A method for preparing AlN-SiC composite ceramics by using oxygen-absorbing flow guide layer to promote reaction infiltration

Abstract

The application relates to a method for preparing AlN-SiC composite ceramics by using an oxygen-absorbing flow guide layer to promote reaction infiltration. The preparation method comprises the following steps: (1) mixing silicon nitride powder, a carbon source, a binder and a solvent by ball milling to obtain slurry; the slurry is obtained by a flow casting process to obtain a slurry sheet, which is dried, cut, pressurized and solidified, and pyrolyzed to obtain an infiltration preform; (2) placing the infiltration preform in a graphite crucible, and sequentially laying a layer of ceramic powder and a fiber on the surface of the graphite crucible to prepare an oxygen-absorbing flow guide layer on the surface of the preform; and (3) placing an Al-Si alloy block on the oxygen-absorbing flow guide layer, and performing high-temperature reaction sintering to obtain dense AlN-SiC composite ceramics.

Description

Technical Field

[0001] This invention belongs to the field of multiphase ceramic preparation, and particularly relates to a method for preparing AlN-SiC multiphase ceramics by utilizing an oxygen-absorbing flow layer to promote reactive melting and infiltration. Background Technology

[0002] SiC ceramic materials possess excellent properties such as high strength, high hardness, high thermal conductivity, corrosion resistance, high temperature resistance, and oxidation resistance, and are often used as corrosion-resistant seals, ceramic engine components, and heat exchanger components. Reactive infiltration is an important method for preparing ceramic materials, offering advantages such as short preparation cycle, low cost, and the ability to achieve near-net-shape molding. It has become one of the most promising methods for preparing SiC ceramic materials. This method typically uses silicon as the infiltration medium and porous carbon formed from the decomposition of organic matter as the infiltration preform. At high temperatures, molten Si infiltrates into the porous carbon preform under capillary force and reacts to form SiC. However, this method struggles to achieve a complete reaction between Si and C, easily leaving residual Si and C in the material, leading to poor mechanical properties.

[0003] Numerous studies have shown that introducing an appropriate amount of AlN into SiC ceramics can significantly improve the material's strength and toughness (~20%). This provides a possibility for reducing the residual Si content in the ceramic after reactive infiltration through alloy and pre-infiltration composition design, while simultaneously generating second-phase dispersed particles in situ to achieve ceramic material strengthening and toughening. Therefore, we proposed using an Al-Si alloy as the infiltration medium, and simultaneously introducing heterogeneous AlN particles generated in situ from the reaction of Si3N4 with Al in a carbon-infiltrated pre-body to achieve ceramic strengthening and toughening. However, research has found that oxygen contamination is unavoidable during reactive infiltration, such as oxidation of metal particle surfaces and oxygen in the infiltration environment. This causes aluminum in the alloy to oxidize at the interface between the pre-infiltrated pre-body and the alloy melt, forming an Al2O3 layer, which hinders reactive infiltration. In addition, the poor wettability of Si in the alloy with Si3N4 in the pre-body makes it difficult for the alloy melt to fully spread on the pre-body surface after melting, hindering the infiltration reaction and affecting the infiltration effect. To address the problems encountered during the low-temperature melting and infiltration process of aluminum-silicon alloys, this invention improves the reactive melting and infiltration process based on the principles of oxide layer formation and the wettability of materials. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for preparing AlN-SiC multiphase ceramics by utilizing an oxygen-absorbing flow-guiding layer to promote reactive melting and infiltration. This method involves laying an oxygen-absorbing flow-guiding layer on the surface of the melting preform to prevent the formation of an oxide layer at the interface of the melting preform, which would hinder the infiltration of the molten metal into the melting preform. Simultaneously, it induces the aluminum-silicon alloy melt to flow directionally and spread uniformly on the surface of the melting preform to increase the reaction sites, thus solving the problem of poor wettability of the Al-Si alloy melt on the melting preform, which affects the melting and infiltration process.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing AlN-SiC multiphase ceramics by utilizing an oxygen-absorbing flow-conducting layer to promote reactive melt infiltration includes the following steps:

[0007] (1) The silicon nitride powder, carbon source, binder and solvent are ball-milled and mixed to obtain a slurry; the slurry is then processed by casting to obtain a slurry sheet, which is then dried, cut, pressure-cured and pyrolyzed to obtain a melt-infiltrated preform;

[0008] (2) Place the melt-infiltrated preform in a graphite crucible, and sequentially lay a layer of ceramic powder and fiber on its surface to prepare an oxygen-absorbing and guiding layer on the surface of the preform.

