A 500 DEG C high-strength alpha+beta titanium alloy and a preparation method thereof

Abstract

The application discloses a high-strength alpha+beta titanium alloy suitable for 500 DEG C and a preparation method thereof, which comprises Ti, Al, V, Mo, Nb, Zr and other impurity elements, and the mass percentage (wt.%) of alloy components is as follows: Al is 6.2-7.2, V is 1.5-2.5, Mo is 1.5-2.5, Nb is 0.5-1.5, Zr is 13.5-14.5, Mn is less than or equal to 0.02, C is less than or equal to 0.02, Ni is less than or equal to 0.01, Si is less than or equal to 0.20, Sn is less than or equal to 0.20, Cr is less than or equal to 0.04, O is less than or equal to 0.02, P is less than or equal to 0.01, S is less than or equal to 0.01, N is less than or equal to 0.006, and Ti is the balance. p The application realizes that the alloy has a specific microstructure of a bimodal structure composed of primary alpha phase and transformed beta phase by alloy design, the primary equiaxial alpha s The content of the secondary alpha s The width of the secondary alpha s The alpha T / beta The application forms an alpha The application has excellent thermal stability and thermal strength, and no harmful phase is generated after aging at 550 DEG C. Meanwhile, the alloy has good mechanical properties and excellent processing deformation capacity, the yield strength at room temperature is more than 1250 MPa, the tensile strength at room temperature is more than 1300 MPa, the plasticity at room temperature is more than 7%, and the tensile strength at 500 DEG C is more than 600 MPa, so the application discloses a new high-strength titanium alloy suitable for 500 DEG C.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically a high-strength α+β titanium alloy suitable for 500℃ and its preparation method, which can maintain the stability of the dual-state structure after aging at 550℃, and the high-temperature strength at 500℃ exceeds 600MPa. Background Technology

[0002] Currently, α+β high-temperature titanium alloys typically operate at high temperatures (350℃~650℃) and under complex stress conditions. This harsh environment places stringent requirements on the alloy's physical, chemical, and mechanical properties. α+β high-temperature titanium alloys must possess high heat resistance, good plasticity, resistance to high-temperature oxidation, corrosion resistance, and long-term thermal stability. With the rapid development of the aerospace industry, the thrust-to-weight ratio of aircraft is increasing, and the operating temperature of engine components is continuously rising, driving the research and application of α+β high-temperature titanium alloys for key components such as compressor disks, blades, and impellers. To improve the alloy's service performance and meet high-temperature strength requirements, large amounts of α-stabilizing elements (Al), β-stabilizing elements (Mo, Nb, V), and neutral elements (Zr) are added to α+β high-temperature titanium alloys used in high-performance compressor disks, blades, and impellers. However, high alloying levels increase the difficulty of alloy processing deformation and microstructure control. Furthermore, excessive addition of elements such as Al and Zr can lead to the formation of precipitates, reducing the alloy's strength and plasticity, which significantly narrows the alloy's applicability.

[0003] The room temperature tensile strength of existing α+β high-temperature titanium alloys used for key components such as compressor discs, blades, and impellers is difficult to exceed 1300 MPa, while their high-temperature tensile strength at 500℃ is also difficult to achieve above 600 MPa. For example, the Ti-6Al-4V alloy, first developed by the United States in 1954, is one of the most widely used α+β titanium alloys and can operate at 350℃. Subsequently, various countries added β isomorphic elements Mo and Nb, neutral element Zr, and β eutectoid element Si to dual-phase alloys to improve their high-temperature performance. Russia developed the BT9 alloy (Ti-6.5Al-1.5Zr-3.5Mo-0.3Si, named TC11 in China) suitable for 500℃ in 1958, and the Ti-6Al-3Mo-2Sn-2Zr-2Nb-1.5Cr-0.1Si alloy (TC21) developed by the Northwest Institute of Nonferrous Metals in 1977 can serve for extended periods at 500℃. It is evident that reasonable composition design is of great significance to material performance.

