JP2023072682A - Ceramic structure and method for manufacturing the same - Google Patents

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 The present invention relates to a ceramics structure obtained by a direct molding method and a manufacturing method thereof.

As a means of manufacturing prototypes and small-lot products, additive manufacturing technology is becoming widespread, in which materials are added based on shape data of a three-dimensional model to be manufactured to obtain a desired structure. In the manufacture of metal articles, a direct molding method is widely employed in which a metal powder is irradiated with a laser beam to solidify the powder for molding. According to this method, various articles can be obtained by effectively melting and solidifying the metal powder.

In recent years, efforts have been made to establish additive manufacturing techniques using ceramic powders. Unlike metals, common ceramics such as aluminum oxide and zirconium oxide have low absorptivity to the wavelength of the laser beam. However, even if a large amount of energy is input, the laser beam spreads and melts unevenly, making it difficult to obtain the necessary molding precision.

Patent Literature 1 discloses a technique of adding an absorber having high absorptivity to the wavelength of a laser beam to be irradiated to a raw material powder to suppress beam diffusion and achieve high molding accuracy. Patent Literature 2 discloses a technique for manufacturing a ceramic structure by a direct molding method using powder containing silicon dioxide as a main component, to which an absorber having high absorbability for the wavelength of the irradiated laser beam is added. ing.

JP 2019-19051 A JP 2021-66177 A

Patent Document 1 describes an Al ₂ O ₃ —ZrO ₂ -based powder and an Al ₂ O ₃ —SiO ₂ -based powder to which Tb ₄ O ₇ is added as an absorber. Further, Patent Document 2 describes an Al ₂ O ₃ —SiO ₂ -based powder to which SiO is added as an absorber. Since SiO ₂ is inexpensive and readily available, Al ₂ O ₃ —SiO ₂ -based powders are particularly preferable in that ceramic structures can be stably produced at low cost.

However, as in Patent Literature 1 and Patent Literature 2, molded objects obtained from raw material powders with a _SiO2 ratio of more than 70 mol% using a direct molding method become porous, and the structures of mechanical parts, medical parts, etc. Mechanical strength tends to be insufficient for use as parts.

A 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 having a higher proportion of Si than the mullite, and a region made of aluminum oxide. and the molar ratio SiO ₂ /Al ₂ O ₃ in terms of oxide satisfies 0.1/0.9 to 0.7/0.3.

Further, the method for producing a ceramic structure according to the present invention includes (i) silicon dioxide particles, aluminum oxide particles, and a higher light absorption than silica or alumina with respect to light of a wavelength contained in an irradiated laser beam. and a powder having a molar ratio of SiO ₂ /Al ₂ O ₃ in terms of oxide satisfying 0.1/0.9 to 0.7/0.3 in terms of oxide. (ii) irradiating the powder with a laser beam to melt and then solidify the powder; and (iii) a shaped object obtained by performing the steps (i) and (ii) multiple times. and a step of heat-treating so that the highest temperature reaches 1595°C or more and less than 1730°C.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to manufacture a ceramic structure with high mechanical strength at low cost using a direct molding method.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic cross-sectional view schematically showing an embodiment of a method for manufacturing a modeled object by a powder bed fusion method; 1 is a schematic cross-sectional view schematically showing an embodiment of a method for manufacturing a modeled object by a cladding method; FIG. (a) is an SEM image of a cross section of a typical ceramic structure of the present invention, (b) is an Al elemental mapping image of the cross section, and (c) is an Si elemental mapping image of the cross section. (a) is an SEM image of a certain cross section of the ceramic structure according to Example 19, (b) is an Al elemental mapping image in the cross section, and (c) is an Si elemental mapping image in the cross section. (a) is an SEM image of a certain cross section of the ceramic structure according to Example 20, (b) is an Al elemental mapping image in the cross section, and (c) is an Si elemental mapping image in the cross section.

Hereinafter, embodiments of the present invention will be described with specific examples and with reference to the drawings, but the present invention is not limited to the following specific examples or drawings.

Among the direct molding methods, the powder bed fusion bonding method and the directed energy lamination method (so-called cladding method) are preferably used in the present invention.

In this specification, silicon dioxide may be described as silica or SiO ₂ , and aluminum oxide may be described as alumina or Al ₂ O ₃ . Silicon dioxide has a plurality of different crystal forms, but when it does not matter whether it is amorphous, crystalline, or has a crystal structure, it is simply referred to as silicon dioxide, silica, or the chemical formula SiO ₂ .

FIG. 1 is a schematic cross-sectional view schematically showing the flow of basic shaping in a manufacturing method based on the powder bed fusion bonding method.

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

FIG. 2 is a schematic cross-sectional view schematically showing the flow of basic shaping in a manufacturing method using the cladding method. Raw material powder is ejected from a plurality of powder supply holes 202 in a cladding nozzle 201, and a laser beam 203 is irradiated to a region where the powder is focused to additionally form a solidified portion 100 based on slice data. (Fig. 2(a)). By continuously performing such steps, a modeled object 110 is obtained (FIGS. 2(b) and 2(c)). Finally, if necessary, the unnecessary parts of the modeled object are removed and the modeled object and the base are separated.

In the case of direct molding methods such as the powder bed fusion method and the cladding method, the particles contained in the raw material powder are melted while the laser beam is being irradiated, and when the laser beam irradiation ends, they are rapidly cooled and solidified from the surroundings. , a solidified portion 100 is formed. Silica powder has a high viscosity when melted and does not spread when wet, so when cooled, it solidifies into particles. Our investigation revealed that a ceramic structure obtained by molding using only silica powder has a large porosity and does not have sufficient mechanical strength.

Therefore, in the present invention, the absorbent contains absorber particles, silicon dioxide particles, and aluminum oxide particles, and the molar ratio SiO ₂ /Al ₂ O ₃ in terms of oxide is 0.1/0.9 to 0.7. A mixed powder of silica powder and alumina powder is used so as to satisfy /0.3. Silicon oxide containing SiO is calculated as SiO ₂ regardless of composition, and aluminum oxide is calculated as Al ₂ O ₃ regardless of composition.

While the thermal conductivity of silica is about 1.5 W/m K, the thermal conductivity of alumina is about 30 W/m K, which is about 20 times higher than that of silica. Alumina particles with a higher . are preferentially melted. When alumina is added to silica at a predetermined ratio, the alumina that is preferentially melted and becomes a melt comes into contact with silica particles or a highly viscous silica melt, and the solutions are mixed together to reduce the viscosity. It will be in a melted state. By reducing the viscosity of the melt in this way, it is possible to obtain a model with a smaller porosity (higher density) and higher mechanical strength than when using a raw material powder with a high proportion of silica. becomes.

During the laser beam irradiation, some of the fused silica reacts with the fused alumina to form mullite, a compound of silica and alumina. However, in the case of molding methods such as the powder bed fusion method and the cladding method, in which the raw material powder is melted and solidified by short-time laser beam irradiation, the particles of alumina and silica may not be completely melted. As long as the amount necessary for modeling is melted, a part of it may remain in the solidified portion without melting or reacting.

Since the portion irradiated with the laser beam melts and solidifies within a short period of time, cracks are often formed in the resulting molded product due to thermal stress. Cracks are distributed throughout the model (structure), ie, on the surface and inside. Most of the cracks have a width of about 5 nm to 50 μm, which causes a decrease in the mechanical strength of the model.

