A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine-grained structure by medium-temperature constant-load deformation

Abstract

A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant load deformation. The present invention relates to the technical field of high-strength titanium alloys. The present invention aims to solve the technical problem of casting defects in alloys. Method: Prepare an alloy ingot according to the composition of the high-strength β titanium alloy; perform high-temperature forging treatment in five heat cycles to obtain a forged high-strength β titanium alloy; perform solution heat treatment in a single-phase region; perform medium-temperature constant load deformation. The present invention obtains a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure, which has excellent plasticity and extremely high strength. In addition, there are no cracks inside and on the surface of the alloy, showing excellent deformation performance; the method of the present invention makes full use of energy, reduces energy consumption, and improves production controllability, and is simple and easy to operate. The present invention prepares a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure.

Description

Technical Field

[0001] The present invention relates to the technical field of high-strength titanium alloys, and particularly to a medium-temperature constant-load deformation method for preparing a high-strength β-titanium alloy with an ultrafine-grained structure having a two-phase mixture of α-phase and β-phase. Background Art

[0002] Titanium and titanium alloys are widely used in fields such as aerospace, biomedicine, petrochemical industry, and marine ships due to their excellent properties. Among them, high-strength β-titanium alloys have attracted much attention due to their excellent mechanical properties such as high specific strength, corrosion resistance, suitable combination of strength and toughness, and good hardenability. They can replace some high-strength steel structural parts, such as aircraft landing gears or fasteners, etc., reducing the weight of structural parts by 30% - 40%. With the development of technology, people's requirements for materials are getting higher and higher, which has promoted the research on high-strength β-titanium alloys with higher strength and better plasticity.

[0003] Generally, the common means to improve the properties of high-strength β-titanium alloys is to control the alloy microstructure, which can be achieved through various methods, such as heat treatment and thermomechanical processing. Heat treatment can significantly improve the alloy microstructure, and aging treatment in heat treatment can significantly strengthen the alloy; in actual production processes, thermomechanical processing procedures such as forging and rolling are often required, which can reduce alloy defects, improve alloy density, and significantly refine the microstructure at the same time. However, both of these means have their limitations. The heat treatment method has limited grain refinement degree and it is difficult to ensure a good match between strength and toughness; while the thermomechanical processing method becomes difficult to determine because of the narrow hot working range of high-strength β-titanium alloys and their extremely high sensitivity to hot working processes. The microstructure morphology before hot working, hot working temperature, and hot working method will all affect the morphology, distribution, size, etc. of α-phase and β-phase. Unreasonable process design not only cannot significantly improve the alloy properties, but may even cause a sharp deterioration of the properties. And preparing fine-grained materials or even ultrafine-grained materials is a very effective means for improving alloy properties. Fine grain strengthening can simultaneously improve the strength and plasticity of materials, but it often requires high requirements in production processes and consumes a large amount of energy. Summary of the Invention

[0004] The present invention provides a method for preparing a high-strength β-titanium alloy with a two-phase mixture ultrafine-grained structure by medium-temperature constant-load deformation in order to solve the technical problem of casting defects existing in the alloy.

[0005] A processing and forming process of medium-temperature constant-load deformation of the present invention, combined with the pre-set high-temperature forging process and heat treatment process, can effectively reduce internal defects of the alloy, control the alloy microstructure, and finally prepare an alloy with an ultrafine-grained structure. This new method is easy to operate and has strong controllability, which has important significance for the application and popularization of high-strength β-titanium alloys.

[0006] A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant-load deformation, which is specifically carried out according to the following steps:

[0007] I. Weigh sponge titanium, high-purity aluminum, high-purity chromium, high-purity tin, aluminum-molybdenum alloy, aluminum-vanadium alloy and iron nails as raw materials according to the atomic percentages: Al is 2.5% - 4.5%, Mo is 4% - 7%, V is 4.5% - 7.5%, Cr is 2.5% - 4.5%, Sn is 1.5% - 3.5%, Fe is 0.3% - 1.0% and the balance is Ti;

[0008] II. Clean the raw materials obtained in step I, press them into multiple electrodes, then weld them into a consumable electrode, and then use the vacuum consumable electrode melting process to prepare an alloy ingot through two meltings;

[0009] Using the metallographic method, determine that the α / β phase transformation temperature of the alloy ingot is T β ;

