Ceramic spheres, ceramic spheres for bearing balls, and method for manufacturing ceramic balls

Abstract

This invention provides a technology to improve the polishing efficiency of ceramic spheres. [Solution] The ceramic sphere is obtained by X-ray diffraction of a region A including the outer periphery of the ceramic sphere, which contains the cross-section, and the integral intensity Pat of the (101) peak of the monoclinic zirconia, the integral intensity Pam1 of the (-111) peak of the monoclinic zirconia, the integral intensity Pam2 of the (111) peak of the monoclinic zirconia, and the integral intensity of the (111) peak of the monoclinic zirconia obtained by X-ray diffraction of a region B inside the outer periphery. The integral intensity Pbt of the (101) peak of monoclinic zirconia, the integral intensity Pbm1 of the (-111) peak of monoclinic zirconia, and the integral intensity Pbm2 of the (111) peak of monoclinic zirconia are given by (Pam1+Pam2) / (Pam1+Pam2+Pat)≦0.035 and |(Pam1+Pam2) / (Pam1+Pam2+Pat)-(Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)|≦0.035.

Description

[Technical Field]

[0001] This invention relates to ceramic spheres, ceramic spheres for bearing balls, and a method for manufacturing ceramic balls. [Background technology]

[0002] Ceramic spheres that can be polished to become ceramic balls have been known for some time (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2024-101045 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, even with prior art such as Patent Document 1, there was still room for improvement in techniques for improving the polishing efficiency of ceramic spheres.

[0005] This invention was made to solve the above-mentioned problems and aims to provide a technology for improving the polishing efficiency of ceramic spheres. [Means for solving the problem]

[0006] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following forms.

[0007] (1) According to one embodiment of the present invention, a ceramic sphere is provided. This ceramic sphere contains alumina crystal particles and zirconia crystal particles, and in a planar region including the cross-section of the ceramic sphere, a circular region with a diameter of 50 μm including the outer periphery of the ceramic sphere is designated as region A, and a circular region with a diameter of 50 μm inside the outer periphery of the ceramic sphere is designated as region B. For each of region A and region B, the (101) peak of tetragonal zirconia obtained by X-ray diffraction for region A is Let Pat be the integrated intensity, Pam1 be the integrated intensity of the (-111) peak of monoclinic zirconia, Pam2 be the integrated intensity of the (111) peak of monoclinic zirconia, Pbt be the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for region B, Pbm1 be the integrated intensity of the (-111) peak of monoclinic zirconia, and Pbm2 be the integrated intensity of the (111) peak of monoclinic zirconia. Then the following equations (1) and (2) are satisfied. (Pam1+Pam2) / (Pam1+Pam2+Pat)≦0.035 ···(1) |(Pam1+Pam2) / (Pam1+Pam2+Pat)-(Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)|≦0.035 ···(2)

[0008] According to this configuration, the zirconia crystal particles contained in the outer periphery of the ceramic sphere contain a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. Furthermore, the proportion of monoclinic zirconia in the zirconia crystal particles contained in the outer periphery of the ceramic sphere is close to the proportion of monoclinic zirconia in the zirconia crystal particles contained inward from the outer periphery. In other words, in the ceramic sphere, the crystalline phase composition of the zirconia crystal particles is similar in both the outer periphery and the inward side. As a result, in the manufacturing process of producing bearing balls by polishing the ceramic sphere, ceramic balls can be produced with less polishing, thereby improving polishing efficiency.

[0009] (2) In the ceramic sphere of the above form, the region B may satisfy the following formula (3). (Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)≦0.035 ···(3) In this configuration, the zirconia crystal particles contained inside the outer periphery of the ceramic sphere contain a larger proportion of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. As a result, by polishing the ceramic sphere, bearing balls with superior mechanical properties can be obtained.

[0010] (3) In the ceramic sphere of the above form, if Sa is the ratio of the area occupied by zirconia crystal particles in the cross-section of the ceramic sphere included in region A, and Sb is the ratio of the area occupied by zirconia crystal particles in the cross-section of the ceramic sphere included in region B, then the following equations (4) and (5) may be satisfied. 0.08 ≤ Sa ≤ 0.30 ···(4) 0.08 ≤ Sb ≤ 0.30 ···(5) In this configuration, both the outer periphery and the inner portion of the ceramic sphere contain more alumina crystal particles than zirconia crystal particles. As a result, the zirconia crystal particles are less likely to transform from tetragonal zirconia to monoclinic zirconia due to the constraint of the alumina crystal particles, thus suppressing the deterioration of the mechanical properties of the ceramic balls obtained by polishing the ceramic spheres.

[0011] (4) In the above-described form of ceramic sphere, if Va is the Vickers hardness of the cross-section of the ceramic sphere included in region A, and Vb is the Vickers hardness of the cross-section of the ceramic sphere included in region B, then the following equations (6) to (8) may be satisfied. Va ≥ 1960 kgf / mm 2 ...(6) Vb ≥ 1960 kgf / mm 2 ...(7) |Va-Vb| ≤ 120 kgf / mm 2 ...(8) With this configuration, the Vickers hardness of the outer periphery of the ceramic sphere and the Vickers hardness of the part inside the periphery are both relatively large, with little difference between them. In ceramic spheres, the Vickers hardness of the outer periphery and the part inside the periphery are both relatively large and almost the same. This makes it possible to manufacture ceramic balls with relatively high hardness with a small amount of polishing.

[0012] (5) The ceramic sphere of the above form may further include a spherical portion made of ceramics and a strip-shaped, annular strip-shaped portion made of ceramics, which is arranged along the outer circumference of the spherical portion. With this configuration, the ceramic sphere has a spherical portion and a strip-shaped portion arranged along the outer circumference of the spherical portion. This makes it possible to manufacture a ceramic ball by polishing the strip-shaped portion and polishing the surface of the spherical portion to a relatively thin degree.

