Method for the fused deposition 3d printing of silicon nitride ceramic parts

Abstract

This invention discloses a method for fused deposition modeling (FDM) 3D printing of silicon nitride ceramic parts. The steps include: ball milling a mixture of silicon powder, silicon nitride powder, sintering aid, reinforcing phase particles, and an organic solvent to obtain a ceramic slurry; drying the ceramic slurry to obtain a dried powder; mixing the dried powder, stearic acid, paraffin wax, polyethylene, polypropylene, and ethylene-vinyl acetate copolymer to obtain a feedstock; preparing the feedstock into a printing consumable, 3D printing it to obtain a green blank, machining it to remove interlayer steps on the surface of the green blank to obtain a preform; coating the surface of the preform with silica sol, drying it, then coating it with phenolic resin solution, and drying it again to obtain a reinforced preform; thermally debinding the reinforced preform, nitriding it in a nitrogen atmosphere at a temperature of 1000℃~1350℃ and a pressure of 2MPa~4MPa, and sintering it to obtain a silicon nitride ceramic part. This method can produce large-size silicon nitride ceramic parts with high yield and excellent performance.

Description

Technical Field

[0001] This invention belongs to the field of ceramic material preparation technology, specifically relating to a fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts. Background Technology

[0002] Silicon nitride ceramics are widely used in aerospace, high-end equipment manufacturing, and electronic semiconductor fields due to their comprehensive advantages such as high strength, high hardness, corrosion resistance, and good thermal shock resistance. However, their inherent high hardness and brittleness make traditional subtractive manufacturing methods difficult to process, especially large-sized parts with intricate internal structures, due to high processing difficulty, long cycle times, and high manufacturing costs. Additive manufacturing (3D printing) technology, as a bottom-up, layer-by-layer additive manufacturing method, can achieve one-piece molding without molds, greatly improving design freedom and offering significant advantages in realizing complex structures, lightweight designs, and shortening R&D cycles. Currently, 3D printing technologies applied to ceramic materials mainly fall into the following categories:

[0003] Photopolymerization technologies such as stereolithography (SLA) and digital light processing (DLP) can achieve high printing accuracy and surface quality, but the cost of photosensitive resin raw materials is high. At the same time, silicon nitride ceramic powder has a strong scattering and absorption effect on ultraviolet light, making it difficult to reliably print large-sized parts, and the post-processing process is complicated.

[0004] Selective laser melting (SLM) and selective laser sintering (SLS) are technologies that use lasers to directly melt or sinter ceramic powder. However, the printing process involves huge temperature gradients and internal stresses, which can easily cause microcracks or even macroscopic cracks inside the formed parts, resulting in low yield.

[0005] Binder jetting is a technique that uses a binder to bond a powder bed into shape. Its advantages include fast forming speed, but the resulting green parts have low density and poor strength, making it difficult to achieve densification during subsequent sintering, ultimately resulting in parts whose mechanical properties fail to meet usage requirements.

[0006] Compared to the technologies mentioned above, fused deposition modeling (FDM) technology has significant advantages, including low equipment cost, simple operation and maintenance, large forming space, ease of manufacturing large-size parts, and strong applicability to various material systems. However, for large-size, thick-walled silicon nitride ceramic parts, the green body contains a large amount of organic binder. During the subsequent thermal debinding process, the decomposition and discharge channels of the binder are lengthy and complex, making it prone to blistering, deformation, or cracking of the green body due to internal pressure accumulation and uneven stress release. This results in an extremely narrow debinding process window for large-size parts and a very low yield. Therefore, how to effectively promote the debinding of large-size silicon nitride ceramic green bodies, avoid defects, and improve the yield is an urgent problem to be solved. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a fused deposition modeling (FDM) method for fabricating silicon nitride ceramic parts with large size and excellent mechanical properties, which addresses the shortcomings of the existing technology.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0009] A method for fabricating silicon nitride ceramic parts by fused deposition modeling includes the following steps:

[0010] S1. Mix and ball-mill silicon powder, silicon nitride powder, sintering aid, reinforcing phase particles and organic solvent to obtain ceramic slurry;

[0011] S2. Dry the ceramic slurry to obtain a dry powder;

[0012] S3. The dried powder, stearic acid, paraffin wax, polyethylene, polypropylene and ethylene-vinyl acetate copolymer are mixed to obtain a feed;

[0013] S4. The feed material is made into printing consumables, and 3D printed to obtain a green blank. The green blank is then machined to remove the interlayer steps on the surface of the green blank to obtain a blank body.

[0014] S5. Apply silica sol to the surface of the green body, dry it, then apply phenolic resin coating, and dry it again to obtain a reinforced green body;

[0015] S6. The reinforced blank is hot degreased, nitrided in a nitrogen atmosphere at a temperature of 1000℃~1350℃ and a pressure of 2MPa~4MPa, and sintered to obtain silicon nitride ceramic parts.

[0016] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, in step S1, the silicon powder is 50%–75% by mass percentage, the silicon nitride powder is 10%–30%, the sintering aid is 10%–20%, and the reinforcing phase particles are 1%–5%.

[0017] In the above-mentioned fused deposition 3D printing method for preparing silicon nitride ceramic parts, preferably, in step S3, the dry powder is 75%–85% by mass percentage, stearic acid is 1%–5%, paraffin is 5%–15%, polyethylene is 1%–5%, polypropylene is 1%–5%, and ethylene-vinyl acetate copolymer is 0.5%–5%.

