Zirconia sintered body

Abstract

Provided is a zirconia sintered body with which both transparency and fracture toughness value can be achieved at high levels and which can be easily manufactured even by pressureless sintering. In this sintered body, the percentage content of Y2O3 in the whole composition is 1.7-2.9 mol%, the area average particle diameter of zirconia crystal particles is 0.6-1.1 μm, the area ratio of a first region composed of zirconia crystal particles having a particle diameter of 0.1 or more and less than 0.8 μm is 10-80%, the area ratio of a second region composed of zirconia crystal particles having a particle diameter of 0.8-3.2 μm is 20-90%, the average Y2O3 concentration C2 of zirconia crystal particles forming the second region is 2.0-3.2 mol%, the average Y2O3 concentration C1 of zirconia crystal particles forming the first region is 1.7-2.3 mol%, and when the difference in Y2O3 concentration is defined as ΔC≡C2-C1, the ΔC / C2 value is 0.1-0.5, the fracture toughness value of the sintered body measured by the IF method is 10.5 MPa·m0.5 or more, and the total light transmittance of the sintered body is 40% or more.

Description

Zirconia sintered body

[0001] This invention relates to a zirconia sintered body, and more particularly to a zirconia sintered body that has good fracture toughness and excellent visible light transmission characteristics.

[0002] As shown in Fig. 9 of Non-Patent Document 1 (referred to as Figure 22 herein), pure ZrO ２ (Zirconium oxide) is converted to CaF at high temperatures. ２ It has polymorphs in the form of cubic phase (C phase), tetragonal phase (T phase), and monoclinic phase (M phase). ２ O ３ Adding stabilizers such as yttrium oxide or calcium oxide (CaO) in concentrations of 2-5 mol% results in partially stabilized zirconia (PSZ) containing a metastable T phase at room temperature, while adding approximately 8 mol% or more results in the C phase, i.e., fully stabilized zirconia (FSZ). PSZ, in particular, has been shown to exhibit excellent mechanical properties due to a martensitic transformation from the high-temperature T phase to the low-temperature M phase. When cracks propagate within a sintered PSZ body, the stress causes a transformation from the T phase to the M phase, resulting in an approximately 4% volume expansion. This expansion applies compressive stress to the crack tip, suppressing crack propagation (hereinafter, this mechanism of strengthening the zirconia sintered body is referred to as "transformation-induced high toughness"). ２ O ３ PSZ, which uses this as a stabilizer, is chemically stable and possesses high strength and toughness, making it widely used as a mechanical structural material such as engine materials, cutting tools, dies, seals, and bearings, as well as a biomaterial such as dental bone material.

[0003] The zirconia sintered body disclosed in Patent Document 1 has a 5 mol% Y phase which is more stable. ２ O ３The composition of [the sintered body] is adopted, and a sintered body manufactured by adopting the HIP method with less air bubble residue is disclosed. The total light transmittance measured at a sample thickness of 1 mm is as high as 41 to 46%. In addition, regarding the sample thickness used for the measurement of the total light transmittance, the cases of 0.5 mm and 1.0 mm are mixed according to the literature. However, in Fig. 3 of Non-Patent Document 2, the values of the total light transmittance when the sample thickness is changed from 0.5 to 1.5 mm for various zirconia sintered body products are disclosed. Referring to this, by multiplying the value of the total light transmittance of the sample with a thickness of 1.0 mm by 1.21 as a coefficient, the total light transmittance of the sample with a thickness of 0.5 mm can be estimated. The numerical values of the total light transmittance disclosed in Patent Document 2 are considered to be as high as 49.6 to 55.7% in the case of a sample thickness of 0.5 mm. On the other hand, the flexural strength of the sintered body is about 800 to 1100 MPa, and the fracture toughness value is about 3.5 to 4.0 MPa·m ０．５ or so. Also, it is disclosed that the average crystal grain size of the sintered body measured by the line intercept method is about 0.49 to 0.95 μm. The raw material powder used has an average particle size of 0.028 to 0.030 μm and a specific surface area value of 15 to 16 m ２ / g and is fine.

[0004] In Patent Document 2, a sintered body manufactured by adopting the HIP method is disclosed for zirconia with a composition of 1.6 to 2 mol% Y ２ O ３ . Due to the fact that a composition with a higher T-phase content, which is a factor in transformation toughening, is adopted, the flexural strength of the sintered body is 1470 to 2140 MPa, and the fracture toughness value is 6.0 to 10.3 MPa·m ０．５ and it has high strength and high toughness. However, the total light transmittance measured at a sample thickness of 1 mm is 27 to 34% (the converted value to a sample thickness of 0.5 mm is estimated to be 32.7 to 41.2%), which is lower compared with Patent Documents 1 to 3. The average crystal grain size of the sintered body measured by the planimetric method is 0.28 to 0.55 μm. The raw material powder used has a bimodal distribution having peaks at 0.14 μm and 0.34 to 0.35 μm respectively, and a median diameter of 0.15 to 0.18 μm, and the specific surface area value is 15.1 to 17.9 m ２ / g (the specific surface area value is 10.3 m ２ / g and 11.6m ２ For the powders in synthesis examples 3 and 6 (at / g), the total light transmittance of the sintered body has not been evaluated.

[0005] Patent Document 3 mainly describes 3 mol% Y ２ O ３ Regarding the composition of zirconia, a sintered body manufactured using an atmospheric pressure sintering method is disclosed. The total light transmittance measured at a sample thickness of 1 mm is high at 34-40% (the converted value to a sample thickness of 0.5 mm is estimated to be 41.2-48.4%), and furthermore, the bending strength of the sintered body is 980-1280 MPa. In addition, the average grain size of the sintered body measured by the planimetric method is 0.30-0.34 μm. The raw material powder used has an average grain size of 0.4-0.7 μm and a specific surface area of ​​11-15 m². ２ The value is / g. The raw material powder used has an average particle size of 0.4 to 0.7 μm and a specific surface area of ​​11 to 15 m². ２ It is / g.

[0006] Patent Document 4 mainly describes 4 mol% Y ２ O ３ Regarding the composition of zirconia, a sintered body manufactured using an atmospheric pressure sintering method is disclosed. The bending strength of the sintered body is 10¹⁶ to 1220 MPa, Y ２ O ３ The content has been increased to a level comparable to that of Patent Document 3, which has a lower content. Furthermore, the fracture toughness value is 4.0 to 4.5 MPa·m. ０．５ The degree is relatively good, but the total light transmittance measured with a sample thickness of 0.5 mm is about 28-30%. The powder used does not disclose the specific surface area value, but according to section 0043, the particle size distribution of the zirconia crystal particles of the raw material powder has at least two peaks, and in the particle size distribution, the first peak is preferably located at 0.05 μm to 0.11 μm (small particle size powder), and the second peak is preferably located at 0.1 μm to 0.7 μm (large particle size powder). As a specific example, a mixture of equal amounts of small particle size powder with a peak of 0.08 μm and large particle size powder with a peak of 0.4 μm is used. This raw material is considered to be similar in concept to the bimodal distribution raw material powder disclosed in Patent Document 2.

[0007] Furthermore, Patent Document 4 describes an analysis of the grain size distribution using SEM observation images of a sintered body. It discloses that, in the circular grain size distribution of each crystal particle observed in the image, it is preferable that the cross-sectional area ratio of zirconia particles in the class less than 0.4 μm is 4% to 35%, the cross-sectional area ratio of zirconia particles in the class between 0.4 μm and less than 0.76 μm is 24% to 57%, and furthermore, the cross-sectional area ratio of zirconia particles in the class of 0.76 μm or more is 16% to 62%. The average grain size value is not disclosed, but it is estimated that this value is in the range of 0.06 μm to 0.085 μm based on the area ratio of crystal particles in each class. Table 1 summarizes the contents of the disclosures in each of the above patent documents.

[0008]

[0009] Japanese Patent Publication No. 5396691, Japanese Unexamined Patent Publication No. 2022-8052, Japanese Patent Publication No. 5608976, Japanese Patent Publication No. 6688838

[0010] "Phase diagram and microstructure of Y203-added partially stabilized ZrO2" (Journal of the Japan Institute of Metals, Vol. 50, No. 12 (1986), pp. 1101-1108) "Evaluation of physical properties of supertransparent zirconia" (Proceedings of the 33rd Annual Meeting of the Japanese Society of Gnathology, p. 34 (2017)) "Evaluation of fracture toughness of zirconia (Y-TZP) by SEVNB and IF methods" (Ann Jpn Prosthodont Soc 5: P165-173, 2013) "Fracture toughness testing method of ceramics by indentation (IF) method" (Synthesiology Vol. 13 No. 1 (2021), pp. 29-44) "Sintering mechanism of yttria-stabilized zirconia: grain boundary segregation effect of yttrium ions (III)" (TOSOH Research & Technology Review) Vol. 55 (2011), pp. 7-18) "Spinodal Decomposition of Ceramics" (Iron and Steel, 73rd Year (1987), No. 11, pp. 1453-1460)

[0011] To improve the mechanical properties of a zirconia sintered body, Y ２ O ３It is considered effective to reduce the content and increase the T-phase ratio that contributes to transformation toughening, and to refine the grain size of the sintered body. However, as is clear from comparing the disclosures of Patent Documents 1 to 3 as shown in Table 1, in zirconia sintered bodies, Y ２ O ３ By reducing the content, a high fracture toughness value can be ensured, especially 10 MPa·m. ０．５ Achieving fracture toughness values ​​exceeding this level has been difficult. For example, paragraph 0071 of Patent Document 4 states that "the distribution balance or area balance of grain size is considered to contribute to improving bending strength, fracture toughness, and phase transition suppression," but judging from the disclosed characteristic values, it is difficult to say that high fracture toughness values ​​have been achieved. As shown in Figure 25, there is almost no correlation between the fracture toughness value and the area ratio of crystal grains smaller than 0.4 μm, indicating that the refinement of crystal grains does not necessarily contribute to the improvement of fracture toughness.

[0012] Furthermore, since the HIP method requires large-scale equipment, it is desirable to use a simpler atmospheric pressure sintering method for dental materials, etc. However, as is clear from the disclosures in Patent Documents 3 and 4, the mechanical properties of zirconia sintered bodies produced by atmospheric pressure sintering have been significantly inferior to those produced by the HIP method. Therefore, there is a need for a zirconia sintered body that can be produced by atmospheric pressure sintering while having particularly high fracture toughness.

