A nano-precipitate phase-reinforced refractory high-entropy alloy and its preparation method

Abstract

The present invention discloses a refractory high-entropy alloy strengthened by a nano-precipitate phase and a preparation method thereof, and relates to the technical field of preparation of new metal materials. The present invention uses NbMoTaW refractory high-entropy alloy as a matrix material, and effectively induces the phase separation phenomenon of the matrix by introducing a high proportion of Zr element into the matrix. Combined with a specific solid solution and aging treatment process, the formation of a uniformly dispersed nano-scale precipitate phase is successfully achieved. The refractory high-entropy alloy prepared by the present invention exhibits excellent performance characteristics, which not only significantly improves the basic properties of the material, but also provides more possibilities for its application in extreme environments. It is expected to promote the wider application and development of refractory high-entropy alloys in aerospace, nuclear industry and other fields.

Description

Technical Field

[0001] The present invention relates to the technical field of novel metal material preparation, and in particular to a nano-precipitation phase-reinforced refractory high-entropy alloy and a preparation method thereof. Background Art

[0002] The concept of refractory high-entropy alloys (RHEAs) was proposed by ON Senkov, chief scientist at the U.S. Air Force Laboratory. After more than a decade of development, these alloys have demonstrated excellent high-temperature mechanical properties, good softening resistance, and unique radiation resistance, garnering widespread attention from researchers worldwide and promising candidates for the next generation of high-temperature structural components. The pursuit of higher high-temperature strength has long been a design goal and research direction for high-temperature structural materials. However, most reported RHEAs have a single-phase body-centered cubic (BCC) structure, relying primarily on solid solution strengthening for strength. This single strengthening method has limited the development of RHEAs' high-temperature strength.

[0003] Existing technology prepares BCC single-phase refractory high-entropy alloys by dissolving a small amount of Zr in a NbMoTaW matrix. However, due to the lack of strengthening effect of the second phase, it is difficult to achieve further breakthroughs in the room temperature or high temperature strength of this single-phase refractory high-entropy alloy, which is not conducive to its industrial application in the field of high-temperature structural materials.

[0004] In traditional nickel-based superalloys, nanoprecipitation strengthening is one of the most effective strengthening mechanisms. Nanoprecipitates can generate strain fields at the interface with the matrix, thereby hindering dislocation motion at high temperatures and improving the alloy's high-temperature mechanical properties. Therefore, constructing nanoprecipitates through rational element selection and heat treatment processes is key to further improving the high-temperature strength of refractory high-entropy alloys. Because Zr and Ta have a positive mixing enthalpy and tend to repel each other, increasing the Zr content is promising for inducing phase separation in NbMoTaW refractory high-entropy alloys. Combined with heat treatments such as solution treatment and aging, Zr-rich nanoprecipitates can be precipitated in the matrix, further enhancing the high-temperature strength of the refractory high-entropy alloy. However, designing the Zr content and selecting a rational preparation process to achieve nanoprecipitation-strengthened ZrNbMoTaW refractory high-entropy alloys remains a significant challenge. Summary of the Invention

[0005] The purpose of the present invention is to provide a nano-precipitate phase strengthened refractory high entropy alloy and a preparation method thereof, so as to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for preparing a nano-precipitated phase-reinforced refractory high-entropy alloy, the chemical formula of which is Zr a Nbb Mo c Ta d W e , a, b, c, d and e are mole percentages of the elements; wherein, 30%≤a≤40%, 15%≤b≤18%, 15%≤c≤18%, 15%≤d≤18%, 15%≤e≤18%, and a+b+c+d+e=100%.

[0008] The present invention also provides a method for preparing the above-mentioned nano-precipitate phase-reinforced refractory high-entropy alloy, comprising the following steps:

[0009] (1) weighing the elements Zr, Nb, Mo, Ta and W according to the molar percentage of the elements in the chemical formula;

[0010] (2) mixing the elemental raw materials of step (1) and arc melting them to obtain a cast alloy ingot;

[0011] (3) The cast alloy ingot obtained in step (2) is kept at 1500° C. for 12 hours, and then quenched in water to obtain a solid solution alloy; then the solid solution alloy is kept at 1000° C. for 1-100 hours, and cooled in the furnace to obtain an aged alloy, which is the refractory high entropy alloy strengthened by the nano-precipitation phase.

[0012] As a further preferred embodiment of the present invention, the values ​​of a, b, c, d and e are as follows: 32%≤a≤36%, 16%≤b≤18%, 16%≤c≤18%, 16%≤d≤18% and 16%≤e≤18%.

