A method for integrally forming an extrusion and forging of a high-performance TiAl alloy blade

Abstract

The application belongs to the technical field of near-net forming manufacturing of lightweight high-temperature TiAl intermetallic compound components, and particularly discloses an integrated extrusion and forging forming method for high-performance TiAl alloy blades. Alpha TiAl alloy profiles with <11-20> wire texture are selected as the base material, and after being sleeved, the base material is kept in the alpha single-phase zone for 10-60 minutes, and then one-way extrusion and die forging combined forming is carried out with an extrusion ratio of 4:1-9:1, so as to directly obtain a blade blank. The method realizes short-process near-net forming of the blade, and forms fine-grained sheet layer organization with <11-20> wire texture after deformation in the alpha single-phase zone. The application solves the short-process manufacturing and wide-temperature-range strength-plasticity inversion problems of the high-performance TiAl alloy blade, and the room-temperature elongation is not less than 2.5%, the room-temperature tensile strength is higher than 850 MPa, and the 800 DEG C tensile strength is as high as 700 MPa.

Description

Technical Field

[0001] This invention belongs to the field of near-net-shape forming manufacturing technology of lightweight, high-temperature resistant TiAl intermetallic compound components, specifically relating to an integrated extrusion and forging forming method for high-performance TiAl alloy blades. Background Technology

[0002] γ-TiAl-based intermetallic compounds (TiAl alloys), with their low density, excellent high-temperature specific strength, creep resistance, and oxidation resistance, have become ideal lightweight materials to replace nickel-based superalloys in the 600–900℃ temperature range, showing broad application prospects in hot-end components such as low-pressure turbine blades for aero-engines. However, the inherent room-temperature brittleness, asynchronous shape-property control, and common challenges of strength-plasticity mismatch over a wide temperature range of TiAl alloys severely hinder their engineering applications and the fabrication of complex components.

[0003] Currently, the manufacturing of TiAl alloy components mainly relies on precision casting technology. However, cast TiAl alloys generally suffer from defects such as low room temperature plasticity (<1.0%), coarse microstructure accompanied by porosity, resulting in uneven component performance, low yield, and insufficient high-temperature strength to meet the requirements of complex working conditions. Although methods such as adding alloying elements such as Nb and Mo, grain refinement, and microstructure isomerization can improve mechanical properties to some extent, these methods often come at the expense of other aspects, making it difficult to fundamentally achieve a synergistic improvement in both strength and plasticity.

[0004] In recent years, the control of lamellar orientation has been considered key to overcoming the performance bottleneck of TiAl alloys. A research team has prepared polylamellar twin (PST) TiAl single crystals with 0° orientation using photo-suspended directional solidification technology, achieving a significant improvement in room temperature plasticity, wide-temperature strength, creep resistance, and thermal stability. However, the PST-TiAl single crystals prepared by directional solidification have limited size, are difficult to prepare, and exhibit strong anisotropy in mechanical properties, failing to meet the manufacturing requirements of low-pressure turbine blades.

[0005] Thermoplastic deformation (such as extrusion and forging) is an important means to improve the microstructure and properties of TiAl alloys. Numerous research institutions both domestically and internationally have conducted extensive fundamental research in this area, confirming that uniaxial extrusion of TiAl alloys can achieve preferred lamellar orientation, resulting in mechanical properties superior to those of conventionally forged and cast alloys. Some processes employ traditional temperature-decreasing multi-step hot-clamping extrusion or a composite processing technique of hot extrusion + forging, with deformation temperatures all below T0. α The phase transition point results in a biphasic microstructure with strong random orientation, low high-temperature strength, and difficulty in exceeding 2.0% room-temperature plasticity. Other processes near the T... αHot extrusion at a specific temperature successfully produced Ti-4822 alloy profiles with 0° lamellar preferred orientation; however, severe coarsening of the lamellar clusters hindered the development of their mechanical properties. Furthermore, some studies have attempted to improve the room-temperature plasticity of TNM and high-niobium TiAl alloys by introducing microtexture, but their elongation remained below 1.0% and 2.0%, respectively, and they exhibited brittleness β. o and ω o The precipitated phase has poor thermal stability.

