Titanium alloy with improved strength and plasticity and preparation method thereof

Abstract

The invention belongs to the technical field of titanium alloy strengthening, and particularly relates to a titanium alloy with improved strength and plasticity and a preparation method thereof. The titanium alloy is composed of a beta phase of a body-centered cubic lattice structure and an alpha phase of a close-packed hexagonal structure. The alpha phase of the close-packed hexagonal structure comprises a primary alpha phase, a grain boundary alpha phase, an intragranular alpha phase and a secondary alpha phase; the alpha phase of the close-packed hexagonal structure further comprises one or more of a grain boundary widmannite alpha-phase nanosheet, a widmannite alpha-phase nanosheet and an alpha variant; the intracrystalline alpha phases form coherent twin boundaries; and nano twin crystals are formed in the intracrystalline alpha phase. The size of the intragranular alpha phase is that the average lamellar thickness is 5 nm to 5 [mu] m; the preparation method comprises the following specific steps: cooling the titanium alloy to room temperature after solid solution heat treatment; and the titanium alloy subjected to solution treatment is treated under the combined action of a magnetic field and aging. The technical problem that the titanium alloy is poor in strength and plasticity is solved, and the technical effect that the strength and plasticity of the titanium alloy are cooperatively improved is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy strengthening, and in particular, relates to a titanium alloy with improved strength and plasticity and a preparation method thereof. Background Art

[0002] Titanium alloy is a high-strength structural material with low density and good corrosion resistance. It has become the preferred material for high-end frontier fields such as aerospace and deep-sea manned submersibles. Although titanium alloy has excellent performance, it is a major challenge to achieve a synergistic match between strength and plasticity under high strength. This has prompted researchers to continuously explore strategies and methods to simultaneously improve strength and plasticity.

[0003] In order to achieve the synergistic improvement of strength and ductility of titanium alloys, innovative strategies such as constructing multi-morphology, multi-scale secondary α phase, and multi-scale hierarchical heterogeneous structure through aging process have shown remarkable potential in achieving strength-plasticity matching. In addition, the use of grain boundary engineering (such as coherent twin boundaries and coherent phase interfaces) is considered to be the preferred strategy for synergistically improving strength and ductility.

[0004] Prior art CN 119082637 A discloses a method for preparing a titanium alloy and a titanium alloy that synergistically improves strength and plasticity. The method is to first perform a solid solution or aging treatment on the titanium alloy, then perform a magnetic field treatment, and finally perform an aging treatment. The method performs a single magnetic field treatment at room temperature. In order to make the dislocation density increased by the magnetic field treatment promote the subsequent precipitation of the α phase during aging, this requires the equipment to generate a larger magnetic field strength value, and the equipment is difficult to meet the technical requirements; when the solid titanium alloy is treated with a magnetic field at room temperature, the weak magnetic field is difficult to promote the dislocation and phase change process of the titanium alloy, resulting in the magnetic field treatment having no substantial effect on the subsequent precipitation of the α phase during aging; the tensile strength of the titanium alloy thus produced is only ~932.39MPa, the improvement effect of the mechanical properties is limited and the plasticity is poor, which is difficult to meet the application requirements of high-performance structural parts. Summary of the invention

[0005] In view of the defects of the prior art, the present invention provides a titanium alloy with improved strength and plasticity and a preparation method thereof, the purpose of which is to solve the technical problems of poor strength and plasticity of titanium alloys in the prior art and to achieve the technical effect of synergistically improving the strength and plasticity of titanium alloys.

[0006] In view of the defects of the prior art, according to the first aspect of the present invention, a titanium alloy with improved strength and plasticity is provided, wherein the titanium alloy is composed of a β phase of a body-centered cubic lattice structure and an α phase of a close-packed hexagonal structure; the α phase of the close-packed hexagonal structure includes a primary α phase, a grain boundary α phase, an intracrystalline α phase, and a secondary α phase; the α phase of the close-packed hexagonal structure also includes one or more of a grain boundary Widmanstatten α phase nanosheet, a Widmanstatten α phase nanosheet, and an α variant; the intracrystalline α phases form coherent twin boundaries with each other; and nanotwins are formed inside the intracrystalline α phase. The size of the intracrystalline α phase is an average sheet thickness of 5nm to 5μm.

