Reactive powder coating method for in-situ generation of interface layer on surface of silicon nitride green body

Abstract

The invention discloses a reactive powder coating method for in-situ generation of an interface layer on the surface of a silicon nitride green body, and relates to the technical field of ceramic preparation, and the reactive powder coating method comprises the following specific steps: S1, raw material preparation, the coating is prepared from 35-45 parts of boron nitride, 25-35 parts of silicon powder, 14-17 parts of yttrium oxide, 10 parts of polyvinyl alcohol, 3-5 parts of glycerinum and 2 parts of sodium dodecyl benzene sulfonate. The preparation method comprises the following steps: step S2, preparing composite powder, step S3, dispersing and defoaming slurry, step S4, coating the surface of a green body, step S5, carrying out gradient drying and curing, and step S6, carrying out sintering reaction, in the preparation method, boron nitride, silicon powder, yttrium oxide, polyvinyl alcohol, glycerol and sodium dodecyl benzene sulfonate are mixed to prepare the slurry, and the cured silicon nitride green body is sintered by utilizing the sintering reaction, so that the silicon nitride green body is obtained. An in-situ generation interface layer is formed, a compact transition layer is formed, and the density, the force performance and the thermal shock resistance of the material can be obviously improved.

Description

Technical Field

[0001] This invention relates to the field of ceramic preparation technology, and specifically to a reactive powder coating method for in-situ generation of an interface layer on the surface of silicon nitride rust. Background Technology

[0002] Silicon nitride ceramics are widely used in semiconductors, aerospace, metallurgy, and other fields due to their high hardness, excellent high-temperature stability, and chemical inertness. However, during the sintering of silicon nitride green blanks, cracking and performance degradation can easily occur due to abnormal grain growth or insufficient interfacial bonding.

[0003] In summary, a reactive powder coating method for in-situ generation of an interface layer on a silicon nitride defective surface is designed. Summary of the Invention

[0004] In order to overcome the above-mentioned shortcomings, the present invention provides a reactive powder coating method for in-situ generation of an interface layer on a silicon nitride substrate.

[0005] The present invention achieves the above objectives through the following technical solutions: A reactive powder coating method for in-situ generation of an interface layer on a silicon nitride defective surface includes the following specific steps: Step S1: Raw material preparation. The raw material formula consists of the following components by weight: 35-45 parts boron nitride, 25-35 parts silicon powder, 14-17 parts yttrium oxide, 10 parts polyvinyl alcohol, 3-5 parts glycerol, and 2 parts sodium dodecylbenzenesulfonate. Step S2: Preparation of composite powder. The raw materials from step S1 are mixed to prepare composite powder. Step S3, Slurry dispersion and degassing: Composite powder, glycerol and sodium dodecylbenzenesulfonate are added to the polyvinyl alcohol solution, followed by dispersion and degassing treatment to obtain the slurry; Step S4: Coating the surface of the green blank. The surface of the silicon nitride green blank is coated using a high-voltage electrostatic spraying device. Step S5: Gradient drying and curing, the silicon nitride raw material is dried and cured by gradient drying method; Step S6: Sintering reaction, sintering the cured silicon nitride substrate to form an in-situ generated interface layer; The specific steps of step S4 are as follows: S41. Coating the surface of the silicon nitride raw material with a high-voltage electrostatic spraying device at a distance of 20cm from the raw silicon nitride surface; S42, silicon nitride raw materials are placed on a moving platform, so that the spraying rate of the high voltage electrostatic spraying equipment is 5mm / s and the coating thickness is controlled at 15-20μm; S43. After spraying, allow the coating to self-level for 5 minutes to ensure that there are no pinholes or missed coating defects. The specific steps of step S6 are as follows: S61, during the debinding stage, the temperature inside the high-temperature furnace is increased to 600℃ at a rate of 5℃ / min and held for 2 hours. The nitrogen flow rate is 5L / min to remove the organic carrier in the silicon nitride substrate, and the weight loss rate is controlled at 8±0.5%. S62. High-temperature sintering: The temperature inside the high-temperature furnace continues to rise to 1850℃ at a rate of 3℃ / min, with a nitrogen pressure of 3MPa, and is held at this temperature for 3-5 hours. An in-situ interface layer is formed on the surface of the silicon nitride raw material, utilizing the in-situ nitriding reaction of silicon powder ( )generate Columnar crystals, which synergistically form a gradient interface layer with boron nitride; S63. Cooling and temperature reduction: The temperature inside the high-temperature furnace is reduced to 800℃ at a rate of 2℃ / min, and then cooled with the furnace to avoid interface cracking caused by thermal shock.

