A method for improving the strength and plasticity of TiAl alloys based on superimposed deformation during cooling and isothermal treatment, and a TiAl alloy with high strength and plasticity

Abstract

The present invention belongs to the technical field of high-temperature light alloy processing, and particularly relates to a method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation and a TiAl alloy with high strength and plasticity. The method of the present invention comprises the following steps: subjecting a specimen of a TiAl alloy ingot to multiple axial compressions; heating the specimen to a set temperature and holding it before each compression, and then performing the compression, and cooling to room temperature after each compression; as the number of compressions increases, the set temperature gradually decreases, and the compression ratio gradually decreases or the compression ratio remains unchanged first and then gradually decreases. The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation of the present invention has stable technology, can greatly reduce the size of brittle β0 phase, and does not overly refine the lamellar cluster grains, and can effectively improve the room temperature plasticity and hot working performance of TiAl alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature light alloy processing, and particularly relates to a method for improving the strength and plasticity of TiAl alloy based on superimposed deformation of cooling and isothermal treatment, and a high-strength and high-plasticity TiAl alloy. Background Art

[0002] γ-TiAl-based alloys have lower density and specific strength, and their high-temperature strength, creep resistance and oxidation resistance have considerable development potential. However, one of the biggest obstacles restricting the practical application and popularization of TiAl-based alloys at present is their poor room-temperature plasticity and hot workability.

[0003] Lamellar clusters with different orientations and a large number of brittle β0 phases are the main restricting factors. The room-temperature plasticity can be effectively improved by refining grains through forging and rolling composite technology, but the high deformation temperature requires high equipment requirements and has poor controllability of deformation parameters. High-temperature long-term heat treatment can eliminate the β0 phase, but also inhibits the lubricating effect of the B2 phase under high-temperature deformation conditions. Therefore, it is worth exploring how to promote the nanocrystallization of β0 phases at the boundaries of lamellar clusters while slightly refining the size of lamellar clusters. This method combines the advantages of coarse grains and fine grains, and makes the alloy contain rich nanostructures, which will help to improve the deficiencies of TiAl alloys under room-temperature and hot-working conditions. There is a literature disclosure of a scheme for refining alloy grains by low-temperature pre-deformation and isothermal heat treatment. However, the isothermal heat treatment temperature (1280-1320 °C) is higher than the pre-deformation temperature (900 °C), and the grains are likely to grow under the heat treatment conditions of high temperature and long time, thus weakening the grain-refining effect of pre-deformation. Another literature discloses a method of making only fine lamellar structures exist in TiAl alloys through creep forming and heat treatment. Although this method helps to improve room-temperature ductility, the beneficial effect of β0 phases on hot workability is also inhibited. In addition, through powder metallurgy, a microstructure with a heterogeneous structure can be designed and prepared, but the mechanical properties of the prepared alloy are unstable due to the influence of the quality of alloy powder and porosity.

[0004] Therefore, it is urgent to seek a processing method with stable technology, which can greatly reduce the size of brittle β0 phases and does not overly refine the grains of lamellar clusters to effectively improve the room-temperature plasticity and hot workability of TiAl alloys. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the strength and plasticity of TiAl alloy based on superimposed deformation of cooling and isothermal treatment, and a high-strength and high-plasticity TiAl alloy, so as to help stably improve the room-temperature plasticity and / or hot workability of TiAl alloys.

[0006] To achieve the above object, the present invention provides the following technical solution: A method for improving the strength and plasticity of TiAl alloy based on superposition of cooling and isothermal deformation, comprising the following steps: subjecting a sample of TiAl alloy ingot to multiple axial compressions; heating the sample to a set temperature and holding it before each compression, and then compressing it, and cooling it to room temperature after each compression; as the number of compressions increases, the set temperature gradually decreases, and the compression ratio gradually decreases or first remains unchanged and then gradually decreases.

[0007] Preferably, the set temperature is a temperature value below the lower limit temperature of the transformation temperature T e at which the sample transforms from the γ phase to the α phase; the cooling method is air cooling.

[0008] Preferably, the number of compressions is 3 - 7 times, the difference in the set temperature before adjacent compressions is 10 - 100 °C; the difference in the compression ratio between adjacent compressions is 0 - 15%, and the difference in the compression ratio between adjacent compressions first increases and then decreases as the number of compressions increases.

[0009] Preferably, the set temperatures are successively 1170 - 1220 °C, 1130 - 1170 °C, 1080 - 1130 °C, 1030 - 1080 °C, and 930 - 980 °C as the number of compressions increases; calculated based on the initial height of the sample, the compression ratios are successively 22% - 27%, 22% - 27%, 12% - 17%, 7% - 12%, and 3% - 7% as the number of compressions increases.

[0010] Preferably, the compression rate for each time is 0.001 - 0.05 s -1 ; the holding time is 10 - 30 min.

[0011] Preferably, the heating and compression are carried out in a heating furnace of a universal testing machine under vacuum conditions.

[0012] Preferably, the sample is cylindrical, a positive thermocouple and a negative thermocouple are welded on the sample, and the upper and lower end faces of the sample are respectively in close contact with nickel-based alloy pads of the universal testing machine; in the height direction of the sample, the positive thermocouple and the negative thermocouple are arranged at the central position of the sample.

[0013] Preferably, the elemental composition of the TiAl alloy ingot includes, in atomic percentage: Al 46% - 50%, Cr 2% - 6%, Re 0.2% - 1.2%, and Ru 0 - 2%.

[0014] Preferably, the TiAl alloy ingot is obtained by vacuum arc melting; the raw materials of the TiAl alloy ingot include: sponge Ti particles or sponge Ti blocks; Al particles with a particle size of 2-3 mm and a purity of 99.99 wt.%; Cr particles with a particle size of 2-3 mm and a purity of 99.99 wt.%; Ru powder with a purity of 99.999 wt.%; Re powder with a purity of 99.999 wt.%.

[0015] The present invention also provides a high-plasticity TiAl alloy, which adopts the following technical solution: a high-plasticity TiAl alloy is processed by the method as described above.

[0016] Beneficial effects:

[0017] The method for improving the high plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation in the present invention is technically stable, can greatly reduce the size of brittle β0 phase, and does not overly refine the lamellar cluster grains, effectively improving the room-temperature plasticity and hot-working performance of TiAl alloy.

