Magnetic short carbon fiber reinforced silicon magnesium nitride ceramic and preparation method thereof

Abstract

The invention relates to a magnetic chopped carbon fiber reinforced silicon magnesium nitride ceramic and a preparation method thereof. According to the technical scheme, the preparation method comprises the following steps: mixing magnesium silicon nitride powder, yttrium oxide powder and absolute ethyl alcohol, and performing ultrasonic dispersion to obtain a mixture I; bombarding the surface of the short carbon fiber by using low-temperature plasma treatment equipment, and then soaking the short carbon fiber in a silane coupling agent aqueous solution to obtain modified short carbon fiber; magnetic short carbon fibers obtained by bombarding a target material through magnetron sputtering are mixed with the mixture I, and a mixture II is obtained; pouring the mixture II into a mold, and directionally arranging the magnetic short carbon fibers along the direction of a magnetic field by using a magnetic field generating device; placing a mold containing the mixture II in the center of a pressing plate of a hydraulic machine for mechanical pressing, and performing vacuum drying to obtain a mixture III; and finally, carrying out segmented low-pressure sintering to obtain the magnetic short carbon fiber reinforced silicon magnesium nitride ceramic. The prepared product is good in interface bonding, and the fracture toughness and the breaking strength stability can be remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of silicon-magnesium nitride ceramics technology. Specifically, it relates to a magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic and its preparation method. Technical Background Magnesium silicon nitride (MgSi) is an orthorhombic group II-IV nitride semiconductor. Its crystal structure is similar to that of aluminum nitride (AN), and can be considered a deformation of the wurtzite structure of AlN. The two Al atoms in this structure... 3+ by a Mg 2+ and a Si 4+ The orderly substitution forms an orthogonal structure composed of interconnected tetrahedral units. This structure endows MgSiN2 with a series of excellent properties, including high thermal stability, good thermal conductivity, high resistivity, low dielectric constant, and a low coefficient of thermal expansion similar to that of AlN, thus attracting the attention of scientists and engineers.

[0002] WA Croen et al. (WA Croen, MJ Kraan. Preparation, et al. Microstructure and Properties of MgSiN2 Ceramics. J Eur Ceram Soc, 1993, 12: 413-420.) prepared MgSiN2 and AlN ceramics at 1500℃ under a nitrogen atmosphere using a pressureless sintering method and systematically compared their mechanical and thermal properties. The study showed that MgSiN2 ceramics exhibited superior overall mechanical properties compared to AlN ceramics. However, the MgSiN2 ceramics prepared by this sintering process also had significant defects, including low fracture toughness, which made the magnesium silicon nitride prone to brittle fracture under external forces.

[0003] Shukiko Tanaka et al. (Shukiko Tanaka, Kiyoshi Itatani, et al. Effect of silicon nitride addition on the thermal and mechanical properties of magnesium silicon nitride ceramics J. Journal of the European Ceramic Society, 2004, 24(7): 2163-2168.) prepared samples using a hot-pressing sintering method. Silicon nitride was added to MgSiN2, and Yb2O3 was used as a sintering aid. During sintering, the presence of the liquid phase caused Si3N4 grains to elongate, hindering crack propagation and thus improving toughness. However, the Si3N4 phase and the MgSiN2 matrix in this method only rely on liquid-phase sintering for physical bonding, resulting in weak interfacial bonding. When subjected to external impact or sudden temperature changes, defects easily appear at the phase interface.

[0004] Shukiko Tanaka et al. (Shukiko Tanaka, Kiyoshi Itatani, et al. The effect of rare-earth oxide addition on the hot-pressing of magnesium siliconnitride. J Eur Ceram Soc, 2002, 22:777-783.) studied the effect of rare-earth oxide content on the properties of MgSiN2 ceramics and prepared MgSiN2 ceramics using hot-pressing sintering. The addition of Y2O3 showed the best effect on improving the relative density and Vickers hardness of the material, while the addition of Yb2O3 was most suitable for improving the thermal conductivity. Hot-pressing sintering has advantages in improving the density of the material, but the high-pressure environment of hot-pressing sintering restricts the escape of gases during sintering, leaving micropores inside the matrix. Under high pressure, these micropores form closed pores, becoming new crack initiations and affecting the stability of the material's flexural strength. Summary of the Invention

[0005] The present invention aims to overcome the shortcomings of existing technologies and provides a magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic with good interfacial bonding and significantly improved fracture toughness and flexural strength stability, as well as its preparation method.

