Ceramic structure and method for manufacturing the same

Abstract

To provide a technology for manufacturing a silica alumina-based ceramic structure having higher densification and more improved in mechanical strength than a silica-based ceramic, using a direct modeling method.SOLUTION: A ceramic structure has a region formed of an oxide including Si and Al, a region formed of mullite, and a region formed of aluminum oxide, wherein a mole ratio SiO2 / Al2O3 in terms of oxide satisfies 0.1 / 0.9 to 0.7 / 0.3.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a laminated structure obtained by a direct molding method and a method for manufacturing the same. [Background technology]

[0002] Additive manufacturing technology, which involves adding material based on the shape data of a three-dimensional model of the object to be manufactured to obtain the desired structure, is becoming increasingly popular as a means of producing prototypes and small quantities of items. In the manufacture of metal articles, direct fabrication, which involves irradiating metal powder with a laser beam to solidify the powder and create the shape, is widely used. This method makes it possible to obtain a wide variety of articles by effectively melting and solidifying the metal powder.

[0003] In recent years, efforts have been made to establish additive manufacturing technology using ceramic powders. Unlike metals, common ceramics such as aluminum oxide and zirconium oxide have low absorption capacity for laser beam wavelengths, so a large amount of high energy is required to melt the ceramic powder. However, even with a large amount of energy, the laser beam diffuses, resulting in uneven melting and making it difficult to obtain the required molding accuracy.

[0004] Patent Document 1 discloses a technique for achieving high fabrication accuracy by adding an absorber with high absorption capacity for the wavelength of the irradiated laser beam to the raw material powder to suppress beam diffusion. Patent Document 2 discloses a technique for manufacturing ceramic structures by a direct fabrication method using a powder mainly composed of silicon dioxide, to which an absorber with high absorption capacity for the wavelength of the irradiated laser beam has been added. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2019-19051 [Patent Document 2] Japanese Patent Publication No. 2021-66177 [Overview of the project] [Problems that the invention aims to solve]

[0006] Patent Document 1 describes Al2O3-ZrO2-based powders and Al2O3-SiO2-based powders with Tb4O7 added as an absorber. Patent Document 2 describes Al2O3-SiO2-based powders with SiO added as an absorber. Since SiO2 is inexpensive and readily available, Al2O3-SiO2-based powders are particularly preferred because they allow for the stable and low-cost production of ceramic structures.

[0007] However, as shown in Patent Documents 1 and 2, molded objects obtained using a direct molding method from raw material powder with a SiO2 content exceeding 70 mol% tend to be porous and lack sufficient mechanical strength for use as structural components such as machine parts and medical parts. [Means for solving the problem]

[0008] The ceramic structure containing Si and Al according to the present invention has a region made of mullite, a region made of an oxide containing Si and Al in a higher proportion of Si than the mullite, and a region made of aluminum oxide, and is characterized in that the molar ratio SiO2 / Al2O3 on an oxide basis satisfies 0.1 / 0.9 to 0.7 / 0.3.

[0009] Furthermore, the method for manufacturing a ceramic structure according to the present invention is characterized by comprising: (i) arranging a powder containing silicon dioxide particles, aluminum oxide particles, and absorber particles that exhibit higher light absorption capacity than silica or alumina for light of wavelengths contained in the irradiated laser beam, wherein the molar ratio SiO2 / Al2O3 on an oxide basis satisfies 0.1 / 0.9 to 0.7 / 0.3 on an oxide basis; (ii) irradiating the powder with a laser beam to melt and then solidify the powder; and (iii) heating the molded object obtained by performing steps (i) and (ii) multiple times so that the maximum temperature reached is 1595°C or higher and less than 1730°C. [Effects of the Invention]

[0010] According to the present invention, it is possible to manufacture ceramic structures with high mechanical strength at low cost using a direct fabrication method. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view illustrating one embodiment of a method for manufacturing a molded object using a powder bed fusion method. [Figure 2] This is a schematic cross-sectional view illustrating one embodiment of a method for manufacturing a molded object using the cladding method. [Figure 3] (a) is an SEM image of a cross-section of a typical ceramic structure of the present invention, (b) is an elemental mapping image of Al in the cross-section, and (c) is an elemental mapping image of Si in the cross-section. [Figure 4] (a) is an SEM image of a cross-section of the ceramic structure according to Example 19, (b) is an elemental mapping image of Al in the cross-section, and (c) is an elemental mapping image of Si in the cross-section. [Figure 5] (a) is an SEM image of a cross-section of a ceramic structure according to Example 20, (b) is an elemental mapping image of Al in the cross-section, and (c) is an elemental mapping image of Si in the cross-section. [Modes for carrying out the invention]

[0012] Hereinafter, embodiments of the present invention will be described with reference to specific examples and drawings, but the present invention is not limited to the following specific examples and drawings at all.

[0013] Among the direct shaping methods, the powder bed fusion bonding method and the directed energy deposition method (so-called cladding method) are preferably used in the present invention.

[0014] In this specification, silicon dioxide may be described as silica or SiO2, and aluminum oxide may be described as alumina or Al2O3. Silicon dioxide has a plurality of different crystal forms, but when the state such as amorphous, crystalline, and crystal structure is not questioned, it is simply described as silicon dioxide, silica, or SiO2 in terms of chemical formula.

[0015] FIG. 1 is a schematic cross-sectional view schematically showing the basic shaping flow of a manufacturing method by the powder bed fusion bonding method.

[0016] First, the raw material powder 101 is placed on the base 130 installed on the stage 151, and is spread evenly to a predetermined thickness by the roller 152 to form a powder layer 102 (FIGS. 1(a) and (b)). The powder layer 102 is irradiated while being scanned by the scanner unit 181 based on the slice data generated from the shape data of the desired three-dimensional model with the laser beam emitted from the laser light source 180. In the irradiation range 182 of the laser beam, the raw material powder melts and then solidifies, and a solidified portion 100 corresponding to the slice data for one layer is formed (FIG. 1(c)). Subsequently, the stage 151 is lowered, a new powder layer 102 is formed on the solidified portion 100 (FIG. 1(d)), and the laser beam is irradiated based on the slice data. These series of steps are repeated the number of times according to the slice data to obtain the shaped object 110 (FIGS. 1(e) and (f)). Finally, the unfixed raw material powder 103 is removed, and if necessary, the unnecessary portion of the shaped object is removed and the shaped object is separated from the base (FIGS. 1(g) and (h)).

[0017] FIG. 2 is a schematic cross-sectional view schematically showing the basic shaping process flow of the manufacturing method by the cladding method. Raw material powder is ejected from a plurality of powder supply holes 202 in a cladding nozzle 201, and while irradiating the laser beam 203 to the region where these powders converge, an additional solidified portion 100 is formed based on the slice data (FIG. 2(a)). By continuously performing such a process, a shaped object 110 is obtained (FIGS. 2(b) and (c)). Finally, if necessary, the unnecessary portions of the shaped object are removed and the shaped object is separated from the base.

[0018] In the case of direct shaping methods such as the powder bed fusion bonding method and the cladding method, the particles contained in the raw material powder melt while the laser beam is irradiated, and when the irradiation of the laser beam ends, they are rapidly cooled from the surroundings and solidify, forming the solidified portion 100. The silica powder has a high viscosity during melting and does not wet and spread, so when cooled, it solidifies in a granular form. Our study has revealed that the ceramic structure obtained by shaping using only silica powder has a large porosity and insufficient mechanical strength.

[0019] Therefore, in the present invention, a mixed powder obtained by mixing silica powder and alumina powder is used, which contains absorber particles, silicon dioxide particles, and aluminum oxide particles, and satisfies a molar ratio SiO2 / Al2O3 in terms of oxides of 0.1 / 0.9 to 0.7 / 0.3. In terms of oxides, silicon oxides containing SiO are calculated as SiO2 regardless of the composition, and aluminum oxides are calculated as Al2O3 regardless of the composition.

[0020] While silica has a thermal conductivity of approximately 1.5 W / m·K, alumina has a thermal conductivity of approximately 30 W / m·K, which is about 20 times higher than silica. Therefore, when irradiated with a laser beam, the alumina particles with higher thermal conductivity preferentially melt. When alumina is added to silica in a predetermined ratio, the alumina that preferentially melts and becomes a molten state comes into contact with the silica particles or the highly viscous silica molten state, and the solutions mix together to form a molten state with reduced viscosity. By reducing the viscosity of the molten state in this way, it becomes possible to obtain molded objects with lower porosity (higher density) and higher mechanical strength compared to when using raw material powders with a high proportion of silica.

