A boron carbide-coated carbon fiber composite material, its preparation method and application

Abstract

This invention discloses a boron carbide-coated carbon fiber composite material, its preparation method, and its application, belonging to the field of composite material preparation technology. The preparation method of this invention is as follows: (1) Disperse chopped C fibers, place them in anhydrous ethanol, and dry; (2) Disperse boron powder in anhydrous ethanol, then add the chopped C fibers obtained in step (1) for impregnation and mixing, and dry; (3) Lay the boron powder, chopped C fibers, and boron powder obtained in step (2) sequentially in a furnace, calcine at high temperature under inert gas, cool to room temperature, wash in anhydrous ethanol, and dry. The prepared C@B4C composite material has high uniformity and good stability, and the B4C coating layer thickness is 0~0.8μm. Pure C@B4C composite material can be obtained using only anhydrous ethanol, which can meet the requirements of toughening B4C-based ceramic materials and reinforcing metal materials.

Description

Technical Field

[0001] This invention relates to the field of composite material preparation technology, and in particular to a boron carbide-coated carbon fiber composite material, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Carbon fiber reinforced boron carbide ceramic matrix composites (C / B4C) have shown broad application prospects in the field of high-end structural components due to their high specific strength, high hardness, and excellent wear and corrosion resistance. However, B4C ceramics are inherently brittle, and there are problems such as poor interfacial compatibility and low bonding strength between them and carbon fibers, which makes it difficult to fully realize the toughening effect of the fibers.

[0004] Existing technologies still have significant drawbacks: First, some methods for coating C fibers with B4C use boron powder and boric acid as boron sources to prepare the coating through high-temperature solid-state reactions. Although this can form a coating layer, it requires complex pretreatment of the C fibers, such as muffle furnace activation and acetone soaking for degumming. Subsequent cleaning requires boiling with concentrated nitric acid, which causes serious environmental pollution and increases process costs and operational complexity. Second... In the technology for directly preparing C fiber reinforced B4C composites, a liquid phenolic resin-anhydrous ethanol system is used to disperse short-cut C fibers and B4C powder. Although this avoids the physical damage to the fibers caused by ball milling, it fails to fundamentally solve the interfacial bonding problem between the C fibers and the B4C matrix. Furthermore, the use of organic substances such as liquid phenolic resin in the preparation process may generate harmful gases during subsequent high-temperature treatment, causing environmental pollution. At the same time, the high-temperature pyrolysis of phenolic resin can easily leave carbon impurities, affecting the purity and mechanical properties of the composite material.

[0005] Therefore, how to prepare B4C-coated C-fiber composites using a simple and stable process with the lowest possible cost and least environmental pollution, while simultaneously improving the performance stability and repeatability of the composite material preparation process, is a pressing technical challenge in the fields of B4C-based ceramic toughening and metal reinforcement. Summary of the Invention

[0006] In view of this, the present invention provides a boron carbide-coated carbon fiber composite material, its preparation method and application. The boron carbide-coated carbon fiber composite material provided by the present invention has high uniformity and good stability, and can meet the requirements of toughening B4C-based ceramic materials and reinforcing metal materials.

[0007] In a first aspect, the present invention provides a method for preparing boron carbide-coated carbon fiber composite material, comprising the following steps: (1) Disperse the short-cut C fibers, place them in anhydrous ethanol, and dry them; (2) Disperse boron powder in anhydrous ethanol, then add the short-cut C fibers obtained in step (1) for impregnation and mixing, and then dry; (3) The boron powder, chopped C fiber and boron powder obtained in step (2) are laid in sequence in the furnace body, calcined at high temperature under inert gas, cooled to room temperature and then washed in anhydrous ethanol and dried.

[0008] Preferably, in step (2), the mass ratio of boron powder to anhydrous ethanol is 1:10~20, and the mass ratio of chopped C fibers to boron powder is 0.5-1:1.5-6.

[0009] Preferably, in step (3), the mass ratio of the first layer of boron powder to the third layer of boron powder is 1:1~2.

