hot isostatic pressing; In step S1, during the preparation of the conventional lamellar structure, heat treatment is performed according to the phase diagram of the TiAl alloy. If the TiAl alloy has an α single-phase region, the TiAl alloy is heated to T. α / (α+γ) The TiAl alloy is held at 5°C to 50°C above the phase transformation point, i.e., in the α single-phase region. If the TiAl alloy does not have an α single-phase region, the TiAl alloy is heated to T. (α+β) / (α+β+γ)The tissue is kept at 5°C to 50°C above the phase transition point, i.e., in the (α+β) two-phase region; kept at this temperature for 5 min to 60 min, and then cooled to room temperature at a slow cooling rate of 5°C / min to 20°C / min to obtain conventional lamellar tissues that are near-lamellar or fully lamellar.

[0023] S2, rapid cooling retains a small amount of coarse lamellar layers; heating the TiAl alloy with conventional lamellar structure to T α / (α+γ) or T (α+β) / (α+β+γ) The temperature is set at 5℃~50℃ below the phase transition point, and the holding time is preferably 5min~120min, for example, 5min, 10min, 20min, 50min, 80min, 100min, or 120min, followed by rapid cooling to obtain a metastable lamellar structure containing a small amount of coarse γ lamellae; wherein, T α / (α+γ) T represents the phase transition temperature between the α single-phase region and the (α+γ) two-phase region. (α+β) / (α+β+γ) The phase transition temperatures are those of the (α+β) two-phase region and the (α+β+γ) three-phase region. Specifically, in step S2, heat treatment is performed according to the phase diagram of the TiAl alloy. If the TiAl alloy has an α single-phase region, the TiAl alloy is preferably heated to T. α / (α+γ) Temperatures 5°C to 50°C below the phase transition point, for example, T. α / (α+γ) 5°C below the phase transition point, T α / (α+γ) 10°C below the phase transition point, T α / (α+γ) 15°C below the phase transition point, T α / (α+γ) 25°C below the phase transition point, T α / (α+γ) 35°C below the phase transition point, T α / (α+γ) 45°C below the phase transition point, T α / (α+γ) The TiAl alloy is held at 50°C below the phase transformation point, i.e., in the (α+γ) two-phase region; if the TiAl alloy does not have an α single-phase region, the TiAl alloy is preferably heated to T. (α+β) / (α+β+γ) Temperatures 5°C to 50°C below the phase transition point, for example, T. (α+β) / (α+β+γ) 5°C below the phase transition point, T (α+β) / (α+β+γ) 10°C below the phase transition point, T (α+β) / (α+β+γ) 15°C below the phase transition point, T (α+β) / (α+β+γ) 25°C below the phase transition point, T (α+β) / (α+β+γ) 35°C below the phase transition point, T (α+β) / (α+β+γ) 45°C below the phase transition point, T (α+β) / (α+β+γ) The temperature is maintained at 50°C below the phase transition point, i.e., in the (α+β+γ) three-phase region; rapid cooling is achieved through air cooling.

[0024] S3. The TiAl alloy with metastable lamellar structure is subjected to low-temperature tempering treatment at a temperature preferably 700°C to 1000°C, such as 700°C, 800°C, 900°C, or 1000°C, and the holding time is preferably 5 min to 300 min, such as 5 min, 50 min, 100 min, 120 min, 150 min, 200 min, 250 min, or 300 min. The alloy is then cooled to room temperature in the furnace to allow fine lamellar layers to precipitate from between the coarse lamellar layers, resulting in a bimodal lamellar structure with alternating coarse and fine lamellar layers.

[0025] The present invention will be further described below with reference to the embodiments.

[0026] Example 1 In this embodiment, the TiAl alloy composition is Ti-43.5Al-4Nb-1Mo-0.1B (at.%). The bimodal lamellar structure was controlled using the following steps: Step S1: Prepare a conventional lamellar structure; The cylindrical small sample of Ti-43.5Al-4Nb-1Mo-0.1B alloy prepared by casting is heat-treated at 1280°C. This temperature is located in the (α+β) two-phase region of the alloy, i.e., T... (α+β) / (α+β+γ) The temperature was set at 25°C above the phase transition point. After holding at this temperature for 60 minutes, the tissue was cooled to room temperature at a controlled cooling rate of 20°C / min to obtain a conventional lamellar tissue composed of coarse γ-lamellae. This conventional lamellar tissue belongs to the near-lamellar tissue category.