[0006] Preferably, the specific steps of step S2 are as follows: S21. Powder mixing: Boron nitride, silicon powder, and yttrium oxide are added to an agate ball mill jar in proportion, and anhydrous ethanol is added as a dispersion medium, wherein the anhydrous ethanol is added at a solid-liquid ratio of 1:2. S22, ball milling into a slurry, using... Grinding balls with a diameter of 5 mm were used to ball mill for 3 hours under an inert atmosphere to prevent silicon powder oxidation and obtain a slurry after ball milling. S23. Evaporation to obtain composite powder: under an environment of 60℃ and a vacuum degree of -0.09MPa, the solvent is removed by rotary evaporation to obtain dry composite powder.

[0007] Preferably, the loose bulk density of the powder in S23 is controlled between 0.8 and 1.0. This avoids uneven buildup during subsequent coating processes.

[0008] Preferably, the specific steps of step S3 are as follows: S31. Dissolve polyvinyl alcohol in deionized water at 80℃, stir until completely dissolved, and then cool to room temperature. S32. Add composite powder, glycerol and sodium dodecylbenzenesulfonate to the polyvinyl alcohol solution and disperse them by high-speed shearing using a high-speed mixer. S33. Ultrasonic degassing method is used to remove air bubbles inside the slurry.

[0009] Preferably, in step S32, the high-speed mixer rotates at 3000 rpm, the mixing duration is 30-35 minutes, and the slurry viscosity is 500-800 ppm. At an ambient temperature of 25°C, the coating uniformity was ensured by measuring the viscosity using a rotational viscometer.

[0010] Preferably, in step S33, the ultrasonic power is 500W and the duration is 20min.

[0011] Preferably, the atomizing pressure of the high-voltage electrostatic spraying equipment is 0.3 MPa.

[0012] Preferably, the specific steps of step S5 are as follows: S51. Initial stage: The temperature inside the drying oven is increased from 30℃ to 60℃ at a rate of 1-2℃ / min, and the temperature is maintained for 1 hour to remove free moisture. S52, Intermediate stage: The temperature inside the drying oven is increased from 60℃ to 120℃ at a rate of 0.5-1℃ / min, and the temperature is maintained for 2 hours to promote the cross-linking and curing of polyvinyl alcohol. S53. Final stage: The temperature inside the drying oven is reduced from 120℃ to 80℃ at a rate of 1℃ / min to avoid thermal stress causing coating cracking.

[0013] Preferably, before step S41, the surface of the silicon nitride green blank is pretreated. First, plasma cleaning is performed with an oxygen flow rate of 20 sccm and a cleaning time of 5-10 min to remove surface grease and adsorbed impurities and improve coating wettability. Then, the surface is roughened by sandblasting with 50 μm white corundum abrasive, a pressure of 0.2 MPa, and a spray angle of 45° to form a uniform pit structure on the surface of the green blank, achieving a roughness Ra of 2.5 μm and increasing the powder contact area.

[0014] The beneficial effects of this invention are as follows: In the reactive powder coating method for in-situ generation of an interface layer on the surface of silicon nitride substrate, boron nitride, silicon powder, yttrium oxide, polyvinyl alcohol, glycerol and sodium dodecylbenzenesulfonate are mixed to form a slurry. At the same time, a sintering reaction is used to sinter the cured silicon nitride substrate to form an in-situ generated interface layer and a dense transition layer, which can significantly improve the material density, mechanical properties and thermal shock resistance. Detailed Implementation

[0015] The invention will now be described in further detail.

