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

Abstract

The invention provides a high-plasticity niobium-tantalum-based refractory medium-entropy alloy and a preparation method thereof, the chemical formula of the alloy is NbaTabHfcModWe, and the atomic percent of elements a: b: c: d: e is equal to (45%-47.5%): (45%-47.5%): (0-5%): (0-5%): (2%-5%). The alloy is prepared by adopting vacuum arc melting. The refractory medium-entropy alloy disclosed by the invention is uniform in alloy structure, has the characteristic of high plasticity, shows excellent comprehensive mechanical properties, can meet the service requirements in an ultra-high-temperature environment, and is expected to be applied to severe service environments such as aerospace and the like.

Description

Technical Field

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

[0002] High-performance metal structural materials are an important factor in promoting the progress of industries such as aerospace and military. With the development of science and technology, the temperature that traditional nickel-based high-temperature alloys can withstand is close to their material limits due to their own melting points, and they cannot meet the requirements of serving in high-temperature and high-pressure harsh environments such as the next generation of aircraft engine propulsion and industrial gas turbines. Therefore, it is urgent to develop a high-strength and high-toughness material that can withstand high temperatures.

[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 5 or more main elements, each of which is in equiatomic ratio or nearly equiatomic ratio. According to the type and content of the main element, the mixing entropy of some alloys is between low entropy alloys and high entropy alloys, so it is called medium entropy alloy. Medium entropy alloys have excellent mechanical and physical and chemical properties due to their four unique effects (medium entropy effect, hysteresis diffusion effect, lattice distortion effect, cocktail effect). One of them is a refractory medium entropy alloy prepared from high melting point metal elements such as Hf, Nb, Ta, Mo, and W. It has excellent mechanical properties and unique properties such as high temperature oxidation resistance and corrosion resistance at room temperature and high temperature. It is expected to replace nickel-based high temperature alloys and has broad application prospects and research value.

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

[0005] After searching, the Chinese invention patent with application publication number CN111363964A discloses a W-Ta-Mo-Nb-Hf-C high temperature high entropy alloy and its preparation method, wherein the high temperature high entropy alloy is composed of W, Ta, Mo, Nb, Hf and C in equal atomic ratios or non-equal atomic ratios. The invention also provides a preparation method of the high temperature high entropy alloy, including: 1) weighing the required weight of W, Ta, Mo, Nb, Hf and C raw materials; 2) performing vacuum arc melting). The patent regulates the phase structure and microstructure of the alloy by introducing the non-metallic element C. This method of adding the C element will cause the Nb-Ta-Mo-Hf-WC system alloy to have great room temperature brittleness. Summary of the invention

[0006] In view of the defects in the prior art, the object of the present invention is 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 invention, a high plasticity niobium-tantalum-based refractory medium entropy alloy is provided, wherein the chemical formula of the alloy is 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%).

[0008] Furthermore, the alloy consists of a single BCC phase.

[0009] Furthermore, the cast microstructure of the alloy exhibits a dendritic growth morphology.

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

[0011] Weigh Nb, Ta, Hf, Mo, and W metal blocks respectively according to the designed atomic molar ratio;

[0012] First put a titanium ingot into the crucible, and then put each metal block in order from low to high melting point, and perform vacuum arc melting to obtain a master alloy ingot, which is a high-plasticity niobium-tantalum-based refractory medium-entropy alloy.

[0013] Optionally, the Nb, Ta, Hf, Mo, and W metal blocks are weighed respectively according to the designed atomic molar 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, the process includes: extracting a vacuum and introducing a protective gas, wherein the vacuum degree is 5.0×10 -3 Pa, the pressure of the protective gas is 0.5kPa.

[0015] Optionally, the vacuum arc melting includes: melting the titanium ingot before melting the metal block raw material each time.

[0016] Optionally, the vacuum arc melting includes: accelerating the homogenization of elements in the alloy melt by applying an external electromagnetic stirring action during the melting process.

