A method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance

Abstract

The invention discloses a preparation method of a FeCoNiMnAl series high entropy alloy powder with wave absorbing performance, the method comprising: step (1), uniformly mixing iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder to obtain alloy raw material powder; step (2), adding the alloy raw material powder, anhydrous ethanol and grinding balls into a ball mill, and performing high and low speed alternating ball milling under the protection of inert gas; step (3), after the ball milling, vacuum drying and grinding the milled alloy raw material powder to obtain an intermediate product A; step (4), adding sodium hydroxide solution to the intermediate product A, and performing corrosion modification by water bath heating; after the water bathing, washing the solid product obtained by solid-liquid separation to neutrality to obtain an intermediate product B; step (5), vacuum drying and grinding the intermediate product B. The FeCoNiMnAl series high entropy alloy powder prepared by the invention has excellent wave absorbing performance in the case of small thickness.

Description

Technical Field

[0001] The present invention relates to the technical field of wave absorbing materials, and more specifically to a method for preparing FeCoNiMnAl series high entropy alloy powder with wave absorbing performance. Background Art

[0002] High entropy alloys have become a potential absorbing material due to their good chemical stability, excellent mechanical properties and high electromagnetic wave absorption efficiency. Thin thickness, strong absorption, wide frequency band, corrosion resistance and wear resistance are the prerequisites for the application of absorbing materials in military and civilian fields. However, the electromagnetic wave absorption effect of conventional high entropy alloy materials is not ideal. Therefore, it is necessary to further improve high entropy alloy materials to meet the application requirements of military and civilian absorbing materials.

[0003] Patent CN114799172A discloses a FeCoNi-based porous high-entropy alloy material for electromagnetic wave absorption and a preparation method thereof. The method can adjust the high-entropy alloy element composition and the size of the pores by adjusting the degree of dealloying, thereby adjusting the electromagnetic parameters of the material. The high-entropy alloy material FeCoNiCuAl prepared by the method of the patent has a maximum reflection loss value of about -54 decibels when the thickness is 3mm, and its effective absorption bandwidth is about 3.5GHz, and a high absorption efficiency is obtained in the low frequency band (6-9 GHz). However, when the material is at other thicknesses (when the thickness is 5mm, the maximum reflection loss value is also less than -25 decibels), especially when the thickness is thin, the maximum reflection loss value is greater than -25 decibels, which shows that its overall average wave absorption performance is not ideal. Therefore, it is necessary to further improve the preparation method of FeCoNi-based porous high-entropy alloy materials to further improve the wave absorption performance of FeCoNi-based porous high-entropy alloy materials. Summary of the invention

[0004] To this end, the technical problem to be solved by the present invention is to provide a method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, so as to solve the technical problem that the FeCoNi-based high entropy alloy material prepared by the existing FeCoNi-based high entropy alloy material preparation method has unsatisfactory microwave absorbing performance when the thickness is relatively thin.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance comprises the following steps:

[0007] Step (1), mixing iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder uniformly to obtain alloy raw material powder; the molar ratio of iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is 1:1:1:(0.5-0.6):(0.4-0.5); the particle size of the iron powder is 100-300 nm, the particle size of the cobalt powder is 1-2 μm, the particle size of the nickel powder is less than or equal to 50 μm, the particle size of the manganese powder is 40-50 μm, and the particle size of the aluminum powder is 3-5 μm;

[0008] Step (2), adding alloy raw material powder, anhydrous ethanol and grinding balls into a ball mill, and performing alternating ball milling under the protection of inert gas, wherein each round of alternating ball milling is first performed at a high speed and then at a low speed, and at least two or more rounds of alternating ball milling are performed;

[0009] Step (3), after the ball milling is completed, vacuum drying the ball-milled alloy raw material powder and grinding it to obtain an intermediate product A;

[0010] Step (4), adding sodium hydroxide solution to the intermediate product A, mixing and stirring, and performing corrosion modification by water bath heating; after the water bath is completed, washing the solid product obtained by solid-liquid separation to neutrality to obtain the intermediate product B;

[0011] Step (5), vacuum drying the intermediate product B and grinding it to obtain FeCoNiMnAl high entropy alloy powder with microwave absorbing performance.

