A method for enhancing the mechanical properties of a 3D-printed porous ceramic framework by printing a filament seal

Abstract

The application relates to a method for enhancing the mechanical properties of a 3D-printed porous ceramic framework by sealing the holes of printing monofilaments, and relates to a method for enhancing the mechanical properties of a 3D-printed porous ceramic framework. The application aims to solve the technical problem that the ceramic formed by preceramic polymer pyrolysis under an air atmosphere has irregular, large-size holes and poor mechanical properties. In the application, a high-temperature melting filler such as boron powder is added, the boron powder is oxidized at high temperature to form boron oxide, and the boron oxide in a molten state causes material migration, thereby sealing the holes of the 3D-printed monofilaments under the air atmosphere, gradually changing the hollow structure and cracks in the monofilaments into a solid structure, and finally significantly improving the overall mechanical properties of the framework formed by the mutual lapping of the monofilaments. The hole sealing process of the application is simple, does not need additional impregnation and filling treatment of the holes of the printing monofilaments, improves the mechanical properties of the printing framework under pyrolysis under the air atmosphere, and widens the application environment of the polymer-derived ceramic.

Description

Technical Field

[0001] This invention relates to a method for enhancing the mechanical properties of 3D-printed porous ceramic frames. Background Technology

[0002] Ceramics and ceramic matrix composites possess advantages such as high-temperature resistance, oxidation resistance, and chemical corrosion resistance, making them indispensable thermal protection materials for extreme aerospace environments. However, with increasing demands for miniaturization, precision, and structural complexity in ceramic materials, the application of traditionally manufactured ceramic materials in high-performance components has become severely limited. Prepolymer-derived ceramics (PDCs) refer to ceramic materials transformed from preceramic polymers (PCPs) through processes such as molding, curing, and pyrolysis. They possess excellent molding capabilities, flexible adjustment of microstructure and composition, and the ability to transform into ceramics at relatively low temperatures. Combining 3D printing technology with polymer derivatization technology can solve the problems faced by traditional ceramic preparation methods.

[0003] Compared to an inert atmosphere, ceramics formed by the pyrolysis of prepolymers in an air atmosphere have irregular, large-sized pores and poorer mechanical properties. This is because during the conversion of prepolymers into ceramics, not only are small-molecule gases released from the matrix itself, but oxygen also continuously reacts with the matrix and the small-molecule substances released from the matrix to form gaseous substances. Therefore, during the sintering process, the substances continuously migrate to the wall to form an irregular, large-sized pore structure. Summary of the Invention

[0004] The present invention aims to address the technical problems of irregularity, large-sized pores, and poor mechanical properties in ceramics formed by the pyrolysis of pre-ceramic polymers in an air atmosphere, and provides a method for sealing the pores of printed monofilaments to enhance the mechanical properties of 3D printed porous ceramic frames.

[0005] The method of the present invention for enhancing the mechanical properties of 3D printed porous ceramic frames by sealing holes in printed monofilaments is carried out according to the following steps:

[0006] I. Preparation of printing paste:

[0007] Mix the first batch of ceramic precursor, crosslinking agent and inhibitor together for 5 min to 10 min; then add the second batch of ceramic precursor and platinum catalyst, and stir for another 5 min to 10 min; then add the fiber, stir for 10 min to 15 min, then add the filler, stir for 5 min to 10 min, then add the silica, the silica is added in two equal portions, the amount added in the two portions is the same, stir for 10 min to 15 min after the first addition, and stir for 30 min to 35 min after the second addition;

[0008] The first batch of ceramic precursors and the second batch of ceramic precursors have the same mass and are made of the same material.

[0009] The mass ratio of the fiber to the first batch of ceramic precursors is 1:(1-3);

[0010] The mass ratio of the filler to the first batch of ceramic precursors is 1:(16-17);

[0011] The total mass ratio of the two additions of silica to the mass ratio of the first batch of ceramic precursor is 1:(2-5);

[0012] II. Printing the ceramic frame preform:

[0013] (1) Use Cinema 4D software to draw a 3D printing model and export the model as an STL file. Import the exported STL file into Cura slicing software to slice it, that is, divide the drawn 3D model into multiple layers of 2D planes.

