A microwave-absorbing high-entropy alloy composite coating and its preparation method

Abstract

The invention relates to the field of composite coatings and discloses a microwave-absorbing high-entropy alloy composite coating and a preparation method thereof. The microwave-absorbing high-entropy alloy composite coating is formed by depositing a mixed powder on a substrate surface by laser cladding to form a pre-coating layer, and then performing ion nitriding treatment on the pre-coating layer. The mixed powder comprises: high-entropy alloy powder, functional additives, core-shell friction-reducing powder, and a binder. The functional additives are prepared by using halloysite, biomass chitosan, and ferric chloride hexahydrate as raw materials, adopting a hydrothermal method to obtain an iron-modified halloysite / carbon material, and then undergoing a carbon thermal reduction reaction. The core-shell friction-reducing powder is prepared by uniformly depositing an outer layer of aluminum oxide on the surface of nano hexagonal boron nitride by a non-uniform nucleation method. The ion nitriding treatment process parameters are: nitriding at a temperature of 540-560°C for 58-62h, and using flow rate thermal decomposition of ammonia as a nitrogen source. The composite coating prepared by the invention has high hardness and good wear resistance, corrosion resistance, and microwave-absorbing properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite coatings, and in particular relates to a microwave-absorbing high-entropy alloy composite coating and a preparation method thereof. Background Art

[0002] Coating is one of the most effective and economical methods for protecting metal parts. Coatings are typically prepared using processes such as atmospheric plasma spraying, vacuum plasma spraying, electron beam physical vapor deposition, and laser cladding. Laser cladding is a low-cost, reliable, and convenient coating preparation method. High-entropy alloys (HEAs), also known as multi-component alloys, contain five or more principal elements and are widely studied for their superior overall properties. While HEAs are relatively expensive to prepare, HEA coatings can maximize their exceptional properties while remaining economical and practical. Their high strength, excellent wear and corrosion resistance, and high-temperature stability have led to their application in cutting-edge fields such as aerospace, medical treatment, and electronics, with promising future applications.

[0003] AlCoCrFeNi, one of the most widely studied high-entropy alloy systems, possesses a single-phase BCC structure, exhibiting high strength and hardness, and excellent high-temperature mechanical properties. AlCoCrFeNi high-entropy alloys typically consist of an Fe-Cr-rich solid solution phase (disordered BCC), an Al-Ni-rich solid solution phase (ordered BCC), and an Fe-Cr-Ni-rich structure (disordered FCC), demonstrating high strength, high hardness, and excellent softening resistance. However, in extreme environments subject to high loads and wear, the mechanical properties, wear resistance, and corrosion resistance of AlCoCrFeNi high-entropy alloy coatings still need to be further enhanced. Furthermore, with the rapid development of wireless communication technology in both military and civilian applications, absorbing materials play an important role in fields such as electromagnetic interference protection. The preparation of composite coatings with excellent absorbing properties holds great promise for future applications. Summary of the Invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a microwave-absorbing high-entropy alloy composite coating and a preparation method thereof. The prepared composite coating has high hardness, good wear resistance, corrosion resistance and microwave absorption performance.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A microwave-absorbing high-entropy alloy composite coating is prepared by depositing a mixed powder on a substrate surface by laser cladding to form a pre-coating layer, which is then polished, cleaned, and then ion nitrided. The mixed powder comprises the following components by weight: 100 parts of high-entropy alloy powder, 2 to 5 parts of a functional additive, 0.1 to 1 part of a core-shell friction-reducing powder, and 1 to 3 parts of a binder.

[0007] The functional additive is prepared by hydrothermally preparing an iron-modified halloysite / carbon material using halloysite, biomass chitosan, and ferric chloride hexahydrate as raw materials, and then undergoing a carbothermal reduction reaction; the core-shell anti-friction powder is prepared by uniformly depositing an outer layer of spherical aluminum oxide on the surface of nano hexagonal boron nitride using a non-uniform nucleation method;

[0008] The process parameters of the ion nitriding treatment are as follows: nitriding treatment is carried out using a pulse plasma multi-element co-nitriding furnace, nitriding for 58 to 62 hours at a temperature of 540 to 560°C, and a flow rate of 0.3 to 0.5 m 3 / h of thermal decomposition of ammonia as a nitrogen source.

