A metastable β titanium alloy with a yield ratio less than 0.6 and a method of making the same

Abstract

The application provides a metastable beta titanium alloy with a yield ratio lower than 0.6 and a preparation method thereof. The titanium alloy comprises the following components and mass percentages: 78-82% of Ti, 18-20% of V, 0.5-1% of Fe, 0.03-0.08% of O, and the balance of inevitable impurities. The preparation method comprises the following steps: vacuum arc melting, vacuum homogenization annealing, hot rolling, cold rolling, vacuum solid solution heat treatment and the like. The titanium alloy provided by the application can generate stress-induced omega phase lath attached with a thin layer of non-identical variant omega phase on the boundary and / or {332}<113> deformation twin attached with a thin layer of omega phase on the twin boundary during deformation. The formation of the omega phase lath or twin can greatly improve the work hardening capacity and plasticity of the corresponding alloy, thereby reducing the yield ratio to 0.6 or less, and under the condition of the optimal component ratio, the yield ratio can be reduced to 0.51. The application solves the problem of high yield ratio of the existing metastable beta titanium alloy, and the titanium alloy is suitable for manufacturing a new type of cold-formed high-strength component for an aircraft.

Description

Technical Field

[0001] This invention belongs to the field of titanium alloy material technology, specifically relating to a metastable β titanium alloy with a yield strength ratio of less than 0.6 and its preparation method. Background Technology

[0002] Titanium alloys possess high specific strength and excellent corrosion resistance, making them crucial materials for aerospace structures. Using titanium alloys to manufacture load-bearing structural components in aircraft not only significantly reduces the overall structural weight but also substantially improves fuel efficiency and extends service life. Cold-formed titanium alloy sheets have much larger dimensional limits than those formed by hot forging, while also offering high forming efficiency and low cost, easily meeting the design and application requirements of large-scale aircraft structural components. Cold forming requires materials with low yield strength for easy deformation, high plasticity to prevent cracking during deformation, and significant work hardening capacity to ensure high tensile strength after deformation; that is, a low yield-to-tensile strength ratio (the ratio of yield strength to tensile strength). Furthermore, a lower yield-to-tensile strength ratio also improves the material's resistance to failure after yielding and before plastic instability, enhancing its reliability during service.

[0003] Titanium alloys, as high fault energy materials, generally suffer from insufficient work hardening capacity, resulting in a high yield strength ratio (close to 1.0). Recent studies have shown that metastable β-titanium alloys with very low β-matrix stability possess high work hardening capacity due to phase transformation and / or twinning-induced plasticity effects during deformation, making them the class of titanium alloys with the lowest yield strength ratios. However, it is worth noting that the phase transformation-induced plasticity effect in most current metastable β-titanium alloys relies on stress-induced β→α” martensite phase transformation. Since α” martensite has limited resistance to dislocation movement, the yield strength ratio of existing metastable β-titanium alloys is generally higher than 0.7, and even the few metastable β-titanium alloys that can produce very hard α” martensite have yield strength ratios no lower than 0.63, limiting the further application of this type of alloy in the field of cold-formed aerospace components.

[0004] Related studies have found that, compared to α” martensite, the ω phase and {332} <113> Twins provide a stronger barrier to dislocations. Furthermore, by analyzing the ω-phase laths and {332}... <113> By controlling the interfacial structure of twins to create a thin layer of ω phase at the interface between the ω phase laths and the twins, their dislocation-resisting ability can be further improved. Therefore, by rationally designing the composition of metastable β-titanium alloys, stress-induced ω phase laths with a thin layer of ω phase attached to the interface can be easily generated during deformation, and / or {332} <113> Deformation twins are a key approach to solving the problem of excessively high yield strength ratio in existing metastable β-titanium alloys.