[0012] Under normal temperature conditions, the three elements of iron, cobalt and nickel exhibit ferromagnetism, and the high entropy alloys composed of them have attracted much attention due to their excellent magnetic properties. This alloy can effectively improve the composite magnetic permeability of the alloy powder, thereby enhancing its ability to absorb electromagnetic waves. Manganese is an antiferromagnetic element. The addition of Al element can inhibit the antiferromagnetism of manganese. By accurately controlling the addition amount of aluminum element, it can be promoted to ferromagnetism, which will increase the actual dielectric constant, conductive loss and eddy current loss of the high entropy alloy, greatly improve the attenuation constant of the high entropy alloy powder, and thus improve the electromagnetic shielding performance. Therefore, the present invention introduces manganese and aluminum elements into the alloy system, which can not only further improve the electromagnetic properties of the alloy, but also significantly enhance its absorption efficiency of electromagnetic waves. In addition, the atomic radius of aluminum is relatively large, and the addition of aluminum element can increase the lattice constant and produce lattice distortion. This lattice distortion can increase the solid solution strengthening effect, and also cause the movement of the natural resonance frequency, which is conducive to improving impedance matching and high-frequency resonance loss. In addition, adding a specific amount of aluminum can form more defects in the structure. These defects become polarization centers and promote polarization. The addition of aluminum is beneficial to increase the aspect ratio of the alloy, resulting in an increase in the specific surface area of ​​flaky particles, which enhances the polarization effect.

[0013] The preparation method of the present invention uses repeated vacuuming and argon filling to ensure that the alloy raw material powder is not oxidized and deteriorated during the ball milling process, and uses a double-tank high-energy swing ball mill for ball milling. Compared with other low-speed ball milling methods, the time for preparing samples is greatly shortened, and energy consumption is reduced to prepare an absorbing material with good electromagnetic shielding performance in a shorter time. The lattice constant is adjusted by accurately adjusting the amount of manganese and aluminum elements, and the resulting lattice distortion can increase the solid solution strengthening effect, so that the natural resonance frequency moves, which is beneficial to improve the impedance matching and high-frequency resonance loss of the high-entropy alloy powder; more defects become polarization centers, the alloy aspect ratio increases, and the specific surface area of ​​flaky particles increases, all of which enhance the polarization effect.

[0014] In the method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, in step (1), the particle size of the iron powder is 150-200 nm, the particle size of the cobalt powder is 1-2 μm, the particle size of the nickel powder is less than or equal to 30 μm, the particle size of the manganese powder is 45 μm, and the particle size of the aluminum powder is 5 μm; the purity of the iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is greater than or equal to 99.5 wt%.

[0015] In the method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, in step (1), the molar ratio of iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is 1:1:1:0.52:0.44.

[0016] The preparation method of the FeCoNiMnAl high entropy alloy powder with microwave absorption performance is as follows: in step (2), the mass volume ratio of the alloy raw material powder to anhydrous ethanol is (6-8) g / L; the mass ratio of the alloy raw material powder to the grinding ball is 1:(1-3); among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm and the grinding balls with a diameter of 2 mm is 1:(3-5):(3-5); before ball milling, the ball mill is repeatedly evacuated and filled with argon gas for 3-5 times; the present invention uses grinding balls with a diameter of 2 mm, which can make several metal single substance powders with different densities mixed together better and more evenly, and the grinding balls with diameters of 4 mm and 8 mm can make the metal single substance powder particles continuously undergo the process of crushing-cold welding, so that the single substance powders with different particle sizes are mutually dissolved together to form a new solid solution; the present invention mixes the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm and the grinding balls with a diameter of 2 mm in a mass ratio of 1: (3-5): (3-5) After mixing, the raw material powder of the alloy is used for ball milling. In the wet milling process, the aluminum powder, which has a large density difference with other metal elements and is used in a small amount, can be evenly dispersed in the other metal element powders, so that it can effectively participate in the alloying to form a flaky structure during the wet milling process, thereby avoiding the unsatisfactory alloying effect caused by the uneven mixing of aluminum and other metal element powders during the alloying process; this method of mixing three different diameter balls for wet milling can crush the granular powder into flakes during the alloying process, and the flake powder has a large specific surface area and better wave absorption performance;

[0017] During ball milling, firstly, ball mill at a high speed of 700-800rpm for 10-12h, then at a low speed of 400-500rpm for 10-12h; then, ball mill at a high speed of 700-800rpm for 10-12h, then at a low speed of 400-500rpm for 10-12h; finally, ball mill at a high speed of 700-800rpm for 10-12h; the ball mill changes direction every 30 minutes. The centrifugal force of different ball milling speeds is different. At 700rpm, the alloy raw material powder can fully contact with the wall of the ball mill, which is conducive to promoting the crushing-cold welding process, while the centrifugal force of 500rpm is smaller, which can better evenly and disperse the grinding balls and metal powders during crushing-cold welding to prevent aggregation;

[0018] The invention uses anhydrous ethanol as a medium, mixes metal powders of specific particle sizes in a certain proportion to obtain alloy raw material powder and three grinding balls with different diameters, and adopts high-speed and low-speed alternating ball milling for two or more rounds, so that not only can iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder be fully alloyed to form a high-entropy alloy powder with a lamellar structure having a relatively large aspect ratio, but also part of the nickel element in the intermediate product A obtained by alloying can be activated, and the reaction energy barrier of the reaction between the metal nickel and the sodium hydroxide solution can be reduced, so that the metal nickel can react with the 1.0-1.5 mol / L sodium hydroxide solution under water bath heating conditions to generate nickel hydroxide, thereby realizing the surface modification of the dealloyed powder.

