A method for preparing a high-strength titanium alloy multi-scale structure

Abstract

The application discloses a preparation method of a titanium alloy multi-scale structure. First, high-energy pulse current rapid heating technology is used to heat the titanium alloy as a whole, and the titanium alloy is air-cooled after heat preservation for a certain time; second, medium-temperature short-time heat preservation treatment is used to obtain micron-sized alpha with sufficient content and size; finally, low-voltage short-time high-energy pulse current treatment is continuously used to promote explosive nucleation of nano-sized alpha, so that fine nano alpha second phase particles are dispersedly distributed, and finally, the titanium alloy with a multi-scale lamellar alpha structure and a fine-grained beta matrix is obtained under room temperature conditions. The method is simple in operation, simple in equipment, and environmental protection and economy in heating method. By adjusting pulse electric heating parameters and time, the multi-scale lamellar alpha structure which is more excellent than that obtained by a traditional resistance furnace heating method can be obtained in a short time, the beta grain coarsening is inhibited, the formation of continuous alpha at the grain boundary is avoided, the comprehensive mechanical properties of the alloy are improved, and the method has wide popularization and application prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium alloy heat treatment, and particularly relates to a preparation method of a titanium alloy multi-scale structure. BACKGROUND

[0002] In recent years, the use amount of titanium alloy in China has rapidly increased, and in the future, the demand for high-performance titanium alloy as a representative of light-weight high-performance materials in the field of aerospace will also show a rapid growth trend. High-strength high-toughness titanium alloy is favored by scientists because it has high specific strength and plasticity, and can meet the needs of lightweight, high-speed and large-scale development of aerospace. Ti55531 titanium alloy is a type of titanium alloy with the most potential to obtain high-strength high-toughness performance. The alloy contains a large number of solid solution elements such as Al, Mo, Cr, Nb, V and Si, which not only have a significant solid solution strengthening effect, but also can precipitate a large amount of alpha phase from the beta matrix to play a precipitation strengthening role. Among them, the lamellar structure or widmanstatten structure is a common type of organizational mode of this type of titanium alloy. However, due to the fact that the microstructure regulation and preparation of the high-strength and high-toughness titanium alloy often uses a traditional resistance furnace for heating treatment, on the one hand, it is easy to cause abnormal coarsening of beta grain size, and on the other hand, alpha phase is easy to preferentially nucleate at the beta grain boundary to form grain boundary continuous coarse alpha phase and parallel coarse alpha colony (alpha colony). Coarse beta grains and grain boundary continuous alpha phase become the main reason for low plasticity and premature fracture of the alloy. Therefore, how to avoid abnormal coarsening of beta grains and reduce the formation and growth of grain boundary continuous alpha phase is a key problem that needs to be solved in the organization preparation and performance regulation of the alloy. SUMMARY

[0003] In view of the deficiencies of the prior art, the purpose of the present application is to provide a preparation method of a high-strength titanium alloy multi-scale structure. The multi-scale organizational structure can organically combine the toughening effect of large-size alpha phase and the strengthening effect of nano alpha phase, thereby improving the strength and plasticity matching of the alloy. The present application provides a new type of heat treatment method for preparing an organizational structure with multi-scale distribution of alpha phase for typical high-strength Ti55531 alloy used in aviation, and provides a heat treatment method for obtaining excellent strength and plasticity matching and preparation of complex multi-phase alloy.

[0004] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0005] A preparation method of a titanium alloy multi-scale structure, comprising the following steps:

[0006] Step 1, using wire electrical discharge machining to prepare a plate-shaped or round bar sample, the sample being a Ti55531 titanium alloy with a nominal composition of Ti-5Al-5Mo-5V-3Cr-1Zr;

[0007] Step 2: Place the plate-shaped or round bar sample described in Step 1 into the glove box and connect the sample to the positive and negative terminals of the high-energy pulse power supply.

[0008] Step 3: Vacuum the glove box and then introduce inert gas for protection to prevent the sample from being oxidized.

[0009] Step 4: Turn on the pulse power supply, adjust the pulse voltage, current and pulse frequency, and perform rapid heating treatment on the titanium alloy sample, then cool it to room temperature.