[0005] Based on this, the present invention provides a metastable β-titanium alloy with a yield strength ratio of less than 0.6 and its preparation method. Summary of the Invention

[0006] Considering the high yield strength ratio of existing metastable β-titanium alloys, which leads to difficulties in cold deformation or insufficient strength after cold deformation, and their susceptibility to premature failure during service, stress-induced ω-phase laths or {332} with thin layers of ω-phase adhering to the interface are introduced into the metastable β-titanium alloy. <113> Deformation twins can effectively improve work hardening ability and plasticity, while significantly reducing yield strength ratio. Therefore, rationally controlling the alloy composition to generate stress-induced ω-phase laths with thin layers of ω-phase adhering to the interface during deformation and / or {332} <113> Deformation twins are a key approach to solving the problem of excessively high yield strength ratio in existing metastable β-titanium alloys.

[0007] The deformation mechanism of metastable β-titanium alloys is closely related to the shear modulus in a specific direction of the β matrix, which in turn is directly affected by the alloy composition. By rationally designing the chemical composition of metastable β-titanium alloys, for example, by using V as the main alloying element and controlling its content within a specific range, stress-induced ω-phase laths and / or {332} phases can be generated in the β matrix during deformation. <113> Deformed twins, and the addition of Fe can further regulate the interfacial structure of ω-phase laths and twins, resulting in the formation of a thin layer of ω-phase at the interface. Stress-induced ω-phase laths or {332} with a thin layer of ω-phase attached to the interface. <113> The formation of a large number of deformation twins can effectively reduce the mean free path of dislocations and promote the accumulation of dislocations, thereby improving the work hardening ability and plasticity of the corresponding alloys and significantly reducing the yield strength ratio of the alloys.

[0008] Based on the above considerations, this invention addresses the problem of excessively high yield strength ratio in existing metastable β-titanium alloys by providing a metastable β-titanium alloy with a yield strength ratio of less than 0.6 and its preparation method.

[0009] Specifically, the first aspect of the present invention provides a metastable β titanium alloy with a yield strength ratio of less than 0.6, wherein the constituent elements and mass percentages of the titanium alloy are: 78%~82%Ti, 18%~20%V, 0.5%~1%Fe, 0.03%~0.08%O, and the balance being unavoidable impurity elements.

[0010] As a further illustration of the present invention, the titanium alloy is composed of 100% β phase, and during the plastic deformation stage, stress-induced ω phase laths with non-identical variant ω phase thin layers attached to the boundaries and / or twin boundaries with a thin layer of ω phase attached {332} are generated. <113> Deformed twins.

[0011] As a further explanation of the present invention, the mass percentage ratio of Ti to V in the titanium alloy is in the range of 4 to 4.5, and the sum of 0.67 times the mass percentage of V and 2.9 times the mass percentage of Fe is in the range of 13.6% to 16.3%. This ensures that the titanium alloy can obtain 100% of the relatively unstable β phase after solution quenching, and that the shear modulus of the β phase in a specific direction is within a suitable range. This allows the titanium alloy to generate a large number of stress-induced ω phase laths and / or {332} during plastic deformation. <113> Deformed twins.

[0012] As a further explanation of the present invention, the mass percentage ratio of V to Fe in the titanium alloy is in the range of 18 to 35, so as to ensure that the titanium alloy generates stress-induced ω-phase laths or {332} during plastic deformation. <113> A thin ω phase forms at the boundary of the deformed twin, which generates a very strong ability to impede dislocation movement, thereby giving the titanium alloy a very strong work hardening ability.

[0013] As a further explanation of the present invention, the sum of the mass percentages of Fe and O elements in the titanium alloy is not higher than 1.05% to ensure that the titanium alloy exhibits a sufficiently low yield strength, thereby facilitating cold deformation and obtaining a low yield strength ratio.

[0014] As a further explanation of the present invention, the mass percentages of interstitial impurity elements H, N, and C in the titanium alloy are less than 0.004%, 0.015%, and 0.02%, respectively, to ensure that the titanium alloy can withstand stress-induced β→ω phase transformation or {332} <113> The atomic motions involved in twinning are not completely hindered by interstitial impurity atoms.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned metastable β-titanium alloy with a yield strength ratio of less than 0.6, comprising the following steps:

[0016] S1. Pure Ti, pure V and pure Fe raw materials are weighed according to the constituent elements and mass percentages of the titanium alloy according to any one of claims 1-4, and titanium alloy ingots are obtained by vacuum arc melting.

