High plasticity niobium-tantalum-based refractory medium-entropy alloy and preparation method thereof

Abstract

The application provides a high-plasticity niobium-tantalum-based refractory medium-entropy alloy and a preparation method thereof. a Ta b Hf c Mo d W e , and the atomic percentage of each element is a:b:c:d:e=(45% to 47.5%):(45% to 47.5%):(0 to 5%):(0 to 5%):(2% to 5%). The alloy is prepared by vacuum arc melting. The refractory medium-entropy alloy has a uniform structure, high plasticity, excellent comprehensive mechanical properties and can meet the service requirements in an ultrahigh-temperature environment, and is expected to be applied to harsh service environments such as aerospace.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of new materials, in particular to a high-plasticity niobium-tantalum-based refractory medium-entropy alloy and a preparation method thereof. BACKGROUND

[0002] High-performance metal structural materials are important factors for promoting the progress of the aerospace, military and other industries. With the development of science and technology, the service temperature of traditional nickel-based high-temperature alloys is close to the material limit under the constraint of their own melting point, and cannot meet the service requirements in high-temperature and high-pressure harsh environments such as next-generation aircraft engine propellers and industrial gas turbines. Therefore, it is urgent to develop a high-temperature-resistant high-strength and high-toughness material.

[0003] In recent years, researchers have proposed a new alloy design idea-high-entropy alloy. High-entropy alloy is a multi-element alloy system composed of five or more than five main elements, and each element is composed of equal atomic ratio or near equal atomic ratio. According to the difference of the main element types and contents, the mixing entropy of part of the alloy is between low-entropy alloy and high-entropy alloy, so it is called medium-entropy alloy. The medium-entropy alloy has excellent mechanical and physical properties due to its four unique effects (medium-entropy effect, delayed diffusion effect, lattice distortion effect and cocktail effect). A refractory medium-entropy alloy prepared from high-melting-point metal elements Hf, Nb, Ta, Mo and W has excellent mechanical properties at room temperature and high temperature, and unique properties such as high-temperature oxidation resistance and corrosion resistance, which is expected to replace nickel-based high-temperature alloys and has broad application prospects and research value.

[0004] However, the most classic NbMoTaW with single-phase BCC structure developed by Senkov et al. exhibits extremely high yield strength (405 MPa) at 1600℃, but only has a fracture compression rate of 2.1% under room temperature compression deformation, which greatly limits its application in the fields of aerospace and the like.

[0005] According to the search, the Chinese invention patent with the application publication number CN111363964A discloses a W-Ta-Mo-Nb-Hf-C high-temperature high-entropy alloy and a preparation method thereof. The high-temperature high-entropy alloy is composed of W, Ta, Mo, Nb, Hf and C in an atomic ratio or a non-equal atomic ratio. The application also provides a preparation method of the high-temperature high-entropy alloy, which comprises the following steps: 1) weighing W, Ta, Mo, Nb, Hf and C raw materials according to the required weight; and 2) performing vacuum arc melting. The patent regulates the phase structure and microstructure of the alloy by introducing the non-metallic element C. This way of adding C element will cause great room temperature brittleness of the Nb-Ta-Mo-Hf-W-C system alloy. SUMMARY

[0006] Aiming at the defects in the prior art, the present application aims to provide a high-plasticity niobium-tantalum-based refractory medium-entropy alloy and a preparation method thereof.

[0007] According to one aspect of the present application, a high-plasticity niobium-tantalum-based refractory medium-entropy alloy is provided, the chemical formula of the alloy being Nb a Ta b Hf c Mo d W e , and the atomic percentage of each element a:b:c:d:e=(45%-47.5%):(45%-47.5%):(0-5%):(0-5%):(2%-5%).

[0008] Further, the alloy is composed of a single BCC phase.

[0009] Further, the as-cast microstructure of the alloy presents dendritic growth morphology.

[0010] According to another aspect of the present application, a preparation method of the above high-plasticity niobium-tantalum-based refractory medium-entropy alloy is provided, the method comprising:

[0011] The Nb, Ta, Hf, Mo and W metal blocks are weighed according to the designed atomic mole ratio;

[0012] The titanium ingot is first placed in the crucible, and then the metal blocks are sequentially placed in the order of low to high melting point, vacuum arc melting is performed, and a master alloy ingot is obtained, i.e. the high-plasticity niobium-tantalum-based refractory medium-entropy alloy.

