A MBNS-GC-Ni2Si reinforced dual-phase SiC composite ceramic and its preparation method

Abstract

This invention discloses an MBNS-GC-Ni2Si reinforced biphase SiC composite ceramic and its preparation method. The method includes adding hexagonal boron nitride to phenolic resin and exfoliating it in a three-roll mill to obtain a first mixture containing multilayer boron nitride nanosheets; dissolving the first mixture in furfural solution, then sequentially adding high-purity silicon powder, nickel nitrate hexahydrate, boron carbide, and α-SiC ceramic powder, and stirring to obtain a second mixture; removing moisture and furfural from the second mixture and then vacuum sintering it at 1900-2100℃. The MBNS-GC-Ni2Si reinforced biphase SiC composite ceramic obtained by this invention achieves high mechanical strength and excellent electromagnetic wave absorption performance. It meets the requirements of high-performance structure-function integrated SiC-based composite ceramics, such as aerospace, stealth fighters, and functionalized armor, and has broad market application prospects.

Description

Technical Field

[0001] This invention relates to the field of dual-phase SiC materials, and more particularly to an MBNS-GC-Ni2Si reinforced dual-phase SiC composite ceramic and its preparation method. Background Technology

[0002] SiC is a wide-bandgap semiconductor with tunable dielectric properties, making it suitable as an electromagnetic absorber under harsh conditions and thus one of the most promising high-performance structural-functional integrated materials. However, the low fracture toughness of SiC limits its wide range of applications. High-performance composite materials, prepared by introducing various zero-dimensional particles, one-dimensional fibers or whiskers, and two-dimensional nanosheets as reinforcing / toughening phases through specific processes, hold the promise of overcoming the rigidity and brittleness of ceramics while expanding their functional applications.

[0003] The brittleness and hardness of structural ceramics severely limit their widespread application. Therefore, maximizing the toughness of ceramic materials without compromising their strength is the fundamental research approach and method in the field of structural ceramics. Furthermore, optimizing the structural strength of ceramic materials to achieve functional applications of composite materials in various fields has significant engineering implications. Especially in harsh environments, such as electromagnetic wave absorption, structural materials like metamaterials and porous materials are often favored by researchers in the field of electromagnetic wave absorption (EMA), due to considerations of multiple reflection and trapping space for electromagnetic waves (EMW), lightweight design, and high design freedom. However, their intrinsic structural strength is often severely compromised by targeted design. Therefore, under certain extreme working conditions, such as high load, high temperature and high pressure, and corrosive radiation environments, their performance often becomes unreliable. There is an urgent need to develop lightweight, thin EMW absorbing materials with high mechanical strength, wide absorption bandwidth, and strong absorption, integrating structure and function. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an MBNS-GC-Ni2Si reinforced biphase SiC composite ceramic and its preparation method. The method utilizes three-roll milling (TRM) technology to introduce 2D multilayer boron nitride nanosheets (MBNS) and performs in-situ catalytic conversion to form an 0D hard glassy carbon GC / metallic ductile phase Ni2Si reinforcing phase. This effectively improves the mechanical strength of the SiC matrix, while the properties of the reinforcing phase itself effectively regulate the electromagnetic properties of the ceramic matrix, resulting in excellent microwave absorption performance in the composite ceramic.

[0005] Specifically, the present invention is achieved through the following technical solution:

[0006] A method for preparing MBNS-GC-Ni2Si reinforced dual-phase SiC composite ceramics, comprising:

[0007] Hexagonal boron nitride was added to phenolic resin and then exfoliated in a three-roll mill to obtain a first mixture containing multilayer boron nitride nanosheets.

[0008] The first mixture was dissolved in furfural solution, and high-purity silicon powder, nickel nitrate hexahydrate, boron carbide and α-SiC ceramic powder were added in sequence. After stirring, a second mixture was obtained.

[0009] After removing moisture and furfural from the second mixture, vacuum sintering is performed to obtain the MBNS-GC-Ni2Si reinforced duplex SiC composite ceramic.

[0010] Furthermore, the mass ratio of the hexagonal boron nitride to the phenolic resin is 0.01-0.7:1.

[0011] Specifically, the ratio is preferably 0.01-0.5:1; more preferably 0.05-0.5:1; and even more preferably 0.2:1.

[0012] Furthermore, the mass ratio of the first mixture, high-purity silicon powder, nickel nitrate hexahydrate, boron carbide, and α-SiC ceramic powder is 1-40:1-40:1-10:0.01-2:60-80.