[0010] Preferably, in step (3), calcination is carried out at 1200~1400℃ for 80~140min, the heating rate is 5~10℃ / min, and the inert gas rate is 3~6mL / min; The preferred calcination temperature is 1300℃, and the preferred calcination time is 120 min; The inert gas is one or a mixture of two or more of helium, neon, argon, xenon, and krypton.

[0011] Preferably, the diameter of the chopped C fibers is 3~4.5μm, and the particle size D50 of the boron powder is 10~20μm.

[0012] Preferably, in step (1), the drying temperature is 60~90℃ and the drying time is 1~5h; In step (2), the drying temperature is 60~90℃ and the drying time is 6~12h; In step (3), the drying temperature is 60~90℃ and the drying time is 1~3h.

[0013] Preferably, in step (1), the dispersion is performed by ultrasonic dispersion, with an ultrasonic frequency of 30~50kHz and an ultrasonic time of 1~3h; In step (2), the dispersion is carried out by grinding dispersion, the grinding time is 5~10 min, and the impregnation time is 1~3 min; In step (3), the cleaning is performed using ultrasonic cleaning with an ultrasonic frequency of 30~50kHz and an ultrasonic time of 10~40min.

[0014] Secondly, the present invention provides a boron carbide-coated carbon fiber composite material prepared by the above preparation method.

[0015] Thirdly, the present invention provides the application of the above-mentioned boron carbide-coated carbon fiber composite material in the preparation of ceramic or metallic materials.

[0016] Compared with the prior art, the present invention has achieved the following beneficial effects: (1) The preparation method of the present invention is simple to operate, has low equipment cost, good repeatability, and low pollution. The present invention utilizes an ethanol whole-process solvent system to completely replace strong acid treatment, reduce pollution, and simplify the cleaning and impurity removal steps.

[0017] (2) This invention achieves uniform and firm coating of B4C on the surface of C fibers by combining pre-dispersion, impregnation mixing, and calcination. First, the fibers and boron powder are dispersed and mixed in ethanol through gentle ultrasonic dispersion and manual grinding, avoiding damage to the fibers from ball milling. Moreover, dispersing the C fibers into a smaller number of fiber bundles increases the contact area between the C fibers and the subsequently added B powder. Then, impregnation allows the B powder particles to adhere uniformly to the surface of each C fiber and the gaps between fiber bundles with the help of the fluidity of ethanol, forming a preliminary mixture of B powder coating on the surface of the C fibers. At the same time, calcination is carried out by constructing a sandwich structure, providing a uniform and sufficient contact environment for the reaction between carbon fibers and boron powder. This structure allows the C fibers to be fully surrounded by B powder during calcination, ensuring uniform contact between the C fibers and B powder in all directions, which is conducive to the uniform generation of B4C on the surface of the C fibers. It can form a B4C layer with controllable thickness (0~0.8μm) and uniform coating on the fiber surface, effectively improving the interfacial bonding strength between the fiber and the matrix. Moreover, calcination temperature is a key factor affecting the quality of composite materials. The temperature range of 1200~1400℃ has been optimized. At this temperature, B powder and C fiber can fully react to generate B4C. If the temperature is too low, the reaction will be incomplete and a sufficient B4C coating layer cannot be formed. If the temperature is too high, it may lead to excessive growth and abnormal aggregation of B4C particles, affecting the uniformity of the coating layer and the performance of the composite material.

[0018] (3) The C@B4C composite material prepared by this method has a uniform surface coating, high purity, and good stability. It can significantly improve the interfacial bonding between C fiber and B4C, and fully meet the application requirements of toughening B4C-based ceramic materials and reinforcing metal materials. Attached Figure Description

[0019] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0020] Figure 1 This is the XRD pattern of the C@B4C composite material prepared in Example 1 of this invention; Figure 2 These are electron microscope images of the C@B4C composite materials synthesized at different calcination temperatures obtained in this invention, wherein (a) is 1250℃, (b) is 1300℃, and (c) is 1350℃. Figure 3 This is an electron microscope image of the C@B4C composite material prepared in Comparative Example 1 of this invention; Figure 4 This is an electron microscope image of the C@B4C composite material prepared in Comparative Example 2 of this invention; Figure 5 This is an electron microscope image of the C@B4C composite material prepared in Comparative Example 3 of this invention; Figure 6 This is an electron microscope image of the C@B4C composite material prepared in Comparative Example 4 of this invention; Figure 7 This is an electron microscope image of the C@B4C composite material prepared in Comparative Example 5 of this invention. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] The technical solution of the present invention will be further described below with reference to specific embodiments. The present invention does not impose any special restrictions on the source of reagents used in the following embodiments; commercially available products well known to those skilled in the art can be used.

