A special glass solder for reaction-bonded silicon carbide welding, its preparation method, and high-strength welded joints

Abstract

This invention belongs to the field of material joining technology, and provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The invention involves preparing a low-melting-point sodium aluminum borosilicate glass matrix as the molten binder phase, boron-containing amorphous nano-silica powder capable of in-situ self-generating a one-dimensional nanowire reinforcement structure during welding heat treatment, BN-coated silicon hexaboride powder for constructing a macroscopic reinforcing skeleton and optimizing interfacial stress, and active metallic silicon powder as the main thermal expansion regulator and interfacial activator. Subsequently, a special glass solder for reaction-bonded silicon carbide welding is prepared through a stepwise masterbatch mixing process. During welding, a staged adhesive removal, welding, and annealing heat treatment are employed, ultimately forming a dense, reinforced weld between the silicon carbide matrix. The welded joint prepared by this invention exhibits thermal expansion properties highly matched to the matrix and excellent mechanical strength.

Description

Technical Field

[0001] This invention belongs to the field of material joining technology, and relates to a special glass solder for reaction sintering silicon carbide welding, its preparation method, and a high-strength welded joint. Background Technology

[0002] Reaction-bonded silicon carbide (SiC), as an advanced ceramic material with excellent performance, is widely used due to its high hardness, high strength, excellent wear resistance, corrosion resistance, and high-temperature stability. However, the strong covalent bond characteristics of SiC make the fabrication of large or complex-shaped monolithic components exceptionally difficult and costly. Therefore, assembling simple-shaped SiC components into large, complex structures using reliable joining techniques has become a key technological approach to expanding its engineering applications. Currently, methods for joining SiC ceramics mainly include mechanical joining, adhesive bonding, and high-temperature welding. Among these, mechanical joining suffers from stress concentration and poor sealing; organic adhesives cannot meet the requirements of harsh operating conditions such as high temperatures and strong corrosion. Therefore, high-temperature welding, especially using glass solder, has attracted much attention due to its ability to form joints with good airtightness and high bonding strength.

[0003] However, existing glass solder joining technologies still face significant challenges. First, silicon carbide has an extremely low coefficient of thermal expansion, making it difficult for traditional glass solders to precisely match its thermal expansion during cooling. The resulting enormous thermal stress easily leads to joint or substrate cracking, causing connection failure. Second, oxide glasses generally have poor wettability on non-oxide silicon carbide substrates, making it difficult to form a strong interfacial bond. Furthermore, welds formed with conventional glass solders are inherently brittle, lacking sufficient fracture toughness and becoming stress-sensitive during service, making reliability difficult to guarantee. While existing technologies have attempted to introduce microcrystalline phases or inert fillers to improve performance, their effectiveness in simultaneously achieving thermal expansion matching, strong interfacial bonding, and weld toughening is often limited. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength weld joint. The present invention combines four functional components—a low-melting-point glass matrix, active metallic silicon powder, boron-containing amorphous nano-silica powder, and BN-coated silicon hexaboride powder—through a stepwise masterbatch mixing process to obtain a multi-scale composite solder. The welding process involves sequentially performing staged adhesive removal, welding, and annealing heat treatment to meet the needs of actual production.

[0005] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a special glass solder for reaction-bonded silicon carbide welding, the method comprising: S1, quartz powder, boric acid, alumina and anhydrous sodium carbonate are mixed and wet ball-milled, dried to obtain dry powder, and then the dry powder is heat-insulated to obtain sodium aluminum borosilicate glass powder. S2, disperse ethyl silicate and triethyl borate in ethanol to obtain solution A, mix anhydrous ethanol, deionized water and ammonia to obtain solution B, add solution A dropwise to solution B and stir to obtain boron-containing amorphous nano silica powder; S3, silicon hexaboride, ammonia borane and tetrahydrofuran are mixed and stirred under reflux, dried to obtain dry powder, and the dry powder is subjected to a heat preservation process to obtain BN-coated silicon hexaboride powder; S4, mix and wet-mill components A, B, sodium aluminum borosilicate glass powder and metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder. Pour out the slurry after mixing and wet-milling, dry and grind to obtain composite solder powder. Mix and grind the composite solder powder, ethyl cellulose and terpineol, and degas to obtain a special glass solder for reaction sintering silicon carbide welding.

[0006] Specifically, it includes: S1, quartz powder, boric acid, alumina and anhydrous sodium carbonate are mixed and wet ball-milled, poured out, dried and ground to obtain dry powder, then the dry powder is heat-preserved, and after heat preservation, glass blocks are made by water quenching, ground and dried to obtain sodium aluminum borosilicate glass powder. S2, disperse ethyl silicate and triethyl borate in ethanol to obtain solution A, mix anhydrous ethanol, deionized water and ammonia to obtain solution B, add solution A dropwise to solution B, seal and stir to obtain gel precursor, centrifuge, wash and freeze dry the gel precursor to obtain boron-containing amorphous nano silica powder. S3, mix silicon hexaboride, ammonia borane and tetrahydrofuran, under nitrogen atmosphere, reflux and stir at the first temperature, rotary evaporate and dry to obtain dry powder, place the dry powder in a tube furnace under nitrogen protection for heat preservation process to obtain BN coated silicon hexaboride powder. S4, mix and wet-mill components A, B, sodium aluminum borosilicate glass powder and metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder. Pour out the slurry after mixing and wet-milling, dry and grind to obtain composite solder powder. Mix and grind the composite solder powder, ethyl cellulose and terpineol, and degas to obtain a special glass solder for reaction sintering silicon carbide welding.

[0007] In a second aspect, the present invention provides a special glass solder for reaction-bonded silicon carbide welding prepared by the preparation method described in the first aspect.

[0008] Thirdly, the present invention provides a method for preparing a high-strength welded joint, the method comprising: The surface of the sample to be welded is uniformly coated with the special glass solder for reaction sintered silicon carbide welding described in the second aspect. Another sample to be welded is aligned with the welding surface and attached. The assembled assembly is placed in the fixture for positioning, and then the adhesive is removed in stages, welding and annealing heat treatment are performed in sequence to obtain a high-strength reaction sintered silicon carbide welded joint.

