Ceramic article manufacturing method, metal component-containing liquid, ceramic article manufacturing kit, and ceramic article

Abstract

To provide, in manufacturing a ceramic article using addition manufacturing technology, a ceramic article manufacturing method and a metal component-containing liquid for achieving an improvement in mechanical strength of a modeled product while achieving a high model accuracy and a shape accuracy.SOLUTION: Provided is a ceramic article manufacturing method, and which is characterized by having: (i) a step in which a ceramic modeled product is obtained by energy beam irradiating a powder containing ceramics as main component to sinter or melt and solidify, and to form a solidified part; (ii) a step in which a metal element-containing inorganic particle-containing metal component-containing liquid is absorbed into the ceramic modeled product; and (iii) a step in which the ceramic modeled product into which the metal component-containing liquid is absorbed is heat treated.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an additive manufacturing technique, particularly a method for manufacturing ceramic articles using a powder bed fusion bonding method or a directed energy deposition method.

Background Art

[0002] In applications where prototypes are produced or small quantities of parts are manufactured in a short time, an additive manufacturing technique is widespread in which an energy beam is irradiated onto raw material powder based on three-dimensional data of an object to be formed, and the raw material powder is bonded to obtain a desired formed object. In forming using metal powder (metal forming), the powder bed fusion bonding method is widely adopted, and dense and diverse metal formed objects are obtained. The high density of the metal formed object is achieved by effectively melting and solidifying the metal powder. Based on the success of such metal forming, the expansion of additive manufacturing technology to ceramic materials has been discussed, and many efforts have been reported.

[0003] However, common metal oxides such as aluminum oxide and zirconium oxide have a low absorption ability for laser light, unlike metals. Therefore, in order to melt metal oxide powder in the same manner as metal powder, more energy needs to be input. However, since the laser light diffuses and melting becomes non-uniform, it has been difficult to obtain high forming accuracy.

[0004] In addition, since metal oxides have a low thermal conductivity, large thermal stresses are generated during solidification, and the cracks formed thereby have led to a decrease in the mechanical strength of the formed object.

[0005] Under such circumstances, Patent Document 1 describes that by heating the powder to be melted and the powder around it to a degree that does not melt with preheating laser light before and after irradiating the shaping laser light, the thermal stress is relaxed. Furthermore, a technique is disclosed in which by using a powder having an Al2O3-ZrO2 eutectic system (eutectic system) composition to lower the melting point, the energy required for melting is reduced to relax the thermal stress, and by forming a phase separation structure, the propagation of cracks is suppressed. Furthermore, a technique is disclosed in which glass powder is melted and infiltrated into the shaped article, and the mechanical strength of the shaped article is improved by filling the cracks with glass.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] According to Patent Document 1, by shaping while preheating, a shaped article with excellent mechanical strength is obtained. However, due to the light diffused from the irradiation part of the shaping laser light, a part of the powder near the irradiation part, which has reached a certain high temperature by preheating, may be heated up and melted. Therefore, it is difficult to selectively melt the irradiation part of the shaping laser light to obtain high shaping accuracy because the part where the shaping laser light is not irradiated is shaped. Also, after shaping without preheating and infiltrating glass, the bending strength of the shaped article is as low as less than 50 MPa even when using a powder having an Al2O3-ZrO2 eutectic system composition.

[0008] In order to address such problems, the present invention provides a method for manufacturing a ceramic article that achieves high shaping accuracy and shape accuracy while improving the mechanical strength of the shaped article in the manufacture of a ceramic article using additive manufacturing technology. Furthermore, a metal component-containing liquid used in such a manufacturing method and a ceramic article manufacturing kit are provided.

[0009] Furthermore, the present invention provides a ceramic article that can have an advantageous free form when the additive manufacturing technique is applied, and has excellent shaping accuracy, dimensional accuracy, and mechanical strength.

Means for Solving the Problems

[0010] A first aspect of the present invention is a method for manufacturing a ceramic article, (i) irradiating a powder mainly composed of ceramics with an energy beam to sinter, melt, and solidify to form a solidified portion, thereby obtaining a ceramic shaped article; (ii) causing the ceramic shaped article to absorb a metal component-containing liquid containing inorganic particles containing a metal element; (iii) heat-treating the ceramic shaped article that has absorbed the metal component-containing liquid, characterized by comprising these steps.

[0011] A second aspect of the present invention is a metal component-containing liquid used for crack repair of a ceramic shaped article formed by an additive manufacturing method using an energy beam, wherein the metal component-containing liquid contains a solvent and inorganic particles containing a metal element with an average particle size of 300 nm or less, and an oxide of the metal element can form a eutectic with at least one kind of compound contained in the ceramic shaped article.

[0012] A third aspect of the present invention is a ceramic article manufacturing kit for manufacturing a ceramic article by an additive manufacturing method using an energy beam, including a powder mainly composed of ceramics and a metal component-containing liquid, wherein the metal component-containing liquid contains inorganic particles containing a metal element and a solvent, and an oxide of the metal element can form a eutectic with at least one kind of compound contained in a ceramic shaped article formed from the powder.

[0013] A fourth aspect of the present invention is a ceramic article manufactured by an additive manufacturing technique, which includes three phases having at least one common metal element, and at least two of the three phases are phases of composite compounds.

Advantages of the Invention

[0014] According to the present invention, it becomes possible to manufacture a ceramic article with high precision and excellent mechanical strength by using an additive manufacturing method.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following specific examples at all.

[0017] The method for manufacturing a ceramic article according to the present invention can provide a ceramic article having excellent shaping accuracy, shape accuracy, and mechanical strength by appropriately treating a ceramic shaped article formed by an additive manufacturing method using a metal component-containing liquid. Specifically, after absorbing the metal component-containing liquid into the cracks of the ceramic shaped article formed by the additive manufacturing method, heat treatment is performed to locally melt only the vicinity of the crack portion, reducing or eliminating the crack.

[0018] The additive manufacturing technology is a process of forming an object by bonding materials based on three-dimensional shape data of a shaping model to be shaped. In many cases, a method of joining materials in layers is used. By using the additive manufacturing technology, it is possible to realize ceramic articles having complex shapes and fine shapes, which were difficult to produce by conventional mold forming methods or subtractive manufacturing methods such as machining. The method for manufacturing a ceramic article according to the present invention includes an additive manufacturing technology of a powder bed fusion bonding method or a directed energy deposition method (so-called cladding method). Further, the metal component-containing liquid of the present invention is preferably used for a shaped article formed by additive manufacturing of a powder bed fusion bonding method or a directed energy deposition method.

[0019] First, after explaining the method for manufacturing a ceramic article including a treatment step using a metal component-containing liquid, the ceramic article manufactured by the manufacturing method and the kit for manufacturing a ceramic article will be explained.

[0020] <Method for Manufacturing Ceramic Article> The method for manufacturing a ceramic article of the present invention will be described. The manufacturing method of the present invention is characterized by having the following three steps. (i) A ceramic shaped article is obtained by irradiating a powder mainly composed of ceramics with an energy beam to sinter, melt, and solidify it to form a solidified portion. (ii) The ceramic shaped article is caused to absorb a metal component-containing liquid containing inorganic particles containing a metal element as a component. (iii) Heat-treat the ceramic shaped article that has absorbed the metal component-containing liquid.

[0021] Hereinafter, taking the case of performing shaping using a powder containing aluminum oxide, which is a general-purpose structural ceramic, as the main component as an example, each step will be specifically described. However, the technical idea is not limited to the powder containing aluminum oxide as the main component. It can also be applied to shaping using a powder containing silicon oxide as the main component or a powder having other ceramics as the main component. Further, it is also applicable to shaping using a powder obtained by mixing a plurality of ceramics (for example, aluminum oxide, silicon oxide, magnesium oxide, etc.) so that a target ceramic (for example, mullite, cordierite, etc.) is formed as the shaped article.

[0022] In the present invention, the powder mainly composed of ceramics for shaping a ceramic shaped article only needs to be composed of inorganic compound powder, and not only ceramics defined as sintered polycrystals but also powders composed of amorphous or single crystals may be used. Further, when sintering or melting and solidifying, it is preferable that the powder does not contain an organic component such as a binder. This is because there is a risk of hindering the bonding between particles. From such a viewpoint, the amount of carbon in the powder is preferably 2000 ppm or less, and more preferably 1000 ppm or less.

[0023] In the present invention, among the objects (powder, shaped article or article) for discussing components, the component contained in the largest molar ratio is called the main component. The notation "main component" is also used synonymously with the main component. The sub-component refers to a component other than the main component, and is added to facilitate shaping, such as a sintering aid or an infrared absorber.

[0024] <Step (i)> This is a step of obtaining a ceramic shaped article by irradiating a powder mainly composed of ceramics with an energy beam to sinter or melt and solidify it to form a solidified portion.

[0025] The basic flow of the shaping procedure using the powder bed fusion bonding method will be described with reference to FIG. 1. First, powder 101 mainly composed of ceramics is placed on a base 130 installed on a stage 151, and a powder layer 102 is formed using a roller 152 (FIGS. 1(a) and (b)). On the surface of the powder layer 102, an energy beam emitted from an energy beam source 180 is irradiated based on three-dimensional shape data of the article to be manufactured while being scanned by a scanner unit 181. In the irradiation range 182 of the energy beam, the powder is sintered, or melted and solidified, and a solidified portion 100 is formed (FIG. 1(c)). Next, the stage 151 is lowered, and a powder layer 102 is newly formed on the shaped article 100 (FIG. 1(d)). The newly formed powder layer 102 is irradiated with an energy beam in the same manner as in FIG. 1(c), and a solidified portion 100 is formed in the irradiation range. At this time, if the output of the energy beam is adjusted to such an extent that the surface layer of the previously formed solidified portion on the side of the newly formed powder layer 102 melts, the previously formed solidified portion and the subsequently formed solidified portion can be joined to each other. By repeating these series of steps, a shaped article 110 having a desired shape in which the solidified portions 100 formed for each layer are joined to each other and integrated is formed (FIGS. 1(e) and (f)). Finally, the unsolidified powder 103 is removed, and if necessary, unnecessary portions of the shaped article are removed and the shaped article is separated from the base (FIGS. 1(g) and (h)).

[0026] Next, the basic flow of the shaping procedure using the cladding method will be described with reference to FIG. 2. In the cladding method, powder is ejected from a plurality of powder supply holes 202 in a cladding nozzle 201, and an energy beam 203 is irradiated to the region where these powders converge, and an additional solidified portion 100 is formed at a desired location (FIG. 2(a)). At this time, similar to the powder bed fusion bonding method, by adjusting the output of the energy beam 203 to such an extent that the surface layer of the base melts, such steps are repeated to obtain a shaped article 110 having a desired shape in which the solidified portions are integrated (FIGS. 2(b) and (c)). Finally, if necessary, unnecessary portions of the shaped article are removed and the shaped article is separated from the base.

[0027] In any method, when a powder is irradiated with an energy beam, the powder absorbs the energy, which is then converted into heat and the powder melts. Then, in the region where the energy beam has passed and the irradiation has ended, the melted part is cooled by the surrounding atmosphere and the adjacent parts and sintered or solidified to form a solidified part. At this time, due to the rapid cooling during the solidification process of the melted part, stress is generated on the surface layer and inside of the shaped object, and innumerable cracks are formed.

[0028] As the energy beam to be used, a light source having an appropriate wavelength is selected in view of the absorption characteristics of the powder. In order to perform high-precision shaping, it is preferable to employ a laser beam or an electron beam with a narrowed beam diameter and high directivity. From the viewpoint of versatility, YAG lasers and fiber lasers in the 1-μm wavelength band, CO2 lasers in the 10-μm wavelength band, etc. can be cited as suitable energy beams.