[0013] Furthermore, even though bending strength and fracture toughness are the same mechanical properties, they are in a trade-off relationship, as mentioned in paragraph 0010 of Patent Document 4, and it is difficult to increase both bending strength and fracture toughness. For example, when the bending strength and fracture toughness values ​​disclosed in Patent Documents 1, 2, and 3 are plotted in two dimensions, the result is as shown in Figure 26, and it is difficult to say that there is a clear correlation between these two properties. The data points enclosed by the dashed line in the figure are the values ​​for the sintered bodies of Patent Documents 1 and 2 manufactured using the HIP method, and for these, there does seem to be a negative correlation between bending strength and fracture toughness. However, the remaining data points for the sintered bodies manufactured using the atmospheric pressure sintering method deviate significantly from the data points for the sintered bodies manufactured using the HIP method, indicating that bending strength and fracture toughness cannot be understood through a unambiguous correlation trend.

[0014] According to Non-Patent Document 4, the fracture of brittle materials occurs when stress concentrates, causing cracks to form, which then rapidly grow and lead to fracture. This rapid crack growth is called unstable fracture, while the fracture achieved by controlling crack propagation in response to slowly applied stress, such as in a bending strength test, is called stable fracture. As mentioned above, when a crack propagates within a zirconia sintered body, the stress concentrated at the crack tip causes the surrounding T phase to undergo martensitic transformation into the M phase. The compressive stress resulting from the volume expansion caused by this transformation prevents further crack propagation. The phenomenon where the crack propagates despite this compressive stress is called unstable fracture, and the fracture toughness value represents the critical stress intensity factor at which unstable fracture begins. On the other hand, once the mode shifts to unstable fracture, the sintered body cannot control crack propagation and fractures; therefore, it is considered that most of the phase transformation during bending strength tests occurs during stable fracture.

[0015] Thus, the way in which phase transformations are involved in the test values ​​differs fundamentally between fracture toughness tests and bending strength tests. It should also be noted that, for example, in cases where the results of the fracture toughness test are not disclosed, as in Patent Document 3, it is fundamentally impossible to estimate the fracture toughness value from the disclosed bending strength test value.

[0016] The object of the present invention is Y as a stabilizer. ２ O ３ The objective is to provide a zirconia sintered body that exhibits good light transmission, achieved by improving the crystal structure while taking into account the distribution of components, thereby achieving a high level of both transparency and fracture toughness, and that can be easily manufactured even by atmospheric pressure sintering.

[0017] The zirconia sintered body of the embodiment that solves the above problems has a total composition of Y in the sintered body. ２ O ３ The content of is 1.7 mol% to 2.9 mol%, and the remainder is ZrO ２ A zirconia sintered body having a relative density of 99% or more, consisting of unavoidable impurities, wherein in an electron microscope image of the sintered body structure, the area-average particle size of the zirconia crystal particles is 0.6 μm or more and 1.2 μm or less, the area ratio of zirconia crystal particles with a particle size of less than 0.1 μm and zirconia crystal particles with a particle size of more than 3.2 μm is both less than 1%, the area ratio of the first region consisting of zirconia crystal particles with a particle size of 0.1 μm or more and less than 0.8 μm is 10% or more and 80% or less, the area ratio of the second region consisting of zirconia crystal particles with a particle size of 0.8 μm or more and 3.2 μm or less is 20% or more and 90% or less, and the average second region Y of the zirconia crystal particles forming the second region ２ O ３ The concentration C2 is 2.0 mol% or more and 3.2 mol% or less, and the average first region Y of the zirconia crystal grains forming the first region ２ O ３ The concentration C1 is 1.7 mol% or more and 2.3 mol% or less, and the second region Y ２ O ３ Concentration C2 and first region Y ２ O ３ Y with concentration C1 ２ O ３ With the concentration difference being ΔC ≡ C2 - C1, the value of ΔC / C2 is between 0.1 and 0.5, and the fracture toughness value measured by the IF method in accordance with JIS Z 2244-1 (2024) is 10.5 MPa·m. ０．５ The above is the characteristic feature.

[0018] The zirconia sintered body of the present invention has a total composition of Y ２ O ３The content of is 1.7 mol% to 2.9 mol%, and the remainder is ZrO ２ A zirconia sintered body having a relative density of 99% or more, consisting of unavoidable impurities, wherein in an electron microscope image of the sintered body structure, the area-average particle size of the zirconia crystal particles is 0.6 μm or more and 1.2 μm or less, the area ratio of zirconia crystal particles with a particle size of less than 0.1 μm and zirconia crystal particles with a particle size of more than 3.2 μm is both less than 1%, the area ratio of the first region consisting of zirconia crystal particles with a particle size of 0.1 μm or more and less than 0.8 μm is 10% or more and 80% or less, the area ratio of the second region consisting of zirconia crystal particles with a particle size of 0.8 μm or more and 3.2 μm or less is 20% or more and 90% or less, and the average second region Y of the zirconia crystal particles forming the second region ２ O ３ The concentration C2 is 2.0 mol% or more and 3.2 mol% or less, and the average first region Y of the zirconia crystal grains forming the first region ２ O ３ The concentration C1 is 1.7 mol% or more and 2.3 mol% or less, and the second region Y ２ O ３ Concentration C2 and first region Y ２ O ３ Y with concentration C1 ２ O ３ The difference in concentration is defined as ΔC ≡ C2 - C1, the value of ΔC / C2 is between 0.1 and 0.5, and the fracture toughness value measured by the IF method is 10.5 MPa·m. ０．５ Therefore, the fracture toughness value measured by the IF method in accordance with JIS Z 2244-1 (2024) is 10.5 MPa·m. ０．５ This material achieves exceptionally high values, while also maintaining a high level of light transmission, and can be easily manufactured even through atmospheric pressure sintering.

[0019] This histogram shows the particle size distribution (volume-based) of the sintering raw material powder measured by a laser scattering particle size analyzer, along with its statistical characteristics, for the production of the zirconia sintered body test specimen of Table 3, No. 3 (Example). This histogram shows the particle size distribution (volume-based) of the sintering raw material powder measured by a laser scattering particle size analyzer, along with its statistical characteristics, for the production of the zirconia sintered body test specimen of Table 3, No. 12 (Example). This histogram shows the particle size distribution (volume-based) of the sintering raw material powder measured by a laser scattering particle size analyzer, along with its statistical characteristics, for the production of the zirconia sintered body test specimen of Table 3, No. 19 (Comparative Example). This is a scanning electron microscope image (magnification 10,000x) of the zirconia sintered body (Example) of Table 3, No. 3. This is a scanning electron microscope image (magnification 10,000x) of the zirconia sintered body (Comparative Example) of Table 3, No. 12. This is a scanning electron microscope image (magnification 20,000x) of the zirconia sintered body (comparative example) shown in Table 3, No. 19. This is a histogram showing the microstructure grain size distribution (area-based) of the zirconia sintered body (Example) shown in Table 3, No. 3, analyzed using the observation image in Figure 2. This is a histogram showing the microstructure grain size distribution (area-based) of the zirconia sintered body (Example) shown in Table 3, No. 12, analyzed using the observation image in Figure 3. This is a histogram showing the microstructure grain size distribution (area-based) of the zirconia sintered body (Comparative Example) shown in Table 3, No. 19, analyzed using the observation image in Figure 4. Y for the crystal grains in the first region and the crystal grains in the second region observed in the image in Figure 4. ２ O ３ This figure shows a typical example of setting the concentration analysis circle. The image shows a scanning electron microscope observation image (magnification 20,000x) of the zirconia sintered body of Table 3 No. 1 (comparative example), and the analysis line crossing multiple particles in the image is Y. ２ O ３ This figure shows the correspondence between the EPMA radiation analysis results for which the concentration was measured and the actual results. It shows a scanning electron microscope image (magnification 10,000x) of the zirconia sintered body of item 3 (Example) in Table 3, and the analysis lines crossing multiple particles in the image along the Y-axis. ２ O ３This figure shows the correspondence between the EPMA radiation analysis results for which the concentration was measured and the actual results. It shows a scanning electron microscope image (magnification 10,000x) of the zirconia sintered body of Table 3, No. 12 (Example), and the analysis lines crossing multiple particles in the image along the Y-axis. ２ O ３ This figure shows the correspondence between the EPMA radiation analysis results for which the concentration was measured and the actual results. It shows a scanning electron microscope image (magnification 20,000x) of the zirconia sintered body of Table 3 No. 18 (comparative example), and the analysis lines crossing multiple particles in the image along the Y-axis. ２ O ３ This figure shows the results of EPMA radiation analysis, which measured the concentration, in correspondence with the actual results. This figure schematically shows the estimated diffusion modes of Zr and Y when small crystal particles with closely spaced particle sizes coalesce during the sintering process of a zirconia sintered body. This is an explanatory diagram schematically showing the initial process of crystal structure formation in the zirconia sintered body of the present invention. In the process of Figure 16, Y ２ O ３ The powder particle component is ZrO ２ This is an explanatory diagram showing how powder particles diffuse, with concentration fluctuations occurring according to their size. This diagram schematically shows the estimated diffusion mode from small crystal particles of various sizes toward the larger crystal particles they come into contact with during the sintering process of the zirconia sintered body of the present invention. This diagram schematically shows the estimated diffusion mode of the Y component when small crystal particles are absorbed by the larger crystal particles. The Y component of the reference raw material powder. ２ O ３ ZrO with components uniformly dissolved in solid solution ２ In powder particles, Y by diffusion ２ O ３ This figure illustrates how fluctuations in component concentration become less likely. This figure illustrates the sintering process of a conventional zirconia sintered body using a reference raw material powder. ZrO is disclosed in Fig. 9 of Non-Patent Document 1. ２ -Y ２ O ３ This is a binary phase diagram. The equivalent cubic area fraction S was determined for each numbered zirconia sintered body in Table 3. （Ｃ）This is a graph plotting the measured fracture toughness values of each sintered body against the value of

[0020] The zirconia sintered body of the embodiment has a Y content rate (central composition) in the total composition of the sintered body of 1.7 mol% or more and 2.9 mol% or less, and the balance is composed of ZrO ２ O ３ and inevitable impurities. Also, the relative density of the zirconia sintered body is ensured to be 99% or more so that sufficient mechanical properties can be obtained. The relative density is desirably 99.5% or more.