A ceramic structure according to the present invention is obtained by heat-treating a shaped article manufactured according to the flow of FIGS. can be done. The reason why the mechanical strength is increased by heat treatment at 1595° C. or more and less than 1730° C. is presumed as follows.

FIG. 3(a) is an example of a secondary electron image (SEM image) obtained by observing a cross section of a ceramic structure that has been heat-treated at 1595° C. or more and less than 1730° C. with a scanning electron microscope. 3(b) and (c) are elemental mapping images (EDS; Energy Dispersive X-ray Spectroscopy, energy dispersive X-ray spectroscopy) of FIG. .

The brightest region in FIG. 3(b) and the darkest region in FIG. 3(c) is the region 301 made of aluminum oxide. The second brightest region in FIG _. 3B and the _second darkest region in _FIG . A region that appears dark in FIG. 3B and bright in FIG. 3B is a region 303 made of an oxide containing Si and Al, and has a composition close to the eutectic composition of silica and mullite. The region having a composition close to the eutectic composition of silica and mullite has an element number ratio Si/Al of 6 to 12, is a region containing more Si than the region made of mullite, and has a molar ratio _SiO / in terms of oxide. Al ₂ O ₃ is the region of 12-24.

When heat treatment is performed in the above temperature range, a region having a composition close to the eutectic composition of silica and mullite (eutectic point 1595 ° C.) whose melting point is within this temperature range (region made of oxide containing Si and Al ) 303 softens or melts. The melted components wet and spread from the region 303 to cracks generated by thermal stress due to capillary action, and the cracks are repaired by oxides containing Si and Al. In addition, even if a composition mixed with other regions is generated in a portion of the wall surface facing the crack, the present invention is not hindered. In the central part of FIG. 3(c), a state in which a streaky region CR is connected to a region 303 made of an oxide containing Si and Al is observed. Since this streaky region corresponds to the position of the crack generated by the thermal stress during molding, the above-described heat treatment melts the components that make up the region 303, penetrates the crack, and wets and spreads the crack. is considered to have been repaired. In this way, cracks are repaired, and the ceramic structure after heat treatment has fewer cracks and improved mechanical strength. From the above, the streaky region CR is included in the region 303 made of oxide containing Si and Al.

Considering the density of cracks that occur during molding, at least one region CR, which is a crack repair location, can be observed by observing a two-dimensional plane of 2 mm×2 mm. Since the region CR has an average width of 1 μm or more and a ratio of length to average width of 10 or more, it can be distinguished from regions not caused by cracks. Here, the average width is an average value obtained by measuring the width of the region CR at five or more points. If the region CR extends in a curved line instead of a straight line, the length measured along the curved line is used.

FIG. 4(a) is an example of a SEM image of a cross section of a ceramic structure subjected to heat treatment at 1595° C. or more and less than 1730° C. under conditions different from those in FIG. 3(a). FIGS. 4(b) and 4(c) are elemental mapping images of FIG. 4(a), showing distributions of Al and Si, respectively.

As in FIG. 3, the brightest region in FIG. 4(b) and the darkest region in FIG. 4(c) is the region 301 made of aluminum oxide. The second brightest region in FIG. 4B and the second darkest region in FIG. 4C is the region 302 made of mullite. The second darkest region in FIG. 4B and the brightest region in FIG. 4B is the region 303 made of oxide containing Si and Al. The darkest region in FIG. 4(b) and the brightest region in FIG. 4(c) is the region 401 made of silicon dioxide. In this way, the shaped object after the heat treatment has at least three regions: a region made of oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide, as shown in FIG. A region 401 made of silicon may be included.

As described above, the region 301 made of aluminum oxide and the region 401 made of silicon dioxide are presumed to be part of the silica particles and alumina particles that remained undissolved during molding and remained as they were after heat treatment. . Composite ceramic structures with shorter heat treatment times tend to include regions made of silicon dioxide.

A ceramic structure containing three or four regions has significantly improved mechanical strength compared to before heat treatment. The reason for this is believed to be due to the following phenomenon in addition to repairing cracks. In the case of a ceramic structure containing three regions, by increasing the heat treatment time, a region made of silicon dioxide changes to a region made of an oxide containing Si and Al or a region made of mullite. It is thought that the mechanical strength is improved because the porosity can be reduced in the process. In the case of a ceramic structure containing four regions, the region made of silicon dioxide changes to a state containing cristobalite as a state prior to changing to a region made of an oxide containing Si and Al or a region made of mullite. do. Of the silicon dioxide regions contained in the shaped article before heat treatment, most of the portions formed by being melted by laser beam irradiation and then solidified have an amorphous structure. Since cristobalite has a higher density and superior mechanical strength than an amorphous structure, it is considered that the mechanical strength of the ceramic structure increases as a result of changing the state of the silicon dioxide region to include cristobalite.

In order to make the region 401 made of silicon dioxide contain cristobalite, it is preferable to adjust the conditions of the heat treatment, the particle size and crystal state of the silicon dioxide particles used in the raw material powder, and the like. By adjusting the particle diameter and crystal state of the silicon dioxide particles, the size and crystal 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. Then, by adjusting the conditions of the heat treatment, it is possible to control whether or not the region 401 made of silicon dioxide is included in the ceramic structure, and if it is included, the final size and crystalline state of the region 401 made of silicon dioxide. be able to.

In order to further improve the mechanical strength of the modeled article, it is preferable to allow cracks in the modeled article to absorb a repair liquid containing a metal component before the heat treatment. In the case of normal firing, the crack becomes the region 303 made of oxide containing Si and Al. However, if the crack is allowed to absorb the repair liquid before the heat treatment, the melt in the region composed of the oxide containing Si and Al reacts with the solid component of the repair liquid to remove the metal component contained in the repair liquid. A containing oxide forms and repairs the crack to form region CR. When the region CR is formed of an oxide containing the metal component contained in the repair liquid, the composition of the modeled article becomes more complicated, and the mechanical strength of the modeled article is improved. In this case, the metal component resulting from the repair liquid provided to the region 302 diffuses not only to the region CR but also to the region 303 made of oxide containing Si and Al connected to the region CR during the heat treatment.

Hereinafter, the raw material powder and the method for producing the ceramic structure used in the present invention will be described in more detail.

[Raw material powder]
The raw material powder contains an absorber, silicon dioxide particles, and aluminum oxide particles, and has a molar ratio of SiO ₂ /Al ₂ O ₃ in terms of oxide of 0.1/0.9 to 0.7/0.3. Fulfill. Here, SiO is converted to oxide as _SiO2 .

The silica particles and alumina particles that make up the raw material powder have a nearly spherical shape in order to spread the raw material powder densely and evenly on the base 130 with a predetermined thickness, in order to obtain sufficient fluidity. is preferred. In addition, in order to suppress aggregation of the powder and manufacture a highly accurate model, the average particle size of each of the silica powder and the alumina powder is preferably 5 μm or more and 200 μm or less, more preferably 10 μm or more and 150 μm or less. The average particle size of the powder in the present invention refers to the median size (median value). The average particle size of the powder is calculated as the circle equivalent diameter of the projected image from the micrograph of the powder.

