A method for improving the performance of ceramic joints by crystallization of the joint interface surface and its applications

Abstract

The application belongs to the technical field of ceramic materials, and discloses a method for improving the performance of a ceramic connecting piece by surface crystallization of a connecting interface and application thereof. The method comprises the following steps: spraying SiO2-TiO2 powder and MgO-Al2O3-SiO2 glass powder on the surfaces of two SiC ceramic blocks in sequence, respectively; connecting the two pretreated SiC ceramics to form a pre-connected ceramic block; and placing the pre-connected ceramic block in an induction heating furnace and heating to 1500-1600 DEG C to obtain a SiC ceramic connecting piece. The application can effectively promote the crystallization of glass in the connecting layer by covering TiO2 on the surface of the SiC ceramic, significantly improves the performance of the SiC joint, and the prepared joint can be widely applied in the fields of heat engines and nuclear energy.

Description

Technical Field

[0001] This invention belongs to the field of ceramic materials technology, and more specifically, relates to a method for improving the performance of ceramic connectors by surface crystallization at the connection interface and its application. Background Technology

[0002] Silicon carbide (SiC) ceramics, due to their high melting point, high strength, high hardness, high thermal conductivity, and excellent radiation and corrosion resistance, are applicable to fields such as heat engines and nuclear energy. However, due to the inherent brittleness and low self-diffusion coefficient of SiC ceramics, it is difficult to produce large and complex-shaped SiC ceramics using traditional processing methods. Furthermore, because of the high melting point of SiC ceramics, traditional welding techniques are not suitable. Therefore, developing SiC ceramic joining technologies is of great significance. Most joining methods, such as precursor joining and nano-wetting transient eutectic phase (NITE) joining, require high joining pressure and are not suitable for joining complex structural components. Glass joining, as a pressureless joining method with mild joining conditions and controllable coefficient of thermal expansion (CTE) of the joint, can be used for joining complex components such as heat engines.

[0003] Before optimization, the joint strength of glass joints is generally between 30 and 80 MPa, while the joint strength obtained by joining with NITE phase is relatively low. Therefore, it is necessary to improve the joint strength of glass joints. Currently, the mainstream methods to improve the joint strength of glass joints include controlling the composition of glass solder, surface treatment of SiC base material, or low-temperature heat treatment. In terms of controlling glass formulation, the CaO-Al2O3 (CA) system has received widespread attention as a core system, but due to its inherently high CTE, there is a significant difference between it and the SiC base material. Hang et al. developed the CaO-Al2O3-SiO2 (CAS) system by adding SiO2 to the CA system, thereby increasing the shear strength of SiC joints by nearly 87%. Fang et al. introduced Li2O into the CAS system, which improved the crystallinity of the glass and thus obtained higher strength. Wang et al. used CaO-Y2O3-Al2O3-SiO2 as the joint system, obtained a high-strength joint while controlling the CTE of the joint layer, thereby improving the adaptability of the joint layer at high temperatures. Regarding the surface treatment of SiC, Fang et al. proposed a two-step process: first, pre-oxidizing the SiC substrate, followed by using a CaO-Al2O3-SiO2-Li2O (CASL) glass solder system to achieve SiC ceramic bonding and obtain a shear strength of 127 MPa, an increase of 119% compared to the unoxidized state. Ma et al. constructed a Si transition layer on the bonding surface of the SiC substrate using laser cladding technology, improving the wettability of the glass solder and the bonded object, thus enhancing the bonding performance and changing the fracture mode to a collaborative fracture process between the matrix and the bonding layer, rather than just the bonding layer fracture. Zhang et al. performed surface texturing treatment on the SiC substrate, thereby increasing the contact area between the glass filler and the substrate and forming an interlocking structure, thus improving the mechanical properties of the joint. Heat treatment refers to improving the joint performance by controlling the heating, holding, and cooling processes to change the internal microstructure of the material (such as phase composition and crystallinity). Shan et al. performed heat treatment on the CAS system, which significantly improved the mechanical properties of the joint. Furthermore, the joint could still maintain a strength of 85 MPa after high-temperature shearing at 800°C.

[0004] However, the aforementioned studies inevitably introduced more diverse systems when controlling the glass formulation, making the crystallization process and kinetics in the bonding layer more uncontrollable. Furthermore, treating the SiC substrate further complicates the bonding process, and heat treatment significantly increases the bonding time. Pure amorphous glass bonding systems are unstable under long-term high-temperature irradiation or neutron irradiation; MgO-Al2O3-SiO2 (MAS) is a typical amorphous system during the bonding process. Therefore, there is an urgent need to develop convenient and integrated bonding methods to give SiC ceramic connectors higher mechanical strength. Summary of the Invention

[0005] In order to overcome the shortcomings and disadvantages of the existing technology, the purpose of this invention is to provide a method for improving the performance of ceramic connectors by surface crystallization at the connection interface.