[0021] While the laser beam is irradiated, some of the molten silica reacts with the molten alumina to produce mullite, a compound of silica and alumina. However, in molding methods that melt and solidify the raw material powder by short-duration laser beam irradiation, such as powder bed fusion and cladding methods, the alumina and silica particles may not melt completely. As long as the amount necessary for molding melts, it is acceptable for some to remain unmelted and unreacted in the solidified area.

[0022] Because the area irradiated by the laser beam undergoes melting and solidification in a short time, cracks due to thermal stress often form in the resulting fabricated object. These cracks are distributed throughout the entire fabricated object (structure), i.e., on the surface and inside. Most cracks are about 5 nm to 50 μm wide and cause a decrease in the mechanical strength of the fabricated object.

[0023] The ceramic structure according to the present invention is obtained by heat-treating a fabricated object according to the flow shown in Figures 1 and 2 at a temperature of 1595°C to less than 1730°C, thereby achieving high mechanical strength. The reason why the mechanical strength increases with heat treatment at 1595°C to less than 1730°C is presumed to be as follows.

[0024] Figure 3(a) is an example of a secondary electron image (SEM image) obtained by scanning electron microscopy of a cross-section of a ceramic structure that has undergone heat treatment between 1595°C and 1730°C. Figures 3(b) and (c) are elemental mapping images (EDS; Energy Dispersive X-ray Spectroscopy) of Figure 3(a), showing the distribution of Al and Si, respectively.

[0025] The region that appears brightest in Figure 3(b) and darkest in Figure 3(c) is region 301, which is composed of aluminum oxide. The region that appears second brightest in Figure 3(b) and second darkest in Figure 3(c) is region 302, which is composed of mullite, and its composition is Al6Si2O 13 This is represented as follows. The dark area in Figure 3(b) and the bright area in Figure 3(b) are regions 303, which consist of oxides containing Si and Al, and have a composition close to that of the eutectic composition of silica and mullite. The region with a composition close to that of the eutectic composition of silica and mullite has an elemental ratio of Si / Al of 6 to 12, contains more Si than the region consisting of mullite, and has a molar ratio of SiO2 / Al2O3 on an oxide basis of 12 to 24.

[0026] When heat treatment is performed within the aforementioned temperature range, the region 303, which has a composition close to the eutectic composition of silica and mullite (eutectic point 1595°C) and whose melting point is within this temperature range (a region consisting of oxides containing Si and Al), softens or melts. The molten components wet and spread from region 303 to cracks generated by thermal stress by capillary action, and the cracks are repaired by oxides containing Si and Al. Furthermore, even if a mixture of compositions with other regions is generated in a part of the wall surface facing the crack, it does not impede the present invention. In the central part of Figure 3(c), a state in which a striated region CR is connected to region 303 consisting of oxides containing Si and Al can be observed. Since this striated region corresponds to the location of cracks generated by thermal stress during molding, it is considered that the components constituting region 303 melted and penetrated into the cracks due to the aforementioned heat treatment, wetting and spreading, and repairing the cracks. In this way, the cracks are repaired, and the ceramic structure after heat treatment has reduced cracks and improved mechanical strength. Based on the above, the striated region CR is included in region 303, which is composed of an oxide containing Si and Al.

[0027] Considering the density of cracks generated during fabrication, at least one crack repair area (CR) can be observed within a 2mm x 2mm two-dimensional plane. Since the CR area has an average width of 1 μm or more and a length-to-average width ratio of 10 or more, it can be distinguished from areas not affected by cracks. Here, the average width is the average value obtained by measuring the width of the CR area at five or more locations. If the CR area extends in a curved shape rather than a straight line, the length measured along the curve is used.

[0028] Figure 4(a) is an example of an SEM image of a cross-section of a ceramic structure that underwent heat treatment at temperatures between 1595°C and 1730°C under different conditions than those in Figure 3(a). Figures 4(b) and (c) are elemental mapping images of Figure 4(a), showing the distribution of Al and Si, respectively.

[0029] Similar to Figure 3, the region that appears brightest in Figure 4(b) and darkest in Figure 4(c) is the region 301 made of aluminum oxide. The region that appears second brightest in Figure 4(b) and second darkest in Figure 4(c) is the region 302 made of mullite. The region that appears second darkest in Figure 4(b) and brightest in Figure 4(b) is the region 303 made of an oxide containing Si and Al. And the region that appears darkest in Figure 4(b) and brightest in Figure 4(c) is the region 401 made of silicon dioxide. Thus, the fabricated object after heat treatment may include at least three regions: the region made of an oxide containing Si and Al, the region made of mullite, and the region made of aluminum oxide, as shown in Figure 4, the region made of silicon dioxide 401.

[0030] As mentioned above, the regions 301, composed of aluminum oxide, and 401, composed of silicon dioxide, are presumed to be areas where some silica and alumina particles that did not dissolve during the molding process remained in their original state after heat treatment. Composite ceramic structures with shorter heat treatment times tend to contain more regions composed of silicon dioxide.

[0031] Ceramic structures containing three or four regions exhibit a significant improvement in mechanical strength compared to before heat treatment. This is thought to be due to crack repair as well as the following phenomena: In the case of ceramic structures containing three regions, increasing the heat treatment time causes the silicon dioxide regions to change into regions composed of oxides containing Si and Al or regions composed of mullite. This change process can reduce porosity, thus improving mechanical strength. In the case of ceramic structures containing four regions, the silicon dioxide regions change into a state containing cristobalite as a preliminary step before changing into regions composed of oxides containing Si and Al or regions composed of mullite. Of the silicon dioxide regions contained in the molded object before heat treatment, the parts that were melted by laser beam irradiation and then solidified are mostly amorphous. Since cristobalite has a higher density and superior mechanical strength compared to amorphous structures, it is thought that the mechanical strength of the ceramic structure increases as a result of the silicon dioxide regions changing into a state containing cristobalite.

[0032] To make the silicon dioxide region 401 contain cristobalite, it is advisable to adjust the heat treatment conditions, the particle size and crystalline state of the silicon dioxide particles used in the raw material powder, etc. By adjusting the particle size and crystalline state of the silicon dioxide particles, the size and crystalline state of the silicon dioxide region before heating can be adjusted. The state of the silicon dioxide region before heating also affects the state of the silicon dioxide region 401 after heat treatment. Furthermore, by adjusting the heat treatment conditions, it is possible to control whether or not the ceramic structure contains the silicon dioxide region 401, and if so, the final size and crystalline state of the silicon dioxide region 401.

[0033] To further improve the mechanical strength of the fabricated object, it is advisable to allow a repair liquid containing metal components to be absorbed into the cracks of the object before heat treatment. In normal firing, cracks become regions 303 consisting of oxides containing Si and Al. However, if the cracks are absorbed with the repair liquid before heat treatment, the molten region consisting of oxides containing Si and Al reacts with the solid components of the repair liquid to generate oxides containing metal components contained in the repair liquid, repairing the cracks and forming region CR. When regions consisting of oxides containing metal components contained in the repair liquid are formed in region CR, the composition of the fabricated object becomes more complex, improving the mechanical strength of the fabricated object. In this case, the metal components from the repair liquid provided to region 302 diffuse not only into region CR during heat treatment, but also into the regions 303 consisting of oxides containing Si and Al that are connected to region CR.

[0034] The raw material powders and ceramic structures used in the present invention will be described in more detail below.

[0035] [Raw material powder] The raw material powder contains an absorbent, silicon dioxide particles, and aluminum oxide particles, and the molar ratio SiO2 / Al2O3, calculated on an oxide basis, satisfies 0.1 / 0.9 to 0.7 / 0.3. Here, SiO is calculated on an oxide basis as SiO2.

