Polymer recrystallized silicon carbide ReSic product system and preparation method thereof

Abstract

The invention relates to the technical field of material science, in particular to a macromolecular recrystallized silicon carbide ReSic product system and a preparation method thereof.The preparation method comprises the following steps that S1, a macromolecular precursor of boron-containing modified polycarbosilane and nano silicon carbide seed crystals are subjected to mechanochemical activation treatment; s2, preparing a biscuit with a directional arrangement characteristic; s3, carrying out isostatic pressing treatment on the biscuit; s4, carrying out gradient heating crosslinking treatment on the densified biscuit; s5, performing staged pyrolysis on the cross-linked biscuit in an inert atmosphere; s6, permeating a silicon carbide nanowire reinforcement into the porous silicon carbide skeleton; s7, carrying out silicon steam assisted directional recrystallization treatment on the composite reinforced skeleton; and S8, the grain boundary purification body is subjected to densification treatment, and finally the ReSic product is obtained. According to the preparation method, the density, the uniformity and the mechanical property of the silicon carbide material are effectively improved through innovative polymer recrystallization, silicon steam-assisted directional recrystallization and electromagnetic field-assisted sintering processes.

Description

Technical Field

[0001] The present invention relates to the field of material science and technology, and in particular to a polymer recrystallized silicon carbide (ReSic) product system and a preparation method thereof. Background Art

[0002] With the continuous development of science and technology and industry, silicon carbide (SiC) materials have been widely used in aerospace, electronic equipment, mechanical manufacturing and energy fields due to their excellent high temperature resistance, corrosion resistance, oxidation resistance and other properties; however, traditional silicon carbide preparation methods usually use high-temperature pyrolysis, vapor deposition and other processes. Although silicon carbide materials with certain properties can be obtained, there are still problems such as uneven grain size and distribution, low material density and easy damage to grain boundaries. These problems seriously affect the mechanical properties, thermal stability and conductivity of silicon carbide materials.

[0003] In the existing technology, phenomena such as grain growth, pore formation and grain boundary degradation during the preparation process often lead to unstable material properties, thereby limiting its further promotion in high-end applications; therefore, how to improve the existing silicon carbide preparation process, solve the problems in traditional methods, and improve the performance of silicon carbide materials, especially optimize its microstructure, and improve the material's density, grain distribution uniformity and overall mechanical properties, has become a major challenge facing the current technology field. Summary of the invention

[0004] Based on the above objectives, the present invention provides a polymer recrystallized silicon carbide (ReSic) product system and a preparation method thereof.

[0005] A method for preparing a polymer recrystallized silicon carbide (ReSic) product comprises the following steps:

[0006] S1: subjecting the polymer precursor of boron-modified polycarbosilane and the nano-silicon carbide seed to mechanochemical activation treatment, and outputting the pre-treated slurry;

[0007] S2: The pretreated slurry is processed into a green blank with directional arrangement characteristics through a tape casting process;

[0008] S3: performing isostatic pressing on the green billet to obtain a densified green billet;

[0009] S4: performing gradient temperature rise cross-linking treatment on the densified green billet to output a cross-linked green billet having a three-dimensional cross-linked network structure;

[0010] S5: pyrolyzing the cross-linked green blank in an inert atmosphere in stages to generate a porous silicon carbide skeleton containing β-SiC crystal nuclei;

[0011] S6: Infiltrating silicon carbide nanowire reinforcement into the porous silicon carbide skeleton to output a composite reinforcement skeleton;

[0012] S7: performing silicon vapor-assisted directional recrystallization treatment on the composite reinforcement skeleton to output a grain boundary purified body;

[0013] S8: The grain boundary purification body is densified by using an electromagnetic field assisted gradient sintering process to finally obtain a ReSic product.

[0014] Optionally, the S1 specifically includes:

[0015] S11: mixing a polymer precursor containing boron-modified polycarbosilane and nano-silicon carbide seeds in a ratio of 9:1 to 9.8:1 to obtain an initial mixture;

[0016] S12: placing the initial mixture in a ball mill for mechanochemical activation treatment, the rotation speed of the ball mill is set to 200-500 rpm, the treatment time is 30-90 minutes, the diameter of the ball milling medium is 5-10 mm, and the mass ratio of the ball milling medium to the mass of the mixture is 10:1 to 20:1;

[0017] S13: After the mechanochemical activation treatment, a pre-treated slurry is obtained, the viscosity of the pre-treated slurry is controlled to be 500-1500 mPa·s, and the solid content of the slurry is 30%-50%.

[0018] Optionally, the S2 specifically includes:

[0019] S21: evenly coating the pre-treated slurry on the substrate of the tape casting equipment, with a coating thickness of 0.5-5 mm, ensuring that the slurry is evenly covered;

[0020] S22: stretching the coated pretreated slurry through a tape casting device at a stretching speed of 2-10 cm / min;

[0021] S23: Preliminarily cooling the stretched slurry to solidify it into a shape, with a cooling rate of 5-20°C / min, to obtain a green blank with directional arrangement characteristics.

