Titanium-yttrium solid-dissolved zirconia sintered body

Abstract

To provide at least one of: a titanium-yttrium solid-dissolved zirconia sintered body exhibiting transparency, in which fracture is hard to progress as compared with a conventional titanium-yttrium solid-dissolved zirconia sintered body exhibiting transparency; a method for producing the same; and an application thereof.SOLUTION: A titanium-yttrium solid-dissolved zirconia sintered body has an yttrium content of 3.5 mol% or more and less than 6.0 mol%, a titanium content of 6.0 mol% or more and 18.5 mol% or less, an in-line transmission of 45% or more at a sample thickness of 1±0.1 mm and a measured wavelength of 600 nm, a ratio of the in-line transmission at the sample thickness of 1±0.1 mm and the measured wavelength of 600 nm to the total light transmission at the sample thickness of 1±0.1 mm and the measured wavelength of 600 nm of 0.70 or more, and a fracture toughness (KIC) of 1.5 MPa m 0.5 or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a sintered body of zirconia in which titanium and yttrium are solid-solved.

Background Art

[0002] A sintered body made of zirconia in which titanium and yttrium are solid-solved and having only a cubic crystal phase is known as a sintered body having high transparency (Patent Document 1). However, such a sintered body has low mechanical properties. Therefore, improvement of the mechanical properties of such a transparent sintered body has been studied.

[0003] For example, in Patent Document 2, by controlling the crystal grain size of a primary sintered body to be subjected to hot isostatic pressing (hereinafter also referred to as "HIP") treatment, a sintered body of zirconia in which titanium and yttrium are solid-solved, having a three-point bending strength of 255 MPa and transparency, can be obtained. Further, in Patent Document 3, by controlling the reduction degree of titanium (Ti) in HIP treatment, a sintered body of titanium and yttrium solid-solved zirconia having a three-point bending strength of 300 MPa or more and transparency can be obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] The sintered compacts disclosed in Patent Documents 2 and 3 exhibit both a linear transmittance that shows transparency and a high three-point bending strength. Therefore, they are less likely to develop defects compared to conventional sintered compacts of zirconia in which titanium and yttrium having transparency are dissolved. On the other hand, since these sintered compacts have a weak resistance to the progression of fracture such as cracks, once a defect occurs, the fracture rapidly progresses.

[0006] An object of the present disclosure is to provide at least one of a sintered compact of zirconia in which titanium and yttrium are dissolved, which is less likely to have fracture progress compared to a conventional sintered compact of zirconia in which titanium and yttrium having transparency are dissolved and which also shows transparency, a method for manufacturing the same, and uses thereof. [Means for Solving the Problems]

[0007] In the present disclosure, a titania - yttria - zirconia sintered compact having transparency was examined. As a result, it was found that by controlling the crystal grain structure, transparency can be maintained even in a composition that was conventionally considered to cause a decrease in transparency. Furthermore, it was found that a sintered compact having such a composition becomes a titania - yttria - zirconia sintered compact with improved resistance to the progression of fracture.

[0008] That is, the present invention is as described in the claims, and the gist of the present disclosure is as follows. [1] A sintered compact of zirconia in which titanium and yttrium are dissolved, comprising cubic crystal grains containing a tetragonal domain, wherein the yttrium content is 3.5 mol% or more and less than 6.0 mol%, and the titanium content is 6.0 mol% or more and 18.5 mol% or less. [2] The sintered compact according to [1] above, containing alumina. [3] The sintered compact according to [1] or [2] above, wherein the crystallite size determined from the half - width of the peak having a peak top at 2θ = 74.0 ± 0.3° in its XRD pattern is 1400 nm or less. [4] The sintered body according to any one of [1] to [3] above, having an average crystal grain size of 5 μm or more and 50 μm or less. [5] The sintered body according to any one of [1] to [4] above, having a linear transmittance of 45% or more at a sample thickness of 1 ± 0.1 mm and a measurement wavelength of 600 nm. [6] The fracture toughness value (K IC ) is 1.5 MPa·m 0.5 or more, and the sintered body according to any one of [1] to [5] above. [7] The sintered body according to any one of [1] to [6] above, having a three-point bending strength of 280 MPa or more. [8] A primary sintering step of obtaining a primary sintered body by subjecting a green body containing a zirconia source, a yttrium source, and a titanium source, with a yttrium content of 3.5 mol% or more and less than 6.0 mol%, and a titanium content of 6.0 mol% or more and 18.5 mol% or less, to atmospheric pressure sintering at 1260 °C or higher in an oxidizing atmosphere; a hot isostatic pressing step of obtaining a pressure-treated body by subjecting the primary sintered body to pressure sintering at 1500 °C or higher in a reducing atmosphere; and a heat treatment step of heat-treating the pressure-treated body in an oxidizing atmosphere, and a method for producing the sintered body according to any one of [1] to [7] above. [9] The production method according to [8] above, wherein the green body is obtained by a forming step of forming raw material powder obtained by a mixing method of mixing a mixed raw material powder of a zirconia source and a yttrium source with a titanium source.

[10] The production method according to [8] or [9] above, wherein the actually measured density of the primary sintered body is 5.35 g / cm 3 or more and 6.00 g / cm 3 or less.

[11] The production method according to any one of [8] to

[10] above, wherein the pressure sintering is a hot isostatic pressing treatment.

[12] The production method according to any one of [8] to

[11] above, wherein the reducing atmosphere is a weak reducing atmosphere.

[13] The production method according to any one of [8] to

[12] above, wherein the temperature reduction rate from the holding temperature in the pressure sintering to 1000 °C is 50 °C / min or more and 300 °C / min or less.

[14] A member containing the sintered body according to any one of [1] to [7] above.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide at least one of a sintered body of zirconia in which titanium and yttrium are solid-dissolved, which is difficult for fracture to progress compared with a conventional sintered body of zirconia in which titanium and yttrium are solid-dissolved and which exhibits transparency, a method for producing the same, and its use.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] Hereinafter, an example of an embodiment of the sintered body of the present disclosure will be shown and described. Each configuration and parameter disclosed in this specification can be arbitrarily combined, and the upper and lower limits of the values disclosed in this specification can be arbitrarily combined.

[0012] A "composition" is a substance having a certain composition, and examples thereof include one or more selected from the group consisting of powders, granules, compacts, green compacts, and sintered bodies.

[0013] A "powder" is an aggregate of powder particles and is a composition having fluidity. A "zirconia powder" is a powder mainly composed of zirconia and is a powder essentially composed of zirconia.

[0014] A "granular powder" is a powder composed of granular particles. The "granular particles" are particles (tertiary particles) in which powder particles (particularly, at least one of primary particles and secondary particles) are slowly aggregated by physical force and may contain an organic component.

[0015] The "formed body" is a composition having a certain shape composed of powder particles aggregated by physical force, and in particular, a composition in a state where heat treatment has not been performed after the shape is imparted (for example, after molding). The "zirconia formed body" is a formed body having zirconia as a main component, and is a formed body essentially composed of zirconia. In this embodiment, the "formed body" and the "compacted powder" are used interchangeably.

[0016] The "sintered body" is a composition having a certain shape composed of crystal particles, and is a composition in a state heat-treated at a temperature equal to or higher than the sintering temperature. The "zirconia sintered body" is a sintered body having zirconia as a main component, and further is a sintered body essentially composed of zirconia.

[0017] The "stabilizing element" is an element having a function of stabilizing the crystal phase of zirconia by dissolving in zirconia.

[0018] The "powder X-ray diffraction pattern" is the XRD pattern of a composition obtained by powder X-ray diffraction (hereinafter also referred to as "XRD") measurement under the following conditions.

[0019] X-ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: continuous scan Scan speed: 1° / min Measurement range: 2θ = 20° to 80° Accelerating voltage and current: 40 kV·40 mA Divergence vertical limiting slit: 10 mm Divergence / incidence slit: 1° Receiving slit: open Detector: semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185 mm XRD measurement can be carried out using a general X-ray diffractometer (e.g., Ultima IV, manufactured by RIGAKU). When the composition is a sintered body, its surface may be polished to a surface roughness Ra ≦ 0.02 μm, and XRD measurement may be performed on the surface.

[0020] Examples of XRD peaks corresponding to each crystal plane of zirconia measured in the above XRD measurement include XRD peaks having peak tops at the following 2θ.

[0021] XRD peak corresponding to monoclinic (111) plane: 2θ = 31 ± 0.5° XRD peak corresponding to monoclinic (11-1) plane: 2θ = 28 ± 0.5° XRD peak corresponding to tetragonal (111) plane: 2θ = 30 ± 0.5° XRD peak corresponding to cubic (111) plane: 2θ = 30 ± 0.5° XRD peak corresponding to tetragonal (400) plane: 2θ = 72.8 ± 0.3° XRD peak corresponding to tetragonal (004) plane: 2θ = 74.8 ± 0.3° XRD peak corresponding to cubic (400) plane: 2θ = 74.0 ± 0.3° Note that the XRD peak corresponding to the tetragonal (111) plane and the XRD peak corresponding to the cubic (111) plane are measured as one overlapping peak.

[0022] The detection of XRD peaks can be obtained by performing profile fitting on the XRD pattern (hereinafter, also referred to as the "processed XRD pattern") after smoothing and background removal processing using a split pseudo-Voigt function. Analyses of XRD patterns such as smoothing processing, background processing, and detection of XRD peaks may be performed under the following conditions using a program such as an analysis program attached to the X-ray diffractometer (for example, integrated powder X-ray analysis software PDXL Ver. 2.2, manufactured by Rigaku Corporation). In this embodiment, the peaks detected thereby are defined as XRD peaks. Note that the XRD pattern and the processed XRD pattern may include minute peaks (so-called noise) that are not detected in the fitting.