[0016] A reactive powder coating method for in-situ generation of an interface layer on a silicon nitride defective surface includes the following specific steps: Step S1: Raw material preparation. The raw material formula consists of the following components by weight: 35-45 parts boron nitride, 25-35 parts silicon powder, 14-17 parts yttrium oxide, 10 parts polyvinyl alcohol, 3-5 parts glycerol, and 2 parts sodium dodecylbenzenesulfonate. Step S2: Preparation of composite powder. The raw materials from step S1 are mixed to prepare composite powder. Step S3, Slurry dispersion and degassing: Composite powder, glycerol and sodium dodecylbenzenesulfonate are added to the polyvinyl alcohol solution, followed by dispersion and degassing treatment to obtain the slurry; Step S4: Coating the surface of the green blank. The surface of the silicon nitride green blank is coated using a high-voltage electrostatic spraying device. Step S5: Gradient drying and curing, the silicon nitride raw material is dried and cured by gradient drying method; Step S6: Sintering reaction, sintering the cured silicon nitride substrate to form an in-situ generated interface layer; The specific steps of step S4 are as follows: S41. Coating the surface of the silicon nitride raw material with a high-voltage electrostatic spraying device at a distance of 20cm from the raw silicon nitride surface; S42, silicon nitride raw materials are placed on a moving platform, so that the spraying rate of the high voltage electrostatic spraying equipment is 5mm / s and the coating thickness is controlled at 15-20μm; S43. After spraying, allow the coating to self-level for 5 minutes to ensure that there are no pinholes or missed coating defects. The specific steps of step S6 are as follows: S61, during the debinding stage, the temperature inside the high-temperature furnace is increased to 600℃ at a rate of 5℃ / min and held for 2 hours. The nitrogen flow rate is 5L / min to remove the organic carrier in the silicon nitride substrate, and the weight loss rate is controlled at 8±0.5%. S62. High-temperature sintering: The temperature inside the high-temperature furnace continues to rise to 1850℃ at a rate of 3℃ / min, with a nitrogen pressure of 3MPa, and is held at this temperature for 3-5 hours. An in-situ interface layer is formed on the surface of the silicon nitride raw material, utilizing the in-situ nitriding reaction of silicon powder ( )generate Columnar crystals, which synergistically form a gradient interface layer with boron nitride; S63. Cooling and temperature reduction: The temperature inside the high-temperature furnace is reduced to 800℃ at a rate of 2℃ / min, and then cooled with the furnace to avoid interface cracking caused by thermal shock.

[0017] Specifically, the steps of step S2 are as follows: S21. Powder mixing: Boron nitride, silicon powder, and yttrium oxide are added to an agate ball mill jar in proportion, and anhydrous ethanol is added as a dispersion medium, wherein the anhydrous ethanol is added at a solid-liquid ratio of 1:2. S22, ball milling into a slurry, using... Grinding balls with a diameter of 5 mm were used to ball mill for 3 hours under an inert atmosphere to prevent silicon powder oxidation and obtain a slurry after ball milling. S23. Evaporation to obtain composite powder: under an environment of 60℃ and a vacuum degree of -0.09MPa, the solvent is removed by rotary evaporation to obtain dry composite powder.

[0018] Specifically, the loose bulk density of the powder in S23 is controlled between 0.8 and 1.0. This avoids uneven buildup during subsequent coating processes.

[0019] Specifically, the steps of step S3 are as follows: S31. Dissolve polyvinyl alcohol in deionized water at 80℃, stir until completely dissolved, and then cool to room temperature. S32. Add composite powder, glycerol and sodium dodecylbenzenesulfonate to the polyvinyl alcohol solution and disperse them by high-speed shearing using a high-speed mixer. S33. Ultrasonic degassing method is used to remove air bubbles inside the slurry.

[0020] Specifically, in step S32, the high-speed mixer rotates at 3000 rpm, the mixing duration is 30-35 minutes, and the slurry viscosity is 500-800 ppm. At an ambient temperature of 25°C, the coating uniformity was ensured by measuring the viscosity using a rotational viscometer.

[0021] Specifically, in step S33, the ultrasonic power is 500W and the duration is 20min.

[0022] Specifically, the atomizing gas pressure of the high-voltage electrostatic spraying equipment is 0.3 MPa.

[0023] Specifically, the steps of step S5 are as follows: S51. Initial stage: The temperature inside the drying oven is increased from 30℃ to 60℃ at a rate of 1-2℃ / min, and the temperature is maintained for 1 hour to remove free moisture. S52, Intermediate stage: The temperature inside the drying oven is increased from 60℃ to 120℃ at a rate of 0.5-1℃ / min, and the temperature is maintained for 2 hours to promote the cross-linking and curing of polyvinyl alcohol. S53. Final stage: The temperature inside the drying oven is reduced from 120℃ to 80℃ at a rate of 1℃ / min to avoid thermal stress causing coating cracking.