[0013] As a further preferred embodiment of the present invention, the purity of the single elements Zr, Nb, Mo, Ta and W is ≥99.9wt%. More preferably, the purity of the raw materials of Mo, Ta and W is 99.9wt%, and the purity of the raw materials of Zr and Nb is 99.95wt%.

[0014] As a further preferred embodiment of the present invention, the current of the arc melting is 500-600A.

[0015] As a further preferred embodiment of the present invention, the arc melting is repeated 5-7 times, each time for 2-3 minutes, with an interval of 2 minutes between each time.

[0016] As a further preferred embodiment of the present invention, the arc melting process is supplemented by electromagnetic stirring.

[0017] As a further preferred embodiment of the present invention, the current frequency of the electromagnetic stirring is 4 to 6 Hz.

[0018] As a further preferred embodiment of the present invention, the heat treatment is carried out in a 99.99% high-purity argon atmosphere.

[0019] More preferably, the smelting process is to put the raw materials into the water-cooled copper crucible of the arc melting furnace in the order of the melting points of the elements from low to high, close the furnace chamber, use a mechanical pump to evacuate to 10Pa, turn on the molecular pump to evacuate to 3×10 -3 Pa, then fill with argon until the furnace chamber pressure is 0.95MPa, strike the arc and start melting, first melt the Ti ingot to absorb the residual oxygen in the furnace chamber, then melt the alloy raw materials and assist with electromagnetic stirring technology to obtain the cast alloy ingot.

[0020] More preferably, when placing the raw materials, Zr and Nb with lower melting points are placed at the bottom of the crucible, and W, Ta, and Mo with higher melting points are placed on the Zr and Nb raw materials to minimize the volatilization of low-melting-point elements during the smelting process.

[0021] More preferably, when melting the Ti ingot, the melting is performed for 3 to 5 times, with each melting lasting 60 to 100 seconds, so as to remove excess oxygen in the chamber as much as possible.

[0022] During the quenching process of the solution treatment of the present invention, the operation time for taking out the alloy ingot does not exceed 60 seconds, so as to prevent the precipitation of the low-temperature brittle phase during the cooling process.

[0023] After aging for 100 hours, the precipitated phase of the refractory high-entropy alloy provided by the present invention still maintains nanoscale, showing good high-temperature structural stability, and can be used as a candidate material for high-temperature structural parts.

[0024] The present invention significantly improves the high temperature yield strength of NbMoTaW series refractory high entropy alloys at 600 to 1000°C. At the same time, the density of the alloy of the present invention is between 11.1 and 11.4 g / cm 3 Compared with the NbMoTaW refractory high entropy alloy matrix, it is reduced by nearly 20%.

[0025] The present invention also provides a nano-precipitate phase-reinforced refractory high-entropy alloy prepared by the above preparation method.

[0026] The nano-precipitation phase-reinforced refractory high-entropy alloy of the present invention is a two-phase alloy composed of two BCC disordered solid solutions.

[0027] The present invention introduces a high proportion of Zr into the NbMoTaW matrix, effectively inducing phase separation of the matrix, and performs solid solution and aging treatment on the alloy, during which a nanoscale Zr-rich second phase is precipitated. The refractory high-entropy alloy prepared by this process has a room temperature yield strength greater than 2200 MPa, a Vickers hardness exceeding 800 HV, a yield strength greater than 1500 MPa at 600°C, and a yield strength greater than 1200 MPa at 1000°C, which greatly improves its comprehensive high-temperature performance and is expected to realize the engineering application of refractory high-entropy alloys in the field of high-temperature structural materials.

[0028] The present invention discloses the following technical effects:

[0029] The present invention uses ZrNbMoTaW refractory high-entropy alloy as the matrix material. By introducing a high proportion of Zr element into the matrix, the phase separation phenomenon of the matrix is ​​effectively induced. Combined with specific solid solution and aging treatment processes, the formation of uniformly dispersed nanoscale precipitates is successfully achieved.