[0009] Preferably, the high entropy alloy powder is AlCoCrFeNi high entropy alloy powder.

[0010] Preferably, the binder is polyvinyl alcohol.

[0011] Preferably, the preparation method of the functional additive comprises the following steps:

[0012] A. Halloysite, chitosan and deionized water are placed in a reactor, stirred and dispersed evenly, and then transferred to a hydrothermal reactor and reacted at 175-185°C for 20-24 hours. After the reaction is completed, the mixture is washed and dried to prepare a halloysite / carbon material;

[0013] B. Take the halloysite / carbon material and the aqueous solution of ferric chloride hexahydrate and stir and mix them evenly, adjust the pH value of the solution to 7.5-8 with ammonia water, continue stirring for 1-1.5 hours, and dry in an oven after stirring to prepare an iron-modified halloysite / carbon material;

[0014] C. The iron-modified halloysite / carbon material is placed in a crucible and sintered in a hot press furnace. An argon atmosphere is introduced, and the temperature of the hot press furnace is raised from room temperature to 250-300°C at a heating rate of 4-5°C / min, and then raised to 1350-1400°C at a heating rate of 8.5-10°C / min. After heating for 2-3 hours, the temperature is gradually lowered to room temperature, and the crucible is removed to prepare a functional additive.

[0015] Preferably, the oxides in the halloysite include the following components by weight percentage: 49.55% silicon dioxide, 43.72% aluminum oxide, 4.48% iron oxide, 0.40% titanium dioxide, 0.34% magnesium oxide, and the rest 1.51%.

[0016] Preferably, the method for preparing the core-shell friction reducing powder comprises the following steps:

[0017] (1) Ultrasonic dispersion of nano hexagonal boron nitride powder in hydrofluoric acid, followed by centrifugation and washing to obtain acidified nano hexagonal boron nitride powder, dissolving polyvinyl pyrrolidone in anhydrous ethanol, adding the acidified nano hexagonal boron nitride powder, and ultrasonically dispersing the powder uniformly to prepare pretreated nano hexagonal boron nitride powder;

[0018] (2) Polyvinyl pyrrolidone was dissolved in a mixed solution of anhydrous ethanol and deionized water, and aluminum nitrate nine hydrate was added and stirred thoroughly. Then, it was added to the pretreated nano hexagonal boron nitride powder, and acetic acid-sodium acetate buffer solution was added. Ultrasonic dispersion was continued, and then the system was placed at 70-80 ° C and ammonia solution was added dropwise to adjust the pH value of the system to 7.5-8. After the addition was completed, stirring was continued for 0.5-1h. After the reaction was completed, the system was allowed to stand for aging, centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain a core-shell precursor powder.

[0019] (3) The core-shell precursor powder was calcined at a heating rate of 4-5°C / min and kept at 1000-1100°C for 1-1.5 h to prepare a core-shell antifriction powder.

[0020] Preferably, the thickness of the nitride layer formed by the ion nitriding process is 10-30 μm.

[0021] A method for preparing a microwave-absorbing high-entropy alloy composite coating comprises the following steps:

[0022] S1. Weigh the raw materials by weight, fully mix the high entropy alloy powder, functional additives, core-shell friction reducing powder, and binder to obtain a mixed powder, pre-place the mixed powder on the surface of the substrate, and perform a laser cladding process to form a pre-coating layer;

[0023] S2. The pre-coating layer is polished and cleaned with anhydrous ethanol, and the surface of the pre-coating layer is ion nitrided in a pulsed plasma multi-element co-diffusion furnace to prepare a microwave-absorbing high-entropy alloy composite coating.

[0024] Preferably, the preset thickness of the mixed powder is 1.2-1.45 mm.