[0013] Specifically, the preferred mass ratio is 20:20:5:1:80.

[0014] Furthermore, the stripping process includes: the rotational speed ratio of the discharge roller, center roller, and feed roller of the three-roll mill is 8-10:3-5:1-2, the rotational speed is set to 200-400 rpm corresponding to the discharge roller, and the stripping is performed 12-28 times. During the cycle, the first gap between the center roller and the feed roller is always greater than the second gap between the discharge roller and the center roller.

[0015] Specifically, the preferred speed ratio is set to 9:3:1, the speed is set to 300 rpm, and the stripping cycle is repeated 24 times.

[0016] Furthermore, the peeling process further includes: first, peeling 3-7 times with the first gap being 22-26 μm and the second gap being 10-14 μm; then peeling 3-7 times with the first gap being 10-14 μm and the second gap being 4-8 μm; next, peeling 3-7 times with the first gap being 4-8 μm and the second gap being 2-3 μm; and finally peeling 3-7 times with the first gap being 2-3 μm and the second gap being 1-1.9 μm, for a total of 12-28 peeling cycles.

[0017] Specifically, the preferred method is to first peel off 6 times with the first gap being 24 μm and the second gap being 12 μm; then peel off 6 times with the first gap being 12 μm and the second gap being 6 μm; then peel off 6 times with the first gap being 6 μm and the second gap being 3 μm; and finally peel off 6 times with the first gap being 3 μm and the second gap being 1 μm, for a total of 24 peelings.

[0018] Furthermore, the process prior to the stripping includes a premixing of hexagonal boron nitride and phenolic resin at 40-60°C.

[0019] Specifically, 50°C is preferred.

[0020] Furthermore, the furfural solution uses water as a solvent, and the mass fraction of furfural is 10%-20%, and the mass-volume relationship between the first mixture and the furfural solution is 1:0.8-1.2 g / mL.

[0021] Specifically, the furfural solution preferably has a mass fraction of 15%, and the mass-volume relationship between the first mixture and the furfural solution is 1:1 g / mL.

[0022] Furthermore, the first mixture is dissolved in a furfural solution by magnetic stirring to ensure complete dissolution.

[0023] Specifically, the preferred magnetic stirring time is 1 hour.

[0024] Further, high-purity silicon powder, nickel nitrate hexahydrate, boron carbide and α-SiC ceramic powder were added and then magnetically stirred.

[0025] Specifically, the preferred stirring time is 6 hours.

[0026] Further, removing moisture and furfural from the second mixture includes: removing moisture by freeze drying and then removing furfural by a forced-air drying oven.

[0027] Specifically, before freeze-drying, the product is pre-frozen in a cold storage room at -5 to -10°C for 8-16 hours, then freeze-dried in a freeze-drying oven for 24-48 hours, and then taken out and dried in a forced-air drying oven at 160-200°C for 2-4 hours.

[0028] Specifically, it is preferable to pre-freeze at -5°C for 12 hours in a cold storage room, then freeze-dry in a freeze dryer for 24 hours, and then take it out and dry it in a forced-air drying oven at 180°C for 3 hours.

[0029] Further, the vacuum sintering includes: increasing the temperature from room temperature to 650-750℃ at a rate of 40-60℃ / min, maintaining a pressure of 10-20MPa; then increasing the temperature to 900-1100℃ at a rate of 40-60℃ / min, maintaining a pressure of 10-20MPa, and holding for 30-60min; then increasing the temperature to 1400-1500℃ at a rate of 40-60℃ / min, maintaining a pressure of 10-20MPa, and holding for 60-180min; then increasing the temperature to 1900-2100℃ at a rate of 40-60℃ / min, maintaining a pressure of 30-60MPa, and holding for 20-40min; finally, slowly depressurizing to 0MPa for 1-3min, and allowing the furnace to cool naturally to room temperature.

[0030] Specifically, the preferred method is as follows: increase the temperature from room temperature to 700°C at a rate of 50°C / min, maintaining a pressure of 15 MPa; then increase the temperature to 1000°C at a rate of 50°C / min, maintaining a pressure of 15 MPa, and hold for 30 min; then increase the temperature to 1450°C at a rate of 50°C / min, maintaining a pressure of 15 MPa, and hold for 120 min; then increase the temperature to 1950°C at a rate of 50°C / min, holding for 30 min, and maintaining a pressure of 50 MPa; finally, slowly depressurize to 0 MPa for 2 min.