[0007] According to another aspect of the present invention, a method for preparing the titanium alloy with improved strength and plasticity is provided, which specifically comprises the following steps:

[0008] S1, subjecting the titanium alloy to solution heat treatment and then cooling to room temperature;

[0009] S2. The titanium alloy after solid solution treatment is treated under the simultaneous action of magnetic field and aging treatment.

[0010] Preferably, in step S2, the magnetic field is selected from a steady-state magnetic field or a pulsed magnetic field;

[0011] Preferably, the titanium alloy is a rectangular parallelepiped, sheet-shaped or rod-shaped sample, and the direction of action of the magnetic field is parallel or perpendicular to the long side direction of the rectangular parallelepiped, sheet-shaped or rod-shaped sample.

[0012] Preferably, in step S2, the conditions for the simultaneous action of the magnetic field and the aging treatment are: the intensity of the magnetic field is 0.2-10T, the temperature of the aging treatment is 300-600°C, and the time for the simultaneous action of the magnetic field and the aging treatment is 1-12h.

[0013] Preferably, in step S1, the solution heat treatment is specifically performed by keeping the temperature at 30 to 100° C. above the β-transus temperature or 30 to 60° C. below the β-transus temperature for 5 to 60 minutes, and then air-cooling, furnace-cooling or water-cooling to room temperature.

[0014] Preferably, step S2 is specifically to perform a separate aging treatment before and / or after the simultaneous action of the magnetic field and the aging treatment; preferably, the time of the separate aging treatment is 1 to 4 hours, and the temperature of the separate aging treatment is 300 to 600°C.

[0015] Preferably, step S2 is specifically, after the magnetic field and aging treatment act simultaneously, a single aging treatment is performed, and finally a second magnetic field and aging treatment are simultaneously performed; preferably, the time of the single aging treatment is 1 to 4 hours, and the temperature of the single aging treatment is 300 to 600°C; the conditions for the simultaneous action of the second magnetic field and aging treatment are: the intensity of the magnetic field is 0.2 to 10T, the aging treatment temperature is 300 to 600°C, and the time is 1 to 4 hours.

[0016] Preferably, step S2 is specifically, after the magnetic field and the aging process act together, then the aging cooling or heating treatment is carried out under the condition that the magnetic field maintains a set value; preferably, the set value is 0.2-10T, the temperature range of the aging cooling or heating is 400-550°C, and the cooling or heating rate is 10-60°C / min.

[0017] Preferably, step S2 is specifically, after the magnetic field and the aging process work together, then the magnetic field strength is increased or decreased while the aging temperature is kept at a set value; preferably, the set value is 300-600°C, the magnetic field strength is increased or decreased in the range of 0.4-8T, and the rate of increase or decrease of the magnetic field strength is 0.013-0.13T / s.

[0018] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0019] 1. The present invention prepares a primary α phase, a grain boundary α phase, an intracrystalline α phase and a secondary α phase, and also includes one or more of grain boundary Widmanstatten α phase nanosheets, Widmanstatten α phase nanosheets, and α variants; a secondary α phase with multiple morphologies and scales is precipitated in the β matrix, and a large number of phase interfaces between the α phase and the β phase can not only hinder the dislocation movement and strengthen the alloy during the plastic deformation process; but also can alleviate the strain incompatibility between the two phases and act as a dislocation source, improve plasticity, and synergistically enhance the strength and plasticity of the titanium alloy.

[0020] 2. The present invention prepares nanotwins of α phase in nanocrystals and coherent twin boundaries formed by α phase in nanocrystals. A semi-coherent interface is maintained between the α phase and the β phase. Due to the strain incompatibility between the two phases, stress concentration occurs at the interface and fractures, which reduces the plasticity of the alloy. After the formation of nanotwins and coherent twin interfaces, the problem of strain incompatibility can be effectively avoided, and strain localization can be further alleviated. Coherent twin boundaries can both hinder dislocation slip and promote dislocation slip transmission, increase the number of slip systems, and deflect the direction of crack propagation, thereby achieving high strength and high plasticity of titanium alloys.

