A high-strength and tough NbTaV-based medium-entropy alloy and preparation method thereof

Abstract

The present invention discloses a high-strength and toughness NbTaV-based medium-entropy alloy and a preparation method thereof. The raw materials are mixed according to atomic percentage to obtain a metal particle mixture; the metal particle mixture is vacuum-melted to obtain an ingot; the alloy is then cold-rolled at room temperature, and then subjected to a heat treatment process at an appropriate temperature to obtain an excellent strength-plasticity combination; the present invention uses a heat treatment process at an appropriate temperature to not only reduce the grain size to produce fine grain strengthening, but also produce solid solution strengthening and dislocation strengthening due to alloy design and processing, while the alloy still maintains a bcc matrix, thereby greatly improving the alloy plasticity while still having good strength. The alloy of the present invention has excellent room temperature mechanical properties. 50 Ta 25 V 20 The total elongation at break of the Ti5 refractory medium entropy alloy is increased by 470% to about 20%, while the yield strength is increased by 11% to about 787MPa and the tensile strength is increased by 15% to about 887MPa. Based on the above characteristics, the alloy of the present invention has a great competitive advantage in single-phase bcc high / medium entropy alloys and has great engineering application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of high-performance alloy materials, and in particular to a high-strength and toughness NbTaV-based medium-entropy alloy and a preparation method thereof. Background Art

[0002] Since the concept of high entropy alloys was formally proposed in 2004, HEAs have broken the design concept of a single main element of traditional alloys, highlighting the breakthrough new concept of using high mixed entropy effects to form simple solid solution phase structures. Through the study of this concept and a large number of experiments, many types of high entropy alloys have been discovered and explored, and the special relationship between material processing technology, microstructure and performance has been found. Through reasonable selection of ingredients and screening of preparation processes, high entropy alloys can form simple organizational structures and exhibit excellent properties, such as high strength, high hardness, high plasticity, wear resistance, corrosion resistance, etc., which gives high entropy alloys broad application prospects.

[0003] Among the many HEAs systems currently available, refractory high / medium entropy alloys (bcc-RHEAs / RMEAs) with a body-centered structure have attracted widespread attention for their excellent high-temperature performance. However, studies have shown that although they have excellent mechanical properties at high temperatures, they have poor ductility at room temperature, and cracking can cause material failure under low strains. These shortcomings have become a bottleneck for the current industrial application of refractory high-entropy alloys as structural materials. This has also become a difficulty that many bcc-structured refractory high-entropy alloys need to face. In previous studies, it was found that research on the microstructure and mechanical properties of NbTaV-based medium-entropy alloys is still scarce. Therefore, how to improve the plasticity of NbTaV-based medium-entropy alloys while maintaining good yield strength is a key issue that needs to be solved urgently. Summary of the invention

[0004] Aiming at the problem that the NbTaV-based medium entropy alloy can improve plasticity while maintaining good yield strength, the present invention provides a high-strength and tough NbTaV-based medium entropy alloy and a preparation method thereof. 50 Ta 25 V 20 The Ti5 medium entropy alloy is cold rolled at room temperature and then quenched to effectively refine the grains and produce dislocation strengthening. At the same time, solid solution strengthening is produced through the design of alloy composition, achieving a good match between the alloy's plasticity and strength.

[0005] The present invention is achieved through the following technical solutions:

[0006] A high-strength and tough NbTaV-based medium-entropy alloy comprises, by atomic percentage, 49-51% of Nb, 24-26% of Ta, 19-21% of V and 4-6% of Ti.

[0007] Preferably, the NbTaV-based mesentropy alloy has a tensile strength greater than 850 MPa, a yield strength greater than 750 MPa, and a total elongation at break greater than 19%.

[0008] Preferably, the NbTaV—Ti based refractory medium entropy alloy has a single-phase bcc structure.

[0009] A method for preparing a high-strength and tough NbTaV-based medium-entropy alloy comprises the following steps:

[0010] Step 1, mixing the raw materials according to atomic percentage to obtain a metal particle mixture;

[0011] Step 2, vacuum melting the metal particle mixture to obtain an ingot;

[0012] Step 3, cold rolling the ingot with a deformation amount of 45-55%;

[0013] Step 4: quenching the cold-rolled ingot to obtain a single-phase bcc structured NbTaV-Ti refractory medium entropy alloy.

[0014] Preferably, the vacuum melting method in step 2 is as follows:

[0015] During the smelting process, the vacuum is first reduced to 5Pa, and then high-purity argon is introduced and the vacuum is evacuated again. The smelting induction current is 395-495A. Electromagnetic stirring is used during the smelting process, and remelting is repeated until the composition is uniform. Finally, the ingot is obtained by water cooling.