[0010] Step 5: After the titanium alloy plate or bar has been heated by pulse current, it is subjected to medium-temperature heat preservation treatment at a temperature of 730-780℃ for 25-30 minutes, and then cooled to room temperature by water.

[0011] Step 6: The sample from Step 5 is subjected to pulsed current heating treatment again and cooled to room temperature. Finally, a high-strength titanium alloy multi-scale structure is obtained at room temperature.

[0012] Furthermore, the cross-sectional area of ​​the Ti55531 alloy sample in step 1 is 4-15 mm². 2 .

[0013] Furthermore, the specific method for connecting the sample to the positive and negative terminals of the pulse power supply in step 2 is as follows: the positive and negative terminals of the pulse power supply are made of copper plates with dimensions of 50×200×5mm, and the two ends of the sample to be heated are clamped stably using the copper plates.

[0014] Furthermore, the specific operation method for vacuuming and argon protection in step 3 is as follows: the vacuum degree is 3.5 kPa, high-purity argon is used, and the gas pressure is maintained at 70-78 kPa.

[0015] Furthermore, the specific process of rapid pulse current heating in step 4 is as follows: pulse voltage 37-45V, continuous heating time 3-8 minutes.

[0016] Furthermore, the specific process of pulse current heating treatment in step 6 is as follows: the pulse voltage is 25-30V, and the heating time is 5-10 minutes.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention does not require changing the alloy composition or performing hot working processes such as forging and rolling. By simply adjusting the pulse electric heating parameters and time, a multi-scale lamellar α structure that is superior to the traditional resistance furnace heating method can be obtained in a short time.

[0019] 2. High-energy pulsed current heating is adopted, which utilizes its Joule heating effect to achieve rapid heating. On the one hand, it can reduce the recrystallization temperature of the alloy and promote the nucleation of new phases; on the other hand, the time required to reach the phase transformation point is extremely short, so that the β grains do not have enough time to grow, effectively suppressing the abnormal coarsening of β grains, and laying a good microstructure foundation for the subsequent precipitation and control of multi-scale α phase.

[0020] 3. Currently, traditional resistance furnace heating is used, which has a slow heating rate and requires long-term heating and holding. During cooling, grain boundaries often become the preferred nucleation sites for new phases, making it difficult to prevent the α phase from preferentially nucleating and growing into a continuous state at grain boundaries. This often leads to a decrease in alloy plasticity and premature fracture. This invention first utilizes pulsed current rapid heating to suppress β coarsening; it employs a medium-temperature quenching process to precipitate a small amount of α phase in the β matrix at the medium temperature stage. A rapid water-cooling method is used to retain a small amount of α, preventing excessive α precipitation due to slow cooling. This small amount of α phase grows into micron-sized lath α phases during subsequent heat treatment, providing sufficient plasticity for the alloy; secondly, it utilizes pulsed current heating with low voltage parameters, taking advantage of the recrystallization nucleation effect of pulsed current heating to ensure uniform nucleation of the α phase at and within the β grain boundaries, effectively suppressing the preferential nucleation of the α phase at the β grain boundaries. Ultimately, this composite processing technology was used to design and prepare a novel multi-scale microstructure with micron and nano-sized α phases, effectively suppressing or avoiding the formation of continuous α phases at grain boundaries.

[0021] 4. This multi-scale lamellar structure consists of hard nano-sized lamellar α phase and softer micro-sized lamellar α phase, combining the toughening effect of the micro-sized α phase with the strengthening effect of the nano-α particles, effectively improving the plasticity and toughness of the alloy without significantly reducing the alloy strength.

[0022] 5. This electric pulse heating method is simple to operate, has a fast heat treatment speed and high efficiency, and produces no harmful gases. It is economical and environmentally friendly, and can improve the production efficiency of materials and reduce energy consumption. It is a new heat treatment technology with great competitive potential and has broad application prospects. Attached Figure Description

[0023] Figure 1 The microstructure of the high-strength titanium alloy multi-scale structure prepared in Example 1 is shown.

