A method for preparing a multi-component alloy

Abstract

The invention provides a preparation method of a multi-component alloy, belonging to the field of multi-component alloys. Raw metals Cr, Fe, Co, Ni and raw metal CrN are selected for batching, and the atomic percentages of the elements Cr, Fe, Co, Ni and N are converted into mass ratios for accurate weighing; the raw materials Cr, Fe, Co and Ni are placed in a crucible from bottom to top in the order of melting points from low to high, the raw material CrN is placed between the raw materials Cr and Fe, arc melting is performed under the protection of an inert atmosphere, and then the button ingot is cooled; the button ingot is turned over, arc melting is repeated, and drop casting is performed to obtain a final product; the invention adds a small amount of N element on the basis of a multi-component alloy of CrFeCoNi with equal atomic ratios, so that the alloy exhibits excellent comprehensive mechanical properties and corrosion resistance without changing the alloy phase structure, thereby achieving the effect of simultaneously improving strength, toughness and corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of multi-component alloys, and in particular to a method for preparing a multi-component alloy. Background Art

[0002] High entropy alloys are multi-component alloys. They are new materials with multiple components based on "chemical disorder". They mainly propose to develop and study alloy materials from the perspective of entropy, breaking through the limitations of the basic elements of alloy materials in the past. Multi-component high-entropy alloys are generally composed of five or more metals or non-metals in equal or nearly equal atomic ratios. Studies have shown that after solidification, multi-component high-entropy alloys will not form a large number of intermetallic compounds, but tend to form a simple solid solution phase, giving the alloy excellent comprehensive properties, such as high strength, high hardness, excellent work hardening ability, resistance to high temperature softening, corrosion resistance and high resistivity, etc. Therefore, multi-component alloys have broad application prospects.

[0003] In traditional alloys, the more elements are added, the more phases are formed and the more complex the composition is. However, the classic CrFeCoNi multi-component alloy has a single-phase face-centered cubic structure. Generally speaking, metals with a face-centered cubic structure have better plasticity than metals with a body-centered cubic structure, but their strength is insufficient. This is mainly because face-centered cubic alloys contain more slip planes and slip directions, which makes the alloys more prone to slip and show good plasticity. The plasticity of single-phase face-centered cubic multi-component alloys is higher.

[0004] At present, the research on CrFeCoNi multi-component alloys mainly involves alloy composition design, phase formation mechanism, and the influence of main components on alloy structure and mechanical properties. The good corrosion resistance of the alloy can effectively resist corrosion in various harsh environments, thereby further expanding the application field of the alloy. Studies have shown that high-strength multi-component high-entropy alloys generally have poor corrosion resistance, while multi-component alloys with excellent corrosion resistance generally have low strength and toughness, and it is difficult to achieve simultaneous improvement of mechanical properties and corrosion resistance. The fundamental measure to improve corrosion resistance lies in the alloying of materials. Invention CN104674103A adds Nb elements to the CrFeCoNi face-centered cubic matrix to form a precipitation phase, and improves the mechanical properties of the alloy by precipitation strengthening, but does not involve the improvement of corrosion performance. Invention CN110172628A prepares a multi-component alloy AlCrFeCoNi with good corrosion resistance, but the addition of alloying element Al will produce B2 precipitation phase, which increases the hardness of the alloy while significantly reducing plasticity. In short, the current multi-component alloys still need to be developed to achieve simultaneous improvement of mechanical properties and corrosion resistance. Summary of the invention

[0005] In view of this, the present invention proposes a method for preparing a multi-component alloy, which is used to solve the problem that the current multi-component alloy still needs to be developed to achieve simultaneous improvement of mechanical properties and corrosion resistance.