[0016] Preferably, the remelting is performed more than 5 times.

[0017] Preferably, the quenching method is as follows:

[0018] The cold rolled ingot is heated at 800-1200°C for 5 minutes for quenching.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] The present invention provides a method for preparing a high-strength and tough NbTaV-based medium-entropy alloy. After the designed NbTaV-based medium-entropy alloy is cold-rolled at room temperature, a heat treatment process at an appropriate temperature can be performed to obtain a substantial plasticity increase compared to the cast state, and an excellent plasticity-strength combination. Under normal circumstances, single-phase bcc refractory high / medium-entropy alloys exhibit poor ductility at room temperature due to the crystallographic characteristics of their bcc structure. In order to obtain a good combination of plasticity and strength, it is necessary to further improve its plasticity without affecting its strength. Through the exploration of alloy composition design, cold rolling and heat treatment processes, the present invention finds that when the heat treatment process is performed at an appropriate temperature, the material properties can be greatly improved compared to the cast state. Further analysis shows that, compared to the cast state, heat treatment at an appropriate temperature not only reduces the grain size and increases the number of dislocations. Under the effects of grain refinement and dislocation strengthening, the alloy plasticity is greatly improved while the strength is slightly increased. The alloy of the present invention has excellent room temperature ductility. 50 Ta 25 V 20 The total elongation at break of the Ti5 refractory medium entropy alloy is increased by 470% to about 20%, while the yield strength is increased by 11% to about 787MPa and the tensile strength is increased by 15% to about 887MPa. Based on the above characteristics, the alloy of the present invention has a great competitive advantage in single-phase bcc refractory high / medium entropy alloys and has great engineering application prospects.

[0021] The preparation method provided by the invention is simple, and the alloy can obtain excellent plasticity-strength matching after smelting, cold rolling and quenching. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a metallographic structure photo of the NbTaV-Ti based medium entropy alloy of the present invention;

[0023] Figure 2 This is a comparison chart of tensile properties of the NbTaV-Ti based medium entropy alloy of the present invention in different heat treatment states;

[0024] Figure 3 It is a strength-plasticity comparison diagram of the NbTaV-Ti based medium entropy alloy of the present invention and other single-phase bcc structure incompatible medium / high entropy alloys. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings, which are intended to explain the present invention rather than to limit it.

[0026] A high-strength and tough NbTaV-based medium-entropy alloy comprises, by atomic percentage (at.%), 49-51% Nb, 24-26% Ta, 19-21% V and 4-6% Ti.

[0027] The above-mentioned Nb, Ta, V and Ti are all high-purity metal particles, and the purity is not less than 99.95%.

[0028] A method for preparing a high-strength and tough NbTaV-based medium-entropy alloy comprises the following steps:

[0029] Step 1: Calculated by atomic percentage, 49-51% of Nb, 24-26% of Ta, 19-21% of V and 4-6% of Ti metal particles are uniformly mixed.

[0030] The raw materials were weighed to an accuracy of 0.01 g.

[0031] Step 2: Smelting the mixed metal particles obtained in step 1 by vacuum arc melting to obtain alloy ingots.

[0032] During the smelting process, the vacuum is first reduced to 5Pa, and then high-purity argon is introduced and then vacuumed. The furnace is washed three times to ensure a high-purity vacuum environment. The smelting induction current is 395-495A. The alloy smelting process is accompanied by electromagnetic stirring, and the alloy is repeatedly remelted 5 times to ensure the uniformity of the composition. Finally, the alloy is cooled in a water-cooled copper crucible to obtain an ingot.

[0033] Step 3, cold rolling the ingot at room temperature, with the deformation amount controlled at 45-55%;

[0034] Step 4: After the cold-rolled ingot is heated at 800-1200° C. for 5 min and subjected to quenching heat treatment, a single-phase bcc structured NbTaV-Ti system medium entropy alloy is obtained.

[0035] Example 1

[0036] A method for preparing a NbTaV-Ti refractory medium entropy alloy comprises the following steps:

[0037] Step 1: Calculated by atomic percentage, 49% Nb, 26% Ta, 19% V, and 6% Ti metal particles are uniformly mixed.

[0038] Step 2, vacuum melting the metal particles. During the melting process, the vacuum is first reduced to 5Pa, and then high-purity argon gas is introduced and then vacuumized. The furnace is washed three times to ensure a high-purity vacuum environment. The melting induction current is 395A. The alloy melting process is accompanied by electromagnetic stirring, and the alloy is repeatedly remelted 5 times to ensure the uniformity of the composition. Finally, the alloy is cooled in a water-cooled copper crucible to obtain an ingot.