[0023] Scherrer constant: 1.000 Smoothing method: Smoothing by β-spline, γ threshold value = 1.50 Background removal method: Straight line connecting endpoints Kα2 line removal method: Intensity ratio = 0.497 Peak search method: Peak top method, α cut-off value = 3.00 Profiling fitting method: Split pseudo-Voigt function [Sintered body] This embodiment is a sintered body of zirconia containing titanium and yttrium, which consists of cubic crystal particles containing a tetragonal domain, with the yttrium content being 3.5 mol% or more and less than 6.0 mol% and the titanium content being 6.0 mol% or more and 18.5 mol% or less. As a result, it has the same transparency as the conventional sintered body of zirconia composed of cubic crystal particles and has a higher mechanical strength than these.

[0024] The sintered body of the present embodiment is a sintered body of zirconia, which is a sintered body having zirconia as the main component (matrix), so-called zirconia sintered body. Among zirconia sintered bodies, the sintered body of the present embodiment is particularly a sintered body of zirconia in which titanium and yttrium are dissolved, so-called titania-yttria-zirconia sintered body. Further, the sintered body of the present embodiment is a sintered body having transparency, and more particularly, a sintered body of zirconia having transparency, so-called transparent zirconia sintered body.

[0025] The fact that titanium and yttrium are dissolved in zirconia, and further that the sintered body of the present embodiment does not contain titanium and yttrium not dissolved in zirconia (undissolved titanium and yttrium) can be determined by the fact that XRD peaks corresponding to titanium compounds and yttrium compounds are not detected in the XRD pattern. Note that it is acceptable to contain undissolved titanium and yttrium within a range that does not impair the effects of the sintered body of the present embodiment, such as containing undissolved titanium and yttrium to such an extent that they are not detected in the XRD pattern. Even in such a case, for convenience, in the present embodiment, it is regarded as not containing undissolved titanium and yttrium.

[0026] Yttrium (Y) functions as a stabilizing element that stabilizes the crystal phase of zirconia by dissolving in zirconia. On the other hand, titanium (Ti) dissolves in zirconia, but in the sintered body of the present embodiment, it is considered not to have a function of stabilizing the crystal phase of zirconia.

[0027] The sintered body of this embodiment has a yttrium content of 3.5 mol% or more and less than 6.0 mol%. When the yttrium content is less than 3.5 mol%, the transparency is low, and even if it has light transmittance, it becomes a sintered body with extremely low transparency. When the yttrium content is 6.0 mol% or more, the resistance to the progress of fracture is low, and it becomes easy to break. As a result, it becomes difficult to apply it to uses such as decorative members and other transparent ceramics. In order to obtain a sintered body having a fracture toughness value and transparency applicable to decorative members and the like, the yttrium content is 4.0 mol% or more, 4.2 mol% or more, 4.35 mol% or more, or 4.5 mol% or more, and also 5.8 mol% or less, 5.5 mol% or less, less than 5.5 mol%, 5.2 mol% or less, 5.0 mol% or less, or 4.7 mol% or less, and it is preferable that it is 4.0 mol% or more and 5.8 mol% or less, 4.0 mol% or more and less than 5.5 mol%, 4.2 mol% or more and 5.5 mol% or less, 4.2 mol% or more and less than 5.5 mol%, 4.2 mol% or more and 5.2 mol% or less, 4.35 mol% or more and 5.2 mol% or less, or 4.5 mol% or more and 5.0 mol% or less.

[0028] The yttrium content in this embodiment is the ratio [mol%] of the amount of substance [mol] of yttrium in terms of Y2O3 to the total amount of substance [mol] of zirconia (ZrO2) and solid-solved elements in terms of oxide.

[0029] Note that the solid solution element in the present embodiment is an element that replaces zirconium (Zr) cations in zirconia, and this is contained in zirconia in the form of cations. Specific solid solution elements include one or more selected from the group consisting of titanium (Ti), yttrium (Y), erbium (Er), terbium (Tb), calcium (Ca), magnesium (Mg), lanthanum (La), cerium (Ce), gadolinium (Gd), praseodymium (Pr), Nd (neodymium), samarium (Sm), europium (Eu), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). It is preferable that the solid solution elements contained in the sintered body of the present embodiment are only yttrium and titanium, and it is preferable that it does not contain lanthanum.

[0030] It is preferable that the sintered body of the present embodiment does not contain un-dissolved solid solution elements, but it may contain un-dissolved solid solution elements as long as the effects of the sintered body of the present embodiment are not impaired. In the present embodiment, the fact that it does not contain un-dissolved solid solution elements may be confirmed by the fact that no XRD peak corresponding to the compound of the solid solution element is detected in the XRD pattern.

[0031] The sintered body of the present embodiment has a titanium content of 6.0 mol% or more and 18.5 mol% or less. When the titanium content is less than 6.0 mol%, crystal particles containing tetragonal crystals are likely to be formed, and it becomes difficult to obtain a sintered body composed of crystal particles composed of cubic crystals. When the titanium content exceeds 18.5 mol%, defects occur during the production (sintering) of the sintered body, and the sintered body cannot be obtained. The titanium content is 7.0 mol% or more, 8.0 mol% or more, 9.0 mol% or more, 9.3 mol% or more, 10.0 mol% or more, or 12.0 mol% or more, and is also 17.0 mol% or less, 15.0 mol% or less, or 13.0 mol% or less, and it is preferable that it is 7.0 mol% or more and 17.0 mol% or less, 8.0 mol% or more and 15.0 mol% or less, 9.0 mol% or more and 13.0 mol% or less, 9.3 mol% or more and 13.0 mol% or less, or 10.0 mol% or more and 13.0 mol% or less.

[0032] The titanium content in this embodiment is the ratio [mol%] of the amount of substance [mol] of titanium in terms of TiO2 to the total amount of substance [mol] of zirconia (ZrO2) and solid-solved elements in terms of oxide.

[0033] In the sintered body of this embodiment, titanium and yttrium may have the above-mentioned contents, but the total content of titanium and yttrium is 9.5 mol% or more, 10.0 mol% or more, 13.0 mol% or more, or 15.0 mol% or more, and is also less than 24.5 mol%, 20.0 mol% or less, 18.0 mol% or less, or 17.0 mol% or less. In addition, examples include 9.5 mol% or more and less than 24.5 mol%, 10.0 mol% or more and 20.0 mol% or less, 13.0 mol% or more and 20.0 mol% or less, or 15.0 mol% or more and 17.0 mol% or less. The total content of the solid-solved elements in this embodiment may also be the same amount.

[0034] The sintered body of this embodiment may be a sintered body composed of zirconia in which titanium and yttrium are solid-solved, but in addition to zirconia in which titanium and yttrium are solid-solved, it may also contain alumina (Al2O3). The strength tends to increase by including alumina.

[0035] The sintered body of this embodiment may not contain alumina (the alumina content is 0% by mass), but may contain alumina. The sintered body of this embodiment only needs to have an alumina content of 0% by mass or more. Examples of the alumina content include 0.15% by mass or less, 0.08% by mass or less, or less than 0.05% by mass. When alumina is contained, the alumina content may be more than 0% by mass, 0.01% by mass or more, or 0.04% by mass or more. The alumina content of the sintered body of this embodiment is preferably 0% by mass or more and 0.15% by mass or less, 0% by mass or more and less than 0.05% by mass, and more preferably more than 0% by mass and 0.15% by mass or less, 0.01% by mass or more and 0.08% by mass or less, or 0.04% by mass or more and 0.08% by mass or less.

[0036] In this embodiment, the alumina content may be determined from the ratio [mass%] of the mass of aluminum converted to Al2O3 to the total mass of the metal elements in the sintered body converted to oxides (hereinafter also referred to as "metal mass").

[0037] The sintered body of this embodiment is a sintered body of zirconia in which titanium and yttrium are solid - dissolved. Since it is a sintered body having zirconia as a matrix, its composition contains, in addition to zirconia, titanium, yttrium, and, if necessary, alumina. That is, the composition of the sintered body of this embodiment is essentially such that the remainder excluding yttrium, titanium, and aluminum is zirconia.

[0038] The sintered body of this embodiment preferably contains no impurities, but may contain impurities as long as the effects are achieved. Specific impurities include, for example, metal elements, and more particularly alkali metal elements. Also, the sintered body of this embodiment may contain hafnia (HfO2), which is an inevitable impurity of zirconia. When obtaining values related to the composition such as density in this embodiment, hafnia may be regarded as zirconia for the calculation.

[0039] For example, in the case of a sintered body of zirconia containing alumina and in which titanium and yttrium are solid - dissolved, the composition of the sintered body of this embodiment may be determined as follows.

[0040] Metal mass [g] =Al2O3 + TiO2+Y2O3 + ZrO2 Content of yttrium [mol%] ={Y2O3 / (ZrO2 + Y2O3+TiO2)}×100 Content of titanium [mol%] ={TiO2 / (ZrO2 + Y2O3+TiO2)}×100 Content of solid - dissolved elements [mol%] ={(Y2O3 + TiO2) / (ZrO2 + Y2O3+TiO2)}×100 Content of aluminum [mass%] ={Al2O3 / (Al2O3+TiO2+Y2O3+ZrO2)}×100 The sintered body of this embodiment is composed of cubic crystal grains, and more specifically, it is composed of cubic crystal grains of zirconia in which yttrium and titanium are solid-solved. Cubic crystals are crystal phases having a shape without anisotropy. Since the sintered body of this embodiment is composed of cubic crystal grains, light scattering caused by the anisotropy of the crystal structure does not occur, so the sintered body exhibits high transparency. In addition, the sintered body of this embodiment may contain alumina crystal grains in addition to the cubic crystal grains (cubic crystal grains of zirconia in which yttrium and titanium are solid-solved).

[0041] In this embodiment, for convenience, the crystal phase of zirconia may be regarded as consisting of three crystal phases: cubic, tetragonal, and monoclinic. Also, if no XRD peaks of tetragonal and monoclinic crystals are detected in the XRD pattern of the sintered body, it may be regarded that the sintered body is composed of cubic crystal grains. The sintered body of this embodiment can be regarded as being composed of cubic zirconia, and further, it may be regarded that the zirconia contained in the sintered body of this embodiment is composed of cubic crystals. Specifically, the fact that the sintered body of this embodiment is composed of cubic crystal grains means that in the XRD pattern, it has a peak with a peak top at 2θ = 74.0 ± 0.3°, and does not have a peak with a peak top at 2θ = 72.8 ± 0.3° or a peak with a peak top at 2θ = 74.8 ± 0.3°. This can be further confirmed.