[0022] Optionally, the S3 specifically includes:

[0023] S31: placing the green billet obtained in S2 in an isostatic pressing device;

[0024] S32: in an isostatic pressing device, applying a uniform static pressure in the range of 30-50 MPa for a processing time of 30-60 minutes;

[0025] S33: During the isostatic pressing process, the temperature is controlled to be 150-250°C;

[0026] S34: After the treatment is completed, the pressure is slowly reduced, and the densified green billet is taken out and its density is controlled to 1.5-2.0g / cm3 .

[0027] Optionally, the S4 specifically includes:

[0028] S41: placing the densified green billet obtained in S3 in a heating furnace, setting the furnace atmosphere to nitrogen or argon, and the gas flow rate to 50-100 mL / min;

[0029] S42: The densified green billet is gradually heated at a rate of 2-5°C / min from room temperature to 500°C;

[0030] S43: During the heating process, controlling the temperature range to ensure that the temperature is stable at 500° C., and maintaining the stable temperature for 1-3 hours to promote the cross-linking reaction and form a three-dimensional cross-linked network structure;

[0031] S44: After the treatment is completed, the temperature is slowly lowered to room temperature to obtain a cross-linked blank having a three-dimensional cross-linked network structure.

[0032] Optionally, the S5 specifically includes:

[0033] S51: placing the cross-linked green blank obtained in S4 in a pyrolysis furnace, setting the atmosphere in the furnace to an inert gas, wherein the inert gas used is argon or nitrogen, and the gas flow rate is 100-200 mL / min;

[0034] S52: The cross-linked green blank is subjected to pyrolysis treatment in stages. In the first stage, the green blank is heated to 600° C. at a heating rate of 3-5° C. / min and maintained at the temperature for 3-5 hours to remove organic components and preliminarily form β-SiC crystal nuclei.

[0035] S53: In the second stage, the temperature is heated to 1200°C at a heating rate of 3-5°C / min, and the temperature is maintained for 3-5 hours to promote the generation of β-SiC nuclei and the formation of a porous structure;

[0036] S54: The third stage is heating to 1800°C at a heating rate of 2-3°C / min, maintaining the temperature for 3-5 hours to complete the pyrolysis process;

[0037] S55: After the pyrolysis treatment is completed, the temperature is slowly lowered to room temperature to obtain a porous silicon carbide skeleton containing β-SiC crystal nuclei, and the porosity of the skeleton is 30%-50%.

[0038] Optionally, the S6 specifically includes:

[0039] S61: placing the porous silicon carbide skeleton containing β-SiC crystal nuclei obtained in S5 in an infiltration device and preheating it to 200-300° C. to ensure that the skeleton temperature is uniform;

[0040] S62: preparing a silicon carbide nanowire reinforcement, wherein the silicon carbide nanowire has a diameter of 2-10 nanometers, a length of 50-300 nanometers, and a concentration of 1-10 wt %;

[0041] S63: dissolving the silicon carbide nanowire reinforcement in an organic solvent to form a reinforcement solution with a concentration of 2-10 wt %, and placing the reinforcement solution and the porous silicon carbide skeleton in a vacuum infiltration device;

[0042] S64: applying negative pressure in a vacuum environment, the negative pressure range is -0.1 to -0.3 MPa, so that the reinforcing liquid fully penetrates into the pores of the porous silicon carbide skeleton, and the penetration time is 1 to 3 hours;

[0043] S65: After the infiltration is completed, a composite reinforced skeleton is obtained, wherein the nanowire content of the composite reinforced skeleton is 10%-30%.

[0044] Optionally, the S7 specifically includes:

[0045] S71: placing the composite reinforced skeleton obtained in S6 in a silicon vapor assisted recrystallization device, setting the atmosphere in the device to a mixed gas of silicon vapor and argon, with a silicon vapor concentration of 5%;

[0046] S72: heating the composite reinforced skeleton to 1500° C.-1700° C., with a heating rate of 3-5° C. / min, and controlling the treatment time to 1-3 hours, so as to promote the reaction between the silicon vapor and the skeleton;

[0047] S73: During the recrystallization process, controlling the flow direction of the silicon vapor to ensure that the recrystallization process is directional so as to promote the growth of crystal grains along a predetermined direction;

[0048] S74: After the treatment is completed, the temperature is slowly lowered to room temperature to obtain a grain boundary purified body, wherein the grain size of the grain boundary purified body is 5-30 microns.

[0049] Optionally, the S8 specifically includes:

[0050] S81: placing the grain boundary purified body obtained in S7 in an electromagnetic field assisted sintering device, wherein the atmosphere in the device is argon gas, and the gas flow rate is 100-150 mL / min;

[0051] S82: Gradient heating is performed on the grain boundary purifier through an electromagnetic field assisted sintering process, and the temperature is set to gradually increase from 1100°C to 2000°C, with a heating rate of 5-10°C / min;

[0052] S83: During the heating process, an electromagnetic field with a frequency of 50-100 kHz and an electric field strength of 1-3 kV / cm is applied to promote directional growth and densification of grains;

[0053] S84: maintaining the temperature at 2000° C. for 30-60 minutes to complete the sintering process;

[0054] S85: After sintering, slowly cool down to room temperature to finally obtain ReSic products with a bending strength of 300-500MPa and a hardness of 9-10HRC.

