Fe2alb2@al2o3 high-temperature absorbent, preparation method and application

Abstract

The application discloses a novel high-efficiency Fe2AlB2@Al2O3 high-temperature absorber, a preparation method and application, the microstructure of the high-temperature absorber is nanometer layer, the micro-layer thickness is 10-50 nm, the layered Fe2AlB2 is coated with an Al2O3 shell layer, and the shell layer thickness is 5-10 nm. The preparation method of the high-temperature absorber is as follows: weighing powder, high-energy ball milling, laser rapid sintering, and plasma ball milling plus in-situ self-generation. The high-temperature absorber can serve in a 600-800 DEG C environment for a long time, exhibits good wave-absorbing performance, has the characteristics of a wide absorption frequency band and high wave-absorbing efficiency, and the preparation method has the advantages of short synthesis time, low energy consumption, high efficiency and high purity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature wave-absorbing materials, and relates to a novel high-efficiency Fe2AlB2@Al2O3 high-temperature absorber, a preparation method and application. BACKGROUND

[0002] Radar wave-absorbing materials can be divided into normal-temperature wave-absorbing materials and high-temperature wave-absorbing materials according to different working temperatures. The high-temperature wave-absorbing materials are mainly applied to the tail nozzles and nose cone caps of aero-engines, warheads and wing parts of cruise missiles and other high-temperature components which are prone to expose position information of weapon equipment. Therefore, how to realize the stealth of high-temperature components of weapon equipment, weaken the characteristic signals and develop high-performance high-temperature wave-absorbing materials has become an important frontier topic in the current military field.

[0003] At present, common high-temperature wave-absorbing materials are mainly dielectric wave-absorbing materials such as carbon materials, SiC and ZnO. The carbon materials have poor high-temperature oxidation resistance and are difficult to serve in an environment higher than 500 DEG C. The SiC and ZnO wave-absorbing materials have low electrical conductivity, and have problems such as narrow absorption frequency band and poor low-frequency wave-absorbing effect. Therefore, in actual use, it is often necessary to increase the thickness of the dielectric wave-absorbing coating to improve its wave-absorbing performance, which is extremely disadvantageous for the design and application of stealth materials of aerospace weapon equipment which pursues the strict requirement of "thin, light, wide and strong". Compared with the dielectric wave-absorbing materials, the magnetic loss type wave-absorbing materials have the outstanding advantage of high wave-absorbing efficiency, but the disadvantage is that they have poor high-temperature stability and are difficult to serve in a high-temperature environment for a long time. Therefore, if a magnetic loss type wave-absorbing material with good high-temperature oxidation resistance and excellent wave-absorbing performance can be developed, it is a key problem to be solved at present.

[0004] Fe2AlB2 is a novel ternary transition metal boride (MAB phase) which has good electrical conductivity, paramagnetic properties and high-temperature oxidation resistance. At present, there is no related report on the application of the material to the wave-absorbing field. At present, the preparation methods of Fe2AlB2 include arc melting plus annealing treatment method and in-situ hot-pressing synthesis method. The arc melting plus annealing treatment method is to press the prepared Fe, Al and B powders into a billet, then perform arc melting, and then place the billet in a quartz glass tube to obtain Fe2AlB2 bulk material at 900 DEG C for 7 days. The problem of this preparation method is that the synthesis time is too long, the process is complex and the energy consumption is high. The in-situ hot-pressing synthesis method is to place the mixed and uniform raw material powders into a vacuum hot-pressing furnace, and then obtain Fe2AlB2 bulk material at 1200 DEG C and 30 MPa for 0.5 h. The problem of this preparation method is that the purity of the bulk material is low, and in addition to the Fe2AlB2 phase, the bulk material also contains FeB, Fe-Al and Al2O3 phases.

[0005] Therefore, it is of important military significance to develop a Fe2AlB2 powder preparation method with short synthesis time, low energy consumption, high efficiency and high purity, and to popularize and apply it as a high-temperature wave-absorbing material in the field of aerospace in China. SUMMARY

[0006] To solve the above problems, the application provides a novel and efficient Fe2AlB2@Al2O3 high-temperature absorber, which can serve in a 600-800 DEG C environment for a long time, exhibits good wave-absorbing performance, and has the characteristics of wide absorption frequency band and high wave-absorbing efficiency.