[0024] Figure 2 The microstructure of the high-strength titanium alloy multi-scale structure prepared in Example 2 is shown. Detailed Implementation

[0025] The following detailed description, in conjunction with the accompanying drawings, illustrates specific embodiments. Taking a Ti55531 alloy sample as an example, this invention further details the specific implementation of preparing a multi-scale lamellar microstructure using pulsed current heating. The specific implementation follows these steps:

[0026] Step 1: Prepare plate-shaped or round bar samples using wire electrical discharge machining. The samples are metastable Ti55531 titanium alloys with a nominal composition of Ti-5Al-5Mo-5V-3Cr-1Zr. The cross-sectional area of ​​the alloy samples is 4-15 mm². 2 ;

[0027] Step 2: Place the plate or round bar sample into the glove box and connect the sample to the positive and negative terminals of the high-energy pulse power supply. The positive and negative terminals of the pulse power supply are made of copper plates with a size of 50×200×5mm. Use the copper plates to clamp the two ends of the sample to be heated.

[0028] Step 3: Evacuate the glove box by introducing inert argon gas for protection. The vacuum level is 3.5 kPa, and the high-purity argon gas pressure is maintained at 70-78 kPa.

[0029] Step 4: Turn on the pulse power supply, adjust the pulse voltage, current and pulse frequency, and perform rapid heating treatment on the titanium alloy sample. The pulse voltage is 37-45V, and the heating is continued for 3-8 minutes. Then cool to room temperature.

[0030] Step 5: Place the titanium alloy plate or bar sample after pulse current heating treatment into a box-type muffle furnace for medium-temperature heat treatment at 730-780℃ for 25-30 minutes, and then cool it to room temperature with water.

[0031] Step 6: The sample from Step 5 is subjected to pulsed current heating treatment again. The pulse voltage is 25-30V, and the heating is continued for 5-10 minutes. After cooling to room temperature, the multi-scale lamellar structure is obtained at room temperature.

[0032] Example 1

[0033] (1) Select a cross-sectional area of ​​15mm 2 Ti55531 titanium alloy plate sample;

[0034] (2) Connect the sample to the positive and negative copper plate electrodes of the pulse power supply and place it in the glove box;

[0035] (3) The glove box was evacuated to a vacuum of 3.5 kPa. Then, argon atmosphere was introduced into the glove box and the pressure was maintained at 78 kPa to prevent the sample from being oxidized.

[0036] (4) Connect the pulse power supply, turn on the pulse power switch, adjust the pulse voltage to 45V, heat for 3 minutes, and then air cool to room temperature;

[0037] (5) After pulse current heating treatment, the sample was kept at 730℃ for 30 minutes and then cooled to room temperature with water.

[0038] (6) Connect the pulse power supply and turn on the pulse power switch. Adjust the pulse heating voltage to 30V, heat continuously for 5 minutes, and then air cool to room temperature.

[0039] After pulsed current heating treatment, the sample was subjected to coarse grinding, fine grinding and electrolytic polishing. Then, it was etched with a mixed solution of HF:HNO3:H2O in a ratio of 1:2:5. The morphology of the sample was observed and analyzed using a scanning electron microscope. Figure 1 The scanned images of the obtained specimens show that the tissue contains micron-sized α phases (average width 0.7 μm), nano-sized fine α phases (average width 140 nm), and residual β phases. The sizes of these phases range from micron to nanometer, forming lamellar tissues of different scales.

[0040] Example 2

[0041] (1) First, cut the original Ti55531 alloy into pieces with a cross-sectional area of ​​10mm. 2 Rod-shaped sample;

[0042] (2) Connect the sample to the positive and negative copper plate electrodes of the pulse power supply and place it in the glove box;

[0043] (3) The glove box was evacuated to a vacuum of 3.5 kPa. Then, argon atmosphere was introduced into the glove box and the pressure was maintained at 70 kPa to prevent the sample from being oxidized.

[0044] (4) Connect the pulse power supply, turn on the pulse power switch, adjust the pulse voltage to 43V, heat for 5 minutes, and then air cool to room temperature;

[0045] (5) After pulse current heating treatment, the sample was kept at 755℃ for 27 minutes and then cooled to room temperature with water.

[0046] (6) Connect the pulse power supply, turn on the pulse power switch, adjust the pulse heating voltage to 25V, heat continuously for 8 minutes, and then air cool to room temperature.