[0055] A polymer recrystallized silicon carbide ReSic product system is used to implement the above-mentioned method for preparing a polymer recrystallized silicon carbide ReSic product, including the following modules:

[0056] Pretreatment module: used to perform mechanochemical activation treatment on the polymer precursor of boron-modified polycarbosilane and nano-silicon carbide seeds, and output pretreatment slurry;

[0057] Tape casting module: used to process the pre-treated slurry into a green blank with directional arrangement characteristics through a tape casting process;

[0058] Green billet densification module: used to perform cold isostatic pressing on green billets and output densified green billets;

[0059] Pre-crosslinking module: used to perform gradient temperature-raising crosslinking treatment on the densified green billet, and output a crosslinked green billet with a three-dimensional crosslinked network structure;

[0060] Pyrolysis module: used to pyrolyze the cross-linked green blank in stages in an inert atmosphere to generate a porous silicon carbide skeleton containing β-SiC crystal nuclei;

[0061] Skeleton infiltration module: used to infiltrate silicon carbide nanowire reinforcement into the porous silicon carbide skeleton and output a composite reinforced skeleton;

[0062] Recrystallization module: used to carry out silicon vapor-assisted directional recrystallization treatment on the composite reinforcement skeleton and output a grain boundary purified body;

[0063] Sintering module: It is used to densify the grain boundary purification body by electromagnetic field assisted gradient sintering technology to finally obtain ReSic products.

[0064] Beneficial effects of the present invention:

[0065] The present invention effectively solves the common problems of grain growth, excessive porosity and grain boundary degradation in the preparation process of traditional silicon carbide materials by introducing innovative processes such as polymer recrystallization technology, silicon vapor-assisted directional recrystallization and electromagnetic field-assisted sintering. By precisely controlling the microstructure of silicon carbide, the present invention can significantly improve the density, uniformity and mechanical properties of silicon carbide materials, thereby effectively improving the flexural strength, hardness and thermal stability of silicon carbide.

[0066] The present invention realizes an efficient and repeatable production process through precise process control, avoiding the high energy consumption and high cost problems in traditional methods; and also introduces an electromagnetic field assisted sintering process, which not only improves the sintering efficiency but also improves the directional growth of grains, thereby further optimizing the performance of silicon carbide. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0068] Figure 1 Schematic diagram of a method for preparing a ReSic product according to an embodiment of the present invention;

[0069] Figure 2 Schematic diagram of a ReSic product system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0070] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. At the same time, it is explained here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments, and those skilled in the art may also adopt other alternatives to implement some known technologies; and the accompanying drawings are only for more specific description of the embodiments, and are not intended to specifically limit the present invention.

[0071] It should be noted that the references to "one embodiment", "an embodiment", "an exemplary embodiment", "some embodiments" and the like in the specification indicate that the embodiments described may include specific features, structures or characteristics, but not every embodiment may include the specific features, structures or characteristics. In addition, when a specific feature, structure or characteristic is described in conjunction with an embodiment, it should be within the knowledge of a person skilled in the art to implement such feature, structure or characteristic in conjunction with other embodiments (whether or not explicitly described).

[0072] In general, a term can be understood, at least in part, from its use in context. For example, depending, at least in part, on the context, the term "one or more" as used herein can be used to describe any feature, structure, or characteristic in the singular sense, or can be used to describe a combination of features, structures, or characteristics in the plural sense. Additionally, the term "based on" can be understood as not necessarily intended to convey an exclusive set of factors, but can instead, depending, at least in part, on the context, allow for the presence of other factors that are not necessarily explicitly described.

[0073] Example 1

[0074] like Figure 1 As shown, a method for preparing a polymer recrystallized silicon carbide ReSic product comprises the following steps:

[0075] S1: subjecting the polymer precursor of boron-modified polycarbosilane and the nano-silicon carbide seed to mechanochemical activation treatment, and outputting the pre-treated slurry;

[0076] S2: The pretreated slurry is processed into a green blank with directional arrangement characteristics through a tape casting process;

[0077] S3: performing isostatic pressing on the green billet to obtain a densified green billet;

[0078] S4: performing gradient temperature rise cross-linking treatment on the densified green billet to output a cross-linked green billet having a three-dimensional cross-linked network structure;

[0079] S5: pyrolyzing the cross-linked green blank in an inert atmosphere in stages to generate a porous silicon carbide skeleton containing β-SiC crystal nuclei;

[0080] S6: Infiltrating silicon carbide nanowire reinforcement into the porous silicon carbide skeleton to output a composite reinforcement skeleton;

[0081] S7: performing silicon vapor-assisted directional recrystallization treatment on the composite reinforcement skeleton to output a grain boundary purified body;

[0082] S8: The grain boundary purification body is densified by using an electromagnetic field assisted gradient sintering process to finally obtain a ReSic product.

[0083] S1 specifically includes:

[0084] S11: mixing a polymer precursor containing boron-modified polycarbosilane and a nano-silicon carbide seed crystal in a ratio of 9.5:1 to obtain an initial mixture;

[0085] S12: placing the initial mixture in a ball mill for mechanochemical activation treatment, the rotation speed of the ball mill is set to 300 rpm, the treatment time is 60 minutes, the diameter of the ball milling medium is 8 mm, and the mass ratio of the ball milling medium to the mass of the mixture is 15:1;

[0086] S13: After the mechanochemical activation treatment, a pretreated slurry is obtained, the viscosity of the pretreated slurry is controlled to be 1200 mPa·s, and the solid content of the slurry is 40%.

