Interlocking microstructure silicon carbide ceramic formed by slender crystal grains and preparation method thereof

Abstract

The invention relates to an interlocking microstructure silicon carbide ceramic formed by slender crystal grains and a preparation method thereof, and belongs to the technical field of ceramic materials. According to the method, alpha-SiC powder is used as a main raw material, and a certain proportion of perhydropolysilazane (PSZ) which is not subjected to crosslinking, curing or pretreatment is added to prepare ceramic composite powder. Then, spark plasma sintering is carried out under specific conditions, and the dense SiC ceramic with the interlocking microstructure formed by the long and thin crystal grains is obtained. In the sintering process, the stability of the alpha-SiC polymorph can be regulated and controlled by trace nitrogen elements generated by pyrolysis of all-hydrogen PSZ, and grains are induced to anisotropically grow along a specific crystal orientation, so that an interlocking microstructure is formed. The structure can influence the fracture toughness of the material through mechanisms such as crack deflection and bridging, so that the self-toughening of the ceramic material is realized.

Description

Technical Field

[0001] This invention relates to a silicon carbide ceramic with an interlocking microstructure formed by slender grains and its preparation method, belonging to the field of ceramic materials technology. Background Technology

[0002] Silicon carbide (SiC) ceramics are widely used in aerospace, defense equipment, nuclear engineering, and semiconductor manufacturing due to their high melting point, high hardness, low density, excellent thermal stability, and oxidation resistance. However, the low fracture toughness and insufficient damage tolerance of traditional SiC ceramics, along with their inherent brittleness, have become a significant factor limiting their further application in harsh service environments.

[0003] To improve the fracture toughness of SiC ceramics, existing technologies mainly employ fiber reinforcement or the introduction of a second phase for toughening. While fiber reinforcement can significantly improve toughness, it suffers from problems such as complex preparation processes, high costs, and significant anisotropy in mechanical properties. Introducing a second phase, such as metals or low-melting-point oxides, often reduces the material's high-temperature performance, hardness, and corrosion resistance, thus weakening the intrinsic advantages of SiC ceramics. Achieving self-toughening by controlling grain morphology without introducing external reinforcing phases is considered an ideal technical approach. The inventors discovered that when SiC grains transform from an equiaxed morphology to slender grains with a high aspect ratio, forming an interlocking structure at the microscale, fracture toughness can be effectively improved through mechanisms such as crack deflection, crack bridging, and grain interlocking. However, because SiC is a strongly covalently bonded material with limited atomic diffusion capabilities, its anisotropic grain growth typically relies on prolonged high-temperature treatment (>1950 °C) or the introduction of sintering aids, making it difficult to directly obtain slender grains and interlocking structures at lower temperatures without sintering aids.

[0004] Therefore, there is an urgent need to provide a new method for preparing SiC ceramics that can achieve the construction of slender grains and interlocked microstructures through direct sintering without the introduction of external reinforcing phases or complex pretreatment processes, thereby improving the comprehensive mechanical properties of the material while ensuring its purity. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a silicon carbide ceramic with an interlocking microstructure formed by slender grains and its preparation method. This method uses α-SiC powder as the main raw material, adding a certain proportion of uncrosslinked, uncured, or unpretreated all-hydrogen polysilazane (PSZ) to prepare a ceramic composite powder. Subsequently, under specific conditions, spark plasma sintering is performed to obtain a dense SiC ceramic with an interlocking microstructure formed by slender grains. During the sintering process, the trace nitrogen element generated by the pyrolysis of all-hydrogen PSZ can regulate the stability of the α-SiC polymorphs, inducing anisotropic grain growth along specific crystal directions, thereby forming an interlocking microstructure. This structure can influence the fracture toughness of the material through mechanisms such as crack deflection and bridging, achieving self-toughening of the ceramic material.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A method for preparing silicon carbide ceramics with interlocking microstructures formed by slender grains, the method comprising the following steps:

[0008] Step (1) Raw material preparation: The raw materials include α-SiC powder and perhydropolysilazane (PSZ), wherein the mass fraction of perhydropolysilazane is 7.5%-15% of the mass of α-SiC powder; Step (2) Slurry preparation: Dissolve all-hydrogen PSZ in an organic solvent and stir to obtain a transparent and uniform PSZ solution; then add α-SiC powder and stir to mix evenly to obtain a mixed slurry; Step (3) Drying: Evaporate and dry the slurry to obtain ceramic composite powder; Step (4) Spark plasma sintering: The ceramic composite powder is loaded into a graphite mold and placed in a spark plasma sintering equipment for sintering: First, when the initial vacuum degree is less than 10 Pa, the temperature is raised to 800-1000 ℃ and held for 1-3 min. Then, when the temperature is raised to 1200±50 ℃, the pressure is increased to 60-80 MPa. Finally, the pressure is kept constant and the temperature is raised to 1700-1750 ℃ ​​and held for 5-15 min. After sintering, the mixture is cooled with the furnace to obtain silicon carbide ceramic with interlocked microstructure formed by fine grains.