[0025] Preferably, the laser cladding process parameters are: laser power 900 W, scanning rate 4 mm / s, overlap rate 30%, spot diameter 2 mm, and argon is used as the protective gas during the cladding process.

[0026] Beneficial effects of the present invention:

[0027] The present invention uses clay mineral halloysite, biomass chitosan and ferric chloride hexahydrate as raw materials, wherein halloysite is used as template, chitosan is used as carbon source, ferric chloride hexahydrate is used as iron source, and iron-modified halloysite / carbon material is prepared by hydrothermal method, and then mullite / silicon carbide / Fe is synthesized in situ by carbothermal reduction reaction. x Siy / Carbon ceramic composite material is used as a functional additive. As the temperature rises, the loaded carbon further pyrolyzes and graphitizes on the halloysite surface. Due to its excellent thermal conductivity, the introduction of carbon promotes the formation of silicon-rich liquid phase and mullite process, thereby improving the mechanical properties of the material. In addition, the introduced carbon reacts with excess silicon dioxide in the halloysite to form silicon carbide by carbon thermal reduction reaction. Carbon and silicon carbide together improve the reflection loss of the material. Ferric chloride hexahydrate reacts with carbon by carbon thermal reduction reaction and then reacts with silicon dioxide to form Fe x Si y , improve the material's wave absorbing properties.

[0028] The present invention uses a non-uniform nucleation method to prepare a core-shell anti-friction powder, in which the outer layer of aluminum oxide is uniformly deposited in the form of small spheres on the surface of nano hexagonal boron nitride. The dense aluminum oxide tightly wraps the nano hexagonal boron nitride particles, improving the material's lubricity and promoting wear resistance. The present invention uses laser cladding combined with ion nitriding technology to compositely treat the substrate surface to generate a pre-coating layer and a nitride layer. The longer nitriding time facilitates the diffusion of active nitrogen atoms into the pre-coating layer. The aluminum and chromium elements in the pre-coating layer react with nitrogen to form high-hardness aluminum nitride and chromium nitride, significantly improving the microhardness of the composite coating. In addition, the nitride layer can effectively prevent the diffusion and erosion of corrosive ions into the substrate, significantly improving the environmental performance of the substrate. DETAILED DESCRIPTION

[0029] 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 embodiments described 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0030] The AlCoCrFeNi high entropy alloy powder in the embodiments and comparative examples of the present invention was prepared by vacuum atomization and produced by Beijing Jiaming Platinum Nonferrous Metals Co., Ltd. with a particle size of 10-50 μm and a purity of ≥99.9%.

[0031] Example 1 A method for preparing a functional additive comprises the following steps:

[0032] A. Halloysite, chitosan, and deionized water in a mass ratio of 9:1:70 were placed in a reactor, stirred and dispersed evenly, and then transferred to a hydrothermal reactor and reacted at 180°C for 24 hours. After the reaction was completed, the materials were washed and dried to obtain a halloysite / carbon material.

[0033] B. Take 10 g of halloysite / carbon material and 100 mL of 8 wt.% ferric chloride hexahydrate aqueous solution and stir and mix them evenly. Use ammonia water to adjust the pH value of the solution to 7.5. Continue stirring for 1 hour. After stirring, place it in an oven and dry it to prepare an iron-modified halloysite / carbon material.

[0034] C. The iron-modified halloysite / carbon material was placed in a crucible and sintered in a hot press furnace. An argon atmosphere was introduced and the temperature of the hot press furnace was raised from room temperature to 300°C at a heating rate of 5°C / min, then to 1400°C at a heating rate of 10°C / min. After heating for 2 hours, the temperature was gradually lowered to room temperature. The crucible was removed to prepare the functional additive.

[0035] Example 2 A method for preparing a core-shell anti-friction powder comprises the following steps:

[0036] (1) 0.5 g of nano hexagonal boron nitride powder was ultrasonically dispersed in 20 mL of hydrofluoric acid, and then centrifuged and washed to obtain acidified nano hexagonal boron nitride powder. 0.7 g of polyvinyl pyrrolidone was dissolved in 100 mL of anhydrous ethanol, and the acidified nano hexagonal boron nitride powder was added and ultrasonically dispersed to obtain pretreated nano hexagonal boron nitride powder.