[0024] Specifically, before step S41, the surface of the silicon nitride green blank is pretreated. First, plasma cleaning is performed with an oxygen flow rate of 20 sccm and a cleaning time of 5-10 min to remove surface grease and adsorbed impurities and improve coating wettability. Then, the surface is roughened by sandblasting with 50 μm white corundum abrasive at a pressure of 0.2 MPa and a spray angle of 45° to form a uniform pit structure on the surface of the green blank, achieving a roughness Ra of 2.5 μm and increasing the powder contact area. Example 1

[0025] A reactive powder coating method for in-situ generation of an interface layer on a silicon nitride defective surface includes the following specific steps: Step S1: Raw material preparation. The raw material formula consists of the following components by weight: 40 parts boron nitride, 30 parts silicon powder, 15 parts yttrium oxide, 10 parts polyvinyl alcohol, 3 parts glycerol, and 2 parts sodium dodecylbenzenesulfonate. Step S2: Preparation of composite powder. The raw materials from step S1 are mixed to prepare composite powder. Step S3, Slurry dispersion and degassing: Composite powder, glycerol and sodium dodecylbenzenesulfonate are added to the polyvinyl alcohol solution, followed by dispersion and degassing treatment to obtain the slurry; Step S4: Coating the surface of the green blank. The surface of the silicon nitride green blank is coated using a high-voltage electrostatic spraying device. Step S5: Gradient drying and curing, the silicon nitride raw material is dried and cured by gradient drying method; Step S6: Sintering reaction, sintering the cured silicon nitride substrate to form an in-situ generated interface layer; The specific steps of step S2 are as follows: S21. Powder mixing: Boron nitride, silicon powder, and yttrium oxide are added to an agate ball mill jar in proportion, and anhydrous ethanol is added as a dispersion medium, wherein the anhydrous ethanol is added at a solid-liquid ratio of 1:2. S22, ball milling into a slurry, using... Grinding balls with a diameter of 5 mm were used to ball mill for 3 hours under an inert atmosphere to prevent silicon powder oxidation and obtain a slurry after ball milling. S23. Evaporation to obtain composite powder: Solvent is removed by rotary evaporation at 60℃ and a vacuum of -0.09MPa to obtain dry composite powder. The loose packing density of the powder is controlled between 0.8 and 1.0. This avoids uneven buildup during subsequent coating processes.

[0026] The specific steps of step S3 are as follows: S31. Dissolve polyvinyl alcohol in deionized water at 80℃, stir until completely dissolved, and then cool to room temperature. S32. Add composite powder, glycerol, and sodium dodecylbenzenesulfonate to the polyvinyl alcohol solution, and disperse by high-speed shearing using a high-speed mixer at 3000 rpm for 30-35 minutes. The slurry viscosity should be 500-800 ppm. At an ambient temperature of 25°C, the coating uniformity was ensured by measuring the viscosity using a rotational viscometer. S33. Use ultrasonic degassing to remove air bubbles from the slurry. The ultrasonic power is 500W and the duration is 20min.

[0027] The specific steps of step S4 are as follows: S41. At a distance of 20cm from the surface of the silicon nitride blank, the surface of the silicon nitride blank is coated using a high-voltage electrostatic spraying device. The atomizing air pressure of the high-voltage electrostatic spraying device is 0.3MPa. Before step S41, the surface of the silicon nitride blank is pretreated. First, plasma cleaning is performed. During cleaning, the oxygen flow rate is 20sccm and the cleaning time is 5-10min. This is used to remove surface grease and adsorbed impurities and improve the wettability of the coating. Then, the surface is roughened by sandblasting. 50μm white corundum abrasive is selected, the pressure is 0.2MPa, and the spraying angle is 45° to form a uniform pit structure on the surface of the blank. The roughness Ra reaches 2.5μm, increasing the powder contact area. S42, the silicon nitride raw material is placed on the moving platform, so that the spraying rate of the high voltage electrostatic spraying equipment is 5mm / s and the coating thickness is controlled at 18μm; S43. After spraying, allow the coating to self-level for 5 minutes to ensure that there are no pinholes or missed coating defects.