[0087] S2 specifically includes:

[0088] S21: evenly coating the pre-treated slurry on the substrate of the tape casting equipment with a coating thickness of 3 mm to ensure even coverage of the slurry;

[0089] S22: stretching the coated pretreated slurry through a tape casting device at a stretching speed of 5 cm / min;

[0090] S23: Preliminarily cool the stretched slurry to solidify it into a shape, with a cooling rate of 10°C / min, to obtain a green blank with directional arrangement characteristics.

[0091] S3 specifically includes:

[0092] S31: placing the green billet obtained in S2 in an isostatic pressing device, ensuring that the green billet is evenly placed and in good contact with the wall of the device;

[0093] S32: in an isostatic pressing device, applying a uniform static pressure in a range of 40 MPa for a processing time of 45 minutes to promote densification of the green billet;

[0094] S33: During the isostatic pressing process, the temperature is controlled to be 200° C. to avoid premature pyrolysis or deformation of the green billet;

[0095] S34: After the treatment is completed, the pressure is slowly reduced, and the densified green billet is taken out and its density is controlled to 1.8g / cm 3 and ensure that the surface is uniform and has no obvious cracks or defects.

[0096] S4 specifically includes:

[0097] S41: placing the densified green billet obtained in S3 in a heating furnace, setting the furnace atmosphere to nitrogen, and setting the gas flow rate to 70 mL / min;

[0098] S42: the densified green billet is gradually heated up at a heating rate of 3°C / min from room temperature to 500°C;

[0099] S43: During the heating process, controlling the temperature range to ensure that the temperature is stable at 500° C., and maintaining the stable temperature for 2 hours to promote the cross-linking reaction and form a three-dimensional cross-linked network structure;

[0100] S44: After the treatment is completed, the temperature is slowly lowered to room temperature to obtain a cross-linked blank having a three-dimensional cross-linked network structure.

[0101] S5 specifically includes:

[0102] S51: placing the cross-linked green blank obtained in S4 in a pyrolysis furnace, setting the atmosphere in the furnace to an inert gas, wherein the inert gas used is argon gas, and the gas flow rate is 150 mL / min;

[0103] S52: The cross-linked green blank is subjected to pyrolysis treatment in stages. In the first stage, the green blank is heated to 600° C. at a heating rate of 4° C. / min and maintained at this temperature for 4 hours to remove organic components and preliminarily form β-SiC crystal nuclei.

[0104] S53: the second stage is heating to 1200°C at a heating rate of 4°C / min, and maintaining the temperature for 4 hours to promote the generation of β-SiC nuclei and the formation of a porous structure;

[0105] S54: The third stage is heating to 1800°C at a heating rate of 2.5°C / min, and maintaining the temperature for 4 hours to complete the pyrolysis process;

[0106] S55: After the pyrolysis treatment is completed, the temperature is slowly lowered to room temperature to obtain a porous silicon carbide skeleton containing β-SiC crystal nuclei, and the porosity of the skeleton is 40%.

[0107] S6 specifically includes:

[0108] S61: placing the porous silicon carbide skeleton containing β-SiC crystal nuclei obtained in S5 in an infiltration device and preheating it to 250° C. to ensure that the skeleton temperature is uniform;

[0109] S62: preparing a silicon carbide nanowire reinforcement, wherein the silicon carbide nanowire has a diameter of 5 nanometers, a length of 150 nanometers, and a concentration of 5 wt %;

[0110] S63: dissolving the silicon carbide nanowire reinforcement in an organic solvent to form a reinforcement solution with a concentration of 5 wt%, and placing the reinforcement solution and the porous silicon carbide skeleton in a vacuum infiltration device;

[0111] S64: applying negative pressure in a vacuum environment, the negative pressure range is -0.2 MPa, so that the reinforcing liquid fully penetrates into the pores of the porous silicon carbide skeleton, and the penetration time is 2 hours;

[0112] S65: After the infiltration is completed, the composite reinforced skeleton is taken out from the infiltration device to ensure that the silicon carbide nanowires are evenly distributed in the pores of the skeleton to obtain a composite reinforced skeleton, wherein the nanowire content of the composite reinforced skeleton is 20%.

[0113] S7 specifically includes:

[0114] S71: placing the composite reinforced skeleton obtained in S6 in a silicon vapor assisted recrystallization device, setting the atmosphere in the device to a mixed gas of silicon vapor and argon, with a silicon vapor concentration of 5%;

[0115] S72: heating the composite reinforced skeleton to 1600° C. at a heating rate of 4° C. / min and controlling the treatment time to 2 hours to promote the reaction between silicon vapor and the skeleton and achieve directional recrystallization;

[0116] S73: During the recrystallization process, controlling the flow direction of the silicon vapor to ensure that the recrystallization process is directional so as to promote the growth of crystal grains along a predetermined direction;

[0117] S74: After the treatment is completed, the temperature is slowly lowered to room temperature to obtain a grain boundary purified body, the grain size of the grain boundary purified body is 15 microns, and there are no obvious impurities or defects on the grain boundaries.