[0014] (2) Set the corresponding printing parameters on the Cura slicing software according to actual needs, and then print to obtain the ceramic frame blank;

[0015] III. Curing and Heat Treatment of the Printed Frame:

[0016] The printed ceramic frame is placed in an oven for curing. The cured ceramic frame is then heat-treated in the following two steps:

[0017] (1) Pre-oxidation at low temperature: Place the cured ceramic frame in a muffle furnace, raise the temperature from room temperature to 320℃~330℃ and keep it at that temperature for 6h~6.5h, and then cool it down to room temperature with the furnace.

[0018] (2) The pre-oxidized ceramic frame is heated from room temperature to 1100℃~1300℃ and held for 2h~3h, and then cooled to room temperature in the furnace to obtain the 3D printed polymer-derived porous ceramic frame.

[0019] The inventive point of this invention:

[0020] Polymer-derived ceramics decompose in an air atmosphere. Due to the oxidizing atmosphere, they continuously react with substances in the matrix. As the sintering temperature increases, these substances migrate towards the monofilament wall, causing dense cracks not only to appear on the surface of the printed ceramic monofilaments but also to form large, irregular pores inside, severely affecting the overall mechanical properties of the framework. For 3D printing monofilaments with a fiber content higher than 50%, the internal cracks and hollow structures gradually decrease with increasing fiber content, which is beneficial to improving the mechanical properties of the 3D printed structure. However, high fiber content often makes it difficult to overcome the problem of fiber deposition in the slurry and can easily cause the slurry to clog the printer nozzles during printing and extrusion, resulting in discontinuous printing or even printing failure. While low fiber content (15%–50%) can overcome problems such as fiber deposition and printing and extrusion clogging, it is difficult to obtain 3D printed structures with high mechanical properties. This invention proposes a method to resolve these two contradictions. Under conditions of low fiber content, a filler such as boron powder that can melt at high temperatures is added. After the boron powder is oxidized at high temperature, it forms boron oxide. The boron oxide, in a molten state at high temperature, drives the migration of matter, and the powder reaction produces volume expansion, thereby sealing the pores of the 3D printed monofilaments in the air atmosphere. This gradually transforms the interior of the monofilaments, which originally had hollow structures and cracks, into a solid structure (mainly cracks, as cracks are the most important factor causing the decline in the mechanical properties of monofilaments). At the same time, the molten state of the oxidized filler can also alleviate stress concentration and offset some of the shrinkage caused by the cracking of the precursor. Ultimately, the overall mechanical properties of the frame composed of interlocking monofilaments are significantly improved.

[0021] Advantages of this invention:

[0022] 1. The method of the present invention is to fill the pores in an air atmosphere, which is more economical and convenient than the enhancement method of atmosphere protection or vacuum heat treatment;

[0023] 2. The sealing process of the present invention is simple and does not require additional impregnation and filling treatment of the printed monofilament holes, which improves the mechanical properties of the printed frame under air atmosphere pyrolysis and broadens the applicable environment of polymer-derived ceramics. Attached Figure Description

[0024] Figure 1 Images of ceramic frames obtained by adding different boron powders in Experiment 1 and Experiment 2;

[0025] Figure 2 This is a SEM image of the internal cross-section of a single filament in the ceramic frame obtained without adding boron powder in Experiment 2.

[0026] Figure 3 The image shows a SEM image of the internal cross-section of a single filament of the ceramic framework obtained when the mass of boron powder filler is 5g in Experiment 2.

[0027] Figure 4 This is a SEM image of one outer end face of a monofilament of a ceramic framework obtained when the mass of boron powder filler is 5g in Experiment 2.

[0028] Figure 5 Comparison graphs of the compressive strength of frames with different boron powder contents at different sintering temperatures in Experiments 1, 2 and 3 are presented. Detailed Implementation

[0029] Specific Implementation Method 1: This implementation method is a method for enhancing the mechanical properties of 3D printed porous ceramic frames by sealing the holes in printed monofilaments, specifically carried out according to the following steps:

[0030] I. Preparation of printing paste:

[0031] Mix the first batch of ceramic precursor, crosslinking agent and inhibitor together for 5 min to 10 min; then add the second batch of ceramic precursor and platinum catalyst, and stir for another 5 min to 10 min; then add the fiber, stir for 10 min to 15 min, then add the filler, stir for 5 min to 10 min, then add the silica, the silica is added in two equal portions, the amount added in the two portions is the same, stir for 10 min to 15 min after the first addition, and stir for 30 min to 35 min after the second addition;

[0032] The first batch of ceramic precursors and the second batch of ceramic precursors have the same mass and are made of the same material.