[0006] Furthermore, existing technological approaches separate "material preparation" (obtaining high-performance billets) from "component forming." This involves first preparing profiles or master alloys with specific microstructures through complex hot working processes, and then forming blades through machining or secondary die forging. This traditional hot working process is lengthy, has low material utilization, and is costly. Moreover, secondary heating and deformation may disrupt the carefully controlled ideal microstructure, leading to a decline in mechanical properties.

[0007] Therefore, there is an urgent need to develop a short-process manufacturing technology that can simultaneously optimize the microstructure and properties of TiAl alloys and achieve near-net-shape forming of complex components. This technology should directly inherit and enhance the microstructure features (lamellar preferred orientation, fine lamellae clusters, and <11-20> filament texture) that play a key role in performance during the forming process, thereby producing high-performance TiAl alloy blade components with high efficiency and low cost. Summary of the Invention

[0008] To address the problems of long manufacturing processes, complex procedures, asynchronous shape-property control, and low room temperature plasticity in existing technologies, this invention proposes an integrated extrusion and forging method for high-performance TiAl alloy blades. This method organically combines the "microstructure-property control" of high-performance TiAl alloys with the "plastic forming" of the blade in the same hot working process. By performing unidirectional constrained extrusion and die forging in the α single-phase region, a blade blank is directly manufactured, simultaneously forming a fine-grained, near-lamellar microstructure with <11-20> filamentary texture. This microstructure endows the blade with excellent room temperature plasticity, high strength over a wide temperature range, higher thermal stability, and creep resistance.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for integrated extrusion and forging forming of high-performance TiAl alloy blades includes the following steps:

[0011] S1. Select α-type TiAl alloy profiles with <11-20> wire texture as the base material and determine the temperature range of its α single-phase region. Specifically, use TiAl alloy extruded or hot-rolled bars and other profiles with a wide α single-phase region as the initial base material, and accurately determine its α phase transformation point Tα and the temperature range of the α single-phase region through thermal analysis and phase diagram calculation. The temperature range of the α single-phase region is greater than 40℃.

[0012] S2. Preform processing and sheathing: Based on the final blade shape, prepare cylindrical or rectangular preforms and sheath them with pure molybdenum to form sheath blanks. The sheath thickness is controlled in the range of 0.2-2mm. At the same time, an anti-oxidation coating is sprayed on the surface.

[0013] S3, α single-phase region preheating: The cladding billet is heated to the α single-phase region of the alloy at a rate of not less than 8℃ / min under an argon protective atmosphere, and the holding time is 10 to 60 minutes;

[0014] S4. Integrated extrusion and forging of blade blanks: The preheated cladding blank is transferred from the heating furnace to the cavity of an extrusion and forging die at a preheated temperature of 1250℃ within 5 seconds. The die cavity is the outline of the blade blank to be formed. Under the α single-phase temperature, the blank is subjected to a continuous, large-deformation extrusion and hot forging composite plastic forming under the unidirectional pressure of a hydraulic press. The extrusion ratio in the α single-phase region is controlled between 4:1 and 9:1, and the blade tenon is at the end.

[0015] S5. After forming, the surface molybdenum cladding layer of the blade blank is removed, and it is then vacuum annealed at (Tα-20℃), held at that temperature for 2 hours, and furnace cooled to room temperature to stabilize the microstructure and generate a lamellar structure. Finally, the heat-treated blank is precision machined on a five-axis CNC machine tool to obtain a blade with accurate dimensions.

[0016] This TiAl blade blank, which utilizes unidirectional constrained deformation in the high-temperature α single-phase region, exhibits plastic deformation dominated by {10-10}<11-20> cylindrical slip, ensuring the final formation of a lamellar structure with <11-20> filamentary texture. The thin cladding made of pure molybdenum demonstrates significant advantages over traditional stainless steel or titanium alloy cladding in terms of insulation performance and dimensional accuracy of the blade blank.