[0013] Optionally, the Nb, Ta, Hf, Mo and W metal blocks are weighed according to the designed atomic mole ratio, wherein the purity of the Nb, Ta, Hf, Mo and W metal blocks is greater than 99.99%.

[0014] Optionally, before the vacuum arc melting, it comprises: extracting vacuum and introducing protective gas, wherein the vacuum degree is less than 5.0*10 -3 Pa, and the gas pressure of the protective gas is 0.5 kPa.

[0015] Optionally, the vacuum arc melting comprises: before each time of melting the metal block raw material, the titanium ingot is first melted.

[0016] Optionally, the vacuum arc melting comprises: during the melting process, the element homogenization of the alloy melt is accelerated by external electromagnetic stirring.

[0017] Optionally, the vacuum arc melting comprises:

[0018] After the titanium ingot is smelted, the metal block raw material is rapidly heated and melted, each alloy button ingot is turned over after being completely cooled after smelting is completed, and the mother alloy ingot is obtained through repeated smelting.

[0019] Optionally, the repeated smelting obtains the mother alloy ingot, wherein: the repeated smelting is performed 6-8 times, each time the smelting time is 2-3 min, and the smelting current is 320-380 A.

[0020] Compared with the prior art, the present application has at least one of the following beneficial effects:

[0021] 1. The high-plasticity niobium-tantalum-based refractory medium-entropy alloy and the preparation method thereof provided by the present application comprehensively consider the effects of various additive elements, and the refractory medium-entropy alloy obtained through the mutual cooperation between the elements Nb, Ta, Mo, Hf and W in the alloy and the content of each element is composed of a single BCC phase and does not contain an intermetallic compound phase, the alloy has a uniform structure and a dendritic growth morphology, the alloy has the strength advantages of the base elements Nb and Ta, and has the characteristics of high plasticity, can meet the service requirements in an ultrahigh-temperature environment, and the alloy composition regulation method is simple and effective, and can effectively reduce the cost of the alloy. a Ta b Hf c Mo d W e The development and application of the system alloy have important values.

[0022] 2. The refractory medium-entropy alloy has excellent tensile plastic deformation capacity at room temperature, and has prominent strength, the tensile yield strength at room temperature can reach 482 Mpa, the tensile strength is close to 580 MPa, and the fracture elongation can reach 13%, and the alloy has excellent comprehensive mechanical properties, can support the engineering application of refractory high-entropy / medium-entropy alloys, and can be applied to the fields of aerospace, military industry and the like. BRIEF DESCRIPTION OF DRAWINGS

[0023] Other characteristics, objects and advantages of the present application will become more apparent through reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings:

[0024] Figure 1 The flowchart shows the preparation of the refractory medium-entropy alloy and the analysis and testing in an embodiment of the present application.

[0025] Figure 2 The X-ray diffraction patterns of the samples prepared in embodiment 1, embodiment 2 and embodiment 3 of the present application are shown.

[0026] Figure 3 The optical microscope photograph of the sample prepared in embodiment 1 of the present application is shown.

[0027] Figure 4Optical microscope photo of the sample prepared for the embodiment 2 of the present application;

[0028] Figure 5 Optical microscope photo of the sample prepared for the embodiment 3 of the present application;

[0029] Figure 6 Engineering stress-strain curve of the tensile test at room temperature for the embodiment 1 of the present application;

[0030] Figure 7 Engineering stress-strain curve of the tensile test at room temperature for the embodiment 2 of the present application;

[0031] Figure 8 Engineering stress-strain curve of the tensile test at room temperature for the embodiment 3 of the present application. DETAILED DESCRIPTION

[0032] The present application will be described in detail below with specific embodiments. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made. These are within the scope of the present application.

[0033] An embodiment of the present application provides a high-plasticity niobium-tantalum-based refractory medium-entropy alloy, which selects five high-melting-point metal elements of Nb, Ta, Hf, Mo and W, takes Nb and Ta as main matrix elements, and has a chemical formula of Nb a Ta b Hf c Mo d W e , and the atomic percentage of each element is a:b:c:d:e=(45%~47.5%):(45%~47.5%):(0~5%):(0~5%):(2%~5%).