[0027] Step S2: Rapid cooling retains a small amount of coarse lamellar layers; the obtained sample with conventional lamellar structure is held at 1250°C for 5 min, then air-cooled to room temperature to obtain a metastable lamellar structure containing a small amount of residual coarse γ-lamellae. Here, 1250°C is located in the (α+β+γ) three-phase region of the alloy, i.e., T... (α+β) / (α+β+γ) 5°C below the phase transition point.

[0028] Step S3: Low-temperature tempering to precipitate fine lamellar layers. The obtained metastable lamellar structure is tempered at 1000°C, held for 5 minutes, and then cooled to room temperature in the furnace to finally obtain a bimodal lamellar structure with alternating γ coarse lamellar layers and γ fine lamellar layers.

[0029] Statistical results show that the average thickness of γ-lamellae in conventional lamellar tissue is approximately 1.9 μm, such as... Figure 1 As shown. The bimodal lamellar structure processed by the method of this invention is as follows: Figure 2 As shown, the volume fraction of coarse γ-lamellae is approximately 20%, with an average thickness of approximately 920 nm; the volume fraction of fine γ-lamellae is approximately 80%, with an average thickness of approximately 23 nm. This structure significantly reduces the overall size of the γ-lamellae, and no discontinuous precipitation regions were observed at the lamellar cluster interfaces.

[0030] Mechanical tests on small cylindrical specimens showed that the room temperature yield strength of the bimodal lamellar structure was 115 MPa higher than that of the conventional lamellar structure. In high-temperature creep tests at 750°C and 200 MPa, the steady-state creep rate of the conventional lamellar structure was 1.9 × 10⁻⁶. -7 s -1 The steady-state creep rate of the bimodal lamellar structure decreased to 3.2 × 10⁻⁶. -8 s -1 The creep performance is significantly improved.

[0031] For the Ti-43.5Al-4Nb-1Mo-0.1B alloy, the traditional process (i.e., step S1) can only obtain a coarse lamellar structure. However, this invention, through two simple subsequent heat treatment steps S2 and S3, can successfully construct a bimodal lamellar structure, which is simple to operate and has a stable process window. Experimental verification shows that this method has high repeatability and can significantly and stably improve the strength and creep properties of the alloy.

[0032] Example 2 In this embodiment, the TiAl alloy composition used is Ti-48Al-2Cr-2Nb (at.%), and the bimodal lamellar structure is controlled. The specific steps are as follows: Step S1: Prepare conventional lamellar structure; The Ti-48Al-2Cr-2Nb blade blank prepared by powder hot isostatic pressing is heat-treated at 1370°C. This temperature is located in the α single-phase region of the alloy, i.e., T α / (α+γ) The temperature was set 5°C above the phase transition point. After holding at this temperature for 5 minutes, the temperature was controlled to cool to room temperature at a cooling rate of 5°C / min, resulting in a conventional lamellar structure composed of coarse γ-lamellae. This conventional lamellar structure is a fully lamellar structure.

[0033] Step S2: Rapid cooling retains a small amount of coarse lamellar layers; the obtained sample with conventional lamellar structure is held at 1330°C for 20 min, then air-cooled to room temperature to obtain a metastable lamellar structure containing a small amount of residual coarse γ-lamellae. Here, 1330°C is located in the (α+γ) two-phase region of the alloy, i.e., T... α / (α+γ) 35°C below the phase transition point.

[0034] Step S3: Low-temperature tempering to precipitate fine lamellar layers. The obtained metastable lamellar structure is tempered at 700°C and held for 300 min, then cooled to room temperature in the furnace to finally obtain a bimodal lamellar structure with alternating γ coarse lamellar layers and γ fine lamellar layers.

[0035] Statistical results show that the average thickness of γ-lamellae in conventional lamellar tissue is approximately 3.3 μm, such as... Figure 3 As shown. The bimodal lamellar structure processed by the method of this invention is as follows: Figure 4As shown, the volume fraction of coarse γ-lamellae is approximately 32%, with an average thickness of approximately 1.2 nm; the volume fraction of fine γ-lamellae is approximately 68%, with an average thickness of approximately 146 nm. This structure significantly reduces the overall size of the γ-lamellae, and no non-equilibrium precipitation was observed at the lamellar cluster interface.