[0021] 3. The present invention couples the magnetic field with the aging process so that the titanium alloy is simultaneously affected by the magnetic field and temperature. The magnetic field can reduce the phase transition point of the titanium alloy, and the temperature can provide energy for the phase transition process, promoting the transformation of the β phase into the α phase; high temperature can accelerate atomic diffusion, reducing the demand for magnetic field energy in the phase transition process; the magnetic field can promote dislocation slip, and high temperature can provide energy for the activation of the slip system, especially the α phase with fewer slip systems. Under the coupling of the magnetic field and the temperature field, the titanium alloy can not only form a heterogeneous structure through the nucleation, precipitation and growth of the α phase, but also activate the slip system and promote dislocation slip. The synergistic effect of the two can not only improve the strength, but also improve the plasticity. Therefore, the magneto-plastic effect generated by the magnetic field and the precipitation strengthening mechanism caused by aging can be synergistically utilized to couple the multi-effects, multi-scales and multi-mechanisms involved in the magnetic-thermal coupling effect, showing a huge promoting effect in breaking through the strength-plasticity matching dilemma of titanium alloys.

[0022] 4. The present invention performs aging treatment before the magnetic field and aging process work together (magnetic-thermal coupling) to give the titanium alloy an initial temperature, which is conducive to converting the metastable phase into the α phase and promoting dislocation slip under the action of magnetic-thermal coupling; separate aging is performed after magnetic-thermal coupling, and magnetic-thermal coupling can promote dislocation slip. When the magnetic field is removed, the dislocations increased by the magnetic field can provide energy and diffusion channels for atomic diffusion, which can promote the nucleation and precipitation of the α phase; after magnetic-thermal coupling, heating and cooling treatments are performed, and the temperature difference is used to provide a driving force for the phase change process and dislocation movement, thereby accelerating the transformation of the second phase; after magnetic-thermal coupling, the magnetic field intensity is increased and decreased, and when the magnetic field intensity changes, the dislocations will be impacted by energy and intensity, accelerating the accumulation and proliferation of dislocations at obstacles, and promoting dislocation movement.

[0023] 5. The present invention can flexibly adjust the synergistic mode and time of the magnetic field and the aging process, can reasonably modify the process parameters according to needs, effectively regulate and customize the microstructure, and provide an effective technical approach and technical solution for achieving high strength and high plasticity of titanium alloys from the perspective of process feasibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a stress-strain curve diagram of the Ti-6554 titanium alloy prepared in Examples 1-4 of the present invention and Comparative Example 1.

[0025] Figure 2 The scanning electron microscope (SEM) images of the microstructural characteristics of the Ti-6554 titanium alloy prepared in Examples 1-4 of the present invention, wherein (a) is Example 1; (b) is Example 2; (c) is Example 3; and (d) is Example 4.

[0026] Figure 3Electron backscatter diffraction (EBSD) analysis diagrams of the Ti-6554 alloy prepared in Examples 2-4 of the present invention, wherein (a) and (b) are Example 2; (c) and (d) are Example 3; (e) and (f) are Example 4.

[0027] Figure 4 It is the orientation difference angle of the Ti-6554 alloy prepared in Examples 2-4 of the present invention.

[0028] Figure 5 The statistical results of the local orientation difference of the Ti-6554 alloy prepared in Examples 2-4 of the present invention.

[0029] Figure 6 These are the statistical results of the α phase diameter of the Ti-6554 alloy prepared in Examples 2-4 of the present invention.

[0030] Figure 7 The transmission electron microscope (TEM) image of the Ti-6554 titanium alloy prepared in Example 4 of the present invention, wherein (a) is the precipitation of α variants with different orientations; (b) is the twin boundary formed by the α phases in the nanocrystal and the nanotwins inside the α phase in the nanocrystal; (c) is the high-resolution TEM image of the twin boundary formed by three adjacent α phases; (c1) is the fast Fourier transform image corresponding to the dotted box area of ​​c1 in (c); (c2) is the dotted box area of ​​c2 in (c) domain; (c3) is the fast Fourier transform image corresponding to the c3 dotted box area in (c); (d) is the fast Fourier transform image of (c), and (e) is the high-resolution TEM image of the twin boundary composed of two adjacent α phases; (e1) is the fast Fourier transform image corresponding to the e1 dotted box area in (e); (e2) is the fast Fourier transform image corresponding to the e2 dotted box area in (e); (f) is the fast Fourier transform image of (e).

[0031] Figure 8 is the integrated intensity analysis, where (a) is Figure 7 The integrated intensity analysis between the blue boxes AB in (e); (b) Figure 7 Integrated intensity analysis between the blue box CDs in (e). DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Example 1

[0034] Taking the forged Ti-6554 metastable β titanium alloy as the material, a rectangular sample with a size of 40×15×20 mm was cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0035] A. The sample was solution treated at 800℃ for 10 min and then air-cooled to room temperature, which is called ST sample.

