CN118234694A

CN118234694A - Ceramic structure and method for manufacturing same

Info

Publication number: CN118234694A
Application number: CN202280074894.1A
Authority: CN
Inventors: 村上俊介; 大志万香菜子; 清水康志; 安居伸浩; 有井千明; 海野知浩; 西川浩司
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2021-11-12
Filing date: 2022-11-10
Publication date: 2024-06-21

Abstract

A ceramic structure comprising at least a region containing mullite, a region containing an oxide containing S i and Al that is more S i than mullite, and a region containing alumina, wherein the oxide conversion molar ratio SiO ₂/Al₂O₃ satisfies 0.1/0.9 to 0.7/0.3.

Description

Ceramic structure and method for manufacturing same

Technical Field

The present invention relates to a ceramic structure obtained by direct shaping and a method for producing the same.

Background

As means for manufacturing prototypes and small numbers of objects, additive manufacturing techniques for obtaining a desired structure by adding materials based on shape data of a three-dimensional model to be manufactured are becoming popular. In the manufacture of metal objects, direct shaping is widely employed in which a laser beam is used to irradiate metal powder and cure the powder to shape. This method can produce various objects by effectively melting and solidifying the metal powder.

In recent years, methods for developing additive manufacturing techniques using ceramic powders have been made. Unlike metals, common ceramics such as alumina and zirconia have low absorption capacity for laser beam wavelengths, and therefore require the application of significantly higher energy to melt the ceramic powder. However, even if high energy is applied, the diffusion of the laser beam makes the melting uneven, and it is difficult to achieve desired manufacturing accuracy.

Patent document 1 discusses a technique of adding an absorber having a high absorption capacity for the wavelength of an irradiation laser beam to a raw material powder to reduce beam spread and achieve high manufacturing accuracy. Patent document 2 discusses a technique for manufacturing a ceramic structure by direct shaping using a powder mainly containing silica as a raw material, to which an absorber having a high absorption capacity for the wavelength of an irradiation laser beam is added.

CITATION LIST

Patent literature

Patent document 1: japanese patent laid-open No. 2019-19051

Patent document 2: japanese patent laid-open No. 2021-66177

Disclosure of Invention

Technical problem

Patent document 1 discusses Al ₂O₃-ZrO₂ powder and Al ₂O₃-S iO₂ powder added with Tb ₄O₇ as an absorber. Patent document 2 discusses Al ₂O₃-S iO₂ powder added with S iO as an absorber. Al ₂O₃-S iO₂ powder is particularly desirable in terms of stable low cost manufacture of ceramic structures, since SiO ₂ is inexpensive and readily available.

However, a shaped article made of a raw material powder having a ratio of S iO ₂ of more than 70mol% using direct shaping methods such as those of patent document 1 and patent document 2 is porous, and tends to lack mechanical strength for use as a structural member such as a mechanical member or a medical member.

Solution to the problem

The ceramic structure according to the present invention includes at least: a region comprising mullite, a region comprising oxides containing Si and Al that are more Si-rich than mullite; and a region containing alumina, wherein the oxide conversion molar ratio SiO ₂/Al₂O₃ satisfies 0.1/0.9 to 0.7/0.3.

The method for manufacturing a ceramic structure according to the present invention comprises the steps of: (i) Providing a powder containing silica particles, alumina particles, and an absorber exhibiting higher light absorption than silica and alumina at a wavelength of light included in the irradiation laser beam, the oxide conversion molar ratio SiO ₂/Al₂O₃ of the powder satisfying 0.1/0.9 to 0.7/0.3; (ii) Irradiating the powder with a laser beam to melt the powder, followed by solidification; and (iii) heat treating the shaped article obtained by performing steps (i) and (ii) a plurality of times so that a maximum temperature of 1595 ℃ or more and below 1730 ℃ is reached.

Advantageous effects of the invention

According to the present invention, a ceramic structure having high mechanical strength can be manufactured at low cost using direct shaping.

Drawings

Fig. 1A is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shaped article by powder bed fusion.

Fig. 1B is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

FIG. 1C is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

FIG. 1D is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

Fig. 1E is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

Fig. 1F is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

Fig. 1G is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

FIG. 1H is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shape by powder bed fusion.

Fig. 2A is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shaped article by cladding.

Fig. 2B is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shaped article by cladding.

Fig. 2C is a schematic cross-sectional view schematically illustrating an exemplary embodiment of a method of manufacturing a shaped article by cladding.

Fig. 3A is a Scanning Electron Microscope (SEM) image of a cross section of a typical ceramic structure according to the present invention.

Fig. 3B is an Al element distribution image of the cross section shown in fig. 3A.

Fig. 3C is a Si element distribution image of the cross section shown in fig. 3A.

Fig. 4A is an SEM image of a cross section of a ceramic structure according to example 19.

Fig. 4B is an Al element distribution image of the cross section shown in fig. 4A.

Fig. 4C is a Si element distribution image of the cross section shown in fig. 4A.

Fig. 5A is an SEM image of a cross section of a ceramic structure according to example 20.

Fig. 5B is an Al element distribution image of the cross section shown in fig. 5A.

Fig. 5C is a Si element distribution image of the cross section shown in fig. 4A.

Detailed Description

Exemplary embodiments of the present invention will be described below with reference to specific examples and with reference to the accompanying drawings. However, the present invention is not limited in any way to the following specific embodiments or the drawings.

In the direct shaping process, powder bed fusion and directed energy deposition (so-called cladding process) are suitable for use in the present invention.

In this specification, silicon dioxide may be referred to as silicon oxide (sii i ica) or SiO ₂. Alumina may be referred to as alumina (aluminum) or Al ₂O₃. Silica has many different crystalline forms, but will be referred to simply as silica or silicon oxide, or if conditions such as amorphous, crystalline and other crystalline structures are not critical, chemical formula SiO ₂ is used.

Fig. 1A to 1H are schematic cross-sectional views schematically illustrating a basic manufacturing process of a manufacturing method using powder bed fusion.

First, the raw material powder 101 is placed on the base 130 mounted on the table 151 and flattened to a predetermined thickness by the roller 152 to form the powder layer 102 (fig. 1A and 1B). The powder layer 102 is irradiated with a laser beam emitted from the laser light source 180, and scanned by the scanner unit 181 based on slice data generated from shape data on 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 (fig. 1C) corresponding to the sliced data layer. Then, the stage 151 is lowered, a new powder layer 102 is formed above the solidified portion 100 (fig. 1D), and the new powder layer 102 is irradiated with a laser beam based on slice data. This series of processes is repeated a plurality of times corresponding to the slice data, thereby obtaining a shaped object 110 (fig. 1E and 1F). Finally, the uncured raw material powder 103 is removed, unwanted portions of the shaped article are removed, and the shaped article and the base are separated as needed (fig. 1G and 1H).

Fig. 2A to 2C are schematic cross-sectional views schematically illustrating a basic manufacturing process using a manufacturing method of cladding. Raw material powder is discharged from a plurality of powder supply holes 202 in a cladding nozzle 201, and a region where the powder is focused is irradiated with a laser beam 203 while the solidified portion 100 is additively formed based on slice data (fig. 2A). The process continues to obtain the shape 110 (fig. 2B and 2C). Finally, the unwanted portions of the shaping object are removed and the shaping object and the abutment are separated as desired.

In the case of direct shaping methods such as powder bed fusion and cladding, particles contained in the raw material powder are melted during laser beam irradiation. When the laser beam irradiation is completed, the particles are rapidly cooled from the surroundings to form the solidified portion 100. The silica powder has a high viscosity when melted so as not to scatter and thus solidifies into a granular form upon cooling. Our studies found that ceramic structures formed only from silica powder have high porosity and do not provide sufficient mechanical strength.