[0004] Furthermore, the microstructure of dual-phase titanium alloys has a significant impact on material properties, especially the dual-state structure consisting of equiaxed primary α(α) p ) particles and β-transformed tissue (β TIt is known to offer a good balance between high strength and ductility, as well as good creep resistance and fatigue properties. It has been reported that Ti-6Al-4V titanium alloy prepared by the LSF process exhibits an elongation of 18% after solution treatment at 920℃ for 2 hours and aging at 550℃ for 4 hours, significantly higher than that of forged samples. Triple heat treatment of the LSF-prepared Ti-6Al-4V-ELI titanium alloy revealed that its microstructure consists of equiaxed α-laminates. p , fine α s The composition of the layered microstructure and the remaining β phase significantly increases the elongation of the sample. Studies show that the strength of the Ti-6Al-2Mo-2Cr alloy with equiaxed microstructure is lower than that with layered microstructure, while its ductility is the opposite. Furthermore, different cooling methods significantly affect the mechanical properties of the alloy. Mechanical property tests on air-cooled and furnace-cooled TC21 alloys revealed that the yield strength and tensile strength of the air-cooled TC21 alloy were superior to those of the furnace-cooled alloy, while the ductility was the opposite. This demonstrates the crucial importance of accurate microstructure control for material properties.

[0005] Existing α+β high-temperature titanium alloy preparation processes are simple and low-cost, but they suffer from high deformation difficulty, poor microstructure uniformity, insufficient temperature resistance, and difficulty in improving overall performance. Therefore, two core issues restricting the current development of α+β high-temperature titanium alloys are: firstly, ensuring excellent room-temperature strength while maintaining high temperature resistance and high-temperature microstructure stability; and secondly, ensuring excellent deformation capacity while improving high-temperature performance. In view of this, this invention provides a high-strength α+β titanium alloy suitable for 500℃ and its preparation method, which can maintain stable bimodal microstructure after aging at 550℃ without harmful phase precipitation, exhibiting a room-temperature tensile yield strength >1250MPa, a room-temperature tensile strength >1300MPa, plasticity >7%, and a high-temperature strength at 500℃ >600MPa. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a high-strength α+β titanium alloy suitable for 500℃ and its preparation method. Compared with existing α+β high-temperature titanium alloys, this alloy exhibits a room temperature tensile yield strength >1250MPa, a room temperature tensile strength >1300MPa, plasticity >7%, and a high-temperature strength at 500℃ >600MPa. After aging at 550℃, the microstructure remains stable with no harmful phase precipitation. The objective of this invention is to develop an aerospace-grade α+β titanium alloy suitable for 500℃, with a room temperature tensile strength >1300MPa and a room temperature elongation >7%, through precise alloy design.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A high-strength α+β titanium alloy suitable for 500℃ is disclosed. This high-strength α+β titanium alloy comprises Ti, Al, V, Mo, Nb, Zr, and other impurity elements. The mass percentage (wt.%) of the alloy composition is as follows: Al: 6.2–7.2, V: 1.5–2.5, Mo: 1.5–2.5, Nb: 0.5–1.5, Zr: 13.5–14.5. Other impurity elements are: Mn≤0.02, C≤0.02, Ni≤0.01, Si≤0.20, Sn≤0.20, Cr≤0.04, O≤0.02, P≤0.01, S≤0.01, N≤0.006, Ti: balance.

[0009] The high-strength α+β titanium alloy suitable for 500℃ is designed to achieve a specific microstructure, namely a bimodal microstructure: consisting of primary equiaxed α... p Phase transition β T Phase composition, wherein, transformation β T The phases include the residual β phase and the secondary α phase. s Phase, primary equiaxed α p Phase content is 10%–40%, diameter is 7.0–9.0 μm, secondary α s Phase width is 50–100 nm; α s α can lead to hindering dislocation motion s The β interface forms, and no harmful phases are generated after aging at 550℃, exhibiting excellent thermal stability and thermal strength.