[0042] Moreover, in the Rietveld analysis with the XRD pattern of the sintered body of this embodiment using, as references respectively, the XRD pattern of a zirconia crystal structure model consisting only of cubic crystals (cubic model) and the XRD pattern of a zirconia crystal structure model consisting of a mixed phase of cubic and tetragonal crystals (mixed crystal model), it is preferable that the cubic model fits. Thereby, it can be confirmed that the sintered body of this embodiment does not contain tetragonal crystal grains and monoclinic crystal grains.

[0043] Rietveld analysis may be performed using an analysis program (e.g., Rietan-FP). For the cubic model and the mixed crystal model, a structural model may be used in which the cubic crystal has a space group Fm-3m as a cubic crystal, and the tetragonal crystal has a space group P42nmc as a tetragonal crystal.

[0044] Thus, in the yttrium content of the sintered body of the present embodiment, it is usually a mixed-phase zirconia composed of tetragonal crystal grains and cubic crystal grains. In contrast, the sintered body of the present embodiment has the above-described yttrium content and has a crystal phase composed only of cubic crystals.

[0045] It is preferable that the sintered body of the present embodiment has a moderately high crystallinity of cubic crystals, and the crystallite size (hereinafter, also simply referred to as "crystallite size") obtained from the half-value width of the peak (hereinafter, also referred to as "FWHM") having a peak top at 2θ = 74.0 ± 0.3° in its XRD pattern is 1400 nm or less, 1050 nm or less, 800 nm or less, or 650 nm or less. The crystallite size can be exemplified as 150 nm or more, 300 nm or more, 400 nm or more, or 500 nm or more, and it is preferably 300 nm or more and 1400 nm or less, 400 nm or more and 800 nm or less, or 400 nm or more and 650 nm or less.

[0046] In the present embodiment, the crystallite size may be obtained by the following formula.

[0047] D = κλ / βcosθ In the above formula, D is the crystallite size (nm), κ is the Scherrer constant (κ = 1.000), λ is the wavelength of the measured X-ray (when using CuKα line as the radiation source, λ = 0.1548 nm), β is the half-value width (°) of the peak having a peak top at 2θ = 74.0 ± 0.3°, and θ is the Bragg angle.

[0048] The half-value width of the peak having a peak top at 2θ = 74.0 ± 0.3° may be obtained by fitting the processed XRD pattern obtained by the above-described method.

[0049] The crystal particles constituting the sintered body of the present embodiment are cubic crystal particles containing a tetragonal domain. By including the tetragonal domain, the resistance to the progress of fracture increases. Even when defects such as cracks occur in the sintered body of the present embodiment, the expansion of the generated defects is suppressed. As a result, the fracture toughness value is higher than that of a conventional sintered body composed of cubic crystal particles, and the sintered body is less likely to be fractured.

[0050] The sintered body of the present embodiment is mainly composed of zirconia crystal particles (more specifically, zirconia crystal particles in which yttrium and titanium are solid-solved). The crystal particles are an aggregate (particles) composed of a plurality of crystallites. The domain (crystal domain) in the present embodiment is a region composed of crystallites having the same crystal structure in the crystal particles. Further, the tetragonal domain is a region composed of crystallites having a tetragonal crystal in the cubic crystal particles. Usually, cubic crystal particles are composed of only crystallites having a cubic crystal (only cubic domains). In contrast, the crystal particles constituting the sintered body of the present embodiment are cubic crystal particles containing a tetragonal domain. Therefore, the crystal particles in the sintered body of the present embodiment are crystal particles containing a tetragonal domain in addition to the cubic domain, and can also be regarded as crystal particles composed of the cubic domain and the tetragonal domain.

[0051] That the sintered body of the present embodiment is composed of cubic crystal particles containing a tetragonal domain can be confirmed by the following method. That is, by detecting the above-described XRD peak, it can be confirmed that the sintered body is composed of cubic crystal particles. In addition to this, an electron diffraction map is obtained for the crystal particles observed in the nano-diffraction mapping by a transmission electron microscope (hereinafter also referred to as "TEM") measured under the following conditions, and an electron diffraction spot (hereinafter also referred to as "spot") corresponding to the tetragonal crystal plane is observed, whereby it can be confirmed that the crystal particles contain a tetragonal domain.

[0052] Analysis orientation: Tetragonal

[0100] Accelerating voltage: 200 Kv Observation magnification: 250,000 times TEM nano-diffraction mapping and electron beam diffraction maps may be obtained using a general TEM (for example, JEM-F200, manufactured by JEOL Ltd.) and a general electron beam diffraction apparatus (for example, 4D-STEM, manufactured by Gatan).

[0053] Figures 1 and 2 are diffraction patterns of cubic crystal particles having a tetragonal domain and cubic crystal particles not having a tetragonal domain, respectively. It can be confirmed that Figure 1 has spots corresponding to the tetragonal crystal (the arrowed part in Figure 1 corresponds to the spots equivalent to the (100) plane of the tetragonal crystal and its equivalent planes). On the other hand, Figure 2 does not have spots corresponding to the tetragonal crystal. As shown in Figure 1, by having spots corresponding to the tetragonal crystal in the diffraction pattern, it can be confirmed that the crystal particles contain a tetragonal domain.

[0054] The average crystal grain size of the sintered body of the present embodiment is 5 μm or more, 10 μm or more, or 15 μm or more, and may be 50 μm or less, 40 μm or less, 30 μm or less, or 20 μm or less. Since the smaller the average crystal grain size, the higher the mechanical strength tends to be, the average crystal grain size of the sintered body of the present embodiment is preferably 5 μm or more and 50 μm or less, 10 μm or more and 40 μm or less, 10 μm or more and 30 μm or less, or 15 μm or more and 30 μm or less.

[0055] The average crystal grain size is the average diameter of the crystal particles constituting the sintered body, and is a value obtained by the planimetric method from the SEM observation diagram obtained by observing the surface of the sintered body with a scanning electron microscope (hereinafter, also referred to as "SEM"). Specifically, in order to suppress the variation in the crystal particles observed due to the difference in the SEM observation locations, two or more, and further two or more and four or less SEM observation diagrams are used, and on each SEM observation diagram, the number of crystal particles (n c ) inside the circle and the total number of crystal particles (N i ) on the circumference are 100 ± 30. Draw two circles. For all the drawn circles, the crystal grain size of each circle is obtained by the planimetric method, and the average value thereof may be taken as the average crystal grain size.

[0056] SEM observation in the measurement of the average crystal grain size may be carried out using a general scanning electron microscope (for example, JSM-IT500LA, manufactured by JEOL Ltd.). The SEM observation may be carried out by appropriately setting the observation magnification so that the number of crystal particles to be analyzed by image analysis (crystal particles in which the crystal grain boundaries are observed without interruption in the SEM observation image) is 450 ± 50. The conditions for the SEM observation may be the following conditions.

[0057] Accelerating voltage: 15 kV Irradiation current: 40 nA Observation magnification: 400 to 10,000 times Prior to the measurement, the sintered body sample may be used after being subjected to surface grinding using a #200 grindstone, followed by lapping using diamond abrasives with particle sizes of 3 μm and 1 μm, and then thermal etching in an air atmosphere at a temperature at which the crystal grain boundaries can be confirmed.

[0058] The shape of the sintered body of the present embodiment includes, for example, at least any one selected from the group consisting of spherical, substantially spherical, elliptical, disk-shaped, columnar, cubic, rectangular parallelepiped-shaped, polyhedral-shaped, and substantially polyhedral-shaped. Further, any shape according to the purpose of various applications and the like may be used.

[0059] The sintered body of the present embodiment has transparency. For example, the linear transmittance (hereinafter, also referred to as "It") at a sample thickness of 1 ± 0.1 mm and a measurement wavelength of 600 nm is 45% or more, and further preferably 50% or more. It is one of the indicators showing transparency, and the higher It is, the higher the transparency is. Therefore, It of the sintered body of the present embodiment is preferably 52% or more or 55% or more. Although it is preferable that It is higher, It of the sintered body of the present embodiment can be exemplified as 75% or less, 70% or less, 65% or less, or 60% or less, and also 45% or more and 75% or less, 50% or more and 75% or less, 52% or more and 70% or less, 52% or more and 65% or less, or 55% or more and 60% or less.

[0060] The sintered body of this embodiment preferably has high translucency. For example, the total light transmittance (hereinafter also referred to as "Tt") at a sample thickness of 1 ± 0.1 mm and a measurement wavelength of 600 nm is preferably 60% or more. Tt is one of the indicators showing translucency, and the higher the Tt, the higher the translucency. The sintered body of this embodiment only needs to satisfy the above-mentioned It, but the Tt may be 65% or more, 70% or more, or 71% or more, and may also be 80% or less, 77% or less, 75% or less, or 73% or less. Further, the Tt of the sintered body of this embodiment may be 60% or more and 80% or less, 65% or more and 80% or less, 70% or more and 75% or less, or 71% or more and 75% or less.

[0061] Since it is easier to obtain a more aesthetically pleasing transparent member, the ratio of It to Tt (hereinafter also referred to as "It / Tt ratio") is preferably high. However, the It / Tt ratio of the sintered body of this embodiment may be 0.95 or less, 0.90 or less, or 0.85 or less. For highly aesthetic transparency, It / Tt may be 0.70 or more or 0.75 or less, and may be 0.70 or more and 0.95 or less, 0.70 or more and 0.90 or less, or 0.75 or more and 0.85 or less.