The bonding state of Si and O in silica particles constituting the powder is not particularly limited, and may be amorphous, crystalline such as cristobalite or quartz, or a mixture thereof.

The absorber refers to a component (element or compound) that exhibits a higher light absorption ability than silica or alumina with respect to light of a wavelength contained in a laser beam irradiated during modeling. The absorber preferably has an absorptance of 10% or more, more preferably 40% or more, and even more preferably 60% or more, with respect to the wavelength of the laser beam used. Absorptivity of an absorber can be measured using a common spectrometer. Specifically, the sample dish filled with an absorber was placed in an integrating sphere and irradiated with an assumed wavelength (near the laser wavelength used in manufacturing) to measure the electromagnetic wave spectrum. Absorption rate is calculated from the ratio with the value.

Such an absorber efficiently absorbs the laser beam used during manufacturing and heats itself up, thereby transferring heat to other components present within an area corresponding to the focal size of the laser beam, raising the temperature. bring. As a result, effective local heating can be realized, and the interface between the process area (the area irradiated with the laser beam) and the non-process area (the area not irradiated with the laser beam) can be clarified, and the molding accuracy can be improved. improves.

It is preferable that the absorber is at least partly changed into another composition having relatively low light absorption ability upon irradiation with a laser beam. For example, there is a composition in which the valence of a metal element changes due to detachment of oxygen accompanying temperature rise, and changes to another metal oxide having a relatively low light absorption ability with respect to a laser beam. If the light absorption capacity is reduced to 5/6 times or less of that before the laser beam irradiation, even if the solidified portion is irradiated with the laser beam, it does not affect the molding accuracy to the extent that it deteriorates. That is, since there is almost no absorber in the solidified portion after laser beam irradiation, the temperature does not rise like before laser beam irradiation. Therefore, even if the powder adjacent to the solidified portion is irradiated with the laser beam, the deformation and deterioration of the solidified portion are suppressed. The impact can be reduced. In order to obtain higher molding accuracy, it is preferable that the light absorption ability after laser beam irradiation is reduced to 1/2 or less of that before laser beam irradiation.

When the absorber is irradiated with a laser beam, it combines with gas in the atmosphere or other composition contained in the powder, or undergoes a decomposition reaction such as desorption of oxygen. Compositions that are incorporated therein may be used.

Suitable compositions for the absorber are SiO, _Tb4O7 , _Pr6O11 , _Ti2O3 , TiO, _ZnO , antimony-doped tin _{oxide (} ATO), indium-doped tin oxide (ITO), MnO, _MnO2. , _Mn2O3 , _Mn3O4 , FeO, _{Fe2O3 , Fe3O4 , Cu2O , CuO} , _Cr2O3 , _CrO3 , _{NiO , V2O3} , _VO2 , _V2O5 , V ₂ O ₄ , Co ₃ O ₄ , CoO, transition metal carbides, transition metal nitrides, Si ₃ N ₄ , AlN, borides, silicides. TiC and ZrC are preferred as the transition metal carbide. Preferred transition metal nitrides are TiN and ZrN. Preferred borides are TiB ₂ , ZrB ₂ and LaB ₆ . Preferred silicides are TiSi ₂ , ZrSi ₂ and MoSi ₂ . It is preferable to use at least one type of absorber selected from the group consisting of these.

For the absorber, it is preferable to select and use a composition that has a high affinity with other compositions that constitute the powder. Since the raw material powder of the present invention contains silica and aluminum, a metal oxide with high affinity is preferable for the absorber, and SiO, which has high affinity with silica, is particularly preferable.

SiO exhibits a brown or black color, and has a higher light absorption ability than aluminum and silica contained in the raw material powder with respect to the wavelength of the laser beam irradiated during modeling. When SiO absorbs the laser light, it changes from divalent to tetravalent and from the metastable state of SiO to the more stable state of _SiO2 . SiO is preferable in that the light absorption ability for the laser beam is lowered, but since it changes to SiO ₂ , which is the main component of the raw material powder, after laser beam irradiation, it is preferable in molding where it is not desired to add extra components. In addition, SiO is available on the market as a negative electrode for lithium-ion secondary batteries, and is therefore preferable in that it can be obtained at a lower cost than other compounds that can be used as absorbers.

An absorber that exhibits good energy absorption with respect to a laser beam is preferably finely and uniformly dispersed in the powder. As a result, the reaction that occurs in the powder when irradiated with the laser beam becomes uniform, and the molding accuracy is further improved. From such a viewpoint, the average particle diameter of the absorber particles (absorbent powder) contained in the powder is preferably 1 μm or more and less than 10 μm, more preferably 1 μm or more and less than 5 μm.

The amount of the absorber to be added is preferably 0.5 vol % or more and 10 vol % or less of the raw material powder. By containing 0.5 vol% or more of the absorber in the raw material powder, one or more absorbers can stochastically exist in the laser beam irradiation part under general laser beam usage conditions. The effect of adding can be obtained. Further, by setting the content to 10 vol % or less, it is possible to avoid a rapid temperature rise of the powder during laser beam irradiation, and to suppress scattering of the melted material to the surroundings, that is, a decrease in modeling accuracy.

In order to adjust the physical properties of the ceramic structure, a composition other than silica, alumina, and absorber may be added to the raw material powder at a rate of less than 10% by mass.

In this specification, the composition may be expressed using chemical formulas such as SiO and Tb ₄ O ₇ , but as long as the gist of the present invention is satisfied, the actual composition ratio of the elements is the ratio of the chemical formula. Exact matching is not required. That is, the valences of the metal elements constituting a certain composition may be slightly different from the valences assumed from the chemical formula, and the error in the ratio of constituent elements within ±30% from the stoichiometric ratio normalized by the metal element is allowed. For example, when the absorber is SiO, the constituent element ratio of the absorber is Si:O=1:1.30, which is included in SiO. When SiO is used as an absorber, a more preferable element composition ratio is within ±20% from the stoichiometric ratio from the viewpoint of obtaining a sufficient light absorption capacity.

[Ceramic structure manufacturing method]
Next, a method for manufacturing a ceramic structure according to the present invention will be described in detail with reference to FIG. A ceramic structure is obtained through the following three steps.
(i) a step of arranging the raw material powder with a predetermined thickness on the molding surface; (ii) a step of irradiating the powder with a laser beam to melt and then solidify the powder; A step of heating the shaped object obtained by repeating (ii) at 1595° C. or more and less than 1730° C.

<Step (i)>
As shown in FIG. 1, raw material powder is placed on the molding surface (base 130) by a recoater (mechanism for laying powder) such as a roller or a blade so as to have a predetermined thickness. The base 130 can be appropriately selected and used from materials such as ceramics, metal, glass, etc. in consideration of the use of the modeled object, manufacturing conditions, and the like.

<Step (ii)>
In step (i), the raw material powder arranged with a predetermined thickness is irradiated with a laser beam while scanning based on slice data generated from the shape data of the three-dimensional model to be manufactured. While the laser beam is being irradiated, the absorber contained in the raw material powder absorbs the light energy and converts it into heat, melting itself and transferring the heat to the surroundings, thereby melting other powders in the laser irradiation area. is triggered.

