Silicon carbide ceramic for stereolithography and its reaction bonding method

Abstract

The application discloses a kind of silicon carbide ceramics for light-cured forming and its reaction bonding method, the reaction bonding method, comprising the following steps: S1.Preparing silicon carbide preform;S2.Silicon powder and pitch are placed in container, silicon carbide preform is placed above silicon powder and pitch, and the whole is placed in vacuum debinding sintering furnace and sintered, so that pitch volatilization is deposited in the pore of silicon carbide preform, pitch deposited in pore is removed impurity, and again silicon vapor and carbon are fully reacted to obtain dense silicon carbide product.The carbon source gasification bonding method of the application can effectively solve the short board that carbon source such as graphite cannot be added in light-cured forming, and can also solve the complex process of repeated carbon penetration and debinding of preform.The application not only effectively increases the carbon source content in preform, but also can ensure that the product structure after sintering is more uniform, the surface quality is excellent, and there is no cracking, deformation and other phenomena.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silicon carbide ceramic sintering, in particular to silicon carbide ceramic for light-cured forming and a reaction bonding method thereof. BACKGROUND

[0002] The basic principle and process of preparing reaction bonded silicon carbide is to uniformly mix alpha-SiC powder with carbon powder, which can be graphite, carbon black, or carbon source obtained by pyrolysis of epoxy resin and phenolic resin, and then to form a green body by mixing the powder. Then, silicon infiltration is performed, and the solid silicon is dissolved into liquid silicon by heating to above 1500 DEG C in vacuum or inert atmosphere, and the liquid silicon penetrates into the green body containing pores through capillary action. The original silicon carbide is bonded by beta-SiC generated in situ by chemical reaction between Si solution or Si vapor and C to form RBSiC.

[0003] The light-cured 3D printing technology is a rapid prototyping technology that creates a 3D printed object by layering and curing a photosensitive polymer liquid through a projector. When light-cured 3D printing is used to form a silicon carbide green body, graphite or carbon black is added to the printing slurry, which will absorb a large amount of printing energy, resulting in poor bonding of the green body, irregular shape, and other problems. Therefore, only a small amount of residual carbon is formed as a carbon source by removing the photosensitive resin, resulting in less in-situ generated beta-SiC, and a large amount of silicon filling the voids, which leads to a rapid decline in the performance of the silicon carbide ceramic. To increase the in-situ generated beta-SiC and reduce free silicon, a carbon infiltration process is required before reaction bonding to increase the carbon source density in the preform.

[0004] A light-cured forming silicon carbide ceramic slurry and application are disclosed in Chinese patent application No. CN115490522A. By using two particle sizes of silicon carbide powder, a ceramic slurry with good light-cured performance is obtained, and excellent light-cured characteristics and forming performance are obtained, and finally a silicon carbide product with good performance is obtained. The preparation of raw materials does not add a carbon source, and the residual silicon content of the ceramic body after sintering is high.

[0005] Chinese patent application No. CN101508570A discloses a reaction bonded silicon carbide ceramic and its production process. After processes including slurry preparation, slurry injection forming, drying, vacuum sintering, and sand removal oxidation, a silicon carbide ceramic is prepared. The prepared sample has a large amount of residual silicon on the surface after vacuum sintering, which needs to be treated subsequently, and the process is complex and difficult to ensure that the silicon on the surface of the sample is not affected.

[0006] In summary, at the present stage, the photo-curing forming silicon carbide ceramic blank cannot add carbon source in the raw material, resulting in too high silicon content in the reaction bonded silicon carbide ceramic. If the carbon source needs to be added in the blank, it is necessary to add the steps of carbon source infiltration and carbon source degreasing in the preform after degreasing, which is complicated and affects the production efficiency and cost. At the same time, the residual silicon on the surface of the traditional reaction bonded silicon carbide is difficult to handle. The present application combines carbon source gasification and reaction bonding at the same time, effectively solves the problem of external carbon source for photo-curing, and effectively increases the production efficiency with simple process. Finally, the surface of the ceramic product is free of residual silicon. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a reaction bonding method for photo-curing forming silicon carbide ceramic to improve the carbon source density in the preform, and to obtain a silicon carbide product with more uniform structure, excellent surface quality, no cracking and deformation.

