A method for producing high performance structural ceramics based on a binder jetting technique

Abstract

The application discloses a method for preparing high-performance structural ceramics based on a binder jetting technology and relates to the technical field of additive manufacturing. The application first uniformly mixes ceramic powder and sintering aids, then adds a mixed suspension containing metal salt, silica sol and glue, performs granulation to prepare coarse powder, uses the binder jetting technology to form the coarse powder into a green body, and performs debinding and sintering on the green body to prepare a ceramic-based core. The application uses ceramic powder with high sintering activity, sintering aid powder, metal salt compound, silica sol and glue to prepare micron-level coarse powder, and then prepares a ceramic printing sample through the binder jetting process, so that a printing green body with high strength can be obtained, the green body can still maintain high strength after debinding, high-temperature sintering is facilitated to prepare structural ceramics with high compactness and high strength, and the problem that the binder jetting additive manufacturing technology is difficult to prepare high-density high-performance ceramics is solved.

Description

Technical Field

[0001] This invention relates to the field of additive manufacturing technology, and in particular to a method for preparing high-performance structural ceramics based on binder spraying technology. Background Technology

[0002] Structural ceramics are advanced ceramics with excellent mechanical, thermal, and chemical properties, such as high temperature resistance, erosion resistance, corrosion resistance, high hardness, high strength, and low creep rate. They are commonly used in various structural components. Materials used to manufacture structural ceramics include alumina, zirconium oxide, and silicon nitride, which, after sintering, exhibit high strength and high hardness.

[0003] Additive manufacturing technology offers a new direction for the fabrication of complex-shaped ceramic components. Among them, binder jet additive manufacturing (BJAM) is based on a powder bed process. A binder is selectively deposited layer by layer onto a powder bed via an inkjet printhead, forming a green part. Subsequent curing, debinding, and sintering processes densify the green part, resulting in a component with excellent mechanical properties. BJAM technology is characterized by its speed, efficiency, low cost, and lack of need for additional support. It not only offers high precision but is also suitable for the fabrication of large components and mass production.

[0004] To achieve good powder spreading results, BJAM technology places high demands on the powder, such as high flowability. Therefore, near-spherical powders with a particle size range of 10-200 μm are typically used. However, the powder characteristics (particle size, specific surface area, etc.) of advanced ceramic materials have a significant impact on their sintering activity. Generally speaking, the smaller the particle size and the larger the specific surface area, the higher the sintering activity and the lower the sintering temperature. In the preparation of high-performance ceramics, submicron and nano-sized powders are usually used as raw materials to provide sufficient sintering activity to ensure complete densification of the material. However, the 10-200 μm particle size ceramic powder used in BJAM significantly reduces the sintering activity of the powder. Powders in this particle size range are usually used for porous ceramics, thermal insulation materials, etc., making it very difficult to prepare high-density, high-performance advanced ceramics using BJAM technology. In addition, due to the influence of powder bed technology, powder bed density and other factors, such as powder characteristics (particle size, distribution, morphology, etc.) and powder spreading technology (powder spreading method, thickness, speed, etc.), powder beds with almost no external force rely on natural accumulation. There are fewer contact points between powder particles and larger pores, which is not conducive to the sintering of high-performance structural ceramics. Summary of the Invention

[0005] The technical problem to be solved by the present invention is how to prepare high-density, high-strength structural ceramics using binder spray molding technology.

[0006] To address the above problems, the present invention proposes the following technical solution:

[0007] On the one hand, this invention proposes a method for preparing high-performance structural ceramics based on binder spraying technology, comprising the following steps:

[0008] S1. By mass, first mix 80-99 parts of ceramic powder and 1-20 parts of sintering aid evenly, then add a mixed suspension containing 20-30 parts of metal salt, 20-30 parts of silica sol and 20-30 parts of glue to the mixed powder, and granulate to prepare coarse powder with a particle size of 0.1um-150um, preferably 0.1-60um;

[0009] S2. The coarse powder is molded into a blank using binder spraying technology;

[0010] S3. Degrease and sinter the green body to obtain a ceramic core.