[0036] B. The ST sample is placed in a 0.6T magnetic field, where the direction of the magnetic field is perpendicular to the sample, and aged at 350°C for 6h. After magnetic-thermal coupling, it is air-cooled to room temperature. The resulting sample is called 350°C-0.6T.

[0037] Example 2

[0038] Taking the forged Ti-6554 metastable β titanium alloy as the material, a rectangular sample with a size of 40×15×20 mm was cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0039] A. The sample was solution treated at 800℃ for 10 min and then air-cooled to room temperature, which is called ST sample.

[0040] B. The ST sample is placed in a 0.6T magnetic field, where the direction of the magnetic field is perpendicular to the sample, and aged at 460°C for 6h. After magnetic-thermal coupling, it is air-cooled to room temperature. The resulting sample is called 460°C-0.6T.

[0041] Example 3

[0042] Taking the forged Ti-6554 metastable β titanium alloy as the material, a rectangular sample with a size of 40×15×20 mm was cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0043] A. The sample was solution treated at 800℃ for 10 min and then air-cooled to room temperature, which is called ST sample.

[0044] B. The ST sample is placed in a 0.6T magnetic field, where the direction of the magnetic field is perpendicular to the sample, and aged at 520°C for 6 hours. After magnetic-thermal coupling, it is air-cooled to room temperature. The resulting sample is called a 520°C-0.6T sample.

[0045] Example 4

[0046] Taking forged Ti-6554 metastable β titanium alloy as the material, a rectangular sample with a size of 40×15×20 mm was cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0047] A. The sample was solution treated at 800℃ for 10 min and then air-cooled to room temperature, which is called ST sample.

[0048] B. The ST sample is placed in a 0.6T magnetic field with the direction of the magnetic field parallel to the sample and aged at 460°C for 6 hours. After magnetic-thermal coupling, it is air-cooled to room temperature. The sample prepared at this time is called 460°C-0.6T-PMF.

[0049] Example 5

[0050] The forged, extruded or rolled Ti-6554 metastable β titanium alloy is used as the material, and a block sample is cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0051] A. The sample was solution treated at 740℃ for 30min and then air-cooled to room temperature. This is called the ST sample.

[0052] B. The ST sample was aged at 520°C for 2 hours.

[0053] C. Then a 10T magnetic field is applied in the direction parallel to the sample, and an aging treatment is performed at 520°C for 6h.

[0054] Example 6

[0055] The forged, extruded or rolled Ti-6554 metastable β titanium alloy is used as the material, and a block sample is cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0056] A. The sample was solution treated at 740℃ for 30min and then air-cooled to room temperature. This is called the ST sample.

[0057] B. The ST sample is subjected to a 10 T magnetic field with the direction of the magnetic field being parallel to the sample, and is simultaneously subjected to an aging treatment at 520° C. for 6 h.

[0058] C. Then remove the magnetic field and continue aging treatment at this temperature for 2 hours.

[0059] Example 7

[0060] The forged, extruded or rolled Ti-6554 metastable β titanium alloy is used as the material, and a block sample is cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0061] A. The sample was solution treated at 800℃ for 30min and then air-cooled to room temperature, which is called ST sample.

[0062] B. The ST sample is subjected to a 10 T magnetic field with the direction of the magnetic field being parallel to the sample, and is subjected to an aging treatment at 460° C. for 6 h.

[0063] C. Then remove the magnetic field and continue the aging treatment for 3 hours.

[0064] D. Finally, a 6T magnetic field is applied with the direction of the magnetic field perpendicular to the sample, and the sample is aged at 460°C for 1h.

[0065] Example 8

[0066] The forged, extruded or rolled Ti-6554 metastable β titanium alloy is used as the material, and a block sample is cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0067] A. The sample was solution treated at 800℃ for 30min and then air-cooled to room temperature, which is called ST sample.

[0068] B. The ST sample is subjected to a 4 T magnetic field with the direction of the magnetic field being parallel to the sample, and is subjected to an aging treatment at 300° C. for 6 h.

[0069] C. Then under the action of this magnetic field, the temperature was increased to 520°C at a rate of 60°C / min.

[0070] Example 9

[0071] The forged, extruded or rolled Ti-6554 metastable β titanium alloy is used as the material, and a block sample is cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0072] A. The sample was solution treated at 800℃ for 30min and then air-cooled to room temperature, which is called ST sample.