[0021] The fracture toughness value adopted in the zirconia sintered body of the embodiment is the value measured by the IF (Indentation Fracture) method. According to Non-Patent Document 3 and Non-Patent Document 4, it has been pointed out as a problem that the fracture toughness value measured and calculated by the IF method is likely to appear lower than the fracture toughness value measured by other methods due to the problem of the reading accuracy at the tip of the crack. On the other hand, when it is difficult to take out a test piece from a sintered body product, the IF method also has the advantage that measurement can be performed without problems. Also, the fact that the measured fracture toughness value appears low can be considered to give a safety margin in order to ensure a larger fracture toughness value of the material. The above-mentioned IF method is a method of using a Vickers hardness tester conforming to JIS Z 2244-1 (2024) (equivalent standard ISO 6507-1:2023), pressing a Vickers indenter into a test piece under the condition of a pressing time of 15 seconds, and measuring the length of the indentation and crack generated. From this measurement, the fracture toughness value "K ＩＣ " is calculated. Fracture toughness value K ＩＣ = 0.018×(E / H)[[ID=P]] ０．５ ×(P / c １．５ ) K ＩＣ : Fracture toughness value (MPa·m​​０．５ E: Young's modulus (GPa), where 205 GPa was used. H: Vickers hardness (HV) = 0.1891 P / (2a) ２ c: Half of the average crack length (m) a: Half of the average indentation length (m) P: Vickers indenter pressure (N) (1 kgf = 9.80665 N)

[0022] The transparency (light transmission) of the zirconia sintered body is evaluated by measuring the total light transmittance of a zirconia sintered body test specimen processed to a thickness of 0.5 mm using the CIE standard light D65 in the visible light wavelength range of 380 nm to 780 nm. The value of this total light transmittance is preferably 40% to 60%, and more preferably 45% to 56%, which is higher than the value disclosed in, for example, Patent Document 4. The total light transmittance is measured using equipment and standards conforming to standards such as JIS K 7375 (2008) and JIS K 7361-1 (1997) (ISO 13468-1:1996).

[0023] In the embodiment, the zirconia sintered body has an area-average particle size of zirconia crystal particles of 0.6 μm or more and 1.2 μm or less in electron microscope images of the sintered body structure. If the area-average particle size is less than 0.6 μm, it leads to a decrease in the total light transmittance and fracture toughness of the sintered body. If the area-average particle size exceeds 1.2 μm, the fracture toughness of the sintered body becomes insufficient. Preferably, the area-average particle size of the zirconia crystal particles is between 0.65 μm and 1.1 μm. Furthermore, the area ratio of zirconia crystal particles with a particle size of less than 0.1 μm and zirconia crystal particles with a particle size of more than 3 μm should both be less than 1%. If the area ratio of zirconia crystal particles with a particle size of more than 3 μm is 1% or more, the fracture toughness of the sintered body becomes insufficient. Moreover, it is difficult to ensure a relative density of 99% or more of the sintered body while having 1% or more zirconia crystal particles with a particle size of less than 1 μm in atmospheric pressure sintering.

[0024] Also, the area ratio of the first region composed of zirconia crystal particles having a particle size of 0.1 μm or more and less than 0.8 μm is 10% or more and 80% or less, while the area ratio of the second region composed of zirconia crystal particles having a particle size of 0.8 μm or more and less than 3.2 μm is 20% or more and 90% or less. And the average Y ２ O ３ concentration of the zirconia crystal particles forming the second region is 2.0 mol% or more and 3.2 mol% or less, while the average Y ２ O ３ concentration of the zirconia crystal particles forming the first region is 1.7 mol% or more and 2.3 mol% or less. And taking the difference in these Y ２ O ３ concentrations as ΔC ≡ C2 - C1, the value of ΔC / C2 is 0.1 or more and 0.5 or less.

[0025] When the area ratio of the zirconia crystal particles in the first region and the area ratio of the zirconia crystal particles in the second region are outside the scope of the present invention, the fracture toughness value of the zirconia sintered body cannot be ensured sufficiently. Also, regarding the average Y ２ O ３ concentrations C1 and C2 of the zirconia crystal particles in the first region and the second region, when ΔC ≡ C2 - C1, if the value of ΔC / C2 becomes less than 0.1, it becomes impossible to ensure that the fracture toughness value of the zirconia sintered body is 10.5 MPa·m ０．５ or more. Also, it is difficult to obtain a sintered body having a value of ΔC / C2 exceeding 0.5, at least by ordinary atmospheric pressure sintering.

[0026] Y ２ O ３ When the central composition of is less than 1.7 mol%, it becomes difficult to ensure that the value of ΔC / C2 is 0.1 or more, and it becomes impossible to ensure that the fracture toughness value is 10.5 MPa·m ０．５ or more. On the other hand, when the central composition of Y ２ O ３ becomes too high, even if the value of ΔC / C2 is ensured to be 0.1 or more, the fracture toughness value may not be ensured sufficiently. In the present invention, in order to surely obtain a fracture toughness value of 10.5 MPa·m ０．５ or more, its upper limit value is set to 2.9 mol%. Y ２ O ３The core composition should preferably be 1.8 mol% or more, and more preferably 1.9 mol% or more. Also, Y ２ O ３ The core composition should preferably be 2.7 mol% or less, and more preferably 2.5 mol% or less.

[0027] There is no particular upper limit to the fracture toughness value of the zirconia sintered body of the embodiment, but by adjusting various conditions of atmospheric pressure sintering, it can be increased to, for example, 15 to 22 MPa·m. ０．５ It is also possible to raise it both forward and backward.

[0028] In the zirconia sintered body of the present invention, the first region consisting of zirconia crystal particles with a particle size of 0.1 μm or more and less than 0.8 μm is a region mainly composed of fine crystal particles, and it has generally been considered advantageous to increase the number of crystal particles in this region in order to improve the mechanical strength of the material. However, from the viewpoint of improving fracture toughness, as is clear from the disclosure in Patent Document 4 (see Figure 25), simply increasing the number of crystal particles in this region will not lead to a significant improvement in fracture toughness. The reason for this is that if the proportion of the T phase, which contributes to suppressing the rapid propagation of cracks, i.e., unstable fracture, is small, even a region with finely milled crystal particles will not lead to an improvement in fracture toughness.

[0029] Here, the raw material powder for the zirconia sintered body disclosed in Patent Document 3 is derived from a method of calcining and pulverizing a coprecipitate obtained by mixing a zirconium salt, a stabilizing agent source, and alkali, etc. This method is a common method widely used in the production of raw material powder for commercially available partially stabilized zirconia, and the resulting powder contains Y in each individual zirconia powder particle. ２ O ３ The components are uniformly dissolved in solid solution (Patent documents 1, 2, and 4 do not disclose the specific manufacturing method of the raw material powder, but since they mention "yttria-containing zirconia powder," etc., it is thought that powder manufactured by a similar method is used). Therefore, the crystalline structure of a zirconia sintered body manufactured using such raw material powder is Y ２ O ３It is thought that fluctuations in component concentration are less likely to occur, and that there is almost no difference in the distribution of T-phase domains and C-phase domains in both the first region, which consists of zirconia crystal particles with a particle size of 0.1 μm or more and less than 0.8 μm, and the second region, which consists of zirconia crystal particles with a particle size of 0.8 μm or more and less than 3.2 μm.

[0030] Even though zirconia sintered bodies are toughened, their fracture mode is essentially brittle fracture, and the cracks associated with fracture propagate through the crystal grains. Furthermore, considering that the toughening mechanism of zirconia sintered bodies involves suppression of unstable fracture due to martensitic transformation of the T-phase domain, it is difficult to significantly improve fracture toughness even by controlling the ratio of the first and second regions when there is no difference in the distribution of the T-phase and C-phase.

[0031] Therefore, in the zirconia sintered body of the embodiment, the average Y of the entire sintered body ２ O ３ While setting the concentration (hereinafter also referred to as "core composition") to a relatively low range of 1.7 mol% to 2.9 mol%, the average Y of the second region, which is mainly composed of large crystal grains, ２ O ３ The concentration is the average Y of the first region, which is mainly composed of small crystalline particles. ２ O ３ A key feature is that the concentration is set higher than the stated value. This configuration results in a fracture toughness value of 10.5 MPa·m for the sintered body. ０．５ It becomes possible to improve to the above high level. From a histological perspective, the mechanism is presumed to be as follows.

[0032] In the composition range where the central composition is between 1.7 mol% and 2.9 mol%, the C phase (equilibrium Y) is present near the sintering temperature (e.g., 1550°C). ２ O ３ (Concentration is around 6.1 mol%) and T phase (equilibrium Y ２ O ３The equilibrium ratio (at a concentration of around 1.6 mol%) is thought to be around 1:10 when the central composition is 2.0 mol% (composition point O). For the T-phase domains formed in the high-temperature range to contribute to improved fracture toughness, they must maintain the T-phase structure in a metastable state down to around room temperature. However, according to the phase diagram in Figure 22, the T→M transformation point ML is Y in the T phase. ２ O ３ As the concentration decreases, the value increases sharply, and it is thought that most of the T phase in the zirconia sintered body obtained in the above central composition range has already transformed into the M phase when cooled to room temperature, so a significant improvement in fracture toughness cannot be expected.

[0033] On the other hand, as described above, the first region Y has fine crystal grains. ２ O ３ As the concentration decreases, the second region Y, where the crystal grains are coarser, appears. ２ O ３ In a situation where the concentration increases, if we consider the phase diagram shown in Figure 22, for example, around 800°C, then the first region Y ２ O ３ The concentration shifts from the central composition towards point A, which indicates the solid solubility limit on the T phase side, and then to the second region Y. ２ O ３ The concentration also shifts towards point B, which indicates the solid solubility limit on the C phase side. In terms of the equilibrium phase diagram, if the shifted compositions fall within the composition range indicated by line segments AB, then the Y of the T and C phases will be the same in both the first and second regions. ２ O ３ The concentration will be the equilibrium concentration indicated by points A and B.

[0034] However, as mentioned in Non-Patent Documents 5 and 6, Y ２ O ３ ZrO with added ２ In ceramics, it is known that the separation of the C phase from the T phase is accompanied by spinodal decomposition-like concentration fluctuations. In a phase separation mechanism accompanied by concentration fluctuations, Y ２ O ３ High concentration of C-phase domain and Y ２ O ３ Y between the low-concentration T-phase domain ２ O ３This facilitates the creation of a modulation structure in which the concentration changes continuously, and Y is formed from the T-phase solid solution line ST in Figure 22. ２ O ３ Even in the high concentration range, supersaturation occurs. ２ O ３ It is thought that a larger amount of the T phase, which is dissolved in solid solution, will remain. In Figure 22, the line indicating the T→M transformation point ML is Y ２ O ３ As the concentration increases, Y emerges from within the T-phase single-phase region. ２ O ３ It has been suggested that the composition decreases monotonically as it enters a supersaturated region exceeding the solid solubility limit ST. Furthermore, it is believed that the transformation toughness of the zirconia sintered body is mainly due to the T phase (hereinafter referred to as the "supersaturated T phase"), which has a composition in this supersaturated region and is maintained metastable without transforming into the M phase at room temperature.