[0006] To achieve the above objectives, the specific steps of the technical solution adopted by the present invention are as follows: Step 1: Mix 95-98 wt% magnesium silicon nitride powder and 2-5 wt% yttrium oxide powder for 5-8 hours to obtain a mixture; then add 100-600 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 20-40 minutes to obtain mixture I.

[0007] Step 2: Using an argon-oxygen mixed gas as the plasma source, bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 15-30 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 30-60 minutes, and then dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 1-4 wt% of the mass of the short-cut carbon fibers.

[0008] Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber.

[0009] Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place a 0.3~0.6T magnetic field generator along the direction of the guide grooves, and then use a scraper to scrape the mixture II 2~5 times along the magnetic field direction to make the magnetic carbon fibers oriented along the magnetic field direction.

[0010] Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.5~0.8MPa and hold for 10~15min, then vacuum dry to obtain mixture III.

[0011] Step 6: Place mixture III in a pneumatic sintering furnace under a nitrogen atmosphere and use a segmented low-pressure sintering process: first, heat the mixture to 1050-1200℃ at a rate of 3-6℃ / min and hold it for 2-5 hours; then heat the mixture to 1500-1650℃ at a rate of 4-7℃ / min and hold it at 5-8MPa for 2-5 hours, and allow it to cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

[0012] The MgSiN2 content of the silicon magnesium nitride powder is ≥98wt%; the particle size of the silicon magnesium nitride powder is ≥100nm.

[0013] The purity of the yttrium oxide powder is ≥99wt%; the particle size of the yttrium oxide powder is ≥50nm.

[0014] The drying process is carried out at a temperature of 60-80℃ and a vacuum of 0.08-0.10MPa for 6-8 hours.

[0015] The magnetic target material is one of iron, cobalt, or nickel.

[0016] The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 3~6:100. The mixture was ultrasonically dispersed for 15~30 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 10~16 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 2-5 wt% of the dispersed magnetic short-cut carbon fibers.

[0017] The inert gas is argon, helium, or a mixture of argon and helium.

[0018] The resin is a thermosetting phenolic resin or a thermoplastic phenolic resin.

[0019] The vacuum drying temperature is 60~80℃, the vacuum degree is 0.08~0.10MPa, and the vacuum drying time is 1~5h.

[0020] By adopting the above technical solution, the present invention has the following advantages compared with the prior art: This invention utilizes chopped carbon fibers as a reinforcing phase. Due to their high aspect ratio and high tensile strength, chopped carbon fibers can significantly increase the energy consumption for matrix crack propagation through multiple mechanisms such as crack deflection, bridging, and fiber pull-out. This fundamentally improves the brittle characteristics of silicon-magnesium nitride ceramics and enhances their fracture toughness, with a toughening effect far superior to single-phase ceramic composites. Simultaneously, the high elastic modulus and high-temperature mechanical stability of chopped carbon fibers precisely complement the excellent high-temperature resistance, high hardness, and chemical corrosion resistance of silicon-magnesium nitride ceramics. Their introduction does not sacrifice the core performance advantages of the matrix; the two work together to bear the load. This allows magnetic chopped carbon fiber-reinforced silicon-magnesium nitride ceramics to retain their intrinsic high-temperature and thermal shock resistance characteristics while also possessing good impact resistance, making them suitable for engineering conditions involving complex high-temperature stresses.

[0021] This invention enhances the bonding performance between chopped carbon fibers and a magnesium silicon nitride ceramic matrix by modifying the surface and directionally arranging short carbon fibers, thereby optimizing the interfacial interaction mechanism. Through surface modification of the chopped carbon fibers and a directional magnetic field-assisted ordered arrangement process, the interfacial bonding strength and structural stability of the magnetically modified chopped carbon fibers reinforced magnesium silicon nitride ceramics are both improved. Plasma and other surface treatment processes promote the formation of a stable chemical bond structure between the chopped carbon fibers and the magnesium silicon nitride ceramic matrix. The directional magnetic field guides the magnetically modified chopped carbon fibers to achieve an ordered arrangement along the direction of stress. This superior interfacial bonding further avoids problems such as uneven interfacial bonding and stress concentration caused by the agglomeration of chopped carbon fibers. The modified chopped carbon fibers, possessing excellent interfacial bonding properties, function uniformly within the matrix, ensuring that the interfacial bonding advantages between the chopped carbon fibers and the magnesium silicon nitride matrix are fully transformed into improved overall mechanical properties of the material. This further optimizes the mechanical properties and structural stability of the magnetically modified magnesium silicon nitride ceramic reinforced with chopped carbon fibers.