[0031] The present invention also provides an MBNS-GC-Ni2Si reinforced dual-phase SiC composite ceramic, which is prepared by the above method.

[0032] Beneficial effects:

[0033] 1. This invention successfully prepared low-cost, high-structure-retention multilayer boron nitride nanosheets (MBNS) in large quantities using a three-roller exfoliation process, and applied them to SiC structural ceramics, verifying their feasibility for structural reinforcement and expanding EMA functionality by combining them with the concept of multi-component reinforcement.

[0034] 2. This invention innovatively designs an effective modification strategy for the composite reinforcing phase dominated by MBNS and the biphase SiC matrix. Specifically, through a precursor transformation step designed in the sintering process, the composite reinforcing phase precursor is transformed at high temperature into a multi-element ceramic reinforcing phase (β-SiC, 0D Ni2Si particles, and 0D glassy carbon GC) uniformly dispersed in the SiC ceramic matrix. β-SiC combines with the main matrix α-SiC to form a biphase α / β-SiC matrix (DS). Subsequently, the DS matrix, GC, and MBNS form chemical bonds, promoting their horizontally ordered arrangement. The remaining 0D reinforcing phase is dispersed in the matrix, ultimately achieving the overall assembly of the composite material. The introduction of the composite reinforcement improves the load-bearing and transfer capabilities of the ceramic matrix and provides various toughening mechanisms (such as crack bifurcation, deflection, and bridging), enabling a comprehensive improvement in the mechanical properties of the composite ceramic. On the other hand, the reinforcement also rationally optimizes the dielectric and magnetic properties of the composite material. With the synergy of multiple loss mechanisms, the test results in the Ku band (12.4-18GHz) show excellent EMA performance, and finally realizes the integration of strength and wave absorption function. This has broad application potential in the fields of multi-functional armor and high-performance spacecraft. Attached Figure Description

[0035] Figure 1 This is a diagram showing the detection results of the stripped MBNS in Embodiment 1 of the present invention;

[0036] Figure 2 The XRD patterns of the final ceramics in Examples 1-6 and Comparative Examples 1-6 of this invention are shown below.

[0037] Figure 3 The images shown are SEM images of the fracture surfaces of the final ceramics in Examples 1-6 and Comparative Examples 1-6 of this invention.

[0038] Figure 4 Images showing the microwave absorption performance of the final ceramics in Examples 1-3 and Comparative Examples 1-3 of the present invention. Detailed Implementation

[0039] The technical solutions provided by the present invention will be described more clearly below with reference to the embodiments and accompanying drawings, but the scope of protection claimed by the present invention is not limited to the following embodiments.

[0040] Example 1:

[0041] Hexagonal boron nitride (h-BN, content ≥ 99.7%) was added to phenolic resin (PF, purity 98%) at a mass ratio of 0.05:1 and premixed under water bath heating at 50°C. The mixture was then poured into a three-roll differential mill for peeling, and after 24 cycles, a first mixture was obtained. The three-roll differential mill includes a discharge roller, a center roller, and a feed roller, with a rotational speed ratio of 9:3:1 and a rotational speed of 300 rpm. The process involved peeling 6 times with a first gap of 24 μm and a second gap of 12 μm; then 6 times with a first gap of 12 μm and a second gap of 6 μm; then 6 times with a first gap of 6 μm and a second gap of 3 μm; and finally 6 times with a first gap of 3 μm and a second gap of 1 μm, for a total of 24 peeling cycles.

[0042] The first mixture was dissolved in a 15% furfural solution and magnetically stirred for 1 hour to ensure complete dissolution. Then, high-purity silicon powder (Si, 1 μm, 99% purity), nickel nitrate hexahydrate (Ni(NO3)2·6H2O, ≥ 99 wt%), boron carbide (B4C, 1 µm, ≥ 99.9%, sintering aid), and α-SiC ceramic powder (1-2 μm, 99% purity) were added sequentially. After vigorous stirring for 6 hours, a second mixture was obtained. The mass-to-volume ratio of the first mixture to the furfural solution was 1:1 g / mL, and the mass ratio of the first mixture, high-purity silicon powder, nickel nitrate hexahydrate, boron carbide, and α-SiC ceramic powder was 20:20:5:1:80.