[0029] (Powder mainly composed of ceramics) Here, a powder mainly composed of aluminum oxide (Al2O3), which is a common structural ceramic (hereinafter sometimes referred to as a raw material powder), will be described in detail as an example. The powder mainly composed of aluminum oxide preferably contains, as a sub-component, an oxide of a rare earth element that forms a eutectic composition with aluminum oxide. Specifically, it is particularly preferable to contain at least one selected from gadolinium oxide (Gd2O3), yttrium oxide (Y2O3), terbium oxide (Tb2O3), and praseodymium oxide (Pr2O3). For example, when the raw material powder contains gadolinium oxide that forms a eutectic composition with aluminum oxide, three eutectic compositions exist, and the eutectic points in the vicinity of each of the three eutectic compositions are lower than the melting point of pure aluminum oxide and the melting point of pure gadolinium oxide. As a result, the powder can be melted with less heat, and the diffusion of energy within the powder is suppressed, so the shaping accuracy is improved. In addition, when the raw material powder contains gadolinium oxide, the shaped article has a phase separation structure composed of two or more phases. Thereby, the propagation of cracks is suppressed, and the mechanical strength of the shaped article is improved. The same effects as in the case of gadolinium oxide can be obtained when other rare earth element oxides such as yttrium oxide are included.

[0030] When the energy beam is a laser beam, sufficient energy absorption by the powder suppresses the spread of heat in the powder and makes it local, reducing the influence of heat on the non-shaped part, so the shaping accuracy is improved. For example, when using a Nd:YAG laser or a fiber laser in the 1μm wavelength band, the powder is doped with terbium oxide (Tb4O7), praseodymium oxide (Pr6O 11)、Ti2O3, TiO, SiO, 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, Si3N4, AlN, borides, silicides, etc., which show good energy absorption, are more preferably contained as sub-components. These components serve as absorbers when using a Nd:YAG laser or a fiber laser in the 1μm wavelength band. The raw material powder contains, in addition to rare earth element compounds such as terbium oxide (Tb4O7) and praseodymium oxide (Pr6O 11 ), other rare earth elements with low energy absorption for the laser beam, which is also preferable. An absorber refers to a component (element or compound) that shows a higher absorption ability than the main component for light with a wavelength contained in the laser used for shaping. The absorption ability of the absorber is preferably 10% or more, more preferably 40% or more, and even more preferably 60% or more for light with a wavelength contained in the laser beam of the wavelength used.

[0031] From the above viewpoints, particularly suitable raw material powders include Al2O3-Gd2O3, Al2O3-GdAlO3, Al2O3-Tb4O7, Al2O3-Gd2O3-Tb4O7, Al2O3-GdAlO3-Tb4O7, Al2O3-Pr6O 11 , Al2O3-Gd2O3-Pr6O 11 , Al2O3-GdAlO3-Pr6O 11 , Al2O3-Y2O3, Al2O3-YAlO3, Al2O3-Y3Al5O 12 , Al2O3-Y2O3-Tb4O7, Al2O3-YAlO3-Tb4O7, Al2O3-Y3Al5O 12 -Tb4O7, Al2O3-Y2O3-Pr6O 11 , Al2O3-YAlO3-Pr6O 11 , Al2O3-Y3Al5O 12 -Pr6O 11, Al2O3-ZrO2, Al2O3-ZrO2-Tb4O7, Al2O3-ZrO2-Pr6O 11 , Al2O3-SiO, Al2O3-Gd2O3-SiO, Al2O3-GdAlO3-SiO, Al2O3-Y2O3-SiO, Al2O3-YAlO3-SiO, Al2O3-Y3Al5O 12 -SiO, Al2O3-ZrO2-SiO, SiO2-Tb4O7, SiO2-Pr6O 11 , (MgO-Al2O3-SiO2)-Tb4O7, (MgO-Al2O3-SiO2)-Pr6O 11 , (Al2O3-SiO2)-Tb4O7, (Al2O3-SiO2)-Pr6O 11 and the like.

[0032] The powder mainly composed of ceramics preferably contains a eutectic-composable composition in a ratio forming a eutectic composition. The eutectic composition is the composition at the eutectic point shown in the phase diagram. However, in the shaping process using an energy beam, since the heating state and the cooling state occur very rapidly, a eutectic structure having a phase separation structure is formed even with a composition deviated from the eutectic point. Therefore, the eutectic composition in the production method of the present invention is preferably defined as a composition range in which a eutectic structure is formed, and includes a range of ±10 mol% with respect to the eutectic composition in the phase diagram. Similarly, in the case of a powder whose main component is other than aluminum oxide, it is preferable that it contains a eutectic-composable composition in a ratio forming a eutectic composition.

[0033] The fact that component X and another component Y can form a eutectic may be expressed as "component X and component Y are in a eutectic relationship". A eutectic is a mixture of two or more crystals that simultaneously crystallize from a liquid containing two or more components. "Component X and component Y can form a eutectic" is synonymous with "component X and component Y have a eutectic state". When having a eutectic state, a eutectic point (also referred to as a eutectic melting point) exists. The eutectic point is the temperature at which a eutectic occurs and corresponds to the minimum value of the liquid-phase curve in a state diagram with temperature on the vertical axis and component composition ratio on the horizontal axis. The composition corresponding to the eutectic point is called the eutectic composition (or eutectic melting composition). Therefore, the eutectic point of component X and component Y is lower than the melting points of component X and component Y respectively.

[0034] In addition, in this specification, when expressing materials using chemical formulas such as the above-mentioned Al2O3 and Tb4O7, etc., as long as the gist of the present invention is satisfied, it is not necessary for the elemental composition ratio of the actual material to exactly match the ratio of the chemical formula. That is, the valence of the metal elements constituting a certain material may be somewhat different from the valence assumed from the chemical formula. For example, in the case of SiO, even if the constituent element ratio of the absorber is Si:O = 1:1.30, it is included in the present invention because it exhibits good energy absorption with respect to the laser beam. From the viewpoint of obtaining sufficient light absorption ability, a more preferable elemental composition ratio is such that the deviation from the stoichiometric ratio is within ±15%.

[0035] <Step (ii)> In step (ii), the ceramic shaped article obtained in step (i) is made to absorb a metal component-containing liquid containing inorganic particles containing a metal element. In the case of a direct shaping method such as a powder bed fusion bonding method or a cladding method, the portion where the powder is melted by the energy beam irradiation is cooled by the surroundings and solidifies, forming a solidified portion. In the case of ceramics, many cracks occur in the solidified portion. This is considered to be due to the thermal stress caused by the temperature difference generated between the non-solidified portion and the solidified portion because the thermal conductivity of the material itself is small. Since such solidified portions are joined to each other to form a shaped article, the cracks are distributed in a random pattern like a chessboard in a shape substantially dependent on the scanning direction of the energy beam over the entire shaped article. When the cross-section of the shaped article is observed with a scanning electron microscope or the like, many of the cracks have a width ranging from several nm to several μm. Also, the lengths of the cracks vary from several μm to several mm. This crack is considered to be the main cause of reducing the mechanical strength of the shaped article.

[0036] When a liquid containing a metal component is brought into contact with a shaped article having a crack as described above, the liquid containing the metal component is absorbed into the crack of the shaped article, and inorganic particles containing metal elements are dispersed. By heating the shaped article that has absorbed the liquid containing the metal component within a predetermined temperature range in step (iii) described below, it is possible to selectively melt only the vicinity of the crack. By performing such treatment, it is possible to reduce the cracks present in the shaped article while suppressing the shape change of the shaped article, and improve the mechanical strength of the shaped article.

[0037] (Liquid containing a metal component) The liquid containing the metal component will be described.

[0038] The liquid containing the metal component used in step (ii) contains at least inorganic particles containing metal elements and a solvent. In the step of causing the shaped article to absorb the liquid containing the metal component, it is not necessary to densely fill the cracks of the shaped article with inorganic particles; it is sufficient to have the inorganic particles present substantially uniformly on the surface of the shaped article facing the cracks of the shaped article. In order for the inorganic particles to cover the entire crack, it is preferable that the liquid containing the metal component contains inorganic particles having a particle size sufficiently smaller than the width of the crack. In the case of direct shaping methods such as the powder bed fusion bonding method and the cladding method, many cracks have widths ranging from several nm to several μm. In order to reduce cracks of a size that contributes to mechanical strength (three-point bending strength) among these, the average particle size of the inorganic particles is preferably 300 nm or less. A preferable average particle size for further reducing cracks and improving mechanical strength is 100 nm or less, and a more preferable average particle size is 50 nm or less. The particle size is the equivalent spherical diameter defined as the diameter of a sphere of the same physical properties. The method for measuring the average particle size is not particularly limited, and methods such as dynamic light scattering method and microscopy can be used. In addition, the average particle size in the present invention is the median diameter, which is the particle size (D 50 ) at which the cumulative frequency becomes 50%.

[0039] The shape of the fine particles is not particularly limited, and examples include spherical, columnar, ellipsoidal, cubic, rectangular parallelepiped, needle-like, plate-like, scaly, pyramid-like shapes, etc.

[0040] The metal element contained in the inorganic particles is preferably one whose oxide can form a eutectic with at least one kind of compound contained in the ceramic shaped article. As described above, the eutectic point at which the eutectic of the oxide of the metal element contained in the inorganic particles and the components of the ceramic shaped article occurs is lower than the melting points of the respective single components. Thereby, the effect of lowering the melting point near the crack of the shaped article in which the inorganic particles are present is enhanced.

[0041] Therefore, after the metal component-containing liquid is absorbed into the shaped article and the inorganic particles in the metal component-containing liquid are distributed in the cracks in the shaped article, the shaped article is heated in step (iii) described later. Then, due to the presence of the inorganic particles and at least one kind of compound of the ceramic shaped article, the melting point is locally lowered, and the shaped article near the crack can be selectively melted. This makes it easy to reduce the cracks in the shaped article while maintaining the shape of the shaped article.

[0042] Examples of the inorganic particles containing a metal element include metal particles, metal oxide particles, metal nitride particles, metal carbide particles, metal boride particles, and metal hydroxide particles. The bonding state of the atoms constituting the inorganic particles is not limited. It may be crystalline or amorphous.

[0043] Among them, it is preferable that the main component of the inorganic particles is a metal oxide. When the main component of the inorganic particles is a metal oxide, volatile components such as carbon dioxide and water vapor are less likely to be generated in the heat treatment step of step (iii), so that stable heat treatment is possible. In addition, the ceramic shaped article formed in step (i) may be in a state where there is less oxygen than the stoichiometric ratio due to an excessive reaction by an energy beam. In this case, the heat treatment in step (iii) is preferably performed in an oxygen-containing atmosphere, which can promote the oxidation of the shaped article and eliminate the oxygen deficiency. Metal oxide particles are less likely to cause an oxidation reaction during heat treatment compared to metal particles and the like, and do not inhibit the supply of oxygen to the shaped article itself. From these viewpoints, inorganic particles mainly composed of a metal oxide are preferable.

[0044] In addition, since there is a possibility of generating toxic gases by heat treatment, the concentration of halogen elements contained in the inorganic particles is preferably at an impurity level of 1000 ppm or less.

[0045] When the compound contained in the ceramic shaped article that absorbs the metal component-containing liquid is defined as component X, and the oxide of the metal element contained in the inorganic particles contained in the metal component-containing liquid is defined as component Y, it is preferable that component X and component Y are in a eutectic state. In this case, the local melting caused by cracks is presumed to be due to the following phenomenon. Component X only needs to be in a eutectic state with component Y, and a complex of a plurality of compounds (such as a phase separation structure) may be collectively regarded as component X. For example, as will be described in detail later, a shaped article formed from an Al2O3-Gd2O3-based raw material powder has a two-component phase separation structure of Al2O3 and GdAlO3. In this case, component X may refer to the two-component phase separation structure of Al2O3 and GdAlO3. Since both Al2O3 and GdAlO3 are in a eutectic state with zirconium oxide, zirconium oxide can be used as component Y.

