Casting core mainly composed of ceramics and manufacturing method of casting product using the same

Abstract

To provide a core for casting which has mechanical strength enough to withstand for a long time during a casting process and is excellent in dissolution to alkaline solution.SOLUTION: A core for casting composed mainly of ceramics has a core, a surface layer, and an intermediate layer between the core and the surface layer. A relative density of the intermediate is lower than that of the surface layer and the core.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a casting core containing ceramics as its main component, which is used for precision casting of metals. [Background technology]

[0002] Ceramic casting cores (ceramic cores) used to create flow paths inside turbine blades used in aircraft engines and the like are required to have shape stability that can withstand the stresses generated during the casting process for a long period of time. Furthermore, the casting cores inserted inside the casting must be eluted in a strong alkaline solution or the like after the casting process is completed. Thus, casting cores are required to have not only high-temperature stability but also elution properties in a strong alkaline solution.

[0003] To meet these demands, conventional casting cores are made of a porous material with a relative density of about 70%, primarily composed of silica, to facilitate penetration by strong alkaline solutions and to improve elution properties in strong alkaline solutions. Patent Document 1 proposes a casting core made of a porous material with a three-layer structure with different relative densities, where the relative density decreases from the surface layer to the core, in order to achieve higher strength and elution properties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-71169 Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional cores for precision casting are made of porous materials and have a three-point bending strength of around 10 to 34 MPa. Casting cores used in long-term casting processes, such as casting of aircraft engine parts, require a three-point bending strength of 40 MPa or more, so these cores for precision casting were insufficient in strength. [Means for solving the problem]

[0006] A casting core whose main component is ceramic, comprising a core, a surface layer, and an intermediate layer between the core and the surface layer, wherein the relative density of the intermediate layer is lower than the relative density of the surface layer and the core. [Effects of the Invention]

[0007] The casting core of the present invention has a core, a surface layer, and an intermediate layer between the core and the surface layer, with the intermediate layer having a lower relative density than the surface layer and the core. According to the present invention, it is possible to provide a casting core that has sufficient mechanical strength to withstand a long period of time during the casting process and excellent elution resistance in an alkaline solution. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are a schematic view and a partial cross-sectional view, respectively, illustrating an embodiment of a casting core of the present invention. [Figure 2] FIG. 1 is a conceptual diagram of a manufacturing apparatus that uses powder bed fusion to manufacture. [Figure 3] 1A and 1B are diagrams showing structures produced in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following specific examples and can be modified within the technical spirit of the present invention. Furthermore, the effects described in the embodiments are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments.

[0010] 1 is a diagram showing a casting core (hereinafter sometimes simply referred to as a core) according to one embodiment of the present invention, and its cross section. As shown in the A-A' and B-B' cross sections, the core has a structure including a surface layer 101, an intermediate layer 102, and a core 103, and is characterized in that the relative density of the intermediate layer 102 is lower than the relative densities of the surface layer 101 and the core 103.

[0011] The density of a casting core is calculated by dividing the mass of the casting core by the volume. The relative density of a casting core is calculated as the ratio of the density to the theoretical density taking into account the phases of the compounds contained in the casting core. The average relative density of a casting core is calculated as the ratio of the value obtained by dividing the mass of the casting core by the volume enclosed by the surface of the casting core to the theoretical density.

[0012] To ensure sufficient mechanical strength to prevent deformation, the core 103 of the casting core 100 is preferably made of dense ceramics, and the surface layer 101 is preferably made of a relatively dense porous or dense ceramics. Furthermore, to improve elution in alkaline solutions, it is preferable to thin the wall thickness of each part of the casting core or make it low-density (porous). In the casting core of the present invention, the intermediate layer 102 has a structure that is lower in density than other parts, allowing sufficient penetration by alkaline solutions. This allows the surface layer 101 in contact with the casting to be efficiently eluted from the inside. The core that is not in contact with the casting can be expelled from the casting together with the eluted surface layer 101 and intermediate layer 102.

[0013] Casting cores that require partial adjustment of wall thickness or density can be manufactured using additive manufacturing technology. In particular, infrared laser melting (or selective laser melting), which involves layer-by-layer manufacturing while sintering, melting, and solidifying raw material powder, is suitable. The density of each part can be controlled by adjusting the degree of sintering or melting by changing the amount of heat input to the raw material powder by a laser beam, or by adjusting the irradiation pitch of the laser beam to sinter, melt, or solidify the raw material powder in a lattice pattern. Hereinafter, "sintering, melting, or solidifying powder" may be expressed as "solidifying powder."

[0014] To ensure sufficient mechanical strength for a casting core, the thickness 104 of the surface layer 101 is preferably at least 0.2 mm, more preferably 0.3 mm to 3 mm. Because the intermediate layer 102 must be able to penetrate a sufficient amount of alkaline solution, the thickness 105 of the intermediate layer 102 is preferably 0.2 mm or greater. For casting cores with complex shapes, the remaining portion, obtained by subtracting the thickness 104 of the surface layer 101 from the thickness 105 of the intermediate layer 102, is preferably the core 103. The core 103 need only constitute at least a portion of the casting core. For example, if the casting core 100 has a shape including a tapered tip region or a thin-walled region, it is not necessary to provide a core 103 in those regions. By providing the core layer 103 inside the surface layer 101 via the intermediate layer 102, strength sufficient to withstand the casting process can be achieved even when the thin surface layer 101 alone is not sufficient. When the casting core includes a core 103, if the thickness 106 of the core 103 is 0.2 mm or more, the effect of reinforcing the strength of the casting core 100 can be obtained. From the viewpoint of reinforcing the strength of the casting core 100, the thickness 106 of the core 103 is preferably 0.3 mm or more, and more preferably 1 mm or more.