[0010] III. Cut off the surface of the alloy ingot obtained in step II, remove the oil stain, and then coat an antioxidant coating on the surface; Keep the alloy ingot at a temperature of (T β + 150 °C) - (T β + 200 °C) for 110 min - 140 min, then carry out ingot forging to make a forged blank, and then air-cool the forged blank to room temperature; Subsequently, keep it at a temperature of (T β + 30 °C) - (T β + 80 °C) for 90 min - 120 min, and then carry out the second forging treatment, and cool it to room temperature with the furnace; At a temperature of (T β - 80 °C) - (T β - 20 °C) for 80 min - 100 min, then carry out the third forging, and cool it to room temperature with the furnace; At a temperature of (T β - 80 °C) - (T β - 20 °C) for 80 min - 100 min, and then carry out the fourth forging, and cool it to room temperature with the furnace; At a temperature of (T β - 100 °C) - (T β - 20 °C) for 80 min - 100 min, and then carry out precision forging to obtain a forged high-strength β titanium alloy; At this time, the structure of the forged high-strength β titanium alloy is uniform and the casting defects are basically eliminated;

[0011] IV. Cut the forged high-strength β titanium alloy obtained in step III to obtain a heat treatment piece, and set the temperature of the heat treatment furnace to (T β + 20 °C) - (T β+(40 °C). After the temperature in the furnace rises to the preset temperature, place the heat-treated part into the heat treatment furnace, keep it warm for 50 min to 120 min, and then air-cool it to room temperature. At this time, the structure of the as-forged high-strength β titanium alloy is a single β phase, and the alloy grain size is coarse.

[0012] V. Process the heat-treated part after the heat treatment in Step IV into several deformed parts. Use an electronic creep and rupture testing machine for the deformation process. Place the deformed part at the exact center position of the indenter of the testing machine, zero the stress, adjust the height of the indenter, then apply a preload pressure of 20 MPa to 50 MPa, fix the deformed part, and then fix a thermocouple at the positions of the upper indenter, lower indenter, and in the middle of the two indenters of the testing machine respectively. Then close the insulation furnace of the testing machine, set the target deformation temperature to 600 °C to 650 °C, and the target load to 450 MPa to 550 MPa. Then heat the furnace at a heating rate of 15 to 20 °C / min. After reaching the target temperature, start to keep it warm. The holding time is 20 to 50 min. Then load to the target load at a load increasing rate of 5 to 8 MPa / s, keep a constant load for compression. After the compression is completed, unload the load within 3 s to 5 s, and cool it to room temperature with the furnace to obtain a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure.

[0013] The alloy showed excellent deformation ability during the entire deformation process in Step V. The workpiece taken out is disc-shaped, without cracks on the surface and inside. The deformed structure is an ultrafine grain structure with a mixture of α phase and β phase, and the grain size is generally less than 1 μm.

[0014] The present invention defines the composition of a high-strength β titanium alloy and prepares a as-cast high-strength β titanium alloy through vacuum consumable electrode melting technology; the as-cast high-strength β titanium alloy is subjected to five-pass hot forging treatment to obtain a forged high-strength β titanium alloy. The purpose of this operation is to eliminate the casting defects in the as-cast alloy, improve the density of the alloy, and improve the performance of the final alloy; then the forged high-strength β titanium alloy is subjected to solution heat treatment in the single-phase region, which not only obtains the alloy structure required before deformation but also eliminates the internal stress generated during forging, facilitating the next deformation; the heat-treated high-strength β titanium alloy is subjected to constant-load deformation at medium temperature and cooled in the furnace after the deformation is completed. The obtained high-strength β titanium alloy has an ultrafine-grained structure with a mixture of α and β phases, and the grain size is generally less than 1 μm, which will endow the alloy with excellent plasticity and extremely high strength. In addition, there are no cracks inside and on the surface of the alloy, showing excellent deformation performance. Compared with the conventional thermomechanical processing method for high-strength β titanium alloys, the present invention can not only obtain an ultrafine-grained structure with a mixture of two phases but also make full use of energy, reduce energy consumption, and improve production controllability, being simple and easy to operate. This method further expands the hot processing technology of high-strength β titanium alloys, reduces production requirements, and the obtained two-phase hybrid ultrafine-grained titanium alloy has excellent mechanical properties, which is of great significance for further improving the performance of high-strength β titanium alloys and further promoting the application scenarios of the alloy.