[0018] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, in step S5, the mass fraction of silicon dioxide in the silica sol is 20% to 40%, the phenolic resin coating is a phenolic resin ethanol solution, and the mass fraction of the phenolic resin in the phenolic resin ethanol solution is 10% to 30%.

[0019] In the above-mentioned fused deposition modeling (FDM) method for fabricating silicon nitride ceramic parts, preferably, the silicon powder has a D... 50 The D of silicon nitride powder is 5μm to 10μm. 50 The size ranges from 0.5μm to 1μm.

[0020] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, the sintering aid is at least one of alumina, magnesium oxide, yttrium oxide, ytterbium oxide, lanthanum oxide, gadolinium oxide, and zirconium oxide; the reinforcing phase particles are at least one of titanium nitride, titanium carbide, and tungsten carbide; and the organic solvent is one or more of ethanol, ethyl acetate, and butyl acetate.

[0021] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, in step S1, the mass ratio of the total mass of silicon powder, silicon nitride powder, sintering aid, and reinforcing phase particles to the mass ratio of organic solvent and ball milling media is 1:1 to 2:1 to 3, the ball milling time is 12h to 48h, and the ball milling speed is 50 rpm to 100 rpm.

[0022] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, in step S2, the drying is vacuum drying, the drying temperature is 50℃~70℃, and the drying time is 12h~24h.

[0023] In the above-mentioned fused deposition modeling method for silicon nitride ceramic parts, preferably, in step S3, the mixing is a intensive mixing process, the intensive mixing temperature is 140℃~180℃, and the intensive mixing time is 2h~6h.

[0024] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, in step S4, the 3D printing temperature is 140℃~180℃, the nozzle diameter is 0.6mm~1.2mm, the layer thickness is 40%~80% of the nozzle diameter, and the printing speed is 15mm / s~45mm / s.

[0025] In the above-mentioned fused deposition 3D printing method for silicon nitride ceramic parts, preferably, in step S5, the drying is vacuum drying, the drying temperature is 40℃~60℃, and the drying time is 4h~12h; the re-drying is natural air drying, the natural air drying temperature is 20℃~40℃, and the natural air drying time is 2h~6h.

[0026] In the above-mentioned fused deposition 3D printing method for silicon nitride ceramic parts, preferably, in step S6, the thermal degreasing is vacuum thermal degreasing, the thermal degreasing temperature is 450℃~600℃, and the holding time at the thermal degreasing temperature is 2h~4h; the heating program for thermal degreasing is: heating to 60℃ at 0.2℃ / min~1℃ / min, heating to 150℃ at 0.05℃ / min~0.2℃ / min, and heating to the thermal degreasing temperature at 0.2℃ / min~0.5℃ / min.

[0027] In the preferred embodiment of the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, in step S6, the sintering temperature is 1700℃~1800℃, and the nitriding and sintering regime is as follows: the temperature is increased to 600℃ at 0.5℃ / min~2℃ / min, then increased to 1000℃ at 2℃ / min~5℃ / min, and nitrogen gas is introduced to 2MPa~4MPa; then the temperature is increased to 1200℃ at 0.5℃ / min~2℃ / min, then increased to 1300℃~1350℃ at 0.1℃ / min~0.5℃ / min, and held at that temperature for 2h~4h; then the temperature is increased to the sintering temperature at 0.5℃ / min~2℃ / min and held at that temperature for 2h~4h.

[0028] In the above-mentioned fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts, preferably, in step S4, the machining is performed using a computer numerical control (CNC) machine tool machining center.

[0029] Compared with the prior art, the advantages of the present invention are as follows:

[0030] (1) The fused deposition modeling (FDM) method for preparing silicon nitride ceramic parts of the present invention employs a simple process design and readily available raw material system, combining FDM molding with a one-step thermal debinding process, effectively reducing equipment investment and process complexity. Compared with traditional solvent debinding, the thermal debinding process completely avoids the use of organic solvents, making it more environmentally friendly and safer, while also reducing post-processing costs. This process can stably prepare large-size silicon nitride ceramic parts, and the obtained parts have excellent comprehensive mechanical properties, possessing high density and good mechanical strength.

[0031] (2) The fused deposition modeling method for silicon nitride ceramic parts of the present invention uses silicon powder as the main raw material. Since the silicon powder particles are relatively coarse, high solid content and high flowability feedstock can be prepared with less binder, which is beneficial for printing and safe debinding, and has a small shrinkage rate. At the same time, silicon nitride powder is used in combination. Since the silicon nitride powder particles are fine, they can act as a diluent or catalyst, which can promote the nitriding reaction at a lower temperature. Combined with low-temperature (1000℃~1350℃) nitriding at a pressure of 2MPa~4MPa, the problem of silicon melting and cracking caused by volume expansion during the nitriding process of silicon powder blanks due to insufficient nitrogen penetration and violent exothermic reaction is successfully solved. Compared with the existing atmospheric pressure or low pressure (0.1MPa) high temperature (1400℃) nitriding, it has more advantages, especially suitable for the safe nitriding of thick-walled and large-sized blanks. Furthermore, the moderate volume expansion and gas-phase diffusion of silicon powder during the nitriding process help to bridge the interlayer interface and enhance the interlayer bonding force, thereby improving the overall integrity of the blank. At the same time, the system has low shrinkage and controllable deformation during sintering, which is beneficial to maintaining shape accuracy.