[0019] The method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorption performance is as follows: in step (2), the mass volume ratio of the alloy raw material powder to anhydrous ethanol is 7.4 g / L; the mass ratio of the alloy raw material powder to the grinding balls is 3.7:6; among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm, and the grinding balls with a diameter of 2 mm is 1:4:4; before ball milling, the ball mill is repeatedly evacuated and filled with argon gas for 3 times;

[0020] During ball milling, first ball mill at a high speed of 700 rpm for 12 hours, then ball mill at a low speed of 500 rpm for 12 hours; then ball mill at a high speed of 700 rpm for 12 hours, then ball mill at a low speed of 500 rpm for 12 hours; finally ball mill at a high speed of 700 rpm for 12 hours; the ball mill changes direction every 30 minutes of operation.

[0021] The preparation method of the FeCoNiMnAl high entropy alloy powder with microwave absorption performance is as follows: in step (4), the concentration of the sodium hydroxide solution is 1.0-1.5 mol / L, and the mass ratio of the intermediate product A to the sodium hydroxide solution is 1:(5-10); the FeCoNiMnAl high entropy alloy powder is corroded by using the sodium hydroxide solution in the concentration range, and the corrosion ability is moderate, which can not only avoid the formation of a passivation film on the powder surface (avoid the oxidation of the alloy element aluminum to form aluminum oxide attached to the powder surface and inhibit the dealloying reaction), but also quickly corrode the powder to form surface defects (mainly due to the participation of metal nickel in the reaction to form nickel hydroxide) and irregular pore structures (mainly due to the participation of aluminum in the reaction and the corrosion left behind), thereby facilitating the formation of defects, increasing the surface area of ​​the high entropy alloy powder, and increasing its multiple reflections; the conditions for water bath heating corrosion modification are: water bath at a temperature of 30-60°C for 1-6h, and a stirring rate of 5-15rpm; and washing with deionized water and anhydrous ethanol alternately for 3-5 times. When the intermediate product A is corroded and modified by a sodium hydroxide solution having a concentration of 1.0 to 1.5 mol / L, the water bath heating and stirring process can effectively avoid oxidation of the powder, better promote the reaction, and make the intermediate product A fully contact with the sodium hydroxide solution, greatly shortening the reaction time of the corrosion modification and improving the corrosion efficiency; the reaction mechanism is: aluminum reacts with hydroxide ions to generate aluminate, so that the powder particles have a porous structure; nickel reacts with the sodium hydroxide solution under water bath conditions to generate nickel hydroxide, and after corrosion, part of the nickel element exists in the form of nickel hydroxide, thereby generating irregular cracks on the surface and increasing defects, and these defects provide polarization centers for polarization, thereby improving the wave absorbing performance.

[0022] In the method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, in step (4), the concentration of the sodium hydroxide solution is 1.0 mol / L; the mass ratio of the intermediate product A to the sodium hydroxide solution is 1:8; the conditions for water bath heating corrosion modification are: water bath at a temperature of 40°C for 5 hours and a stirring rate of 10 rpm; and deionized water and anhydrous ethanol are used for alternating washing 3 times.

[0023] In the above-mentioned method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, in step (3), the vacuum drying conditions are: vacuum drying at a temperature of 40 to 70°C for 18 to 24 hours, and the particle size of the intermediate product A is 60 to 120 μm; in step (5), the vacuum drying conditions are: vacuum drying at a temperature of 40 to 70°C for 18 to 24 hours, and the particle size of the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance is 10 to 40 μm.

[0024] In the above-mentioned method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, in step (3), the vacuum drying conditions are: vacuum drying at 50°C for 24 hours, and the particle size of the intermediate product A is 60 to 120 μm; in step (5), the vacuum drying conditions are: vacuum drying at 50°C for 24 hours, and the particle size of the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance is 10 to 40 μm.