[0046] When a shaped object absorbs a liquid containing a metal component, not only the surface of the shaped object but also the surfaces that make up the cracks in the shaped object will have a certain amount of inorganic particles contained in the liquid containing the metal component. When heat treatment is performed in this state, on the surfaces that make up the cracks in the shaped object, either the main component of the inorganic particles is a metal oxide or the metal elements contained in the inorganic particles are oxidized to become metal oxides during the heat treatment process, resulting in the presence of a certain amount of component Y. In the vicinity of component Y present on the surface of the crack, component X in an amount that gives a eutectic composition or a composition ratio close to the eutectic composition melts at a temperature lower than the melting point of the shaped object. Then, by further fusing with component X that makes up the surrounding shaped object, the proportion of component X in the fused composition increases. When the proportion of component X increases, the melting point of the fused portion relatively rises and exceeds the heat treatment temperature, and it is considered that recrystallization occurs and contributes to crack repair. As a result, it is considered that only the region near the crack softens and recrystallizes while maintaining the shape of the shaped object, obtaining an effect of reducing or eliminating the crack. Also, since this process progresses simply by maintaining the heating temperature at a constant state, there is an advantage that control is easy.

[0047] Therefore, it is considered that in the portion where the crack is repaired, the bond between the tissues is stronger compared to the method of filling the crack by glass infiltration or the like, and a shaped object having high mechanical strength is obtained. Also, compared to the method of filling the crack with a material such as glass, the extreme compositional bias is reduced, so a shaped object that is relatively homogeneous with respect to physical properties other than mechanical strength is obtained.

[0048] Although several combinations of component X and Y are conceivable, among them, the melting point T of component Y, which is an oxide of the metal element contained in the inorganic particles i is the melting point T of component X, which is a compound contained in the ceramic shaped object that can form a eutectic with component Y mIt is preferably in a higher relationship. Fig. 3 shows an example of a phase diagram representing the composition ratio of component X and component Y when component X and component Y are in a eutectic relationship, and the relationship between the temperature and state at each composition ratio. The horizontal axis represents the composition ratio, with component X being 100% at the left end, and the proportion of component X decreasing and the proportion of component Y increasing as approaching the right end.

[0049] Let the melting point of component X be T m and the melting point of component Y be T i , and the eutectic point of component X and component Y be T E . Then, each temperature satisfies the relationship of T E < T m , T E < T i . In this case, the maximum temperature T S that the shaped article reaches by the heat treatment performed after absorbing the metal component-containing liquid is set to satisfy the relationship of T E ≤ T S < T m . T E and T S are set to be lower than the melting point T a of the shaped article, respectively. Further, if T m < T i , high effects can be obtained even with a small number of times of absorbing the metal component-containing liquid or heating. This is because, as shown in Fig. 3, since T m < T i , the eutectic composition of component X and component Y becomes a state with a high ratio of component X and a low ratio of component Y, and the vicinity of the crack can be melted at the eutectic temperature. Note that T m < T i is a preferable condition, not an essential condition.

[0050] For example, when the main component of the shaped article is aluminum oxide (Al2O3; melting point T m = 2070 °C), the main component of the inorganic particles contained in the metal component-containing liquid is zirconium oxide (ZrO2; melting point T iComponents that reach a temperature of 2715 °C are preferred. In this case, the metal element contained in the inorganic particles is zirconium. Candidates for inorganic particles that turn into zirconium oxide by heating include zirconium (metal), zirconium oxide, zirconium hydroxide, zirconium chloride, etc. Although zirconium chloride is a sublimable solid, it can turn into zirconium oxide through hydrated zirconium chloride hydroxide, etc. Al2O3 and ZrO2 are in a relationship where they can form a eutectic, and the eutectic point T E is approximately 1840 °C. That is, Al2O3 and ZrO2 are a combination that satisfies the aforementioned preferred relationship, T m <T i . Therefore, when ZrO2 is generated near the crack from the metal element contained in the metal component-containing liquid, the maximum temperature T S during the heat treatment can be set in the range of 1840 °C ≤ T S < 2070 °C. And by selectively melting the vicinity of the crack at a temperature sufficiently lower than the melting point of Al2O3, the crack can be reduced or eliminated.

[0051] When the shaped article contains two components of Al2O3 and GdAlO3, the melting point of the shaped article is determined according to the composition ratio of these two components. For example, if the shaped article contains the two components in a eutectic composition, the melting point T a of the shaped article is approximately 1720 °C (eutectic point). In such a case, it is preferable that the metal component-containing liquid contains inorganic particles mainly composed of components that turn into zirconium oxide by heating. Although the melting point T i of ZrO2 is 2715 °C, since the eutectic point T E of the three components of Al2O3, GdAlO3, and ZrO2 is approximately 1662 °C, by heating at a temperature T a sufficiently lower than approximately 1720 °C for the melting point T S of the shaped article, it becomes possible to reduce or eliminate the crack.

[0052] In this way, other combinations are also conceivable for the combination of at least one kind of compound constituting the shaped article and the metal oxide that is the oxide of the metal element contained in the inorganic particles. The melting point T m <T iExamples of combinations that satisfy the relationship include [SiO2] and ZrO2, [SiO2] and Al2O3, [Al2O3] and MgO, [Al2O3] and HfO2, [Al2O3 and ReAlO3 (Re is a rare earth)] and ZrO2, [Al2O3 and Re3Al5O 12 (Re is a rare earth)] and ZrO2, [Al2O3 and ReAlO3 (Re is a rare earth)] and HfO2, [Al2O3 and Re3Al5O 12 (Re is a rare earth)] and HfO2, [Mg2Al4Si5O 18 and Mg2SiO4, [Mg2Al4Si5O 18 and MgSiO3, etc., but are not limited thereto. In the above description, within [ ], the components that can correspond to component X and are the phases constituting the shaped article are shown, and following [ ], the phases of metal oxides that are metal oxides of the metal elements contained in the inorganic particles are shown.

[0053] Note that the metal component-containing liquid containing the metal element that becomes component Y is preferably used for a ceramic shaped article in which the content rate of component Y is less than 3 mol%. With such a combination, it becomes easier to locally melt only near the crack by heating, and deformation of the shaped article can be suppressed. The content rate of component Y in the ceramic shaped article that absorbs the metal component-containing liquid is more preferably less than 2 mol%, and even more preferably less than 1 mol%.

[0054] As described above, in order to eliminate the crack, it is necessary to have an appropriate amount of component Y present on the surface of the shaped article facing the crack. The amount of component Y present on the surface of the shaped article facing the crack may be adjusted according to the number of times of absorbing the metal component-containing liquid into the shaped article, the content and particle diameter of the inorganic particles in the metal component-containing liquid, and the size and shape of the shaped article to be absorbed.

[0055] In the present invention, the content of the inorganic particles in the metal component-containing liquid is not particularly limited, but there may be a preferred content depending on the purpose.

[0056] When the content of inorganic particles in the metal component-containing liquid is high, by performing step (ii) once, a large amount of component Y can be applied to the surface of the shaped object facing the crack. Therefore, even if the number of times of performing step (ii) and step (iii) is small, the crack can be sufficiently reduced or eliminated. From this perspective, the content of inorganic particles in the metal component-containing liquid is preferably 25% by weight or more, and more preferably 30% by weight or more. On the other hand, when the content of inorganic particles in the metal component-containing liquid is high, the amount of component Y applied to the surface of the shaped object facing the crack per one-time performance of step (ii) becomes too large, and the melting of the shaped object may easily reach a wide range around the crack. In order to maintain the shape accuracy of the shaped object, a metal component-containing liquid with an inorganic particle content of 80% by weight or less is preferable, and more preferably 75% by weight or less.

[0057] In summary, although it varies depending on the components constituting the shaped object and the size of the shaped object, in order to shorten the heat treatment time while maintaining the shape of the shaped object, the content of inorganic particles in the metal component-containing liquid is preferably 25% by weight or more and 80% by weight or less. More preferably, it is 30% by weight or more and 75% by weight or less.

[0058] The content of inorganic particles in the metal component-containing liquid applied to a shaped object having a fine shape is preferably less than 50% by weight, and more preferably less than 40% by weight.

[0059] From the above viewpoints, at the initial stage of the process for repairing cracks, after reducing the cracks to some extent efficiently using a dispersion liquid with a high content of inorganic particles, it is also preferable to reduce or eliminate the cracks using a dispersion liquid with a low content of inorganic particles at the finishing stage. In this way, by combining and using a plurality of types of metal component-containing liquids with different contents of inorganic particles, the cracks can be reduced or eliminated more efficiently while ensuring the shape accuracy.

[0060] The inorganic particles may be produced by crushing each material by the top-down method, may be synthesized from metal salts, hydrates, hydroxides, carbonates, etc. using a method such as hydrothermal reaction by the bottom-up method, or may be commercially available products.

[0061] The liquid containing a metal component contains any one of an organic solvent, water, and a mixture thereof as a solvent for dispersing inorganic particles. Specifically, it contains alcohols, ketones, esters, ethers, ester-modified ethers, hydrocarbons, halogenated hydrocarbons, amides, water, oils, or a mixed solvent of two or more of these. As alcohols, for example, methanol, ethanol, 2-propanol, isopropanol, 1-butanol, ethylene glycol, etc. are preferable. As ketones, for example, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc. are preferable. As esters, for example, ethyl acetate, propyl acetate, butyl acetate, 4-butyrolactone, propylene glycol monomethyl ether acetate, methyl 3-methoxypropionate, etc. are preferable. As ethers, for example, ethylene glycol monomethyl ether, diethylene glycol monobutyl ether, butyl carbitol, 2-ethoxyethanol, 1-methoxy-2-propanol, 2-butoxyethanol, etc. are preferable. As modified ethers, for example, propylene glycol monomethyl ether acetate is preferable. As hydrocarbons, for example, benzene, toluene, xylene, ethylbenzene, trimethylbenzene, hexane, cyclohexane, methylcyclohexane, etc. are preferable. As halogenated hydrocarbons, for example, dichloromethane, dichloroethane, chloroform are preferable. As amides, for example, dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone are preferable. As oils, for example, mineral oil, vegetable oil, wax oil, silicone oil are preferable.

[0062] Furthermore, in order to uniformly absorb particles into the cracks, it is preferable that the particles do not aggregate or sediment in the dispersion liquid and maintain high dispersibility. Therefore, the liquid containing a metal component preferably further contains a dispersant.

[0063] As the dispersant, it is preferable to contain at least one of an organic acid, a silane coupling agent, and a surfactant. Examples of the organic acid include acrylic acid, 2-hydroxyethyl acrylate, 2-acryloxyethyl succinic acid, 2-acryloxyethyl hexahydrophthalic acid, 2-acryloxyethyl phthalic acid, 2-methylhexanoic acid, 2-ethylhexanoic acid, 3-methylhexanoic acid, 3-ethylhexanoic acid, etc. Examples of the silane coupling agent include 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, hexyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, etc. Examples of the surfactant include ionic surfactants such as sodium oleate, potassium fatty acid, sodium alkyl phosphate ester, alkylmethylammonium chloride, alkylaminocarboxylate, etc., and nonionic surfactants such as polyoxyethylene lauric fatty acid ester, polyoxyethylene alkyl phenyl ether, etc.

[0064] In order to absorb the metal component-containing liquid to the central part of the shaped article and to suppress the thick deposition of the metal component-containing liquid on the surface of the shaped article, it is preferable that the viscosity of the metal component-containing liquid is lower, and it is particularly preferable that the viscosity at 20 °C is 12 mPa·s or less.