[0007] Another object of the application is to provide a preparation method of the novel and efficient Fe2AlB2@Al2O3 high-temperature absorber, which has the advantages of short synthesis time, low energy consumption, high efficiency and high purity.

[0008] A third object of the application is to provide an application of the novel and efficient Fe2AlB2@Al2O3 high-temperature absorber in stealth of high-temperature parts of aerospace equipment.

[0009] The technical scheme adopted by the application is a novel and efficient Fe2AlB2@Al2O3 high-temperature absorber, the microstructure of the high-temperature absorber is nanolayer, the micro-layer thickness of Fe2AlB2 is 10-50 nm, Fe2AlB2 is coated with an Al2O3 shell layer, and the shell layer thickness is 5-10 nm.

[0010] Further, the Fe2AlB2 is in a sheet structure as a whole, and the thickness is 3-5 microns.

[0011] The absorber has the following outstanding advantages:

[0012] (1) Fe2AlB2 is a novel ternary transition metal boride (MAB phase), which has the characteristics of metal and ceramic, has high resistivity and paramagnetic characteristics, is a magnetic loss type absorber, and can utilize eddy current loss and natural resonance loss electromagnetic waves.

[0013] (2) The microstructure of Fe2AlB2 powder is a unique nanolayer, which has the advantages of inhibiting skin effect, increasing natural resonance frequency, breaking through the Snoek limit, improving the wave-absorbing efficiency of the absorber in the high-frequency band, and expanding the frequency width.

[0014] (3) The Al2O3 shell layer generated in-situ on the outer side of the Fe2AlB2 nanolayer is an electric loss type absorber. On the one hand, the impedance matching characteristics of the absorber can be further improved, so that more electromagnetic waves are transmitted to the interior of the absorber powder; on the other hand, the electromagnetic waves can be attenuated by using various polarization mechanisms such as Debye dipole polarization relaxation loss, interface polarization and conductance loss, so as to fully exert the coupling effect of dielectric loss and magnetic loss, and achieve the purposes of expanding the frequency width and improving the wave absorption efficiency.

[0015] (4) The nanoscale Al2O3 shell layer obtained by the in-situ generation technology can further improve the high-temperature oxidation resistance of the Fe2AlB2 flaky powder, hinder the invasion of oxygen atoms, and ensure that the absorber can serve for a long time in an environment of 600-800 DEG C, so as to be used as a high-temperature wave absorption material.

[0016] Another technical solution adopted by the present application is a preparation method of a Fe2AlB2@Al2O3 high-temperature absorber, comprising the following steps:

[0017] Step one: dry iron powder, aluminum powder and boron powder are weighed according to the proportion as raw materials;

[0018] Step two: the mixed powder of step one and agate grinding balls are put into a ball mill tank filled with inert gas, and are loaded into a planetary ball mill to perform high-energy ball milling, so as to obtain Fe-Al-B mixed powder with uniform composition;

[0019] Step three: the Fe-Al-B mixed powder obtained in step two is laid on the surface of the substrate of a laser sintering machine, and is rapidly sintered by a high-energy laser beam, so as to obtain Fe2AlB2 powder;

[0020] Step four: the Fe2AlB2 powder obtained in step three is put into a plasma ball mill to be broken, and is in-situ generated by plasma ball milling, so as to obtain Fe2AlB2@Al2O3 absorber.

[0021] Further, in step one, the purity of the raw material powder is more than 99%, the particle size is 3-10 μm, and the molar ratio of Fe:Al:B is 2:x:2, wherein x=1.1-1.5. In the present application, the designed molar ratio of Fe:Al:B powder ensures that not only the expected Fe2AlB2 phase is obtained, but also sufficient Al source is provided for the in-situ generation of Al2O3 in step four.

[0022] Further, step two is specifically as follows: the powder is loaded into a sealed ball mill tank, vacuumized, and then inert gas is introduced into the ball mill tank to protect the powder from being oxidized during the ball milling process; the mass ratio of the powder to the agate grinding balls is 1:5-1:20, the ball milling time is 1-5 h, and the ball milling speed is 300-500 r / min.

[0023] The main purpose of this step is to ensure that the Fe powder, Al powder and B powder are fully mixed and the components are uniform.

[0024] The ratio of the powder to the grinding ball and the speed of the ball mill are matched, which directly affects the uniformity of the powder mixing and the degree of refinement, and indirectly affects the reaction degree of the subsequent step three.

