Method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening

Abstract

This invention discloses a method for preparing ultra-high strength titanium alloys through high-temperature annealing strengthening, belonging to the field of titanium alloy material microstructure control and high-performance preparation technology. The chemical composition of the titanium alloy, by weight percentage, is: Al, Cu, Nb, Mo, V, Zr, with the balance being Ti and unavoidable impurities. The method first involves annealing the alloy ingot at a β-phase transformation temperature T... β Single-phase forging is performed at 50-150℃, followed by T... β The following processes involve multi-pass hot working deformation in the α+β two-phase region at 50-150℃, and finally at T... β The titanium alloy is subjected to high-temperature annealing at 50-150℃, held at that temperature for 0.5-4 hours, and then air-cooled or controlled-cooled to room temperature. This invention does not require solution quenching and aging treatment, and the process is simple. It is particularly suitable for large-size forgings, thick-section components, and powder metallurgy components. The resulting titanium alloy can achieve a tensile strength of over 1400MPa while maintaining good plasticity.

Description

Technical Field

[0001] This invention relates to the field of microstructure control and high-performance preparation technology of titanium alloy materials, specifically to a method for preparing ultra-high strength titanium alloys by high-temperature annealing strengthening. Background Technology

[0002] Titanium alloys possess low density, high specific strength, and excellent corrosion resistance, making them widely used in aerospace, weaponry, marine engineering, energy equipment, biomedicine, and high-end manufacturing. As next-generation equipment continues to evolve towards lightweight, high load-bearing capacity, and high reliability, higher requirements are being placed on the strength levels of titanium alloys. In typical applications such as aerospace structural components, high-strength fasteners, load-bearing connectors, and complex formed components, the material not only needs to possess ultra-high strength but also retain a certain degree of plasticity and work hardening capacity to ensure service safety margins.

[0003] Currently, most technical approaches for preparing ultra-high-strength titanium alloys are based on solution treatment and subsequent aging treatment. The principle is to obtain a metastable structure or supersaturated solid solution through rapid cooling after solution treatment, and then use the aging process to precipitate strengthening phases to improve strength. This route requires high hardenability of the material. For small-sized bars, plates, or thin-walled components, achieving uniform rapid cooling is practically feasible. However, for large-sized forgings, thick-section components, and complex-shaped components, rapid quenching faces significant challenges in practice, including uneven cross-sectional structure, high residual stress, increased tendency to deformation and cracking, and poor performance consistency. Traditional solution aging processes also involve long process chains, strict requirements for equipment conditions and process control, and high energy and time costs.

[0004] It should also be noted that, in traditional understanding, high-temperature annealing is mainly used to eliminate processing stress, improve plasticity, or stabilize the microstructure, usually accompanied by a decrease in strength. This approach shows significant limitations in the preparation of ultra-high-strength titanium alloys. This invention, based on a specific multi-element alloy system, utilizes the strain energy accumulated during hot working deformation to induce a dispersion transformation of the β phase to the fine-scale α phase during high-temperature annealing and subsequent cooling. This achieves a significant increase in strength without solution quenching, while maintaining good elongation and work hardening ability, exhibiting a microstructure evolution characteristic of high-temperature annealing strengthening rather than annealing softening. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing ultra-high strength titanium alloys by high-temperature annealing strengthening.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing ultra-high strength titanium alloys by high-temperature annealing strengthening includes the following steps: (1) Alloy design and smelting: The chemical composition of the prepared titanium alloy by weight percentage is: Al: 5.0-6.2%, Cu: 3.5-6.5%, Nb: 2.0-2.8%, Mo: 1.0-1.8%, V: 1.0-2.5%, Zr: 1.0-2.5%, with the balance being Ti and unavoidable impurity elements; the alloy is prepared into ingots by vacuum consumable melting or other smelting methods that can achieve the same purity; (2) Multi-stage hot working deformation: The ingot obtained in step (1) is subjected to multi-stage hot working deformation treatment, including single-phase region billet forging and two-phase region hot working deformation, in order to construct a non-equilibrium structure with high dislocation density and high strain energy storage. (3) High-temperature annealing treatment: The titanium alloy component deformed in step (2) is heated to the β phase transformation temperature T. β Annealing is performed within the range of 50-150℃. After holding at that temperature for 0.5-4 hours, the mixture is then air-cooled or controlled-cooled to room temperature.