[0023] Example 1 (1) C fiber dispersion: Weigh 1g of short-cut C fiber and sonicate at 50kHz for 1h to disperse the C fiber into single / multiple C fiber bundles, wherein the number of C fibers in each bundle does not exceed 20. Then, place the separated C fiber in an evaporating dish containing anhydrous ethanol, with the volume of anhydrous ethanol accounting for 1 / 3 of the volume of the evaporating dish. Then, transfer the evaporating dish to a forced-air drying oven for complete drying at 70℃ for 3h.

[0024] (2) Dispersion of amorphous boron powder: Weigh 3g of boron powder and place it in an agate mortar. Add 50ml of anhydrous ethanol and grind manually for 10min to disperse the amorphous boron powder evenly in the anhydrous ethanol.

[0025] (3) Mixing and drying: The dispersion suspension of amorphous boron powder and anhydrous ethanol in step (2) is completely added to the evaporating dish obtained in step (1) so that the dispersed C fiber is completely immersed in the amorphous boron powder suspension for 2 minutes. Then the evaporating dish is transferred to a forced-air drying oven for complete drying at a temperature of 70°C for 3 hours.

[0026] (4) High-temperature calcination: The mixture of C fiber and amorphous boron powder obtained in step (3) is collected at room temperature. Then, 1 / 2 of the boron powder in the evaporating dish is evenly spread to the bottom of the crucible. Next, the C fiber is evenly placed on top of the boron powder so that the C fiber and the boron powder are in full contact. Then, the remaining 1 / 2 of the boron powder in the evaporating dish is evenly covered on top of the C fiber to form a "sandwich" structure. Finally, the crucible is covered and placed in a tube furnace and calcined at 1300℃ for 120min to synthesize C@B4C composite material. The heating rate of the tube furnace is 8℃ / min, and the high-purity Ar gas rate is 50mL / min.

[0027] (5) Cleaning and removing impurities: After natural cooling, the C@B4C composite material after calcination in step (4) is taken out of the crucible and placed in a 500ml beaker containing 100ml of anhydrous ethanol. The boron powder adhering to the surface of the C@B4C composite material is removed by ultrasonication at 50kHz for 10min. Then, the C@B4C composite material is placed in a forced-air drying oven for complete drying at 70℃ for 3h to obtain boron carbide coated carbon fiber composite material.

[0028] Figure 1 This is the XRD pattern of the C@B4C composite material prepared in Example 1 of this invention. Figure 1 The XRD diffraction peaks are highly consistent with the standard cards C-PDF:00-026-1076 and B4C-PDF#00-001-1163. This result fully confirms the successful synthesis of C@B4C composite material, and that B4C and C phases are present with no impurity peaks.

[0029] like Figure 2 As shown in (b), the C fiber has a regular morphology, and the B4C coating has the highest uniformity, with a B4C thickness of 0~0.8μm.

[0030] Example 2 Compared with Example 1, the difference in this embodiment is that the calcination temperature in step (4) of this embodiment is 1250℃.

[0031] The remaining steps and process conditions are the same as in Example 1.

[0032] like Figure 2 As shown in (a), the C fiber has a regular morphology and the B4C coating is highly uniform.

[0033] Example 3 The difference between this embodiment and embodiment 1 is that the calcination temperature in step (4) of this embodiment is 1350℃.

[0034] The remaining steps and process conditions are the same as in Example 1.

[0035] like Figure 2 As shown in (c), the C fiber has a regular morphology, a high degree of uniformity of B4C coating, and contains some B4C particles aggregated.

[0036] Comparative Example 1 The difference between this comparative example and Example 1 is that in step (4) of this comparative example, the mixture of C fiber and amorphous boron powder obtained in step (3) is placed directly in the crucible.

[0037] The remaining steps and process conditions are the same as in Example 1.