[0009] Preferably, in step (1), the particle size of the α-SiC powder is 40-50 μm.

[0010] Preferably, in step (1), the mass fraction of the all-hydrogen PSZ is 7.5%-8.5% of the mass of the α-SiC powder.

[0011] Preferably, in step (2), the organic solvent is butyl ether, and a transparent and uniform PSZ solution is obtained by stirring at a speed of 450-800 r / min for 30-60 min.

[0012] Preferably, in step (2), after adding α-SiC powder, the mixture is stirred continuously at 800-1000 r / min for 2-4 h to obtain a mixed slurry.

[0013] Preferably, in step (3), the mixed slurry is placed in a rotary evaporator and dried by oil bath heating under negative pressure. The evaporation temperature is 110-120 ℃, the flask rotation speed is 30-40 r / min, and the drying time is 1-2 h to obtain dried ceramic composite powder.

[0014] Preferably, in step (4), when the initial vacuum degree is less than 10 Pa, the temperature is first raised to 800-1000 ℃ at a heating rate of 40-60 ℃ / min and held for 1-3 min. This stage is the key stage of all-hydrogen PSZ cracking. A large amount of gas will be generated during the cracking process. If the heating rate is too fast or the vacuum degree is insufficient, the precursor cracking will be insufficient, thereby reducing the effective ceramicization yield and hindering the formation of slender grains. The sintering process is carried out in a vacuum atmosphere to avoid nitrogen-containing gas or inert gas from changing the cracking path of the precursor and the composition of cracking products, thereby affecting the formation of slender grains. Then, when the temperature is increased to 1200±50 ℃ at a heating rate of 50-100 ℃ / min, the pressure is increased to 60-80 MPa when the temperature is increased to 1600±50 ℃ at a heating rate of 50-100 ℃ / min. Finally, while maintaining constant pressure, continue heating at a rate of 30-40 ℃ / min to 1700-1750 ℃ ​​and hold for 5-10 min. After sintering, cool with the furnace to obtain silicon carbide ceramics with interlocked microstructures formed by slender grains.

[0015] A silicon carbide ceramic with an interlocking microstructure formed by slender grains was prepared by the above method.

[0016] Preferably, the silicon carbide grains in the interlocked microstructure are elongated and have an average grain aspect ratio greater than 2.

[0017] Preferably, the interlocking microstructure silicon carbide ceramic formed by the slender grains has a density ≥99%, a hardness of 25-30 GPa, and a fracture toughness of 5.5-8 MPa·m. 1 / 2 .

[0018] Beneficial effects In this invention, the trace nitrogen elements generated by the sintering and pyrolysis of all-hydrogen polysilazane under controlled heating rate and high vacuum conditions may influence the relative stability of α-SiC polymorphs, thereby inducing anisotropic grain growth along specific crystal orientations during sintering, forming slender grains with an aspect ratio greater than 2. These slender grains interlock on a microscale, constructing a stable interlocking structure and achieving a self-toughening effect.

[0019] The preparation method of the present invention does not require the introduction of additional sintering aids, nor does it require thermal crosslinking or curing treatment, thus simplifying the process and reducing the preparation cost. In the preparation method of this invention, the all-hydrogen PSZ is mainly converted into SiC after cracking, which is beneficial to maintaining the high purity of the ceramic material; By synergistically controlling the composition and sintering process, the aspect ratio and size of SiC grains can be designed in a controllable manner. The interlocking structure formed by slender grains achieves a self-toughening effect, resulting in SiC ceramics with high density and high mechanical properties at a lower sintering temperature. Attached Figure Description

[0020] Figure 1 The microstructure of the SiC ceramic with a content of 7.5 wt.% PSZ at 1750 °C for 5 min in Example 1 is shown.

[0021] Figure 2 The microstructure of the SiC ceramic with a content of 7.5 wt.% PSZ at 1750 °C for 15 min in Example 2 is shown.