[0006] The technical solution of the present invention is implemented as follows: The present invention provides a method for preparing a multi-component alloy, comprising the following steps: Step 1, selecting raw metals Cr, Fe, Co, Ni and raw metal CrN for batching, and converting the atomic percentage of each element of Cr, Fe, Co, Ni and N into a mass ratio, and accurately weighing the raw metals with an electronic balance; The present invention adopts a composite strengthening method, adding N element to Cr, Fe, Co and Ni, and the interstitial solid solution effect of N element on the multi-component alloy is mainly manifested in the following aspects: 1) Microstructure influence: After adding N element, a single face-centered cubic (fcc) structure phase appears in the alloy, and no precipitation of nitride phase is observed. This indicates that the addition of N element forms a nitrogen-containing solid solution and is evenly distributed in the matrix of the alloy. Through electron probe analysis, it is found that all elements are evenly distributed in the alloy, and no segregation phenomenon is observed. Interstitial elements have a significant effect on the expansion of the face-centered cubic (fcc) structure lattice. In fact, interstitial elements diffuse into the interstitial position of the crystal structure, resulting in an increase in the lattice constant. This phenomenon is common in both stainless steel and high entropy alloys. Compared with stainless steel, the expansion of the lattice constant of high entropy alloys is more significant. In terms of the specific mechanism, the addition of interstitial elements will cause the deformation of the lattice structure. These elements occupy the empty positions between atoms in the lattice, driving the lattice to transform into a larger structure, thereby increasing the spacing of the lattice, which in turn leads to an increase in the lattice constant. This effect is particularly significant in high entropy alloys because high entropy alloys have a complex crystal structure and are more sensitive to changes in lattice constants. 2) Grain refinement effect: After adding N elements, the grain size of the alloy is significantly reduced, and the average grain size is about 30% lower than that of the alloy without N elements. This shows that the addition of N elements leads to the refinement effect of alloy grains. The refinement effect of grain size is of great significance for improving the strength and hardness of the alloy. Smaller grain size means that when subjected to force, the grain boundary hinders the movement of dislocations, thereby increasing the alloy's resistance to deformation. 3) Improved mechanical properties: After adding N elements, the mechanical properties of the alloy are significantly improved. Compared with conventional CrFeCoNi alloys, the alloy with N added has better Vickers hardness and tensile properties, and the addition of N can make the alloy show better ductility. Step 2, place the raw materials Cr, Fe, Co, and Ni in a crucible from bottom to top in order of melting point from low to high, place the raw material CrN between the raw materials Cr and Fe, and perform vacuum non-consumable arc melting under the protection of an inert atmosphere. The current intensity of the arc melting is 200-300 amperes, the voltage is 40-60 volts, and the melting temperature is 1800-2000 degrees Celsius. Cooling obtains a button ingot; Step 3, flip the button ingot and repeat the arc melting and cooling operations at least 5 times, and use a copper mold for drop casting to obtain a cast multi-component alloy.

[0007] On the basis of the above technical solution, preferably, in step 2 and step 3, when the arc melting operation is performed, the melting equipment uses an arc furnace to apply a magnetic field to stir the molten raw materials in the crucible. The stirring effect of the arc furnace's external magnetic field can make the raw materials more fully and evenly mixed in a molten state. The magnetic field strength of the magnetic field stirring device is set according to the equipment specifications, usually 1000-5000 Gauss.

[0008] More preferably, during the arc melting operation, the raw material is placed in a sealed crucible, and the molten raw material in the crucible is pressurized by inputting an inert gas into the crucible. The inert gas is helium or argon. Compared with the situation where the pressure in the crucible is lower than one atmosphere during conventional vacuum arc melting, the principle of this pressurization method is similar to hot isostatic pressing, which can enhance the stirring effect of the external magnetic field and enhance the interstitial solid solution effect of the N element in the high entropy alloy for a longer period of time.

[0009] More preferably, the environmental pressure in the crucible is increased to 2-5 MPa by introducing an inert gas into the crucible, so that the environmental pressure in the crucible is high enough to enhance the magnetic field stirring effect and the interstitial solid solution effect of the N element.

[0010] On the basis of the above technical scheme, preferably, in step one, block raw metals Cr, Fe, Co, Ni and powdered raw metal CrN are selected for batching. The thickness of the block raw material is usually 3-10mm, and its shape is circular in accordance with the internal shape of the crucible, and the inner diameter of its circular section is 5-10cm. The reason why Cr, Fe, Co, and Ni use metal blocks is that under normal circumstances, the elements are provided in block form, which is relatively easy to obtain in block form, and the block raw materials are easier to operate and handle. In addition, the block raw materials are relatively stable, not easily affected by the environment, and suitable for long-term storage. The mesh number of the powder raw material is usually 50-100 mesh, but powders with larger mesh numbers can also be used to improve the uniformity during mixing. CrN uses metal powder, which makes it easier to mix with other raw materials, which is conducive to achieving uniform batching. In addition, the surface area of ​​the powdered raw material is larger and it is easier to react with other raw materials, thereby improving the uniformity and reaction rate of the alloy. The reason for using CrN metal powder is that its properties are relatively stable, and the atomic ratio of nitrogen to chromium is 1:1; in comparison, iron nitride exists in four forms: Fe 2 N, Fe 3 N 1+x , Fe 4 N and Fe 16 N 2 , not only is the property unstable, but also the atoms are relatively complex, which is not conducive to the preparation of raw materials; nickel nitride Ni 3N is difficult to obtain and the cost is high; cobalt nitride will introduce other elements besides N and Co, and its high hardness and brittleness also make it difficult to process, requiring special processes to achieve. In addition, the melting point of CrN is between Cr and Fe, so when CrN powder is filled between the metal blocks Cr and Fe, CrN and Cr can be more fully mixed during smelting, which improves the mixing consistency of the N element in the alloy.