[0009] (3) The Al-Si alloy block is placed on the oxygen absorption and flow guiding layer, and a dense AlN-SiC multiphase ceramic is obtained by high-temperature reaction sintering.

[0010] Preferably, in step (1), the silicon nitride powder has a particle size of 0.01–50 μm, more preferably 0.2–10 μm; the carbon source is an inorganic carbon source and an organic carbon source, the inorganic carbon source is carbon powder, the carbon powder has a particle size of 5–100 nm, more preferably 20–80 nm; the organic carbon source is at least one of phenolic resin, epoxy resin or sugar alcohol resin, preferably phenolic resin; the amount of carbon source added is 40–80 wt% of the total mass of carbon source and silicon nitride powder; the binder is at least one of polyvinyl alcohol, polyvinyl butyral or polymethyl methacrylate; the solvent is at least one of ethanol, isopropanol or xylene, preferably ethanol; the mass ratio of silicon nitride powder, carbon source, binder and solvent is 10–50:5–25:5–20:30–60.

[0011] Preferably, in step (1), the ball milling time is 24 to 48 hours.

[0012] Preferably, in step (1), the specific steps of the casting process are as follows:

[0013] (a) Prepare a slurry by mixing silicon nitride powder, carbon source, dispersant, plasticizer and solvent and ball milling for 12 to 24 hours at a ball milling speed of 150 to 300 r / min. Then add binder and ball mill for another 12 to 24 hours to obtain a uniform and stable casting slurry.

[0014] (b) Pour the cast slurry into a beaker and place it in a vacuum environment to remove bubbles for 30-60 minutes;

[0015] (c) The defoamed slurry is poured into a casting machine for casting, and the thickness of the resulting slurry sheet is 0.1 to 0.5 mm; wherein the casting speed is 120 to 480 mm / min and the scraper height is 0.2 to 1 mm.

[0016] Preferably, in step (1), the drying temperature is 18-35°C and the drying time is 12-36 hours.

[0017] Preferably, in step (1), the curing temperature is 100-150℃, the curing pressure is 0.1-20MPa, and the holding time is 2-4 hours; the thermal decomposition temperature is 700-1200℃, the holding time is 0.5-1 hours, the decomposition atmosphere is nitrogen or argon, preferably argon, and the argon flow rate is 5-10L / min.

[0018] Preferably, in step (2), the ceramic powder is at least one of boron nitride, silicon nitride, boron carbide, and silicon carbide, with a thickness of 0.5 to 3 mm and a particle size of 5 to 100 μm.

[0019] Preferably, in step (2), the fiber is at least one of C fiber, SiC fiber and BN fiber, and the fiber diameter is 1 to 3 mm.

[0020] Preferably, in step (2), the mass fraction of Al in the Al-Si alloy is 10 to 40 wt%.

[0021] Preferably, in step (3), the high-temperature reaction sintering temperature is 1200-1500℃, the vacuum degree in the furnace is 0.5-10Pa, and the holding time is 0.1-2h.

[0022] Beneficial effects

[0023] This invention provides a method for preparing AlN-SiC multiphase ceramics by utilizing an oxygen-absorbing flow-guiding layer to promote reactive infiltration. An oxygen-absorbing flow-guiding layer is deposited on the surface of the preform to prevent the formation of an oxide layer at the interface, which would hinder the infiltration of the molten metal. Simultaneously, it induces the aluminum-silicon alloy melt to flow directionally and spread uniformly on the surface of the preform, thereby increasing the number of reaction sites. This solves the problem of poor wettability of the Al-Si alloy melt on the preform, which affects the infiltration process, and improves the efficiency of reactive infiltration. With the oxygen-absorbing flow-guiding layer, the oxide layer at the interface of the preform disappears, allowing the alloy melt to spread uniformly on the surface of the preform, enabling complete infiltration and successful preparation of AlN-SiC multiphase ceramics. Attached Figure Description

[0024] Figure 1 (a) is a SEM image of a porous C-Si3N4 melt-infiltrated preform. Figure 1(b), (c), (d), and (e) are the surface distribution maps of C, O, Si, and N elements, respectively.