[0032] (3) The fused deposition modeling method for silicon nitride ceramic parts of the present invention first removes the interlayer steps on the surface of the green body by mechanical processing before debinding, effectively avoiding stress concentration caused by geometric abrupt changes during debinding and inhibiting the initiation of cracks from the source. At the same time, a dual reinforcing coating of silica sol and phenolic resin is introduced. Phenolic resin effectively enhances the toughness of the green body at low temperature (50℃~200℃), alleviating deformation or cracking caused by binder softening and volatilization and decomposition of low molecular weight binders; silica sol further strengthens the green body structure in the mid-temperature range (200℃~400℃), preventing the risk of cracking caused by stress generated by the decomposition of macromolecular binders. After this composite strengthening treatment, the debinded green body has sufficient mechanical strength and can be safely transferred to the sintering process, avoiding damage caused by handling collisions, thus providing a key guarantee for the reliable preparation of large-size complex structure ceramic parts. In addition, silica sol and phenolic resin can also generate silicon nitride in situ through reduction nitriding reaction during the subsequent high-temperature sintering process. The reaction products are pure and will not contaminate the ceramic body, while effectively inhibiting the decomposition of silicon nitride at high temperatures. The reaction products of silica in the silica sol, carbon from the high-temperature decomposition of phenolic resin, and nitrogen further regulate sintering kinetics. By hindering excessively rapid surface shrinkage, it promotes uniform densification of the entire body, thereby effectively preventing the "white core" phenomenon caused by uneven shrinkage, and ultimately ensuring a comprehensive improvement in the structural uniformity and mechanical properties of the product.

[0033] In summary, this invention, through comprehensive optimization of raw material selection, process design, and preform reinforcement, achieves the preparation of high-performance silicon nitride ceramics while taking into account process feasibility, cost control, and the molding reliability of large-size parts, and has significant engineering application value. Detailed Implementation

[0034] The present invention will be further described below with reference to the specification and specific preferred embodiments, but this does not limit the scope of protection of the present invention. Unless otherwise specified, the materials and instruments used in the following embodiments are commercially available. The silicon powder was purchased from Hebei Gaofu Silicon Nitride Materials Co., Ltd., D 50 =8μm; silicon nitride powder was purchased from Qingdao Cixing New Materials Co., Ltd. (CX-B08E), D 50 =0.7μm; Alumina and yttrium oxide were purchased from Qingdao MCC New Material Technology Co., Ltd., D 50 =500nm; Titanium carbide was purchased from Qingdao Zhongye New Material Technology Co., Ltd., D 50=50 nm; Paraffin wax (PW), polyethylene (PE), and polypropylene (PP) were purchased from China National Petroleum Corporation; stearic acid (SA) was purchased from Hangzhou Zanyu Oils & Fats Technology Co., Ltd.; ethylene-vinyl acetate copolymer (EVA) was purchased from Fujian Gulei Petrochemical Co., Ltd.; phenolic resin was purchased from Henan Borun Foundry Materials, grade BR2130.

[0035] Example 1

[0036] A method for fabricating silicon nitride ceramic parts by fused deposition modeling includes the following steps:

[0037] (1) Weigh 4200g of silicon powder, 2000g of silicon nitride powder, 500g of alumina, 500g of yttrium oxide, 100g of titanium carbide and organic solvent and place them in a ball mill jar for ball milling and mixing to obtain a ceramic slurry. The organic solvent is ethanol, the ball milling medium is silicon nitride balls, the mass ratio of the mixed powder, ethanol and silicon nitride balls is 1:1.5:2, the ball milling time is 12 h and the rotation speed is 75 rpm.

[0038] (2) The ceramic slurry obtained in step (1) is placed in a vacuum oven and dried at 60°C for 12 hours to obtain dried powder;

[0039] (3) Weigh 6000g of dry powder, 100g of stearic acid, 720g of paraffin wax, 300g of polyethylene, 120g of polypropylene, and 80g of ethylene-vinyl acetate copolymer and mix them in a mixer to obtain the feed. The mixing temperature is 160℃ and the mixing time is 3h.

[0040] (4) Use an extruder to extrude the feed obtained in step (3) and cut it into small segments to obtain printing consumables with a diameter of 1 mm and a length of 2 mm to 5 mm.

[0041] (5) Model the model using CAD software and print it using an FDM 3D printer to obtain a green model. The printing temperature is 160℃, the nozzle diameter is 1mm, the layer thickness is 0.6mm, the printing speed is 20mm / s, and the model is a hollow cylinder with an outer diameter of 52cm, an inner diameter of 50cm, and a height of 80cm. 3D printing is a process of layering and stacking, and the layer thickness refers to the thickness of each layer.

[0042] (6) Use a computer numerical control machine tool (CNC) machining center to machine the printed blank obtained in step (5) to remove the interlayer steps on the surface and obtain the blank.

[0043] (7) Spray a layer of silica sol on the surface of the processed blank. The silica sol contains 30% silica by mass and is dried in a vacuum oven at 50°C for 6 hours.