[0062] In this embodiment, both Tt and It are light transmittance values obtained by measuring in accordance with JIS K 7361-1. The ratio of the transmitted light (the sum of the linearly transmitted light and the diffusely transmitted light) to the incident light is the total light transmittance [%], and the ratio of the linearly transmitted light to the incident light is the linear transmittance [%]. Also, there is a relationship that total light transmittance [%] = linear transmittance [%] + diffuse transmittance [%]. As the measurement sample, a disk-shaped sintered body with a sample thickness of 1.0 ± 0.1 mm and a surface roughness Ra of both surfaces ≦ 0.02 μm is used, and as the measurement device, a general spectrophotometer (for example, spectrophotometer V-650, manufactured by JASCO Corporation) may be used.

[0063] In addition to having high transparency, the sintered body of this embodiment has high resistance to the progress of fracture. The sintered body of this embodiment has a fracture toughness value (K IC ) which is one of the indicators of the resistance to the progress of fracture, and is 1.5 MPa·m0.5 2.0 MPa·m or more 0.5 or 2.2 MPa·m or more 0.5 Preferably, it is 2.0 MPa·m or more, 2.2 MPa·m or more. Although a high fracture toughness value is preferable, the fracture toughness value of the sintered body of the present embodiment is 3.0 MPa·m 0.5 or less, 2.8 MPa·m or less 0.5 or 2.6 MPa·m or less 0.5 or less, and 1.5 MPa·m or more and 3.0 MPa·m 0.5 or less, 2.0 MPa·m or more and 3.0 MPa·m 0.5 or less, or 2.2 MPa·m or more and 2.8 MPa·m 0.5 or less, or 2.2 MPa·m or more and 2.8 MPa·m 0.5 or less, or 2.2 MPa·m or more and 2.8 MPa·m 0.5 or 2.8 MPa·m or more 0.5 Preferably, it is 2.8 MPa·m or less.

[0064] The "fracture toughness value (K IC )" in the present embodiment is the value of fracture toughness [MPa·m 0.5 measured by a method according to the SEPB method defined in JIS R 1607. The fracture toughness value is measured using a columnar sintered body sample with a span of 30 mm, a width of 4 mm, and a thickness of 3 mm, and the average value of 10 measurements may be used as the fracture toughness value of the sintered body of the present embodiment. Also, a general strength tester (for example, Instron tester model 5582, manufactured by Instron Corporation) may be used for the measurement. Note that JIS R 1607 defines two methods for measuring fracture toughness: the IF method and the SEPB method. The value measured by the IF method tends to be larger than that measured by the SEPB method. Furthermore, since the IF method is a simple measurement method, the variation in measurement values for each measurement is large. Therefore, the fracture toughness value in the present embodiment and the fracture toughness value measured by the IF method cannot be compared in terms of the absolute value of the values. Similarly, the fracture toughness value measured by a method other than the SEPB method and the fracture toughness value measured by the SEPB method cannot be compared in terms of the absolute value of the values.

[0065] Since the sintered body of the present embodiment is less likely to break when processed, it preferably has high strength. It is preferable that the three-point bending strength of the sintered body of the present embodiment is 280 MPa or more, 310 MPa or more, 350 MPa or more, or 420 MPa or more. The strength of the sintered body of the present embodiment only needs to have a strength suitable for processing, and examples include that the three-point bending strength is 800 MPa or less, 750 MPa or less, 700 MPa or less, or 600 MPa or less, and it can be exemplified that it is 280 MPa or more and 800 MPa or less, 310 MPa or more and 700 MPa or less, or 420 MPa or more and 600 MPa or less.

[0066] The "three-point bending strength" in the present embodiment is a value measured by a method according to JIS R 1601. As the measurement sample, a columnar shape with a width of 4 mm, a thickness of 3 mm, and a length of 45 mm is used, the distance between the fulcrums is 30 mm, and a load may be applied in the horizontal direction of the measurement sample for measurement. A general strength tester (for example, a tabletop universal precision tester AGX-10kNX, manufactured by Shimadzu Corporation) may be used for the measurement.

[0067] The sintered body of the present embodiment may be a sintered body (hereinafter, also referred to as "composite sintered body") composed of the sintered body of the present embodiment and a sintered body other than the sintered body of the present embodiment. The composite sintered body is a sintered body in a state where the sintered body of the present embodiment and a sintered body other than the sintered body of the present embodiment are integrated by sintering, whereby a member with higher aesthetic properties is obtained. Here, the "state integrated by sintering" is different from a state integrated by a physical structure such as the use of an adhesive or fitting, or other physical actions, and means that the sintered body of the present embodiment and a sintered body other than the sintered body of the present embodiment form an interface and are integrated.

[0068] The sintered body other than the sintered body of the present embodiment contained in the composite sintered body may be a sintered body having an aesthetic property different from that of the sintered body of the present embodiment, but is preferably a sintered body of zirconia, and more preferably an opaque zirconia sintered body. Examples of the opaque zirconia sintered body include zirconia sintered bodies in which It is 0% or more and 5% or less, further 0% or more and 3% or less, still further 0% or more and 1% or less, and particularly 0% or more and 0.5% or less. Examples of the sintered body other than the sintered body of the present embodiment contained in the composite sintered body include, for example, sintered bodies of zirconia exhibiting colored or achromatic colors. Examples of the sintered body of zirconia exhibiting achromatic colors include white, gray, or black zirconia sintered bodies. On the other hand, examples of the colored zirconia sintered body include sintered bodies of zirconia exhibiting red, orange, yellow, green, blue, indigo, or violet colors, and further sintered bodies of zirconia exhibiting black color.

[0069] The sintered body of the present embodiment can be applied to uses as transparent ceramics, and can be used, for example, in one or more selected from the group of optical members, exterior members, and decorative members. Further, the sintered body of the present embodiment may be used as a member including the same. [Manufacturing method of sintered body] The manufacturing method of the sintered body of the present embodiment may be any manufacturing method as long as a sintered body satisfying the above-described configuration is obtained. As a preferable manufacturing method, there is a method for manufacturing a sintered body (hereinafter, also referred to as "the manufacturing method of the present embodiment") including a primary sintering step of obtaining a primary sintered body by subjecting a molded body containing a zirconia source, a yttrium source, and a titanium source, having a yttrium content of 3.5 mol% or more and less than 6.0 mol%, and a titanium content of 6.0 mol% or more and 18.5 mol% or less to atmospheric pressure sintering at 1260°C or higher in an oxidizing atmosphere, a pressure sintering step of obtaining a pressure-treated body by subjecting the primary sintered body to pressure sintering at 1500°C or higher in a reducing atmosphere, and a heat treatment step of heat-treating the pressure-treated body in an oxidizing atmosphere. By the manufacturing method of the present embodiment, a sintered body of zirconia composed of only cubic crystal phases can be obtained, although the composition was conventionally considered to be such that only a sintered body of zirconia having a mixed phase of tetragonal crystal and cubic crystal could be obtained.

[0070] The manufacturing method of this embodiment includes a primary sintering step of subjecting a green compact containing a zirconia source, a yttrium source, and a titanium source to atmospheric pressure sintering to obtain a primary sintered body, where the yttrium content is 3.5 mol% or more and less than 6.0 mol%, and the titanium content is 6.0 mol% or more and 18.5 mol% or less. Thereby, a primary sintered body to be subjected to a pressure sintering treatment is obtained.

[0071] In the primary sintering step, a green compact is provided, where the yttrium content is 3.5 mol% or more and less than 6.0 mol%, the titanium content is 6.0 mol% or more and 18.5 mol% or less, and it contains a zirconia source, a yttrium source, and a titanium source.

[0072] The zirconia source may be zirconia (ZrO2).

[0073] The yttrium source may be a yttrium compound, and examples include one or more selected from the group of oxides, hydroxides, oxyhydroxides, and halides containing yttrium. At least one of yttrium chloride and oxide is preferred, and more preferably yttrium oxide (yttria; Y2O3) and at least one of yttrium chloride (YCl3).

[0074] In addition to zirconia and a yttrium compound, or instead of zirconia and a yttrium compound, the green compact may contain yttrium solid-solution zirconia (yttrium-stabilized zirconia). Furthermore, it is preferable that the green compact contains yttrium solid-solution zirconia instead of zirconia and a yttrium compound (that is, the zirconia source and the yttria source are yttrium solid-solution zirconia). Yttrium solid-solution zirconia is zirconia stabilized by the solid solution of yttrium, so-called yttrium-stabilized zirconia.

[0075] The titanium source may be any titanium compound, and examples include one or more selected from the group of titanium-containing oxides, hydroxides, oxyhydroxides, and halides. At least one of titanium-containing chlorides and oxides, further at least one of titanium oxide (titania; TiO2) and titanium chloride (TiCl4), and still further, it may be titanium oxide.

[0076] The molded body may contain an alumina source. The alumina source may be at least one of alumina and its precursors, and is preferably alumina (Al2O3).

[0077] The molded body may contain a binder. By containing a binder, the operability (handling) and shape retention are improved. The binder may be any binder that can be used for granulation and molding of ceramics, and is preferably an organic binder. Examples of the organic binder include one or more selected from the group of polyvinyl alcohol, polyvinyl butyrate, wax, and acrylic resins, preferably at least one of polyvinyl alcohol and acrylic resins, and more preferably acrylic resins. In this embodiment, the acrylic resin is a polymer containing at least one of acrylic ester and methacrylic ester. Specific examples of the binder include one or more selected from the group of AS-1100, AS-1800, and AS-2000 (all are product names, manufactured by Toagosei Co., Ltd.).

[0078] The composition of the molded body has a yttrium content of 3.5 mol% or more and less than 6.0 mol%, and a titanium content of 6.0 mol% or more and 18.5 mol% or less. Further, it may contain a metal element in a composition similar to that of the target sintered body, and it may contain a metal element in a composition similar to that of the above-mentioned sintered body.

[0079] When containing a binder, the content of the binder can be exemplified as 0.5 mass% or more or 1 mass% or more, and also 10 mass% or less or 5 mass% or less. The content of the binder may be determined as follows.