[0022] This invention employs segmented low-pressure sintering. Segmented sintering, through precise temperature control, specifically alleviates the thermal stress caused by the difference in thermal expansion coefficients between chopped carbon fibers and the ceramic matrix. Based on the differences in the thermal expansion characteristics of the two phases, appropriate heating rates are set in stages. In critical temperature ranges where the thermal expansion difference is significant and thermal stress is prone to concentration, a gentle heating method is used, effectively avoiding problems such as pyrolysis, fracture, and interfacial microcracks in chopped carbon fibers caused by mismatched thermal expansion rates. While ensuring the sintering density of the material, the structural integrity of the chopped carbon fibers is preserved to the maximum extent, significantly improving the interfacial structural stability and flexural strength stability of magnetic chopped carbon fiber reinforced silicon magnesium nitride ceramics. This effectively solves the technical defects of existing sintering processes that easily cause fiber thermal damage and interfacial bonding failure. This invention utilizes magnetic short-cut carbon fibers to reinforce magnesium silicon nitride, thereby enhancing the interfacial bonding strength between the magnetic carbon fibers and magnesium silicon nitride, effectively improving the mechanical properties of the product. The magnetic short-cut carbon fiber reinforced magnesium silicon nitride ceramic prepared by this invention has been tested and found to have a flexural strength of 400~450 MPa at room temperature and a fracture toughness of 6.2~7 MPa·m. 1 / 2 .

[0023] Therefore, the magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic prepared by this invention has the characteristics of good interfacial bonding and can significantly improve fracture toughness and flexural strength stability. Attached Figure Description

[0024] Figure 1 This is a SEM image of a magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic prepared according to the present invention. Detailed Implementation

[0025] The following detailed description of the embodiments further illustrates the present invention, but is not intended to limit its scope of protection.

[0026] A magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic and its preparation method. The steps of the preparation method described in this specific embodiment are as follows: Step 1: Mix 95-98 wt% magnesium silicon nitride powder and 2-5 wt% yttrium oxide powder for 5-8 hours to obtain a mixture; then add 100-600 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 20-40 minutes to obtain mixture I.

[0027] Step 2: Using an argon-oxygen mixed gas as the plasma source, bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 15-30 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 30-60 minutes, and then dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 1-4 wt% of the mass of the short-cut carbon fibers.

[0028] Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber.

[0029] Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place a 0.3~0.6T magnetic field generator along the direction of the guide grooves, and then use a scraper to scrape the mixture II 2~5 times along the magnetic field direction to make the magnetic carbon fibers oriented along the magnetic field direction.

[0030] Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.5~0.8MPa and hold for 10~15min, then vacuum dry to obtain mixture III.

[0031] Step 6: Place mixture III in a pneumatic sintering furnace under a nitrogen atmosphere and use a segmented low-pressure sintering process: first, heat the mixture to 1050-1200℃ at a rate of 3-6℃ / min and hold it for 2-5 hours; then heat the mixture to 1500-1650℃ at a rate of 4-7℃ / min and hold it at 5-8MPa for 2-5 hours, and allow it to cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

[0032] The MgSiN2 content of the silicon magnesium nitride powder is ≥98wt%.

[0033] The purity of the yttrium oxide powder is ≥99wt%.

[0034] The drying process is carried out at a temperature of 60-80℃ and a vacuum of 0.08-0.10 MPa for 6-8 hours.

[0035] The magnetic target material is one of iron, cobalt, or nickel.

[0036] The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 3~6:100. The mixture was ultrasonically dispersed for 15~30 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 10~16 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 2-5 wt% of the dispersed magnetic short-cut carbon fibers.

[0037] The inert gas is argon, helium, or a mixture of argon and helium.

