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. The Y2O3 content in the entire composition of the sintered body is 2.5-6 mol%, the remainder comprising ZrO2 and unavoidable impurities. The zirconia crystal grains have an area-average grain size of 0.4-0.9 μm. The area ratio of a first region ranging in grain size from 0.1 μm to less than 0.5 μm is 5-80%, the area ratio of a second region ranging in grain size from 0.8 μm to less than 2 μm is 5-80%, and the area ratio of a third region ranging in grain diameter from 0.5 μm to less than 0.8 μm is 10% to less than 55%. The zirconia crystal grains forming the second region have an average Y2O3 concentration of 3.5-7.0 mol%, and the zirconia crystal grains forming the first region have an average Y2O3 concentration C1 of 1.7-5 mol%.

Description

[Technical Field]

[0001] The present invention relates to a zirconia sintered body, and more particularly to a zirconia sintered body that has a good fracture toughness value and is also excellent in visible light transmittance. [Background technology]

[0002] As shown in Fig. 9 of Non-Patent Document 1 (cited herein as Fig. 15), pure ZrO2 (zirconium oxide) has polymorphic forms of CaF2-type cubic phase (C phase), tetragonal phase (T phase), and monoclinic phase (M phase) from high temperatures. When 2 to 5 mol% of a stabilizer such as Y2O3 (yttrium oxide) or CaO (calcium oxide) is added to this, partially stabilized zirconia (PSZ) containing the metastable T phase at room temperature is formed, and when approximately 8 mol% or more is added, the C phase, i.e., fully stabilized zirconia (FSZ), is formed. The excellent mechanical properties of PSZ are due to the fact that it can be easily converted from the high-temperature T phase to the low-temperature M phase. phase It has been revealed that this is due to a martensitic transformation into the M phase. When a crack propagates within a PSZ sintered body, the resulting 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, the toughening of zirconia sintered bodies through this mechanism will be referred to as "transformation toughening"). In particular, PSZ using Y2O3 as a stabilizer is chemically stable and has high strength and toughness, making it widely used in engine materials, cutting tools, dies, seals, bearings, and other machine structural materials, as well as in dental bone and other biomaterials.

[0003] Incidentally, industrial products using zirconia sintered bodies made of PSZ (hereinafter simply referred to as "zirconia sintered bodies" in this specification) may require a certain level of transparency in order to improve their appearance and aesthetics. Examples of such industrial products include dental materials and decorative items such as accessories. For example, in the case of dental materials, if the transparency of the zirconia sintered body used is too low, the difference in appearance from actual teeth will be significant, impairing aesthetics and making it unsuitable.

[0004] The zirconia sintered body disclosed in Patent Document 1 employs a 5 mol% Y2O3 composition, which further stabilizes the C phase, and is manufactured using a HIP process with minimal residual bubbles. The total light transmittance measured with a 1 mm sample thickness is high, ranging from 41 to 46%. While the sample thickness used for total light transmittance measurement varies between 0.5 mm and 1.0 mm depending on the literature, Figure 3 in Non-Patent Document 2 discloses the total light transmittance values ​​for various zirconia sintered body products when the sample thickness is varied from 0.5 to 1.5 mm. By referring to this, the total light transmittance value for a 1.0 mm sample can be estimated by multiplying the total light transmittance value for a 1.0 mm sample by a coefficient of 1.21. The total light transmittance values ​​disclosed in Patent Document 2 are considered to be as high as 49.6 to 55.7% for a 0.5 mm sample thickness. On the other hand, the bending strength of the sintered body is about 800M to 1100MPa, and the fracture toughness is 3.5 to 4.0MPa m 0.5 It is also 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 grain size of 0.028 to 0.030 μm and a specific surface area of ​​15 to 16 m. 2 / g and finer ones are used.

[0005] Patent Document 2 discloses a sintered body manufactured by HIP using zirconia with a composition of 1.6 to 2 mol% Y2O3. Because a composition with a higher T-phase content, which contributes to high transformation toughness, is used, the sintered body has a bending strength of 1470 MPa to 2140 MPa and a fracture toughness of 6.0 to 10.3 MPa m 0.5It has high strength and toughness. However, the total light transmittance measured with a sample thickness of 1 mm is 27-34% (the converted value for a sample thickness of 0.5 mm is estimated to be 32.7-41.2%), which is lower than those in Patent Documents 1-3. The average crystal grain size of the sintered body measured by the planimetric method is 0.28-0.55 μm. The raw material powder used has a bimodal distribution with peaks at 0.14 μm and 0.34-0.35 μm, a median diameter of 0.15-0.18 μm, and a specific surface area of ​​15.1-17.9 m. 2 / g (specific surface area is 10.3m 2 / g and 11.6m 2 For the powders of Synthesis Examples 3 and 6 with a porosity of 1 / g, the total light transmittance of the sintered body was not evaluated).

[0006] Patent Document 3 discloses a sintered body produced by employing a pressureless sintering method, mainly using zirconia with a 3 mol% Y2O3 composition. The total light transmittance measured with a sample thickness of 1 mm is high at 34-40% (the equivalent value for a sample thickness of 0.5 mm is estimated to be 41.2-48.4%), and the bending strength of the sintered body is 980-1280 MPa. The average crystal 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 m 2 The raw powder used had an average particle size of 0.4 to 0.7 μm and a specific surface area of ​​11 to 15 m 2 / g.

[0007] Patent Document 4 discloses a sintered body produced by pressureless sintering using zirconia mainly having a 4 mol% Y2O3 composition. The bending strength of the sintered body is 1016 to 1220 MPa, which is as high as that of Patent Document 3, which has a lower Y2O3 content. The fracture toughness value is also 4.0 to 4.5 MPa m 0.5Although the optical transmittance measured with a sample thickness of 0.5 mm was relatively good, the total optical transmittance measured with a sample thickness of 0.5 mm was approximately 28-30%. Although the specific surface area of ​​the powder used is not disclosed, the description in 0043 states that the particle size distribution of the zirconia crystal particles in the raw material powder has at least two peaks, with the first peak preferably existing between 0.05 μm and 0.11 μm (small particle size powder) and the second peak preferably existing between 0.1 μm and 0.7 μm (large particle size powder). Specifically, a mixture of equal amounts of a small particle size powder with a peak of 0.08 μm and a large particle size powder with a peak of 0.4 μm is used. This raw material is thought to be similar in concept to the raw material powder with a bimodal distribution disclosed in Patent Document 2.

[0008] Patent Document 4 also analyzes the crystal grain size distribution using SEM images of sintered bodies, and discloses that, in the circular equivalent particle size distribution of each crystal grain observed in the image, the cross-sectional area ratio of zirconia particles in the class of less than 0.4 μm is preferably 4% to 35%, the cross-sectional area ratio of zirconia particles in the class of 0.4 μm to less than 0.76 μm is preferably 24% to 57%, and the cross-sectional area ratio of zirconia particles in the class of 0.76 μm or more is preferably 16% to 62%. Although the average crystal grain size is not disclosed, it is estimated from the area ratio of each class of crystal grain that this value is in the range of 0.06 μm to 0.085 μm. Table 1 summarizes the disclosures of the above patent documents.

[0009] [Table 1] [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-222450 [Patent Document 2] Japanese Patent Publication No. 2022-008052 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-150063 [Patent Document 4] Japanese Patent Application Publication No. 2018-165243 [Non-patent literature]

[0011] [Non-Patent Document 1] "Phase diagram and structure of partially stabilized ZrO2 with Y2O3 addition" (Journal of the Japan Institute of Metals, Vol. 50, No. 12 (1986), pp. 1101-1108) [Non-patent document 2] "Evaluation of the physical properties of ultra-translucent zirconia" (Proceedings of the 33rd Annual Meeting of the Japanese Academy of Dentistry, P-34 (2017)) [Non-patent document 3] "Evaluation of fracture toughness of zirconia (Y-TZP) by SEVNB and IF methods" (Ann Jpn Prosthodont Soc 5: P165-173, 2013) [Non-patent document 4] "Indentation-Fitting (IF) Method for Fracture Toughness Testing of Ceramics" (Synthesiology Vol.13 No.1 (2021) P29-44) [Non-patent document 5] "Sintering Mechanism of Yttria-Stabilized Zirconia: Effect of Grain Boundary Segregation of Yttrium Ions (III)" (TOSOH Research & Technology Review Vol. 55 (2011) pp. 7-18) [Non-patent document 6] "Spinodal Decomposition of Ceramics" (Iron and Steel, 73rd Annual Meeting (1987), Vol. 11, pp. 1453-1460) Summary of the Invention [Problem to be solved by the invention]

[0012] To improve the mechanical properties of zirconia sintered bodies, it is believed that reducing the Y2O3 content to increase the proportion of the T phase, which contributes to transformation toughening, and refining the crystal grain size of the sintered body are effective. On the other hand, to improve transparency, it is believed that increasing the proportion of crystal grains grown to a level larger than the wavelength of visible light and reducing the proportion of fine crystal grains that cause light scattering, and increasing the Y2O3 content to further stabilize the C phase and suppress the formation of fine crystalline domains of the T phase or M phase within the grown crystal grains are effective.

[0013] However, as is clear from a comparison of the disclosures of Patent Documents 1 to 3 (see Table 1), in zirconia sintered bodies, there is often a trade-off between transparency and mechanical properties such as strength and fracture toughness, making it difficult to simultaneously improve both. Meanwhile, paragraph 0071 of Patent Document 4 states, "It is believed that the balance of grain size distribution or area contributes to improving bending strength, fracture toughness, and phase transition suppression." However, based on the disclosed property values, it is difficult to say that transparency and mechanical properties (especially fracture toughness) are compatible at a high level. For example, as shown in Figure 30, the total light transmittance value of Patent Document 4 tends to increase with increasing area fraction of crystal grains 0.76 μm or larger, but the rate of increase in light transmittance relative to this area fraction is not very high. Furthermore, as shown in Figure 31, there is almost no correlation between fracture toughness and the area fraction of crystal grains smaller than 0.4 μm, suggesting that grain refinement does not necessarily contribute to improved fracture toughness.