[0013] (6) In the ceramic sphere of the above form, the variation in the diameter of the spherical part may be within 2%. With this configuration, since the variation in the diameter of the spherical part is relatively small, the amount of polishing required to manufacture ceramic balls of a predetermined diameter can be reduced. Therefore, in the manufacturing process of producing ceramic balls by polishing ceramic spheres, ceramic balls can be manufactured with an even smaller amount of polishing, thereby further improving polishing efficiency.

[0014] (7) According to another embodiment of the present invention, ceramic spheres for bearing balls are provided. These ceramic spheres for bearing balls consist of the ceramic spheres described above. With this configuration, bearing balls can be manufactured with a relatively small amount of polishing. That is, the polishing efficiency can be improved, and thus the manufacturing cost of bearing balls can be reduced.

[0015] (8) According to another aspect of the present invention, a method for manufacturing ceramic balls is provided. The method for manufacturing ceramic balls includes a step of preparing the above-mentioned ceramic green balls and a step of polishing the ceramic green balls. According to this configuration, in the step of polishing the ceramic green balls, ceramic balls can be manufactured with a relatively small amount of polishing. That is, since the polishing efficiency can be improved, the manufacturing cost of the ceramic balls can be reduced.

[0016] Note that the present invention can be realized in various aspects, and can be realized in the form of a method for manufacturing ceramic green balls, a manufacturing apparatus used for the method for manufacturing ceramic green balls, a ceramic ball manufactured from the ceramic green balls, a method for manufacturing ceramic green balls for bearing balls, a computer program for causing a manufacturing apparatus to execute the manufacturing of ceramic green balls, etc.

Brief Description of the Drawings

[0017] [Figure 1] It is a schematic diagram of a bearing according to the first embodiment. [Figure 2] It is a schematic external view of a ceramic green ball for bearing balls. [Figure 3] It is a cross-sectional SEM image of a ceramic green ball for bearing balls. [Figure 4] It is a cross-sectional schematic diagram of a ceramic green ball for bearing balls. [Figure 5] It is a first diagram for explaining an evaluation test of a ceramic green ball. [Figure 6] It is a second diagram for explaining an evaluation test of a ceramic green ball.

Embodiments for Carrying Out the Invention

[0018] <First Embodiment> Figure 1 is a schematic diagram of a bearing 100 according to a first embodiment. The bearing 100 comprises an inner ring 110, an outer ring 120, and a plurality of bearing balls P10. The bearing balls P10 are held by a cage (not shown) and sandwiched between the inner ring 110 and the outer ring 120. The bearing balls P10 stably hold the rotation axis of the inner ring 110, to which a rotating shaft (not shown) is fixed, with respect to the outer ring 120, which is fixed to a machine or the like. However, the method of using the bearing 100 is not limited to this.

[0019] The bearing ball P10 is a ceramic ball formed from ceramics. The bearing ball P10 is formed by polishing a ceramic sphere intended for bearing balls.

[0020] Figure 2 is a schematic diagram of the external appearance of a ceramic sphere 10 for bearing balls. Figure 3 is a cross-sectional SEM image of the ceramic sphere 10 for bearing balls, and is a cross-sectional SEM image including the outer surface S10 of the ceramic sphere 10. As shown in Figure 3, the ceramic sphere 10 contains alumina crystal grains CPa and zirconia crystal grains CPz. The ceramic sphere 10 comprises a spherical portion 11 formed of ceramics and a band-shaped, annular band-shaped portion 12 arranged along the outer circumference of the spherical portion 11, and the band-shaped portion 12 formed of ceramics. In Figure 2, the direction along the central axis Ca 10 of the ceramic sphere 10 is defined as the z-axis direction, and the x-axis is perpendicular to the z-axis, and the y-axis is perpendicular to the z-axis and x-axis. Figure 2 shows a schematic diagram of the external appearance of the ceramic sphere 10 as seen from the y-axis direction and a schematic diagram of the external appearance of the ceramic sphere 10 as seen from the z-axis direction. In the ceramic sphere 10 of this embodiment, the diameter d11 of the spherical portion 11 is 0.5 mm or more. Preferably, the diameter d11 of the spherical portion 11 is 1 mm or more, and more preferably 2 mm or more. Preferably, the diameter of the spherical portion 11 is 25 mm or less. In this embodiment, the variation in the diameter d11 of the spherical portion 11 is within 2%. The ceramic sphere 10 shown in Figure 2 is manufactured by the method for manufacturing the bearing ball P10 described later, and is an unpolished (unpolished) ceramic member. Note that "polishing" here does not include barrel polishing.

[0021] Figure 4 is a schematic cross-sectional view of a ceramic sphere 10 for bearing balls. The cross-section of the ceramic sphere 10 shown in Figure 4 is a cross-section passing through the center Cs 10 of the ceramic sphere 10, and is, for example, a cross-section perpendicular to the x-axis and the y-axis. In the planar region including the cross-section of the ceramic sphere 10, a circular region with a diameter of 50 μm including the outer periphery of the ceramic sphere 10 is designated as "Region A," and a circular region with a diameter of 50 μm inside the outer periphery of the ceramic sphere is designated as "Region B." For each of "Region A" and "Region B," the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for "Region A" is denoted as Pat. Let Pam1 be the integrated intensity of the (-111) peak of clinocrystalline zirconia, and Pam2 be the integrated intensity of the (111) peak of monoclinic zirconia. If Pbt is the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for "Region B", Pbm1 be the integrated intensity of the (-111) peak of monoclinic zirconia, and Pbm2 be the integrated intensity of the (111) peak of monoclinic zirconia, then the following equations (1) and (2) are satisfied. The value obtained by the left side of equation (1) is called the "m-phase ratio" in "Region A". The m-phase ratio indicates the proportion of monoclinic zirconia in the zirconia crystal grains CPz contained in the target region. (Pam1+Pam2) / (Pam1+Pam2+Pat)≦0.035 ···(1) |(Pam1+Pam2) / (Pam1+Pam2+Pat)-(Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)|≦0.035 ···(2)