[0028] The specific steps of step S5 are as follows: S51. Initial stage: The temperature inside the drying oven is increased from 30℃ to 60℃ at a rate of 1-2℃ / min, and the temperature is maintained for 1 hour to remove free moisture. S52, Intermediate stage: The temperature inside the drying oven is increased from 60℃ to 120℃ at a rate of 0.5-1℃ / min, and the temperature is maintained for 2 hours to promote the cross-linking and curing of polyvinyl alcohol. S53. Final Stage: The temperature inside the drying oven is reduced from 120℃ to 80℃ at a rate of 1℃ / min to prevent thermal stress from causing coating cracking. The specific steps of step S6 are as follows: S61, during the debinding stage, the temperature inside the high-temperature furnace is increased to 600℃ at a rate of 5℃ / min and held for 2 hours. The nitrogen flow rate is 5L / min to remove the organic carrier in the silicon nitride substrate, and the weight loss rate is controlled at 8±0.5%. S62. High-temperature sintering: The temperature inside the high-temperature furnace continues to rise to 1850℃ at a rate of 3℃ / min, with a nitrogen pressure of 3MPa, and is held at this temperature for 3-5 hours. An in-situ interface layer is formed on the surface of the silicon nitride raw material, utilizing the in-situ nitriding reaction of silicon powder ( )generate Columnar crystals, which synergistically form a gradient interface layer with boron nitride; S63. Cooling and temperature reduction: The temperature inside the high-temperature furnace is reduced to 800℃ at a rate of 2℃ / min, and then cooled with the furnace to avoid interface cracking caused by thermal shock.

[0029] Effect verification Silicon nitride insulating substrates used in high-power semiconductor devices require enhanced interfacial bonding to withstand thermal cycling stress, with an interfacial layer hardness of 18 GPa and thermal shock cycling (1000℃) capability. No cracking after 100 cycles at 25℃. Example 2

[0030] A reactive powder coating method for in-situ generation of an interface layer on a silicon nitride defective surface includes the following specific steps: Step S1: Raw material preparation. The raw material formula consists of the following components by weight: 40 parts boron nitride, 30 parts silicon powder, 15 parts yttrium oxide, 10 parts polyvinyl alcohol, 3 parts glycerol, and 2 parts sodium dodecylbenzenesulfonate. Step S2: Preparation of composite powder. The raw materials from step S1 are mixed to prepare composite powder. Step S3, Slurry dispersion and degassing: Composite powder, glycerol and sodium dodecylbenzenesulfonate are added to the polyvinyl alcohol solution, followed by dispersion and degassing treatment to obtain the slurry; Step S4: Coating the surface of the green blank. The surface of the silicon nitride green blank is coated using a high-voltage electrostatic spraying device. Step S5: Gradient drying and curing, the silicon nitride raw material is dried and cured by gradient drying method; Step S6: Sintering reaction, sintering the cured silicon nitride substrate to form an in-situ generated interface layer; The specific steps of step S2 are as follows: S21. Powder mixing: Boron nitride, silicon powder, and yttrium oxide are added to an agate ball mill jar in proportion, and anhydrous ethanol is added as a dispersion medium, wherein the anhydrous ethanol is added at a solid-liquid ratio of 1:2. S22, ball milling into a slurry, using... Grinding balls with a diameter of 5 mm were used to ball mill for 3 hours under an inert atmosphere to prevent silicon powder oxidation and obtain a slurry after ball milling. S23. Evaporation to obtain composite powder: Solvent is removed by rotary evaporation at 60℃ and a vacuum of -0.09MPa to obtain dry composite powder. The loose packing density of the powder is controlled between 0.8 and 1.0. This avoids uneven buildup during subsequent coating processes.

[0031] The specific steps of step S3 are as follows: S31. Dissolve polyvinyl alcohol in deionized water at 80℃, stir until completely dissolved, and then cool to room temperature. S32. Add composite powder, glycerol, and sodium dodecylbenzenesulfonate to the polyvinyl alcohol solution, and disperse by high-speed shearing using a high-speed mixer at 3000 rpm for 30-35 minutes. The slurry viscosity should be 500-800 ppm. At an ambient temperature of 25°C, the coating uniformity was ensured by measuring the viscosity using a rotational viscometer. S33. Use ultrasonic degassing to remove air bubbles from the slurry. The ultrasonic power is 500W and the duration is 20min.