[0017] S2. Vacuum homogenization annealing treatment is performed on the titanium alloy ingot;

[0018] S3. The titanium alloy ingot after vacuum homogenization annealing is hot rolled into a hot rolled plate. After hot rolling, it is water-quenched to room temperature, and then the hot rolled plate is cold rolled into a cold rolled plate through multiple cold rolling processes.

[0019] S4. The cold-rolled sheet is subjected to vacuum solution heat treatment, and after solution treatment, it is water-quenched to room temperature to complete the preparation of titanium alloy.

[0020] As a further explanation of the present invention, in S1, the raw materials are pure Ti, pure V and pure Fe with a purity higher than 99.95%, and the ingredients are formulated according to the mass percentage of each element.

[0021] As a further explanation of the present invention, in S1, the vacuum arc melting is repeated 3 to 5 times, and after each melting is completed, the titanium alloy ingot is flipped over for the next melting.

[0022] As a further explanation of the present invention, in S2, the titanium alloy ingot is placed in a vacuum with a degree higher than 3 × 10⁻⁶. -4 The furnace is heated in a vacuum environment of Pa and held at 1050℃ for more than 10 hours, and then cooled to room temperature in the furnace.

[0023] As a further explanation of the present invention, in S3, the titanium alloy ingot after vacuum homogenization annealing is placed in a vacuum with a degree higher than 3×10⁻⁶. -4 The furnace is heated in a vacuum environment of Pa and held at 900℃ for more than 30 minutes. Then, it is immediately hot rolled in one pass using a twin-roll strip mill with a deformation of 30% to 60%. After hot rolling, it is water-cooled and quenched to room temperature.

[0024] As a further explanation of the present invention, in S3, the hot-rolled sheet is subjected to multiple cold rolling passes using a twin-roll strip mill at room temperature, with each pass having a roll reduction of no more than 0.3 mm and a total deformation of 30% to 70%.

[0025] As a further explanation of the present invention, in S4, the cold-rolled sheet is placed in a vacuum with a degree higher than 1×10⁻⁶. -3 It is heated in a vacuum environment of Pa at 800℃~900℃ for 30 minutes, and then water-quenched to room temperature.

[0026] As a further explanation of the present invention, after the vacuum solution heat treatment described in step S4, the microstructure of the titanium alloy material is an equiaxed β-grain structure with an average grain size in the range of 80μm to 150μm.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] This invention, through rational composition design and precise control of the preparation process, yields a metastable β-titanium alloy with a yield strength ratio below 0.6. This titanium alloy, during plastic deformation, can generate stress-induced ω-phase laths with thin layers of non-isomorphic ω-phase adhering to their boundaries and / or twin boundaries with a thin layer of ω-phase adhering to them {332}. <113> Deformation twins. This interface has a thin layer of stress-induced ω-phase laths or {332} attached to it. <113> Deformation twins possess a very strong ability to hinder dislocation movement, which can significantly improve the work hardening ability and plasticity of the corresponding alloys, and significantly reduce the yield strength ratio. The titanium alloy provided achieves a tensile strength of over 690 MPa and a fracture elongation of over 36% with a yield strength not exceeding 460 MPa, and a yield strength ratio of less than 0.6. Under optimal composition conditions, the yield strength ratio can be further reduced to 0.51, making it suitable for manufacturing cold-formed high-strength components for new aerospace vehicles. Attached Figure Description

[0029] Figure 1 The image shows the initial microstructure backscattered electron images of the titanium alloys prepared in Examples 1, 2 and Comparative Example 3 of this invention.

[0030] Figure 2 The table shows the room temperature tensile stress-strain curves of the titanium alloys prepared in Examples 1, 2 and Comparative Example 3 of this invention.