[0025] The preparation method of the FeCoNiMnAl high entropy alloy powder with microwave absorption performance also includes the following steps: vacuum drying the intermediate product B and then annealing it, and the annealing conditions are: keeping warm at 500°C for 2 hours in an argon atmosphere; after the annealing is completed, an intermediate product C is obtained; the intermediate product C and grinding balls are added to a ball mill for ball milling; the mass ratio of the intermediate product C to the grinding balls is 1:1; among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm and the grinding balls with a diameter of 2 mm is 1:4:4; before ball milling, the ball mill is repeatedly vacuumed and filled with argon for 3 times; the ball mill speed is 500 rpm, the ball mill changes direction every 30 minutes, and the ball milling time is 1 hour. When preparing FeCoNiMnAl high entropy alloy powder with microwave absorption performance, annealing after corrosion modification of alloyed powder can effectively remove the internal stress inside FeCoNiMnAl high entropy alloy, effectively enhance the saturation magnetization (Ms) of high entropy alloy powder, reduce coercivity, increase actual dielectric constant, conductive loss and eddy current loss, greatly improve the attenuation constant of high entropy alloy powder, and thus improve electromagnetic shielding performance. It was also found in the experiment that if annealing is performed before corrosion modification of alloyed powder (i.e., annealing after alloying and then corrosion modification), the minimum reflection loss of the FeCoNiMnAl high entropy alloy powder prepared will increase, affecting its overall microwave absorption performance.

[0026] The technical solution of the present invention achieves the following beneficial technical effects:

[0027] 1. The preparation method of the FeCoNiMnAl high entropy alloy powder with wave absorbing performance of the present invention uses anhydrous ethanol as a medium, mixes various metal powders of specific particle sizes in a certain proportion to obtain alloy raw material powder, mixes it with three grinding balls of different diameters in proportion, adopts high speed and low speed to alternately ball mill for two or more rounds, and then adds a sodium hydroxide solution of a specific concentration to perform corrosion modification under water bath conditions, so that the prepared FeCoNiMnAl high entropy alloy powder has lower reflection loss at a thinner thickness, and has excellent magnetic loss capacity at different thicknesses, and its wave absorbing performance is comprehensively improved. When the thickness of the FeCoNiMnAl high entropy alloy powder prepared by the present invention is 1.5mm, the reflection loss value is as low as -36.71dB, and the effective absorption bandwidth is 4.40GHz, showing good wave absorbing performance, and the minimum reflection loss at the thickness of 1.5mm, 2.5mm, 3.0mm, and 3.5mm is less than -25dB.

[0028] 2. Compared with the traditional preparation method, the preparation method of the FeCoNiMnAl high entropy alloy powder with wave absorbing performance of the present invention not only reduces the amount of metal raw materials used, but also has the advantages of high efficiency, energy saving and environmental protection. The prepared FeCoNiMnAl high entropy alloy powder has the synergistic effect of multiple electromagnetic loss mechanisms, enhances dielectric loss, magnetic loss and impedance matching, so that electromagnetic waves are absorbed to the greatest extent, achieving the effect of increasing reflection loss and wide absorption bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 XRD diffraction pattern of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0030] Figure 2 SEM morphology of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder in Example 1 of the present invention (20.0 μm);

[0031] Figure 3 SEM morphology of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder in Example 1 of the present invention (10.0 μm);

[0032] Figure 4 SEM morphology of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder in Example 1 of the present invention (5.00 μm);

[0033] Figure 5 SEM morphology of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention (20.0 μm);

[0034] Figure 6SEM morphology of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention (10.0 μm);

[0035] Figure 7 SEM morphology of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention (5.00 μm);

[0036] Figure 8 SEM morphology of the FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention (20.0 μm);

[0037] Fig. 9 SEM morphology of the FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention (10.0 μm);

[0038] Fig.10 SEM morphology of the FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention (5.00 μm);

[0039] Fig.11 General magnetization curve of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder in Example 1 of the present invention;

[0040] Fig.12 General magnetization curve of FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0041] Fig.13 General magnetization curve of FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention;

[0042] Fig.14 Magnetic hysteresis loop of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder according to Example 1 of the present invention;

[0043] Fig.15 Magnetic hysteresis loop of FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0044] Fig.16 Magnetic hysteresis loop of FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention;

[0045] Fig.17 The dielectric constant of the intermediate product A when preparing FeCoNiMnAl high entropy alloy powder according to Example 1 of the present invention;

[0046] Fig.18 The dielectric constant of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0047] Fig.19 The dielectric constant of the FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention;

[0048] Fig. 20 The magnetic permeability of the intermediate product A when preparing FeCoNiMnAl high entropy alloy powder in Example 1 of the present invention;

[0049] Fig.21 The magnetic permeability of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0050] Fig. 22 Magnetic permeability of the FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention;

[0051] Fig.23 Reflection loss of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder in Example 1 of the present invention;

[0052] Fig.24 Reflection loss of the FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0053] Fig.25 Reflection loss of the FeCoNiMnAl high entropy alloy powder prepared in Example 2 of the present invention;