[0011] More preferably, in step 1, the purity of the bulk raw metals Cr, Fe, Co, Ni and the powdered raw metal CrN is greater than 99.9wt.% to ensure the purity of the prepared product.

[0012] On the other hand, the present invention also provides a multi-component alloy, which is prepared by the above-mentioned method for preparing a multi-component alloy, and the chemical formula of the multi-component alloy is calculated in atomic percentage: (Fe a Cr b Ni c Co d ) 100-x N x For multi-component high entropy alloys, the range of each main component element is generally 5% to 35%. The added N element plays a role of solid solution strengthening and is a non-main component element, so 1≤x≤5.

[0013] On the basis of the above technical solution, preferably, in the chemical expression of the multi-component alloy, a=b=c=d.

[0014] On the basis of the above technical solution, preferably, the yield strength of the multi-component alloy is not less than 210 MPa, the tensile strength is not less than 520 MPa, and the elongation is not less than 56%.

[0015] The preparation method of a multi-component alloy of the present invention has the following beneficial effects compared with the prior art:

[0016] (1) The present invention adopts a composite strengthening method. Since the atomic radius of the N element is relatively small compared to that of the metal atom, on the one hand, the alloying of N will form interstitial solid solution in CrFeCoNi, causing serious lattice distortion and a large strain field. On the other hand, the binding enthalpy of N atoms and dislocations is very high. Both of these situations can hinder the movement of dislocations, thereby achieving the purpose of improving strength and toughness.

[0017] (2) The present invention adopts a design concept to avoid the generation of harmful precipitate phases. In a multi-component alloy matrix, dissolving a large amount of Cr elements will form a thin and dense passivation layer, which is beneficial for resisting various types of corrosion. However, the Cr-containing precipitate phase will become a defect of the passivation layer, thereby causing the deterioration of corrosion resistance. The present invention avoids the generation of precipitate phases by adding N elements so that they exist in the gaps between the metal atoms of Cr, Fe, Co, and Ni. In addition, N can also improve the local corrosion resistance of the alloy by increasing the breakdown potential.

[0018] (3) The method of the present invention adds a small amount of N element to the equiatomic ratio CrFeCoNi alloy to prepare a multi-component alloy, which exhibits excellent comprehensive mechanical properties; the electrochemical curve of the alloy is studied and analyzed, and the corrosion resistance to 5.6wt.% KOH is better than that of stainless steel SUS304, and the alloy exhibits excellent corrosion resistance. Therefore, the present invention achieves the effect of improving both strength and toughness and corrosion resistance.

[0019] (4) The present invention adopts a vacuum arc melting furnace to prepare a multi-component alloy containing the N element. The alloy has excellent comprehensive performance in a wide temperature range and has excellent practicality. The preparation technology obtained by this invention has wide applicability, convenient operation and high efficiency, and is an advanced multi-component alloy preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. 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 creative work.

[0021] Figure 1 is the X-ray diffraction pattern of the multi-component alloy of the present invention;

[0022] Figure 2 is a tensile stress-strain curve diagram of the multi-component alloy of the present invention at room temperature;

[0023] Figure 3 is an electrochemical polarization curve diagram of the multi-component alloy of the present invention;

[0024] Figure 4 It is an electrochemical performance data diagram of the polarization curve of the multi-component alloy of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] The chemical formula of the multi-component alloy of this embodiment is CrFeCoNi, which includes, in terms of atomic percentage, Cr: 25%, Fe: 25%, Co: 25%, and Ni: 25%.

[0028] The preparation method of the multi-component alloy of this embodiment comprises the following steps:

[0029] Step 1, raw material preparation. The raw material components are selected and converted into mass ratios according to atomic percentages, and the bulk raw material metals Cr: 25%, Fe: 25%, Co: 25%, Ni: 25% are accurately weighed using an electronic balance. The purity of the bulk raw material metals Cr, Fe, Co and Ni is 99.95wt.%. This embodiment uses a conventional bowl-shaped crucible, and the shape of the bulk raw material matches the shape of the interior of the crucible to be circular, and the inner diameter of the circular section is 10cm and the thickness is 10mm.