[0038] The resin is a thermosetting phenolic resin or a thermoplastic phenolic resin.

[0039] The vacuum drying temperature is 60~80℃, the vacuum degree is 0.08~0.10 MPa, and the vacuum drying time is 1~5h.

[0040] In this specific implementation: The particle size of the silicon magnesium nitride powder is ≥100nm.

[0041] The particle size of the yttrium oxide powder is ≥50nm.

[0042] The details will not be repeated in the examples.

[0043] Example 1 A magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic and its preparation method are disclosed. The steps of the preparation method described in this embodiment are as follows: Step 1: Mix 95 wt% magnesium silicon nitride powder and 5 wt% yttrium oxide powder for 5 h to obtain a mixture; then add 100 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 20 min to obtain mixture I.

[0044] Step 2: Using an argon-oxygen mixed gas as the plasma source, bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 15 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 30 minutes, and then dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 1 wt% of the mass of the short-cut carbon fibers.

[0045] Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber.

[0046] Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place the 0.3T magnetic field generator along the direction of the guide grooves, and then scrape the mixture II twice along the magnetic field direction with a scraper to make the magnetic carbon fibers oriented along the magnetic field direction.

[0047] Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.5 MPa and hold for 10 minutes, then vacuum dry to obtain mixture III.

[0048] Step 6: Place mixture III in a gas pressure sintering furnace under a nitrogen atmosphere and use a segmented low-pressure sintering process: first, heat to 1050℃ at a rate of 3℃ / min and hold for 2 hours; then heat to 1500℃ at a rate of 4℃ / min and hold for 2 hours under 5MPa conditions, and then cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

[0049] The MgSiN2 content of the silicon magnesium nitride powder is 98 wt%.

[0050] The purity of the yttrium oxide powder is 99 wt%.

[0051] The drying process was carried out at a temperature of 60°C and a vacuum of 0.08 MPa for 6 hours.

[0052] The magnetic target material is an iron target.

[0053] The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 3:100. The mixture was ultrasonically dispersed for 15 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 10 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 2 wt% of the dispersed magnetic short-cut carbon fibers.

[0054] The inert gas is argon.

[0055] The resin is a thermosetting phenolic resin.

[0056] The vacuum drying temperature is 60℃, the vacuum degree is 0.08MPa, and the vacuum drying time is 1h.

[0057] The magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic prepared in this embodiment was tested and found to have a room-temperature flexural strength of up to 400 MPa and a fracture toughness of 6.2 MPa·m. 1 / 2 .

[0058] Example 2 A magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic and its preparation method are disclosed. The steps of the preparation method described in this embodiment are as follows: Step 1: Mix 96 wt% magnesium silicon nitride powder and 4 wt% yttrium oxide powder for 6 hours to obtain a mixture; then add 200 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 25 minutes to obtain mixture I.

[0059] Step 2: Using an argon-oxygen mixed gas as the plasma source, bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 20 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 40 minutes, and then dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 2 wt% of the mass of the short-cut carbon fibers.

[0060] Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber.

[0061] Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place the 0.4T magnetic field generator along the direction of the guide grooves, and then use a scraper to scrape the mixture II three times along the magnetic field direction so that the magnetic carbon fibers are oriented along the magnetic field direction.

[0062] Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.6 MPa and hold for 12 minutes, then vacuum dry to obtain mixture III.

[0063] Step 6: Place mixture III in a gas pressure sintering furnace under a nitrogen atmosphere and use a segmented low-pressure sintering process: first, heat to 1100℃ at a rate of 4℃ / min and hold for 3 hours; then heat to 1550℃ at a rate of 5℃ / min and hold for 3 hours under 6MPa conditions, and then cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

[0064] The MgSiN2 content of the silicon magnesium nitride powder is 98.5 wt%.

[0065] The purity of the yttrium oxide powder is 99.5 wt%.

[0066] The drying process was carried out at a temperature of 65°C and a vacuum of 0.085 MPa for 6.5 hours.

[0067] The magnetic target is a cobalt target.

[0068] The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 4:100. The mixture was ultrasonically dispersed for 20 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 12 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 3 wt% of the dispersed magnetic short-cut carbon fibers.

[0069] The inert gas is helium.

[0070] The resin is a thermoplastic phenolic resin.