[0035] In the zirconia sintered body of the embodiment, the lower limit of the central composition is set to 1.7 mol%, and the upper limit is also relatively low at 2.9 mol%. For the first region, Y ２ O ３ Since the concentration is even lower than the central composition described above, the proportion of the T phase, which has a high transformation point to the M phase, increases, and its contribution to improving fracture toughness decreases. However, Y ２ O ３ Concentration Y ２ O ３ In the second region, which has a higher composition than the central region, the proportion of the supersaturated T phase, in which the transformation point to the M phase is lowered, increases compared to the first region, and is expected to contribute to improved fracture toughness. The supersaturated T phase is found near the boundary between the second region, which is mainly composed of large crystal grains, and the first region, which is mainly composed of small crystal grains (as described later, for example, the peripheral region of large crystal grains within the second region), Y ２ O ３ It is thought that this region is likely to form mainly in areas where the concentration gradually decreases. Therefore, by forming the above-mentioned second region in the sintered body with an appropriate area ratio, a supersaturated T phase with a large crack propagation inhibition effect based on stress-induced martensitic transformation is uniformly dispersed and formed in the sintered body, resulting in a fracture toughness value of 10.5 MPa·m. ０．５ This achieves a significantly higher level of toughness through transformation.

[0036] Next, the zirconia sintered body of the embodiment can be manufactured by atmospheric pressure sintering using the following specific zirconia raw material powder. That is, the zirconia raw material powder is (1) Y ２ O ３ ZrO without any components ２ Powder (e.g., pure ZrO) ２ (Powder) and pure Y which constitutes the stabilizing component ２ O ３ This zirconia raw material powder is obtained by mixing and grinding powders and other materials in a ball mill, and satisfies the following two conditions in the particle size distribution measured by volume using a laser scattering particle size analyzer: - The arithmetic mean particle size is 0.10 μm or more and 0.15 μm or less, - The value of the arithmetic standard deviation is 0.03 μm or more and 0.05 μm or less, - No particles with a particle size greater than 0.8 μm or less and no particles with a particle size less than 0.03 μm are measured, and - The measured values ​​of particles with a particle size greater than 0.4 μm and particles with a particle size of 0.04 μm or less are both 0.5% or less (such zirconia raw material powder will be referred to as "recommended zirconia raw material powder" below).

[0037] When raw material powder deviating from condition (2) is used, the average first region Y of the zirconia crystal grains forming the first region ２ O ３ Concentration C1 corresponds to the average second region Y of the zirconia crystal grains that make up the second region. ２ O ３ It becomes difficult to obtain a characteristic concentration distribution pattern where the concentration is lower than C2 (specifically, where ΔC ≡ C2 - C1, and the value of ΔC / C2 is between 0.1 and 0.5). Furthermore, considering the formation of secondary particles in the powder, the specific surface area of ​​the raw material powder measured by the BET method is set to 13 m² to more reliably exclude particles smaller than 0.04 μm at the primary particle level. ２ It is preferable to keep it below / g. Furthermore, the specific surface area value of the raw material powder should be 8m, in relation to keeping the arithmetic mean particle size between 0.10 μm and 0.15 μm. ２ It is best to set it to / g or higher.

[0038] According to the above condition (1), the zirconia raw material powder contains Y in the powder. ２ O ３ Components and ZrO２ The components will separate at the particle level. Therefore, Y ２ O ３ The component is ZrO ２ The step of forming a solid solution state in the substrate must depend on diffusion during sintering. A zirconia sintered body produced using such zirconia raw material powder is Y ２ O ３ ZrO with components uniformly dissolved in solid solution ２ Due to the difficulty in obtaining the substrate, conventional zirconia sintered bodies are produced using methods such as the coprecipitation method disclosed in Patent Document 3, where Y is produced during the chemical synthesis stage of the powder raw material. ２ O ３ The component is ZrO ２ It has been manufactured using zirconia raw material powder (hereinafter referred to as "reference zirconia raw material powder") prepared by a method of solid solution in a substrate.

[0039] However, as a result of detailed investigation by the present inventors, Y occurs between two regions with different average crystal grain sizes in the sintered body. ２ O ３ From the viewpoint of obtaining a sintered body that produces a difference in concentration, as described in (1) above, Y ２ O ３ Components and ZrO ２ It was found to be advantageous to use zirconia raw material powder from which the components have been separated. However, in order to obtain a sintered body with good fracture toughness, the zirconia raw material powder must be finely ground by a ball mill until the particle size distribution is sufficiently sharpened at the arithmetic mean particle size, so as to satisfy condition (2).

[0040] In this case, the starting material for the recommended zirconia raw material powder is ZrO ２ Powder particles are Y ２ O ３ It has significantly higher hardness compared to powder particles. Therefore, in ball mill grinding, not only the media (e.g., zirconia spheres) introduced into the pot along with the raw material, but also the ZrO added as a raw material ２ Powder particles are also Y ２ O ３ It functions as a fine media for powder particles. In this case, Y ２ O ３ The powder particles are fine ZrO２ Through contact with the powder particles, the large-diameter grinding media is subjected to high-energy grinding impact forces, and in the final raw material powder, Y ２ O ３ This makes it easier to obtain a state in which the powder particles are uniformly mixed and distributed. Y in the recommended zirconia raw material powder obtained in this way ２ O ３ The powder particles are ZrO ２ It is believed that the material has been ground down to an average particle size smaller than that of powder particles.

[0041] The aforementioned condition (2) is Y ２ O ３ Powder particles are ZrO ２ This is necessary to obtain a state in which the powder particles are sufficiently and uniformly mixed and distributed. In order to finely grind the starting material to this level, it is effective to set the grinding time in the ball mill to a correspondingly long time. However, according to the inventors' research, it has been found that using a mixture of multiple spherical media of different sizes as input media is effective in shortening the grinding time.

[0042] Figure 1 shows the particle size distribution measurement results for an example of a recommended zirconia raw material powder. This raw material powder is Y ２ O ３ The content is 2.0 mol%, and the particle size distribution measured by volume using a laser scattering particle size analyzer (device used: HORIBA LA-960) shows the following: - Arithmetic mean particle size: 0.128 μm - Arithmetic standard deviation: 0.038 μm - Measured values ​​for particles larger than 0.4 μm and particles smaller than 0.04 μm are zero (therefore, measured values ​​for particles larger than 0.8 μm and particles smaller than 0.03 μm are also zero). More specifically, the maximum value of the particle size class in which particles were measured is 0.339 μm, and the class exceeding 0.35 μm, which is the large diameter peak of the bimodal powder in Patent Document 2, is less than 1% (zero in Figure 1). The powder is a commercially available pure ZrO ２ Powder and pure Y ２ O ３ A total of 1 kg of powder, 7.7 kg of 2 mm diameter zirconia media, and 3 mm diameter zirconia media (Y ２ O ３This material was obtained by placing 2.3 kg of a partially stabilized zirconia sintered body containing 2.75 mol% (totaling 10 kg) and 1.7 kg of pure water into a pot with an inner diameter of approximately 245 mm and grinding it at a rotation speed of 78 rpm for 20 hours.

[0043] Furthermore, as another example of a recommended zirconia raw material powder, Y ２ O ３ Figure 2 shows the particle size distribution measurement results for the raw material powder with a content of 2.5 mol%. In the particle size distribution measured by volume using a laser scattering particle size analyzer (device used: HORIBA LA-960), the following was observed: - Arithmetic mean particle size: 0.126 μm - Arithmetic standard deviation: 0.036 μm - Measured values ​​for particles larger than 0.4 μm and particles smaller than 0.04 μm were zero (therefore, the measured values ​​for particles larger than 0.8 μm and particles smaller than 0.03 μm were also zero). More specifically, the maximum value of the particle size class in which particles were measured was 0.296 μm, and the class exceeding 0.35 μm, which is the large diameter peak of the bimodal powder in Patent Document 2, was less than 1% (zero in Figure 1). The grinding conditions for this powder were the same as those for the powder in Figure 1.

[0044] On the other hand, Figure 3 shows the particle size distribution measurement results for an example of reference zirconia raw material powder. This raw material powder is Y ２ O ３ The content is 3.0 mol%, and in the particle size distribution measured by volume using a laser scattering particle size analyzer, the following was observed: - Arithmetic mean particle size: 0.404 μm - Arithmetic standard deviation: 0.666 μm - There were zero measured values ​​for particles smaller than 0.04 μm, but 19.31% of the measured values ​​for particles larger than 0.4 μm. The powder is obtained by adding yttrium chloride to a hydrated zirconia sol obtained by hydrolyzing an aqueous solution of zirconium oxychloride, followed by drying and calcination. ２ O ３ This product was obtained by placing 1 kg of calcined zirconia powder, 15 kg of similar zirconia media with a diameter of 3 mm, and 1.7 kg of pure water into a pot with an inner diameter of approximately 245 mm, and grinding it at a rotation speed of 78 rpm for 10 hours.

[0045] Table 2 shows the application volume frequency for each particle size class value of each raw material powder in Figure 1 (recommended zirconia raw material powder) and Figure 3 (reference zirconia raw material powder), along with the total surface area per gram of powder and the surface area ratio for each class, calculated by approximating the crystal particles as spheres. The left column of Table 2 shows the raw material powder in Figure 1, and the right column shows the raw material powder in Figure 3.

[0046]

[0047] Furthermore, the zirconia powder particles contained in the recommended zirconia raw material powder are Y as a solid solution component. ２ O ３ If the amount is less than 1.5 mol%, it does not prevent it from being included. Zirconia powder particles within this composition range are Y ２ O ３ Due to the low solid solubility of the components, transformation toughening is less likely to occur, resulting in a partially stabilized zirconia sintered body (Y ２ O ３ Compared to tough zirconia media with a solid solution content of, for example, 2.0 mol% to 5.0 mol%, this material has lower hardness and fracture cracks propagate more easily. Therefore, fine pulverization due to impact force from the zirconia media is more likely to occur, and the average diameter of the powder particles can be reduced by pulverization in a relatively short time, and the residue of coarse powder particles is less likely to occur.

[0048] Figure 4 shows a zirconia sintered body manufactured by atmospheric pressure sintering at 1550°C for 2 hours using the recommended zirconia raw material powder shown in Figure 1 (see Table 3 below: No. 3 (Y) ２ O ３ Figure 5 shows a scanning electron microscope image of the surface of a zirconia sintered body (content: 2.0 mol%) (magnification 10,000x). It can be seen that the structure consists of a mixture of relatively fine crystalline particles of 0.8 μm or less (first region) and slightly coarser crystalline particles of 0.8 μm or more (second region). Figure 5 also shows a zirconia sintered body (Table 3: No. 12 (Y) described later) manufactured by atmospheric pressure sintering at 1550°C for 2 hours using the recommended zirconia raw material powder shown in Figure 2. ２ O ３This is a scanning electron microscope image of the surface of a sample containing 2.5 mol%) (magnification 10,000x). Crystal grains larger than 0.8 μm (second region) have grown somewhat compared to the sintered body in Figure 4, but it can be seen that a relatively fine structure is still maintained.