Accordingly, the present invention uses a mixed powder of silica powder and alumina powder, which contains absorber particles, silica particles, and alumina particles, such that the oxide conversion molar ratio sio ₂/Al₂O₃ satisfies 0.1/0.9 to 0.7/0.3. For oxide equivalent conversion, silicon oxide composition including sio is calculated as sio ₂ and aluminum oxide composition is calculated as Al ₂O₃.

The thermal conductivity of silica is about 1.5W/mK. The thermal conductivity of alumina is about 30W/mK, which is about 20 times that of silica. The alumina particles having high thermal conductivity are preferentially melted by the laser beam irradiation. If a predetermined ratio of alumina is added to silica, the preferentially melted alumina melt is contacted with a silica melt or silica particles having a high viscosity and the melt is mixed into a molten state of low viscosity. Since the melt viscosity is reduced in this way, a shaped article of low porosity (high compactability) and high mechanical strength can be obtained as compared with the case of using a silica-rich raw material powder.

During laser beam irradiation, a portion of the fused silica reacts with the fused alumina to form mullite, which is a silica-alumina compound. However, in the case of a manufacturing method in which raw material powder is melted and solidified by short pulse laser beam irradiation (such as powder bed fusion and cladding), alumina and silica particles may not be completely melted. Some of the particles may be unreacted and remain only in the solidified portion as long as the amount required for manufacturing is melted.

Since the portion irradiated with the laser beam is melted and solidified in a short time, the resulting shaped article is often cracked due to thermal stress. The cracks are distributed throughout the shape (structure), i.e. both surface and interior. Most cracks have a width of about 5nm to 50 μm and can lead to a decrease in the mechanical strength of the shaped article.

The ceramic structure according to the present invention is obtained by heat-treating the shaped article manufactured through the steps of fig. 1A to 1H or fig. 2A to 2C at a temperature of 1595 ℃ or more and less than 1730 ℃, and can provide high mechanical strength. The reason why the mechanical strength is improved by heat treatment at a temperature of 1595 ℃ or more and less than 1730 ℃ is as follows:

Fig. 3A is an example of a secondary electron image (scanning electron microscope [ SEM ] image) of a cross section of a ceramic structure subjected to heat treatment at 1595 ℃ or higher and below 1730 ℃ observed under SEM. Fig. 3B and 3C are element distribution images (energy dispersive X-ray spectroscopy [ EDS ]) showing the distribution of Al and Si, respectively.

The alumina containing region 301 appears brightest in fig. 3B and darkest in fig. 3C. The mullite-containing region 302 appears to be sub-bright in fig. 3B and sub-dark in fig. 3C. The composition of this region is denoted as Al ₆S i₂O₁₃. The region 303 containing the oxide containing S i and Al appears dark in fig. 3B and bright in fig. 3B. The composition of region 303 approximates 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 S i/Al of 6 to 12 and is more Si-rich than the region containing mullite, with an oxide-converted molar ratio sio ₂/Al₂O₃ of 12 to 24.

The heat treatment in the above temperature range causes a region (region containing an oxide containing S i and Al) 303 having a composition close to the eutectic composition (eutectic point: 1595 ℃) of silica and mullite to soften or melt, and its melting point is in the temperature range. Cracks caused by thermal stress of the molten composition propagate from the region 303 by capillary action, thereby repairing the cracks with oxides containing Si and Al. Even if a composition mixed with other regions is formed on a portion of the wall surface facing the crack, the present invention is not affected. In fig. 3C, a striped region CR is observed in the middle portion, which leads to a region 303 containing an oxide containing S i and Al. The striped region corresponds to the location of a crack caused by thermal stress during manufacture, and is therefore considered to be a crack repaired by the intrusion and propagation of the molten component constituting the region 303 through the crack during the aforementioned heat treatment. By the cracks thus repaired, the ceramic structure after heat treatment has fewer cracks and improved mechanical strength. For this reason, a striped region CR is included in the region 303, the region 303 containing an oxide containing Si and Al.

At least one region CR or repair crack can be observed in a two-dimensional region of 2mm×2mm, taking into account the crack density occurring during manufacture. The region CR has an average width of 1 μm or more and a ratio of its length to the average width of 10 or more. Thus, it can be distinguished from areas not originating from cracks. Here, the average width is an average value of the widths of the regions CR measured at five or more positions. If the region CR extends not in a straight but in a curved shape, a length measured along the curve is used.

Fig. 4A is an example of an SEM image of a cross section of a ceramic structure heat-treated at 1595 ℃ or higher and below 1730 ℃ under different conditions from fig. 3A. Fig. 4B and 4C are element distribution images of fig. 4A, showing the distribution of Al and S i, respectively.

As with fig. 3A to 3C, the alumina containing region 301 appears brightest in fig. 4B and darkest in fig. 4C. The mullite-containing region 302 appears to be sub-bright in fig. 4B and sub-dark in fig. 4C. The region 303 comprising the oxide containing S i and Al appears to be sub-dark in fig. 4B and bright in fig. 4B. The region 401 comprising silicon dioxide appears darkest in fig. 4B and brightest in fig. 4C. In this way, the shaped article after the heat treatment may include the region 401 including silica as shown in fig. 4A to 4C, in addition to at least three regions including a region including oxides including Si and Al, a region including mullite, and a region including alumina.

As described above, the alumina-containing region 301 and the silica-containing region 401 are considered to be regions in which some of the silica particles and alumina particles that remain unmelted during manufacture remain unchanged even after heat treatment. The shorter the duration of the heat treatment, the more silica-containing regions the composite ceramic structure tends to include.

The mechanical strength of the ceramic structure comprising three or four regions is significantly improved compared to before the heat treatment. This is believed to be due to the following phenomena in addition to the repair of the crack: for ceramic structures having three regions, the region containing silica is believed to be transformed into a region containing oxides containing Si and Al or a region containing mullite over an extended duration of heat treatment. During this transition, the porosity can be reduced to improve the mechanical strength. For a ceramic structure having four regions, the region containing silica is converted into a state containing cristobalite as a preliminary stage of conversion into a region containing oxides containing Si and Al or a region containing mullite. In the region containing silicon dioxide included in the shaped article before the heat treatment, most of the portion that was melted by the laser beam irradiation and then solidified has an amorphous structure. The cristobalite has a higher density and a higher mechanical strength than those of the amorphous structure, and it is considered that the mechanical strength of the ceramic structure is improved due to the transition of the region containing silicon dioxide into a state containing cristobalite.

In order to convert the region 401 containing silica into a state containing cristobalite, the heat treatment conditions, and the particle diameter and crystalline state of silica particles used in the raw material powder may be adjusted. By adjusting the particle diameter and the crystalline state of the silica particles, the size and the crystalline state of the region containing silica before heating can be adjusted. The morphology of the region comprising silicon dioxide before heating also affects the state of the region 401 comprising silicon dioxide after heat treatment. Whether the region 401 containing silicon dioxide is included in the ceramic structure, and if included, the final size and crystalline state of the region 401 containing silicon dioxide can be controlled by adjusting the heat treatment conditions.

In order to further improve the mechanical strength of the shaped article, the shaped article may be impregnated with a repair solution containing a metal component prior to the heat treatment. The ordinary sintering converts the cracks into a region 303 comprising oxides containing S i and Al. In contrast, if the crack is impregnated with the repair solution before the heat treatment, the melt including the region containing the oxides of S i and Al and the solid component of the repair solution react to generate the oxide containing the metal component included in the repair solution, thereby repairing the crack to form the region CR. If a region including an oxide containing a metal component included in the repair solution is formed in the region CR, the composition of the shaped article becomes more complicated, and the mechanical strength of the shaped article improves. In this case, the metal component derived from the repair solution supplied to the region 302 is dispersed not only into the region CR but also into the region 303 containing the oxide containing S i and Al associated with the region CR during the heat treatment.