[0036] Mechanical tests on the blade blanks showed that the room temperature yield strength of the bimodal lamellar structure was increased by 80 MPa compared to the conventional lamellar structure. In high-temperature creep tests at 700°C and 150 MPa, the steady-state creep rate of the conventional lamellar structure was 4.2 × 10⁻⁶. -8 s -1 The steady-state creep rate of the bimodal lamellar structure decreased to 1.5 × 10⁻⁶. -9 s -1 The creep performance is significantly improved.

[0037] For Ti-48Al-2Cr-2Nb alloys, traditional processes (i.e., step S1) can only produce coarse lamellar structures. However, this invention, through two simple subsequent heat treatments (steps S2 and S3), can successfully construct a bimodal lamellar structure, offering ease of operation and a stable process window. Experimental verification shows that this method has high repeatability and can significantly and stably improve the strength and creep properties of the alloy.

[0038] Example 3 In this embodiment, the TiAl alloy composition is Ti-47Al-6Nb-1Zr-1.1B (at.%), and the bimodal lamellar structure is controlled. The specific steps are as follows: Step S1: Prepare a conventional lamellar structure; the Ti-47Al-6Nb-1Zr-1.1B alloy valve prepared by additive manufacturing is heat-treated at 1380°C. This temperature is located in the α single-phase region of the alloy, i.e., T α / (α+γ) The temperature was set at 50°C above the phase transition point. After holding at this temperature for 30 minutes, the tissue was cooled to room temperature at a controlled cooling rate of 10°C / min to obtain a conventional lamellar structure composed of coarse γ-lamellae. This conventional lamellar structure belongs to the whole lamellar structure category.

[0039] Step S2: Rapid cooling retains a small amount of coarse lamellar layers; the obtained sample with conventional lamellar structure is held at 1280°C for 120 min, and then air-cooled to room temperature to obtain a metastable lamellar structure containing a small amount of residual coarse γ lamellar layers. Here, 1280°C is located in the (α+γ) two-phase region of the alloy, i.e., T... α / (α+γ) 50°C below the phase transition point.

[0040] Step S3: Low-temperature tempering to precipitate fine lamellar layers. The obtained metastable lamellar structure is tempered at 800°C and held for 200 min, then cooled to room temperature in the furnace to finally obtain a bimodal lamellar structure with alternating γ coarse lamellar layers and γ fine lamellar layers.

[0041] Statistical results show that the average thickness of γ-lamellae in conventional lamellar structures is approximately 2.6 μm. However, in the bimodal lamellar structures treated by the method of this invention, the volume fraction of coarse γ-lamellae is approximately 51%, with an average thickness of approximately 1.4 nm; the volume fraction of fine γ-lamellae is approximately 49%, with an average thickness of approximately 68 nm. This structure significantly reduces the overall size of the γ-lamellae, and no non-equilibrium tissue precipitation was observed at the lamellar cluster interface.

[0042] Mechanical testing of the valves showed that the room temperature yield strength of the bimodal lamellar structure was increased by 51 MPa compared to that of the conventional lamellar structure. In high-temperature creep testing at 800°C and 200 MPa, the steady-state creep rate of the conventional lamellar structure was 4.2 × 10⁻⁶. -7 s -1 The steady-state creep rate of the bimodal lamellar structure decreased to 7.6 × 10⁻⁶. -8 s -1 The creep performance is significantly improved.

[0043] For the Ti-47Al-6Nb-1Zr-1.1B alloy, the traditional process (i.e., step S1) can only obtain a coarse lamellar structure. However, this invention, through two simple subsequent heat treatment steps S2 and S3, can successfully construct a bimodal lamellar structure, which is simple to operate and has a stable process window. Experimental verification shows that this method has high repeatability and can significantly and stably improve the strength and creep properties of the alloy.

[0044] Example 4 This embodiment uses a TiAl alloy with the same composition as in Example 1 to control the bimodal lamellar structure. The specific steps are as follows: Step S1: Prepare a conventional lamellar structure; The cylindrical sample of Ti-43.5Al-4Nb-1Mo-0.1B alloy prepared by forging is heat-treated at 1270°C. This temperature is located in the (α+β) two-phase region of the alloy, i.e., T... (α+β) / (α+β+γ) The temperature was set 15°C above the phase transition point. After holding at this temperature for 20 minutes, the tissue was cooled to room temperature at a controlled cooling rate of 10°C / min to obtain a conventional lamellar tissue composed of coarse γ-lamellae. This conventional lamellar tissue belongs to the near-lamellar tissue category.

