A metastable beta titanium alloy of the Ti-Al-V-Mo-Cr-Zr-Nb system and a method for producing the same

Abstract

The application relates to the technical field of titanium alloys, in particular to a Ti-Al-V-Mo-Cr-Zr-Nb metastable beta titanium alloy and a preparation method thereof. The Ti-Al-V-Mo-Cr-Zr-Nb metastable beta titanium alloy comprises 3.8-4.6% of aluminum in terms of weight percentage, 5.7-6.5% of vanadium in terms of weight percentage, 4.2-5.2% of molybdenum in terms of weight percentage, 3.0-3.7% of chromium in terms of weight percentage, 1.0-2.2% of zirconium in terms of weight percentage, <=1.0% of niobium in terms of weight percentage, <=0.05% of carbon in terms of weight percentage, <=0.05% of nitrogen in terms of weight percentage, <=0.015% of hydrogen in terms of weight percentage, <=0.15% of oxygen in terms of weight percentage, and the balance is titanium and impurity elements. The purpose of the Ti-Al-V-Mo-Cr-Zr-Nb metastable beta titanium alloy and the preparation method thereof is to solve the problem that the comprehensive performance such as strength, plasticity and toughness of the current super-high-strength titanium alloy is difficult to realize good matching.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy technology, specifically to a Ti-Al-V-Mo-Cr-Zr-Nb metastable β titanium alloy and its preparation method. Background Technology

[0002] The application of titanium and titanium alloys in aircraft airframe structures can achieve significant weight reduction benefits, meeting the design requirements of high maneuverability, high reliability, and long service life. The amount of titanium used is considered one of the important indicators of the sophistication of aircraft material selection. Titanium alloys have undergone a development process from low-strength to medium-strength to high-strength, and currently, ultra-high-strength titanium alloys have become an important trend in titanium alloy development worldwide. High-strength titanium alloys generally refer to titanium alloys with a tensile strength of over 1100 MPa. Their applications in aircraft mainly include key components such as fuselage load-bearing beams, landing gear components, wing-to-pylon connections, and joints.

[0003] Currently, the alloying characteristics of high-strength titanium alloys include the addition of Al and a significant amount of β-stabilizing elements such as Mo, Cr, Mn, V, Fe, and Nb. Some alloy systems also incorporate neutral elements such as Zr or Sn. Because high-strength titanium alloys contain sufficient amounts of β-stabilizing elements, the β-phase microstructure can be retained to room temperature after quenching. Further aging treatment causes the metastable β-phase retained at room temperature to decompose into dispersed fine secondary α-phase. These precipitated fine secondary α-strengthening phases provide a large number of α / β grain boundaries, greatly enhancing the resistance to dislocation movement, thus achieving the high strength of the titanium alloy. Based on the Mo equivalent, β-titanium alloys can be divided into four categories: when the Mo equivalent is greater than 30, they are stable β-type titanium alloys; when the Mo equivalent is 30–10, they are metastable β-type titanium alloys; when the Mo equivalent is 10–5, they are near-β-type titanium alloys; and when the Mo equivalent is 0–5, they are α+β-type titanium alloys rich in β-stabilizing elements. High-strength titanium alloys, especially metastable β-titanium alloys, often combine the performance advantages of α+β two-phase alloys and β alloys. They possess high hardenability, ultra-high strength, and a wide range of controllable microstructure and properties, making them an important development direction for ultra-high-strength structural titanium alloys and attracting widespread attention both domestically and internationally. Currently, representative high-strength titanium alloys both domestically and internationally include β-type titanium alloys Ti-1023 (TB6), β-21S (TB8), Ti-15-3 (TB5), and Ti-5553, as well as α+β-type titanium alloy BT22 (TC18), which have been practically applied in the aerospace field, playing a significant role in reducing the weight of aircraft structures.

[0004] The design principles of lightweight, long-life, and high-reliability in new aircraft have placed more urgent demands on weight reduction in the main load-bearing structures. This requires titanium alloys to possess higher levels of strength in addition to their excellent overall performance, ensuring both fatigue performance and reliability while achieving greater weight reduction, thereby obtaining better overall technical and economic benefits. However, although metastable β-titanium alloys can achieve extremely high strength, like conventional metals, they typically exhibit an inverse relationship between strength and toughness / ductility. This means that as strength increases, toughness / ductility usually decreases, making it difficult for their damage tolerance at high strength levels to fully meet the design requirements of new aircraft. This severely restricts the further application of such high-strength titanium alloys under even higher strength conditions.