The raw material powder and the method of manufacturing the ceramic structure used in the present invention will now be described in more detail.

[ Raw material powder ]

The raw material powder contains an absorber, silica particles, and alumina particles. The oxide conversion molar ratio SiO ₂/Al₂O₃ satisfies 0.1/0.9 to 0.7/0.3. Here, S iO is regarded as S iO ₂ for oxide equivalent conversion.

The silica particles and alumina particles constituting the raw material powder desirably have a nearly spherical shape to obtain sufficient fluidity to compactly planarize the raw material powder to a predetermined thickness on the base 130. In order to reduce powder aggregation and manufacture a molded article with high accuracy, the average particle diameters of both the silica particles and the alumina particles are desirably 5 μm or more and 200 μm or less, preferably 10 μm or more and 150 μm or less. The average particle size of the powder according to the invention is referred to as the median diameter (median). The average particle diameter of the powder was calculated as the equivalent circle diameter of the projected image from the powder micrograph.

The bonding state of S i and O in the silica particles constituting the powder is not particularly limited, and may be an amorphous state, a crystalline state (such as cristobalite and quartz), or a mixed state thereof.

The absorber refers to a component (element or compound) having a high light absorbing ability at a wavelength of light included in the irradiation laser beam during manufacturing as compared with silicon dioxide and aluminum oxide. The absorption capacity or absorption rate of the absorber for the wavelength of the laser beam used is desirably higher than or equal to 10%, preferably higher than or equal to 40%, and still preferably higher than or equal to 60%. The absorption rate of the absorber can be measured using a conventional spectrometer. Specifically, a sample disk filled with an absorber is mounted in an integrating sphere as a sample, and irradiated at a desired wavelength (near the laser wavelength used in manufacturing) to measure the value of the electromagnetic spectrum. The absorbance was calculated from the ratio of this value to the measured value without the sample.

Such an absorber effectively absorbs the laser beam used during manufacturing and raises its own temperature, thereby conducting heat to other compositions in the region corresponding to the focal size of the laser beam, resulting in an increase in temperature. This achieves effective local heating, and can clarify the interface between the treated region (region irradiated with the laser beam) and the untreated region (region not irradiated with the laser beam) to achieve improved manufacturing accuracy.

The absorber desirably converts at least partially into another composition having a low light absorption capacity due to laser beam irradiation. Examples include a composition of another metal oxide in which the valence state of a metal element is changed due to oxygen desorption caused by a temperature increase to be converted into a relatively low light absorption capacity for a laser beam. Even when the cured portion is irradiated with the laser beam, the light absorption capacity is reduced to 5/6 times or less before the laser beam is irradiated, and adverse effects on the manufacturing accuracy are prevented. In other words, there is almost no absorber in the cured portion after the laser beam irradiation, and a temperature rise as before the laser beam irradiation will not occur. If the powder adjacent to the cured portion is irradiated with a laser beam, the cured portion can be thereby prevented from being deformed or transformed. This increases the process margin of the irradiation condition of the laser light, and can reduce the influence of fluctuation of the irradiation condition on the manufacturing accuracy. For higher manufacturing accuracy, the light absorption capacity after laser beam irradiation desirably falls below 1/2 of that before laser beam irradiation.

As the absorber, a composition that is converted into another composition by being combined with another composition included in an atmosphere gas or powder or by causing a decomposition reaction (e.g., oxygen desorption) under laser beam irradiation and incorporated into a molded article can be used.

Suitable compositions for the absorber include SiO, tb ₄O₇、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、V₂O₄、Co₃O₄、CoO、 transition metal carbides, transition metal nitrides, S i ₃N₄, alN, borides and silicides. Suitable transition metal carbides include TiC and ZrC. Suitable transition metal nitrides include TiN and ZrN. Suitable borides include TiB ₂、ZrB₂ and LaB ₆. Suitable silicides include TiSi ₂、ZrS i₂ and MoSi ₂. At least one selected from these may be used as the absorber.

It is desirable to select a composition having a high affinity with other compositions constituting the powder and use it as an absorber. Since the raw material powder of the present invention contains silica and aluminum, a metal oxide having a high affinity for an absorber is desirable. S iO with high affinity for silica is particularly desirable.

The color of sio is brown or black, and has a high light absorbing ability to the wavelength of the irradiation laser beam during manufacturing, compared with aluminum and silicon dioxide included in the raw material powder. When the SiiO absorbs the laser, si is converted from divalent to tetravalent, and metastable SiiO is converted to stable SiiO ₂. SiO is also desirable because of its reduced light absorption capacity for laser light. For manufacturing purposes where no additional components are required, it is desirable to convert S iO to S iO ₂ (the main component of the raw material powder) after laser beam irradiation. In addition, S iO is commercially available as a negative electrode of a lithium ion secondary battery, and is therefore also advantageous in that it can be obtained inexpensively compared with other compounds that can be used as an absorber.

The absorber exhibiting good energy absorption for the laser beam is preferably finely and uniformly dispersed together with the powder. This uniformizes the reaction of the powder upon laser beam irradiation, and further improves the manufacturing accuracy. In view of this, the average particle diameter of the absorber particles (absorber powder) included in the powder is desirably 1 μm or more and less than 10 μm, preferably 1 μm or more and less than 5 μm.

The amount of the absorber added is desirably 0.5% by volume or more and 10% by volume or less of the raw material powder. If the raw material powder contains 0.5% by volume or more of the absorber, at least one or more absorber particles may be statistically present in the region irradiated with the laser beam under typical laser beam use conditions, and the effect of adding the absorber may be obtained. The addition of the absorber of 10% by volume or less can prevent the temperature of the powder from rising sharply during laser beam irradiation, so that splashing of the surrounding molten material, i.e., a decrease in manufacturing accuracy, can be avoided.

In order to adjust the properties of the ceramic structure, a composition other than silica, alumina or an absorber may be added to the raw material powder up to a proportion of less than 10 mass%.

Although the present specification expresses compositions using chemical formulas such as SiO and Tb ₄O₇, the actual elemental composition ratios need not be exactly matched to the stoichiometric ratios so long as the intended purpose of the present invention is met. In other words, the valence of the metal element constituting the composition may be slightly different from those expected from the chemical formula. From the stoichiometric ratio specified for the metal element, a constituent element ratio error of at most ±30% is acceptable. For example, if the absorber is SiO, the absorber having a composition element ratio of Si: o=1:1.30 is included in SiO. If SiO is used as the absorber, the deviation of the element composition ratio from the stoichiometric ratio is more desirable within.+ -. 20% in terms of providing sufficient light absorption capacity.

[ Method for producing ceramic Structure ]

Next, a method of manufacturing a ceramic structure according to the present invention will be described in detail with reference to fig. 1A to 1H. The ceramic structure is obtained by the following three steps:

(i) Disposing the raw material powder on a manufacturing surface to a predetermined thickness;

(ii) Irradiating the powder with a laser beam to melt the powder, followed by solidification; and

(Iii) Heating the shaped article obtained by repeating steps (i) and (ii) above 1595 ℃ and below 1730 ℃.

< Step (i) >

As shown in fig. 1A to 1H, raw material powder is set on a manufacturing surface (base 130) to a predetermined thickness using a recoater (mechanism for laying powder) such as a roller and a doctor blade. The material of the substrate 130 may be appropriately selected from ceramics, metals, and glasses according to the intended use purpose of the mold and manufacturing conditions.

< Step (ii) >

Irradiating the raw material powder set to a predetermined thickness in step (i) with a laser beam, the laser beam being scanned based on slice data generated from shape data on a three-dimensional model to be manufactured. During laser beam irradiation, an absorber included in the raw material powder absorbs light energy, converts the light energy into heat, melts itself and transfers the heat to the surroundings, thereby melting other powders in the laser irradiation region.