[0025] If the ball milling time is too short, the powder activation degree is insufficient and the component uniformity is poor; if the ball milling time is too long, the powder is cold-welded and re-agglomerated, and energy is wasted.

[0026] Further, in step three, the process parameters of high-energy laser beam rapid sintering are: spot diameter 50-100 μm, laser power 100-200 W, scanning speed 300-500 mm / s, and during the high-energy laser beam rapid sintering process, the cavity is first evacuated and then filled with inert gas protection.

[0027] The laser power determines the reaction degree. If the laser power is too small, the temperature is too low, the powder cannot be completely melted, the reaction cannot occur, and the Fe2AlB2 phase cannot be formed; if the laser power is too high, the grains grow too much, and the expected nanosheet structure cannot be formed.

[0028] The scanning speed and the laser power are matched, which are the key factors affecting the effect of laser rapid sintering. Too slow scanning speed leads to over-burning of the powder, the powder is agglomerated into blocks, and the wave absorption efficiency is affected; too fast scanning speed affects the reaction degree, resulting in low powder purity.

[0029] Further, step four is: the powder is loaded into a sealed ball mill tank, vacuumized, and then a mixture of oxygen and argon gas is introduced into the ball mill tank, wherein the volume fraction of oxygen is 1-5%, the mass ratio of the powder to the stainless steel grinding ball is 1:20-1:50, the rotation speed is 800-900 r / min, the discharge voltage is 15-25 kV, the discharge current is 1-2 A, the discharge frequency is 10-30 kHz, the ball milling time is 1-5 h, and the temperature in the ball mill tank during ball milling is 500-700℃.

[0030] Only when the ball mill tank is in an inert gas atmosphere containing 1-5 vol% oxygen, the Al atoms in the powder will be better than Fe and B, and a dense Al2O3 protective layer of 5-10 nm can be formed on the surface of the Fe2AlB2 particles. The role of this nanoscale protective layer is to hinder the intrusion of external oxygen atoms, further improving the oxidation resistance of the Fe2AlB2 powder in a high-temperature environment.

[0031] The discharge voltage, discharge current and discharge frequency parameters match together to form important factors affecting the discharge effect of dielectric barrier plasma. The plasma is excited in the ball milling process, which improves the energy of the reaction system, promotes the generation of a large number of high-energy electrons and active particles, and bombards the powder surface to introduce a large number of defects and active sites, improve the surface activity of the powder, and accelerate the reaction rate of the in-situ generation of uniform and dense Al2O3 shell on the surface of Fe2AlB2 powder.

[0032] The appropriate ball-to-powder ratio, ball milling time and ball milling speed are selected and matched to refine the powder organization, effectively shorten the process time and improve the production efficiency; meanwhile, the mechanical energy and plasma energy are coupled in the ball milling process to improve the atomic diffusion capacity and promote the in-situ generation of Al2O3.

[0033] The plasma ball milling and in-situ self-generation technology is used, which has the following effects: on the one hand, the 'thermal shock' effect of plasma and the crushing effect of high-energy ball milling make the Fe2AlB2 powder obtained by laser rapid sintering be refined, the powder sheet thickness is reduced and the diameter-thickness ratio is increased under the premise of ensuring the micro-nano layered structure, which is beneficial to the improvement of the wave absorption performance of the powder; on the other hand, due to the plasma activation effect and the strong impact of the stainless steel milling ball, the powder system temperature rapidly reaches 500-700 DEG C, and a large number of active sites are generated on the surface of the Fe2AlB2 powder, which improves the powder activity and atomic diffusion capacity, and provides growth conditions for the in-situ generation of Al2O3 protective shell on the surface.

[0034] Further, in the step four, the content of the in-situ self-generated Al2O3 shell is 5-10wt%, and the content of Fe2AlB2 is 90-95wt%, and the expected Fe2AlB2@Al2O3 absorber is obtained.

[0035] Another technical solution adopted by the application is the application of a new type of efficient Fe2AlB2@Al2O3 high-temperature absorber in the stealth of high-temperature parts of aerospace equipment.

