Pressureless Sintered Silicon Carbide Ceramics Facilitating Machining and Its Preparation Method

Abstract

The present invention discloses a pressureless sintered silicon carbide ceramic convenient for processing and its preparation method, which relates to the technical field of ceramics. Taking the total mass of the remaining components except the binder, dispersant, plasticizer, lubricant, and water as 100%, the binder, dispersant, plasticizer, lubricant, and water are calculated as percentages of the total mass of the remaining components: 91-95% of α-SiC ultrafine powder, 3-5% of β-SiC ultrafine powder, 0.5-1% of boron carbide micropowder, 0.5-2.5% of carbon fiber, 0.5-2.5% of carbon nanotube, 6-9% of water-soluble phenolic resin as the binder, 0.5-1.5% of dispersant, 1-3% of plasticizer composed of polyvinyl alcohol and carboxymethyl cellulose with a mass ratio of 1:1, 1-3% of lubricant, 100% of water; the total mass of the binder and the plasticizer is 7-10%, and the mass ratio of the binder to the plasticizer is 18:(2-9). The present invention is beneficial to improving the processing precision and processing efficiency of products and reducing processing defects.

Description

Technical Field

[0001] The present invention relates to the field of ceramic technology, and particularly to pressureless sintered silicon carbide ceramics that are easy to process and a preparation method thereof. Background Art

[0002] The outstanding features of pressureless sintered silicon carbide ceramics are superhardness and wear resistance (Mohs hardness reaches 9 - 9.5, close to diamond), high-temperature stability (performance remains stable at 1600°C), chemical corrosion resistance (strong resistance to corrosive media such as acids, alkalis, and molten metals), and good thermal shock resistance (low thermal expansion rate, can withstand rapid temperature changes).

[0003] Pressureless sintered silicon carbide ceramics have a wide range of application fields, mainly including industrial manufacturing (cutting tools, wear-resistant linings, seals), electronics and semiconductors (high-temperature radiators, insulators, precision stages for lithography machines, substrates for energy storage battery modules), national defense and security (bulletproof armor, high-temperature components in aerospace), new energy and environmental protection (furnace linings, crucibles, heat exchangers), etc.

[0004] However, due to the superhardness characteristics of pressureless sintered silicon carbide ceramics themselves, their processing is difficult, the processing time is long, and the finished product rate is low. The formed green bodies are brittle, and it is very easy to cause chipping and corner breakage of the workpieces during the processing, making it difficult to perform pre-processing. At the same time, solid-phase sintering used in the existing technology easily leads to abnormal grain growth (grain size > 10μm), reducing the fracture toughness of the product (about 3.5 MPa·m¹ / ²); the residual bonding phase in liquid-phase sintering (such as the Al 2 O 3 -Y 2 O 3 system) weakens the grain boundary bonding, affects the overall strength of the material, and the mixing of the additive and the silicon carbide powder is uneven, forming an additive enrichment area, resulting in uneven liquid-phase distribution and affecting the densification effect. Although hot-press sintering can improve the density of the product (> 99%), it requires high-pressure equipment and is costly, making it difficult to be applied on a large scale. Obviously, the coarse grains, additive residues, and process limitations of the product are still the core bottlenecks restricting the improvement of its toughness.

[0005] Chinese invention patent CN102537510B discloses a preparation process of a pressureless sintered silicon carbide ceramic valve core. The raw material composition is as follows: 80 - 100 parts by weight of silicon carbide, 0.1 - 1 part of boron carbide powder with a particle size less than 200 mesh, 0.5 - 3 parts of polyvinyl alcohol, an appropriate amount of dispersant, and 0.1 - 1 part of water-soluble polyoxyethylene resin. After the configuration of raw materials, spray granulation, mold loading, pressure forming, drying, rough machining, high-temperature sintering, and finish machining to size, the finished valve core and valve seat are obtained. However, in this preparation process, the added single binder is less, and the strength and toughness of the formed green body are low. Performing pre-processing in advance will cause defects such as chipping and corner breakage of the green body.