[0036] The silica and alumina particles constituting the raw material powder preferably have a shape close to spherical in order to obtain sufficient fluidity, as the raw material powder is densely spread on the base 130 to a predetermined thickness. Furthermore, in order to suppress powder aggregation and manufacture highly accurate molded objects, the average particle diameter of the silica powder and alumina powder, respectively, is preferably 5 μm to 200 μm, and more preferably 10 μm to 150 μm. In this invention, the average particle diameter of the powder refers to the median diameter (median value). The average particle diameter of the powder is calculated as the equivalent circle diameter of the projection image from a micrograph of the powder.

[0037] The bonding state of Si and O in the silica particles constituting the powder is not particularly limited; it may be amorphous, crystalline (such as cristobalite or quartz), or a mixture of these.

[0038] An absorber refers to a component (element or compound) that exhibits higher light absorption capacity than silica or alumina for light of wavelengths contained in the laser beam irradiated during fabrication. The absorber's absorption capacity is preferably 10% or more of the wavelength of the laser beam used, more preferably 40% or more, and even more preferably 60% or more. The absorption rate of the absorber can be measured using a general spectrometer. Specifically, a sample filled with the absorber is placed in an integrating sphere, and the absorption rate is calculated from the ratio of the electromagnetic wave spectrum measured by irradiating it with a assumed wavelength (near the laser wavelength used in manufacturing) to the value measured without the sample.

[0039] Such absorbers efficiently absorb the laser beam used during manufacturing, and by becoming hot themselves, they transfer heat to other compositions within a region equivalent to the focal size of the laser beam, causing a temperature increase. This enables effective localized heating, clarifying the interface between the process area (the area irradiated by the laser beam) and the non-process area (the area not irradiated by the laser beam), and improving the accuracy of the fabrication.

[0040] The absorber is preferably one in which at least a portion changes to another composition with relatively lower light absorption capacity upon irradiation with a laser beam. For example, a composition in which the valence state of the metal element changes due to the release of oxygen accompanying the rise in temperature, and it changes to another metal oxide with relatively lower light absorption capacity to the laser beam. If the light absorption capacity decreases to 5 / 6 or less of what it was before irradiation with the laser beam, even if the laser beam is irradiated onto the solidified part, it will not have an effect that would worsen the molding accuracy. In other words, since there is almost no absorber in the solidified part after irradiation with the laser beam, the temperature rise that occurred before irradiation with the laser beam does not occur. Therefore, even if the powder adjacent to the solidified part is irradiated with a laser beam, deformation and alteration of the solidified part are suppressed, so the process margin such as the laser light irradiation conditions is widened, and the impact of fluctuations in irradiation conditions on molding accuracy can be reduced. To obtain higher molding accuracy, it is preferable that the light absorption capacity after irradiation with the laser beam decreases to 1 / 2 or less of what it was before irradiation with the laser beam.

[0041] The absorber may be a composition that, upon irradiation with a laser beam, combines with other compositions contained in the gas or powder in the atmosphere, or undergoes decomposition reactions such as the release of oxygen, thereby changing into a different composition and being incorporated into the fabricated object.

[0042] Suitable compositions for absorbers include SiO, Tb4O7, and Pr6O 11 These include Ti2O3, TiO, ZnO, antimond-doped tin oxide (ATO), indium-doped tin oxide (ITO), MnO, MnO2, Mn2O3, Mn3O4, FeO, Fe2O3, Fe3O4, Cu2O, CuO, Cr2O3, CrO3, NiO, V2O3, VO2, V2O5, V2O4, Co3O4, CoO, transition metal carbides, transition metal nitrides, Si3N4, AlN, borides, and silicides. Preferably, the transition metal carbides are TiC and ZrC. Preferably, the transition metal nitrides are TiN and ZrN. Preferably, the borides are TiB2, ZrB2, and LaB6. Preferably, the silicides are TiSi2, ZrSi2, and MoSi2. The absorber should be at least one selected from the group consisting of these.

[0043] The absorbent should be a composition that has high affinity with the other components of the powder. Since the raw material powder of the present invention contains silica and aluminum, a metal oxide with high affinity is preferred for the absorbent, and SiO2, which has high affinity with silica, is particularly preferred.

[0044] SiO exhibits a brown or black color and has a higher light absorption capacity than aluminum or silica contained in the raw material powder for the wavelength of the laser beam irradiated during fabrication. When SiO absorbs laser light, Si changes from divalent to tetravalent, changing from a metastable state of SiO to a more stable state of SiO2. SiO is preferable not only because its light absorption capacity for laser light decreases, but also because it changes to SiO2, the main component of the raw material powder, after laser beam irradiation, making it preferable in fabrication where the addition of extra components is undesirable. In addition, SiO is available on the market as a negative electrode for lithium-ion secondary batteries, making it preferable because it can be obtained at a lower cost compared to other compounds that can be used as absorbers.

[0045] Absorbers that exhibit good energy absorption from a laser beam are preferably finely and uniformly dispersed in the powder. This ensures that the reaction that occurs in the powder when irradiated with a laser beam is uniform, thereby improving the accuracy of the fabrication. From this viewpoint, the average particle size of the absorber particles (absorber powder) contained in the powder is preferably 1 μm or more and less than 10 μm, and more preferably 1 μm or more and less than 5 μm.

[0046] The amount of absorber added is preferably 0.5 vol% to 10 vol% of the raw material powder. By including 0.5 vol% or more of the absorber in the raw material powder, it is possible to probabilistically ensure that one or more absorbers are present in the laser beam irradiation area under typical laser beam usage conditions, thereby achieving the effect of adding an absorber. Furthermore, by keeping the amount at 10 vol% or less, a rapid temperature rise of the powder during laser beam irradiation can be avoided, suppressing the scattering of molten material into the surrounding area, and thus preventing a decrease in molding accuracy.

[0047] To adjust the physical properties of the ceramic structure, compositions other than silica, alumina, and absorbents may be added to the raw material powder in a proportion of less than 10% by mass.

[0048] In this specification, compositions are sometimes expressed using chemical formulas, such as SiO and Tb4O7. However, the actual elemental composition ratio does not need to strictly match the ratio in the chemical formula, as long as it satisfies the spirit of the present invention. That is, the valence of the metal elements constituting a certain composition may differ slightly from the valence assumed from the chemical formula, and an error in the elemental composition ratio of within ±30% from the stoichiometric ratio normalized by the metal elements is acceptable. For example, if the absorber is SiO, the elemental composition ratio of the absorber is Si:O = 1:1.30 and is included in SiO. When SiO is used as the absorber, a more preferable elemental composition ratio from the viewpoint of obtaining sufficient light absorption capacity is one in which the deviation from the stoichiometric ratio is within ±20%.

[0049] [Method for manufacturing ceramic structures] Next, the method for manufacturing the ceramic structure according to the present invention will be described in detail with reference to Figure 1. The ceramic structure is obtained through the following three steps. (i) A step of placing raw material powder on the molding surface to a predetermined thickness. (ii) A step of irradiating the powder with a laser beam to melt the powder and then solidify it. (iii) A step of heating the molded object obtained by repeating steps (i) and (ii) above at a temperature of 1595°C or higher and less than 1730°C.

[0050] <Process (i)> As shown in Figure 1, raw material powder is placed on the molding surface (base 130) using a recoater (a mechanism for laying powder) such as a roller or blade to achieve a predetermined thickness. The base 130 can be appropriately selected and used from materials such as ceramics, metal, and glass, taking into consideration the intended use of the molded object and manufacturing conditions.

[0051] <Process (ii)> In step (i), a laser beam is scanned and irradiated onto the raw material powder, which is arranged to a predetermined thickness, based on slice data generated from the shape data of the three-dimensional model to be manufactured. While the laser beam is irradiated, absorbers contained in the raw material powder absorb light energy and convert it into heat, causing them to melt and transfer heat to the surroundings, which in turn causes other powders in the laser-irradiated area to melt.

[0052] Once the laser beam has passed and irradiation has ended, the heat from the molten area dissipates into the atmosphere and surroundings, causing it to cool and form a solidified area. At this time, because the temperature change during the melting and solidification process is rapid, most of the silicon dioxide region and the region containing oxides such as Si and Al in the formed object will have an amorphous structure. In addition, the rapid temperature change generates stress in the surface and interior of the object, causing cracks to form.