[0033] The mass ratio of the fiber to the first batch of ceramic precursors is 1:(1-3);

[0034] The mass ratio of the filler to the first batch of ceramic precursors is 1:(16-17);

[0035] The total mass ratio of the two additions of silica to the mass ratio of the first batch of ceramic precursor is 1:(2-5);

[0036] II. Printing the ceramic frame preform:

[0037] (1) Use Cinema 4D software to draw a 3D printing model and export the model as an STL file. Import the exported STL file into Cura slicing software to slice it, that is, divide the drawn 3D model into multiple layers of 2D planes.

[0038] (2) Set the corresponding printing parameters on the Cura slicing software according to actual needs, and then print to obtain the ceramic frame blank;

[0039] III. Curing and Heat Treatment of the Printed Frame:

[0040] The printed ceramic frame is placed in an oven for curing. The cured ceramic frame is then heat-treated in the following two steps:

[0041] (1) Pre-oxidation at low temperature: Place the cured ceramic frame in a muffle furnace, raise the temperature from room temperature to 320℃~330℃ and keep it at that temperature for 6h~6.5h, and then cool it down to room temperature with the furnace.

[0042] (2) The pre-oxidized ceramic frame is heated from room temperature to 1100℃~1300℃ and held for 2h~3h, and then cooled to room temperature in the furnace to obtain the 3D printed polymer-derived porous ceramic frame.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the first batch of ceramic precursors mentioned in step one is PDMS. Everything else is the same as in Specific Implementation Method One.

[0044] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the crosslinking agent mentioned in step one is hydrogen-containing silicone oil. Everything else is the same as in Specific Implementation Method One or Two.

[0045] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the inhibitor mentioned in step one is 1-ethynyl-1-cyclohexanol. Everything else is the same as in Specific Implementation Methods One to Three.

[0046] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that the fiber mentioned in step one is alumina fiber. Everything else is the same as in Specific Implementation Method Four.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that the filler mentioned in step one is boron powder, Al, Ti, or MoSi. Everything else is the same as in Specific Implementation Method Five.

[0048] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the printing parameters in step two (2) are: needle diameter is 0.84mm, the interlayer spacing is 70% of the needle diameter, the printing speed is 20mm / s, the frame infill rate is 43%, the size of the printed green body is 25mm long × 25mm wide × 20mm high, the filling pattern is serrated, and the interlayer angle is 90°. Everything else is the same as in Specific Implementation Method Six.

[0049] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that the curing temperature in step three is 130℃ and the time is 1 hour. Everything else is the same as in Specific Implementation Method Seven.

[0050] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that the heating rate in step three (1) is 1℃ / min. Everything else is the same as in Specific Implementation Method Eight.

[0051] Specific Implementation Method 10: This implementation method differs from Specific Implementation Method 9 in that the heating rate in step 3 (2) is 2℃ / min. Everything else is the same as in Specific Implementation Method 9.

[0052] The invention was verified using the following experiments:

[0053] Experiment 1: This experiment demonstrates a method for enhancing the mechanical properties of 3D-printed porous ceramic frames by sealing the holes in printed monofilaments. The specific steps are as follows:

[0054] I. Preparation of printing paste:

[0055] Mix 50g of ceramic precursor PDMS, 3g of crosslinking agent hydrogen-containing silicone oil, and 0.17g of inhibitor 1-ethynyl-1-cyclohexanol together and stir for 5 minutes at a speed of 6500 rpm. Then add 50g of ceramic precursor PDMS and 0.1g of platinum catalyst, and stir for another 5 to 10 minutes at a speed of 6500 rpm. Then add 20g of alumina fiber and stir for 10 minutes. Add 3g of filler boron powder and stir for 5 minutes. Then add 25g of silica. Add silica in two equal portions. Stir for 10 minutes after the first addition and 30 minutes after the second addition at a speed of 10000 rpm to ensure that the slurry is mixed evenly.