[0006] Chinese invention patent CN105198434A discloses a high-performance pressureless sintered silicon carbide bulletproof ceramic and its preparation method. The components and their weight ratios are as follows: 96 - 99 parts of ultra-fine silicon carbide powder, 1 - 2 parts of ultra-fine boron carbide powder, 0.2 - 1 part of nano-titanium boride, 10 - 20 parts of water-soluble phenolic resin, and 0. - 0.5 part of high-efficiency dispersant. After mixing, ball milling, spray granulation, dry pressing, green body curing, and vacuum sintering, the final product is obtained. In the production process of this patent, a large amount of water-soluble phenolic resin and excessive organic binder are used, which will lead to too high viscosity of the slurry, uneven distribution of each raw material during the homogenization process, agglomeration of the slurry, defects in the green body after forming, reduction of the strength and toughness of the material, and defects are also likely to occur during the processing of the green body.

[0007] In summary, it is necessary to develop a new pressureless sintered silicon carbide ceramic and its preparation method to solve the above problems. Summary of the Invention

[0008] The technical problem to be solved by the present invention is: overcoming the deficiencies of the prior art, providing a pressureless sintered silicon carbide ceramic that is easy to process and its preparation method, which not only improves the strength of the green body of the pressureless sintered silicon carbide ceramic, but also has good toughness of the product after sintering. According to the size requirements of the product, pre-processing of the green body can be carried out in advance without breakage, and only simple grinding is required during subsequent finishing to reach the product size, which is beneficial to improving the processing accuracy and efficiency of the product and reducing processing defects.

[0009] The technical solution of the present invention is as follows:

[0010] On the one hand, the present invention provides a pressureless sintered silicon carbide ceramic that is easy to process, including the following components by mass percentage. The total mass of the remaining components except the binder, dispersant, plasticizer, lubricant, and water is counted as 100%, and the binder, dispersant, plasticizer, lubricant, and water are counted as the percentage of the total mass of the remaining components: 91 - 95% of α-SiC ultrafine powder, 3 - 5% of β-SiC ultrafine powder, 0.5 - 1% of boron carbide micropowder, 0.5 - 2.5% of carbon fiber, 0.5 - 2.5% of carbon nanotube, 6 - 9% of binder, 0.5 - 1.5% of dispersant, 1 - 3% of plasticizer, 1 - 3% of lubricant, and 100% of water; the total mass of the binder and the plasticizer is 7 - 10%, and the mass ratio of the binder to the plasticizer is 18:(2 - 9); wherein, the binder is water-soluble phenolic resin, and the plasticizer is a mixture of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) with a mass ratio of 1:1.

[0011] Preferably, the purity of the α-SiC ultrafine powder > 99.5wt.%, and the median diameter is 0.5 - 0.7μm.

[0012] Preferably, the purity of the β-SiC ultrafine powder is >99.5 wt.%, and the median diameter is 0.1-0.2 μm.

[0013] Preferably, the purity of the boron carbide micropowder is >99 wt.%, and the median diameter is 0.5-1 μm; the purity of the carbon fiber is ≥98 wt.%, the diameter is 50-200 nm, and the length is 5-7 μm; the purity of the carbon nanotube is ≥98 wt.%, the diameter is 10-25 nm, and the length is 0.5-0.6 μm.

[0014] Preferably, the dispersant is ammonium polyacrylate.

[0015] Preferably, the lubricant is oleic acid.

[0016] On the other hand, the present invention provides a method for preparing the above-mentioned pressureless sintered silicon carbide ceramic which is easy to process, comprising the following steps:

[0017] S1 Batching and grinding: Add water, binder, dispersant, plasticizer, and lubricant into a stirring mill for grinding, then add boron carbide micropowder, carbon fiber, and carbon nanotube for grinding, and finally add α-SiC ultrafine powder and β-SiC ultrafine powder for grinding;

[0018] S2 Screen the slurry after grinding in step S1 using a sieve;

[0019] S3 Granulate the slurry screened in step S2 to obtain granular material;

[0020] S4 Screen the granular material to obtain granulated powder;

[0021] S5 Isostatically press the granulated powder to obtain a green body;

[0022] S6 Dry the green body;

[0023] S7 Pre-process the dried green body;

[0024] S8 Sinter the pre-processed green body to obtain the pressureless sintered silicon carbide ceramic which is easy to process.

