Method for introducing high-density twin crystals into tantalum-tungsten alloy

Abstract

The invention discloses a method for introducing high-density twin crystals into a tantalum-tungsten alloy, which is characterized in that the tantalum-tungsten alloy prepared by vacuum electron beam melting is selected as a raw material, and a high-density twin crystal structure is introduced by adopting a method of combining thermal mechanical treatment with multi-pass high-strain-rate impact, so that the tantalum-tungsten alloy with uniform high-density twin crystals is obtained. Thermal mechanical treatment is adopted to homogenize the structure, reduce the dislocation density and remove the machining deformation stress, then multi-pass high-strain-rate impact deformation is adopted to regulate and control the microstructure in the tantalum-tungsten alloy, a high-density and uniformly-distributed twin crystal structure is introduced into the tantalum-tungsten alloy, controllable preparation of the twin crystal density is achieved, and the preparation process is simple. And the method is reasonable in design, simple and efficient in process and wide in application range.

Description

Technical Field

[0001] This invention belongs to the field of tantalum alloy preparation and structure control technology, specifically relating to a method for introducing high-density twins in tantalum-tungsten alloys. Background Technology

[0002] Tantalum-tungsten alloy is a binary solid solution alloy with tantalum as the matrix and tungsten as the additive element. It possesses excellent properties such as high melting point, high density, corrosion resistance, and high high-temperature strength, and is often used to manufacture key components in aerospace, nuclear industry, and weaponry. With the development of modern technology, increasingly higher requirements are being placed on the service performance of tantalum-tungsten alloys in extreme environments, which in turn places greater demands on the microstructure control of tantalum-tungsten alloys. Currently, tantalum-tungsten alloy ingots are generally plastically deformed through forging and rolling, and the grain size of the tantalum-tungsten alloy is refined by controlling the forging / rolling parameters and combining them with subsequent annealing. While this method refines the grain size to some extent, it is difficult to further control complex structures.

[0003] Twins, as an important crystal defect structure, can significantly improve the strength, plasticity, and toughness matching of materials. Especially under dynamic loading conditions, the formation of twin structures can enhance the self-sharpening property of tantalum-tungsten alloys, enabling them to maintain a sharp penetration head during high-penetration processes and greatly improving penetration capability. However, introducing high-density twins into body-centered cubic tantalum-tungsten alloys faces significant technical challenges, especially with the addition of high W content, which further increases the difficulty of twin introduction. The high melting point and high rheological stress of tantalum-tungsten alloys make it difficult for traditional plastic processing methods to generate sufficient strain energy to drive twin deformation; moreover, the formation of twins exhibits a significant orientation correlation, with grains of different orientations potentially activating different numbers of slip systems. Summary of the Invention

[0004] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a method for introducing high-density twins in tantalum-tungsten alloys. This invention employs a combination of thermomechanical treatment and multi-pass high-strain-rate impact deformation to achieve a uniform structure, reduce dislocation density, and control the microstructure of the tantalum-tungsten alloy, thereby introducing a uniform high-density twin structure within the alloy and overcoming the difficulty of introducing twins in traditional deformation treatments of tantalum-tungsten alloys.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for introducing high-density twins into a tantalum-tungsten alloy, characterized in that a tantalum-tungsten alloy prepared by vacuum electron beam melting is selected as the raw material, and a high-density twin structure is introduced by thermomechanical treatment combined with multi-pass high strain rate impact to obtain a tantalum-tungsten alloy with uniform high-density twins; the element mass percentage in the tantalum-tungsten alloy is: Ta ≥ 75% and W ≤ 15%.

[0006] The above-mentioned method for introducing high-density twins into a tantalum-tungsten alloy is characterized by comprising the following steps: Step 1: The tantalum-tungsten alloy ingot prepared by vacuum electron beam melting is forged and then recrystallized and annealed, then hot rolled, and then recrystallized and annealed again to obtain a tantalum-tungsten alloy billet with a recrystallized structure having uniform grain size in the initial structure. Step 2: The deformation rate of the tantalum-tungsten alloy billet from Step 2 is higher than 1×10⁻⁶. 3 Multiple high strain rate impacts per second yielded a tantalum-tungsten alloy with uniform high-density twins.

[0007] Typically, in this invention, after removing the surface oxide layer and defects from the tantalum-tungsten alloy billet in step one, it is machined into a cylinder with the same diameter and height. The machining marks on the surface are then removed using sandpaper, and the sides and ends of the cylinder are polished. The cylinder is then used as a sample for multiple high strain rate impacts in step two.