[0014] Furthermore, since the HIP method requires large-scale equipment, it would be desirable to adopt the simple atmospheric sintering method in the case of dental materials, etc. However, as is clear from the disclosures of Patent Documents 3 and 4, there is a problem in that the mechanical properties of zirconia sintered bodies obtained by atmospheric sintering have been significantly inferior to those of zirconia sintered bodies obtained by HIP. Therefore, there is a particular demand for zirconia sintered bodies that combine high levels of mechanical properties and translucency and that can be realized by atmospheric sintering.

[0015] Although bending strength and fracture toughness are the same mechanical property, as mentioned in 0010 of Patent Document 4, there is a trade-off between them, making it difficult to increase both. For example, a two-dimensional plot of the bending strength and fracture toughness values ​​disclosed in Patent Documents 1, 2, and 3 is shown in Figure 32, which makes it difficult to say that a clear correlation exists between these two properties. The data points enclosed by dashed lines in the figure are values ​​for the sintered bodies of Patent Documents 1 and 2 manufactured using the HIP method, and it appears that there is indeed a negative correlation between bending strength and fracture toughness. However, the remaining data points for the sintered bodies manufactured using the atmospheric sintering method are significantly different from the data points for the sintered bodies manufactured using the HIP method, indicating that a clear correlation between bending strength and fracture toughness cannot be understood.

[0016] According to Non-Patent Document 4, fracture of brittle materials occurs when stress concentrates, causing cracks to form, which then grow rapidly and lead to fracture. This rapid crack growth is called unstable fracture, while stable fracture occurs when fracture is achieved by controlling crack propagation in response to slowly applied stress, as in bending strength tests. As mentioned above, when a crack propagates within a zirconia sintered body, the stress concentrated at the crack tip causes the T phase around the tip to transform into martensitic M phase. The volume expansion caused by this transformation results in compressive stress, which prevents crack propagation. Unstable fracture occurs when a crack propagates despite this compressive stress, and fracture toughness indicates the critical stress intensity factor at which unstable fracture begins. On the other hand, if the mode shifts to unstable fracture, the sintered body cannot control crack propagation and ultimately fractures. Therefore, it is believed that most phase transformations during bending strength tests occur during stable fracture.

[0017] As described above, the contribution of phase transformation to test values ​​in fracture toughness tests and bending strength tests is fundamentally different. It is important to note that, for example, in cases where the results of fracture toughness tests are not disclosed, as in Patent Document 3, it is fundamentally impossible to estimate the fracture toughness value from the disclosed value of the bending strength test.

[0018] The object of the present invention is to provide a zirconia sintered body that can achieve high levels of both transparency and fracture toughness by improving the crystal structure while taking into consideration the distribution of the YO component as a stabilizer, and that can be easily produced by atmospheric sintering. [Means for solving the problem]

[0019] In order to solve the above problems, the zirconia sintered body of the present invention is a zirconia sintered body having a relative density of 99% or more, in which the content of Y2O3 in the entire composition of the sintered body is 2.5 mol% or more and 6 mol% or less, the remainder being ZrO2 and unavoidable impurities, and in an electron microscope image of the sintered body structure, the area average grain size of the zirconia crystal grains is 0.4 μm or more and 0.9 μm or less, the area ratios of zirconia crystal grains less than 0.1 μm and zirconia crystal grains having a grain size of more than 2 μm are both less than 1%, the area ratio of first regions consisting of zirconia crystal grains having a grain size of 0.1 μm or more and less than 0.5 μm is 5% or more and 80% or less, and the grain size The area ratio of the second region consisting of zirconia crystal particles having a particle size of 0.8 μm or more and less than 2 μm is 5% or more and 80% or less, the area ratio of the third region consisting of zirconia crystal particles having a particle size of 0.5 μm or more and less than 0.8 μm is 10% or more and less than 55%, the average Y2O3 concentration of the zirconia crystal particles forming the second region is 3.5 mol% or more and 7.0 mol% or less, the average Y2O3 concentration C1 of the zirconia crystal particles forming the first region is 1.7 mol% or more and 5 mol% or less, and when the difference in the Y2O3 concentrations is ΔC≡C2-C1, the value of ΔC / C2 is 0.2 or more and 0.5 or less, and the fracture toughness value measured by the IF method is 4.5 MPa m 0.5 More than 12MPa m 0.5 The present invention is characterized by the following: [Effects of the Invention]

[0020] According to the above-described configuration of the zirconia sintered body of the present invention, both high levels of transparency and fracture toughness can be achieved, and the body can be easily produced by atmospheric sintering. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a histogram showing the powder particle size distribution (volume basis) of a sintering raw material powder having a Y2O3 concentration of 4.5 mol% measured by a laser scattering particle size analyzer for producing a zirconia sintered body test piece according to an example, together with its statistical characteristic values. [Figure 2] 1 is a histogram showing the powder particle size distribution (volume basis) of a sintering raw material powder having a Y2O3 concentration of 4.5 mol% measured by a laser scattering particle size analyzer for producing a zirconia sintered body test piece of a comparative example, together with its statistical characteristic values. [Figure 3] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body (example product) No. 10 in Table 3, which was produced by atmospheric sintering at 1500°C for 2 hours in the air using the sintering raw material powder of FIG. [Figure 4] 3 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body (comparison example) No. 22 in Table 3, which was produced by atmospheric sintering at 1,500°C for 2 hours in the atmosphere using the sintering raw material powder of FIG. 2. [Figure 5] 4 is a diagram showing an example of setting crystal grain sampling lines on the observation image of FIG. 3 together with the concept of measuring crystal grain dimensions. FIG. [Figure 6] 4 is a diagram showing typical crystal grains in the first region and crystal grains in the second region observed in the observation image of FIG. 3, marked together with an example of setting a Y2O3 concentration analysis circle. FIG. [Figure 7] 4 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) No. 10 in Table 3, analyzed using the observation image of FIG. 3. [Figure 8] 5 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body No. 22 (comparative example) in Table 3, analyzed using the observation image in FIG. 4. [Figure 9] FIG. 10 is a diagram showing a scanning electron microscope image (magnification: 10,000 times) of the zirconia sintered body (Example product) No. 10 in Table 3, taken in a different field of view, in association with the results of EPMA line analysis in which the Y2O3 concentration was measured along an analysis line that crosses the background region and multiple coarse dispersed particles in that field of view. [Figure 10] FIG. 2 is an explanatory diagram schematically showing the process of forming a crystal structure of the zirconia sintered body of the example. [Figure 11] FIG. 1 is an explanatory diagram schematically showing the process of forming a crystal structure of a conventional zirconia sintered body. [Figure 12] FIG. 1 is a diagram showing a schematic diagram of the estimated diffusion mode of Zr and Y when small crystal grains having similar grain sizes coalesce and grow during the sintering process of a zirconia sintered body. [Figure 13] FIG. 1 is a diagram schematically illustrating an estimated diffusion pattern from small crystal particles of various sizes toward large crystal particles in contact with them during the sintering process of a zirconia sintered body according to an embodiment, which is performed using a raw material powder having a narrow particle size distribution width. [Figure 14] FIG. 1 is a diagram showing an estimated diffusion pattern when most of the small crystal grains, which have a larger particle size difference than the large crystal grains, are absorbed during the sintering process of a conventional zirconia sintered body using raw material powder with a wide particle size distribution. [Figure 15] This is a ZrO2-Y2O3 binary phase diagram disclosed in Fig. 9 of Non-Patent Document 1. [Figure 16] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body of No. 1 in Table 3 (Example product: 3 mol% Y2O3-0 mol% La2O3). [Figure 17] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body of No. 3 in Table 3 (Example product: 3 mol% Y2O3-0.4 mol% La2O3). [Figure 18] 15 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) of No. 1 in Table 3, analyzed using the observation image of FIG. 14. [Figure 19] 16 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) of No. 3 in Table 3, analyzed using the observation image of FIG. 15. [Figure 20] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body No. 5 in Table 3 (Example product: 4 mol% Y2O3-0 mol% La2O3). [Figure 21] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body No. 7 in Table 3 (Example product: 4 mol% Y2O3-0.4 mol% La2O3). [Figure 22] 19 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) of No. 5 in Table 3, analyzed using the observation image of FIG. 18. [Figure 23] 20 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) of No. 7 in Table 3, analyzed using the observation image of FIG. 19. [Figure 24] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body No. 13 in Table 3 (Example product: 4 mol% Y2O3-0 mol% La2O3). [Figure 25] 1 is a scanning electron microscope image (magnification 10,000 times) of the zirconia sintered body No. 15 in Table 3 (Example product: 4 mol% Y2O3-0.4 mol% La2O3). [Figure 26] 23 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) No. 13 in Table 3, analyzed using the observation image of FIG. 22. [Figure 27] 24 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body (Example product) No. 15 in Table 3, analyzed using the observation image of FIG. 23. [Figure 28] 1 is a graph plotting the measured values ​​of fracture toughness of each zirconia sintered body against the value of the converted tetragonal area fraction PT in the first region obtained for each zirconia sintered body numbered in Tables 3 and 4. [Figure 29] 1 is a graph plotting the measured values ​​of the total light transmittance of each zirconia sintered body against the value of the converted cubic area fraction SC in the second region obtained for each zirconia sintered body of each number in Tables 3 and 4. [Figure 30] 1 is a graph in which the values ​​of total light transmittance of the zirconia sintered body disclosed in Patent Document 4 are plotted against the area ratio of crystal grains of 0.76 μm or more. [Figure 31]1 is a graph in which the fracture toughness values ​​of the zirconia sintered bodies disclosed in Patent Document 4 are plotted against the area ratio of crystal grains smaller than 0.4 μm. [Figure 32] 1 is a graph in which the bending strength and fracture toughness values ​​of the zirconia sintered bodies disclosed in Patent Documents 1, 2, and 3 are two-dimensionally plotted. DETAILED DESCRIPTION OF THE INVENTION

[0022] In the zirconia sintered body of the embodiment, the Y2O3 content in the overall composition of the sintered body is 2.5 mol% to 6 mol%, with the remainder consisting of ZrO2 and inevitable impurities. If the Y2O3 content is less than 2.5 mol%, the amount of T phase produced will be excessive, making the sintered body more susceptible to cracking during room-temperature sintering. Furthermore, excessive grain refinement will make it difficult to ensure the transparency of the sintered body. On the other hand, if the Y2O3 content exceeds 6 mol%, the amount of T phase produced will be small, making it more likely that excessive grain growth will occur, making it difficult to ensure the fracture toughness of the sintered body. The Y2O3 content is more preferably 3.0 mol% to 5.5 mol%, and even more preferably 3.5 mol% to 5.2 mol%. The aforementioned C phase refers to a CaF2-type cubic phase, and the later-mentioned T phase refers to a tetragonal phase, and the later-mentioned M phase refers to a monoclinic phase.