[0030] The refractory high-entropy alloy prepared by the present invention exhibits excellent performance characteristics, which not only significantly improves the basic properties of the material, but also provides more possibilities for its application in extreme environments. It is expected to promote the wider application and development of refractory high-entropy alloys in aerospace, nuclear industry and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 is Zr in Example 1 32 Nb 17 Mo 17 Ta 17 W 17 Microscopic morphology photos of refractory high entropy alloys;

[0033] Figure 2 is Zr in Example 1 32 Nb 17 Mo 17 Ta 17 W 17 XRD spectrum of refractory high entropy alloy;

[0034] Figure 3 is Zr in Example 1 32 Nb 17 Mo 17 Ta 17 W 17 Compressive engineering stress-engineering strain curve of refractory high entropy alloy;

[0035] Figure 4 is Zr in Example 2 36 Nb 16 Mo 16 Ta 16 W 16 Microscopic morphology photos of refractory high entropy alloys;

[0036] Figure 5 is Zr in Example 236 Nb 16 Mo 16 Ta 16 W 16 XRD spectrum of refractory high entropy alloy;

[0037] Figure 6 is Zr in Example 2 36 Nb 16 Mo 16 Ta 16 W 16 Compressive engineering stress-engineering strain curve of refractory high-entropy alloy. DETAILED DESCRIPTION

[0038] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0039] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0041] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0042] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0043] Example 1

[0044] This embodiment provides a nano-precipitate phase strengthened refractory high entropy alloy, which is represented by the molar percentage of the element and has the chemical formula Zr 32 Nb 17 Mo 17 Ta 17 W 17 , the specific preparation method is as follows:

[0045] Step 1: Raw material pretreatment: Mo particles, Ta particles, W particles with a purity of 99.9% and Zr particles and Nb particles with a purity of 99.95% are selected as raw materials, and their surfaces are polished with sandpaper to remove oxide scale and stains on the surface of the raw materials.

[0046] Step 2. Weighing: The selected raw materials were weighed according to the molar ratio of each component in the general formula. Based on a 50g alloy ingot, each elemental raw material was weighed using an electronic balance. The weighed masses of the elemental raw materials Zr, Nb, Mo, Ta, and W were 11.837g, 6.404g, 6.613g, 12.473g, and 12.673g, respectively, with a weighing error of ±0.001g.

[0047] Step 3, melting: Place Zr and Nb with lower melting points at the bottom of the crucible, and place W, Ta, and Mo with higher melting points on top of the Zr and Nb raw materials to minimize the volatilization of low-melting-point elements during the melting process. Close the furnace chamber, use a mechanical pump to evacuate to 10Pa, and turn on the molecular pump to evacuate to 3×10 -3 Pa, then fill with argon until the furnace chamber pressure reaches 0.95MPa. The arc is struck to begin melting. First, the Ti ingot is melted to absorb the residual oxygen in the furnace chamber. This process is repeated three times, each melting for 100 seconds. The alloy ingot is melted with a current controlled at 500A and repeated seven times. Each melting arc lasts for 2 minutes, with a 2-minute interval between each melting. A robotic arm is used to turn the alloy over to ensure uniform composition of the alloy ingot. Each melting arc should last for 2 minutes and be supplemented by electromagnetic stirring technology with a current frequency of 5Hz to ensure that the alloy is fully mixed.

[0048] Step 4, heat treatment: The ingot is placed in a vacuum tube furnace, vacuumed for 10 minutes using a mechanical pump, and high-purity argon is introduced. The temperature is raised to 1500°C at a heating rate of 10°C / min, kept at this temperature for 12 hours, and then taken out and immediately quenched in water to obtain a solid solution alloy. During the quenching process of the solid solution treatment, the operation time for taking out the alloy ingot does not exceed 60 seconds to prevent the precipitation of low-temperature brittle phases during the cooling process. The solid solution alloy is aged in a vacuum tube furnace, vacuumed for 10 minutes using a mechanical pump, and high-purity argon is introduced. The temperature is raised to 1000°C at a heating rate of 10°C / min, kept at this temperature for 1 to 100 hours, and cooled with the furnace to obtain an aged alloy.

[0049] The nano-precipitate phase strengthened refractory high entropy alloy provided in Example 1 was subjected to various organizational characterizations and performance tests. Figure 1 The Zr provided in Example 1 32 Nb 17 Mo 17 Ta 17 W 17 The microstructure photos of the refractory high entropy alloy in the aged state show that the alloy of Example 1 contains uniformly dispersed equiaxed and elongated nano-precipitates with a size distribution between 100 and 500 nm.

[0050] Figure 2 The Zr provided in Example 1 32 Nb 17 Mo 17 Ta 17 W 17 The XRD spectrum of the refractory high entropy alloy shows that Example 1 is composed of two BCC phases with different lattice constants.

[0051] Figure 3 The Zr provided in Example 1 32 Nb 17 Mo 17 Ta 17 W 17 The compressive stress-strain curve of the refractory high-entropy alloy is strengthened by the uniformly dispersed nano-precipitates, and its yield strength is as high as 2250MPa.