[0053] The type of laser beam is not particularly limited, but general-purpose lasers such as YAG lasers and fiber lasers in the 1 μm wavelength band, and CO2 lasers in the 10 μm wavelength band are preferred. When using SiO as the absorber, YAG lasers and fiber lasers that emit light in the 1 μm wavelength band, where SiO exhibits high absorption, are particularly preferred.

[0054] <Step (iii)> In step (iii), the molded object, which is created by repeating steps (i) and (ii) a predetermined number of times, is heat-treated to reach a maximum temperature of 1595°C or higher and less than 1730°C. The number of repetitions of steps (i) and (ii) corresponds to the number of slices in the slice data.

[0055] The heating temperature range for step (iii), 1595°C to less than 1730°C, is the temperature range in which the region consisting of oxides containing Si and Al melts. Therefore, step (iii) causes the oxides containing Si and Al to melt and spread into the cracks through capillary action.

[0056] This heat treatment makes it possible to create a molded object that is stable at high temperatures and has excellent mechanical strength. The molded object after the heat treatment in step (iii) is a ceramic structure that includes at least three regions: a region made of oxides containing Si and Al, a region made of mullite, and a region made of aluminum oxide. Specifically, it is a composite ceramic structure consisting of three regions: a region made of oxides containing Si and Al, a mullite region, and a region made of aluminum oxide, or a ceramic structure consisting of four regions, including a region made of silicon dioxide. The region made of oxides containing Si and Al is a region with an elemental ratio of Si / Al of 6 to 12. The region made of silicon dioxide is often included in ceramic structures with a short heat treatment time.

[0057] The proportion of the three or four regions mentioned above in the ceramic structure depends on the mixing ratio of silicon dioxide and aluminum oxide in the raw material powder and the heat treatment conditions. Since region 302, which consists of mullite, has relatively high mechanical strength, it is preferable for it to make up a larger proportion of the ceramic structure. Specifically, it is preferable for it to be 75 volume% or more of the maximum amount of mullite (referred to as the maximum mullite generation amount) calculated from the molar ratio SiO2 / Al2O3 contained in the ceramic structure. More preferably, it is 80 volume% or more. Even more preferably, it is 90 volume% or more. However, the actual amount of mullite generated is determined by the laser irradiation conditions in step (ii) and the heat treatment conditions in step (iii). When comparing structures of the same composition, those with a mullite generation amount of 75 volume% or more of the maximum mullite generation amount can obtain higher mechanical strength.

[0058] Table 1 shows an example of the maximum mullite generation amount calculated from the Si and Al ratio contained in the ceramic structure of the present invention. The maximum amounts of the region consisting of oxides containing Si and Al, and the maximum amounts of the region consisting of aluminum oxide, calculated using a similar method, are also listed. As assumptions for the calculations, the molecular weight of silicon dioxide is 60.08 and the density is 2.3 g / cm³. 3 The molecular weight of aluminum oxide is 101.977, and its density is 3.96 g / cm³.3 For the region consisting of oxides containing Si and Al, assuming an elemental ratio of Si / Al = 10, the molecular weight calculated using the aforementioned values ​​is 62.09 and the density is 2.38 g / cm³. 3 The molecular weight of mullite is 426.05, and its density is 3.0 g / cm³. 3 I used it.

[0059] [Table 1]

[0060] Depending on the combination of heat treatment conditions in process (iii) and the state of silicon dioxide used in the raw material powder, the silicon dioxide region, which is mainly amorphous silica immediately after molding, can be transformed into cristobalite by heat treatment. Cristobalite has a higher density than amorphous silicon dioxide and therefore has superior mechanical strength. For this reason, when a ceramic structure contains a region of silicon dioxide, it is desirable to optimize the conditions so that the region of silicon dioxide contains cristobalite.

[0061] The maximum temperature reached in step (iii) is preferably 1600°C or higher and less than 1720°C, and more preferably 1650°C or higher and less than 1700°C. Furthermore, to create a ceramic structure consisting of three regions: a region made of oxides containing Si and Al, a region made of mullite, and a region made of aluminum oxide, the heat treatment time should be extended. As a guideline for the heat treatment time to create the three regions, for example, if the molar ratio of the molded material is SiO2 / Al2O3 is 0.56 / 0.44, when the temperature is raised to 1690°C, the maximum temperature should be maintained for 40 minutes or more and 120 minutes or less.

[0062] As long as the highest temperature reached near the crack in step (iii) reaches the above temperature range, cracks can be reduced, and therefore the holding time may be short. However, if the heating time within the above temperature range is too long, or if the heat treatment is performed at a temperature higher than the above temperature range, the average grain size in each region tends to become too large, and the mechanical strength of the ceramic structure tends to decrease. Therefore, it is preferable to adjust the heating time within a few hours. The heat treatment time to avoid reducing the mechanical strength of the ceramic structure is preferably 1 minute to 4 hours, more preferably 5 minutes to 120 minutes, and even more preferably 10 minutes to 80 minutes.

[0063] The heating method is not particularly limited. The object may be heated again by irradiating it with an energy beam, or it may be heated in an electric furnace. When heating with an energy beam, it is advisable to determine the relationship between the amount of heat input from the energy beam and the temperature of the object beforehand using a thermocouple or similar device, so that the object is heated to the preferred temperature described above.

[0064] Heat treatment is generally performed by placing the molded object on a setter, but during heating, the surface layer or the area near cracks in the molded object may melt and solidify after the heat treatment, causing it to adhere to the setter. Therefore, it is preferable that the setter used for heat treatment be inert. As materials for inert setters, for example, platinum can be used in an atmospheric environment, and iridium can be used in a low-oxygen atmosphere.

[0065] Cracks in the fabricated object can also be repaired by absorbing a repair liquid (a liquid containing a metal component) into the fabricated object and then heating it before heat treatment. Preferably, the metal component is such that, upon heat treatment, it generates a metal oxide and a phase that can form a eutectic with the phase constituting the fabricated object. In particular, it is preferable that the eutectic temperature of the metal oxide and silicon dioxide is lower than the maximum temperature reached by the fabricated object during the heat treatment in step (iii). This makes it possible to set the maximum temperature reached by the fabricated object during the heat treatment in step (iii) below the melting point of silicon dioxide and higher than the eutectic temperature of the metal oxide and silicon dioxide.

[0066] When such a repair liquid is absorbed into cracks before heat treatment, the area near the cracks into which the metal components have penetrated melts at a lower temperature than the melting point of the rest of the object, and the metal components diffuse into the interior of the object. Then, as the temperature decreases after heating is complete, crystals containing the metal components recrystallize within the object. As a result, the shape of the object is maintained, but only the area near the cracks softens, reducing or eliminating the cracks. At this time, an oxide phase containing metal components precipitates, and the mechanical strength of the object may be further improved as the phase structure of the object becomes more complex.

[0067] Furthermore, even if metal components used for crack repair are pre-added to the raw material powder, the effect of reducing cracks in the molded object cannot be obtained. If the raw material powder contains a large amount of metal components used for crack repair, it will not be possible to locally lower the melting point near the crack, and the entire molded object may melt during the heat treatment, potentially causing deformation of the molded object. Therefore, it is preferable that the metal elements contained in the repair liquid are not present in the raw material powder, or if present, be less than 3.0% by mass. More preferably, it is less than 2.0% by mass.

[0068] Thus, when using a repair fluid to reduce cracks, it is important to allow the repair fluid to be absorbed into the fabricated object, thereby locally increasing the concentration of metallic elements in the cracks, and then applying heat treatment. This method allows for crack reduction with high fabrication precision and improves the mechanical strength of the fabricated object.

[0069] The method for absorbing the repair liquid into the object is not particularly limited, as long as a sufficient amount of metallic components can be interposed throughout the entire object. The object may be immersed in the repair liquid to impregnate it, or the repair liquid may be sprayed onto the object in a mist or applied to the surface with a brush to allow absorption. Multiple of these methods may be combined, or the same method may be repeated multiple times.

[0070] Metal elements can be added to a liquid in the form of metal alkoxides, metal salt compounds, metal ions, or particles containing metal elements.

[0071] The metal component contained in the repair fluid may be one selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, and other rare earth elements.