[0049] Figure 6 shows a scanning electron microscope image (magnification 10,000x) of a zirconia sintered body (corresponding to Table 3: No. 19, a comparative example of the present invention) manufactured by atmospheric pressure sintering at 1500°C for 2 hours using the reference zirconia raw material powder shown in Figure 3.

[0050] In this specification, the grain size distribution on electron microscope images is quantified using the following method. First, 300 to 400 crystal particles are randomly selected from the image. In this specification, as shown in Figure 4, multiple sampling lines SL are set on the image, and the crystal particles that each sampling line crosses are selected as the target for extraction. At this time, the setting interval is adjusted so that no single crystal particle is passed through by multiple sampling lines. Then, for each crystal particle that passes through each sampling line, parallel lines tangent to the outline of the crystal particle are drawn on the image in the vertical and horizontal directions, and when the intervals between the parallel lines are D1 and D2, the value Dm = (D1 + D2) / 2 is calculated, and the diameter of a circle having the same area as Dm is determined as the particle size of each extracted crystal particle.

[0051] Figure 7 is a histogram showing the microstructure grain size distribution (area-based) for the zirconia sintered body number 3 in Table 3, analyzed using the observation image in Figure 4 and the method described above. Figure 8 is a histogram showing the microstructure grain size distribution (area-based) for the zirconia sintered body number 12 in Table 3, analyzed using the observation image in Figure 5 and the method described above. Figure 9 is a histogram showing the microstructure grain size distribution (area-based) for the zirconia sintered body number 19 in Table 3, similarly analyzed using the observation image in Figure 6. For the zirconia sintered bodies manufactured using the recommended zirconia raw material powder mentioned above (histograms: Figures 7 and 8), the area ratio of crystal grains in the first region with a crystal grain diameter of 0.8 μm or less is 47% to 73.5%, and the area-average grain size of the crystal grains is 0.840 μm and 0.722 μm. On the other hand, for the comparative zirconia sintered body (histogram: Figure 9), the area ratio of crystal grains in the first region was 74.8%, and the area-average grain size of the crystal grains was 0.660 μm.

[0052] Furthermore, since all sintered bodies exhibited relatively smooth surface conditions, no polishing was performed, and the sintered surface was directly observed under magnification. For confirmation, the grain size distribution of a microstructure obtained by mirror polishing the surface of a sintered body and then thermal etching it at a temperature 50°C lower than the sintering temperature for 1 hour was also measured using the same method. Within the scope of the study described herein, it should be noted that the calculation results of the area ratios of the first and second regions were in agreement with the results obtained using observation images of the unpolished sintered body surface within ±5%.

[0053] Also, the average Y of the first and second regions ２ O ３ The concentrations can be analyzed using a field emission electron probe microanalyzer (EPMA) in the following manner. Specifically, as shown in Figure 10, in the first region where crystal particles smaller than 0.8 μm are densely packed in the observation field of the electron microscope (magnification 10,000x), the spot diameter is adjusted within the range of 0.8 to 1.2 μm so that multiple crystal particles smaller than 0.8 μm are contained within the spot of the irradiated electron beam, as indicated by the dashed white circle AC1, and the concentrations of Zr, Y, and O are analyzed. The same measurement is then performed five times while changing the spot position in the field of view, and the average value of these results is used to determine the concentration of Y.２ O ３ The concentration should be recorded.

[0054] On the other hand, for crystal grains in the second region exceeding 0.8 μm, as shown by the dashed white circle AC2 in Figure 10, the spot diameter of the irradiated electron beam is adjusted within the range of 0.8 to 2.0 μm so that the spot sufficiently covers the region including the center inside the crystal grain, and the concentrations of Zr, Y, and O are analyzed. Then, the same measurement is performed for 10 crystal grains while changing the spot position in the field of view, and the average value of these results is used to determine Y ２ O ３ The concentration was calculated.

[0055] Figures 7 to 9 show the average Y for the first and second regions. ２ O ３ The analysis results of the concentration are added along with the measurement results of the fracture toughness value and total light transmittance. For the zirconia sintered body manufactured using the raw material powder in Figure 1 (recommended zirconia raw material powder) (histogram in Figure 7), the average first region Y of the first region with a crystal grain size of 0.8 μm or less ２ O ３ The concentration C1 is 1.84 mol%, which is lower than the central composition of 2.00 mol%. In contrast, the average second region Y of the second region, where the crystal grain size is greater than 0.8 μm, is... ２ O ３ The concentration of C2 is 2.17 mol%, which is higher than the central composition described above. First region Y ２ O ３ Concentration C1 and second region Y ２ O ３ Y in both regions of concentration C2 ２ O ３ If the difference in concentration is ΔC ≡ C2 - C1, then the value of ΔC / C2 is 0.15, which is sufficiently larger than the lower limit of 0.1 set by the present invention. Furthermore, the fracture toughness value of the zirconia sintered body is 15.0 MPa·m ０．５ It is extremely high, and the total light transmittance is also good at 42.9%.

[0056] Similarly, for the zirconia sintered body produced using the raw material powder in Figure 2 (histogram in Figure 8), the average first region Y ２ O ３The concentration C1 is 2.18 mol%, which is lower than the central composition of 2.5 mol%. On the other hand, the average second region Y ２ O ３ The concentration of C2 is 3.03 mol%, which is higher than the central composition mentioned above. Furthermore, the ΔC / C2 value is 0.28, and the fracture toughness value of the zirconia sintered body is 11.7 MPa·m. ０．５ The light transmittance is high, and the total light transmittance is also good at 43.1%.

[0057] On the other hand, for the zirconia sintered body produced using the raw material powder shown in Figure 3 (reference zirconia raw material powder) (histogram in Figure 9), the area ratio of the first region is low, and the average first region Y ２ O ３ Concentration C1 is 2.98 mol%, the average second region Y ２ O ３ The concentration C2 is 3.01 mol%, and in all cases, it is almost the same as the central composition described above. As a result, the value of ΔC / C2 is 0.01, which is less than the lower limit of 0.1 for the present invention, and the fracture toughness value of the zirconia sintered body is 5.9 MPa·m ０．５ And it remains at a low value.

[0058] Furthermore, detailed analysis using EPMA revealed that the crystalline particles constituting the structure of the zirconia sintered body of the embodiment (particularly the crystalline particles in the second region) have a central Y ２ O ３ The concentration is Y at the outer edge. ２ O ３ It has been found that some exist with concentrations significantly higher than the standard concentration. Crystal grains with such a concentration structure are called Y ２ O ３ In the central region with high concentration, the proportion of the C phase increases, and from there towards the periphery of the crystal grain, the Y phase develops. ２ O ３ A region of gradually decreasing concentration is formed. The supersaturated T phase, which is mainly responsible for the transformation toughness of the zirconia sintered body, is Y at the periphery of these crystal grains. ２ O ３ In the region of decreasing concentration, Y ２ O ３ It is thought that these deposits tend to form in areas where the concentration is within a specific range.

[0059] As a result of detailed investigation by the present inventors, Y ２ O ３ Effective Y has a specific concentration range of 2.0 mol% to 2.4 mol%. ２ O ３ It was found that a zirconia sintered body with particularly good fracture toughness can be obtained when the area ratio of the concentration region is 17% or more. ２ O ３ The area ratio of the concentration region is presumed to reflect the area ratio of the supersaturated T phase formation, and Y is set in the zirconia sintered body. ２ O ３ It is thought that the formation morphology and absolute amount change depending on the central composition (see Figure 24 below).

[0060] Figure 11 shows Y as a recommended zirconia raw material powder. ２ O ３ The following are images of the surface of a zirconia sintered body (Table 3: No. 1 described later) manufactured by atmospheric pressure sintering at 1450°C for 2 hours using a raw material powder with a central composition of 1.6 mol% (less than the lower limit of the embodiment), as observed by a scanning electron microscope (magnification 20,000x), and an analysis line along the large particles belonging to the second region in the field of view. ２ O ３ This shows the results of EPMA radiation analysis, which measured the concentration. ２ O ３ The region where the concentration is 1.5 mol% belongs to the T(M) single-phase region, which is close to the solid solubility limit on the T(M) phase side in the phase diagram of Figure 22, and the formation of the C phase is hardly expected.

[0061] The EPMA radiation analysis results shown in Figure 11 below indicate that Y does not distinguish between large and small particles. ２ O ３ The concentration profile shows small concentration fluctuations near the central composition. In the graph, the two horizontal dashed lines represent the effective Y-axis mentioned above. ２ O ３ Y corresponding to the concentration range ２ O ３ The concentration interval (2.0 mol% to 2.4 mol%) is shown, but the line analysis profile is mostly effective Y ２ O ３Located below the lower limit of the concentration interval, effective Y ２ O ３ It can be seen that the area ratio of the concentration region also decreases. The fracture toughness value is 4.9 MPa·m ０．５ This falls outside the scope of the present invention.

[0062] Figure 12 shows Y ２ O ３ A scanning electron microscope image (magnification 10,000x) of the surface of a zirconia sintered body (Table 3: No. 3 described later) manufactured by atmospheric pressure sintering at 1550°C for 2 hours using a recommended zirconia raw material powder with a central composition set to 2.0 mol% (within the range of the embodiment), and an analysis line along the Y line that crosses the large particles belonging to the second region in the field of view. ２ O ３ This shows the results of EPMA radiation analysis, which measured the concentration. ２ O ３ The region where the concentration is 2.0 mol% occupies a position close to the solid solubility limit on the T(M) phase side within the T(M) + C phase multiphase region in the phase diagram of Figure 22, and is a region where the T(M) phase is predominant, but the formation of a certain amount of C phase is expected. The sintered body structure can be seen to have a background region consisting of zirconia crystal particles belonging to the second region with a particle size of 0.8 μm or more, with zirconia crystal particles belonging to the second region having a particle size of 0.8 μm or more dispersed between the background region consisting of zirconia crystal particles in the first region with a particle size of less than 0.8 μm.

[0063] According to the EPMA line analysis results in Figure 12 (bottom), a continuous Y-shaped pattern radiates outward from the maximum point formed within the large particle. ２ O ３ A concentration profile with varying concentrations has been obtained. Looking at it in more detail, at the position of large particles belonging to the second region, Y ２ O ３ While the concentration increases significantly compared to the central composition, the background region, which is mainly composed of first-region particles, exhibits a profile with gradual concentration fluctuations near the lower limit of the effective Y concentration interval. ２ O ３ The concentration interval is Y, from the center of the large particle to the periphery. ２ O ３ The profile section, where the concentration decreases with a significant gradient, is cropped over a relatively long distance, and the background region is also effectively captured by Y. ２ O３ Profile portions that fall within the concentration range are present in various places. The area ratio of the effective Y concentration region in this zirconia sintered body is a large value of 25.2%, and the fracture toughness value is 15.0 MPa·m. ０．５ And it has become extremely large. Effective Y in the sintered body structure ２ O ３ The concentration region is thought to be dispersed in a network-like manner along the boundary between the large particles and the background region. ２ O ３ Since a supersaturated T phase, which can inhibit the propagation of fracture cracks, is thought to be dispersed and formed in a network-like manner in corresponding to the concentration range, it can be said that this is more advantageous for improving fracture toughness.