[0065] The production method of the metal component-containing liquid is not limited. It is preferable to prepare by mixing inorganic particles, a dispersant, and a solvent, but it may also be prepared by mixing all at once. Alternatively, the particles and the dispersant may be mixed first and then the solvent may be added and mixed, or the particles and the solvent may be mixed first and then the dispersant may be added and mixed, or the dispersant and the solvent may be mixed first and then the particles may be mixed for preparation.

[0066] The metal component-containing liquid is as described above. When the ceramic shaped article has aluminum oxide as the main component, a metal component-containing liquid containing inorganic particles having zirconium oxide as the main component is suitable.

[0067] If inorganic particles can be uniformly interposed on the surface constituting the crack of the shaped article, the method of absorbing the metal component-containing liquid into the shaped article is not particularly limited. The shaped article may be immersed in the metal component-containing liquid for impregnation, or the metal component-containing liquid may be atomized and sprayed onto the shaped article, or applied to the surface with a brush or the like for absorption. Further, a plurality of these methods may be combined, or the same method may be repeated a plurality of times.

[0068] When the volume of the shaped article obtained by repeating step (i) many times is large, in order to sufficiently distribute the inorganic particles to the inside of the shaped article, it is preferable to immerse the shaped article in the metal component-containing liquid and perform vacuum degassing. Alternatively, after putting the shaped article in a sealed container and performing vacuum degassing, it may be immersed in the metal component-containing liquid.

[0069] <Step (iii)> In step (iii), the ceramic shaped article that has absorbed the metal component-containing liquid is heat-treated.

[0070] By step (ii), the inorganic particles are widely distributed on the surface layer of the shaped article and in the cracks inside the shaped article. For example, in a shaped article mainly composed of aluminum oxide, in a shaped article in a state where it has absorbed a metal component-containing liquid in which zirconium oxide particles are dispersed, only the vicinity of the crack locally approaches the eutectic composition of Al2O3 and ZrO2. Therefore, the melting point is lower only in the vicinity of the crack portion compared to the portion away from the crack portion. Utilizing this difference in melting point, the shaped article is heated at a temperature equal to or higher than the eutectic point of at least one kind of compound contained in the shaped article and a metal oxide composed of a metal element contained in the inorganic particles and lower than the melting point of the material constituting the shaped article.

[0071] Here, it is heated at a temperature equal to or higher than the eutectic point of Al2O3 and ZrO2 and lower than the melting point of Al2O3. As a result, while maintaining the shape of the shaped article, only the portion where the inorganic particles exist in the shaped article, that is, only the vicinity of the crack of the shaped article partially melts.

[0072] If the shaped article is composed of two types of compounds and these two components and zirconium oxide form a eutectic (three-phase eutectic) relationship among the three components, the eutectic point of these three components will be at a lower temperature than the eutectic point of the two components. In this case, step (iii) can be carried out at a lower temperature than when the shaped article is composed of one type of compound, and even for a relatively large-sized shaped article, the temperature unevenness during heating within the shaped article can be reduced, which is more preferable. Also, when the article to be manufactured is an oxide, if the temperature is relatively low, step (iii) can be simply carried out in an electric furnace in an air atmosphere or the like.

[0073] For example, Al2O3-Gd2O3 is a material that can form a three-phase eutectic with zirconium oxide. Therefore, when a metal component-containing liquid containing inorganic particles containing zirconium elements is absorbed into a shaped article formed from a powder containing Al2O3-Gd2O3 as a component, a certain amount of inorganic particles containing zirconium elements is imparted to the surface constituting the crack of the shaped article. When heat treatment is performed in this state, the zirconium elements present on the surface constituting the crack of the shaped article become zirconium oxide, for example, during the heat treatment process. In the vicinity of the zirconium oxide on the surface of the shaped article facing the crack, the amount of zirconium oxide and the amount of Al2O3-Gd2O3 having a composition ratio at which a three-phase eutectic can be formed or a composition ratio in its vicinity melt at a temperature lower than the melting point of the shaped article. Then, recrystallization occurs thereafter, contributing to the repair of the crack.

[0074] In this way, if the composition ratio near the crack is made close to the composition ratio at which a three-phase eutectic can be formed, the melting point can be locally greatly reduced. Utilizing this difference in melting point, heating can be carried out at a temperature above the eutectic point of the three phases and below the melting point of the shaped article, and only the vicinity of the crack can be selectively locally melted.

[0075] Specifically, by heat-treating a shaped article formed from a powder containing Al2O3-Gd2O3 as a component such that the maximum temperature near the crack of the shaped article after step (ii) is 1600 °C or higher and 1710 °C or lower, the crack can be reduced or eliminated. In this case, from the viewpoint of being higher than the eutectic point of the three phases of Al2O3, Gd2O3, and ZrO2 and lower than the lowest melting point (about 1720 °C) that a shaped article of the Al2O3-Gd2O3 system can have, it is more preferably 1662 °C or higher and 1710 °C or lower. As described above, in order to melt only near the crack, it is necessary to appropriately set the temperature of the heat treatment performed after absorbing the metal component-containing liquid into the crack of the shaped article. When the component X constituting the shaped article and the inorganic oxide component Y that is the main component of the particles are in the eutectic relationship shown in the phase diagram of FIG. 3, the maximum temperature T S that the shaped article reaches by the heat treatment performed in step (iii) E is preferably set such that T S ≦ T m < T E ≦ T S < T m -(T m -T E ) / 2. Thereby, since the vicinity of the crack can be selectively melted at a temperature sufficiently lower than the melting point T m of the shaped article, and the crack can be reduced or eliminated, the shape of the shaped article is likely to be maintained.

[0076] As long as the vicinity of the crack reaches the above maximum temperature, the heating time does not matter. Specifically, the shaped article may be heated at the temperature at which it is desired to reach the vicinity of the crack in step (iii). By heating at such a temperature, the crack and its vicinity melt and move in the direction of decreasing surface energy, so it is considered that the crack decreases or disappears. Then, as the heating further progresses, it is considered that the crack diffuses into the crystalline and amorphous interior of the shaped article and the crystal recrystallizes in a state containing the metal oxide component. It is presumed that such an action has an effect of further enhancing the mechanical strength of the shaped article compared to the method of simply infiltrating and filling the crack with glass.

[0077] If inorganic particles are present on the surface constituting the crack of the shaped article, as described above, the vicinity of the crack melts, and there is an effect of reducing or eliminating the crack.

[0078] The amount of inorganic particles in the vicinity of the crack may be adjusted by the content of inorganic particles in the metal component-containing liquid, the method of absorbing the metal component-containing liquid into the crack, the number of times, etc.

[0079] For example, in the case of a shaped article mainly composed of aluminum oxide, by bringing the vicinity of the crack closer to the eutectic composition in which zirconium oxide is 38 mol% with respect to 62 mol% of aluminum oxide, the vicinity of the crack becomes more easily melted. To selectively melt the vicinity of the crack to reduce or eliminate the crack, when the eutectic point of aluminum oxide and zirconium oxide is about 1840 °C, it is preferable to heat at a temperature of 1840 °C or higher and lower than 2070 °C. More preferably, it is 1850 °C or higher and 2060 °C or lower.

[0080] Also, in the case of a shaped article formed from a powder containing Al2O3-Gd2O3, it contains a phase mainly composed of Al2O3 and a phase mainly composed of GdAlO3. As described above, it is preferable to absorb the zirconium oxide metal component-containing liquid into this shaped article (step (ii)) and heat at a temperature of 1662 °C or higher and 1710 °C or lower (step (iii)). The components of the zirconium oxide particles that have entered the shaped article from the crack diffuse into the crystalline and amorphous interiors of the shaped article and recrystallize. As a result, in the obtained ceramic article, a three-phase eutectic of a phase mainly composed of ZrO2 with a fluorite structure, a phase mainly composed of Al2O3, and a phase mainly composed of GdAlO3 is formed. Further, when a powder of terbium oxide (Tb4O7) is added as a subcomponent to the powder containing Al2O3-Gd2O3, the shaped article contains a phase mainly composed of Al2O3 and a phase mainly composed of (Gd,Tb)AlO3 in which a part of the Gd sites are substituted with Tb. Also in this case, heating at a temperature of 1662 °C or higher and 1710 °C or lower (step (iii)) can reduce or eliminate the crack.

[0081] Since the shaped article immediately after being formed by step (i) is rapidly cooled and solidified after melting by energy beam irradiation, it contains a large amount of amorphous components. By appropriately selecting the metal component-containing liquid to be absorbed in step (ii) based on the components constituting the shaped article, most of the amorphous components contained in the shaped article can be changed into crystalline ones during the heat treatment process of step (iii). Also, during the heat treatment process, by heating the shaped article for a certain period of time or more, and sufficiently diffusing and recrystallizing the oxides of the metal elements contained in the inorganic particles inside the crystals of the shaped article, high mechanical strength can be obtained. The holding time of the maximum temperature Ts in step (iii) is preferably 1 minute or more in total, and more preferably 5 minutes or more. On the other hand, if the heat treatment time is too long, the particle size of the crystal particles constituting the ceramic shaped article may become too large, leading to a decrease in mechanical strength. Therefore, the holding time of the maximum temperature Ts in step (iii) is preferably 2 hours or less in total, and more preferably 1 hour or less. Even more preferably, it is 30 minutes or less.

[0082] In the present invention, unless otherwise specified, the heat treatment time refers to the holding time at the maximum heat treatment temperature Ts in step (iii). Also, the total heat treatment time refers to the holding time at the maximum heat treatment temperature Ts when step (iii) is carried out once, and when step (iii) is repeatedly carried out a predetermined number of times, it refers to the sum of the holding times at the maximum temperature Ts for each time.

[0083] The heating method is not particularly limited. The ceramic shaped article that has absorbed the metal component-containing liquid may be heated by irradiating it with an energy beam again, or it may be heated by placing it in an electric furnace. When heating with an energy beam, it is necessary to grasp in advance the relationship between the input heat amount of the energy beam and the temperature of the shaped article with a thermocouple or the like so that the shaped article is heated within the above-mentioned preferred temperature range. An electric furnace that can adjust the cooling rate after heating can heat the entire shaped article and further control the cooling temperature, so the formation of new cracks is suppressed and it is suitable.

[0084] When steps (ii) and (iii) are repeatedly carried out, as long as cracks do not disappear from the shaped article, the oxide of the metal element contained in the inorganic particles diffuses into the shaped article each time it is repeated. Then, the concentration difference of the components caused by the particles becomes smaller between the vicinity of the crack of the shaped article and the other parts, and the difference between the melting point (eutectic point) of the vicinity of the crack of the shaped article and the melting point of the other parts becomes smaller. From the viewpoint of melting only the vicinity of the crack, it is preferable that the difference in the melting points is 20 °C or more, more preferably 30 °C or more. For example, for a shaped article formed from a powder mainly composed of aluminum oxide, if the zirconium oxide component in the shaped article is less than 3 mol%, it is preferable because the shape change of the shaped article can be suppressed and only the vicinity of the crack can be melted. More preferably, it is less than 2 mol%. Even more preferably, it is less than 1 mol%. A ceramic article having small crystal particle diameters and sufficiently reduced cracks contributing to mechanical strength has particularly excellent mechanical strength. Such a ceramic article can be realized by shortening the heat treatment time required for crack reduction as much as possible and suppressing grain growth.

[0085] Furthermore, when using a powder composed of a plurality of types of compounds including a main component and sub-components such as an absorber, the integrated time of the heat treatment in step (iii) is preferably shorter. Thereby, a ceramic article having a phase separation structure in which a plurality of phases are intertwined can be obtained. Specifically, a ceramic article having a phase separation structure including three phases having at least one common metal element, and at least two of the three phases being phases of composite compounds can be obtained. As will be described in detail later, a ceramic article having such a phase separation structure has better mechanical strength than a ceramic article composed of one phase or two phases.