[0011] The particle size range of the ceramic powder is 1 nm to 10 μm; the metal salt is selected from alkaline earth metal nitrates and / or rare earth metal nitrates.

[0012] The ceramic powder has a particle size range of 1 nm to 10 μm, preferably 100 nm to 1 μm. Within this particle size range, the ceramic powder has higher sintering activity.

[0013] It should be noted that the mixed suspension solution is prepared by pre-dissolving the metal salt in a solvent, and then adding silica sol and glue. The solvent used can be anhydrous ethanol.

[0014] The preferred granulation method of this invention is extrusion mixing granulation, the principle of which is described in [link to invention]. Figure 2 Specifically, ceramic powder and sintering aids are mixed, and while the mixed powder is extruded and stirred, a mixed suspension containing metal salts, silica sol, and adhesive is sprayed from a nozzle as needed, followed by drying to obtain coarse powder. This granulation method ensures that the addition of the mixed suspension does not affect the packing of the powder raw materials during granulation. At the same time, the components in the mixed suspension help increase the density of the coarse powder, thereby increasing the density of the green body. The higher the density of the green body, the higher the density of the sintered ceramic. Furthermore, during binder jet printing, the binder jet adhesive enters the powder bed and mixes with the silica sol and metal salts in the coarse powder. The binder jet adhesive wetting the powder bed helps the silica sol and metal salts uniformly fill the pores of the green body. After debinding, the metal salts decompose into metal oxides and form a core-shell structure and crystal bridges, strengthening the solid bridging between the powder raw materials, ensuring the strength of the green body after debinding, and forming a relatively uniform internal structure of the green body, which is conducive to sintering into a dense structural ceramic.

[0015] A further technical solution is that the ceramic powder is at least one of alumina, zirconium oxide, silicon nitride, and aluminum nitride.

[0016] A further technical solution is that the metal salt is selected from one or more of the following: nitrate compounds of Mg, nitrate compounds of Al, nitrate compounds of Zr, nitrate compounds of Ca, nitrate compounds of Y, nitrate compounds of Ce, nitrate compounds of Eu, nitrate compounds of La, and nitrate compounds of Lu.

[0017] A further technical solution is that the sintering aid is selected from alkaline earth metal oxides and / or rare earth metal oxides.

[0018] A further technical solution is that the sintering aid is selected from one or more of MgO, Al2O3, ZrO2, CaO, SiO2, Cr2O3, Y2O3, La2O3, Ce2O3, Sm2O3, Eu2O3, Gd2O3, and Lu2O3.

[0019] A further technical solution is that the particle size range of the sintering aid is 1 nm to 10 μm, preferably 100 nm to 1 μm.

[0020] A further technical solution is that the mass fraction of SiO2 in the silica sol is 1-50%, preferably 15%-30%, and the average particle size of SiO2 is in the range of 1nm-500nm, preferably 10nm-150nm.

[0021] A further technical solution is that the adhesive is an adhesive curing adhesive, which can be selected from one or more of epoxy resin adhesives, furan resin adhesives, acrylic ester adhesives, phenolic adhesives, polyvinyl alcohol adhesives, cellulose adhesives, and sodium silicate adhesives. Those skilled in the art can also select other adhesives to achieve similar effects.

[0022] A further technical solution is that, in step S2, the powder thickness is 60µm to 200µm. Those skilled in the art can optimize printing parameters (powder spreading speed, adhesive spraying amount, etc.) to ensure that problems such as part pushing, layer displacement, and deformation do not occur, thereby obtaining a printed blank with good shape and precision.

[0023] It should be noted that in this invention, degreasing refers to the removal of organic matter from the printed body. Depending on the thermal decomposition of the organic matter, the degreasing temperature should be around 300-600℃. The degreasing method is not limited to one-step air degreasing, vacuum and air two-step degreasing, etc. The degreased sample is then sintered at a temperature of 1300-1900℃ to obtain a highly dense, high-performance ceramic. The sintering temperature should be determined according to the type of ceramic material. In this invention, degreasing and sintering are conventional preparation processes for ceramic materials. Those skilled in the art can use appropriate equipment and sintering processes depending on the specific ceramic material. For example, alumina and zirconia ceramic materials can be sintered using a muffle furnace, and silicon nitride ceramic materials can be sintered using an atmosphere furnace, pressure furnace, etc., but are not limited to these methods.