[0018] The method for improving the high plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation in the present invention can retain the micro / nano defects such as nano twins and dislocations formed in the TiAl alloy after each compression, and will not annihilate due to the re-elevation of temperature. Therefore, the finally prepared alloy specimens accumulate abundant micro-nano defects, and these nano structures are beneficial to activating more dislocation slips and fully coordinating the plastic deformation of the alloy under external force.

[0019] The present invention adopts the method of sequential cooling and isothermal axial compression to promote the corresponding changes in the microstructure of TiAl alloy under different compression conditions, that is, the continuous accumulation of micro-nano defects (these abundant defects are the channels of dislocation slip, the nucleation sites of stacking faults and nano twins, and important factors for improving the room-temperature and high-temperature plasticity of the alloy), the refinement of lamellar cluster grains, the gradual nanocrystallization of B2 phase, and the dynamic recrystallization of equiaxed γ phase. These microstructure changes provide room for the improvement of room-temperature plasticity and hot-working performance.

[0020] The method for improving the high plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation provided by the present invention combines heat treatment and hot deformation at the same time, enabling the alloy to experience timely heat preservation and low-degree deformation at a temperature below the γ→α phase transformation, avoiding the cracking of the alloy caused by uneven heating and severe deformation. The compression deformation temperature and deformation amount are sequentially reduced to ensure that the micro-nano defects induced by each compression deformation are retained, which is beneficial to improving the room-temperature and high-temperature plasticity of the alloy below 950 °C.

[0021] The preparation method provided by the present invention has a simple process. The heating-up time and heat-preservation time can be accurately set by a computer. The cost of the preparation process is low and the energy consumption is small. Multiple deformed alloy specimens can be prepared quickly.

[0022] The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation in the present invention can enable the prepared high-strength and high-plasticity TiAl alloy to have good room-temperature compression and high-temperature tensile properties. This deformation method that improves strength and plasticity simultaneously enriches the hot working technology of TiAl alloy, improves the shortcoming of TiAl alloy in room-temperature plasticity, and is expected to promote the multi-directional application of TiAl alloy in military fields such as aerospace, automobiles, and airplanes.

[0023] The high-strength and high-plasticity TiAl alloy of the present invention has a network structure formed by nano B2 phase and equiaxed γ phase wrapping fine lamellar clusters. Compared with the as-cast TiAl alloy, its room-temperature compression strength is increased from 1919.4 MPa to 2536.5 MPa, and the compression strain is significantly increased from 32.9% to 42.6%; at 850 °C, the tensile strength of the TiAl alloy is increased from 403.5 MPa to 505.7 MPa, and the elongation is increased from 3.5% to 5.3%. The room-temperature and high-temperature mechanical properties of the alloy are significantly improved. Description of the Drawings

[0024] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention. Among them:

[0025] Figure 1 is a flow chart of the method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation according to an embodiment of the present invention;

[0026] Figure 2 is a comparison diagram of the macroscopic microstructures of the TiAl alloys in Comparative Example 1 and Example 1; among them, (a) is the macroscopic microstructure photo of the TiAl alloy in Comparative Example 1, and (b) is the macroscopic microstructure photo of the high-strength and high-plasticity TiAl alloy in Example 1;

[0027] Figure 3 is a comparison diagram of the macroscopic microstructures of the TiAl alloys in Comparative Example 2 and Example 1; among them, (a) is the macroscopic microstructure photo of the TiAl alloy in Comparative Example 2, and (b) is the macroscopic microstructure photo of the high-strength and high-plasticity TiAl alloy in Example 1;

[0028] Figure 4 is the microscopic microstructure photo of the TiAl alloy under the original as-cast condition; among them, (a) is the scanning electron microscope image, and (b) is the partial enlarged image of the red square area in (a);

[0029] Figure 5 At 1200 °C, under a constant strain rate of 0.01 s -1 , after holding for 20 min, the TiAl alloy was compressed downward by 25% of the original height, and the obtained microstructure group picture of the TiAl alloy; among them, (a) is a scanning electron microscope image, and (b) is a partial enlarged image of the red box area in (a);

[0030] Figure 6 At 950 °C, under a constant strain rate of 0.01 s -1 , after holding for 20 min, after the first four compression deformations, the TiAl alloy was further compressed downward by 5% of the original height, and the obtained microstructure picture of the TiAl alloy; among them, (a) is a scanning electron microscope image, (b) is a partial enlarged image of the red box area in (a); (c) is a bright field image of dislocations and nano-twins in the deformed TiAl alloy taken by a transmission electron microscope;

[0031] Figure 7 It is a graph of the mechanical property test results of the TiAl alloy in the comparative example and the example; among them, (a) is the room temperature compression property test results of the as-cast TiAl alloy, the TiAl alloys of Comparative Examples 1-4, and the high-strength and ductile TiAl alloy of Example 1; (b) is the tensile property test results of the as-cast TiAl alloy, the TiAl alloys of Comparative Examples 1-4, and the high-strength and ductile TiAl alloy of Example 1 at 850 °C. Detailed implementation manners

[0032] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0033] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0034] Aiming at at least one of the problems existing in the current TiAl alloy, such as poor room temperature plasticity and / or hot working performance, limited improvement effect of the existing process on the room temperature plasticity and / or hot working performance of the TiAl alloy, and poor stability of the existing improvement process, the present invention provides a method for improving the high strength and ductility of the TiAl alloy based on the superposition of cooling and isothermal deformation and a high-strength and ductile TiAl alloy.

[0035] The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation in the embodiments of the present invention includes the following steps: performing multiple axial compressions on the specimen of the TiAl alloy ingot. Before each compression, first heat the specimen to a set temperature and hold it for a certain time, and then perform the compression. After each compression, cool the specimen to room temperature. As the number of compressions increases, the set temperature gradually decreases, and the compression ratio gradually decreases or first remains unchanged and then gradually decreases. Among them, there are two purposes for cooling to room temperature after each compression: on the one hand, cooling to room temperature can obtain room temperature structure, and the structure is more stable. If cooled to a higher temperature, the retained structure is a metastable structure, and the microstructure and mechanical properties are unstable. On the other hand, cooling to room temperature after each compression is convenient for comparing between microstructures, and there is no variable of cooling temperature.