[0009] Fourthly, the present invention provides a high-strength welded joint prepared by the preparation method described in the third aspect.

[0010] In the preparation of sodium aluminum borosilicate glass powder, during the heating process, boric acid first undergoes a dehydration reaction, losing its water of crystallization and gradually transforming into boron trioxide. Simultaneously, anhydrous sodium carbonate undergoes a metathesis reaction with silica provided by quartz powder at high temperature, generating sodium silicate and releasing carbon dioxide gas. Sodium silicate further integrates into the glass network constructed by silica and boron trioxide during subsequent heating, with the sodium oxide component distributed in the melt as a network modifier. In the subsequent high-temperature melting stage, silica provided by quartz powder acts as the main network formant, reacting chemically with boron trioxide, alumina, and sodium oxide. Silica and boron trioxide together construct the amorphous network framework of the glass, while alumina enters the network as an intermediate. Sodium oxide acts as a network modifier; its sodium ions can break some silicon-oxygen or boron-oxygen bridges, forming non-bridged oxygen, a process that reduces the degree of polymerization of the glass network and the melting temperature of the system. Water quenching instantly freezes this disordered liquid structure at high temperature, forming a glassy solid.

[0011] For the preparation of boron-containing amorphous silica nanoparticles, in the presence of the alkaline catalyst ammonia, both tetraethyl silicate and triethyl borate precursors participate in the hydrolysis-condensation process. Since the hydrolysis rate of triethyl borate is higher than that of tetraethyl silicate, during the dropwise addition of solution A to solution B, the dropping rate is controlled to maintain a very low instantaneous concentration of triethyl borate in the system, thereby suppressing its tendency for excessively rapid hydrolysis and self-condensation. This allows the newly generated boric acid (or borol) groups to be sufficiently diluted and captured in the silanol group environment formed by the gradual hydrolysis of tetraethyl silicate, promoting the formation of Si-OB chemical bonds rather than the independent aggregation of BOB. In the subsequent sealed stirring stage, condensation reactions occur between the hydrolyzed silanol and borol groups, as well as between these hydroxyl groups and unhydrolyzed ethoxy groups, removing water or ethanol molecules to form silicon-oxygen-silicon, boron-oxygen-boron, and silicon-oxygen-boron chemical bonds. Continuous condensation reactions lead to the formation and growth of a silicon-boron inorganic polymer network, ultimately constituting boron-containing amorphous nanoparticles with boron atoms uniformly doped in the silica framework.

[0012] In the preparation of BN-coated silicon hexaboride powder, during the reflux heating process, the ammonia borane precursor is physically adsorbed and uniformly coated on the surface of the silicon hexaboride particles. In the subsequent high-temperature heat treatment under an inert atmosphere, the partially positively charged hydrogen atoms (usually hydrogen atoms bonded to nitrogen) on the ammonia borane molecules attract the partially negatively charged hydrogen atoms (usually hydrogen atoms bonded to boron) on the adjacent ammonia borane molecules. These two hydrogen atoms combine to form a hydrogen molecule and detach from the system. Simultaneously, a new chemical bond forms between the remaining portions of the two ammonia borane molecules, connecting the two molecules to form a dimer or a longer chain polymer, consisting of alternating boron and nitrogen atoms forming a chain-like, cyclic, or more complex three-dimensional network. During the formation of the polymer network, the original, relatively weak coordination bonds in the ammonia borane molecules gradually transform into more stable and stronger covalent σ bonds during pyrolysis. Because the pyrolysis process is carried out at a relatively low temperature, and the dehydrogenation process may not be complete, the final solid product is structurally disordered. Boron and nitrogen atoms do not have enough time and energy to arrange themselves into a hexagonal boron nitride lattice with a long-range ordered structure. Instead, they form an amorphous network with disordered atomic arrangement.

[0013] In the staged adhesive removal process, the organic carrier undergoes thermal decomposition and combustion under an oxidizing atmosphere. After the atmosphere is switched, the welding stage begins under a micro-oxygen nitrogen atmosphere. First, the low-melting-point component A glass matrix transforms into a liquid phase, wetting and filling the spaces between solid particles through capillary action. As the temperature continues to rise, the free silicon on the surface of component B active metallic silicon powder and the surface of the reaction-sintered silicon carbide substrate oxidizes under controlled micro-oxygen conditions, generating a highly chemically active silicon oxide or sub-silica thin layer in situ. This thin layer rapidly reacts with and integrates into the molten glass phase, forming a strong chemical bond interface between the solder and the substrate. Simultaneously, sodium ions in the molten glass act as a flux or catalyst, forming localized eutectic liquid phase points on the surface of the boron-containing amorphous nano-silica powder. These liquid phase points act as mediators for mass transport, dissolving, diffusing, and reprecipitating from the surrounding solid / glass phase. When supersaturation is reached, this facilitates the formation of elongated fibrous or nanowire-like silicon-rich phases locally. At this temperature, the amorphous boron nitride (BN) shell undergoes a controlled interfacial reaction with the glass liquid phase in a micro-oxygen nitrogen atmosphere: the surface layer of the BN shell is gradually oxidized to B2O3 by trace amounts of oxygen. The generated B2O3 rapidly integrates into the surrounding sodium aluminum borosilicate glass liquid phase, replenishing the boron component of the glass network. Due to the extremely low oxygen partial pressure in the micro-oxygen atmosphere, and the fact that the B2O3 glass layer generated by BN oxidation itself has a certain inhibitory effect on further inward diffusion of oxygen, this oxidation-dissolution process is gradual and self-limiting, and can continue to occur during the welding holding time without instantly depleting the BN coating. This controlled consumption mechanism of the BN coating, on the one hand, effectively releases residual interfacial stress by forming a gradient transition interfacial layer between the silicon hexaboride particles and the glass substrate through volume change; on the other hand, the BN coating provides chemical protection for the silicon hexaboride core before it is completely consumed, preventing direct corrosion reaction between the silicon hexaboride and the oxide glass melt. The silicon hexaboride core ultimately exists in the weld as a stable, low-expansion rigid framework. Its coefficient of thermal expansion is similar to that of the reaction-bonded silicon carbide matrix, which helps to suppress the overall shrinkage mismatch of the weld during cooling. In the final high-temperature homogenization stage, solid particles diffuse to form sintered necks, while the elemental distribution throughout the weld tends to be uniform. The final annealing and slow cooling process is a physical stress release process to ensure that the formed complex composite structure remains intact after cooling.