[0008] The above-mentioned method for introducing high-density twins into tantalum-tungsten alloy is characterized in that, in step one, a tantalum-tungsten alloy ingot is prepared by two vacuum electron beam melting processes. After peeling, the tantalum-tungsten alloy ingot is first forged at a forging temperature of 1000℃~1200℃ with an upsetting ratio of 1.5, and then radially drawn at a drawing ratio of 2.0. After two upsetting and drawing processes, the forged billet is squared. The recrystallization annealing treatment after forging is performed at a temperature of 1300℃~1500℃, and the hot rolling temperature is 1000℃~1200℃. The rolling method is cross rolling, that is, the first pass is rolled along the length direction of the billet, and then the billet is rotated 90° and rolled along the width direction for the second pass, and then rotated back to the original length direction. The rolling process is repeated alternately, and the number of hot rolling passes is more than 8, with a total deformation of 50%~80%. After hot rolling, recrystallization annealing treatment is performed. More preferably, the forging temperature is 1000℃, the recrystallization annealing temperature after forging is 1300℃, the hot rolling temperature is 1000℃, the total deformation of hot rolling is 70%, and the recrystallization annealing temperature after hot rolling is 1500℃ for 2 hours.

[0009] The above-mentioned method for introducing high-density twins into a tantalum-tungsten alloy is characterized in that the multi-pass high strain rate impact in step two is performed using a Hopkinson bar.

[0010] The above-mentioned method for introducing high-density twins in tantalum-tungsten alloy is characterized in that the Hopkinson rod uses limiting rings of different specifications to perform multiple impacts on the tantalum-tungsten alloy billet. The height of the limiting rings is lower than that of the specimen to be impacted and the height decreases sequentially. The outer diameter of the limiting rings is consistent with that of the incident rod, and the inner diameter increases sequentially and is greater than that of the outer diameter of the specimen after impact. The total deformation of the multiple high strain rate impacts is 50% to 80%.

[0011] Typically, high-strength steel is used to process the limiting ring.

[0012] The above-mentioned method for introducing high-density twins into a tantalum-tungsten alloy is characterized in that the multi-pass high strain rate impact includes the following steps: Step 201: Cut the tantalum-tungsten alloy billet into cylinders with equal diameter and height and polish them as a sample. Then place the sample in the center of the first limiting ring with the first height, avoiding contact with the inner wall of the first limiting ring. Then place the whole sample between the two shims of the incident rod and the transmission rod of the Hopkinson rod and use glycerin to bond them together. Step 202: After ensuring that the center of the Hopkinson rod, the specimen to be impacted, and the transmission rod are on the same axis as in step 201, adjust the emission gas pressure of the Hopkinson rod and start the incident rod to perform the first impact on the specimen and the first limiting ring, so that the specimen impacts to the first height of the first limiting ring. Step 203: Take out the sample and the first limiting ring after the first impact in step 202, and replace them with the second limiting ring with the second height. Repeat the process of placing, bonding and ensuring that the center is on the same axis in step 201. Then adjust the emission gas pressure of the Hopkinson rod to be higher than the emission gas pressure of the first impact, and start the incident rod to perform a second impact on the sample and the second limiting ring after the first impact, so that the sample impacts to the second height of the second limiting ring. Step 204: Take out the sample and the second limiting ring after the second impact in step 203, and replace them with the third limiting ring with the third height. Repeat the process of placing, bonding and ensuring that the center is on the same axis in step 201. Then adjust the emission gas pressure of the Hopkinson rod to be higher than the emission gas pressure of the second impact, and start the incident rod to perform the third impact on the sample and the third limiting ring after the second impact. By repeating this process three or more times with high strain rate impacts and a total deformation of 50% to 80%, a tantalum-tungsten alloy with uniform high-density twins is obtained.

[0013] The heights of the limiting rings used in this impact process decrease sequentially in the order of first height, second height, third height, and so on. More preferably, the sample is machined into a cylinder with a diameter of 6 mm and a height of 6 mm, and subjected to three high strain rate impacts with a total deformation of 60%. The corresponding heights of the first, second, and third limiting rings are 4.8 mm, 3.6 mm, and 2.4 mm, respectively.

[0014] The method for introducing high-density twins into a tantalum-tungsten alloy described above is characterized in that the twin density in the tantalum-tungsten alloy with uniform high-density twins is 20% to 50%, and the twins are uniformly distributed. More preferably, the twin density is 35%.