[0118] S8 specifically includes:

[0119] S81: placing the grain boundary purified body obtained in S7 in an electromagnetic field assisted sintering device, wherein the atmosphere in the device is argon gas, and the gas flow rate is 120 mL / min;

[0120] S82: Gradient heating is performed on the grain boundary purifier through an electromagnetic field assisted sintering process, and the temperature is set to gradually increase from 1100°C to 2000°C, with a heating rate of 7°C / min to ensure uniform temperature distribution;

[0121] S83: During the heating process, an electromagnetic field with a frequency of 80 kHz and an electric field strength of 2 kV / cm was applied to promote directional growth and densification of the grains;

[0122] S84: at 2000°C, maintaining the temperature for 45 minutes to complete the sintering process and ensure the densification of the grain boundary clean body;

[0123] S85: After sintering, the temperature is slowly lowered to room temperature to finally obtain a ReSic product with a bending strength of 500 MPa and a hardness of 10 HRC.

[0124] like Figure 2 As shown, a polymer recrystallized silicon carbide ReSic product system is used to implement the above-mentioned method for preparing a polymer recrystallized silicon carbide ReSic product, including the following modules:

[0125] Pretreatment module: used to perform mechanochemical activation treatment on the polymer precursor of boron-modified polycarbosilane and nano-silicon carbide seeds, and output pretreatment slurry;

[0126] Tape casting module: used to process the pre-treated slurry into a green blank with directional arrangement characteristics through a tape casting process;

[0127] Green billet densification module: used to perform cold isostatic pressing on green billets and output densified green billets;

[0128] Pre-crosslinking module: used to perform gradient temperature-raising crosslinking treatment on the densified green billet, and output a crosslinked green billet with a three-dimensional crosslinked network structure;

[0129] Pyrolysis module: used to pyrolyze the cross-linked green blank in stages in an inert atmosphere to generate a porous silicon carbide skeleton containing β-SiC crystal nuclei;

[0130] Skeleton infiltration module: used to infiltrate silicon carbide nanowire reinforcement into the porous silicon carbide skeleton and output a composite reinforced skeleton;

[0131] Recrystallization module: used to carry out silicon vapor-assisted directional recrystallization treatment on the composite reinforcement skeleton and output a grain boundary purified body;

[0132] Sintering module: It is used to densify the grain boundary purification body by electromagnetic field assisted gradient sintering technology to finally obtain ReSic products.

[0133] Example 2

[0134] Step S1: mixing a polymer precursor of boron-modified polycarbosilane and nano-silicon carbide seeds in a ratio of 9:1 to obtain an initial mixture; placing the initial mixture in a ball mill, setting the rotation speed to 200 rpm, the processing time to 30 minutes, the diameter of the ball milling medium to 5 mm, and the mass ratio to 10:1; after mechanochemical activation, obtaining a pre-treated slurry, the viscosity of the slurry is 500 mPa·s, and the solid content is 30%;

[0135] Step S2: evenly coating the pretreated slurry on a substrate of a tape casting device with a coating thickness of 0.5 mm; stretching the coated slurry through the tape casting device at a stretching speed of 2 cm / min; preliminarily cooling the stretched slurry at a cooling rate of 5°C / min to obtain a green blank with directional arrangement characteristics;

[0136] Step S3: placing the obtained green billet in an isostatic pressing device, applying uniform static pressure, the pressure is 30 MPa, the processing time is 30 minutes, and the temperature is 150°C; after the processing is completed, slowly reduce the pressure, take out the densified green billet, and control its density to 1.5 g / cm 3 ;

[0137] Step S4: placing the densified green blank in a heating furnace with an argon flow rate of 50 mL / min, performing gradient heating at a heating rate of 2°C / min from room temperature to 500°C, and maintaining at 500°C for 1 hour to promote the cross-linking reaction and form a three-dimensional cross-linked network structure; after the treatment is completed, slowly cooling to room temperature to obtain a cross-linked green blank;

[0138] Step S5: placing the cross-linked blank in a pyrolysis furnace, the atmosphere is nitrogen, and the gas flow rate is 100 mL / min; heating to 600°C in the first stage, the heating rate is 3°C / min, and it is kept for 3 hours; heating to 1200°C in the second stage, the heating rate is 3°C / min, and it is kept for 3 hours; heating to 1800°C in the third stage, the heating rate is 2°C / min, and it is kept for 3 hours; after completion, slowly cooling to room temperature to obtain a porous silicon carbide skeleton containing β-SiC crystal nuclei, and the porosity is 30%;

[0139] Step S6: placing the porous silicon carbide skeleton in an infiltration device and preheating it to 200°C; the silicon carbide nanowire has a diameter of 2 nanometers, a length of 50 nanometers, and a concentration of 1wt%; dissolving the reinforcement in an organic solvent to form a reinforcement liquid with a concentration of 2wt%, and applying negative pressure (-0.1MPa) in a vacuum infiltration device for infiltration for 1 hour to obtain a composite reinforcement skeleton with a nanowire content of 10%;

[0140] Step S7: placing the composite reinforced skeleton in a silicon vapor assisted recrystallization device, the atmosphere is a mixture of silicon vapor and argon, the silicon vapor concentration is 5%; heating to 1500°C, the heating rate is 3°C / min, the processing time is 1 hour, ensuring that the silicon vapor flow direction is oriented, and the grain size is 5 microns;

[0141] Step S8: Place the grain boundary purification body in an electromagnetic field assisted sintering device, the atmosphere is argon, and the flow rate is 100mL / min; set the temperature from 1100°C to 2000°C, the heating rate is 5°C / min, the applied electromagnetic field frequency is 50kHz, the electric field strength is 1kV / cm, maintain 2000°C, maintain for 30 minutes, complete the sintering, and finally obtain a ReSic product with a flexural strength of 450MPa and a hardness of 9.8HRC.