[0039] Step 3, cold rolling the ingot at room temperature, with the deformation amount controlled at 50%;

[0040] Step 4: The cold-rolled ingot is heated at 1000° C. for 5 min to obtain a single-phase bcc alloy through quenching heat treatment.

[0041] Nb50 Ta 25 V 20 After the Ti5 refractory medium entropy alloy is subjected to the above deformation heat treatment, the microstructure obtained is as follows Figure 1 As shown, the structure is a typical single-phase bcc structure with an average grain size of about 37μm. This structure allows the alloy to have excellent plasticity and high strength. According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as follows: tensile strength σ UTS is 887MPa, and the yield strength σ y is 787MPa, and the elongation at break ε T The alloy has excellent strength and plasticity.

[0042] Example 2

[0043] A method for preparing a NbTaV-Ti refractory medium entropy alloy comprises the following steps:

[0044] Step 1: Calculated by atomic percentage, 51% Nb, 25% Ta, 20% V and 4% Ti metal particles are uniformly mixed.

[0045] Step 2, vacuum melting the metal particles. During the melting process, the vacuum is first reduced to 5Pa, and then high-purity argon gas is introduced and then vacuumized. The furnace is washed three times to ensure a high-purity vacuum environment. The melting induction current is 395A. The alloy melting process is accompanied by electromagnetic stirring, and the alloy is repeatedly remelted 5 times to ensure the uniformity of the composition. Finally, the alloy is cooled in a water-cooled copper crucible to obtain an ingot.

[0046] Step 3, cold rolling the ingot at room temperature, with the deformation amount controlled at 48%;

[0047] Step 4: The cold-rolled ingot is heated at 900° C. for 5 min to obtain a single-phase bcc alloy through quenching heat treatment.

[0048] According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as follows: tensile strength σ UTS is 1015MPa, and the yield strength σ y is 864MPa, and the elongation at break ε T It is 17.5%, and the alloy has excellent strength and plasticity.

[0049] Example 3

[0050] A Nb 50 Ta 25 V 20 The preparation method of Ti5 refractory medium entropy alloy is as follows:

[0051] Step 1: Calculated by atomic percentage, 50% Nb, 24% Ta, 21% V, and 5% Ti metal particles are uniformly mixed.

[0052] Step 2, vacuum melting the metal particles. During the melting process, the vacuum is first reduced to 5Pa, and then high-purity argon is introduced and vacuumized again. The furnace is washed three times to ensure a high-purity vacuum environment. The melting induction current is 445A. The alloy melting process is accompanied by electromagnetic stirring, and the alloy is repeatedly remelted 6 times to ensure the uniformity of the composition. Finally, the alloy is cooled in a water-cooled copper crucible to obtain an ingot.

[0053] Step 3, cold rolling the ingot at room temperature, and controlling the deformation amount to 51%;

[0054] Step 4: The cold-rolled ingot is heated at 1100° C. for 5 min to obtain a single-phase bcc alloy through quenching heat treatment.

[0055] According to the requirements of GB / T228.1-2010 standard, the mechanical properties of the alloy are measured as follows: tensile strength σ UTS is 868MPa, and the yield strength σ y is 697MPa, and the elongation at break ε T The alloy has excellent strength and plasticity.

[0056] Comparative Example 1

[0057] A Nb 50 Ta 25 V 20 The preparation method of Ti5 refractory medium entropy alloy is as follows:

[0058] Step 1: Calculated by atomic percentage, 50% Nb, 24% Ta, 21% V, and 5% Ti metal particles are uniformly mixed.

[0059] Step 2, vacuum melting the metal particle mixture, first vacuum to 5Pa during the melting process, then introduce high-purity argon gas and evacuate again, repeat the furnace washing three times to ensure a high-purity vacuum environment, the melting induction current is 445A, the alloy melting process is accompanied by electromagnetic stirring, and repeated remelting 6 times to ensure the uniformity of the composition, and finally cooled in a water-cooled copper crucible to obtain an alloy ingot;

[0060] The grain size of the cast structure of the alloy was measured, and the mechanical properties were tested. The alloy was a single-phase bcc alloy with an average grain size of 53 μm, which was larger than that of Example 1.

[0061] According to the requirements of GB / T228.1-2010 standard, the measured mechanical properties of the alloy are as follows Figure 2 As shown in curve 3, the tensile strength σ UTS is 774, the yield strength σy is 711MPa, and the elongation at break ε T In general, compared with the examples, the alloy of Comparative Example 1 has very low strength and very low elongation.

[0062] Comparative Example 2

[0063] A Nb 50 Ta 25 V 20 The preparation method of Ti5 refractory medium entropy alloy is as follows:

[0064] Step 1: Calculated by atomic percentage, 50% Nb, 24% Ta, 21% V, and 5% Ti metal particles are uniformly mixed.