[0071] The vacuum drying temperature is 65℃, the vacuum degree is 0.085 MPa, and the vacuum drying time is 2 hours.

[0072] The magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic prepared in this embodiment was tested and found to have a room-temperature flexural strength of 429 MPa and a fracture toughness of 6.5 MPa·m. 1 / 2 .

[0073] Example 3 A magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic and its preparation method are disclosed. The steps of the preparation method described in this embodiment are as follows: Step 1: Mix 97 wt% magnesium silicon nitride powder and 3 wt% yttrium oxide powder for 7 h to obtain a mixture; then add 400 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 35 min to obtain mixture I.

[0074] Step 2: Using an argon-oxygen mixed gas as the plasma source, bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 25 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 50 minutes, and then dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 3 wt% of the mass of the short-cut carbon fibers.

[0075] Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber.

[0076] Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place the 0.5T magnetic field generator along the direction of the guide grooves, and then use a scraper to scrape the mixture II 4 times along the magnetic field direction so that the magnetic carbon fibers are oriented along the magnetic field direction.

[0077] Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.7 MPa and hold for 13 minutes, then vacuum dry to obtain mixture III.

[0078] Step 6: Place mixture III in a gas pressure sintering furnace under a nitrogen atmosphere and use a segmented low-pressure sintering process: first, heat to 1150℃ at a rate of 5℃ / min and hold for 4 hours; then heat to 1600℃ at a rate of 6℃ / min and hold for 4 hours under 7MPa conditions, and then cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

[0079] The MgSiN2 content of the silicon magnesium nitride powder is 99 wt%.

[0080] The purity of the yttrium oxide powder is 99.9 wt%.

[0081] The drying process was carried out at a temperature of 70°C and a vacuum of 0.09 MPa for 7 hours.

[0082] The magnetic target is a nickel target.

[0083] The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 5:100. The mixture was ultrasonically dispersed for 25 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 14 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 4 wt% of the dispersed magnetic short-cut carbon fibers.

[0084] The inert gas is a mixture of argon and helium.

[0085] The resin is a thermosetting phenolic resin.

[0086] The vacuum drying temperature is 70℃, the vacuum degree is 0.09 MPa, and the vacuum drying time is 4 hours.

[0087] The magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic prepared in this embodiment was tested and found to have a room-temperature flexural strength of 435 MPa and a fracture toughness of 6.8 MPa·m. 1 / 2 .

[0088] Example 4 A magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic and its preparation method are disclosed. The steps of the preparation method described in this embodiment are as follows: Step 1: Mix 98 wt% magnesium silicon nitride powder and 2 wt% yttrium oxide powder for 8 hours to obtain a mixture; then add 600 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 40 minutes to obtain mixture I.

[0089] Step 2: Using an argon-oxygen mixed gas as the plasma source, bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 30 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 60 minutes, and then dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 4 wt% of the mass of the short-cut carbon fibers.

[0090] Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber.

[0091] Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place the 0.6T magnetic field generator along the direction of the guide grooves, and then use a scraper to scrape the mixture II 5 times along the magnetic field direction to make the magnetic carbon fibers oriented along the magnetic field direction.

[0092] Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.8 MPa and hold for 15 minutes, then vacuum dry to obtain mixture III.

[0093] Step 6: Place mixture III in a gas pressure sintering furnace under a nitrogen atmosphere and use a segmented low-pressure sintering process: first, heat to 1200℃ at a rate of 6℃ / min and hold for 5 hours; then heat to 1650℃ at a rate of 7℃ / min and hold for 5 hours under 8MPa conditions, and then cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

[0094] The MgSiN2 content of the silicon magnesium nitride powder is 98.7 wt%.

[0095] The purity of the yttrium oxide powder is 99.3 wt%.

[0096] The drying process was carried out at a temperature of 80°C and a vacuum of 0.10 MPa for 8 hours.

[0097] The magnetic target is a nickel target.

[0098] The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 6:100. The mixture was ultrasonically dispersed for 30 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 16 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 5 wt% of the dispersed magnetic short-cut carbon fibers.

[0099] The inert gas is argon.

[0100] The resin is a thermoplastic phenolic resin.

[0101] The vacuum drying temperature is 80℃, the vacuum degree is 0.10 MPa, and the vacuum drying time is 5 hours.