[0064] Figure 13 shows Y ２ O ３ A scanning electron microscope image (magnification 10,000x) of the surface of a zirconia sintered body (Table 3: No. 12, described later) manufactured by atmospheric pressure sintering at 1550°C for 2 hours using a similar raw material powder with a central composition set to 2.5 mol% (within the scope of the embodiment), and an analysis line along the Y line that crosses the large particles belonging to the second region in the field of view. ２ O ３ This shows the results of EPMA radiation analysis, which measured the concentration. ２ O ３ The region where the concentration is 2.5 mol% is a region within the T-phase (M) + C-phase mixed region of the phase diagram in Figure 22, slightly away from the solid solubility limit of the T-phase (M). This region is expected to be predominantly T-phase (M) but with a greater amount of C-phase formation.

[0065] The EPMA radiation analysis profile shown in Figure 13 (bottom) shows that the large particle position belonging to the second region is Y ２ O ３ As shown in Figure 12, the concentration increases significantly from the central composition, while a considerable portion of the background region, mainly composed of first-region particles, falls outside the upper limit of the effective Y concentration range. The area ratio of the effective Y concentration region in this zirconia sintered body is 20.1%, and the fracture toughness value is 11.7 MPa·m. ０．５ While this is good, it is lower than that of the zirconia sintered body in Figure 12.

[0066] Figure 14 shows Y ２O ３ A scanning electron microscope image (magnification 20,000x) of the surface of a zirconia sintered body (Table 3: No. 18 described later) manufactured by atmospheric pressure sintering at 1500°C for 2 hours using a similar raw material powder with a central composition set to 5.0 mol% (outside the scope of the embodiment), and an analysis line along the Y line that crosses the large particles belonging to the second region in the field of view. ２ O ３ This shows the results of EPMA radiation analysis, which measured the concentration. ２ O ３ The region where the concentration is 5.0 mol% is the region within the T-phase (M) + C-phase multiphase region of the phase diagram in Figure 22 where the amount of C-phase formation is expected to be greater than that of the T-phase (M).

[0067] As is clear from the observed images, the proportion of coarse particles with a diameter of 1 μm or more, belonging to the second region, is increasing. Furthermore, the EPMA radiation analysis profile shows a Y-shape with a maximum point within the coarse particles and a minimum point within the background region formed by the surrounding group of small particles. ２ O ３ The concentration changes in a continuously wave-like pattern, but it can be seen that almost the entire profile, including its minimum point, falls outside the upper limit of the effective Y concentration range. The area ratio of the effective Y concentration region in this zirconia sintered body is almost zero, and the fracture toughness value is 4.6 MPa·m ０．５ And it's low.

[0068] Next, the region where the supersaturated T phase is formed in close proximity to the C phase is the average Y ２ O ３ It can be said that it is more likely to appear in the larger crystal grains of the second region, where the concentration is higher than that of the central composition, but the average Y ２ O ３ Even in the first region where the concentration is lower than the central composition, Y is locally present. ２ O ３ If the concentration is high, the amount formed will be less than in the second region, but it can still appear. The important point is Y in the overall composition of the sintered body. ２ O ３ Content (Y ２ O ３ In the zirconia sintered body of the embodiment in which the core composition is set to a relatively low 1.7 mol% to 2.9 mol%, the C phase is likely to appear. ２ O３ The high-concentration region and the region where the supersaturated T phase can appear are closely related, and there is a specific relationship between the amount of C phase formation inferred from the phase diagram, the amount of supersaturated T phase formation, and consequently the fracture toughness value of the sintered body.

[0069] Specifically, S1 is the area ratio of the first region in the sintered body structure, and Y is the average first region. ２ O ３ C1 represents the concentration, S2 represents the area ratio of the second region, and Y represents the average of the second region. ２ O ３ Let the concentration be C2, S （Ｃ） The converted cubic area fraction S is calculated using the formula: = S1 × {(7.4 - C1) / 6} × 100 + S2 × {(7.4 - C2) / 6} × 100 （Ｃ） When the percentage is between 5% and 25%, particularly high fracture toughness values ​​are achieved (details are explained in the "Experimental Examples" section).

[0070] The following describes how, by using the recommended zirconia raw material powder having the central composition of the embodiment, the average Y of the first and second regions can be obtained. ２ O ３ Concentration (first area Y ２ O ３ Concentration, second area Y ２ O ３ The presumed mechanism for obtaining a characteristic structure that shows differences in concentration will be explained. First, the raw material powder contains almost no particles with a particle size exceeding 0.4 μm, and almost all powder particles have a sharp peak that falls within the range of 0.06 to 0.3 μm. When such raw material powder is molded and sintering is started, in the initial stage of sintering, as shown in Figure 15, there are almost no large crystalline particles exceeding 0.4 μm, and small crystalline particles SG are the main component. At this stage, the main mechanism is the bonding and fusion of adjacent small crystalline particles SG, and it is thought that the material continues to grow slowly and uniformly for a while without generating any protruding large particles.

[0071] However, as shown in Figure 16 (left), Y in the raw material powder ２ O ３ Powder particles Y are ZrO ２It is thought that the pulverization has progressed to an average particle size considerably smaller than that of the powder particles BG and SG, and in the initial stage of sintering, the finely pulverized Y ２ O ３ Powder particles Y are ZrO ２ It appears that a reaction involving diffusion and solid solution of powder particles BG and SG is likely to proceed.

[0072] As shown with reference to Figure 18, according to the known theory of solid-state sintering neck formation, the larger the dimensional difference between the small crystal grains SG and large crystal grains BG that are in contact with each other, the smaller the radius of curvature ρ of the neck N, which is the joint between them, and the lower the vapor pressure. This results in an excess vacancy concentration increase ΔD in the neck N compared to the bulk. The vacancy concentration gradient in the neck N is expressed as ΔD / ρ, and this acts as a driving force, causing vacancies to diffuse into the interior of the crystal grains, while in exchange, constituent atoms of the crystal grains flow into the voids V between the crystal grains. This causes the voids V to contract, and solid-state sintering proceeds.

[0073] According to the above neck formation theory, in Figure 16, Y ２ O ３ Since the atomic diffusion velocity of powder particles Y towards the large crystal particles BG is expected to be high and the atomic diffusion velocity towards the small crystal particles SG is expected to be low, as shown in Figures 16 and 17, ZrO ２ In the early stages of sintering, when the growth of powder particles BG and SG is not progressing significantly, Y is present in the large crystal particles BG. ２ O ３ The concentration is slightly high, and Y is present in small crystalline grains SG. ２ O ３ It is presumed that a gradient structure with slightly lower concentrations is formed as a preliminary step.

[0074] Next, as solid-phase sintering progresses further, as shown in Figure 18, the excess vacancy concentration increment ΔD is thought to concentrate on the small crystal particles SG with a smaller surface curvature radius. Therefore, atomic diffusion proceeds in a direction that fills the voids V, causing the small crystal particles SG to contract and the large crystal particles BG to grow. At this time, the smaller crystal particles SG(3) have a higher atomic diffusion velocity toward the large crystal particles BG, and are absorbed and disappear. Both the small crystal particles SG(3) and the large crystal particles BG are made of ZrO ２ The main component is ZrO, which is included in the starting material.２ Powder particles and Y ２ O ３ Y ２ O ３ Since no concentration difference is created, even if a certain number of small crystal particles SG(3) are absorbed entirely by the large crystal particles BG, the Y of the large crystal particles BG ２ O ３ This does not lead to a significant increase in concentration.

[0075] On the other hand, the atomic diffusion velocity of the larger crystal particles SG(1) or SG(2) toward the larger crystal particles BG is relatively small, and most of them remain without being absorbed by the larger crystal particles BG. In this case, although there is no literature to support this, the inventors speculate that the atomic diffusion coefficient of Y toward the larger crystal particles BG from the smaller crystal particles SG(1) and SG(2) is larger than that of Zr. According to this speculation, it is thought that the larger the particle size of the smaller crystal particles SG(1), the more likely Y diffusion toward the larger crystal particles BG will occur.

[0076] Large crystal grains BG Y that have grown from small crystal grains as seeds ２ O ３ If we assume that the concentration is increased by the mechanism hypothesized by the inventors, then the large crystal particles will be in contact with smaller crystal particles that have a lower Y concentration than the large crystal particles. In other words, the concentration gradient of Y atoms will be formed in the direction from the large crystal particles to the small crystal particles, that is, in the opposite direction to the estimated diffusion direction of Y atoms. However, judging from the analysis results in Figure EPMA, there is no doubt that Y is diffusing from the small crystal particles to the large crystal particles, overcoming this concentration gradient.

[0077] According to the equilibrium phase diagram in Figure 22, ZrO ２ -Y ２ O ３ The binary system composition is ZrO ２ On the side, there is a tendency for the free energies to separate into a T(M) phase and a C phase, which are different from each other. According to Fig. 10 of Non-Patent Literature 1, which is the source of this information, the Y phase assumed in the embodiment is ２ O ３ In the concentration range, the T phase has a lower free energy ΔGv than the C phase, and the difference between the two is Y ２ O３ The concentration increases, and the size decreases. When the size of the crystal grains is taken into account, the total energy of the crystal can be expressed as the sum of the phase free energy term and the interfacial tension energy term. As the crystal grains become finer, the contribution of the interfacial tension energy term to the total energy increases. At this time, a portion of the C phase decomposes into the T(M) phase, which has a lower phase free energy, lowering the total energy of the crystal and making it thermodynamically stable. Therefore, it can be considered that the small crystal grains release the Y component toward the large crystal grains, accompanied by the decomposition of the T phase from the C phase.

[0078] If the outflow of Y component from small crystal particles SG to large crystal particles BG progresses, the Y component of large crystal particles BG will increase. ２ O ３ The concentration increased, and the Y of the small crystalline particles SG ２ O ３ The concentration decreases. As mentioned above, this is compounded by the fact that differences in the concentration of the Y component already exist between the small crystal particles SG and the large crystal particles BG in the initial stages of sintering, and the smaller crystal particles SG that are left behind have a higher concentration of Y. ２ O ３ The concentration decreases significantly. As a result, as shown in Figures 12 and 13, the larger crystal grains have a Y-type distribution, especially in the outer regions that are thickened later in time. ２ O ３ The concentration is expected to decrease.