[0080] {(W2 - W1) / W2} × 100 In the above formula, W1 is the mass [g] of the formed body after heat treatment at 250°C or higher and 400°C or lower in an air atmosphere, and W2 is the mass [g] of the formed body before the heat treatment. Note that due to differences in the calculation method, the composition of the formed body including the binder may not appear to be 100% by mass.

[0081] Regarding the formed body, as long as a formed body in which a zirconia source, a yttrium source, a titanium source, and, if necessary, an alumina source are uniform can be obtained, the manufacturing method thereof is arbitrary. For example, as a manufacturing method of the formed body, a manufacturing method of the formed body having a forming step of forming a powder containing a zirconia source, a yttrium source, and a titanium source can be mentioned.

[0082] For the forming step, the same powder as the above-mentioned zirconia source, yttrium source, and titanium source (hereinafter, also referred to as "starting materials" respectively, and collectively referred to as "raw material powder") may be used. The raw material powder may contain an alumina source. Further, the manufacturing method of the present embodiment has a pressure sintering step. In pressure sintering, since it is hardly affected by the sinterability of the starting materials, the starting materials may be commercially available powders (for example, reagent-grade powders) or granular powders.

[0083] The starting materials (zirconia source, yttrium source, titanium source, and alumina source) are preferably powders having similar particle sizes, and each may have an average particle diameter of 0.2 μm or more or 0.4 μm or more, and can be exemplified as 0.6 μm or less or 0.5 μm or less, and preferably 0.4 μm or more and 0.6 μm or less, or 0.4 μm or more and 0.5 μm or less.

[0084] The average particle size of the raw material powder may be an average particle size equivalent to that of the starting material, and is preferably 0.4 μm or more and 0.6 μm or less, or 0.4 μm or more and 0.5 μm or less. Further, in order to obtain a primary sintered body in which a tetragonal domain is likely to be generated in the pressure sintering under the conditions described later, the ratio of the standard deviation of the particle size [μm] to the average particle size [μm] of the raw material powder (hereinafter also referred to as "particle size standard deviation") is preferably 0.5 or less or 0.3 or less. Since actual powders have a distribution in particle size, the particle size standard deviation of the raw material powder is preferably more than 0 or 0.01 or more, and more preferably more than 0 and 0.5 or less, more than 0 and 0.3 or less, or 0.01 or more and 0.3 or less.

[0085] The raw material powder may be mixed by at least one of dry and wet methods so that the starting materials become uniform, and wet mixing is preferred. Specifically, for example, it may be mixed by at least one of the methods of stirring and mixing, ball milling, and bead milling.

[0086] Preferred mixing methods of the starting materials include a mixing method of mixing a mixed raw material powder of a zirconia source and a yttrium source with a titanium source. The mixed raw material powder may contain an alumina source. The raw material powder is a precursor of a molded body containing a zirconia source as a main component, a yttrium source, a titanium source, and an alumina source. By mixing a titanium source into zirconia in a state where a yttrium source and an alumina source are incorporated, it is considered that titanium is likely to be dissolved in zirconia in a state where a tetragonal domain is likely to be generated in the subsequent primary sintering and pressure sintering. Further, a more preferred mixing method includes a mixing method of mixing a slurry containing a mixed raw material powder of a zirconia source and a yttrium source with a slurry containing a titanium source. By mixing slurries with controlled grinding particle sizes, the physical properties of the resulting raw material powder are more easily controlled, and it is considered that a tetragonal domain of the sintered body obtained by the subsequent primary sintering and pressure sintering is likely to be stably generated.

[0087] The forming method may be any known forming method for a ceramic formed body (compressed powder), as long as it is a forming method suitable for the shape of the target formed body. Examples of the forming method include one or more selected from the group consisting of uniaxial pressing, injection molding, slip casting, sheet forming, and cold isostatic pressing (hereinafter also referred to as "CIP"). One or more selected from the group consisting of uniaxial pressing, injection molding, and CIP are preferred, and primary pressing and CIP are more preferred.

[0088] The formed body to be subjected to the primary sintering step is preferably a formed body obtained by a forming step of forming raw material powder obtained by a mixing method of mixing a mixed raw material powder of a zirconia source and a yttrium source and a titanium source. More preferably, it is a formed body obtained by a forming step of forming raw material powder obtained by a mixing method of mixing a slurry containing a mixed raw material powder of a zirconia source and a yttrium source and a slurry containing a titanium source.

[0089] In the primary sintering step, the above-mentioned formed body is sintered at normal pressure in an oxidizing atmosphere at 1260 °C or higher to obtain a primary sintered body. In the composition of the formed body to be subjected to the primary sintering step, such primary sintering results in a primary sintered body as a sintered body having no open pores. In the present embodiment, normal pressure sintering is a method of sintering by heating the object to be sintered (formed body, green body, etc.) without applying an external force during sintering. In the composition of the formed body to be subjected to the primary sintering step, when sintered at less than 1260 °C, the sintered body obtained after pressure sintering has extremely low transparency or no transparency. The holding temperature of the primary sintering (hereinafter also referred to as "primary sintering temperature") is preferably 1300 °C or higher or 1325 °C or higher. The upper limit of the primary sintering temperature can be exemplified as 1500 °C or lower or 1400 °C or lower. The following conditions are given as preferred normal pressure sintering conditions.

[0090] Sintering atmosphere: Oxidizing atmosphere, preferably air atmosphere Primary sintering temperature: 1260 °C or higher, 1300 °C or higher or 1325 °C or higher, and 1500 °C or lower or 1400 °C or lower The heating rate is 50°C / hour or more, or 80°C / hour or more, and 200°C / hour or less, or 120°C / hour or less The holding time at the holding temperature may be appropriately adjusted according to the size of the compact to be subjected to the primary sintering process and the performance of the primary sintering furnace. Examples thereof include 30 minutes or more and 15 hours or less, and further 1 hour or more and 1.5 hours or less.

[0091] The primary sintered body obtained by the primary sintering process is preferably a sintered body containing only closed pores, and it is preferably that the relative density is 90% or more. Although the relative density in this embodiment varies depending on the composition, the relative density of the primary sintered body may be 90% or more and 98% or less. This is because the measured density in the composition range of the sintered body of this embodiment is 5.35 g / cm 3 or more, 5.40 g / cm 3 or more, 5.60 g / cm 3 or more, or 5.80 g / cm 3 or more, and also 6.00 g / cm 3 or less, 5.90 g / cm 3 or less, or 5.85 g / cm 3 or less. It is preferable that it is 5.35 g / cm 3 or more and 6.00 g / cm 3 or less, 5.40 g / cm 3 or more and 5.9 g / cm 3 or less, 5.60 g / cm 3 or more and 5.85 g / cm 3 or less, 5.80 g / cm 3 or more and 5.85 g / cm 3 or less.

[0092] The "measured density" in this embodiment is a value [g / cm 3 obtained from the mass [g] with respect to the sample volume [cm 3 . For the mass, the mass obtained by weighing the sample may be used, and for the volume, the volume obtained by the Archimedes method according to JIS R 1634 may be used. As the Archimedes method, deionized water may be used as the solvent, and the pretreatment may be performed by the boiling method.

[0093] The average crystal grain size of the primary sintered body may be a crystal grain size at which pores are easily eliminated in pressure sintering, and is preferably 1.0 μm or less, more preferably 0.8 μm or less. The average crystal grain size of the primary sintered body may be 0.1 μm or more or 0.3 μm or more, and may be exemplified as 0.1 μm or more and 1.0 μm or less, or 0.3 μm or more and 0.8 μm or less.

[0094] The manufacturing method of the present embodiment includes a pressure sintering step of obtaining a pressure-treated body by pressure-sintering a primary sintered body in a reducing atmosphere. By pressure sintering, the closed pores contained in the primary sintered body are eliminated by mass transfer. As a result, the sintered body after heat treatment is densified to such an extent that the primary sintered body exhibits high transparency. When the primary sintered body is sintered in a reducing atmosphere without applying pressure, a sintered body having translucency may be obtained, but such a sintered body does not have transparency or has extremely low transparency.

[0095] Pressure sintering is performed in a reducing atmosphere. By pressure sintering in a reducing atmosphere, titanium contained in the primary sintered body is reduced, and the generation of trivalent titanium (Ti 3+ ) and the formation of oxygen vacancies due to this occur. The formation of oxygen vacancies promotes mass transfer, and as a result, closed pores are efficiently eliminated, and a dense sintered body is obtained. Further, by passing through the subsequent heat treatment step, a sintered body having high transparency is obtained. Even when the primary sintered body is sintered at normal pressure, the obtained sintered body may have translucency, but a sintered body having both high translucency and high transparency cannot be obtained.

[0096] Since mass transfer suitable for efficient elimination of closed pores easily occurs, the reducing atmosphere is preferably a weak reducing atmosphere, and more preferably an inert atmosphere in which a reducing member coexists. The inert gas atmosphere may be an argon atmosphere or a nitrogen atmosphere, and an argon atmosphere is preferred. The reducing member may be a member made of a reducing substance, and a carbon member is preferred.

[0097] In pressure sintering, a green compact is placed in a container and pressure sintered. At least one of the members constituting the pressure sintering furnace (hereinafter also referred to as the "furnace member") and the container for placing the green compact (hereinafter also referred to as the "sintering container") may be a reducing member, and examples include that at least one of the furnace member and the sintering container is a carbon member, and it is preferable that the furnace member and the sintering container are carbon members.

[0098] Preferred weakly reducing atmospheres include an argon atmosphere or a nitrogen atmosphere in which one or more selected from the group consisting of a heating element, a heat insulating material, and a sintering container are carbon members, and a more preferred weakly reducing atmosphere is an argon atmosphere in which the heating element and the sintering container are carbon members.

[0099] Pressure sintering includes at least one of hot press treatment and hot isostatic pressing (HIP treatment), and HIP treatment is preferable.