[0045] Step S2: Rapid cooling retains a small amount of coarse lamellar layers; the obtained sample with conventional lamellar structure is held at 1230°C for 20 min, then air-cooled to room temperature to obtain a metastable lamellar structure containing a small amount of residual coarse γ-lamellae. Here, 1230°C is located in the (α+β+γ) three-phase region of the alloy, i.e., T... (α+β) / (α+β+γ) 25°C below the phase transition point.

[0046] Step S3: Low-temperature tempering to precipitate fine lamellar layers. The obtained metastable lamellar structure is tempered at 850°C and held for 120 min, then cooled to room temperature in the furnace to finally obtain a bimodal lamellar structure with alternating γ coarse lamellar layers and γ fine lamellar layers.

[0047] Statistical results show that the average thickness of γ-lamellae in conventional lamellar structures is approximately 1.6 μm. However, in the bimodal lamellar structure treated by the method of this invention, the volume fraction of coarse γ-lamellae is approximately 35%, with an average thickness of approximately 810 nm; the volume fraction of fine γ-lamellae is approximately 65%, with an average thickness of approximately 21 nm. This structure significantly reduces the overall size of the γ-lamellae, and no discontinuous precipitation regions were observed at the lamellar cluster interfaces.

[0048] Mechanical tests on small cylindrical specimens showed that the room temperature yield strength of the bimodal lamellar structure was 176 MPa higher than that of the conventional lamellar structure. In high-temperature creep tests at 750°C and 200 MPa, the steady-state creep rate of the conventional lamellar structure was 3.1 × 10⁻⁶. -8 s -1 The steady-state creep rate of the bimodal lamellar structure decreased to 8.6 × 10⁻⁶. -9 s -1 The creep performance is significantly improved.

[0049] For the Ti-43.5Al-4Nb-1Mo-0.1B alloy, the traditional process (i.e., step S1) can only obtain a coarse lamellar structure. However, this invention, through two simple subsequent heat treatment steps S2 and S3, can successfully construct a bimodal lamellar structure, which is simple to operate and has a stable process window. Experimental verification shows that this method has high repeatability and can significantly and stably improve the strength and creep properties of the alloy.

[0050] Comparative Example 1 This comparative example uses a TiAl alloy with the same composition as in Example 1.

[0051] This comparative example did not perform the rapid cooling in step S2 to retain a small amount of coarse flakes; the remaining steps were the same as in Example 1.

[0052] In this comparative example, after undergoing only low-temperature tempering following a conventional lamellar structure, the resulting microstructure remained a conventional lamellar structure composed of coarse γ-lamellae, failing to form a bimodal lamellar structure. Mechanical property testing results demonstrate that the properties of the low-temperature tempered sample in this comparative example are similar to those of the conventional lamellar structure, proving that a single tempering process did not lead to performance improvement.

[0053] Comparative Example 2 This comparative example uses a TiAl alloy with the same composition as in Example 1.

[0054] The cooling method in step S2 is furnace cooling, which slowly cools the material to room temperature. The remaining steps are the same as in Example 1.

[0055] The tissues obtained in the comparative example all consisted of coarse γ-lamellae, which could not form bimodal lamellar tissue.

[0056] Comparative Example 3 The obtained sample with conventional lamellar structure was held at 1260°C for 5 min, and then air-cooled to room temperature. 1260°C is located in the (α+β) two-phase region of this alloy, i.e., T... (α+β) / (α+β+γ) The temperature is 5°C above the phase transition point. The remaining steps are the same as in Example 1.

[0057] The tissues obtained in the comparative example consisted entirely of fine γ-lamellae, which could not form bimodal lamellar tissue.

[0058] Comparative Example 4 This comparative example uses a TiAl alloy with the same composition as in Example 2.

[0059] This comparative example did not perform the rapid cooling in step S2 to retain a small amount of coarse flakes; the remaining steps were the same as in Example 2.