[0022] The "region A" and "region B" defined in relation to equations (1) and (2) will be explained using Figure 4. "Region A" refers to a circular region with a diameter of 50 μm within the planar region D10 that includes the cross-section of the ceramic sphere 10 as shown in Figure 4, and includes the outer peripheral portion 10a having the outer surface S10 of the ceramic sphere 10. In Figure 4, the part corresponding to "Region A" is the part inside the annular dashed line indicated by the symbol Fa. That is, "Region A" includes at least the cross-section of the outer peripheral portion 10a of the ceramic sphere 10. In the diffraction chart obtained by X-ray diffraction analysis of "Region A" as defined in this way, if we let Pat be the integrated intensity of the (101) peak of tetragonal zirconia, Pam1 be the integrated intensity of the (-111) peak of monoclinic zirconia, and Pam2 be the integrated intensity of the (111) peak of monoclinic zirconia, then the ceramic sphere 10 satisfies equation (1). In other words, a ceramic sphere 10 that satisfies equation (1) contains a large amount of tetragonal zirconia, which has superior mechanical properties than monoclinic zirconia, among the zirconia crystal grains CPz contained in the outer periphery 10a of the ceramic sphere 10. Here, "superior mechanical properties" refers to, for example, a relatively high Vickers hardness. In this embodiment, the outer periphery 10a of the ceramic sphere 10 is also the outer periphery 11a of the spherical portion 11. In Figure 4, for the sake of explanation, the size of the portion inside the annular dashed line indicated by the symbol Fa, which corresponds to "region A," is shown to be larger than its actual size.

[0023] "Region B" refers to a circular region with a diameter of 50 μm within the planar region D10, which includes the cross-section of the ceramic sphere 10 as shown in Figure 4, and is located inside the outer periphery 10a of the ceramic sphere 10. In Figure 4, the portion corresponding to "Region B" is the part inside the annular dashed line indicated by the symbol Fb. In other words, "Region B" includes only the portion of the cross-section of the ceramic sphere 10 inside the outer periphery 10a, i.e., the central part 10b of the ceramic sphere 10. In this embodiment, the central part 10b of the ceramic sphere 10 is also the central part 11b of the spherical part 11. In Figure 4, an example of the central part 10b of the ceramic sphere 10 is shown as a range where the distance from the center Cs10 is within 95% of the diameter d11 of the spherical part 11, but the range of the central part 10b of the ceramic sphere 10 is not limited to this. "Region B" is preferably the area near the center Cs10 of the ceramic sphere 10, for example, it is preferably the area within 10% of the diameter d11 of the spherical part 11 from the center Cs10 of the ceramic sphere 10. In Figure 4, for the sake of explanation, the size of the area inside the annular dashed line indicated by the symbol Fb, which corresponds to "Region B," is shown to be larger than its actual size. Note that "Region A" and "Region B" set with respect to equations (1) and (2) do not have to be cross-sections passing through the center Cs10 of the ceramic sphere 10, but may be set in cross-sections passing near the center Cs10 of the ceramic sphere 10.

[0024] In the diffraction chart obtained by X-ray diffraction analysis for the "region B" set up in this way, the ceramic sphere 10 satisfies equation (2) when Pbt is the integrated intensity of the (101) peak of tetragonal zirconia, Pbm1 is the integrated intensity of the (-111) peak of monoclinic zirconia, and Pbm2 is the integrated intensity of the (111) peak of monoclinic zirconia. The ceramic sphere 10 that satisfies equation (2) has a relatively close ratio of monoclinic zirconia in the zirconia crystal grains CPz contained in the outer periphery 10a and the ratio of monoclinic zirconia in the zirconia crystal grains CPz contained in the central part 10b. In other words, the ceramic sphere 10 that satisfies equation (2) has a similar crystalline phase composition in the zirconia crystal grains CPz in the outer periphery 10a and the central part 10b. Therefore, the ceramic sphere 10 can be said to be relatively homogeneous with respect to zirconia crystal grains CPz.

[0025] In this embodiment, the ceramic sphere 10 satisfies the following equation (3) for "region B" in the planar region D10 that includes the cross-section of the ceramic sphere 10 as shown in Figure 4. The value obtained by the left side of equation (3) is called the "m-phase ratio" in "region B". (Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)≦0.035 ···(3) Equation (3) shows that the zirconia crystal grains CPz contained in the central part 10b of the ceramic sphere 10 contain a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. In other words, a ceramic sphere 10 that satisfies equation (3) contains a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia, in the zirconia crystal grains CPz contained in the central part 10b.

[0026] Here, the method for calculating the m-phase fraction in "region A" and "region B" of the ceramic sphere 10 of this embodiment will be specifically explained. First, the ceramic sphere 10 is cut so as to pass through the center Cs 10 of the ceramic sphere 10, forming a circular cross-section as shown in Figure 4. Next, the cross-section is polished to a mirror finish. The amount of polishing when polishing the cross-section to a mirror finish is arbitrary, but a maximum of about 50 μm is sufficient. For the final finishing polish to make the cross-section a mirror finish, for example, buff polishing using a 0.5 μm diamond spray may be performed. Micro-X-ray diffraction is performed on the mirror-polished cross-section to identify the crystalline phase of the zirconia crystal grains CPz, and the content of each crystalline phase is measured. The diameter of the incident X-ray beam irradiated by the collimator used for micro-X-ray diffraction is 50 μm. Using the diffraction charts of "Region A" and "Region B" of the ceramic sphere 10 obtained by this method, the integrated intensity of the (101) peak of tetragonal zirconia, the integrated intensity of the (-111) peak of monoclinic zirconia, and the integrated intensity of the (111) peak of monoclinic zirconia are calculated. Finally, using these calculated values, the m-phase fractions of "Region A" and "Region B" are calculated.