[0100] The holding temperature in pressure sintering (hereinafter also referred to as the "pressure sintering temperature") may be any temperature at which the elimination of closed pores can be promoted by mass transfer, is 1500°C or higher, and preferably 1525°C or higher or 1550°C or higher. When the pressure sintering temperature is less than 1500°C, the mechanical strength may increase in some cases, but a sintered body with extremely low transparency is obtained. As the pressure sintering temperature increases, the transparency tends to increase. Since a general-purpose HIP treatment apparatus can be used, the holding temperature may be 1700°C or lower, 1650°C or lower, or 1645°C or lower.

[0101] In order to obtain a sintered body with a higher fracture toughness value, the pressure sintering temperature is preferably 1600 °C or lower, more preferably less than 1600 °C, and even more preferably 1575 °C or lower. If the pressure sintering temperature is within the above range, a sintered body having both a linear transmittance and a fracture toughness value can be obtained. On the other hand, when the pressure sintering temperature is appropriately low within the above range, a sintered body having both a linear transmittance and a fracture toughness value and a higher fracture toughness value is likely to be obtained. Therefore, the pressure sintering temperature is preferably 1500 °C or higher and 1645 °C or lower, more preferably 1500 °C or higher and 1600 °C or lower, and even more preferably 1525 °C or higher and 1575 °C or lower.

[0102] The pressure in the pressure treatment may be any pressure as long as the elimination of closed pores by the pressure treatment can proceed, and examples include 50 MPa or higher or 100 MPa or higher, and 200 MPa or lower or 170 MPa or lower, and 50 MPa or higher and 200 MPa or lower, or 100 MPa or higher and 170 MPa or lower.

[0103] The treatment time at the pressure sintering temperature may be appropriately adjusted according to the size of the primary sintered body and the characteristics of the pressure sintering furnace, and examples include 10 minutes or longer and 10 hours or shorter, or 30 minutes or longer and 5 hours or shorter.

[0104] In pressure sintering, the temperature may be raised to the pressure sintering temperature at a rate of 5 °C / min or higher or 10 °C / min or higher. There is no upper limit to the heating rate, but since a general-purpose pressure sintering furnace can be used, examples of the heating rate include 100 °C / min or lower or 50 °C / min or lower.

[0105] Since tetragonal domains are likely to be formed in the cubic crystal grains, the cooling rate from the pressure sintering temperature to 1000 °C is preferably 50 °C / min or higher or 70 °C / min or higher. The upper limit of the cooling rate may be appropriately set according to the pressure sintering furnace used, and examples include 300 °C / min or lower or 150 °C / min or lower. In this embodiment, the cooling rate from the pressure sintering temperature to 1000 °C may be 50 °C / min or higher and 300 °C / min or lower, 70 °C / min or higher and 150 °C / min or lower, or 70 °C / min or higher and 100 °C / min or lower.

[0106] The manufacturing method of this embodiment includes a heat treatment step of heat-treating a processing body in an oxidizing atmosphere. As a result, trivalent titanium (Ti 3+ ) contained in the processing body is oxidized to tetravalent titanium (Ti 4+ ), eliminating oxygen defects and obtaining the sintered body of this embodiment with transparency.

[0107] The oxidizing atmosphere includes an oxygen atmosphere or an air atmosphere, and an air atmosphere is preferred.

[0108] The holding temperature in the heat treatment (hereinafter, also referred to as "heat treatment temperature") may be any temperature at which the oxidation of titanium proceeds efficiently, which is 800°C or higher, or 850°C or higher, and may be less than 1200°C or 1100°C or lower. A range of 800°C or higher and less than 1200°C, or 850°C or higher and 1100°C or lower is preferred.

[0109] The holding time at the heat treatment temperature may be appropriately adjusted according to the size of the processing body and the performance of the heat treatment furnace. Examples include 30 minutes or more and 10 hours or less, or 45 minutes or more and 3 hours or less.

Examples

[0110] Hereinafter, the present disclosure will be described in detail by way of examples. However, the present disclosure is not limited to these examples.

[0111] (Composition analysis) The composition of the composition was measured by ICP analysis.

[0112] (XRD measurement) An XRD pattern of the sintered body was obtained by XRD measurement under the following conditions using an X-ray diffractometer (for example, Ultima IV, manufactured by Rigaku Corporation).

[0113] X-ray source: CuKα ray (λ = 0.15418 nm) Measurement mode: Continuous scan Scan speed: 1° / min Measurement range: 2θ = 20° to 80° Accelerating voltage and current: 40 mA · 40 kV Divergence vertical limiting slit: 10 mm Divergence / incidence slit: 1° Light-receiving slit: open Detector: Semiconductor detector (D / teX Ultra) Filter: Ni filter Goniometer radius: 185 mm Prior to measurement, a sintered body surface polished to a surface roughness Ra ≤ 0.02 μm was used as the measurement sample, and XRD measurement was performed on its surface.

[0114] Using an analysis program (product name: Integrated Powder X-ray Analysis Software PDXL Ver. 2.2, manufactured by Rigaku), smoothing processing and background removal processing were performed, and the XRD pattern (processed XRD pattern) was analyzed by performing profile fitting with a split pseudo-Voigt function. The smoothing processing, background removal processing, and analysis conditions are shown below.

[0115] Scherrer constant: 1.000 Smoothing method: Smoothing by β-spline, γ threshold value = 1.50 Background removal method: Straight line connecting endpoints Kα2 line removal method: Intensity ratio = 0.497 Peak search method: Peak top method, α cut-off value = 3.00 Profiling fitting method: Split pseudo-Voigt function Prior to measurement, the surface of the sintered body was polished using sandpaper with a particle size of #400 according to JIS R 6001-2, and then lapping and polishing was performed using a diamond abrasive with a particle size of 3 μm.

[0116] For the obtained XRD pattern, using an analysis program (Rietan-FP), for the cubic model and the mixed crystal model, a structural model with a cubic crystal having a space group of Fm-3m as a cubic crystal and a tetragonal crystal having a space group of P42nmc as a tetragonal crystal was used, and Rietveld analysis was performed.

[0117] (Crystallite size) In this embodiment, the crystallite size was determined by the following formula.

[0118] D = κλ / βcosθ In the above formula, D is the crystallite size (nm), κ is the Scherrer constant (κ = 1.000), λ is the wavelength of the measured X-ray (when using CuKα line as the radiation source, λ = 0.1548 nm), β is the full width at half maximum (°) of the peak having a peak top at 2θ = 74.0 ± 0.3°, and θ is the Bragg angle.

[0119] The full width at half maximum of the peak having a peak top at 2θ = 74.0 ± 0.3° was determined by analyzing under the same conditions as the above-described XRD measurement.

[0120] (Measured density) The measured density was determined from the mass [g] with respect to the sample volume [cm 3 . The mass used was the mass obtained by weighing the sample, and the volume used was the volume determined by the Archimedes' method according to JIS R 1634. For the Archimedes' method, ion-exchanged water was used as the solvent, and the pretreatment was performed by the boiling method.

[0121] (TEM nanodiffraction) A field emission type transmission electron microscope (equipment name: JEM-F200, manufactured by JEOL Ltd.) and an electron beam diffraction device (equipment name: 4D-STEM, manufactured by Gatan Inc.) were used to obtain a TEM nanodiffraction mapping and a diffraction pattern analyzed from the

[0100] orientation of cubic crystals for the crystal particles observed in the TEM nanodiffraction mapping, and cubic spots were confirmed.

[0122] Accelerating voltage: 200 Kv Observation magnification: 250,000 times (Total light transmittance and linear transmittance) Tt and It were measured under the following conditions using a general UV-VIS spectrophotometer (device name: Spectrophotometer V-650, manufactured by JASCO Corporation). In the obtained spectrum, the total light transmittance and linear transmittance at a wavelength of 600 nm were defined as Tt and It, respectively. As the measurement sample, a disc-shaped sintered body with a sample thickness of 1 ± 0.1 mm and a surface roughness Ra ≤ 0.02 μm on both sides was used.

[0123] Measurement method: UV-VIS spectrophotometric measurement Measurement mode: Double-beam mode Light source: D2 / WI Measurement wavelength range: 200 nm to 900 nm Data acquisition interval: 0.5 nm (Three-point bending strength) The three-point bending strength was measured by a method according to JIS R 1601. As the measurement sample, a columnar shape with a width of 4 mm, a thickness of 3 mm, and a length of 45 mm was used, the distance between the fulcrums was 30 mm, and a load was applied in the horizontal direction of the measurement sample for measurement. A strength tester (device name: Desktop Universal Precision Tester AGX-10kNX, manufactured by Shimadzu Corporation) was used for the measurement.

[0124] (Fracture toughness value) The fracture toughness value (K IC ) [MPa·m 0.5 was measured. The measurement was performed with a distance between the fulcrums of 30 mm using a columnar sintered body sample with a width of 4 mm and a thickness of 3 mm, and the average value of 10 measurements was taken as the fracture toughness value of the sintered body of this embodiment. Also, a strength tester (for example, Instron tester model 5582, manufactured by Instron Corporation) was used for the measurement.

[0125] (Average crystal grain size) The average crystal grain size was determined from the SEM observation image observed under the following conditions using a scanning electron microscope (device name: JSM-IT500LA, manufactured by JEOL Ltd.).

[0126] Accelerating voltage: 15 kV Irradiation current: 40 nA Observation magnification: 400 to 10,000 times Prior to the measurement, the sintered body sample was first flat-ground using a #200 grinding wheel, then lapped and polished using diamond abrasives with particle sizes of 3 μm and 1 μm, and finally heat-etched in an air atmosphere for 1 hour. The heat etching temperature was set 100 °C lower than the sintering temperature.

[0127] Three SEM observation images were used. On each SEM observation image, two circles were drawn such that the total number of crystal particles (n c ) inside the circle and the number of crystal particles (N i ) on the circumference was 100 ± 30. For all the drawn circles, the crystal grain sizes of each circle were determined by the planimetric method, and the average value was taken as the average crystal grain size.