[0024] On the other hand, the present invention provides a structural ceramic core prepared by adhesive spraying, which is prepared by the method for preparing high-performance structural ceramics based on adhesive spraying technology.

[0025] Compared with the prior art, the technical effects achieved by the present invention include:

[0026] This invention utilizes highly sinterable ceramic powder, sintering aid powder, metal salt compounds, silica sol, and adhesive to prepare micron-sized coarse powder. Then, ceramic printing samples are prepared using a binder jetting process, resulting in a high-strength printed green body. Furthermore, the green body retains high strength even after debinding, which is beneficial for high-temperature sintering to produce highly dense and high-strength structural ceramics. This invention leverages the combined effects of highly sinterable ceramic powder raw materials, nano-silica in silica sol, sintering aids, and nano-oxides from metal salt decomposition to improve the sintering performance of the binder-jetted green body through liquid-phase sintering. This results in a high-density, high-strength printed ceramic green body; the higher the density of the sintered body, the better its mechanical properties. This solves the problem of the difficulty in preparing high-density, high-performance ceramics using binder jetting additive manufacturing technology. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the process flow for preparing ceramic coarse powder and binder sprayed ceramic in Example 1 of the present invention;

[0029] Figure 2This is a schematic diagram of the extrusion mixing granulator used in the preparation of ceramic coarse powder in Embodiment 1 of the present invention. As can be seen from the figure, when the ceramic mixed powder is subjected to high-speed stirring by the extrusion plate, the mixed suspension is sprayed out as needed through the nozzle, and then the coarse powder is obtained through the drying process. Detailed Implementation

[0030] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0032] It should also be understood that the terminology used in this specification of embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of the invention. As used in this specification of embodiments of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0033] Example 1

[0034] This embodiment provides a method for preparing high-performance structural ceramics based on binder spraying technology, wherein the powder raw material used is nano-alumina powder with a medium particle size of 200 nm. The sintering aid is magnesium oxide with a medium particle size of 50 nm.

[0035] In the mixed suspension: the metal salt is yttrium nitrate hexahydrate; the silica sol is silica sol with a silica content of 29-31% and an average particle size of 10-16 nm; the glue is a 5% (w / w) aqueous solution of polyvinyl alcohol; and the solvent in the mixed suspension is anhydrous ethanol.

[0036] See Figure 1 This embodiment describes a method for preparing high-performance structural ceramics using binder spraying technology, comprising the following steps:

[0037] S1: Take 99 parts of alumina and 1 part of magnesium oxide by mass, add alumina grinding balls with anhydrous ethanol as medium, ball mill and mix for 12 hours, and then dry with a rotary evaporator to obtain a uniformly mixed powder.

[0038] By weight, take 20 parts of yttrium nitrate hexahydrate, 20 parts of anhydrous ethanol, 20 parts of silica sol and 20 parts of polyvinyl alcohol aqueous solution, mix them, stir and sonicate for 30 minutes to obtain a uniformly mixed suspension.

[0039] S2: See also Figure 2 Granulation was carried out by extrusion mixing. A mixed suspension was added to the mixed powder at a concentration of 10% of the powder mass. The powder was then dried, and particles larger than 74 μm were removed using a sieve to obtain coarse powder. The loose density and tapped density of the coarse powder were measured.

[0040] S3: Using a commercial adhesive jet printer and commercial glue to print parts, the powder thickness is set to 100um, and the printing parameters (powder spreading speed, glue spraying amount, etc.) are optimized to finally print an alumina print with good shape and precision.

