A method for preparing an alumina-based ceramic based on a 3D printing process

Abstract

The application discloses a method for preparing an alumina-based ceramic based on a 3D printing process. The method comprises the following steps: preparing Ce-loaded polylactic acid (Ce-PLA) particles by adopting an emulsion-solvent evaporation method; then, TiO2 and the Ce-PLA particles are ball-milled at low temperature to obtain TiO2-Ce-PLA composite powder; the TiO2-Ce-PLA composite powder is mixed with alpha-Al2O3 powder, photosensitive resin, a photoinitiator and a dispersing agent in sequence to obtain ceramic slurry; the ceramic slurry is printed by adopting a digital light processing technology to obtain a green body; and after the green body is subjected to ultraviolet light irradiation, degreasing and sintering treatment, the alumina-based ceramic is obtained. The alumina-based ceramic prepared by the method has an open porosity of 41.3% to 43.1% and a bending strength of 93.39 to 97.98 MPa, and is suitable for manufacturing ceramic cores for hollow blades of an aero-engine.

Description

Technical Field

[0001] This invention belongs to the field of ceramic preparation technology, and relates to a method for preparing alumina-based ceramics based on 3D printing technology. Background Technology

[0002] With the continuous improvement of aero-engine performance, the internal cooling structure of blades is becoming increasingly complex. Traditional hot press molding processes are facing significant challenges due to limitations such as the need for mold making, long production cycles of 100-300 days, and difficulty in manufacturing complex structures. Digital light processing (DLP) photopolymerization 3D printing technology provides a new solution for the fabrication of complex ceramic core structures. This technology cures the entire layer in one pass using an ultraviolet projector, offering significant advantages such as high printing speed, high precision, good surface quality, and no need for molds.

[0003] However, DLP-molded ceramic green bodies contain a large amount of photosensitive resin, typically accounting for about 45% by volume. In the subsequent debinding-sintering process, this resin needs to be removed through thermal decomposition, simultaneously achieving sintering densification of the ceramic particles and the formation of a porous structure. During the debinding stage, the thermal decomposition of the resin leaves pore channels, but this process is highly susceptible to defects such as cracking and deformation. The debinding heating rate has a decisive influence on the formation of the final pore structure: an excessively fast heating rate leads to a rapid release of resin decomposition gases, causing excessive internal pressure in the green body and resulting in cracks; an excessively slow heating rate, on the other hand, affects production efficiency.

[0004] During the sintering stage, sintering necks form between ceramic particles, and the pores gradually become rounded, smaller, or even closed. This process is essentially a spontaneous process of reducing the surface energy of the sintered body, but the densification of pores inevitably leads to a decrease in porosity. For ceramic cores that need to simultaneously meet the requirements of high strength and high porosity, the core technical challenge lies in how to achieve a balance between precisely controlling the sintering temperature and holding time to ensure sufficient growth of the sintering necks to provide adequate strength, while maintaining sufficient open porosity for core removal. Summary of the Invention

[0005] To address the problems and shortcomings of the existing technologies, a method for preparing alumina-based ceramics based on 3D printing technology is proposed.

[0006] In a first aspect, the present invention provides a method for preparing alumina-based ceramics based on 3D printing technology, comprising: ball milling and combining a pore-forming aid Ce-PLA and a mineralizer TiO2 to obtain TiO2-Ce-PLA composite powder; mixing a matrix material α-Al2O3 with the TiO2-Ce-PLA composite powder to obtain ceramic powder; sequentially adding ceramic powder, a photoinitiator, and a dispersant to a photosensitive resin to obtain a ceramic slurry; printing and forming a green body using digital light processing technology; and subjecting the green body to ultraviolet irradiation, degreasing, and sintering treatments to obtain alumina-based ceramics.

[0007] The Ce-PLA is cerium-supported polylactic acid;

[0008] The photosensitive resin is a mixture of hydroxyethyl methacrylate, polyethylene glycol diacrylate, and trimethylolpropane triacrylate;

[0009] The photoinitiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide;

[0010] The dispersant is TEGO-685.