[0031] Figure 3 The electron backscatter diffraction patterns of the deformed microstructures of the titanium alloys prepared in Examples 1, 2 and Comparative Example 3 of this invention are shown.

[0032] Figure 4 The electron backscatter diffraction patterns are shown for the deformation bands in the deformed microstructures of the titanium alloys prepared in Examples 1, 2 and Comparative Example 3 of this invention. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This invention addresses the problem of excessively high yield strength ratio in existing metastable β-titanium alloys by providing a metastable β-titanium alloy with a yield strength ratio below 0.6. The constituent elements and mass percentages of the titanium alloy are: 78%~82%Ti, 18%~20%V, 0.5%~1%Fe, 0.03%~0.08%O, with the balance being unavoidable impurity elements.

[0035] Specifically, in the aforementioned titanium alloy, the mass percentage of Ti can be, for example, 78%, 79%, 80%, 81%, 82%, or any value between the two aforementioned values; the mass percentage of V can be, for example, 18%, 19%, 20%, or any value between the two aforementioned values; the mass percentage of Fe can be, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any value between the two aforementioned values; and the mass percentage of O can be, for example, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, or any value between the two aforementioned values.

[0036] Furthermore, the mass percentage ratio of Ti to V in the aforementioned titanium alloy is in the range of 4 to 4.5, for example, it can be 4, 4.1, 4.2, 4.3, 4.4, 4.5, or any value between these two values; and the sum of 0.67 times the mass percentage of V and 2.9 times the mass percentage of Fe is in the range of 13.6% to 16.3%, for example, it can be 13.6%, 14%, 15%, 16%, 16.3%, or any value between these two values, to ensure that the titanium alloy can obtain 100% of the relatively unstable β phase after solution quenching, and that the shear modulus of the β phase in a specific direction is within a suitable range, so that the titanium alloy can generate a large number of stress-induced ω phase laths and / or {332} during plastic deformation. <113> Deformed twins.

[0037] The mass percentage ratio of V to Fe in the titanium alloy is in the range of 18 to 35, for example, it can be 18, 20, 23, 25, 27, 30, 32, 35, or any value between the two above, to ensure that the titanium alloy generates stress-induced ω-phase laths or {332} during plastic deformation. <113> A thin ω phase forms at the boundary of the deformed twin, which generates a very strong ability to impede dislocation movement, thereby giving the titanium alloy a very strong work hardening ability.

[0038] The sum of the mass percentages of Fe and O in the titanium alloy should not exceed 1.05%, for example, it can be 0.53%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.05%, or any value between the two values ​​mentioned above, in order to ensure that the titanium alloy exhibits a sufficiently low yield strength, thereby facilitating cold deformation and obtaining a low yield strength ratio.

[0039] The mass percentages of interstitial impurity elements H, N, and C in the titanium alloy are less than 0.004%, 0.015%, and 0.02%, respectively, to ensure that the titanium alloy can withstand stress-induced β→ω phase transformation or {332} <113> The atomic motions involved in twinning are not completely hindered by interstitial impurity atoms.

[0040] The preparation method of the metastable β-titanium alloy with a yield strength ratio of less than 0.6 includes the following steps:

[0041] S1. Weigh pure Ti, pure V and pure Fe raw materials according to the above-mentioned constituent elements and mass percentages of titanium alloy, and obtain titanium alloy ingots by vacuum arc melting.

[0042] In S1, the raw materials are pure Ti, pure V, and pure Fe with a purity higher than 99.95%, and the ingredients are proportioned according to the mass percentage of each element. Vacuum arc melting is repeated 3 to 5 times, and after each melting, the titanium alloy ingot is flipped over for the next melting.

[0043] S2. Vacuum homogenization annealing treatment is performed on the titanium alloy ingot.

[0044] In S2, the titanium alloy ingot is placed in a vacuum with a degree higher than 3×10⁻⁶. -4 The furnace is heated in a vacuum environment of Pa and held at 1050℃ for more than 10 hours, and then cooled to room temperature in the furnace.