[0017] Optionally, the vacuum arc melting comprises:

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

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

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

[0021] 1. The high-plasticity niobium-tantalum-based refractory medium-entropy alloy and preparation method thereof provided by the present invention comprehensively consider the effects of various added elements. Through the interaction between the elements Nb, Ta, Mo, Hf, W and the content of each element in the alloy, the obtained refractory medium-entropy alloy is composed of a single BCC phase, does not contain an intermetallic compound phase, has a uniform alloy structure, and the microstructure presents a dendrite growth morphology. The alloy has the strength advantages of the matrix elements Nb and Ta, and has the characteristics of high plasticity, and can meet the service requirements under ultra-high temperature environments; the alloy composition control method is simple and effective, and the Nb content is controlled. a Ta b Hf c Mo d W e The development and application of system alloys are of great value.

[0022] 2. The refractory medium-entropy alloy of the present invention has excellent tensile plastic deformation ability at room temperature and has relatively outstanding strength. The tensile yield strength at room temperature can reach 482 MPa, the tensile strength is nearly 580 MPa, and the elongation at break can reach 13%. It has excellent comprehensive mechanical properties and can support the engineering application of refractory high-entropy / medium-entropy alloys, and can be used in aerospace, military industry and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0024] Figure 1 A schematic diagram of a process for preparing a refractory medium entropy alloy and conducting analysis and testing in one embodiment of the present invention;

[0025] Figure 2 X-ray diffraction patterns of samples obtained in Example 1, Example 2 and Example 3 of the present invention;

[0026] Figure 3 This is an optical microscope photo of the sample obtained in Example 1 of the present invention;

[0027] Figure 4This is an optical microscope photo of the sample obtained in Example 2 of the present invention;

[0028] Figure 5 This is an optical microscope photograph of the sample obtained in Example 3 of the present invention;

[0029] Figure 6 The engineering stress-strain curve of the tensile test at room temperature of Example 1 of the present invention;

[0030] Figure 7 The engineering stress-strain curve of the tensile test at room temperature of Example 2 of the present invention;

[0031] Figure 8 This is the engineering stress-strain curve of the tensile test at room temperature of Example 3 of the present invention. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0033] An embodiment of the present invention provides a high plasticity niobium-tantalum-based refractory medium entropy alloy. The alloy is composed of five high melting point metal elements, namely Nb, Ta, Hf, Mo, and W, with Nb and Ta as the main matrix elements. The chemical formula is 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 invention, the alloy is composed of a single BCC phase, and the alloy structure is uniform. The cast microstructure of the alloy presents a dendrite growth morphology. The alloy has the strength advantages of the matrix elements Nb and Ta, and has the characteristics of high plasticity, and has excellent comprehensive mechanical properties. 47 Ta 47 The tensile yield strength of Hf2Mo2W2 alloy at room temperature can reach 482MPa, the tensile strength is nearly 580MPa, and the elongation at break can reach 13%.

[0035] The high-plasticity niobium-tantalum-based refractory medium-entropy alloy in the embodiment of the present invention has a composition obtained by phase diagram calculation-assisted component design. Starting from the excellent plasticity and corrosion resistance of the Nb and Ta matrix elements, the Hf element is easy to process and can absorb impurity elements such as O and C, and the Mo and W elements can improve the melting point and high-temperature strength. 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, can meet the harsh service requirements in ultra-high temperature environments such as aerospace, and can be used in high-temperature and high-pressure harsh environments such as aircraft engine propulsion and industrial gas turbines.

[0036] Another embodiment of the present invention further provides a method for preparing the above-mentioned high plasticity niobium-tantalum-based refractory medium entropy alloy, wherein the method adopts a vacuum arc melting method to prepare the high plasticity niobium-tantalum-based refractory medium entropy alloy, referring to Figure 1 The preparation method of the high plasticity niobium-tantalum-based refractory medium entropy alloy comprises:

[0037] Weigh Nb, Ta, Hf, Mo, and W metal blocks respectively according to the designed atomic molar ratio;

[0038] First put the titanium ingot in the crucible, and then put the metal blocks in order from low to high melting points, that is, before smelting, put the low melting point metal block in the crucible first as a cushion, and then put the metal block with relatively higher melting point on it, and then put them in order for vacuum arc melting to ensure that the metal block with the highest melting point is closest to the arc during melting, so that it can be completely melted at the highest temperature, ensuring that the blocks of refractory metal elements are completely melted and smelted evenly, reducing the occurrence of casting defects, and obtaining a master alloy ingot (small-sized button ingot), which is a high-plasticity niobium-tantalum-based refractory medium entropy alloy.