[0054] Fig.26 Reflection loss of the FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention;

[0055] Fig. 27 Reflection loss of FeCoNiMnAl high entropy alloy powder prepared in the comparative example of the present invention;

[0056] Fig.28 Attenuation constant of intermediate product A when preparing FeCoNiMnAl high entropy alloy powder according to Example 1 of the present invention;

[0057] Fig.29 Attenuation constant of FeCoNiMnAl high entropy alloy powder prepared in Example 1 of the present invention;

[0058] Fig.30 Attenuation constant of FeCoNiMnAl high entropy alloy powder prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0059] Example 1

[0060] In this embodiment, the preparation method of FeCoNiMnAl high entropy alloy powder with microwave absorbing performance includes the following steps:

[0061] Step (1), mixing metal element powders in a molar ratio of Fe:Co:Ni:Mn:Al=1:1:1:0.52:0.44, specifically, mixing 9.659 g of iron powder, 10.194 g of cobalt powder, 10.152 g of nickel powder, 4.942 g of manganese powder and 2.054 g of aluminum powder to obtain alloy raw material powder; the particle size of the iron powder is 150-200 nm, the particle size of the cobalt powder is 1-2 μm, the particle size of the nickel powder is less than or equal to 30 μm, the particle size of the manganese powder is 45 μm, and the particle size of the aluminum powder is 5 μm; the purity of the iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is greater than or equal to 99.5wt%;

[0062] Step (2), adding the above alloy raw material powder, 50 mL of anhydrous ethanol and 60 g of grinding balls into a ball mill, and ball milling is performed under the protection of inert gas; among the grinding balls, the mass ratio of grinding balls with a diameter of 8 mm, grinding balls with a diameter of 4 mm and grinding balls with a diameter of 2 mm is 1:4:4; before ball milling, the ball mill is repeatedly evacuated and filled with argon gas for 3 times; during ball milling, high speed and low speed are used for alternating ball milling, that is, first ball milling at a high speed of 700 rpm for 12 h, then ball milling at a low speed of 500 rpm for 12 h; then ball milling at a high speed of 700 rpm for 12 h, then ball milling at a low speed of 500 rpm for 12 h; finally ball milling at a high speed of 700 rpm for 12 h; the ball mill used in this embodiment is a double-tank high-energy swing ball mill, and the ball mill changes direction every 30 minutes of operation;

[0063] Step (3), after the ball milling is completed, the alloy raw material powder after ball milling is vacuum dried at 50°C for 24 hours and ground to a particle size of 60 to 120 μm to obtain an intermediate product A;

[0064] Step (4), adding a sodium hydroxide solution with a concentration of 1.0 mol / L to the intermediate product A, mixing and stirring, and performing corrosion modification by water bath heating method; the mass ratio of the intermediate product A to the sodium hydroxide solution is 1:8; the conditions for water bath heating corrosion modification are: water bath at a temperature of 40° C. for 3 hours, and a stirring rate of 10 rpm; after the water bath ends, the solid product obtained by solid-liquid separation is washed alternately with deionized water and anhydrous ethanol for 3 times until it is neutral, to obtain an intermediate product B;

[0065] Step (5), vacuum drying the intermediate product B at 50° C. for 24 h and grinding it to a particle size of 10 to 40 μm to obtain a FeCoNiMnAl high entropy alloy powder with microwave absorbing properties.

[0066] Example 2

[0067] The difference between this embodiment and embodiment 1 is that in step (4), the conditions for water bath heating corrosion modification are: water bath at a temperature of 40° C. for 2 h and a stirring rate of 10 rpm.

[0068] The other steps, raw materials and process involved are the same as those in Example 1.

[0069] Example 3

[0070] The difference between this embodiment and embodiment 1 is that in step (4), the conditions for water bath heating corrosion modification are: water bath at a temperature of 40° C. for 5 hours and a stirring rate of 10 rpm.

[0071] The other steps, raw materials and process involved are the same as those in Example 1.

[0072] Example 4

[0073] The difference between this embodiment and embodiment 3 is that: it also includes the following steps: vacuum drying the intermediate product B and then annealing it, and the annealing conditions are: keeping warm at 500°C for 2 hours under argon atmosphere; after the annealing is completed, an intermediate product C is obtained; the intermediate product C and grinding balls are added to a ball mill for ball milling; the mass ratio of the intermediate product C to the grinding balls is 1:1; among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm and the grinding balls with a diameter of 2 mm is 1:4:4; before ball milling, the ball mill is repeatedly evacuated and filled with argon for 3 times; the ball mill speed is 500 rpm, the ball mill changes direction every 30 minutes, and the ball milling time is 1 hour; after the ball milling is completed, a FeCoNiMnAl high entropy alloy powder with microwave absorbing performance is obtained.