[0086] <Ceramic article> The ceramic article of the present invention is an article mainly composed of ceramics manufactured using an additive manufacturing technique, and is characterized by achieving both the free form which is a feature of the additive manufacturing technique and excellent mechanical strength. Among the additive manufacturing techniques, it is preferably manufactured by a powder bed fusion bonding method or a directed energy deposition method.

[0087] As described above, a ceramic article having excellent mechanical strength can be realized by performing laminated modeling using powders composed of a plurality of types of materials, and shortening the integrated time of heat treatment after absorbing the obtained modeled article into a metal component-containing liquid having an appropriate component. The ceramic article thus obtained having particularly excellent mechanical strength has a phase separation structure including three phases having at least one common metal element. At least two of the three phases having at least one common metal element are phases of composite compounds. When the metal element common to the three phases is contained in the compound that is the main component of the ceramic article, the ceramic article has a phase separation structure composed of three or more phases, including the phase of the main component and the phases of two composite compounds containing at least one metal element constituting the main component. In other words, it has a phase separation structure including three phases having at least one common metal element.

[0088] Preferably, the main component is aluminum oxide, rare earth aluminate, silicon oxide, mullite, cordierite, etc. Among them, aluminum oxide is widely used as a general-purpose structural ceramic, and because of its relatively high thermal conductivity, it is suitable for the additive manufacturing technology of the direct modeling method.

[0089] Hereinafter, a ceramic article having aluminum oxide as the main component will be described as an example, but the technical idea is not limited to the ceramic article having aluminum oxide as the main component.

[0090] For example, consider the case where a powder containing aluminum oxide powder and gadolinium oxide powder as a sub-component is irradiated with an energy beam and solidified. Since aluminum oxide and gadolinium oxide are in a relationship where they can form a eutectic, a modeled article mainly composed of Al2O3 phase, GdAlO3 phase, and Gd2O3 phase can be formed.

[0091] After the shaped article absorbs the liquid containing a metal component and is then heat-treated, the ceramic article obtained may contain, in addition to the Al2O3 phase, a GdAlO3 phase, a Gd4Al2O9 phase, a Gd2O3 phase, a phase derived from inorganic particles of the liquid containing a metal component, etc., when the integrated time of the heat treatment is short. At this time, when the cracks in the ceramic article are sufficiently reduced, it exhibits mechanical strength superior to that of a ceramic article obtained by heat treatment for a long time.

[0092] As factors for obtaining excellent mechanical strength, there are considered to be the particle size of the crystal particles constituting the ceramic article and the presence of a composite compound phase.

[0093] When the integrated time of the heat treatment in step (iii) is short, the heat treatment ends before coarse grains are formed, so a ceramic article having excellent mechanical strength and composed of small particle sizes can be obtained. The preferred average particle size is 20 μm or less, more preferably 15 μm or less, and still more preferably 10 μm or less.

[0094] In addition, the presence of a plurality of composite compounds forms a complex phase separation structure composed of many types of phases in the ceramic article. Also, generally, a composite compound often has higher toughness than the main component. Therefore, it is considered that these complex phase separation structures contribute to the improvement of mechanical strength.

[0095] The composite compound is considered to be formed from the main component and the sub-component of the powder during the melting and solidification in step (i) and / or during the heat treatment in step (iii). For example, when using a powder containing gadolinium oxide powder as a sub-component in aluminum oxide powder as the main component, the above-mentioned GdAlO3 phase and Gd4Al2O9 phase correspond to the composite compound. GdAlO3 is considered to be mainly formed by eutectic with Al2O3 in step (i). On the other hand, the Gd4Al2O9 phase is considered to be mainly formed during the heat treatment in step (iii) in the process of solid-phase diffusion of atoms between the remaining undissolved Gd2O3 phase of the raw material and the Al2O3 phase and the GdAlO3 phase. Therefore, when the integrated time of the heat treatment in step (iii) is long, the Gd4Al2O9 phase disappears, and the phase composition of the ceramic article reaches an equilibrium state, but the mechanical strength decreases. Here, if the composite compound formed by eutectic with the main component in step (i) is defined as composite compound 1, and the composite compound transiently formed in step (iii) is defined as composite compound 2, it is considered that the higher the proportion of composite compound 2, the higher the mechanical strength of the ceramic article.

[0096] In the case of a ceramic article formed by an additive manufacturing technique from a powder containing a main component and a sub-component, although the mechanical strength obtained varies depending on the type of the main component, the mechanical strength can be further enhanced by crack repair with short-time heating by the above-mentioned mechanism. As the main component of the powder, in addition to aluminum oxide, silicon oxide, mullite, cordierite, etc. are applicable. Further, as the sub-component of the powder, components that can form a eutectic with the main component, absorber components, sintering aid components, other compounds, etc. can be mentioned.

[0097] Preferred combinations of the main component and the sub-component are Al2O3-Gd2O3, Al2O3-Tb4O7, Al2O3-Gd2O3-Tb4O7, Al2O3-GdAlO3-Tb4O7, Al2O3-Pr6O 11 、Al2O3-Gd2O3-Pr6O 11 、Al2O3-GdAlO3-Pr6O 11, Al2O3 - Y2O3, Al2O3 - YAlO3, Al2O3 - Y2O3 - Tb4O7, Al2O3 - YAlO3 - Tb4O7, Al2O3 - Y3Al5O 12 -Tb4O7, Al2O3 - Y2O3 - Pr6O 11 , Al2O3 - YAlO3 - Pr6O 11 , Al2O3 - Y3Al5O 12 -Pr6O 11 , Al2O3 - ZrO2 - Tb4O7, Al2O3 - ZrO2 - Pr6O 11 , Al2O3 - SiO, Al2O3 - Gd2O3 - SiO, Al2O3 - GdAlO3 - SiO, Al2O3 - Y2O3 - SiO, Al2O3 - YAlO3 - SiO, Al2O3 - Y3Al5O 12 -SiO, Al2O3 - ZrO2 - SiO, SiO2 - Tb4O7, SiO2 - Pr6O 11 , (MgO - Al2O3 - SiO2) - Tb4O7, (MgO - Al2O3 - SiO2) - Pr6O 11 , (Al2O3 - SiO2) - Tb4O7, (Al2O3 - SiO2) - Pr6O 11 etc. are exemplified. In the above combinations, the first component refers to the main component and the subsequent components refer to the sub-components. In the case of these combinations, as the composite compound, a composite oxide is formed.

[0098] The ceramic article of the present invention preferably further includes a phase different from the three phases in which at least one of the above-described metal elements is common. When the metal element common to the three phases is included in the compound that is the main component of the ceramic article, it has three phases: the phase of the main component and the phases of two composite compounds containing at least one metal element constituting the main component, and preferably further includes another phase. Another phase may also be expressed as a different phase. The another phase is preferably a component derived from the inorganic particles of the metal component-containing liquid used in step (ii) and has a relationship that can form a eutectic with at least one of the main component and the two composite compounds contained in the shaped article. The presence of a certain amount or more of the component derived from the inorganic particles of the metal component-containing liquid means that the cracks are sufficiently repaired. Further, by further including such another phase, the phase separation structure of the ceramic article becomes more complex and the mechanical strength is improved. From such a viewpoint, more preferably, the component derived from the inorganic particles of the metal component-containing liquid has a relationship that can form a eutectic with the main component. In order to obtain sufficient mechanical strength and high shape accuracy, the metal element derived from the inorganic particles contained in the ceramic article is preferably contained in the range of 0.3 mol% or more and 5 mol% or less with respect to all the metal elements contained in the ceramic article. More preferably, it is 0.5 mol% or more and 3 mol% or less. If the component derived from the inorganic particles contained in the ceramic article is too much, the shape accuracy of the article tends to decrease.

[0099] For example, a ceramic article obtained by repairing cracks in a shaped article formed by irradiating a powder containing aluminum oxide powder as a main component and gadolinium oxide powder as a sub-component with an energy beam using a metal component-containing liquid containing zirconium oxide particles will be described. The ceramic article thus obtained may contain, in addition to the Al2O3 phase, the GdAlO3 phase, the Gd4Al2O9 phase, the Gd2O3 phase, the ZrO2 phase having a fluorite structure, and the like. The ZrO2 phase having a fluorite structure is a phase derived from the inorganic particles of the metal component-containing liquid and corresponds to the above-described another phase. The ZrO2 phase having a fluorite structure becomes a stable phase by substituting a part of the Zr sites with rare earth elements (here Gd).

[0100] The ZrO2 phase with a fluorite structure, which is a phase derived from inorganic particles in the metal component-containing liquid, is preferably composed of crystal particles with a smaller particle size compared to the phase that is the main component of the ceramic article. This is because another phase with a relatively smaller particle size than the main component phase functions to connect the main component phases to each other and is considered to contribute to the mechanical strength of the ceramic article. The particle size of the other phase is preferably 1 / 2 or less, more preferably 1 / 3 or less, of the particle size of the main component phase.

[0101] From the perspective that the phase separation structure becomes more complex, it is preferable that at least one of the composite compounds and the main component can form a eutectic.

[0102] <Evaluation Method> The evaluation method of the shaped article in the present invention will be described.

[0103] (Mechanical Strength) The mechanical strength of the shaped article was evaluated by a three-point bending test based on JIS standard R1601 for the room-temperature bending strength test of fine ceramics. The three-point bending strength, for each of the five test pieces, when the maximum load at the time of fracture is P [N], the external fulcrum distance is L [mm], the width of the test piece is w [mm], and the thickness of the test piece is t [mm], 3×P×L / (2×w×t2) (Equation 1) was calculated using this formula, and the average value of these was used.

[0104] (Relative Density) The relative density [%] was calculated by dividing the bulk density (weight divided by volume) of the shaped article by the theoretical density. The theoretical density was calculated from the crystal structure. The crystal structure was specified by performing Rietveld analysis by carrying out X-ray diffraction measurement.

[0105] (Crystal Structure) The ceramic article was polished to a mirror finish, and the crystal structure and composition of the phases in the article were examined by X-ray diffraction (XRD), electron diffraction, scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX), and transmission electron microscopy-energy dispersive X-ray analysis (TEM-EDX). Then, the phase separation structure was analyzed by scanning electron microscopy-electron backscatter diffraction (SEM-EBSD).

[0106] Furthermore, simultaneous analysis of SEM-EDX and EBSD was performed at 10 different locations with a field size of 100 μm × 100 μm on the measurement surface to map the composition and crystal phase. When small phases are included, the composition and crystal structure can be similarly analyzed by using a transmission electron microscope (TEM).

[0107] The particle size of the crystal particles constituting the phase was calculated by using EBSD to observe more than 300 crystal particles within the same phase observed on the measurement surface and calculating the median value of the equivalent circle diameter of each crystal particle.

[0108] (Composition analysis) The content of metal elements in the powder, shaped article, or ceramic article was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES), GDMS, ICP-MS, X-ray fluorescence analysis (XRF), SEM-EDX, etc.

[0109] Also, the composition ratio of each phase in the shaped article and ceramic article was measured and calculated by combining the above-described crystal structure analysis and composition analysis.

Example

[0110] (Example 1) α-Al2O3 powder with an average particle size of about 20 μm, Gd2O3 powder with an average particle size of about 35 μm, and Tb2O 3.5 powder (Tb4O7 powder) were prepared, and each powder was weighed so that the molar ratio was Al2O3:Gd2O3:Tb2O 3.5 = 77.4:20.8:1.8. Each weighed powder was mixed in a dry ball mill for 30 minutes to obtain a mixed powder (raw material powder).