[0008] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a reaction bonding method for photo-curing forming silicon carbide ceramic, comprising the following steps:

[0009] S1. Preparing a silicon carbide preform;

[0010] S2. Placing silicon powder and pitch in a container, placing the silicon carbide preform above the silicon powder and pitch, vacuum sintering, allowing the pitch to volatilize and deposit in the pores of the silicon carbide preform, removing impurities from the pitch deposited in the pores, and then forming silicon vapor and carbon to fully react, to obtain a dense silicon carbide product.

[0011] The present application allows the pitch to evaporate and be adsorbed in the pores of the silicon carbide preform, and further deposits the pitch during the process of removing impurities from the pitch deposited in the pores, so that the carbon source density in the preform continues to increase, and a preform with higher and more uniform carbon source density is obtained.

[0012] Then a large amount of silicon vapor is generated in the crucible, the silicon vapor penetrates into the preform interstice and reacts with the residual carbon to form a beta-SiC phase combined preform. After sufficient reaction, the silicon vapor is slowly cooled to form a liquid metal to fill the interstice, and a dense reaction bonded silicon carbide product is obtained.

[0013] In the present application, the preform carbonization and reaction bonding are carried out at the same time, which effectively increases the carbon content in the preform, and optimizes the complex process of repeated carbonization and degreasing. The process of increasing carbon content is effectively simplified, the content of metallic silicon in the reaction bonded silicon carbide product is reduced, and the high temperature performance of the reaction bonded silicon carbide is improved.

[0014] In order to be used for photo-curing ceramic, carbon powder cannot be used, because the use of carbon powder will result in low printing precision and will absorb printing energy. Therefore, pitch is used in the present application.

[0015] In a preferred embodiment of the present application, the vacuum sintering conditions in S2 are as follows:

[0016] holding at 250-350℃ for 3-5 hours;

[0017] holding at 450-600℃ for 3-5 hours;

[0018] holding at 1600-1750℃ for 3-5 hours.

[0019] The first stage of 250-350℃ makes the pitch continuously volatilize and deposit in the pores of the preform;

[0020] The second stage of 450-600℃ makes the pitch deposited in the pores remove impurities and continuously deposit; the impurities in the pitch are fully volatilized, otherwise, the impurities in the pitch will react to produce gas during the deposition of silicon, which will cause the product to crack and produce cracks in the dense silicon carbide part. The temperature in the second stage needs to be kept at 450-600℃ to fully volatilize the impurities in the pitch, and exceeding 600℃ will cause the product to crack.

[0021] The third stage of heating to the melting point of metallic silicon 1600-1750℃ obtains dense silicon carbide ceramic, and the silicon particles form silicon vapor and fully react with carbon to fill the pores and obtain dense silicon carbide parts.

[0022] In a preferred embodiment of the present application, the heating rate at 250-350℃ is 0.5-1.5℃ / min.

[0023] In a preferred embodiment of the present application, the heating rate at 450-600℃ is 0.5-1.5℃ / min.

[0024] In a preferred embodiment of the present application, the heating rate at 1600-1750℃ is 1-5℃ / min.

[0025] The heating rate needs to be kept in the above range respectively, and too fast heating will cause temperature difference in the silicon carbide part, which directly leads to uneven volatilization of volatilization and cracking.

[0026] In a preferred embodiment of the present application, the silicon carbide preform in S2 is placed above the silicon powder and pitch by using a graphite frame. The silicon carbide preform is placed 1-10cm above the silicon powder and pitch. Too far distance will affect the deposition of pitch in the pores of the preform.

[0027] In a preferred embodiment of the present application, the preparation method of the silicon carbide preform in S1 is to perform debinding on the silicon carbide ceramic green body, and the debinding is completed to obtain the silicon carbide preform.

[0028] The silicon carbide ceramic blank is a ceramic slurry prepared from a photosensitive resin and silicon carbide, and is formed by photo-curing 3D printing.