[0015] Advantages of the present invention:

[0016] (1) Through pre-alloy microstructure regulation, the present invention realizes the compression deformation of the alloy at medium temperature and obtains an ultrafine-grained structure with a mixture of α and β phases. This method further expands the hot processing technology of high-strength β titanium alloys, reduces production requirements, significantly shortens the production cycle, and the obtained two-phase hybrid ultrafine-grained titanium alloy will have excellent mechanical properties, with a strength of over 1700 MPa at room temperature and an elongation of not less than 7%, which is of great significance for further improving the performance of high-strength β titanium alloys and further promoting the application scenarios of the alloy.

[0017] (2) The deformation temperature of the present invention is controlled at medium temperature, which not only obtains a two-phase hybrid structure but also realizes the smooth progress of the deformation process while reducing energy consumption. In addition, the furnace cooling process after the deformation is completed can further stabilize the alloy microstructure, reduce the residual stress, and achieve the full utilization of energy.

[0018] (3) The method of medium-temperature constant-load deformation for preparing high-strength β titanium alloy with an ultrafine-grained structure with a mixture of two phases proposed by the present invention has a simple process, strong overall controllability, and a short processing cycle, which is conducive to the large-scale application of high-strength β titanium alloys.

[0019] The present invention prepares a high-strength β titanium alloy with an ultrafine-grained structure with a mixture of two phases. Brief Description of the Drawings

[0020] Figure 1 It is a scanning electron microscope image of the forged high-strength β titanium alloy after five times of high-temperature forging treatment in Step 3 of Example 1; Figure b is a high-magnification image of the white square area in Figure a;

[0021] Figure 2 It is a scanning electron microscope image of the heat-treated part after the treatment in Step 4 of Example 1, and Figure b is a high-magnification image of the white square area in Figure a;

[0022] Figure 3 It is a microstructural image of the high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure obtained in Example 1; Figure a is a scanning electron microscope image, Figure b is an electron backscatter diffraction image, Figure c is a transmission electron microscope image, and Figure d is an enlarged transmission electron microscope image;

[0023] Figure 4 It is a microstructural image of the high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure obtained in Example 2; Figure a is a scanning electron microscope image and Figure b is an electron backscatter diffraction image. Detailed Description of the Invention

[0024] Detailed Description of the Invention 1: A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant-load deformation is as follows:

[0025] 1. Weigh sponge titanium, high-purity aluminum, high-purity chromium, high-purity tin, aluminum-molybdenum alloy, aluminum-vanadium alloy, and iron nails as raw materials according to the atomic percentage: Al is 2.5% - 4.5%, Mo is 4% - 7%, V is 4.5% - 7.5%, Cr is 2.5% - 4.5%, Sn is 1.5% - 3.5%, Fe is 0.3% - 1.0%, and the balance is Ti;

[0026] 2. Clean the raw materials obtained in Step 1, press them into multiple electrodes, then weld them into a consumable electrode, and then use the vacuum consumable electrode melting process to obtain an alloy ingot through two meltings;

[0027] Use the metallographic method to measure the α / β phase transformation temperature of the alloy ingot as T β ;

[0028] 3. Cut off the surface of the alloy ingot obtained in Step 2, remove the oil stain, and then coat an antioxidant coating on the surface; Keep the alloy ingot at a temperature of (T β + 150 °C) - (T β + 200 °C) for 110 min - 140 min, then perform cogging forging to make a forging blank, and then air-cool the forging blank to room temperature; Subsequently, at a temperature of (T β(+30 °C) to (T β Keep warm for 90 min to 120 min at (+80 °C), then conduct the second forging process and cool in the furnace to room temperature; at a temperature of (T β (-80 °C) to (T β (-20 °C) and keep warm for 80 min to 100 min, then conduct the third forging and cool in the furnace to room temperature; at a temperature of (T β (-80 °C) to (T β (-20 °C) and keep warm for 80 min to 100 min, then conduct the fourth forging and cool in the furnace to room temperature; at a temperature of (T β (-100 °C) to (T β (-20 °C) and keep warm for 80 min to 100 min, then conduct precision forging to obtain a forged high-strength β titanium alloy;