[0102] The magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic prepared in this embodiment was tested and found to have a room-temperature flexural strength of up to 450 MPa and a fracture toughness of 7.0 MPa·m. 1 / 2 .

[0103] This specific implementation method has the following advantages compared with the prior art: This specific embodiment utilizes chopped carbon fibers as a reinforcing phase. Due to their high aspect ratio and high tensile strength, chopped carbon fibers can significantly increase the energy consumption for matrix crack propagation through multiple mechanisms such as crack deflection, bridging, and fiber pull-out. This fundamentally improves the brittle characteristics of silicon-magnesium nitride ceramics and enhances their fracture toughness, with a toughening effect far superior to single-phase ceramic composites. Simultaneously, the high elastic modulus and high-temperature mechanical stability of chopped carbon fibers precisely complement the excellent high-temperature resistance, high hardness, and chemical corrosion resistance of silicon-magnesium nitride ceramics. Their introduction does not sacrifice the core performance advantages of the matrix. The two work together to bear the load, allowing magnetic chopped carbon fiber-reinforced silicon-magnesium nitride ceramics to retain both their intrinsic high-temperature and thermal shock resistance characteristics and possess good impact resistance, making them suitable for engineering conditions involving complex high-temperature stresses.

[0104] This specific embodiment optimizes the interfacial interaction mechanism by modifying and orienting the surface of chopped carbon fibers to enhance the bonding performance between the chopped carbon fibers and the silicon-magnesium nitride ceramic matrix. By performing surface modification treatment on the chopped carbon fibers and combining it with an ordered arrangement process assisted by a directional magnetic field, both the interfacial bonding strength and structural stability of the magnetically chopped carbon fiber-reinforced silicon-magnesium nitride ceramic are improved. The magnetically chopped carbon fiber-reinforced silicon-magnesium nitride ceramic prepared according to this specific embodiment is shown in the attached figure. Figure 1 The magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic prepared in Example 1, from Figure 1 It can be seen that by employing surface treatment processes such as plasma, a stable chemical bond structure is formed between the short-cut carbon fibers and the silicon-magnesium nitride ceramic matrix. Furthermore, the magnetically modified short-cut carbon fibers are guided by a directional magnetic field to achieve an orderly arrangement along the direction of stress. This results in good interfacial bonding, further avoiding problems such as uneven interfacial bonding and stress concentration caused by the agglomeration of short-cut carbon fibers. This allows the modified short-cut carbon fibers, with their excellent interfacial bonding properties, to function uniformly within the matrix, ensuring that the interfacial bonding advantages between the short-cut carbon fibers and the silicon-magnesium nitride matrix are fully transformed into an improvement in the overall mechanical properties of the material. This further optimizes the mechanical properties and structural stability of the magnetically modified silicon-magnesium nitride ceramic.

[0105] This specific implementation method employs segmented low-pressure sintering. Segmented sintering, through precise temperature control, specifically alleviates the thermal stress caused by the difference in thermal expansion coefficients between chopped carbon fibers and the ceramic matrix. Based on the differences in the thermal expansion characteristics of the two phases, appropriate heating rates are set in stages. In the critical temperature range where the thermal expansion difference is significant and thermal stress is prone to concentration, a gentle heating method is used, effectively avoiding problems such as pyrolysis, fracture, and interfacial microcracks in chopped carbon fibers caused by mismatched thermal expansion rates. While ensuring the sintering density of the material, the structural integrity of the chopped carbon fibers is preserved to the maximum extent, significantly improving the interfacial structural stability and flexural strength stability of magnetic chopped carbon fiber reinforced silicon magnesium nitride ceramics. This effectively solves the technical defects of existing sintering processes that easily cause fiber thermal damage and interfacial bonding failure. This specific embodiment utilizes magnetic short-cut carbon fibers to reinforce magnesium silicon nitride, thereby enhancing the interfacial bonding strength between the magnetic carbon fibers and magnesium silicon nitride, effectively improving the mechanical properties of the product. The magnetic short-cut carbon fiber reinforced magnesium silicon nitride ceramic prepared according to this specific embodiment was tested and found to have a flexural strength of 400~450 MPa at room temperature and a fracture toughness of 6.2~7 MPa·m. 1 / 2 The Vickers hardness is stable at 16~20 GPa.