[0014] In a preferred embodiment of the present invention, in S1, the mass ratio of quartz powder, boric acid, alumina, and anhydrous sodium carbonate is (340-350):(400-420):(80-100):(180-200), for example, it can be (340, 341, 342, 343, 344, 345, 346, 347, 348, 349 or 350):(400, 402, 404). 406, 408, 410, 412, 414, 416, 418 or 420: (80, 82, 84, 86, 88, 90, 92, 94, 96, 98 or 100): (180, 182, 184, 186, 188, 190, 192, 194, 196, 198 or 200), but not limited to the listed values; other unlisted values ​​within this range also apply.

[0015] In some optional embodiments, the wet ball milling time is 4-6 hours, for example, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5.0 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours, or 6.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the heat preservation treatment is as follows: the dry powder is placed in a high-alumina crucible and placed in an air atmosphere resistance furnace, heated to 400-410°C at 3°C / min and held for 1-1.5 hours, then heated to 900-910°C at 3°C / min and held for 1-1.5 hours, and then heated to 1300-1320°C at 3°C / min and held for 1.5-2 hours. For example, it could be: Place the dried powder into a high-alumina crucible, put it in an air atmosphere resistance furnace, and heat it at 3℃ / min to (400, 401, 402, 403, 404, 405, 406, 407, 408, 409, or 410)℃, hold it at that temperature for (1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5) h, then heat it at 3℃ / min to (900, 901, 902, 903, 904, 905, 906, 907, 908, 909, or 910)℃, and hold it at that temperature for (1.0 h). (1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45 or 1.5) h, continue to increase the temperature at 3℃ / min to (1300, 1302, 1304, 1306, 1308, 1310, 1312, 1314, 1316, 1318 or 1320)℃, and hold at that temperature for (1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.9, 1.95 or 2.0) h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0017] In some optional embodiments, the sodium aluminum borosilicate glass powder has a D50 < 5 μm and a D90 < 15 μm.

[0018] As a preferred embodiment of the present invention, in S2, the mass ratio of ethyl silicate, triethyl borate, and ethanol is (42-44):(3-4):200, for example, it can be (42, 42.2, 42.4, 42.6, 42.8, 43.0, 43.2, 43.4, 43.6, 43.8 or 44):(3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9 or 4.0):200, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0019] In some optional embodiments, the mass ratio of anhydrous ethanol, deionized water, and ammonia is 400:(20-22):(40-42), for example, it can be 400:(20, 20.2, 20.4, 20.6, 20.8, 21.0, 21.2, 21.4, 21.6, 21.8 or 22):(40, 40.2, 40.4, 40.6, 40.8, 41.0, 41.2, 41.4, 41.6, 41.8 or 42), but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the mass ratio of the ethyl silicate to anhydrous ethanol is (42-44):400, for example, it can be (42, 42.2, 42.4, 42.6, 42.8, 43.0, 43.2, 43.4, 43.6, 43.8 or 44):400, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0021] In some optional embodiments, the mass fraction of the ammonia water is 25-28 wt.%, for example, it can be 25 wt.%, 25.3 wt.%, 25.6 wt.%, 25.9 wt.%, 26.2 wt.%, 26.5 wt.%, 26.8 wt.%, 27.1 wt.%, 27.4 wt.%, 27.7 wt.%, or 28 wt.%, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0022] In some optional embodiments, the dripping time is 30-60 min, for example, it can be 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0023] In some optional embodiments, the sealed stirring time is 12-13 hours, for example, 12.0 hours, 12.1 hours, 12.2 hours, 12.3 hours, 12.4 hours, 12.5 hours, 12.6 hours, 12.7 hours, 12.8 hours, 12.9 hours, or 13.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0024] As a preferred technical solution of the present invention, in S3, the mass ratio of silicon hexaboride, ammonia borane and tetrahydrofuran is (50-55):(5-6):200, for example, it can be (50, 50.5, 51, 51.5, 52, 52.5, 53, 53.5, 54, 54.5 or 55):(5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0):200, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0025] In some alternative embodiments, the first temperature is 60-65°C, for example, it can be 60°C, 60.5°C, 61°C, 61.5°C, 62°C, 62.5°C, 63°C, 63.5°C, 64°C, 64.5°C or 65°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0026] In some optional embodiments, the reflux stirring time is 4-5 hours, for example, 4.0 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, or 5.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the heat preservation procedure is as follows: the dry powder is placed in an alumina boat, placed in a tube furnace under high-purity nitrogen protection, heated to 500-510°C at 2°C / min, held at this temperature for 2-2.5 hours, and then ground after naturally cooling to room temperature with the furnace. For example, it can be: the dry powder is placed in an alumina boat, placed in a tube furnace under high-purity nitrogen protection, heated to (500, 501, 502, 503, 504, 505, 506, 507, 508, 509 or 510)°C at 2°C / min, held at this temperature for (2.0, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45 or 2.5) hours, and then ground after naturally cooling to room temperature with the furnace. However, this is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0028] As a preferred embodiment of the present invention, in S4, the mass ratio of component A, component B, sodium aluminum borosilicate glass powder, and metallic silicon powder is (15-18):(20-22):10:(45-50), for example, it can be (15, 15.3, 15.6, 15.9, 16.2, 16.5, 16.8, 17.1, 17.4, 17.7 or 18):(20, 20.2, 20.4, 20.6, 20.8, 21.0, 21.2, 21.4, 21.6, 21.8 or 22):10:(45, 45.5, 46, 46.5, 47, 47.5, 48, 48.5, 49, 49.5 or 50), but it is not limited to the listed values; other unlisted values ​​within this range are also applicable. In some optional embodiments, the purity of the metallic silicon powder is not less than 99.5%, the D50 particle size is 4-12μm, the D90 particle size is not greater than 30μm, the particle morphology is irregular polyhedral or spherical, and the surface oxygen content is not greater than 1.0%.