[0056] II. Printing the ceramic frame preform:

[0057] (1) Use Cinema 4D software to draw a 3D printing model and export the model as an STL file. Import the exported STL file into Cura slicing software to slice it, that is, divide the drawn 3D model into multiple layers of 2D planes.

[0058] (2) Set the corresponding printing parameters on the Cura slicing software according to actual needs. The printing parameters are: needle diameter is 0.84mm, the interlayer spacing is 70% of the needle diameter, the printing speed is 20mm / s, the frame infill rate is 43%, the size of the printed green body is 25mm long × 25mm wide × 20mm high, the filling pattern is serrated, and the interlayer angle is 90°. Then print. The needle extrudes monofilaments along the preset printing path. After printing one layer, the printing platform descends one layer height distance along the Z axis. The monofilaments printed in the second layer are rotated 90° based on the monofilaments printed in the first layer to form an overlapping unit between monofilaments. Repeat this printing process to obtain the entire ceramic frame green body.

[0059] III. Curing and Heat Treatment of the Printed Frame:

[0060] The printed ceramic frame is placed in an oven for curing at 130℃ for 1 hour. The cured ceramic frame is then trimmed at all four sides, resulting in dimensions of 15mm (length) x 15mm (width) x 19mm (height). The frame is then subjected to heat treatment in the following two steps:

[0061] (1) Pre-oxidation at low temperature: The cured ceramic frame is placed in a muffle furnace, heated from room temperature to 320℃ and held for 6 hours at a rate of 1℃ / min, and then cooled to room temperature with the furnace.

[0062] (2) The pre-oxidized ceramic frame is heated from room temperature to 1300℃ and held for 2 hours. The heating rate is 2℃ / min. The frame is then cooled to room temperature in the furnace to obtain a 3D printed polymer-derived porous ceramic frame. The frame size is 15mm long × 15mm wide × 15mm high.

[0063] Experiment 2: This experiment differs from Experiment 1 in that the mass of boron powder added in step one is 0, 5g, 7g, 9g, and 11g, respectively. Everything else is the same as Experiment 1.

[0064] Figure 1 Images of ceramic frames obtained by adding different amounts of boron powder in Experiments 1 and 2 are provided. The images show that when the boron powder content is between 3% and 7% (the mass fraction of boron powder in PDMS), it effectively reduces the longitudinal (height) shrinkage of the frame after sintering. Further increasing the boron powder content (9% and 11%) significantly reduces the frame height, while varying degrees of melting occur at the bottom of the frame. This is because the boron powder, introduced into the matrix, undergoes an oxidation reaction in air to generate liquid B2O3, producing a volume expansion effect that inhibits the longitudinal shrinkage of the precursor ceramic. Then, as the boron powder content increases, the amount of liquid B2O3 generated gradually increases. While causing volume expansion, the excessive liquid phase leads to melting at the bottom of the frame, resulting in a phenomenon where the longitudinal shrinkage rate initially decreases but then increases again.

[0065] Figure 2 The image shows a SEM image of the internal cross-section of the ceramic frame obtained without adding boron powder in Experiment 2. The interior of the single filament was not in direct contact with the air atmosphere during heat treatment. It can be seen that the ceramic frame is severely cracked after high-temperature sintering, and large irregular pores appear inside. Under the action of thermal stress, the cracks tend to extend into the inner wall of the single filament, thus causing the single filament to split into two halves.

[0066] Figure 3The image shows a SEM image of the internal cross-section of a single filament of a ceramic frame obtained when the mass of boron powder filler is 5g in Experiment 2. The interior of the single filament was not in direct contact with the air atmosphere during heat treatment. It can be seen that the introduction of boron powder gradually filled the original irregular voids, but some small pores still exist.

[0067] Figure 4 This is a SEM image of the outer end face of a ceramic frame monofilament obtained with 5g of boron powder as filler in Experiment 2. The outer end face of the monofilament was in direct contact with air during heat treatment. It can be seen that the pores in the monofilament have completely disappeared, and the cross-section is very smooth. This is likely because the boron powder, in direct contact with oxygen, reacts first to form B2O3, which spreads on the surface of the monofilament, repairing cracks formed after the matrix decomposes. Simultaneously, it hinders further oxygen diffusion into the monofilament, resulting in insufficient oxygen supply inside. Only a portion of the boron powder reacts with oxygen to generate liquid B2O3, allowing the internal material to flow and fill the pores. However, due to incomplete boron powder reaction, the amount of liquid phase generated is insufficient to drive a large flow of material to completely fill the pores, so some small pores still exist inside the monofilament. In contrast, the portion in direct contact with oxygen shows a more complete boron powder reaction, significantly improving the pore-sealing efficiency.