[0015] Compared with the prior art, the present invention has the following advantages: 1. This invention employs a combination of thermomechanical treatment and multi-pass high-strain-rate impact deformation. First, thermomechanical treatment is used to regulate the original structure of the tantalum-tungsten alloy, including parameters such as grain size, grain orientation, and dislocation density, to achieve a uniform structure and reduce dislocation density. Then, heat treatment is used to remove internal processing stress. Next, multi-pass high-strain-rate impact deformation is performed, and the deformation amount and rate of each pass are further controlled to regulate the microstructure of the tantalum-tungsten alloy. This introduces a high-density and uniformly distributed twin structure into the tantalum-tungsten alloy, effectively improving its strength, wear resistance, and penetration resistance, making it suitable for aerospace or military applications.

[0016] 2. In the early stage, the present invention used thermomechanical treatment to obtain a uniformly oriented recrystallized structure, which effectively avoided the significant influence of orientation correlation in twin formation and laid the foundation for the introduction of high-density twins.

[0017] 3. This invention achieves multi-pass high strain rate impact using Hopkinson bars by adopting limiting rings of different heights. The deformation amount and deformation pass under high strain rate can be adjusted by adjusting the size, height and number of limiting rings, further realizing controllable twin density preparation. Moreover, the limiting rings are simple to process, can be reused, have low equipment requirements, and improve preparation efficiency.

[0018] 4. The high-density twin introduction method of the present invention is reasonably designed, the process is simple and efficient, and it has a wide range of applications.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the thermomechanical treatment and multi-pass high strain rate impact deformation process used in this invention.

[0021] Figure 2This is an EBSD characterization diagram of the tantalum-tungsten alloy obtained after three impact deformation passes in Example 1 of the present invention.

[0022] Figure 3 This is a cross-sectional EBSD characterization diagram of the tantalum-tungsten alloy obtained after a single-pass impact deformation in Comparative Example 1 of the present invention. Detailed Implementation

[0023] like Figure 1 As shown, the process of the present invention is as follows: a tantalum-tungsten alloy ingot is forged to obtain a forging billet and then subjected to recrystallization annealing treatment, and then rolled into a hot rolled material, which is then annealed and processed to produce a tantalum-tungsten alloy rolled billet sample; then the tantalum-tungsten alloy rolled billet sample is subjected to multiple high strain rate impacts to introduce high twinning, so as to obtain a tantalum-tungsten alloy with uniform high-density twinning.

[0024] Example 1 This embodiment includes the following steps: Step 1: A tantalum-tungsten alloy ingot was prepared by two vacuum electron beam melting processes. The melting power of the melting furnace was 120kW, the crucible diameter was 90mm, and the diameter × height of the tantalum-tungsten alloy ingot was 87mm × 150mm. The element mass percentage was: Ta 88%, W 12%. After peeling the tantalum-tungsten alloy ingot, an anti-oxidation glass powder coating is applied to the surface of the ingot, and it is heated to 1000℃ for rough forging with an upsetting ratio of 1.5. Then, it is radially drawn with an elongation ratio of 2.0. After two upsetting and drawing processes, the forging blank is squared to obtain a forging blank with a height of 20mm, and then placed at 1300℃ for recrystallization annealing treatment. After recrystallization annealing, the forging billet is ground and pickled to remove surface oxide scale and crack defects, and then hot rolled at a temperature of 1000℃. The rolling method is cross rolling, that is, the first pass is rolled along the length of the billet, and then the billet is rotated 90° and rolled along the width direction for the second pass, and then rotated back to the original length direction. The rolling process is repeated alternately, and the total number of hot rolling passes is 10, with a total deformation of 70%, to obtain hot rolled material. The surface of the hot-rolled material was polished to remove the oxide scale. Then, it was subjected to recrystallization annealing in a high-temperature vacuum annealing furnace at 1500℃ for 2 hours. The material was then processed into a cylinder with a diameter of 6mm and a height of 6mm using an electrical discharge machining (EDM) machine. The sides and two end faces of the cylinder were polished using a special grinding and polishing fixture to obtain a tantalum-tungsten alloy billet with a recrystallized structure of uniform grain size as a sample. Step 2: The tantalum-tungsten alloy rolled billet sample from Step 2 is subjected to multiple high-strain-rate impacts using a Hopkinson bar. The Hopkinson bar uses three high-strength steel retaining rings (first retaining ring, second retaining ring, and third retaining ring) to impact the tantalum-tungsten alloy rolled billet sample three times. The heights of the three retaining rings are 4.8 mm, 3.6 mm, and 2.4 mm, respectively, and their outer diameters are all 20 mm. Their inner diameters are 7.5 mm, 9 mm, and 11 mm, respectively, all larger than the outer diameter of the sample. The steps include: Step 201: Install the 20mm diameter incident rod and transmission rod into the Hopkinson rod device. Place the sample in the center of the first limiting ring with a height of 4.8mm, avoiding contact with the inner wall of the first limiting ring. Then, place the whole sample between the two gaskets of the Hopkinson rod incident rod and transmission rod and use glycerin to bond them together. Step 202: After ensuring that the centers of the Hopkinson rod's incident rod, the specimen to be impacted, and the transmission rod are aligned on the same axis as in Step 201, adjust the firing pressure of the Hopkinson rod to 0.2 MPa, release the projectile, and allow the projectile to impact the incident rod, causing the incident rod to perform the first impact on the specimen and the first limiting ring. The deformation rate is calculated to be 4.9 × 10⁻⁶. 3 / s, so that the height of the sample impacted by the first limiting ring is limited to the limiting ring, that is, the height of the sample after the first impact is 4.8mm; Step 203: Remove the sample and the first limiting ring from Step 202 after the first impact, and replace them with a second limiting ring with a height of 3.6 mm. Repeat the process of placing, bonding, and ensuring the center is on the same axis as in Step 201. Then, adjust the firing pressure of the Hopkinson rod to 0.24 MPa, release the bullet, and let the bullet impact the incident rod, so that the incident rod will perform a second impact on the sample and the second limiting ring after the first impact. The deformation rate is calculated to be 6.3 × 10⁻⁶. 3 / s, so that the sample impacts to the height of the second limiting ring, limiting the deformation height within the limiting ring, that is, the sample height after the second impact is 3.6mm; Step 204: Remove the sample and the second limiting ring from Step 203 after the second impact, and replace them with a third limiting ring with a height of 2.4 mm. Repeat the process of placing, bonding, and ensuring the center is on the same axis as in Step 201. Then, adjust the firing pressure of the Hopkinson rod to 0.28 MPa, release the bullet, and let the bullet impact the incident rod, so that the incident rod impacts the sample and the third limiting ring after the second impact a third time. The deformation rate is calculated to be 7.8 × 10⁻⁶. 3 / s, so that the sample impacts to the height of the third limiting ring, limiting the deformation height within the third limiting ring, that is, the height of the sample after the third impact is 2.4mm; the total deformation of the three impacts is 60%, and a tantalum-tungsten alloy with uniform high-density twins is obtained.