[0029] IV. Cut the forged high-strength β titanium alloy obtained in Step III to obtain a heat treatment piece, set the heat treatment furnace temperature to (T β (+20 °C) to (T β (+40 °C). After the temperature in the furnace rises to the preset temperature, put the heat treatment piece into the heat treatment furnace, keep warm for 50 min to 120 min, and then air-cool to room temperature;

[0030] V. Process the heat treatment piece after the heat treatment in Step IV into several deformation processed pieces, perform the deformation process using an electronic creep and rupture testing machine. Place the deformation processed piece at the exact center of the indenter of the testing machine, zero the stress, adjust the height of the indenter, then apply a preload pressure of 20 MPa to 50 MPa, fix the deformation processed piece. Subsequently, fix a thermocouple at the positions of the upper indenter, lower indenter, and in the middle of the two indenters of the testing machine. Then close the insulation furnace of the testing machine, set the target deformation temperature to 600 °C to 650 °C, the target load to 450 MPa to 550 MPa, then heat up in the insulation furnace at a heating rate of 15 to 20 °C / min. After reaching the target temperature, start to keep warm, the holding time is 20 to 50 min, then load to the target load at a load increasing rate of 5 to 8 MPa / s, maintain a constant load for compression. After compression is completed, unload the load within 3 s to 5 s and cool in the furnace to room temperature to obtain a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure.

[0031] Specific Embodiment 2: The difference between this embodiment and Specific Embodiment 1 is that: the mass purity of the titanium sponge in Step 1 is 99%, the mass purity of the high-purity aluminum is 99%, the mass purity of the high-purity chromium is 99.9%, the mass purity of the high-purity tin is 99%, the molybdenum element content in the aluminum-molybdenum alloy is 50.5 wt.%, and the vanadium element content in the aluminum-vanadium alloy is 47.44 wt.%. Others are the same as Specific Embodiment 1.

[0032] Specific Embodiment 3: The difference between this embodiment and Specific Embodiment 1 or 2 is that: when weighing in Step 1, the mass of Al element is increased by 1-3%, and the mass of Sn element is increased by 4-7% to compensate for the loss during melting. Others are the same as Specific Embodiment 1 or 2.

[0033] Specific Embodiment 4: The difference between this embodiment and any one of Specific Embodiments 1 to 3 is that: in Step 2, the raw materials are ultrasonically cleaned with absolute ethanol. Others are the same as any one of Specific Embodiments 1 to 3.

[0034] Specific Embodiment 5: The difference between this embodiment and any one of Specific Embodiments 1 to 4 is that: the antioxidant coating in Step 3 is TB1030 glass powder. Others are the same as any one of Specific Embodiments 1 to 4.

[0035] Specific Embodiment 6: The difference between this embodiment and any one of Specific Embodiments 1 to 5 is that: in Step 4, a resistance type heat treatment furnace is used for treatment. Others are the same as any one of Specific Embodiments 1 to 5.

[0036] Specific Embodiment 7: The difference between this embodiment and any one of Specific Embodiments 1 to 6 is that: the indenter material used in Step 5 is a nickel-based superalloy. Others are the same as any one of Specific Embodiments 1 to 6.

[0037] Specific Embodiment 8: The difference between this embodiment and any one of Specific Embodiments 1 to 7 is that: in Step 5, the temperature change during the compression process is monitored in real time through a thermocouple, and the temperature fluctuation during the compression process is controlled to be less than ±10°C. Others are the same as any one of Specific Embodiments 1 to 7.

[0038] Specific Embodiment 9: The difference between this embodiment and any one of Specific Embodiments 1 to 8 is that: in Step 5, the compression amount is controlled to be 50% - 80%. Others are the same as any one of Specific Embodiments 1 to 8.

[0039] Specific Embodiment 10: The difference between this embodiment and any one of Specific Embodiments 1 to 9 is that: the high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure obtained in Step 5 has an ultrafine grain structure with a hybrid of α phase and β phase, and the grain size is less than 1μm. Others are the same as any one of Specific Embodiments 1 to 9.

[0040] The content of the present invention is not limited to the content of the above embodiments, and the combination of one or several specific embodiments can also achieve the purpose of the invention.

