A high-strength titanium alloy and its preparation method

Abstract

The present invention belongs to the technical field of titanium alloys, and specifically relates to a high-strength titanium alloy and a preparation method thereof. The present invention provides a high-strength titanium alloy, comprising: 0.01-0.3% silicon, 0.01-0.49% scandium and 0.01-0.49% lutetium, with the remainder being titanium and unavoidable impurities, calculated in terms of mass percentage. The alloy adds appropriate amounts of silicon, scandium and lutetium elements to a titanium matrix, and the silicon and scandium elements can be dissolved into the matrix, which strengthens titanium and titanium alloys, and can form oxide particles with oxygen elements in the melt, strengthening the creep properties of the matrix; in addition, the added lutetium element can reduce the grain boundary segregation of the scandium element, which has a great strengthening effect on the titanium alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloys, and particularly relates to a high-strength titanium alloy and a preparation method thereof. Background Art

[0002] Due to advantages such as high specific strength, fatigue resistance, good corrosion resistance, and good biocompatibility, pure titanium is widely used in many fields such as aeroengines, rockets, and missiles. However, compared with titanium alloys and other commonly used engineering structural materials such as automotive steel, die steel, and stainless steel, pure titanium has lower strength and a lower recrystallization temperature, which limits its application fields.

[0003] High alloying is a traditional idea for strengthening pure titanium. However, on the one hand, high alloying will significantly increase the raw material cost of the material, and on the other hand, it will also make the processing difficulty of the material larger, resulting in a substantial increase in the comprehensive cost. Fine grain strengthening is an idea for strengthening pure titanium. Especially when refined to the nanoscale, it can significantly strengthen the mechanical properties of metals. The severe plastic deformation technology can significantly refine metal grains to the submicron and nanometer levels and is considered to be one of the most effective technologies for preparing bulk nanomaterials. However, the severe plastic deformation technology pursues a high proportion of nanocrystals, requires a large deformation amount to be applied to the material, the prepared sample size is small, and the equipment requirements are high, and it has not been popularized in industrial production. In addition to being used in a conventional room-temperature working environment, pure titanium is also used in high-temperature environments of several hundred degrees Celsius. The high-volume fraction of nanocrystalline grains prepared by severe plastic deformation is prone to recovery, recrystallization, and growth, resulting in a significant reduction in material properties and failure.

[0004] Therefore, it is of great significance to develop a process for titanium materials that has lower equipment requirements and can prepare materials with high strength, good plasticity, good heat resistance, and low cost. Summary of the Invention

[0005] The present invention is made based on the inventor's discovery and recognition of the following facts and problems:

[0006] Elements such as silicon and scandium have a certain beneficial effect on titanium and titanium alloys. On the one hand, silicon and scandium elements can dissolve into the matrix and play a strengthening role on titanium and titanium alloys. On the other hand, silicon and scandium elements can purify the melt and reduce the behavior of titanium inclusions. At the same time, silicon and scandium can form oxide particles with oxygen elements in the melt to strengthen the creep performance of the matrix. However, the scandium element has the problem of grain boundary segregation, which is not conducive to the improvement of the strength of titanium alloys. Moreover, the existing preparation processes of titanium alloys cannot effectively improve the strength and plasticity of titanium alloys. Therefore, it is necessary to conduct in-depth research on titanium alloys and their preparation processes.

[0007] The present invention aims to solve at least one of the technical problems in the related art to some extent. To this end, an embodiment of the present invention provides a high-strength titanium alloy and a preparation method thereof. In the titanium matrix, appropriate amounts of silicon, scandium, and lutetium elements are added, effectively reducing the grain boundary segregation of scandium elements, improving the strength of the titanium alloy, and the prepared titanium alloy has good plasticity.

[0008] A high-strength titanium alloy according to an embodiment of the present invention comprises 0.01-0.3% of silicon, 0.01-0.49% of scandium, and 0.01-0.49% of lutetium, with the balance being titanium and inevitable impurities, by mass percentage.