[0128] Example 1 Powder of yttrium-stabilized zirconia containing alumina with a yttrium content of 5.5 mol% and an aluminum content of 0.05 mass% was mixed with pure water. After mixing, wet grinding was performed using a ball mill until the average particle size was 0.5 μm and the standard deviation of the particle size was 0.1 μm, obtaining a zirconia slurry with a powder content (solid content concentration) of 45 mass%. The standard deviation of the particle size of the obtained powder was 0.2.

[0129] On the other hand, powder of titania was mixed with pure water, and wet grinding was performed using a ball mill until the average particle size was 0.5 μm and the standard deviation of the particle size was 0.1 μm, obtaining a titania slurry with a powder content (solid content concentration) of 20 mass%. The standard deviation of the particle size of the obtained powder was 0.2.

[0130] The obtained zirconia slurry and titania slurry were mixed such that the mass ratio of the zirconia powder to the titania powder was 92:8, obtaining a mixed slurry containing powder of yttrium-stabilized zirconia containing alumina and titania with a yttrium content of 4.67 mol%, an aluminum content of 0.046 mass%, and a titania content of 8 mass% (12.29 mol%).

[0131] The obtained mixed slurry was spray-dried at 180 °C to obtain a granular powder of yttrium-stabilized zirconia containing alumina and titania, with a yttrium content of 4.67 mol%, an aluminum content of 0.046 mass%, and a titania content of 8 mass%.

[0132] After filling 3 g of the obtained granular powder into a mold with an inner diameter of 25 mm, uniaxial pressing was performed at a pressure of 98 MPa. After molding, CIP treatment was performed at a pressure of 196 MPa to obtain a disk-shaped molded body with a diameter of 25 mm.

[0133] The obtained molded body was sintered for the first time under the following conditions to obtain a first sintered body composed of titanium and yttrium solid-solution zirconia containing alumina, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046 mass%. The first sintered body had an average crystal grain size of 0.6 μm and an actual measured density of 5.82 g / cm 3 and was as follows.

[0134] First sintering atmosphere: Air atmosphere Heating rate: 100 °C / hour Holding temperature: 1350 °C Holding time: 2 hours The obtained first sintered body was placed in a carbon container with a lid, and the carbon container was placed in a HIP apparatus equipped with a carbon heating element. Then, a HIP-treated body was obtained by performing HIP treatment in a weakly reducing atmosphere under the following conditions.

[0135] Pressure medium: Argon gas (purity: 99.9%) Heating rate: 10 °C / min Holding temperature: 1550 °C Holding pressure: 150 MPa Holding time: 1 hour After holding, the cooling rate to 1000 °C was 80 °C / min.

[0136] The obtained HIP-treated body was heat-treated in an air atmosphere at 900 °C for 1 hour to obtain a sintered body of this example composed of titanium and yttrium solid-solution zirconia containing alumina, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046% by mass.

[0137] Fig. 1 shows the TEM diffraction mapping results of the sintered body of this example. In Fig. 1, spots of the tetragonal (100) plane and equivalent tetragonal crystal planes were confirmed (the circled part in Fig. 1), and it was confirmed that all were tetragonal spots of 5 nm or less. Also, from the Rietveld analysis results of the XRD pattern of the sintered body of this example shown in Fig. 3, it was confirmed that the sintered body of this example was 100% cubic crystal. From this, it was confirmed that the sintered body of this embodiment was a sintered body composed of cubic crystal particles having tetragonal domains. The sintered body of this example had an average crystal grain size of 18 μm and a crystallite size of 448 nm.

[0138] Example 2 A sintered body of this example composed of titania and yttrium solid-solution zirconia containing alumina, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046% by mass, was obtained in the same manner as in Example 1 except that the primary sintering temperature was 1300 °C. The measured density of the obtained primary sintered body was 5.40 g / cm 3 and the crystallite size of the sintered body of this example was 934 nm.

[0139] Example 3 A sintered body of this example composed of titania and yttrium solid-solution zirconia containing alumina, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046% by mass, was obtained in the same manner as in Example 1 except that the holding temperature in the HIP treatment was 1500 °C. The measured density of the obtained primary sintered body was 5.82 g / cm 3 and the crystallite size of the sintered body of this example was 804 nm.

[0140] Example 4 A sintered body of this example composed of titania containing alumina and yttrium solid-solution zirconia, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046 mass%, was obtained in the same manner as in Example 1 except that the holding temperature in the HIP treatment was 1600°C. The measured density of the obtained primary sintered body was 5.82 g / cm 3 It was, and the average crystal grain size of the sintered body of this example was 36.0 μm, and the crystallite size was 678 nm. It was.

[0141] Comparative Example 1 A sintered body of this comparative example composed of titanium containing alumina and yttrium solid-solution zirconia, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046 mass%, was obtained in the same manner as in Example 1 except that the primary sintered body was treated by atmospheric-pressure sintering with an atmosphere of 600°C / hour heating rate, a holding temperature of 1550°C, and a holding time of 1 hour instead of HIP treatment.

[0142] The sintered body of this comparative example was a sintered body composed of cubic crystal particles and tetragonal crystal particles, had low translucency, and did not have transparency.

[0143] Comparative Example 2 A sintered body of this comparative example composed of titanium containing alumina and yttrium solid-solution zirconia, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046 mass%, was obtained in the same manner as in Example 1 except that the primary sintering temperature was 1250°C. The sintered body of this comparative example had translucency but had a low Tt and did not have transparency.

[0144] Comparative Example 3 The green compact was sintered under normal pressure (reductive normal-pressure sintering) in a mixed gas atmosphere of 95% argon - 5% hydrogen as a reducing atmosphere, at a holding temperature of 1550°C, and for a holding time of 1 hour, and the sintered body of this comparative example was obtained in the same manner as in Example 1 except that HIP treatment was not performed. Despite being a sintered body obtained by sintering in a reducing atmosphere, the sintered body of this comparative example had low translucency and no transparency.

[0145] Comparative Example 4 A sintered body of this comparative example composed of titanium and yttrium solid-solution zirconia containing alumina, with a yttrium content of 4.67 mol%, a titanium content of 12.29 mol%, and an alumina content of 0.046 mass%, was obtained in the same manner as in Example 1 except that the treatment temperature in HIP treatment was 1450°C. The sintered body of this comparative example had low translucency and no transparency.

[0146] Comparative Example 5 A sintered body of yttrium and titania-stabilized zirconia with a yttrium content of 9.0 mol% and a titanium content of 10 mol% was obtained by the same method as in Example 3 of JP-A-2011-102227. That is, commercially available zirconia powder (product name: TZ-10Y, manufactured by Tosoh Corporation) and titania powder (product name: PT-401M, manufactured by Ishihara Sangyo Co., Ltd.) were weighed so that the yttrium content was 9.0 mol% and the titania content was 10 mol%, and ball-milled and mixed for 72 hours using zirconia balls with a diameter of 10 mm as a grinding medium, and the dried powder was prepared as a raw material powder.

[0147] After the raw material powder was molded by die pressing at a pressure of 50 MPa, it was further consolidated at a pressure of 200 MPa using a cold isostatic pressing apparatus to obtain a cylindrical molded body with a diameter of 20 mm.

[0148] The molded body was subjected to primary sintering at 1325°C for 2 hours in an air atmosphere to obtain a primary sintered body having a composition of TiO2:Y2O3:ZrO2 = 0.1:0.09:0.81 (molar ratio). The obtained primary sintered body had a relative density of 90% or more, an average particle size of 2 μm or less, and a crystal phase of a mixed phase of cubic and tetragonal phases.

[0149] The obtained green compact was placed in a carbon container with a lid, and the carbon container was placed in a HIP apparatus equipped with a carbon heating element. Then, a HIP-treated body was obtained by performing HIP treatment in a weakly reducing atmosphere under the following conditions.

[0150] Pressure medium: Argon gas (purity: 99.9%) Holding temperature: 1500 °C Holding pressure: 150 MPa Holding time: 1 hour After holding, the cooling rate to 1000 °C was 80 °C / min.

[0151] The obtained HIP-treated body was heat-treated in an air atmosphere at 1000 °C for 2 hours to obtain a sintered body of this comparative example composed of titanium and yttrium solid-solution zirconia with a yttrium content of 9 mol% and a titanium content of 10 mol%. The sintered body of this comparative example was a sintered body of cubic zirconia composed of cubic crystal grains, and its crystallite size was 1409 nm.

[0152] The results of the examples and comparative examples are shown in the following table. The compositions in the following table are in terms of oxides.

[0153]

Table 1

[0154] All the sintered bodies of the examples had high transparency with It of 50% or more and also had a strength of 280 MPa or more. Furthermore, the sintered bodies of the examples had a fracture toughness value of 1.5 MPa·m 0.5 or more, and further 2.2 MPa·m 0.5As described above, it was confirmed that the sintered body has high transparency and high resistance to the progress of fracture. In addition, all of the sintered bodies of the examples have a peak having a peak top at 2θ = 74.0 ± 0.3°, and do not have a peak having a peak top at 2θ = 72.8 ± 0.3° or a peak having a peak top at 2θ = 74.8 ± 0.3°. On the other hand, the sintered bodies of Comparative Examples 3 and 4 have translucency but no transparency, and the fracture toughness value of the sintered body of Comparative Example 5 is 1.4 MPa·m 0.5 0.5 and it was confirmed that, although the It and the three-point bending strength are high, the resistance to the progress of fracture is about half that of the examples.

[0155] Example 5 A mixed slurry containing a powder of yttrium-stabilized zirconia containing alumina and titania, with a yttrium amount of 4.75 mol%, an aluminum amount of 0.047 mass%, and a titania amount of 7 mass% (10.82 mol%), was obtained in the same manner as in Example 1 except that a zirconia slurry and a titania slurry were mixed so that the mass ratio of the zirconia powder and the titania powder was 93:7. A sintered body of this example composed of titanium and yttrium solid-solution zirconia containing alumina, having a yttrium amount of 4.75 mol%, a titanium amount of 10.82 mol%, and an alumina amount of 0.047 mass%, was obtained. The measured density of the obtained primary sintered body was 5.84 g / cm 3 3 , and the sintered body of this example had an average crystal grain size of 18 μm and a crystallite size of 693 nm.