[0044] (8) Use anhydrous ethanol to dilute phenolic resin to obtain phenolic resin coating liquid (i.e. phenolic resin ethanol solution). The mass fraction of phenolic resin in phenolic resin ethanol solution is 20%. Spray it onto the surface of the green body obtained in step (7), and air dry it naturally at a temperature of 30°C for 2 hours to obtain a reinforced green body.

[0045] (9) The blank obtained in step (8) is placed in a vacuum degreasing furnace for hot degreasing. The hot degreasing temperature is 500℃. The temperature is increased to 60℃ at a heating rate of 1℃ / min, to 150℃ at a heating rate of 0.1℃ / min, and to 500℃ at a heating rate of 0.35℃ / min and held for 2 hours.

[0046] (10) The blank obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃ and the sintering temperature is 1780℃. The nitriding and sintering process is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 2 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min and held for 3 hours. Then the temperature is increased to 1780℃ at 1℃ / min and sintered for 3 hours.

[0047] (11) Use a machining center to perform fine machining on the sintered silicon nitride parts to obtain silicon nitride ceramic parts.

[0048] Example 2

[0049] A method for fabricating silicon nitride ceramic parts by fused deposition modeling includes the following steps:

[0050] (1) Weigh 4800g of silicon powder, 1000g of silicon nitride powder, 500g of alumina, 500g of yttrium oxide, 100g of titanium carbide, and an organic solvent and place them in a ball mill jar for ball milling and mixing to obtain a ceramic slurry. The organic solvent is ethanol, the ball milling medium is silicon nitride balls, the mass ratio of the mixed powder, ethanol, and silicon nitride balls is 1:1.5:2, the ball milling time is 12 h, and the rotation speed is 75 rpm.

[0051] (2) The ceramic slurry obtained in step (1) is placed in a vacuum oven and dried at 60°C for 12 hours to obtain dried powder;

[0052] (3) Weigh 6000g of dry powder, 90g of stearic acid, 770g of paraffin wax, 300g of polyethylene, 130g of polypropylene, and 70g of ethylene-vinyl acetate copolymer and mix them in an internal mixer to obtain the feed. The mixing temperature is 160℃ and the mixing time is 3h.

[0053] (4) Use an extruder to extrude the feed obtained in step (3) and cut it into small segments to obtain printing consumables with a diameter of 1 mm and a length of 2-5 mm.

[0054] (5) Model the model using CAD software and print it using an FDM 3D printer to obtain a green model. The printing temperature is 160℃, the nozzle diameter is 0.8mm, the layer thickness is 0.5mm, the printing speed is 20mm / s, and the model is a hollow cylinder with an outer diameter of 52cm, an inner diameter of 50cm, and a height of 80cm. 3D printing is a process of layering and stacking, and the layer thickness refers to the thickness of each layer.

[0055] (6) Use a CNC machining center to machine the printed blank obtained in step (5) to remove the interlayer steps on the surface and obtain the blank.

[0056] (7) Spray a layer of silica sol on the surface of the processed blank. The silica sol contains 30% silica by mass and is dried in a vacuum oven at 50°C for 6 hours.

[0057] (8) Phenolic resin is diluted with anhydrous ethanol to obtain phenolic resin coating liquid (i.e. phenolic resin ethanol solution). The mass fraction of phenolic resin in phenolic resin ethanol solution is 25%. It is sprayed onto the surface of the green body obtained in step (7) and air-dried at 30°C for 2 hours to obtain a reinforced green body.

[0058] (9) The blank obtained in step (8) is placed in a vacuum degreasing furnace for hot degreasing. The hot degreasing temperature is 500℃. The temperature is increased to 60℃ at a rate of 1℃ / min, to 150℃ at a rate of 0.1℃ / min, and to 500℃ at a rate of 0.35℃ / min, and then kept at that temperature for 2 hours.

[0059] (10) The blank obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃ and the sintering temperature is 1780℃. The nitriding and sintering process is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 2 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min and held for 3 hours. Then the temperature is increased to 1780℃ at 1℃ / min and sintered for 3 hours.

[0060] (11) Use a machining center to perform fine machining on the sintered silicon nitride parts to obtain silicon nitride ceramic parts.

[0061] Example 3

[0062] A method for fabricating silicon nitride ceramic parts by fused deposition modeling includes the following steps:

[0063] (1) Weigh 4200g of silicon powder, 2000g of silicon nitride powder, 100g of magnesium oxide, 450g of aluminum oxide, 450g of yttrium oxide, and 150g of titanium carbide and organic solvent, and place them in a ball mill jar for ball milling and mixing to obtain a ceramic slurry. The organic solvent is ethanol, the ball milling medium is silicon nitride balls, the mass ratio of the mixed powder, ethanol and silicon nitride balls is 1:1.5:2, the ball milling time is 12h, and the rotation speed is 75 rpm.

[0064] (2) The slurry obtained in step (1) is placed in a vacuum oven and dried at 60°C for 12 hours to obtain dried powder;

[0065] (3) Weigh 6000g of dry powder, 100g of stearic acid, 720g of paraffin wax, 300g of polyethylene, 120g of polypropylene, and 80g of ethylene-vinyl acetate copolymer and mix them in a mixer to obtain the feed. The mixing temperature is 160℃ and the mixing time is 3h.

[0066] (4) Use an extruder to extrude the feed obtained in step (3) and cut it into small segments to obtain printing consumables with a diameter of 1 mm and a length of 2-5 mm.