[0007] Furthermore, the single-phase region forging described in step (2) involves heating the ingot to the β phase transformation temperature T. β At 50-150℃, hold for 2-6 hours, and perform single-phase β-zone forging. The deformation amount in a single pass is not less than 20%, and the cumulative deformation amount is 40%-70%.

[0008] Furthermore, the two-phase region hot working deformation mentioned in step (2) is as follows: the forging billet after the single-phase region is cooled to the α+β two-phase region, and at T β The temperature range is 50-150℃. Multiple hot working deformations are performed, with a cumulative deformation of 40%-80%.

[0009] Furthermore, after hot working deformation in the two-phase region, it also includes T β Supplementary temperature processing deformation is carried out in the following temperature range of 150-250℃.

[0010] Furthermore, the annealing temperature in step (3) is T. β Below 80-120℃.

[0011] Furthermore, the heat preservation time mentioned in step (3) is 1-3 hours.

[0012] Furthermore, the cooling method described in step (3) is air cooling.

[0013] Furthermore, the chemical composition of the titanium alloy mentioned in step (1) is: Al: 5.5-6.2%, Cu: 4.5-5.5%, Nb: 2.2-2.8%, Mo: 1.2-1.8%, V: 1.5-2.0%, Zr: 1.5-2.0%, with the balance being Ti and unavoidable impurities.

[0014] Furthermore, the chemical composition of the titanium alloy mentioned in step (1) is: Al: 6.0%, Cu: 5.0%, Nb: 2.5%, Mo: 1.5%, V: 1.5%, Zr: 1.5%, with the balance being Ti and unavoidable impurities.

[0015] An ultra-high strength titanium alloy is prepared by the method described above for high-temperature annealing strengthening to prepare ultra-high strength titanium alloy.

[0016] The beneficial effects of this invention are as follows: 1. Breaking through the traditional strengthening route of titanium alloys that relies on solution quenching and aging precipitation, a new strengthening path is established by combining hot working energy storage with high-temperature annealing to induce fine-scale α-phase dispersion precipitation. This achieves ultra-high strength without the need for rapid cooling, fundamentally solving the problem of uneven microstructure and properties caused by incomplete quenching in large-size and complex structural parts.

[0017] 2. The prepared titanium alloy has a tensile strength of over 1400 MPa and an elongation of not less than 10%. It also has a high work hardening capacity, achieving a synergistic improvement in ultra-high strength and good plasticity, which greatly improves the safety margin and failure resistance of the material during service.

[0018] 3. It eliminates the traditional processes of solution quenching and long-term aging, significantly shortening the heat treatment cycle, reducing energy consumption and equipment requirements, and making the process simpler and more stable, which helps to reduce production costs and improve production efficiency.

[0019] 4. The method of the present invention is more adaptable to the size and shape of components. It is not only applicable to conventional forgings, but also to powder metallurgy formed parts and metal injection molded parts, providing a new material solution for the lightweight design and manufacturing of key structural components of high-end equipment. Attached Figure Description

[0020] Figure 1 The image shows the microstructure of the Ti-6Al-5Cu-2.5Nb-1.5Mo-1.5V-1.5Zr alloy in Example 1 after annealing at 850℃ for 2 hours.

[0021] Figure 2 The graph shows the mechanical properties of the Ti-6Al-5Cu-2.5Nb-1.5Mo-1.5V-1.5Zr alloy in Example 1 after annealing at 850℃ for 2 hours. Detailed Implementation

[0022] The present invention will be further described in detail below through embodiments and comparative examples. It should be understood that these embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention. All equivalent changes or modifications made to the technical solutions by those skilled in the art without departing from the technical concept of the present invention should fall within the scope of protection of the present invention.

[0023] Example 1 The chemical composition of the titanium alloy in this embodiment, by weight percentage, is: Al: 6.0%, Cu: 5.0%, Nb: 2.5%, Mo: 1.5%, V: 1.5%, Zr: 1.5%, with the balance being Ti and unavoidable impurity elements. The measured β-phase transformation point T of this alloy is... β It is 950℃.