[0030] Step 2: Melting: Place the raw materials Cr, Fe, Co, and Ni in a crucible from bottom to top in the order of their melting points from low to high, wherein the melting points of Cr, Fe, Co, and Ni are 1907°C, 1538°C, 1495°C, and 1455°C, respectively.

[0031] The arc furnace is used for smelting. The furnace is first evacuated to 5Pa, and then backfilled with inert gas, argon, to raise the pressure in the furnace to 3×10 4 Pa; after repeated charging and discharging three times, fill with inert gas to make the pressure in the furnace reach 3MPa.

[0032] Vacuum non-consumable arc melting technology is used for melting, with a current intensity of 300 amperes and a voltage of 60 volts. The arc furnace is started and the current intensity is adjusted to begin melting the raw materials. The melting time is 30 minutes and the melting temperature is 2000 degrees Celsius. After 30 minutes, the arc is stopped and the alloy is allowed to cool naturally in the melting furnace until the ambient temperature in the crucible drops to 500 degrees Celsius, so that the alloy solidifies.

[0033] During the arc melting process, a magnetic field is applied outside the arc furnace to stir the molten raw materials in the crucible. The magnetic field stirring device is started to ensure that the metals are fully mixed during the melting process; the magnetic field strength of the magnetic field stirring device is 5000 Gauss.

[0034] Step three, use a copper mold for drop casting to cast the alloy into a button ingot. Take out the cooled alloy button ingot, turn the button ingot over, and repeat arc melting, stirring and cooling. Each button ingot is remelted 5 times to ensure that the materials are fully mixed and the alloy is uniform. The resulting alloy is subsequently cleaned, polished, and other treatments are performed to improve the appearance quality, and the alloy is tested and analyzed in terms of mechanical properties and corrosion resistance.

[0035] Example 2

[0036] Compared with Example 1, the multi-component alloy of this embodiment has N element added. The chemical formula of the multi-component alloy is (CrFeCoNi) 99 N 1 , calculated by atomic percentage, including: Cr: 24.75%, Fe: 24.75%, Co: 24.75%, Ni: 24.75%, N: 1%.

[0037] Among them, according to the chemical formula of the multi-component alloy (CrFeCoNi) 100-x N x Calculate the proportion of each raw material (at%), where CrN (at%) is assumed to be x, then:

[0038] Fe(at%)=Co(at%)=Ni(at%)=(100-x) / 4,

[0039] Cr(at%)=(100-x) / 4-x,

[0040] The mass proportion of each raw material is obtained by multiplying the raw material proportion by the atomic mass of each raw material.

[0041] The difference between the preparation method of the multi-component alloy in this embodiment and that in embodiment 1 is that:

[0042] Step 1: When preparing the raw materials, in addition to the bulk metal raw materials Cr, Fe, Co and Ni, a powdered metal raw material CrN is also added, and the purity of the powdered metal raw material is greater than 99.9wt.%. The mesh size of the powdered metal raw material is 100 meshes.

[0043] Step 2: Put the raw materials into the crucible in turn, wherein the melting point of the raw material CrN is 1650° C., and place the powdered raw material CrN between the block raw materials Cr and Fe.

[0044] Example 3

[0045] Compared with Example 2, the multi-component alloy of this embodiment has the chemical formula (CrFeCoNi) 97 N 3 , calculated by atomic percentage, including: Cr: 24.25%, Fe: 24.25%, Co: 24.25%, Ni: 24.25%, N: 3%.

[0046] Example 4

[0047] Compared with Example 2, the multi-component alloy of this embodiment has the chemical formula (CrFeCoNi) 95 N 5 , calculated by atomic percentage, including: Cr: 23.75%, Fe: 23.75%, Co: 23.75%, Ni: 23.75%, N: 5%.

[0048] The microstructure, mechanical properties and electrochemical properties of the multi-component alloys of Examples 1 to 4 above were tested, and the test information is as follows:

[0049] (1) Phase analysis: X-ray diffraction analysis was performed using an X-ray diffractometer with a 2θ scanning range of 10-90° and a scanning speed of 3° / min. The results are shown in Figure 1 shown.

[0050] (2) Mechanical properties: A room temperature (28°C) tensile test was conducted according to the relevant requirements of GB / T228.1-2021 Metal Material Room Temperature Tensile Test Method. Three tests were conducted for each component alloy to ensure that the stress-strain curve was accurate and stable. The results are as follows: Figure 2 shown.