[0067] (5) Model the model using CAD software and print it using an FDM 3D printer to obtain a green model. The printing temperature is 160℃, the nozzle diameter is 1mm, the layer thickness is 0.6mm, the printing speed is 20mm / s, and the model is a hollow cylinder with an outer diameter of 52cm, an inner diameter of 50cm, and a height of 80cm. 3D printing is a process of layering and stacking, and the layer thickness refers to the thickness of each layer.

[0068] (6) Use a CNC machining center to machine the printed blank obtained in step (5) to remove the interlayer steps on the surface and obtain the blank.

[0069] (7) Spray a layer of silica sol on the surface of the processed blank. The silica sol contains 30% silica by mass and is dried in a vacuum oven at 50°C for 6 hours.

[0070] (8) Use anhydrous ethanol to dilute phenolic resin to obtain phenolic resin coating liquid (i.e. phenolic resin ethanol solution). The mass fraction of phenolic resin in phenolic resin ethanol solution is 20%. Spray it onto the surface of the green body obtained in step (7), and air dry it naturally at a temperature of 30°C for 2 hours to obtain a reinforced green body.

[0071] (9) The blank obtained in step (8) is placed in a vacuum degreasing furnace for hot degreasing. The hot degreasing temperature is 500℃. The temperature is increased to 60℃ at a rate of 1℃ / min, to 150℃ at a rate of 0.1℃ / min, and to 500℃ at a rate of 0.35℃ / min, and then kept at that temperature for 2 hours.

[0072] (10) The blank obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃ and the sintering temperature is 1780℃. The nitriding and sintering process is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 2 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min and held for 3 hours. Then the temperature is increased to 1780℃ at 1℃ / min and sintered for 3 hours.

[0073] (11) Use a machining center to perform fine machining on the sintered silicon nitride parts to obtain silicon nitride ceramic parts.

[0074] Example 4

[0075] A method for fabricating silicon nitride ceramic parts by fused deposition modeling includes the following steps:

[0076] (1) Weigh 4800g of silicon powder, 1000g of silicon nitride powder, 500g of alumina, 500g of yttrium oxide, 200g of titanium carbide, and an organic solvent and place them in a ball mill jar for ball milling and mixing to obtain a ceramic slurry. The organic solvent is ethanol, the ball milling medium is silicon nitride balls, the mass ratio of the mixed powder, ethanol, and silicon nitride balls is 1:1.5:2, the ball milling time is 12 h, and the rotation speed is 75 rpm.

[0077] (2) The slurry obtained in step (1) is placed in a vacuum oven and dried at 60°C for 12 hours to obtain dried powder;

[0078] (3) Weigh 6000g of dry powder, 90g of stearic acid, 770g of paraffin wax, 300g of polyethylene, 130g of polypropylene, and 70g of ethylene-vinyl acetate copolymer and mix them in an internal mixer to obtain the feed. The mixing temperature is 160℃ and the mixing time is 3h.

[0079] (4) Use an extruder to extrude the feed obtained in step (3) and cut it into small segments to obtain printing consumables with a diameter of 1 mm and a length of 2-5 mm.

[0080] (5) Model the model using CAD software and print it using an FDM 3D printer to obtain a green model. The printing temperature is 160℃, the nozzle diameter is 0.8mm, the layer thickness is 0.5mm, the printing speed is 20mm / s, and the model is a hollow cylinder with an outer diameter of 52cm, an inner diameter of 50cm, and a height of 80cm. 3D printing is a process of layering and stacking, and the layer thickness refers to the thickness of each layer.

[0081] (6) Use a CNC machining center to machine the printed blank obtained in step (5) to remove the interlayer steps on the surface and obtain the blank.

[0082] (7) Spray a layer of silica sol on the surface of the processed blank. The silica sol contains 30% silica by mass and is dried in a vacuum oven at 50°C for 6 hours.

[0083] (8) Phenolic resin is diluted with anhydrous ethanol to obtain phenolic resin coating liquid (i.e. phenolic resin ethanol solution). The mass fraction of phenolic resin in phenolic resin ethanol solution is 25%. It is sprayed onto the surface of the green body obtained in step (7) and air-dried at 30°C for 2 hours to obtain a reinforced green body.

[0084] (9) The blank obtained in step (8) is placed in a vacuum degreasing furnace for hot degreasing. The hot degreasing temperature is 500℃, and the heating rate is 1℃ / min to 60℃, 0.1℃ / min to 150℃, 0.35℃ / min to 500℃ and held for two hours.

[0085] (10) The green body obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃, and the sintering temperature is 1800℃. The nitriding and sintering regime is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 2.5 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min, and held for 3 hours. Then the temperature is increased to 1800℃ at 1℃ / min and sintered for 3 hours.

[0086] (11) Use a machining center to perform fine machining on the sintered silicon nitride parts to obtain silicon nitride ceramic parts.

[0087] Comparative Example 1

[0088] A 3D printing method for silicon nitride ceramic parts is basically the same as that in Example 1, the main difference being that silicon powder is not added. The specific steps include:

[0089] (1) Weigh 9000g of silicon nitride powder (to maintain the composition of the ceramic powder as in Example 1, silicon nitride powder was used to make up the amount of silicon powder not added; approximately 7000g of silicon nitride powder was obtained after nitriding 4200g of silicon powder), 500g of alumina, 500g of yttrium oxide, 100g of titanium carbide, and an organic solvent, and place them in a ball mill jar for ball milling and mixing to obtain a ceramic slurry. The organic solvent was ethanol, the ball milling medium was silicon nitride balls, the mass ratio of the mixed powder, ethanol, and silicon nitride balls was 1:1.5:2, the ball milling time was 12h, and the rotation speed was 75 rpm.