[0017] Further, in step S4, the extrusion direction is parallel to the main load-bearing axis of the blade (approximately parallel to the blade direction), resulting in a blade blank with a lamellar cluster content greater than 80%, and at least 60% of the α2 / γ lamellar clusters having an angle between the lamellar interface and the extrusion direction within the range of 0°±15°, an average lamellar cluster size less than 50 μm, and a microstructure containing no or only a very small amount of brittle βo phase. The obtained high-niobium TiAl alloy with a near-fully lamellar microstructure exhibiting <11-20> filament texture characteristics has a room temperature elongation of 2.5%–4.5%, a yield strength of not less than 700 MPa, a tensile strength of 850–980 MPa, and a tensile strength at 800℃ higher than 700 MPa.

[0018] The basic design concept of this invention is to break through the traditional serial process path of "preparing high-performance blanks first, and then shaping them through plastic processing or machining" in the manufacturing of TiAl alloy components, and innovatively propose a parallel manufacturing method of "shape and property synergy, one-time forming". This method completes the microstructure construction that determines the core properties of the material and the near-net-shape forming process of complex components in a continuous and controllable thermo-mechanical coupling field. Specifically, for high-niobium TiAl alloys with a wide α single-phase region, directional extrusion and die forging are integrated in its α single-phase region to simultaneously achieve two key objectives: first, to prefabricate a filamentary structure with the {0001} base plane parallel to the extrusion direction; and second, to directly obtain the complex shape of the blade blank in the same thermodynamic process. Subsequently, through controllable cooling and heat treatment in the α+γ two-phase region, a near-fully lamellar structure with preferred lamellar orientation is obtained. This design enables the component to have the optimal microstructure in the initial stage of forming, providing a new approach to solving the long-standing problem in the manufacturing of TiAl alloy components where shape and property control are mutually constrained, and performance potential and geometric complexity are difficult to achieve simultaneously.

[0019] The beneficial effects of this invention are: by integrating extrusion and forging into a single thermodynamic process, the precision forming and high-performance microstructure control of TiAl alloy turbine blades are simultaneously achieved. This technology boasts high production efficiency, controllable processes, and applicability to the manufacturing of large-size components, with significantly better yield and material utilization than traditional methods. Employing simultaneous forming and precision CNC machining via "directional extrusion and die forging" allows the blades to fully retain the <11-20> filamentary texture characteristics of the base material while incorporating fine crystalline layer microstructure characteristics. The blades exhibit both high room-temperature plasticity and excellent high-temperature performance, with significantly weaker anisotropy in mechanical properties compared to PST-TiAl single crystals. This new technology effectively solves the current challenges of TiAl turbine blades, such as "casting instead of forging," poor room-temperature plasticity, and low high-temperature strength, establishing a high-end TiAl blade and impeller manufacturing technology with independent intellectual property rights, serving the aerospace equipment manufacturing industry.

[0020] This invention presents a groundbreaking new technology for the synergistic manufacturing of typical TiAl alloy components with high strength and high plasticity over a wide temperature range, offering significant social, economic, and ecological benefits. The engineering application of high-performance, low-cost TiAl alloy turbine blades will replace current TiAl precision castings and high-temperature alloys used at temperatures below 850°C. This will expand the application from the low-pressure turbine end of aero-engines to 4-7 stage turbine blades, and drive their application in high-pressure compressor blades and integral bladed disks. A single aero-engine is expected to reduce weight by more than 150 kg. These applications will contribute to improved equipment reliability, lightweighting, thrust-to-weight ratio, and maneuverability, while effectively improving fuel efficiency, reducing exhaust emissions, and decreasing noise. Attached Figure Description

[0021] Figure 1Top view of the integrated extrusion and forging die structure used to implement this invention;

[0022] Figure 2 A front view of the integrated extrusion and forging die structure used to implement this invention;

[0023] Figure 3 Cross-sectional view of the integrated extrusion and forging die structure used to implement this invention;

[0024] Figure 4 Images of blade blanks formed by extrusion and forging and finished blades after CNC machining.