[0023] Furthermore, the zirconia sintered body must have a relative density of 99% or more, preferably 99.5% or more, so that it can obtain sufficient mechanical properties.

[0024] In the zirconia sintered body of the embodiment, the area-average particle size of the zirconia crystal particles is 0.4 μm or more and 0.9 μm or less in an electron microscope image of the sintered body structure. If the area-average particle size is less than 0.4 μm, it becomes difficult to ensure the transparency of the sintered body, and if it exceeds 0.8 μm, the fracture toughness value of the sintered body becomes insufficient. The area-average particle size of the zirconia crystal particles is preferably 0.5 μm or more and 0.8 μm or less. Furthermore, the area ratios of zirconia crystal particles less than 0.1 μm and zirconia crystal particles greater than 2 μm are both less than 1%. If the area ratio of zirconia crystal particles greater than 2 μm becomes 1% or more, the fracture toughness value of the sintered body becomes insufficient. Furthermore, it is difficult to achieve 1% or more of zirconia crystal particles less than 0.1 μm in normal pressure sintering.

[0025] 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 0.5 μm is 5% or more and 80% or less, while the area ratio of the second region consisting of zirconia crystal particles with a particle size of 0.8 μm or more and less than 2 μm is 5% or more and 80% or less. The average Y2O3 concentration of the zirconia crystal particles constituting the second region is 3.5 mol% or more and 7.0 mol% or less, while the average Y2O3 concentration of the zirconia crystal particles constituting the first region is 1.7 mol% or more and 5 mol% or less, and the difference between these Y2O3 concentrations is ΔC≡C2-C1, where ΔC / C2 is 0.2 or more and 0.5 or less.

[0026] In the zirconia sintered body of the embodiment, the first region, which is composed of zirconia crystal grains with a grain size of 0.1 μm or more and less than 0.5 μm, is a region mainly composed of fine crystal grains, and increasing the number of crystal grains in this region has generally been considered advantageous for improving the mechanical strength of the material. However, from the perspective of improving fracture toughness, as is clear from the disclosure of Patent Document 4 (see Figure 31), simply increasing the number of crystal grains in this region is not expected to significantly improve fracture toughness. The reason for this is that if the proportion of the T phase, which contributes to suppressing rapid crack propagation, i.e., unstable fracture, is low, even a refined crystal grain region is not thought to lead to improved fracture toughness.

[0027] On the other hand, the second region, which is made up of zirconia crystal grains with a grain size of 0.8 μm or more but less than 2 μm, is a region mainly composed of coarse crystal grains larger than the wavelength of visible light, and an increase in the crystal grains in this region is considered to be advantageous in improving the effect of light scattering at the crystal grain boundaries. However, as mentioned above, even in the test sample of the zirconia sintered body disclosed in Patent Document 4 in which the area ratio of the crystal grains in this region was increased to about 60%, the total light transmittance at a thickness of 0.5 mm was at most about 30%, and it is difficult to say that the transparency was dramatically improved. For example, in the case of a composition near 4 mol% YO in Patent Document 4, as is clear from Figure 15, the equilibrium ratio of the C phase (equilibrium YO concentration near 6.3 mol%) to the M phase (equilibrium YO concentration near 1.5 mol%) at the sintering temperature (e.g., 1500°C) is close to 1:1. This suggests that a modulated structure is created in the crystal grains of the sintered compact, with a fine mixture of C-phase domains with high YO concentration and T-phase domains with low YO concentration (see, for example, Non-Patent Documents 5 and 6). The two domains have different YO concentrations and lattice constants, which can cause significant light scattering. As a result, even if the crystal grain size itself is large, the contribution to improving transparency is thought to be relatively small, with a relatively small effect on suppressing light scattering at the grain boundaries.

[0028] In the structure shown in Patent Document 4, in which a first region with fine crystal grains and a second region with coarse crystal grains are mixed, it is believed that there is almost no difference in the distribution of T-phase domains and C-phase domains in each region. Although the zirconia sintered body is toughened, the fracture morphology is essentially brittle, and the cracks accompanying the fracture propagate through the crystal grains. Considering that the toughening mechanism of the zirconia sintered body is the prevention of unstable fracture due to martensitic transformation of the T-phase domains, it is believed that, in a state in which there is no difference in the distribution of the T-phase and C-phase, it is difficult to achieve high levels of fracture toughness and transparency, even if the ratio of the first region to the second region is controlled.

[0029] Therefore, the zirconia sintered body of the embodiment is characterized in that the Y2O3 concentration in the first region having fine crystal grains is adjusted to be lower by a certain level than the Y2O3 concentration in the second region having coarse crystal grains. By configuring in this way, it is possible to realize a zirconia sintered body that achieves both high levels of transparency and fracture toughness. From a microstructural perspective, the mechanism is presumed to be as follows.

[0030] That is, as described above, the difference in YO concentration between the first region with fine crystal grains and the second region with coarse crystal grains results in a significant difference in the distribution of T-phase and C-phase domains between the first and second regions. Specifically, the proportion of T-phase, which contributes to toughening by transforming into the M-phase, is high in the first region with a low YO concentration and low in the second region with a high YO concentration. Conversely, the proportion of stable C-phase, which does not transform into the M-phase, is high in the second region with a high YO concentration and low in the first region with a low YO concentration. In the second region with a high YO concentration, the proportion of highly stable C-phase is high, reducing the T-phase domain boundaries and reducing the influence of the strain field due to martensitic transformation to the T-phase. This reduces light scattering and significantly contributes to translucency. Therefore, if the second region has such a structure, increasing its area fraction can significantly improve the transparency of the sintered body.

[0031] On the other hand, cracks propagate relatively easily within the coarse crystal grains of the second region, which has a low T-phase domain density. However, when the crack tip reaches the fine crystal grains of the first region surrounding it, the increased T-phase domain density in the first region increases the probability that the crack propagation will be stopped by martensitic transformation of the T-phase. As a result, even if the area ratio of the second region is increased to some extent to improve transparency, the fracture toughness value is unlikely to be impaired because the crystal grains of the first region, which have a strong crack propagation prevention effect, are dispersed at an appropriate area ratio. Therefore, it is expected that high levels of transparency and fracture toughness can be achieved.

[0032] If the area ratio of zirconia crystal particles in the first region is less than 5% or if the area ratio of zirconia crystal particles in the second region exceeds 80%, the fracture toughness of the zirconia sintered body cannot be sufficiently ensured. Furthermore, if the area ratio of zirconia crystal particles in the first region exceeds 80% or if the area ratio of zirconia crystal particles in the second region is less than 5%, the transparency of the sintered body cannot be sufficiently ensured. The area ratio of zirconia crystal particles in the first region is more preferably 10% to 45%, and the area ratio of the second region is more preferably 20% to 50%. Furthermore, when the area ratios of zirconia crystal particles in the first region and the second region are adjusted to fall within the above-mentioned ranges, the area ratio of the third region, which is made up of zirconia crystal particles having a particle size of 0.5 μm to less than 0.8 μm, is 10% to less than 55%. Here, the total area ratio of the first, second and third regions is 98% or more (the remainder is, for example, a region occupied by zirconia crystal particles having a particle size of less than 0.1 μm or zirconia crystal particles having a particle size of more than 2 μm).