[0043] The second mixture was pre-frozen at -5°C for 12 hours in a cold storage room, then freeze-dried in a freeze-drying oven for 24 hours. Afterward, it was removed and dried at 180°C for 3 hours in a forced-air drying oven to form composite ceramic powder. The powder was then poured into a graphite mold, and the mold walls were isolated using carbon felt. It was then placed in a rapid sintering hot press furnace for vacuum sintering. The temperature-pressure regime was as follows: the temperature was increased from room temperature to 700°C at 50°C / min, maintaining a pressure of 15 MPa; then increased to 1000°C at 50°C / min, held for 30 minutes, maintaining a pressure of 15 MPa; then increased to 1450°C at 50°C / min, held for 120 minutes, maintaining a pressure of 15 MPa; then increased to 1950°C at 50°C / min, held for 30 minutes, maintaining a pressure of 50 MPa; finally, after the holding period, the pressure was slowly released to 0 MPa for 2 minutes, and the furnace was allowed to cool naturally to room temperature, thus obtaining the dual-phase SiC composite ceramic of Example 1.

[0044] Test results: The bulk density of the dual-phase SiC composite ceramic in Example 1 is 3.17 g·cm³. -3It has a hardness of 28.4 GPa, a flexural strength of 369 MPa, and a fracture toughness of 5.16 MPa·m. 1 / 2 The lowest reflection loss is -45.12dB, and the maximum effective absorption bandwidth is 1.77GHz.

[0045] Example 2:

[0046] The only difference from Example 1 is that the mass ratio of hexagonal boron nitride to phenolic resin is 0.1:1. This ultimately yields the duplex SiC composite ceramic of Example 2.

[0047] Test results: The bulk density of the dual-phase SiC composite ceramic in Example 2 is 3.13 g·cm³. -3 It has a hardness of 27.7 GPa, a flexural strength of 421 MPa, and a fracture toughness of 5.18 MPa·m. 1 / 2 The lowest reflection loss is -18.16dB, and the maximum effective absorption bandwidth is 2.2GHz.

[0048] Example 3:

[0049] The only difference from Example 1 is that the mass ratio of hexagonal boron nitride to phenolic resin is 0.2:1. This ultimately yields the duplex SiC composite ceramic of Example 3.

[0050] Test results: The bulk density of the dual-phase SiC composite ceramic in Example 3 is 3.16 g·cm³. -3 It has a hardness of 28.8 GPa, a flexural strength of 477 MPa, and a fracture toughness of 6.02 MPa·m. 1 / 2 The lowest reflection loss is -52.59dB, and the maximum effective absorption bandwidth is 5.6GHz.

[0051] Example 4:

[0052] The only difference from Example 1 is that the mass ratio of hexagonal boron nitride to phenolic resin is 0.3:1. This ultimately yields the duplex SiC composite ceramic of Example 4.

[0053] Test results: The bulk density of the dual-phase SiC composite ceramic in Example 4 is 3.14 g·cm³. -3 It has a hardness of 27.5 GPa, a flexural strength of 442 MPa, and a fracture toughness of 5.52 MPa·m. 1 / 2 The lowest reflection loss is -44.26dB, and the maximum effective absorption bandwidth is 5.5GHz.

[0054] Example 5:

[0055] The only difference from Example 1 is that the mass ratio of hexagonal boron nitride to phenolic resin is 0.4:1. This ultimately yields the duplex SiC composite ceramic of Example 5.

[0056] Test results: The bulk density of the dual-phase SiC composite ceramic in Example 5 is 3.10 g·cm³. -3 It has a hardness of 27.1 GPa, a flexural strength of 427 MPa, and a fracture toughness of 5.22 MPa·m. 1 / 2 The lowest reflection loss is -39.72dB, and the maximum effective absorption bandwidth is 4.9GHz.

[0057] Example 6:

[0058] The only difference from Example 1 is that the mass ratio of hexagonal boron nitride to phenolic resin is 0.5:1. The resulting duplex SiC composite ceramic of Example 6 was thus obtained.

[0059] Test results: The bulk density of the dual-phase SiC composite ceramic in Example 6 is 3.05 g·cm³. -3 It has a hardness of 26.2 GPa, a flexural strength of 383 MPa, and a fracture toughness of 4.76 MPa·m. 1 / 2 The lowest reflection loss is -32.62dB, and the maximum effective absorption bandwidth is 4.3GHz.