[0036] When the method of the present invention modifies the original as-cast structure (TiAl alloy ingot), it can not only slightly refine the lamellar colony size and retain a small amount of B2 phase, but also retain nano-structures such as dislocations and nano-twins (the method of the present invention can retain the micro / nano defects such as nano-twins and dislocations formed in the TiAl alloy after each compression deformation, and will not annihilate due to the increase in temperature again. Therefore, the finally prepared alloy specimen accumulates rich micro-nano defects, and these nano-structures are beneficial to activating more dislocation slips and fully coordinating the plastic deformation of the alloy under external force). The present invention adopts the method of sequential cooling and isothermal axial compression to promote the corresponding changes in the microstructure of the TiAl alloy under different deformation conditions, that is, the continuous accumulation of micro-nano defects, the refinement of lamellar colony grains, the gradual nano-sizing of the B2 phase, and the dynamic recrystallization of equiaxed γ phase. These microstructure changes provide room for improving the room temperature plasticity and hot working performance. Among them, the sequential decrease of the set temperature (i.e., the compression temperature of the specimen) and the compression ratio is to ensure that the micro-nano defects induced by each compression deformation are retained, which is beneficial to improving the room temperature and high temperature plasticity below 950 °C of the alloy.

[0037] In addition, the present invention realizes large plastic deformation by stepwise compressing the as-cast TiAl alloy, avoids excessive work hardening and cracking of the alloy during a single deformation process, helps to reduce stress concentration, and ensures the macroscopic uniformity of the microstructure.

[0038] The present invention accumulates the micro-nano defects generated in each cooling-isothermal deformation process through the process of sequential cooling and then isothermal compression at this temperature. These rich defects are the channels for dislocation slip, the nucleation sites of stacking faults and nano-twins, and are important factors for improving the room temperature and high temperature plasticity of the alloy. The method of the present invention has a simple process, the heating and holding time can be accurately set by a computer, the cost of the preparation process is low, the energy consumption is small, and the efficiency is high (it can quickly process multiple specimens).

[0039] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposed deformation of the present invention, the set temperature is determined according to the transformation temperature T of the specimen from the γ phase to the α phase e and its upper and lower limit temperatures (i.e., the lowest temperature and the highest temperature for the transformation of the γ phase to the α phase).

[0040] Preferably, the set temperature is a temperature value below the lower limit temperature of the transformation temperature T of the specimen from the γ phase to the α phase e . The method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposed deformation of the present invention combines heat treatment and hot deformation at the same time, enabling the alloy to undergo timely heat preservation and low-degree deformation at a temperature below the γ→α phase transformation, avoiding cracking of the alloy caused by uneven heating and severe deformation. In addition, by making the set temperature lower than the lower limit temperature of T e (i.e., lower than the lowest temperature for the transformation of the γ phase to the α phase), it helps to ensure that no γ→α phase transformation occurs during the deformation of the TiAl alloy, enabling a sufficient amount of γ phase to form a large number of nano-defects such as dislocations and nano-twins.

[0041] Preferably, the lower limit temperature of T e - 10°C ≤ set temperature ≤ the lower limit temperature of T e - 300°C.

[0042] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposed deformation of the present invention, the cooling method is air cooling. Among them, the cooling method or rate has a great influence on the microstructure of the TiAl alloy; when water cooling or a greater cooling rate is adopted, the solidification path of the alloy often deviates from equilibrium solidification to a greater extent, so metastable phases or intermediate phases will form, and due to their instability, the microstructure and mechanical properties of the alloy are greatly affected by temperature or solidification rate. Secondly, a higher cooling rate generates greater phase transformation stress, which may cause cracking of the alloy; while a smaller cooling rate will increase the grain size in the alloy, resulting in a coarser microstructure of the alloy, and due to the lower driving force, some precipitation phase formation conditions may not be met, and the mechanical properties of the alloy cannot be further enhanced.

[0043] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposed deformation of the present invention, the number of compressions is 3 - 7 times, the difference in the set temperature before two adjacent compressions is 10 - 100°C; the difference in the ratio of two adjacent compressions is 0 - 15%, and as the number of compressions increases, the difference in the ratio of two adjacent compressions first increases and then decreases. Among them, the number of compressions will affect the performance of the TiAl alloy, because increasing the number of compressions will further refine the microstructure of the alloy, but this refinement of the microstructure has a limited effect on improving the mechanical properties. Beyond a certain range, the refinement of the microstructure brought about by increasing the number of compressions has a smaller impact on the mechanical properties.

[0044] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation of the present invention, the set temperatures are successively 1170 - 1220 °C (for example, 1170 °C, 1180 °C, 1190 °C, 1200 °C, 1210 °C or 1220 °C), 1130 - 1170 °C (for example, 1130 °C, 1140 °C, 1150 °C, 1160 °C or 1170 °C), 1080 - 1130 °C (for example, 1080 °C, 1090 °C, 1100 °C, 1110 °C, 1120 °C or 1130 °C), 1030 - 1080 °C (for example, 1030 °C, 1040 °C, 1050 °C, 1060 °C, 1070 °C or 1080 °C) and 930 - 980 °C (for example, 930 °C, 940 °C, 950 °C, 960 °C, 970 °C or 980 °C) as the number of compression times increases; calculated based on the initial height of the specimen, the compression ratios are successively 22% - 27% (for example, 22%, 23%, 24%, 25%, 26% or 27%), 22% - 27% (for example, 22%, 23%, 24%, 25%, 26% or 27%), 12% - 17% (for example, 12%, 13%, 14%, 15%, 16% or 17%), 7% - 12% (for example, 7%, 8%, 9%, 10%, 11% or 12%) and 3% - 7% (for example, 3%, 4%, 5%, 6% or 7%) as the number of compression times increases. The method of the present invention enables the TiAl alloy to be pressed down by 80% of the original height under the condition of multiple superpositions of cooling and isothermal (if not limited by the experimental equipment itself, the TiAl alloy can undergo more than 80% plastic deformation by adopting this deformation method); appropriate heat preservation is carried out before each isothermal compression, and the amount of downward pressure decreases successively, effectively avoiding cracking of the TiAl alloy due to stress concentration.