[0041] S4: The printed sample was degreased using a muffle furnace with air degreasing followed by holding at 600℃ for 2 hours. The compressive strength of the degreased green body was measured. The degreased green body was then sintered in a muffle furnace at 1600℃ for 2 hours, resulting in a highly dense, high-performance alumina structural ceramic. The flexural strength of the sintered part was measured.

[0042] Example 2

[0043] The difference between this embodiment and Example 1 is that the metal salts in the mixed suspension are yttrium nitrate hexahydrate and zirconium nitrate. The mixed suspension in this embodiment consists of 10 parts yttrium nitrate hexahydrate, 10 parts zirconium nitrate, 20 parts anhydrous ethanol, 20 parts silica sol, and 20 parts polyvinyl alcohol aqueous solution. Other parameters and preparation processes are the same as in Example 1.

[0044] Example 3

[0045] The difference between this embodiment and Example 1 is that the powder raw material used is alumina with a medium particle size of 200 nm. The sintering aids are magnesium oxide and zirconium oxide with medium particle sizes of 50 nm and 50 nm, respectively. Other parameters and preparation processes are the same as in Example 1.

[0046] Comparative Example 1

[0047] The powder used in this comparative example was only alumina powder with a medium particle size of 45 μm. This powder was used as the coarse powder for printing, and its loose density and tap density were measured. Then, a commercial adhesive jet printer and commercial glue were used to print the parts. The powder thickness was set at 100 μm, and printing parameters (powder spreading speed, adhesive application rate, etc.) were optimized. Finally, an alumina print was produced. The printed sample was further degreased using a muffle furnace with air degreasing and a holding time of 600℃ for 2 hours. The compressive strength of the degreased blank was measured. The degreased blank was then sintered in a muffle furnace at 1600℃ for 2 hours to obtain a sintered part. The flexural strength of the sintered part was measured.

[0048] Comparative Example 2

[0049] The powder raw material used in this comparative example is alumina with a medium particle size of 45 μm. The sintering aids are magnesium oxide with a medium particle size of 50 nm and silicon dioxide with a medium particle size of 50 nm.

[0050] The preparation method for this comparative example is as follows:

[0051] By weight, 98 parts alumina, 1 part magnesium oxide, and 1 part silicon dioxide were added to anhydrous ethanol as a medium. The mixture was then ball-milled for 12 hours and dried using a rotary evaporator to obtain a uniformly mixed powder. This mixed powder was used as coarse powder for printing, and its loose density and tap density were measured.

[0052] The parts were printed using a commercial adhesive jet printer and commercial glue, with the powder layer thickness set at 100µm and printing parameters (powder spreading speed, glue application rate, etc.) optimized. Finally, an alumina print was produced. The printed sample was then degreased using a muffle furnace with air degreasing and a holding time of 600℃ for 2 hours. The compressive strength of the degreased blank was measured. The degreased blank was then sintered in a muffle furnace at 1600℃ for 2 hours to obtain a sintered part. The flexural strength of the sintered part was measured.

[0053] Comparative Example 3

[0054] The powder used in this comparative example is only alumina powder with a medium particle size of 200 nm. This powder was used as the coarse powder for printing, and its loose density and tapped density were measured. Then, loose-pack sintering was performed in a muffle furnace (the mixed powder was poured into a crucible without applying pressure or tapping). The sintering process was sintering at 1600℃ for 2 hours, resulting in alumina sintered parts. The density of the sintered parts was measured.

[0055] It should be noted that the raw material powder used in this comparative example is nano powder, which has very poor flowability and cannot be spread on the adhesive jet printer. Therefore, this comparative example uses loose-pack sintering for simulation.

[0056] Comparative Example 4

[0057] The powder raw material used in this comparative example is alumina with a medium particle size of 200 nm. The sintering aids are magnesium oxide with a medium particle size of 50 nm and silicon dioxide with a medium particle size of 50 nm.

[0058] The mixed suspension in this comparative example does not contain silica sol. The mixed suspension consists of 20 parts of yttrium nitrate hexahydrate, 20 parts of anhydrous ethanol, and 20 parts of polyvinyl alcohol aqueous solution.