When the laser beam passes through and the irradiation ends, the heat of the melted portion is cooled by escaping into the atmosphere and surroundings, and a solidified portion is formed. At this time, since temperature changes are abrupt in the process of melting and solidification, most of the region made of silicon dioxide and the region made of oxide containing Si and Al of the shaped object to be formed has an amorphous structure. In addition, stress is generated in the surface layer and inside of the model due to a sudden temperature change, and cracks are formed.

Although the type of laser beam is not particularly limited, general-purpose lasers such as a YAG laser or fiber laser with a 1 μm wavelength band and a CO 2 laser with a 10 μm wavelength band are suitable. When SiO is used as the absorber, a YAG laser or a fiber laser that emits light in the 1 μm wavelength band that SiO exhibits high absorption is particularly preferable.

<Step (iii)>
In step (iii), the modeled object produced by repeating steps (i) and (ii) a predetermined number of times is heat-treated so that the highest temperature reaches 1595°C or higher and lower than 1730°C. The number of repetitions of steps (i) and (ii) corresponds to the number of slices of slice data.

The range of the heating temperature in step (iii), 1595° C. or more and less than 1730° C., is a temperature range in which the region made of the oxide containing Si and Al melts. It melts and spreads over cracks by capillary action.

By such heat treatment, it is possible to realize a modeled object that is stable at high temperatures and has excellent mechanical strength. The shaped article after the heat treatment in step (iii) is a ceramic structure including three regions: a region made of an oxide containing at least Si and Al, a region made of mullite, and a region made of aluminum oxide. Specifically, a composite ceramic structure consisting of three regions, a region consisting of an oxide containing Si and Al, a mullite region, and a region consisting of aluminum oxide, or a composite ceramic structure comprising four regions including a region consisting of silicon dioxide becomes a ceramic structure. A region made of an oxide containing Si and Al has an element number ratio Si/Al of 6-12. Regions made of silicon dioxide are often included in ceramic structures that require a short heat treatment time.

Which of the three or four regions mentioned above is included more in the ceramic structure depends on the compounding ratio of silicon dioxide and aluminum oxide contained in the raw material powder and the heat treatment conditions. Since the region 302 made of mullite has relatively high mechanical strength, it is preferable that the region 302 occupy a large proportion of the ceramic structure. Specifically, it is preferably 75% by volume or more of the maximum amount of mullite calculated from the molar ratio SiO ₂ /Al ₂ O ₃ contained in the ceramic structure (described as the maximum amount of mullite produced). More preferably 80% by volume or more. More preferably, it is 90% by volume or more. However, the actual amount of mullite produced is determined by the laser irradiation conditions in step (ii) and the heat treatment conditions in step (iii). When structures with the same composition are compared, higher mechanical strength can be obtained when the amount of mullite produced is 75% by volume or more of the maximum amount of mullite produced.

Table 1 shows an example of the maximum amount of mullite produced calculated from the ratio of Si and Al contained in the ceramic structure of the present invention. The maximum amount of the oxide region containing Si and Al and the maximum amount of the aluminum oxide region calculated by the same method are also described. As assumptions for the calculation, the molecular weight of silicon dioxide is 60.08 and the density is 2.3 g/cm ³ , and the molecular weight of aluminum oxide is 101.977 and the density is 3.96 g/cm ³ . For the region composed of oxides containing Si and Al, the element number ratio Si/Al is assumed to be 10, and the molecular weight calculated using the above values is 62.09, and the density is 2.38 g/cm ³ . Mullite having a molecular weight of 426.05 and a density of 3.0 g/cm ³ was used.

Depending on the combination of the heat treatment conditions in step (iii) and the state of silicon dioxide used in the raw material powder, the silicon dioxide region, which was mainly amorphous silica immediately after shaping, can be changed to cristobalite by heat treatment. Since cristobalite has a higher density than amorphous silicon dioxide, it has excellent mechanical strength. Therefore, when the ceramic structure includes a silicon dioxide region, the conditions should be optimized so that the silicon dioxide region contains cristobalite.

The highest temperature reached in step (iii) is preferably 1600°C or higher and lower than 1720°C, more preferably 1650°C or higher and lower than 1700°C. Further, in order to obtain a ceramic structure composed of three regions, that is, a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide, it is preferable to lengthen the heat treatment time. For example, when the molar ratio SiO ₂ /Al ₂ O ₃ of the modeled product is 0.56/0.44, when the temperature is raised to 1690 ° C., the maximum temperature is maintained. The time should be 40 minutes or more and 120 minutes or less.

As long as the maximum temperature near the crack in step (iii) reaches the above temperature range, cracks can be reduced, so the holding time may be short. However, if the heating time in 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 of each region becomes too large, and the mechanical strength of the ceramic structure decreases. Tend. Therefore, it is preferable to adjust the heating time within several hours. The heat treatment time for not lowering the mechanical strength of the ceramic structure is preferably 1 minute or longer and 4 hours or shorter, more preferably 5 minutes or longer and 120 minutes or shorter, and even more preferably 10 minutes or longer and 80 minutes or shorter.

A heating method is not particularly limited. The modeled object may be heated by irradiating the energy beam again, or may be heated by placing it in an electric furnace. When heating with an energy beam, the relationship between the amount of heat input by the energy beam and the temperature of the modeled object should be grasped in advance using a thermocouple or the like so that the modeled object is heated to the preferred temperature described above.

Heat treatment is generally performed by placing a modeled object on a setter, but the surface layer of the modeled object and the vicinity of cracks may melt during heating, and solidify after heat treatment and adhere to the setter. . Therefore, the setter used for heat treatment is preferably inert. As a material constituting the inert setter, for example, platinum can be applied under an air atmosphere, and iridium can be applied under a low-oxygen atmosphere.

Cracks in the modeled article can also be repaired by allowing the modeled article to absorb a repair liquid (liquid containing a metal component) and heating the article before heat treatment. It is preferable that the metal component generates a metal oxide and a phase that can form a eutectic with the phase that constitutes the shaped article by heat treatment. In particular, it is preferable that the eutectic temperature between the metal oxide and silicon dioxide is lower than the maximum temperature reached by the shaped article in the heat treatment of step (iii). This allows the maximum temperature reached by the shaped article in the heat treatment of step (iii) to be below the melting point of silicon dioxide and above the eutectic temperature of the metal oxide and silicon dioxide.

If such a repair liquid is allowed to absorb into the cracks before heat treatment, the vicinity of the cracks into which the metal components have penetrated will melt at a temperature lower than the melting point of other parts of the model, and the metal components will melt into the model. diffuse inside. Then, as the heating is finished and the temperature is lowered, the crystals are recrystallized in the composition containing the metal component in the modeled object. As a result, while the shape of the modeled object is maintained, only the area near the crack is softened, and the crack can be reduced or eliminated. At this time, an oxide phase containing a metal component is precipitated, and the phase structure of the shaped article becomes more complicated, which may further improve the mechanical strength of the shaped article.

Even if a metal component used for repairing cracks is added to the raw material powder in advance, the effect of reducing cracks in the model cannot be obtained. If the raw material powder contains a large amount of metal components used for repairing cracks, the melting point near the cracks cannot be locally lowered, and the entire model melts due to heat treatment, resulting in deformation of the model. there is a risk of Therefore, it is preferable that the metal element contained in the repair liquid is not contained in the raw material powder, or if it is contained, it is less than 3.0% by mass. More preferably, it is less than 2.0% by mass.