[0072] A preferred example of a repair fluid is a liquid containing a zirconium component and a solvent, and optionally containing stabilizers and dispersants. Most of the zirconium component in the liquid is converted to zirconium oxide (ZrO2) by heat treatment. The eutectic temperature of SiO2 and ZrO2 is 1683°C, the eutectic temperature of Al2O3 and ZrO2 is 1720°C, and the eutectic temperature of mullite and ZrO2 is 1700°C. These eutectic temperatures are within the range of heating temperatures in step (iii) of 1595°C to less than 1730°C, and are lower than the melting points of silica (1730°C), alumina (2070°C), and mullite (1850°C). Therefore, at temperatures where the melting of regions composed of silicon dioxide, aluminum oxide, and mullite that make up the molded object is suppressed, the repair fluid can selectively melt the cracked regions into which it has penetrated, thereby reducing cracks.

[0073] As the zirconium component, zirconium alkoxide, zirconium salt compounds, zirconium ions, and particles containing zirconium can be used. Suitable stabilizers include organic acids, surfactants, and chelating agents.

[0074] A suitable solution containing zirconium alkoxide is one selected from the group consisting of zirconium tetraethoxide, zirconium tetra-n-propoxide, zirconium tetraisopropoxide, zirconium tetra-n-butoxide, and zirconium tetra-t-butoxide, along with an organic solvent and a stabilizer.

[0075] A suitable solution containing a zirconium salt compound is one comprising an alkoxide chloride or alkoxide nitrate, an organic solvent, and a stabilizer.

[0076] As the solution containing zirconium ions, a solution containing zirconium ions and water can be used, and a stabilizer may be added as needed. The amount of water in the solution is preferably 10% by mass or more relative to the solution excluding the metal ions. In addition to water, an organic solvent may also be included. Zirconium ions can be produced by dissolving a raw material containing zirconium ions, such as a zirconium salt or zirconium alkoxide, in a solvent.

[0077] A preferred liquid containing zirconium particles is one that includes zirconium particles or zirconium oxide particles, a solvent, and a dispersant. The particle size is preferably 300 nm or less, and more preferably 50 nm or less, in order to penetrate cracks. The dispersant is preferably at least one of organic acids, silane coupling agents, and surfactants. The solvent is preferably alcohols, ketones, esters, ethers, ester-modified ethers, hydrocarbons, halogenated hydrocarbons, amides, water, oils, or a mixture of two or more of these.

[0078] If a repair solution containing zirconium is absorbed before step (iii), regions containing zirconium oxide will be formed in the fabricated object after step (iii). The formation of regions containing zirconium oxide in addition to the three or four regions mentioned above increases the number of regions forming the ceramic structure, which may improve the mechanical strength of the ceramic structure.

[0079] <Ceramic Structures> The ceramic structure of the present invention obtained by the method described above has low porosity and contains three regions: a region composed of oxides containing Si and Al, a region composed of mullite, and a region composed of aluminum oxide. The molar ratio of SiO2 / Al2O3 contained in the ceramic structure of the present invention satisfies 0.1 / 0.9 to 0.7 / 0.3 in terms of oxides. The elemental ratio Si / Al in the region composed of oxides containing Si and Al is 6 to 12. As mentioned above, depending on the heat treatment time, a region composed of silicon dioxide may also be included.

[0080] Such ceramic structures can be obtained by directly fabricating them using raw material powders with a molar ratio of SiO2 / Al2O3 satisfying 0.1 / 0.9 to 0.7 / 0.3 in terms of oxides, and then by heat treatment within the aforementioned temperature range.

[0081] If the ceramic structure includes regions made of silicon dioxide, it is preferable that it also contains cristobalite. Cristobalite has superior mechanical strength because it has a higher density than amorphous silica.

[0082] If the cracks are impregnated with a repair solution before heat treatment, the number of regions increases from three to four, and from four to five. If a zirconium-containing solution is used as the repair solution, the ceramic structure will contain four or five regions, including the region containing zirconium oxide. Such a ceramic structure may have greater mechanical strength than when the cracks are repaired without a repair solution, due to the crack propagation suppression effect caused by the presence of multiple different regions.

[0083] The porosity of the ceramic structure of the present invention is preferably 10% or less. A porosity of 10% or less allows for mechanical strength suitable for use as a structural component. As will be described in detail later, porosity refers to open porosity.

[0084] [Method for evaluating physical properties] <Mechanical strength> The mechanical strength of the structure is evaluated by a three-point bending test based on R1601, the JIS standard for room-temperature bending strength testing of fine ceramics. Specifically, the test specimen is placed on two supports spaced L[mm] apart, a load P[N] is applied to the center point between the supports, and the strength can be calculated from the maximum bending stress at which the test specimen breaks. The three-point bending strength is calculated for each of the 10 test specimens, where P[N] is the maximum load at which it breaks, L[mm] is the distance between the external supports, w[mm] is the width of the test specimen, and t[mm] is the thickness of the test specimen. 3 × P × L / (2 × W × T 2 ) (Formula 1) Calculate using these methods and take the average value.

[0085] <Porosity> The porosity of the fabricated object was evaluated using a method based on JIS standard R1634, which is the measurement method for the density and open porosity of sintered fine ceramics. Specifically, for three ceramic structures similar to the samples used for measuring mechanical strength, the dry mass of the fabricated object was denoted as W1, the mass in water as W2, and the mass saturated with water as W3. The porosity was then calculated using {(W3-W1) / (W3-W2)}×100 and averaged.

[0086] <Percentage of regions containing mullite in the crystal structure> The crystal structure of a region constituting a ceramic object is determined by polishing the cross-section of the central part of the object to be measured to create a measurement surface, and then determining it by X-ray diffraction measurement. If the location and crystal structure need to be identified, EBSD can be used, and if smaller regions (phases) are included, a transmission electron microscope (TEM) can be used to similarly analyze the composition and crystal structure.

[0087] The content of each region in the fabricated object can be calculated by extracting an area of ​​approximately 230 x 145 μm from the Al and Si elemental mapping images obtained by SEM-EDS analysis. However, the area size does not have to be limited to this, but calculating over a total area of ​​200 μm x 100 μm or more can suppress variability. The proportion of region 301, which consists of aluminum oxide, can be calculated as a percentage of the total area by binarizing the Si elemental mapping image (Si mapping image) so that only the black areas remain.

[0088] The proportion occupied by the mullite region 302 can be determined by the following procedure. First, the Al elemental mapping image (Al mapping image) is binarized by setting a threshold higher than the brightness of the mullite region 302, and the sum of the aluminum oxide region 301 and the mullite region 302 is calculated. Then, this value is divided by the proportion occupied by the aluminum oxide region 301 in the Si mapping image mentioned earlier.

[0089] The proportion of silicon dioxide region 401 can be calculated by binarizing the image so that only the black regions in the Al mapping image are extracted, and then expressing it as a percentage of the total area.

[0090] The proportion of region 303, which consists of oxides containing Si and Al, can be calculated by first setting a threshold brightness higher than that of region 303 in the Si mapping image and binarizing it. Then, the sum of region 401 (silicon dioxide) and region 301 (silicon dioxide) is calculated, and this sum is divided by the proportion of region 401 (silicon dioxide) in the Al mapping image.

[0091] To maintain high mechanical strength, it is preferable to have a larger proportion of regions 302 composed of mullite, which has relatively high mechanical strength, rather than regions composed of silicon dioxide or regions composed of oxides containing Si and Al. Referring to the maximum mullite generation amount values ​​listed in Table 1, it is possible to determine the size of the mullite region by determining what volume percentage of the maximum mullite generation amount is actually accounted for by the mullite generated within the ceramic structure. Specifically, first, the percentage of the area occupied by regions 302 composed of mullite is calculated in each of the multiple cross-sections of the ceramic structure using the method described above. Next, the obtained values ​​are calculated as a percentage of the maximum mullite generation amount listed in Table 1, calculated from the same molar ratio SiO2 / Al2O3 as the ceramic structure, and the size of the mullite region can be determined by averaging these values. Here, a value equivalent to volume percentage is obtained by averaging the area percentages calculated from multiple cross-sections.

[0092] If the ratio of the region 302 consisting of mullite to the maximum amount of mullite generated is 75 volume% or more, a three-point bending strength of 80 [MPa] or more can be obtained, and an easy-to-handle component can be realized. For example, in the ceramic structure according to the present invention shown in Figure 4 (Example 20), the ratio of the region 302 consisting of mullite to the maximum amount of mullite generated is calculated to be 76.0 volume%. In the ceramic structure according to the present invention shown in Figure 5 (Example 19), the ratio of the region 302 consisting of mullite to the maximum amount of mullite generated is calculated to be 95.0 volume%.