[0011] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the ceramic slurry comprises, by mass percentage: 17%~25% photosensitive resin, 2%~4% photoinitiator, 2%~4% dispersant, and the balance being ceramic powder.

[0012] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the photosensitive resin is prepared by mixing hydroxyethyl methacrylate, polyethylene glycol diacrylate and trimethylolpropane triacrylate in a mass ratio of 8~10:5~7:9~11.

[0013] The ceramic powder is prepared by mixing α-Al2O3 and TiO2-Ce-PLA composite powder in a mass ratio of 9~10:1~1.5.

[0014] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the preparation method of Ce-PLA includes: adding sodium lactate to a cerium nitrate solution to obtain a mixture; stirring the mixture and adjusting the pH; allowing it to stand, centrifuging, filtering, and drying to obtain cerium lactate; ultrasonically dispersing cerium lactate in a polylactic acid dichlorotoluene solution to obtain a dispersion; and under an ice-water bath, dropping the dispersion into a polyacryl alcohol aqueous solution and ultrasonically emulsifying to obtain an emulsion; stirring the emulsion, centrifuging, washing, and freeze-drying to obtain Ce-PLA.

[0015] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the molar ratio of cerium nitrate and sodium lactate is 1:3;

[0016] The mixing temperature of the mixture is 35℃, the mixing time is 3~5h, and the pH of the mixture is 7.

[0017] The mixture is allowed to stand for 10-14 hours.

[0018] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the mass ratio of polylactic acid to cerium lactate is 18~20:1;

[0019] The mass concentration of the polyacrylol aqueous solution is 5%;

[0020] The ultrasonic emulsification power is 200~300W, and the time is 2~3 minutes;

[0021] The emulsion is stirred at a speed of 400-500 rpm for 8-10 hours.

[0022] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the preparation method of the TiO2-Ce-PLA composite powder includes: pre-cooling TiO2 and Ce-PLA at -20℃ for 0.5~1h, ball milling at 300~400rpm for 2~3h, and sieving to obtain TiO2-Ce-PLA composite powder;

[0023] The mass ratio of TiO2 to Ce-PLA is 9~10:1.

[0024] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the ultraviolet irradiation includes: irradiating the green blank with a wavelength of 365nm for 30 minutes, then irradiating it with a wavelength of 254nm for 30 minutes, and turning it over every 15 minutes.

[0025] Furthermore, in the method for preparing alumina-based ceramics based on 3D printing technology provided by the present invention, the degreasing includes: heating to 350°C at a rate of 2°C / min and holding for 2 hours in an air atmosphere; heating to 500°C at a rate of 2°C / min and holding for 2 hours; and heating to 600°C at a rate of 2°C / min and holding for 2 hours.

[0026] The sintering process includes: heating to 1200°C at a rate of 3°C / min and holding at that temperature for 2 hours.

[0027] Secondly, the present invention provides an alumina-based ceramic, which is prepared by the above-described method for preparing alumina-based ceramics based on 3D printing technology.

[0028] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0029] This invention uses Ce-PLA (cerium-supported polylactic acid) as a pore-forming agent and pre-composites it with TiO2 at low temperature to obtain TiO2-Ce-PLA composite powder. After photopolymerization 3D printing, staged ultraviolet irradiation treatment is performed. Utilizing the photocatalytic activity of TiO2 under ultraviolet light, and with the synergistic catalytic effect of Ce, the polylactic acid (PLA) undergoes preliminary decomposition. While deeply curing the photosensitive resin and stabilizing the green body structure, ultraviolet irradiation also creates voids within the green body through photocatalytic pre-decomposition, promoting the release of gases during the degreasing stage and effectively preventing cracking of the green body caused by the rapid decomposition of organic matter. The remaining PLA is completely thermally removed during high-temperature sintering, completing the pore-forming process. The dissociated Ce acts as an active sintering aid, accumulating in the neck of the framework and significantly strengthening the sintering connection between particles. Ultimately, the alumina-based ceramics prepared by this invention have an open porosity of 41.3%~43.1%, a flexural strength of 93.39~97.98 MPa, and uniform shrinkage in all directions (9.3%~10.5%), successfully achieving a synergistic effect of high porosity, high strength, and high dimensional accuracy. Detailed Implementation

[0030] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials can be purchased commercially.