[0036] The beneficial effects of the application are:

[0037] The application provides a new type of high-efficiency high-temperature wave-absorbing material with good high-temperature oxidation resistance, which can serve in a 600-800 DEG C environment for a long time. The application first mixes the powder by high-energy ball milling, then performs laser rapid sintering, and finally uses the plasma ball milling and in-situ self-generation technology to obtain the Fe2AlB2@Al2O3 high-temperature wave-absorbing powder, and the steps are closely matched.

[0038] The Fe2AlB2@Al2O3 prepared by the application is a new type of high-temperature absorber with oxidation resistance and high-efficiency wave absorption. On the one hand, the unique lamellar microstructure and electromagnetic properties of the Fe2AlB2@Al2O3 can make it fully exert various loss mechanisms such as dipole polarization, electric conduction loss, eddy current loss, natural resonance, and greatly attenuate electromagnetic waves. On the other hand, the excellent high-temperature oxidation resistance of the Fe2AlB2@Al2O3 can still maintain good wave absorption performance at a high temperature of 600-800 DEG C. The Fe2AlB2@Al2O3 can not only avoid the problem of easy oxidation failure of traditional magnetic loss type absorbers at high temperature, but also avoid the defect of low wave absorption efficiency of traditional dielectric type absorbers.

[0039] Meanwhile, the nanoscale Al2O3 protective shell generated in situ by the application not only helps to adjust the impedance matching ability of the Fe2AlB2 absorber powder, but also can dissipate electromagnetic waves through interface polarization to further improve the ability to attenuate electromagnetic waves. At the same time, the shell layer can also block oxygen from entering, thereby improving the service life of the absorber powder at high temperature. This has important scientific significance and application prospect for improving the stealth performance of key high-temperature components in today's aerospace weapon equipment. BRIEF DESCRIPTION OF DRAWINGS

[0040] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0041] Figure 1 is the XRD pattern of the Fe2AlB2@Al2O3 high-temperature absorber obtained in Example 1.

[0042] Figure 2 is the scanning electron microscope pattern of the Fe2AlB2@Al2O3 high-temperature absorber obtained in Example 1.

[0043] Figure 3 is the appearance morphology pattern of the Fe2AlB2@Al2O3 high-temperature absorber obtained in Example 1.

[0044] Figure 4 is the transmission electron microscope pattern of the Fe2AlB2@Al2O3 high-temperature absorber obtained in Example 1.

[0045] Figure 5 is the reflection loss curve pattern of the Fe2AlB2@Al2O3 high-temperature absorber obtained in Example 1 at 25 DEG C and 800 DEG C.

[0046] Figure 6 is the reflection loss curve pattern of the Fe2AlB2@Al2O3 high-temperature absorber obtained in Example 2 at 25 DEG C and 600 DEG C.

[0047] Figure 7 This is a reflection loss curve of the Fe2AlB2@Al2O3 high-temperature absorbent obtained in Example 3 at 25℃ and 700℃.

[0048] Figure 8 This is a morphology diagram of the Fe-Al-B powder obtained in Comparative Example 1.

[0049] Figure 9 This is the XRD pattern of the Fe-Al-B powder obtained in Comparative Example 1.

[0050] Figure 10 This is a reflection loss diagram of the Fe-Al-B powder obtained in Comparative Example 1 at 25℃.

[0051] Figure 11 This is a morphology diagram of the Fe2AlB2 powder obtained in Comparative Example 2.

[0052] Figure 12 This is the XRD pattern of the Fe2AlB2 powder obtained in Comparative Example 2.

[0053] Figure 13 This is a reflection loss diagram of the Fe2AlB2 powder obtained in Comparative Example 2 at 25℃. Detailed Implementation

[0054] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0055] Example 1,

[0056] The preparation method of the novel high-efficiency Fe2AlB2@Al2O3 high-temperature absorbent is carried out according to the following steps:

[0057] Step 1: Weigh dry iron powder, aluminum powder and boron powder as raw materials, with a purity of over 99% and a particle size of 5μm, and prepare powder according to the molar ratio of Fe:Al:B = 2:1.2:2;

[0058] Step 2: Using high-energy ball milling technology, the prepared powder and agate grinding balls are placed in a ball mill jar filled with inert gas, and then loaded into a planetary ball mill for thorough mixing. The mass ratio of powder to agate grinding balls is set to 1:10, the rotation speed is 400 r / min, and the milling time is 2 hours.