[0034] In the embodiment of the present application, the alloy is composed of a single BCC phase, and the alloy organization is uniform. The as-cast microstructure of the alloy presents dendritic growth morphology. The alloy has the strength advantages of matrix elements Nb, Ta, and has the characteristics of high plasticity, and has excellent comprehensive mechanical properties, wherein the Nb 47 Ta 47 Hf2Mo2W2 alloy has a tensile yield strength of 482 MPa at room temperature, a tensile strength of nearly 580 MPa, and a fracture elongation of 13%.

[0035] The high-plasticity niobium-tantalum-based refractory medium-entropy alloy in the embodiment of the present application is obtained through phase diagram calculation assisted component design. Starting from the excellent plasticity and corrosion resistance of the Nb and Ta matrix elements, the medium-entropy alloy with the above composition takes into account the strength and room temperature tensile plasticity of the Nb-Ta-Hf-Mo-W system, has excellent comprehensive mechanical properties, and can meet the harsh service requirements in aerospace and other ultra-high temperature environments, and can be applied to high-heat and high-pressure harsh environments such as aircraft engine propellers and industrial gas turbines.

[0036] Another embodiment of the present application also provides a preparation method of the high-plasticity niobium-tantalum-based refractory medium-entropy alloy described above. The method uses a vacuum arc melting method to prepare the high-plasticity niobium-tantalum-based refractory medium-entropy alloy, and refers to Figure 1 The preparation method of the high-plasticity niobium-tantalum-based refractory medium-entropy alloy includes the following steps.

[0037] The Nb, Ta, Hf, Mo, and W metal blocks are weighed according to the designed atomic mole ratio.

[0038] The titanium ingot is first placed in the crucible, and then the metal blocks are sequentially placed in the crucible according to the order from low to high melting point, that is, before melting, the low-melting-point metal blocks are first placed in the crucible to pad, and then the metal blocks with relatively higher melting points are placed on them, and the metal blocks are sequentially placed and padded, and vacuum arc melting is performed, so that the metal block with the highest melting point is closest to the electric arc during melting, so that it is completely melted at the highest temperature, ensuring that the blocks of each refractory metal element are completely melted and uniformly melted, reducing the generation of casting defects, and obtaining a master alloy ingot (small-size button ingot), which is the high-plasticity niobium-tantalum-based refractory medium-entropy alloy.

[0039] In some embodiments, the Nb, Ta, Hf, Mo, and W metal blocks are weighed according to the designed atomic mole ratio, wherein the purity of the Nb, Ta, Hf, Mo, and W metal blocks is greater than 99.99%. In order to remove impurities on the surface of the metal blocks, the surface of the raw material is treated before weighing, and high-purity Nb, Ta, Hf, Mo, and W metal blocks are taken, cleaned with an alcohol solution, and dried. In order to ensure the ratio of each metal element, a precision electronic balance with a precision of 0.001 g is used for weighing.

[0040] Because the refractory high-entropy alloy is easily oxidized at high temperature, in some embodiments, before vacuum arc melting, the method includes: extracting vacuum and introducing protective gas, wherein the vacuum degree is 5.0*10 -3Pa, the pressure of the protective gas is 0.5 kPa. The protective gas can be argon or other kinds of inert gas, so as to prevent the oxygen in the environment from entering the alloy during the smelting process and avoid affecting the performance of the alloy. It should be noted that the vacuum degree and the pressure of the protective gas are related to the vacuum smelting furnace used, and in other embodiments, the vacuum degree and the pressure of the protective gas can also be appropriately adjusted according to the performance of the equipment and considering the oxygen content in the smelting environment.

[0041] In some embodiments, the vacuum arc smelting is performed, including: before each time the metal block raw material is smelted, the titanium ingot is first smelted to absorb the oxygen that can be left in the smelting furnace. Preferably, the titanium ingot is smelted for 2-3 times to achieve the effect of more thoroughly eliminating oxygen and avoiding the oxidation of the alloy during the subsequent smelting of the alloy.