[0065] Step 2, vacuum melting the metal particles. During the melting process, the vacuum is first reduced to 5Pa, and then high-purity argon is introduced and vacuumized again. The furnace is washed three times to ensure a high-purity vacuum environment. The melting induction current is 445A. The alloy melting process is accompanied by electromagnetic stirring, and the alloy is repeatedly remelted 6 times to ensure the uniformity of the composition. Finally, the alloy is cooled in a water-cooled copper crucible to obtain an ingot.

[0066] Step 3: cold rolling the ingot at room temperature, controlling the deformation amount to 51%, and obtaining a rolled alloy after cold rolling.

[0067] The grain size of the rolled structure of the alloy was measured, and the mechanical properties were tested. The alloy is a single-phase bcc alloy with an average grain size of 26 μm, which is smaller than that of Example 1.

[0068] According to the requirements of GB / T228.1-2010 standard, the measured mechanical properties of the alloy are as follows Figure 2 As shown in curve 3, the tensile strength σ UTS is 1148, yield strength σ y is 1088MPa, elongation at break ε T In general, compared with the embodiment, the strength of the alloy of comparative example 2 is greatly improved, but the elongation is seriously reduced.

[0069] Figure 3 The strength-plasticity comparison diagram of the NbTaV-Ti medium entropy alloy in the cast state of comparative example 1, the rolled state of comparative example 2, and the rolled state + 1000℃ quenching heat treatment for 5 min of Examples 1-3 with other bcc refractory medium / high entropy alloys. It can be seen that the NbTaV-Ti medium entropy alloy has excellent plasticity-strength matching after being rolled + 1000℃ quenching heat treatment for 5 min.

[0070] The present invention discloses a high-strength and tough NbTaV-based medium-entropy alloy and a preparation method, and designs a new solid solution-strengthened NbTaV-Ti medium-entropy alloy. After smelting, cold rolling and appropriate temperature quenching heat treatment, the alloy can obtain excellent plasticity-strength matching. On the one hand, the high yield strength is due to the addition of V elements with small atomic radius, which leads to severe lattice distortion and strong solid solution strengthening. On the other hand, compared with the cast alloy, high-density dislocation entanglements are generated after cold rolling, and the number of dislocations is greatly increased, resulting in work hardening of the alloy and increased strength. After quenching heat treatment, dislocation entanglements are resolved, the average grain size is reduced, the number of grains is increased, fine grain strengthening is generated, the material strength is improved, and the plasticity of the material is significantly improved. Based on the above characteristics, the NbTaV-Ti refractory medium-entropy alloy has excellent plasticity-strength matching. The Nb element selected in the alloy of the present invention has good high-temperature stability, the Ta element improves the ability to resist high-temperature creep and oxidation, the V element is small in size and light in density, which is conducive to the formation of lattice distortion, and the Ti element improves the oxidation resistance. Therefore, the NbTaV-Ti system medium entropy alloy of the present invention not only has excellent comprehensive mechanical properties, but also has great potential in other properties. This alloy has great prospects for engineering application.

[0071] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A high-strength and tough NbTaV-based medium-entropy alloy, characterized in that: In terms of atomic percentage, it includes 49-51% Nb, 24-26% Ta, 19-21% V and 4-6% Ti; The method for preparing the high-strength and toughness NbTaV-based medium-entropy alloy comprises the following steps: Step 1, mixing the raw materials according to atomic percentage to obtain a metal particle mixture; Step 2, vacuum melting the metal particle mixture to obtain an ingot; Step 3, cold rolling the ingot with a deformation amount of 45-55%; Step 4: quenching the cold-rolled ingot to obtain a single-phase bcc structured NbTaV-Ti refractory medium entropy alloy.

2. A high-strength and tough NbTaV-based medium-entropy alloy according to claim 1, characterized in that: The tensile strength of the NbTaV-based medium-entropy alloy is greater than 850 MPa, the yield strength is greater than 750 MPa, and the total elongation at break is greater than 19%.

3. A high-strength and tough NbTaV-based medium-entropy alloy according to claim 1, characterized in that: The method of vacuum melting in step 2 is as follows: During the smelting process, the vacuum is first reduced to 5Pa, and then high-purity argon is introduced and the vacuum is evacuated again. The smelting induction current is 395-495A. Electromagnetic stirring is used during the smelting process, and remelting is repeated until the composition is uniform. Finally, the ingot is obtained by water cooling.

4. A high-strength and tough NbTaV-based medium-entropy alloy according to claim 3, characterized in that: The number of remelting is greater than 5 times.

5. The high-strength and tough NbTaV-based medium-entropy alloy according to claim 1, characterized in that: The quenching method is as follows: The cold rolled ingot was heated at 800-1200°C for 5 min for quenching.

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