[0059] Step three: The Fe-Al-B mixed powder obtained in the previous step is laid on the surface of the laser sintering machine substrate by laser sintering technology. The spot diameter is set to 70 μm, the laser power is set to 150 W, and the scanning speed is set to 350 mm / s to perform high-energy laser beam rapid sintering; during the sintering process, the cavity is first evacuated and then filled with argon gas protection.

[0060] Step four: The Fe2AlB2 powder obtained in the previous step is loaded into a closed ball mill tank and vacuumized, and then a mixture of oxygen and argon gas is introduced into the ball mill tank, wherein the volume fraction of oxygen is 3%, the ball mill medium is stainless steel balls, the mass ratio of the powder to the stainless steel balls is 1:40, the rotation speed is 850 r / min, the discharge voltage is 20 kV, the discharge current is 1.5 A, the discharge frequency is 20 kHz, the ball milling time is 2 h, and the temperature in the ball mill tank during ball milling is 600 ℃, thereby preparing the Fe2AlB2@Al2O3 high-temperature absorber.

[0061] The phase composition and microstructure thereof are shown in Figures 1-4 The X-ray diffraction pattern of Figure 1 indicates that the obtained powder is composed of Fe2AlB2, and the in-situ generated Al2O3 content on the surface of the powder is too low to be detected. From Figure 2 it can be directly observed that the microstructure of the Fe2AlB2@Al2O3 high-temperature absorber obtained according to the above steps is layered, and the layer thickness is 20-30 nm. From Figure 3 it can be seen that the overall macrostructure of the Fe2AlB2@Al2O3 is a flaky structure, and the thickness thereof is about 3-4 μm.

[0062] From the Figure 4 transmission electron microscopy image, it can be clearly seen that the outer layer of the Fe2AlB2 powder is in-situ generated with a nanoscale Al2O3 shell layer, and the thickness thereof is 5-10 nm. The in-situ generated Al2O3 shell layer content is 8 wt%, and the Fe2AlB2 content is 92 wt%.

[0063] The wave absorption performance of the obtained Fe2AlB2@Al2O3 high-temperature absorber is tested, Figure 5The absorbent was mixed with paraffin after oxidation at 25℃ and 800℃ for 2h, respectively, and the reflection loss-frequency curve in the frequency range of 2-18GHz was tested. As shown in the figure, the wave absorbing material obtained by mixing the Fe2AlB2@Al2O3 absorbent with paraffin has a peak absorption efficiency of -18.2dB at a frequency of 13.8GHz at room temperature when the thickness is 1.5mm, and the effective absorption bandwidth with a reflection loss less than -10dB is 2.68GHz; the Fe2AlB2@Al2O3 absorbent after oxidation at 800℃ for 2h has a peak absorption efficiency of -20.6dB at a frequency of 14.8GHz, and the effective absorption bandwidth with a reflection loss less than -10dB is 2.75GHz.

[0064] Example 2,

[0065] The preparation method of the novel high-efficiency Fe2AlB2@Al2O3 high-temperature absorbent is specifically as follows:

[0066] Step one: dry iron powder, aluminum powder and boron powder were weighed as raw materials, the purity was more than 99%, and the particle size was 3μm, and the powder was prepared according to the molar ratio of Fe:Al:B=2:1.5:2;

[0067] Step two: the prepared powder and agate grinding balls were put into a ball mill tank filled with inert gas, and were fully mixed in a planetary ball mill. The mass ratio of the powder to the agate grinding balls was set to 1:5, the rotation speed was 300r / min, and the ball milling time was 1h.

[0068] Step three: the Fe-Al-B mixed powder obtained in the previous step was laid flat on the surface of the laser sintering machine substrate. The spot diameter was set to 50μm, the laser power was 200W, the scanning speed was 500mm / s, and the cavity was first evacuated and then filled with argon gas during the sintering process.

[0069] Step four: the Fe2AlB2 powder obtained in the previous step was put into a sealed ball mill tank, vacuumized, and then a mixture of oxygen and argon gas was introduced into the ball mill tank, wherein the volume fraction of oxygen was 5%, stainless steel grinding balls were used as the ball mill medium, the ratio of the powder to the stainless steel grinding balls was 1:20, the rotation speed was 800r / min, the discharge voltage was 15kV, the discharge current was 1A, the discharge frequency was 10kHz, the ball milling time was 5h, and the temperature in the ball mill tank during ball milling was 700℃. The prepared Fe2AlB2@Al2O3 high-temperature absorbent has a micro-layer thickness of 10-20nm and a macroscopic flake thickness of about 3-3.5μm. The in-situ self-generated Al2O3 shell layer contains 5wt%, and the Fe2AlB2 content is 95wt%.