[0045] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposed deformation of the present invention, the number of compressions is 5 times, and the set temperatures are successively 1200 °C, 1150 °C, 1100 °C, 1050 °C and 950 °C as the number of compressions increases; calculated based on the initial height of the specimen, the compression ratios are successively 25%, 25%, 15%, 10% and 5% as the number of compressions increases. The method of the present invention enables the TiAl alloy to be pressed down by 80% of the original height under the condition of multiple cooling and isothermal superposition; appropriate heat preservation is carried out before each isothermal compression, and the pressing amount decreases successively, effectively avoiding cracking of the TiAl alloy due to stress concentration. If not limited by the experimental equipment itself, the TiAl alloy can undergo plastic deformation of more than 80% by adopting this deformation method. Among them, in this preferred embodiment, the step of compression at 1000 °C is omitted; however, when the compression temperature is reduced from 1050 °C to 950 °C (that is, the temperature is reduced by 100 °C), the TiAl alloy still has good plastic deformation ability and does not crack. In addition, the step of compression at 1000 °C can also be added as needed.

[0046] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposed deformation of the present invention, the compression rate for each time is 0.001 - 0.05 s -1 (for example, 0.001 s -1 , 0.003 s -1 , 0.005 s -1 , 0.008 s -1 , 0.01 s -1 , 0.02 s -1 , 0.03 s -1 , 0.04 s -1 or 0.05 s -1 ); the heat preservation time is 10 - 30 min (for example, 10 min, 15 min, 20 min, 25 min or 30 min). Among them, the compression rate is one of the important factors affecting the mechanical properties of the alloy. It mainly affects the mechanical properties such as the yield strength, compressive strength and plasticity of the alloy by influencing the mechanisms such as dislocation movement, solute atom diffusion and microstructure evolution inside the alloy; in TiAl alloy, a reasonable compression rate range can significantly improve the plasticity and yield strength of the alloy. The heat preservation time will affect the microstructure, mechanical properties and possible defect formation of the alloy, etc.; as the heat preservation time increases, the phases inside the alloy can gradually transform into a more stable γ phase, and the fracture mechanism of the alloy may also change from brittle fracture to the nucleation and aggregation of pores. In addition, too long heat preservation time may lead to the generation of microcracks inside the TiAl alloy. Therefore, the compression rate and heat preservation time during the deformation of TiAl alloy should be reasonably controlled.

[0047] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superimposed deformation of the present invention, heating and compression are carried out under vacuum conditions in the heating furnace of a universal testing machine. The present invention integrates heat treatment technology and hot deformation technology (both heating and compression of the specimen are carried out in the universal testing machine), avoiding heat dissipation during the transfer of TiAl alloy from multiple devices. Each deformation operation is independent, and the actual temperature during specimen compression deformation can be accurately evaluated, ensuring stable plastic deformation of TiAl alloy at a stable deformation temperature.

[0048] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superimposed deformation of the present invention, the specimen is cylindrical, with a positive thermocouple and a negative thermocouple welded to the specimen. The upper and lower end faces of the specimen are in close contact with nickel-based alloy pads of the universal testing machine; in the height direction of the specimen, the positive thermocouple and the negative thermocouple are arranged at the central position of the specimen.

[0049] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superimposed deformation of the present invention, the elemental composition of the TiAl alloy ingot includes, in atomic percentage: Al 46% - 50%

[0050] (e.g., 46%, 47%, 48%, 49% or 50%), Cr 2% - 6% (e.g., 2%, 3%, 4%, 5% or 6%), Re 0.2% - 1.2% (0.2%, 0.4%, 0.6%, 0.8%, 1.0% or 1.2%) and Ru 0 - 2% (e.g., 0, 0.4%, 0.8%, 1.2%, 1.6% or 2%). Among them, an appropriate amount of Cr element can refine the microstructure of the alloy, improve the strength and plasticity of the alloy; the Re element helps to improve the metallurgical quality of the TiAl alloy, reduce the content of defects and impurities, and improve the overall performance and reliability of the alloy; the Ru element promotes the formation of the B2 phase, helps to improve the microstructure, and an appropriate amount of the Ru element can also stabilize the microstructure of the alloy, prevent the precipitation of harmful phases, and thus improve the high-temperature mechanical properties of the alloy; the Al element is the basic element of the TiAl alloy, and the combination of Al and Ti forms intermetallic compounds TiAl and Ti3Al with relatively high strength; in addition, different contents of the Al element will make the alloy have different solidification microstructures, because the Al content will affect the phase composition of the alloy. Therefore, in the present invention, when the Al content varies from 46% to 50%, the corresponding alloy will experience different solidification paths, resulting in different room-temperature solidification microstructures, but within this Al content range, the alloy can be compressed and deformed by the method of the present invention, indicating that its microstructure has good compatibility with deformation. Al has a significant impact on the properties of the alloy in multiple aspects such as strengthening effect, reducing density, improving thermal stability, improving weldability, improving oxidation resistance, and affecting crack propagation mechanism and mechanical properties in the TiAl alloy.

[0051] It should also be noted that the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superimposed deformation of the present invention is also applicable to other titanium-aluminum alloys with element compositions different from those of the above preferred embodiments. This is because the method of the present invention uses a slower compression rate, performs appropriate heat preservation before each compression, and uses a smaller deformation amount for each compression. Therefore, even though the microstructures of the alloy are slightly different under different Al contents, such a deformation method can effectively avoid cracking and high work hardening of the alloy, help the alloy to continuously undergo plastic deformation, and is less sensitive to the microstructure.

[0052] In the preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superimposed deformation of the present invention, the TiAl alloy ingot is obtained by vacuum arc melting; the TiAl alloy ingot is obtained by vacuum arc melting; the raw materials of the TiAl alloy ingot include: sponge Ti particles or sponge Ti blocks; Al particles, the particle size of the Al particles is 2 - 3 mm, and the purity is 99.99 wt.%; Cr particles, the particle size of the Cr particles is 2 - 3 mm, and the purity is 99.99 wt.%; Ru powder, the purity of the Ru powder is 99.999 wt.%; Re powder, the purity of the Re powder is 99.999 wt.%.