[0015] The surface layer 101 is preferably dense or relatively dense and porous, and preferably has a relative density of 82% or more. The surface layer 101 may be porous, but preferably has a relative density at least sufficiently higher than that of the intermediate layer 102.

[0016] The relative density of the intermediate layer 102 is preferably 20% to 67%, and more preferably 50% to 67%. This value ensures the permeability and fluidity of the solution when dissolving the core in an alkaline solution after the casting process. The fluidity of the solution is important to prevent the core components dissolved in the alkaline solution from saturating, allowing fresh alkaline aqueous solution to be appropriately refluxed. To maintain the relative density of the intermediate layer 102 at 67% or less, it is preferable for the intermediate layer 102 to have a lattice structure. The thickness 300 of the beams constituting the lattice structure is preferably 0.2 mm or more, and more preferably 0.3 mm or more. Furthermore, the maximum thickness of the beams is not particularly specified, but it is preferably 1 mm or less, at least at the points in contact with the surface layer 101.

[0017] When intermediate layer 102 has a lattice structure, it is preferable that core thickness 106 be thicker than the thickness of the beams of the lattice of intermediate layer 102. There are no particular restrictions on the design of the contact portion between the lattice structure of intermediate layer 102 and core 103.

[0018] The casting core has an exposed portion 107 where the intermediate layer 102 and the core 103 are exposed, and after the casting process, an alkaline solution is supplied from the exposed portion 107. This allows the alkaline solution to quickly return to every corner of the core inside the casting via the intermediate layer 102.

[0019] Considering the reflux of the alkaline solution, it is preferable that a plurality of exposed portions 107 are provided as inlet and outlet ports for the alkaline solution. Furthermore, when intermediate layer 102 and core 103 have portions with a thickness of 1 mm or more, they are preferably arranged and shaped so that they can be dissolved in the alkaline solution to be disintegrated and removed from exposed surface 107. For example, one method is to provide partially discontinuous portions or thin, easily eluted portions so that intermediate layer 102 and core 103 are divided into portions of a size that can be removed from exposed portion 107 by elution.

[0020] The alkaline solution used to elute the casting core can be an aqueous solution containing sodium hydroxide, potassium hydroxide, or the like as a main component. There are no particular restrictions on the concentration of the aqueous solution, but it is preferably about 10 to 35 wt%, more preferably 20 to 30 wt%, and particularly preferably 23 to 27 wt%. The content of carbonates, chlorides, iron impurities, and the like contained in the aqueous solution is preferably less than 0.1 wt%.

[0021] During leaching, heating may be performed at temperatures between room temperature and 300°C, as long as the temperature does not affect the metal casting. When heating to 100°C or higher, it is important to apply pressure to prevent the solution from volatilizing. Furthermore, it is preferable to repeatedly apply pressure and reduce pressure during the core leaching process in order to remove any bubbles that may be generated during leaching.

[0022] When the intermediate layer 102 has a lattice structure, it can have various lattice shapes. It may be an asymmetrical lattice structure, a repeating unit structure, or a combination of multiple structures. Specifically, a diamond structure lattice or a gyroid structure lattice, which are widely used in additive manufacturing, are suitable. By changing the thickness of the beams in the lattice structure or the spacing between the beams, the relative density of the intermediate layer 102 can be adjusted to a desired value.

[0023] In addition to having the intermediate layer 102 have a lattice structure, it is also preferable to provide a flow path for the alkaline solution within the porous structure. In this case, the relative density of the entire intermediate layer 102 is set to 67% or less. The difference between the lattice structure and the porous structure is the size of the pores: in the lattice structure, the space between the beams is 0.2 mm or more, while in the porous structure, the average pore diameter is less than 0.2 mm.

[0024] A coating layer may be provided on the outermost surface of the surface layer 101 to impart functionality to the surface of the surface layer 101 that comes into contact with the casting. The coating layer does not need to be provided over the entire surface layer 101, but may be provided in a desired area. The relative density of the coating layer is preferably 82% or more. The coating layer can be formed by applying or spraying a glaze-like substance onto the surface and firing it after completing the shaping using additive manufacturing. Alternatively, the coating layer may be formed using thermal spraying, vacuum deposition, sputtering, CVD, or other similar methods. There are no particular restrictions on the thickness of the coating layer, and in order to impart functionality, it is preferably 20 nm or more and 1 mm or less.

[0025] Next, a manufacturing process for a casting core according to the present invention and a manufacturing process for a cast part using the casting core according to the present invention will be described.

[0026] [Casting core manufacturing process] Although there are no limitations on the manufacturing method as long as it can realize the structure including the three parts according to the present invention, it is preferable to manufacture using a method called powder bed fusion, which is characterized by spreading powder to a predetermined thickness on a substrate and irradiating the powder with a laser beam to sinter or melt and solidify the powder multiple times to form the shape.

[0027] Figure 2 is a conceptual diagram of a molding apparatus that uses powder bed fusion. The molding apparatus comprises a powder container 11, a molding unit 13, a recoater unit 15, a laser light source 16, and a scanner unit 17 that scans the laser beam generated by the laser light source 16. Based on slice data generated from three-dimensional data of the ceramic article, a laser beam 18 generated by the laser light source 16 is scanned by the scanner unit 14, and an image is directly drawn on powder 20 spread on a substrate 19. The drawn area is solidified by sintering or melting and solidifying, and this process is repeated to obtain a molded object 21 in which solidified areas are layered one on top of the other.

[0028] Each step using the apparatus shown in FIG. 2 will be described below.

[0029] <Step 1: Spreading the powder evenly to the specified thickness> In step 1, the bottom 12 of the powder container 11 is raised to push up the material powder 19, and the stage 14 on which the substrate 19 of the molding section 13 is set is lowered a predetermined distance. Next, the material powder 19 is supplied to the molding section 12 by the coater section 15, and the powder 20 is spread evenly to a predetermined thickness over an area larger than the intended ceramic article.