[0074] Experimental tests found that the reflection loss of the FeCoNiMnAl high-entropy alloy powder prepared by annealing the intermediate product B was reduced at different thicknesses, and the minimum value reached -55dB when the thickness was 1.5mm. The effective absorption bandwidth was 4.5 GHz, and the minimum reflection loss of the high-entropy alloy powder at other thicknesses was below -30 dB.

[0075] Comparative Example

[0076] The difference between this embodiment and embodiment 1 is that in step (2), during ball milling, the diameter of the grinding balls is 8 mm; the rotation speed of the ball mill is 500 rpm, the ball milling time is 60 h, and the direction is changed every 30 min during the ball milling process; in step (4), the concentration of the sodium hydroxide solution is 2 mol / L, and the water bath conditions are: water bath at a temperature of 65°C for 4 h, and the stirring rate is 20 rpm.

[0077] The other steps, raw materials and process involved are the same as those in Example 1.

[0078] The microwave absorbing performance of the FeCoNiMnAl high entropy alloy powders prepared in Examples 1 to 3 and the comparative example was evaluated, and the results are shown in Figures 1 to 30.

[0079] from Figure 1 It can be seen that the FeCoNiMnAl high entropy alloy prepared by the preparation method of Example 1 has both FCC and BCC phase structures, and a diffraction peak of Ni(OH)2 appears near 20°. This indicates that part of the nickel reacts with NaOH to generate Ni(OH)2 during the corrosion modification process. The presence of Ni(OH)2 will also make the surface of the FeCoNiMnAl high entropy alloy uneven.

[0080] from Figures 2 to 10 It can be seen that the use of three diameters of grinding balls to alternately ball mill the alloy raw material powder at high and low speeds can not only enable the alloy raw materials to complete the alloying efficiently, but also obtain a high-entropy alloy powder with a thin-flaky structure with a relatively large aspect ratio. After the intermediate product A is surface-corroded and modified with a 1 mol / L sodium hydroxide solution, the microstructure grains of the FeCoNiMnAl high-entropy alloy are further refined (and some of the thin-flaky structures are curled or semi-curled), which not only increases the specific surface area, but also increases multiple reflections, thereby increasing the interfacial polarization effect, which is beneficial to the absorption of microwaves.

[0081] contrast Figures 11 to 13 It can be seen from the general magnetization curve that the saturation magnetization of the FeCoNiMnAl high entropy alloy obtained by surface corrosion modification of the intermediate product A with a 1 mol / L sodium hydroxide solution is significantly improved, and the saturation magnetization is increased from 78.16 emu / g to 108.5 emu / g. This is because after being corroded by a 1 mol / L sodium hydroxide solution, the high entropy alloy powder particles are refined, the surface becomes uneven, and cracks are formed, with a higher specific surface area and more defect sites, so its saturation magnetization is greatly improved.

[0082] The hysteresis loops of FeCoNiMnAl high entropy alloy powders before and after corrosion in the range of -20000Oe to 20000Oe at room temperature were further measured. Figures 14 to 16 Compare Figures 14 to 16It can be seen that the high entropy alloy powders before and after corrosion show typical soft magnetic properties; compared with the uncorroded intermediate product A, the saturation magnetization (Ms) of the FeCoNiMnAl high entropy alloy powder obtained after corrosion by 1mol / L NaOH solution has been significantly improved. This is because part of the Al in the alloy structure reacts with the NaOH solution to form metaaluminate during the corrosion process, and the effective magnetization volume of the powder increases (since Al is a non-magnetic material, the content of elemental aluminum in the powder decreases after dealloying, which enhances its magnetism), thereby increasing the saturation magnetization; soft magnetic materials have the characteristics of easy magnetization and demagnetization, and can generate heat during the magnetization process in the magnetic field, corresponding to the conversion of electromagnetic energy into thermal energy, which is suitable for electromagnetic wave scattering. Therefore, the FeCoNiMnAl high entropy alloy powder after corrosion has good electromagnetic wave absorption performance, and its coercive force decreases from 132.48Oe to 46.32Oe. This is because the grain size of the alloy powder decreases after corrosion. For roughly spherical grains, the coercivity usually increases as the grain size decreases. After reaching a maximum value, the coercivity decreases as the grain size further decreases.

[0083] The electromagnetic parameters (complex permittivity and complex magnetic permeability) of absorbing materials determine the absorbing ability of the materials. Optimizing the electromagnetic parameters of absorbing materials is an effective means to improve the absorbing ability of materials. The real part of the complex permittivity (ε=ε′-jε″) and the complex magnetic permeability (μ=μ′-jμ″) represent the storage capacity of the material, and the imaginary part represents the energy loss capacity of the material under the action of an external electric field or magnetic field.