[0038] like Figure 3 As shown, boron carbide particles are located on the surface of carbon fibers but do not form an obvious coating structure.

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (4) of this comparative example, the boron powder in the evaporating dish in step (3) is evenly spread to the bottom of the crucible, and then the C fiber is evenly placed on top of the boron powder.

[0040] The remaining steps and process conditions are the same as in Example 1.

[0041] like Figure 4 As shown, a small amount of carbon fiber surface is coated, but the vast majority is not coated with boron carbide.

[0042] Comparative Example 3 The difference between this comparative example and Example 1 is that no impregnation is performed in step (3) of this comparative example, and the mixture of C fiber and amorphous boron powder obtained in step (3) is placed directly in the crucible in step (4).

[0043] The remaining steps and process conditions are the same as in Example 1.

[0044] like Figure 5 As shown, no obvious boron carbide-coated carbon fiber structure was observed.

[0045] Comparative Example 4 The difference between this comparative example and Example 1 is that the calcination temperature in step (4) of this example is 1100℃.

[0046] The remaining steps and process conditions are the same as in Example 1.

[0047] like Figure 6 As shown, the B4C coating is uneven.

[0048] Comparative Example 5 The difference between this comparative example and Example 1 is that the calcination temperature in step (4) of this example is 1500℃.

[0049] The remaining steps and process conditions are the same as in Example 1.

[0050] like Figure 7 As shown, a large number of B4C particles are aggregated.

[0051] Performance testing When 1-3 wt% of the boron carbide-coated carbon fibers prepared in Examples 1-3 and Comparative Examples 1-5 were added respectively, the bending strength, fracture toughness and Vickers hardness of the boron carbide-coated carbon fiber-boron carbide composite ceramic materials prepared by spark plasma sintering at 1750℃ / 10min were tested as follows.

[0052] The flexural strength of boron carbide-coated carbon fiber-boron carbide composites was tested according to GB / T6569-2006, the fracture toughness according to GB / T44537-2024, and the Vickers hardness according to GB / T16534-2009. The optimal test results for each embodiment are shown in the table below.

[0053] Table 1. Testing of flexural strength, fracture toughness and Vickers hardness

[0054] As shown in Table 1, the boron carbide-coated carbon fiber-boron carbide composite material prepared in Example 2 exhibits the best overall performance in terms of flexural strength, fracture toughness, and Vickers hardness. Specifically, the flexural strength is 305±20 MPa, and the fracture toughness is 3.4±0.1 MPa. m 1 / 2 The Vickers hardness was 33±2 GPa, significantly better than all comparative examples. Although the performance of Examples 1 and 3 was slightly lower than that of Example 2, it still maintained a high level, with flexural strength exceeding 280 MPa and fracture toughness not less than 2.7 MPa. m 1 / 2 The Vickers hardness is above 28 GPa, which demonstrates the stability and reliability of the preparation process of this invention.

[0055] A comparison of the results from Examples 1-3 and Comparative Examples 1-2 shows that the mechanical properties of B4C-based ceramics significantly decrease when the sandwich-layout structure is removed. Comparative Example 1 shows a lower flexural strength (265±10 MPa) and fracture toughness (2.4±0.2 MPa). m 1 / 2Compared to Example 1, the flexural strength (250±10MPa) and Vickers hardness (22±3GPa) of Comparative Example 2 decreased by approximately 7.6% and 20%, respectively; compared to Example 1, the flexural strength (250±10MPa) and Vickers hardness (22±3GPa) of Comparative Example 2 decreased by approximately 12.9% and 21.4%, respectively. This difference confirms that the sandwich structure of bottom boron powder-C fiber-top boron powder is a key process. This structure allows the C fiber to be surrounded by boron powder in all directions during calcination, ensuring uniform contact between the two in all directions and providing the necessary environment for uniform B4C coating; without this structure, the fiber and boron powder do not have sufficient contact, and a complete coating layer cannot be formed, resulting in weak interfacial bonding and a significant decline in the mechanical properties of the ceramic material.