[0037] (2) 11.4 g of polyvinyl pyrrolidone was dissolved in a mixed solution of 70 mL of anhydrous ethanol and 30 mL of deionized water, 7.6 g of aluminum nitrate nine hydrate was added and stirred thoroughly, and then added to the pretreated nano hexagonal boron nitride powder, 25 mL of acetic acid-sodium acetate buffer solution with a concentration of 0.1 mol / L was added, and ultrasonic dispersion was continued. Subsequently, ammonia solution was added dropwise at 80 ° C to adjust the pH value of the system to 7.5. After the addition was completed, stirring was continued for 0.5 h. After the reaction was completed, the core-shell precursor powder was prepared by standing and aging, centrifugal separation, anhydrous ethanol washing, and vacuum drying;

[0038] (3) The obtained core-shell precursor powder was calcined at a heating rate of 5°C / min and kept at 1100°C for 1 hour to prepare a core-shell anti-friction powder.

[0039] Example 3 A mixed powder comprises the following components in parts by weight: 100 parts of AlCoCrFeNi high entropy alloy powder, 2.4 parts of the functional additive prepared in Example 1, 0.2 parts of the core-shell antifriction powder prepared in Example 2, and 1.5 parts of polyvinyl alcohol as a binder;

[0040] A method for preparing a microwave-absorbing high-entropy alloy composite coating comprises the following steps:

[0041] S1. Weigh all the raw materials by weight, mix the high entropy alloy powder, functional additives, core-shell anti-friction powder and binder thoroughly to obtain mixed powder, and pre-place the mixed powder in a container with a size of 150×60×8mm.3 The surface of the 40cr steel substrate was prepared with a thickness of 1.2mm and laser cladding process was carried out with a laser power of 900W, a scanning rate of 4mm / s, an overlap rate of 30%, and a spot diameter of 2mm. Argon was used as a protective gas during the cladding process to form a pre-coating layer.

[0042] S2. The pre-coating layer was polished and cleaned with anhydrous ethanol. The surface of the pre-coating layer was ion nitrided in a pulsed plasma multi-element co-nitriding furnace at a temperature of 550 ° C for 62 hours at a flow rate of 0.4m 3 / h of thermally decomposed ammonia as a nitrogen source to form a nitride layer with a thickness of 20 μm, and thus a microwave-absorbing high-entropy alloy composite coating was prepared.

[0043] Example 4 A mixed powder comprises the following components in parts by weight: 100 parts of AlCoCrFeNi high entropy alloy powder, 3.5 parts of the functional additive prepared in Example 1, 0.5 parts of the core-shell antifriction powder prepared in Example 2, and 2.5 parts of polyvinyl alcohol as a binder;

[0044] The preparation method of a microwave-absorbing high-entropy alloy composite coating is the same as that of Example 3.

[0045] Example 5 A mixed powder comprises the following components in parts by weight: 100 parts of AlCoCrFeNi high entropy alloy powder, 4 parts of the functional additive prepared in Example 1, 0.8 parts of the core-shell antifriction powder prepared in Example 2, and 2.7 parts of polyvinyl alcohol as a binder;

[0046] The preparation method of a microwave-absorbing high-entropy alloy composite coating is the same as that of Example 3.

[0047] Comparative Example 1 A mixed powder comprises the following components in parts by weight: 100 parts of AlCoCrFeNi high entropy alloy powder, 0.8 parts of the core-shell anti-friction powder prepared in Example 2, and 2.7 parts of polyvinyl alcohol as a binder;

[0048] The preparation method of a microwave-absorbing high-entropy alloy composite coating is the same as that of Example 3.

[0049] Comparative Example 2 A mixed powder comprises the following components in parts by weight: 100 parts of AlCoCrFeNi high entropy alloy powder, 4 parts of the functional additive prepared in Example 1, 0.8 parts of nano hexagonal boron nitride powder, and 2.7 parts of polyvinyl alcohol as a binder;

[0050] The preparation method of a microwave-absorbing high-entropy alloy composite coating is the same as that of Example 3.