[0031] Examples 1-3

[0032] Examples 1-3 provide alumina-based ceramics and their preparation methods.

[0033] The matrix material of the alumina-based ceramic is α-Al₂O₃ (2~4 μm), the mineralizer is TiO₂ (0.1~0.5 μm, anatase phase, Qinghe County Ruijiang Metal Materials Co., Ltd.), the photosensitive resin is a mixture of hydroxyethyl methacrylate (HEMA), polyethylene glycol diacrylate (PEG(200)DA), and trimethylolpropane triacrylate (TMPTA), the photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO), the dispersant is polyether siloxane copolymer (TEGO-685), and the pore-forming aid is Ce-PLA (cerium-supported polylactic acid). The preparation method of the alumina-based ceramic is as follows:

[0034] (1) Preparation of Ce-PLA: 0.1 mol of cerium nitrate (Ce(NO3)3·6H2O) was dissolved in 100 mL of deionized water to obtain a cerium nitrate solution; then 0.3 mol of sodium lactate (Na-LA) was added to the cerium nitrate solution to obtain a mixed solution. The mixed solution was stirred at 35℃ for 4 h, then the pH of the mixed solution was adjusted to 7 with ammonia water, and the solution was allowed to stand for 12 h. After centrifugation, filtration and drying, cerium lactate (Ce-LA) was obtained.

[0035] 9.5 g of polylactic acid (PLA, Mn = 100,000~200,000 g / mol) was dissolved in 100 mL of dichloromethane, and 0.5 g of Ce-LA was added. The mixture was stirred until completely dispersed to obtain a dispersion. Under ice-water bath conditions, the dispersion was slowly added dropwise to 200 mL of a 5% (w / v) aqueous solution of polyacrylamide (PVA), and the mixture was ultrasonically emulsified at 300 W for 2 min to obtain an emulsion. The emulsion was stirred at 400 rpm for 10 h at room temperature, centrifuged, washed, and freeze-dried to obtain Ce-PLA particles (0.5~2 μm).

[0036] (2) Preparation of alumina-based ceramic slurry: 10g TiO2 powder and 1g Ce-PLA particles were pre-cooled at -20℃ for 1h, and then transferred to a low-temperature planetary ball mill and ball-milled at 300 rpm for 2h. The ball milling media were zirconia balls (3~5mm), and the ball-to-powder ratio was 3:1. After ball milling, the powder was passed through a 0.5~2μm sieve to obtain TiO2-Ce-PLA composite powder.

[0037] α-Al₂O₃ powder and TiO₂-Ce-PLA composite powder were mixed at a mass ratio of 9:1 to obtain ceramic powder. HEMA, PEG(200)DA, and TMPTA were mixed at a mass ratio of 9:6:10 to obtain photosensitive resin. Ceramic powder, photoinitiator, and dispersant were added to the photosensitive resin in sequence to obtain a mixed slurry. The mixed slurry was transferred to a planetary ball mill and ball-milled at 300 rpm for 8 hours to obtain an alumina-based ceramic slurry. The composition of the alumina-based ceramic slurry by mass percentage is shown in Table 1.