[0029] The present application carries out pitch degreasing in a vacuum environment, and prepares a silicon carbide preform, and then evaporates and adsorbs the pitch in the voids of the silicon carbide preform, so that the density of the carbon source in the preform continuously increases, and a preform with higher and more uniform carbon source density is obtained.

[0030] The silicon carbide preform is a ceramic sample composed of residual carbon and silicon carbide obtained after vacuum degreasing of the silicon carbide blank.

[0031] In a preferred embodiment of the present application, the degreasing conditions in S1 are to heat to 500-700 DEG C at 0.5-1.5 DEG C / min.

[0032] The present application also discloses a silicon carbide ceramic for photo-curing molding prepared by the reaction bonding method of the silicon carbide ceramic.

[0033] The mass ratio of the silicon carbide preform to the silicon powder and pitch is 1:10-20:5-10.

[0034] The vacuum degree in S1 and S2 is 0.1-1 pa.

[0035] The container in S2 is a graphite crucible.

[0036] Compared with the prior art, the present application has the beneficial effects that:

[0037] The present application optimizes the problem of insufficient carbon source density after degreasing of the 3D printing molded silicon carbide blank, effectively increases the carbon source content in the preform, and also ensures that the product structure after sintering is more uniform, the surface quality is excellent, and there is no cracking, deformation and other phenomena, so that a silicon carbide product with better performance is obtained.

[0038] The carbon source gasification combined with the gas phase silicon infiltration method of the present application can effectively solve the shortcoming that graphite and other carbon sources cannot be added in photo-curing molding, and can also solve the complex process of repeated carbonization and degreasing of the preform. The present application synchronously carries out pitch impregnation and gas phase silicon infiltration reaction, and greatly simplifies the process.

[0039] Compared with the traditional carbon source impregnation process, the present application has the advantages of simple process, short process time, more uniform carbon source density, etc., and the gas phase silicon infiltration makes the silicon carbide ceramic sample more uniform in quality and free of residual silicon on the surface. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The present application is a photo-curing 3D printing silicon carbide substrate blank.

[0041] Figure 2 The present application is a silicon carbide preform after degreasing of the blank.

[0042] Figure 3 A silicon carbide substrate sample after sintering of the preform by the carbon source gasification and vapor silicon infiltration composite process;

[0043] Figure 4 A flow chart of the carbon source gasification and vapor silicon infiltration composite process of the present application.

[0044] Figure 5 A photo of the silicon carbide substrate sample prepared in Comparative Example 1. DETAILED DESCRIPTION

[0045] Example 1

[0046] Preparation of a silicon carbide ceramic substrate:

[0047] (1) First, a 10 g silicon carbide substrate green body was obtained by light-cured 3D printing forming, as shown in Figure 1 .

[0048] (2) The silicon carbide green body was placed in a vacuum debinding furnace, the furnace door was closed, the furnace was evacuated to 0.5 Pa, the temperature was raised to 600°C at a rate of 1°C / min, and the temperature was maintained for 2 h to obtain a silicon carbide substrate preform, as shown in Figure 2 .

[0049] (3) 120 g of silicon powder and 60 g of pitch were placed in a graphite crucible, and then the silicon carbide substrate preform was placed on the powder 5 cm above using a graphite holder, and placed in the middle part of the debinding sintering furnace.

[0050] (4) The temperature was raised to 300°C at a rate of 1°C / min, and the temperature was maintained for 4 h to allow the pitch to melt completely and generate a large amount of steam that was adsorbed in the voids of the silicon carbide substrate preform.

[0051] (5) The temperature was raised to 500°C at a rate of 1°C / min, and the temperature was maintained for 4 h to allow the pitch adsorbed in the voids of the silicon carbide substrate preform to slowly carbonize, while the pitch vapor continued to be adsorbed, gradually increasing the carbon content, and the direct pitch was completely evaporated and reacted.