[0042] In some embodiments, the vacuum arc smelting is performed, including: during the smelting process, the element homogenization of the alloy melt is accelerated by the external electromagnetic stirring effect.

[0043] In some embodiments, the vacuum arc smelting is performed, including: after the titanium ingot is smelted, the metal block raw material is rapidly heated and melted, each alloy button ingot (refractory medium-entropy alloy) is turned over after being completely cooled after the smelting is completed, and the mother alloy ingot is obtained by repeated smelting.

[0044] In some embodiments, the mother alloy ingot is obtained by repeated smelting, wherein: the repeated smelting is performed for 6-8 times, the smelting time is 2-3 min each time, and the smelting current is 320-380 A. The repeated smelting can reduce or even avoid the influence of the difference in smelting time and smelting current on the structure and performance of the sample. The melting point span of the alloy composition used in the embodiments of the present application is about 2600℃-2750℃, and the melting points of different alloy compositions are different. The smelting time, current and other parameters are set according to the different melting points, so that each metal block raw material is fully melted and uniformly smelted, thereby realizing the uniformity of the structure of the final alloy product.

[0045] In the above embodiments of the present application, the strength advantages of refractory elements Nb and Ta are retained, the content of Mo, W and Hf is adjusted by alloy design, and a refractory medium-entropy alloy with high plasticity is obtained by vacuum arc smelting technology, which has good comprehensive mechanical properties and can be applied to the fields of aerospace, military industry and the like.

[0046] To illustrate the performance of the refractory medium-entropy alloy material with high plasticity in the embodiments of the present application, high-purity (99.99%) metal blocks are used as initial raw materials, and vacuum arc smelting technology is used to prepare Nb (45％～47.5％) Ta (45％～47.5％) Hf (0％～5％) Mo (0％～5％) W (2％～5％)The alloy was analyzed for phase composition and microstructure, and its room temperature tensile properties were tested. The details are as follows:

[0047] Example 1

[0048] The medium-entropy alloy of this example contains four high-melting-point metal elements of Nb, Ta, Mo, and W, and has a chemical formula of Nb 47.5 Ta 47.5 Mo 2.5 W 2.5 .

[0049] The preparation process of the quaternary medium-entropy alloy of this example is as follows: according to the atomic molar ratio of each element in the quaternary medium-entropy alloy Nb 47.5 Ta 47.5 Mo 2.5 W 2.5 , high-purity raw material blocks with a purity of more than 99.99% are selected, cleaned with an alcohol solution, dried, and then weighed according to the designed atomic molar ratio using a precision electronic balance (accuracy of 0.001 g); then the treated high-purity metal raw materials are sequentially placed in the water-cooled copper crucible of a WK-II non-consumable vacuum arc melting furnace in order of melting point from low to high, the furnace door is closed, the arc melting furnace is pumped to a vacuum (5.0 x 10 -3 Pa or below) and argon protection gas (0.5 kPa) is introduced, before each melting of raw materials, the titanium ingot is melted for 2-3 times; during melting, the electromagnetic stirring effect is used to accelerate the homogenization of the alloy melt, and after each alloy button ingot is completely solidified after melting, it is turned over and repeatedly melted for 6-8 times, the single melting time is 2-3 min, and the melting current is 380 A; after the melting is completed, the water-cooled copper crucible is cooled for 30 min, the furnace is opened and the alloy ingot is taken out.

[0050] It is observed that the surface of the quaternary medium-entropy alloy button ingot of this example is bright and has no visible defects. The phase composition and microstructure of the quaternary medium-entropy alloy button ingot are detected by X-ray diffractometer and optical microscope, and the results are shown in Figure 2 and Figure 3 It can be seen from Figure 2 that the quaternary medium-entropy alloy button ingot is composed of a single BCC phase. It can be seen from Figure 3 that the as-cast microstructure of the quaternary medium-entropy alloy button ingot presents a dendritic growth morphology.

[0051] The room temperature tensile properties of the quaternary medium-entropy alloy button ingot are tested by a universal testing machine, and the results are shown in Figure 6 . It can be seen from Figure 6 that the quaternary medium-entropy alloy Nb 47.5 Ta 47.5 Mo 2.5 W 2.5The tensile yield strength of the button ingot is 397 MPa, the tensile strength is 424 MPa, and the elongation at break is 10%.