[0090] (2) The slurry obtained in step (1) is placed in a vacuum oven and dried at 60°C for 12 hours to obtain dried powder;

[0091] (3) Weigh 6000g of dry powder, 150g of stearic acid, 900g of paraffin wax, 370g of polyethylene, 160g of polypropylene, and 100g of ethylene-vinyl acetate copolymer and mix them in a mixer to obtain the feed. The mixing temperature is 160℃ and the mixing time is 3h. Since silicon nitride powder is fine and has a higher specific surface area than silicon powder, more binder is required. In order to achieve smooth mixing, the amount of binder system (including stearic acid, paraffin wax, polyethylene, polypropylene, and ethylene-vinyl acetate copolymer) has been increased proportionally. These binders can be removed by thermal degreasing later.

[0092] (4) Use an extruder to extrude the feed obtained in step (3) and cut it into small segments to obtain printing consumables with a diameter of 1 mm and a length of 2-5 mm.

[0093] (5) Model the model using CAD software and print it using an FDM 3D printer to obtain a printed blank. The printing temperature is 160℃, the nozzle diameter is 1mm, the layer thickness is 0.6mm, the printing speed is 20mm / s, the model is a hollow cylinder with an outer diameter of 52cm, an inner diameter of 50cm, and a height of 80cm.

[0094] (6) Use a CNC machining center to process the printed blank obtained in step (5) to remove the interlayer steps on the surface and obtain the blank.

[0095] (7) Spray a layer of silica sol on the surface of the processed blank. The silica sol contains 30% silica by mass and is dried in a vacuum oven at 50°C for 6 hours.

[0096] (8) Use anhydrous ethanol to dilute phenolic resin to obtain phenolic resin coating liquid (i.e. phenolic resin ethanol solution). The mass fraction of phenolic resin in phenolic resin ethanol solution is 20%. Spray it onto the surface of the green body obtained in step (7), and air dry it naturally at a temperature of 30°C for 2 hours to obtain a reinforced green body.

[0097] (9) The blank obtained in step (8) is placed in a vacuum degreasing furnace for hot degreasing. The hot degreasing temperature is 500℃. The temperature is increased to 60℃ at 1℃ / min, to 150℃ at 0.1℃ / min, and to 500℃ at 0.35℃ / min and kept at that temperature for 2 hours.

[0098] (10) The blank obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃ and the sintering temperature is 1780℃. The nitriding and sintering process is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 2 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min and held for 3 hours. Then the temperature is increased to 1780℃ at 1℃ / min and sintered for 3 hours.

[0099] (11) Use a machining center to perform fine machining on the sintered silicon nitride parts to obtain silicon nitride ceramic parts.

[0100] Comparative Example 2

[0101] A 3D printing method for silicon nitride ceramic parts is basically the same as that in Example 1, except that mechanical processing is not performed to remove the interlayer steps on the surface of the printed blank, i.e., step (6) is omitted.

[0102] Comparative Example 3

[0103] A 3D printing method for silicon nitride ceramic parts is basically the same as that in Example 1, except that silica sol is not sprayed, i.e., step (7) is omitted.

[0104] Comparative Example 4

[0105] A 3D printing method for silicon nitride ceramic parts is basically the same as that in Example 1, except that phenolic resin coating is not sprayed, i.e., step (8) is omitted.

[0106] Comparative Example 5

[0107] A 3D printing method for silicon nitride ceramic parts is basically the same as that in Example 1, the main difference being that the timing of filling with high nitrogen pressure in step (10) is different, as follows:

[0108] The green body obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃ and the sintering temperature is 1780℃. The nitriding and sintering process is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 0.1 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min, nitrogen is introduced to 2 MPa and held for 3 hours. Then the temperature is increased to 1780℃ at 1℃ / min and sintered for 3 hours.

[0109] Comparative Example 6

[0110] A 3D printing method for silicon nitride ceramic parts is basically the same as that in Example 1, the main difference being that silicon nitride powder is not added. The specific steps include:

[0111] (1) Weigh 5400g of silicon powder (to maintain the composition of the ceramic powder as in Example 1, 1200g of silicon powder is used to make up the difference; after nitriding the 1200g of silicon powder into silicon nitride, it will become 1.667 times the original mass, equivalent to 2000g of silicon nitride), 500g of alumina, 500g of yttrium oxide, and 100g of titanium carbide, and place them in a ball mill jar for ball milling and mixing to obtain a ceramic slurry. The organic solvent is ethanol, the ball milling medium is silicon nitride balls, the mass ratio of the mixed powder, ethanol, and silicon nitride balls is 1:1.5:2, the ball milling time is 12 h, and the rotation speed is 75 rpm.

[0112] (2) The slurry obtained in step (1) was placed in a vacuum oven and dried at 60°C for 12 hours to obtain dried powder.