[0029] In some optional embodiments, the mass ratio of boron-containing amorphous nano-silica powder to sodium aluminum borosilicate glass powder in component A is (5-6):10, for example, it can be (5.0, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6.0):10, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the mass ratio of BN-coated silicon hexaboride powder to sodium aluminum borosilicate glass powder in component B is (10-11):10, for example, it can be (10.0, 10.1, 10.2, 10.3, 10.4, 10.5, 10.6, 10.7, 10.8, 10.9 or 11.0):10, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the mass ratio of the composite solder powder, ethyl cellulose and terpineol is (82-83):2:18, for example, it can be (82, 82.1, 82.2, 82.3, 82.4, 82.5, 82.6, 82.7, 82.8, 82.9 or 83):2:18, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] As a preferred technical solution of the present invention, the thickness of the special glass solder for coating reaction sintering silicon carbide welding is 100-150μm, for example, it can be 100μm, 105μm, 110μm, 115μm, 120μm, 125μm, 130μm, 135μm, 140μm, 145μm or 150μm, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the staged debinding process is as follows: In an air atmosphere, the temperature is increased to 450-500°C at a rate of 2°C / min, held for 60-90 minutes, then the oven temperature is reduced to 350-400°C, and the oven is continuously purged with nitrogen for 30-60 minutes. The atmosphere is then adjusted to a micro-oxygen nitrogen atmosphere containing nitrogen and 1000-1500 ppm oxygen. For example, it can be: In an air atmosphere, the temperature is increased to (450, 455, 460, 465, 470, 475, 480, 485, 490, 495, or 500)°C at a rate of 2°C / min, held for (60, 63, 66, 69, 72, 75, 78, 81, 84, 87, or 90) minutes, and then the oven temperature is reduced to (350, 355, 360, 365, 370, 375, 380, 385, 390, 395, or 40) minutes. At 0°C, continuously purge with nitrogen for (30, 33, 36, 39, 42, 45, 48, 51, 54, 57 or 60) min, then adjust to a micro-oxygen nitrogen atmosphere with (1000, 1050, 1100, 1150, 1200, 1250, 1300, 1350, 1400, 1450 or 1500) ppm oxygen. However, this is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the welding is performed as follows: this step immediately follows the staged glue removal step, heating to 850-860°C at a heating rate of 3°C / min, holding at that temperature for 30-40 min, then heating to 1050-1060°C at a heating rate of 3°C / min, holding at that temperature for 60-70 min, and then heating to 1100-1120°C at a heating rate of 3°C / min, holding at that temperature for 15-20 min. For example, this step could be: immediately following the staged glue removal step, heating at a rate of 3℃ / min to (850, 851, 852, 853, 854, 855, 856, 857, 858, 859, or 860)℃, holding at that temperature for (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40) min, and then heating at 3℃ / min to (1050, 1051, 1052, 1053, 1054, 1055, 1056, 1057, 1058, 1059, or 1060)℃. Hold at (60, 61, 62, 63, 64, 65, 66, 67, 68, 69 or 70) min, then increase the temperature at 3℃ / min to (1100, 1102, 1104, 1106, 1108, 1110, 1112, 1114, 1116, 1118 or 1120)℃, and hold at (15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5 or 20) min, but not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0035] In some optional embodiments, the annealing heat treatment is as follows: This step immediately follows the welding step, cooling to 650-700°C at a rate of 3°C / min, holding at that temperature for 30-60 min, and then continuing to cool to below 400°C at a rate of 5°C / min, followed by natural cooling to room temperature in the furnace. For example, this step immediately follows the welding step, cooling to (650, 655, 660, 665, 670, 675, 680, 685, 690, 695 or 700)°C at a rate of 3°C / min, holding at that temperature for (30, 33, 36, 39, 42, 45, 48, 51, 54, 57 or 60) min, and then continuing to cool to below 400°C at a rate of 5°C / min, followed by natural cooling to room temperature in the furnace. However, this is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0036] Compared with existing technologies, the beneficial effects of this invention are as follows: First, by combining active metallic silicon powder, which serves as the main thermal expansion regulator, with BN-coated silicon hexaboride powder, this invention achieves a high degree of matching between the overall thermal expansion coefficient of the solder and the silicon carbide matrix, solving the problem of joint cracking caused by thermal mismatch. Second, this invention utilizes the interfacial activation reaction between the active metallic silicon powder and the substrate during the welding process, as well as the stress buffer and chemical bonding transition layer formed, to enhance the bonding strength between the weld and the substrate. Third, this invention introduces boron-containing amorphous nano-silica powder to improve the fracture toughness and crack propagation resistance of the weld. Finally, through the synergistic design of multiple components, this invention obtains a high-performance welded joint with high strength and high toughness, expanding the application potential of reaction-bonded silicon carbide under extreme working conditions. Attached Figure Description

[0037] Figure 1 Metallographic micrograph of the high-strength welded joint provided in Embodiment 1 of the present invention. Detailed Implementation

[0038] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0039] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment. Example