[0051] (3) Electrochemical performance: A potentiodynamic polarization experiment was performed on a potentiostat workstation, and the sample was immersed in a 5.6wt.% KOH solution. The electrochemical test used a three-electrode system, with the working electrode being the test sample, the reference electrode being a saturated calomel electrode, and the counter electrode being a pure platinum sheet. The scanning rate was 5mV / s, and the scanning potential range was -1.5V to 0.5V. When the current density exceeded 1mA / cm 2 Stop the experiment and repeat the scan 3 times to ensure accuracy. The results are as follows Figure 3 As shown and drawn Figure 4 Electrochemical performance data of the polarization curves shown.

[0052] See also Figure 1 , it can be seen that CrFeCoNi and (CrFeCoNi) 100-x N x Multi-component high entropy alloys all have a face-centered cubic structure, and no precipitate phase is produced therein.

[0053] See also Figure 2 The results can be seen in Table 1. It can be seen that after adding N element, (CrFeCoNi) 100-x N x The alloy has excellent mechanical properties at room temperature, with a yield strength of not less than 210 MPa, a tensile strength of not less than 520 MPa, and an elongation of not less than 56%. Especially (CrFeCoNi) in Example 495 N 5 The alloy exhibits more excellent mechanical properties and achieves a good combination of strength and toughness and plasticity.

[0054] Table 1 Tensile mechanical properties after adding different N contents

[0055]

[0056] See also Figure 3 The results can be seen in Table 2. Among them (CrFeCoNi) 99 N 1 The corrosion potential is the lowest, (CrFeCoNi) 97 N 3 The corrosion potential is high, indicating that (CrFeCoNi) 99 N 1 The corrosion resistance is the worst, (CrFeCoNi) 97 N 3 The corrosion resistance is the best.

[0057] Table 2 Electrochemical performance after adding different N contents

[0058]

[0059] See also Figure 4 It can be found that with the increase of N content, the corrosion potential first increases and then decreases, among which (CrFeCoNi) 97 N 3 The corrosion potential is the highest and the corrosion performance is the best.

[0060] By comparing the above examples 1 to 4, it can be seen that (CrFeCoNi) 97 N 3 The multi-component high entropy alloy achieves simultaneous improvement of strength, toughness and corrosion resistance. It not only has good mechanical properties, but also achieves a combination of strength and plasticity, with a yield strength of 224.6MPa, a tensile strength of 528.6MPa, and an elongation of 65%. It also has good corrosion resistance, which can provide ideas for the development of metal materials that require both mechanical properties and corrosion resistance. Therefore, the present invention can prepare a multi-component alloy that simultaneously improves strength, toughness and corrosion resistance by more reasonably and effectively controlling the amount of N element added in the equiatomic ratio CrFeCoNi multi-component alloy.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a multi-component alloy, characterized in that: The following steps are involved: Step 1: Select raw metals Cr, Fe, Co, Ni and raw metal CrN for mixing, and convert the atomic percentage of each element of Cr, Fe, Co, Ni and N into a mass ratio, and accurately weigh the raw metals with an electronic balance; the chemical formula of the multi-component alloy is calculated in atomic percentage: (FeCrNiCo) 97 N3; Step 2, placing raw materials Cr, Fe, Co, and Ni in a crucible from bottom to top in order of melting points from low to high, placing raw material CrN between block raw materials Cr and Fe, and performing vacuum non-consumable arc melting under the protection of an inert atmosphere, and cooling to obtain a button ingot; when performing the arc melting operation, the melting equipment uses an arc furnace to apply a magnetic field to stir the molten raw materials in the crucible; when performing the arc melting operation, the raw materials are placed in a sealed crucible, and the molten raw materials in the crucible are pressurized by inputting an inert gas into the crucible, so that the environmental pressure in the crucible is increased to 2-5MPa; Step 3: After the button ingot is turned over, arc melting and cooling operations are repeated for at least 5 times, and drop casting is performed using a copper mold to obtain a cast multi-component alloy.

2. The method for preparing a multi-component alloy according to claim 1, characterized in that: In the step 1, bulk raw metals Cr, Fe, Co, Ni and powdered raw metal CrN are selected for batching.

3. The method for preparing a multi-component alloy according to claim 2, characterized in that: In the step 1, the purity of the bulk raw metals Cr, Fe, Co, Ni and the powdered raw metal CrN is greater than 99.9wt.%.

4. The method for preparing a multi-component alloy according to claim 1, characterized in that: The yield strength of the multi-component alloy is not less than 210 MPa, the tensile strength is not less than 520 MPa, and the elongation is not less than 56%.

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