[0025] Figure 5 This is a scanning electron microscope image of the silk texture characteristics taken in Example 1;

[0026] Figure 6 The table shows the room temperature tensile properties of three parallel specimens from Example 1. Detailed Implementation

[0027] This invention provides an integrated extrusion and forging method for high-performance TiAl alloy blades. The core steps include: using an α-type TiAl alloy profile with filamentous texture as the base material, determining the temperature range of its α single-phase region; performing a cladding treatment on the filamentous texture profile; rapidly heating the clad profile to the α single-phase region and holding it at that temperature; and integrating extrusion and forging to form the blade blank.

[0028] The innovation of this invention lies in its deep integration of microstructure control, which determines the final properties of materials, with the near-net-shape forming process of complex blades, into a continuous and controlled thermo-mechanical coupling process. By performing integrated extrusion and forging within the α single-phase region of a high-niobium TiAl alloy, two key objectives are simultaneously achieved: first, to induce preferred orientation of high-temperature α grains, pre-fabricating a strong basal filament texture; and second, to transfer the preheated cladding blank from the α single-phase region to a composite extrusion and forging die, completing the integrated extrusion and forging forming of the blade blank and directly obtaining its complex geometry. The blade blank obtained by this invention has a lamellar cluster content exceeding 80%, and the α2 / γ lamellar interface is preferentially parallel to the extrusion direction.

[0029] Compared to the traditional process of "preparing high-performance billets first, then machining or forging," this invention achieves a "shape-property control" collaborative manufacturing technology, completing the transition from material to component in one step. This significantly shortens the manufacturing process, improves material utilization, and reduces costs. Compared to conventional multi-directional forging in the α+γ two-phase region, the integrated deformation in the α single-phase region of this invention more effectively excites and retains the texture of the α phase, providing a fundamental guarantee for obtaining a high-strength lamellar preferred orientation microstructure. Compared to directionally solidified single crystals, the polycrystalline blades prepared by this invention inherit excellent performance while significantly weakening mechanical anisotropy, making them more adaptable to complex service environments. Furthermore, the process is simpler, lower in cost, and more suitable for manufacturing large-size components.

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0031] Example 1:

[0032] This embodiment provides an integrated extrusion and forging method for high-performance TiAl alloy blades. The alloy used is a high-niobium TiAl alloy with a composition of Ti-45Al-6Nb-0.1B (atomic ratio). This alloy exhibits a <11-20> filament texture. Thermodynamic calculations show that the α-phase transformation point Tα of this alloy is approximately 1300℃, and the temperature range of the α single-phase region is approximately 100℃. A homogeneous alloy ingot is prepared through three melting processes in a vacuum arc remelting furnace.

[0033] First, the preform is processed and encapsulated. The ingot is machined into a cylindrical preform similar in shape to the target blade, and then encapsulated using a 2mm thick molybdenum sheet. The inside of the encapsulation is wrapped with fiberglass insulation felt, and the surface of the encapsulation is sprayed with an anti-oxidation coating.

[0034] The packaged billet was placed in a high-temperature argon-atmosphere mortar furnace and heated to 1320°C at a rate of 9°C / min, and held for 60 minutes to completely transform the billet microstructure into a uniform high-temperature α phase. The thoroughly heated billet was then transferred within 5 seconds to a TZM molybdenum alloy mold preheated to 1250°C. The mold cavity was a near-net-shape of a turbine blade, including the profile of the blade body and tenon. Figure 1-3 This is a schematic diagram of the integrated forming mold structure for blade extrusion and forging used in this invention. This process can achieve integrated forming from cylindrical blank to blade blank in a single thermal cycle, wherein the extrusion ratio is 4:1. Figure 4 This shows the blade blank formed by integrated extrusion and forging, as well as the finished blade after CNC machining.

[0035] After forming, the surface molybdenum cladding layer of the blade blank is removed, and it is then vacuum annealed at 1280℃ (Tα-20℃), held at that temperature for 2 hours, and furnace cooled to room temperature to stabilize the microstructure and generate a lamellar structure. Finally, the heat-treated blank is precision machined on a five-axis CNC machine tool to obtain a blade with accurate dimensions.