[0005] Therefore, the inventors provide a Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy and its preparation method. Summary of the Invention

[0006] (1) Technical problems to be solved

[0007] This invention provides a Ti-Al-V-Mo-Cr-Zr-Nb metastable β titanium alloy and its preparation method, which solves the technical problem that it is difficult to achieve a good match between the comprehensive properties such as strength, plasticity and toughness of ultra-high strength titanium alloys.

[0008] (2) Technical solution

[0009] The first aspect of the present invention provides a Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy comprising 3.8% to 4.6% by weight of aluminum, 5.7% to 6.5% by weight of vanadium, 4.2% to 5.2% by weight of molybdenum, 3.0% to 3.7% by weight of chromium, 1.0% to 2.2% by weight of zirconium, ≤1.0% by weight of niobium, ≤0.05% by weight of carbon, ≤0.05% by weight of nitrogen, ≤0.015% by weight of hydrogen, ≤0.15% by weight of oxygen, with the balance being titanium and impurity elements.

[0010] Furthermore, the titanium alloy has a static strength ≥1500MPa, elongation ≥6%, and fracture toughness ≥50MPa·m. 1 / 2 .

[0011] A second aspect of the present invention provides a method for preparing a Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy, comprising the following steps:

[0012] The components of the Ti-Al-V-Mo-Cr-Zr-Nb metastable β titanium alloy were prepared into titanium alloy ingots with uniform microstructure and chemical composition by multiple vacuum arc remelting processes.

[0013] The titanium alloy ingot is subjected to multi-fire forging in the high-temperature β phase region to obtain the first forged titanium alloy.

[0014] The first forged titanium alloy is subjected to repeated upsetting and drawing forging at a temperature of 15 to 55°C below the phase transformation point to obtain the second forged titanium alloy.

[0015] The second forged titanium alloy was subjected to a single upsetting and drawing process at a temperature 30–70°C above the phase transformation point to obtain a third forged titanium alloy with uniform and fine β grains.

[0016] The third forged titanium alloy is subjected to repeated upsetting and drawing forging at a temperature of 25-55°C below the phase transformation point to obtain a fourth forged titanium alloy with completely broken billet structure.

[0017] The fourth forged titanium alloy was subjected to post-forging solution aging treatment to obtain a metastable β titanium alloy with well-matched comprehensive properties.

[0018] Furthermore, the temperature of the high-temperature β-phase region is 900–1050 °C.

[0019] Furthermore, the vacuum self-consumption melting process is performed three times.

[0020] Furthermore, the number of forging operations is three.

[0021] Furthermore, the first forged titanium alloy is subjected to repeated upsetting and drawing forging 2 to 5 times.

[0022] Furthermore, the second forged titanium alloy is subjected to single-pass upsetting forging at a temperature of 35–65°C above the phase transformation point.

[0023] Furthermore, the third forged titanium alloy is subjected to repeated upsetting and drawing forging 3 to 5 times.

[0024] Furthermore, before performing multi-fire forging on the titanium alloy ingot in the high-temperature β-phase region, the method further includes: determining the β-transformation temperature of the titanium alloy ingot by metallographic method.

[0025] Furthermore, the fourth forged titanium alloy is subjected to solution treatment at a temperature of 15–55°C below the β transformation temperature.

[0026] (3) Beneficial effects

[0027] In summary, this invention achieves a good match of comprehensive properties for titanium alloys with a main component system of Ti-Al-V-Mo-Cr-Zr-Nb. This provides a material technology foundation for promoting the engineering application of ultra-high strength titanium alloys, further enriching my country's aerospace titanium alloy material system, and meeting future demand for ultra-high strength titanium alloy materials. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a microstructure of a titanium alloy in a solution-treated and aged state, as provided in Embodiment 1 of the present invention.