[0093] <Composition analysis> The Si, Al, Zr, Tb, and Pr content in powders, fabricated objects, or ceramic structures is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), GDMS, or ICP-MS. [Examples]

[0094] (Example 1) Amorphous SiO2 powder with an average particle size of approximately 28 μm, Al2O3 powder with an average particle size of approximately 20 μm, and SiO powder with an average particle size of 4 μm were prepared. Each powder was weighed so that SiO2 powder accounted for 44.4% by mass, Al2O3 powder for 53.5% by mass, and SiO powder for 2.1% by mass (see Table 2). The composition of these raw material powders was 60 mol% SiO2 and 40 mol% Al2O3 in terms of SiO2 equivalent. Each weighed powder was mixed in a dry ball mill for 30 minutes to obtain a mixed powder.

[0095] Next, an object was fabricated using the same process as shown in Figure 1. The shape of the fabricated object was a rectangular prism measuring 5 mm × 42 mm × 6 mm. A 3D Systems ProXDMP 100 (product name), equipped with a fiber laser with a maximum power of 50 W (beam diameter 65 μm, oscillation wavelength 1070 mm), was used to form the object.

[0096] First, a 20 μm thick first powder layer made of raw material powder was formed on an alumina base 130 using a roller (Figure 1(a), (b)).

[0097] Next, a 47.5W laser beam was irradiated onto the powder layer while scanning, melting and solidifying the material powder in a rectangular area of ​​5mm x 42mm, forming a solidified area 100 (Figure 1(c)). The drawing speed at this time was 60mm / s, and the drawing pitch was 80μm. The drawing lines were scanned in a direction that intersected each side of the rectangle at a 45-degree angle.

[0098] Next, a 20 μm thick powder layer was newly formed on the solidification section 100 using a roller, and the powder layer was irradiated with a scanning laser beam to melt and solidify the material powder in a rectangular area of ​​5 mm × 42 mm, thereby forming the solidification section 100 (Figures 1(d), (e)). At this time, the laser was scanned in a direction perpendicular to the drawing line of the first layer. This process was repeated until the height of the solidification section reached 6 mm, and 14 objects measuring 42 mm × 5 mm × 6 mm were fabricated.

[0099] The fabricated objects were separated from the alumina base and subjected to heating in an electric furnace. Specifically, they were heated to 1690°C in an air atmosphere over 2.5 hours, held at 1690°C for 20 minutes, then the power was turned off and they were cooled to below 200°C over 5.0 hours to obtain 14 ceramic structures.

[0100] Three of the obtained ceramic structures were used as samples for porosity measurement, and the porosity was evaluated to be 6.8%.

[0101] The composition of the obtained ceramic structure was measured by ICP-AES and found to be 43.9 mass% Si (in terms of SiO2) and 56.1 mass% Al (in terms of Al2O3), with a molar ratio of SiO2 / Al2O3 of 0.57 / 0.43 (see Table 3).

[0102] Next, in order to analyze the regions constituting the ceramic structure and to perform three-point bending strength tests and porosity measurements, the remaining 11 ceramic structures were cut and polished to create 40mm × 4mm × 3mm samples. One of the processed samples was cut along both sides of its long edge with a wire saw, leaving the center of the ceramic structure intact, to obtain a 10mm × 4mm × 3mm test piece. This piece was then roughly polished until the 3mm edge was approximately 1.5mm, and then polished to a mirror finish to obtain a 10mm × 4mm observation surface.

[0103] X-ray diffraction, SEM observation, SEM-EDS, and EBSD were performed on the aforementioned observation surface. For SEM-EDS and EBSD, analysis was performed at 10 different locations with a field size of 100 μm × 100 μm to obtain composition and crystal structure mapping. Comprehensive analysis of the results confirmed that the ceramic structure contained four regions: a region composed of silica (SiO2), a region composed of oxides containing Si and Al, a region composed of mullite, and a region composed of aluminum oxide. In addition, a region composed of oxides containing Si and Al, presumably the area where the cracks had been repaired, was also observed. In Table 3, "○" is indicated in the column for regions where the presence was confirmed, and "×" is indicated in the column for regions where the presence was not confirmed. According to the analysis, the silica in the region composed of silicon dioxide was cristobalite, and the regions composed of mullite and aluminum oxide were both crystalline.

[0104] Bending strength tests were performed on the remaining 10 test specimens for strength testing, and the three-point bending strength was calculated to be 103 MPa.

[0105] Table 3 shows the results of evaluating the Si, Al, Tb, Pr, and Zr content (mass %) in terms of oxides, the molar ratio of SiO2 / Al2O3 in terms of oxides, porosity, and three-point bending strength of the ceramic structure.

[0106] Table 2 shows the raw material powders SiO2, Al2O3, SiO, Tb4O7, and Pr6O 11 The weighing values ​​are shown. Table 3 shows the Si, Al, Tb, Pr, and Zr content, expressed as values ​​converted to SiO2, Al2O3, Tb2O3, Pr2O3, and ZrO2, respectively.

[0107] [Table 2]

[0108] [Table 3]

[0109] (Examples 2-6) Ceramic structures were fabricated in the same manner as in Example 1, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder in the raw material powder was changed. The mass ratios of the raw material powders for each example are shown in Table 2. The porosity, mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, and three-point bending strength of the obtained ceramic structures are shown in Table 3, along with the firing temperature. Furthermore, Table 3 also shows the presence or absence of four regions in the ceramic structures: regions composed of silicon dioxide, regions composed of oxides containing Si and Al, regions composed of mullite, and regions composed of aluminum oxide. According to the analysis of the crystal structure, in all ceramic structures, the regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. In addition, regions composed of oxides containing Si and Al, which are presumed to be areas where cracks have been repaired, were observed in all ceramic structures.

[0110] (Example 7) A ceramic structure was fabricated in the same manner as in Example 1, except that the average particle size of the SiO2 powder was changed to 17 μm. Table 3 shows the mass ratio and molar ratio of SiO2 to Al2O3 of the obtained ceramic structure, the presence or absence of four regions, porosity, and three-point bending strength, along with the firing temperature. Analysis of the crystal structure revealed that the regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. In addition, regions composed of oxides containing Si and Al, which are presumed to be areas where cracks had been repaired, were also observed. The porosity was 5.0%, which was lower than that of Examples 1-6. Furthermore, the ratio of the regions composed of actual mullite to the maximum amount of mullite produced was high at 78.9 volume%, and showed a correlation with the three-point bending strength of 108 [MPa].

[0111] (Example 8) A ceramic structure was fabricated in the same manner as in Example 1, except that the average particle size of the SiO2 powder was set to 10 μm. Table 3 shows the mass ratio of SiO2 to Al2O3, the molar ratio of SiO2 / Al2O3, the presence or absence of four regions, the porosity, and the three-point bending strength of the obtained ceramic structure, along with the firing temperature. Analysis of the crystal structure revealed that the regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. Regions composed of oxides containing Si and Al, which are presumed to be areas where cracks had been repaired, were also observed.

[0112] The porosity was 3.1%, lower than in other examples, and the three-point bending strength was also high at 113 MPa. In this case as well, the ratio of the region consisting of mullite to the maximum amount of mullite generated was 91.8% by volume, showing a correlation with high strength.

[0113] (Example 9) A ceramic structure was fabricated in the same manner as in Example 1, except that the average particle size of the SiO2 powder was cristobalite with a diameter of 38 μm, and the firing temperature in step (iii) was changed to 1680°C. The obtained ceramic structure was evaluated in the same manner as in the other examples, and the results are shown in Table 3. According to the analysis of the crystal structure, the region consisting of silicon dioxide contained cristobalite, and the regions consisting of mullite and aluminum oxide also contained crystalline material. In addition, a region consisting of oxides containing Si and Al, which is presumed to be a part where a crack had been repaired, was also observed.