[0052] (6) The temperature was raised to 1650°C at a rate of 3°C / min, and the temperature was maintained for 3 h to allow the silicon powder to melt and form silicon vapor, which first reacted with the residual carbon in the silicon carbide substrate preform to form silicon carbide, and then filled the voids of the preform to obtain a dense silicon carbide substrate sample, as shown in Figure 3 .

[0053] Example 2

[0054] Preparation of a silicon carbide ceramic substrate:

[0055] (1) First, a 10 g silicon carbide substrate green body was obtained by light-cured 3D printing forming.

[0056] (2) Put the silicon carbide green body into the vacuum debinding furnace, close the door, vacuumize the furnace, 1 Pa, 1 °C / min, heat to 700 °C, keep for 2 h to obtain the silicon carbide substrate preform.

[0057] (3) Put 180 g of silicon powder and 90 g of pitch into a graphite crucible, then put the silicon carbide substrate preform on the powder 5 cm above using a graphite holder, and put it into the middle part of the debinding sintering furnace.

[0058] (4) Heat to 350 °C at 1 °C / min, keep for 4 h, so that the pitch is fully melted and a large amount of steam is adsorbed in the voids of the silicon carbide substrate preform.

[0059] (5) Heat to 600 °C at 1 °C / min, keep for 4 h, the pitch adsorbed in the voids of the silicon carbide substrate preform is slowly carbonized, and the pitch steam continues to be adsorbed, so that the carbon content gradually increases, and the direct pitch is completely evaporated and reacted.

[0060] (6) Heat to 1750 °C at 3 °C / min, keep for 3 h, so that the silicon powder is melted to form silicon vapor, which first reacts with the residual carbon in the silicon carbide substrate preform to form silicon carbide phase, and then fills the voids of the preform through the silicon vapor to obtain a dense silicon carbide substrate sample.

[0061] Comparative Example 1

[0062] The difference between the comparative example and the example is that step (5) is not included. The silicon carbide substrate sample prepared in the comparative example has surface cracks, because the impurities in the pitch are not completely removed, and in the subsequent silicon deposition process, the impurities react to produce gas, which causes cracks in the silicon carbide substrate sample, as shown in Figure 5 .

Claims

1. A reaction-bonding process for silicon carbide ceramics for light solidification molding, characterized by The method comprises the following steps: S1. Preparing a silicon carbide preform; S2. Placing silicon powder and pitch in a container, placing the silicon carbide preform above the silicon powder and pitch, vacuum sintering, so that the pitch volatilizes and deposits in the pores of the silicon carbide preform, the pitch deposited in the pores is impurity-removed, and silicon vapor and carbon are fully reacted again to obtain a dense silicon carbide product; The vacuum sintering conditions in S2 are: First, heat preservation at 250-350℃ for 3-5 hours; Then, heat preservation at 450-600℃ for 3-5 hours; Then, heat preservation at 1600-1750℃ for 3-5 hours; The heating rate at 450-600℃ is 0.5-1.5℃ / min; The heating rate at 250-350℃ is 0.5-1.5℃ / min; The heating rate at 1600-1750℃ is 1-5℃ / min; The preparation method of the silicon carbide preform in S1 is to perform debinding on a silicon carbide ceramic green body, and the debinding is completed to obtain the silicon carbide preform; The silicon carbide ceramic green body is a ceramic slurry prepared from photosensitive resin and silicon carbide, and is obtained by light curing 3D printing.

2. The reaction-bonded method for silicon carbide ceramics for light solidification molding according to claim 1, characterized by, In S2, the silicon carbide preform is placed above the silicon powder and pitch by using a graphite frame.

3. The reaction-bonded method for silicon carbide ceramics for light solidification molding according to claim 2, characterized by, The silicon carbide preform is placed 1-10 cm above the silicon powder and pitch.

4. The reaction-bonded method for silicon carbide ceramics for light solidification molding according to claim 1, characterized by, The debinding conditions in S1 are to heat to 500-700℃ at a rate of 0.5-1.5℃ / min.

5. A silicon carbide ceramic prepared by the reaction bonding method of the silicon carbide ceramic according to any one of claims 1-4.

Images