[0025] Preferably, in step S5, the isostatic pressing pressure is 150-200 MPa.

[0026] Preferably, in step S6, the drying temperature is 120-180 °C, and the time is 6-12 h.

[0027] Preferably, in step S8, the sintering process is: at a vacuum degree of 10 -2Under a pressure of [[Pa]], heat from room temperature to 600 - 800 °C at a rate of 20 - 40 °C / h and hold for 4 - 8 h. Subsequently, introduce argon and heat to 2100 - 2250 °C at a rate of 10 - 30 °C / h and hold for 1 - 3 h, then cool naturally to obtain pressureless sintered silicon carbide ceramics that are easy to process.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The pressureless sintered silicon carbide ceramics prepared by the present invention have very high green strength, and the sintered body has a high density (bulk density ≥ 3.13 g / cm 3 ), and at the same time has very high fracture toughness (fracture toughness ≥ 5.6 MPa·m 1 / 2 ), which greatly reduces the pre-processing time of the green body, reduces the complex processing procedures of the sintered product and the phenomenon of chipping and corner breaking during the processing. The finished product rate after fine processing after sintering is ≥ 95%, significantly improving the processing efficiency and product qualification rate.

[0030] 2. The present invention adds water-soluble phenolic resin, polyvinyl alcohol, and carboxymethyl cellulose, which are fully dispersed through high-speed grinding by a stirred mill to form a network structure, enhancing the binding force between powder particles, improving the forming performance and initial strength of the green body after forming, and providing a basic condition for the feasible processing of the green body.

[0031] 3. The present invention adds nano-cubic β-SiC ultrafine powder, so that α-SiC (high-temperature stable type) ultrafine powder and β-SiC (low-temperature stable type) ultrafine powder can form a grain boundary strengthening effect. The fine grains (nanoscale) of β-SiC ultrafine powder can be used as sintering active sites to promote the diffusion reaction between α-SiC ultrafine powder particles; at the same time, the high-temperature stable α-SiC ultrafine powder can inhibit abnormal grain growth, making the sintered body maintain a fine grain structure, thereby improving strength and toughness, and reducing the complex processing procedures of the sintered product, only fine processing is required.

[0032] 4. The present invention adds a composition of boron carbide micropowder, carbon fiber, and carbon nanotubes, which improves toughness by bridging cracks and dispersing stress, thus acting as a toughening agent. Specific Embodiments

[0033] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention.

[0034] Example 1

[0035] The formula of the pressureless sintered silicon carbide ceramics that are easy to process in this example is shown in Table 1, and the preparation method includes the following steps:

[0036] S1 Ingredient grinding: Add water, binder, dispersant, plasticizer, and lubricant into a stirring mill and grind for 1 h. Then add boron carbide micropowder, carbon fiber, and carbon nanotubes and grind for 1 h. Finally, add α-SiC ultrafine powder and β-SiC ultrafine powder and grind for 2 h;

[0037] S2 Use a 180-mesh sieve to screen the slurry after grinding in step S1 to remove agglomerates in the slurry;

[0038] S3 Pour the screened slurry in step S2 into a stirring barrel and start granulation to obtain granular materials;

[0039] S4 Screen the granular materials through an 80-mesh sieve to remove large particles and obtain homogenized granulated powder;

[0040] S5 Pour the granulated powder into a mold and perform isostatic pressing at a forming pressure of 150 MPa to obtain a green body;

[0041] S6 Keep the green body at 120 °C for 8 h for drying;

[0042] S7 Pre-process the dried green body according to the designed shape and size;

[0043] S8 Load the pre-processed green body into a vacuum furnace and protect it with a sagger for sintering: Evacuate to 10 -2 Pa at room temperature, heat up to 800 °C at a rate of 20 °C / h and keep it for 4 h for degreasing, then introduce argon and heat up to 2100 °C at a rate of 30 °C / h and keep it for 3 h, and cool down naturally to obtain pressureless sintered silicon carbide ceramics that are easy to process;

[0044] S9 Perform finish machining on the pressureless sintered silicon carbide ceramics to obtain the required product parts, and the pressureless sintered silicon carbide ceramics do not crack or break corners during the machining process.