[0114] (Example 10) The ceramic structure was produced in the same manner as in Example 7, except that the absorber was changed to Tb4O7 powder with an average particle diameter of 4 μm, and SiO2 powder, Al2O3 powder, and Tb4O7 powder were mixed at the mass ratios described in Table 2, and the firing temperature in step (iii) was changed to 1680°C. The mass ratio of SiO2 to Al2O3, the molar ratio SiO2 / Al2O3, the presence or absence of four regions, the porosity, and the three-point bending strength of the obtained ceramic structure are shown in Table 3 together with the firing temperature. According to the analysis of the crystal structure, the region composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline substances. In addition, a region composed of an oxide containing Si and Al, which was presumed to be a part where cracks were repaired, was also observed.

[0115] (Example 11) The ceramic structure was produced in the same manner as in Example 8, except that the absorber was changed to Pr6O powder with an average particle diameter of μm. The mass ratio of Si to Al, the molar ratio SiO2 / Al2O, the presence or absence of four regions, the porosity, and the three-point bending strength of the obtained ceramic structure are shown in Table 3 together with the firing temperature. According to the analysis of the crystal structure, the region composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline substances. In addition, a region composed of an oxide containing Si and Al, which was presumed to be a part where cracks were repaired, was also observed.

[0116] (Example 12) It should be noted that there seems to be an incomplete expression in "吸収体を平均粒子径が4μmのPr6O", where the formula after Pr6O is not fully written. This may affect the accuracy of the overall translation. You can check and correct it if necessary.A ceramic structure was fabricated in the same manner as in Example 1, except that the zirconium-containing solution was absorbed into the cracks of the fabricated structure before the firing process in step (iii). The zirconium-containing solution was prepared as follows: A solution was prepared by dissolving 85% by mass of zirconium butoxide (zirconium(IV) butoxide (hereinafter referred to as Zr(On-Bu)4)) in 1-butanol. The Zr(On-Bu)4 solution was dissolved in 2-propanol (IPA), and ethyl acetoethyl (EAcAc) was added as a stabilizer. The molar ratio of each component was Zr(On-Bu)4:IPA:EAcAc = 1:15:2. The zirconium-containing solution was then prepared by stirring at room temperature for about 3 hours.

[0117] Table 3 shows the mass ratio of SiO2 to Al2O3, the molar ratio of SiO2 / Al2O3, the presence or absence of four regions, the porosity, and the three-point bending strength of the obtained ceramic structures, along with the firing temperature. Analysis of the crystal structure revealed that the regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. Furthermore, regions composed of oxides containing Si and Al, presumably areas where cracks had been repaired, were observed. In addition, regions composed of zirconium oxide were observed to be dispersed within the regions composed of oxides containing Si and Al, or within the regions where cracks had been repaired or connected to those regions.

[0118] Except for the fact that the repair liquid was not absorbed into the fabricated object, a higher three-point bending strength was obtained compared to Example 1, which had the same fabrication conditions. This is presumed to be due to the increased complexity of the regions constituting the ceramic structure as the area composed of zirconium oxide increased.

[0119] (Example 13) A ceramic structure was fabricated in the same manner as in Example 7, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder contained in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. Analysis of the crystal structure revealed that the region composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material.

[0120] Within the ceramic structure, five regions were observed: a region composed of silicon dioxide, a region composed of an oxide containing Si and Al, a region composed of mullite, a region composed of aluminum oxide, and a region composed of zirconium oxide. A region composed of an oxide containing Si and Al, presumably where a crack had been repaired, was also observed. Furthermore, a higher three-point bending strength was obtained compared to Example 2, which had the same manufacturing conditions except that the repair liquid was not absorbed into the fabricated object.

[0121] (Example 14) A ceramic structure was fabricated in the same manner as in Example 7, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder contained in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. The regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material.

[0122] Within the ceramic structure, five regions were observed: a region composed of silicon dioxide, a region composed of an oxide containing Si and Al, a region composed of mullite, a region composed of aluminum oxide, and a region composed of zirconium oxide. In addition, a region composed of an oxide containing Si and Al, which is presumed to be a repaired area of ​​a crack, was also observed. Furthermore, a higher three-point bending strength was obtained compared to Example 3, which had the same manufacturing conditions except that the repair liquid was not absorbed into the fabricated object.

[0123] (Example 15) A ceramic structure was fabricated in the same manner as in Example 7, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder contained in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. Analysis of the crystal structure revealed that the region composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material.

[0124] Within the ceramic structure, five regions were observed: a region composed of silicon dioxide, a region composed of an oxide containing Si and Al, a region composed of mullite, a region composed of aluminum oxide, and a region composed of zirconium oxide. A region composed of an oxide containing Si and Al, presumably a repaired crack, was also observed. Furthermore, a higher three-point bending strength was obtained compared to Example 4, which had the same manufacturing conditions except that the repair liquid was not absorbed into the fabricated object and the silica particle size was different.

[0125] (Example 16) A ceramic structure was fabricated in the same manner as in Example 1, except that the firing temperature in step (iii) was changed to 1650°C. Table 3 shows the mass ratio of SiO2 to Al2O3, the molar ratio of SiO2 / Al2O3, the presence or absence of four regions, the porosity, and the three-point bending strength of the obtained ceramic structure, along with the firing temperature. Analysis of the crystal structure revealed that the regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. In addition, regions composed of oxides containing Si and Al, which are presumed to be areas where cracks had been repaired, were also observed.

[0126] (Examples 17-19) In Examples 17, 18, and 19, ceramic structures were fabricated in the same manner as in Example 7, except that the firing temperature maintenance time in step (iii) was 40 minutes, 80 minutes, and 120 minutes, respectively. Table 3 shows the mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structures, along with the firing temperature.

[0127] In the ceramic structures of Examples 17-19, no region consisting of silicon dioxide was detected. Instead, it was observed that the structures consisted of three regions: a region consisting of an oxide containing Si and Al, a region consisting of mullite, and a region consisting of aluminum oxide.

[0128] Analysis of the crystal structure revealed that both the mullite region and the aluminum oxide region contained crystalline material. Additionally, regions composed of oxides containing Si and Al, presumably representing areas where cracks had been repaired, were observed.

[0129] Specifically, the proportion of the region composed of mullite relative to the amount of mullite that can be generated in Example 17 was high at 83.3 volume%, and showed a correlation with a three-point bending strength of 111 [MPa]. Figures 5(a) to 5(c) show the SEM image of the ceramic structure obtained in Example 19 and the elemental mapping images of Al and Si obtained by EDS. Calculated using Figures 5(b) and 5(c), the proportion of the region composed of mullite relative to the amount of mullite that can be generated in Example 19 was high at 95.0 volume%, and it showed a high three-point bending strength of 107 [MPa].

[0130] In Examples 7, 17, and 19, the longer the firing time, the higher the proportion of the region consisting of mullite tended to be, exceeding 75% by volume, and the three-point bending strength also remained at a high level. Furthermore, in Examples 17-19, it was confirmed that increasing the heat treatment time reduced the porosity compared to Example 7.

[0131] Thus, it was confirmed that the region composed of mullite, which has relatively high mechanical strength, occupies a larger area than the region composed of silicon dioxide, which has relatively low mechanical strength, and the region composed of oxides containing Si and Al. This condition is particularly desirable for maintaining high mechanical strength.

[0132] (Example 20) In Example 20, a ceramic structure was fabricated in the same manner as in Example 7, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder contained in the raw material powder was changed. The mass ratios of the raw material powders for each example are shown in Table 2. The porosity, SiO2 / Al2O3 mass ratio, molar ratio of SiO2 / Al2O3, and three-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. Furthermore, Table 3 also shows the presence or absence of four regions in the ceramic structure: a region composed of silicon dioxide, a region composed of oxides containing Si and Al, a region composed of mullite, and a region composed of aluminum oxide. SEM images of the obtained ceramic structure are shown in Figure 4(a), and elemental mapping images of Al and Si by EDS are shown in Figures 4(b) and (c).

[0133] Crystal structure analysis and SEM-EDS analysis revealed that the ceramic structure contained cristobalite in region 401, which is composed of silicon dioxide, and also contained crystalline material in region 302, which is composed of mullite, and region 301, which is composed of aluminum oxide. Region 303, composed of an oxide containing Si and Al, was also present, which is presumed to be the CR portion where the cracks were repaired.