After the laser beam passes and completes irradiation, heat of the melted region dissipates into the atmosphere and the surrounding environment, thereby cooling the melted region to form a solidified region. Since the temperature change in melting and solidification is abrupt, most of the region containing silicon dioxide and the region containing oxides containing Si and Al in the shape become amorphous structures. The sharp temperature changes also create stresses on the surface and inside the shape, thereby forming cracks.

The type of laser beam is not particularly limited. A general-purpose laser such as a Yttrium Aluminum Garnet (YAG) laser of a1 μm band or a fiber laser and a CO ₂ laser of a10 μm band is suitably used. A YAG laser or a fiber laser that emits light in the 1 μm band is particularly desirable if SiO is used as an absorber, siO exhibiting high absorption of the light.

< Step (iii) >

In step (iii), the shaped article produced by repeating steps (i) and (ii) a predetermined number of times is heat treated so that the maximum temperature reached is 1595 ℃ or higher and below 1730 ℃. The number of repetitions of steps (i) and (ii) corresponds to the number of slices of the slice data.

The heating temperature range (1595 ℃ or more and less than 1730 ℃) of step (iii) is a temperature range in which oxides containing Si and Al melt. The oxide containing Si and Al is thus melted in step (iii) and propagates through the crack due to capillary action.

Such heat treatment can produce a shaped article that is stable at high temperatures and has excellent mechanical strength. The shape after the heat treatment of step (iii) is a ceramic structure comprising at least three regions, the at least three regions being a region comprising oxides comprising Si and Al, a region comprising mullite, and a region comprising alumina. Specifically, the shaping object is a composite ceramic structure including three kinds of regions, which are a region containing oxides containing Si and Al, a region containing mullite, and a region containing alumina, or a ceramic structure including four kinds of regions, which further include a region containing silica. The region containing oxides containing Si and Al is a region having an element number ratio Si/Al of 6 to 12. The regions comprising silica are typically included in ceramic structures having short heat treatment times.

The ceramic structure includes at most one of the three or fourth regions described above, depending on the mixing ratio of silica and alumina contained in the raw material powder and the heat treatment conditions. The mullite-containing region 302 has relatively high mechanical strength and its proportion in the ceramic structure is therefore desirably high. In particular, the ratio is desirably greater than or equal to 75 volume percent of the maximum amount of mullite calculated from the molar ratio SiO ₂/Al₂O₃ in the ceramic structure (referred to as the maximum amount of mullite formation). The proportion is preferably greater than or equal to 80% by volume, and is also preferably greater than or equal to 90% by volume. The actual amount of mullite formation is determined by the laser irradiation conditions in step (ii) and the heat treatment conditions in step (iii). Comparison of structures having the same composition shows that ceramic structures having a mullite formation amount of greater than or equal to 75% by volume of the maximum mullite formation can provide high mechanical strength.

Table 1 lists examples of maximum mullite formation calculated from the ratio of Si and Al included in the ceramic structure according to the present invention. The maximum amount of the region containing oxides of Si and Al and the maximum amount of the region containing alumina calculated by the same technique are also listed. The assumptions used for the calculations are as follows: silica has a molecular weight of 60.08 and a density of 2.3g/cm ³, and alumina has a molecular weight of 101.977 and a density of 3.96g/cm ³. The region containing oxides of Si and Al was assumed to have an element number ratio Si/al=10, and the molecular weight calculated using the above values was 62.09, and the density was 2.38g/cm ³. Mullite has a molecular weight of 426.05 and a density of 3.0g/cm ³.

TABLE 1

According to the combination of the heat treatment conditions in step (iii) and the state of the silica used for the raw material powder, the amorphous silica-dominant silica-containing region is converted into cristobalite by heat treatment immediately after the production. Cristobalite has a high density and excellent mechanical strength compared with amorphous-structured silica. If the ceramic structure includes a silica-containing region, the conditions are therefore desirably optimized such that the silica-containing region becomes cristobalite-containing.

The maximum temperature reached in step (iii) is desirably above 1600 ℃ and below 1720 ℃, preferably above 1650 ℃ and below 1700 ℃. In order to manufacture a ceramic structure including three regions, which are a region including an oxide containing S i and Al, a region including mullite, and a region including alumina, a heat treatment time may be increased. As a guideline for the heat treatment time to form these three regions, for example, if the shaped article has a molar ratio SiO ₂/Al₂O₃ of 0.56/0.44 and is heated to 1690 ℃, the maximum temperature holding time is desirably kept at 40 minutes to 120 minutes.

The holding time may be short, since the cracks may be reduced once the highest temperature near the cracks in step (iii) reaches the above temperature range. Note that if the heating time in the above temperature range is excessively long or the heat treatment is performed at a high temperature exceeding the above temperature range, the average particle diameter in each region tends to be large, so that the mechanical strength of the ceramic structure is lowered. Thus, the heating time is desirably adjusted within several hours. In order to prevent the mechanical strength of the ceramic structure from decreasing, the heat treatment time is desirably 1 minute or more and 4 hours or less, preferably 5 minutes or more and 120 minutes or less, and more preferably 10 minutes or more and 80 minutes or less.

The heating method is not particularly limited. The shaping object may be irradiated again with the energy beam for heating or heated in an electric furnace. In the case of energy beam heating, it is desirable to find in advance the relationship between the heat input by the energy beam and the temperature of the shaping object using a thermocouple so that the shaping object can be heated to the above-described desirable temperature.

The heat treatment is typically performed with the shaped article placed on the mounting body. However, the shape may melt at the surface or near the crack during heating, and solidify and adhere to the mount after the heat treatment. Thus, the mount for heat treatment is desirably an inert mount. Examples of materials suitable for forming the inert susceptor include platinum in an atmospheric environment and iridium in a low oxygen atmosphere.

Cracks in the shape can be repaired by: the shaped article is impregnated with a repair solution (a solution containing a metal component) prior to heat treatment, and then heated. The metal component is desirably a metal component that generates a metal oxide and a phase capable of forming a eutectic with a phase constituting the shaping object when subjected to heat treatment. In particular, it is desirable that the eutectic temperature of the metal component and silica is below the maximum temperature reached by the former during the heat treatment of step (iii). Thus, the maximum temperature reached by the shaping during the heat treatment of step (iii) may be set below the melting point of silica and above the eutectic temperature of the metal oxide and silica.

For cracks impregnated with such a repair solution prior to heat treatment, the vicinity of the crack penetrated by the metal component melts at a temperature lower than the melting point of the other parts of the shape, and the metal component diffuses inside the shape. When the temperature decreases after heating, crystals having a composition including the metal component are recrystallized inside the shaped article. As a result, only the crack vicinity can be softened to reduce or eliminate the crack, and the shape of the molded article can be maintained. Here, the phase precipitation of the metal component-containing oxide makes the phase composition of the shaped article more complex, which can improve the mechanical strength of the shaped article.

By adding a metal component for repairing cracks to the raw material powder in advance, the effect of reducing cracks in the shaped article cannot be obtained. If the raw material powder is rich in a metal component for repairing cracks, the melting point cannot be locally lowered in the vicinity of the cracks, and the entire shape can be melted and deformed by heat treatment. Thus, the raw material powder desirably does not contain any metal element included in the repair solution, or its content is less than 3.0 mass%, if any. The raw material powder preferably contains less than 2.0 mass% of metal elements.

As described above, in order to reduce cracks using the repair solution, it is important to heat treat the shaped article impregnated with the repair solution to locally increase the density of the metal element in the cracks. This technique can reduce cracks, has high manufacturing accuracy, and can improve the mechanical strength of the molded article.

The technique of impregnating the shaped article with the repair solution is not particularly limited, provided that a sufficient amount of the metal component is able to penetrate the entire shaped article. The shaped article may be immersed in the repair solution for impregnation. The repair solution may be sprayed onto the shape or applied to the surface with a brush and then absorbed. A plurality of such techniques may be used in combination. The same technique may be repeated multiple times.