[0009] The advantages and technical effects brought by the high-strength titanium alloy according to the embodiment of the present invention are as follows: 1. In the embodiment of the present invention, by adding a small amount of scandium element, the recrystallization temperature, high-temperature strength, and structural stability of the titanium alloy can be effectively improved; 2. In the embodiment of the present invention, by adding silicon element and scandium element to the alloy simultaneously, the two can form a solid solution or a precipitation phase in the matrix. On the one hand, it can hinder the growth of titanium grains, increase the proportion of nanocrystals in the product to about 75%, effectively improving the comprehensive performance of the alloy. On the other hand, the solid solution or precipitation phase formed by silicon and scandium can strengthen the alloy, greatly improving the mechanical properties of the titanium alloy. However, if the addition amounts of silicon and scandium are too large, coarse precipitation phases will be formed, reducing the performance of the titanium alloy; 3. In the embodiment of the present invention, adding an appropriate amount of lutetium element to the alloy can reduce or even eliminate the grain boundary segregation of scandium element. Even introducing a small amount of scandium element can greatly improve the strength of the titanium alloy, and to a certain extent, it allows increasing the addition amount of scandium element, which has a great strengthening effect on the nano-structured titanium alloy.

[0010] In some embodiments, the mass percentages of silicon, scandium, and lutetium satisfy the relationship: 0.24% ≤ [Si] + [Sc] + [Lu] ≤ 1.2%.

[0011] In some embodiments, the high-strength titanium alloy comprises: 0.01-0.2% of silicon, 0.3-0.4% of scandium, and 0.2-0.3% of lutetium.

[0012] The embodiment of the present invention also provides a preparation method of a high-strength titanium alloy, comprising vacuum melting, ingot forging, hot rolling thinning, asynchronous rolling, accumulative roll bonding, and heat treatment in sequence.

[0013] Advantages and technical effects brought by the preparation method of the high-strength titanium alloy according to the embodiments of the present invention: 1. In the method according to the embodiments of the present invention, asynchronous rolling and accumulative roll bonding are used to perform plastic deformation with a large deformation amount to achieve the purpose of breaking the precipitated phases and refining the grains, forming micron-sized grains; 2. In the method according to the embodiments of the present invention, repeated rolling can effectively refine the grains of pure titanium to the sub-micron and nano scales, and make the precipitated phases uniformly distributed at the sub-micron scale between the fine grains of pure titanium, effectively improving the high-temperature mechanical properties and fatigue and creep properties of the alloy. At the same time, the nano-sized grains and the micron-sized grains formed by nucleation and growth after annealing produce a synergistic effect, improving the low-temperature plasticity while maintaining the high-temperature strength of the material; 3. In the method according to the embodiments of the present invention, asynchronous rolling is combined with accumulative roll bonding. Repeated asynchronous rolling ensures the formation of a layered coarse grain band during the final local recrystallization heat treatment, increasing the interface between the coarse grains and the nano grains, and giving full play to the synergistic strengthening effect of the coarse grains and the nano grains in the nano-heterogeneous structure; 4. The method according to the embodiments of the present invention can prepare nano-scale precipitated phases, titanium grains, and micron-scale lamellar titanium grains embedded therein, which can be realized only by using conventional equipment and tooling, and has great industrial application prospects.

[0014] In some embodiments, the cogging forging includes: heating the ingot obtained by vacuum melting to 925 - 950 °C, holding for 1 - 3 h, then taking it out of the furnace for 1 - 2 passes of forging to complete reverse three-upsetting and three-drawing, with the deformation amount per pass being greater than 50%; and / or, before performing the cogging forging, holding the ingot obtained by vacuum melting at 450 - 550 °C for 0.5 - 5 h.

[0015] In some embodiments, the hot rolling and thinning includes forging the ingot obtained by cogging forging into a slab and then hot rolling it at 650 - 800 °C to obtain a thin sheet with a thickness of 1 - 2 mm.

[0016] In some embodiments, the ratio of the upper and lower rolling speeds in the asynchronous rolling is 1.1 - 1.4, the thickness change per pass is not less than 0.1 mm, and the thin sheet is reversed and rolled between passes until the thickness is halved to obtain a thin sheet. Preferably, the asynchronous rolling is completed at room temperature.