[0025] Comparative Example 1 The difference between this comparative example and Example 1 is that, instead of using a limiting ring to perform multi-pass impact deformation on the tantalum-tungsten alloy billet, a Hopkinson bar is directly used with the firing gas pressure adjusted to 0.28 MPa to perform a single-pass impact deformation on the tantalum-tungsten alloy billet sample until the sample reaches its maximum deformation under that gas pressure. The deformation rate is calculated to be 7.8 × 10⁻⁶. 3 / s, the deformation of a single impact is about 63%, and tantalum-tungsten alloy is obtained.

[0026] Figure 2 This is an EBSD characterization image of the tantalum-tungsten alloy obtained after three passes of impact deformation in Example 1 of this invention. Figure 2 It can be seen that the twin volume content in the tantalum-tungsten alloy is as high as 38%, and the twins appear on the sample surface and in the core (the red line represents the twin boundaries). The overall distribution is uniform, indicating that the method of the present invention successfully introduces twins with high density and uniform distribution into the tantalum-tungsten alloy.

[0027] Figure 3 This is an EBSD characterization image of the tantalum-tungsten alloy obtained after a single-pass impact deformation in Comparative Example 1 of this invention. Figure 3 and Figure 2 Comparison shows that although the total deformation amount of impact deformation in Comparative Example 1 is close to that in Example 1, the twin content in the tantalum-tungsten alloy obtained in Comparative Example 1 is less, only 8%, which is about one-quarter of that in Example 1. Moreover, the twins appear in the middle region, while the twin content in the upper and lower regions is extremely low.

[0028] In summary, this invention employs a combination of thermomechanical treatment and multi-pass high-strain-rate impact deformation. The multi-pass impact deformation process involves applying restraining rings of varying heights during the impact process to achieve the desired deformation height and number of passes, resulting in uniformly distributed and high-density twins. This allows for rational and effective control of the tantalum-tungsten alloy structure. Furthermore, the internal structure can be adjusted by modifying the amount of deformation per pass through adjusting the height and number of restraining rings. This method is simple, efficient, and highly operable.