[0111] When the composition of the raw material powder was analyzed by ICP emission spectrometry, the content of zirconium oxide was less than 1 mol%. Next, through the same process as shown in FIG. 1 described above, a rectangular parallelepiped of 5 mm × 42 mm × 6 mm was produced as the shaped object of Example 1 (step (i)).

[0112] For the formation of the shaped object, ProX DMP 100 (trade name) manufactured by 3D SYSTEMS equipped with a 50 W fiber laser was used.

[0113] First, using a roller, a first powder layer with a thickness of 20 μm made of the raw material powder was formed on an alumina base 130 (FIGS. 1(a) and (b)). Next, a laser beam of 30 W was scanned at a drawing speed of 140 mm / s and a drawing pitch of 100 μm. As shown in FIG. 4(a), while scanning the laser beam so that the drawing line was at an angle of 45 degrees to each side of the rectangle, the powder in the 5 mm × 42 mm rectangular area was melted and solidified to form a solidified part 100 (FIG. 1(c)).

[0114] Next, a powder layer with a thickness of 20 μm was newly formed with a roller so as to cover the solidified part 100, and while scanning the laser beam, the powder layer was irradiated, and the material powder in the 5 mm × 42 mm rectangular area was melted and solidified to form a solidified part 100 (FIGS. 1(d) and (e)). At this time, as shown in FIG. 4(b), the laser was scanned in a direction perpendicular to the drawing line of the first layer, and the powder was melted and solidified. Such a process was repeated until the height of the solidified part reached 6 mm, and five shaped objects of 42 mm × 5 mm × 6 mm were produced.

[0115] When the surfaces of these shaped objects were observed with an optical microscope, the Ra of the unevenness on the surface of the shaped object was 20 μm or less. The image obtained with the optical microscope is shown in FIG. 5. As can be seen from FIG. 5, cracks were formed depending on the drawing direction of the laser beam. That is, there were cracks extending in a direction that was approximately 45 degrees to each side of the rectangle.

[0116] Each of the shaped articles was separated from the alumina base, and by polishing, a shaped article of W40 mm × D4 mm × H3 mm for a three-point bending strength test was obtained. When the polished surface was observed with an SEM, cracks with a width of several nm to several μm depending on the drawing direction of the laser beam were formed. That is, similar to the observation result with an optical microscope, lattice-like cracks were formed in a direction that was approximately 45 degrees oblique to each side of the rectangle.

[0117] Zirconium oxide-containing liquid 1 containing zirconium oxide particles was used as the metal component-containing liquid. Zirconium oxide can form a eutectic with aluminum oxide, which is the main component of the shaped article.

[0118] Zirconium oxide particles with an average particle diameter of 10 nm (manufactured by Kanto Chemical Co., Inc.) were used as the particles, 2-hydroxyethyl acrylate and 3-acryloxypropyltrimethoxysilane were used as the dispersants, and propylene glycol monomethyl ether acetate was used as the solvent. These were mixed so that the content of zirconium oxide in the dispersion liquid was 70% by weight, and were uniformly stirred to obtain zirconium oxide-containing liquid 1.

[0119] The above-mentioned shaped article processed for the test was immersed in the zirconium oxide-containing liquid 1, degassed under reduced pressure for 1 minute to absorb the liquid into the shaped article, and then naturally dried for 1 hour (step (ii)).

[0120] Subsequently, the shaped article that had absorbed the zirconium oxide-containing liquid 1 was placed in an electric furnace and heated. In an air atmosphere, the temperature was raised to 1670°C, which is above the eutectic point (1662°C) of the three phases of aluminum oxide, gadolinium oxide, and zirconium oxide and below the melting point (1720°C) of the shaped article, over 2 hours, and held at 1670°C for 10 minutes (step (iii)). Then, the power supply was terminated and it was cooled by natural air cooling to obtain the ceramic article of Example 1. In Example 1, by performing the step of absorbing the zirconium oxide-containing liquid 1 (step (ii)) and the heat treatment step (step (iii)) once each on each shaped article, 5 ceramic articles for a three-point bending strength test were produced.

[0121] For the obtained ceramic article, the dimensional accuracy was evaluated. Specifically, the rate of change in the length of each side of the article obtained after the implementation with respect to the length of each side of the shaped article before performing steps (ii) and (iii) is defined as the dimensional accuracy (sometimes referred to as shape accuracy). The dimensional accuracy of Example 1 was within 1% for each side with respect to the dimensions of the polished shaped article (W40 mm × D4 mm × H3 mm) before performing steps (ii) and (iii). Also, before and after the implementation of steps (ii) and (iii), the ratio of the lengths of each side of the shaped article was almost the same, no warping or surface irregularities were observed, and the shaped article and the ceramic article had similar shapes.

[0122] The average value of the relative density was 95.9%.

[0123] For the three-point bending test, a compression testing machine manufactured by Instron was used. When five ceramic articles of Example 1 were tested, the average value of the three-point bending strength was 173 MPa.

[0124] The phases contained in the ceramic article were analyzed. As a result, five phases were confirmed: a phase composed of Al2O3 (main component), a phase composed of GdAlO3 (composite compound 1), a phase composed of Gd4Al2O9 (composite compound 2), a phase composed of Gd2O3, and a phase mainly composed of zirconium oxide with a fluorite structure (corresponding to the other phase mentioned above). The Gd4Al2O9 phase, which is considered to greatly contribute to the mechanical strength, was present in the ceramic article at a ratio of 4 wt% according to the XRD results. The main metal elements constituting the phase mainly composed of zirconium oxide with a fluorite structure were Zr, Gd, and Tb, and the metal elements other than Zr, Gd, and Tb were less than 1 mol%. Also, among the metal elements contained in the phase mainly composed of zirconium oxide with a fluorite structure, the average ratio of the rare earth elements Gd and Tb was 30 mol%. No bias was observed in the distribution of the phase mainly composed of zirconium oxide within the article, and it was found that the zirconium oxide component diffused from the crack part into the shaped article and recrystallized as a phase separation structure while incorporating rare earth elements.

[0125] When examining the amount of Zr contained in the ceramic article, among the metallic elements constituting the ceramic article of this example, the amount of Zr was 0.7 mol%. Further, the articles obtained in this example and the following examples may contain a state in which Tb is dissolved in the Gd site in the phase composed of the aforementioned Gd as a constituent element.

[0126] The average particle size of the crystal particles constituting the ceramic article measured by EBSD was 4.5 μm.

[0127] From the above results, it is considered that a ceramic article with high mechanical strength was obtained due to the presence of a phase separation structure in which a plurality of phases were intricately intertwined and a composite compound having higher toughness than the main component, and the fact that the crystal particles had a small particle size.

[0128] (Example 2) Except that the shaping conditions were adjusted using ProX DMP 200 (trade name) manufactured by 3D SYSTEMS equipped with a 300W fiber laser for the formation of the shaped article, five shaped articles of W40mm × D4mm × H3mm were produced in the same manner as in Example 1 for the three-point bending strength test (step (i)). The shaping conditions were set such that the output of the laser beam was 294W (98% of 300W), the drawing speed was 1000mm / s, and the drawing pitch was 100μm.

[0129] When the surfaces of these shaped articles were observed with an optical microscope, the Ra of the unevenness on the surface of the shaped article was 20μm or less.

[0130] Subsequently, each of the five shaped articles was separated from the alumina base and polished to obtain a shaped article of W40mm × D4mm × H3mm for the three-point bending strength test. When the polished surface was observed with SEM, cracks with a width ranging from several nm to several μm were formed depending on the drawing direction of the laser beam. That is, similar to the observation results with the optical microscope, lattice-like cracks were formed in a direction that was approximately 45 degrees to each side of the rectangle.

[0131] In the same manner as in Example 1, step (ii) of causing the shaped article to absorb the zirconium oxide-containing liquid 1 and step (iii) of heating were carried out to produce five ceramic articles. For the obtained ceramic articles, in the same manner as in Example 1, three-point bending strength, dimensional accuracy, relative density, and analysis of the crystal structure and composition of the phases constituting the ceramic articles were performed.

[0132] The dimensional accuracy of the ceramic articles obtained in Example 2 was excellent, being 1% or less. Also, similar to the ceramic articles of Example 1, the shape of the shaped article hardly changed before and after carrying out step (ii) and step (iii), and the similar shape was maintained.

[0133] The phases contained in the ceramic articles were analyzed. As a result, five phases were confirmed: a phase composed of Al2O3 (main component), a phase composed of GdAlO3 (composite compound 1), a phase composed of Gd4Al2O9 (composite compound 2), a phase composed of Gd2O3, and a phase mainly composed of zirconium oxide having a fluorite structure (corresponding to the other phase described above). The phase of Gd4Al2O9 (composite compound 2), which is considered to greatly contribute to the mechanical strength, was present in the ceramic articles at a ratio of 4% by weight according to the XRD results. The main metal elements constituting the phase mainly composed of zirconium oxide having a fluorite structure were Zr, Gd, and Tb, and the metal elements other than Zr, Gd, and Tb were less than 1 mol%. Also, among the metal elements contained in the phase mainly composed of zirconium oxide having a fluorite structure, the average ratio of the rare earth elements was 30 mol%. It was found that there was no bias in the distribution of the phase mainly composed of zirconium oxide, and the zirconium oxide component diffused from the crack portion into the shaped article and recrystallized as a phase separation structure while taking in rare earth elements. When the amount of Zr contained in the ceramic articles was examined, among the metal elements constituting the ceramic articles of this example, the amount of Zr was 0.7 mol%.

[0134] The particle size of the crystal particles constituting the ceramic articles measured by EBSD was 4.0 μm.

[0135] The presence of a phase separation structure in which these multiple phases are intricately intertwined and a composite compound having higher toughness than the main component, and due to the small particle size, it is considered that a ceramic article with high mechanical strength was obtained.

[0136] (Example 3) In the same manner as in Example 1, a shaped article of W40 mm × D4 mm × H3 mm was produced for the three-point bending strength test (step (i)). When the surface of the shaped article of Example 3 was observed with an optical microscope, the Ra of the unevenness on the surface of the shaped article was 20 μm or less.

[0137] Zirconia fine particles with an average particle size of 10 nm (manufactured by Kanto Chemical Co., Inc.) were mixed with 2-hydroxyethyl acrylate and 3-acryloxypropyltrimethoxysilane as a dispersant and uniformly stirred. To this, propylene glycol monomethyl ether acetate was added as a solvent so that the zirconia content in the dispersion liquid became 70% by weight, and uniformly stirred to obtain zirconium oxide-containing liquid 2.

[0138] The process (ii) of absorbing the above zirconium oxide-containing liquid 2 into the shaped article and the process (iii) of heating were carried out under the same conditions as in Example 1, and five ceramic articles of Example 3 were produced.

[0139] For the obtained ceramic articles, in the same manner as in Example 1, analysis was performed on the three-point bending strength, dimensional accuracy, relative density, and the crystal structure and composition of the phases constituting the ceramic articles.

[0140] The evaluation results of the three-point bending strength, relative density, crystal grain size, and the abundance ratio of the Gd4Al2O9 phase of Example 3 are shown in Table 1 together with the results of Example 1.

[0141] The dimensional accuracy of the ceramic article of Example 3 was excellent at 1% or less. Also, similar to the ceramic article of Example 1, the shape of the shaped article did not change before and after the implementation of steps (ii) and (iii), and the similar shape was maintained.

[0142] The ceramic article of Example 3 had a phase separation structure similar to that of Example 1. That is, five phases were confirmed: a phase composed of Al2O3, a phase composed of GdAlO3 (composite compound 1), a phase composed of Gd4Al2O9 (composite compound 2), a phase composed of Gd2O3, and a phase mainly composed of zirconium oxide with a fluorite structure. The Gd4Al2O9 phase, which is considered to greatly contribute to the mechanical strength, was present in the ceramic article at a ratio of 4% by weight according to the XRD results. The main metal elements constituting the phase mainly composed of zirconium oxide with a fluorite structure were Zr, Gd, and Tb.