[0045] S3. The titanium alloy ingot after vacuum homogenization annealing is hot rolled into a hot rolled plate. After hot rolling, it is water-quenched to room temperature, and then the hot rolled plate is cold rolled into a cold rolled plate through multiple cold rolling processes.

[0046] In S3, the titanium alloy ingot after vacuum homogenization annealing is placed in a vacuum with a degree higher than 3×10⁻⁶. -4 The plate is heated in a vacuum environment at 900°C for at least 30 minutes, and then immediately hot-rolled in one pass using a twin-roll strip mill, with a deformation of 30% to 60%. After hot rolling, it is water-quenched to room temperature. At room temperature, the hot-rolled plate is then cold-rolled in multiple passes using a twin-roll strip mill, with each pass's roll deflection not exceeding 0.3 mm, and the total deformation being 30% to 70%.

[0047] S4. Perform vacuum solution heat treatment on the cold-rolled sheet, and after solution treatment, quench it in water to room temperature to complete the preparation of the titanium alloy.

[0048] In S4, cold-rolled sheet metal is placed in a vacuum with a degree higher than 1×10⁻⁶. -3 It is heated in a vacuum environment of Pa at 800℃~900℃ for 30 minutes, and then water-quenched to room temperature.

[0049] After the vacuum solution heat treatment in step S4, the microstructure of the titanium alloy material is an equiaxed β-grain structure with an average grain size in the range of 80μm to 150μm.

[0050] The following is a description with reference to specific embodiments: Example 1

[0051] The main constituent elements and mass percentages of the metastable β-titanium alloy with a yield strength ratio of less than 0.6 provided in this embodiment are: 80.4%Ti, 18.95%V, 0.58%Fe, 0.036%O, 0.0023%H, 0.011%N, 0.02%C, with the balance being unavoidable impurity elements.

[0052] The preparation process of this titanium alloy includes the following steps:

[0053] S1. Using high-purity Ti (99.995%), high-purity V (99.95%), and high-purity Fe (99.95%) as raw materials, the titanium alloy ingot is smelted in a vacuum electric arc melting furnace. The smelting is repeated 5 times. After each smelting, the titanium alloy ingot is flipped over for the next smelting.

[0054] S2. Seal the titanium alloy ingot into a glass tube, with a vacuum degree of 3.5 × 10⁻⁶. -4 Pa, the sealed titanium alloy ingot is placed in a resistance furnace, first heated to 1050℃, held at this temperature for 12 hours for vacuum homogenization annealing, and then cooled to room temperature in the furnace.

[0055] S3. Place the glass tube containing the vacuum homogenized annealed titanium alloy ingot in a resistance furnace. First, heat the furnace to 900℃ and hold at this temperature for 30 minutes. Then, quickly break the glass tube and perform a single hot rolling operation on the titanium alloy ingot using a twin-roll strip mill. The total deformation is 53.8%. After hot rolling, water-quench the ingot to room temperature. Then, perform multiple cold rolling operations on the hot-rolled titanium alloy sheet at room temperature using a twin-roll strip mill. The roll reduction in each pass is 0.3 mm, and the total deformation is 64.7%.

[0056] S4. Seal the cold-rolled titanium alloy sheet into a glass tube, with a vacuum degree of 1×10⁻⁶. -3 Pa, the sealed titanium alloy plate is placed in a resistance furnace, held at 830℃ for 30 minutes, and then water-quenched to room temperature.

[0057] The initial microstructure of the titanium alloy prepared in this embodiment was characterized using scanning electron microscopy, and the results are shown in the attached figure. Figure 1 As shown. The results indicate that the initial microstructure of the titanium alloy prepared in this embodiment is an equiaxed β-grain microstructure with an average grain size of 102.7 ± 0.9 μm.