[0073] B. The ST sample is subjected to an aging treatment at 460° C. for 6 h under the action of a 6 T magnetic field with the direction of the magnetic field being parallel to the sample.

[0074] C. Then, under the action of this aging temperature, the magnetic field intensity is reduced to 2T at a rate of 0.13T / s.

[0075] Comparative Example 1

[0076] Taking forged Ti-6554 metastable β titanium alloy as the material, a rectangular sample with a size of 40×15×20 mm was cut from the forged Ti-6554 alloy bar by wire cutting. The preparation method includes the following steps:

[0077] A. The sample was solution treated at 800℃ for 10 min and then air-cooled to room temperature, which is called ST sample.

[0078] B. Aging at 350℃ for 6h without magnetic field, and air cooling to room temperature. The sample in this heat treatment state is called 350℃-0T sample.

[0079] The obtained 350℃-0.6T sample, 460℃-0.6T sample, 520℃-0.6T sample and 460℃-0.6T-PMF sample were subjected to scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and mechanical properties tests, respectively.

[0080] Figure 1 The mechanical properties of Ti-6554 samples in different states are shown in Table 1. The yield strength of the 350℃-0.6T sample prepared in Example 1 is ~965.9MPa, the ultimate tensile strength is ~976.9MPa, and the total elongation at break is ~5.6%; the strength of the 460℃-0.6T sample prepared in Example 2 is significantly improved, with a yield strength of ~1289.4MPa and an ultimate tensile strength of ~1312.3MPa, but the total elongation at break is reduced to ~2.9%. As the aging temperature increases again, the yield strength and ultimate tensile strength of the 520℃-0.6T sample prepared in Example 3 decrease to ~1097.4MPa and ~1126.0MPa, respectively, but the total elongation at break increases to ~5.9%. From the above analysis, it can be seen that under the same magnetic field strength, as the aging temperature increases, the strength first increases and then decreases, while the total elongation at break shows the opposite trend. The aging temperature of 460℃ reflects the turning point of strength and plasticity. Based on this, the mechanical properties under different magnetic field directions at 460℃ and 0.6T were further analyzed. Compared with the 460℃-0.6T sample prepared in Example 2, the 460℃-0.6T-PMF sample prepared in Example 4 has a significantly increased total elongation at break to ~9.4% (belonging to the high plasticity range) under the condition of equivalent strength, and the increase is ~224.1%. Figure 1 It can be seen that the 460℃-0.6T-PMF sample has a better combination of high strength and high ductility than other samples. Compared with the 350℃-0T sample prepared in Comparative Example 1, the tensile strength of the 460℃-0.6T-PMF sample prepared in Example 4 increased by 63.4%, and the total elongation at break increased by 27.0%. Through the present invention, the titanium alloy achieves a synergistic improvement in strength and plasticity, and can meet the requirements of high strength and high plasticity.

[0081] Table 1 Mechanical properties of Ti-6554 alloy prepared in Examples 1-4 and Comparative Example 1 under different treatment processes

[0082]

[0083] In order to analyze the effects of different magnetic-thermal processes on mechanical properties, it is necessary to further understand the microstructures under different magnetic-thermal states, such as Figure 2 As shown in the SEM picture. Figure 2 (a) is the 350℃-0.6T sample prepared in Example 1, where the α phase (α GB ) and intragranular α phase, their average length and width are ~1.17μm and ~0.43μm, respectively, and the aspect ratio is ~2.72. Figure 2 (b) shows the precipitation of primary α phase (α p ), intracrystalline α phase, α GB , secondary α phase (α s ) and grain boundary Widmanstattenite α phase (α WGBs ) nanosheets. p The average length and width of α are ∼0.87 μm and ∼0.47 μm, respectively, with an aspect ratio of ∼1.85; GB It is continuously distributed at the grain boundary, with an average width of about 0.45 μm; needle-shaped α s ; α WGBs Distributed in the local area extending from the grain boundary to the grain. The α phase precipitates unevenly at the grain boundary to form a continuous α GB layer, which can significantly sacrifice the ductility of the alloy. Figure 2 (c) is the 520℃-0.6T sample prepared in Example 3, and the microstructure is distributed with α p , intracrystalline α phase, α GB , α s and Widmanstatten α phase (α WM ) nanosheets. p The average length and width of the α-alternatives are ∼0.89 μm and ∼0.52 μm, respectively, with an aspect ratio of ∼1.71. The two and three α-alternatives inside the grains form V-shaped and triangular clusters, respectively, as shown in Figure 2 As shown by the yellow dotted line in (c). Figure 2 (d) is the 460℃-0.6T-PMF sample prepared in Example 4. α p , intracrystalline α phase, α GB , α s and α WGBs Nanosheets. α GB and α p The average length and width were ∼1.03 μm and ∼0.62 μm, respectively, with an aspect ratio of ∼1.66.