[0033] Furthermore, with regard to the average Y2O3 concentrations C1 and C2 of the zirconia crystal grains in the first and second regions, because the crystal grains of the zirconia sintered body are composed of two phases, C and T, at the sintering temperature and the Y2O3 content in the overall composition of the sintered body is 2.5 mol% to 6 mol%, the average Y2O3 concentration C2 of the zirconia crystal grains in the second region, which has a high C-phase ratio, falls within the range of 3.5 mol% to 7.0 mol%, and the average Y2O3 concentration C1 of the zirconia crystal grains in the first region, which has a high T-phase ratio, falls within the range of 1.7 mol% to 5 mol%. If the difference between these Y2O3 concentrations is ΔC≡C2-C1, and the value of ΔC / C2 is less than 0.2, the T-phase ratio in the first region becomes insufficient, and the zirconia sintered body will not have sufficient fracture toughness. Furthermore, it is difficult to obtain a sintered body by normal atmospheric sintering in which the average Y2O3 concentration C1 of the first region is determined so that ΔC / C2 exceeds 0.5. The value of ΔC / C2 is more preferably 0.25 or more and 0.5 or less, and even more preferably 0.3 or more and 0.45 or less. By satisfying these requirements, the fracture toughness value of the zirconia sintered body of the embodiment is 4.5 MPa m0.5 More than 12MPa m 0.5 The fracture toughness is preferably 5.5 MPa m 0.5 More than 10MPa m 0.5 It should be the following:

[0034] The fracture toughness values ​​used in this embodiment are values ​​measured by the IF (Indentation Fracture) method. According to Non-Patent Documents 3 and 4, it has been pointed out that fracture toughness values ​​measured and calculated by the IF method tend to appear lower than fracture toughness values ​​measured by other methods due to issues with the accuracy of reading the crack tip. On the other hand, the IF method has the advantage that it can be measured without any problems even when it is difficult to remove a test piece from a sintered product. In addition, the fact that the measured fracture toughness value appears low can be considered to provide a safety margin in ensuring a higher fracture toughness value of the material. The above-mentioned IF method is a method in which a Vickers hardness tester conforming to JIS R 1607 is used to press a Vickers indenter into a test piece under conditions of a load of 30 kgf and an indentation time of 15 seconds, and the length of the indentation and crack generated are measured. From this measurement, the fracture toughness value "K IC " is calculated. Fracture toughness value K IC =0.018×(E / H) 0.5 ×(P / c 1.5 ) K IC : Fracture toughness value (MPa m 0.5 ) E: Young's modulus (GPa), where 205 GPa was applied to the Young's modulus. H: Vickers hardness (HV) = 0.1891P / (2a) 2 c: Half the average crack length (m) a: Half the average length of the indentation (m) P: Vickers indenter pressure (N) (1 kgf = 9.80665 N)

[0035] Regarding the transparency of zirconia sintered body, a test piece of zirconia sintered body processed to a thickness of 0.5 mm was measured using CIE standard light D65 in the visible light wavelength range of 380 nm to 780 nm. below The total light transmittance is preferably 40% or more and 60% or less, which is higher than the value disclosed in Patent Document 4, for example, and more preferably 45% or more and 56% or less.

[0036] The zirconia sintered body of the above embodiment can be produced by atmospheric sintering using a zirconia raw material powder having the following specific particle size distribution. That is, the zirconia powder has a particle size distribution measured on a volume basis using a laser scattering particle sizer: -Arithmetic mean particle size is 0.10 μm or more and 0.15 μm or less, The arithmetic standard deviation is between 0.03 μm and 0.05 μm, Particles with a particle size of over 0.8 μm and particles with a particle size of less than 0.03 μm are not measured. And the measured values ​​of particles with a particle size of over 0.4 μm and particles with a particle size of 0.04 μm or less are both 0.5% or less It is manufactured using raw material powder as follows.

[0037] The particle size distribution measurement results for an example of a zirconia raw material powder that satisfies the above conditions (hereinafter referred to as the "recommended zirconia raw material powder") are shown in Figure 1. The raw material powder has a Y2O3 content of 4.5 mol%, and the particle size distribution measured on a volume basis using a laser scattering particle size analyzer (apparatus used: HORIBA LA-960) was as follows: ·Arithmetic mean particle size: 0.129μm ·Arithmetic standard deviation: 0.040μm The measured values ​​for particles larger than 0.4 μm and particles smaller than 0.04 μm were zero (thus, 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 class in which particles were measured was 0.39 μm, and the class exceeding 0.35 μm, which is the larger diameter peak of the bimodal powder of Patent Document 2, was also less than 1% (zero in Figure 1). The powder was obtained by placing 1 kg of commercially available pure zirconia powder and pure Y2O3 powder in total, 15 kg of 3 mm diameter zirconia media, and 1.7 kg of pure water into a pot with an inner diameter of approximately 800 mm, and grinding it at a rotation speed of 78 rpm for 20 hours.

[0038] On the other hand, the particle size distribution measurement results for an example of a zirconia raw material powder (hereinafter referred to as "reference zirconia raw material powder") that does not satisfy the above conditions are shown in Figure 2. The raw material powder had a Y2O3 content of 4.5 mol%, and in the particle size distribution measured on a volume basis using a laser scattering particle size analyzer, ·Arithmetic mean particle size: 0.251μm ·Arithmetic standard deviation: 0.124μm The measured value of particles smaller than 0.04 μm was zero, while the measured value of particles larger than 0.4 μm was 10.28%. The powder is a Y2O3-containing zirconia obtained by adding yttrium chloride to a hydrated zirconia sol obtained by hydrolyzing an aqueous solution of zirconium oxychloride, followed by drying and calcination. mosquito The powder was obtained by placing 1 kg of calcined powder, 15 kg of zirconia media with a diameter of 3 mm, and 1.7 kg of pure water in a pot with an inner diameter of approximately 800 mm, and grinding it at a rotation speed of 78 rpm for 10 hours.

[0039] In both cases, the zirconia media used consisted of a partially stabilized zirconia sintered body with a Y2O3 content of 4.5 mol%. Table 2 shows the volumetric frequency of each particle size class for each raw powder shown in Figures 1 and 2, as well as the surface area and surface area ratio for each class per gram of powder, calculated by approximating the crystal particles to spheres.

[0040] [Table 2]

[0041] The recommended zirconia raw material powder contains the zirconia component in the form of zirconia particles that do not contain Y2O3 (i.e., pure zirconia powder particles) before milling. The Y2O3 component, which will be contained as a stabilizer for the zirconia phase after firing, is also contained in the form of pure Y2O3 powder particles. In other words, the recommended zirconia raw material powder is obtained by blending zirconia powder particles with a Y2O3 content of less than 1.2 mol% as a solid solution component (including 0 mol%: the region in Figure 15 where the M-phase is the only phase at room temperature) and yttria powder particles with a zirconia content of less than 1.0 mol% as a solid solution component (including 0 mol%), and milling the blend in a ball mill.

[0042] The zirconia powder particles in the recommended zirconia raw material powder have a low amount of YO in solid solution, making them less likely to exhibit transformation toughening. Compared to tough zirconia media made of partially stabilized zirconia sintered bodies (e.g., with a YO in solution content of 2.0 mol% to 5.0 mol%), they are less hard and more susceptible to fracture cracking. Therefore, fine pulverization by the impact force from the zirconia media is facilitated, allowing the average particle size to be reduced in a relatively short pulverization time, and coarse particles are less likely to remain. This is extremely advantageous for obtaining zirconia raw material powder with the characteristic particle size distribution described above (see Figure 1), which is characterized by a sharp particle size distribution. Furthermore, because yttria powder particles are even less hard than zirconia powder particles, pulverization also progresses upon contact with the zirconia powder particles contained in the raw material, resulting in greater refinement than zirconia powder particles and more uniform mixing with the zirconia powder particles. The concept of such a recommended zirconia raw material powder can also be adopted in the production of a zirconia sintered body in a composition range (Y2O3 content less than 2.5 mol%) where a high total light transmittance is not required but a higher level of fracture toughness is required.

[0043] On the other hand, in the reference zirconia raw powder, the zirconia powder particles are solid-solubilized with the Y2O3 component through calcination, which is thought to be why transformation toughening is already present at the particle stage. Therefore, the zirconia powder particles to be milled have a high hardness comparable to that of the zirconia media, and even if fracture cracks attempt to occur within the particles, their propagation is suppressed by the transformation toughening mechanism. Therefore, fine grinding due to the impact force from the zirconia media is difficult to progress, and coarse powder particles are likely to remain. Therefore, it is thought that it is difficult to obtain zirconia raw powder with the aforementioned characteristic particle size distribution (see Figure 1), which has a sharp particle size distribution, using conventional ball milling.

[0044] In addition to being prepared using pure zirconia powder and pure yttria powder as described above, the recommended zirconia raw material powder may also be prepared using zirconia powder in which a Y2O3 component is dissolved or yttria powder in which a zirconia component is dissolved within the aforementioned composition range. However, since the grinding of zirconia powder particles becomes easier the lower the amount of yttria component dissolved, if one aims to further refine the resulting zirconia raw material powder and sharpen the particle size distribution, it is more desirable to use pure zirconia powder and pure yttria powder.

[0045] Figure 3 shows a zirconia sintered body (see Table below) manufactured by atmospheric pressure sintering at 1500°C for 2 hours in air using the raw powder for the sintered body shown in Figure 1. 3 4 shows a surface image of a zirconia sintered body (see Table 1 below) manufactured by atmospheric pressure sintering at 1500°C for 2 hours in the air using the raw powder of the sintered body shown in FIG. 2. 33: Image of sample No. 22 (corresponding to a comparative example of the present invention) observed with a scanning electron microscope (magnification: 10,000 times). It can be seen that, although the same raw material powder was used in terms of composition, the sample exhibited a structure completely different from that of the sintered body shown in FIG. 3. The sintered body structure of the comparative example exhibited an equiaxed crystal structure in which closely spaced crystal grains exceeding 0.4 μm in size were uniformly observed, with almost no fine crystal grains being observed.

[0046] In this specification, the crystal grain size distribution on an electron microscope image is quantified using the following method. First, 300 to 400 crystal grains are randomly extracted from the image. In this specification, as shown in Figure 5, multiple sampling lines SL are set on the image, and crystal grains that each sampling line crosses are selected as extraction targets. At this time, the intervals between the sampling lines are adjusted so that multiple sampling lines do not pass through a single crystal grain. Then, for each crystal grain that passes through each sampling line, parallel lines are drawn vertically and horizontally on the image, circumscribing the outline of the crystal grain. 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 defined as the particle size of each extracted crystal grain.

[0047] Figure 7 shows the table 3 8 is a histogram showing the structure crystal grain size distribution (area basis) of the zirconia sintered body No. 10 analyzed by the above method using the observation image of FIG. 3. 3 7 is a histogram showing the texture crystal grain size distribution (area basis) of the zirconia sintered body No. 22 analyzed in the same manner using the observation image of Fig. 4. It can be seen that the area ratio of the crystal grains in the first region having a crystal grain size of 0.4 µm or less reaches 14.5% for the zirconia sintered body of the example product of the embodiment (Fig. 7), whereas the area ratio of the crystal grains in the first region for the zirconia sintered body of the comparative example product (Fig. 8) is significantly lower at 4.9%.