[0113] (3) Weigh 6000g of dry powder, 88g of stearic acid, 680g of paraffin wax, 280g of polyethylene, 112g of polypropylene, and 72g of ethylene-vinyl acetate copolymer and mix them in an internal mixer to obtain the feed. The mixing temperature is 160℃ and the mixing time is 3h. Since the silica powder is coarse and has a smaller specific surface area than the silicon nitride powder, the required binder is also reduced accordingly. In order to obtain a suitable mixture, the amount of binder system (including stearic acid, paraffin wax, polyethylene, polypropylene, and ethylene-vinyl acetate copolymer) has been reduced proportionally. These binders can be removed by thermal degreasing later.

[0114] (4) Use an extruder to extrude the feed obtained in step (3) and cut it into small segments to obtain printing consumables with a diameter of 1 mm and a length of 2-5 mm.

[0115] (5) Model the model using CAD software and print it using an FDM 3D printer to obtain a printed blank. The printing temperature is 160℃, the nozzle diameter is 1mm, the layer thickness is 0.6mm, the printing speed is 20mm / s, the model is a hollow cylinder with an outer diameter of 52cm, an inner diameter of 50cm, and a height of 80cm.

[0116] (6) Use a CNC machining center to process the printed blank obtained in step (5) to remove the interlayer steps on the surface and obtain the blank.

[0117] (7) Spray a layer of silica sol on the surface of the processed blank. The silica sol contains 30% silica by mass and is dried in a vacuum oven at 50°C for 6 hours.

[0118] (8) Use anhydrous ethanol to dilute phenolic resin to obtain phenolic resin coating liquid (i.e. phenolic resin ethanol solution). The mass fraction of phenolic resin in phenolic resin ethanol solution is 20%. Spray it onto the surface of the green body obtained in step (7), and air dry it naturally at a temperature of 30°C for 2 hours to obtain a reinforced green body.

[0119] (9) The blank obtained in step (8) is placed in a vacuum degreasing furnace for hot degreasing. The hot degreasing temperature is 500℃. The temperature is increased to 60℃ at 1℃ / min, to 150℃ at 0.1℃ / min, and to 500℃ at 0.35℃ / min and kept at that temperature for 2 hours.

[0120] (10) The blank obtained after hot degreasing in step (9) is transferred to a gas pressure sintering furnace for sintering. The nitriding temperature is 1000℃~1300℃ and the sintering temperature is 1780℃. The nitriding and sintering process is as follows: the temperature is increased to 600℃ at 1℃ / min, then increased to 1000℃ at 4℃ / min, and nitrogen is introduced to 2 MPa. Then the temperature is increased to 1200℃ at 1℃ / min, then increased to 1300℃ at 0.4℃ / min and held for 3 hours. Then the temperature is increased to 1780℃ at 1℃ / min and sintered for 3 hours.

[0121] (11) Use a machining center to perform fine machining on the sintered silicon nitride parts to obtain silicon nitride ceramic parts.

[0122] Table 1. Comparison of product performance between Examples 1-4 and Comparative Examples 1-6

[0123]

[0124] Table 1 shows the performance of Examples 1-4 and Comparative Examples 1-5 during the debinding and sintering processes. Examples 1-4 all achieved a relative density of over 99%, a stable shrinkage rate of around 14%, and a flexural strength exceeding 850 MPa, demonstrating excellent mechanical properties. In contrast, Comparative Example 1, which used only silicon nitride powder, failed to achieve sintering densification and exhibited debinding cracking, with a flexural strength of only 554 MPa and a relatively high shrinkage rate. Comparative Examples 2 and 4, which were not machined or coated with phenolic resin, cracked during the debinding stage, resulting in a decrease in mechanical properties. Although Comparative Example 3, which was not coated with silica sol, did not crack during the debinding process, it cracked during transfer due to insufficient green body strength and could not complete sintering. Furthermore, Comparative Example 5 only introduced nitrogen gas required for nitriding at 1000℃, with a low pressure (only 0.1 MPa). High nitrogen pressure (2 MPa) was introduced only at 1300℃, resulting in severe exothermic reaction and silicon melting. This prevented the material from densifying, leading to a decrease in mechanical properties. In contrast, Example 1 introduced high-pressure nitriding starting at 1000℃, a low-temperature, high-pressure nitriding process that allows for gradient nitriding and effectively prevents silicon melting. Comparative Example 6 did not add silicon nitride powder. Although high-pressure nitrogen gas was introduced at a lower temperature, the actual nitriding temperature was higher, leading to concentrated nitriding. Since nitriding is exothermic, this resulted in a sudden increase in local temperature, causing melting and preventing material densification, resulting in lower mechanical properties. Example 1, with silicon nitride powder as a diluent or catalyst, allowed the nitriding reaction to occur at a lower temperature, achieving gradient nitriding, avoiding concentrated nitriding, and thus preventing melting. In summary, the fused deposition modeling method for large-size silicon nitride ceramic parts proposed in this invention can effectively suppress cracking during debinding and sintering processes, has a low shrinkage rate, and helps prevent part deformation.