As described above, in order to reduce cracks using a repair liquid, it is important to apply the heat treatment in a state in which the repair liquid is absorbed into the model and the concentration of the metal element in the crack is locally increased. By such a method, it is possible to reduce cracks with high modeling accuracy and improve the mechanical strength of the model.

As long as a sufficient amount of metal component can be interposed over the entire shaped article, there is no particular limitation on the method of causing the shaped article to absorb the repair fluid. The modeled object may be impregnated by immersing it in the repair fluid, or the repair fluid may be atomized and sprayed onto the modeled object, or applied to the surface with a brush or the like to be absorbed. Moreover, these methods may be combined multiple times, and the same method may be repeated multiple times.

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

Any one selected from the group consisting of lithium, sodium, potassium, magnesium, calcium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, and other rare earth elements shall be used as the metal component contained in the repair liquid. can be done.

A preferable example of the repair liquid includes a liquid containing a zirconium component and a solvent, and optionally a stabilizer and a dispersant. Most of the zirconium component contained in the liquid becomes zirconium oxide (ZrO ₂ ) 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 the heating temperature of 1595 ° C. or more and less than 1730 ° C. in the step (iii), and the melting point of silica (1730 ° C.), the melting point of alumina (2070 ° C.), the melting point of mullite (1850 ° C. ). Therefore, at a temperature that suppresses the melting of the silicon dioxide region, aluminum oxide region, and mullite region that constitute the model, the crack region into which the repair liquid has penetrated is selectively melted to reduce cracks. be able to.

Zirconium alkoxides, zirconium salt compounds, zirconium ions, particles containing zirconium, and the like can be used as the zirconium component. Suitable stabilizers include organic acids, surfactants and chelating agents.

As the liquid containing zirconium alkoxide, any one selected from the group consisting of zirconium tetraethoxide, zirconium tetra-n-propoxide, zirconium tetraisopropoxide, zirconium tetra-n-butoxide, and zirconium tetra-t-butoxide; A liquid comprising an organic solvent and a stabilizing agent is preferred.

As the liquid containing the zirconium salt compound, a liquid containing an alkoxide chloride or alkoxide nitrate, an organic solvent, and a stabilizer is suitable.

As the liquid containing zirconium ions, a solution containing zirconium ions and water can be used, and a stabilizer may be added as necessary. The amount of water contained in the liquid is preferably 10% by mass or more relative to the liquid excluding metal ions. An organic solvent may be included in addition to water. Zirconium ions can be generated by dissolving a raw material containing zirconium ions such as zirconium salts and zirconium alkoxides in a solvent.

The liquid containing particles containing zirconium is preferably a liquid containing zirconium particles or zirconium oxide particles, a solvent, and a dispersant. The particle size is preferably 300 nm or less, more preferably 50 nm or less, in order to penetrate cracks. The dispersant preferably contains at least one of organic acids, silane coupling agents, and surfactants. As the solvent, alcohols, ketones, esters, ethers, ester-modified ethers, hydrocarbons, halogenated hydrocarbons, amides, water, oils, or mixed solvents of two or more thereof are preferred.

If a repair fluid containing a zirconium component is absorbed before step (iii), regions containing zirconium oxide are formed in the model after step (iii). By forming a region containing zirconium oxide in addition to the above three regions or four regions, the number of regions forming the ceramic structure increases, and the mechanical strength of the ceramic structure may be improved.

<Ceramic structure>
The ceramic structure of the present invention obtained by the above-described method has a low porosity and contains three regions: a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide. The molar ratio SiO ₂ /Al ₂ O ₃ contained in the ceramic structure of the present invention satisfies 0.1/0.9 to 0.7/0.3 in terms of oxide. The element number ratio Si/Al in the region made of the oxide containing Si and Al is 6-12. As mentioned above, depending on the heat treatment time, regions further comprising silicon dioxide may be included.

Such a ceramic structure was molded by a direct molding method using a raw material powder satisfying a molar ratio SiO ₂ /Al ₂ O ₃ of 0.1/0.9 to 0.7/0.3 in terms of oxide. After that, it can be obtained by heat-treating in the above temperature range.

If the ceramic structure contains regions made of silicon dioxide, it preferably contains cristobalite. Since cristobalite has a higher density than amorphous silica, it has excellent mechanical strength.

If the crack is impregnated with a repair fluid before heat treatment, the three areas increase to four areas, and the four areas increase to five areas. When a liquid containing zirconium is used as the repair liquid, the ceramic structure will include four or five regions including the region containing zirconium oxide. In such a ceramic structure, due to the effect of suppressing crack propagation due to the presence of a plurality of different regions, the mechanical strength may be increased compared to the case where cracks are repaired without using a repair liquid.

The porosity of the ceramic structure of the present invention is preferably 10% or less. If the porosity is 10% or less, it is possible to achieve a mechanical strength that allows it to be used as a structural component. As will be described in detail later, the porosity refers to the open porosity.

[Evaluation method of physical property value]
<Mechanical strength>
The mechanical strength of the structure is evaluated by a three-point bending test based on R1601, which is a JIS standard for room temperature bending strength testing of fine ceramics. Specifically, the test piece is placed on two fulcrums separated by L [mm], a load of P [N] is applied to one point in the center between the fulcrums, and the maximum bending stress when the test piece breaks can be calculated from For each of the 10 test pieces, the three-point bending strength is P [N] for the maximum load when broken, L [mm] for the distance between the external fulcrums, w [mm] for the width of the test piece, and w [mm] for the width of the test piece. When the thickness is t [mm],
3×P×L/(2×w×t ² ) (Formula 1)
and average them.

<Porosity>
The porosity of the shaped article was evaluated by a method based on R1634, which is a JIS standard for measuring the density and open porosity of sintered bodies of fine ceramics. Specifically, for three ceramic structures similar to the sample used to measure the mechanical strength, when the dry mass of the shaped product is W1, the underwater mass is W2, and the saturated water mass is W3, {(W3-W1 )/(W3−W2)}×100 and average them.

<Proportion of region containing crystal structure/mullite>
The crystal structure of the region that constitutes the ceramic model is specified by X-ray diffraction measurement on a cross section of the central portion of the object to be measured which is polished to form a measurement surface. EBSD can be used to identify the position and crystal structure, and transmission electron microscopy (TEM) can be used to similarly analyze the composition and crystal structure when smaller regions (phases) are involved.

The content rate of each region included in the model can be calculated by cutting out a region of about 230×145 μm from the elemental mapping image of Al and Si in SEM-EDS analysis. However, although it is not necessary to be limited to this area size, variation can be suppressed by calculating for an area of 200 μm×100 μm or more in total. The proportion of the region 301 made of aluminum oxide can be calculated as a proportion of the total area by binarizing the image so that only the black regions of the Si elemental mapping image (Si mapping image) remain.

The proportion occupied by the region 302 made of mullite can be obtained by the following procedure. First, a threshold value is set to a brightness higher than the mullite region 302 in the Al element mapping image (Al mapping image), binarization is performed, and the total value of the aluminum oxide region 301 and the mullite region 302 is calculated. . Then, it can be calculated by subtracting the proportion of the area 301 made of aluminum oxide in the previous Si mapping image from this value.

The ratio occupied by the silicon dioxide region 401 can be calculated as a ratio of the total area by binarizing the image so that only black regions in the Al mapping image can be extracted.