[0030] While various compositions can be applied to the powder for core making of ceramic casting cores depending on the application, it is preferable to use a metal oxide as the main component. Using a metal oxide as the main component of the powder for core making is preferable because it prevents decomposition or gasification caused by irradiation with an energy beam, which can lead to molding defects. This is because powders with a high ratio of resin components or carbon-containing materials can burn, decompose, gasify, etc. due to sudden heating, resulting in the formation of many voids in the solidified parts and poor bonding between the solidified parts.

[0031] The main component of the metal constituting the metal oxide is preferably an oxide containing at least one element selected from the group consisting of silicon, aluminum, and zirconium. In particular, it is preferable that aluminum oxide, silicon oxide, and zirconium oxide (including stabilized zirconia) total 50 mol % or more. This total value can also include composite oxides of these oxides.

[0032] Furthermore, the powder for core formation preferably contains as little alkali metals and alkaline earth metals as possible, down to the level of impurities, and preferably does not contain the main components that make up the metal to be cast.

[0033] The powder for core formation can be composed of a desired combination of main and sub-components. The sub-component preferably contains, for example, a rare earth oxide or a material that acts as an absorber that absorbs infrared laser light and converts it into heat. A preferred example of the rare earth oxide is an oxide of any one metal selected from the group consisting of Sc, Y, La, Ce, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu. The rare earth oxide may be contained in the form of a composite oxide consisting of a main component and a sub-component. Examples of absorbers include Tb4O7 and Pr6O 11 , Ti2O3, TiO, SiO, ZnO, antimony-doped tin oxide (ATO), indium-doped tin oxide (ITO), TiC, ZrC, NbC, VC, HfC, WC, Mo2C, TaC, WC-TiC, WC-TaC, WC-TiC-TaC, TiN, ZrN, VN, NbN, TaN, Cr2N, HfN, Si3N4, AlN, TiB2, ZrB2, VB2, NbB2, TaB2, CrB, MoB, WB, LaB6, HfB2, TiSi2, ZrSi2, NbSi2, TaSi2, CrSi2, MoSi2, WSi2, FeSi2, HfSi2, and the like are preferred.

[0034] For example, a preferred example of a core-making powder is one that contains aluminum oxide as the main component and at least one of gadolinium oxide and terbium oxide and praseodymium oxide. The inclusion of gadolinium oxide in the powder gives it a lower melting point than aluminum oxide alone, near the Al2O3-Gd2O3 eutectic composition. This allows the powder to be melted with less heat, suppresses laser beam diffusion within the powder, and improves molding accuracy. Furthermore, the inclusion of gadolinium oxide results in a phase-separated structure containing multiple phases in the molded object. This suppresses crack propagation and improves the mechanical strength of the molded object. The same effect as gadolinium oxide can be achieved when oxides of other rare earth elements (excluding terbium and praseodymium) are included instead of gadolinium oxide. Furthermore, terbium oxide (Tb4O7) and praseodymium oxide (Pr6O 11) functions as an absorber that absorbs near-infrared lasers such as Nd:YAG lasers and Yb fiber lasers and converts them into heat. By adding these as secondary ingredients to powder for core molding, the spread of heat within the powder is suppressed, causing it to melt and solidify locally, reducing the impact of heat on non-molded areas and improving molding accuracy.

[0035] Another preferred example of a powder for core making is a powder containing silicon oxide as its main component. Powders containing silicon oxide as their main component may further contain at least one material selected from materials such as aluminum oxide and zirconium oxide that function as absorbents. It is particularly preferable that the powder contains silicon monoxide as an absorbent. Powders containing silicon oxide and aluminum oxide form a SiO2-Al2O3 compound in the molded product, which is expected to improve strength due to the composite structure.

[0036] Although the powder for core formation is not limited to these examples, a mixed powder of three types of Al2O3, Gd2O3, and Tb4O7, or a mixed powder of three types of SiO2, Al2O3, and SiO are preferred material systems. Furthermore, in order to achieve the composition and structure required for the core after production, it is possible to appropriately devise a mixture of multiple types of powder of individual materials, or to use powders that have already been compounded and combined.

[0037] In <Step 1>, it is preferable to spread the powder to a thickness of 5 μm or more and 100 μm or less. A thickness of 20 μm or more and 30 μm or less is particularly preferable. The powder for core formation may be a mixture of multiple types of powders with different average particle sizes, and there are no restrictions as long as fluidity is ensured. For example, fluidity is ensured when the angle of repose is 45 degrees or less. It is preferable that the powders of the main component and subcomponent have an average particle size of 5 μm or more and 100 μm or less. From the viewpoint of mobility, it is preferable that the main component is nearly spherical. It is preferable that the absorber that absorbs infrared laser and converts it into heat has an average particle size of 10 μm or less. The average particle size is the D50 value of the median diameter.

[0038] The material of the substrate 19 placed on the stage 14 of the molding unit 13 can be appropriately selected from ceramics, metals, glass, etc., taking into consideration the application of the molded object, manufacturing conditions, etc. The surface of the substrate preferably has a flatness of 100 μm or less, but some unevenness is acceptable as long as the solidified part can be bonded to the substrate after the core-forming powder is spread evenly on the surface and solidified by irradiating it with a laser beam.

[0039] <Step 2: A step of irradiating the powder with a laser beam to solidify it> In <Step 2>, the powder 20 that has been spread evenly to a predetermined thickness on the substrate 19 in <Step 1> is scanned by the scanner unit 14 with a laser beam 18 generated from a laser light source 16 based on the three-dimensional data of the casting core to be manufactured, thereby performing direct drawing.