[0032] The specific steps of step S4 are as follows: S41. At a distance of 20cm from the surface of the silicon nitride green blank, the surface of the silicon nitride green blank is coated using a high-voltage electrostatic spraying device. The atomizing air pressure of the high-voltage electrostatic spraying device is 0.3MPa. Before step S41, the surface of the silicon nitride green blank is pretreated. First, plasma cleaning is performed. During cleaning, the oxygen flow rate is 20sccm and the cleaning time is 5-10min. This is used to remove surface grease and adsorbed impurities and improve the wettability of the coating. Then, the surface is roughened by sandblasting. 50μm white corundum abrasive is selected, the pressure is 0.2MPa, and the spray angle is 45° to form a uniform pit structure on the surface of the green blank. The roughness Ra is less than 0.1μm, which increases the contact area of ​​the powder. S42, silicon nitride raw materials are placed on a moving platform, so that the spraying rate of the high voltage electrostatic spraying equipment is 5mm / s and the coating thickness is controlled at 15-20μm; S43. After spraying, allow the coating to self-level for 5 minutes to ensure that there are no pinholes or missed coating defects.

[0033] The specific steps of step S5 are as follows: S51. Initial stage: The temperature inside the drying oven is increased from 30℃ to 60℃ at a rate of 1-2℃ / min, and the temperature is maintained for 1 hour to remove free moisture. S52, Intermediate stage: The temperature inside the drying oven is increased from 60℃ to 120℃ at a rate of 0.5-1℃ / min, and the temperature is maintained for 2 hours to promote the cross-linking and curing of polyvinyl alcohol. S53. Final Stage: The temperature inside the drying oven is reduced from 120℃ to 80℃ at a rate of 1℃ / min to prevent thermal stress from causing coating cracking. The specific steps of step S6 are as follows: S61, during the debinding stage, the temperature inside the high-temperature furnace is increased to 600℃ at a rate of 5℃ / min and held for 2 hours. The nitrogen flow rate is 5L / min to remove the organic carrier in the silicon nitride substrate, and the weight loss rate is controlled at 8±0.5%. S62. High-temperature sintering: The temperature inside the high-temperature furnace continues to rise to 1850℃ at a rate of 3℃ / min, with a nitrogen pressure of 3MPa, and is held at this temperature for 5 hours. An in-situ interface layer is formed on the surface of the silicon nitride substrate, utilizing the in-situ nitriding reaction of silicon powder. )generate Columnar crystals, which synergistically form a gradient interface layer with boron nitride; S63. Cooling and temperature reduction: The temperature inside the high-temperature furnace is reduced to 800℃ at a rate of 2℃ / min, and then cooled with the furnace. Below 800℃, the temperature is reduced by 50℃ per hour to avoid interface cracking caused by thermal shock.

[0034] Effect verification: This material is used to improve the surface wear resistance and fatigue resistance of silicon nitride bearing balls, reducing the wear rate by 40% and increasing the fatigue life to 2×10⁻⁶. 7 The loop continues. Example 3

[0035] A reactive powder coating method for in-situ generation of an interface layer on a silicon nitride defective surface includes the following specific steps: Step S1: Raw material preparation. The raw material formula consists of the following components by weight: 40 parts boron nitride, 30 parts silicon powder, 15 parts yttrium oxide, 15 parts polyvinyl alcohol, 3 parts glycerol, and 2 parts sodium dodecylbenzene sulfonate. Polyvinyl alcohol can be replaced with polyethylene glycol to improve high-temperature adhesion. Step S2: Preparation of composite powder. The raw materials from step S1 are mixed to prepare composite powder. Step S3, Slurry dispersion and degassing: Composite powder, glycerol and sodium dodecylbenzenesulfonate are added to the polyvinyl alcohol solution, followed by dispersion and degassing treatment to obtain the slurry; Step S4: Coating the surface of the green blank. The surface of the silicon nitride green blank is coated using a high-voltage electrostatic spraying device. Step S5: Gradient drying and curing, the silicon nitride raw material is dried and cured by gradient drying method; Step S6: Sintering reaction, sintering the cured silicon nitride substrate to form an in-situ generated interface layer; The specific steps of step S2 are as follows: S21. Powder mixing: Boron nitride, silicon powder, and yttrium oxide are added to an agate ball mill jar in proportion, and anhydrous ethanol is added as a dispersion medium, wherein the anhydrous ethanol is added at a solid-liquid ratio of 1:2. S22, ball milling into a slurry, using... Grinding balls with a diameter of 5 mm were used to ball mill for 3 hours under an inert atmosphere to prevent silicon powder oxidation and obtain a slurry after ball milling. S23. Evaporation to obtain composite powder: Solvent is removed by rotary evaporation at 60℃ and a vacuum of -0.09MPa to obtain dry composite powder. The loose packing density of the powder is controlled between 0.8 and 1.0. This avoids uneven buildup during subsequent coating processes.