[0024] Alloy ingots with the above composition were prepared by vacuum arc melting process. After peeling, removing risers and bottoms, cylindrical ingots with suitable diameters were obtained.

[0025] The ingot was heated to 1050℃ and held for 4 hours to ensure a fully homogenized microstructure. Subsequently, it underwent single-phase β-zone forging on a high-speed forging mill, involving multiple upsetting and drawing operations. The deformation per pass was controlled at 25%-35%, with a cumulative deformation of 65%. After forging, the original as-cast coarse β grains were fully broken up, and the microstructure became more homogeneous.

[0026] Once the billet temperature drops to 850℃, multiple hot forging deformations are carried out in the two-phase region, with the single-pass reduction controlled at 15%-25%, and the cumulative deformation reaching 65%. During this process, the primary α phase is elongated and broken, and high-density dislocations, subgrain boundaries, and deformation bands accumulate in the β matrix, storing a high level of strain energy within the material.

[0027] The alloy components that have undergone the above-mentioned hot working deformation are placed in a box-type resistance furnace, heated to 850°C for annealing, and held at that temperature for 2 hours before being air-cooled to room temperature.

[0028] Microscopic observation of the annealed alloy, its metallographic photographs are as follows: Figure 1 As shown. From Figure 1 It is evident that a large number of fine-scale α phases are dispersed and precipitated in the matrix. These phases are small in size, uniformly distributed, and the α / β interface is clear.

[0029] Standard tensile specimens of the alloy in this condition were subjected to room temperature tensile tests using a Zwick Z150 tensile testing machine at a tensile rate of 0.3 mm / min. The obtained stress-strain curves are shown below. Figure 2 As shown, the specific performance indicators are: yield strength 1282MPa, tensile strength 1429MPa, elongation 10.5%, and work hardening capacity up to 147MPa.

[0030] Example 2 This embodiment uses the exact same alloy composition as Example 1, namely Al: 6.0%, Cu: 5.0%, Nb: 2.5%, Mo: 1.5%, V: 1.5%, Zr: 1.5%, with the balance being Ti and unavoidable impurities. The alloy's β-phase transformation point T... β It is 950℃.

[0031] The ingot smelting and preparation process is the same as in Example 1. The ingot is heated to 1040℃ and held for 3 hours. Forging is then performed in the single-phase β region, with single-pass deformation controlled at 20%-30%, and cumulative deformation reaching 60%. The forged billet is then cooled to 840℃ and subjected to multi-pass hot working deformation in the two-phase region, with cumulative deformation reaching 60%. After deformation, the component is heated to 870℃ for high-temperature annealing, held for 2 hours, and then air-cooled to room temperature.

[0032] Samples of the alloy in this state were subjected to room temperature tensile tests under the same conditions as in Example 1. The measured mechanical properties were: yield strength 1265 MPa, tensile strength 1412 MPa, elongation 11.2%, and work hardening capacity 147 MPa. This example also achieved a tensile strength exceeding 1400 MPa under slightly higher annealing temperatures, and the elongation was improved compared to Example 1.

[0033] Example 3 This embodiment continues to use the same alloy composition as Example 1, namely Al: 6.0%, Cu: 5.0%, Nb: 2.5%, Mo: 1.5%, V: 1.5%, Zr: 1.5%, with the balance being Ti. The alloy's β-phase transformation point T... β It is 950℃.

[0034] The ingot smelting and preparation process is the same as before. The ingot is heated to 1060℃ and held for 2 hours. Forging is then performed in the single-phase β region, with single-pass deformation controlled at 25%-35%, and cumulative deformation reaching 70%. The forged billet is then cooled to 840℃ and subjected to multi-pass hot working deformation in the two-phase region, with cumulative deformation reaching 70%. After deformation, the component is heated to 830℃ for high-temperature annealing, held for 2 hours, and then air-cooled to room temperature.

[0035] The alloy in this condition was subjected to a room temperature tensile test under constant tensile conditions. The measured mechanical properties were: yield strength 1298 MPa, tensile strength 1456 MPa, elongation 10.1%, and work hardening capacity 158 MPa.

[0036] Example 4 The chemical composition of the titanium alloy in this embodiment is: Al: 5.5%, Cu: 4.5%, Nb: 2.8%, Mo: 1.8%, V: 1.8%, Zr: 1.8%, with the balance being Ti and unavoidable impurities. The measured β-phase transformation point T of this alloy is... β It is approximately 945℃.