[0017] In some embodiments, the accumulative roll bonding includes cutting the thin sheet obtained by asynchronous rolling into two halves, stacking the thin sheets, heating them to 200 - 500 °C, holding for 5 - 10 min, and symmetrically rolling them until the thickness is halved to bond them.

[0018] In some embodiments, the above processes of asynchronous rolling and accumulative roll bonding are repeated until the thickness of the last rolling is 0.2 - 0.4 mm.

[0019] In some embodiments, the heat treatment includes cooling the obtained sheet and then annealing it at 400 - 500 °C for 4 - 6 min. Description of the Drawings

[0020] Figure 1 It is a transmission electron microscope image of the titanium alloy obtained in Example 1. Detailed Embodiments

[0021] The embodiments of the present invention will be described in detail below. The examples are shown in the accompanying drawings. The embodiments described below with reference to the drawings are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0022] A high-strength titanium alloy according to an embodiment of the present invention comprises 0.01 - 0.3% of silicon, 0.01 - 0.49% of scandium, and 0.01 - 0.49% of lutetium, with the balance being titanium and inevitable impurities, by mass percentage.

[0023] By adding a trace amount of scandium element, the high-strength titanium alloy according to an embodiment of the present invention can effectively increase the recrystallization temperature, high-temperature strength, and structural stability of the titanium alloy; by adding silicon element and scandium element simultaneously in the alloy, the two can form a solid solution or precipitation phase in the matrix. On the one hand, it can hinder the growth of titanium grains, increasing the proportion of nanocrystals in the product to about 75%, effectively improving the comprehensive performance of the alloy. On the other hand, both the solid solution or precipitation phase formed by silicon and scandium can strengthen the alloy, significantly improving the mechanical properties of the titanium alloy. However, if the addition amounts of silicon and scandium are too much, coarse precipitation phases will be formed, reducing the performance of the titanium alloy; adding an appropriate amount of lutetium element in the alloy can reduce or even eliminate the grain boundary segregation of scandium element. Even if a small amount of scandium element is introduced, the strength of the titanium alloy can be greatly improved, and to a certain extent, the addition amount of scandium element can be increased, which has a great strengthening effect on the nano-structured titanium alloy.

[0024] In some embodiments, preferably, the mass percentages of silicon, scandium, and lutetium satisfy the relationship: 0.24% ≤ [Si] + [Sc] + [Lu] ≤ 1.2%.

[0025] In the embodiments of the present invention, making the usage amounts of silicon, scandium, and lutetium elements satisfy the above relationship is beneficial to exert the synergistic effect between the elements and further improve the comprehensive performance of the titanium alloy.

[0026] In some embodiments, preferably, the high-strength titanium alloy comprises: 0.01 - 0.2% of silicon, 0.3 - 0.4% of scandium, and 0.2 - 0.3% of lutetium.

[0027] In the embodiments of the present invention, the contents of scandium and lutetium elements are optimized, which can further improve the performance of the titanium alloy; if the addition amount of scandium is too small, it is easily burned out, and the strengthening effect is very limited; when the lutetium content is within a suitable range, even if the content of scandium element is increased, the plasticity of the alloy does not decrease significantly, which is beneficial to improving the comprehensive performance of the titanium alloy.

[0028] The embodiment of the present invention also provides a preparation method of a high-strength titanium alloy, which includes vacuum melting, cogging forging, hot rolling thinning, asynchronous rolling, accumulative roll bonding, and heat treatment in sequence.

[0029] In the preparation method of the high-strength titanium alloy according to the embodiment of the present invention, large-deformation plastic deformation is carried out through asynchronous rolling and accumulative roll bonding to achieve the purpose of crushing the precipitated phase and refining the grains, forming micron-sized grains; repeated rolling can effectively refine the pure titanium grains to the sub-micron and nano scales, and make the precipitated phase uniformly distributed between the fine pure titanium grains at the sub-micron scale, effectively improving the high-temperature mechanical properties, fatigue and creep properties of the alloy. At the same time, the nano-grains and the micron-sized grains formed by nucleation and growth after annealing produce a synergistic effect, improving the low-temperature plasticity while maintaining the high-temperature strength of the material; combining asynchronous rolling with accumulative roll bonding, repeated asynchronous rolling ensures the formation of a layered coarse-grain band during the last-step local recrystallization heat treatment, increasing the interface between the coarse grains and the nano-grains, and giving full play to the synergistic strengthening effect of the coarse grains and the nano-grains in the nano-heterogeneous structure; it can prepare nano-scale precipitated phases, titanium grains and micron-scale lamellar titanium grains embedded therein, which can be realized only by using conventional equipment and tooling, and has great industrial application prospects.