[0058] The mechanical properties of the titanium alloy prepared in this embodiment were tested according to GB / T 228.1–2010 "Metallic materials, tensile testing—Part 1: Test at room temperature". Its stress-strain curves are attached. Figure 2As shown in the figure. The results show that the upper yield strength of the alloy is 401±33MPa, the lower yield strength is 367±14MPa, the tensile strength is 713±1MPa, the elongation at break is 41±8%, and the yield-to-tensile ratio is 0.51.

[0059] The deformed microstructure of the titanium alloy prepared in this embodiment was characterized by electron backscatter diffraction using scanning electron microscopy, as shown in the attached figure. Figure 3 As shown. The results indicate that the dominant deformation mechanism of this alloy is stress-induced β→ω phase transformation, {332} <113> Twins and dislocation slip.

[0060] The deformation bands in the deformed microstructure of the titanium alloy prepared in this embodiment were characterized by electron backscatter diffraction using scanning electron microscopy, as shown in the attached figure. Figure 4 As shown. The results indicate that a thin layer of ω phase adheres to the boundary of the stress-induced ω phase laths formed during the plastic deformation process of this alloy. This ω phase is a different variant from the internal stress-induced ω phase laths. Example 2

[0061] The main constituent elements and mass percentages of the metastable β-titanium alloy with a yield strength ratio of less than 0.6 provided in this embodiment are: 79.61%Ti, 19.35%V, 0.94%Fe, 0.07%O, 0.0011%H, 0.007%N, 0.014%C, with the balance being unavoidable impurity elements.

[0062] The preparation process of this titanium alloy includes the following steps:

[0063] S1. Using high-purity Ti (99.995%), high-purity V (99.95%), and high-purity Fe (99.95%) as raw materials, the titanium alloy ingot is smelted in a vacuum electric arc melting furnace. The smelting is repeated 5 times. After each smelting, the titanium alloy ingot is flipped over for the next smelting.

[0064] S2. Seal the titanium alloy ingot into a glass tube, with a vacuum degree of 3.5 × 10⁻⁶. -4 Pa, the sealed titanium alloy ingot is placed in a resistance furnace, first heated to 1050℃, held at this temperature for 12 hours for vacuum homogenization annealing, and then cooled to room temperature in the furnace.

[0065] S3. Place the glass tube containing the vacuum homogenized annealed titanium alloy ingot in a resistance furnace. First, heat the furnace to 900℃ and hold at this temperature for 30 minutes. Then, quickly break the glass tube and perform a single hot rolling operation on the titanium alloy ingot using a twin-roll strip mill. The total deformation is 39.7%. After hot rolling, water-quench the ingot to room temperature. Then, perform multiple cold rolling operations on the hot-rolled titanium alloy sheet at room temperature using a twin-roll strip mill. The roll reduction in each pass is 0.3 mm, and the total deformation is 67.4%.

[0066] S4. Seal the cold-rolled titanium alloy sheet into a glass tube, with a vacuum degree of 1×10⁻⁶. -3 Pa, the sealed alloy plate is placed in a resistance furnace, held at 830℃ for 30 minutes, and then water-quenched to room temperature.

[0067] The initial microstructure of the titanium alloy prepared in this embodiment was characterized using scanning electron microscopy, and the results are shown in the attached figure. Figure 1 As shown. The results indicate that the initial microstructure of the titanium alloy prepared in this embodiment is an equiaxed β-grain microstructure with an average grain size of 105.5 ± 2.3 μm.

[0068] The mechanical properties of the titanium alloy prepared in this embodiment were tested according to GB / T 228.1–2010 "Metallic materials, tensile testing—Part 1: Test at room temperature". Its stress-strain curves are attached. Figure 2 As shown in the figure. The results show that the alloy has an upper yield strength of 456±57MPa, a lower yield strength of 398±31MPa, a tensile strength of 696±16MPa, a fracture elongation of 38±2%, and a yield-to-tensile ratio of 0.57.

[0069] The deformed microstructure of the titanium alloy prepared in this embodiment was characterized by electron backscatter diffraction using scanning electron microscopy, as shown in the attached figure. Figure 3 As shown. The results indicate that the dominant deformation mechanism of this alloy is {332}. <113> Twins and dislocation slip.