[0006] Another object of the present invention is to produce a SiC ceramic connector using the method described above, which has excellent mechanical properties.

[0007] Another object of the present invention is to provide the application of the above-mentioned SiC ceramic connector.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A method for improving the performance of ceramic connectors by surface crystallization at the interface includes the following steps:

[0010] S1. Polish the two SiC ceramic blocks separately using a polishing machine, a polishing disc, and diamond polishing powder to obtain pretreated SiC ceramic blocks;

[0011] S2. Mix SiO2-TiO2 powder with anhydrous ethanol at a mass ratio of 1:(4~5) evenly, and spray it onto the surface of the pretreated SiC ceramic block, and mark it as SiC ceramic block 1.

[0012] S3. Mix MgO-Al2O3-SiO2 glass powder with anhydrous ethanol at a mass ratio of 1:(4~5) evenly, spray it onto the surface of the dry SiC ceramic block 1, and mark it as SiC ceramic block 2.

[0013] S4. Two SiC ceramic blocks 2 are combined to form a pre-connected ceramic block, which is then placed in an induction heating furnace and heated to 1500~1600℃ and held to obtain a SiC ceramic connector.

[0014] Preferably, the SiC ceramic block in step S1 is prepared by liquid phase sintering with Al2O3-Y2O3 as a sintering aid, and the surface roughness of the pretreated SiC ceramic block is less than 0.05.

[0015] Preferably, in step S2, the mass ratio of SiO2 powder to TiO2 powder in the SiO2-TiO2 powder is (17~19):(1~3), and the amount of powder used in the spraying is 10~12 mg / cm³. 3 In step S3, the mass ratio of MgO powder, Al2O3 powder, and SiO2 powder in the MgO-Al2O3-SiO2 glass powder is (1~2):(2~3):(5~7), and the amount of powder used for spraying is 200~300 mg / cm³. 3 .

[0016] Preferably, in step S2, the purity of the SiO2 powder is above 99%, the purity of the TiO2 powder is above 99%, and the particle size of both the SiO2 powder and the TiO2 powder is 1~5 μm; in step S3, the purity of the MgO powder is above 99%, the particle size is 1~5 μm, the purity of the Al2O3 powder is above 99%, the particle size is 100~150 μm, and the purity of the SiO2 powder is above 99%, the particle size is 1~5 μm.

[0017] Preferably, the nozzle diameter of the spray gun used for spraying in steps S2 and S3 is 0.3~0.5 mm.

[0018] Preferably, the heating rate in step S4 is 100~200 ℃ / min, and the holding time is 10~15 min.

[0019] Preferably, the nozzle diameter of the spray gun used for spraying in steps S2 and S3 is 0.3~0.5 mm.

[0020] A SiC ceramic connector is prepared by the method described above.

[0021] Preferably, the SiC ceramic connector has a room temperature shear strength of 100~127 MPa and a shear strength at 800℃ of 95~117.6 MPa.

[0022] The SiC ceramic connector described herein is used in the fields of nuclear energy or thermal engines.

[0023] Compared with the prior art, the present invention has the following beneficial effects;

[0024] 1. The SiC ceramic connector of the present invention promotes the crystallization of the connector layer (joint) at the connection interface through TiO2, resulting in crystallization in the non-crystalline connector layer, and significantly improving the shear performance of the connector layer at high temperature, thus broadening the application range of the connector layer.

[0025] 2. The SiC ceramic connector of the present invention has a room temperature shear strength of 100~127 MPa and a shear strength of 95~124.46 MPa at 800℃, and can be applied to the connection of ceramic parts in heat engines.

[0026] 3. This invention promotes the crystallization of glass powder on the surface of the bonding layer by spraying a typical nucleating agent TiO2 onto the surface of SiC ceramic. However, since pure TiO2 results in poor wettability of glass on the ceramic surface, SiO2, which has better wettability on the ceramic surface, is introduced. The coupling between TiO2 and SiO2 promotes crystallization at the bonding interface without weakening the strength at the bonding interface, thereby improving the high-temperature performance of the bonding layer and maintaining the original bonding strength. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the SiC ceramic connector of the present invention.

[0028] Figure 2 This is an electron microscope image of the connecting layer formed on the surface of the connecting interface in Example 1.