[0038] (3) Preparation of alumina-based ceramics: Alumina-based ceramic green bodies were prepared using a 3D printer (PC5003A-50, Xi'an Dianyun Biotechnology Co., Ltd.). The green body was a cube of 50mm × 4mm × 5mm. Based on the curing depth of the slurry, the layer thickness was set to 50μm, and the curing time was 4s. A bottom-up forming method was adopted, with each layer being photocured and accumulated to finally obtain the green body. After printing, the surface of the green body was cleaned with alcohol to remove residual slurry and allowed to air dry naturally. The green body was placed under ultraviolet light and irradiated in stages at a distance of 10cm from the light source. First, it was irradiated with a wavelength of 365nm for 30min, and then with a wavelength of 254nm for 30min. During the irradiation process, the green body was turned over every 15min to ensure uniform light absorption on all sides. During the ultraviolet irradiation process, air cooling was required to reduce the surface temperature of the green body. The green body was transferred to a tube furnace and heated to 350°C at a rate of 2°C / min under air atmosphere, held for 2 hours, then heated to 500°C at a rate of 2°C / min, and held for 2 hours. Finally, the temperature was increased to 600°C at a rate of 2°C / min and held for 2 hours. The final temperature was increased to 1200°C at a rate of 3°C / min and held for 2 hours to obtain alumina-based ceramics.

[0039] Table 1 Composition of alumina-based ceramic slurry

[0040]

[0041] Comparative Example 1

[0042] This comparative example is the same as Example 2, except that the ceramic powder in this comparative example is prepared by mixing α-Al2O3 powder and TiO2 powder in a mass ratio of 9:1.

[0043] Comparative Example 2

[0044] This comparative example is the same as Example 2, except that in this comparative example, 10g of TiO2 powder and 1g of PLA are ball-milled to obtain TiO2-PLA composite powder, and α-Al2O3 powder and TiO2-PLA composite powder are mixed in a mass ratio of 9:1 to obtain ceramic powder.

[0045] Comparative Example 3

[0046] This comparative example is the same as Example 2, except that the ceramic powder in this comparative example is prepared by mixing α-Al2O3 powder, TiO2 powder and Ce-PLA particles in a mass ratio of 9:1:0.1.

[0047] Comparative Example 4

[0048] This comparative example is the same as Example 2, except that the green body in this comparative example was not subjected to ultraviolet light treatment.

[0049] Three alumina-based ceramic samples from each embodiment were placed in a beaker and dried in a 100°C oven. The dry weight M1 of the alumina-based ceramic was measured, and the average of the three measurements was taken. The alumina-based ceramic was then labeled and placed in a glass bottle, with deionized water added until the alumina-based ceramic was completely submerged. After sealing the bottle, the glass bottle was connected to a vacuum pump, and a vacuum was drawn until no air bubbles were generated. The vacuuming was then stopped. The alumina-based ceramic was removed, and its buoyant weight M3 was measured, and the average of the three measurements was taken. The alumina-based ceramic was removed, and the surface moisture was wiped off with filter paper. The wet weight M2 was measured, and the average of the three measurements was taken. The formulas for calculating the open porosity (B) and bulk density (d) of the alumina-based ceramic are as follows:

[0050]

[0051]

[0052] In the formula, d 水 The density of water (g / cm³) 3 ).

[0053] Firing shrinkage refers to the percentage change in size of the green body before and after sintering. The measurement standard is HB5353.2-2004. The dimensions of each alumina-based ceramic green body and the sintered alumina-based ceramic were measured using a vernier caliper with an accuracy of 0.02 mm. The average of three measurements at different locations was taken for each dimension. Three samples were randomly selected from each experimental group for measurement. The formula for calculating the firing shrinkage (δ) is as follows:

[0054]

[0055] In the formula, L is the length (mm) of the alumina-based ceramic green body, and L1 is the length (mm) of the sintered alumina-based ceramic.

[0056] The room temperature strength and flexural strength (σ) of alumina-based ceramics were measured using the three-point bending method. W The formula for calculating (MPa) is as follows:

[0057]

[0058] In the formula, P is the load (N) when the alumina-based ceramic fractures, L is the span between the two support points (mm), b is the width of the alumina-based ceramic (mm), and h is the thickness of the alumina-based ceramic (mm).