[0045] Example 2

[0046] The formula of the pressureless sintered silicon carbide ceramics that are easy to process in this example is shown in Table 1, and the preparation method includes the following steps:

[0047] S1 Ingredient grinding: Add water, binder, dispersant, plasticizer, and lubricant into a stirring mill and grind for 1 h. Then add boron carbide micropowder, carbon fiber, and carbon nanotubes and grind for 1 h. Finally, add α-SiC ultrafine powder and β-SiC ultrafine powder and grind for 2 h;

[0048] S2 Use a 180-mesh sieve to screen the slurry after grinding in step S1 to remove agglomerates in the slurry;

[0049] S3 Pour the screened slurry in step S2 into a stirring barrel and start granulation to obtain granular materials;

[0050] S4 Sieved the granular material through a 80-mesh sieve to remove large particles, obtaining homogenized granulated powder;

[0051] S5 Poured the granulated powder into a mold for isostatic pressing at a forming pressure of 180 MPa to obtain a green body;

[0052] S6 Dried the green body by heat preservation at 150 °C for 12 h;

[0053] S7 Pre-processed the dried green body according to the designed shape and size;

[0054] S8 Loaded the pre-processed green body into a vacuum furnace and protected it with a sagger for sintering: evacuated to 10 -2 Pa at room temperature, heated to 700 °C at a rate of 30 °C / h and held for 6 h for debinding, then introduced argon and heated to 2150 °C at a rate of 20 °C / h and held for 2 h, and cooled naturally to obtain pressureless sintered silicon carbide ceramics convenient for processing;

[0055] S9 Finished machining the pressureless sintered silicon carbide ceramics to obtain the required product parts, and no chipping or corner breakage occurred to the pressureless sintered silicon carbide ceramics during the machining process.

[0056] Example 3

[0057] The formula of the pressureless sintered silicon carbide ceramics convenient for processing in this example is shown in Table 1, and the preparation method includes the following steps:

[0058] S1 Batching and grinding: Added water, binder, dispersant, plasticizer, and lubricant into a stirring mill for grinding for 1 h, then added boron carbide micropowder, carbon fiber, and carbon nanotube for grinding for 1 h, and finally added α-SiC ultrafine powder and β-SiC ultrafine powder for grinding for 2 h;

[0059] S2 Sieved the slurry ground in step S1 through a 180-mesh sieve to remove agglomerates in the slurry;

[0060] S3 Poured the sieved slurry in step S2 into a stirring barrel and started granulation to obtain granular material;

[0061] S4 Sieved the granular material through a 80-mesh sieve to remove large particles, obtaining homogenized granulated powder;

[0062] S5 Poured the granulated powder into a mold for isostatic pressing at a forming pressure of 200 MPa to obtain a green body;

[0063] S6 Dried the green body by heat preservation at 180 °C for 6 h;

[0064] S7 Pre-processed the dried green body according to the designed shape and size;

[0065] Load the pre-processed green body into a vacuum furnace and protect it with a sagger for sintering: evacuate to 10 -2 Pa at room temperature, heat up to 600 °C at a rate of 40 °C / h and hold for 8 h for debinding, then introduce argon and heat up to 2250 °C at a rate of 10 °C / h and hold for 1 h, and cool naturally to obtain pressureless sintered silicon carbide ceramics that are easy to process;

[0066] S9 Finish machining the pressureless sintered silicon carbide ceramics to obtain the required product parts, and the pressureless sintered silicon carbide ceramics do not crack or break during the machining process.