[0084] Depend on Figure 2 It can be seen that (1)α p The aspect ratio of α decreases with the increase of aging temperature; (2) When the aging temperature increases from 460℃ to 520℃, s(3) With the increase of aging temperature, the α phase inside the grain changes from micron-sized lath to nano-sized needle-shaped and flake-shaped α s ; (4) α GB The continuous phase in the 460℃-0.6T sample changes to discontinuous phase in the 520℃-0.6T and 460℃-0.6T-PMF samples; (5) Multi-morphological and multi-scale α phases, including micron-sized α p and α GB , nanoscale α WGBs Sheet and nano-needle α s It is worth noting that more and finer nanoscale α s . Multi-modal and multi-scale α s The precipitation increases the interface content of α phase and β phase. On the one hand, it can hinder dislocation slip and strengthen the alloy; on the other hand, it can alleviate the strain incompatibility at the interface, act as a dislocation source, and improve the plasticity of the alloy.

[0085] Use EBSD analysis to further understand microstructural features such as Figure 3 shown. Figure 3 (a) and (b) are EBSD analyses of the 460°C-0.6T sample prepared in Example 2; Figure 3 (c) and (d) are EBSD analyses of the 520°C-0.6T sample prepared in Example 3; Figure 3 (e) and (f) are EBSD analyses of the 460℃-0.6T-PMF sample prepared in Example 4.

[0086] Depend on Figure 4 , Figure 5 , Figure 6It can be seen that the 460℃-0.6T sample contains 9.3% low-angle grain boundaries, the precipitation volume fraction is 22.7% of the α phase, the average diameter is ~0.71μm, and the average local orientation differences of the α phase and the β phase are ~1.36 and ~0.82, respectively. The low-angle grain boundary content of the 520℃-0.6T sample is 13.2%, the average local orientation differences of the α phase and the β phase are ~0.65 and ~0.58, respectively, the volume fraction of the α precipitate phase is 16.3%, and the average diameter of the α phase is ~0.85μm. Compared with the 460℃-0.6T sample, the low-angle grain boundary and average diameter of α phase of the 460℃-0.6T-PMF sample increased to 19.5% and ~0.91μm, respectively, and the average local orientation difference of β phase and volume fraction of α phase decreased to ~0.73 and 17.1%, respectively; although the low-angle grain boundary content of the 460℃-0.6T-PMF sample increased, its average local orientation difference decreased, which is beneficial to improve plasticity. The above results show that the 460℃-0.6T sample precipitates more and finer α phase, which can significantly improve the strength of the alloy.

[0087] like Figure 7 As shown, TEM was used to further analyze the strengthening and toughening mechanism of the alloy prepared in Example 4. Figure 7 As shown in (a), the alloy precipitates three α variants α1, α2 and α3 that grow along different orientations. The angle between a1 and a2 is 84°, and the angle between a1 and a3 is 90°. The average thickness of the α phase is measured to be 30nm. Figure 7 In (a), in addition to the nanoscale α phase, high-density dislocations are also distributed in the β matrix, where the α phase is a hard phase that can hinder dislocation movement and strengthen the alloy. Figure 7 In (b), V-shaped clusters and twin boundaries composed of α variants, as well as nanotwins inside the nano-α phase, were observed. The twin boundaries were analyzed using high-resolution TEM and fast Fourier transform images. Figure 7 (c) shows the Three α variants with axis orientation, by Figure 7 The fast Fourier transform images of (c), (c1), (c2), (c3) and (d) confirm that they belong to two α variants. The (0001) planes of adjacent α variants form an angle of 120° with each other and present a completely coherent interface, so they belong to Coherent twin boundary. Figure 7 (e) shows the coherent twin boundary between two α variants. The angle between the (0001) planes of these variants is about 120°, showing a typical Symmetrical structure of the surface. Figure 8(a) and (b) show that the peak distances between AB and CD of the two α variants are 2.307 nm and 2.379 nm, respectively, and their average peak distance is about 0.23 nm, which is close to the interplanar spacing of the α phase (0001) plane. Figure 8 (a) and (b) further confirm that Figure 7 The (0001) plane in (e). The introduction of coherent twin interfaces in titanium alloys can achieve good strain compatibility, which in turn makes the alloy exhibit excellent ductility.