[0040] When the laser beam 18 is irradiated onto the powder 20, the energy of the laser beam absorbed by the powder 20 is converted into heat, melting the powder 20. When the irradiation of the laser beam 18 is completed, the molten powder is cooled and solidified by the atmosphere and its adjacent surroundings, forming a solidified portion corresponding to one cross section of the casting core.

[0041] In shaping by laser beam irradiation, the laser beam is preferably a line scan, and preferably a surface is formed by scanning multiple adjacent lines. The thickness of the powder layer (the set value of the stage lowering width) is preferably 5 μm or more and 100 μm or less. From the viewpoint of obtaining shaping accuracy, when shaping a surface shape, the laser output and drawing speed are adjusted so that the line width is approximately 50 to 200 μm, and the average distance between adjacent lines is preferably 20 μm or more and 400 μm or less. More preferably, it is 50 μm or more and 200 μm or less. The ratio of the thickness of the powder layer to the distance between the lines irradiated with the laser beam (drawing pitch) (line distance / powder layer thickness) is preferably 4 μm or more and 6 μm or less. However, this does not apply when a lattice-like structure or a porous structure other than a surface shape is realized by the shape elements of the core.

[0042] The casting core is made by alternately repeating the above-mentioned <Step 1> and <Step 2> multiple times to produce a molded object 21. When the powder spread evenly in <Step 1> on top of the solidified portion formed in <Step 2> is irradiated with a laser beam according to three-dimensional data, the powder in the irradiated portion sinters or melts and solidifies, and the solidified portion melts near its interface with the powder. Then, during solidification, the previously formed solidified portion and the later formed solidified portion are joined, forming a molded object in which they are integrated.

[0043] <Step 3: Firing step> After completion of Step 3, the molded object 21 is separated from the substrate 19, and supports and other components added for shaping are removed from the molded object 21 as needed, completing the shape of the casting core. If the molded object meets the requirements for a casting core, it can be used in the casting process in this state. To further increase structural stability, it is preferable to perform a firing process.

[0044] The firing process is carried out to repair voids and cracks that occurred in the casting core during production and to eliminate oxygen deficiency caused by laser irradiation. It is also preferable to impregnate the casting core with a material required to repair cracks before firing.

[0045] Casting cores made from powders composed of Al2O3, Gd2O3, and Tb4O7 can be impregnated with a liquid (repair liquid) containing a material that can become zirconia and then fired to repair cracks. Repeating the impregnation and firing process multiple times enhances the crack repair effect, so it is also preferable to repeat the process multiple times as needed. The firing temperature should be between 1662°C and 1710°C. Examples of liquids containing a material that can become zirconia include an 85% by weight zirconia butoxide-1-butanol solution diluted 16 times with 2-propanol and stabilized with a stabilizer, or a zirconium acetate solution or a zirconia particle dispersion with a stabilizer. After molding, the impregnated and fired cores can be composed of components such as Al2O3, (GdTb)AlO3, (GdTb)Al2O9, and stabilized ZrO2. The core may contain some powder or remnants of the impregnating material.

[0046] For casting cores made from powders consisting of SiO2, Al2O3, and SiO, crack repair effects can be achieved simply by firing without impregnating them with a repair liquid. Also, to increase the strength of the cracked area, the casting core can be impregnated with the same repair liquid as above before firing. In this case, it is preferable to fire at a temperature that matches the mixture ratio of SiO2 and Al2O3, and a desirable effect can be obtained in the range of approximately 1660°C or higher and 1950°C or lower. In this way, cores that are impregnated with repair liquid after molding and then fired have a high degree of strength, and the cores are made of SiO2, Al2SiO5, Al6SiO2O. 13 It may be composed of components such as Al2O3, ZrSiO4, etc. It is also acceptable for some powder or residues of repair liquid to remain.

[0047] <Process 4: Processing process> The machining process may be carried out to improve the surface smoothness of the casting core, or to make the shape of the casting core fall within a specified tolerance.

[0048] To achieve the specified tolerances, it is preferable to apply grinding, blasting, or other processes. Furthermore, to improve surface smoothness, it is advisable to provide a coating layer on the surface in addition to grinding, blasting, or other processes. For example, it is also preferable to coat the surface with a material such as glaze and then bake it, or to apply a coating by thermal spraying. Because the surface of the casting core comes into contact with the casting metal, it is preferable that the coating layer have the same components as the core, or a material that does not react with the metal and can ensure alkali solubility.

[0049] [Casting parts manufacturing process] <Process 5: Casting process> The casting process using the casting core of the present invention is no different from that using conventional cores. To create an integral mold with the wax, the core is placed in a mold, and wax is poured in and solidified. After demolding, an oxide shell is formed on the wax surface. The wax is then heated to dissolve, creating an area for metal injection. This can then be applied to various types of casting by adding a filter to capture debris in the molten metal during pouring or a grain selection area to control the metal solidification structure. The casting core of the present invention has a dense surface layer and core, making it stronger than conventional cores. Therefore, it can withstand long casting processes and is suitable for casting aircraft engine parts.

[0050] <Step 6: Casting core elution process> Once casting is complete, the outer shell is destroyed and removed, and the integrated body of the cast metal and casting core is placed in a leaching device and immersed in an alkaline solution for the core leaching process. In the leaching process, repeated pressurization and depressurization are preferably performed, as this allows the alkaline solution to penetrate through exposed areas of the casting core and facilitates reflux within the intermediate layer. [Example]

[0051] The casting core structure according to the present invention was subjected to a bending strength test and an evaluation of its elution in an alkaline solution. For the evaluation, seven types of columnar structures 400, each measuring 4 mm wide, 3 mm high, and 38 mm long, were fabricated, three for each type, as shown in Fig. 3. All seven types of structures 400 had in common the design of a surface layer 410 with a thickness of 0.5 mm, an intermediate layer with a thickness of 0.5 mm, and a core with dimensions of 2 mm x 1 mm x 38 mm, but the structural combinations of the surface layer 410, intermediate layer 420, and core 430 were different from one another.