[0037] The ingot was heated to 1045℃ and held for 4 hours for single-phase forging, with single-pass deformation controlled at 20%-30%, and cumulative deformation reaching 65%. The forged billet was then cooled to 845℃ and subjected to multi-pass hot working deformation in the two-phase region, with cumulative deformation reaching 65%. The component was then heated to 845℃ for annealing, held for 2 hours, and air-cooled to room temperature. Room temperature tensile tests showed that the alloy had a yield strength of 1271 MPa, a tensile strength of 1405 MPa, and an elongation of 10.9%.

[0038] Example 5 The chemical composition of the titanium alloy in this embodiment is: Al: 5.8%, Cu: 5.5%, Nb: 2.2%, Mo: 1.2%, V: 1.8%, Zr: 2.0%, with the balance being Ti and unavoidable impurities. The measured β-phase transformation point T of this alloy is... β It is approximately 940℃.

[0039] The ingot was heated to 1040℃ and held for 4 hours for single-phase forging, with a cumulative deformation of 65%. The forged billet was then cooled to 840℃ and subjected to multiple hot working deformations in the two-phase region, with a cumulative deformation of 65%. The component was then annealed at 840℃ for 2 hours and air-cooled. The yield strength measured at room temperature was 1258 MPa, the tensile strength was 1401 MPa, and the elongation was 10.6%.

[0040] Example 6 The same alloy composition and smelting method as in Example 1 were used. After completing the two-phase region hot working deformation, an additional secondary temperature working deformation was added: the component was cooled to 750°C (i.e., T). β The temperature was below 200℃, and the deformation was 20%. It was then annealed at 850℃ for 2 hours and air-cooled. Test results showed that the tensile strength increased to 1465 MPa, and the elongation was 10.2%.

[0041] Comparative Example 1 The chemical composition of this comparative titanium alloy, by weight percentage, is: Al: 5.0%, Cu: 3.5%, Nb: 2.0%, Mo: 1.5%, V: 2.0%, Zr: 1.5%, with the balance being Ti and unavoidable impurities. The measured β-phase transformation point T of the alloy is... β It is approximately 955℃.

[0042] The ingot was heated to 1050℃ and held for 2 hours for single-phase β-zone forging, with single-pass deformation controlled at 20%-30% and cumulative deformation reaching 65%. The forged billet was then cooled to 850℃ and subjected to multi-pass hot working deformation in the two-phase region, with cumulative deformation reaching 65%. After deformation, the comparative alloy was not subjected to subsequent high-temperature annealing and was directly air-cooled to room temperature.

[0043] The results of the room temperature tensile test showed that the yield strength of the comparative alloy was only 986 MPa, the tensile strength was 1123 MPa, and the elongation was 8.3%.

[0044] Comparative Example 2 The chemical composition of this comparative titanium alloy is: Al: 5.0%, Cu: 6.5%, Nb: 3.0%, Mo: 1.5%, V: 1.5%, Zr: 2.0%, with the balance being Ti and unavoidable impurities. The measured β-phase transformation point T of the alloy is... β It is approximately 960℃.

[0045] The ingot was heated to 1150℃ and held for 2 hours for single-phase forging, which was significantly higher than the recommended temperature. The cumulative deformation after forging reached 65%. Subsequently, the forged billet was cooled to 850℃ for two-phase hot working deformation, with a cumulative deformation of 65%. After deformation, the component was heated to 850℃ for annealing for 2 hours and then air-cooled to room temperature.

[0046] The room temperature tensile test results showed that the yield strength was 1052 MPa, the tensile strength was 1189 MPa, and the elongation was only 7.5%.

[0047] Comparative Example 3 The chemical composition of this comparative titanium alloy is: Al: 6.5%, Cu: 5.0%, Nb: 3.0%, Mo: 2.0%, V: 1.5%, Zr: 1.5%, with the balance being Ti and unavoidable impurities. The measured β-phase transformation point T of the alloy is... β The temperature is approximately 958℃. The alloy contains relatively high levels of Al, Nb, and Mo. When these elements exceed the optimization range suggested in this invention, the strengthening effect of high-temperature annealing weakens, and the tensile strength cannot consistently reach above 1400 MPa.