[0079] Returning to Figure 18, as the void V decreases, the shrinkage of the sintered body slows down, and the vacancy concentration, which is the driving force for atomic diffusion, also decreases. Therefore, the small crystal particles SG remaining at that point are less likely to coalesce and be absorbed with the large crystal particles BG. In this way, Y forms between the small crystal particles SG and the large crystal particles BG. ２ O ３ It is thought that the formation of tissues with large concentration differences is largely complete. Also, Y ２ O ３ As the concentration of small crystal particles SG decreases, the T(M) phase ratio increases, and the phase free energy difference with large crystal particles BG, which have a high C phase ratio, widens. Therefore, it is thought that accretion with large crystal particles BG becomes less likely.

[0080] Next, when using reference zirconia raw material powder, Y corresponds to the crystal grain size.２ O ３ The reason why concentration differences are less likely to occur can be estimated as follows. First, as shown in Figure 19, in the reference zirconia raw material powder, the Y component is already solid-solved at roughly the same concentration between the large crystal particles BG and the small crystal particles SG at the raw material stage. Therefore, even in the initial stage of sintering when this powder is molded and sintered, the Y component is still present between the large and small crystal particles. ２ O ３ No concentration differences occur. When such raw material powders are used, a large number of large crystalline particles that are initially present in the raw material powder are already included in the early stages of sintering, and their dimensions are considerably larger than when the recommended zirconia raw material powder is used. In particular, when bimodal powders having two peaks at positions of 0.3 to 0.5 μm and below 0.15 μm are used, as in Patent Documents 2 and 4, the proportion of large crystalline particles exceeding 0.4 μm becomes especially high.

[0081] And then, the Y of the large crystal grain BG ２ O ３ The concentration is close to the composition at the time of formulation, Y ２ O ３ The proportion of particles whose concentration is increasing irregularly is considered to be small. In this case, as shown in Figure 20, in the initial sintering stage where many voids remain, the number ratio of minute powder particles FG and small crystal particles SG with a small growth degree to the particles in contact with such large crystal particles BG increases, and most of them are absorbed and disappear into the large crystal particles BG. In such a case, the Y of the large crystal particles BG ２ O ３ As already explained, the concentration does not increase easily.

[0082] Therefore, until the large crystal particles BG reach a critical size where absorption by them becomes less likely, the process of surrounding small crystal particles SG being absorbed and disappearing into one of the many large crystal particles BG continues for a long time. Thus, until the large crystal particles BG grow to a considerable size, there is not much influx of Y from the small crystal particles SG, and the Y between the large crystal particles BG and the small crystal particles SG continues. ２ O ３ The concentration difference remains relatively small. When using a bimodal distribution raw material powder as described in Patent Document 2 or 4, Y２ O ３ Sintering is completed with a relatively large amount of small crystalline particles SG remaining between the large crystalline particles BG, where the concentration has not decreased significantly (see left side of Figure 21). Furthermore, when a raw material powder with a relatively large average particle size and a broad particle size distribution with one peak is used, the growth of the large crystalline particles BG progresses further until it has almost completely consumed the small crystalline particles SG, and it is thought to reach an equiaxed structure with a large average crystal grain size (see right side of Figure 21). It has been confirmed that in zirconia sintered bodies exhibiting such an equiaxed structure, Y segregates near the grain boundaries where the large crystalline particles are adjacent to each other (Non-Patent Literature 5). ２ O ３ It should be added that the concentration distribution shows a trend completely opposite to that of the embodiment of the present invention shown in Figure 9, where the Y concentration is lower in the outer periphery of the large crystal particle BG and in the surrounding small crystal particles.

[0083] In the zirconia sintered body of the embodiment, the remainder is ZrO ２ A portion of it is Al at a concentration of 0.2 mol% or less (preferably 0.15 mol% or less) ２ O ３ It may be substituted with (aluminum oxide). Also, 0.1 mol% or less (preferably 0.075 mol% or less) of TiO ２ It may be substituted with (titanium dioxide). Al in such a composition range ２ O ３ or TiO ２ The inclusion of this substance does not particularly hinder the realization of the characteristic structure and component distribution morphology of the zirconia sintered body of the present invention as detailed above, and consequently, the resulting fracture toughness value and total light transmittance.

[0084] Furthermore, in the embodiment, "unavoidable impurities" refer to components that can be included in a range that does not impair the characteristics of the zirconia sintered body of the embodiment (so-called contamination), and do not necessarily mean only residual components that cannot be actively removed in the raw material powder or manufacturing process of the zirconia sintered body, but their total will not exceed 0.5 mol%. For example, in the embodiment, Y is used as a stabilizer. ２ O ３While it uses [a specific type of stabilizer], other stabilizers include CaO, MgO (magnesium oxide), and CeO ２ Cerium oxide may be included as an unavoidable impurity in this concept. Also, SiO ２ Silicon dioxide can also be included as an unavoidable impurity, and it is desirable that its content in the overall composition of the sintered body be 0.1% by mass or less.

[0085] The Vickers hardness Hv of the zirconia sintered body configured as described above should be 1100 or higher, preferably 1150 or higher. Furthermore, assuming the use of atmospheric pressure sintering, it is desirable that the bending strength be at least 600 MPa when a three-point bending strength test is performed. The three-point bending strength test is measured in accordance with standards such as JIS R 1601 (2008) (ISO 14704:2000).

[0086] The method for manufacturing the zirconia sintered body of the embodiment has already been partially explained. To explain further, first, pure zirconia powder (average particle size: for example, 20 μm or less) and pure Y, which is a stabilizing powder. ２ O ３ The powder (and other oxide powders making up the components) are blended to achieve the desired composition. Zirconia media with a diameter of 1.5 mm to 9 mm (preferably 1.5 mm to 5 mm) and a solvent (e.g., pure water) are blended and placed in a pot of a grinding device such as a ball mill, and the contents are ground at a predetermined rotational speed that causes an avalanche phenomenon. After grinding, an appropriate amount of water-soluble binder is added. The ground material is dried in a spray dryer or the like to prepare a composition for molding.

[0087] The composition may be formed into a green molded body by press molding (green processing), and if necessary, the green molded body may be subjected to secondary processing such as cutting, and then immediately subjected to main sintering. Alternatively, a calcined body may be created first, and then the calcined body may be subjected to secondary processing such as cutting before main sintering. The sintering temperature when creating the calcined body should be, for example, 800°C to 1200°C, preferably 900°C to 100°C. The main sintering of the green molded body should be, for example, 1475°C to 1650°C, preferably 1490°C to 1625°C. Both calcination and main sintering can be carried out in an atmospheric atmosphere at normal pressure.

[0088] When the green molded body is immediately subjected to sintering, the sintering time required to obtain a sufficiently dense sintered body is, for example, 70 to 180 minutes after degreasing the water-soluble binder required during molding at 300 to 500°C. On the other hand, if a calcined body is manufactured using raw material powder with a particle size distribution that satisfies the aforementioned conditions, the time required for densifying the calcined body can be significantly reduced. When using such a calcined body, the time required for sintering is 60 minutes or less, preferably 30 minutes or less, and more preferably 20 minutes or less.

[0089] Furthermore, the method for manufacturing the zirconia sintered body in the embodiment can be modified as appropriate, as long as it does not particularly hinder the securing of the characteristic structure and component distribution morphology of the zirconia sintered body of the present invention, and consequently the resulting fracture toughness and total light transmittance.

[0090] Furthermore, the zirconia sintered body of the embodiment can be used in a variety of applications, such as dental materials like prosthetic materials, optical fiber connectors like ferrules and sleeves, various tools (e.g., grinding balls, grinding tools), various parts (e.g., screws, bolts and nuts, bearing balls), various sensors, electronic components, and decorative items (e.g., watch bands). When the zirconia sintered body is used as a dental material, it can be used, for example, in copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, onlays, onlays, orthodontic wires, laminate veneers, etc.

[0091] (Experimental Examples) Below, we will describe more detailed experimental examples to support the effects of the embodiments. First, as raw material powders to obtain zirconia sintered bodies with various central compositions shown in Table 3, pure Y is added to commercially available pure zirconia powder in various proportions. ２ O ３ A total of 1 kg of the powder mixture, 7.7 kg of 2 mm diameter zirconia media and 2.3 kg of 3 mm diameter zirconia media (totaling 10 kg), and 1.7 kg of pure water were placed in a pot with an inner diameter of approximately 245 mm. After grinding at a rotation speed of 78 rpm for 20 hours, an appropriate amount of water-soluble binder was added, and the slurry was dried with a spray dryer to obtain raw material powders adjusted to various values. In addition, among the compositions numbered 1 to 13 in Table 3, Y ２ O ３ For concentrations of 1.9 and 2.0 mol%, ZrO ２ A portion of it is 0.1 mol% Al ２ O ３ (Numbers 14, 15), and 0.05 mol% TiO ２ The raw material powders substituted with (numbers 16 and 17) were prepared in the same manner.

[0092] For comparison, Y is used as a reference zirconia raw material powder. ２ O ３For a composition with a concentration of 3.0 mol%, yttrium chloride is added to the hydrated zirconia sol obtained by hydrolyzing an aqueous solution of zirconium oxychloride, and then dried and calcined to obtain Y ２ O ３ To prepare the slurry, 15 kg of 3 mm diameter zirconia media and 1.7 kg of pure water were placed in a pot with an inner diameter of approximately 245 mm with 1 kg of calcined zirconia powder. The mixture was ground at a rotation speed of 78 rpm for 10 hours, then an appropriate amount of water-soluble binder was added, and the slurry was dried with a spray dryer (see Table 3 below: No. 19). A portion of the slurry before the addition of the water-soluble binder was not dried and was used to measure the particle size distribution of the powder using a laser scattering particle size analyzer. Except for No. 19, all powders obtained a particle size distribution that was almost the same as that shown in Figure 1, and it was confirmed that the arithmetic mean particle size was between 0.10 μm and 0.15 μm, and the arithmetic standard deviation was between 0.03 μm and 0.05 μm.

[0093] Next, the raw material powder was appropriately molded into compacts using a hydraulic press to create N=3 compacts, which were then sintered at a temperature of 1450-1600°C in atmospheric pressure to produce zirconia sintered bodies. The dimensions of the sintered bodies were 40 mm x 30 mm x 3 mm in the shape of a plate. The density of the sintered bodies was measured by the Archimedes method, and by comparing it with the calculated true density for each composition, it was confirmed that all were densified to over 99.5%.

[0094] Next, one of the three sintered bodies was cut into a first specimen measuring 30 mm × 30 mm × 3 mm and a second specimen measuring 30 mm × 10 mm × 3 mm. The sintered surface forming one of the main surfaces of the second specimen was observed using a Schottky electron microscope (HITACHI: SU5000) in low vacuum mode at magnifications of 5000x, 10000x, and 20000x to obtain microstructure images.