[0052] Example 2

[0053] The medium-entropy alloy in this example contains four high-melting-point metal elements of Nb, Ta, Hf and W, and the chemical formula is Nb 47.5 Ta 47.5 Hf 2.5 W 2.5 .

[0054] The preparation process of the quaternary medium-entropy alloy in this example is as follows: according to the atomic molar ratio of each element in the quaternary medium-entropy alloy Nb 47.5 Ta 47.5 Hf 2.5 W 2.5 , high-purity raw material blocks with a purity of more than 99.99% are selected, cleaned with an alcohol solution, dried, and then weighed according to the designed atomic molar ratio using a precision electronic balance (accuracy of 0.001 g); then the treated high-purity metal raw materials are sequentially placed in the water-cooled copper crucible of the WK-II non-consumable vacuum arc melting furnace in order of melting point from low to high, the furnace door is closed, the arc melting furnace is pumped to vacuum (5.0 x 10 -3 Pa or below) and argon protection gas (0.5 kPa) is introduced, before each melting of raw materials, the titanium ingot is melted for 2-3 times; during melting, the electromagnetic stirring effect is used to accelerate the homogenization of the alloy melt, and after each alloy button ingot is completely solidified after melting, it is turned over and repeatedly melted for 6-8 times, the single melting time is 2-3 min, and the melting current is 320 A; after the melting is completed, the water-cooled copper crucible is cooled for 30 min, the furnace is opened and the mother alloy ingot is taken out.

[0055] It is observed that the surface of the quaternary medium-entropy alloy button ingot in this example is bright and has no visible defects. The phase composition and microstructure of the quaternary medium-entropy alloy button ingot are detected by X-ray diffractometer and optical microscope, and the results are shown in Figure 2 and Figure 4 . As can be seen from Figure 2 , the quaternary medium-entropy alloy button ingot is composed of a single BCC phase. As can be seen from Figure 4 , the as-cast microstructure of the quaternary medium-entropy alloy button ingot presents dendritic growth morphology.

[0056] The room temperature tensile properties of the quaternary medium-entropy alloy button ingot are tested by a universal testing machine, and the results are shown in Figure 7 . As can be seen from Figure 7 , the quaternary medium-entropy alloy Nb 47.5 Ta 47.5 Hf 2.5 W 2.5The tensile yield strength of the button ingot is 450 MPa, the tensile strength is 527 MPa, and the elongation at break is 10%.

[0057] Example 3

[0058] The medium-entropy alloy in this example contains five high-melting-point metal elements of Nb, Ta, Hf, Mo and W, and the chemical formula is Nb 47 Ta 47 Hf2Mo2W2.

[0059] The preparation process of the five-element medium-entropy alloy in this example is as follows: according to the atomic molar ratio of each element in the five-element medium-entropy alloy Nb 47 Ta 47 Hf2Mo2W2, after cleaning with an alcohol solution and drying, the elements are weighed according to the designed atomic molar ratio using a precision electronic balance (accuracy of 0.001 g); then the treated high-purity metal raw materials are sequentially placed in the water-cooled copper crucible of the WK-II non-consumable vacuum arc melting furnace in order of melting point from low to high, the furnace door is closed, the arc melting furnace is pumped to vacuum (5.0 x 10 - 3 Pa and argon protection gas (0.5 kPa) is introduced, before each time of melting raw materials, the titanium ingot is first melted for 2-3 times. During melting, the electromagnetic stirring is used to accelerate the homogenization of the alloy melt, and after each alloy button ingot is completely solidified after melting, it is turned over and repeatedly melted for 6-8 times. The single melting time is 2-3 min, and the melting current is 360 A; after the melting is completed, the water-cooled copper crucible is cooled for 30 min, the furnace is opened and taken out, and the master alloy ingot is obtained.

[0060] It is observed that the surface of the five-element medium-entropy alloy button ingot in this example is bright and has no visible defects. The phase composition and microstructure of the five-element medium-entropy alloy button ingot are detected by X-ray diffractometer and optical microscope, and the results are shown in Figure 2 and Figure 5 It can be seen from Figure 2 that the four-element medium-entropy alloy button ingot is composed of a single BCC phase. It can be seen from Figure 5 that the as-cast microstructure of the five-element medium-entropy alloy button ingot presents dendritic growth morphology.