[0010] The high-strength titanium alloy suitable for 500℃ has the following typical properties: room temperature yield strength >1250MPa, room temperature tensile strength >1300MPa, room temperature elongation >7%, and high temperature tensile strength at 500℃ >600MPa.

[0011] A method for preparing a high-strength titanium alloy suitable for 500℃ includes the following steps:

[0012] First, weigh out the high-purity alloy material according to the mass percentage, and add it to the vacuum arc melting furnace according to the melting point of the elements from high to low. Melt it repeatedly at least 5 times, and turn on the electromagnetic stirring system 3 to 4 times during the process to ensure that the alloy ingot composition is uniform.

[0013] Next, the alloy ingot is heated in a muffle furnace to the β phase transformation point temperature and held for 25-35 minutes. The alloy ingot after holding is then subjected to 5-10 passes of unidirectional rolling. The deformation amount of each pass in the multi-pass rolling process is 10%-15%, and the total reduction is 85-90%.

[0014] Finally, the product is subjected to solution treatment at 800–850℃ for 1–1.5 hours, air-cooled to room temperature, and then aged at 530–560℃ for 3–5 hours, followed by air-cooling to room temperature to obtain the final product.

[0015] The concept behind the above technical solution is to utilize the applicant's cluster-based composition design method to design the composition of a novel high-strength titanium alloy suitable for 500℃. This method constructs cluster-based structural units based on inter-element interactions, namely [clusters] (connecting atoms). x That is, it consists of a cluster and x connecting atoms. The cluster is a coordination polyhedron formed by any solute atom as the center and matrix atoms in the nearest neighbor shell. The connecting atoms in the next nearest neighbor shell are used to match the average density of the alloy. For the HCP crystal structure, the cluster part is determined to be a CN12 twin cubic octahedron with 3 connecting atoms. The cluster formula is expressed as: [AB 12 [C3], where A, B, and C represent the center, shell, and connecting atom positions, respectively. For the BCC crystal structure, the coordination number of the cluster is CN14 rhombic dodecahedron, and the number of connecting atoms C ranges from 1 to 8. The cluster structure is most stable when C = 3, and the cluster formula is expressed as: [AB] 14 (C3). This cluster-based composition design method has been successfully applied to the design of various solid solution alloys, such as nickel-based superalloys, magnesium alloys, and high-entropy alloys, providing new ideas and methods for the composition design of high-performance alloys.

[0016] Based on the applicant's preliminary work, in the α+β high-temperature titanium alloy system, elements can be classified into three categories according to their roles and the mixing enthalpy between the elements and the matrix elements: Category T elements (including Ti and Zr), Category A elements (including Al), and Category B elements (including Mo, Nb, and V). For simplicity, the three elements entering the cluster structure will be represented by T, A, and B. Through analysis of numerous α+β high-temperature titanium alloys, a novel high-strength titanium alloy cluster formula suitable for 500℃ can be obtained as α-{[AT...} 12 ](A 1.2 T 1.8 )} 12 +β-{[AT 14 ](T 0.5 A 0.5 B2)}5.

[0017] In novel high-strength titanium alloys suitable for 500℃, Al primarily promotes the β-α transformation, increasing the strength of the titanium alloy and helping to reduce its density. Simultaneously, it forms a protective film on the metal surface at high temperatures, improving the alloy's oxidation and corrosion resistance. However, excessive Al content leads to the precipitation of the Ti3Al phase, negatively impacting the alloy's plasticity and fracture toughness. Zr belongs to the same transition group as Ti, possessing similar chemical properties and unlimited solubility. The addition of Zr causes lattice distortion, increasing the alloy's strength and ductility, resulting in solid solution strengthening. Furthermore, it enhances the high-temperature performance of the titanium alloy. Mo readily accumulates in the β phase, thus improving its stability. Mo also reduces the alloy's notch sensitivity. Nb significantly improves high-temperature strength and oxidation resistance; however, excessive Nb content causes severe segregation and the formation of harmful phases. Using the β-stabilizing elements Mo and Nb in multi-element alloying achieves solid solution strengthening of the β phase, while further stabilizing the β phase to improve room-temperature plasticity. Therefore, the high-strength titanium alloy suitable for 500℃ was finally determined to be: Ti-(71.8~76.8)Al-(6.2~7.2)V-(1.5~2.5)Mo-(1.5~2.5)Nb-(0.5~1.5)Zr-(13.5~14.5).