[0048] Since all sintered bodies had relatively smooth surfaces, the as-sintered surfaces were directly observed under magnification without any special polishing. To be sure, the surfaces of the sintered bodies were mirror-polished, and then thermally etched for 1 hour at 1450°C, 50°C lower than the sintering temperature, and the grain size distribution was measured using the same method on the structures. It should be noted that, within the scope of the study in this specification, the calculation results for the area ratios of the first and second regions agreed within ±5% with the results obtained using observation images of the unpolished sintered body surfaces.

[0049] The average YO concentrations in the first and second regions were analyzed using a field emission electron probe microanalyzer (EPMA: JXA-8530F (JEOL Ltd.)) as follows. Specifically, as shown in Fig. 6, in the observation field of the electron microscope (magnification 10,000x), for the first region (area PA surrounded by a white dashed line in the figure; each region PA also contains some intermediate-sized crystal grains from the third region, and the area of ​​region PA does not mean that it is the area of ​​the first region alone), the spot diameter of the irradiated electron beam was adjusted in the range of 0.3 to 0.8 μm so that 3 to 4 crystal grains of 0.4 μm or less were contained within the spot, as indicated by the solid white circle AC1 in Fig. 6, and the concentrations of Zr, Y, and O were analyzed. The same measurement was performed five times while changing the spot position in the field of view, and the YO concentration was calculated from the average of the results.

[0050] On the other hand, for the crystal grains in the second region larger than 0.8 μm (crystal grains SA illustrated by white arrows in the figure), as shown by the solid black circle AC2 in Figure 6, the spot diameter was adjusted in the range of 0.5 to 0.8 μm so that the spot of the irradiated electron beam sufficiently covered the region inside the crystal grain, including the center, and the concentration analysis of Zr, Y, and O was performed. The same measurement was then performed on 10 crystal grains while changing the spot position in the field of view, and the Y2O3 concentration was calculated from the average of these results. Note that for the zirconia sintered body of the comparative example, which had a small area ratio of crystal grains of 0.4 μm or less, 10 crystal grains of 0.4 μm or less were individually selected, and the spot diameter was adjusted so that the spot of the irradiated electron beam was contained within each crystal grain, and analysis was performed.

[0051] 7 and 8 show the first region and No. The analysis results of the average YO concentration in the two regions are also shown, along with the fracture toughness and total light transmittance measurements. For the zirconia sintered body of the example (Fig. 7), the average YO concentration in the first region, where the crystal grain size is 0.4 μm or less, is 3.6 mol%, lower than the YO concentration of the entire sintered body (4.5 mol%). Meanwhile, the average YO concentration in the second region, where the crystal grain size is greater than 0.8 μm, is 5.7 mol%, higher than the YO concentration of the entire sintered body. For the zirconia sintered body of the comparative example (Fig. 8), the average YO concentration in the first region is 4.7 mol%, and the average YO concentration in the second region is 4.4 mol%, both of which are similar to the YO concentration of the entire sintered body (4.5 mol%), and no significant difference in YO concentration is observed between the regions. It can also be seen that the zirconia sintered bodies of the examples of the embodiment have significantly higher fracture toughness and total light transmittance than the zirconia sintered bodies of the comparative examples.

[0052] Furthermore, further detailed analysis using EPMA revealed that the zirconia sintered body of the example had a lower Y2O3 concentration in the zirconia crystal grains that constituted the second region of the sintered body structure, compared to the Y2O3 concentration in the center. As already explained, the crystal grains in the second region are 0.8 μm or larger, which is larger than the wavelength of visible light, and have a high proportion of the highly stable C phase with a high Y2O3 concentration. This reduces the T-phase domain boundaries, significantly contributing to translucency. With the above structure, the center of the crystal grains in the second region is occupied by the highly stable C phase, which is thought to be even more beneficial in improving the transparency of the sintered body.

[0053] figure 9 As shown in Figure 1, the sintered body structure has a rock-garden-like structure in which zirconia crystal particles SA (crystal particles outlined by a white dashed line) belonging to the second region are dispersed as coarse dispersed particles against a background region consisting of zirconia crystal particles PA (crystal particles surrounded by a white solid line) belonging to the first region and zirconia crystal particles belonging to the third region. The structure of this zirconia sintered body can be said to be morphologically similar to that disclosed in Patent Document 4. On the other hand, the sintered body of Patent Document 4 has a composition similar to that of the Examples, but its fracture toughness and total light transmittance are significantly inferior to those of the Examples. Therefore, although no specific disclosure is made, the YO concentration distribution within the structure is thought to be significantly different from that of the Examples.

[0054] Figure 9 shows a scanning electron microscope image (magnification 10,000x) of the zirconia sintered body of the above example in a different field of view, along with the results of EPMA line analysis, in which the YO concentration was measured along an analysis line that crossed the background region and multiple coarse dispersed particles in that field of view. A notable feature is the concentration profile in which the YO concentration changes continuously in a wave-like pattern, with maximum points within each coarse dispersed particle and minimum points within the background region. This unique YO concentration profile is particularly noticeable when the area fraction of the second region is 15% to 50%. Resistance to crack propagation is relatively low in coarse dispersed particles (crystal particles of the second region) that are primarily composed of C-phase domains. However, it is believed that a region in which the Y2O3 concentration is reduced by the crystal particles belonging to the first region (and the third region), i.e., a region in which the T-phase domain ratio increases, is formed around the coarse dispersed particles, and a structure in which the amount of Y2O3 concentration reduction increases with increasing distance from the coarse dispersed particles based on the concentration profile described above, i.e., a structure in which the T-phase domain ratio increases gradually with increasing distance from the coarse dispersed particles, can be formed, making it easier to ensure a good fracture toughness value.

[0055] The mechanism by which a characteristic structure that produces a difference in the average Y2O3 concentration between the first and second regions is obtained by using a raw material powder with a sharp particle size distribution as shown in Figure 1 can be assumed as follows. That is, the raw material powder has a sharp particle size distribution peak with almost no particles with a particle size exceeding 0.4 μm, and almost all powder particles fall within the range of 0.06 to 0.3 μm. When such raw material powder is molded and sintering is started, at the initial stage of sintering, as shown in State 1 in Figure 10, particles exceeding 0.4 μm are present. large There are almost no crystal grains, and small crystal grains SG are the main constituent. At this stage, as shown in Figure 12, the mechanism by which adjacent small crystal grains SG bond and coalesce is the main mechanism, and it is thought that the slow, uniform growth continues for a while without generating protruding large grains.

[0056] However, a small number of relatively large powder particles near the large particle size tail of the particle size distribution tend to grow larger than the others. When the particle size exceeds a certain critical value, they rapidly grow into large crystal particles BG, consuming the surrounding fine crystal particles FG, as shown in State 2. However, because the number of these large crystal particles BG is small, they form islands of their own. On the other hand, small crystal particles SG that are separated from the large crystal particles BG continue to grow relatively slowly, primarily through the coalescence mechanism shown in Figure 12. Because the number of islands of large crystal particles BG is limited, they do not contribute to the coarsening of the entire structure, as shown in State 3. Meanwhile, small crystal particles FG that do not reach the large crystal particles to which they coalesce remain stranded between the large crystal particles BG. These become crystal particles in the first or third regions that form the background region, and the large crystal particles BG become crystal particles (coarse dispersed particles) SA in the second region, dispersed in island-like shapes in the background region (see Figure 6).

[0057] If there are few large crystal grains BG that grow excessively large, the average difference in particle size between the large crystal grains BG and the adjacent small crystal grains SG (SG(1)-(3)) will remain relatively small, as shown in Figure 13. According to the known theory of neck formation in solid-state sintering, the larger the dimensional difference between the adjacent large crystal grains SG and the adjacent large crystal grains BG, the smaller the radius of curvature ρ of the neck N at the junction, which is the junction, and the lower the vapor pressure. This results in an increment of vacancy concentration ΔC in the neck N that is greater than that in the bulk. The vacancy concentration gradient at the neck N is expressed as ΔC / ρ, which acts as the driving force for vacancies to diffuse into the interior of the crystal grains, while the constituent atoms of the crystal grains flow into the voids V between the crystal grains. This causes the voids V to shrink and solid-state sintering to proceed. Since the excess vacancy concentration increase ΔC is thought to be concentrated on the small crystal grain SG side, which has a small radius of surface curvature, atomic diffusion proceeds in the direction of filling the void V, shrinking the small crystal grain SG, and growing the large crystal grain BG.

[0058] At this time, the smaller small crystal particles SG(3), which have a large size difference from the large crystal particles BG, have a large atomic diffusion flux toward the large crystal particles BG, and are absorbed and disappear. Because the small crystal particles SG(3) are entirely absorbed into the large crystal particles BG, they do not significantly increase the Y2O3 concentration in the large crystal particles BG. This is also true when fine crystal particles FG (or small crystal particles SG) coalesce as shown in Figure 12.

[0059] On the other hand, the atomic diffusion flux of the larger small crystal grains SG(1) and SG(2) toward the large crystal grains BG is relatively small, and many remain without being absorbed by the large crystal grains BG. In this case, it is presumed that the atomic diffusion coefficient from the small crystal grains SG(1) and SG(2) toward the large crystal grains BG is larger for Y than for Zr. In other words, it is thought that the larger the grain size of the small crystal grains SG(1), the more likely Y diffusion occurs toward the large crystal grains BG.