[0059] The preparation method for this comparative example is as follows:

[0060] By weight, take 98 parts of alumina, 1 part of magnesium oxide, and 1 part of silicon dioxide. Using anhydrous ethanol as a medium, add alumina grinding balls and mix by roller ball milling for 12 hours. After drying with a rotary evaporator, a uniform mixed powder is obtained.

[0061] Granulation was performed using an extrusion mixing method. A mixed suspension was added to the mixed powder at a concentration of 10% of the powder mass. The powder was then dried, and particles larger than 74 μm were removed using a sieve to obtain coarse powder. The loose density and tapped density of the coarse powder were measured.

[0062] The parts were printed using a commercial adhesive jet printer and commercial glue, with the powder layer thickness set at 100µm and printing parameters (powder spreading speed, glue application rate, etc.) optimized. Finally, an alumina print was produced. The printed sample was then degreased using a muffle furnace with air degreasing and a holding time of 600℃ for 2 hours. The compressive strength of the degreased blank was measured. The degreased blank was then sintered in a muffle furnace at 1600℃ for 2 hours to obtain a sintered part. The flexural strength of the sintered part was measured.

[0063] Comparative Example 5

[0064] The difference between this comparative example and Example 1 is that the mixed suspension does not contain yttrium nitrate hexahydrate (a metal salt) or silica sol. The mixed suspension in this comparative example consists of 20 parts anhydrous ethanol and 20 parts polyvinyl alcohol aqueous solution. Other parameters are the same as in Example 1.

[0065] Comparative Example 6

[0066] The difference between this comparative example and Example 1 is that the mixed suspension does not contain silica sol. The mixed suspension in this example consists of 20 parts yttrium nitrate hexahydrate, 20 parts anhydrous ethanol, and 20 parts a polyvinyl alcohol aqueous solution. Other parameters and preparation processes are the same as in Example 1.

[0067] Comparative Example 7

[0068] The difference between this comparative example and Example 1 is that the mixed suspension does not contain the metal salt yttrium nitrate hexahydrate. The mixed suspension in this example consists of 20 parts silica sol, 20 parts anhydrous ethanol, and 20 parts polyvinyl alcohol aqueous solution. Other parameters and preparation processes are the same as in Example 1.

[0069] The relevant data of Examples 1 to 3 and Comparative Examples 1 to 7 of the present invention are compared and shown in Table 1.

[0070] Table 1. Experimental data from Example 1 of the present invention and Comparative Examples 1-7.

[0071]

[0072]

[0073] In Table 1, the prints of Comparative Examples 1, 2, 5, and 7 have virtually no strength after degreasing, while Comparative Examples 3 and 4 were not printed. The compressive strength of these examples will not be measured again and is indicated by / .

[0074] The results in Table 1 above show that, by optimizing the particle size of ceramic raw material powder and adding metal salts and silica sol to regranulate the ceramic powder, the coarse powder prepared in Examples 1-3 can achieve a high powder bed filling density. Furthermore, by promoting sintering through liquid phase sintering, high-density and high-strength alumina ceramics can be obtained. At the same time, using the method of this invention, the coarse powder can be used to form blanks with binder technology, and after debinding, it has a certain compressive strength. This is a unique advantage of this invention, which is conducive to the production of high-performance structural ceramics.

[0075] The ceramic raw material powders in Comparative Examples 1 and 2 have relatively coarse particle sizes. Although they can obtain higher loose density and tap density, the sintering performance of the spherical alumina powder with a particle size of 45 μm is too low. Even with the addition of sintering aids, the relative density is far lower than that of Example 1.

[0076] Comparative Example 3 used 200nm alumina powder as raw material, but it did not add a mixed suspension to re-granulate the powder raw material, resulting in a lower loose density and tap density of the powder used for printing, and a lower density after sintering, which was significantly different from the relative density of Example 1.

[0077] Comparative Example 4 uses nano-silica to replace the silica sol in the mixed suspension. The preparation process is the same as in Example 1. Although the granulated powder can have a higher loose density and tap density, it is not as good as in Example 1. The density and strength of the sintered ceramic are not as good as in Example 1.