[0047] After pulsed current heating treatment, the sample was subjected to coarse grinding, fine grinding and electrolytic polishing. Then, it was etched with a mixed solution of HF:HNO3:H2O in a ratio of 1:2:5. The morphology of the sample was observed and analyzed using a scanning electron microscope. Figure 2The scanned images of the obtained specimens show that the tissue contains micron-sized α phases (average width 0.8 μm), nano-sized fine α phases (average width 70 nm), and residual β phases. The sizes of these phases range from micron to nanometer, forming lamellar structures of different scales, and the scale differences between coarse and fine lamellar α phases are obvious.

[0048] Example 3

[0049] (1) First, the original Ti55531 alloy was cut into pieces with a cross-sectional area of ​​4mm. 2 Round bar sample;

[0050] (2) Connect the sample to the positive and negative copper plate electrodes of the pulse power supply and place it in the glove box;

[0051] (3) The glove box was evacuated to a vacuum of 3.5 kPa. Then, argon atmosphere was introduced into the glove box and the pressure was maintained at 74 kPa to prevent the sample from being oxidized.

[0052] (4) Connect the pulse power supply, turn on the pulse power switch, adjust the pulse voltage to 37V, heat for 8 minutes, and then air cool to room temperature;

[0053] (5) After the pulse current heating treatment, the sample was kept at 780℃ for 25 minutes and then cooled to room temperature with water.

[0054] (6) Connect the pulse power supply and turn on the pulse power switch. Adjust the pulse heating voltage to 26V, heat continuously for 10 minutes, and then air cool to room temperature.

[0055] After pulsed current heating treatment, the sample was subjected to coarse grinding, fine grinding and electrolytic polishing. Then, it was etched with a mixed solution of HF:HNO3:H2O in a ratio of 1:2:5. The microstructure contained micron-sized α phase (average width 0.3 μm), nano-sized fine α phase (average width 50 nm), and residual β phase. The sizes of these phases ranged from micron to nanometer, forming lamellar structures of different scales, and the lamellars were evenly and finely distributed.

[0056] In this invention, Ti55531 alloy was subjected to high-energy pulsed current heating composite treatment technology to obtain multi-scale lamellar structure. Compared with traditional lamellar structure, the size scale of this lamellar structure is different, which is conducive to achieving excellent strength and plasticity matching.

[0057] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a multi-scale structure of titanium alloy, characterized in that, Includes the following steps: Step 1: Prepare plate-shaped or round bar samples using wire electrical discharge machining. The sample is a Ti55531 titanium alloy with a nominal composition of Ti-5Al-5Mo-5V-3Cr-1Zr. Step 2: Place the plate-shaped or round bar sample described in Step 1 into the glove box and connect the sample to the positive and negative terminals of the high-energy pulse power supply. Step 3: Vacuum the glove box and then introduce inert gas for protection to prevent the sample from being oxidized. Step 4: Turn on the pulse power supply, adjust the pulse voltage, current and pulse frequency, and perform rapid heating treatment on the titanium alloy sample. Cool it to room temperature. The pulse voltage is 37-45V and the heating time is 3-8 minutes. Step 5: After the titanium alloy plate or bar has been heated by pulse current, it is subjected to medium-temperature heat preservation treatment at a temperature of 730-780℃ for 25-30 minutes, and then cooled to room temperature by water. Step 6: The sample from Step 5 is subjected to pulsed current heating treatment again. The pulse voltage is 25-30V and the heating time is 5-10 minutes. After cooling to room temperature, a high-strength titanium alloy multi-scale structure is finally obtained at room temperature.

2. The method for preparing a multi-scale titanium alloy structure according to claim 1, characterized in that, The cross-sectional area of ​​the Ti55531 alloy sample in step 1 is 4-15 mm². 2 .

3. The method for preparing a multi-scale titanium alloy structure according to claim 1, characterized in that, The specific method for connecting the sample to the positive and negative terminals of the pulse power supply in step 2 is as follows: the positive and negative terminals of the pulse power supply are made of copper plates with a size of 50×200×5mm. The copper plates are used to hold the two ends of the sample to be heated stably.

4. The method for preparing a multi-scale titanium alloy structure according to claim 1, characterized in that, The specific operating method for vacuuming and argon protection in step 3 is as follows: the vacuum degree is 3.5 kPa, high-purity argon is used, and the gas pressure is maintained at 70-78 kPa.

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