[0060] Comparative Example 1:

[0061] The only difference from Example 1 is that hexagonal boron nitride, phenolic resin, furfural, high-purity silicon powder, and nickel nitrate hexahydrate are not added; instead, boron carbide and α-SiC ceramic powder are mixed and sintered as in Example 1. The single-phase SiC ceramic of Comparative Example 1 is thus obtained.

[0062] Test results: The bulk density of the single-phase SiC ceramic in Comparative Example 1 is 3.20 g·cm³. -3 It has a hardness of 25.2 GPa, a flexural strength of 245 MPa, and a fracture toughness of 4.01 MPa·m. 1 / 2 The lowest reflection loss is -25.32dB, and the maximum effective absorption bandwidth is 1.74GHz.

[0063] Comparative Example 2:

[0064] The only difference from Example 1 is that hexagonal boron nitride and nickel nitrate hexahydrate are not added. The resulting duplex SiC ceramic is Comparative Example 2.

[0065] In Comparative Example 2, the dual-phase SiC composite ceramic does not contain MBNS and does not form a Ni2Si reinforcing phase.

[0066] Test results: The bulk density of the dual-phase SiC composite ceramic in Comparative Example 2 is 3.16 g·cm³. -3 The hardness is 28.1 GPa, the flexural strength is 420 MPa, and the fracture toughness is 4.43 MPa·m.1 / 2 The lowest reflection loss is -2.63dB, and the maximum effective absorption bandwidth is 0GHz.

[0067] Comparative Example 3:

[0068] The only difference from Example 1 is that hexagonal boron nitride is not added. The resulting dual-phase SiC composite ceramic is Comparative Example 3.

[0069] The biphase SiC composite ceramic in Comparative Example 3 does not contain the MBNS reinforcing phase.

[0070] Test results: The bulk density of the dual-phase SiC composite ceramic in Comparative Example 3 is 3.14 g·cm³. -3 It has a hardness of 26.9 GPa, a flexural strength of 409 MPa, and a fracture toughness of 5.43 MPa·m. 1 / 2 The lowest reflection loss is -3.75dB, and the maximum effective absorption bandwidth is 0GHz.

[0071] Comparative Example 4:

[0072] The only difference from Example 3 is that nickel nitrate hexahydrate is not added, and hexagonal boron nitride is not stripped. The resulting dual-phase SiC composite ceramic is Comparative Example 4.

[0073] The dual-phase SiC composite ceramic in Comparative Example 4 contains h-BN raw material, but no exfoliated MBNS, and does not form a Ni2Si reinforcing phase.

[0074] Test results: The bulk density of the dual-phase SiC composite ceramic in Comparative Example 4 is 3.15 g·cm³. -3 It has a hardness of 28.1 GPa, a flexural strength of 426 MPa, and a fracture toughness of 5.07 MPa·m. 1 / 2 The lowest reflection loss is -3.92dB, and the maximum effective absorption bandwidth is 0GHz.

[0075] Comparative Example 5:

[0076] The only difference from Example 3 is that the hexagonal boron nitride is not stripped. The resulting dual-phase SiC composite ceramic is shown in Comparative Example 5.

[0077] Comparative Example 5 shows a dual-phase SiC composite ceramic with h-BN raw material but without stripped MBNS.

[0078] Test results: The bulk density of the dual-phase SiC composite ceramic in Comparative Example 5 is 3.15 g·cm³. -3 It has a hardness of 27.9 GPa, a flexural strength of 353 MPa, and a fracture toughness of 4.27 MPa·m. 1 / 2 The minimum reflection loss is -4.50dB, and the maximum effective absorption bandwidth is 0GHz.

[0079] Comparative Example 6:

[0080] The only difference from Example 3 is that nickel nitrate hexahydrate is not added. The resulting dual-phase SiC composite ceramic is Comparative Example 6.

[0081] The biphase SiC composite ceramic in Comparative Example 6 contains an MBNS reinforcing phase but no Ni2Si reinforcing phase.

[0082] Test results: The bulk density of the dual-phase SiC composite ceramic in Comparative Example 6 is 3.14 g·cm³. -3 It has a hardness of 27.4 GPa, a flexural strength of 356 MPa, and a fracture toughness of 5.63 MPa·m. 1 / 2 The lowest reflection loss is -12.40dB, and the maximum effective absorption bandwidth is 1.8GHz.