[0078] In Comparative Examples 5 to 7, the mixed suspensions contained only metal salts or silica sols or contained no metal salts or silica sols. The loose density and tap density of the coarse powder obtained by regranulation were both lower than those in Example 1, and the density after sintering was also lower.

[0079] The above embodiments are only used as examples of preparing alumina ceramics. This invention utilizes ceramic powder with high sintering activity, sintering aid powder, metal salt compound, silica sol and glue to prepare micron-sized coarse powder. By using binder spraying technology, a green body with high compressive strength can be obtained. After sintering, a high-performance ceramic is obtained. Those skilled in the art can also obtain similar effects by using zirconium oxide, silicon nitride or aluminum nitride ceramic powders.

[0080] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0081] The above description describes specific embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing high-performance structural ceramics based on binder spraying technology, characterized in that, Includes the following steps: S1. By mass, first mix 80-99 parts of ceramic powder and 1-20 parts of sintering aid evenly. Then add a mixed suspension containing 20-30 parts of metal salt, 20-30 parts of silica sol and 20-30 parts of glue to the mixed powder. Extrusion, stirring and granulation are carried out to prepare coarse powder with a particle size of 0.1μm-150μm. S2. The coarse powder is formed into a blank using binder spraying technology; the loose density of the coarse powder is 35%, and the tapped density is 42% or 45%; S3. Degrease and sinter the green body to obtain a ceramic core. In the process of binder jet printing, the binder jet adhesive enters the powder bed and mixes with the silica sol and metal salts in the coarse powder. The binder jet adhesive wets the powder bed and helps the silica sol and metal salts to uniformly fill the pores of the preform. After degreasing, the metal salts decompose into metal oxides and form a core-shell structure and crystal bridges, which strengthens the solid bridging between the powder raw materials and obtains a degreased preform with a compressive strength of 5MPa or 6MPa. The ceramic powder has a particle size range of 1 nm to 10 μm, and the metal salt is selected from one or more of the following: nitrate compounds of Mg, nitrate compounds of Al, nitrate compounds of Zr, nitrate compounds of Ca, nitrate compounds of Y, nitrate compounds of Ce, nitrate compounds of Eu, nitrate compounds of La, and nitrate compounds of Lu. The adhesive is selected from one or more of the following: epoxy resin adhesives, furan resin adhesives, acrylic ester adhesives, phenolic adhesives, polyvinyl alcohol adhesives, cellulose adhesives, and sodium silicate adhesives.

2. The method for preparing high-performance structural ceramics based on binder spraying technology as described in claim 1, characterized in that, The ceramic powder is at least one of alumina, zirconium oxide, silicon nitride, and aluminum nitride.

3. The method for preparing high-performance structural ceramics based on binder spraying technology as described in claim 1, characterized in that, The sintering aid is selected from alkaline earth metal oxides and / or rare earth metal oxides.

4. The method for preparing high-performance structural ceramics based on binder spraying technology as described in claim 1, characterized in that, The sintering aid is selected from one or more of MgO, Al2O3, ZrO2, CaO, SiO2, Cr2O3, Y2O3, La2O3, Ce2O3, Sm2O3, Eu2O3, Gd2O3, and Lu2O3.

5. The method for preparing high-performance structural ceramics based on binder spraying technology as described in claim 1, characterized in that, The particle size range of the sintering aid is 1 nm to 10 μm.

6. The method for preparing high-performance structural ceramics based on binder spraying technology as described in claim 1, characterized in that, The silica sol contains 1-50% SiO2 by mass, and the average particle size of SiO2 is 1 nm-500 nm.

7. The method for preparing high-performance structural ceramics based on binder spraying technology as described in claim 1, characterized in that, In step S2, the powder thickness is 60μm to 200μm.

8. A structural ceramic substrate core prepared by adhesive spraying, characterized in that, The high-performance structural ceramics are prepared by the method for preparing high-performance structural ceramics based on binder spraying technology as described in any one of claims 1-7.

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