[0052] [Modeling powder] Two types of material systems A and B were prepared as powders for molding.

[0053] (Materials A) This powder is made by mixing Al2O3, Gd2O3, and Tb4O7 in the following ratio, where Al2O3 is the main component, Gd2O3 and Tb4O7 are secondary components, and Tb4O7 functions as an absorber. Weight ratio: Al2O3:Gd2O3:Tb4O7=49.1:46.7:4.2 Molar ratio: Al2O3:Gd2O3:Tb4O7 = 78.2:20.9:0.9

[0054] The following powders were used as raw materials for Al2O3, Gd2O3, and Tb4O7. Spherical Al2O3 powder (median diameter: approx. 20 μm) Spherical Gd2O3 powder (median diameter: approx. 30μm) Tb4O7 crushed powder (median diameter: approx. 4 μm)

[0055] (Materials B) This powder is made by mixing SiO2, Al2O3, and SiO in the following ratio. The three main components are SiO2, Al2O3, and SiO, and SiO functions as an absorbent. Weight ratio: SiO2:Al2O3:SiO=44.3:53.6:2.1 Molar ratio: SiO2:Al2O3:SiO = 56.3:40.1:3.6

[0056] The following powders were used as raw materials for Al2O3, Gd2O3, and Tb4O7. Spherical SiO2 powder (median diameter: approx. 38 μm) Spherical Al2O3 powder (median diameter: approx. 20 μm) SiO pulverized powder (median diameter: approx. 5 μm)

[0057] [Repair fluid] The liquid (repair liquid) used for the impregnation of the zirconium component in the firing process was an 85 wt% zirconia butoxide·1-butanol solution diluted 16 times with 2-propanol and a stabilizer added, resulting in a Zr concentration of 13 wt%. The firing temperature after impregnation was 1680°C for 20 minutes in all cases.

[0058] [Modeling method] The 3Dsystems ProX DMP200 was used for the modeling. The substrate was an alumina plate measuring 110mm x 120mm x 3mm, and the raw material powder was spread to a thickness of 25μm. The modeling was performed in a direction parallel to the substrate and a 5mm x 38mm surface.

[0059] To fabricate structure 40, a cube measuring 5 mm × 6 mm × 38 mm was first fabricated. During fabrication, the central 2 mm × 1 mm × 38 mm area of ​​the internal 4 mm × 3 mm × 38 mm area was designated as the core, and the area excluding the core was designated as the intermediate layer.

[0060] The molded object was separated from the base, and the process of impregnating it with repair liquid and firing it was repeated until it was confirmed that there were no cracks or other imperfections.Then, the outer periphery of the intermediate layer was ground down to a size of 4 mm x 3 mm x 38 mm, so that an evenly distributed surface layer of 0.5 mm thickness remained.

[0061] The conditions for fabricating a dense body using material system A were an infrared fiber laser output of 294 W, a laser scan speed of 1500 mm / sec, and a scan pitch of 130 μm. When fabricating a relatively dense porous body, the scan pitch was changed to 180 μm.

[0062] The conditions for forming a dense body using material system B were an infrared fiber laser output of 294 W, a laser scanning speed of 1000 mm / sec, and a scanning pitch of 130 μm.

[0063] [Evaluation of Structure] The seven types of structures produced were subjected to measurements of three-point bending strength at room temperature and 1500°C, and evaluation of elution in alkaline solutions. To evaluate elution, each sample was immersed in a 25 wt% aqueous solution of sodium hydroxide at 160°C for 48 hours, and a cycle of pressurizing to 0.5 MPa and returning to normal pressure was repeated in seven-minute cycles to promote penetration, diffusion, and reflux of the aqueous solution into the fine details. Visual inspection was performed to determine whether there was any thinning or collapse from the original shape, and a score of ◯ was given if the shape had collapsed after 48 hours, and an × if the shape was maintained.

[0064] Material system A was used for the molding powder, and samples were produced in which the surface layer 410 was a dense body and the structures of the intermediate layer 420 and core 430 were changed, and then evaluated.

[0065] (Comparative Example 1) The surface layer 410, intermediate layer 420, and core 430 were all molded under conditions that would result in a dense body. The molded object was separated from the base material, impregnated with a repair liquid, and fired. This process was repeated four times to confirm that cracks had disappeared. The object was then ground to a size of 4 mm x 3 mm x 38 mm.

[0066] The structure of this comparative example is a dense body without any distinction between a surface layer, an intermediate layer, and a core. When converted using the theoretical density of 5.72 g / cm3, the relative density of the dense body was 99.1%.

[0067] (Comparative Example 2) The intermediate layer 420 and core 430 were molded to have a lattice structure, and the surface layer 410 was molded to have a dense body. The lattice structure was a diamond structure with a relative density of 10.3%. The molding conditions for both were the dense body forming conditions for material system A.

[0068] After separating the molded object from the base material, the process of impregnating it with a repair liquid and firing it was repeated twice. After confirming that there were no cracks, the object was ground. The lattice structure of the intermediate layer 420 and core 430 was exposed on a 4 mm x 3 m surface of the structure.

[0069] In the structure of this comparative example, the surface layer 410 is a dense body having a thickness of 0.5 mm, and the intermediate layer 420 and the core 430 have a uniform lattice structure with no distinction therebetween.

[0070] The overall average relative density was 59.5%, so if the dense body portion had the same relative density as Comparative Example 1, the relative density of the lattice region was 19.9%, which was larger than the expected 10.3%. This is thought to be because the lattice beams were made slightly thicker.