[0027] In this embodiment, the ceramic sphere 10 satisfies the following equations (4) and (5) when the planar region D10 containing the cross-section of the ceramic sphere 10 as shown in Figure 4 is divided into "region A" and "region B", where Sa is the proportion of the area occupied by zirconia crystal particles CPz in the cross-section of the ceramic sphere 10 contained in "region A", and Sb is the proportion of the area occupied by zirconia crystal particles CPz in the cross-section of the ceramic sphere contained in "region B". 0.08 ≤ Sa ≤ 0.30 ···(4) 0.08 ≤ Sb ≤ 0.30 ···(5) Equation (4) shows that in "region A," there are more alumina crystal particles CPa than zirconia crystal particles CPz. Equation (5) shows that in "region B," there are more alumina crystal particles CPa than zirconia crystal particles CPz. In other words, the ceramic elementary sphere 10 that satisfies equations (4) and (5) contains more alumina crystal particles CPa than zirconia crystal particles CPz overall.

[0028] In this embodiment, the ceramic sphere 10 satisfies the following equations (6) to (8) when the planar region D10 containing the cross-section of the ceramic sphere 10 as shown in Figure 4 is divided into "region A" and "region B", with Va being the Vickers hardness of the cross-section of the ceramic sphere 10 included in "region A" and Vb being the Vickers hardness of the cross-section of the ceramic sphere 10 included in "region B". Va ≥ 1960 kgf / mm 2 ...(6) Vb ≥ 1960 kgf / mm 2 ...(7) |Va-Vb| ≤ 120 kgf / mm 2 ...(8) Equations (6) and (7) show that the Vickers hardness is relatively high in "region A" and "region B," respectively. Equation (8) shows that there is no significant difference between the Vickers hardness in "region A" and the Vickers hardness in "region B." In other words, the ceramic sphere 10 that satisfies equations (5) to (8) has a relatively high Vickers hardness overall.

[0029] Next, the manufacturing method for the ceramic balls, which are bearing balls P10, will be described. In the manufacturing method for ceramic balls, first, ceramic spheres 10 are manufactured. In the manufacturing of ceramic spheres 10, alumina powder (Al2O3, average particle size: 0.5 μm) and yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm) are used as raw material powders. In the manufacturing of ceramic spheres 10, first, the alumina powder and yttria-stabilized zirconia powder are weighed out so that the content of alumina in the ceramic spheres 10 is 80% by weight and zirconia is 20% by weight (weighing step).

[0030] The weighed raw material powder is placed in a resin pot along with alumina spheres, pure water is added as a solvent, and ball milling is performed at a rotation speed of 60 revolutions per minute for 72 hours to pulverize and mix the raw material powder, thereby producing a mixed slurry (slurry production process). In the manufacturing method of the ceramic spheres 10 of this embodiment, a polycarboxylic acid-based dispersant is added when producing the mixed slurry. Among polycarboxylic acid-based dispersants, ammonium polycarboxylic acid salt is suitable for hydrophilic oxides, and can appropriately disperse the alumina powder and yttria-stabilized zirconia powder while reducing the amount of water in the mixed slurry.

[0031] A binder is added to the prepared mixed slurry, and after mixing for a further 30 minutes, the mixed slurry is dried by spray drying to produce a mixed powder (powder production step). In the manufacturing method of the ceramic sphere 10 of this embodiment, PVA (polyvinyl alcohol) or PVB (polyvinyl acetal) is used as the binder when producing the mixed powder. As a result, the mixed slurry becomes an aggregated slurry with relatively low viscosity. Since the ceramic sphere 10 of this embodiment is an alumina-zirconia composite material with alumina crystal particles CPa as the matrix, when the mixed slurry becomes an aggregated slurry, the alumina crystal particles CPa can more easily restrain the zirconia crystal particles CPz, and the phase transformation of the zirconia crystal particles CPz to monoclinic zirconia can be suppressed. In addition, when the mixed slurry becomes an aggregated slurry with relatively low viscosity, the mixed powder produced by spray drying becomes solid, so relatively large pores are less likely to be formed when pressing with a mold as described later. This suppresses the phase transformation of zirconia crystal grains CPz to monoclinic zirconia, which tends to progress easily during firing due to the lack of restraining force in the direction toward the inside of the pores. As a result, the formation of monoclinic zirconia, which has inferior mechanical properties compared to tetragonal zirconia and is prone to grain shedding due to volume expansion associated with the phase transformation, becomes less likely. In addition, the resulting slurry becomes a relatively low-viscosity, aggregated slurry, making spray drying easier.

[0032] In the manufacturing method of the ceramic spheres 10 of this embodiment, plasticizers such as PEG (polyethylene glycol) and glycerin are used when preparing the mixed powder. This makes the mixed powder more easily crushed during powder press molding using a mold. In this embodiment of the manufacturing method of the ceramic spheres 10, the plasticizer is added to the mixed slurry before the binder is added. This makes it easier for the plasticity effect to be exhibited.

[0033] Next, the prepared mixed powder is filled into a mold, and a preliminary molded body is produced by powder press molding using a uniaxial press (press pressure: 30 MPa) (preliminary molding process). Next, the preliminary molded body is placed in a special sheet bag and subjected to main molding by CIP (cold isostatic pressing, press pressure: 150 MPa) to produce a molded body (main molding process). The produced molded body is degreased by heat treatment in air at a maximum temperature of 800°C (degreasing process).

[0034] Next, the degreased molded body is fired in the air (firing temperature 1450°C, firing time: 2 hours), followed by hot isostatic pressing (HIP, processing temperature 1400°C, processing pressure 150 MPa, argon atmosphere, processing time: 2 hours) (firing process). This produces the ceramic sphere 10.