The metal element may be added to the solution in the form of a metal alkoxide, a metal salt compound, a metal ion, or particles containing the metal element.

As the metal component included in the repair solution, a metal component selected from lithium, sodium, potassium, magnesium, calcium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, and other rare earth elements may be used.

An advantageous example of a repair solution is a solution containing a zirconium component and a solvent, and optionally a stabilizer and/or dispersant. The majority of the zirconium component included in the solution is converted to zirconia by heat treatment (the eutectic temperature of ZrO ₂).SiO₂ and ZrO ₂ is 1683 ℃, the eutectic temperature of Al ₂O₃ and ZrO ₂ is 1720 ℃, the eutectic temperature of mullite and ZrO ₂ is 1700 ℃, these eutectic temperatures fall within the range of the heating temperature in step (iii), 1595 ℃ or higher and lower than 1730 ℃ and lower than the melting point of silica (1730 ℃), the melting point of alumina (2070 ℃) and the melting point of mullite (1850 ℃), the crack region infiltrated with the repair solution can be selectively melted at a temperature at which the melting of the silica-containing region, the alumina-containing region and the mullite-containing region can be prevented to reduce the cracks.

Zirconium alkoxides, zirconium salt compounds, zirconium ions and zirconium-containing particles can be used as the zirconium component. For the stabilizer, organic acids, surfactants and chelating agents are suitable.

For the solution containing zirconium alkoxide, a solution containing zirconium alkoxide selected from zirconium tetraethoxide, zirconium tetra-n-propoxide, zirconium tetra-isopropoxide, zirconium tetra-n-butoxide and zirconium tetra-t-butoxide, and an organic solvent and a stabilizer are suitable.

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

For the zirconium ion-containing solution, a solution containing zirconium ions and water, optionally with a stabilizer, may be used. The amount of water in the solution is desirably greater than or equal to 10 mass% of the solution (excluding metal ions). In addition to water, the solution may contain an organic solvent. The zirconium ion may be generated by dissolving a zirconium ion-containing material such as zirconium salt and zirconium alkoxide in a solvent.

For the solution containing zirconium-containing particles, a solution containing zirconium particles or zirconium oxide particles, a solvent and a dispersant is desirable. For crack penetration, the particle size is desirably 300nm or less, preferably 50nm or less. The dispersant desirably comprises at least one of an organic acid, a silane coupling agent, and a surfactant. Advantageous solvents include alcohols, ketones, esters, ethers, ester-modified ethers, hydrocarbons, halogenated hydrocarbons, amides, water, oils, and mixtures of two or more thereof.

If a repair solution containing a zirconium component is impregnated before step (iii), a region including zirconia is formed in the shape after step (iii). In addition to the above three or four kinds of regions, the formation of the region including zirconia increases the number of regions formed in the ceramic structure, so that the mechanical strength of the ceramic structure can be improved.

< Ceramic Structure >)

The ceramic structure according to the present invention obtained by the above method has low porosity and includes three regions, which are: a region containing oxides containing Si and Al, a region containing mullite, and a region containing alumina. The oxide conversion molar ratio SiO ₂/Al₂O₃ in the ceramic structure is 0.1/0.9 to 0.7/0.3. In the region containing oxides containing Si and Al, the element number ratio Si/Al is 6 to 12. As described above, depending on the heat treatment time, a region containing silicon dioxide is also included.

Such a ceramic structure can be obtained by: the raw material powder satisfying the oxide conversion mole ratio SiO ₂/Al₂O₃ of 0.1/0.9 to 0.7/0.3 is directly shaped and then heat-treated in the above temperature range.

If the ceramic structure includes regions comprising silica, then cristobalite is desirably included. Cristobalite has a high density and excellent mechanical strength as compared with amorphous silica.

If the crack is impregnated with the repair solution prior to the heat treatment, the number of areas is increased from three to four, or from four to five. If a zirconium-containing solution is used as the repair solution, the ceramic structure includes four or five regions, with the additional regions comprising zirconium oxide. The mechanical strength of such a ceramic structure may be higher than in the case of repairing a crack without using the repair solution, because of the effect of inhibiting crack growth due to the presence of a plurality of different regions.

The porosity of the ceramic structure according to the present invention is desirably 10% or less. At a porosity of 10% or less, the ceramic structure may provide sufficient mechanical strength for use as a structural member. As will be described in detail below, porosity refers to open porosity.

Evaluation method of performance value

< Mechanical Strength >

The mechanical strength of the structure was evaluated by a 3-point bending test of Japanese Industrial Standard (JIS) R1601 based on a room temperature bending strength test of the fine ceramics. Specifically, the mechanical strength can be calculated from the maximum bending stress at which the specimen breaks, in which the specimen is placed on two supports spaced apart by L [ mm ], and a load P [ N ] is applied to the center point between the supports. The 3-point bending strength was determined by averaging the results of the calculation for 10 samples, each using:

3 XPxL/(2 Xw x t ²) (equation 1)

Where PN is the maximum load at break, L mm is the distance between the external supports, w mm is the width of the specimen, and t mm is the thickness of the specimen.

< Porosity >

The porosity of the shaped article was evaluated by a method of JIS R1634 based on a measurement method of the density and the open porosity of the sintered fine ceramic. Specifically, the porosity can be determined by averaging the calculation results of three ceramic structures similar to the sample used in measuring the mechanical strength using { (W3-W1)/(W3-W2) } ×100, where W1 is the dry mass of the shaped article, W2 is the mass in water, and W3 is the saturated mass.

< Proportion of regions containing Crystal Structure and mullite >

The crystal structure of the region constituting the ceramic shaped article is identified by X-ray diffraction measurement, wherein the measurement surface is prepared by polishing the cross section of the middle portion of the shaped article to be measured. Electron Back Scattering Diffraction (EBSD) can be used to identify the position and crystal structure. If smaller regions (phases) are included, the composition and crystal structure can be analyzed in a similar manner using a Transmission Electron Microscope (TEM).

The content of each region in the shape can be calculated by extracting an area of about 230×145 μm from the Al and S i element distribution image obtained by SEM-EDS analysis. The area size is not limited thereto. By calculating the content in the area of 200 μm×100 μm or more in total, variation can be suppressed. The proportion of the region 301 containing alumina, which is a ratio to the entire area, can be calculated by binarizing the Si element distribution image (S i distribution image) so that only the black region remains.

The proportion of the mullite-containing region 302 may be determined by the following procedure. First, an Al element distribution image (Al distribution image) is binarized, a threshold value is set to a higher luminance than that of the mullite-containing region 302, and the total value of the alumina-containing region 301 and the mullite-containing region 302 is calculated. The proportion of the region 302 containing mullite can be calculated by subtracting the proportion of the region 301 containing alumina in the foregoing S i distribution image from this value.

The proportion of the region 401 containing silicon dioxide, which is a ratio to the entire area, can be calculated by binarizing the Al distribution image so that only the black region is extracted.

In order to calculate the proportion of the region 303 containing oxides containing Si and Al, the S i distribution image is first binarized, and the threshold value is set to a luminance higher than that of the region 303 containing oxides containing Si and A1. The total value of the region 401 containing silicon dioxide and the region 303 containing oxide containing S i and Al is then calculated. This ratio can be calculated by subtracting the ratio of the region 401 containing silicon dioxide in the above Al distribution image from the total value.