[0029] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for introducing high-density twins into a tantalum-tungsten alloy, characterized in that, A tantalum-tungsten alloy prepared by vacuum electron beam melting was selected as the raw material. A high-density twin structure was introduced by thermomechanical treatment combined with multiple high strain rate impacts to obtain a tantalum-tungsten alloy with uniform high-density twins. The elemental mass percentages in the tantalum-tungsten alloy were: Ta ≥ 75% and W ≤ 15%.

2. The method for introducing high-density twins into a tantalum-tungsten alloy according to claim 1, characterized in that, The method includes the following steps: Step 1: The tantalum-tungsten alloy ingot prepared by vacuum electron beam melting is forged and then recrystallized and annealed, then hot rolled, and then recrystallized and annealed again to obtain a tantalum-tungsten alloy billet with a recrystallized structure having uniform grain size in the initial structure. Step 2: The deformation rate of the tantalum-tungsten alloy billet from Step 2 is higher than 1×10⁻⁶. 3 Multiple high strain rate impacts per second yielded a tantalum-tungsten alloy with uniform high-density twins.

3. The method for introducing high-density twins into a tantalum-tungsten alloy according to claim 2, characterized in that, In step one, a tantalum-tungsten alloy ingot is prepared by two vacuum electron beam melting processes. After peeling, the ingot is first forged at a temperature of 1000℃~1200℃ with an upsetting ratio of 1.5, and then radially drawn at a drawing ratio of 2.

0. After two upsetting and drawing processes, the forged billet is squared. The recrystallization annealing treatment after forging is performed at a temperature of 1300℃~1500℃, and the hot rolling temperature is 1000℃~1200℃. The rolling method is cross rolling, that is, the first pass is rolled along the length of the billet, and then the billet is rotated 90° and rolled along the width direction for the second pass, and then rotated back to the original length direction. The rolling process is repeated alternately, and the number of hot rolling passes is more than 8, with a total deformation of 50%~80%. After hot rolling, recrystallization annealing treatment is performed.

4. The method for introducing high-density twins into a tantalum-tungsten alloy according to claim 2, characterized in that, The multi-pass high strain rate impacts described in step two are performed using a Hopkinson bar.

5. A method for introducing high-density twins into a tantalum-tungsten alloy according to claim 4, characterized in that, The Hopkinson bar uses limiting rings of different specifications to perform multiple impacts on tantalum-tungsten alloy billets. The height of the limiting rings is lower than that of the specimen to be impacted and the height decreases sequentially. The outer diameter of the limiting rings is consistent with that of the incident bar, and the inner diameter increases sequentially and is greater than the outer diameter of the specimen after impact. The total deformation of the multiple high strain rate impacts is 50% to 80%.

6. The method for introducing high-density twins in a tantalum-tungsten alloy according to claim 5, characterized in that, The multi-stage high strain rate impact includes the following steps: Step 201: Cut the tantalum-tungsten alloy billet into cylinders with equal diameter and height and polish them as a sample. Then place the sample in the center of the first limiting ring with the first height, avoiding contact with the inner wall of the first limiting ring. Then place the whole sample between the two shims of the incident rod and the transmission rod of the Hopkinson rod and use glycerin to bond them together. Step 202: After ensuring that the center of the Hopkinson rod, the specimen to be impacted, and the transmission rod are on the same axis as in step 201, adjust the emission gas pressure of the Hopkinson rod and start the incident rod to perform the first impact on the specimen and the first limiting ring, so that the specimen impacts to the first height of the first limiting ring. Step 203: Take out the sample and the first limiting ring after the first impact in step 202, and replace them with the second limiting ring with the second height. Repeat the process of placing, bonding and ensuring that the center is on the same axis in step 201. Then adjust the emission gas pressure of the Hopkinson rod to be higher than the emission gas pressure of the first impact, and start the incident rod to perform a second impact on the sample and the second limiting ring after the first impact, so that the sample impacts to the second height of the second limiting ring. Step 204: Remove the sample and the second limiting ring after the second impact in step 203, and replace them with a third limiting ring with a third height. Repeat the process of placing, bonding, and ensuring that the center is on the same axis in step 201. Then, adjust the emission gas pressure of the Hopkinson rod to be higher than the emission gas pressure of the second impact, and start the incident rod to perform a third impact on the sample and the third limiting ring after the second impact, so that the sample impacts to the second height of the second limiting ring. By repeating this process three or more times with high strain rate impacts and a total deformation of 50% to 80%, a tantalum-tungsten alloy with uniform high-density twins is obtained.

7. The method for introducing high-density twins into a tantalum-tungsten alloy according to claim 1, characterized in that, The tantalum-tungsten alloy with uniform high-density twins has a twin density of 20% to 50% and the twins are uniformly distributed.

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