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JP-2026075875-A - Zirconia sintered body

JP2026075875AJP 2026075875 AJP2026075875 AJP 2026075875AJP-2026075875-A

Abstract

[Problem] To provide a zirconia sintered body that can achieve a high level of both transparency and fracture toughness, and can be easily manufactured even by atmospheric pressure sintering. [Solution] The Y₂O₃ content in the total composition of the sintered body is 1.7 to 2.9 mol% or less, the area-average particle size of the zirconia crystal particles is 0.6 to 1.1 μm or less, the area ratio of the first region consisting of zirconia crystal particles with a particle size of 0.1 to less than 0.8 μm is 10 to 80% or less, the area ratio of the second region consisting of zirconia crystal particles with a particle size of 0.8 to 3.2 μm or less is 20 to 90% or less, the average Y₂O₃ concentration C2 of the zirconia crystal particles forming the second region is 2.0 to 3.2 mol% or less, the average Y₂O₃ concentration C1 of the zirconia crystal particles forming the first region is 1.7 to 2.3 mol% or less, and the difference in Y₂O₃ concentration is ΔC ≡ C2 - C1, the value of ΔC/C2 is 0.1 to 0.5 or less, and the fracture toughness value measured by the IF method is 10.5 MPa·m The total light transmittance of the sintered body is 40% or higher, and the ratio is 0.5 or higher. [Selection Diagram] Figure 12

Inventors

  • 江田 智一
  • 角田 航介
  • 中島 幹夫
  • 中島 僚紀

Assignees

  • ノリタケ株式会社
  • 中島産業株式会社

Dates

Publication Date
20260511
Application Date
20241023

Claims (10)

  1. A zirconia sintered body having a total composition in which the Y₂O₃ content is 1.7 mol% or more and 2.9 mol% or less, with the remainder being ZrO₂ and unavoidable impurities, and having a relative density of 99% or more. In the electron microscope image of the sintered structure of the zirconia sintered body, The area-average particle size of the zirconia crystal particles is 0.6 μm or more and 1.2 μm or less. The area ratio of zirconia crystal particles with a particle size of less than 0.1 μm and zirconia crystal particles with a particle size of more than 3.2 μm is both less than 1%. The area ratio of the first region, which consists of zirconia crystal particles with a particle size of 0.1 μm or more and less than 0.8 μm, is 10% or more and 80% or less. The area ratio of the second region, which consists of zirconia crystal particles with a particle size of 0.8 μm or more and 3.2 μm or less, is 20% or more and 90% or less. The average Y₂O₃ concentration C₂ of the zirconia crystal particles forming the second region is 2.0 mol% or more and 3.2 mol % or less. The average Y₂O₃ concentration C1 of the zirconia crystal particles forming the first region is 1.7 mol% or more and 2.3 mol% or less. Furthermore, the difference in Y2O3 concentration between the second region Y2O3 concentration C2 and the first region Y2O3 concentration C1 is defined as ΔC ≡ C2 - C1, and the value of ΔC/C2 is 0.1 or greater and 0.5 or less. A zirconia sintered body characterized by having a fracture toughness value of 10.5 MPa· m² or higher, as measured by the IF method in accordance with JIS Z 2244-1 (2024).
  2. The zirconia sintered body according to claim 1, wherein in the sintered body structure, the zirconia crystal grains forming the second region have a lower Y2O3 concentration in the outer periphery than in the center.
  3. The sintered structure has a structure in which zirconia crystal particles belonging to the second region are dispersed in a background region consisting of zirconia crystal particles belonging to the first region, and when the Y2O3 concentration is measured along an analysis line crossing the background region and the plurality of large particles, it exhibits a concentration profile in which the Y2O3 concentration changes continuously from a maximum point formed within each large particle toward the surrounding area.
  4. The zirconia sintered body according to claim 1, wherein the area ratio of the effective Y2O3 concentration region in the sintered body structure, in which the Y2O3 concentration is 2.0 mol% or more and 2.4 mol % or less, is 17% or more.
  5. The zirconia sintered body according to claim 4, wherein the effective Y2O3 concentration region in the sintered body structure is dispersed in a network-like manner along the boundary between the large particles and the background region .
  6. The zirconia sintered body according to claim 1, wherein S1 is the area ratio of the first region in the sintered body structure, CM1 is the average first region Y2O3 concentration in the first region, S2 is the area ratio of the second region, and CM2 is the average second region Y2O3 concentration in the second region, and the converted cubic area ratio S (C) (%) calculated by S (C) = S1 × {(7.4 - CM1) / 6} × 100 + S2 × {(7.4 - CM2) / 6} × 100 is 5% or more and 25% or less.
  7. The zirconia sintered body according to claim 1, wherein a portion of the remaining ZrO2 is replaced with Al2O3 at a content of 0.2 mol% or less in the total composition of the sintered body.
  8. The zirconia sintered body according to claim 1, wherein a portion of the remaining ZrO2 is replaced with TiO2 at a content of 0.1 mol% or less in the total composition of the sintered body.
  9. The zirconia sintered body according to claim 1, wherein the Vickers hardness Hv of the sintered body structure is 1100 or higher.
  10. The zirconia sintered body according to claim 1, wherein a test specimen of the zirconia sintered body processed to a thickness of 0.5 mm has a total light transmittance value of 40% or more and 60% or less, measured using CIE standard light D65 in the visible light wavelength range of 380 nm to 780 nm.