[0022] Figure 3 The microstructure of the SiC ceramic with a content of 10 wt.% PSZ at 1750 °C for 5 min in Example 3 is shown.

[0023] Figure 4 The microstructure of SiC ceramic with 1750 °C × 5 min and 7.5 wt.% vinyl PSZ content in Comparative Example 1 is shown. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments.

[0025] Example 1 Step (1) Raw material preparation: The raw materials include 10 g of α-SiC spherical powder and 0.75 g of all-hydrogen PSZ. The particle size of the SiC spherical powder is 40 μm and the purity is greater than 99%.

[0026] Step (2) Slurry preparation: Weigh the total hydrogen PSZ and put it into a flat-bottomed flask. Add butyl ether solvent and magnetic stir bar, and stir at 450 r / min for 30 min to obtain a transparent and uniform total hydrogen PSZ solution.

[0027] Subsequently, α-SiC spherical powder was added to the above solution, the stirring speed was increased to 800 r / min, and stirring was continued for 3 hours to obtain a uniformly mixed slurry.

[0028] Step (3) Rotary evaporation drying: The mixed slurry obtained in step (2) is placed in a rotary evaporator and dried under negative pressure by oil bath heating. The evaporation temperature is 120 ℃, the flask rotation speed is 30 r / min, and the drying time is 1 h to obtain dried ceramic powder.

[0029] Step (4) Spark Plasma Sintering: The ceramic powder obtained in step (3) is loaded into a graphite mold and placed in a spark plasma sintering apparatus. Sintering is carried out according to the following process: The initial vacuum degree is 6 Pa. First, heat to 1000 ℃ at a heating rate of 50 ℃ / min and hold for 2 min, with a vacuum degree of 10 Pa; then heat to 1200 ℃ at a heating rate of 100 ℃ / min and start applying pressure while continuing to heat to 1650 ℃ at a heating rate of 50 ℃ / min, at which time the sintering pressure is 80 MPa; keep the pressure constant and continue to heat to 1750 ℃ ​​at a heating rate of 30 ℃ / min and hold for 5 min. After sintering, cool with the furnace to obtain SiC ceramic products.

[0030] The microstructure of the SiC sample obtained by sintering in this embodiment is as follows: Figure 1 As shown in the figure, an interlocking microstructure formed by slender grains (aspect ratio of 2.6) can be observed. The sample has a density of 99.0%, a hardness of 27.5 GPa, and a fracture toughness of 6.8 MPa·m. 1 / 2 The above data demonstrate that high-performance dense SiC ceramics were successfully prepared through direct sintering.

[0031] Example 2 Steps (1)-(3) are the same as in Example 1.

[0032] Step (4) Spark Plasma Sintering: The ceramic powder obtained in step (3) is loaded into a graphite mold and placed in a spark plasma sintering apparatus. Sintering is carried out according to the following process: The initial vacuum degree is 8 Pa. First, heat to 1000 ℃ at a heating rate of 50 ℃ / min and hold for 1 min, with a vacuum degree of 10 Pa; then heat to 1200 ℃ at a heating rate of 100 ℃ / min and start applying pressure while continuing to heat to 1650 ℃ at a heating rate of 50 ℃ / min, at which time the sintering pressure is 80 MPa; keep the pressure constant and continue to heat to 1750 ℃ ​​at a heating rate of 30 ℃ / min and hold for 15 min. After sintering, cool with the furnace to obtain SiC ceramic products.

[0033] The microstructure of the SiC sample obtained by sintering in this embodiment is as follows: Figure 2 As shown in the figure, an interlocking microstructure formed by slender grains can be observed. Extending the holding time increased the grain aspect ratio to 5.5, achieving controllable design of the grain morphology. The sample exhibited a density of 99%, a hardness of 27.1 GPa, and a fracture toughness of 5.8 MPa·m. 1 / 2 The above data demonstrate that high-performance dense SiC ceramics were successfully prepared through direct sintering.

[0034] Example 3 Step (1) Raw material preparation: The raw materials include 10 g of α-SiC spherical powder and 1 g of PSZ. The particle size of the SiC spherical powder is 40 μm and the purity is greater than 99%.

[0035] Steps (2)-(4) are the same as in Example 1.