[0041] Example 1:

[0042] A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant load deformation is specifically carried out according to the following steps:

[0043] 1. By atomic percentage: Weigh spongy titanium (purity > 99%), high-purity aluminum (purity > 99%), high-purity chromium (purity > 99.9%), high-purity tin (purity > 99%), aluminum-molybdenum alloy (Mo content 50.5 wt.%), aluminum-vanadium alloy (V content 47.44 wt.%) and iron nails as raw materials, where Al is 3.5%, Mo is 5%, V is 6%, Cr is 3%, Sn is 2%, Fe is 0.5% and the balance is Ti;

[0044] 2. Ultrasonically clean the raw materials obtained in step 1 with anhydrous ethanol, press them into multiple electrodes, then weld them into a consumable electrode, and then use the vacuum consumable electrode melting process to obtain alloy ingots through two meltings;

[0045] Use the metallographic method to measure the α / β phase transformation temperature T β of the alloy ingot to be 815 °C;

[0046] 3. Cut off the surface of the alloy ingot obtained in step 2, remove the oil stain, and then coat an antioxidant coating on the surface; Keep the alloy ingot at 980 °C for 120 min, then perform cogging forging to make a forged blank, and then air-cool the forged blank to room temperature; Subsequently, keep it at 870 °C for 100 min, then perform the second forging treatment, and cool it to room temperature with the furnace; Keep it at 780 °C for 90 min, then perform the third forging, and cool it to room temperature with the furnace; Keep it at 780 °C for 90 min, then perform the fourth forging, and cool it to room temperature with the furnace; Keep it at 780 °C for 90 min, then perform finish forging to obtain a forged high-strength β titanium alloy;

[0047] 4. Cut the forged high-strength β titanium alloy obtained in step 3 to obtain a heat treatment piece. Set the temperature of the heat treatment furnace to 840 °C. After the temperature in the furnace rises to the preset temperature, put the heat treatment piece into the heat treatment furnace, keep it for 60 min, and then air-cool it to room temperature;

[0048] V. Process the heat-treated parts after Step IV into several deformed parts with a size of Ф6mm×9mm. Use an RDL-50 electronic creep rupture testing machine for the deformation process. The indenter material used is a nickel-based superalloy. Place the deformed parts at the exact center of the indenter of the testing machine, zero the stress, adjust the height of the indenter, then apply a preload pressure of 20 MPa, fix the deformed parts. Subsequently, fix a thermocouple at the positions of the upper indenter, lower indenter, and in the middle of the two indenters of the testing machine respectively. Monitor the temperature change during the compression process in real time through the thermocouple, and control the temperature fluctuation during the compression process to be less than ±10°C. Then, close the insulation furnace of the testing machine, set the target deformation temperature to 600°C, and the target load to 500 MPa. Then, heat up in the insulation furnace at a heating rate of 15°C / min. After reaching the target temperature, start insulation for 30 min. Then, load to the target load at a load increase rate of 6 MPa / s, and perform compression while maintaining a constant load. The compression amount is 55% - 60%. After the compression is completed, unload the load within 3 s, and cool in the furnace to room temperature to obtain a high-strength β titanium alloy (Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe) with a two-phase hybrid ultrafine grain structure.

[0049] Figure 1 Figure a is a scanning electron microscope image of the forged high-strength β titanium alloy after five times of high-temperature forging treatment in Step III of Example 1; Figure b is a high-magnification image of the white square area in Figure a. It can be seen from the figure that the microstructure of the forged high-strength β titanium alloy consists of β grains, continuous grain boundary α (α GB ) phases at the grain boundaries, and a small amount of fine secondary α (α s ) phases in the grains. Moreover, the β grains are significantly flattened, and the size in the length direction is significantly larger than that in the height direction. After measurement, the grain length is generally greater than 50 μm.

[0050] Figure 2 Figure a is a scanning electron microscope image of the heat-treated parts after Step IV of Example 1, and Figure b is a high-magnification image of the white square area in Figure a. It can be found that after solution treatment, the alloy microstructure becomes a single β phase, and the grain size significantly increases. After calculation, the average size is about 75.1 μm.

[0051] Figure 3 Figure a is a scanning electron microscope image, Figure b is an electron backscatter diffraction image, Figure c is a transmission electron microscope image, and Figure d is an enlarged transmission electron microscope image of the high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure obtained in Example 1. It can be found that after deformation, the alloy microstructure becomes α phase and β phase, and the grains are extremely refined. After calculation, the average grain size is 0.47 μm.