[0035] In the method for manufacturing ceramic balls, the surface of the ceramic sphere 10 prepared by the manufacturing method described above is polished to remove the strip-shaped portion 12 while polishing the outer surface of the spherical portion 11 (polishing step). This produces a bearing ball P10 as a ceramic ball.

[0036] Next, we will describe the evaluation test of ceramic spheres. In this evaluation test, samples of ceramic spheres made with different raw materials and manufacturing methods were prepared, and the influence of the raw materials and manufacturing method on the physical properties of the ceramic spheres was evaluated.

[0037] Figure 5 is the first diagram illustrating the evaluation test of ceramic spheres. Figure 5 is a diagram illustrating the items related to the manufacturing method for each of the 11 types of samples used in this evaluation test. Each of the 11 types of samples used in this evaluation test was manufactured using a method similar to the manufacturing method of the ceramic sphere 10 of this embodiment.

[0038] The "raw material (wt%)" shown in Figure 5 indicates the weight percentage of the raw materials used in the preparation of each of the 11 samples. Samples 1 to 5 and samples 9 to 11 use alumina powder (Al2O3, average particle size: 0.5 μm) and yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm), and contain both aluminum oxide sintered bodies and zirconium oxide sintered bodies. Sample 6 uses alumina powder (Al2O3, average particle size: 0.5 μm), silicon nitride powder (Si3N4, average particle size: 0.9 μm), and yttria powder (Y2O3, average particle size: 1.0 μm), and contains a silicon nitride sintered body. Sample 7 uses alumina powder (Al2O3, average particle size: 0.5 μm) and magnesia powder (MgO, average particle size: 0.5 μm), and contains an aluminum oxide sintered body. Sample 8 uses yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm) and contains a zirconium oxide sintered body. Thus, samples 6 to 8 differ from samples 1 to 5 and samples 9 to 11 in the type of sintered body they contain, and are treated as comparative examples in this evaluation test.

[0039] Figure 5 shows the "additives" for each of the 11 samples, indicating the type of "binder" and "plasticizer" added during preparation, as well as the "timing of addition" of the binder and plasticizer during preparation. For the "binder," PVB (polyvinyl acetal) or wax-based materials were used. For the "plasticizer," PEG (polyethylene glycol) or glycerin was used, except for sample 10, which had no plasticizer added. Regarding the "timing of addition," for samples 1 to 9, the plasticizer was added "before" the binder, while for sample 11, the plasticizer was added "after" the binder. Sample 10, which had no plasticizer added, is indicated with "-".

[0040] Figure 6 is the second diagram illustrating the evaluation test of ceramic spheres. Figure 6 shows the density (g / cm³) of each of the 11 samples produced under the manufacturing conditions shown in Figure 5.3 )」, 「m-phase ratio (%)」, 「zirconia area ratio (%)」, and 「Vickers hardness (kgf / mm 2 )」 are shown.

[0041] The 「density (g / cm 3 )」 shown in Fig. 6 indicates the density of each of the 11 types of samples. The 「m-phase ratio (%)」 shown in Fig. 6 indicates the proportion of monoclinic zirconia in the zirconia crystal particles in each of the 11 types of samples. Specifically, it shows the m-phase ratio of the portion corresponding to 「Region A」, the m-phase ratio of the portion corresponding to 「Region B」, and the 「difference」 between the m-phase ratio of the portion corresponding to 「Region A」 and the m-phase ratio of the portion corresponding to 「Region B」, which are set for the m-phase ratio in the ceramic spherical element 10 of this embodiment. The calculation of the 「m-phase ratio (%)」 shown in Fig. 6 was performed on the samples by micro X-ray diffraction on the polished cut surface, similar to the calculation method of the m-phase ratio in the ceramic spherical element 10 of this embodiment. Note that for Sample 6 containing a silicon nitride sintered body and Sample 7 containing an aluminum oxide sintered body, since they do not contain zirconia crystal particles and the m-phase ratio cannot be calculated, it is shown as 「-」.

[0042] The "Zirconia Area Ratio (%)" shown in Figure 6 represents the zirconia area ratio of "Region A," the zirconia area ratio of "Region B," and the "difference" between the zirconia area ratio of "Region A" and the zirconia area ratio of "Region B" for each of the 11 types of samples. Here, we will explain the method for calculating the zirconia area ratio of the target region. In this evaluation test, the zirconia area ratio was calculated by observing the cross-section of the sample. Specifically, an SEM image at a magnification of 1500x was taken using a FE-SEM (Field Emission Scanning Electron Microscope) on the mirror-polished cross-section of the sample prepared for the calculation of the "m-phase ratio (%)." Next, taking advantage of the fact that zirconia crystal particles appear brighter than alumina crystal particles due to the difference in elemental amounts (see Figure 3) in the acquired SEM image, the ratio of the area of ​​zirconia crystal particles to the area of ​​the cross-section of the ceramic sphere in the SEM image was calculated using image processing software. The imaging range using FE-SEM was defined as a rectangular area with sides of 50 μm, and cross-sections of the portions corresponding to "Region A" and "Region B," which were defined for the m-phase fraction of the ceramic elementary sphere 10 in this embodiment, were imaged. Sample 6, which contains a silicon nitride sintered body, sample 7, which contains an aluminum oxide sintered body, and sample 8, which does not contain an alumina sintered body but contains a zirconium oxide sintered body, are indicated with "-".