[0053] In a preferred embodiment of the method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation of the present invention, the preparation of the TiAl alloy ingot includes the following steps:

[0054] (1) Melting: Wrap Re powder and Ru powder with aluminum foil and place them at the bottom of a water-cooled copper crucible in a vacuum arc melting furnace. Spread Al particles and Cr particles above the aluminum foil, and place sponge titanium blocks at the upper part of the crucible. Close the furnace door of the vacuum arc melting furnace and turn on the circulating cooling water.

[0055] (2) Vacuum pumping treatment: Pump the vacuum arc melting furnace to a vacuum of below 3×10 -3 Pa, and then fill the vacuum arc melting furnace with high-purity argon gas until the pressure in the furnace is 0.05 Pa.

[0056] (3) Arc ignition and temperature rising melting:

[0057] A. After ignition, soften and connect the raw materials by increasing the current from 30 A to 150 A, and then evenly increase the current to 550 A to completely melt all the raw materials to form a homogeneous melt. Slowly reduce the current to 0 A, turn off the power supply, and the first melting is completed.

[0058] B. After the melt obtained from the first melting solidifies and takes shape, turn it over and repeat the melting process 3 times with the same process to ensure the uniformity of chemical composition.

[0059] C. After the melt obtained from step B solidifies and takes shape, perform the last melting: After melting evenly, reduce the current from 550 A to 450 A, and then reduce the current by 30 A every 10 s; when the current is reduced to 300 A, start to slowly lift the tungsten electrode arc gun away from the molten pool and dock it towards the edge of the crucible. Stop retracting the gun until the current is reduced to 150 A, and then reduce the current to 0 A and turn off the power supply.

[0060] D. After the melting is completed, cool it to room temperature to obtain the TiAl alloy ingot.

[0061] Among them, if the pressure in the furnace is lower than 0.05 Pa after filling with high-purity argon in step (2), various elements of the alloy composition during the melting process are likely to volatilize due to the existence of saturated vapor pressure; specifically, due to the relatively large saturated vapor pressure of the Al element, it is more likely to volatilize; this causes the alloy composition after final solidification to deviate from the nominal composition, affecting the microstructure and mechanical properties of the alloy. If the pressure in the melting furnace is higher than 0.05 Pa after filling with argon, the heat generated during the melting process will increase the pressure in the furnace, resulting in air leakage in the furnace, which will increase the oxygen content and have an adverse effect on the alloy. In step C, by making the "current decrease by 30 A every 10 s" (until the current reaches 300 A), the purpose of this is to maintain a uniform decrease in the current, so that the temperature drop of the alloy melt itself is also uniform; "when the current is reduced to 300 A, start to slowly lift the tungsten electrode arc gun away from the molten pool and dock it towards the edge of the crucible", the purpose of this is to slowly raise the arc gun and move it away from the molten pool. The top of the alloy ingot is the last solidified area, which can avoid the formation of pits due to the blowing force of the arc gun and ensure that the top morphology of the alloy ingot is flat and smooth.

[0062] The present invention also proposes a high-strength and ductile TiAl alloy, and the high-strength and ductile TiAl alloy of the embodiment of the present invention is processed by the method as described above. The high-strength and ductile TiAl alloy of the present invention has a room-temperature microstructure in which fine lamellar clusters are surrounded by a network structure composed of a coupled nano B2 phase and recrystallized γ grains (this special structure generates back stress strengthening during stress deformation, which helps to reduce the stress concentration at a single constituent phase or phase interface and promotes the coordinated plastic deformation ability of the alloy). Compared with the original as-cast alloy, it has considerable room-temperature and high-temperature mechanical properties, and the room-temperature plasticity is significantly increased.

[0063] In the following examples: all raw materials are sourced from Beijing Yanbang New Materials Technology Co., Ltd. Among them, the Ti particles are 4N 3×3 mm, the specification model of the Al particles is 4N 3×3 mm, the specification model of the Cr particles is 3N 3-10 mm, the specification model of the Re powder is 4N-325 mesh, and the specification model of the Ru powder is 4N-325 mesh. The titanium particles are obtained by wire drawing and forging after the self-consumption melting of sponge titanium, the aluminum particles are obtained by wire drawing and forging after the remelting of the ingots prepared by the electrolysis method, the chromium particles are obtained by crushing electrolytic chromium blocks, and the Re powder and Ru powder are obtained by redox reactions.

[0064] Example 1

[0065] The method for improving the high-strength and ductility of TiAl alloy based on the superposition of cooling and isothermal deformation in this embodiment includes the following steps:

[0066] Step 1. Calculate the raw material content by atomic percentage, where Al is 48%, Cr is 3%, Re is 0.8%, Ru is 1%, and the balance is Ti. Weigh sponge titanium granules, high-purity Al granules (particle size 2 - 3 mm, purity 99.99 wt.%), high-purity Cr granules (particle size 1 - 2 mm, purity 99.99 wt.%), high-purity Re powder (purity 99.999 wt.%) and high-purity Ru powder (purity 99.999 wt.%), with a total atomic percentage of 100%. Screen and classify the weighed raw materials, and dry the granules in a drying oven to avoid the influence of attached water vapor or other impurities on the melting process.

[0067] Step 2. Melting

[0068] ① Since there are large differences in melting points between Al element and elements such as Re and Ru, the loss of Al element during the heating process is inevitable. Therefore, when configuring the raw materials, set the compensation amount of Al element to 2 wt.% of its added mass. Wrap the weighed Re powder and Ru powder with aluminum foil and place them at the bottom of the water-cooled copper crucible to prevent them from being blown off by the tungsten electrode arc gun during melting. Spread the fine Al granules and Cr granules above the Re powder and Ru powder, and finally place the larger sponge titanium block at the upper part of the crucible. Align the arc gun with the raw materials to be melted, close the furnace door of the arc furnace, and turn on the circulating cooling water. Use the non-consumable vacuum arc melting technology to melt the raw materials and prepare a TiAl alloy ingot.