[0039] In some embodiments, Nb, Ta, Hf, Mo, and W metal blocks are weighed according to the designed atomic molar 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 raw material surface 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 an accuracy of 0.001g is used for weighing.

[0040] Since refractory high entropy alloys are easily oxidized at high temperatures, in some embodiments, before vacuum arc melting, the process includes: extracting a vacuum and introducing a protective gas, wherein the vacuum degree is 5.0×10 -3The protective gas is argon or other types of inert gases to prevent oxygen in the environment from entering the alloy during the smelting process and affecting the alloy properties. It should be noted that the vacuum degree and the pressure of the protective gas are related to the vacuum melting furnace used. In some other embodiments, the vacuum degree and the pressure of the protective gas can be appropriately adjusted according to the equipment performance and the oxygen content in the smelting environment.

[0041] In some embodiments, vacuum arc melting is performed, including: melting the titanium ingot before each melting of the metal block raw material to absorb the residual oxygen that may be in the melting furnace. Preferably, the titanium ingot is melted 2 to 3 times to achieve a more thorough elimination of oxygen and avoid oxidation of the alloy during subsequent melting of the alloy.

[0042] In some embodiments, vacuum arc melting is performed, including: accelerating the homogenization of elements in the alloy melt by applying an external electromagnetic stirring effect during the melting process.

[0043] In some embodiments, vacuum arc melting is performed, including: after melting the titanium ingot, the metal block raw material is quickly heated and melted, each alloy button ingot (refractory medium entropy alloy) is turned over after the melting is completed and completely cooled, and the mother alloy ingot is repeatedly melted.

[0044] In some embodiments, the master alloy ingot is obtained by repeated smelting, wherein: the smelting is repeated 6 to 8 times, each smelting time is 2 to 3 minutes, and the smelting current is 320 to 380A. The repeated smelting can reduce or even avoid the influence of each smelting time, smelting current difference, etc. on the sample structure and performance. The melting point span of the alloy components used in the embodiment of the present invention is about 2600°C to 2750°C, and the melting points of different alloy components are different. The parameters such as smelting time and current are considered to have different melting point settings, so that each metal raw material block is fully melted and smelted evenly, thereby achieving the uniformity of the structure of the final alloy product.

[0045] The above-mentioned embodiment of the present invention, while retaining the strength advantage of the refractory elements Nb and Ta, adjusts the composition content of Mo, W and Hf through alloy design, and obtains a refractory medium-entropy alloy with high plasticity through vacuum arc melting technology. At the same time, it has good comprehensive mechanical properties and can be applied to the fields of aerospace, military industry, etc.

[0046] In order to illustrate the performance of the high-plasticity refractory medium-entropy alloy material in the embodiment of the present invention, a high-purity (99.99%) metal block was used as the initial raw material and vacuum arc melting technology was used to prepare Nb (45％～47.5％) Ta (45％～47.5％) Hf (0％～5％) Mo (0％～5％) W (2％～5％)Alloy, analyze its phase composition and microstructure, and test its room temperature tensile properties. Details are as follows:

[0047] Example 1

[0048] The medium entropy alloy in this embodiment contains four high melting point metal elements: Nb, Ta, Mo, and W. The chemical formula is Nb 47.5 Ta 47.5 Mo 2.5 W 2.5 .