[0018] The microstructure and structure of the alloy were examined using metallographic microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron probe microanalysis (EPMA). Tensile mechanical properties at room temperature and 500℃ were tested using a UTM5504 electronic universal tensile testing machine. Based on this, the present invention is determined to be the aforementioned high-strength titanium alloy suitable for 500℃. The alloy composition by mass percentage (wt.%) is: Al: 6.2–7.2, V: 1.5–2.5, Mo: 1.5–2.5, Nb: 0.5–1.5, Zr: 13.5–14.5, Mn≤0.02, C≤0.02, Ni≤0.01, Si≤0.20, Sn≤0.20, Cr≤0.04, O≤0.02, P≤0.01, S≤0.01, N≤0.006, Ti: balance. The microstructure and performance indicators of the material are: room temperature yield strength R... p0.2 >1250MPa, tensile strength R m >1300MPa, elongation A>7%; tensile strength R at 500℃ m >600MPa; After solution treatment and aging, it exhibits a specific microstructure as a bimodal structure, composed of primary α phase and transformed β phase, with primary equiaxed α phase... p The phase content is approximately 10%–40%, and the diameter is 7.0–9.0 μm, secondary α s The phase width is approximately 50–100 nm; no harmful phases are formed after aging at 550 °C, exhibiting excellent thermal stability.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) This invention designs and develops a high-strength α+β titanium alloy suitable for 500℃ based on the applicant's self-developed cluster composition method. Compared with existing α+β high-temperature titanium alloys, the room temperature tensile strength R of the alloy of this invention is significantly higher. m >1300MPa, far exceeding the current representative α+β high-temperature titanium alloys, such as TC21 titanium alloy (1284MPa) and TC4 titanium alloy (999MPa).

[0021] (2) The microstructure of this series of high-strength titanium alloys suitable for 500℃ exhibits a specific bimodal structure, consisting of primary α phase and transformed β phase, with primary equiaxed α phase... p The phase content is approximately 10%–40%, and the diameter is 7.0–9.0 μm, secondary α s The phase width is approximately 50–100 nm; α s α can lead to hindering dislocation motion s The formation of the / β interface gives the alloy excellent tensile properties, and no harmful phases are formed after aging at 550℃, resulting in excellent thermal stability.

[0022] (3) The series of alloys can have a tensile strength of over 600 MPa at 500℃ in the absence of high-temperature elements such as W, Ta, and Si, and have excellent thermal strength. Attached Figure Description

[0023] Figure 1 The SEM microstructure of the alloy prepared in Example 1 shows a specific bimodal microstructure, consisting of a primary α phase and a transformed β phase. The primary α phase is equiaxed. p The phase content is approximately 33.4%, and the diameter is 8.0 μm, secondary α s The phase width is approximately 50 nm.

[0024] Figure 2 The SEM microstructure of the alloy prepared in Example 2 shows a specific bimodal microstructure, consisting of a primary α phase and a transformed β phase. The primary α phase is equiaxed. p The phase content is approximately 12.2%, and the diameter is 7.3 μm, secondary α s The phase width is approximately 90 nm.

[0025] Figure 3 The SEM microstructure of the alloy prepared in Example 3 shows a specific bimodal microstructure, consisting of a primary α phase and a transformed β phase. The primary α phase is equiaxed. p The phase content is approximately 36.8%, and the diameter is 8.6 μm, secondary αs The phase width is approximately 100 nm. Detailed Implementation

[0026] The specific embodiments of the present invention will be described in detail below with reference to the technical solution.