[0069] ② Vacuum pumping treatment: Turn on the power of the multifunctional arc melting system, and successively use a mechanical pump and a high-speed molecular pump to pump the vacuum degree in the furnace to 3×10 -3 Pa. When the vacuum degree drops below 3×10 -3 Pa, stop running the molecular pump, close the vacuum gauge. After the molecular pump speed reaches 0, fill the furnace with high-purity argon gas until the pressure in the furnace is 0.05 Pa. Filling argon gas can not only remove the residual oxygen in the furnace but also ionize and initiate an arc.

[0070] ③Arc ignition and temperature rise for melting: After ignition during operation, increase the current from 30 A to 150 A to soften and interconnect the raw materials. Then evenly increase it to 550 A to completely melt all the raw materials and form a homogeneous melt. Subsequently, slowly reduce the current to 0 A and turn off the melting power supply, marking the end of the first melting. After the alloy solidifies and takes shape, use a turning ladle to flip the ingot and repeat the melting process 3 times with the same process to ensure the uniformity of the alloy's chemical composition. After the ingot solidifies, conduct the final melting. First, slowly increase the current to 550 A to ensure complete melting of the alloy, then reduce the current to 450 A and start timing. Every 10 s, reduce the current by 30 A. When the current is reduced to 300 A, start slowly lifting the tungsten electrode arc gun away from the molten pool and docking it towards the edge of the crucible. Stop retracting the gun until the current is reduced to 150 A, then reduce the current to 0 A and turn off the power supply. The melting is completed. After the alloy ingot cools to room temperature, open the furnace door to take out the alloy ingot, clean the arc furnace, close the furnace door and re-pump the vacuum to a negative pressure state, and turn off the circulating cooling water. The preparation of the as-cast TiAl alloy ingot is completed.

[0071] Step 3. Determine the compression deformation temperature: Analyze the TiAl alloy sample obtained in Step 2 using differential scanning calorimetry to measure the transformation temperature T of the γ→α phase e and its upper and lower limit temperatures (T e is 1250 °C, its upper limit temperature is 1280 °C, and its lower limit temperature is 1230 °C).

[0072] Step 4. Isothermal / variable temperature compression deformation: Cut several cylindrical specimens with a diameter of 8 mm and a height of 12 mm from the alloy ingot melted in Step 2 using wire cutting. Use sandpaper to polish off the wire cutting marks on the side and upper and lower end faces of the cylinder, and dry it after ultrasonic cleaning. Weld two thermocouples, one positive and one negative, at the center of the cylindrical specimen in the height direction. Place the specimen in the heating furnace, with the upper and lower end faces of the cylinder closely attached to nickel-based alloy pads. After the vacuum degree in the heating furnace on the universal testing machine reaches the standard, raise the furnace temperature to 1200 °C at a rate of 7 °C / s, hold the specimen at this temperature for 20 min, then adjust the compression rate to 0.01 s -1 , and prepare to start compression deformation. When the height of the specimen decreases by 25%, stop compression, take out the specimen and air-cool it.

[0073] Step 5: After the temperature in the furnace drops to 1150 °C, put the alloy specimen cooled to room temperature into the heating furnace again. After holding for 20 min, continue to press down 25% of the original height of the specimen at the same compression rate. After the compression is completed, take out the specimen and air-cool it. After the temperature in the furnace drops to 1100 °C, 1050 °C, and 950 °C respectively, repeat the above operations, but the compression amount is successively reduced to 15%, 10%, and 5%. Until the isothermal compression at 950 °C is completed, take out the alloy specimen and air-cool it to room temperature. The deformed alloy is prepared, and the highly plastic TiAl alloy of this embodiment is obtained. The highly plastic TiAl alloy obtained in this embodiment has been reduced by 80% relative to the original height of the specimen (the original height of the specimen is 12 mm). Turn off the computer, and then turn off the universal testing machine.

[0074] Example 2

[0075] The difference between this embodiment and Example 1 is as follows: In the universal testing machine described in Step 4, the heating rate, heating time, and holding time need to be set at the computer program end, and the compression amount is converted into true strain value and input into the calculation program. Weld two platinum-rhodium thermocouples in the middle of the cylindrical specimen by spot welding to ensure accurate measurement of temperature changes during the hot compression process. The other ends of the two thermocouples are connected to the electrodes on the thermo-mechanical simulation testing machine. Others are the same as in Example 1.

[0076] Example 3

[0077] Figure 1 is a flow chart of a method for improving the high plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation according to an embodiment of the present invention. Refer to Figure 1 , raise the temperature to 1200 °C at a rate of 10 °C / s, hold the prepared TiAl alloy cylindrical specimen (the same as in Example 1) for 20 min, then press down 25% along the height direction, and then air-cool it to room temperature. On this basis, continue to place the cooled alloy specimen at 1150 °C for 20 min, continue to press down 25% of the original height and then air-cool it to room temperature; on this basis, successively hold the alloy specimen at 1100 °C, 1050 °C, and 950 °C for 20 min and then press down 15%, 10%, and 5% of the original height according to the above steps, so that the total compression amount reaches 80% or more. After each compression deformation, air-cool the specimen to room temperature.

[0078] Example 4

[0079] The difference between this embodiment and Example 1 is only that: in Step 1, the raw material content is calculated by atomic percentage, Al is 46%, Cr is 3%, Re is 0.8%, Ru is 1%, and the balance is Ti; the rest are the same as in Example 1.

[0080] Example 5

[0081] The difference between this embodiment and Embodiment 1 is only in Step 1. The raw material content is calculated by atomic percentage, with Al being 50%, Cr being 3%, Re being 0.8%, Ru being 1%, and the balance being Ti; the rest are the same as in Embodiment 1.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Embodiment 1 is only that: in Step 4, after the TiAl alloy is heated to 1200 °C and held for 20 min, it is compressed at a compression rate of 0.01 s -1 to 80% (the height of the specimen decreases by 80% relative to that before compression), and the alloy undergoes one compression deformation (Step 5 is omitted); the rest are the same as in Embodiment 1.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Embodiment 1 is only that: in Steps 4 and 5, the compression ratio each time is 16% (the height of the specimen decreases by 16% each time relative to the original height); the rest are the same as in Embodiment 1.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Embodiment 1 is only that: in Steps 4 and 5, after each compression, the step of cooling the specimen to room temperature is omitted. After the previous compression is completed, the specimen directly undergoes the next compression after the furnace temperature drops to the next set value and is held for 20 min; the rest are the same as in Embodiment 1.