[0030] In some embodiments, preferably, the cogging forging includes: heating the ingot obtained by vacuum melting to 925-950 °C, holding for 1-3 h, then taking it out of the furnace for 1-2 forging passes, with the deformation amount per pass being greater than 50%, and completing three upsetting and three drawing operations with reversed directions; and / or, before performing the cogging forging, holding the ingot obtained by vacuum melting at 450-550 °C for 0.5-5 h.

[0031] In the method of the embodiment of the present invention, a unidirectional deformation amount greater than 50% per pass is adopted in the cogging forging, which can effectively promote grain deformation and achieve nano-scale dynamic recrystallization. If the unidirectional deformation amount per pass is less than 50%, the insufficient deformation amount makes it difficult to obtain nano-scale grains.

[0032] In some embodiments, preferably, the hot rolling thinning includes hot rolling the ingot obtained by cogging forging into a slab at 650-800 °C to obtain a thin plate with a thickness of 1-2 mm.

[0033] In some embodiments, preferably, the upper and lower rolling speeds of the asynchronous rolling are in the ratio of 1.1-1.4, the thickness change per pass is not less than 0.1 mm, and the thin plate is reversed and rolled between each pass until the thickness is halved to obtain a thin sheet. Preferably, the asynchronous rolling is completed at room temperature.

[0034] In the embodiments of the present invention, a thickness change of not less than 0.1 mm per pass is adopted in each rolling, which can effectively promote grain deformation and achieve nano-scale dynamic recrystallization. If the thickness change per pass is less than 0.1 mm, the deformation is insufficient and it is difficult to obtain nano-scale grains. Further preferably, rolling at room temperature can effectively prevent the growth of recrystallized grains, enabling more grains to be maintained at the nano-scale and strengthening the material more effectively.

[0035] In some embodiments, preferably, the accumulative roll bonding includes cutting the thin sheet obtained by asynchronous rolling in half, stacking the thin sheets, heating them to 200 - 500 °C and holding for 5 - 10 min, and symmetrically rolling to half the thickness to bond them.

[0036] In some embodiments, preferably, the above processes of asynchronous rolling and accumulative roll bonding are repeated until the final rolling thickness is 0.2 - 0.4 mm.

[0037] In some embodiments, preferably, the heat treatment includes annealing the obtained sheet at 400 - 500 °C for 4 - 6 min after cooling.

[0038] In the embodiments of the present invention, annealing the sheet can promote the growth of some nano-grains to the micron scale while eliminating internal stress. The temperature and time of the heat treatment can be adjusted according to the specifications of the sample. Samples with smaller weight and volume can be heat-treated at a lower temperature for a shorter time, while samples with larger weight and volume can be heat-treated at a higher temperature for a longer time to ensure that the internal stress of the sample can be completely eliminated by the heat treatment.

[0039] The present invention will be described in detail below with reference to specific embodiments and drawings.

[0040] Example 1

[0041] (1) Vacuum melting is carried out by a vacuum consumable arc furnace, and then the obtained ingot is held at 500 °C for 5 hours.

[0042] (2) Blooming forging: The ingot is heated to 925 °C, taken out of the furnace for forging after holding for 3 hours, and three upsetting and three drawing operations are completed with two heat treatments, and the unidirectional deformation amount per heat treatment is 51%.

[0043] (3) Hot rolling and thinning: The ingot obtained by blooming forging is forged into a slab and then hot-rolled to obtain a thin sheet with a thickness of 2 mm.