[0043] Figure 6 shows the Vickers hardness (kgf / mm²). 2The table shows the Vickers hardness in "Region A," the Vickers hardness in "Region B," and the difference between the Vickers hardness in "Region A" and the Vickers hardness in "Region B" for each of the 11 types of samples. Here, we will explain the method for measuring Vickers hardness. In this evaluation test, Vickers hardness was measured on the mirror-polished cross-section of the sample prepared in the calculation of "m-phase ratio (%)" using a Vickers hardness measuring device. The measuring device used for measuring Vickers hardness was a dynamic ultramicrohardness tester manufactured by Shimadzu Corporation, which is capable of applying loads from 100mN to 1000mN. For measuring Vickers hardness, a rectangular area with sides of 50 μm was set for each of the cross-sections of the parts corresponding to "Region A" and "Region B" set for the m-phase fraction of the ceramic sphere 10 in this embodiment. This area was similar to the imaging range by FE-SEM used to calculate the "zirconia area ratio (%)". A load of 200 mN was applied to five locations within the set area, and the average value was calculated. Note that for sample 6, which contains a silicon nitride sintered body, a volatile layer was formed in the part corresponding to "Region A," making it impossible to measure the Vickers hardness in "Region A." Therefore, the value for "Region A" is "-" and the "difference" is also "-".

[0044] As shown in Figure 6, the "m-phase ratio (%)" indicates that in samples 1 to 5, the m-phase ratio in "Region A" was 3.5% or less, confirming that the zirconia crystal grains contained in "Region A" contained a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. Furthermore, in samples 1 to 5, the difference between the m-phase ratio in "Region A" and the m-phase ratio in "Region B" was 3.5% or less, confirming that the crystalline phase composition of the zirconia crystal grains was similar in the outer and central parts of the ceramic spheres.

[0045] As shown in Figure 6, the "m-phase ratio (%)" indicates that in samples 1 to 5, the m-phase ratio in "Region B" is 3.5% or less. This confirms that the zirconia crystal grains contained in "Region B" contain a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. In other words, samples 1 to 5 as a whole contain tetragonal zirconia, which has superior mechanical properties.

[0046] As shown in Figure 6, "Zirconia Area Ratio (%)", it was confirmed that samples 1 to 5 contained more alumina crystal particles than zirconia crystal particles in both "Region A" and "Region B". This confirmed that in samples 1 to 5, the zirconia crystal particles were less likely to transform from tetragonal zirconia to monoclinic zirconia due to the constraint of the alumina crystal particles.

[0047] Figure 6 shows "Vickers hardness (kgf / mm²)". 2 As shown in the above, samples 1 to 5 showed a reading of 1960 kgf / mm² in "Region A". 2 It has a Vickers hardness of 1960 kgf / mm² in "Region B". 2 It has the above Vickers hardness. Also, the difference between the Vickers hardness of "Area A" and the Vickers hardness of "Area B" is 120 kgf / mm². 2 The following is the result: Samples 1 through 5, overall, can be said to have relatively high Vickers hardness.

[0048] Thus, Samples 1 to 5, overall, contain a large amount of tetragonal zirconia, which has excellent mechanical properties, and the crystalline phase of the zirconia crystal grains is homogeneous. As a result, the ceramic spheres of Samples 1 to 5 can be easily manufactured as relatively hard ceramic balls with a small amount of polishing, thereby improving polishing efficiency.

[0049] Sample 6 contains a silicon nitride sintered body, and a volatile layer has been formed in the area corresponding to "Region A". It was confirmed that it has different physical properties from Samples 1 to 5, which contain both aluminum oxide sintered body and zirconium oxide sintered body. Sample 7 contains an aluminum oxide sintered body but does not contain a zirconia sintered body, and the Vickers hardness of the area corresponding to "Region A" is considerably lower than the Vickers hardness of the area corresponding to "Region B". Therefore, Sample 7 is not in a homogeneous state, and there is a risk that the amount of material to be polished will increase. Sample 8 contains a zirconia sintered body but does not contain an alumina sintered body, so the zirconia crystal particles are not constrained by the alumina crystal particles. Therefore, in the area corresponding to the center of Sample 8, the zirconia crystal particles are more likely to undergo phase transformation to monoclinic zirconia, and in the area corresponding to "Region A", they are even more likely to undergo phase transformation to monoclinic zirconia. Therefore, as shown in Figure 6, the m-phase ratio in "Region A" tends to be larger than that in "Region B," and the Vickers hardness of the portion corresponding to "Region A" becomes considerably smaller than that of the portion corresponding to "Region B."

[0050] Sample 9 uses a wax-based material as a binder during the fabrication of ceramic spheres. As a result, the mixing slurry becomes a dispersion-based slurry, and the mixed powder has a hollow shape. When the mixed powder has a hollow shape, it is expected that the zirconia crystal particles will be less constrained by the alumina crystal particles in the hollow portion of "Region A" that remained uncrushed during the preliminary molding process, and it was confirmed that the m-phase ratio of "Region A" is significantly larger than that of "Region B".

[0051] In Sample 10, no plasticizer was added during the fabrication of the ceramic spheres, which is thought to have resulted in poor crushability of the mixed powder. Therefore, in the hollow portion of "Region A" that remained uncrushed during the preliminary molding process, it is expected that the zirconia crystal particles will be less constrained by the alumina crystal particles, and it was confirmed that the m-phase ratio of "Region A" is significantly larger than that of "Region B".

[0052] In Sample 11, the plasticizer was added after the binder during the fabrication of the ceramic sphere. Therefore, it is thought that the plasticizer interacted with the binder before it could spread throughout the entire mixed slurry, preventing it from exhibiting sufficient plasticity. Consequently, in the hollow portion of "Region A" that remained uncrushed during the preliminary molding process, the zirconia crystal particles were less constrained by the alumina crystal particles, and it was confirmed that the m-phase ratio of "Region A" was significantly larger than that of "Region B".