[0029] Figure 3 This is an electron microscope image of the connecting layer at the interface surface without nucleation, as shown in Comparative Example 1. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but these should not be construed as limiting the invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0031] In the embodiments of the present invention, the purity of SiO2 powder is above 99%, the purity of TiO2 powder is above 99%, and the particle size of both SiO2 powder and TiO2 powder is 1~5μm; the purity of MgO powder is above 99%, the particle size is 1~5 μm, the purity of Al2O3 powder is above 99%, the particle size is 100~150μm, and the purity of SiO2 powder is above 99%, the particle size is 1~5 μm. Example 1

[0032] 1. Polish the two SiC ceramic blocks separately using a polishing machine. Use a 400-mesh polishing disc for rough polishing, then use a 1000-mesh iron disc to remove scratches from the surface of the SiC blocks. Finally, use 10-mesh, 5-mesh, and 2.5-mesh diamond polishing powders in combination with polishing cloth discs for polishing to obtain pretreated SiC ceramic blocks.

[0033] 2. SiO2 and TiO2 powders with a mass ratio of 17:3 were magnetically stirred or ultrasonically vibrated. SiO2-TiO2 powders with a mass ratio of 1:4 were then mixed uniformly with anhydrous ethanol to obtain a slurry. The spraying amount of SiO2-TiO2 was 10 mg / cm³. 3 The slurry was sprayed (using a spray gun with a nozzle diameter of 0.3 mm) onto the surface of the pretreated SiC block and marked as SiC ceramic block 1.

[0034] 3. MgO-Al2O3-SiO2 glass powder (MgO, Al2O3, and SiO2 mass percentages of 10%:20%:70%) was mixed with anhydrous ethanol in a mass ratio of 1:4 using magnetic stirring until homogeneous. A 200 mg / cm³ solution was then sprayed onto the surface of the SiC ceramic block 1, which had been dried at 80℃ for 24 hours. 3 The glass powder was labeled as SiC ceramic bulk 2.

[0035] 4. After merging the sprayed surfaces of two SiC ceramic blocks 2, they are bonded together with adhesive tape to form a pre-connected ceramic block. The pre-connected ceramic block is placed in a tungsten carbide mold and heated in an induction heating furnace at 1500℃ for 15 minutes to obtain a SiC ceramic connector, the structure of which is as follows. Figure 1 As shown, SiO2-TiO2 and MgO-Al2O3-SiO2 glass (MAS) are sequentially sprayed onto each SiC ceramic (SiC base material).

[0036] Comparative Example 1

[0037] 1. Polish the two SiC ceramic blocks separately using a polishing machine. Use a 400-mesh polishing disc for rough polishing, then use a 1000-mesh iron disc to remove scratches from the surface of the SiC blocks. Finally, use 10-mesh, 5-mesh, and 2.5-mesh diamond polishing powders in combination with polishing cloth discs for polishing to obtain pretreated SiC ceramic blocks.

[0038] 2. Mix MgO-Al2O3-SiO2 glass powder (MgO, Al2O3, and SiO2 in a mass ratio of 10%:20%:70%) with anhydrous ethanol using magnetic stirring until homogeneous. Then, spray a 200 mg / cm³ mixture onto the surface of the pretreated SiC ceramic block. 3 The glass powder was labeled as SiC ceramic bulk 3;

[0039] 3. After merging two SiC ceramic blocks 3, they are glued together with adhesive tape to form a pre-connected ceramic block. The pre-connected ceramic block is placed in a tungsten carbide mold and placed in an induction heating furnace and kept at 1500℃ for 15 minutes to obtain the SiC ceramic connector.

[0040] The SiC ceramic connector prepared in Example 1 has a dense bonding layer. The SiC ceramic connector has a room temperature shear strength of 100 MPa and a high temperature shear performance retention rate of 95% at 800℃, with a shear strength of 95 MPa. Figure 2 Electron micrographs of the connecting layer nucleated at the interface surface in Example 1 are shown. (a) is a low-magnification (500) electron microscope image, and (b) is a high-magnification (1500) electron microscope image. Figure 2 As can be seen, a crystalline phase exists at the interface and grows along the interface. Figure 3 The images shown are electron microscope (EM) images of the connecting layer at the interface surface without nucleation in Comparative Example 1. (a) is a low-magnification (1500) EEM image, and (b) is a high-magnification (2500) EEM image. Figure 3 As can be seen, the bonding between the surface of the connecting layer and the interface is good at this time, but no crystalline phase is found at the connecting interface. Example 2

[0041] The difference from Example 1 is that the SiO2-TiO2 spraying amount in step 2 is 10 mg / cm². 3 The mass ratio of SiO2 to TiO2 is 19:1, and the spraying amount of MgO-Al2O3-SiO2 glass powder in step 3 is 200 mg / cm³. 3 The mass percentages of MgO, Al2O3 and SiO2 in the MgO-Al2O3-SiO2 glass powder are 15%:20%:65%, and the joining temperature in step 4 is 1500℃, resulting in a SiC ceramic connector.