[0060] If we consider that the Y2O3 concentration of the large crystal grains BG, which grew using small crystal grains as seeds, is increased by this estimated mechanism, then the large crystal grains are in contact with small crystal grains with a lower Y concentration. In other words, a concentration gradient of Y atoms is formed in the direction from the large crystal grains to the small crystal grains, i.e., in the opposite direction to the estimated diffusion direction of Y atoms. However, the EPMA analysis results shown in the figure strongly suggest that Y is diffusing from the small crystal grains to the large crystal grains, overcoming this concentration gradient.

[0061] According to the equilibrium phase diagram in Figure 13, a ZrO2-Y2O3 binary composition tends to separate into T and C phases, which have different phase free energies, at the ZrO2 side. According to Figure 10 of Non-Patent Document 1, which is the source of this diagram, in the Y2O3 concentration range assumed in this embodiment, the T phase has a lower free energy ΔGv than the C phase, and the difference between the two decreases as the Y2O3 concentration increases. Furthermore, 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 above-mentioned phase free energy term (volume energy) and the interfacial tension energy term (area energy). As the crystal grains become finer, the contribution of the interfacial tension energy term to the total energy increases. Therefore, if a large amount of the T phase, which has a low phase free energy, is produced, the total energy of the crystal decreases, resulting in energy stability. Therefore, it can be considered that small crystal grains induce Y to flow toward large crystal grains in order to increase the T phase ratio.

[0062] As Y flows out from the small crystal grains SG to the large crystal grains BG, the Y2O3 concentration in the large crystal grains BG increases and decreases. In this case, the smaller the crystal grains SG that are left behind, the more rapidly the Y2O3 concentration decreases, so it is thought that the Y2O3 concentration will be lower in the outer regions of the large crystal grains BG, which are filled in later in time.

[0063] If the void V decreases, the shrinkage of the sintered body slows down, and the vacancy concentration that acts as the driving force for atomic diffusion also decreases, so that the remaining small crystal grains SG are less likely to coalesce or absorb into the large crystal grains BG. 9 It is thought that the formation of a structure with a large difference in Y2O3 concentration between the small crystal grains SG and the large crystal grains BG is largely completed as the wave-shaped Y2O3 concentration profile shown in Figure 1 is formed. Furthermore, the smaller the Y2O3 concentration of the small crystal grains SG, the higher the T phase ratio, which increases the phase free energy difference with the large crystal grains BG, which has a high C phase ratio, making it more difficult for them to coalesce with the large crystal grains BG.

[0064] Next, the reason why the difference in Y2O3 concentration according to the crystal grain size is less likely to occur when a raw material powder with a broad particle size distribution as shown in Figure 2 is used can be presumed as follows. As shown in State 1 of Figure 11, when such a raw material powder is used, a large number of large crystal grains BG, which are originally present in the raw material powder, are already present at the early stage of sintering, and as shown in Figure 14, their size is considerably larger than when the raw material powder of Figure 1 is used. In particular, in the case of bimodal powders having two peaks, one at 0.3 to 0.5 μm and the other at 0.15 μm or less, as in Patent Documents 2 and 4, the content ratio of large crystal grains exceeding 0.4 μm is particularly high.

[0065] The YO concentration of these large crystal particles BG, which originate from large powder particles at the raw material stage, is close to the composition at the time of blending, and the proportion of irregular increases in the YO concentration is thought to be small. In this case, as shown in Figure 14, in the early stages of sintering when many voids remain, the number ratio of fine powder particles FG and small crystal particles SG with low growth rates among the particles in contact with these large crystal particles BG becomes much higher than in Figure 13, and most of them are absorbed into the large crystal particles BG and disappear, similar to the small crystal particles SG (3) in Figure 13. As already explained, in such cases, the YO concentration of the large crystal particles BG is unlikely to increase.

[0066] Therefore, until the critical size is reached at which absorption into the large crystal particles BG becomes difficult, the surrounding small crystal particles SG are absorbed into one of the many large crystal particles BG and disappear, and this process continues for a long time, resulting in state 2 in Figure 11. Therefore, until the large crystal particles BG grow considerably large, there is not much inflow of Y from the small crystal particles SG, and the Y2O3 concentration in the large crystal particles BG and small crystal particles SG remains small. When a raw material powder with a bimodal distribution such as that in Patent Document 2 or 4 is used, sintering is completed in a state where a relatively large number of small crystal particles SG, in which the Y2O3 concentration has not decreased significantly, remain between the large crystal particles BG (Figure 11: state 3). right). Furthermore, when a raw material powder with a relatively large average grain size and a broad, single-peak grain size distribution is used as shown in Figure 2 of the present invention, the growth of the large crystal grains BG continues until they have almost completely consumed the small crystal grains SG, and it is thought that an equiaxed crystal structure with a large average crystal grain size is reached (Figure 11: left of State 3). It has been confirmed that in zirconia sintered bodies exhibiting an equiaxed crystal structure such as the latter, Y segregates near the grain boundaries where large crystal grains are adjacent to each other (Non-Patent Document 5). It should be noted that such a Y2O3 concentration distribution exhibits a tendency that is completely opposite to that of the embodiment shown in Figure 9, in that the Y concentration is low in the outer periphery of the large crystal grains BG and in the surrounding small crystal grains.

[0067] The raw material powder for producing the zirconia sintered body of the above embodiment is -Arithmetic mean particle size is 0.10 μm or more and 0.15 μm or less, - The arithmetic standard deviation is between 0.03 μm and 0.05 μm, Particles with a particle size of more than 0.8 μm and less than 0.03 μm are not measured. - The measured values ​​of particles with a particle size of more than 0.4 μm and particles with a particle size of 0.04 μm or less are both 0.5% or less. If any of the above conditions is exceeded, the average Y2O3 concentration C1 (first Y2O3 concentration C1) of the zirconia crystal particles constituting the first region will be lower than the average Y2O3 concentration C2 (second Y2O3 concentration C2) of the zirconia crystal particles constituting the second region (specifically, the value of ΔC / C2 is 0.2 or more and 0.5 or less, where ΔC≡C2-C1), making it difficult to obtain a characteristic concentration distribution form. Taking into consideration the formation of secondary particles in the powder, the specific surface area of ​​the raw material powder measured by the BET method was set to 13 m 2 The specific surface area of ​​the raw material powder should be 8 m / g or less in relation to the arithmetic mean particle size being 0.10 μm or more and 0.15 μm or less. 2 It is recommended to set it to / g or higher.

[0068] Next, in the zirconia sintered body of the embodiment, a portion of the remaining ZrO2 can be substituted with La2O3 (lanthanum oxide) in a content of 0.1 mol% to 1 mol% in the total composition of the sintered body. By adding La2O3 in this composition range, the total light transmittance of the zirconia sintered body can be further improved compared to a zirconia sintered body without adding La2O3. The amount of La2O3 substituted for ZrO2 is preferably 0.15 mol% to 0.8 mol%, more preferably 0.15 mol% to 0.6 mol%, in terms of the content in the total composition of the sintered body.

[0069] In the zirconia sintered body of the embodiment, a portion of the remaining ZrO may be substituted with 0.2 mol% or less of AlO (aluminum oxide). It may also be substituted with 0.1 mol% or less of TiO (titanium oxide). The inclusion of AlO or TiO within such a composition range does not particularly hinder the realization of the characteristic structure and component distribution of the zirconia sintered body of the embodiment described above in detail, and thus the fracture toughness value and total light transmittance resulting therefrom.

[0070] In the embodiments, the term "unavoidable impurities" refers to components that can be contained within a range that does not impair the characteristics of the zirconia sintered body of the embodiment. It does not necessarily refer only to residual components that cannot be actively removed during the raw material powder or manufacturing process for the zirconia sintered body, but the total of these does not exceed 0.5 mol%. For example, in the embodiments, Y2O3 is used as a stabilizer, but other stabilizers such as CaO, MgO (magnesium oxide), and CeO2 (cerium oxide) may also be included as inevitable impurities within this concept. SiO2 (silicon dioxide) can also be contained as an inevitable impurity, and its content in the total composition of the sintered body is preferably 0.1 mass% or less.

[0071] The zirconia sintered body of the embodiment configured as described above preferably has a Vickers hardness Hv of 1150 or more, more preferably 1200 or more. As for bending strength, it is desirable that a three-point bending strength test be carried out to ensure a strength of 600 MPa or more, assuming that atmospheric sintering is employed.

[0072] Although some aspects of the manufacturing method for the zirconia sintered body of the embodiment have already been described, it is preferable to proceed as follows. First, pure zirconia powder (average particle size: e.g., 5 μm or less) and pure YO powder (and other oxide powders) as a stabilizer powder are blended to obtain the desired composition, and then 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, where they are pulverized at a predetermined rotation speed that causes an avalanche phenomenon in the contents. At this time, an appropriate amount of water-soluble binder is added, and after pulverization, the mixture is dried using a spray dryer or the like to obtain a composition for molding.

[0073] The composition may be press-molded into a green body, which may then be subjected to secondary processing such as cutting as necessary, followed immediately by sintering. Alternatively, a calcined body may be first prepared, which may then be subjected to secondary processing such as cutting, followed by sintering. When preparing a calcined body, the sintering temperature is preferably 800°C or higher and 1200°C or lower, and more preferably 900°C or higher and 1000°C or lower. The sintering temperature is preferably 1400°C or higher and 1580°C or lower, and more preferably 1420°C or higher and 1550°C or lower. Both the calcination and the sintering can be carried out in an atmospheric atmosphere at normal pressure.

[0074] When the green compact is immediately sintered, the sintering time required to obtain a sufficiently dense sintered body is, for example, 70 to 180 minutes. On the other hand, if a calcined body is produced using a raw material powder with a particle size distribution that satisfies the above-mentioned conditions, the sintering time required to densify the calcined body can be significantly reduced. When using such a calcined body, the sintering time is 60 minutes or less, preferably 30 minutes or less, and more preferably 20 minutes or less.