[0088] Comparative Example 4

[0089] The difference between this comparative example and Embodiment 1 is only that: in Steps 4 and 5, after each compression, the specimen is cooled to room temperature by water cooling; the rest are the same as in Embodiment 1.

[0090] Experimental Example

[0091] 1. The as-cast TiAl alloy (rectangular parallelepiped specimen, 8 mm in length, 6 mm in width, and 4 mm in thickness) obtained by melting in Step 2 and the compressed TiAl alloy are respectively cut by wire cutting technology for microstructure observation. The surface to be observed is polished with sandpaper to 2000#, ultrasonically cleaned and dried after mechanical polishing, and the microstructures of the TiAl alloy obtained after the first, first two, first three, first four, and a total of five compression deformations are respectively observed under a scanning electron microscope.

[0092] Figure 2 (a) shows that in Comparative Example 1 at 1200 °C and 0.01 s -1The macroscopic structure of the TiAl alloy obtained by undergoing a 80% compression deformation at a strain rate once. Figure 2 (b) shows the macroscopic structure of the TiAl alloy in Example 1 under a strain rate of 0.01 s -1 and undergoing multi-step cooling / isothermal compression. By comparison, after a large-scale compression deformation once, severe shear cracking occurs at the edge of the alloy, while the TiAl alloy undergoing multi-step cooling / isothermal compression still has a complete edge. This indicates that the method provided by the present invention ensures the ability of the alloy to have continuous plastic deformation without cracking.

[0093] Figure 3 (a) shows the macroscopic structure of the TiAl alloy obtained after undergoing five identical compression ratio deformations in Comparative Example 2. Figure 3 (b) shows the macroscopic structure of the TiAl alloy in Example 1 under a strain rate of 0.01 s -1 and undergoing multi-step cooling / isothermal compression. By comparison, for TiAl alloys undergoing the same compression ratio deformation at different temperatures, their edges still have a tendency to crack. On the contrary, for the TiAl alloy undergoing multi-step cooling / isothermal compression, its edge has a complete contour. The alloy prepared by the method of the present invention has the characteristic of uniform plastic deformation.

[0094] Figure 4 (a) shows the microstructural photograph of the as-cast TiAl alloy obtained by melting in Step 2 in Example 1. Figure 4 (b) is Figure 4 the partial enlarged image of the red box area in (a). The as-cast TiAl alloy is mainly composed of coarse lamellar clusters and γ-phase and B2-phase distributed in a coupled manner. After measurement, the average lamellar size is about 85.20 μm, and the average size of the strip-shaped B2-phase is 10.70 - 14.20 μm. A large number of strip-shaped B2-phases are distributed along the boundaries of the lamellar clusters, dividing the lamellar matrix.

[0095] Figure 5 shows the microstructural photograph of the TiAl alloy (compressed by 25% relative to the as-cast TiAl alloy) obtained by isothermal compression at 1200 °C in Examples 1 - 3. Figure 5 (b) is Figure 5 (a) the partial enlarged image of the red box area in. The as-cast TiAl alloy at 1200 °C, with a strain rate of 0.01 s -1After being compressed by 25% along the height direction at a strain rate of, the lamellae are twisted and bent, and the microstructure is significantly refined. The size of the lamellar clusters is statistically 72.50 μm. The original banded B2 phase appears split and fragmented and is no longer continuously distributed at the boundaries of the lamellar clusters, with an average size of approximately 5.35 μm. And a small amount of recrystallization occurs in the equiaxed γ phase. The TiAl alloy after compression deformation still consists of lamellar clusters, B2 phase, and equiaxed γ phase.

[0096] Figure 6 It is the microstructure of the TiAl alloy obtained by successively isothermally compressing Examples 1 - 3 at 1200 °C, 1150 °C, 1100 °C, and 1050 °C four times and then continuing to compress 5% of the original height after the temperature is reduced to 950 °C. Figure 6 (b) is Figure 6 A partial enlarged view of the red boxed area in (a). Figure 6 (c) is a transmission electron microscope image of the severely plastic TiAl alloy obtained after 5 compression deformations.

[0097] It can be seen from Figure 6 that: after five isothermal compressions, the alloy does not crack and uniform plastic deformation still occurs. Perpendicular to the compression direction, the microstructure has a reticular structure, the size of the lamellar clusters is about 37.70 μm, the average size of the B2 phase is 0.92 μm, and the average size of the equiaxed γ phase is 1.33 μm. The B2 phase at the nanoscale and the fine equiaxed γ phase are alternately distributed around the lamellar clusters, forming a significant size difference with the lamellar clusters. By means of multiple cooling / isothermal superimposed compression deformation, the size of the lamellar clusters can be slightly refined while the B2 phase can be significantly refined to the nanoscale. Such a multi-sized constituent phase promotes the significant diffusion of dislocations, realizes the redistribution of stress, and has a synergistic strengthening and strain localization alleviation effect during the deformation process. From Figure 6 it can be observed in (c) that a large number of dislocations and nano-twins are distributed around the lamellar clusters and nano B2 phase. The aggregation and recovery of dislocations can promote the transformation of the B2 phase and γ grains into recrystallization or substructure during subsequent plastic deformation. During the continuous isothermal / cooling plastic deformation process, defects such as dislocations and nano-twins are retained, and new dislocations and nano-twins are activated and nucleated on the existing defects, releasing excessive deformation stress, which is beneficial to improving the ductility of the alloy.

[0098] 2. Cut three specimens for room-temperature compression and three specimens for high-temperature tension from the TiAl alloy to be tested using wire cutting technology. Conduct mechanical property tests on an electronic universal testing machine respectively, and test each mechanical property three times to reduce experimental errors. Among them, the compression rate selected for room-temperature compression is 0.5 mm / min; for high-temperature tension, the tensile property is tested at 850 °C (this temperature is lower than 950 °C, which can retain the high-density micro-nano defects accumulated after deformation and is also within the service temperature range of the TiAl alloy), and the tensile rate is set at 0.3 mm / min.

[0099] Figure 7 are the room-temperature compression and 850 °C high-temperature tensile property diagrams of the as-cast TiAl alloy, the TiAl alloys of Comparative Examples 1-4, and the TiAl alloy after compression deformation (compressed by 80% relative to the as-cast TiAl alloy) in Example 1.