[0040] This embodiment provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The preparation method specifically includes the following steps: S1, 340g of quartz powder, 420g of boric acid, 80g of alumina and 200g of anhydrous sodium carbonate are mixed and wet-milled for 4 hours. The mixture is then poured out, dried and ground to obtain a dry powder. The dry powder is then subjected to a heat preservation treatment. The heat preservation treatment is as follows: the dry powder is placed in a high-alumina crucible and placed in an air atmosphere resistance furnace. The temperature is increased to 410℃ at 3℃ / min and held for 1 hour. Then the temperature is increased to 900℃ at 3℃ / min and held for 1.5 hours. The temperature is then increased to 1320℃ at 3℃ / min and held for 1.5 hours. After the heat preservation treatment, a glass block is obtained by water quenching. The block is then ground and dried to obtain sodium aluminum borosilicate glass powder. The sodium aluminum borosilicate glass powder has a D50 < 5μm and a D90 < 15μm. S2, 42g of ethyl silicate and 4g of triethyl borate were dispersed in 200g of ethanol to obtain solution A. 400g of anhydrous ethanol, 20g of deionized water and 42g of 25wt.% ammonia water were mixed to obtain solution B. Solution A was added dropwise to solution B over a period of 60min. The mixture was then sealed and stirred for 12h to obtain a gel precursor. The gel precursor was centrifuged, washed and freeze-dried to obtain boron-containing amorphous nano-silica powder. S3, 55g silicon hexaboride, 5g ammonia borane and 200g tetrahydrofuran are mixed, and under a nitrogen atmosphere, the mixture is refluxed and stirred at 65°C for 4 hours. The mixture is then rotary evaporated and dried to obtain a dry powder. The dry powder is placed in a tube furnace under nitrogen protection for a heat preservation process. The heat preservation process is as follows: the dry powder is placed in an alumina boat, placed in a tube furnace under high-purity nitrogen protection, heated to 510°C at 2°C / min, and held for 2 hours. After the furnace is naturally cooled to room temperature, the powder is ground to obtain BN-coated silicon hexaboride powder. S4, mix and wet-mill 180g of component A, 200g of component B, 100g of sodium aluminum borosilicate glass powder and 500g of metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder in a mass ratio of 5:10. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder in a mass ratio of 11:10. The purity of the metallic silicon powder is not less than 99.5%, the D50 particle size is 4μm, the D90 particle size is not greater than 30μm, the particle morphology is irregular polyhedral, and the surface oxygen content is not greater than 1.0%. Pour out the slurry after mixing and wet-milling, dry and grind to obtain composite solder powder. Mix and grind 820g of composite solder powder, 20g of ethyl cellulose and 180g of terpineol, and degas to obtain special glass solder for reaction sintering silicon carbide welding. A special glass solder for reaction-bonded silicon carbide welding is uniformly coated onto the surface of the sample to be welded. The thickness of the coating is 150 μm. Another sample to be welded is aligned with the welding surface and attached. The assembled assembly is placed in a fixture for positioning, and then subjected to staged debonding, welding, and annealing heat treatment. The staged debonding process is as follows: in an air atmosphere, the temperature is increased to 450°C at a rate of 2°C / min, held for 90 min, the furnace temperature is reduced to 400°C, and the furnace is continuously purged with nitrogen for 30 min. Then, the temperature is adjusted to a mixture of nitrogen and 1000 ppm oxygen. Oxygen and nitrogen atmosphere; the welding process is as follows: this step follows the staged glue removal step, heating to 860℃ at a heating rate of 3℃ / min, holding for 30min, then heating to 1060℃ at a heating rate of 3℃ / min, holding for 60min, then heating to 1120℃ at a heating rate of 3℃ / min, holding for 15min; the annealing heat treatment is as follows: this step follows the welding step, cooling to 700℃ at a heating rate of 3℃ / min, holding for 30min, then continuing to cool to below 400℃ at a heating rate of 5℃ / min, and then naturally cooling to room temperature in the furnace to obtain a high-strength welded joint.

[0041] Figure 1 The metallographic micrograph of the high-strength welded joint provided in this embodiment shows that the weld zone is dense, without through-holes or cracks, the glass phase is uniformly distributed, and the weld is well bonded to the matrix. Example

[0042] This embodiment provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The preparation method specifically includes the following steps: S1. Mix 350g of quartz powder, 400g of boric acid, 100g of alumina and 180g of anhydrous sodium carbonate and wet ball mill for 6 hours. Pour out, dry and grind to obtain dry powder. Then, heat-preservation treatment is performed on the dry powder. The heat-preservation treatment is as follows: put the dry powder into a high-alumina crucible, place it in an air atmosphere resistance furnace, heat it to 400℃ at 3℃ / min, hold it for 1.5 hours, then heat it to 910℃ at 3℃ / min, hold it for 1 hour, and continue to heat it to 1300℃ at 3℃ / min, hold it for 2 hours. After heat preservation treatment, glass blocks are obtained by water quenching, grinding and drying to obtain sodium aluminum borosilicate glass powder. The sodium aluminum borosilicate glass powder has D50 < 5μm and D90 < 15μm. S2, 44g of ethyl silicate and 3g of triethyl borate were dispersed in 200g of ethanol to obtain solution A. 400g of anhydrous ethanol, 22g of deionized water and 40g of 28wt.% ammonia water were mixed to obtain solution B. Solution A was added dropwise to solution B over 30min. The mixture was sealed and stirred for 13h to obtain a gel precursor. The gel precursor was centrifuged, washed and freeze-dried to obtain boron-containing amorphous nano-silica powder. S3, 50g silicon hexaboride, 6g ammonia borane and 200g tetrahydrofuran are mixed and stirred under nitrogen atmosphere at 60℃ for 5h under reflux, and then dried by rotary evaporation to obtain dry powder. The dry powder is placed in a tube furnace under nitrogen protection for a heat preservation process. The heat preservation process is as follows: the dry powder is placed in an alumina boat and placed in a tube furnace under high-purity nitrogen protection. The temperature is increased to 500℃ at 2℃ / min and held for 2.5h. After cooling naturally to room temperature with the furnace, it is ground to obtain BN-coated silicon hexaboride powder. S4, mix and wet grind 150g of component A, 220g of component B, 100g of sodium aluminum borosilicate glass powder and 450g of metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder in a mass ratio of 6:10. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder in a mass ratio of 10:10. The purity of the metallic silicon powder is not less than 99.5%, the D50 particle size is 12μm, the D90 particle size is not greater than 30μm, the particle morphology is spherical, and the surface oxygen content is not greater than 1.0%. Pour out the slurry after mixing and wet grinding, dry and grind to obtain composite solder powder. Mix and grind 830g of composite solder powder, 20g of ethyl cellulose and 180g of terpineol, and degas to obtain special glass solder for reaction sintering silicon carbide welding. A special glass solder for reaction-bonded silicon carbide welding is uniformly coated onto the surface of the sample to be welded. The thickness of the coating is 100 μm. Another sample to be welded is aligned with the welding surface and attached. The assembled assembly is placed in a fixture for positioning, and then subjected to staged debonding, welding, and annealing heat treatment. The staged debonding process is as follows: in an air atmosphere, the temperature is increased to 500°C at a rate of 2°C / min, held for 60 min, the furnace temperature is reduced to 350°C, and the furnace is continuously purged with nitrogen for 60 min. Then, the furnace is adjusted to a micro-environment of nitrogen and 1500 ppm oxygen. Oxygen and nitrogen atmosphere; the welding process is as follows: this step follows the staged glue removal step, heating to 850℃ at a heating rate of 3℃ / min, holding for 40min, then heating to 1050℃ at a heating rate of 3℃ / min, holding for 70min, then heating to 1100℃ at a heating rate of 3℃ / min, holding for 20min; the annealing heat treatment is as follows: this step follows the welding step, cooling to 650℃ at a heating rate of 3℃ / min, holding for 60min, then continuing to cool to below 400℃ at a heating rate of 5℃ / min, and then naturally cooling to room temperature in the furnace to obtain a high-strength welded joint. Example