[0075] The method for producing a zirconia sintered body according to the embodiment can be appropriately modified and carried out as long as it does not particularly hinder the realization of the characteristic structure and component distribution form of the zirconia sintered body, and furthermore, the fracture toughness value and total light transmittance brought about thereby.

[0076] Furthermore, the zirconia sintered body of the embodiment can be used for various purposes such as dental materials such as prosthetic materials, optical fiber connection parts such as ferrules and sleeves, various tools (e.g., grinding balls, grinding tools), various parts (e.g., screws, bolts and nuts), various sensors, electronic parts, decorative items (e.g., watch bands), etc. When the zirconia sintered body is used as a dental material, it can be used for, for example, copings, frameworks, crowns, crown bridges, abutments, implants, implant screws, implant fixtures, implant bridges, implant bars, brackets, denture bases, inlays, etc. 、 It can be used for onlays, orthodontic wires, laminate veneers, etc. [Example]

[0077] Hereinafter, a more detailed example will be described using experiments carried out to confirm the effects and the results thereof. First, as raw powder, 1 kg of commercially available pure zirconia powder mixed with pure Y2O3 powder and pure La2O3 powder in various ratios, 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 244 mm and milled at a rotation speed of 78 rpm for 20 hours. After adding and mixing an appropriate amount of binder, the slurry was dried in a spray dryer to obtain raw powders of various compositions. For comparison, a composition with a Y2O3 concentration of 4.5 mol% was obtained by adding yttrium chloride to a hydrated zirconia sol obtained by hydrolyzing an aqueous zirconium oxychloride solution, followed by drying and mosquito Y2O3-containing zirconia obtained by calcination mosquito A sample was also prepared using 3 mm diameter zirconia media for 1 kg of calcined powder, with a milling time of 10 hours (see Table below). 3(No. 22). A portion of the slurry was not dried and was subjected to measurement of the powder particle size distribution using a laser scattering particle size analyzer. All of the powders, except for No. 22, had particle size distributions almost identical to those shown in Figure 1, and it was confirmed that the arithmetic mean diameter was within the range of 0.115 to 0.130 μm and the arithmetic standard deviation was within the range of 0.035 to 0.042 μm.

[0078] The raw powder was then pressed into a mold using a hydraulic press to create a green compact (N=3), which was then fired at 1500°C in atmospheric air to produce a zirconia sintered body. The sintered body was a plate measuring 40mm x 30mm x 3mm. The density of the sintered body was measured using the Archimedes method, and a comparison with the calculated true density for each composition confirmed that all were densified to over 99.5%.

[0079] Next, one of the three sintered bodies was cut into a first test piece measuring 30 mm × 30 mm × 3 mm and a second test piece measuring 30 mm × 10 mm × 3 mm. The sintered surface of one major surface of the second test piece was observed using a Schottky electron microscope (HITACHI: SU5000) in low vacuum mode at 10,000x magnification to obtain a microstructure image. Using the obtained microstructure image, the grain size distribution was measured as described above to create a histogram. The area ratios of the first region consisting of grains with grain sizes of 0.1 μm to less than 0.5 μm, the third region consisting of grains with grain sizes of 0.5 μm to less than 0.8 μm, and the second region consisting of grains with grain sizes of 0.8 μm or more were calculated as a ratio to the total area of ​​the grains sampled for grain size measurement. The measured grain size distribution data was also used to calculate the area-average diameter of the sampled grains (the value obtained by weighting the grain size of each grain by the equivalent circular grain area on the image, adding up the sum, and dividing by the total area of ​​the sampled grains). For the second test piece, the average Y2O3 concentration CM1 in the first region and the average Y2O3 concentration CM2 in the second region were measured using the EPMA according to the method described above, and the value of ΔCM / CM2 was calculated.

[0080] Next, both sides of the first test piece were ground to a thickness of 0.5 mm, and then both sides were mirror-polished using diamond abrasive grains. Using this test piece, a commercially available ultraviolet-visible spectrophotometer (Japan Spectroscopy: V-780) was used to measure the visible light wavelength range of 380 nm to 780 nm. below The total light transmittance was measured using CIE standard illuminant D65 at 1000 kJ / cm2. Furthermore, the Vickers hardness and fracture toughness were measured using a commercially available Vickers hardness tester at a load of 49 N on one mirror-polished surface of the first test piece. The Vickers hardness and fracture toughness were measured at 12 different positions per sample, and the maximum and minimum measured values ​​were excluded and averaged.

[0081] The remaining two sintered bodies were processed into bending test pieces measuring 3 mm x 4 mm x 40 mm, and a bending strength test was performed using three-point bending. The bending strength was measured at 10 points per sample, and the maximum and minimum measured values ​​were excluded to calculate the average value. The results are shown in Table 2 (in the table, * indicates that the value is outside the scope of the embodiment (present invention)).

[0082] [Table 3]

[0083] For test pieces Nos. 1 to 19 in which the area ratio of the first region and the area ratio of the second region are within the ranges described in the claims of the present invention and the value of ΔCM / CM2 is 0.3 or more, the fracture toughness value is 4.5 MPa m 0.5 More than 12MPa m 0.5The results are as follows: The total light transmittance was found to be high, exceeding 40%. Among the test pieces with a YO concentration of 5.5 mol%, the area ratio of the first region in No. 20 was below the lower limit of the range of the present invention, while the area ratio of the second region exceeded the upper limit of the range. Furthermore, the area ratio of the first region in No. 21 was below the lower limit of the range of the present invention, while the area ratio of the second region exceeded the upper limit of the range. While the total light transmittance of these test pieces was good, the fracture toughness remained low. Furthermore, the test piece with a YO concentration of 2 mol% in No. 23 had significant cracking in the sintered body, and evaluation was abandoned. A comparison of the results of No. 10 (Example) and No. 22 (Comparative Example) has already been described in detail, so it is omitted here.

[0084] Figures 16 and 17 show electron microscope images of test samples Nos. 1 and 3, and Figures 18 and 19 are histograms showing the results of measuring the grain size distribution of those test samples. Figures 20 and 21 show electron microscope images of test samples Nos. 5 and 7, and Figures 22 and 23 are histograms showing the results of measuring the grain size distribution of those test samples. Furthermore, Figures 24 and 25 show electron microscope images of test samples Nos. 13 and 15, and Figures 26 and 27 are histograms showing the results of measuring the grain size distribution of those test samples.

[0085] The Y2O3 concentrations are 3 mol%, 4 mol%, and 5 mol%, respectively, and numbers 1, 5, and 13 have a La2O3 concentration of 0 mol%, while numbers 3, 7, and 15 have La2O3 concentrations of 0 and 4 mol%. Comparing these results, when compared at the same firing temperature, it can be seen that the higher the Y2O3 concentration, the easier it is for crystal grain growth to proceed, and furthermore, there is a tendency for crystal grain growth to proceed more easily with the addition of La2O3 compared to the samples without it.

[0086] Of the test sample compositions numbered 1 to 21 in Table 3, except for numbers 3 and 4, the same raw material powder was used, and several raw material powders (numbers 45 to 47) with compositions having different Y2O3 and La2O3 concentrations were added to these, and the samples were fired at slightly lower temperatures of 1425°C to 1475°C, and the resulting test samples were evaluated in the same manner. The results are shown in Table 4.

[0087] [Table 4]

[0088] It can be seen that by slightly lowering the firing temperature, the area fraction of the first region increased and the fracture toughness values ​​were better than those of the samples fired at 1500°C in Table 3. Furthermore, for the two test samples (Nos. 43 and 44: corresponding to Nos. 20 and 21 in Table 3) with a YO concentration of 5.5 mol%, which had an insufficient area fraction of the first region and thus had fracture toughness values ​​outside the range of the present invention when fired at 1500°C, these samples, along with No. 45, in which the LaO concentration was increased to 0.8 mol%, achieved fracture toughness values ​​within the range of the present invention. On the other hand, for test sample 46, in which the YO concentration was 3 mol% and the firing temperature was lowered to 1425°C, both the area fraction and area-average diameter of the second region were below the lower limit of the present invention, indicating an insufficient total light transmittance. Furthermore, for test sample No. 47, in which the YO concentration exceeded the upper limit of the present invention, the area fraction of the first region was insufficient and the fracture toughness value was insufficient.

[0089] Next, for six of the test sample compositions numbered 1 to 21 in Table 3, which had a Y2O3 concentration of 3, 4, or 5 mol% and a La2O3 concentration of 0 or 0.4 mol%, raw material powders were used in which part of the ZrO2 was replaced with 0.1 mol% Al2O3 (numbers 51 to 56) and 0.05 mol% TiO2 (numbers 57 to 62), and the test samples were fired at 1500°C and the resulting test samples were evaluated in the same way. The results are shown in Table 5.

[0090] [Table 5]

[0091] The evaluation results for these test items are shown in Table 3 The results are almost the same as those of the corresponding compositions, and it can be seen that there is no adverse effect due to the addition of Al2O3 and TiO2.

[0092] Regarding the above results, the area ratio of the first region in the sintered compact structure is S1, and the average Y2O3 concentration of the first region is CM1. PT(%)=S1×{(7.4-CM1) / 6}×100 (A) The value PT calculated by the above formula, the area ratio of the second region in the sintered compact structure is S2, and the average Y2O3 concentration of the second region is CM2. SC(%)=S1×{(CM2-1.4) / 6}×100 (B) Tables 3 to 5 show the SC values ​​calculated by the above formulas. In both formulas A and B, the denominator value "6" indicates the distance between point A (YO concentration: approximately 1.4 mol%), which represents the solid solubility limit of YO in ZrO at 800°C, where atomic diffusion slows to a certain degree, and point B (YO concentration: approximately 7.4 mol%), which represents the solid solubility limit of ZrO in YO. In FIG. 15, when a given composition point is O, the abundance ratio of C phase in a phase equilibrium state can be expressed by AO / AB, and the abundance ratio of T phase can be expressed by BO / AB. Therefore, the right side of formula (A) gives the upper limit of the area fraction of T phase in the first region expected in the equilibrium state, and the right side of formula (B) gives the upper limit of the area fraction of C phase in the second region expected in the equilibrium state. PT is the converted tetragonal area fraction, and SC is the converted cubic area fraction. These values ​​do not directly indicate the amount of T phase or C phase actually present in the zirconia sintered body. However, it is expected from the perspective of phase equilibrium that the larger the value of PT, the larger the area fraction of the actual tetragonal crystals, and the larger the value of SC, the larger the area fraction of the actual cubic crystals.