[0044] (4) Asynchronous rolling: The obtained thin sheet is subjected to asynchronous rolling at room temperature with an upper and lower rolling speed ratio of 1.3, the thickness change per pass is 0.1 mm, and the thin sheet is flipped and reversed for rolling between each pass until the thickness is halved to obtain a thin sheet.

[0045] (5) Cumulative roll bonding: Cut the thin sheet into two halves, stack the thin sheets, heat them to 500 °C and keep them at this temperature for 10 minutes, then symmetrically roll them until the thickness is halved. Then repeat the above asynchronous rolling process, and continue to repeat the processes of slicing and stacking, annealing, adhesive rolling, and asynchronous rolling for several times. Finally, roll them to a thickness of 0.3 mm in the last rolling;

[0046] (6) After cooling the obtained sheet, anneal it at 475 °C for 5 minutes to obtain a titanium alloy.

[0047] Perform scanning electron microscope characterization on the titanium alloy prepared in Example 1, and the results are as Figure 1 shown. It can be seen from this figure that the prepared titanium alloy has a nano-structured heterogeneous structure, which can effectively improve the high-temperature strength, low-temperature plasticity, fatigue, and creep properties of the titanium alloy.

[0048] The alloy composition of the alloy prepared in Example 1 is shown in Table 1, and the performance is shown in Table 2.

[0049] Example 2

[0050] (1) Conduct vacuum melting through a vacuum consumable arc furnace, and then keep the obtained ingot at 500 °C for 0.5 hour.

[0051] (2) Blooming forging: Heat the ingot to 950 °C, take it out of the furnace for forging after keeping it at this temperature for 1 hour, complete three upsetting and three drawing operations with reverse direction in one heat, and the unidirectional deformation amount for each heat is 65%;

[0052] (3) Hot rolling for thickness reduction: Forge the ingot obtained by blooming forging into a slab, and then hot roll it to obtain a thin sheet with a thickness of 2 mm;

[0053] (4) Asynchronous rolling: Perform asynchronous rolling on the obtained thin sheet at room temperature with an upper and lower rolling speed ratio of 1.1. The thickness change per pass is 0.3 mm, and the thin sheet is flipped and rolled in the reverse direction between each pass until the thickness is halved to obtain a thin sheet;

[0054] (5) Cumulative roll bonding: Cut the thin sheet into two halves, stack the thin sheets, heat them to 450 °C and keep them at this temperature for 11 minutes, then symmetrically roll them until the thickness is halved. Then repeat the above asynchronous rolling process, and continue to repeat the processes of slicing and stacking, annealing, adhesive rolling, and asynchronous rolling for several times. Finally, roll them to a thickness of 0.2 mm in the last rolling;

[0055] (6) After cooling the obtained sheet, anneal it at 400 °C for 6 minutes to obtain a titanium alloy.

[0056] The alloy composition of the alloy prepared in Example 2 is shown in Table 1, and the performance is shown in Table 2.

[0057] Example 3

[0058] (1) Conduct vacuum melting through a vacuum consumable arc furnace, and then keep the obtained ingot at 500 °C for 3 hours;

[0059] (2) Blooming forging: Heat the ingot to 935 °C, keep it warm for 2 hours and then take it out of the furnace for forging. Complete the three-upsetting and three-drawing with reverse direction in one heat, and the single-direction deformation amount for each heat is 60%;

[0060] (3) Hot rolling and thinning: Forge the ingot obtained by blooming forging into a slab and then hot roll it to obtain a thin sheet with a thickness of 2 mm;

[0061] (4) Asynchronous rolling: Complete the asynchronous rolling with a rolling speed ratio of 1.4 between the upper and lower rolls at room temperature for the obtained thin sheet. The thickness change amount for each pass is 0.2 mm. Flip the thin sheet between each pass for reverse rolling until the thickness is halved to obtain a thin sheet;

[0062] (5) Accumulative roll bonding: Cut the thin sheet in half, stack the thin sheets, heat them to 350 °C and keep them warm for 8 minutes, symmetrically roll them until the thickness is halved, and then repeat the above asynchronous rolling process. Continue to repeat the processes of slicing, stacking, annealing, adhesive rolling, and asynchronous rolling for several times. Finally, roll it to a thickness of 0.4 mm;

[0063] (6) Cool the obtained sheet and anneal it at 500 °C for 4 hours to obtain a titanium alloy.