[0095] Using the obtained microstructure images, the grain size distribution was measured and a histogram was created using the method already described. The area ratios of the first region, consisting of grains with a grain size of 0.1 μm or more and less than 0.8 μm, and the second region, consisting of grains with a grain size of 0.8 μm or more and 3.2 μm or less, were calculated as ratios to the total area of ​​the sampled grains for particle size measurement. Furthermore, using the measured grain size distribution data, the area-average grain size of the sampled grains (a value obtained by weighting the particle diameter of each grain by its circular particle area on the image, summing them, and dividing by the total area of ​​the sampled grains) was calculated. Additionally, for the second specimen, using EPMA (equipment used: JXA-8530F (JEOL Ltd.)), the average Y of the first region was measured using the method described above. ２ O ３ Concentration C1 and the average Y of the second region ２ O ３ The concentration C2 was measured, and the value of ΔC / C2 was calculated. EPMA surface analysis was also performed, and based on the results, the aforementioned effective Y ２ O ３ The area ratio of the region was also calculated.

[0096] Next, both sides of the first test specimen were ground to a thickness of 0.5 mm, and then both sides were mirror-polished using diamond abrasive grains. Using this test specimen, the total light transmittance was measured using a commercially available ultraviolet-visible spectrophotometer (JASCO: V-780) with the CIE standard light D65 in the visible light wavelength range of 380 nm to 780 nm. In addition, the Vickers hardness and fracture toughness value were measured using a commercially available Vickers hardness tester on one of the mirror-polished surfaces of the first test specimen. For each sample, Vickers hardness and fracture toughness value were measured at 12 points at different positions, and the maximum and minimum measured values ​​were excluded to obtain the average value.

[0097] Furthermore, the remaining two sintered bodies were processed into 3 mm × 4 mm × 40 mm bending test specimens, and bending strength tests were performed by three-point bending. Ten bending strength measurements were taken for each specimen, and the maximum and minimum measurements were excluded to obtain the average value. The results are shown in Table 3 (in the table, * indicates that it is outside the scope of the present invention).

[0098]

[0099] For test specimens numbered 2 to 17, where the central composition, the area ratio of the first region, and the area ratio of the second region are within the range described in the claims of the present invention, and the value of ΔC / C2 is 0.1 or greater, the fracture toughness value is 10.5 MPa·m ０．５ The values ​​are as high as above, and it can be seen that the total light transmittance values ​​are high, exceeding 40%. Furthermore, test samples numbered 2 to 17 also have good total light transmittance values ​​of 40% or higher. In addition, Al ２ O ３ and TiO ２ The evaluation results for test samples numbered 9 to 12, to which Al was added, were all as follows: ２ O ３ and TiO ２ The corresponding Y that is not added ２ O ３ The results obtained were almost identical to those of compositions (numbers 3 and 4), and Al ２ O ３ and TiO ２ It appears that there have been no adverse effects from the additives.

[0100] On the other hand, in test specimen No. 1, whose central composition is less than the lower limit of the present invention (1.7 mol%), the area ratio of the first region exceeds the upper limit of the claimed range (80%), the area ratio of the second region is less than the lower limit (10%), and the area-average particle size is less than the lower limit of the present invention (0.6 μm). Furthermore, the value of ΔC / C2 is below the lower limit of the claimed range (0.1), and the fracture toughness value is 4.9 MPa·m ０．５ This is low and outside the scope of the claims (the present invention). On the other hand, test specimen No. 18, whose core composition exceeds the upper limit of the claims (2.9 mol%), has a ΔC / C2 value within the claims, but its fracture toughness value is 4.6 MPa·m. ０．５ This value is low and falls outside the scope of the claims (the present invention). Furthermore, test specimen No. 19, manufactured using reference zirconia raw material powder, had a ΔC / C2 value below the lower limit of the claims (0.1), and its fracture toughness value was 5.9 MPa·m ０．５ This is low and falls outside the scope of the claims (of the present invention).

[0101] Based on the above results, let S1 be the area ratio of the first region in the sintered body structure, and Y be the average of the first region.２ O ３ Let the concentration be C1, then S （Ｃ） Table 3 shows the values ​​of the converted cubic area fraction S(C) calculated using the formula (%) = S1 × {(7.4 - C1) / 6} × 100 + S2 × {(7.4 - C2) / 6} × 100. In the above formula, the denominator value "6" represents the ZrO at 800°C where atomic diffusion slows down to some extent in the equilibrium phase diagram in Figure 22. ２ Y ２ O ３ Point A(Y) represents the solid solubility limit. ２ O ３ Concentration: approximately 1.4 mol%, and Y ２ O ３ ZrO ２ Point B(Y) represents the solid solubility limit. ２ O ３ This shows the distance to a concentration of approximately 7.4 mol%). In Figure 22, when the given composition point is O, the abundance ratio of the C phase in the phase equilibrium state can be expressed as AO / AB. The first term on the right-hand side of the above equation gives the area ratio of the C phase in the first region, and the second term gives the area ratio of the C phase in the second region. S is defined as the sum of these two. （Ｃ） Y is in the first and second regions. ２ O ３ This refers to the expected cubic area ratio in the entire zirconia sintered body when a concentration difference exists, and this is referred to as the "converted cubic area ratio" in this specification. These values ​​do not immediately represent the amount of C phase actually present in the zirconia sintered body, however S （Ｃ） From a phase equilibrium perspective, it can be expected that a larger value of will result in a larger area ratio of tetragonal crystals present within the sintered zirconia.

[0102] Y adopted in the claims (of the present invention) ２ O ３ In the central composition region, as mentioned above, it is thought that a supersaturated T phase is likely to form in close proximity to the C phase formation region. Therefore, the fracture toughness values ​​(K) in Table 3. ＩＣ ) is the tetragonal area fraction S converted above. （Ｃ） Figure 23 shows the results plotted against the value of S. （Ｃ）When the percentage is between 5% and 15%, the fracture toughness value measured by the IF method (JIS Z 2244-1 (2024) (corresponding standard ISO 6507-1:2023)) is 12 MPa·m. ０．５ It can be seen that particularly high values ​​have been achieved. This is due to the converted cubic crystal area ratio S （Ｃ） It is presumed that if the value is too large or too small, the formation of the supersaturated T phase mentioned above will be insufficient. Also, the fracture toughness value (K) in Table 3 ＩＣ ) Enable Y ２ O ３ Figure 24 shows the results plotted against the area fraction values ​​of the concentration region. The effective Y is presumed to reflect the amount of supersaturated T phase formation. ２ O ３ It can be seen that the fracture toughness value measured by the IF method increases monotonically as the area ratio of the concentration region increases. As is clear from the experimental examples, it has been demonstrated that zirconia sintered bodies, by satisfying the composition and conditions adopted in the claims (the present invention), possess good fracture toughness values ​​as well as good light transmittance (total light transmittance). Therefore, zirconia sintered bodies are effective materials in fields where an optical appearance of the zirconia sintered body itself is required, and where strength is also required.

Claims

1. The content of Y in the entire composition of the sintered body O ３ is 1.7 mol% or more and 2.9 mol% or less, and the balance is ZrO ２ and an impurity-inevitable zirconia sintered body with a relative density of 99% or more. In the electron microscope observation image of the sintered body structure of the zirconia sintered body, ２ O ３ the area-average particle size of zirconia crystal particles is 0.6 μm or more and 1.2 μm or less, ２ O ３ the area ratio of zirconia crystal particles with a particle size of less than 0.1 μm and zirconia crystal particles with a particle size of more than 3.2 μm are both less than 1%, ２ O ３ the area ratio of the first region composed of zirconia crystal particles with a particle size of 0.1 μm or more and less than 0.8 μm is 10% or more and 80% or less, ２ O ３ the area ratio of the second region composed of zirconia crystal particles with a particle size of 0.8 μm or more and 3.2 μm or less is 20% or more and 90% or less, ２ O ３ the average Y ０．５ O concentration C2 in the zirconia crystal particles forming the second region is 2.0 mol% or more and 3.2 mol% or less, the average Y ２ O concentration C1 in the zirconia crystal particles forming the first region is 1.7 mol% or more and 2.3 mol% or less, and, taking the difference in Y ３ O concentration between the second region and the first region as ΔC ≡ C2 - C1, the value of ΔC / C2 is 0.1 or more and 0.5 or less, and the fracture toughness value measured by the IF method in accordance with JIS Z 2244-1 (2024) is 10.5 MPa·m ２ or more. A zirconia sintered body characterized by the above.

2. In the sintered body structure, the zirconia crystal grains forming the second region are more Y-shaped in the outer periphery than in the center. ２ O ３ A zirconia sintered body according to claim 1 with a low concentration.

3. The sintered body structure has a background region consisting of zirconia crystal particles belonging to the first region, with zirconia crystal particles belonging to the second region dispersed within it, and along the analysis line that crosses the background region and the plurality of large particles, Y ２ O ３ When the concentration is measured, a continuous Y-shaped pattern is observed from the maximum point formed within each large particle toward the surrounding area. ２ O ３ A zirconia sintered body according to claim 2, which exhibits a concentration profile in which the concentration changes.

4. In the sintered body structure, Y ２ O ３ Effective Y with a concentration of 2.0 mol% or more and 2.4 mol% or less ２ O ３ The zirconia sintered body according to claim 1, wherein the area ratio of the concentration region is 17% or more.

5. In the sintered body structure, the effective Y ２ O ３ The zirconia sintered body according to claim 4, wherein the concentration region is dispersed in a network-like manner along the boundary between the large particles and the background region.

6. The area ratio of the first region in the sintered body structure is S1, and the average first region Y is the area ratio of the first region. ２ O ３ CM1 is the concentration, S2 is the area ratio of the second region, and Y is the average of the second region. ２ O ３ Let the concentration be CM2, S （Ｃ） The converted cubic area fraction S is calculated using the formula: = S1 × {(7.4 - CM1) / 6} × 100 + S2 × {(7.4 - CM2) / 6} × 100 （Ｃ） A zirconia sintered body according to claim 1, wherein the percentage is 5% or more and 25% or less.

7. The remaining ZrO ２ A portion of it is Al, which has a content of 0.2 mol% or less in the total composition of the sintered body. ２ O ３ A zirconia sintered body according to claim 1, which is substituted with [the specified substance].

8. The remaining ZrO ２ A portion of it is TiO, which is present in a concentration of 0.1 mol% or less in the total composition of the sintered body. ２ A zirconia sintered body according to claim 1, which is substituted with [the specified substance].

9. The zirconia sintered body according to claim 1, wherein the Vickers hardness Hv of the sintered body structure is 1100 or more.

10. The zirconia sintered body according to claim 1, wherein the total light transmittance value measured using CIE standard light D65 in the visible light wavelength range of 380 nm to 780 nm on a test piece processed to a thickness of 0.5 mm is 40% to 60%.

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