[0059] As shown in Table 2, the alumina-based ceramics prepared in Examples 1-3 have an open porosity of 41.3%-43.1% and a bulk density of 2.02-2.15 g / cm³. 3The flexural strength ranges from 93.39 to 97.98 MPa. This indicates that by using TiO2-Ce-PLA composite powder and combining it with photopolymerization 3D printing, a connected porous network was successfully constructed. Furthermore, the introduction of the pore-forming agent (Ce-PLA) and its pre-ball-milling composite with the mineralizer (TiO2) strengthened the sintering neck connections of the matrix framework, significantly improving the mechanical load-bearing capacity of the alumina-based ceramic.

[0060] Comparative Example 1, without the addition of pore-forming agents, showed an alumina-based ceramic with an open porosity of 27.7% and a bulk density of 1.32 g / cm³. 3 The flexural strength was 16.75 MPa, indicating that the absence of Ce-PLA resulted in insufficient pore-forming effect, poor sintering activity, and a loose skeletal structure. In Comparative Example 2, the pore-forming aid was not loaded with Ce; the alumina-based ceramic had an open porosity of 39.9% and a bulk density of 1.93 g / cm³. 3 The flexural strength was 40.02 MPa, indicating that Ce can strengthen the sintered neck and improve the skeleton strength. In Comparative Example 3, TiO2 and Ce-PLA were not pre-composite, and the alumina-based ceramic had an open porosity of 39.4% and a bulk density of 1.95 g / cm³. 3 The flexural strength was 53.60 MPa, indicating that the pre-composite effect of TiO2 and Ce-PLA can promote the uniform distribution of α-Al2O3, TiO2, and Ce-PLA, thereby optimizing the pore structure and sintering behavior. Comparative Example 4, without UV irradiation, showed an alumina-based ceramic with an open porosity of 38.0% and a bulk density of 1.81 g / cm³. 3 The bending strength was 81.23 MPa, indicating that ultraviolet light treatment can stabilize the green body structure and reduce sintering defects.

[0061] Table 2. Porosity, bulk density, and flexural strength of alumina-based ceramics

[0062]

[0063] In Examples 1-3, the alumina-based ceramics exhibited a firing shrinkage rate of 9.3%-9.5% in the X direction, 9.7%-9.9% in the Y direction, and 10.3%-10.5% in the Z direction. The small difference in shrinkage rate among the X, Y, and Z directions indicates that the uniform dispersion of the TiO2-Ce-PLA composite powder ensures that the shrinkage in each direction tends to be synchronized during sintering. This effectively avoids defects such as warping and cracking caused by uneven shrinkage, which is beneficial for ensuring the dimensional accuracy and structural integrity of complex structural parts.

[0064] Comparative Example 1 showed a firing shrinkage rate of 1.5% in the X direction, 2.0% in the Y direction, and 1.2% in the Z direction, indicating that the alumina-based ceramics hardly underwent effective densification during sintering, resulting in a loose skeletal structure and severely insufficient sintering activity. Comparative Example 2 had firing shrinkage rates of 9.0% in the X direction, 9.5% in the Y direction, and 10.0% in the Z direction; Comparative Example 3 had firing shrinkage rates of 9.0% in the X direction, 9.6% in the Y direction, and 10.0% in the Z direction; and Comparative Example 4 had firing shrinkage rates of 8.6% in the X direction, 9.4% in the Y direction, and 9.9% in the Z direction, all close to those of Examples 1-3.

[0065] Table 3. Firing shrinkage rate of alumina-based ceramics

[0066]

[0067] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for preparing alumina-based ceramics based on 3D printing technology, characterized in that, include: TiO2-Ce-PLA composite powder was prepared by ball milling and compounding pore-forming agent Ce-PLA and mineralizer TiO2; ceramic powder was prepared by mixing matrix material α-Al2O3 with TiO2-Ce-PLA composite powder; ceramic powder, photoinitiator and dispersant were added to photosensitive resin in sequence to obtain ceramic slurry; green body was obtained by printing using digital light processing technology; alumina-based ceramic was obtained after ultraviolet irradiation, degreasing and sintering of green body. The Ce-PLA is cerium-supported polylactic acid; The photosensitive resin is a mixture of hydroxyethyl methacrylate, polyethylene glycol diacrylate, and trimethylolpropane triacrylate; The photoinitiator is 2,4,6-trimethylbenzoyldiphenylphosphine oxide; The dispersant is TEGO-685.