[0125] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method of fused deposition 3D printing of a silicon nitride ceramic part, characterized in that, Includes the following steps: S1. Mix and ball-mill silicon powder, silicon nitride powder, sintering aid, reinforcing phase particles and organic solvent to obtain ceramic slurry, wherein the silicon powder is 50% to 75% and the silicon nitride powder is 10% to 30% by mass percentage; S2. Dry the ceramic slurry to obtain a dry powder; S3. The dried powder, stearic acid, paraffin wax, polyethylene, polypropylene and ethylene-vinyl acetate copolymer are mixed to obtain a feed; S4. The feed material is made into printing consumables, and 3D printed to obtain a green blank. The green blank is then machined to remove the interlayer steps on the surface of the green blank to obtain a blank body. S5. Apply silica sol to the surface of the green body, dry it, then apply phenolic resin coating, and dry it again to obtain a reinforced green body; S6. The reinforced blank is subjected to hot degreasing, nitriding, and sintering to obtain silicon nitride ceramic parts. The nitriding is carried out in a nitrogen atmosphere at a temperature of 1000℃~1350℃ and a pressure of 2MPa~4MPa. The nitrogen is pressurized to 2MPa~4MPa when the system temperature rises to 1000℃.

2. The method for fabricating silicon nitride ceramic parts by fused deposition modeling according to claim 1, characterized in that, In step S1, the sintering aid is 10%–20% by mass percentage, and the reinforcing phase particles are 1%–5%. In step S3, by mass percentage, the dry powder comprises 75%–85%, stearic acid comprises 1%–5%, paraffin comprises 5%–15%, polyethylene comprises 1%–5%, polypropylene comprises 1%–5%, and ethylene-vinyl acetate copolymer comprises 0.5%–5%.

3. The method for fabricating silicon nitride ceramic parts by fused deposition modeling according to claim 1, characterized in that, In step S5, the silica sol contains 20% to 40% silica by mass, the phenolic resin coating is a phenolic resin ethanol solution, and the phenolic resin in the phenolic resin ethanol solution contains 10% to 30% phenolic resin by mass.

4. The method for fabricating silicon nitride ceramic parts by fused deposition 3D printing according to claim 1, characterized in that, The D50 of the silicon powder is 5 μm to 10 μm, the D50 of the silicon nitride powder is 0.5 μm to 1 μm. 50 The D50 of the silicon powder is 5 μm to 10 μm, the D50 of the silicon nitride powder is 0.5 μm to 1 μm. 50 The D50 of the silicon 5. The method for fabricating silicon nitride ceramic parts by fused deposition modeling according to claim 1, characterized in that, The sintering aid is at least one of alumina, magnesium oxide, yttrium oxide, ytterbium oxide, lanthanum oxide, gadolinium oxide, and zirconium oxide; the reinforcing phase particles are at least one of titanium nitride, titanium carbide, and tungsten carbide; and the organic solvent is one or more of ethanol, ethyl acetate, and butyl acetate.

6. The method for fabricating silicon nitride ceramic parts by fused deposition modeling according to claim 1, characterized in that, In step S1, the total mass ratio of silicon powder, silicon nitride powder, sintering aid and reinforcing phase particles to organic solvent and ball milling media is 1:1 to 2:1 to 3, the ball milling time is 12h to 48h, and the ball milling speed is 50 rpm to 100 rpm. In step S2, the drying is vacuum drying, the drying temperature is 50℃~70℃, and the drying time is 12h~24h. In step S3, the mixing is a intensive mixing process, the temperature of which is 140℃~180℃ and the time of which is intensive mixing is 2h~6h.

7. The method for fabricating silicon nitride ceramic parts by fused deposition modeling according to claim 1, characterized in that, In step S4, the 3D printing temperature is 140℃~180℃, the nozzle diameter is 0.6mm~1.2mm, the layer thickness is 40%~80% of the nozzle diameter, and the 3D printing speed is 15mm / s~45mm / s. In step S5, the drying is vacuum drying, the drying temperature is 40℃~60℃, and the drying time is 4h~12h; the re-drying is natural air drying, the natural air drying temperature is 20℃~40℃, and the natural air drying time is 2h~6h.

8. The method for fabricating silicon nitride ceramic parts by fused deposition 3D printing according to any one of claims 1 to 7, characterized in that, In step S6, the hot degreasing is vacuum hot degreasing, the hot degreasing temperature is 450℃~600℃, and the holding time at the hot degreasing temperature is 2h~4h; the heating program for hot degreasing is: heating to 60℃ at 0.2℃ / min~1℃ / min, heating to 150℃ at 0.05℃ / min~0.2℃ / min, and heating to the hot degreasing temperature at 0.2℃ / min~0.5℃ / min.

9. The method for fabricating silicon nitride ceramic parts by fused deposition 3D printing according to any one of claims 1 to 7, characterized in that, In step S6, the sintering temperature is 1700℃~1800℃, and the nitriding and sintering process is as follows: the temperature is increased to 600℃ at 0.5℃ / min~2℃ / min, then increased to 1000℃ at 2℃ / min~5℃ / min, and nitrogen gas is introduced to 2MPa~4MPa. Then the temperature is increased to 1200℃ at 0.5℃ / min~2℃ / min, then increased to 1300℃~1350℃ at 0.1℃ / min~0.5℃ / min, and held at that temperature for 2h~4h. Then the temperature is increased to the sintering temperature at 0.5℃ / min~2℃ / min and held at that temperature for 2h~4h.

10. The method for fabricating silicon nitride ceramic parts by fused deposition 3D printing according to any one of claims 1 to 7, characterized in that, In step S4, the machining is performed using a computer numerical control (CNC) machine tool machining center.

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