[0106] Therefore, the magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic prepared in this specific embodiment has the characteristics of good interfacial bonding and can significantly improve fracture toughness and flexural strength stability.

Claims

1. A method for preparing magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramics, characterized in that, The preparation method is as follows Step 1: Mix 95-98 wt% magnesium silicon nitride powder and 2-5 wt% yttrium oxide powder for 5-8 hours to obtain a mixture; then add 100-600 wt% anhydrous ethanol to the mixture and ultrasonically disperse for 20-40 minutes to obtain mixture I. Step 2: Bombard the surface of the short-cut carbon fiber with a low-temperature plasma treatment device for 15-30 minutes; immerse the bombarded short-cut carbon fiber in a silane coupling agent aqueous solution for 30-60 minutes, and dry it to obtain modified short-cut carbon fiber. The silane coupling agent is 1-4 wt% of the mass of the chopped carbon fibers; Step 3: Place the modified short-cut carbon fiber in a DC magnetron sputtering device and bombard the target material by magnetron sputtering. A uniform magnetic coating is deposited on the surface of the modified short-cut carbon fiber to obtain magnetic short-cut carbon fiber. Mix the magnetic short-cut carbon fiber with mixture I to obtain mixture II containing magnetic short-cut carbon fiber. Step 4: Select a mold with parallel guide grooves, pour the mixture II containing magnetic short-cut carbon fibers into the mold, place a 0.3~0.6T magnetic field generator along the direction of the guide grooves, and then scrape the mixture II with a scraper 2~5 times along the magnetic field direction to make the magnetic carbon fibers oriented along the magnetic field direction. Step 5: Place the mold containing mixture II in the center of the pressure plate of the hydraulic press, pressurize to 0.5~0.8MPa and hold for 10~15min, then vacuum dry to obtain mixture III; Step 6: Place mixture III in a gas pressure sintering furnace under a nitrogen atmosphere. First, heat the mixture to 1050-1200℃ at a rate of 3-6℃ / min and hold for 2-5 hours. Then, heat the mixture to 1500-1650℃ at a rate of 4-7℃ / min and hold for 2-5 hours under a pressure of 5-8MPa. Allow the mixture to cool naturally to obtain magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic.

2. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 1, characterized in that, The MgSiN2 content of the silicon magnesium nitride powder is ≥98wt%; the particle size of the silicon magnesium nitride powder is ≥100nm.

3. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 1, characterized in that, The purity of the yttrium oxide powder is ≥99wt%; the particle size of the yttrium oxide powder is ≥50nm.

4. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 1, characterized in that, The drying process is carried out at a temperature of 60-80℃ and a vacuum of 0.08-0.10 MPa for 6-8 hours.

5. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 1, characterized in that, The magnetic target material is one of iron, cobalt, or nickel.

6. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 1, characterized in that, The method for mixing the magnetic short-cut carbon fibers with mixture I is as follows: The magnetic short-cut carbon fibers were dispersed by blowing with an inert gas. Then, the dispersed magnetic short-cut carbon fibers were added to mixture I at a mass ratio of 3~6:

100. The mixture was ultrasonically dispersed for 15~30 minutes to obtain dispersed magnetic short-cut carbon fibers. Then, phenolic resin was added to the dispersed magnetic short-cut carbon fibers and allowed to stand for 10~16 minutes to obtain mixture II containing magnetic short-cut carbon fibers. The amount of phenolic resin added is 2-5 wt% of the dispersed magnetic short-cut carbon fibers.

7. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 6, characterized in that, The inert gas is argon, helium, or a mixture of argon and helium.

8. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 6, characterized in that, The resin is a thermosetting phenolic resin or a thermoplastic phenolic resin.

9. The method for preparing magnetic short-cut carbon fiber reinforced silicon magnesium nitride ceramic according to claim 1, characterized in that, The vacuum drying temperature is 60~80℃, the vacuum degree is 0.08~0.10 MPa, and the vacuum drying time is 1~5h.

10. A magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic, characterized in that, The magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic is prepared according to any one of the preparation methods of magnetic short-cut carbon fiber reinforced silicon-magnesium nitride ceramic in claims 1 to 9.

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