[0084] Depend on Figures 17 to 19 It can be seen that the real part of the dielectric constant of the intermediate product A after being corroded by 1 mol / L NaOH solution for 3h and 5h is lower than that before corrosion, while the imaginary part is higher than that before corrosion, indicating that the ability of FeCoNiMnAl high entropy alloy powder to consume electromagnetic waves has been enhanced, which is conducive to promoting the eddy current loss effect. This is because new defects are generated during the corrosion process, and the grain refinement leads to an increase in specific surface area. These defects provide new polarization centers, promote polarization, and enhance the polarization effect of FeCoNiMnAl high entropy alloy powder.

[0085] For alloy electromagnetic wave absorbers, the natural resonance caused by spin and the eddy current effect are the main factors affecting the magnetic loss capacity. Figure 20 to Figure 22It can be seen that after being corroded by 1mol / L NaOH solution for 3h and 5h, the real part of the dielectric permeability of the FeCoNiMnAl high entropy alloy powder has increased compared with that before corrosion, and the imaginary part has also increased compared with that before corrosion. The higher imaginary part of the magnetic permeability can convert the bundled magnetic flux into latent heat consumption, thereby improving the magnetic loss capacity of the material. This shows that the FeCoNiMnAl high entropy alloy powder after corrosion modification has a strong response to the magnetic field and has strong magnetic conductivity; and the high entropy alloy powder after corrosion has a higher magnetic loss capacity, which can effectively absorb electromagnetic wave energy, thereby reducing reflection and improving the wave absorption performance of the material.

[0086] Compare the reflection losses of the FeCoNiMnAl alloy powders prepared in Examples 1 to 3. Figure 23 to Figure 27 It can be seen that the reflection loss value of the FeCoNiMnAl alloy powder before corrosion is as low as -29.92dB (when the thickness is 2.5mm), and the effective absorption bandwidth is 2.32GHz; after the FeCoNiMnAl alloy powder is corroded by 1mol / L NaOH solution for 2h, its reflection loss value is as low as -32.43dB (when the thickness is 3.5mm), and the effective absorption bandwidth is as wide as 4.00GHz; after the FeCoNiMnAl alloy powder is corroded by 1mol / L NaOH solution for 3h, its reflection loss value is as low as -47.92dB (when the thickness is 3mm), and the effective absorption bandwidth is 2.00GHz; after the FeCoNiMnAl alloy powder is corroded by 1mol / L NaOH solution for 5h, its reflection loss value is as low as -36.71dB (when the thickness is 1.5mm), and the effective absorption bandwidth is 4.40GHz, and the minimum reflection loss of the high entropy alloy powder at other thicknesses (except 2mm) is all within -25 The FeCoNiMnAl alloy powder prepared in the comparative example, after being corroded by 2mol / L NaOH solution for 4h, has a minimum reflection loss value of -31.17dB (when the thickness is 1.5mm), and an effective absorption bandwidth of 3.52GHz; the minimum reflection loss values ​​of other thicknesses (except 3.5mm) are all above -15dB.

[0087] By testing the attenuation constant (see Figures 28 to 30 ), it can be seen that the attenuation constant is significantly improved after corrosion treatment with 1 mol / L NaOH solution. This is because the surface of the alloy powder particles is uneven after corrosion, and the specific surface area increases. When the electromagnetic wave is incident on the surface of the material, multiple reflections and refractions will occur, thereby increasing the attenuation constant and improving the wave absorption performance.