[0143] Also in the ceramic article obtained in this example, there was no bias in the distribution of the phase mainly composed of zirconium oxide, and it is considered that the zirconium oxide component diffused from the crack part into the shaped article and recrystallized as a phase separation structure while incorporating rare earth elements. When the amount of Zr contained in the ceramic article was examined, among the metal elements constituting the ceramic article of this example, the amount of Zr was 0.7 mol%.

[0144] (Example 4) In the same manner as in Example 1, a shaped article of W40 mm × D4 mm × H3 mm was produced for the three-point bending strength test (step (i)). When the surface of the shaped article was observed with an optical microscope, the Ra of the unevenness on the surface of the shaped article was 20 μm or less.

[0145] In step (ii) of this example, a 15% by weight zirconium oxide-containing liquid 3 was prepared and used using the same dispersant and solvent as in Example 1. The step of absorbing the zirconium oxide-containing liquid 3 into the shaped article (step (ii)) and the step of heating the shaped article that had absorbed the zirconium oxide-containing liquid (step (iii)) were also carried out under the same conditions as in Example 1.

[0146] In Example 4, steps (ii) and (iii) were alternately repeated three times each. In this way, five ceramic articles for strength tests were obtained for Example 4.

[0147] Similar to Example 1, for the ceramic article of Example 4, three-point bending strength, relative density, dimensional accuracy, and analysis of the crystal structure and composition of the phases constituting the shaped article were also performed.

[0148] The evaluation results of the three-point bending strength, relative density, particle size, and the proportion of the phase of Gd4Al2O9 (composite compound 2) in the ceramic article of Example 4 are shown in Table 1 together with the results of Example 1.

[0149] The dimensional accuracy of the ceramic article of Example 4 was excellent at 1% or less. Also, similar to the shaped article of Example 1, the shape of the shaped article did not change before and after the implementation of steps (ii) and (iii), and maintained a similar shape.

[0150] Also, the ceramic article of Example 4 had a phase separation structure similar to that of Example 1. That is, five phases were confirmed: a phase composed of Al2O3, a phase composed of GdAlO3 (composite compound 1), a phase composed of Gd4Al2O9 (composite compound 2), a phase composed of Gd2O3, and a phase mainly composed of zirconium oxide with a fluorite structure. The phase composed of Gd4Al2O9 (composite compound 2), which is considered to greatly contribute to the mechanical strength, was present in the ceramic article at a ratio of 2% by weight according to the XRD results. The main metal elements constituting the phase mainly composed of zirconium oxide with a fluorite structure were Zr, Gd, and Tb.

[0151] There was no bias in the distribution of the phase mainly composed of zirconium oxide in the ceramic article of Example 4 either. It is considered that the zirconium oxide component diffused from the crack part into the shaped article and recrystallized as a phase separation structure while taking in rare earth elements. When the amount of Zr contained in the ceramic article was examined, among the metal elements constituting the ceramic article of this example, the amount of Zr was 0.4 mol%.

[0152] (Examples 5 and 6) In the same manner as in Example 1, a shaped article of W40 mm × D4 mm × H3 mm was produced for the three-point bending strength test (step (i)). When the surface of the shaped article was observed with an optical microscope, the Ra of the unevenness on the surface of the shaped article was 20 μm or less.

[0153] The mixed solution of zirconium hydroxide aqueous solution and HNO3 was heated at 90 °C for 30 minutes, and then the mixed solution was filtered and dried to obtain a precursor powder. By calcining the precursor powder at 1000 °C, a zirconium oxide raw material powder with an average particle size of 40 nm was obtained.

[0154] Similarly, by calcining the precursor powder at 1030 °C, a zirconium oxide raw material powder with an average particle size of 90 nm was obtained.

[0155] Using the zirconium oxide raw material powder, in the same manner as in Example 1, a zirconium oxide-containing liquid 4 containing particles with an average particle size of 40 nm and a zirconium oxide-containing liquid 5 containing particles with an average particle size of 90 nm were prepared. The zirconium oxide-containing liquid 4 was formulated so that the content of zirconium oxide in the liquid was 30% by weight. The zirconium oxide-containing liquid 5 was formulated so that the content of zirconium oxide in the liquid was 15% by weight.

[0156] In Example 5, zirconium oxide-containing liquid 4 was used as the metal component-containing liquid. The step of absorbing zirconium oxide-containing liquid 4 into the shaped article (step (ii)), and the step of heating the shaped article that had absorbed zirconium oxide-containing liquid 4 (step (iii)) were carried out under the same conditions as in Example 1. In Example 5, steps (ii) and (iii) were repeated alternately three times each.

[0157] In Example 6, zirconium oxide-containing liquid 5 was used as the metal component-containing liquid. The step of absorbing zirconium oxide-containing liquid 5 into the shaped article (step (ii)), and the step of heating the shaped article that had absorbed zirconium oxide-containing liquid 5 (step (iii)) were carried out under the same conditions as in Example 1. In Example 6, steps (ii) and (iii) were repeated alternately five times each.

[0158] In this way, for each of Example 5 and Example 6, five ceramic articles for strength testing were obtained.

[0159] Similar to Example 1, for each of the ceramic articles of Example 5 and Example 6, three-point bending strength, relative density, dimensional accuracy, and analysis of the crystal structure and composition of the phases constituting the shaped article were performed. The evaluation results are shown in Table 1 together with the results of Example 1.

[0160] In both Example 5 and Example 6, the dimensional accuracy of the ceramic article was excellent at 1% or less. Also, similar to the shaped article of Example 1, the shape of the shaped article did not change before and after the implementation of steps (ii) and (iii), and similar shapes were maintained.

[0161] The ceramic articles of Example 5 and Example 6 had a phase separation structure similar to that of Example 1. That is, it contained five phases: a phase composed of Al2O3, a phase composed of GdAlO3 (composite compound 1), a phase composed of Gd4Al2O9 (composite compound 2), a phase composed of Gd2O3, and a phase mainly composed of zirconium oxide with a fluorite structure. The main metal elements constituting the phase mainly composed of zirconium oxide with a fluorite structure were Zr, Gd, and Tb.

[0162] There was no bias in the distribution of the phase mainly composed of zirconium oxide, and the zirconium oxide component diffused from the crack part into the shaped article and recrystallized as a phase separation structure while taking in rare earth elements. When the amount of Zr contained in each of the ceramic articles of Example 5 and Example 6 was examined, the amount of Zr in Example 5 was 1.1 mol%, and the amount of Zr in Example 6 was 0.5 mol%.

[0163] (Examples 7 and 8) SiO2 powder with an average particle size of about 38 μm and Tb4O7 powder with an average particle size of 4 μm were prepared, and each powder was weighed so that Si was 96.5 mol% in terms of oxide and Tb was 3.5 mol% in terms of oxide. The weighed powders were mixed in a dry ball mill for 30 minutes to obtain a mixed powder (raw material powder). When the composition analysis of the raw material powder was performed by ICP emission spectroscopic analysis, the content of aluminum oxide was less than 1 mol%.

[0164] Next, except for the points where the output of the laser beam was 47.5 W, the drawing speed was 60 mm / s, and the drawing pitch was 80 μm, in the same manner as in Example 1, a rectangular parallelepiped of 5 mm × 42 mm × 6 mm was produced as the shaped objects of Example 7 and Example 8. When the surface of the shaped object was observed with an optical microscope, the shaped object was porous, and the Ra of the portion excluding the concave and convex holes on the surface of the shaped object was 20 μm or less.

[0165] The produced shaped object was separated from the alumina base, and by polishing, a shaped object of W40 mm × D4 mm × H3 mm for a three-point bending strength test was obtained.

[0166] As the metal component-containing liquid, an aluminum oxide-containing liquid was adopted. Silicon oxide and aluminum oxide, which are the main components of the shaped object, are in a eutectic relationship. Alumina fine particles with an average particle diameter of 25 nm (manufactured by Kanto Chemical Co., Inc.), 2-hydroxyethyl acrylate and 3-acryloxypropyltrimethoxysilane as dispersants, and methyl ethyl ketone as a solvent were mixed so that the content of alumina in the dispersion liquid was 70% by weight, and uniformly stirred to obtain aluminum oxide-containing liquid 1.

[0167] The above-mentioned shaped object processed for testing was made to absorb the aluminum oxide-containing liquid 1, degassed under reduced pressure for 1 minute, impregnated with the liquid up to the inside of the shaped object, and then naturally dried for 1 hour (step (ii)).

[0168] Subsequently, the shaped object that had absorbed the aluminum oxide-containing liquid 1 was placed in an electric furnace and heated. The temperature was raised to 1610 °C, which is above the eutectic point of silicon oxide and aluminum oxide and below the melting point of silicon oxide, in 2.5 hours in an air atmosphere, held at 1610 °C for 50 minutes, then the power supply was terminated and cooled to 200 °C or lower in 5.0 hours (step (iii)).

[0169] In Example 7, the step of making the shaped object absorb the aluminum oxide-containing liquid 1 (step (ii)) and the heat treatment step (step (iii)) were alternately repeated twice each to produce 5 ceramic articles.

[0170] In Example 8, alumina fine particles with an average particle diameter of 25 nm (manufactured by Kanto Chemical Co., Inc.) were calcined at 1100 °C and then pulverized to produce aluminum oxide particles with an average particle diameter of 90 nm, which were used as a raw material for the metal component-containing liquid 2 of aluminum oxide. Five ceramic articles of Example 8 were produced in the same manner as in Example 7, except that the aluminum oxide particles were changed.

[0171] Similar to Example 1, for each of the ceramic articles of Example 7 and Example 8, three-point bending strength, relative density, dimensional accuracy, and analysis of the crystal structure and composition of the phases constituting the shaped article were performed. The results of Example 7 and Example 8 are shown in Table 1.

[0172] In both Example 7 and Example 8, the dimensional accuracy of the ceramic articles was excellent at 1% or less. Also, similar to the shaped articles of other examples, the shape of the shaped article hardly changed before and after the implementation of steps (ii) and (iii), and similar shapes were maintained.

[0173] The ceramic articles of Example 7 and Example 8 had a phase separation structure including a SiO2 (cristobalite) phase, a Si2Tb2O7 phase, and a phase composed of Al2O3. Furthermore, a non-stoichiometric composite oxide composed of Al2O3 - SiO2 also existed. The Si2Tb2O7 phase and the non-stoichiometric composite oxide composed of Al2O3 - SiO2 corresponded to the phases of the two kinds of composite oxides, and the Al2O3 phase corresponded to the phase derived from the inorganic particles of the metal component-containing liquid.

[0174] There was no bias in the distribution of the phase composed of aluminum oxide, and the aluminum oxide component diffused from the crack part into the shaped article and recrystallized as a phase separation structure. When the amount of Al contained in each of the ceramic articles of Example 7 and Example 8 was examined, the amount of Al in Example 7 was 0.8 mol%, and the amount of Al in Example 8 was 0.4 mol%.

[0175] (Comparative Example 1) In the same manner as in Example 1, five shaped articles with W40 mm × D4 mm × H3 mm were produced. When the surface of the shaped article was observed with an optical microscope, the Ra of the unevenness on the surface of the shaped article was 20 μm or less.

[0176] An article was produced in the same manner as in Example 1, except that the step of causing the produced shaped article to absorb the metal component-containing liquid (step (ii)) and the step of heating the shaped article impregnated with the metal component-containing liquid (step (iii)) were not carried out.