[0064] The alloy composition obtained in Example 3 is shown in Table 1, and the performance is shown in Table 2.

[0065] Examples 4-6

[0066] The method is the same as that of Example 1, except that the alloy compositions are different. Specifically, see Table 1 for the alloy compositions and Table 2 for the performance.

[0067] Comparative Example 1

[0068] The preparation method is the same as that of Example 1, except that the alloy elements are different: the Si element accounts for 0.75 wt.% of the total weight, the Sc element accounts for 0.6 wt.% of the total weight, and the Lu element accounts for 0.5 wt.% of the total weight. The titanium alloy composition obtained in Comparative Example 1 is shown in Table 1, and the performance is shown in Table 2.

[0069] Comparative Example 2

[0070] The method is the same as that of Example 1, except that the alloy elements are different: no Si, Sc, and Lu elements are added. The titanium alloy composition obtained in Comparative Example 2 is shown in Table 1, and the performance is shown in Table 2.

[0071] Comparative Example 3

[0072] The method is the same as that of Example 1, the difference is that no Lu element is added. The titanium alloy composition obtained in Comparative Example 3 is shown in Table 1, and the performance is shown in Table 2.

[0073] Comparative Example 4

[0074] The method is the same as that of Example 1, except that: in step (2), the single-pass deformation amount during cogging forging is 45%, and the properties of the titanium alloy obtained in Comparative Example 4 are shown in Table 2.

[0075] Comparative Example 5

[0076] The method is the same as that of Example 1, except that: in step (4), the thickness change amount per pass during asynchronous rolling is 0.4 mm, and the properties of the titanium alloy obtained in Comparative Example 5 are shown in Table 2.

[0077] Comparative Example 6

[0078] The method is the same as that of Example 1, except that: in step (4), asynchronous rolling is changed to synchronous rolling, and the properties of the titanium alloy obtained in Comparative Example 6 are shown in Table 2.

[0079] Table 1

[0080] Si (%) Sc (%) Lu (%) Titanium and impurities [Si] + [Sc] + [Lu] Example 1 0.11 0.3 0.2 Remainder 0.61 Example 2 0.22 0.35 0.35 Remainder 0.92 Example 3 0.2 0.3 0.2 Remainder 0.7 Example 4 0.1 0.1 0.04 Remainder 0.24 Example 5 0.22 0.25 0.18 Remainder 0.65 Example 6 0.3 0.45 0.42 Remainder 1.17 Comparative Example 1 0.75 0.6 0.5 Remainder 1.85 Comparative Example 2 0 0 0 Remainder 0 Comparative Example 3 0.11 0.12 0 Remainder 0.23 Comparative Example 4 0.11 0.3 0.2 Remainder 0.61 Comparative Example 5 0.11 0.3 0.2 Remainder 0.61 Comparative Example 6 0.11 0.3 0.2 Remainder 0.61

[0081] Table 2

[0082]

[0083] Note: The test conditions for the fatigue limit are: the test frequency is 30 - 50 Hz, and the stress ratio is -1;

[0084] The creep rate refers to the deformation amount per hour under the stress value of 60% of the yield strength at 400°C. For example, 0.0392 / h means the deformation amount per hour is 3.92%; the larger the value, the worse the creep resistance of the material.

[0085] It can be seen from the data in the above table that in Examples 1 - 6, appropriate amounts of silicon, scandium, and lutetium elements are added, and when their contents satisfy the relationship 0.24 ≤ [Si] + [Sc] + [Lu] ≤ 1.2, the alloy has excellent tensile strength while having certain plasticity, and the tensile strength of the alloy at room temperature can reach more than 980 MPa; and the recrystallization temperature of the alloy is increased to more than 440°C, the fatigue limit reaches more than 340 MPa, and the alloy has good creep resistance.