[0156] Example 6 The zirconia slurry and the titania slurry were mixed so that the mass ratio of the zirconia powder to the titania powder was 94:6, and a mixed slurry containing a powder of yttrium-stabilized zirconia containing alumina and titania with a yttrium amount of 4.83 mol%, an aluminum amount of 0.047 mass%, and a titania amount of 6 mass% (9.33 mol%) was obtained. In the same manner as in Example 1, except for the above, a sintered body of this example composed of titanium and yttrium solid-solution zirconia containing alumina with a yttrium amount of 4.83 mol%, a titanium amount of 9.33 mol%, and an alumina amount of 0.047 mass% was obtained. The measured density of the obtained primary sintered body was 5.85 g / cm 3 and the sintered body of this example had an average crystal grain size of 15 μm and a crystallite size of 584 nm.

[0157] Example 7 A powder of yttrium-stabilized zirconia containing alumina with a yttrium amount of 5.0 mol% and an aluminum amount of 0.05 mass% was mixed with pure water. After mixing, wet grinding was performed with a ball mill until the average particle size was 0.5 μm and the standard deviation of the particle size was 0.1 μm, and a zirconia slurry with a powder content (solid content concentration) of 45 mass% was obtained. In the same manner as in Example 1, except for using the obtained zirconia slurry, a sintered body of this example composed of titanium and yttrium solid-solution zirconia containing alumina with a yttrium amount of 4.35 mol%, a titanium amount of 12.26 mol%, and an alumina amount of 0.046 mass% was obtained. The measured density of the obtained primary sintered body was 5.84 g / cm 3 and the sintered body of this example had a crystallite size of 312 nm.

[0158] Example 8 Powder of yttrium-stabilized zirconia containing alumina with a yttrium content of 6.5 mol% and an aluminum content of 0.05 mass% was mixed with pure water. After mixing, it was wet-milled with a ball mill until the average particle size became 0.5 μm and the standard deviation of the particle size became 0.1 μm, and a zirconia slurry with a powder content (solid content concentration) of 45 mass% was obtained. Except for using the obtained zirconia slurry, in the same manner as in Example 1, a sintered body of this example composed of titanium and yttrium solid-solution zirconia containing alumina with a yttrium content of 5.65 mol%, a titanium content of 12.39 mol% and an alumina content of 0.046 mass% was obtained. The measured density of the obtained primary sintered body was 5.84 g / cm 3 and the sintered body of this example had a crystallite size of 1039 nm.

[0159] Example 9 Except for mixing a zirconia slurry and a titania slurry so that the mass ratio of the zirconia powder to the titania powder became 90:10, in the same manner as in Example 1, a sintered body of this example composed of titanium and yttrium solid-solution zirconia containing alumina with a yttrium content of 4.52 mol%, a titanium content of 15.18 mol% and an alumina content of 0.045 mass% was obtained. The measured density of the obtained primary sintered body was 5.81 g / cm 3 and the sintered body of this example had a crystallite size of 940 nm.

[0160] Example 10 Powder of yttrium-stabilized zirconia with a yttrium content of 5.5 mol% was mixed with pure water. After mixing, it was wet-milled with a ball mill until the average particle size became 0.5 μm and the standard deviation of the particle size became 0.1 μm, and a zirconia slurry with a powder content (solid content concentration) of 45 mass% was obtained. Except for using the obtained zirconia slurry, in the same manner as in Example 1, a sintered body of this example composed of titanium and yttrium solid-solution zirconia with a yttrium content of 4.67 mol% and a titanium content of 12.29 mol% was obtained. The measured density of the obtained primary sintered body was 5.84 g / cm 3 and the sintered body of this example had a crystallite size of 781 nm.

[0161] Comparative Example 6 A powder of yttrium-stabilized zirconia containing alumina with a yttrium content of 4.0 mol% and an aluminum content of 0.05 mass% was mixed with pure water and wet-milled with a ball mill until the average particle diameter became 0.5 μm and the standard deviation of the particle diameter became 1.0 μm, to obtain a zirconia slurry having a solid content of 45 mass%.

[0162] A sintered body of this comparative example composed of titanium- and yttrium-solid solution zirconia containing alumina, having a yttrium content of 3.40 mol%, a titanium content of 0.23 mol%, and an alumina content of 0.046 mass%, was obtained in the same manner as in Example 1, except that the obtained zirconia slurry and a titania slurry were mixed so that the mass ratio of the zirconia powder to the titania powder was 92:8, to obtain a mixed slurry containing a powder of yttrium-stabilized zirconia containing alumina and titania, having a yttrium content of 3.40 mol%, an aluminum content of 0.046 mass%, and a titania content of 8 mass% (0.23 mol%). The crystallite size of the sintered body of this comparative example was 223 nm.

[0163] Comparative Example 7 The zirconia slurry and the titania slurry were mixed so that the mass ratio of the zirconia powder to the titania powder was 87.5:12.5, to obtain a mixed slurry containing a powder of yttrium-stabilized zirconia containing alumina and titania, having a yttrium content of 4.33 mol%, an aluminum content of 0.044 mass%, and a titania content of 12.5 mass% (18.71 mol%). Primary sintering, HIP treatment, and heat treatment were performed in the same manner as in Example 1.

[0164] However, in this comparative example, cracks occurred during the heat treatment after the HIP treatment, and no sintered body was obtained.

[0165] The results are shown in the following table. The compositions in the following table are in terms of oxides. Also, in Comparative Example 7, since cracks occurred during the heat treatment and no sintered body was obtained, evaluations such as Tt could not be performed.

[0166]

Table 2

[0167] With the decrease in the titanium content, It decreased while Tt showed no specific trend. Also, it was confirmed that with the decrease in the titanium content, the fracture toughness value tended to improve. Further, from Examples 1 and 10, it was confirmed that while the bending strength increased by containing alumina, there was no effect on the fracture toughness value.

[0168] On the other hand, in the comparative example, it was confirmed that when the titanium content exceeded 18.5 mol%, no sintered body could be obtained.

[0169] Example 11 In the same manner as in Example 1, yttrium-stabilized zirconia granule powder containing alumina and titania, with a yttrium amount of 4.67 mol%, an aluminum amount of 0.046 mass%, and a titania amount of 8 mass%, was obtained.

[0170] Alumina powder, iron oxide powder, cobalt oxide powder, 4 mol% yttria-containing zirconia powder, and titania powder were wet-mixed in an ethanol solvent using a ball mill with zirconia balls to obtain a mixed powder containing 2 mass% alumina, 0.4 mass% iron oxide, and 0.3 mass% cobalt oxide, with the balance being zirconia containing 4 mol% yttria and 4.5 wt% titania. The mixed powder was dried at 110°C in the air and then sieved, and this was used as the black raw material powder.

[0171] A disc-shaped primary mold with a diameter of 25 mm and an uneven shape was filled with yttrium-stabilized zirconia granular powder, and by uniaxially pressing it at a pressure of 25 MPa, a disc-shaped green compact with a thickness of 2 mm and a diameter of 25 mm, made of yttrium-stabilized zirconia granular powder, was obtained. This was placed in a disc-shaped secondary mold with a diameter of 50 mm such that the convex shape of the green compact became the upper surface. Black raw material powder was filled so as to cover the entire upper surface of the green compact. Then, by uniaxially pressing and molding this at a pressure of 50 MPa, a secondary green compact in which the green compact and the compact made of black raw material powder were laminated was obtained. The obtained secondary green compact was subjected to CIP treatment at a pressure of 200 MPa. As a result, a disc-shaped secondary green compact with a thickness of 3.5 mm and a diameter of 50 mm was obtained.

[0172] The obtained secondary green compact was subjected to primary sintering, HIP treatment, and heat treatment in the same manner as in Example 1, whereby a composite sintered body of the present embodiment in which a sintered body of transparent zirconia and a sintered body of black zirconia (opaque zirconia) were integrally sintered was obtained. Incidentally, It of the black zirconia sintered body was 0.5% or less.

[0173] Example 12 A composite sintered body of the present embodiment in which a sintered body of transparent zirconia and a sintered body of black zirconia (opaque zirconia) were integrally sintered was obtained in the same manner as in Example 11, except that yttrium-stabilized zirconia granular powder containing alumina and titania, having a yttrium content of 4.75 mol%, an aluminum content of 0.047 mass%, and a titania content of 7 mass% (10.82 mol%), obtained by the same method as in Example 5, was used.

[0174] For the obtained composite sintered body, the biaxial bending strength was measured in accordance with the biaxial bending strength measurement specified in ISO / DIS6872. The results are shown in the table below.

[0175]

Table 3

[0176] The biaxial flexural strength of the composite sintered body of this example all exceeded 500 MPa. From this, it was confirmed that the sintered body of this embodiment can be a member having high mechanical strength.

Claims

1. a sintered body of zirconia in which yttrium is contained in an amount of 3.5 mol% or more and less than 6.0 mol%, and titanium is contained in an amount of 6.0 mol% or more and 18.5 mol% or less, having a linear transmittance of 45% or more at a sample thickness of 1 ± 0.1 mm and a measurement wavelength of 600 nm, having a ratio of the linear transmittance at a sample thickness of 1 ± 0.1 mm and a measurement wavelength of 600 nm to the total light transmittance at a sample thickness of 1 ± 0.1 mm and a measurement wavelength of 600 nm of 0.70 or more, and having a fracture toughness value (KIC) of 1.5 MPa·m0.5 or more, wherein titanium and yttrium are dissolved in the zirconia.

2. The sintered body according to claim 1, comprising alumina.

3. The sintered body according to claim 1 or 2, wherein the crystallite size determined from the half-width of the peak having a peak top at 2θ = 74.0 ± 0.3° in the XRD pattern thereof is 1400 nm or less.

4. The sintered body according to claim 1 or 2, having a three-point bending strength of 280 MPa or more.

5. A member comprising the sintered body according to claim 1 or 2.

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