[0036] The leaf blade portion prepared in this embodiment was observed using a scanning electron microscope, and the microstructure results are shown in the figure. Figure 5 The obtained microstructure was found to be a typical lamellar-preferred-orientation fine-grained near-fully lamellar structure, with the lamellar interfaces basically parallel to the blade axis. Approximately 70% of the lamellar clusters had lamellar interfaces with an angle between the lamellar interface and the axis within the range of 0°±15°, and the average cluster size was less than 35μm. No brittle βo phase precipitation was found in the microstructure.

[0037] Three parallel specimens (1), (2), and (3) were taken from the blade blank and subjected to tensile property testing. The test results are shown in Figure 6 As can be seen, the average yield strength at room temperature reaches 760 MPa, the average tensile strength reaches 970 MPa, and the average elongation reaches 3.3%; the tensile strength at 800℃ reaches 780 MPa. These results verify that the method of this invention can prepare TiAl alloy blades with both good room temperature plasticity and excellent high-temperature strength, demonstrating its feasibility.

[0038] Example 2:

[0039] This embodiment provides a method for manufacturing a lamellar preferred-oriented, ultra-high plasticity, high-niobium TiAl alloy, Ti-45Al-6Nb-1Cr-0.1B (atomic ratio). According to the phase diagram, the Tα phase transformation point of this alloy is calculated to be 1285℃, the temperature span of the single α phase region is 90℃, and there exists an α+γ dual-phase region below Tα with a temperature span of approximately 180℃. The addition of Cr element extends this phase region to some extent, but the alloy composition design avoids the precipitation of βo and ωo phases.

[0040] The difference between this embodiment and specific embodiment 1 is that trace element Cr is added to the high-niobium TiAl alloy. Cr, as a β-stabilizing element, is controlled at a content of 1% in this alloy system.

[0041] The difference between this embodiment and specific embodiment 1 is that the packaged billet is placed in a high-temperature argon atmosphere gravitational furnace and held for 10 minutes to avoid excessive grain coarsening.

[0042] The difference between this embodiment and specific embodiment 1 is that, in the process of integrated extrusion and forging, the extrusion ratio is 9:1 to ensure the forming effect.

[0043] The difference between this embodiment and specific embodiment 1 lies in the post-annealing treatment, which is completed by furnace cooling after holding at Tα-25℃ (approximately 1260℃) for 2 hours. The purpose is to appropriately introduce a certain proportion of equiaxed γ grains while maintaining the preferred orientation of the lamellar layers, forming a microstructure with fine-grained bimorphic microstructure characteristics, in order to further optimize room temperature plasticity.

[0044] The advantages of this embodiment are as follows: the generated lamellar preferred-oriented high-niobium TiAl alloy exhibits a fine-grained bimorphic microstructure, with grain sizes generally less than 30 μm and lamellar grain content of approximately 85%. Fine equiaxed γ grains are uniformly distributed throughout the microstructure. The addition of Cr element improves the strength level of the matrix to a certain extent. Simultaneously, due to the reduction in stacking fault energy, twinning activity is enhanced during deformation, which is beneficial for coordinating plastic deformation. Mechanical property tests revealed that the alloy achieves a room temperature elongation of 3.0%, a tensile strength of 1050 MPa, and a tensile strength of 850 MPa at 800℃, demonstrating a good balance between strength and plasticity.

[0045] Comparative Example 1:

[0046] This comparative example provides a method for manufacturing a lamellar preferred-oriented high-niobium TiAl alloy, Ti-43Al-6Nb-1Cr (atomic ratio). The difference between this comparative example and specific example 1 lies in process step S1, where a TiAl alloy with an α + β two-phase region but not an α single-phase region is selected for integrated extrusion and die forging.

[0047] After the process in this comparative example, a fine-grained near-fully lamellar microstructure containing a large amount of βo was generated. Although the preferred lamellar orientation was maintained, the microstructure contained a large amount of hard and brittle βo phase. Tensile property tests revealed that this fine-grained near-fully lamellar high-niobium TiAl alloy with a preferred lamellar orientation had a room temperature elongation of only 1.7%, a tensile strength of 900 MPa, and a tensile strength of 690 MPa at 800℃.