[0083] Figure 1 The results of the detection of MBNS after exfoliation in Example 1 are shown. SEM images (a)-(d) show that the micrometer-thick disk-shaped h-BN was thinned to nanometer-thick MBNS. AFM height curves (e)-(f) show that the thickness is concentrated at 5 nm. XRD and FT-IR spectra (g)-(h) indicate the consistency of phase composition and molecular structure of the BN sheets before and after exfoliation. Simultaneously, the exfoliated MBNS exhibits a small leftward shift at the (002) lattice plane, which is related to the increased interlayer spacing d along the c-axis of the crystal space. The TEM images of MBNS (i)-(j) show the magnitude of d (d...). MBNS =0.346 nm > d BN This was further verified by the finding that the wavelength was 0.333 nm.

[0084] Figure 2 The XRD patterns of the final ceramics from Examples 1-6 and Comparative Examples 1-6 are shown. Except for Comparative Example 1, which is composed of single-phase α-SiC, the other samples are composed of α / β-SiC. In addition, characteristic peaks of graphite and hexagonal boron nitride on the (002) lattice plane were observed in the characteristic region of 26°-27° on the right. The graphite peak is likely formed by the amorphous carbon of the phenolic resin remaining during sintering, which undergoes atomic rearrangement after high-temperature treatment to form hard glassy carbon (GC) with a certain degree of crystallinity, and the catalytic effect of Ni helps to improve its crystallinity. The characteristic peak at around 26.7° corresponds to h-BN and MBNS, so MBNS still maintains its phase composition after continuous high-temperature treatment. Subsequently, in the characteristic region of 34.5-35.5°, more obvious peak intensity fluctuations than the initial samples were observed, which corresponds to the SFs characteristics of β-SiC on the (111) lattice plane.

[0085] Figure 3 SEM images of the fracture surfaces of the final ceramics from Examples 1-6 and Comparative Examples 1-6 are shown. (a) I )-(a III (b) is the comparative example 1. I )-(b III (c) is for comparative example 2. I )-(c III The image shown is for Comparative Example 3, and the subsequent images follow the same pattern. It can be seen that the matrix of Comparative Example 1 exhibits a large area of ​​smooth shear fracture morphology, which corresponds to its brittle characteristics. Subsequently, two-phase SiC samples Comparative Examples 2-3 were formed based on Comparative Example 1. It can be seen that Comparative Examples 2-3 exhibit a self-toughening mechanism of the matrix compared to Comparative Example 1, with multiple stepped tear paths displayed at the fracture surface. The appearance of the stepped morphology means that the crack propagation path becomes more tortuous, increasing the energy consumption required for crack propagation, thus hindering rapid crack propagation and improving the toughness of the material. Figure (g) I )-(g III (h) is from Example 1. I )-(h III (i) is from Example 2. I )-(i III Example 3 is shown in (j)-(l), and Examples 4-6 are shown in (j)-(l). The cross-section clearly shows the torn MBNS embedded within the ceramic matrix, and their near-horizontal arrangement effectively intercepts the direction of crack attack. In contrast, Comparative Examples 4-5, reinforced with the same amount of unexfoliated h-BN, have a much smaller distribution of MBNS, a difference of orders of magnitude. Furthermore, large chunks of h-BN easily cause large-scale mismatch with the matrix, leading to weakened bonding and stress concentration, thus affecting the composite material's performance. Meanwhile, Comparative Example 6, which did not add nickel hexahydrate but added MBNS, lacks the 0D Ni2Si particles that play a toughening role as a ductile phase. In contrast, the biphase SiC matrix of Examples 1-6, which added nickel hexahydrate, has a diffusely distributed 0D metallic ductile phase Ni2Si and hard particles GC, which play a toughening role in microcrack derivation and deflection within the matrix, a key reason for its superior matrix mechanical properties.

[0086] Combining the mechanical properties of the final ceramics from Examples 1-6 and Comparative Examples 1-6, it can be seen that, compared to the initial single-phase α-SiC comparative sample, the mechanical properties of the other samples were improved under varying degrees of modification. Compared to Comparative Examples 2-6 without the addition of nickel hexahydrate or without the addition of exfoliated MBNS, the flexural strength and fracture toughness of Examples 1-6 were mostly enhanced, showing a trend of initial increase followed by decrease. This illustrates the key regulatory role of nickel hexahydrate as a catalyst and MBNS as a 2D reinforcement in terms of mechanical properties.