To maintain high mechanical strength, the region 302 comprising mullite, which is relatively high in mechanical strength, is desirably larger than the region comprising silica or the region comprising oxides comprising Si and Al. Whether the mullite-containing region is large or small can be determined by: the maximum amount of mullite formation, based on the volume of the maximum amount of mullite formation occupied by the mullite actually formed in the ceramic structure, was calculated by referring to the values of the maximum amounts of mullite formation listed in table 1. Specifically, in each of the plurality of cross sections of the ceramic structure, the area ratio of the mullite-containing region 302 was calculated by the above-described method. Next, the obtained values were converted into ratios of the maximum amount of mullite formation calculated with respect to the same molar ratio SiO ₂/Al₂O₃ as the ceramic structure, as shown in table 1. Whether the mullite-containing region is large or small is determined based on the average value of the ratio. Here, the area percentages calculated in the plurality of cross sections are averaged to a value corresponding to the volume percentage.

If the ratio of the mullite-containing region 302 to the maximum amount of mullite formation is 75% by volume or more, a 3-point bending strength of 80[ MPa ] or more can be obtained to construct an easy-to-handle member. For example, the ratio of the mullite-containing region 302 to the maximum amount of mullite formation in the ceramic structure according to the invention shown in fig. 4A to 4C (example 20) was calculated to be 76.0 vol%. The ratio of the mullite-containing region 302 to the maximum amount of mullite formation in the ceramic structure according to the invention shown in fig. 5A to 5C (example 19) was calculated to be 95.0 vol%.

< Analysis of composition >

The content of Si, al, zr, tb and Pr in the powder, shaped article, or ceramic structure is measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), glow Discharge Mass Spectrometry (GDMS), or inductively coupled plasma mass spectrometry (ICP-MS).

Examples

Example 1

Amorphous SiO ₂ powder having an average particle diameter of about 28 μm, al ₂O₃ powder having an average particle diameter of about 20 μm, and SiO powder having an average particle diameter of 4 μm were prepared. The powder was weighed so that SiO ₂ powder was 44.4 mass%, al ₂O₃ powder was 53.5 mass%, and SiO powder was 2.1 mass% (see table 2). The raw material powder had a composition comprising 60 mol% of SiO ₂ converted value and 40 mol% of Al ₂O₃. The weighed powders were mixed in a dry ball mill for 30 minutes to obtain mixed powders.

Next, a shaped article is manufactured by the same process as shown in fig. 1A to 1H. The molded article produced had a rectangular parallelepiped shape of 5mm×42mm×6 mm. The shaped article was formed using 3D SYSTEMS ProX DMP 100 (trade name) equipped with a fiber laser (beam diameter 65 μm, oscillation wavelength 1070 mm) having a maximum power of 50W.

First, a first powder layer of raw material powder of 20 μm thickness was formed on an alumina-based stage 130 using a roller (fig. 1A and 1B).

Next, the powder layer was irradiated with a scanning laser beam of 47.5-W to melt and solidify the raw material powder in a rectangular area of 5mm×42mm, thereby forming a solidified portion 100 (fig. 1C). The drawing speed was 60mm/s and the drawing pitch was 80. Mu.m. The laser beam is scanned so that the drawn line intersects the sides of the rectangle at 45 °.

Next, a new 20 μm thick powder layer was formed on the solidified portion 100 using a roller. The powder layer was irradiated with the scanned laser beam to melt and solidify the raw material powder in a rectangular area of 5mm×42mm, thereby forming a solidified portion 100 (fig. 1D and 1E). Here, the laser light is scanned in a direction orthogonal to the drawing line of the first layer. This procedure was repeated until the cured portion reached a height of 6mm, thereby producing 14 moldings of 42mm×5mm×6mm.

The fabricated shaped article was separated from the alumina-based stage and heated in an electric furnace. Specifically, the shaped article was heated to 1690 ℃ in an atmospheric environment for 2.5 hours and held at 1690 ℃ for 20 minutes. Then, the energization was terminated, and the molded article was cooled to 200 ℃ or lower within 5.0 hours, whereby 14 ceramic structures were obtained.

Three of the obtained ceramic structures were used as samples for porosity measurement. The porosity evaluation showed a porosity of 6.8%.

The composition of the resulting ceramic structure was measured by ICP-AES. S i was found to be a calculated amount of 43.9 mass% of S iO ₂ and Al was found to be a calculated amount of 56.1 mass% of Al ₂O₃. The molar ratio of SiO ₂/Al₂O₃ was 0.57/0.43 (see Table 3).

Next, in order to analyze the region constituting the ceramic structure and perform a 3-point bending strength test and a porosity measurement, the remaining 11 ceramic structures were cut and polished into 40mm×4mm×3mm samples. Two long sides of one processed sample were cut out using a wire saw to leave the middle portion of the ceramic structure, thereby obtaining a 10mm×4mm×3mm specimen. The sample was rough-ground to reduce the 3mm side to about 1.5mm, and then mirror-polished to obtain an observation surface of 10mm×4 mm.

X-ray diffraction, SEM observation, SEM-EDS and EBSD were performed on the observation surface. SEM-EDS and EBSD were performed to analyze 10 different positions with field of view dimensions of 100 μm by 100 μm, to map the composition and crystal structure. Comprehensive analysis of the results shows that the ceramic structure includes four regions, namely, a region containing silica (SiO ₂), a region containing an oxide containing S i and Al, a region containing mullite, and a region containing alumina. A region containing an oxide containing S i and Al, which is presumed to be a crack-repairing region, was also observed. In table 3, the presence of a region is indicated by "Σ", and the presence of a region is not indicated by "×". Analysis showed that the silica in the silica-containing region was cristobalite and that both the mullite-containing region and the alumina-containing region were crystalline.

The remaining 10 samples for the strength test were subjected to the flexural strength test. The 3-point bending strength was calculated to be 103[ MPa ].

Table 3 shows the evaluation of Si, al, tb, pr and Zr contents (mass percent in terms of oxide), the oxide conversion molar ratio S iO ₂/Al₂O₃, the porosity and the 3-point bending strength of the ceramic structure.

Table 2 shows the weighing values of the raw material powders SiO ₂、Al₂O₃、SiO、Tb₄O₇ and Pr ₆O₁₁. Table 3 shows the contents of Si, al, tb, pr and Zr, expressed as values converted to S iO ₂、Al₂O₃、Tb₂O₃、Pr₂O₃ and ZrO ₂, respectively.

TABLE 2

TABLE 3 Table 3

Examples 2 to 6

A ceramic structure was produced in a similar manner to example 1, except that the mass ratio of the sio ₂ powder, the Al ₂O₃ powder, and the sio powder included in the raw material powder was changed. Table 2 lists the mass ratios of the raw material powders in the respective examples. Table 3 lists the porosity, mass ratio of SiO ₂ and Al ₂O₃, S iO ₂/Al₂O₃ molar ratio and 3 point flexural strength and sintering temperature of the obtained ceramic structures. Table 3 also lists the presence or absence of four regions, namely, a region comprising silica, a region comprising oxides comprising Si and Al, a region comprising mullite, and a region comprising alumina. Analysis of the crystal structure showed that all ceramic structures contained cristobalite in the silica-containing region and crystals in the mullite-containing region and alumina-containing region. In all the ceramic structures, a region including a region containing oxides of Si and Al was observed, and this region was presumed to be a crack repairing portion.

Example 7

A ceramic structure was produced in a similar manner to example 1, except that the average particle size of the sio ₂ powder was changed to 17 μm. Table 3 shows the mass ratio of SiO ₂ and Al ₂O₃, the SiO ₂/Al₂O₃ molar ratio, the presence or absence of the four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the regions containing silica contained cristobalite, the regions containing mullite and the regions containing alumina contained crystals as well. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion. The porosity was 5.0%, which is lower than in examples 1-6. The ratio of the actual area containing mullite to the maximum amount of mullite formed is as high as 78.9 volume percent and shows a correlation with the 3-point flexural strength of 108[ mpa ].

Example 8

A ceramic structure was produced in a similar manner to example 1, except that the average particle size of the sio ₂ powder was changed to 10 μm. Table 3 shows the mass ratio of SiO ₂ and Al ₂O₃, the SiO ₂/Al₂O₃ molar ratio, the presence or absence of the four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion.