[0061] The room temperature tensile properties of the four-element medium-entropy alloy button ingot are tested by a universal testing machine, and the results are shown in Figure 8 . It can be seen from Figure 8 that the tensile yield strength of the four-element medium-entropy alloy button ingot Nb 47 Ta 47 Hf2Mo2W2 is 450 MPa, the tensile strength is 527 MPa, and the elongation at break is 10%.

[0062] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The above preferred features can be combined in any manner without conflict, and used.

Claims

1. A high ductility niobium-tantalum based refractory medium entropy alloy characterized in that, The chemical formula of the alloy is Nb a Ta b Hf c Mo d W e , and the atomic percentage composition of each element satisfies any one of the following conditions: - 45%≤a≤47.5%, 45%≤b≤47.5%, 0<c≤5%, 0<d≤5%, 2%≤e≤5%, and a+b+c+d+e=100%; - 45%≤a≤47.5%, 45%≤b≤47.5%, c=0, 0<d≤5%, 2%≤e≤5%, and a+b+d+e=100%; - 45%≤a≤47.5%, 45%≤b≤47.5%, 0<c≤5%, d=0, 2%≤e≤5%, and a+b+c+e=100%.

2. The high plasticity niobium-tantalum based refractory medium entropy alloy of claim 1, wherein, The alloy is composed of a single BCC phase.

3. The high plasticity niobium-tantalum based refractory medium entropy alloy of claim 1, wherein, The as-cast microstructure of the alloy presents dendritic growth morphology.

4. A method of producing the high plasticity niobium tantalum based refractory medium entropy alloy of any one of claims 1-3, characterized in that, The method comprises the following steps: According to the designed atomic molar ratio, each element metal block is weighed; In the crucible, titanium ingot is first placed, and then each metal block is placed in order from low to high melting point, vacuum arc melting is carried out, and the master alloy ingot is obtained, that is, the high plasticity niobium-tantalum-based refractory medium-entropy alloy.

5. The method of claim 4, wherein the high plasticity refractory medium entropy niobium tantalum based alloy is prepared by the steps of: melting the alloying elements in a vacuum induction furnace; pouring the molten alloy into a graphite crucible; and casting the molten alloy into a graphite mold. According to the designed atomic molar ratio, each element metal block is weighed, wherein: the purity of each element metal block is greater than 99.99%.

6. The method of claim 4, wherein the high plasticity refractory medium entropy niobium-tantalum based alloy is prepared by the steps of: melting the alloying elements in a vacuum induction furnace; pouring the molten alloy into a graphite crucible; and casting the molten alloy into a mold. Before the vacuum arc melting, including: vacuum extraction and into the protective gas, wherein the vacuum degree is 5.0 x 10 -3 The pressure of the protective gas is 0.5 kPa.

7. The method of claim 4, wherein the high plasticity refractory medium entropy niobium-tantalum based alloy is prepared by the steps of: melting the alloying elements in a vacuum induction furnace; pouring the molten alloy into a graphite crucible; and casting the molten alloy into a mold. The vacuum arc melting comprises the following steps:

8. The method of claim 4, wherein the high plasticity refractory medium entropy niobium-tantalum based alloy is characterized by, The vacuum arc melting comprises the following steps:

9. The method of claim 4, wherein the high plasticity refractory medium entropy niobium-tantalum based alloy is characterized by, The vacuum arc melting comprises the following steps: After the titanium ingot is melted, the metal block raw material is rapidly heated and melted, each alloy button ingot is turned over after being completely cooled after melting, and the master alloy ingot is obtained by repeated melting.

10. The method of claim 9, wherein the high plasticity refractory medium entropy niobium-tantalum based alloy is prepared by the steps of: providing a niobium-tantalum based alloy; and hot working the niobium-tantalum based alloy. The repeated melting obtains the master alloy ingot, wherein: the repeated melting is 6-8 times, the melting time is 2-3 min each time, and the melting current is 320-380 A.

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