The ratio of the region 303 made of oxide containing Si and Al is first binarized by setting a brightness higher than that of the region 303 made of oxide containing Si and Al in the Si mapping image as a threshold value. Then, the total value of the silicon dioxide region 401 and the region 301 made of oxide containing Si and Al is calculated, and the ratio of the silicon dioxide region 401 in the previous Al mapping image is divided from this total value. can do.

In order to maintain a state of high mechanical strength, it is preferable that there are many regions 302 made of mullite, which has relatively high mechanical strength, rather than regions made of silicon dioxide or regions made of oxides containing Si and Al. With reference to the values of the maximum mullite production amount listed in Table 1, the size of the mullite region is determined by what volume percent of the maximum mullite production amount the mullite actually produced in the ceramic structure occupies. It is possible to Specifically, first, in each of a plurality of cross sections of the ceramic structure, the ratio of the area occupied by the region 302 made of mullite is calculated by the method described above. Next, the obtained value was calculated as a ratio to the maximum mullite production amount shown in Table 1, which was calculated from the same molar ratio SiO ₂ /Al ₂ O ₃ as the ceramic structure, and the average value was used to calculate the mullite It is possible to judge the size of the area consisting of. Here, a value corresponding to volume % is obtained by averaging area % calculated from a plurality of cross sections.

If the ratio of the region 302 made of mullite to the maximum amount of mullite produced is 75% by volume or more, a three-point bending strength of 80 [MPa] or more can be obtained, and a member that is easy to handle can be realized. For example, the ratio of the region 302 made of mullite to the maximum amount of mullite produced in the ceramic structure according to the present invention in FIG. 4 (Example 20) is calculated to be 76.0% by volume. The ratio of the region 302 made of mullite to the maximum amount of mullite produced in the ceramic structure according to the present invention in FIG. 5 (Example 19) is calculated to be 95.0% by volume.

<Composition analysis>
The Si, Al, Zr, Tb, and Pr contents contained in the powder, shaped article, or ceramic structure are measured by inductively coupled plasma emission spectroscopy (ICP-AES), GDMS, or ICP-MS.

(Example 1)
Amorphous SiO ₂ powder with an average particle size of about 28 μm, Al ₂ O ₃ powder with an average particle size of about 20 μm, and SiO powder with an average particle size of 4 μm were prepared. Each _powder was weighed so that _SiO2 powder was 44.4 wt%, _Al2O3 powder was 53.5 wt%, and SiO powder was 2.1 wt% (see Table 2). The components of this raw material powder are 60 mol % and Al ₂ O ₃ are 40 mol % in terms of SiO ₂ . Each weighed powder was mixed in a dry ball mill for 30 minutes to obtain a mixed powder.

Next, a modeled object was produced in the same process as in FIG. The shape of the fabricated object was a rectangular parallelepiped of 5 mm×42 mm×6 mm. ProXDMP 100 (trade name) manufactured by 3D SYSTEMS equipped with a fiber laser with a maximum power of 50 W (beam diameter of 65 μm, oscillation wavelength of 1070 mm) was used to form the modeled object.

First, on a base 130 made of alumina, a roller was used to form a 20 μm-thick first powder layer made of raw material powder (FIGS. 1(a) and 1(b)).

Next, the powder layer was irradiated with a scanning laser beam of 47.5 W to melt and solidify the material powder in a rectangular region of 5 mm×42 mm to form a solidified portion 100 (FIG. 1(c)). The drawing speed at this time was 60 mm/s, and the drawing pitch was 80 μm. A line of drawing was scanned in a direction that intersects each side of the rectangle at 45 degrees.

Next, a new powder layer with a thickness of 20 μm is formed on the solidified part 100 with a roller, and the powder layer is irradiated with a scanning laser beam to melt and solidify the material powder in a rectangular area of 5 mm×42 mm. to form a solidified portion 100 (FIGS. 1(d) and 1(e)). At this time, the laser was scanned in a direction orthogonal to the drawing lines of the first layer. Such a process was repeated until the height of the solidified portion reached 6 mm, and 14 molded objects of 42 mm×5 mm×6 mm were produced.

The formed object was separated from the base made of alumina, placed in an electric furnace, and subjected to heat treatment. Specifically, the temperature was raised to 1690° C. in 2.5 hours in an air atmosphere, and the temperature was maintained at 1690° C. for 20 minutes. A ceramic structure was obtained.

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

When the composition of the obtained ceramic-based structure was measured by ICP-AES, Si was 43.9% by mass in terms of SiO ₂ , Al was 56.1% by mass in terms of Al ₂ O ₃ , and the molar ratio was SiO _{2 .} / _Al2O3 was 0.57/0.43 (see Table ₃ ).

Next, the remaining 11 ceramic structures were cut and polished to obtain samples of 40 mm × 4 mm × 3 mm in order to analyze the regions constituting the ceramic structures and to perform three-point bending strength tests and porosity measurements. processed into One of the processed samples was cut with a wire saw on both sides of the long side leaving the center of the ceramic structure to obtain a test piece of 10 mm×4 mm×3 mm. Then, after roughly polishing until the side of 3 mm became about 1.5 mm, by polishing to a mirror surface, an observation surface of 10 mm×4 mm was obtained.

The observation surface was subjected to X-ray diffraction, SEM observation, SEM-EDS, and EBSD. SEM-EDS and EBSD were analyzed at 10 different locations with a field size of 100 μm×100 μm to obtain mapping of composition and crystal structure. After comprehensively analyzing the results, the ceramic structure contained four regions: a region made of silica (SiO ₂ ), a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide. It was confirmed that A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion. In Table 3, "O" is entered in the column of the area where the existence is confirmed, and "X" is entered in the column of the area where the existence is not confirmed. According to the analysis, the silica in the silicon dioxide region was cristobalite, and both the mullite region and the aluminum oxide region were crystalline.

A flexural strength test was performed on the remaining 10 specimens for the strength test, and the 3-point flexural strength was calculated to be 103 [MPa].

Results of evaluating the contents of Si, Al, Tb, Pr, and Zr (mass % in terms of oxides), the molar ratio SiO ₂ /Al ₂ O ₃ in terms of oxides, the porosity, and the three-point bending strength of the ceramic structure are shown in Table 3.

Table 2 shows _the weight values of the raw material powders _{SiO2 , Al2O3 ,} SiO, _Tb4O7 and _Pr6O11 . Table 3 shows the contents of Si, Al, Tb, Pr, and Zr as numerical values converted into SiO ₂ , Al ₂ O ₃ , Tb ₂ O ₃ , Pr ₂ O ₃ , and ZrO ₂ , respectively.

(Examples 2-6)
A ceramic structure was produced in the same manner as in Example 1, except that the mass ratio of SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed. Table 2 shows the mass ratio of the raw material powder in each example. Table 3 shows the porosity, the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , and the three-point bending strength of the obtained ceramic structure together with the firing temperature. Table 3 also shows whether or not there are four regions in the ceramic structure: a region made of silicon dioxide, a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide. According to the analysis of the crystal structure, in all ceramic structures, the silicon dioxide region contained cristobalite, and the mullite region and the aluminum oxide region contained crystalline. In addition, in all the ceramic structures, a region composed of an oxide containing Si and Al, which is presumed to be a repaired portion of cracks, was also observed.