[0068] Experiment 3: The difference between this experiment and Experiment 2 is that the heat treatment temperatures in step 3 (2) are 1100℃, 1200℃ and 1300℃ respectively. Everything else is the same as Experiment 2.

[0069] Figure 5 Comparative strength graphs of frames with different boron powder contents at different sintering temperatures in Experiments 1, 2, and 3 are presented. It can be seen that the compressive strength of the frames gradually increases with increasing boron powder content, and this trend becomes more pronounced with increasing sintering temperature. At 1300℃, the compressive strength of the frame containing 11% boron powder reaches 1.39 MPa, while the compressive strength of the frame containing 0% boron powder is only 0.15 MPa, an increase of almost an order of magnitude. This demonstrates that sealing the printing monofilaments with filler can effectively improve the mechanical properties of the printed frames.

Claims

1. A method for improving the mechanical properties of a 3D-printed porous ceramic framework with printing of filament-pinhole reinforcement, characterized by The method for printing single filament hole sealing to enhance the mechanical properties of 3D printed porous ceramic framework is carried out according to the following steps: I. Configuration of printing slurry: The first batch of ceramic precursor, crosslinking agent and inhibitor are mixed and stirred for 5-10 minutes; then the second batch of ceramic precursor and platinum catalyst are added and stirred for 5-10 minutes; then the fiber is added and stirred for 10-15 minutes, then the filler is added and stirred for 5-10 minutes, then the white carbon black is added, the white carbon black is added in two equal amounts, after the first addition, stir for 10-15 minutes, and after the second addition, stir for 30-35 minutes; The filler is boron powder; The first batch of ceramic precursor and the second batch of ceramic precursor are the same material and have the same mass; The mass ratio of the fiber to the first batch of ceramic precursor is 1:(1-3); The mass ratio of the filler to the first batch of ceramic precursor is 1:(16-17); The total mass of the two times of white carbon black added is 1:(2-5) times the mass of the first batch of ceramic precursor; II. Printing of ceramic framework embryo: (1) Use Cinema 4D software to draw a three-dimensional printing model and export the model to an STL format file, import the exported STL format file into Cura slicing software for slicing, i.e. divide the drawn three-dimensional model into multiple two-dimensional planes; (2) Set the corresponding printing parameters on the Cura slicing software according to the actual needs, then print, and obtain the ceramic framework embryo; III. Printing framework solidification and heat treatment: Place the printed ceramic framework in an oven for solidification, and then heat treat the solidified ceramic framework in the following two steps: (1) Pre-oxidation at low temperature: place the solidified ceramic framework in a muffle furnace, raise the temperature from room temperature to 320-330 DEG C and keep it for 6-6.5 hours, then cool it to room temperature with the furnace; (2) Raise the temperature of the pre-oxidized ceramic framework from room temperature to 1100-1300 DEG C and keep it for 2-3 hours, then cool it to room temperature with the furnace, i.e. obtain a 3D printed polymer-derived porous ceramic framework.

2. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The first batch of ceramic precursor in step one is PDMS.

3. The method of claim 1, wherein the method is characterized by The crosslinking agent in step one is hydrogen-containing silicone oil.

4. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The inhibitor in step one is 1-ethynyl-1-cyclohexanol.

5. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The fiber in step one is alumina fiber.

6. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The printing parameters in step two (2) are: needle diameter is 0.84 mm, printing layer spacing is 70% of needle diameter, printing speed is 20 mm / s, framework filling rate is 43%, printing embryo size is 25 mm long x 25 mm wide x 20 mm high, filling pattern is zigzag, and layer angle is 90 DEG.

7. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The solidification temperature in step three is 130 DEG C, and the time is 1 hour.

8. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The heating rate in step three (1) is 1 DEG C / min.

9. The method of claim 1, wherein the method is for enhancing the mechanical properties of a 3D-printed porous ceramic framework with a printed filament hole sealing. The heating rate in step three (2) is 2 DEG C / min.

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