[0086] In Comparative Example 1, excessive amounts of silicon, scandium, and lutetium elements are added, forming coarse precipitation phases in the alloy. Compared with the alloy obtained in Example 1, it not only reduces the tensile strength of the alloy, and the tensile strength at room temperature is only 710 MPa, but also does not have plasticity, and the fatigue limit is reduced to 270 MPa.

[0087] In Comparative Example 2, silicon, scandium, and lutetium elements were not added. Compared with the alloy prepared in Example 1, the comprehensive performance was obviously poor. Although the toughness was improved to a certain extent, the tensile strength decreased, failing to meet the usage requirements. Moreover, the creep rate increased to 0.0464 / h, and the creep resistance was poor.

[0088] In Comparative Example 3, only silicon and scandium elements were added. Its plasticity and creep rate were comparable to those of the alloy prepared in Example 1, but the tensile strength decreased significantly, being only 840 MPa at room temperature, and the fatigue limit also decreased to 300 MPa. The reason is that after not adding lutetium element, there is grain boundary segregation of scandium element in the alloy, which is not conducive to improving the strength of the alloy.

[0089] Comparative Examples 4 to 6 used the same alloying elements as in Example 1, and the only difference was that the relevant preparation parameters were adjusted, and the alloy properties also decreased to varying degrees.

[0090] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0091] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A method for preparing a high-strength titanium alloy, characterized in that, It includes vacuum melting, cogging forging, hot rolling thinning, asynchronous rolling, accumulative roll bonding and heat treatment in sequence. The cogging forging includes: heating the ingot obtained by vacuum melting to 925 - 950 °C, holding for 1 - 3 h, then taking it out of the furnace for 1 - 2 heats of forging, completing three upsetting and three drawing operations with reverse direction, and the deformation amount per heat is greater than 50%. The high-strength titanium alloy includes: 0.01 - 0.3% of silicon, 0.01 - 0.49% of scandium and 0.01 - 0.49% of lutetium, with the balance being titanium and inevitable impurities, by mass percentage.

2. The preparation method of the high-strength titanium alloy according to claim 1, characterized in that, The mass percentages of silicon, scandium and lutetium satisfy the relational expression: 0.24% ≤ [Si] + [Sc] + [Lu] ≤ 1.2%.

3. The preparation method of the high-strength titanium alloy according to claim 1, characterized in that, The high-strength titanium alloy includes: 0.01 - 0.2% of silicon, 0.3 - 0.4% of scandium and 0.2 - 0.3% of lutetium.

4. The preparation method of the high-strength titanium alloy according to claim 1, characterized in that, Before carrying out the cogging forging, the ingot obtained by vacuum melting is held at 450 - 550 °C for 0.5 - 5 h.

5. The preparation method of the high-strength titanium alloy according to claim 1, wherein, The hot rolling thinning includes forging the ingot obtained by cogging forging into a slab and then hot rolling it at 650 - 800 °C to obtain a thin sheet with a thickness of 1 - 2 mm.

6. The preparation method of the high-strength titanium alloy according to claim 1, characterized in that The upper and lower rolling speed ratio of the asynchronous rolling is 1.1 - 1.4, the thickness change per pass is not less than 0.1 mm, and the thin sheet is reversed and rolled in the reverse direction between each pass until the thickness is halved to obtain a thin slice.

7. The preparation method of the high-strength titanium alloy according to claim 1, characterized in that, The asynchronous rolling is completed at room temperature.

8. The preparation method of the high-strength titanium alloy according to claim 1, characterized in that, The accumulative roll bonding includes cutting the thin slice obtained by asynchronous rolling into two halves, stacking the thin slices, heating them to 200 - 500 °C and holding for 5 - 10 min, and symmetrically rolling them until the thickness is halved to make them bond.

9. The preparation method of the high-strength titanium alloy according to any one of claims 1 to 8, characterized in that, Repeat the above processes of asynchronous rolling and accumulative roll bonding until the thickness of the last rolling is 0.2 - 0.4 mm.

10. The preparation method of the high-strength titanium alloy according to claim 9, characterized in that, The heat treatment includes cooling the obtained sheet and then annealing it at 400 - 500 °C for 4 - 6 min.

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