[0052] Example 2:

[0053] A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant-load deformation, which is specifically carried out according to the following steps:

[0054] I. Weigh sponge titanium (purity > 99%), high-purity aluminum (purity > 99%), high-purity chromium (purity > 99.9%), high-purity tin (purity > 99%), aluminum-molybdenum alloy (Mo content 50.5 wt.%), aluminum-vanadium alloy (V content 47.44 wt.%) and iron nails as raw materials according to the atomic percentages: 3.5% for Al, 5% for Mo, 6% for V, 3% for Cr, 2% for Sn, 0.5% for Fe and the balance of Ti;

[0055] II. Ultrasonically clean the raw materials obtained in step I with absolute ethanol, press them into multiple electrodes, then weld them into a consumable electrode, and then use the vacuum consumable electrode melting process to obtain an alloy ingot after two meltings;

[0056] Using the metallographic method, measure the α / β phase transformation temperature T β of the alloy ingot to be 815 °C;

[0057] III. Cut the surface of the alloy ingot obtained in step II, remove the oil stain, and then coat an antioxidant coating on the surface; keep the alloy ingot at a temperature of 980 °C for 120 min, then perform open-die forging to make a forging blank, and then air-cool the forging blank to room temperature; then keep it at a temperature of 870 °C for 100 min, perform the second forging treatment, and cool it to room temperature in the furnace; keep it at a temperature of 780 °C for 90 min, then perform the third forging, and cool it to room temperature in the furnace; keep it at a temperature of 780 °C for 90 min, perform the fourth forging, and cool it to room temperature in the furnace; keep it at a temperature of 780 °C for 90 min, then perform precision forging to obtain a forged high-strength β titanium alloy;

[0058] IV. Cut the forged high-strength β titanium alloy obtained in step III to obtain a heat treatment piece, set the temperature of the heat treatment furnace to 840 °C, and after the temperature in the furnace rises to the preset temperature, put the heat treatment piece into the heat treatment furnace, keep it for 60 min, and then air-cool it to room temperature;

[0059] V. Process the heat-treated parts after Step IV into several deformed parts with a size of Ф6mm×9mm. Use an RDL-50 electronic creep rupture testing machine for the deformation process. The indenter material used is a nickel-based superalloy. Place the deformed part at the exact center of the indenter of the testing machine, zero the stress, adjust the height of the indenter, then apply a preload pressure of 20 MPa, fix the deformed part. Subsequently, fix a thermocouple at the positions of the upper indenter, lower indenter, and in the middle of the two indenters of the testing machine respectively. Real-time monitor the temperature change during the compression process through the thermocouple, and control the temperature fluctuation during the compression process to be less than ±10°C. Then turn off the insulation furnace of the testing machine, set the target deformation temperature to 650°C, the target load to 500 MPa, then heat up in the insulation furnace at a heating rate of 15°C / min. After reaching the target temperature, start insulation for 30 min, then load to the target load at a load increasing rate of 6 MPa / s, maintain a constant load for compression, the compression amount is 75% - 80%. After the compression is completed, unload the load within 3 s, and cool in the furnace to room temperature to obtain a high-strength β titanium alloy (Ti-3.5Al-5Mo-6V-3Cr-2Sn-0.5Fe) with a two-phase hybrid ultrafine grain structure.

[0060] Figure 4 It is the microstructural image of the high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure obtained in Example 2; Figure a is a scanning electron microscope image, and Figure b is an electron backscatter diffraction image. It can be found that after deformation, the alloy microstructure becomes α phase and β phase, and the grains are extremely refined. After calculation, the average grain size is 0.64 μm.