[0043] This embodiment provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The preparation method specifically includes the following steps: S1, 345g of quartz powder, 410g of boric acid, 90g of alumina and 190g of anhydrous sodium carbonate are mixed and wet-milled for 5h. The mixture is then poured out, dried and ground to obtain a dry powder. The dry powder is then subjected to a heat preservation treatment. The heat preservation treatment is as follows: the dry powder is placed in a high-alumina crucible and placed in an air atmosphere resistance furnace. The temperature is increased to 405℃ at 3℃ / min and held for 1.2h. Then the temperature is increased to 905℃ at 3℃ / min and held for 1.2h. The temperature is then increased to 1310℃ at 3℃ / min and held for 1.8h. After the heat preservation treatment, a glass block is obtained by water quenching. The block is then ground and dried to obtain sodium aluminum borosilicate glass powder. The sodium aluminum borosilicate glass powder has a D50 < 5μm and a D90 < 15μm. S2, 43g of ethyl silicate and 3.5g of triethyl borate were dispersed in 200g of ethanol to obtain solution A. 400g of anhydrous ethanol, 21g of deionized water and 41g of 26wt.% ammonia water were mixed to obtain solution B. Solution A was added dropwise to solution B over a period of 45min. The mixture was then sealed and stirred for 12.5h to obtain a gel precursor. The gel precursor was centrifuged, washed and freeze-dried to obtain boron-containing amorphous nano-silica powder. S3, 52g silicon hexaboride, 5.5g ammonia borane and 200g tetrahydrofuran were mixed and stirred under nitrogen atmosphere at 62℃ for 4.5h. The mixture was then rotary evaporated and dried to obtain a dry powder. The dry powder was placed in a tube furnace under nitrogen protection for a heat preservation process. The heat preservation process was as follows: the dry powder was placed in an alumina boat and placed in a tube furnace under high-purity nitrogen protection. The temperature was increased to 505℃ at 2℃ / min and held for 2.2h. After the furnace cooled naturally to room temperature, the powder was ground to obtain BN-coated silicon hexaboride powder. S4, mix and wet grind 165g of component A, 210g of component B, 100g of sodium aluminum borosilicate glass powder and 480g of metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder in a mass ratio of 5.5:10. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder in a mass ratio of 10.5:10. The purity of the metallic silicon powder is not less than 99.5%, the D50 particle size is 6μm, the D90 particle size is not greater than 30μm, the particle morphology is irregular polyhedral, and the surface oxygen content is not greater than 1.0%. Pour out the slurry after mixing and wet grinding, dry and grind to obtain composite solder powder. Mix and grind 825g of composite solder powder, 20g of ethyl cellulose and 180g of terpineol, degas and obtain special glass solder for reaction sintering silicon carbide welding. A special glass solder for reaction-bonded silicon carbide welding is uniformly coated onto the surface of the sample to be welded. The thickness of the coating is 120 μm. Another sample to be welded is aligned with the welding surface and attached. The assembled assembly is placed in a fixture for positioning, and then subjected to staged debonding, welding, and annealing heat treatment. The staged debonding process is as follows: in an air atmosphere, the temperature is increased to 480°C at a rate of 2°C / min and held for 75 min. The furnace temperature is then reduced to 380°C, and the furnace is continuously purged with nitrogen for 45 min. Finally, the furnace is adjusted to a micro-environment of nitrogen and 1200 ppm oxygen. Oxygen and nitrogen atmosphere; the welding process is as follows: this step follows the staged glue removal step, heating to 855℃ at a heating rate of 3℃ / min, holding for 35min, then heating to 1055℃ at a heating rate of 3℃ / min, holding for 65min, then heating to 1110℃ at a heating rate of 3℃ / min, holding for 18min; the annealing heat treatment is as follows: this step follows the welding step, cooling to 680℃ at a heating rate of 3℃ / min, holding for 45min, then continuing to cool to below 400℃ at a heating rate of 5℃ / min, and then naturally cooling to room temperature in the furnace to obtain a high-strength welded joint. Example