[0051] Comparative Example 3 A mixed powder comprises the following components in parts by weight: 100 parts of AlCoCrFeNi high entropy alloy powder, 4 parts of the functional additive prepared in Example 1, 0.8 parts of the core-shell antifriction powder prepared in Example 2, and 2.7 parts of polyvinyl alcohol as a binder;

[0052] A method for preparing a microwave-absorbing high-entropy alloy composite coating comprises the following steps:

[0053] Weigh the raw materials according to weight, fully mix the high entropy alloy powder, functional additives, core-shell antifriction powder and binder to obtain mixed powder, and pre-place the mixed powder in a container with a size of 150×60×8mm. 3 The surface of the 40cr steel substrate is preset to a thickness of 1.2mm and is subjected to laser cladding process with a laser power of 900W, a scanning rate of 4mm / s, an overlap rate of 30%, and a spot diameter of 2mm. Argon is used as a protective gas during the cladding process to form a wave-absorbing high-entropy alloy composite coating.

[0054] Performance testing

[0055] The performance of the microwave-absorbing high-entropy alloy composite coatings prepared in Examples 3-5 and Comparative Examples 1-3 was tested: the microhardness of the coating was measured using a microhardness tester; a friction and wear test was carried out using a reciprocating friction and wear tester, with Si3N4 balls as the grinding pair, a friction load of 20N, a friction frequency of 4Hz, and a test time of 30min. After the test, the wear rate and the wear scar depth were detected using a three-dimensional profilometer; the electrochemical corrosion experiment was tested in accordance with GB / T 40299-2021; and the microwave absorbing performance was tested using a vector network analyzer in a test frequency band of 2~18GHz. The data results are shown in Table 1.

[0056] Table 1 Sample performance test results

[0057]

[0058] As can be seen from the data results in Table 1, the composite coatings prepared in Examples 3-5 of the present invention have high hardness and excellent wave absorption, wear resistance, and corrosion resistance. In Comparative Example 1, no functional additives were added, and the measured microhardness, wear resistance, and wave absorption performance were lower than those of Examples 3-5, indicating that the addition of functional additives can improve the mechanical properties and wave absorption performance of the material. In Comparative Example 2, the core-shell anti-friction powder was replaced with nano hexagonal boron nitride powder in equal amounts, and the measured wear scar depth and volume wear rate were significantly increased compared to Examples 3-5, indicating that the addition of the core-shell anti-friction powder can further improve the wear resistance of the material. In Comparative Example 3, no ion nitriding treatment was performed, and the measured microhardness and corrosion resistance were significantly lower than those of Examples 3-5.

[0059] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0060] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A microwave-absorbing high-entropy alloy composite coating, characterized in that: A pre-coating layer is formed by depositing a mixed powder on the substrate surface by laser cladding, and then the pre-coating layer is polished, cleaned, and then ion nitrided. The mixed powder comprises the following components by weight: 100 parts of high entropy alloy powder, 2 to 5 parts of functional additives, 0.1 to 1 part of core-shell anti-friction powder, and 1 to 3 parts of binder. The functional additive is prepared by hydrothermally preparing an iron-modified halloysite / carbon material using halloysite, biomass chitosan, and ferric chloride hexahydrate as raw materials, and then undergoing a carbothermal reduction reaction; the core-shell anti-friction powder is prepared by uniformly depositing an outer layer of spherical aluminum oxide on the surface of nano hexagonal boron nitride using a non-uniform nucleation method; The process parameters of the ion nitriding treatment are as follows: nitriding treatment is carried out using a pulse plasma multi-element co-nitriding furnace, nitriding for 58 to 62 hours at a temperature of 540 to 560°C, and a flow rate of 0.3 to 0.5 m 3 / h of thermal decomposition of ammonia as nitrogen source; The high entropy alloy powder is AlCoCrFeNi high entropy alloy powder; the binder is polyvinyl alcohol.