[0067] Example 4

[0068] The formula of the pressureless sintered silicon carbide ceramics that are easy to process in this example is shown in Table 1, and the preparation method includes the following steps:

[0069] S1 Batching and grinding: Add water, binder, dispersant, plasticizer, and lubricant to a stirring mill and grind for 1 h, then add boron carbide micropowder, carbon fiber, and carbon nanotube and grind for 1 h, and finally add α-SiC ultrafine powder and β-SiC ultrafine powder and grind for 2 h;

[0070] S2 Screen the slurry after grinding in step S1 using a 180-mesh sieve to remove agglomerates in the slurry;

[0071] S3 Pour the screened slurry in step S2 into a stirring barrel and start granulation to obtain granular material;

[0072] S4 Screen the granular material through an 80-mesh sieve to remove large particles and obtain homogenized granulated powder;

[0073] S5 Pour the granulated powder into a mold and perform isostatic pressing at a forming pressure of 150 MPa to obtain a green body;

[0074] S6 Keep the green body at 150 °C for 8 h for drying;

[0075] S7 Pre-process the dried green body according to the designed shape and size;

[0076] S8 Load the pre-processed green body into a vacuum furnace and protect it with a sagger for sintering: evacuate to 10 -2 Pa at room temperature, heat up to 700 °C at a rate of 30 °C / h and hold for 6 h for debinding, then introduce argon and heat up to 2200 °C at a rate of 20 °C / h and hold for 3 h, and cool naturally to obtain pressureless sintered silicon carbide ceramics that are easy to process;

[0077] S9 Finish machining the pressureless sintered silicon carbide ceramics to obtain the required product parts, and the pressureless sintered silicon carbide ceramics do not crack or break during the machining process.

[0078] Table 1 Formulation of Pressureless Sintered Silicon Carbide Ceramics Facilitating Processing for Examples 1 - 4

[0079]

[0080] Comparative Examples 1 - 7

[0081] The formulations of the pressureless sintered silicon carbide ceramics for Comparative Examples 1 - 7 are shown in Table 2, and the preparation method is the same as that of Example 1.

[0082] Comparative Examples 8 - 14

[0083] The formulations of the pressureless sintered silicon carbide ceramics for Comparative Examples 8 - 14 are shown in Table 3, and the preparation method is the same as that of Example 1.

[0084] Table 2 Formulation of Pressureless Sintered Silicon Carbide Ceramics for Comparative Examples 1 - 7

[0085]

[0086] Table 3 Formulation of Pressureless Sintered Silicon Carbide Ceramics for Comparative Examples 8 - 14

[0087]

[0088] Perform performance tests on the pressureless sintered silicon carbide ceramics prepared in Examples 1 - 4 and Comparative Examples 1 - 14. The test results are shown in Tables 4 - 6. Among them, the apparent porosity and bulk density are tested in accordance with "GB / T 2997 - 2015 Test Methods for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products", and the fracture toughness is tested in accordance with "GB / T 23806 - 2009 Test Method for Fracture Toughness of Fine Ceramics - Single - Edge Pre - cracked Beam (SEPB) Method".

[0089] Table 4 Performance Test Results of Pressureless Sintered Silicon Carbide Ceramics Facilitating Processing Prepared in Examples 1 - 4

[0090]

[0091] Table 5 Performance Test Results of Pressureless Sintered Silicon Carbide Ceramics Prepared in Comparative Examples 1 - 7

[0092]

[0093] Table 6 Performance Test Results of Pressureless Sintered Silicon Carbide Ceramics Prepared in Comparative Examples 8 - 14

[0094]

[0095] As can be seen from Table 4, the sintered density of the pressureless sintered silicon carbide ceramics prepared in Examples 1-4 of the present invention is high, with the apparent porosity ≤ 0.2% and the bulk density ≥ 3.13 g / cm 3 , and the fracture toughness reaches 5.6 - 5.8 MPa·m 1 / 2 , and the green body is not prone to chipping and corner breakage during the processing of green body and finish machining.

[0096] Compared with Example 1, in Comparative Example 1, an excessive amount of β-SiC ultrafine powder was added, and the toughness of the green body was good, and no chipping and corner breakage occurred during the processing of the green body; however, the excessive β-SiC ultrafine powder would promote the abnormal growth of SiC grains during the sintering process, reduce the strength of the material, hinder the discharge of pores, form closed pores, reduce the density of the material, and was not conducive to the finish machining of the product, and chipping and corner breakage were prone to occur.