(Example 7)
A ceramic structure was produced 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 of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of four regions, the porosity, and the three-point bending strength of the resulting ceramic structure together with the firing temperature. . Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion. The porosity was 5.0%, which was smaller than those of Examples 1-6. Moreover, the ratio of the region composed of actual mullite to the maximum amount of mullite produced was as high as 78.9% by volume, and showed a correlation with the three-point bending strength of 108 [MPa].

(Example 8)
A ceramic structure was produced in the same manner as in Example 1, except that the SiO ₂ powder had an average particle size of 10 μm. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

The porosity was 3.1%, which was lower than those of other examples, and the three-point bending strength was also high, 113 [MPa]. Also in this case, the ratio of the region composed of mullite to the maximum amount of mullite produced was 91.8% by volume, showing a correlation with high strength.

(Example 9)
A ceramic structure was produced in the same manner as in Example 1, except that the average particle size of the SiO ₂ powder was cristobalite of 38 μm and the firing temperature in step (iii) was changed to 1680°C. Table 3 shows the results of evaluating the obtained ceramic structures in the same manner as in other examples. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

(Example 10)
The absorber was changed to Tb ₄ O ₇ powder having an average particle size of 4 μm, and SiO ₂ powder, Al ₂ O ₃ powder, and Tb ₄ O ₇ powder were mixed at the mass ratio shown in Table 2; ) was changed to 1680° C., a ceramic structure was produced in the same manner as in Example 7. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

(Example 11)
A ceramic structure was produced in the same manner as in Example 8, except that the absorber was changed to Pr ₆ O ₁₁ powder having an average particle size of 4 μm. Table 3 shows the mass ratio of Si and Al, the molar ratio of SiO ₂ /Al ₂ O, the presence or absence of four regions, the porosity and the three-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

(Example 12)
A ceramic structure was produced in the same manner as in Example 1, except that the zirconium component-containing liquid was absorbed into the cracks of the shaped article before the firing process of step (iii). A zirconium component-containing liquid 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 acetoacetate (EAcAc) was added as a stabilizer. The molar ratio of each component was Zr(On-Bu)4:IPA:EAcAc=1:15:2. After that, the mixture was stirred at room temperature for about 3 hours to prepare a zirconium component-containing liquid.

Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion. Furthermore, it was observed that regions made of zirconium oxide were dispersed in the portion where the crack was repaired or in the region made of oxide containing Si and Al connected to the portion.

A higher three-point bending strength was obtained than in Example 1, in which the manufacturing conditions were the same, except that the repair liquid was not absorbed into the modeled article. It is presumed that this is due to the fact that the regions forming the ceramic structure are complicated by the increase in the regions made of zirconium oxide.

(Example 13)
A ceramic structure was produced in the same manner as in Example 7, except that the mass ratio of SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Analysis of the crystal structure showed that the silicon dioxide regions contained cristobalite, the mullite regions and the aluminum oxide regions also contained crystalline.

Five regions were observed in the ceramic structure: a silicon dioxide region, an oxide region containing Si and Al, a mullite region, an aluminum oxide region, and a zirconium oxide region. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion. A higher 3-point bending strength was obtained than in Example 2, which was manufactured under the same manufacturing conditions, except that the repair liquid was not absorbed into the modeled object.

(Example 14)
A ceramic structure was produced in the same manner as in Example 7, except that the mass ratio of SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. The regions of silicon dioxide contained cristobalite, and the regions of mullite and aluminum oxide also contained crystalline.

Five regions were observed in the ceramic structure: a silicon dioxide region, an oxide region containing Si and Al, a mullite region, an aluminum oxide region, and a zirconium oxide region. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion. A higher three-point bending strength was obtained than in Example 3, in which the manufacturing conditions were the same, except that the repair liquid was not absorbed into the modeled object.

(Example 15)
A ceramic structure was produced in the same manner as in Example 7, except that the mass ratio of SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline.

Five regions were observed in the ceramic structure: a silicon dioxide region, an oxide region containing Si and Al, a mullite region, an aluminum oxide region, and a zirconium oxide region. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion. A higher 3-point bending strength was obtained than in Example 4, in which the manufacturing conditions were the same, except that the repair liquid was not absorbed into the shaped object and that the particle size of silica was different.

(Example 16)
A ceramic structure was produced 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 SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

(Examples 17-19)
In Examples 17, 18, and 19, ceramic structures were produced in the same manner as in Example 7, except that the firing temperature maintenance time in step (iii) was set to 40 minutes, 80 minutes, and 120 minutes, respectively. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature.

In the ceramic structures of Examples 17 to 19, no region composed of silicon dioxide was detected, and from three regions: a region composed of an oxide containing Si and Al, a region composed of mullite, and a region composed of aluminum oxide. It was observed that

According to the analysis of the crystal structure, both the mullite region and the aluminum oxide region contained crystallinity. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

Specifically, the ratio of the mullite region to the mullite-producible amount of Example 17 was as high as 83.3% by volume, and showed a correlation with the three-point bending strength of 111 [MPa]. 5A to 5C are SEM images of the ceramic structure obtained in Example 19 and elemental mapping images of Al and Si by EDS, respectively. The ratio of the region composed of mullite to the mullite-producible amount of Example 19, which is calculated using FIGS. showed strength.

As in Examples 7, 17, and 19, the longer the firing time, the higher the ratio of the mullite region to 75% by volume or more, and the three-point bending strength was maintained at a high level. Moreover, in Examples 17 to 19, it was confirmed that the porosity was reduced compared to Example 7 by lengthening the heat treatment time.

Thus, the region occupied by the region made of mullite, which has relatively high mechanical strength, is larger than the region occupied by the region made of silicon dioxide, which has relatively low mechanical strength, and the region made of oxide containing Si and Al. was confirmed to be wide. Such a state is particularly preferable for maintaining high mechanical strength.

(Example 20)
In Example 20, a ceramic structure was produced in the same manner as in Example 7, except that the mass ratio of SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed. Table 2 shows the mass ratio of the raw material powder in each example. Table 3 shows the porosity, SiO ₂ /Al ₂ O ₃ mass ratio, SiO ₂ /Al ₂ O ₃ molar ratio, and three-point bending strength of the obtained ceramic structure together with the firing temperature. Table 3 also shows whether or not there are four regions in the ceramic structure of the structure: a region made of silicon dioxide, a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide. . An SEM image of the obtained ceramic structure is shown in FIG. 4(a), and elemental mapping images of Al and Si by EDS are shown in FIGS. 4(b) and 4(c).

According to the crystal structure analysis and SEM-EDS analysis, in this ceramic structure, the region 401 made of silicon dioxide contains cristobalite, and the region 302 made of mullite and the region 301 made of aluminum oxide also contain crystals. board. A region 303 made of an oxide containing Si and Al was also present, which is presumed to be a crack-repaired portion CR.

Furthermore, the ratio of the mullite region to the mullite-producible amount was as high as 76.0% by volume, showing a correlation with the three-point bending strength of 93 [MPa].

(Comparative example 1)
A ceramic structure was produced in the same manner as in Example 1, except that the mass ratio of the SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. In addition, a region composed of an oxide containing Si and Al was observed, which is presumed to be a crack-repaired portion.