Claims

1. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine-grained structure by medium-temperature constant-load deformation, characterized in that The method is specifically carried out according to the following steps: I. Weigh spongy titanium, high-purity aluminum, high-purity chromium, high-purity tin, aluminum-molybdenum alloy, aluminum-vanadium alloy and iron nails as raw materials according to the atomic percentages: Al is 2.5% - 4.5%, Mo is 4% - 7%, V is 4.5% - 7.5%, Cr is 2.5% - 4.5%, Sn is 1.5% - 3.5%, Fe is 0.3% - 1.0% and the balance is Ti. II. Clean the raw materials obtained in step I, press them into multiple electrodes, then weld them into a consumable electrode, and then use the vacuum consumable electrode melting process to prepare an alloy ingot through two meltings. The α / β phase transformation temperature of the alloy ingot was measured to be T by metallographic method β ; III. Cut the surface of the alloy ingot obtained in Step II, remove the oil stain, and then coat an antioxidant coating on the surface; Heat the alloy ingot at a temperature of (T β + 150 °C) to (T β + 200 °C) for 110 min to 140 min, then perform cogging forging to make a forging blank, and then air-cool the forging blank to room temperature; Subsequently, heat at a temperature of (T β + 30 °C) to (T β + 80 °C) for 90 min to 120 min, and then perform the second forging treatment, and cool to room temperature with the furnace; Heat at a temperature of (T β - 80 °C) to (T β - 20 °C) for 80 min to 100 min, then perform the third forging, and cool to room temperature with the furnace; Heat at a temperature of (T β - 80 °C) to (T β - 20 °C) for 80 min to 100 min, then perform the fourth forging, and cool to room temperature with the furnace; Heat at a temperature of (T β - 100 °C) to (T β - 20 °C) for 80 min to 100 min, and then perform finish forging to obtain a forged high-strength β titanium alloy; IV. Cut the as-forged high-strength β titanium alloy obtained in Step III to obtain a heat treatment piece, and set the heat treatment furnace temperature to (T β + 20°C) to (T β + 40°C). After the temperature in the furnace rises to the preset temperature, put the heat treatment piece into the heat treatment furnace, keep it warm for 50 min to 120 min, and then air cool it to room temperature; V. Process the heat-treated parts in step IV into several deformed parts, perform the deformation process using an electronic creep rupture testing machine. Place the deformed parts at the exact center of the indenter of the testing machine, zero the stress, adjust the height of the indenter, then apply a preload pressure of 20 MPa - 50 MPa, fix the deformed parts. Subsequently, fix a thermocouple at the positions of the upper indenter, lower indenter and in the middle of the two indenters of the testing machine. Then close the insulation furnace of the testing machine, set the target deformation temperature to 600°C - 650°C, the target load to 450 MPa - 550 MPa, and then heat up in the insulation furnace at a heating rate of 15 - 20°C / min. After reaching the target temperature, start insulation, and the insulation time is 20 - 50 min. Then load to the target load at a load increasing rate of 5 - 8 MPa / s, maintain a constant load for compression. After compression is completed, unload the load within 3 s - 5 s, and cool with the furnace to room temperature to obtain a high-strength β-titanium alloy with a two-phase hybrid ultrafine grain structure.

2. The method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant load deformation according to claim 1, wherein The mass purity of the spongy titanium described in step I is 99%, the mass purity of the high-purity aluminum is 99%, the mass purity of the high-purity chromium is 99.9%, the mass purity of the high-purity tin is 99%, the molybdenum element content in the aluminum-molybdenum alloy is 50.5 wt.%, and the vanadium element content in the aluminum-vanadium alloy is 47.44 wt.%.

3. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine-grained structure by medium-temperature constant-load deformation according to claim 1, characterized in that When weighing in step I, increase 1% - 3% of the mass of the Al element and 4% - 7% of the mass of the Sn element to compensate for the loss during the melting process.

4. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant-load deformation according to claim 1, characterized in that In step II, the raw materials are ultrasonically cleaned with anhydrous ethanol.

5. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant load deformation according to claim 1, characterized in that The antioxidant coating described in step III is TB1030 glass powder.

6. The method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant-load deformation according to claim 1, characterized in that In step IV, a resistance-type heat treatment furnace is used for treatment.

7. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine-grained structure by medium-temperature constant-load deformation according to claim 1, characterized in that The indenter material used in step V is a nickel-based superalloy.

8. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine-grained structure by medium-temperature constant-load deformation according to claim 1, characterized in that In step V, the temperature change during the compression process is monitored in real time through a thermocouple, and the temperature fluctuation during the compression process is controlled to be less than ±10°C.

9. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine-grained structure by medium-temperature constant-load deformation according to claim 1, characterized in that In step V, the compression amount is controlled to be 50% - 80%.

10. A method for preparing a high-strength β titanium alloy with a two-phase hybrid ultrafine grain structure by medium-temperature constant-load deformation according to claim 1, characterized in that The high-strength β-titanium alloy with a two-phase hybrid ultrafine grain structure obtained in step V has an ultrafine grain structure with α-phase and β-phase hybrid, and the grain size is less than 1 μm.

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