[0030] Figure 2 This is a room temperature tensile stress-strain curve of a titanium alloy provided in Embodiment 1 of the present invention;

[0031] Figure 3 This is a microstructure of a titanium alloy in a solution-treated and aged state, as provided in Embodiment 2 of the present invention.

[0032] Figure 4 This is a room temperature tensile stress-strain curve of a titanium alloy provided in Embodiment 2 of the present invention;

[0033] Figure 5 This is a microstructure of a titanium alloy in a solution-treated and aged state, provided in Embodiment 3 of the present invention.

[0034] Figure 6 This is a room temperature tensile stress-strain curve of a titanium alloy provided in Embodiment 3 of the present invention;

[0035] Figure 7 This is a schematic flowchart of a method for preparing a Ti-Al-V-Mo-Cr-Zr-Nb metastable β titanium alloy according to an embodiment of the present invention. Detailed Implementation

[0036] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention, but should not be used to limit the scope of the present invention.

[0037] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0038] This invention provides a Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy, comprising 3.8%–4.6% aluminum, 5.7%–6.5% vanadium, 4.2%–5.2% molybdenum, 3.0%–3.7% chromium, 1.0%–2.2% zirconium, ≤1.0% niobium, ≤0.05% carbon, ≤0.05% nitrogen, ≤0.015% hydrogen, and ≤0.15% oxygen, with the balance being titanium and impurity elements.

[0039] In the above embodiments, the active optimization design of the composition of a novel multi-component ultra-high-strength titanium alloy is achieved. The composition design is based on the critical Mo equivalent, employing a multi-component strengthening approach. Phase diagram calculations, supplemented by crystal structure design methods, prioritize ensuring that the alloying of the β phase satisfies the minimum homogeneous structural unit rule during the alloy design process, thereby initially determining the types and range of principal components in the novel ultra-high-strength titanium alloy. Then, the nominal composition of the initially obtained ultra-high-strength titanium alloy is verified using Mo equivalent, Bo value, and Md value, thereby screening and determining the core composition system of the novel ultra-high-strength titanium alloy. This metastable β-titanium alloy exhibits a static strength ≥1500 MPa, elongation ≥6%, and fracture toughness ≥50 MPa·m. 1 / 2 .

[0040] Figure 7 This is a schematic flowchart illustrating a method for preparing a Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to an embodiment of the present invention. Figure 7 As shown, the method may include the following steps:

[0041] S100: The components of the Ti-Al-V-Mo-Cr-Zr-Nb metastable β titanium alloy are prepared into titanium alloy ingots with uniform microstructure and chemical composition by multiple vacuum self-consumption melting processes.

[0042] S200: The titanium alloy ingot is subjected to multiple forging processes in the high-temperature β phase region to obtain the first forged titanium alloy.

[0043] S300. The first forged titanium alloy is subjected to repeated upsetting and drawing forging at a temperature of 15-55°C below the phase transformation point to obtain the second forged titanium alloy.

[0044] S400, the second forged titanium alloy is subjected to single-pass upsetting and drawing forging at a temperature 30-70°C above the phase transformation point to obtain a third forged titanium alloy with uniform and fine β grains.

[0045] S500, the third forged titanium alloy is subjected to repeated upsetting and drawing forging at a temperature of 25-55°C below the phase transformation point to obtain the fourth forged titanium alloy with completely broken billet structure.

[0046] S600, after forging, solution and aging treatment is performed on the fourth forged titanium alloy to obtain a metastable β titanium alloy with well-matched comprehensive properties.

[0047] In the above embodiment, in step S100, a titanium alloy ingot with uniform microstructure and chemical composition is prepared by three vacuum self-consumable melting processes.

[0048] In step S200, the initial forging can break the original coarse grains of the ingot, and the uniformity and directionality of the ingot's structure are initially improved; three-stage forging is carried out above the phase transformation point (temperature range of 900-1050℃).

[0049] In step S300, through multiple forging processes in this stage, static and dynamic recrystallization of the alloy structure is achieved, the grains are fully refined, and the uniformity of the titanium alloy billet structure is further controlled; the first-forged titanium alloy is subjected to repeated upsetting and drawing forging processes of 2 to 5 times.