[0044] This embodiment provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The preparation method specifically includes the following steps: S1. Mix 342g of quartz powder, 415g of boric acid, 95g of alumina and 195g of anhydrous sodium carbonate and wet ball mill for 4.5h. Pour out, dry and grind to obtain dry powder. Then, heat-preservation treatment is performed on the dry powder. The heat-preservation treatment is as follows: put the dry powder into a high-alumina crucible, place it in an air atmosphere resistance furnace, heat to 408℃ at 3℃ / min, hold for 1.4h, then heat to 908℃ at 3℃ / min, hold for 1.4h, and continue to heat to 1315℃ at 3℃ / min, hold for 1.6h. After heat preservation treatment, glass blocks are obtained by water quenching, grinding and drying to obtain sodium aluminum borosilicate glass powder. The sodium aluminum borosilicate glass powder has D50<5μm and D90<15μm. S2, 43.5g of ethyl silicate and 3.8g of triethyl borate were dispersed in 200g of ethanol to obtain solution A. 400g of anhydrous ethanol, 21.5g of deionized water and 41.5g of 27wt.% ammonia water were mixed to obtain solution B. Solution A was added dropwise to solution B over 50min. The mixture was then sealed and stirred for 12.8h to obtain a gel precursor. The gel precursor was centrifuged, washed, and freeze-dried to obtain boron-containing amorphous nano-silica powder. S3, 54g silicon hexaboride, 5.8g ammonia borane and 200g tetrahydrofuran were mixed and stirred under nitrogen atmosphere at 64℃ for 4.8h. The mixture was then rotary evaporated and dried to obtain a dry powder. The dry powder was placed in a tube furnace under nitrogen protection for a heat preservation process. The heat preservation process was as follows: the dry powder was placed in an alumina boat and placed in a tube furnace under high-purity nitrogen protection. The temperature was increased to 508℃ at 2℃ / min and held for 2.4h. After the furnace cooled naturally to room temperature, the powder was ground to obtain BN-coated silicon hexaboride powder. S4, mix and wet grind 170g of component A, 215g of component B, 100g of sodium aluminum borosilicate glass powder and 460g of metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder in a mass ratio of 5.8:10. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder in a mass ratio of 10.8:10. The purity of the metallic silicon powder is not less than 99.5%, the D50 particle size is 10μm, the D90 particle size is not greater than 30μm, the particle morphology is spherical, and the surface oxygen content is not greater than 1.0%. Pour out the slurry after mixing and wet grinding, dry and grind to obtain composite solder powder. Mix and grind 828g of composite solder powder, 20g of ethyl cellulose and 180g of terpineol, and degas to obtain special glass solder for reaction sintering silicon carbide welding. A special glass solder for reaction-bonded silicon carbide welding is uniformly coated onto the surface of the sample to be welded. The thickness of the coating is 140 μm. Another sample to be welded is aligned with the welding surface and attached. The assembled assembly is placed in a fixture for positioning, and then subjected to staged debonding, welding, and annealing heat treatment. The staged debonding process is as follows: in an air atmosphere, the temperature is increased to 460°C at a rate of 2°C / min and held for 80 min. The furnace temperature is then reduced to 360°C, and the furnace is continuously purged with nitrogen for 50 min. Finally, the furnace is adjusted to a micro-environment of nitrogen and 1400 ppm oxygen. Oxygen and nitrogen atmosphere; the welding process is as follows: this step follows the staged glue removal step, heating to 852℃ at a heating rate of 3℃ / min, holding for 38min, then heating to 1052℃ at 3℃ / min, holding for 68min, then heating to 1115℃ at 3℃ / min, holding for 16min; the annealing heat treatment is as follows: this step follows the welding step, cooling to 660℃ at a rate of 3℃ / min, holding for 50min, then continuing to cool to below 400℃ at a rate of 5℃ / min, and then naturally cooling to room temperature in the furnace to obtain a high-strength welded joint.

[0045] Comparative Example 1 This comparative example provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The difference between this example and Example 1 is that the mass of sodium aluminum borosilicate glass powder in component A of S4 is 0, while other process parameters and operating conditions are exactly the same as in Example 1.

[0046] Comparative Example 2 This comparative example provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The difference between this example and Example 1 is that the mass of boron-containing amorphous nano-silica powder in component A of S4 is 0, while other process parameters and operating conditions are exactly the same as in Example 1.

[0047] Comparative Example 3 This comparative example provides a special glass solder for reaction-bonded silicon carbide welding, its preparation method, and a high-strength welded joint. The difference between this example and Example 1 is that the mass of BN-coated silicon hexaboride powder in component B of S4 is 0, while other process parameters and operating conditions are exactly the same as in Example 1.

[0048] Comparative Example 4 This comparative example provides a special glass solder for reaction sintering silicon carbide welding and a high-strength welded joint and its preparation method. The difference between this example and Example 1 is that, when preparing the high-strength welded joint, the staged debinding, welding and annealing heat treatment are not performed. The temperature is increased to 1100℃ at 10℃ / min and held for 60 minutes. After the holding time is completed, the joint is cooled to room temperature with the furnace. Other process parameters and operating conditions are exactly the same as in Example 1.

[0049] The four-point bending strength (room temperature) test method is ASTM C1161; the four-point bending strength (800℃) test method is ASTM C1211; the joint shear strength test method is ASTM C1469; and the fracture toughness test method is ASTM C1421.

[0050] The test results are shown in Table 1.

[0051] Table 1 Test results of welded joints in Examples 1-4 and Comparative Examples 1-4 Example 1 280 230 78 3.0 Example 2 274 226 76 2.9 Example 3 283 220 79 3.1 Example 4 270 224 78 3.0 Comparative Example 1 214 177 56 2.1 Comparative Example 2 232 193 60 2.3 Comparative Example 3 195 164 52 1.9 Comparative Example 4 148 112 38 1.4 As shown in Table 1, compared with Example 1, the four-point bending strength (room temperature), four-point bending strength (800°C), joint shear strength, and fracture toughness of Comparative Example 1 decreased; the four-point bending strength (room temperature), four-point bending strength (800°C), joint shear strength, and fracture toughness of Comparative Example 2 decreased; the four-point bending strength (room temperature), four-point bending strength (800°C), joint shear strength, and fracture toughness of Comparative Example 3 decreased; and the four-point bending strength (room temperature), four-point bending strength (800°C), joint shear strength, and fracture toughness of Comparative Example 4 decreased.

[0052] This is because the mass of sodium aluminum borosilicate glass powder in component A of Comparative Example 1 is 0, which weakens local liquid phase wetting and adhesion, making it easier to form residual porosity, thus reducing four-point bending, shear strength, and fracture toughness. In Comparative Example 2, the mass of boron-containing amorphous nano-silica powder in component A is 0, lacking a high specific surface area and easily nucleating boron-doped silicon-oxygen framework, making it difficult to form fine and uniform nano-bridging structures in the transition layer, thus reducing structural strength. In Comparative Example 3, the mass of BN-coated silicon hexaboride powder in component B is 0, resulting in a lack of low-expansion, high-stiffness connections within the weld, weakening the thermal expansion coefficient gradient between the glass phase and the substrate, significantly increasing residual tensile stress during thermal cycling and high-temperature stages, and easily generating microcracks near the interface. In Comparative Example 4, without staged glue removal, welding, and annealing heat treatment, the organic carrier decomposes and releases a large amount of gas before the glass softens. The gas is difficult to expel in time, forming closed pores and carbon residue. At the same time, rapid heating and no annealing cooling cause huge thermal stress, and through cracks are prone to appear at the interface. Therefore, the four-point bending, shear strength, and fracture toughness decrease.