[0070] The wave-absorbing performance of the obtained Fe2AlB2@Al2O3 high-temperature absorber was tested, Figure 6 The Fe2AlB2@Al2O3 absorber was mixed with paraffin wax at 25°C and 600°C for 2h, and the reflection loss-frequency curve of the wave-absorbing material in the frequency range of 2-18GHz was tested. It can be seen from the figure that Figure 6 The wave-absorbing material obtained by mixing the Fe2AlB2@Al2O3 absorber with paraffin wax has a peak absorption efficiency of -19.8dB at a frequency of 13.3GHz at room temperature when the thickness is 1.5mm, and the effective absorption bandwidth with a reflection loss less than -10dB is 2.41GHz; after oxidation at 600°C for 2h, the Fe2AlB2@Al2O3 absorber has a peak absorption efficiency of -19.5dB at a frequency of 14.7GHz, and the effective absorption bandwidth with a reflection loss less than -10dB is 2.61GHz.

[0071] Example 3,

[0072] The preparation method of the novel and efficient Fe2AlB2@Al2O3 high-temperature absorber is carried out according to the following steps:

[0073] Step one: dry iron powder, aluminum powder and boron powder are weighed as raw materials, the particle size is 10μm, and the powder is prepared according to the molar ratio of Fe:Al:B=2:1.1:2;

[0074] Step two: the prepared powder and agate grinding balls are put into a ball mill tank filled with inert gas through high-energy ball milling technology, and are loaded into a planetary ball mill for thorough mixing. The mass ratio of powder to agate grinding ball is set to 1:20, the rotation speed is 500r / min, and the ball milling time is 5h.

[0075] Step three: the Fe-Al-B mixed powder obtained in the previous step is laid flat on the surface of the laser sintering machine substrate through laser sintering technology. The spot diameter is set to 100μm, the laser power is 100W, and the scanning speed is 300mm / s. The cavity is first evacuated and then filled with argon gas during the sintering process.

[0076] Step four: The Fe2AlB2 powder obtained in the previous step was loaded into a closed ball mill tank and vacuumized, and then a mixture of oxygen and argon gas was introduced into the ball mill tank, wherein the volume fraction of oxygen was 1%, the ball mill medium was stainless steel ball, the mass ratio of powder to stainless steel ball was 1:50, the rotation speed was 900 r / min, the discharge voltage was 25 kV, the discharge current was 2 A, the discharge frequency was 30 kHz, the ball milling time was 1 h, and the temperature in the ball mill tank during ball milling was 500 ℃. The prepared Fe2AlB2@Al2O3 high-temperature absorber had a micro-layer thickness of 30-50 nm and a whole macroscopic flake thickness of about 4-5 μm. The in-situ self-generated Al2O3 shell layer content was 10 wt%, and the Fe2AlB2 content was 90 wt%.

[0077] The wave-absorbing performance of the obtained Fe2AlB2@Al2O3 high-temperature absorber was tested, Figure 7 After the absorber was oxidized at 25 ℃ and 700 ℃ for 2 h, it was mixed with paraffin, and the reflection loss-frequency change curve graph of the wave-absorbing performance in the frequency range of 2-18 GHz was tested. It can be seen from Figure 7 that the wave-absorbing material obtained by mixing the Fe2AlB2@Al2O3 absorber with paraffin had a peak absorption efficiency of -19.3 dB at a frequency of 12.5 GHz at room temperature when the thickness was 1.5 mm, and the effective absorption bandwidth with a reflection loss less than -10 dB was 2.62 GHz; after being oxidized at 700 ℃ for 2 h, the Fe2AlB2@Al2O3 absorber had a peak absorption efficiency of -19.8 dB at a frequency of 15.4 GHz, and the effective absorption bandwidth with a reflection loss less than -10 dB was 3.25 GHz.