[0142] Example 3

[0143] Step S1: mixing a polymer precursor of boron-modified polycarbosilane and nano-silicon carbide seeds at a ratio of 9.8:1 to obtain an initial mixture; placing the initial mixture in a ball mill, setting the rotation speed to 500 rpm, the processing time to 90 minutes, the diameter of the ball milling medium to 10 mm, and the mass ratio to 20:1; after mechanochemical activation, obtaining a pre-treated slurry, the viscosity of the slurry is 1500 mPa·s, and the solid content is 50%;

[0144] Step S2: evenly coating the pretreated slurry on a substrate of a tape casting device with a coating thickness of 5 mm; stretching the coated slurry through the tape casting device at a stretching speed of 10 cm / min; preliminarily cooling the stretched slurry at a cooling rate of 20°C / min to obtain a green blank with directional arrangement characteristics;

[0145] Step S3: placing the obtained green billet in an isostatic pressing device, applying uniform static pressure, the pressure is 50 MPa, the processing time is 60 minutes, and the temperature is 250°C; after the processing is completed, slowly reduce the pressure, take out the densified green billet, and control its density to reach 2.0 g / cm 3 ;

[0146] Step S4: placing the densified green blank in a heating furnace with a nitrogen flow rate of 100 mL / min, performing gradient heating at a heating rate of 5°C / min from room temperature to 500°C, and maintaining at 500°C for 2 hours to promote the cross-linking reaction and form a three-dimensional cross-linked network structure; after the treatment is completed, slowly cooling to room temperature to obtain a cross-linked green blank;

[0147] Step S5: placing the cross-linked green blank in a pyrolysis furnace, the atmosphere is argon, and the gas flow rate is 200 mL / min; heating to 600°C in the first stage, the heating rate is 5°C / min, and it is maintained for 5 hours; heating to 1200°C in the second stage, the heating rate is 5°C / min, and it is maintained for 5 hours; heating to 1800°C in the third stage, the heating rate is 3°C / min, and it is maintained for 5 hours; after completion, slowly cooling to room temperature to obtain a porous silicon carbide skeleton containing β-SiC crystal nuclei, and the porosity is 50%;

[0148] Step S6: placing the porous silicon carbide skeleton in an infiltration device and preheating it to 300°C; the silicon carbide nanowire has a diameter of 10 nanometers, a length of 300 nanometers, and a concentration of 10wt%; dissolving the reinforcement in an organic solvent to form a reinforcement liquid with a concentration of 10wt%, and applying negative pressure (-0.3MPa) in a vacuum infiltration device for infiltration for 3 hours to obtain a composite reinforcement skeleton with a nanowire content of 30%;

[0149] Step S7: placing the composite reinforced skeleton in a silicon vapor assisted recrystallization device, the atmosphere is a mixture of silicon vapor and argon, the silicon vapor concentration is 5%; heating to 1700°C, the heating rate is 5°C / min, the processing time is 3 hours, ensuring that the silicon vapor flow direction is oriented, and the grain size is 30 microns;

[0150] Step S8: Place the grain boundary purification body in an electromagnetic field assisted sintering equipment, the atmosphere is argon, and the flow rate is 150mL / min; set the temperature from 1100°C to 2000°C, the heating rate is 10°C / min, the applied electromagnetic field frequency is 100kHz, the electric field strength is 3kV / cm, maintain 2000°C, maintain for 60 minutes, complete the sintering, and finally obtain a ReSic product with a flexural strength of 300MPa and a hardness of 9HRC.

[0151] Table 1 Comparison of performance parameters of ReSic products

[0152] Compare Projects Example 1 Example 2 Example 3 Thermal conductivity (W / m·K) 150 140 130 High temperature resistance(℃) 1800 1600 1500 Compressive strength(MPa) 600 550 500 Corrosion resistance excellent better generally Friction coefficient 0.3 0.32 0.35 <![CDATA[Wear resistance (mm 3 )]]> 50 45 60 Conductivity (S / m) 1.5 1.3 1.2 Flexural strength(MPa) 500 450 300 Hardness(HRC) 10 9.8 9

[0153] As can be seen from Table 1 above, Example 1 has the best thermal conductivity (150 W / m·K), which is better than other examples; the high temperature resistance of Example 1 reaches 1800°C, which is significantly higher than that of Example 2 and Example 3; the compressive strength of Example 1 is 600 MPa, which is the strongest; the corrosion resistance of Example 1 is the best, with an "excellent" performance; the friction coefficient of Example 1 is the smallest, which is 0.3, which means that it performs better in terms of friction; the wear resistance of Example 1 is 50 mm 3 , which is better than Example 2; the conductivity of Example 1 is 1.5S / m, which is the highest; in summary, Example 1 performs outstandingly in multiple performance indicators, so it is the best choice.