[0088] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A titanium alloy with improved strength and plasticity, characterized in that: The titanium alloy is composed of a β phase with a body-centered cubic lattice structure and an α phase with a close-packed hexagonal structure; The α phase of the close-packed hexagonal structure includes a primary α phase, a grain boundary α phase, an intracrystalline α phase and a secondary α phase; The α phase of the close-packed hexagonal structure also includes one or more of grain boundary Widmanstatten α phase nanosheets, Widmanstatten α phase nanosheets, and α variants; The intracrystalline α phases form coherent twin boundaries with each other; nano twins are formed inside the intracrystalline α phases; and the size of the intracrystalline α phases is an average lamella thickness of 5 nm to 5 μm.

2. A method for preparing a titanium alloy with improved strength and plasticity according to claim 1, characterized in that: The specific steps include: S1, subjecting the titanium alloy to solution heat treatment and then cooling to room temperature; S2. The titanium alloy after solid solution treatment is treated under the simultaneous action of magnetic field and aging treatment.

3. The method for preparing a high-strength and high-plasticity titanium alloy according to claim 2, characterized in that: In step S2, the magnetic field is selected from a steady-state magnetic field or a pulsed magnetic field.

4. The method for preparing a high-strength and high-plasticity titanium alloy according to claim 2, characterized in that: The titanium alloy is a rectangular parallelepiped, sheet-shaped or rod-shaped sample, and the action direction of the magnetic field is parallel or perpendicular to the long side direction of the rectangular parallelepiped, sheet-shaped or rod-shaped sample.

5. The method for preparing a high-strength and high-plasticity titanium alloy according to claim 2, characterized in that: In step S2, the conditions for the simultaneous action of the magnetic field and the aging treatment are: the intensity of the magnetic field is 0.2-10T, the temperature of the aging treatment is 300-600°C, and the time for the simultaneous action of the magnetic field and the aging treatment is 1-12h.

6. The method for preparing a high-strength and high-plasticity titanium alloy according to claim 2, characterized in that: In step S1, the solution heat treatment is specifically performed by keeping the temperature at 30 to 100° C. above the β-transus temperature or 30 to 60° C. below the β-transus temperature for 5 to 60 minutes, and then air-cooling, furnace-cooling or water-cooling to room temperature.

7. The method for preparing a titanium alloy with improved strength and plasticity according to claim 2, characterized in that: Specifically, step S2 is to perform a separate aging treatment before and / or after the simultaneous action of the magnetic field and the aging treatment; preferably, the time of the separate aging treatment is 1 to 4 hours, and the temperature of the separate aging treatment is 300 to 600°C.

8. The method for preparing a titanium alloy with improved strength and plasticity according to claim 2, characterized in that: Step S2 specifically comprises: performing a single aging treatment after the magnetic field and aging treatment are applied simultaneously, and finally performing a second magnetic field and aging treatment simultaneously; preferably, the time of the single aging treatment is 1 to 4 hours, and the temperature of the single aging treatment is 300 to 600° C.; the conditions for the second magnetic field and aging treatment to act simultaneously are: the intensity of the magnetic field is 0.2 to 10T, the aging treatment temperature is 300 to 600° C., and the time is 1 to 4 hours.

9. The method for preparing a titanium alloy with improved strength and plasticity according to claim 2, characterized in that: Step S2 specifically includes, after the magnetic field and the aging process act together, then implementing aging cooling or heating treatment under the condition that the magnetic field maintains a set value; preferably, the set value is 0.2-10T, the temperature range of the aging cooling or heating is 400-550°C, and the cooling or heating rate is 10-60°C / min.

10. The method for preparing a titanium alloy with improved strength and plasticity according to claim 2, characterized in that: Step S2 specifically includes, after the magnetic field and the aging process work together, then increasing or decreasing the magnetic field strength while maintaining the set value of the aging temperature; preferably, the set value is 300-600°C, the magnetic field strength is increased or decreased in the range of 0.4-8T, and the rate of increase or decrease of the magnetic field strength is 0.013-0.13T / s.

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