[0025] Figure 2 This is a SEM image of the cross-section of the material after melting and infiltration using the oxygen-absorbing flow guide layer in Example 2;

[0026] Figure 3 for Figure 2 Scan the spectrum along the element lines in the direction of the arrows;

[0027] Figure 4 (a) is a SEM image of the cross-section of the material after melt infiltration in Comparative Example 1 without the use of an oxygen-absorbing flow-guiding layer. Figure 4 (b) is a scan of the element lines in the direction of the arrows. Detailed Implementation

[0028] The present invention will be further illustrated below with specific examples, but the scope of protection of the present invention is not limited to the content described herein.

[0029] A method for preparing AlN-SiC multiphase ceramics by utilizing an oxygen-absorbing flow-conducting layer to promote reactive melt infiltration includes the following steps:

[0030] (1) Silicon nitride powder, carbon source, binder and solvent are ball-milled and mixed to obtain a uniform and stable slurry: the silicon nitride powder has a particle size of 0.01-50 μm, the carbon source has a mass fraction of 40-80 wt%, the carbon powder has a particle size of 5-100 nm, and the mass ratio of silicon nitride powder, carbon source, binder and solvent is 10-50:5-25:5-20:30-60. After being mechanically stirred evenly, the mixture is poured into a ball mill jar and ball-milled for 24-48 hours to obtain a uniform and stable silicon nitride slurry. Then, the slurry is used to form a cast sheet with a uniform thickness of 0.5 mm using a casting equipment. Finally, the sheet is laid flat and dried at a temperature of 18-35℃ for 12-36 hours to obtain a silicon nitride slurry sheet with a thickness of 0.4 mm.

[0031] (2) The slurry sheets obtained in step (1) are cut and stacked (20 layers in total), placed in a mold, and cured under pressure and heat. The cured preform is then placed in a carbon tube furnace for pyrolysis treatment to obtain a C-Si3N4 melt-infiltrated preform. The curing pressure is 0.1-20 MPa, the curing temperature is 100-150℃, and the curing holding time is 2-4 hours; the pyrolysis temperature is 700-1200℃, the pyrolysis holding time is 0.5-1 hour, and the pyrolysis atmosphere is argon.

[0032] (3) The C-Si3N4 melt-infiltrating preform obtained in step (2) is placed in a graphite crucible, and a layer of ceramic powder with a thickness of 0.5-3 mm and a particle size of 5-100 μm is spread on its surface. Then, a layer of fibers with a length of 60 mm and a diameter of 1-3 mm is spread on the surface of the powder, with one fiber placed at a interval of 0.5-2 mm. Subsequently, an aluminum-silicon alloy (Al mass fraction of 10-40 wt%) is placed on the oxygen-absorbing and guiding layer, and AlN-SiC multiphase ceramic is obtained by high-temperature reaction sintering. The reaction sintering temperature is 1200-1500℃, the sintering holding time is 0.1-2 h, and the vacuum degree in the melt-infiltrating furnace is 0.5-10 Pa.

[0033] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0034] Example 1

[0035] (1) Silicon nitride powder, carbon source, binder, and solvent were ball-milled and mixed to obtain a uniform and stable slurry: the silicon nitride powder had a particle size of 0.5 μm, the carbon powder had a particle size of 20 nm, the phenolic resin had a mass fraction of 18 wt%, polyvinyl butyral (PVB) and ethanol were the binder and solvent, respectively, and the mass ratio of silicon nitride powder, carbon source, binder, and solvent was 70:60:40:240. After being mechanically stirred evenly, the mixture was poured into a ball mill jar and ball-milled for 24 hours to obtain a uniform and stable silicon nitride slurry. The slurry was then used to make a cast sheet with a uniform thickness of 0.5 mm using a casting equipment. Finally, the sheet was laid flat and dried at room temperature for 12 hours to obtain a silicon nitride slurry sheet with a thickness of 0.4 mm.