[0097] Compared with Example 1, in Comparative Example 2, an excessively small amount of water-soluble phenolic resin and plasticizer were added, resulting in insufficient network structure formation inside the formed green body, reducing the strength of the green body, causing chipping and corner breakage during the processing of the green body, and making it impossible to perform pre-processing on the product.

[0098] Compared with Example 1, in Comparative Example 3, an excessive amount of water-soluble phenolic resin and plasticizer were added, which would lead to too high viscosity of the slurry, uneven distribution of carbon in silicon carbide, local aggregation and growth of silicon carbide particles and pores, and the non-uniformity would damage the grain boundary bonding, cause microcracks and void defects, reduce the fracture toughness of the material, and cause chipping and corner breakage during the processing.

[0099] Compared with Example 1, in Comparative Example 4, an excessively small amount of carbon fiber and carbon nanotube were added, resulting in insufficient toughening phase quantity, uneven distribution around silicon carbide, and difficulty in forming a continuous bridging network, and the material after sintering could not reach the expected toughening effect, and chipping and corner breakage occurred during the processing.

[0100] Compared with Example 1, in Comparative Example 5, an excessive amount of carbon fiber and carbon nanotube were added, resulting in difficulty in their uniform dispersion, easy formation of local stress concentration points, which would significantly increase the microcracks and pore defects inside the material, and these defects might become the preferential paths for crack propagation, instead reducing the fracture toughness; the excessive addition of carbon fiber and carbon nanotube might damage the grain boundary structure, leading to grain coarsening, and grain coarsening would reduce the grain boundary volume fraction, reduce the probability of crack deflection and bridging, thereby weakening the toughness.

[0101] Compared with Example 1, in Comparative Example 6, boron carbide micropowder was not added, and no solution strengthening effect could be achieved during the sintering process, and the material could not be densified, with insufficient density; without the protection of boron carbide, the silicon carbide grains would grow excessively, damaging the strength and toughness of the material, and chipping and corner breakage occurred during the finish machining process.

[0102] Compared with Example 1, in Comparative Example 7, boron carbide micropowder was used instead of carbon fiber and carbon nanotube. After sintering, the product achieved a densification effect, but excessive increase in strength could not significantly achieve a toughening effect, and edge chipping and corner breaking occurred during the processing.

[0103] Compared with Example 1, in Comparative Examples 8 - 10, the mutual substitution of polyvinyl alcohol and carboxymethyl cellulose or the imbalance of their proportions led to the inability to achieve their synergistic effect, the failure to form a strong molecular network, the reduction of the fluidity and plasticity of the granulated powder, the decrease in the strength of the green body after molding, and edge chipping and corner breaking occurred during the processing.

[0104] Compared with Example 1, in Comparative Example 11, the addition amounts of the binder and the plasticizer were excessive, and in Comparative Example 12, the proportion between them was imbalanced, which would lead to too high a consistency of the slurry, uneven distribution of carbon in silicon carbide, local aggregation and growth of silicon carbide particles and pores. The non-uniformity would damage the grain boundary bonding, cause microcracks and void defects, reduce the fracture toughness of the material, and edge chipping and corner breaking occurred during the processing.

[0105] Compared with Example 1, in Comparative Example 13, using water-soluble phenolic resin instead of polyvinyl alcohol and carboxymethyl cellulose would cause too high a viscosity of the slurry, poor fluidity, was not conducive to forming a dense green body during molding, the toughness of the green body was poor, and at the same time, the synergistic regulation of polyvinyl alcohol and carboxymethyl cellulose could not be realized during the sintering heating process, the pyrolysis temperature was too concentrated, causing local overheating and cracking of the green body.

[0106] Compared with Example 1, in Comparative Example 14, using α-SiC ultrafine powder instead of β-SiC ultrafine powder, the activity of the material was not high, densification could not be achieved, there was no volume effect during the high-temperature sintering of β-SiC ultrafine powder, the fracture toughness of the material was reduced, and edge chipping and corner breaking occurred during the material processing.