[0134] Furthermore, the proportion of the region composed of mullite relative to the amount of mullite that can be generated was high at 76.0 volume%, and it showed a correlation with the three-point bending strength of 93 MPa.

[0135] (Comparative Example 1) A ceramic structure was fabricated in the same manner as in Example 1, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. Analysis of the crystal structure revealed that the region composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. In addition, a region composed of oxides containing Si and Al, which is presumed to be a part where a crack had been repaired, was observed.

[0136] Four regions were observed within the ceramic structure: a region composed of silicon dioxide, a region composed of oxides containing Si and Al, a region composed of mullite, and a region composed of aluminum oxide. However, the three-point bending strength was low at 25 MPa, making it unsuitable for use in structural components.

[0137] Compared to the examples, the porosity was high at 16.3%, suggesting that the ceramic structure had high porosity, meaning low density, which resulted in lower three-point bending strength. The reason for the high porosity is presumed to be that the amount of aluminum oxide contained in the raw material powder was small, so the molten aluminum oxide during laser beam irradiation in process (ii) did not spread throughout the entire fabricated object, and the silica did not melt sufficiently.

[0138] (Comparative Example 2) A ceramic structure was fabricated in the same manner as in Example 1, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. The regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. In addition, regions composed of oxides containing Si and Al, which are presumed to be areas where cracks had been repaired, were also observed.

[0139] Four regions were observed within the ceramic structure: a region composed of silicon dioxide, a region composed of oxides containing Si and Al, a region composed of mullite, and a region composed of aluminum oxide. However, the three-point bending strength was low at 28 MPa, making it unsuitable for application as a structural component.

[0140] Comparative Example 2 also had a high porosity of 13.4%, suggesting that, similar to Comparative Example 1, the molar ratio of the raw material powder (SiO2 / Al2O3) was 0.75 / 0.25, meaning that the amount of aluminum oxide contained in the raw material powder was small, and therefore the silica could not be sufficiently melted.

[0141] (Comparative Example 3) A ceramic structure was fabricated in the same manner as in Example 1, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the firing temperature. Analysis of the crystal structure revealed that the regions composed of silicon dioxide contained cristobalite, and the regions composed of mullite and aluminum oxide also contained crystalline material. In addition, regions composed of oxides containing Si and Al, which are presumed to be areas where cracks had been repaired, were observed. However, the number of such regions was extremely small compared to those in Examples 1 to 16.

[0142] The three-point bending strength of Comparative Example 3 was also low at 41 MPa, a value unsuitable for application in structural components. This is thought to be because the amount of silicon dioxide contained in the raw material powder was small, so the composition of the region consisting of molten Si and Al oxides during the heat treatment in step (iii) did not reach the cracks, resulting in insufficient crack repair and increased porosity.

[0143] (Comparative Example 4) A ceramic structure was fabricated in the same manner as in Example 1, except that the mass ratio of SiO2 powder, Al2O3 powder, and SiO powder in the raw material powder was changed to the values ​​shown in Table 2. The mass ratio of SiO2 to Al2O3, molar ratio of SiO2 / Al2O3, presence or absence of 4 regions, porosity, and 3-point bending strength of the obtained ceramic structure are shown in Table 3, along with the heating temperature. Furthermore, no regions consisting of oxides containing Si and Al, which are presumed to be areas where cracks were repaired, were observed.

[0144] The three-point bending strength of Comparative Example 4 was also low at 41 MPa, a value unsuitable for application in structural components. This is thought to be because the molar ratio of SiO2 / Al2O3 in the raw material powder was 0.03 / 0.97, meaning that the raw material powder contained almost no silicon dioxide. As a result, the phenomenon of crack repair in the molded object did not occur sufficiently during the heat treatment in process (iii), leading to a high porosity. [Industrial applicability]

[0145] According to the present invention, it is possible to provide ceramic structures at low cost while retaining the characteristics of the direct fabrication method, which allows for the creation of complex shapes, and improving the density and mechanical strength of the fabricated objects. [Explanation of Symbols]

[0146] 100 Solidified section 101 powder 102 Powder layer 103 Unsolidified powder 110 Sculptures 130 base 151 stages 152 Rollers 180 Laser beam sources 181 Scanner section 190 Liquid spray nozzles 201 Cladding Nozzle 202 Powder supply hole 203 Laser beam 301 Region made of aluminum oxide 302 Regions consisting of mullite 303 Regions consisting of oxides containing Si and Al 401 Region made of silicon dioxide CR crack repaired area

Claims

1. A ceramic structure, a first region made of an oxide containing Si and Al; a second region made of an oxide containing Si and Al; a third region made of an oxide containing Al, the second region has a higher proportion of Si than the first region, the third region has a lower proportion of Si than the first region, at least one of the first region and the third region is crystalline; The molar ratio of oxides in the part is SiO ２ / Al ２ O ３ A ceramic structure characterized in that the ratio satisfies 0.1 / 0.9 to 0.7 / 0.

3.

2. 2. The ceramic structure according to claim 1, wherein a cross section of the ceramic structure includes a region having an average width of 1 μm or more and a ratio of length to average width of 10 or more, the region being made of an oxide containing Si and Al.

3. The proportion of the first region in the portion is a molar ratio SiO ２ / Al ２ O ３ 2. The ceramic structure according to claim 1, wherein the content of mullite is 75% by volume or more of the maximum amount of mullite calculated from the above formula (1).

4. The molar ratio of the second region in terms of oxide is SiO ２ / Al ２ O ３ 4. The ceramic structure according to claim 1, wherein the tensile strength of the ceramic structure is 12 to 24.

5. 2. The ceramic structure according to claim 1, wherein the first region is crystalline.

6. 2. The ceramic structure according to claim 1, wherein the third region is crystalline.

7. A ceramic structure as described in claim 1, characterized in that the portion has a fourth region consisting of an oxide containing Si, and the fourth region has a lower proportion of Al than the second region.

8. The ceramic structure of claim 1, wherein the portion has a fifth region made of an oxide containing Zr.

9. The ceramic structure of claim 1, wherein the first region is made of a compound of silica and alumina.

10. The ceramic structure of claim 1, wherein the first region is made of mullite.

11. A ceramic structure as described in claim 1, characterized in that the second region is surrounded by the first region and the third region.

12. The ceramic structure of claim 7, wherein the fourth region is crystalline.

13. The ceramic structure of claim 7, wherein the fourth region contains cristobalite.

14. A method for manufacturing a ceramic structure, comprising: (i) a laser beam absorber that contains silicon dioxide particles, aluminum oxide particles, and an absorber that exhibits a higher light absorption ability than silica or alumina for light of a wavelength contained in the irradiated laser beam, and has a molar ratio of SiO ２ / Al ２ O ３ disposing a powder satisfying a ratio of 0.1 / 0.9 to 0.7 / 0.3; (ii) irradiating the powder with a laser beam to melt and then solidify the powder; (iii) a step of heat-treating the shaped object obtained by carrying out steps (i) and (ii) multiple times so that the maximum temperature reached is 1595°C or higher but lower than 1730°C; and a shaped product after the heat treatment, the shaped product having a crystalline region made of an oxide containing at least Al;

15. 15. The method for manufacturing a ceramic structure according to claim 14, wherein in the step (iii), the holding time at the maximum temperature is set to be 1 minute or more and 4 hours or less.

16. 15. The method for manufacturing a ceramic structure according to claim 14, wherein the absorber has an absorptivity of 10% or more for light of a wavelength included in the laser beam.

17. The method for manufacturing a ceramic structure according to claim 14, wherein the absorber is SiO.

18. The average particle size of the silicon dioxide particles is 5 μm or more and 200 μm or less, and the average particle size of the absorber is 1 μm or more and less than 10 μm, 15. The method for manufacturing a ceramic structure according to claim 14, wherein the amount of the absorber added is 0.5 vol % or more and 10 vol % or less of the powder.

19. 15. The method for producing a ceramic structure according to claim 14, wherein the shaped article heat-treated in step (iii) has a region made of a component containing a metal element selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, and rare earth elements.

20. 20. The method for producing a ceramic structure according to claim 19, wherein a maximum temperature reached by the shaped object in the heat treatment in step (iii) is lower than the melting point of silicon dioxide and higher than the eutectic temperature of the oxide of the metal element and silicon dioxide.

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