[0036] (2) The slurry sheets obtained in step (1) are cut and stacked (20 layers in total), placed in a mold, and cured under pressure and heat. The cured preform is then placed in a carbon tube furnace for pyrolysis treatment to obtain a C-Si3N4 melt-infiltrated preform. The curing pressure is 2 MPa, the curing temperature is 140℃, and the curing holding time is 3 h. The pyrolysis temperature is 700℃, the pyrolysis holding time is 1 h, and the pyrolysis atmosphere is argon.

[0037] (3) The C-Si3N4 melt-infiltrating preform obtained in step (2) was placed in a graphite crucible, and a layer of Si3N4 powder with a thickness of 1 mm and a particle size of 10 μm was spread on its surface. Then, a layer of SiC fibers with a length of 60 mm and a diameter of 2 mm was spread unidirectionally on the powder surface in the same direction, with one fiber placed every 1 mm. Subsequently, an aluminum-silicon alloy (30 wt% Al by mass) was placed on the oxygen-absorbing and guiding layer, and AlN-SiC multiphase ceramic was obtained by high-temperature reaction sintering. The reaction sintering temperature was 1350 °C, the sintering holding time was 40 min, and the vacuum degree in the melt-infiltrating furnace was 5 Pa.

[0038] Example 2

[0039] In this Example 2, the process of preparing AlN-SiC multiphase ceramics by using an oxygen-absorbing flow layer to promote reactive melting and infiltration is the same as in Example 1, except that: in step (3), the ceramic powder of the oxygen-absorbing flow layer is SiC ceramic powder with a thickness of 1 mm and a particle size of 20 μm.

[0040] Example 3

[0041] In this Example 3, the process of preparing AlN-SiC multiphase ceramics by using an oxygen-absorbing flow-guiding layer to promote reactive melting and infiltration is the same as in Example 1, except that: in step (1), the mass fraction of phenolic resin in the slurry is 24wt%, and the mass ratio of silicon nitride powder, carbon source, binder and solvent is 70:90:40:240.

[0042] Example 4

[0043] In this embodiment 4, the process of preparing AlN-SiC multiphase ceramics by using an oxygen-absorbing flow layer to promote reactive melting and infiltration is the same as in embodiment 1, except that: the thickness of the oxygen-absorbing layer in step (3) is 2 mm, and the oxygen-absorbing flow layer is arranged in a cross pattern.

[0044] Example 5

[0045] In this Example 5, the process of preparing AlN-SiC multiphase ceramics by using an oxygen-absorbing flow-guiding layer to promote reactive melting and infiltration is the same as in Example 1, except that: the thickness of the oxygen-absorbing layer in step (3) is 2 mm, and the oxygen-absorbing flow-guiding layer is arranged in a cross pattern. The mass fraction of Al in the aluminum-silicon alloy is 20 wt%, and the reaction sintering temperature is 1400 °C.

[0046] Example 6

[0047] In this Example 6, the process of preparing AlN-SiC multiphase ceramics by using an oxygen-absorbing flow layer to promote reactive melting and infiltration is the same as in Example 1, except that: in step (3), the fibers of the oxygen-absorbing flow layer are C fibers with a length of 60 mm and a diameter of 1.5 mm, and a group is placed at 0.5 mm intervals.

[0048] Comparative Example 1

[0049] The process of preparing AlN-SiC multiphase ceramics by reactive melting in Comparative Example 1 is the same as that in Example 1, except that ceramic powder and fibers are not spread on the surface of the preform.

[0050] Figure 1 (a) is a SEM image of the C-Si3N4 porous melt-infiltrated preform in Example 1. Figure 1 (b), (c), (d), and (e) are the surface distribution maps of C, O, Si, and N elements, respectively.

[0051] Figure 2 This is a SEM image of the cross-section of the material after melting and infiltration using the oxygen-absorbing flow-guiding layer in Example 2. Figure 3 for Figure 2 According to the elemental line scan spectrum in the direction of the arrow, it can be seen that no Al2O3 layer appeared at the interface between the alloy and the preform after the oxygen-absorbing and guiding layer was spread and infiltrated on the surface, and SiC-AlN multiphase ceramic was successfully prepared.