[0036] The specific steps of step S3 are as follows: S31. Dissolve polyvinyl alcohol in deionized water at 80℃, stir until completely dissolved, and then cool to room temperature. S32. Add composite powder, glycerol, and sodium dodecylbenzenesulfonate to the polyvinyl alcohol solution, and disperse by high-speed shearing using a high-speed mixer at 3000 rpm for 30-35 minutes. The slurry viscosity should be 500-800 ppm. At an ambient temperature of 25°C, the coating uniformity was ensured by measuring the viscosity using a rotational viscometer. S33. Use ultrasonic degassing to remove air bubbles from the slurry. The ultrasonic power is 500W and the duration is 20min.

[0037] The specific steps of step S4 are as follows: S41. At a distance of 20cm from the surface of the silicon nitride blank, the surface of the silicon nitride blank is coated using a high-voltage electrostatic spraying device. The atomizing air pressure of the high-voltage electrostatic spraying device is 0.3MPa. Before step S41, the surface of the silicon nitride blank is pretreated. First, plasma cleaning is performed. During cleaning, the oxygen flow rate is 20sccm and the cleaning time is 5-10min. This is used to remove surface grease and adsorbed impurities and improve the wettability of the coating. Then, the surface is roughened by sandblasting. 50μm white corundum abrasive is selected, the pressure is 0.2MPa, and the spraying angle is 45° to form a uniform pit structure on the surface of the blank. The roughness Ra reaches 2.5μm, increasing the powder contact area. S42, silicon nitride raw materials are placed on a moving platform, so that the spraying rate of the high voltage electrostatic spraying equipment is 5mm / s and the coating thickness is controlled at 15-20μm; S43. After spraying, allow the coating to self-level for 5 minutes to ensure that there are no pinholes or missed coating defects.

[0038] The specific steps of step S5 are as follows: S51. Initial stage: The temperature inside the drying oven is increased from 30℃ to 60℃ at a rate of 1-2℃ / min, and the temperature is maintained for 1 hour to remove free moisture. S52, Intermediate stage: The temperature inside the drying oven is increased from 60℃ to 120℃ at a rate of 0.5-1℃ / min, and the temperature is maintained for 2 hours to promote the cross-linking and curing of polyvinyl alcohol. S53. Final Stage: The temperature inside the drying oven is reduced from 120℃ to 80℃ at a rate of 1℃ / min to prevent thermal stress from causing coating cracking. The specific steps of step S6 are as follows: S61, during the debinding stage, the temperature inside the high-temperature furnace is increased to 600℃ at a rate of 5℃ / min and held for 2 hours. The nitrogen flow rate is 5L / min to remove the organic carrier in the silicon nitride substrate, and the weight loss rate is controlled at 8±0.5%. S62. High-temperature sintering: The temperature inside the high-temperature furnace continues to rise to 1850℃ at a rate of 3℃ / min, with a nitrogen pressure of 3MPa, and is held at this temperature for 3-5 hours. An in-situ interface layer is formed on the surface of the silicon nitride raw material, utilizing the in-situ nitriding reaction of silicon powder ( )generate Columnar crystals, which synergistically form a gradient interface layer with boron nitride; S63. Cooling and temperature reduction: The temperature inside the high-temperature furnace is reduced to 800℃ at a rate of 2℃ / min, and then cooled with the furnace to avoid interface cracking caused by thermal shock.

[0039] Effect verification: The problem of erosion and hot cracking of the separation ring in continuous casting of molten steel was solved, and the service life of continuous casting was increased from 200 heats to 500 heats.

[0040] In summary, this reactive powder coating method for in-situ generation of interface layers on silicon nitride defective surfaces can be flexibly changed according to the requirements of on-site process parameters.