[0071] Example 1 The intermediate layer 42 had a lattice structure, and the surface layer 410 and core 430 were dense bodies. Both parts were molded under conditions that would result in a dense body. The lattice structure of the intermediate layer 42 was a diamond structure with a relative density of 10.3%. After the molded object was separated from the substrate, the process of impregnating it with repair material and firing was repeated twice. After confirming that there were no cracks or other imperfections, the object was then machined. The lattice structure of the intermediate layer 420 was exposed on a surface measuring 4 mm x 3 m of the structure.

[0072] The structure of this example has a surface layer made of a dense body with a thickness of 0.5 mm, a lattice-shaped middle layer, and a core made of a dense body with a thickness of 1 mm. Since the average relative density of the entire structure was 73.7%, assuming that the dense body portion had the same relative density as Comparative Example 1, the relative density of the lattice-shaped region was 22.9%, which was larger than the expected 10.3%. This is thought to be because the lattice beams were made slightly thicker.

[0073] Example 2 Material system A was used for the molding powder. The intermediate layer 420 was molded to be porous with flow paths, and the surface layer 410 and core 430 were molded to be dense. When molding the intermediate layer 42, conditions were adopted to mold a relatively dense porous body, and the other parts were molded under conditions to become dense bodies.

[0074] Six flow paths equivalent to φ0.4 mm were provided along a 38 mm side of the intermediate layer 420 at the four corners of the intermediate layer 420 and around the center of the 2 mm side of the core. The design relative density of the intermediate layer 420 in this example can be converted to 66.5%, which is below the preferred relative density of 67% for an intermediate layer.

[0075] After separating the molded object from the base material, the process of impregnating it with a repair liquid and firing it was repeated twice. After confirming that there were no cracks, the molded object was then machined. The porous surface of the intermediate layer 420 and the flow paths were exposed on a 4 mm x 3 m surface of the structure.

[0076] The structure of this example has a surface layer 41 made of a dense body with a thickness of 0.5 mm, an intermediate layer 42 made of a structure consisting of relatively dense pores and flow channels, and a dense body 1 mm thick in the core 430. Since the average relative density of the entire structure was 88.3%, assuming that the dense body is the same as in Comparative Example 1, the region made of the structure consisting of pores and flow channels is estimated to have a relative density of 66.7%, which is equivalent to the converted value.

[0077] The three-point bending strength was measured and the elution property in an alkaline solution was evaluated for the prepared samples of Comparative Examples 1 and 2 and Examples 1 and 2. The results are shown in Table 1. The relative density is shown in parentheses in the table.

[0078] [Table 1]

[0079] It was found that Comparative Example 1, being entirely dense, had poor elution properties and did not dissolve within a practically acceptable time. Comparative Example 2, in which intermediate layer 420 and core 430 have a lattice structure, had a lower bending strength than Comparative Example 1, which is a dense body, but there was no problem with elution properties.

[0080] In Examples 1 and 2, in which the core 430 was a dense body, the bending strength was improved by about 20% at room temperature and 10% in the range close to the casting temperature of 1500°C compared to Comparative Example 2, and furthermore, the alkali solubility was equivalent.

[0081] From this, it was confirmed that by constructing the surface layer 410 and the core 430 so that their relative density is higher than that of the intermediate layer 420, as in the present invention, it is possible to improve the bending strength at room temperature and at high temperatures while maintaining the solubility in alkaline solutions.

[0082] Next, samples were produced and evaluated using material system A as the molding powder, with the surface layer 410 being a relatively dense porous body and the structures of the intermediate layer 420 and core 430 being changed.

[0083] (Comparative Example 3) The surface layer 41, the intermediate layer 42, and the core 43 were all molded to be relatively dense and porous. After separating the molded object from the base material, the process of impregnating it with a repair liquid and firing it was repeated four times. After confirming that there were no cracks or other imperfections, the object was ground.

[0084] The structure of this comparative example is a relatively dense porous structure without any distinction between the surface layer, intermediate layer, and core. When converted using the theoretical density of 5.72 g / cm3, the relative density of the porous body was 82.4%.

[0085] Comparative Example 4 The intermediate layer 42 was shaped to have a lattice structure, while the surface layer 41 and core 43 were shaped to have relatively dense porous structures. The lattice structure of the intermediate layer 42 was a diamond structure with a relative density of 10.3%. The shaping conditions for both were the same as for forming a dense material for material system A.

[0086] After separating the molded object from the base material, the process of impregnating it with a repair liquid and firing it was repeated twice. After confirming that there were no cracks, the object was ground. The lattice structure of the intermediate layer 42 was exposed on a 4 mm x 3 m surface of the structure.

[0087] The structure of this comparative example has a surface layer 41 that is a dense body with a thickness of 0.5 mm, and a uniform lattice structure with no distinction between the intermediate layer 42 and the core 43. The relative density of the entire object was calculated to be 48.5%. If the relatively dense porous portion has the same relative density as Comparative Example 3, the relative density of the lattice region is 14.5%, which is larger than the expected 10.3%. This is thought to be because the lattice beams were made slightly thicker.

[0088] Example 3 The intermediate layer 42 was shaped to have a lattice structure, while the other areas were relatively dense and porous. The lattice structure was a diamond structure with a relative density of 10.3%, the same as in Example 1. After separating the structure from the substrate, the process of impregnating it with a repair liquid and firing it was repeated twice. After confirming that there were no cracks or other imperfections, the structure was then machined. The lattice structure of the intermediate layer 42 was exposed on a surface measuring 4 mm x 3 m.