[0052] Figure 4 (a) is a SEM image of the cross-section of the material after melt infiltration in Comparative Example 1 without the use of an oxygen-absorbing flow-guiding layer. Figure 4 (b) is the elemental line scan spectrum in the direction of the arrow. As can be seen from the figure, after the oxygen absorption and flow guiding layer is not spread on the surface, an Al2O3 layer appears at the interface between the alloy and the preform, which hinders the reaction and infiltration.

Claims

1. A method for preparing AlN-SiC multiphase ceramics by utilizing an oxygen-absorbing flow-guiding layer to promote reactive melting and infiltration, characterized in that, Includes the following steps: (1) The silicon nitride powder, carbon source, binder and solvent are ball-milled and mixed to obtain a slurry; the slurry is then processed by casting to obtain a slurry sheet, which is then dried, cut, pressure-cured and pyrolyzed to obtain a melt-infiltrated preform; (2) Place the melt-infiltrated preform in a graphite crucible, and sequentially lay a layer of ceramic powder and fiber on its surface to prepare an oxygen-absorbing and guiding layer on the surface of the preform; (3) The Al-Si alloy block is placed on the oxygen absorption and flow guiding layer, and a dense AlN-SiC multiphase ceramic is obtained by high-temperature reaction sintering.

2. The preparation method according to claim 1, characterized in that, In step (1), the particle size of the silicon nitride powder is 0.01~50μm; the carbon source is an inorganic carbon source and an organic carbon source, the inorganic carbon source is carbon powder, the particle size of the carbon powder is 5~100nm; the organic carbon source is at least one of phenolic resin, epoxy resin or sugar alcohol resin; the amount of carbon source added is 40~80wt% of the total mass of carbon source and silicon nitride powder; the binder is at least one of polyvinyl alcohol, polyvinyl butyral or polymethyl methacrylate; the solvent is at least one of ethanol, isopropanol or xylene; the mass ratio of silicon nitride powder, carbon source, binder and solvent is 10~50:5~25:5~20:30~60.

3. The preparation method according to claim 2, characterized in that, The silicon nitride powder has a particle size of 0.2~10μm; the carbon powder has a particle size of 20~80nm; the organic carbon source is phenolic resin; and the solvent is ethanol.

4. The preparation method according to claim 1, characterized in that, In step (1), the ball milling time is 24 to 48 hours.

5. The preparation method according to claim 1, characterized in that, In step (1), the specific steps of the casting process are as follows: (a) Prepare a slurry by mixing silicon nitride powder, carbon source, dispersant, plasticizer and solvent and ball mill for 12 to 24 hours at a speed of 150 to 300 r / min. Then add binder and ball mill for another 12 to 24 hours to obtain a uniform and stable casting slurry. (b) Pour the cast slurry into a beaker and place it in a vacuum environment to remove bubbles for 30-60 minutes; (c) Pour the defoamed slurry into a casting machine for casting, and the thickness of the resulting slurry sheet is 0.1~0.5mm; wherein the casting speed is 120~480mm / min and the scraper height is 0.2~1mm.

6. The preparation method according to claim 1, characterized in that, In step (1), the drying temperature is 18~35℃ and the drying time is 12~36 hours.

7. The preparation method according to claim 1, characterized in that, In step (1), the curing temperature is 100~150℃, the curing pressure is 0.1~20MPa, and the holding time is 2~4 hours; the thermal decomposition temperature is 700~1200℃, the holding time is 0.5~1 hours, and the decomposition atmosphere is nitrogen or argon.

8. The preparation method according to claim 7, characterized in that, The pyrolysis atmosphere is argon, and the argon flow rate is 5~10L / min.

9. The preparation method according to claim 1, characterized in that, In step (2), the ceramic powder is at least one of boron nitride, silicon nitride, boron carbide and silicon carbide, with a thickness of 0.5~3mm and a particle size of 5~100μm.

10. The preparation method according to claim 1, characterized in that, In step (2), the fiber is at least one of C fiber, SiC fiber and BN fiber, and the fiber diameter is 1~3mm.

11. The preparation method according to claim 1, characterized in that, In step (2), the mass fraction of Al in the Al-Si alloy is 10~40wt%.

12. The preparation method according to claim 1, characterized in that, In step (3), the high-temperature reaction sintering temperature is 1200~1500℃, the vacuum degree in the furnace is 0.5~10Pa, and the holding time is 0.1~2 hours.

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