[0041] Based on the above description, those skilled in the art can make various changes and modifications without departing from the technical concept of this invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface, characterized by: Comprise the following specific steps: Step S1, raw material preparation, the raw material formula consists of the following components by weight parts, boron nitride 35-45 parts, silicon powder 25-35 parts, yttria 14-17 parts, polyvinyl alcohol 10 parts, glycerol 3-5 parts and sodium dodecyl benzene sulfonate 2 parts; Step S2, composite powder configuration, the raw materials of step S1 are mixed to prepare a composite powder; Step S3, slurry dispersion and defoaming, adding composite powder, glycerol and sodium dodecyl benzene sulfonate to polyvinyl alcohol solution, then carrying out dispersion and defoaming treatment to obtain slurry; Step S4, green body surface coating, coating the surface of the silicon nitride green body by high voltage electrostatic spraying equipment; Step S5, gradient drying and curing, drying and curing the silicon nitride green body by gradient drying method; Step S6, sintering reaction, sintering the cured silicon nitride green body to form an in-situ generated interface layer; The specific steps of step S4 are as follows: S41, at a distance of 20 cm from the surface of the silicon nitride green body, the surface of the silicon nitride green body is coated by high voltage electrostatic spraying equipment; S42, the silicon nitride green body is placed on a moving platform, the spraying rate of the high voltage electrostatic spraying equipment is 5 mm / s, and the coating thickness is controlled at 15-20 μm; S43, self-leveling for 5 min after spraying to ensure that the coating has no pinhole and missing coating defects; The specific steps of step S6 are as follows: S61, degassing stage, the temperature in the high temperature furnace is increased to 600℃ at a rate of 5℃ / min, and the temperature is kept for 2h, the nitrogen flow is 5L / min, which is used to remove the organic carrier in the silicon nitride green body, and the weight loss rate is controlled at 8±0.5%; S62, high temperature sintering, the temperature in the high temperature furnace is continuously increased to 1850℃ at a rate of 3℃ / min, the nitrogen pressure is 3MPa, and the temperature is kept for 3-5h to form an in-situ generated interface layer on the surface of the silicon nitride green body; S63, cooling, the temperature in the high temperature furnace is decreased to 800℃ at a rate of 2℃ / min, and then the furnace is cooled.

2. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 1, wherein: The specific steps of step S2 are as follows: S21, powder mixing, boron nitride, silicon powder and yttria are put into agate ball mill tank according to the proportion, and anhydrous ethanol is added as dispersion medium; S22, ball milling into slurry, using milling balls, under the protection of inert atmosphere, ball milling for 3h, obtaining post-milling slurry; S23, evaporation to obtain composite powder, the solvent is removed by rotary evaporation under the condition of temperature 60℃ and vacuum degree-0.09MPa to obtain dry composite powder.

3. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 2, wherein: The bulk density of the powder of S23 is controlled at 0.8-1.0 .

4. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 1, wherein: The specific steps of step S3 are as follows: S31, polyvinyl alcohol is dissolved in deionized water at 80℃, stirred until completely dissolved, and then cooled to room temperature; S32, adding composite powder, glycerol and sodium dodecyl benzene sulfonate to the polyvinyl alcohol solution, and shearing and dispersing by high speed stirrer; S33, removing the air bubbles in the slurry by ultrasonic defoaming method.

5. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 3, wherein: The S32 step, the speed of the high-speed mixer is 3000 rpm, the stirring duration is 30-35 min, and the slurry viscosity is 500-800 .

6. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface of claim 3, wherein: In step S33, the ultrasonic power is 500W, and the duration is 20min.

7. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 1, wherein: The atomization gas pressure of the high voltage electrostatic spraying equipment is 0.3MPa.

8. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 1, wherein: The specific steps of step S5 are as follows: S51, initial stage: the temperature in the drying furnace is increased from 30℃ to 60℃ at a rate of 1-2℃ / min, and the temperature is kept for 1h; S52, intermediate stage: the temperature in the drying furnace is increased from 60℃ to 120℃ at a rate of 0.5-1℃ / min, and the temperature is kept for 2h; S53, final stage: the temperature in the drying furnace is decreased from 120℃ to 80℃ at a rate of 1℃ / min to avoid thermal stress leading to coating cracking.

9. The reactive dusting process for in-situ generation of an interface layer on a silicon nitride green surface as claimed in claim 1, wherein: Before the step S41, the surface of the green body is pretreated. First, the surface of the green body is cleaned by plasma cleaning, the oxygen flow rate is 20sccm, and the cleaning time is 5-10min. Then, the surface of the green body is roughened by sand blasting, 50μm white corundum sand is selected, the pressure is 0.2MPa, and the spraying angle is 45°, so that the surface of the green body forms a uniform pit structure, and the roughness Ra reaches 0.1-2.5μm.