[0087] Figure 4 The microwave absorption performance of the final ceramics of Examples 1-6 and Comparative Examples 1-6 is shown. The lowest reflection loss (RL) of Comparative Example 1 is also shown. min The absorption rate was -30.27 dB, and the EAB coverage range was 1.57 GHz. It can be seen that, even though a two-phase SiC matrix was formed, the comparative examples 2-5 without MBNS stripping resulted in poor microwave absorption performance due to the modification. min >-5dB. Although the introduction of unstripped hexagonal boron nitride improved the RL of Comparative Examples 4-5 min The value decreased slightly compared to Comparative Examples 2-3; however, the large particle size inevitably resulted in a sparse distribution within the ceramic matrix, thus the improvement was not significant. Subsequently, after adding exfoliated MBNS to Comparative Example 6, the absorption performance was significantly improved. Looking back at Examples 1-6, it can be seen that the absorption performance was sufficiently improved after adding nickel nitrate hexahydrate and exfoliated MBNS. As in Example 1, an RL of -45.12 dB was obtained compared to Comparative Example 1. min A dual improvement over the 1.77 GHz EAB. The best performing RL implementation is 3. min It was significantly reduced to -52.59 dB, and the maximum EAB range was expanded to 5.6 GHz, covering the entire Ku band.

[0088] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing MBNS-GC-Ni2Si reinforced dual-phase SiC composite ceramics, characterized in that, include: Hexagonal boron nitride was added to phenolic resin and then exfoliated in a three-roll mill to obtain a first mixture containing multilayer boron nitride nanosheets. The first mixture was dissolved in furfural solution, and high-purity silicon powder, nickel nitrate hexahydrate, boron carbide and α-SiC ceramic powder were added in sequence. After stirring, a second mixture was obtained. After removing the moisture and furfural from the second mixture, vacuum sintering was performed to obtain the MBNS-GC-Ni2Si reinforced duplex SiC composite ceramic. The mass ratio of the hexagonal boron nitride to the phenolic resin is 0.01-0.7:1; The mass ratio of the first mixture, high-purity silicon powder, nickel nitrate hexahydrate, boron carbide, and α-SiC ceramic powder is 1-40:1-40:1-10:0.01-2:60-80; The furfural solution uses water as a solvent and has a furfural mass fraction of 10%-20%. The mass-volume relationship between the first mixture and the furfural solution is 1:0.8-1.2 g / mL. The vacuum sintering includes: raising the temperature from room temperature to 650-750°C at a rate of 40-60°C / min, while maintaining a pressure of 10-20 MPa; Then, increase the temperature at 40-60℃ / min to 900-1100℃, maintain the pressure at 10-20MPa, and hold for 30-60min; then increase the temperature at 40-60℃ / min to 1400-1500℃, maintain the pressure at 10-20MPa, and hold for 60-180min; then increase the temperature at 40-60℃ / min to 1900-2100℃, maintain the pressure at 30-60MPa, and hold for 20-40min; finally, slowly depressurize to 0MPa over 1-3min, and allow the furnace to cool naturally to room temperature.

2. The method according to claim 1, characterized in that, The stripping process includes: the rotational speed ratio of the discharge roller, center roller, and feed roller of the three-roll mill is 8-10:3-5:1-2, the rotational speed is set to 200-400 rpm corresponding to the discharge roller, and the stripping is repeated 12-28 times. During the cycle, the first gap between the center roller and the feed roller is always greater than the second gap between the discharge roller and the center roller.

3. The method according to claim 2, characterized in that, The peeling process further includes: first, peeling 3-7 times with the first gap being 22-26 μm and the second gap being 10-14 μm; then peeling 3-7 times with the first gap being 10-14 μm and the second gap being 4-8 μm; next, peeling 3-7 times with the first gap being 4-8 μm and the second gap being 2-3 μm; and finally peeling 3-7 times with the first gap being 2-3 μm and the second gap being 1-1.9 μm, for a total of 12-28 peeling cycles.

4. The method according to claim 1, characterized in that, The process prior to the stripping also includes a premixing of hexagonal boron nitride and phenolic resin at 40-60°C.

5. The method according to claim 1, characterized in that, The removal of moisture and furfural solution from the second mixture includes: removing moisture by freeze drying and then removing furfural by a forced-air drying oven.

6. An MBNS-GC-Ni2Si reinforced dual-phase SiC composite ceramic, characterized in that, Prepared by the method described in any one of claims 1-5.

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