[0048] The ingot is heated to 1050℃ and held for 2 hours for single-phase forging, with the deformation per pass controlled at 20%-30%, and the cumulative deformation reaching 65%. The forged billet is then cooled to 850℃ for two-phase hot working deformation, with the cumulative deformation reaching 65%. After deformation, the component is heated to 870℃ for annealing, held for 2 hours, and then air-cooled to room temperature.

[0049] The yield strength was 1145 MPa, the tensile strength was 1268 MPa, and the elongation was 8.8% when measured at room temperature.

[0050] Based on the experimental results of Examples 1-5 and Comparative Examples 1-3, it is evident that only when the alloy composition range, hot working deformation regime, and high-temperature annealing process conditions defined by this invention are simultaneously satisfied can titanium alloys achieve tensile strength exceeding 1400 MPa, elongation of not less than 10%, and high work hardening capacity through high-temperature annealing. Examples 4 and 5 further confirm that, within the claimed alloy composition range, various element ratios can achieve the aforementioned annealing strengthening effects under appropriate process conditions. The method of this invention simplifies the preparation process of ultra-high-strength titanium alloys, avoids the limitations imposed by the quenching process on the size and shape of components, and has significant industrial application value in the production and manufacturing of large-size and complex-shaped components.

Claims

1. A method for preparing ultra-high strength titanium alloys by high-temperature annealing strengthening, characterized in that, Includes the following steps: (1) Alloy design and smelting: The chemical composition of the prepared titanium alloy by weight percentage is: Al: 5.0-6.2%, Cu: 3.5-6.5%, Nb: 2.0-2.8%, Mo: 1.0-1.8%, V: 1.0-2.5%, Zr: 1.0-2.5%, with the balance being Ti and unavoidable impurity elements; the alloy is prepared into ingots by vacuum consumable melting or other smelting methods that can achieve the same purity; (2) Multi-stage hot working deformation: The ingot obtained in step (1) is subjected to multi-stage hot working deformation treatment, including single-phase region billet forging and two-phase region hot working deformation, in order to construct a non-equilibrium structure with high dislocation density and high strain energy storage. (3) High-temperature annealing treatment: The titanium alloy component deformed in step (2) is heated to the β phase transformation temperature T. β Annealing is performed within the range of 50-150℃. After holding at that temperature for 0.5-4 hours, the mixture is then air-cooled or controlled-cooled to room temperature.

2. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The single-phase forging described in step (2) involves heating the ingot to the β-phase transformation temperature T. β At 50-150℃, hold for 2-6 hours, and perform single-phase β-zone forging. The deformation amount in a single pass is not less than 20%, and the cumulative deformation amount is 40%-70%.

3. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The two-phase region hot working deformation mentioned in step (2) is as follows: the forging billet after the single-phase region is cooled to the α+β two-phase region, and at T β The temperature range is 50-150℃. Multiple hot working deformations are performed, with a cumulative deformation of 40%-80%.

4. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 3, characterized in that, After hot working deformation in the two-phase region, it also includes T β Supplementary temperature processing deformation is carried out in the following temperature range of 150-250℃.

5. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The annealing temperature in step (3) is T. β Below 80-120℃.

6. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The heat preservation time mentioned in step (3) is 1-3 hours.

7. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The cooling method described in step (3) is air cooling.

8. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The chemical composition of the titanium alloy mentioned in step (1) is: Al: 5.5-6.2%, Cu: 4.5-5.5%, Nb: 2.2-2.8%, Mo: 1.2-1.8%, V: 1.5-2.0%, Zr: 1.5-2.0%, with the balance being Ti and unavoidable impurities.

9. The method for preparing ultra-high strength titanium alloy by high-temperature annealing strengthening according to claim 1, characterized in that, The chemical composition of the titanium alloy mentioned in step (1) is: Al: 6.0%, Cu: 5.0%, Nb: 2.5%, Mo: 1.5%, V: 1.5%, Zr: 1.5%, with the balance being Ti and unavoidable impurities.

10. An ultra-high strength titanium alloy, characterized in that, It is prepared by the method for preparing ultra-high strength titanium alloy by high temperature annealing strengthening according to any one of claims 1 to 9.

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