[0027] Example 1:

[0028] α+β high-temperature titanium alloy with Ti-6.58Al-2.19V-2.06Mo-0.66Nb-14.39Zr (wt.%)

[0029] Step 1: Alloy Preparation

[0030] High-purity raw materials were used. 80g of raw materials were mixed according to mass percentage and placed in a vacuum arc furnace, with elements having similar melting points placed close together. The raw materials were repeatedly melted five times under an argon atmosphere, with an electromagnetic stirring system activated four times during the melting process, resulting in a homogeneous alloy ingot. Next, the alloy ingot was heated to the β-phase transformation point temperature in a muffle furnace and held for 30 minutes. The ingot after this holding period was then subjected to six passes of unidirectional rolling. In this multi-pass rolling process, the deformation per pass was 15%, and the total reduction was 90%, yielding a sheet sample with a thickness of approximately 2mm. Subsequently, a solution treatment was performed at 800℃ for 1 hour, followed by air cooling to room temperature. An aging process was then carried out at 550℃ for 4 hours, followed by air cooling to room temperature.

[0031] Step Two: Organizational Structure and Mechanical Property Testing

[0032] The microstructure and structure of the alloy after solution treatment and aging were examined using OM, SEM, TEM, and EPMA. The results showed that the alloy consists of primary α phase and transformed β phase, with primary equiaxed α phase. p The phase content is approximately 33.4%, and the diameter is 8.0 μm, secondary α s The phase width is approximately 50 nm, see attached image. Figure 1 Tensile properties at room temperature and 500℃ were measured using an MTS universal tensile testing machine: Room temperature yield strength R p0.2 =1258MPa, tensile strength R m =1295MPa, elongation after fracture A = 9.8%; high-temperature tensile strength R at 500℃ m =627MPa.

[0033] Example 2:

[0034] Ti-6.2Al-1.5V-1.5Mo-0.5Nb-13.5Zr (wt.%) α+β high-temperature titanium alloy

[0035] Step 1: Alloy Preparation

[0036] High-purity raw materials were used. 80g of raw materials were mixed according to mass percentage and placed in a vacuum arc furnace, with elements having similar melting points placed close together. The raw materials were repeatedly melted five times under an argon atmosphere, with an electromagnetic stirring system activated three times during the melting process, resulting in a homogeneous alloy ingot. Next, the alloy ingot was heated to the β-phase transformation point temperature in a muffle furnace and held for 25 minutes. The ingot was then subjected to five passes of unidirectional rolling, with a single-pass deformation of 15% and a total reduction of 85%, yielding a plate sample with a thickness of approximately 2.5mm. Subsequently, a solution treatment was performed at 840℃ for 1.5 hours, followed by air cooling to room temperature. An aging process was then carried out at 550℃ for 3 hours, followed by air cooling to room temperature.

[0037] Step Two: Organizational Structure and Mechanical Property Testing

[0038] The microstructure and structure of the alloy after solution treatment and aging were examined using OM, SEM, TEM, and EPMA. The results showed that the alloy consists of primary α phase and transformed β phase, with primary equiaxed α phase. p The phase content is approximately 12.2%, and the diameter is 7.3 μm, secondary α s The phase width is approximately 90 nm, see attached image. Figure 2 Tensile properties at room temperature and 500℃ were measured using an MTS universal tensile testing machine: Room temperature yield strength R p0.2 =1330MPa, tensile strength R m =1366MPa, elongation after fracture A = 7.3%; high-temperature yield strength R at 500℃ m =658MPa.