[0177] For the shaped article of Comparative Example 1 as well, in the same manner as in Example 1, the three-point bending strength, the relative density, and the evaluation of the crystal structure and composition of the phases constituting the shaped article were carried out. The evaluation results of the three-point bending strength and the relative density are shown in Table 1. Since the heating step (step (iii)) was not carried out in Comparative Example 1, there were regions in a partially amorphous state. Therefore, the particle size evaluation was carried out only on the crystalline part.

[0178] The shaped article of Comparative Example 1 was composed mainly of a phase composed of Al2O3, a phase composed of GdAlO3, a Gd2O3 phase that was the undissolved residue of the raw material, and an amorphous phase with compositional fluctuations. Cracks depending on the drawing direction of the laser beam were formed in the shaped article of Comparative Example 1. That is, there were cracks extending in a direction that was approximately 45 degrees diagonal to each side of the rectangle. The width of the cracks was from several nm to several μm.

[0179] (Comparative Example 2) In the same manner as in Example 1, five shaped articles of W40 mm × D4 mm × H3 mm were produced. When the surface of the shaped article was observed with an optical microscope, the Ra of the unevenness on the surface of the shaped article was 20 μm or less.

[0180] An article of W40 mm × D4 mm × H3 mm for a three-point bending strength test was produced in the same manner as in Example 1, except that the step of causing the obtained shaped article to absorb the inorganic oxide metal component-containing liquid (step (ii)) was omitted and only step (iii) was carried out. That is, after shaping, the shaped article was placed in an electric furnace and only heat treatment was performed. The temperature was raised to 1670 °C in 2.5 hours in an air atmosphere, held at 1670 °C for 50 minutes, then the power supply was terminated and the cooling process by natural cooling was repeated three times to produce five ceramic articles.

[0181] Similar to Example 1, for the ceramic article of Comparative Example 2, three-point bending strength, relative density, and analysis of the crystal structure and composition of the phases constituting the ceramic article were also performed.

[0182] The measurement results of the three-point bending strength and relative density are shown in Table 1. As a result of the analysis, the ceramic article of Comparative Example 2 was composed of two phases, a phase composed of Al2O3 and a phase composed of GdAlO3. In addition, cracks depending on the drawing direction of the laser beam remained in the comparative ceramic article of Comparative Example 2. That is, cracks extending in a direction that was approximately 45 degrees to each side of the rectangle remained. The width of the cracks was from several nm to several μm.

[0183] (Comparative Examples 3 and 4) α-Al2O3 powder with an average particle size of about 20 μm was prepared. When the composition of the raw material powder was analyzed by ICP emission spectroscopic analysis, the content of zirconium oxide was less than 1 mol%. Next, five shaped articles each according to Comparative Examples 3 and 4 were produced through the same process as that of FIG. 1 described above.

[0184] For the formation of the comparative shaped article, shaped articles of W50 mm × D10 mm × H8 mm were produced under the same conditions as in Example 1 except that the output of the laser was 50 W, the irradiation speed of the laser was 50 mm / s, and the drawing pitch of the laser was 50 μm. The unevenness on the surface of the comparative shaped article was so large that it could be visually confirmed, and Ra was unmeasurable.

[0185] The shape of the shaped article was adjusted to W40 mm × D4 mm × H3 mm by polishing. When the surface of the polished shaped article was observed with an optical microscope, cracks depending on the drawing direction of the laser beam were formed. That is, cracks extending in a direction that was approximately 45 degrees to each side of the rectangle were present.

[0186] Fe2O3 particles (manufactured by Kanto Chemical Co., Inc.) with a particle size of 25 nm were mixed with 2-hydroxyethyl acrylate and 3-acryloxypropyltrimethoxysilane as dispersants and stirred uniformly. To this, propylene glycol monomethyl ether acetate was added as a solvent so that the iron oxide content in the dispersion was 70% by weight, and it was stirred uniformly to obtain an iron oxide-containing solution.

[0187] Note that aluminum oxide, which is a component constituting the shaped article of this comparative example, does not form a eutectic with iron oxide in the dispersion.

[0188] In Comparative Example 3, referring to the phase diagram of the Al2O3-Fe2O3 system, the maximum temperature of the heat treatment was set to 1800 °C, a temperature higher than 1700 °C at which a phase change occurs. Otherwise, after absorbing the iron oxide-containing solution into the shaped article under the same conditions as in Example 1, heat treatment was performed to obtain 5 ceramic articles.

[0189] Also, in Comparative Example 4, 5 ceramic articles were produced in the same manner as in Comparative Example 3, except that the maximum temperature of the heat treatment was set to 1650 °C, a temperature lower than 1700 °C at which a phase change occurs in the Al2O3-Fe2O3 system.

[0190] Regarding the ceramic articles of Comparative Example 3 and Comparative Example 4 as well, in the same manner as in Example 1, three-point bending strength, dimensional accuracy, relative density, and analysis of the crystal structure and composition of the phases constituting the ceramic article were performed. The evaluation results are shown in Table 1.

[0191] The dimensional accuracy of the ceramic articles of Comparative Example 3 and Comparative Example 4 was both 1% or less.

[0192] Further, when the cross-section near the center of the ceramic articles of Comparative Example 3 and Comparative Example 4 was polished and observed by SEM, cracks depending on the drawing direction remained in both ceramic articles. In the ceramic article of Comparative Example 3, it was composed of (Al, Fe)2O3 with a corundum structure, and a large amount of Fe was detected near the crack, and no phase separation structure was observed. Most of the ceramic article of Comparative Example 4 was composed of Al2O3 with a corundum structure, and AlFe2O4 with a spinel structure was partially formed near the crack.

[0193] (Comparative Example 5) Except for not performing the step of absorbing the metal component-containing liquid into the shaped article (step (ii)), in the same manner as in Example 7, a shaped article of W40 mm × D4 mm × H3 mm was produced for the three-point bending strength test. That is, only the step of absorbing the metal component-containing liquid (step (ii)) was omitted, and the shaped article was placed in an electric furnace for heat treatment (step (iii)). The temperature was raised to 1610°C in 2.5 hours in an air atmosphere, held at 1610°C for 50 minutes, then the power supply was terminated and the cooling process by natural cooling was repeated twice to produce five ceramic articles.

[0194] For the ceramic article of Comparative Example 5 as well, in the same manner as in Example 7, analysis of the three-point bending strength, relative density, and the crystal structure and composition of the phases constituting the comparative ceramic article was performed. The measurement results are shown in Table 1.

[0195] As a result of the analysis, the ceramic article of Comparative Example 5 was composed of two phases, the SiO2 (cristobalite) phase and the Si2Tb2O7 phase. Further, cracks extending in a direction that was approximately 45 degrees to each side of the square and depending on the drawing direction of the laser beam also remained in the ceramic article of Comparative Example 5. The width of the cracks was from several nm to several μm.

[0196] [Table 1]

[0197] (Discussion) From the results shown in Table 1, the following was found.

[0198] The ceramic articles according to Examples 1 to 6, which were made using the metal component-containing liquid of the present invention and whose main component is aluminum oxide, had a significantly improved three-point bending strength compared to the ceramic articles of Comparative Examples 1 to 4 that did not use the metal component-containing liquid of the present invention. From this, it was confirmed that by using the metal component-containing liquid according to the present invention, the mechanical strength of the shaped article can be significantly improved.

[0199] In addition, in Comparative Examples 3 and 4, which were made using a metal component-containing liquid containing particles mainly composed of iron oxide that does not form a eutectic with aluminum oxide constituting the shaped article, cracks remained almost as they were during shaping, and high mechanical strength as in Examples 1 to 6 could not be obtained. In Comparative Examples 3 and 4, it is considered that only the Fe component in the iron oxide particles diffused into the shaped article and melting of the crack portion did not occur.

[0200] On the other hand, in Examples 1 to 6 using a metal component-containing liquid of zirconium oxide that can form a eutectic with aluminum oxide constituting the shaped article, melting occurred only near the cracks, and it is considered that the cracks were reduced or eliminated while maintaining the shape and dimensions of the shaped article. In addition, since it was recrystallized in a form incorporating the zirconium oxide particle component, it is considered that a high mechanical strength (three-point bending strength) of 100 MPa or more was obtained in the ceramic parts mainly composed of aluminum oxide.

[0201] In addition, in Examples 1 to 5 where the integrated time of the heat treatment was as short as 30 minutes or less, the particle size of the crystal particles constituting the ceramic article was as small as 10 μm or less, and a higher mechanical strength was obtained compared to Example 6 where the integrated time of the heat treatment was as long as 50 minutes.

[0202] Furthermore, in Examples 1 to 6, there was a tendency that the greater the abundance ratio of the composite compound Gd4Al2O9 phase, the better the mechanical strength obtained.

[0203] The ceramic articles mainly composed of silicon oxide in Examples 7 and 8 were porous with relative densities of 82.2% and 80.3%. It is presumed that this was due to the high viscosity of the silicon oxide component during melting by laser irradiation, resulting in a porous state. Despite the fabricated shaped articles being porous, mechanical strengths of around 20 MPa were obtained by using the metal component-containing liquid of the present invention. In contrast, Comparative Example 5, which did not use the dispersion liquid of the present invention, had a low three-point bending strength of 7 MPa.

[0204] Comparing Example 7 and Example 8, Example 7 using a dispersion liquid with a smaller particle size obtained higher mechanical strength than Example 8 using a dispersion liquid with a larger particle size. This is considered to be because the smaller particles penetrated deep into the cracks and exerted an effect.

[0205] From the comparison of Examples 1 to 4, it can be seen that when the content of inorganic oxide particles in the dispersion liquid is large, high mechanical strength can be obtained even with a small number of executions of steps (ii) and (iii).

[0206] Furthermore, comparing Example 3 and Example 4, it can be seen that the three-point bending strength of the shaped article improves as steps (ii) and (iii) are repeated a larger number of times. This is considered to be because the proportion of repaired cracks increased.

[0207] In all the examples and Comparative Examples 1 and 2, a high shaping accuracy with an Ra of the surface unevenness of the shaped article of 20 μm or less was obtained. In contrast, in Comparative Examples 3 and 4, unevenness visible to the naked eye (presumed to be 100 to 300 μm) was observed on the surface and side surfaces of the shaped article. This is recognized to be because the ceramic powder, which is the raw material powder used in each example, did not contain a component with high energy absorption with respect to the irradiated laser beam, specifically, Tb2O 3.5 powder (Tb4O7 powder).

[0208] By using the metal component-containing liquid of the present invention as described above, in additive manufacturing, it is possible to achieve high shape accuracy while improving the mechanical strength of the shaped article, and to obtain a ceramic article having high mechanical strength despite its complex or fine shape. Furthermore, the ceramic article according to the present invention can be easily manufactured by using a ceramic article manufacturing kit including a powder mainly composed of ceramics, the above-described solvent, and the metal component-containing liquid containing inorganic particles containing a metal element.

Industrial Applicability

[0209] According to the present invention, it is possible to provide a metal component-containing liquid that can improve the mechanical strength of a shaped article while taking advantage of the characteristics of the direct shaping method in which a dense and complex-shaped shaped article can be obtained. In addition, it is possible to provide a method for manufacturing a ceramic article using the metal component-containing liquid.

Explanation of Signs

[0210] 100 Solidification part 101 Powder 102 Powder layer 103 Uncured powder 110 Shaped article 130 Base 151 Stage 152 Roller 180 Energy beam source 181 Scanner unit 201 Cladding nozzle 202 Powder supply hole 203 Energy beam

Claims

【Claim 1】 A ceramic article manufactured by an additive manufacturing technique, having a phase separation structure including three phases having at least a first type of metal element in common, wherein the first phase among the three phases is a phase of an oxide of the first type of metal element, and the second phase and the third phase among the three phases are phases of a composite oxide of the first type of metal element. A ceramic article characterized by this.

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