2. The microwave-absorbing high-entropy alloy composite coating according to claim 1, characterized in that: The preparation method of the functional additive comprises the following steps: A. Halloysite, chitosan and deionized water are placed in a reactor, stirred and dispersed evenly, and then transferred to a hydrothermal reactor and reacted at 175-185°C for 20-24 hours. After the reaction is completed, the mixture is washed and dried to prepare a halloysite / carbon material; B. Take the halloysite / carbon material and the aqueous solution of ferric chloride hexahydrate and stir and mix them evenly, adjust the pH value of the solution to 7.5-8 with ammonia water, continue stirring for 1-1.5 hours, and dry in an oven after stirring to prepare an iron-modified halloysite / carbon material; C. The iron-modified halloysite / carbon material is placed in a crucible and sintered in a hot press furnace. An argon atmosphere is introduced, and the temperature of the hot press furnace is raised from room temperature to 250-300°C at a heating rate of 4-5°C / min, and then raised to 1350-1400°C at a heating rate of 8.5-10°C / min. After heating for 2-3 hours, the temperature is gradually lowered to room temperature, and the crucible is removed to prepare a functional additive.

3. The microwave-absorbing high-entropy alloy composite coating according to claim 2, characterized in that: The oxides in the halloysite include the following components by weight percentage: 49.55% silicon dioxide, 43.72% aluminum oxide, 4.48% iron oxide, 0.40% titanium dioxide, 0.34% magnesium oxide, and the rest 1.51%.

4. The microwave-absorbing high-entropy alloy composite coating according to claim 1, characterized in that: The preparation method of the core-shell friction reducing powder comprises the following steps: (1) Ultrasonic dispersion of nano hexagonal boron nitride powder in hydrofluoric acid, followed by centrifugation and washing to obtain acidified nano hexagonal boron nitride powder, dissolving polyvinyl pyrrolidone in anhydrous ethanol, adding the acidified nano hexagonal boron nitride powder, and ultrasonically dispersing the powder uniformly to prepare pretreated nano hexagonal boron nitride powder; (2) Polyvinyl pyrrolidone was dissolved in a mixed solution of anhydrous ethanol and deionized water, and aluminum nitrate nine hydrate was added and stirred thoroughly. Then, it was added to the pretreated nano hexagonal boron nitride powder, and acetic acid-sodium acetate buffer solution was added. Ultrasonic dispersion was continued, and then the system was placed at 70-80 ° C and ammonia solution was added dropwise to adjust the pH value of the system to 7.5-8. After the addition was completed, stirring was continued for 0.5-1h. After the reaction was completed, the system was allowed to stand for aging, centrifuged, washed with anhydrous ethanol, and vacuum dried to obtain a core-shell precursor powder. (3) The core-shell precursor powder was calcined at a heating rate of 4-5°C / min and kept at 1000-1100°C for 1-1.5 h to prepare a core-shell antifriction powder.

5. The microwave-absorbing high-entropy alloy composite coating according to claim 1, characterized in that: The thickness of the nitride layer formed by the ion nitriding process is 10-30 μm.

6. A method for preparing a microwave-absorbing high-entropy alloy composite coating according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Weigh the raw materials by weight, fully mix the high entropy alloy powder, functional additives, core-shell friction reducing powder, and binder to obtain a mixed powder, pre-place the mixed powder on the surface of the substrate, and perform a laser cladding process to form a pre-coating layer; S2. The pre-coating layer is polished and cleaned with anhydrous ethanol, and the surface of the pre-coating layer is ion nitrided in a pulsed plasma multi-element co-diffusion furnace to prepare a microwave-absorbing high-entropy alloy composite coating.

7. The method for preparing the microwave-absorbing high-entropy alloy composite coating according to claim 6, wherein: The preset thickness of the mixed powder is 1.2-1.45 mm.

8. The method for preparing the microwave-absorbing high-entropy alloy composite coating according to claim 6, wherein: The laser cladding process parameters are: laser power 900 W, scanning rate 4 mm / s, overlap rate 30%, spot diameter 2 mm, and argon is used as the protective gas during the cladding process.

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