[0039] Example 3:

[0040] Ti-7.2Al-2.5V-2.5Mo-1.5Nb-14.5Zr (wt.%) α+β high-temperature titanium alloy

[0041] Step 1: Alloy Preparation

[0042] High-purity raw materials were used. 80g of raw materials were mixed according to mass percentage and placed in a vacuum arc furnace, with elements having similar melting points placed close together. The raw materials were repeatedly melted five times under an argon atmosphere, with an electromagnetic stirring system activated four times during the melting process, resulting in a homogeneous alloy ingot. Next, the alloy ingot was heated to the β-phase transformation point temperature in a muffle furnace and held for 35 minutes. The ingot after this holding period was then subjected to nine passes of unidirectional rolling. In this multi-pass rolling process, the deformation per pass was 10%, and the total reduction was 90%, yielding a plate sample with a thickness of approximately 2.5mm. Subsequently, a solution treatment was performed at 800℃ for 1 hour, followed by air cooling to room temperature. An aging process was then carried out at 550℃ for 5 hours, followed by air cooling to room temperature.

[0043] Step Two: Organizational Structure and Mechanical Property Testing

[0044] The microstructure and structure of the alloy after solution treatment and aging were examined using OM, SEM, TEM, and EPMA. The results showed that the alloy consists of primary α phase and transformed β phase, with primary equiaxed α phase. p The phase content is approximately 36.8%, and the diameter is 8.6 μm, secondary α s The phase width is approximately 100 nm, see appendix. Figure 3 Tensile properties at room temperature and 500℃ were measured using an MTS universal tensile testing machine: Room temperature yield strength R p0.2 =1280MPa, tensile strength R m =1321MPa, elongation after fracture A = 8.3%; high temperature yield strength R at 500℃ m =638MPa.

[0045] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A high-strength α+β titanium alloy suitable for 500℃, characterized in that, The high-strength α+β titanium alloy suitable for 500℃ comprises the main alloying components Ti, Al, V, Mo, Nb, Zr, and other impurity elements. The mass percentages (wt.%) of the main alloying components are as follows: Al: 6.2~7.2, V: 1.5~2.5, Mo: 1.5~2.5, Nb: 0.5~1.5, Zr: 13.5~14.5, Ti: balance. The mass percentages (wt.%) of the other impurity elements are: Mn ≤ 0.02, C ≤ 0.02, Ni ≤ 0.01, Si ≤ 0.20, Sn ≤ 0.20, Cr ≤ 0.04, O ≤ 0.02, P ≤ 0.01, S ≤ 0.01, N ≤ 0.

006. The high-strength α+β titanium alloy suitable for 500℃ achieves a bimodal microstructure through alloy design: from primary equiaxed α... p Phase transition β T Phase composition, wherein, transformation β T The phases include the residual β phase and the secondary α phase. s Phase, primary equiaxed α p Phase content is 10%~40%, diameter is 7.0~9.0μm, secondary α s Phase width is 50 ~ 100 nm; α s α can lead to hindering dislocation motion s The β interface forms, and no harmful phases are generated after aging at 550℃, exhibiting excellent thermal stability and thermal strength.

2. The high-strength α+β titanium alloy suitable for 500℃ according to claim 1, characterized in that, The high-strength titanium alloy suitable for 500℃ has the following typical properties: room temperature yield strength >1250 MPa, room temperature tensile strength >1300 MPa, room temperature elongation >7%, and high temperature tensile strength at 500℃ >600 MPa.

3. A method for preparing a high-strength titanium alloy suitable for 500℃ as described in any one of claims 1-2, characterized in that, Includes the following steps: The first step is to weigh out the high-purity alloy material according to the mass percentage, and add it into the vacuum arc melting furnace according to the melting point of the elements from high to low. The materials are repeatedly melted to obtain alloy ingots with uniform composition. The second step is to heat the alloy ingot in a muffle furnace to the β phase transformation point temperature and hold it there. After holding, the alloy ingot is subjected to 5 to 10 passes of unidirectional rolling. In the multi-pass rolling process, the deformation amount of each pass is 10% to 15%, and the total reduction is 85% to 90%. The third step involves solution treatment at 800~850℃ for 1~1.5 hours, followed by air cooling to room temperature, and then aging treatment at 530~560℃ for 3~5 hours, followed by air cooling to room temperature to obtain the final product.

4. The method for preparing a high-strength titanium alloy suitable for 500℃ according to claim 3, characterized in that, In the second step, the heat preservation time is 25 min to 35 min.

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