Four regions were observed in the ceramic structure: a region made of silicon dioxide, a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide. MPa], which is not suitable for application to structural parts.

Since the porosity is as high as 16.3% compared to the examples, the three-point bending strength is low due to the high porosity of the ceramic structure, that is, the low compactness. it is conceivable that. The reason for the large porosity is that the amount of aluminum oxide contained in the raw material powder was small, so that the aluminum oxide melted during the laser beam irradiation in step (ii) did not spread throughout the model, and the silica was not sufficiently melted. guessed.

(Comparative example 2)
A ceramic structure was produced in the same manner as in Example 1, except that the mass ratio of the SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. The regions of silicon dioxide contained cristobalite, and the regions of mullite and aluminum oxide also contained crystalline. A region composed of an oxide containing Si and Al was also observed, which is presumed to be a crack-repaired portion.

Four regions were observed in the ceramic structure: a region made of silicon dioxide, a region made of an oxide containing Si and Al, a region made of mullite, and a region made of aluminum oxide. MPa], which is not suitable for application to structural parts.

Comparative Example 2 _also has _a high porosity of 13.4% _. It is presumed that the silica could not be sufficiently melted because the amount of aluminum oxide contained was small.

(Comparative Example 3)
A ceramic structure was produced in the same manner as in Example 1, except that the mass ratio of the SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of 4 regions, the porosity and the 3-point bending strength of the obtained ceramic structure together with the firing temperature. Crystal structure analysis showed that the silicon dioxide region contained cristobalite, and the mullite and aluminum oxide regions also contained crystalline. In addition, a region composed of an oxide containing Si and Al was observed, which is presumed to be a crack-repaired portion. However, the number was extremely less than that of Examples 1-16.

The three-point bending strength of Comparative Example 3 was also as low as 41 [MPa], a value unsuitable for application to structural parts. This is because the amount of silicon dioxide contained in the raw material powder was small, so that the composition in the region composed of oxides containing Si and Al melted during the heat treatment in step (iii) did not reach the cracks, and the cracks were sufficiently repaired. It is considered that this is because the porosity was increased.

(Comparative Example 4)
A ceramic structure was produced in the same manner as in Example 1, except that the mass ratio of the SiO ₂ powder, Al ₂ O ₃ powder, and SiO powder contained in the raw material powder was changed to the value shown in Table 2. Table 3 shows the mass ratio of SiO ₂ and Al ₂ O ₃ , the molar ratio SiO ₂ /Al ₂ O ₃ , the presence or absence of four regions, the porosity, and the three-point bending strength of the resulting ceramic structure together with the heating temperature. Moreover, no region composed of oxide containing Si and Al, which is presumed to be a repaired portion of cracks, was observed.

The three-point bending strength of Comparative Example 4 was also as low as 41 [MPa], a value unsuitable for application to structural parts. This is because the molar ratio SiO ₂ /Al ₂ O ₃ of the raw material powder was 0.03/0.97, and the raw material powder contained almost no silicon dioxide. This is probably because the phenomenon of repairing the crack did not occur sufficiently and the porosity increased.

According to the present invention, it is possible to provide, at a low cost, a ceramic structure in which the compactness and mechanical strength of the shaped product are improved while taking advantage of the features of the direct shaping method, in which a shaped product with a complicated shape can be obtained.

100 solidified part 101 powder 102 powder layer 103 unsolidified powder 110 shaped object 130 base 151 stage 152 roller 180 laser beam source 181 scanner part 190 liquid injection nozzle 201 cladding nozzle 202 powder supply hole 203 laser beam 301 made of aluminum oxide Region 302 Region made of mullite Region 303 Region made of oxide containing Si and Al Region 401 Region made of silicon dioxide CR Crack-repaired portion

Claims (20)

A ceramic structure,
It has a region made of at least mullite, a region made of an oxide containing Si and Al having a higher proportion of Si than the mullite, and a region made of aluminum oxide,
A ceramic structure characterized by satisfying a molar ratio SiO ₂ /Al ₂ O ₃ of 0.1/0.9 to 0.7/0.3 in terms of oxide. 2. The method according to claim 1, wherein the cross section of the ceramic structure includes a region made of an oxide containing Si and Al and having an average width of 1 μm or more and a ratio of length to average width of 10 or more. ceramic structure. The ratio of the mullite region to the entire region satisfies 75% by volume or more of the maximum amount of mullite calculated from the oxide-equivalent molar ratio SiO ₂ /Al ₂ O ₃ of the ceramic structure. The ceramic structure according to claim 1, wherein 4. The region according to any one of claims 1 to 3, wherein the oxide-equivalent molar ratio SiO ₂ /Al ₂ O ₃ of the region made of the oxide containing Si and Al is 12 to 24. ceramic structure. 2. The ceramic structure according to claim 1, wherein said mullite region is crystalline. 2. The ceramic structure according to claim 1, wherein said region made of aluminum oxide is crystalline. 2. The ceramic structure of claim 1, further comprising a region of silicon dioxide. 2. The ceramic structure according to claim 1, further comprising a region made of zirconium oxide. A method for manufacturing a ceramic structure,
(i) containing silicon dioxide particles, aluminum oxide particles, and an absorber exhibiting a higher light absorption capacity than silica or alumina with respect to the light of the wavelength contained in the irradiated laser beam; disposing a powder satisfying a molar ratio SiO ₂ /Al ₂ O ₃ 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 article obtained by performing the steps (i) and (ii) a plurality of times so that the maximum temperature reaches 1595° C. or more and less than 1730° C.;
A method for manufacturing a ceramic structure, comprising: 10. The method of manufacturing a ceramic structure according to claim 9, wherein in said step (iii), the heat treatment is performed so that the maximum temperature reaches 1600[deg.] C. or more and less than 1720[deg.] C. 10. The method for manufacturing a ceramic structure according to claim 9, wherein in said step (iii), the holding time at the highest temperature is 1 minute or more and 4 hours or less. 10. The method of manufacturing a ceramic structure according to claim 9, wherein said absorber has an absorptance of 10% or more for light of a wavelength contained in said laser beam. 13. The method of manufacturing a ceramic structure according to claim 12, wherein said absorber has an absorptivity of 40% or more for light of a wavelength contained in said laser beam. 10. The method of manufacturing a ceramic structure according to claim 9, wherein said absorber is SiO. 10. The method for producing a ceramic structure according to claim 9, wherein the silicon dioxide particles have an average particle size of 5 [mu]m or more and 200 [mu]m or less, and the absorber has an average particle size of 1 [mu]m or more and less than 10 [mu]m. 10. The method of manufacturing a ceramic structure according to claim 9, wherein the amount of said absorber added is 0.5 vol % or more and 10 vol % or less of said powder. 10. The method of manufacturing a ceramic structure according to claim 9, further comprising the step of allowing said shaped article to absorb a liquid containing a metal element before said step (iii). 18. The method of manufacturing a ceramic structure according to claim 17, wherein the liquid containing the metal element contains zirconium. 17. The maximum temperature reached by the shaped article in the heat treatment in step (iii) is lower than the melting point of silicon dioxide and higher than the eutectic temperature between the oxide of the metal element and silicon dioxide. 2. A method for producing a ceramic structure according to 1. 18. The method of manufacturing a ceramic structure according to claim 17, wherein the content of said metal element in said powder is less than 3.0% by mass.

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