[0049] The preparation process of the quaternary medium entropy alloy in this embodiment is as follows: 47.5 Ta 47.5 Mo 2.5 W 2.5 The atomic molar ratio of each element in the mixture is determined by selecting high-purity raw material blocks with a purity greater than 99.99%. After being washed and dried with an alcohol solution, they are weighed using a precision electronic balance (with an accuracy of 0.001g) according to the designed atomic molar ratio. The treated high-purity metal raw materials are then placed in the water-cooled copper crucible of a WK-Ⅱ type non-consumable vacuum arc melting furnace in the order of melting point from low to high. The furnace door is closed to evacuate the arc melting furnace to a vacuum of 5.0×10 -3 Pa or less) and argon protective gas (0.5kPa) is introduced. Before each smelting of the raw materials, the titanium ingot is smelted 2 to 3 times. During smelting, the electromagnetic stirring effect is used to accelerate the homogenization of the alloy melt. At the same time, each alloy button ingot is turned over after the smelting is completed and completely solidified. The smelting is repeated 6 to 8 times to obtain a mother alloy ingot. The single smelting time is 2 to 3 minutes, and the smelting current is 380A. After the smelting is completed, it is cooled in a water-cooled copper crucible for 30 minutes, and the furnace is opened and taken out to obtain a mother alloy ingot.

[0050] The quaternary medium entropy alloy button ingot of this embodiment has a bright surface and no visible defects. The phase composition and microstructure of the quaternary medium entropy alloy button ingot were tested by X-ray diffractometer and optical microscope respectively. The results are as follows: Figure 2 and Figure 3 As shown. Figure 2 It can be seen that the quaternary medium entropy alloy button ingot is composed of a single BCC phase. Figure 3 It can be seen that the as-cast microstructure of the quaternary medium-entropy alloy button ingot shows a dendritic growth morphology.

[0051] The room temperature tensile properties of quaternary medium entropy alloy button ingots were tested using a universal testing machine. Figure 6 .Depend on Figure 6 It can be seen that: the quaternary medium entropy alloy Nb 47.5 Ta 47.5 Mo 2.5 W 2.5The button ingot has a tensile yield strength of 397 MPa, a tensile strength of 424 MPa, and an elongation at break of 10%.

[0052] Example 2

[0053] The medium entropy alloy of this embodiment contains four high melting point metal elements: Nb, Ta, Hf, and W. 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 embodiment is as follows: 47.5 Ta 47.5 Hf 2.5 W 2.5 The atomic molar ratio of each element in the mixture is determined by selecting high-purity raw material blocks with a purity greater than 99.99%. After being washed and dried with an alcohol solution, they are weighed using a precision electronic balance (with an accuracy of 0.001g) according to the designed atomic molar ratio. The treated high-purity metal raw materials are then placed in the water-cooled copper crucible of a WK-Ⅱ type non-consumable vacuum arc melting furnace in the order of melting point from low to high. The furnace door is closed to evacuate the arc melting furnace to a vacuum of 5.0×10 -3 Pa or less) and introduce argon protective gas (0.5kPa). Before each smelting of the raw materials, the titanium ingot is smelted 2 to 3 times first; during smelting, the electromagnetic stirring effect is used to accelerate the homogenization of the alloy melt. At the same time, each alloy button ingot is turned over after the smelting is completed and completely solidified. The smelting is repeated 6 to 8 times to obtain a mother alloy ingot. The single smelting time is 2 to 3 minutes, and the smelting current is 320A; after the smelting is completed, it is cooled in a water-cooled copper crucible for 30 minutes, and the furnace is opened and taken out to obtain a mother alloy ingot.

[0055] The quaternary medium entropy alloy button ingot of this embodiment has a bright surface and no visible defects. The phase composition and microstructure of the quaternary medium entropy alloy button ingot were tested by X-ray diffractometer and optical microscope respectively. The results are as follows: Figure 2 and Figure 4 As shown. Figure 2 It can be seen that the quaternary medium entropy alloy button ingot is composed of a single BCC phase. Figure 4 It can be seen that the as-cast microstructure of the quaternary medium-entropy alloy button ingot shows a dendritic growth morphology.

[0056] The room temperature tensile properties of quaternary medium entropy alloy button ingots were tested using a universal testing machine. Figure 7 .Depend on Figure 7 It can be seen that: the quaternary medium entropy alloy Nb 47.5 Ta 47.5 Hf 2.5 W 2.5The button ingot has a tensile yield strength of 450MPa, a tensile strength of 527MPa, and an elongation at break of 10%.