[0078] Comparative Example 1,

[0079] The preparation method of the Fe-Al-B powder was specifically carried out according to the following steps:

[0080] Step one: Dry iron powder, aluminum powder and boron powder were weighed as raw materials, the purity was more than 99%, and the particle size was 5 μm, and the powder was prepared according to the molar ratio of Fe:Al:B = 2:1.2:2;

[0081] Step two: The prepared powder and agate ball were put into a ball mill tank filled with inert gas, and then loaded into a planetary ball mill for thorough mixing. The mass ratio of powder to agate ball was set to 1:10, the rotation speed was 400 r / min, and the ball milling time was 2 h. The obtained Fe-Al-B powder had flaky characteristics, and the micro-morphology, phase composition and wave-absorbing performance related results were as shown in Figures 8-10 .

[0082] From Figures 8-10The microstructure of the material obtained after high-energy ball milling is shown to be sheet-like, and its phase is Fe(Al,B) solid solution. Its microwave absorption performance in the frequency range of 2–18 GHz was tested. The results show that the microwave absorbing material obtained by mixing Fe-Al-B powder and paraffin, with a thickness of 1.5 mm, exhibits a peak absorption efficiency of -13.6 dB at 3.3 GHz at room temperature, with an effective absorption bandwidth of 1.15 GHz and a reflection loss of less than -10 dB. Since this is only a Fe(Al,B) solid solution and not the MAB phase Fe2AlB2, a layered structure is not observed at this stage. Therefore, obtaining a layered microstructure of the MAB phase Fe2AlB2 while maintaining a thin sheet-like overall appearance presents significant technical challenges.

[0083] Comparative Example 2,

[0084] The preparation method of Fe2AlB2 powder is carried out according to the following steps:

[0085] Step 1: Weigh dry iron powder, aluminum powder and boron powder as raw materials, with a purity of over 99% and a particle size of 5μm, and prepare powder according to the molar ratio of Fe:Al:B = 2:1.2:2;

[0086] Step 2: Using high-energy ball milling technology, the prepared powder and agate grinding balls are placed in a ball mill jar filled with inert gas, and then loaded into a planetary ball mill for thorough mixing. The mass ratio of powder to agate grinding balls is set to 1:10, the rotation speed is 400 r / min, and the milling time is 2 hours.

[0087] Step 3: Using laser sintering technology, the Fe-Al-B mixed powder obtained in the previous step is spread evenly onto the surface of the laser sintering machine substrate. The spot diameter is set to 70 μm, the laser power to 150 W, and the scanning speed to 350 mm / s. During the sintering process, the cavity is first evacuated and then filled with argon gas for protection. The resulting absorbent is a blocky Fe2AlB2 with a relatively large thickness of 5–10 μm. Its microstructure exhibits a layered structure with a microlayer thickness of 100–200 nm. The experimental results are as follows: Figures 11-13 As shown.

[0088] from Figure 11 The enlarged view in the upper right corner shows that the obtained powder microstructure is a typical layered structure. Combined with... Figure 12 XRD pattern analysis revealed that the phase was Fe2AlB2. Its microwave absorption performance in the frequency range of 2–18 GHz was tested. The results showed that the microwave absorbing material obtained by mixing Fe2AlB2 powder and paraffin, with a thickness of 1.5 mm, exhibited a peak absorption efficiency of -11.5 dB at 5.6 GHz at room temperature, with an effective absorption bandwidth of 2.13 GHz and a reflection loss of less than -10 dB.

[0089] At this time, the MAB phase Fe2AlB2absorbent is obtained, and the microstructure also presents a layered feature. However, the problem is that the ratio of the macroscopic morphology diameter to thickness is too large, which affects the transmission of electromagnetic waves in the absorbent powder and the impedance matching characteristics, resulting in low wave absorption efficiency. Meanwhile, the stability under high temperature service needs to be further improved.

[0090] On this basis, the fourth step of the embodiment of the present application is further added, that is, the plasma ball milling and in-situ self-generation technology are used, the plasma activation and thermal shock effect are coupled with the strong impact of high-energy ball milling, so that the blocky Fe2AlB2absorbent is broken and peeled off, not only the thickness of the flaky powder is further reduced to 3-5 μm in macroscopic view, but also the layered spacing of Fe2AlB2is further expanded, the flaky thickness is reduced, and the flaky thickness is reduced to 10-50 nm. From the perspective of wave absorption mechanism, compared with the bulk, the special microstructure can break through the Snoek limit and expand the wave absorption frequency width. Meanwhile, in the inert gas environment containing 1-5 vol% oxygen, a 5-10 nm Al2O3protective shell can be generated in-situ on the surface of the layered Fe2AlB2absorbent powder, which is extremely beneficial to improve the service life of the absorbent in the high temperature environment of 600-800℃.