[0089] The structure produced in this example consisted of a surface layer 41 that was a relatively dense porous body with a thickness of 0.5 mm, an intermediate layer 42 with a lattice structure, and a core 43 that was 1 mm thick and relatively dense and porous. The average relative density of the entire structure was 61.4%. Assuming that the relatively dense porous body had the same relative density as Comparative Example 1, the relative density of the intermediate layer 42 region was 19.3%, which was larger than the expected 10.3%. This is thought to be because the lattice beams were made slightly thicker.

[0090] The three-point bending strength was measured and the elution property in an alkaline solution was evaluated for the prepared samples of Comparative Examples 3 and 4 and Example 3. The results are shown in Table 2. The relative density is shown in parentheses in the table.

[0091] [Table 2]

[0092] Comparative Example 3 was composed of a relatively dense porous body, and therefore the elution rate was slightly improved compared to Comparative Example 1. However, the shape did not collapse within the time, and the elution rate was still insufficient within the allowable time. Furthermore, the bending strength was lower than that of Comparative Example 1, which was entirely dense.

[0093] Both Comparative Example 4 and Example 3, in which the intermediate layer 420 has a lattice structure, exhibited excellent elution properties in an alkaline solution. The bending strength was lower than that of Comparative Example 1, in which the entire body was dense. However, Example 3, which had a structure according to the present invention, exhibited bending strength that was improved by about 20% at room temperature and 10% in the range close to the casting temperature of 1500°C compared to Comparative Example 4.

[0094] From the above results, it was confirmed that by constructing the surface layer 410 and the core 430 so that their relative density is higher than that of the intermediate layer 420, as in the present invention, it is possible to improve the bending strength at room temperature and at high temperatures while maintaining the solubility in alkaline solutions.

[0095] Material system B was used for the molding powder, and samples were produced in which the surface layer 410 was a dense body and the structures of the intermediate layer 420 and core 430 were changed, and then evaluated.

[0096] (Comparative Example 5) The surface layer 410, the intermediate layer 420, and the core 430 were all shaped to be dense bodies. After separating the molded object from the base material, it was impregnated with repair liquid and baked once. After confirming that there were no cracks or other imperfections, it was ground.

[0097] The structure of this comparative example was a columnar dense body measuring 4 mm x 3 mm x 38 mm, with no distinction between a surface layer, an intermediate layer, or a core. The relative density of the dense body was 92.7%.

[0098] (Comparative Example 6) The intermediate layer 42 and the core 43 were shaped to have a lattice structure, and the surface layer 410 was shaped to have a dense body. The lattice structure was a gyroid structure with a density of 66.3%.

[0099] After separating the molded object from the base material, it was impregnated with a repair liquid and baked once. After confirming that there were no cracks, it was ground. The lattice structure of the intermediate layer 420 and core 430 was exposed on a 4 mm x 3 m surface of the structure.

[0100] The structure of this comparative example has a surface layer 410 that is a dense body with a thickness of 0.5 mm, and a uniform lattice structure with no distinction between the intermediate layer 420 and the core 430. The average relative density of the entire structure was 78.2%.

[0101] Assuming that the dense body has the same relative density as Comparative Example 1, the relative density of the lattice-like region is 63.7%, which is smaller than the assumed 66.3%, but this is thought to be because the lattice beams were shaped to be slightly thinner.

[0102] Example 4 Material system B was used for the molding powder. The intermediate layer 42 was molded to have a lattice structure, and the other parts were molded to be dense. The lattice structure was a gyroid structure with a relative density of 66.3%.

[0103] After separating the molded object from the substrate, the object was impregnated with a repair liquid and baked once. After confirming that there were no cracks, the object was ground. The lattice structure of the intermediate layer 42 was exposed on a 4 mm x 3 m surface of the structure.

[0104] The structure of this example has a surface layer made of a dense body with a thickness of 0.5 mm, a lattice-shaped intermediate layer, and a core made of a dense body with a thickness of 1 mm. Since the average relative density of the entire structure was 83.9%, if the dense body had the same relative density as Comparative Example 1, the relative density of the lattice-shaped region was 66.3%, as expected.

[0105] The samples prepared in Comparative Examples 3 and 4 and Example 3 were subjected to measurement of three-point bending strength and evaluation of elution in alkaline solution. The results are shown in Table 3. The relative density is shown in parentheses in the table.

[0106] [Table 3]

[0107] It was found that Comparative Example 5, which was entirely dense, had poor elution properties and did not dissolve within a practically acceptable time. Comparative Example 6, in which intermediate layer 420 and core 430 had a lattice structure, had a lower bending strength than Comparative Example 5, which was dense, but there was no problem with elution properties.

[0108] Example 4, in which the core 430 was a dense body, had a bending strength that was approximately 20% higher at room temperature and 10% higher in the range close to the casting temperature of 1500°C than Comparative Example 6, and furthermore, the alkali solubility was equivalent.

[0109] From this, it was confirmed that by constructing the surface layer 410 and the core 430 so that their relative density is higher than that of the intermediate layer 420, as in the present invention, it is possible to improve the bending strength at room temperature and at high temperatures while maintaining the solubility in alkaline solutions.

[0110] Next, it was confirmed that the configuration of the present invention can also be applied to the shape of a casting core.

[0111] (Comparative Example 7) Under the same conditions as in Comparative Example 2, a structure having the shape shown in Figure 1(a) was formed with the exposed surface 107 in contact with the substrate. That is, the structure of Comparative Example 7 has a surface layer 101 made of a dense body with a thickness of 0.5 mm, and an indistinguishable lattice structure between the intermediate layer 102 and the core 103. The approximate size of Figure 1(a) is 30 mm x 8 mm x 60 mm.

[0112] First, during the separation process before firing, a portion of the surface where the diamond-structured lattice structure and the base material come into contact broke due to its fragile strength and the thinness of the beams that make up the lattice. After separating the model from the base material, the process of impregnating it with repair liquid and firing it was repeated twice, and it was confirmed that the cracks had disappeared.