[0088] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance, characterized in that: The steps include: Step (1), mixing iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder uniformly to obtain alloy raw material powder; the molar ratio of iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is 1:1:1:(0.5-0.6):(0.4-0.5); the particle size of the iron powder is 100-300 nm, the particle size of the cobalt powder is 1-2 μm, the particle size of the nickel powder is less than or equal to 50 μm, the particle size of the manganese powder is 40-50 μm, and the particle size of the aluminum powder is 3-5 μm; Step (2), adding alloy raw material powder, anhydrous ethanol and grinding balls into a ball mill, and performing alternating ball milling under the protection of inert gas, wherein each round of alternating ball milling is first performed at a high speed and then at a low speed, and more than two rounds of alternating ball milling are performed; Step (3), after the ball milling is completed, vacuum drying the ball-milled alloy raw material powder and grinding it to obtain an intermediate product A; Step (4), adding sodium hydroxide solution to the intermediate product A, mixing and stirring, and performing corrosion modification by water bath heating method; After the water bath is finished, the solid product obtained by solid-liquid separation is washed to neutrality to obtain intermediate product B; Step (5), vacuum drying and grinding the intermediate product B to obtain FeCoNiMnAl high entropy alloy powder with microwave absorbing performance; In step (2), the mass volume ratio of the alloy raw material powder to anhydrous ethanol is (6-8) g / L; the mass ratio of the alloy raw material powder to the grinding balls is 1:(1-3); among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm, and the grinding balls with a diameter of 2 mm is 1:(3-5):(3-5); before ball milling, the ball mill is repeatedly evacuated and filled with argon gas for 3-5 times; During ball milling, firstly, ball mill at a high speed of 700-800 rpm for 10-12 hours, then ball mill at a low speed of 400-500 rpm for 10-12 hours; then ball mill at a high speed of 700-800 rpm for 10-12 hours, then ball mill at a low speed of 400-500 rpm for 10-12 hours; finally, ball mill at a high speed of 700-800 rpm for 10-12 hours; the ball mill changes direction every 30 minutes; In step (4), the concentration of the sodium hydroxide solution is 1.0-1.5 mol / L; the mass ratio of the intermediate product A to the sodium hydroxide solution is 1:(5-10); the conditions for water bath heating corrosion modification are: water bath at a temperature of 30-60° C. for 1-6 hours, and a stirring rate of 5-15 rpm; and deionized water and anhydrous ethanol are used for alternating washing for 3-5 times.

2. The method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to claim 1, characterized in that: In step (1), the particle size of the iron powder is 150-200 nm, the particle size of the cobalt powder is 1-2 μm, the particle size of the nickel powder is less than or equal to 30 μm, the particle size of the manganese powder is 45 μm, and the particle size of the aluminum powder is 5 μm; the purity of the iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is greater than or equal to 99.5 wt%.

3. The method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to claim 1, characterized in that: In step (1), the molar ratio of iron powder, cobalt powder, nickel powder, manganese powder and aluminum powder is 1:1:1:0.52:0.

44.

4. The method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to claim 1, characterized in that: In step (2), the mass volume ratio of the alloy raw material powder to anhydrous ethanol is 7.4 g / L; the mass volume ratio of the alloy raw material powder to the grinding balls is 3.7:6; among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm, and the grinding balls with a diameter of 2 mm is 1:4:4; before ball milling, the ball mill is repeatedly evacuated and filled with argon gas for 3 times; During ball milling, first ball mill at a high speed of 700 rpm for 12 hours, then ball mill at a low speed of 500 rpm for 12 hours; then ball mill at a high speed of 700 rpm for 12 hours, then ball mill at a low speed of 500 rpm for 12 hours; finally ball mill at a high speed of 700 rpm for 12 hours; the ball mill changes direction every 30 minutes of operation.

5. The method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to claim 1, characterized in that: In step (4), the concentration of the sodium hydroxide solution is 1.0 mol / L; the mass ratio of the intermediate product A to the sodium hydroxide solution is 1:8; the conditions for water bath heating corrosion modification are: water bath at a temperature of 40° C. for 5 h, and a stirring rate of 10 rpm; and deionized water and anhydrous ethanol are used for alternating washing 3 times.

6. The method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to claim 1, characterized in that: In step (3), the vacuum drying conditions are: vacuum drying at a temperature of 40 to 70° C. for 18 to 24 hours, and the particle size of the intermediate product A is 60 to 120 μm; In step (5), the vacuum drying conditions are: vacuum drying at a temperature of 40 to 70° C. for 18 to 24 hours, and the particle size of the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance is 10 to 40 μm.

7. The method for preparing FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to claim 6, characterized in that: In step (3), the vacuum drying conditions are: vacuum drying at 50°C for 24 hours, and the particle size of the intermediate product A is 60 to 120 μm; In step (5), the vacuum drying conditions are: vacuum drying at 50° C. for 24 hours, and the particle size of the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance is 10 to 40 μm.

8. The method for preparing the FeCoNiMnAl high entropy alloy powder with microwave absorbing performance according to any one of claims 1 to 7, characterized in that: The following steps are also included: The intermediate product B is vacuum dried and then annealed. The annealing conditions are: keeping the temperature at 500°C for 2 hours under an argon atmosphere. After the annealing is completed, the intermediate product C is obtained. The intermediate product C and grinding balls are added to a ball mill for ball milling; the mass ratio of the intermediate product C to the grinding balls is 1:1; among the grinding balls, the mass ratio of the grinding balls with a diameter of 8 mm, the grinding balls with a diameter of 4 mm and the grinding balls with a diameter of 2 mm is 1:4:4; before ball milling, the ball mill is repeatedly evacuated and filled with argon for 3 times; the ball mill speed is 500 rpm, the ball mill changes direction every 30 minutes, and the ball milling time is 1 hour.

Images