[0036] The microstructure of the SiC sample obtained by sintering in this embodiment is as follows: Figure 3 As shown in the figure, an interlocking microstructure formed by slender grains (aspect ratio of 2.9) can be observed. The sample has a density of 99.1%, a hardness of 27.4 GPa, and a fracture toughness of 6.7 MPa·m. 1 / 2 The above data demonstrate that high-performance dense SiC ceramics were successfully prepared through direct sintering.

[0037] Comparative Example 1 Step (1) Raw material preparation: The raw materials include 10 g α-SiC spherical powder and 0.75 g vinyl PSZ. The particle size of the SiC spherical powder is 40 μm and the purity is greater than 99%.

[0038] Steps (2)-(4) are the same as in Example 1.

[0039] The microstructure of the SiC sample obtained by sintering in this comparative example is as follows: Figure 4As shown, the grains exhibit an equiaxed morphology, and no elongated grain interlocking structure was observed. The grain size is approximately 1.2 μm.

[0040] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A method for preparing a silicon carbide ceramic with an interlocking microstructure formed by slender grains, characterized in that: The method steps include: Step (1) Raw material preparation: The raw materials include α-SiC powder and all-hydrogen PSZ, wherein the mass fraction of all-hydrogen PSZ is 7.5%-15% of the mass of α-SiC powder; Step (2) Slurry preparation: Dissolve all-hydrogen PSZ in an organic solvent and stir to obtain a transparent and uniform PSZ solution; then add α-SiC powder and stir to mix evenly to obtain a mixed slurry; Step (3) Drying: Evaporate and dry the slurry to obtain ceramic composite powder; Step (4) Spark plasma sintering: The ceramic composite powder is loaded into a graphite mold and placed in a spark plasma sintering equipment for sintering: First, when the initial vacuum degree is less than 10 Pa, the temperature is raised to 800-1000 ℃ and held for 1-3 min. Then, when the temperature is raised to 1200±50 ℃, the pressure is increased to 60-80 MPa. Finally, the pressure is kept constant and the temperature is raised to 1700-1750 ℃ ​​and held for 5-15 min. After sintering, the mixture is cooled with the furnace to obtain silicon carbide ceramic with interlocked microstructure formed by fine grains.

2. The method for preparing a silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 1, characterized in that: In step (1), the particle size of the α-SiC powder is 40-50 μm.

3. The method for preparing a silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 1, characterized in that: In step (1), the mass fraction of the all-hydrogen PSZ is 7.5%-8.5% of the mass of the α-SiC powder.

4. The method for preparing a silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 1, characterized in that: In step (2), the organic solvent is butyl ether, and a transparent and uniform PSZ solution is obtained by stirring at a speed of 450-800 r / min for 30-60 min.

5. The method for preparing a silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 1, characterized in that: In step (2), after adding α-SiC powder, the mixture is stirred continuously at 800-1000 r / min for 2-4 h to obtain a mixed slurry.

6. The method for preparing a silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 1, characterized in that: In step (3), the mixed slurry is placed in a rotary evaporator and dried under negative pressure by oil bath heating. The evaporation temperature is 110-120 ℃, the flask rotation speed is 30-40 r / min, and the drying time is 1-2 h to obtain dried ceramic composite powder.

7. The method for preparing a silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 1, characterized in that: In step (4), when the initial vacuum degree is less than 10 Pa, heat to 800-1000 ℃ at a heating rate of 40-60 ℃ / min and hold for 1-3 min; then heat to 1200±50 ℃ at a heating rate of 50-100 ℃ / min and start pressurizing; heat to 1600±50 ℃ at a heating rate of 50-100 ℃ / min and increase the pressure to 60-80 MPa; finally, keep the pressure constant and continue heating to 1700-1750 ℃ ​​at a heating rate of 30-40 ℃ / min and hold for 5-10 min. After sintering, cool with the furnace to obtain interlocked microstructure silicon carbide ceramic with fine grains.

8. A silicon carbide ceramic with an interlocking microstructure formed by slender grains, characterized in that: It is prepared by any one of the methods of claims 1 to 7.

9. The silicon carbide ceramic with an interlocking microstructure formed by elongated grains as described in claim 8, characterized in that: The interlocked microstructure contains elongated silicon carbide grains with an average grain aspect ratio greater than 2.

10. The silicon carbide ceramic with interlocking microstructure formed by elongated grains as described in claim 8, characterized in that: The interlocking microstructure silicon carbide ceramic formed by the slender grains has a density ≥99%, a hardness of 25-30 GPa, and a fracture toughness of 5.5-8 MPa·m. 1 / 2 .

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