[0056] The difference between Comparative Example 3 and Example 1 confirms that the impregnation step affects the properties of the composite material. After omitting the impregnation step in Comparative Example 3, the flexural strength (252±10 MPa) and fracture toughness (2.4±0.2 MPa) of the B4C-based ceramic were significantly improved. m 1 / 2 Compared with Example 1, the content was reduced by approximately 12.2% and 20%, respectively, and no obvious encapsulation structure was formed (e.g., Figure 5 (As shown). This is because the impregnation step, with the help of the fluidity of ethanol, allows the boron powder particles to adhere evenly to the surface of each C fiber and the gaps between fiber bundles, forming a preliminary structure of "fiber-wrapped boron powder". Without this step, the boron powder and fiber are not evenly dispersed, and an effective coating cannot be formed during calcination, ultimately resulting in a significant reduction in the toughening effect of the ceramic material.

[0057] A comparison of the results of Comparative Examples 4-5 with those of Examples 1-3 shows that when the calcination temperature exceeds the optimized range of 1200~1400℃, the properties of the composite material exhibit a precipitous decline: the flexural strength (255±10MPa) and fracture toughness (2.3±0.1MPa) of Comparative Example 4 are significantly reduced. The B4C coating thickness (m¹ / ²) was the lowest among all test groups because the low temperature resulted in incomplete reaction between the boron powder and C fiber, preventing the formation of a sufficiently thick B4C coating layer. Comparative Example 5, while having a slightly higher flexural strength (269±15MPa) than the other comparative examples, had a lower fracture toughness (2.5±0.1MPa). The m¹ / ² was still lower than that of Examples 1-3, and a large number of B4C particles aggregated. Excessive high temperature destroyed the uniformity of the coating layer and weakened the interfacial bonding ability between the fiber and the matrix.

[0058] The results above show that the boron carbide-coated carbon fiber composite material prepared by this invention exhibits excellent mechanical property enhancement when reinforcing B4C-based ceramics, fully meeting the toughening requirements of B4C-based ceramic materials.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing boron carbide-coated carbon fiber composite material, characterized in that, Includes the following steps: (1) Disperse the short-cut C fibers, place them in anhydrous ethanol, and dry them; (2) Disperse boron powder in anhydrous ethanol, then add the short-cut C fibers obtained in step (1) for impregnation and mixing, and then dry; (3) The boron powder, chopped C fiber and boron powder obtained in step (2) are laid in sequence in the furnace body, calcined at high temperature under inert gas, cooled to room temperature and then washed in anhydrous ethanol and dried.

2. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of boron powder to anhydrous ethanol is 1:10~20, and the mass ratio of chopped C fibers to boron powder is 0.5-1:1.5-6.

3. The preparation method according to claim 1, characterized in that, In step (3), the mass ratio of the first layer of boron powder to the third layer of boron powder is 1:1~2.

4. The preparation method according to claim 1, characterized in that, In step (3), calcination is carried out at 1200~1400℃ for 80~140min, the heating rate is 5~10℃ / min, and the inert gas rate is 3~6mL / min; The inert gas is one or a mixture of two or more of helium, neon, argon, xenon, and krypton.

5. The preparation method according to claim 4, characterized in that, The calcination temperature was 1300℃ and the calcination time was 120 min.

6. The preparation method according to claim 1, characterized in that, The diameter of the chopped C fibers is 3~4.5μm, and the particle size D50 of the boron powder is 10~20μm.

7. The preparation method according to claim 1, characterized in that, In step (1), the drying temperature is 60~90℃ and the drying time is 1~5h; In step (2), the drying temperature is 60~90℃ and the drying time is 6~12h; In step (3), the drying temperature is 60~90℃ and the drying time is 1~3h.

8. The preparation method according to claim 1, characterized in that, In step (1), the dispersion is performed by ultrasonic dispersion, with an ultrasonic frequency of 30~50kHz and an ultrasonic time of 1~3h; In step (2), the dispersion is carried out by grinding dispersion, the grinding time is 5~10 min, and the impregnation time is 1~3 min; In step (3), the cleaning is performed using ultrasonic cleaning with an ultrasonic frequency of 30~50kHz and an ultrasonic time of 10~40min.

9. The boron carbide-coated carbon fiber composite material prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the boron carbide-coated carbon fiber composite material as described in claim 9 in the preparation of ceramic or metallic materials.

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