[0048] Comparative Example 2:

[0049] This embodiment provides a method for manufacturing a high-niobium TiAl alloy Ti-45Al-6Nb-0.1B (atomic ratio) with random lamellar orientation. The difference between this comparative example and specific embodiment 1 is that the obtained cladding billet is subjected to conventional hot forging. The subsequent modification involves cooling the extruded billet to room temperature, then reheating it to the forging temperature (usually also in the α-phase region), placing it in a die forging process, and finally obtaining the blade blank.

[0050] After the process was completed, this comparative example exhibited a conventional coarse-grained, nearly fully lamellar microstructure. The preferred orientation of the 0° lamellae disappeared, the proportion of lamellar interfaces parallel to the principal stress direction was less than 20%, and the lamellar clusters showed significant coarsening. Tensile property tests revealed that this conventional coarse-grained, nearly fully lamellar high-niobium TiAl alloy had a room temperature elongation of only 1.5%, a tensile strength of 800 MPa, and a tensile strength of 600 MPa at 800°C.

[0051] In summary, the high-performance TiAl alloy blade extrusion and forging integrated forming method provided by this invention, through process design, completes the forming of the blade and the construction of the preferred orientation fine crystalline layer cluster structure in the α single-phase region in one step. It provides an effective way to solve the problems of "difficulty in balancing shape and properties" and "long process and high cost" in the manufacturing of high-performance TiAl alloy components, and provides an efficient near-net-shape forming technology path for the large-scale and reliable application of TiAl alloy in advanced aero engines.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for integrated extrusion and forging forming of high-performance TiAl alloy blades, characterized in that, Includes the following steps: S1. Select α-type TiAl alloy profiles with <11-20> filament texture characteristics as the base material, and determine the temperature range of its α single-phase region; S2. The base material is encapsulated to form an encapsulated blank. S3. Heat the cladding blank to the α single-phase region under a protective atmosphere and hold for 10 to 60 minutes; S4. The heat-insulated cladding blank is transferred to an integrated extrusion and forging die. At the α single-phase temperature, unidirectional extrusion and die forging are performed at an extrusion ratio of 4:1 to 9:1 to directly obtain the blade blank. S5. After forming, the surface cladding layer of the blade blank is removed, and it is vacuum annealed at (Tα-20℃). After holding at this temperature for 2 hours, it is furnace cooled to room temperature to stabilize the microstructure and generate a lamellar structure. Finally, the heat-treated blank is precision machined on a five-axis CNC machine tool to obtain a blade with accurate dimensions.

2. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, The α-phase of the parent material has a temperature range greater than 40℃ and is an α-phase with <11-20> filament texture characteristics.

3. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, The encapsulation process described in step S2 involves wrapping the base material with a 0.2-2 mm thick molybdenum sheet and sealing it, followed by spraying an anti-oxidation coating.

4. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, The protective atmosphere described in step S3 is argon, and the heating method is to heat to the α single-phase region at a rate of not less than 8°C / min.

5. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, The transfer described in step S4 involves transferring the heat-insulated cladding billet from the heating furnace to the mold within 5 seconds. During the transfer process, a heat-insulating container is used to maintain the billet temperature within the α single-phase region.

6. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, The preheating temperature of the extrusion and forging die in step S4 is controlled at 1250°C.

7. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, In the unidirectional extrusion and die forging composite forming process described in step S4, the extrusion direction is parallel to the main load-bearing axis of the blade, so that the content of lamellar clusters in the formed blade blank is higher than 80%, and the α2 / γ lamellar interface is preferentially parallel to the extrusion direction, forming a <11-20> filament texture.

8. The integrated extrusion and forging forming method for high-performance TiAl alloy blades according to claim 1, characterized in that, After processing in steps S1 to S4, the average size of the lamellar clusters in the obtained blade blank is less than 50 μm, the room temperature elongation is not less than 2.5%, the room temperature tensile strength is higher than 850 MPa, and the 800℃ tensile strength is not less than 700 MPa.

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