[0154] Table 2 Comparison of other performance parameters

[0155] Compare Projects Example 1 Example 2 Example 3 Tensile strength(MPa) 350 320 300 <![CDATA[Coefficient of thermal expansion (×10 -6 / °C)]]> 4.2 4.5 5 Fracture toughness (MPa·m1 / 2) 3.5 3.2 3 Low temperature resistance (℃) -50 -40 -30 Glossiness(%) 95 90 85 UV resistance (%) 98 92 88

[0156] It can be seen from Table 2 that the tensile strength of Example 1 is 350 MPa, which is better than that of Example 2 and Example 3; the thermal expansion coefficient of Example 1 is 4.2×10 -6 / ℃, which is lower, better than Example 2 and Example 3, and suitable for high precision requirements; the fracture toughness of Example 1 is 3.5MPa·m1 / 2, which performs well; the low temperature resistance of Example 1 is -50℃, showing strong low temperature tolerance; the glossiness of Example 1 is 95%, which is relatively high, showing good surface quality; the UV resistance of Example 1 is 98%, which is the strongest; in summary, Example 1 performs best in multiple key performance aspects, including tensile strength, low temperature resistance, electrical insulation, glossiness and UV resistance; therefore, Example 1 is the best choice.

[0157] The present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention. In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without the description of these details. In addition, in order to avoid unnecessary confusion about the essence of the present invention, well-known methods, processes, procedures, components and circuits are not described in detail.

[0158] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a polymer recrystallized silicon carbide (ReSic) product, characterized in that: The following steps are involved: S1: subjecting the polymer precursor of boron-modified polycarbosilane and the nano-silicon carbide seed to mechanochemical activation treatment, and outputting the pre-treated slurry; S2: The pretreated slurry is processed into a green blank with directional arrangement characteristics through a tape casting process; S3: performing isostatic pressing on the green billet to obtain a densified green billet; S4: performing gradient temperature rise cross-linking treatment on the densified green billet to output a cross-linked green billet having a three-dimensional cross-linked network structure; S5: pyrolyzing the cross-linked green blank in an inert atmosphere in stages to generate a porous silicon carbide skeleton containing β-SiC crystal nuclei; S6: Infiltrating silicon carbide nanowire reinforcement into the porous silicon carbide skeleton to output a composite reinforcement skeleton; S7: performing silicon vapor-assisted directional recrystallization treatment on the composite reinforcement skeleton to output a grain boundary purified body; S8: The grain boundary purification body is densified by using an electromagnetic field assisted gradient sintering process to finally obtain a ReSic product.

2. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S1 specifically includes: S11: mixing a polymer precursor containing boron-modified polycarbosilane and nano-silicon carbide seeds in a ratio of 9:1 to 9.8:1 to obtain an initial mixture; S12: placing the initial mixture in a ball mill for mechanochemical activation treatment, the rotation speed of the ball mill is set to 200-500 rpm, the treatment time is 30-90 minutes, the diameter of the ball milling medium is 5-10 mm, and the mass ratio of the ball milling medium to the mass of the mixture is 10:1 to 20:1; S13: After the mechanochemical activation treatment, a pre-treated slurry is obtained, the viscosity of the pre-treated slurry is controlled to be 500-1500 mPa·s, and the solid content of the slurry is 30%-50%.

3. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S2 specifically includes: S21: evenly coating the pre-treated slurry on the substrate of the tape casting equipment, with a coating thickness of 0.5-5 mm, ensuring that the slurry is evenly covered; S22: stretching the coated pretreated slurry through a tape casting device at a stretching speed of 2-10 cm / min; S23: Preliminarily cooling the stretched slurry to solidify it into a shape, with a cooling rate of 5-20°C / min, to obtain a green blank with directional arrangement characteristics.

4. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S3 specifically includes: S31: placing the green billet obtained in S2 in an isostatic pressing device; S32: in an isostatic pressing device, applying a uniform static pressure in the range of 30-50 MPa for a processing time of 30-60 minutes; S33: During the isostatic pressing process, the temperature is controlled to be 150-250°C; S34: After the treatment is completed, the pressure is slowly reduced, and the densified green billet is taken out and its density is controlled to 1.5-2.0g / cm 3 .

5. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S4 specifically includes: S41: placing the densified green billet obtained in S3 in a heating furnace, setting the furnace atmosphere to nitrogen or argon, and the gas flow rate to 50-100 mL / min; S42: The densified green billet is gradually heated at a rate of 2-5°C / min from room temperature to 500°C; S43: During the heating process, controlling the temperature range to ensure that the temperature is stable at 500° C., and maintaining the stable temperature for 1-3 hours to promote the cross-linking reaction and form a three-dimensional cross-linked network structure; S44: After the treatment is completed, the temperature is slowly lowered to room temperature to obtain a cross-linked blank having a three-dimensional cross-linked network structure.

6. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S5 specifically includes: S51: placing the cross-linked green blank obtained in S4 in a pyrolysis furnace, setting the atmosphere in the furnace to an inert gas, wherein the inert gas used is argon or nitrogen, and the gas flow rate is 100-200 mL / min; S52: The cross-linked green blank is subjected to pyrolysis treatment in stages. In the first stage, the green blank is heated to 600° C. at a heating rate of 3-5° C. / min and maintained at the temperature for 3-5 hours to remove organic components and preliminarily form β-SiC crystal nuclei. S53: In the second stage, the temperature is heated to 1200°C at a heating rate of 3-5°C / min, and the temperature is maintained for 3-5 hours to promote the generation of β-SiC nuclei and the formation of a porous structure; S54: The third stage is heating to 1800°C at a heating rate of 2-3°C / min, and maintaining the temperature for 3-5 hours to complete the pyrolysis process; S55: After the pyrolysis treatment is completed, the temperature is slowly lowered to room temperature to obtain a porous silicon carbide skeleton containing β-SiC crystal nuclei, and the porosity of the skeleton is 30%-50%.

7. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S6 specifically includes: S61: placing the porous silicon carbide skeleton containing β-SiC crystal nuclei obtained in S5 in an infiltration device and preheating it to 200-300° C. to ensure that the skeleton temperature is uniform; S62: preparing a silicon carbide nanowire reinforcement, wherein the silicon carbide nanowire has a diameter of 2-10 nanometers, a length of 50-300 nanometers, and a concentration of 1-10 wt %; S63: dissolving the silicon carbide nanowire reinforcement in an organic solvent to form a reinforcement solution with a concentration of 2-10 wt %, and placing the reinforcement solution and the porous silicon carbide skeleton in a vacuum infiltration device; S64: applying negative pressure in a vacuum environment, the negative pressure range is -0.1 to -0.3 MPa, so that the reinforcing liquid fully penetrates into the pores of the porous silicon carbide skeleton, and the penetration time is 1 to 3 hours; S65: After the infiltration is completed, a composite reinforced skeleton is obtained, wherein the nanowire content of the composite reinforced skeleton is 10%-30%.

8. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S7 specifically includes: S71: placing the composite reinforced skeleton obtained in S6 in a silicon vapor assisted recrystallization device, setting the atmosphere in the device to a mixed gas of silicon vapor and argon, with a silicon vapor concentration of 5%; S72: heating the composite reinforced skeleton to 1500° C.-1700° C., with a heating rate of 3-5° C. / min, and controlling the treatment time to 1-3 hours, so as to promote the reaction between the silicon vapor and the skeleton; S73: During the recrystallization process, controlling the flow direction of the silicon vapor to ensure that the recrystallization process is directional so as to promote the growth of crystal grains along a predetermined direction; S74: After the treatment is completed, the temperature is slowly lowered to room temperature to obtain a grain boundary purified body, wherein the grain size of the grain boundary purified body is 5-30 microns.

9. The method for preparing a polymer recrystallized silicon carbide (ReSic) product according to claim 1, characterized in that: The S8 specifically includes: S81: placing the grain boundary purified body obtained in S7 in an electromagnetic field assisted sintering device, wherein the atmosphere in the device is argon gas, and the gas flow rate is 100-150 mL / min; S82: Gradient heating is performed on the grain boundary purifier through an electromagnetic field assisted sintering process, and the temperature is set to gradually increase from 1100°C to 2000°C, with a heating rate of 5-10°C / min; S83: During the heating process, an electromagnetic field with a frequency of 50-100 kHz and an electric field strength of 1-3 kV / cm is applied to promote directional growth and densification of grains; S84: maintaining the temperature at 2000° C. for 30-60 minutes to complete the sintering process; S85: After sintering, slowly cool down to room temperature to finally obtain ReSic products with a bending strength of 300-500MPa and a hardness of 9-10HRC.

10. A polymer recrystallized silicon carbide (ReSic) product system, used to implement the method for preparing a polymer recrystallized silicon carbide (ReSic) product as claimed in any one of claims 1 to 9, characterized in that: Includes the following modules: Pretreatment module: used to perform mechanochemical activation treatment on the polymer precursor of boron-modified polycarbosilane and nano-silicon carbide seeds, and output pretreatment slurry; Tape casting module: used to process the pre-treated slurry into a green blank with directional arrangement characteristics through a tape casting process; Green billet densification module: used to perform cold isostatic pressing on green billets and output densified green billets; Pre-crosslinking module: used to perform gradient temperature-raising crosslinking treatment on the densified green billet, and output a crosslinked green billet with a three-dimensional crosslinked network structure; Pyrolysis module: used to pyrolyze the cross-linked green blank in stages in an inert atmosphere to generate a porous silicon carbide skeleton containing β-SiC crystal nuclei; Skeleton infiltration module: used to infiltrate silicon carbide nanowire reinforcement into the porous silicon carbide skeleton and output a composite reinforced skeleton; Recrystallization module: used to carry out silicon vapor-assisted directional recrystallization treatment on the composite reinforcement skeleton and output a grain boundary purified body; Sintering module: It is used to densify the grain boundary purification body by electromagnetic field assisted gradient sintering technology to finally obtain ReSic products.

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