[0100] From Figure 7 (a), it can be seen that compared with the as-cast alloy, the compression strength of the TiAl alloy prepared in Example 1 increased from 1919.4 MPa to 2536.5 MPa, and the compression strain increased from 32.9% to 42.6% (the properties of the high-strength and high-ductility TiAl alloys obtained in Examples 2 and 3 are equivalent to those in Example 1). The room-temperature compression properties of the TiAl alloys prepared in Comparative Examples 1 and 2 are even lower than those of the as-cast alloy. For Comparative Example 1, the decrease in room-temperature compression performance is due to the stress caused by the high compression ratio exceeding the load-bearing capacity of the alloy. Even if microdefects are formed, their beneficial effects are severely inhibited by stress concentration, and the alloy cracks. For Comparative Example 2, due to the gradual decrease in compression temperature, the ability of the alloy to undergo plastic deformation also decreases. When the same compression ratio is used, severe stress concentration tends to form at low temperatures, and these stress concentration areas are also where cracks initiate and propagate, so the compression strength and compression strain of the alloy cannot be further improved. For Comparative Example 3, since the alloy is cooled to the next compression temperature before reaching room temperature, it will cause the alloy to crack due to uneven internal and external temperatures during cooling. Such a deformation method exacerbates grain coarsening and makes the alloy brittle. For Comparative Example 4, the alloy is water-cooled to room temperature, and compared with air-cooling, the internal stress of the alloy is greater and the compression performance is relatively reduced.

[0101] From Figure 7It can be seen from (b) that, compared with the as-cast alloy, the tensile strength of the deformed TiAl alloy at 850 °C increases from 403.5 MPa to 505.7 MPa, and the elongation increases from 3.5% to 5.3%. Since multi-step isothermal / variable-temperature compression deformation combines heat treatment and hot deformation, rich substructures and defects are introduced when the microstructure changes with deformation, which is more conducive to dislocation slip and multi-configuration coordinated deformation of the alloy during deformation. In addition, as the deformation temperature decreases, the amount of deformation applied to the alloy also decreases. This milder plastic deformation method can ensure that the alloy undergoes large plastic deformation without cracking. The finally obtained microstructure with a reticular structure indeed contains high-density defects. This heterogeneous structure not only improves the strength of the alloy at room temperature and high temperature but also retains good plasticity through the back stress strengthening effect. However, the tensile strength and elongation of the TiAl alloys prepared in Comparative Examples 1, 2, 3, and 4 are relatively reduced.

[0102] The method for improving the strength and plasticity of TiAl alloys based on the superposition of cooling and isothermal deformation provided by the present invention can promote the process parameter design and diversification of the preparation process of TiAl alloys in the field of hot processing, providing a new idea for promoting the application and popularization of TiAl alloys in military engineering fields such as aerospace, automobiles, and airplanes in the future.

[0103] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for improving the strength and plasticity of TiAl alloy based on superposition of cooling and isothermal deformation, characterized in that, The TiAl alloy is compressed axially for multiple times under the condition of superimposing multiple cooling and isothermal processes, with the total compression being more than 80% of the original height, including the following steps: subjecting a sample of the TiAl alloy ingot to multiple axial compressions; heating the sample to a set temperature and holding it before each compression, and then performing the compression, and air-cooling to room temperature after each compression; the strain rate for each compression is 0.001 - 0.05 s -1 ; As the number of compressions increases, the set temperature gradually decreases, and the compression ratio gradually decreases or first remains unchanged and then gradually decreases; The set temperature is a temperature value below the lower limit temperature of the transformation temperature T at which the specimen transforms from the γ phase to the α phase. e ​ 2. The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation according to claim 1, characterized in that The number of compressions is 3 - 7 times, and the difference in the set temperature before adjacent compressions is 10 - 100 °C; the difference in the compression ratio between adjacent compressions is 0 - 15%, and the difference in the compression ratio between adjacent compressions first increases and then decreases as the number of compressions increases.

3. The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation according to claim 2, characterized in that, The set temperatures are successively 1170 - 1220 °C, 1130 - 1170 °C, 1080 - 1130 °C, 1030 - 1080 °C, and 930 - 980 °C as the number of compressions increases; Calculated based on the initial height of the specimen, the compression ratios are successively 22% - 27%, 22% - 27%, 12% - 17%, 7% - 12%, and 3% - 7% as the number of compressions increases.

4. The method for improving the strength and plasticity of TiAl alloy based on cooling and isothermal superposition deformation according to claim 1, characterized in that The heat preservation time is 10 - 30 min.

5. The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation as claimed in claim 1, wherein The heating and compression are carried out in a heating furnace of a universal testing machine under vacuum conditions.

6. The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation as claimed in claim 5, wherein, The specimen is cylindrical, and a positive thermocouple and a negative thermocouple are welded on the specimen, and the upper and lower end faces of the specimen are respectively in close contact with the nickel-based alloy pads of the universal testing machine; In the height direction of the specimen, the positive thermocouple and the negative thermocouple are arranged at the central position of the specimen.

7. The method for improving the strength and plasticity of TiAl alloy based on superposition of cooling and isothermal deformation as claimed in any one of claims 1-6, characterized in that, The elemental composition of the TiAl alloy ingot includes, by atomic percentage: Al 46% - 50%, Cr 2% - 6%, Re 0.2% - 1.2%, and Ru 0 - 2%.

8. The method for improving the strength and plasticity of TiAl alloy based on the superposition of cooling and isothermal deformation according to claim 7, characterized in that The TiAl alloy ingot is obtained by vacuum arc melting; The raw materials of the TiAl alloy ingot include: Sponge Ti particles or sponge Ti blocks; Al particles with a particle size of 2 - 3 mm and a purity of 99.99 wt.%; Cr particles with a particle size of 2 - 3 mm and a purity of 99.99 wt.%; Ru powder with a purity of 99.999 wt.%; Re powder with a purity of 99.999 wt.%.

9. A strong plastic TiAl alloy, characterized in that, The high-strength and high-plasticity TiAl alloy is processed by the method according to any one of claims 1 - 8.

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