[0093] Figure 28 shows the results of plotting the fracture toughness values ​​(KIC) in Tables 3 and 4 against the above-mentioned PT values. In the figure, the white plot points represent data for test samples without La2O3 added, and the black plot points represent data for test samples with La2O3 added (the shape of the black plot points is displayed differently depending on the amount of La2O3 added). Regardless of whether La2O3 is added or not, the fracture toughness value increases almost linearly with the PT value, clearly demonstrating that the above inference is not incorrect. From these results, for example, when the converted tetragonal crystal area fraction PT (%) in the first region is between 7% and 32%, the fracture toughness value measured by the IF method is 5.5 MPa m 0.5 More than 10MPa m 0.5 It can be seen that the converted tetragonal area fraction PT can be satisfactorily secured within the following range. In addition, in order to adjust the converted tetragonal area fraction PT within the above range, it is preferable that the Y2O3 content be 3.7 mol% or more and 5.3 mol% or less, and that the area fraction of the first region in the sintered compact structure be 10% or more and 45% or less.

[0094] Next, Figure 29 shows the results of plotting the total light transmittance in Tables 3 and 4 against the SC values. The white plot points in the figure represent data for test samples without La2O3 added, while the black plot points represent data for test samples with La2O3 added (the shape of the black plot points varies depending on the amount of La2O3 added). It can be said that the total light transmittance tends to increase monotonically as the PT value increases, but this increase varies depending on the amount of La2O3 added. Furthermore, upon closer inspection, it can be seen that the data points for the total light transmittance of test samples with La2O3 added are almost always on the higher side of the data points for the total light transmittance of test samples without La2O3 added. Furthermore, the results of logarithmic regression analysis for each La2O3 content are shown in the figure. The solid line represents the logarithmic regression curve for 0 mol% La2O3, the dashed line represents the logarithmic regression curve for 0.2 mol% La2O3, and the dashed lines represent the logarithmic regression curves for 0.4 mol% and 0.8 mol% La2O3 (the curves for 0.4 mol% and 0.8 mol% La2O3 content almost overlap). These results suggest that the total light transmittance of the sintered body tends to increase with La2O3 content up to approximately 0.4 mol% to 0.6 mol%, but the improvement in total light transmittance plateaus at higher La2O3 content levels. Therefore, when adding La2O3 to improve the total light transmittance of a sintered body, it is recommended that a portion of the remaining ZrO2 be replaced with La2O3 at a content of 0.1 mol% to 0.8 mol% in the total composition of the sintered body.

[0095] From this result, for example, when the converted cubic crystal area ratio SC (%) in the second region is 15% or more and 45% or less, a test piece of zirconia sintered body processed to a thickness of 0.5 mm is used for the visible light wavelength range of 380 nm to 780 nm using CIE standard light D65. below It can be seen that the total light transmittance measured by can be satisfactorily secured in the range of 45% or more. In addition, in order to adjust the converted cubic crystal area fraction SC to the above range, it is preferable that the Y2O3 content be 3.7 mol% or more and 5.3 mol% or less, and the area fraction of the second region in the sintered body structure be 20% or more and 50% or less.

[0096] In addition, when preparing the raw material powder, 15 kg of 3 mm diameter zirconia media was replaced with a mixture of 11.6 kg of 3 mm diameter zirconia media and 3.4 kg of 2 mm diameter zirconia media, and the same grinding was performed using the same pot as above with 1 kg of raw material and 1.5 kg of pure water.For both raw material compositions, raw material powders with approximately the same particle size distribution were obtained in a grinding time 50 to 60% shorter than when 3 mm diameter zirconia media was used.These raw material powders were then fired under the same conditions as above, and sintered bodies with approximately the same properties were obtained.

Claims

1. Y in the overall composition of the sintered body ２ O ３ The content of is 2.5 mol % or more and 6 mol % or less, and the balance is ZrO ２ and a zirconia sintered body having a relative density of 99% or more, which consists of inevitable impurities, In the electron microscope image of the sintered body structure, The area average particle size of the zirconia crystal particles is 0.4 μm or more and 0.9 μm or less, the area ratios of zirconia crystal particles having a particle size of less than 0.1 μm and zirconia crystal particles having a particle size of more than 2 μm are both less than 1%; an area ratio of the first region consisting of zirconia crystal grains having a grain size of 0.1 μm or more and less than 0.5 μm being 5% or more and 80% or less; an area ratio of the second region consisting of zirconia crystal grains having a grain size of 0.8 μm or more and less than 2 μm is 5% or more and 80% or less; an area ratio of the third region composed of zirconia crystal grains having a grain size of 0.5 μm or more and less than 0.8 μm is 10% or more and less than 55%; The average Y of the zirconia crystal grains forming the second region ２ O ３ The concentration C2 is 3.5 mol% or more and 7.0 mol% or less, The average Y of the zirconia crystal grains forming the first region ２ O ３ The concentration C1 is 1.7 mol% or more and 5 mol% or less, and ２ O ３ The difference in concentration is ΔC≡C2−C1, and the value of ΔC / C2 is 0.2 or more and 0.5 or less, The fracture toughness measured by the IF method was 4.5 MPa m ０．５ 12MPa・m or more ０．５ A zirconia sintered body characterized by the following:

2. The remainder is ZrO ２ A part of the sintered body has a La content of 0.1 mol % or more and 1 mol % or less in the total composition of the sintered body. ２ O ３ The zirconia sintered body according to claim 1, wherein the zirconia sintered body is substituted with

3. The remainder is ZrO ２ A part of the sintered body has an Al content of 0.2 mol% or less in the total composition of the sintered body. ２ O ３ The zirconia sintered body according to claim 1, wherein the zirconia sintered body is substituted with

4. The remainder is ZrO ２ A part of the sintered body has a TiO content of 0.1 mol% or less in the total composition of the sintered body. ２ The zirconia sintered body according to claim 1, wherein the zirconia sintered body is substituted with

5. 2. The zirconia sintered body according to claim 1, having a Vickers hardness Hv of 1150 or more.

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

7. The area ratio of the first region in the sintered body structure is S1, and the average Y ２ O ３ PT is calculated by PT=S1×{(7.4−CM1) / 6}×100, where CM1 is the concentration. The zirconia sintered body according to claim 1, wherein the converted tetragonal area ratio PT (%) in the first region is 3% or more and 60% or less.

8. The area ratio of the second region in the sintered body structure is S2, and the average Y of the second region is ２ O ３ The concentration is CM2, and SC is calculated as SC=S2×{(CM2−1.4) / 6}×100. The zirconia sintered body according to claim 1, wherein the converted cubic crystal area ratio SC (%) in the second region is 4% or more and 70% or less.

9. In the sintered body structure, the zirconia crystal grains constituting the second region have a Y at the center of the zirconia crystal grains. ２ O ３ The outer Y ２ O ３ The zirconia sintered body according to claim 1, wherein the concentration is low.

10. The sintered body structure has an area ratio of the second region of 15% or more and 50% or less, and has a rock garden-like structure in which the zirconia crystal particles belonging to the second region are dispersed as coarse dispersed particles against a background region consisting of zirconia crystal particles belonging to the first region and zirconia crystal particles belonging to the second region, and has a Y line along an analysis line crossing the background region and a plurality of the coarse dispersed particles. ２ O ３ When the density is measured, a maximum point is shown in each of the coarse dispersed particles, and a minimum point is shown in the background region. ２ O ３ The zirconia sintered body according to claim 9, which exhibits a concentration profile in which the concentration changes in a wave shape.

11. Y ２ O ３ The content of is 3.7 mol% or more and 5.3 mol% or less, an area ratio of the first region in the sintered body structure is 10% or more and 45% or less; The area ratio of the first region in the sintered body structure is S1, The average Y of the first region ２ O ３ The concentration is CM1, PT = S1 × {(7.4 - CM1) / 6} × 100 a converted tetragonal area ratio PT (%) in the first region is 7% or more and 32% or less, The fracture toughness measured by the IF method was 5.5 MPa m ０．５ 10MPa・m or more ０．５ The zirconia sintered body according to claim 1, wherein the zirconia sintered body is:

12. Y ２ O ３ The content of is 3.7 mol% or more and 5.3 mol% or less, an area ratio of the second region in the sintered body structure is 20% or more and 50% or less; The area ratio of the second region in the sintered body structure is S2, The average Y of the second region ２ O ３ The concentration is CM2, SC = S2 × {(CM2 - 1.4) / 6} × 100 a converted cubic crystal area ratio SC (%) in the second region is 15% or more and 45% or less, 2. The zirconia sintered body according to claim 1, wherein a test piece of the zirconia sintered body processed to a thickness of 0.5 mm has a total light transmittance of 45% or more measured in a visible light wavelength range of 380 nm to 780 nm using CIE standard illuminant D65.

13. The remainder is ZrO ２ A part of the sintered body has a La content of 0.1 mol % or more and 0.8 mol % or less in the total composition of the sintered body. ２ O ３ is replaced by The zirconia sintered body according to claim 11, wherein the total light transmittance is 50% or more.

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