[0070] The deformation bands in the deformed microstructure of the titanium alloy prepared in this embodiment were characterized by electron backscatter diffraction using scanning electron microscopy, as shown in the attached figure. Figure 4 As shown. The results indicate that the {332} formed during the plastic deformation process of this alloy <113> A thin layer of ω phase is attached to the boundary of the deformed twin.

[0071] Comparative Example 3

[0072] The metastable β-titanium alloy provided in this comparative example has the following main constituent elements and mass percentages: 76.83% Ti, 21.34% V, 1.75% Al, 0.005% Fe, 0.044% O, 0.003% H, 0.008% N, 0.019% C, with the balance being unavoidable impurity elements.

[0073] The preparation process of this titanium alloy includes the following steps:

[0074] S1. Using high-purity Ti (99.995%), high-purity V (99.95%), and high-purity Al (99.95%) as raw materials, the titanium alloy ingot is smelted in a vacuum electric arc melting furnace. The smelting is repeated 5 times. After each smelting, the titanium alloy ingot is flipped over for the next smelting.

[0075] S2. Seal the titanium alloy ingot into a glass tube, with a vacuum degree of 3.5 × 10⁻⁶. -4 Pa, the sealed titanium alloy ingot is placed in a resistance furnace, first heated to 1050℃, held at this temperature for 12 hours for vacuum homogenization annealing, and then cooled to room temperature in the furnace.

[0076] S3. Place the glass tube containing the vacuum homogenized annealed titanium alloy ingot in a resistance furnace. First, heat the furnace to 900℃ and hold at this temperature for 30 minutes. Then, quickly break the glass tube and perform a single hot rolling operation on the titanium alloy ingot using a twin-roll strip mill. The total deformation is 43.5%. After hot rolling, water-quench the ingot to room temperature. Then, perform multiple cold rolling operations on the hot-rolled titanium alloy sheet at room temperature using a twin-roll strip mill. The roll reduction in each pass is 0.3 mm, and the total deformation is 62.2%.

[0077] S4. Seal the cold-rolled titanium alloy sheet into a glass tube, with a vacuum degree of 1×10⁻⁶. -3 Pa, the sealed titanium alloy plate is placed in a resistance furnace and held at 860℃ for 30 minutes, and then water-quenched to room temperature.

[0078] The initial microstructure of the titanium alloy prepared in this comparative example was characterized using scanning electron microscopy, and the results are shown in the attached figure. Figure 1 As shown. The results indicate that the initial microstructure of the titanium alloy prepared in this comparative example is an equiaxed β-grain microstructure with an average grain size of 104.7 ± 1 μm.

[0079] The mechanical properties of the titanium alloy prepared in this comparative example were tested according to GB / T 228.1–2010 "Metallic materials, tensile testing—Part 1: Test at room temperature". The stress-strain curves are attached. Figure 2 As shown in the figure. The results show that the alloy has a yield strength of 462±8 MPa, a tensile strength of 590±1 MPa, a fracture elongation of 40±3%, and a yield-to-tensile ratio of 0.78.

[0080] The deformed microstructure of the titanium alloy prepared in this comparative example was characterized by electron backscatter diffraction using scanning electron microscopy, as shown in the attached figure. Figure 3 As shown. The results indicate that the dominant deformation mechanism of this alloy is {332}. <113> Twins and dislocation slip.

[0081] The deformation bands in the deformed microstructure of the titanium alloy prepared in this comparative example were characterized by electron backscatter diffraction using scanning electron microscopy, as shown in the attached figure. Figure 4 As shown. The results indicate that the {332} formed during the plastic deformation process of this alloy <113> The boundary of the deformed twin contains only a small amount of α” phase and no ω phase thin layer.