[0107] In summary, the green body and the finish-machined product of the pressureless-sintered silicon carbide ceramic prepared by the present invention have high density and good toughness, which is beneficial to improving the precision and processing efficiency of the product.

Claims

1. Easy-to-process pressureless sintered silicon carbide ceramics, characterized in that: The invention comprises the following components in percentage by mass, wherein the total mass of the remaining components except the binder, dispersant, plasticizer, lubricant and water is calculated as 100%, and the binder, dispersant, plasticizer, lubricant and water are calculated as the percentage of the total mass of the remaining components: 91-95% of α-SiC ultrafine powder, 3-5% of β-SiC ultrafine powder, 0.5-1% of boron carbide powder, 0.5-2.5% of carbon fiber, 0.5-2.5% of carbon nanotube, 6-9% of binder, 0.5-1.5% of dispersant, 1-3% of plasticizer, 1-3% of lubricant and 100% of water; the total mass of the binder and the plasticizer is 7-10%, and the mass ratio of the binder to the plasticizer is 18:(2-9); wherein the binder is a water-soluble phenolic resin, and the plasticizer is polyvinyl alcohol and carboxymethyl cellulose in a mass ratio of 1:

1.

2. The pressureless sintered silicon carbide ceramic that is easy to process as claimed in claim 1, characterized in that: The purity of the α-SiC ultrafine powder is greater than 99.5wt.%, and the median diameter is 0.5-0.7μm.

3. The pressureless sintered silicon carbide ceramic that is easy to process as claimed in claim 1, characterized in that: The purity of the β-SiC ultrafine powder is greater than 99.5wt.%, and the median diameter is 0.1-0.2μm.

4. The pressureless sintered silicon carbide ceramic that is easy to process as claimed in claim 1, characterized in that: The purity of the boron carbide powder is greater than 99wt.%, with a median diameter of 0.5-1μm; the purity of the carbon fiber is greater than or equal to 98wt.%, with a diameter of 50-200nm and a length of 5-7μm; the purity of the carbon nanotube is greater than or equal to 98wt.%, with a diameter of 10-25nm and a length of 0.5-0.6μm.

5. The pressureless sintered silicon carbide ceramic that is easy to process as claimed in claim 1, characterized in that: The dispersant is ammonium polyacrylate.

6. The pressureless sintered silicon carbide ceramic that is easy to process as claimed in claim 1, characterized in that: The lubricant is oleic acid.

7. The method for preparing pressureless sintered silicon carbide ceramics that is easy to process as claimed in any one of claims 1 to 6, characterized in that: The steps include: S1 Ingredient grinding: add water, binder, dispersant, plasticizer, lubricant into a stirred mill for grinding, then add boron carbide powder, carbon fiber, carbon nanotubes for grinding, and finally add α-SiC ultrafine powder and β-SiC ultrafine powder for grinding; S2 uses a screen to screen the mud ground in step S1; S3 granulating the slurry screened in step S2 to obtain granular material; S4 sieving the granular material to obtain granulated powder; S5 isostatically pressing the granulated powder to obtain a green body; S6 drying the green body; S7 performs pre-processing on the green body after drying; S8 sintering the pre-processed green body to obtain pressureless sintered silicon carbide ceramics that are easy to process.

8. The method for preparing pressureless sintered silicon carbide ceramics that is easy to process as claimed in claim 7, characterized in that: In step S5, the isostatic pressing pressure is 150-200 MPa.

9. The method for preparing pressureless sintered silicon carbide ceramics that is easy to process as claimed in claim 7, characterized in that: In step S6, the drying temperature is 120-180° C. and the drying time is 6-12 hours.

10. The method for preparing pressureless sintered silicon carbide ceramics that is easy to process as claimed in claim 7, characterized in that: In step S8, the sintering process is as follows: at a vacuum degree of 10 -2 Pa, the temperature is raised from room temperature to 600-800°C at a rate of 20-40°C / h and kept for 4-8h, then argon is introduced to raise the temperature to 2100-2250°C at a rate of 10-30°C / h and kept for 1-3h, and the temperature is naturally lowered to obtain pressureless sintered silicon carbide ceramics that are easy to process.

Images