2. The method for preparing alumina-based ceramics based on 3D printing technology according to claim 1, characterized in that, The ceramic slurry comprises, by weight percentage: 17%~25% photosensitive resin, 2%~4% photoinitiator, 2%~4% dispersant, and the balance being ceramic powder.

3. The method for preparing alumina-based ceramics based on 3D printing technology according to claim 1, characterized in that, The photosensitive resin is prepared by mixing hydroxyethyl methacrylate, polyethylene glycol diacrylate and trimethylolpropane triacrylate in a mass ratio of 8~10:5~7:9~11; The ceramic powder is prepared by mixing α-Al2O3 and TiO2-Ce-PLA composite powder in a mass ratio of 9~10:1~1.

5.

4. The method for preparing alumina-based ceramics based on 3D printing technology according to claim 1, characterized in that, The preparation method of Ce-PLA includes: adding sodium lactate to a cerium nitrate solution to obtain a mixture; stirring the mixture and adjusting the pH; allowing it to stand, centrifuging, filtering, and drying to obtain cerium lactate; ultrasonically dispersing cerium lactate in a polylactic acid dichlorotoluene solution to obtain a dispersion; adding the dispersion dropwise to a polyacryl alcohol aqueous solution under an ice-water bath, ultrasonically emulsifying to obtain an emulsion; stirring the emulsion, centrifuging, washing, and freeze-drying to obtain Ce-PLA.

5. The method for preparing alumina-based ceramics based on 3D printing process according to claim 4, characterized in that, The molar ratio of cerium nitrate to sodium lactate is 1:3; The mixing temperature of the mixture is 35℃, the mixing time is 3~5h, and the pH of the mixture is 7. The mixture is allowed to stand for 10-14 hours.

6. The method for preparing alumina-based ceramics based on 3D printing process according to claim 4, characterized in that, The mass ratio of polylactic acid to cerium lactate is 18~20:1; The mass concentration of the polyacrylol aqueous solution is 5%; The ultrasonic emulsification power is 200~300W, and the time is 2~3 minutes; The emulsion is stirred at a speed of 400-500 rpm for 8-10 hours.

7. The method for preparing alumina-based ceramics based on 3D printing technology according to claim 1, characterized in that, The preparation method of the TiO2-Ce-PLA composite powder includes: pre-cooling TiO2 and Ce-PLA at -20℃ for 0.5~1h, ball milling at 300~400rpm for 2~3h, and sieving to obtain TiO2-Ce-PLA composite powder; The mass ratio of TiO2 to Ce-PLA is 9~10:

1.

8. The method for preparing alumina-based ceramics based on 3D printing process according to claim 1, characterized in that, The ultraviolet irradiation includes: irradiating the green blank with a wavelength of 365nm for 30 minutes, then irradiating it with a wavelength of 254nm for 30 minutes, and turning it over every 15 minutes.

9. The method for preparing alumina-based ceramics based on 3D printing process according to claim 1, characterized in that, The degreasing process includes: heating to 350°C at a rate of 2°C / min and holding for 2 hours in air; heating to 500°C at a rate of 2°C / min and holding for 2 hours; and heating to 600°C at a rate of 2°C / min and holding for 2 hours. The sintering process includes: heating to 1200°C at a rate of 3°C / min and holding at that temperature for 2 hours.

10. An alumina-based ceramic, characterized in that, It is prepared by the method for preparing alumina-based ceramics based on 3D printing process according to any one of claims 1 to 9.

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