[0052] Example 2

[0053] This embodiment provides a nano-precipitate phase strengthened refractory high entropy alloy, which is represented by the molar percentage of the element and has the chemical formula Zr 36 Nb 16 Mo 16 Ta 16 W 16 The preparation method of the alloy is the same as that of Example 1.

[0054] Figure 4 The Zr provided in Example 2 36 Nb 16 Mo 16 Ta 16 W 16 The microstructure photos of the refractory high entropy alloy in the aged state show that there are a large number of uniformly dispersed equiaxed and elongated nano-precipitates in the alloy of Example 2, with a size distribution between 50 and 300 nm.

[0055] Figure 5 The Zr provided in Example 2 36 Nb 16 Mo 16 Ta16 W 16 The XRD spectrum of the refractory high entropy alloy shows that Example 2 is composed of two BCC phases with different lattice constants.

[0056] Figure 6 The Zr provided in Example 2 36 Nb 16 Mo 16 Ta 16 W 16 The compressive stress-strain curve of the refractory high-entropy alloy is strengthened by the uniformly dispersed nano-precipitates, and its yield strength is as high as 2493MPa.

[0057] Comparative Example 1

[0058] The cast single-phase Zr alloy reported in Chinese patent 202110348397.3 0.3 The NbMoTaW alloy was used as comparative example 1.

[0059] Comparative Example 2

[0060] The cast single-phase Zr alloy reported in Chinese patent 202110348397.3 0.5 As Comparative Example 2, a NbMoTaW alloy was used.

[0061] Comparative Example 3

[0062] The unheat-treated cast Zr 32 Nb 17 Mo 17 Ta 17 W 17 The alloy was used as Comparative Example 3.

[0063] Comparative Example 4

[0064] The unheat-treated cast Zr 36 Nb 16 Mo 16 Ta 16 W 16 The alloy was used as Comparative Example 4.

[0065] Table 1 is the Zr content of Example 1 32 Nb 17 Mo 17 Ta 17 W 17 Refractory high entropy alloy and Zr of Example 2 36 Nb 16 Mo 16 Ta 16 W 16Room temperature yield strength and room temperature / high temperature Vickers hardness of refractory high entropy alloys. Clearly, Examples 1 and 2, which have higher Zr contents and have undergone solution aging heat treatment, exhibit superior overall mechanical properties, outperforming Comparative Examples 2 and 3, which have lower Zr contents, and also outperforming Comparative Examples 3 and 4, which have not undergone heat treatment.

[0066] Table 1

[0067]

[0068] The present invention addresses the problem of lack of strengthening phases in NbMoTaW-based refractory high-entropy alloys. By rationalizing the composition ratio and heat treatment process, a nano-precipitated phase is constructed, significantly improving the high-temperature strength of the alloy. The alloy has excellent strength and hardness at both room and high temperature conditions, and can be industrially produced on a large scale, making it expected to become the next generation of high-temperature structural material.

[0069] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for preparing a refractory high entropy alloy strengthened by nano-precipitation phase, characterized in that: The chemical formula of the nano-precipitated phase-strengthened refractory high entropy alloy is Zr a Nb b Mo c Ta d W e , a, b, c, d and e are mole percentages of the elements; where 32%≤a≤36%, 16%≤b≤18%, 16%≤c≤18%, 16%≤d≤18% and 16%≤e≤18%, and a+b+c+d+e=100%; The preparation method comprises the following steps: (1) Weighing the elements Zr, Nb, Mo, Ta and W according to the molar percentage of the elements in the chemical formula; (2) mixing the elemental raw materials of step (1) and arc melting them to obtain a cast alloy ingot; (3) The cast alloy ingot obtained in step (2) is kept at 1500° C. for 12 hours, and then quenched in water to obtain a solid solution alloy; the solid solution alloy is then kept at 1000° C. for 1-100 hours and cooled in the furnace to obtain an aged alloy, namely the nano-precipitate phase strengthened refractory high entropy alloy; The purity of the single elements Zr, Nb, Mo, Ta and W is ≥99.9wt%; the current of the arc melting is 500-600A; The arc melting process is supplemented by electromagnetic stirring; the current frequency of the electromagnetic stirring is 4-6 Hz; The heat treatment is carried out in a 99.99% high purity argon atmosphere.

2. The preparation method according to claim 1, characterized in that The arc melting is repeated 5-7 times, each time for 2-3 minutes, with an interval of 2 minutes between each time.

3. A refractory high entropy alloy strengthened by nano-precipitation phase prepared by the preparation method according to any one of claims 1 to 2.

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