[0042] The SiC ceramic connector prepared in this embodiment has a room temperature shear strength of 107 MPa; at a high temperature of 800℃, the shear performance retention rate is 97%, and the shear strength is 104 MPa. Example 3

[0043] The difference from Example 1 is that the SiO2-TiO2 spraying amount in step 2 is 12 mg / cm². 3 The mass ratio of SiO2 to TiO2 is 19:1, and the spraying amount of MgO-Al2O3-SiO2 glass powder in step 3 is 300 mg / cm³. 3 The mass percentages of MgO, Al2O3 and SiO2 in the MgO-Al2O3-SiO2 glass powder are 15%:25%:60%, and the bonding temperature in step 4 is 1500℃, resulting in a SiC ceramic connector.

[0044] The SiC ceramic connector prepared in this embodiment has a room temperature shear strength of 112 MPa; at a high temperature of 800℃, the shear performance retention rate is 96%, and the shear strength is 107 MPa. Example 4

[0045] The difference from Example 1 is that the SiO2-TiO2 spraying mass in step 2 is 12 mg / cm³. 3 The mass ratio of SiO2 to TiO2 is 19:1, and the weight of the MgO-Al2O3-SiO2 glass powder sprayed in step 3 is 200 mg / cm³. 3 The mass percentages of MgO, Al2O3 and SiO2 in the MgO-Al2O3-SiO2 glass powder are 20%:20%:60%, and the joining temperature in step 4 is 1600℃, resulting in a SiC ceramic connector.

[0046] The SiC ceramic connector prepared in this embodiment has a room temperature shear strength of 120 MPa; at a high temperature of 800℃, the shear performance retention rate is 98%, and the shear strength is 117.6 MPa.

[0047] The SiC ceramic connector of this invention has a room temperature shear strength of 100~127 MPa and a shear strength of 95~124.46 MPa at 800℃, and can be applied to the connection of ceramic parts in heat engines.

[0048] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for improving the performance of ceramic connectors by surface crystallization at the interface, characterized in that, Includes the following steps: S1. Polish the two SiC ceramic blocks separately using a polishing machine, a polishing disc, and diamond polishing powder to obtain pretreated SiC ceramic blocks; S2. SiO2 powder and TiO2 powder in a mass ratio of (17~19):(1~3) are magnetically stirred or ultrasonically vibrated to obtain SiO2-TiO2 powder. The SiO2-TiO2 powder in a mass ratio of 1:(4~5) is mixed uniformly with anhydrous ethanol and sprayed onto the surface of a pretreated SiC ceramic block, which is then labeled as SiC ceramic block 1. The amount of the sprayed powder is 10~12 mg / cm³. 3 ; S3. Mix MgO-Al2O3-SiO2 glass powder with anhydrous ethanol at a mass ratio of 1:(4~5) until homogeneous, and spray the mixture onto the surface of a dry SiC ceramic block 1 to mark it as SiC ceramic block 2; the mass ratio of MgO powder, Al2O3 powder and SiO2 powder in the MgO-Al2O3-SiO2 glass powder is (1~2):(2~3):(5~7), and the spraying dosage is 200~300 mg / cm³. 3 ; S4. Two SiC ceramic blocks 2 are combined to form a pre-connected ceramic block, and then placed in an induction heating furnace and heated to 1500~1600℃ and held at that temperature to obtain a SiC ceramic connector; the heating rate is 100~200 ℃ / min, and the holding time is 10~15 min.

2. The method for improving the performance of ceramic connectors by surface crystallization at the connection interface according to claim 1, characterized in that, In step S2, the purity of SiO2 powder is above 99%, the purity of TiO2 powder is above 99%, and the particle size of both SiO2 powder and TiO2 powder is 1~5μm; in step S3, the purity of MgO powder is above 99%, the particle size is 1~5μm, the purity of Al2O3 powder is above 99%, the particle size is 100~150μm, and the purity of SiO2 powder is above 99%, the particle size is 1~5μm.

3. The method for improving the performance of ceramic connectors by surface crystallization at the connection interface according to claim 1, characterized in that, The nozzle diameter of the spray gun used for spraying in steps S2 and S3 is 0.3~0.5mm.

4. A SiC ceramic connector, characterized in that, The ceramic connector is made by the method described in any one of claims 1-3.

5. The SiC ceramic connector according to claim 4, characterized in that, The SiC ceramic connector has a room temperature shear strength of 100~127 MPa and a shear strength of 95~117.6 MPa at 800℃.

6. The application of the SiC ceramic connector as described in claim 4 or 5 in the field of nuclear energy or thermal engines.

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