[0060] In this comparative example, after undergoing only low-temperature tempering following a conventional lamellar structure, the resulting microstructure remained a conventional lamellar structure composed of coarse γ-lamellae, failing to form a bimodal lamellar structure. Mechanical property testing results demonstrate that the properties of the low-temperature tempered sample in this comparative example are similar to those of the conventional lamellar structure, proving that a single tempering process did not lead to performance improvement.

[0061] Comparative Example 5 This comparative example uses a TiAl alloy with the same composition as in Example 3.

[0062] This comparative example did not perform the rapid cooling in step S2 to retain a small amount of coarse flakes; the remaining steps were the same as in Example 3.

[0063] In this comparative example, after undergoing only low-temperature tempering following a conventional lamellar structure, the resulting microstructure remained a conventional lamellar structure composed of coarse γ-lamellae, failing to form a bimodal lamellar structure. Mechanical property testing results demonstrate that the properties of the low-temperature tempered sample in this comparative example are similar to those of the conventional lamellar structure, proving that a single tempering process did not lead to performance improvement.

[0064] Comparative Example 6 This comparative example uses a TiAl alloy with the same composition as in Example 4.

[0065] This comparative example did not perform the rapid cooling in step S2 to retain a small amount of coarse flakes; the remaining steps were the same as in Example 4.

[0066] In this comparative example, after undergoing only low-temperature tempering following a conventional lamellar structure, the resulting microstructure remained a conventional lamellar structure composed of coarse γ-lamellae, failing to form a bimodal lamellar structure. Mechanical property testing results demonstrate that the properties of the low-temperature tempered sample in this comparative example are similar to those of the conventional lamellar structure, proving that a single tempering process did not lead to performance improvement.

[0067] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0068] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0069] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for controlling the bimodal lamellar structure of a TiAl alloy, characterized in that, Includes the following steps: S1. Prepare TiAl alloy and heat it to T α / (α+γ) or T (α+β) / (α+β+γ) Hold at 5℃~50℃ above the phase transition point for 5min~60min, then slowly cool to room temperature to obtain a conventional lamellar tissue composed of coarse γ-lamellae. S2. Heat the TiAl alloy with a conventional lamellar structure to T. α / (α+γ) or T (α+β) / (α+β+γ) The temperature was set at 5°C to 50°C below the phase transition point, held for 5 to 120 minutes, and then rapidly cooled to obtain a metastable lamellar structure containing a small amount of coarse γ lamellae; the T α / (α+γ) The phase transition temperature between the α single-phase region and the (α+γ) two-phase region; T (α+β) / (α+β+γ) The phase transition temperatures are those of the (α+β) two-phase region and the (α+β+γ) three-phase region. S3. The TiAl alloy with metastable lamellar structure is subjected to low-temperature tempering treatment, held at 700°C~1000°C for 5min~300min, and then cooled to room temperature in the furnace to obtain a TiAl alloy with bimodal lamellar structure.

2. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S1, the TiAl alloy is composed of elements with the following atomic percentages: Al 40 at.%~50 at.% and alloying elements 0~10 at.%; the alloying elements are one or more of Nb, Mo, V, Cr, Zr, Mn, Ni, Fe, Hf, Ta, W, Re, C, Si, B, Y and O.

3. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S1, the prepared TiAl alloy includes small TiAl alloy samples, component blanks, or components prepared by plastic deformation, powder metallurgy, or additive manufacturing processes.

4. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S1, if the TiAl alloy has an α single-phase region, the TiAl alloy is heated to T. α / (α+γ) If the TiAl alloy does not have an α single-phase region, and is heated to T at a temperature 5°C to 50°C above the phase transformation point. (α+β) / (α+β+γ) 5℃~50℃ above the phase transition point.

5. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S1, the slow cooling rate is 5°C / min to 20°C / min.

6. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S1, the conventional lamellar tissue is either a full lamellar tissue or a near-lamellar tissue.

7. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S2, if the TiAl alloy has an α single-phase region, the TiAl alloy is heated to T. α / (α+γ) If the TiAl alloy does not have an α single-phase region, and is heated to T at 5℃~50℃ below the phase transformation point. (α+β) / (α+β+γ) 5℃~50℃ below the phase transition point.

8. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S2, the rapid cooling method is air cooling.

9. The method for controlling the bimodal lamellar structure of a TiAl alloy according to claim 1, characterized in that, In step S3, the coarse lamellar layers and fine lamellar layers are distributed alternately in the bimodal lamellar structure.

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