[0050] In step S400, the principle of phase transformation recrystallization is used to return the temperature range of 35-65°C above the phase transformation point and perform single-pass upsetting and drawing forging to generate new uniform and fine β grains.

[0051] In step S500, the fine and uniform billet structure is completely broken down to achieve further homogenization and refinement of the billet structure, thereby achieving active control over the forged structure of the ultra-high strength titanium alloy; the third forged titanium alloy is subjected to repeated upsetting and drawing forging 3 to 5 times.

[0052] In step S600, the forged titanium alloy is subjected to post-forging solution aging treatment to achieve active control over the final microstructure of the ultra-high strength titanium alloy material.

[0053] As an optional implementation, before performing multi-fire forging on the titanium alloy ingot in the high-temperature β-phase region, the method further includes: determining the β-transformation temperature of the titanium alloy ingot by metallographic method.

[0054] As an optional implementation, the fourth-forged titanium alloy is solution-treated at a temperature 15–55°C below the β transformation temperature. This solution treatment at 15–55°C below the β transformation temperature allows for the formation of a large number of metastable β phases in the microstructure, while the primary α phase obtained during forging inhibits the growth of β grains. Based on this, by designing different aging process steps and parameters, the size, morphology, distribution, and quantity of the secondary α phase in the titanium alloy proposed in this invention can be actively controlled, thereby achieving a good balance between its ultra-high strength and its comprehensive properties such as plasticity and toughness.

[0055] Example 1

[0056] A method for preparing a Ti-Al-V-Mo-Cr-Zr-Nb system ultra-high strength metastable β-titanium alloy, the specific implementation steps of which are as follows:

[0057] 1. The novel ultra-high strength titanium alloy composition system proposed in this invention is as follows: aluminum 3.8%–4.6%, vanadium 5.7%–6.5%, molybdenum 4.2%–5.2%, chromium 3.0%–3.7%, zirconium 1.0%–2.2%, niobium ≤1.0%, carbon ≤0.05%, nitrogen ≤0.05%, hydrogen ≤0.015%, oxygen ≤0.15%, with the balance being titanium and unavoidable impurity elements. A titanium alloy ingot with uniform chemical composition and microstructure is prepared by three-stage vacuum arc remelting. The β-transformation temperature of the ingot is tested to be 810–815℃. Three-stage forging is then performed within the temperature range of 900–1050℃ to break up the original coarse ingot grains.

[0058] 2. Lower the forging temperature to below the phase transformation point, and perform five rounds of repeated upsetting and drawing forging within a temperature range of 770–800℃. Through this stage of multiple forging processes, static and dynamic recrystallization of the alloy structure is achieved, the grains are fully refined, and the uniformity of the titanium alloy billet structure is further controlled.

[0059] 3. Within a temperature range of 850–880℃, a single upsetting and drawing process is performed to generate new, uniform, and fine β grains. Then, the temperature is lowered again to below the phase transformation point, and five repeated upsetting and drawing processes are performed within a temperature range of 760–790℃. This process completely breaks down the fine and uniform billet structure, further refining and homogenizing the billet structure, thereby achieving active control over the forged structure of the ultra-high strength titanium alloy.

[0060] 4. The forged titanium alloy obtained in the above steps is subjected to post-forging solution treatment and aging to further achieve active control over the final microstructure of the ultra-high strength titanium alloy material. Through solution treatment at 780℃, a large number of metastable β phases are formed in the microstructure, while the primary α phase obtained during forging inhibits excessive growth of β grains. Then, aging treatment is carried out at 520–540℃ for 4–8 hours, resulting in the dispersed precipitation of secondary α phases, thereby achieving precipitation strengthening.

[0061] Mechanical property tests showed that its tensile strength was 1503 MPa, yield strength was 1435 MPa, elongation was 10.2%, reduction of area was 31.1%, and fracture toughness was 51.5 MPa·m. 1 / 2 This achieves an excellent balance of strength, plasticity, and toughness in titanium alloys.

[0062] The ultra-high strength titanium alloy solution-aged microstructure prepared in this embodiment is as follows: Figure 1 As shown, its tensile stress-strain curve at room temperature is as follows: Figure 2 As shown.