The porosity was 3.1%, which is lower than in the other examples. The 3-point bending strength is as high as 113[ MPa ]. Also, the ratio of the actual region containing mullite to the maximum amount of mullite formed was 91.8 vol%, and showed a correlation with high strength.

Example 9

A ceramic structure was produced in a similar manner to example 1, except that the average particle size of the sio ₂ powder was changed to an average particle size of cristobalite of 38 μm, and the sintering temperature of step (iii) was changed to 1680 ℃. The obtained ceramic structures were evaluated in a similar manner to the other examples, and table 3 shows the evaluation results. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing an oxide containing S i and Al was also observed, and this region was presumed to be a crack-repairing portion.

Example 10

A ceramic structure was produced in a similar manner to example 7, except that the absorber was changed to Tb ₄O₇ powder having an average particle diameter of 4 μm, and SiO ₂ powder, al ₂O₃ powder and Tb ₄O₇ powder were mixed in the mass ratio shown in table 2, and the sintering temperature of step (iii) was changed to 1680 ℃. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing an oxide containing S i and Al was also observed, and this region was presumed to be a crack-repairing portion.

Example 11

A ceramic structure was produced in a similar manner to example 8, except that the absorber was changed to Pr ₆O₁₁ powder having an average particle diameter of 4 μm. Table 3 shows the mass ratio of S i and Al, the SiO ₂/Al₂ O molar ratio, the presence or absence of the four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing an oxide containing S i and Al was also observed, and this region was presumed to be a crack-repairing portion.

Example 12

A ceramic structure was produced in a similar manner to example 1, except that the cracks in the shaped article were impregnated with a solution containing a zirconium component prior to step (iii). The solution containing the zirconium component was prepared in the following manner. A solution was prepared by dissolving 85 mass% of zirconium butoxide (zirconium (IV) butoxide [ hereinafter referred to as Zr (O-n-Bu) 4 ]) in 1-butanol. Zr (O-n-Bu) 4 solution was dissolved in 2-propanol (isopropyl alcohol [ IPA ]), and ethyl acetoacetate (EAcAc) was added as a stabilizer. The molar ratio of the components was Zr (O-n-Bu) 4:IPA: EAcAc=1:15:2. The solution was then stirred at room temperature for about 3 hours, thereby preparing a solution containing the zirconium component.

Table 3 shows the mass ratio of SiO ₂ and Al ₂O₃, the SiO ₂/Al₂O₃ molar ratio, the presence or absence of the four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. The analysis of the crystal structure showed that the regions containing silica contained cristobalite, the regions containing mullite and the regions containing alumina contained crystals as well. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion. Further, it was observed that a region containing zirconia was dispersed with a crack-repairing portion and a connecting region containing an oxide containing S i and Al.

A high 3-point flexural strength was obtained compared to example 1, in which the shaping article was not impregnated with the repair solution, under the same manufacturing conditions but with the difference. This is presumably due to an increase in the area containing zirconia, which leads to an increase in the complexity of the area constituting the ceramic structure.

Example 13

A ceramic structure was manufactured in a similar manner to example 7, except that the mass ratios of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder were changed to the values shown in table 2. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well.

It was observed that the ceramic structure included five regions, namely, a region containing silicon dioxide, a region containing oxides containing Si and Al, a region containing mullite, a region containing alumina, and a region containing zirconia. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion. A high 3-point flexural strength was obtained compared to example 2, in which the shaped article was not impregnated with the repair solution, with the same manufacturing conditions.

Example 14

A ceramic structure was manufactured in a similar manner to example 7, except that the mass ratios of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder were changed to the values shown in table 2. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. The silica-containing region contains cristobalite, and the mullite-containing region and the alumina-containing region also contain crystals.

It was observed that the ceramic structure included five regions, namely, a region containing silicon dioxide, a region containing oxides containing Si and Al, a region containing mullite, a region containing alumina, and a region containing zirconia. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion. A high 3-point flexural strength was obtained compared to example 3, in which the shaped article was not impregnated with the repair solution, with the same manufacturing conditions.

Example 15

It was observed that the ceramic structure included five regions, namely, a region containing silicon dioxide, a region containing oxides containing Si and Al, a region containing mullite, a region containing alumina, and a region containing zirconia. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion. A high 3-point flexural strength was obtained compared to example 4, which was identical in manufacturing conditions except that the shaped article was not impregnated with the repair solution and the particle size of the silica was different.

Example 16

A ceramic structure was produced in a similar manner to example 1, except that the sintering temperature of step (iii) was changed to 1650 ℃. Table 3 shows the mass ratio of SiO ₂ and Al ₂O₃, the SiO ₂/Al₂O₃ molar ratio, the presence or absence of the four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing an oxide containing S i and Al was also observed, and this region was presumed to be a crack-repairing portion.

Examples 17 to 19

In examples 17, 18 and 19, ceramic structures were produced in a similar manner to example 7, except that the sintering temperature holding times in step (iii) were set to 40 minutes, 80 minutes and 120 minutes, respectively. Table 3 shows the mass ratio of SiO ₂ and Al ₂O₃, the SiO ₂/Al₂O₃ molar ratio, the presence or absence of the four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure.

In the ceramic structures according to examples 17 to 19, no region containing silica was detected, and three regions, i.e., a region containing oxides containing Si and Al, a region containing mullite, and a region containing alumina were observed.

Analysis of the crystal structure showed that both the mullite-containing region and the alumina-containing region included crystals. A region containing an oxide containing S i and Al was also observed, and this region was presumed to be a crack-repairing portion.

Specifically, in example 17, the ratio of the mullite-containing region to the producible amount of mullite was as high as 83.3 vol%, and the correlation with the 3-point bending strength of 111[ mpa ] was shown. Fig. 5A to 5C are an SEM image, an EDS Al element distribution image, and an EDS Si element distribution image, respectively, of the ceramic structure obtained in example 19. The ratio of mullite-containing region to mullite producibility in example 19 calculated using fig. 5B and 5C is as high as 95.0 vol%, and the 3-point flexural strength is as high as 107[ mpa ].

In examples 7, 17 and 19, the proportion of the mullite-containing region was 75% by volume or higher, and tended to increase as the sintering time increased. In addition, the 3-point bending strength is kept at a high level. In examples 17 and 19, it was confirmed that increasing the heat treatment time reduced the porosity compared to example 7.

It was thus confirmed that the mullite-containing region having a relatively high mechanical strength occupies a wider area than the silica-containing region having a relatively low mechanical strength and the region containing the oxide containing Si and Al. This state is particularly desirable in terms of maintaining high mechanical strength.

Example 20

In example 20, a ceramic structure was produced in a similar manner to example 7, except that the mass ratio of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder was changed. Table 2 shows the mass ratios of the raw material powders in the respective examples. Table 3 shows the porosity, mass ratio of sio ₂ and Al ₂O₃, sio ₂/Al₂O₃ molar ratio and 3-point bending strength of the obtained ceramic structure, and sintering temperature. Table 3 further shows the presence or absence of four regions, namely, a region containing silica, a region containing oxides containing S i and Al, a region containing mullite, and a region containing alumina. Fig. 4A shows an SEM image of the obtained ceramic structure. Fig. 4B and 4C show EDS Al element distribution images and EDS si element distribution images, respectively.

The crystal structure analysis and SEM-EDS analysis revealed that, in the ceramic structure, the region 401 containing silica contained cristobalite, and the region 302 containing mullite and the region 301 containing alumina contained crystals as well. There is also a region 303 containing an oxide containing S i and Al, which is presumed to be a crack-repairing portion CR.

The ratio of mullite-containing region to mullite producible amount is as high as 76.0 vol% and shows a correlation with 3-point flexural strength of 93[ mpa ].