[0082] Compared to Examples 1 and 2, although the same preparation process was used, the titanium alloy composition provided in this comparative example exceeds the scope of protection of this patent application, which leads to the formation of {332} in the corresponding alloy during plastic deformation. <113> A thin ω-phase layer cannot be formed at the boundary of the deformed twin, so this type of twin can only provide limited work hardening capability, which in turn leads to a significantly higher yield strength ratio of the alloy.

[0083] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0084] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A metastable β-titanium alloy with a yield strength ratio of less than 0.6, characterized in that, The titanium alloy has the following composition and mass percentage: 78%~82%Ti, 18%~20%V, 0.5%~1%Fe, 0.03%~0.08%O, with the balance being unavoidable impurity elements; The titanium alloy is composed of 100% β phase, and during the plastic deformation stage, stress-induced ω phase laths with non-identical ω phase thin layers attached to the boundaries and / or twin boundaries with a thin layer of ω phase attached {332} are generated. <113> Deformed twins; The mass percentage ratio of Ti to V in the titanium alloy is in the range of 4 to 4.5, and the sum of 0.67 times the mass percentage of V and 2.9 times the mass percentage of Fe is in the range of 13.6% to 16.3%; the mass percentage ratio of V to Fe in the titanium alloy is in the range of 18 to 35; and the sum of the mass percentages of Fe and O in the titanium alloy is not higher than 1.05%.

2. The metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in claim 1, characterized in that, The mass percentages of interstitial impurity elements H, N, and C in the titanium alloy are less than 0.004%, 0.015%, and 0.02%, respectively.

3. A method for preparing a metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Weigh pure Ti, pure V and pure Fe raw materials according to the constituent elements and mass percentages of the titanium alloy according to any one of claims 1-2, and obtain titanium alloy ingots by vacuum arc melting. S2. Vacuum homogenization annealing treatment is performed on the titanium alloy ingot; S3. The titanium alloy ingot after vacuum homogenization annealing is hot rolled into a hot rolled plate. After hot rolling, it is water-quenched to room temperature, and then the hot rolled plate is cold rolled into a cold rolled plate through multiple cold rolling processes. S4. The cold-rolled sheet is subjected to vacuum solution heat treatment, and after solution treatment, it is water-quenched to room temperature to complete the preparation of titanium alloy.

4. The method for preparing metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in claim 3, characterized in that, In S1, the raw materials are pure Ti, pure V and pure Fe with a purity higher than 99.95%; the vacuum arc melting is repeated 3 to 5 times, and after each melting is completed, the titanium alloy ingot is flipped over for the next melting.

5. The method for preparing metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in claim 3, characterized in that, In S2, the titanium alloy ingot is placed in a vacuum with a degree higher than 3×10⁻⁶. -4 The furnace is heated in a vacuum environment of Pa and held at 1050℃ for more than 10 hours, and then cooled to room temperature in the furnace.

6. The method for preparing metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in claim 3, characterized in that, In S3, the titanium alloy ingot after vacuum homogenization annealing is placed in a vacuum with a degree higher than 3×10⁻⁶. -4 The plate is heated in a vacuum environment at 900°C for more than 30 minutes, and then immediately hot-rolled in one pass using a twin-roll strip mill with a deformation of 30% to 60%. After hot rolling, the plate is water-cooled and quenched to room temperature. At room temperature, the hot-rolled plate is then cold-rolled in multiple passes using a twin-roll strip mill, with each pass having a roll reduction of no more than 0.3 mm and a total deformation of 30% to 70%.

7. The method for preparing metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in claim 3, characterized in that, In S4, the cold-rolled sheet is placed under a vacuum degree higher than 1×10⁻⁶. -3 It is heated in a vacuum environment of Pa at 800℃~900℃ for 30 minutes, and then water-quenched to room temperature.

8. The method for preparing metastable β-titanium alloy with a yield strength ratio of less than 0.6 as described in claim 3, characterized in that, After the vacuum solution heat treatment described in step S4, the microstructure of the titanium alloy material is an equiaxed β-grain structure with an average grain size in the range of 80μm to 150μm.

Images