[0053] As described above, the ceramic sphere 10 of this embodiment satisfies equations (1) and (2), so the zirconia crystal particles CPz contained in the outer periphery 10a contain a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. Furthermore, the proportion of monoclinic zirconia in the zirconia crystal particles CPz contained in the outer periphery 10a of the ceramic sphere 10 is close to the proportion of monoclinic zirconia in the zirconia crystal particles CPz contained inside the outer periphery 10a of the ceramic sphere 10. In other words, in the ceramic sphere 10, the crystalline phase composition of the zirconia crystal particles CPz is similar in the outer periphery 10a and the central part 10b inside the outer periphery 10a. As a result, in the manufacturing process of producing bearing balls P10 by polishing the ceramic sphere 10, ceramic balls can be produced with a small amount of polishing, thereby improving polishing efficiency.

[0054] Furthermore, according to the ceramic ball 10 of this embodiment, ceramic balls can be manufactured with a small amount of polishing, thus reducing the process load when manufacturing bearing balls P10. In addition, by reducing the process load, the amount of energy required when manufacturing bearing balls P10 can be reduced.

[0055] Furthermore, according to the ceramic sphere 10 of this embodiment, equation (3) is satisfied, so the zirconia crystal grains CPz contained in "region B" contain a large amount of tetragonal zirconia, which has superior mechanical properties compared to monoclinic zirconia. As a result, by polishing the ceramic sphere 10, a bearing ball P10 with superior mechanical properties can be obtained.

[0056] Furthermore, according to the ceramic sphere 10 of this embodiment, equations (4) and (5) are satisfied, so in both "region A" and "region B", alumina crystal particles CPa are present in greater quantities than zirconia crystal particles CPz. As a result, the zirconia crystal particles CPz are less likely to transform from tetragonal zirconia to monoclinic zirconia due to the constraint of alumina crystal particles CPa, thus suppressing the deterioration of the mechanical properties of the ceramic ball obtained by polishing the ceramic sphere 10.

[0057] Furthermore, according to the ceramic sphere 10 of this embodiment, equations (6) to (8) are satisfied, so the Vickers hardness of "region A" and the Vickers hardness of "region B" are both relatively large values ​​and there is no significant difference between them. In the ceramic sphere 10, the Vickers hardness of the outer circumference 10a and the central part 10b are both relatively large and almost the same. As a result, ceramic balls with relatively high hardness can be manufactured with a small amount of polishing.

[0058] Furthermore, according to the ceramic sphere 10 of this embodiment, the ceramic sphere 10 has a spherical portion 11 and a strip-shaped portion 12 arranged along the outer circumference of the spherical portion 11. As a result, a ceramic ball can be manufactured by polishing the strip-shaped portion 12 and polishing the surface of the spherical portion 11 to a relatively thin degree.

[0059] Furthermore, according to the ceramic sphere 10 of this embodiment, the variation in the diameter d11 of the spherical portion 11 is within 2%. This makes it possible to reduce the amount of polishing required to manufacture ceramic balls of a preset diameter. Therefore, in the manufacturing process of producing bearing balls P10 by polishing the ceramic sphere 10, ceramic balls can be manufactured with an even smaller amount of polishing, thereby further improving polishing efficiency.

[0060] Furthermore, the ceramic ball 10 for bearing balls of this embodiment allows for the manufacture of bearing balls P10 with a relatively small amount of polishing. In other words, since the polishing efficiency can be improved, the manufacturing cost of bearing balls P10 can be reduced.

[0061] Furthermore, according to the ceramic ball manufacturing method of this embodiment, in the process of polishing the ceramic sphere 10, ceramic balls that become bearing balls P10 can be manufactured with a relatively small amount of polishing. In other words, since the polishing efficiency can be improved, the manufacturing cost of ceramic balls can be reduced.

[0062] <Modified form of this embodiment> The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit, for example, the following modifications are also possible.

[0063] [Example 1] In the above-described embodiment, the ceramic sphere 10 is made into a bearing ball P10 by polishing. The technical field to which ceramic balls obtained by polishing ceramic spheres are applied is not limited to this.

[0064] [Differentiation 2] In the above embodiment, the ceramic sphere 10 is assumed to satisfy equation (3) for the crystalline phase structure of the zirconia crystal grains contained in "region B". The ceramic sphere does not have to satisfy equation (3), but by satisfying equation (3), a bearing ball P10 with excellent mechanical properties can be obtained by polishing the ceramic sphere 10.

[0065] [Difference 3] In the above-described embodiment, the ceramic sphere 10 was assumed to satisfy equations (4) and (5) in the comparison of the area ratio of zirconia crystal particles and alumina crystal particles in cross-section. The ceramic sphere does not have to satisfy equations (4) and (5), but by satisfying equations (4) and (5), the zirconia crystal particles are less likely to transform from tetragonal zirconia to monoclinic zirconia, thereby suppressing the deterioration of the mechanical properties of the ceramic ball obtained by polishing the ceramic sphere.

[0066] [Differentiation Example 4] In the above embodiment, the ceramic sphere 10 was assumed to satisfy equations (6) to (8) for the Vickers hardness of its cross-section. The ceramic sphere does not have to satisfy any of equations (6) to (8), but by satisfying equations (6) to (8), it is possible to manufacture ceramic balls with relatively high hardness with a small amount of polishing.

[0067] [Difference 5] In the above-described embodiment, the ceramic sphere 10 has a spherical portion 11 and a strip-shaped portion 12 arranged along the outer circumference of the spherical portion 11. The shape of the ceramic sphere is not limited to this.

[0068] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.