[0063] Example 2

[0064] The difference between this embodiment and Embodiment 1 is that:

[0065] Step 2: Forging temperature range 760~780℃, forging times 4 times; Step 4: Solution temperature 800℃, aging adopts ascending two-stage aging system, the first step low temperature aging temperature is 300℃, the second step high temperature aging temperature is 510~530℃.

[0066] Performance test results show that its tensile strength is 1523 MPa, yield strength is 1446 MPa, elongation is 7.0%, reduction of area reaches 14.3%, and fracture toughness is 50.01 MPa·m. 1 / 2 The other steps are the same as in Example 1.

[0067] The ultra-high strength titanium alloy solution-aged microstructure prepared in this embodiment is as follows: Figure 3 As shown, its tensile stress-strain curve at room temperature is as follows: Figure 4 As shown.

[0068] Example 3

[0069] The difference between this embodiment and Embodiment 1 is that:

[0070] Step 3: The forging temperature range below the phase transformation point is 770-790℃, and the forging is carried out 3 times; Step 4: The solution temperature is 790℃, and the aging adopts a descending two-stage aging system, with the first step being a high-temperature aging temperature of 510-530℃ and the second step being a low-temperature aging temperature of 350℃.

[0071] Performance test results show that its tensile strength is 1458 MPa, yield strength is 1398 MPa, elongation is 6.0%, reduction of area reaches 22.8%, and fracture toughness is 56.8 MPa·m. 1 / 2 The other steps are the same as in Example 1.

[0072] The ultra-high strength titanium alloy solution-aged microstructure prepared in this embodiment is as follows: Figure 5 As shown, its tensile stress-strain curve at room temperature is as follows: Figure 6 As shown.

[0073] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. Furthermore, for the sake of brevity, detailed descriptions of known methods and techniques are omitted here.

[0074] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art without departing from the scope of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of this application should be included within the scope of the claims of this application.

Claims

1. A method for preparing a Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy, characterized in that, The Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy comprises 3.8%–4.6% aluminum, 5.7%–6.5% vanadium, 4.2%–5.2% molybdenum, 3.0%–3.7% chromium, 1.0%–2.2% zirconium, ≤1.0% niobium, ≤0.05% carbon, ≤0.05% nitrogen, ≤0.015% hydrogen, and ≤0.15% oxygen, with the balance being titanium and impurity elements. The method includes the following steps: The components of the Ti-Al-V-Mo-Cr-Zr-Nb metastable β titanium alloy were prepared into titanium alloy ingots with uniform microstructure and chemical composition by multiple vacuum arc remelting processes. The titanium alloy ingot is subjected to multi-fire forging in the high-temperature β phase region to obtain the first forged titanium alloy. The first forged titanium alloy is subjected to repeated upsetting and drawing forging at a temperature of 15 to 55°C below the phase transformation point to obtain the second forged titanium alloy. The second forged titanium alloy was subjected to a single upsetting and drawing process at a temperature 30–70°C above the phase transformation point to obtain a third forged titanium alloy with uniform and fine β grains. The third forged titanium alloy is subjected to repeated upsetting and drawing forging at a temperature of 25-55°C below the phase transformation point to obtain a fourth forged titanium alloy with completely broken billet structure. The fourth forged titanium alloy was subjected to post-forging solution and aging treatment to obtain a metastable β titanium alloy with well-matched comprehensive properties. The fourth forged titanium alloy was subjected to solution treatment at a temperature of 15–55°C below the β transformation temperature.

2. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The temperature of the high-temperature β-phase region is 900–1050 °C.

3. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The vacuum self-consumption melting process is performed three times.

4. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The number of forging cycles is three.

5. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The first forged titanium alloy is subjected to repeated upsetting and drawing forging 2 to 5 times.

6. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The second forged titanium alloy was subjected to single-pass upsetting forging at a temperature of 35–65°C above the phase transformation point.

7. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The third forged titanium alloy is subjected to repeated upsetting and drawing forging 3 to 5 times.

8. The method for preparing the Ti-Al-V-Mo-Cr-Zr-Nb metastable β-titanium alloy according to claim 1, characterized in that, The static strength of the titanium alloy is ≥1500MPa, the elongation is ≥6%, and the fracture toughness is ≥50MPa·m. 1 / 2 .

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