[0053] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing a special glass solder for reaction-bonded silicon carbide welding, characterized in that, The preparation method includes: S1, quartz powder, boric acid, alumina and anhydrous sodium carbonate are mixed and wet ball-milled, dried to obtain dry powder, and then the dry powder is heat-insulated to obtain sodium aluminum borosilicate glass powder. S2, disperse ethyl silicate and triethyl borate in ethanol to obtain solution A, mix anhydrous ethanol, deionized water and ammonia to obtain solution B, add solution A dropwise to solution B and stir to obtain boron-containing amorphous nano silica powder; S3, silicon hexaboride, ammonia borane and tetrahydrofuran are mixed and stirred under reflux, dried to obtain dry powder, and the dry powder is subjected to a heat preservation process to obtain BN-coated silicon hexaboride powder; S4, mix and wet-mill components A, B, sodium aluminum borosilicate glass powder and metallic silicon powder. Component A includes boron-containing amorphous nano-silica powder and sodium aluminum borosilicate glass powder. Component B includes BN-coated silicon hexaboride powder and sodium aluminum borosilicate glass powder. Pour out the slurry after mixing and wet-milling, dry and grind to obtain composite solder powder. Mix and grind the composite solder powder, ethyl cellulose and terpineol, and degas to obtain a special glass solder for reaction sintering silicon carbide welding. The mass ratio of boron-containing amorphous nano-silica powder to sodium aluminum borosilicate glass powder in component A is (5-6):10; The mass ratio of BN-coated silicon hexaboride powder to sodium aluminum borosilicate glass powder in component B is (10-11):10; The mass ratio of component A, component B, sodium aluminum borosilicate glass powder to metallic silicon powder is (15-18):(20-22):10:(45-50); The purity of the silicon metal powder is not less than 99.5%, the D50 particle size is 4-12μm, the D90 particle size is not greater than 30μm, the particle morphology is irregular polyhedral or spherical, and the surface oxygen content is not greater than 1.0%.

2. The method for preparing a special glass solder for reaction-bonded silicon carbide welding according to claim 1, characterized in that, In S1: The mass ratio of the quartz powder, boric acid, alumina and anhydrous sodium carbonate is (340-350):(400-420):(80-100):(180-200).

3. The method for preparing a special glass solder for reaction-bonded silicon carbide welding according to claim 1, characterized in that, In S1: The heat preservation treatment is as follows: the dry powder is loaded into a high-alumina crucible, placed in an air atmosphere resistance furnace, heated to 400-410℃ at 3℃ / min, and held for 1-1.5h, then heated to 900-910℃ at 3℃ / min, and held for 1-1.5h, and then heated to 1300-1320℃ at 3℃ / min, and held for 1.5-2h.

4. The method for preparing a special glass solder for reaction-bonded silicon carbide welding according to claim 1, characterized in that, In S2: The mass ratio of ethyl silicate, triethyl borate and ethanol is (42-44):(3-4):200; The mass ratio of anhydrous ethanol, deionized water and ammonia is 400:(20-22):(40-42).

5. The method for preparing a special glass solder for reaction-bonded silicon carbide welding according to claim 1, characterized in that, In S3: The mass ratio of silicon hexaboride, ammonia borane and tetrahydrofuran is (50-55):(5-6):200; The heat preservation process is as follows: place the dry powder in an alumina boat, place it in a tube furnace protected by high-purity nitrogen, heat it to 500-510℃ at 2℃ / min, keep it at that temperature for 2-2.5h, and then grind it after it cools naturally to room temperature with the furnace.

6. The method for preparing a special glass solder for reaction-bonded silicon carbide welding according to claim 1, characterized in that, In S4: The mass ratio of the composite solder powder, ethyl cellulose and terpineol is (82-83):2:

18.

7. A special glass solder for reaction-bonded silicon carbide welding, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

8. A method for preparing a high-strength welded joint, characterized in that, The preparation method includes: The surface of the sample to be welded is coated with the special glass solder for reactive sintered silicon carbide welding as described in claim 7. Another sample to be welded is aligned with the welding surface and attached. The assembled assembly is placed in the fixture for positioning and then subjected to staged glue removal, welding and annealing heat treatment in sequence to obtain a high-strength welded joint. The staged debinding process is as follows: in an air atmosphere, the temperature is increased to 450-500℃ at a rate of 2℃ / min, held for 60-90min, the furnace temperature is reduced to 350-400℃, and the furnace is continuously flushed with nitrogen for 30-60min. Then, the furnace is adjusted to a micro-oxygen nitrogen atmosphere containing nitrogen and 1000-1500ppm oxygen. The welding process is as follows: This step is immediately followed by the staged glue removal step. The temperature is increased to 850-860℃ at a rate of 3℃ / min, and held for 30-40 minutes. Then, the temperature is increased to 1050-1060℃ at a rate of 3℃ / min, and held for 60-70 minutes. Finally, the temperature is increased to 1100-1120℃ at a rate of 3℃ / min, and held for 15-20 minutes. The annealing heat treatment is as follows: This step is immediately after the welding step. The temperature is cooled to 650-700℃ at a rate of 3℃ / min, held for 30-60min, and then cooled to below 400℃ at a rate of 5℃ / min. The temperature is then allowed to cool naturally to room temperature in the furnace.

9. The method for preparing a high-strength welded joint according to claim 8, characterized in that: The thickness of the special glass solder used for coating reactive sintered silicon carbide welding is 100-150 μm.

10. A high-strength welded joint, characterized in that, It is prepared by the preparation method described in claim 8 or 9.

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