[0057] Example 3

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

[0059] The preparation process of the five-element medium-entropy alloy in this embodiment is as follows: 47 Ta 47 The atomic molar ratio of each element in Hf2Mo2W2 was weighed according to the designed atomic molar ratio using a precision electronic balance (accuracy of 0.001g) after washing and drying with an alcohol solution; then the treated high-purity metal raw materials were placed in the water-cooled copper crucible of the WK-Ⅱ type non-consumable vacuum arc melting furnace in the order of melting point from low to high, and the furnace door was closed to evacuate the arc melting furnace to a vacuum (5.0×10 - 3 Pa or less) and argon protective gas (0.5kPa) is introduced. Before each smelting of raw materials, the titanium ingot is smelted 2 to 3 times. During smelting, the homogenization of the alloy melt is accelerated by electromagnetic stirring. At the same time, each alloy button ingot is turned over after smelting and complete solidification. The mother alloy ingot is smelted repeatedly for 6 to 8 times. The single smelting time is 2 to 3 minutes, and the smelting current is 360A; after the smelting is completed, it is cooled in a water-cooled copper crucible for 30 minutes, and the furnace is opened to take out to obtain the mother alloy ingot.

[0060] The five-element medium-entropy alloy button ingot of this embodiment has a bright surface and no visible defects. The phase composition and microstructure of the five-element medium-entropy alloy button ingot were tested by X-ray diffractometer and optical microscope respectively. The results are as follows: Figure 2 and Figure 5 As shown. Figure 2 It can be seen that the quaternary medium entropy alloy button ingot is composed of a single BCC phase. Figure 5 It can be seen that the as-cast microstructure of the five-element medium-entropy alloy button ingot shows a dendritic growth morphology.

[0061] The room temperature tensile properties of quaternary medium entropy alloy button ingots were tested using a universal testing machine. Figure 8 .Depend on Figure 8 It can be seen that the five-element medium-entropy alloy Nb 47 Ta 47 The tensile yield strength of Hf2Mo2W2 button ingot is 482MPa, the tensile strength is 580MPa, and the elongation at break is 13%.

[0062] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A high plasticity 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 of each element is a:b:c:d:e = (45%~47.5%):(45%~47.5%):(0~5%):(0~5%):(2%~5%).

2. The high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 1, characterized in that: The alloy consists of a single BCC phase.

3. The high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 1, characterized in that: The cast microstructure of the alloy exhibits a dendritic growth morphology.

4. A method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to any one of claims 1 to 3, characterized in that: include: Weigh Nb, Ta, Hf, Mo, and W metal blocks respectively according to the designed atomic molar ratio; First put a titanium ingot into the crucible, and then put each metal block in order from low to high melting point, and perform vacuum arc melting to obtain a master alloy ingot, which is a high-plasticity niobium-tantalum-based refractory medium-entropy alloy.

5. The method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 4, characterized in that: The Nb, Ta, Hf, Mo and W metal blocks are weighed respectively according to the designed atomic molar ratio, wherein the purity of the Nb, Ta, Hf, Mo and W metal blocks is greater than 99.99%.

6. The method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 4, characterized in that: Before the vacuum arc melting is performed, the process includes: extracting a vacuum and introducing a protective gas, wherein the vacuum degree is 5.0×10 -3 Pa, the pressure of the protective gas is 0.5kPa.

7. The method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 4, characterized in that: The vacuum arc melting comprises: melting the titanium ingot before melting the metal block raw material each time.

8. The method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 4, characterized in that: The vacuum arc melting comprises: accelerating the homogenization of elements in the alloy melt by applying an external electromagnetic stirring action during the melting process.

9. The method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 4, characterized in that: The vacuum arc melting comprises: After the titanium ingot is smelted, the metal block raw material is quickly heated and melted. Each alloy button ingot is turned over after the smelting is completed and completely cooled, and the mother alloy ingot is obtained by repeated smelting.

10. The method for preparing a high plasticity niobium-tantalum-based refractory medium entropy alloy according to claim 9, characterized in that: The repeated smelting obtains a master alloy ingot, wherein the repeated smelting is performed 6 to 8 times, each smelting time is 2 to 3 minutes, and the smelting current is 320 to 380A.

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