[0091] The Fe2AlB2@Al2O3high temperature absorbent prepared by the present application can be used for stealth of high temperature parts in aerospace equipment. For example, the key high temperature parts of major weapon equipment, such as the tail nozzle and nose cone cap of an aero-engine, the warhead and wing of a cruise missile, and the like, which are extremely easy to expose the location information of the equipment.

[0092] The above only describes the preferred embodiments of the present application and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of the present application are included in the protection scope of the present application.

Claims

1. Fe2AlB2@Al2O3 high-temperature wave absorber, characterized in that, The microstructure of the high-temperature wave absorber is nanometer layered, the micro-layer thickness of Fe2AlB2 is 10-50 nm, and the Fe2AlB2 is externally coated with an Al2O3 shell layer with a thickness of 5-10 nm; The Fe2AlB2 as a whole is in a sheet structure, and the thickness is 3-5 μm; The Fe2AlB2@Al2O3 wave absorber can serve in an environment of 600-800 ℃.

2. The preparation method of Fe2AlB2@Al2O3 high-temperature wave absorber according to claim 1, characterized in that, The method comprises the following steps: Step one: dry iron powder, aluminum powder and boron powder are weighed according to a proportion as raw materials; Step two: the mixed powder of step one and agate grinding balls are put into a ball mill tank filled with inert gas, and are loaded into a planetary ball mill to perform high-energy ball milling, so as to obtain Fe-Al-B mixed powder with uniform composition; Step three: the Fe-Al-B mixed powder obtained in step two is laid on the surface of a laser sintering machine substrate, and is rapidly sintered by a high-energy laser beam, so as to obtain Fe2AlB2 powder; Step four: the Fe2AlB2 powder obtained in step three is put into a plasma ball mill to be broken, and is generated in-situ by plasma ball milling, so as to obtain Fe2AlB2@Al2O3 wave absorber.

3. The preparation method of Fe2AlB2@Al2O3 high-temperature wave absorber according to claim 2, characterized in that, In step one, the purity of the raw material powder is more than 99%, and the particle size is 3-10 μm; the powder is mixed according to a molar ratio of Fe:Al:B=2:x:2, wherein x=1.1-1.

5.

4. The preparation method of Fe2AlB2@Al2O3 high-temperature wave absorber according to claim 2, characterized in that, In step two, the powder is loaded into a sealed ball mill tank, vacuum is drawn, and then inert gas is introduced into the ball mill tank to protect the powder from being oxidized during the ball milling process; the mass ratio of the powder to the agate grinding balls is 1:5-1:20, the ball milling time is 1-5 h, and the ball milling speed is 300-500 r / min.

5. The preparation method of Fe2AlB2@Al2O3 high-temperature wave absorber according to claim 2, characterized in that, In step three, the process parameters of the high-energy laser beam rapid sintering are as follows: the spot diameter is 50-100 μm, the laser power is 100-200 W, and the scanning speed is 300-500 mm / s; during the high-energy laser beam rapid sintering process, the cavity is first vacuumed and then filled with inert gas for protection.

6. The preparation method of Fe2AlB2@Al2O3 high-temperature wave absorber according to claim 2, characterized in that, In step four, the powder is loaded into a sealed ball mill tank, vacuum is drawn, and then a mixture of oxygen and argon gas is introduced into the ball mill tank, wherein the volume fraction of oxygen is 1-5%; the mass ratio of the powder to the stainless steel grinding balls is 1:20-1:50, the speed is 800-900 r / min, the discharge voltage is 15-25 kV, the discharge current is 1-2 A, the discharge frequency is 10-30 kHz, the ball milling time is 1-5 h, and the temperature in the ball mill tank during the ball milling process is 500-700 ℃.

7. The preparation method of Fe2AlB2@Al2O3 high-temperature wave absorber according to claim 2, characterized in that, In step four, the content of the in-situ generated Al2O3 shell layer is 5-10 wt%, and the content of Fe2AlB2 is 90-95 wt%.

8. Application of the Fe2AlB2@Al2O3 high-temperature wave absorber of claim 1 to stealth of high-temperature components of aerospace equipment.

Images