[0069] <Application Example 1> These are ceramic spheres, It contains alumina crystal particles and zirconia crystal particles. If, within the planar region including the cross-section of the ceramic sphere, a circular region with a diameter of 50 μm including the outer periphery of the ceramic sphere is designated as region A, and a circular region with a diameter of 50 μm inside the outer periphery of the ceramic sphere is designated as region B, For each of the aforementioned regions A and B, Let Pat be the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for the region A, Pam1 be the integrated intensity of the (-111) peak of monoclinic zirconia, and Pam2 be the integrated intensity of the (111) peak of monoclinic zirconia. If we denote the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for the region B as Pbt, the integrated intensity of the (-111) peak of monoclinic zirconia as Pbm1, and the integrated intensity of the (111) peak of monoclinic zirconia as Pbm2, then The following equations (1) and (2) are satisfied, Ceramic spheres. (Pam1+Pam2) / (Pam1+Pam2+Pat)≦0.035 ···(1) |(Pam1+Pam2) / (Pam1+Pam2+Pat)-(Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)|≦0.035 ···(2) <Application Example 2> A ceramic sphere as described in Application Example 1, The region B is characterized by satisfying the following equation (3): Ceramic spheres. (Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)≦0.035 ···(3) <Application Example 3> A ceramic sphere as described in Application Example 1 or Application Example 2, If Sa is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres contained in region A, and Sb is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres contained in region B, then the following equations (4) and (5) are satisfied, Ceramic spheres. 0.08 ≤ Sa ≤ 0.30 ···(4) 0.08 ≤ Sb ≤ 0.30 ···(5) <Application Example 4> A ceramic sphere as described in any one of Application Examples 1 to 3, Let Va be the Vickers hardness of the cross-section of the ceramic sphere contained in region A, and Vb be the Vickers hardness of the cross-section of the ceramic sphere contained in region B. The following equations (6) to (8) are satisfied, and the following conditions are met. Ceramic spheres. Va ≥ 1960 kgf / mm 2 ...(6) Vb ≥ 1960 kgf / mm 2 ...(7) |Va-Vb| ≤ 120 kgf / mm 2 ...(8) <Application Example 5> A ceramic sphere described in any one of Application Examples 1 to 4, A spherical part formed from ceramics, The invention is characterized by comprising a strip-shaped, annular strip-shaped portion, which is arranged along the outer circumference of the spherical portion and is formed of ceramics, Ceramic spheres. <Application Example 6> A ceramic sphere as described in Application Example 5, The variation in the diameter of the spherical portion is characterized by being within 2%. Ceramic spheres. <Application Example 7> These are ceramic ball bearings, The invention is characterized by comprising ceramic spheres as described in any one of the examples from Application Example 1 to Application Example 6. Ceramic ball bearings. <Application Example 8> A method for manufacturing ceramic balls, The process involves preparing a ceramic sphere as described in any one of the examples from Application Example 1 to Application Example 7, The invention is characterized by comprising a polishing step for polishing the aforementioned ceramic spheres. A method for manufacturing ceramic balls. [Explanation of Symbols]

[0070] 10…Ceramic spheres 10a...Outer periphery 10b…Center 11...Spherical part 12...band-shaped area 100...bearings 110...Inner circle 120... Outer ring CPa... Alumina crystal grains CPz... Zirconia crystal grains D10…Plane area P10...Bearing ball S10…Outer surface d11…Diameter

Claims

1. These are ceramic spheres, It contains alumina crystal particles and zirconia crystal particles. If, within the planar region including the cross-section of the ceramic sphere, a circular region with a diameter of 50 μm including the outer periphery of the ceramic sphere is designated as region A, and a circular region with a diameter of 50 μm inside the outer periphery of the ceramic sphere is designated as region B, For each of the aforementioned regions A and B, Let Pat be the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for the region A, let Pam1 be the integrated intensity of the (-111) peak of monoclinic zirconia, and let Pam2 be the integrated intensity of the (111) peak of monoclinic zirconia. If Pbt is the integrated intensity of the (101) peak of tetragonal zirconia obtained by X-ray diffraction for the region B, Pbm1 is the integrated intensity of the (-111) peak of monoclinic zirconia, and Pbm2 is the integrated intensity of the (111) peak of monoclinic zirconia, then The following equations (1) and (2) are satisfied, Ceramic spheres. (Pam1+Pam2) / (Pam1+Pam2+Pat)≦0.035...(1) |(Pam1+Pam2) / (Pam1+Pam2+Pat)-(Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)|≦0.035...(2)

2. A ceramic sphere according to claim 1, The region B is characterized by satisfying the following equation (3): Ceramic spheres. (Pbm1+Pbm2) / (Pbm1+Pbm2+Pbt)≦0.035...(3)

3. A ceramic sphere according to claim 1 or claim 2, If Sa is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres included in region A, and Sb is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres included in region B, then the following equations (4) and (5) are satisfied, Ceramic spheres. 0.08 ≤ Sa ≤ 0.30 ... (4) 0.08 ≤ Sb ≤ 0.30 ... (5)

4. A ceramic sphere according to claim 1 or claim 2, If Va is the Vickers hardness of the cross-section of the ceramic sphere contained in region A, and Vb is the Vickers hardness of the cross-section of the ceramic sphere contained in region B, then the following equations (6) to (8) are satisfied, Ceramic spheres. Va≧1960kgf / mm 2 ・・・(6) Vb≧1960kgf / mm 2 ・・・(7) |Va-Vb|≦120kgf / mm 2 ・・・(8)

5. A ceramic sphere according to claim 1 or claim 2, A spherical part formed from ceramics, The invention is characterized by comprising a strip-shaped, annular strip-shaped portion, which is arranged along the outer circumference of the spherical portion and is formed of ceramics, Ceramic spheres.

6. A ceramic sphere according to claim 5, The variation in the diameter of the spherical portion is characterized by being within 2%. Ceramic spheres.

7. These are ceramic ball bearings, A ceramic sphere characterized by being made up of the ceramic sphere described in claim 1 or claim 2. Ceramic ball bearings.

8. A method for manufacturing ceramic balls, A step of preparing a ceramic sphere according to claim 1 or claim 2, The invention is characterized by comprising a polishing step for polishing the aforementioned ceramic spheres. A method for manufacturing ceramic balls.

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