[0113] After the firing process was completed, the structure of the molded object was observed. In the wider part of the lattice structure (approximately 7 mm), there were areas where the lattice beams had slightly collapsed due to the slight pressure applied when spreading and leveling the powder during molding. In the molded object produced in Comparative Example 2, this was not apparent because the width of the molded surface of the lattice part was narrow, but it was confirmed that if both the intermediate layer 102 and the core 103 had a lattice structure in the original shape of a core, the molded object would be fragile and difficult to handle before firing.

[0114] Example 5 1(a) was fabricated under the same conditions as in Example 1, with the exposed surface 107 in contact with the substrate. The structure was shaped so that the surface layer 101 was a dense body with a thickness of 0.5 mm, the intermediate layer 102 had a lattice structure with a thickness of 2 mm from the inner surface of the surface layer, and the entire portion thicker than 2.5 mm was a dense body serving as the core 103.

[0115] During the process of separating the substrate, the lattice-shaped portion did not break, and the structure had sufficient strength. After separation, the process of impregnating with the zirconium component and firing was repeated three times, and it was confirmed that there were no cracks or other defects.

[0116] After firing was completed, the structure of the molded object was inspected and no particular structural defects were found.

[0117] Example 6 A shaped object was produced in the same shape as in Example 5, except that the thickness of the surface layer 101 was set to 0.4 mm. Thereafter, a coating layer of aluminum oxide was applied to the surface of the shaped object by plasma spraying to a thickness of 0.1 mm.

[0118] When the surface was observed, no significant cracks were found. The object was cut to observe the cross-sectional structure of the surface layer, and it was confirmed that the sprayed aluminum oxide coating layer was tightly attached to the surface of the surface layer 101.

[0119] From the above, it was confirmed that by providing three parts - a casting core, a core, an intermediate layer, and a structure in which the relative density of the intermediate layer is lower than the relative density of the surface layer and the core - it is possible to achieve high mechanical strength and excellent leaching properties, and that this is superior to conventional cores. [Industrial Applicability]

[0120] According to the present invention, a three-layer structure in which the surface layer and core are dense bodies and the middle layer has a lattice structure can improve the mechanical strength while maintaining the alkali solubility of ceramic cores for metal casting, thereby enabling production with a good yield even when the casting time is long. [Explanation of symbols]

[0121] 100 Casting core 101, 410 surface layer 102, 420 middle class 103,430 cores 104 Surface layer width 105 Middle layer width 106 Core Width 107 Exposed surface

Claims

1. 1. A ceramic article used as a casting core, comprising: a core; a surface layer; and an intermediate layer between the core and the surface layer, wherein the relative density of the intermediate layer is lower than the relative densities of the surface layer and the core; the relative densities of the core and the surface layer are 82% or more; the relative density of the intermediate layer is 20% or more and 67% or less; the thickness of the surface layer is 0.2 mm or more and 3 mm or less; the thickness of the intermediate layer is 0.2 mm or more; and the thickness of the core is 0.2 mm or more.

2. 2. The ceramic article according to claim 1, wherein the core has a thickness of 1 mm or more.

3. 3. The ceramic article according to claim 1, wherein the core and the intermediate layer have portions exposed on the surface.

4. 4. The ceramic article according to claim 1, wherein the intermediate layer has a lattice structure having voids of 0.2 mm or more in size.

5. 4. The ceramic article according to claim 1, wherein the intermediate layer has a porous structure having voids of less than 0.2 mm in size.

6. 6. The ceramic article according to claim 5, wherein the intermediate layer is provided with a flow channel.

7. 7. The ceramic article according to claim 1, wherein the ceramic is an oxide containing at least one element selected from the group consisting of silicon, aluminum, and zirconium.

8. 8. The ceramic article according to claim 1, wherein a coating layer is provided on at least a portion of the surface of the surface layer.

9. 9. A method for manufacturing a ceramic article according to any one of claims 1 to 8, comprising the steps of: Spread the oxide-containing powder evenly, forming a shaped object from a portion of the powder by powder bed fusion; forming the ceramic article from the shaped object; 1. A method for producing a ceramic article, comprising:

10. 10. The method for producing a ceramic article according to claim 9, wherein the powder contains at least one of aluminum oxide, silicon oxide, and zirconium oxide.

11. 11. The method for manufacturing a ceramic article according to claim 9, wherein the powder is irradiated with a laser beam in forming the shaped article.

12. The method for manufacturing a ceramic article according to any one of claims 9 to 11, wherein the formation of the ceramic article includes a firing step of firing the shaped article.

13. 13. The method for manufacturing a ceramic article according to claim 12, wherein the formation of the ceramic article includes a grinding step or a blasting step after the firing step.

14. 14. The method for manufacturing a ceramic article according to claim 9, wherein a coating layer is provided on the surface layer in forming the ceramic article.

15. A method for manufacturing a casting, comprising: arranging the ceramic article according to any one of claims 1 to 8 and an outer shell with a region into which metal is injected, injecting metal into the region to cast the ceramic article, and then eluting the ceramic article.

16. The method for manufacturing a casting according to claim 15, characterized in that an alkaline solution is used for the elution.

17. A method for manufacturing a casting, comprising: A step of placing the ceramic article according to any one of claims 1 to 8 in a mold, pouring wax into the mold, and allowing it to solidify; forming an oxide shell on the wax surface after removing the mold; a step of heating the wax to dissolve it, and then injecting a molten metal into a space between the ceramic article and the outer shell to perform casting; After removing the outer shell, immersing the cast metal and the ceramic article in an alkaline solution to dissolve the ceramic article; A method for manufacturing a casting, comprising:

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