Comparative example 1

A ceramic structure was manufactured in a similar manner to example 1, except that the mass ratios of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder were changed to the values shown in table 2. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion.

Four kinds of regions were observed in the ceramic structure, namely, a region containing silicon dioxide, a region containing oxides containing Si and Al, a region containing mullite, and a region containing alumina. However, the 3-point bending strength is as low as 25[ mpa ], which is not a suitable value for application as a structural member.

The porosity of 16.3% is higher than in the examples. Therefore, the low 3-point bending strength is considered to be due to the high porosity or low compactability of the ceramic structure. The high porosity is believed to be due to the low alumina content in the raw powder. During the laser beam irradiation of step (ii), it is presumed that the molten alumina cannot diffuse around the shape, resulting in insufficient melting of the silica.

Comparative example 2

A ceramic structure was manufactured in a similar manner to example 1, except that the mass ratios of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder were changed to the values shown in table 2. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. The silica-containing region contains cristobalite, and the mullite-containing region and the alumina-containing region also contain crystals. A region containing oxides containing Si and Al was also observed, and this region was presumed to be a crack repairing portion.

Four kinds of regions were observed in the ceramic structure, namely, a region containing silicon dioxide, a region containing oxides containing Si and Al, a region containing mullite, and a region containing alumina. However, the 3-point bending strength is as low as 28[ mpa ], which is not a suitable value for application as a structural member.

In comparative example 2, the porosity was as high as 13.4%. As in comparative example 1, it is presumed that this is due to insufficient melting of silica, which is caused by low alumina content in the raw material powder having a molar ratio of SiO ₂/Al₂O₃ of 0.75/0.25.

Comparative example 3

A ceramic structure was manufactured in a similar manner to example 1, except that the mass ratios of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder were changed to the values shown in table 2. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the sintering temperature of the obtained ceramic structure. Analysis of the crystal structure showed that the silica-containing region contained cristobalite, the mullite-containing region and the alumina-containing region contained crystals as well. A region containing an oxide containing S i and Al was also observed, and this region was presumed to be a crack-repairing portion. However, the number of such areas is very small compared to examples 1 to 16.

The 3-point bending strength of comparative example 3 is as low as 41[ MPa ], which is not a suitable value for application as a structural member. The high porosity is believed to be due to the low silica content in the raw material powder, which prevents the composition melted during the heat treatment of step (iii) that contains the regions containing S i and the oxides of Al from diffusing throughout the crack and prevents the crack from being sufficiently repaired.

Comparative example 4

A ceramic structure was manufactured in a similar manner to example 1, except that the mass ratios of SiO ₂ powder, al ₂O₃ powder, and SiO powder included in the raw material powder were changed to the values shown in table 2. Table 3 shows the mass ratio of sio ₂ and Al ₂O₃, the sio ₂/Al₂O₃ molar ratio, the presence or absence of four regions, the porosity and 3-point bending strength, and the heating temperature of the obtained ceramic structure. No region containing the oxide containing S i and Al was observed, and this region was presumed to be a crack-repairing portion.

The 3-point bending strength of comparative example 4 is as low as 41[ MPa ], which is not a suitable value for application as a structural member. The reason for the high porosity is considered to be that the phenomenon of repairing cracks in the shaped article does not sufficiently occur during the heat treatment of step (iii) because the raw material powder having a SiO ₂/Al₂O₃ molar ratio of 0.03/0.97 contains little silica.

The present invention is not limited to the foregoing exemplary embodiments, and various changes and modifications may be made without departing from the spirit and scope of the present invention. Accordingly, the following claims are appended to illustrate the scope of the invention.

The present application claims priority based on Japanese patent application Nos. 2021-184895 and 2022-No. 11-No. 9 filed on 11/12 of 2021 and 2022, which are incorporated herein by reference in their entireties.

Reference numerals

100. Curing part

101. Powder

102. Powder layer

103. Uncured powder

110. Shaping article

130. Base station

151 Workbench

152. Roller

180. Laser beam source

181. Scanner unit

190. Liquid nozzle

201. Cladding nozzle

202. Powder supply hole

203. Laser beam

301. Regions comprising alumina

302. Areas containing mullite

303 Comprises a region comprising oxides of Si and Al

401 Region comprising silicon dioxide

CR crack repairing part

Claims

1. A ceramic structure comprising at least:

a region comprising mullite;

a region containing oxides of Si and Al that are more rich in Si than mullite; and

A region comprising aluminum oxide and having a surface,

Wherein the oxide conversion molar ratio SiO ₂/Al₂O₃ satisfies 0.1/0.9 to 0.7/0.3.

2. The ceramic structure of claim 1, wherein a cross section of the ceramic structure comprises: the region containing an oxide containing Si and Al has an average width of 1 μm or more and a ratio of a length to an average width of 10 or more.

3. The ceramic structure according to claim 1, wherein a ratio of a region containing mullite to the entire ceramic structure satisfies 75 vol.% or more of a maximum amount of mullite calculated from an oxide-converted molar ratio SiO ₂/Al₂O₃ of the ceramic structure.

4. A ceramic structure according to any one of claims 1 to 3, wherein the region containing oxides containing Si and Al has an oxide conversion molar ratio SiO ₂/Al₂O₃ of 12 to 24.

5. The ceramic structure of claim 1, wherein the region comprising mullite is crystalline.

6. The ceramic structure of claim 1, wherein the region comprising alumina is crystalline.

7. The ceramic structure of claim 1, further comprising a region comprising silica.

8. The ceramic structure of claim 1, further comprising a region comprising zirconia.

9. A method for manufacturing a ceramic structure, comprising the steps of:

(i) Providing a powder containing silica particles, alumina particles, and an absorber exhibiting higher light absorption than silica and alumina at a wavelength of light included in the irradiation laser beam, the oxide conversion molar ratio SiO ₂/Al₂O₃ of the powder satisfying 0.1/0.9 to 0.7/0.3;

(Iii) The shaped article obtained by carrying out steps (i) and (ii) a plurality of times is subjected to a heat treatment such that a maximum temperature of 1595 ℃ or more and below 1730 ℃ is reached.

10. The method for producing a ceramic structure according to claim 9, wherein in step (iii), the heat treatment is performed so that the maximum temperature reached is 1600 ℃ or higher and lower than 1720 ℃.

11. The method for producing a ceramic structure according to claim 9, wherein in step (iii), the maximum temperature reached is maintained for one minute or more and four hours or less.

12. The method for manufacturing a ceramic structure according to claim 9, wherein the absorption capacity of the absorber for a wavelength of light included in the laser beam is 10% or more.

13. The method for manufacturing a ceramic structure according to claim 12, wherein the absorption capacity of the absorber for a wavelength of light included in the laser beam is 40% or more.

14. The method for manufacturing a ceramic structure according to claim 9, wherein the absorber is SiO.

15. The method for producing a ceramic structure according to claim 9, wherein the silica particles have an average particle diameter of 5 μm or more and 200 μm or less, and the absorber has an average particle diameter of 1 μm or more and less than 10 μm.

16. The method for producing a ceramic structure according to claim 9, wherein the absorber is added in an amount of 0.5% by volume or more and 10% by volume or less of the powder.

17. The method for manufacturing a ceramic structure according to claim 9, further comprising a step of impregnating the shaped article with a solution containing a metal element before step (iii).

18. The method for producing a ceramic structure according to claim 17, wherein the solution containing a metal element contains zirconium.

19. The method for manufacturing a ceramic structure according to claim 17, wherein the highest temperature reached by the shaping object in the heat treatment of step (iii) is lower than the melting point of silica and higher than the eutectic temperature of the oxide of the metal element and silica.

20. The method for manufacturing a ceramic structure according to claim 17, wherein the metal element content in the powder is less than 3.0 mass%.