Description

This invention relates to a zirconia sintered body, specifically one that exhibits excellent fracture toughness and superior visible light transmission characteristics. As shown in Fig. 9 of Non-Patent Literature 1 (referred to as Figure 22 in this specification), pure ZrO₂ (zirconium oxide) has polymorphs of CaF₂- type cubic phase (C phase), tetragonal phase (T phase), and monoclinic phase (M phase) from high temperatures. When a stabilizer such as Y₂O₃ (yttrium oxide) or CaO (calcium oxide) is added in an amount of 2 to 5 mol%, it becomes partially stabilized zirconia (PSZ) containing the metastable T phase at room temperature, and when an amount of 8 mol% or more is added, it becomes the C phase, i.e., fully stabilized zirconia (FSZ). In particular, it has been shown that PSZ exhibits excellent mechanical properties due to the martensitic transformation from the high-temperature T phase to the low-temperature M phase. When a crack propagates within the sintered body of PSZ, the stress causes a transformation from the T phase to the M phase, and at that time, the volume expands by about 4%. This expansion applies compressive stress to the crack tip , suppressing crack propagation (hereinafter, this mechanism of strengthening of zirconia sintered bodies will be referred to as "transformation-induced high toughness"). PSZ using Y2O3 as a stabilizer is chemically stable and possesses high strength and toughness, making it widely used as a mechanical structural material such as engine material, cutting tool, die, seal material, and bearing, as well as a biomaterial such as dental bone material. The zirconia sintered body disclosed in Patent Document 1 employs a composition of 5 mol% Y₂O₃ , which further stabilizes the C phase, and is manufactured using the HIP method, which minimizes bubble retention. The total light transmittance measured at a sample thickness of 1 mm is high, ranging from 41 to 46%. While the sample thickness used for measuring total light transmittance varies between 0.5 mm and 1.0 mm in different 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. Referring to this, the total light transmittance of a 0.5 mm thick sample can be estimated by multiplying the total light transmittance value of a 1.0 mm thick 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 sample thickness of 0.5 mm. On the other hand, the bending strength of the sintered body is approximately 800 M to 1100 MPa, and the fracture toughness is approximately 3.5 to 4.0 MPa· m0.5 . Furthermore, it has been disclosed that the average grain size of the sintered body, measured by the line intercept method, is approximately 0.49 to 0.95 μm. The raw material powder used is fine, with an average grain size of 0.028 to 0.030 μm and a specific surface area of 15 to 16 m² /g. Patent Document 2 discloses a sintered body of zirconia with a composition of 1.6 to 2 mol% Y₂O₃ , manufactured using the HIP method. Due to the adoption of a composition with a higher T phase content, which is a factor in transformation and increased toughness, the sintered body exhibits high strength and toughness, with a bending strength of 1470 to 2140 MPa and a fracture toughness of 6.0 to 10.3 MPa· m⁰.5 . However, the total light transmittance measured at a sample thickness of 1 mm is 27 to 34% (estimated to be 32.7 to 41.2% when converted to a sample thickness of 0.5 mm), which is lower compared to Patent Documents 1 to 3. The average grain size of the sintered body measured by the planimetric method is 0.28 to 0.55 μm. The raw material powders used had a bimodal distribution with peaks at 0.14 μm and 0.34–0.35 μm, respectively, and a median diameter of 0.15–0.18 μm, with a specific surface area of 15.1–17.9 m² /g (for the powders in synthesis examples 3 and 6, with specific surface area values of 10.3 m² /g and 11.6 m² /g, the total light transmittance of the sintered bodies was not evaluated). Patent Document 3 discloses a sintered body manufactured using an atmospheric pressure sintering method, mainly for zirconia with a 3 mol% Y₂O₃ composition. The total light transmittance measured at a sample thickness of 1 mm is high at 34-40% (the converted value to a sample thickness of 0.5 mm is estimated to be 41.2-48.4%), and furthermore, the bending strength of the sintered body is 980-1280 MPa. In addition, the average grain size of the sintered body measured by the planimetric method is 0.30-0.34 μm. The raw material powder used has an average grain size of 0.4-0.7 μm and a specific surface area of 11-15 m² / g. Patent Document 4 discloses a sintered body produced by employing an atmospheric pressure sintering method, mainly for zirconia with a 4 mol% Y₂O₃ composition. The bending strength of the sintered body is 10¹⁶ to