JP4514563B2 - Alumina / zirconia ceramics and process for producing the same - Google Patents

Description

  The present invention relates to an alumina / zirconia ceramic and a method for producing the same, and more particularly, to an alumina / zirconia ceramic suitable for use in various structural members, cutting tools, medical instruments and biomaterials, and a method for producing the same.

  In recent years, alumina / zirconia ceramics have been widely used as structural members that require high strength, wear resistance, and corrosion resistance. In particular, alumina / zirconia ceramics containing alumina and zirconia at a certain ratio are attracting attention because of the effect of refining crystal grains, higher strength than the individual ceramics can be obtained (see Non-Patent Document 1). . However, the above-mentioned alumina / zirconia ceramics have a drawback of low fracture toughness.

On the other hand, it is known that the above-mentioned alumina / zirconia-based ceramics can improve strength and fracture toughness by giving anisotropy to the particle shape of the sintered body. For example, in the 12CeZrO ₂ · Al ₂ O ₃ composite material It has been reported that fracture toughness is greatly improved by adding Mn to form a compound MnCeAl ₁₁ O ₁₉ having a magnetoplumbite structure (Non-patent Document 2). Furthermore, it has been reported that fracture toughness is greatly improved by the same mechanism by adding Mg instead of the above Mn (Non-patent Document 3).
Ryoichi Shikata et al., “Powder and Powder Metallurgy”, Powder Powder Metallurgy Association Jing / Fong Tsai, “J.Am.Ceram.Soc”, American Ceramic Society Masahiro Nawa et al., “Ceramics”, Ceramics Association

  However, even if a compound having a magnetoplumbite structure disclosed in Non-Patent Documents 2 and 3 is deposited on alumina / zirconia ceramics, it is required in the fields of cutting tools, medical instruments, biomaterials, and the like. For example, in zirconia-rich alumina / zirconia-based ceramics, the strength and Although fracture toughness can be improved, it has a problem that its hardness is low and its use as a material requiring wear resistance such as an artificial joint is particularly limited.

  On the other hand, alumina-rich alumina / zirconia ceramics have improved hardness and strength, but are not sufficiently effective in improving fracture toughness, and are required to be further improved in fracture toughness in order to be applied to the above applications. It was.

  Therefore, the present invention satisfies desired characteristics in all of strength, wear resistance (hardness) and toughness, and in particular, alumina that is suitably used for various structural members, cutting tools, medical instruments, and biomaterials. -An object is to provide zirconia ceramics.

According to the present invention, 5 to 30 wt% zirconia containing 8-12 mol% of CeO _2, alumina 67-90% by weight and zinc oxide from 0.3 to 3 wt% titanium oxide 0.2 to 2 weight % and with consists has the CeO ₂ and the portion of the zinc oxide solid solution precipitated needles and zirconia crystal phase and alumina phase to the alumina, and the average crystal size of the zirconia crystal phase is 1μm An alumina / zirconia ceramic characterized by the following is provided.

In the alumina / zirconia ceramic of the present invention, the average crystal diameter of the alumina phase is preferably 2 μm or less, and the needle-like crystals are preferably ZnCeAl ₁₁ O ₁₉ .

According to the present invention, a step of preparing a Ce-stabilized zirconia powder in which Ce ₂ O ₃ is a solid solution, an alumina powder, a zinc oxide powder, and a titanium oxide powder , all having an average particle diameter of 1 μm or less, and said Ce-stabilized zirconia powder and the alumina powder and the zinc oxide powder and the titanium oxide powder, the following conditions (a), (b), conditions: (a) the Ce-stabilized zirconia powder 5-30 wt% the alumina powder 67-90 wt%, the zinc oxide powder 0. 3-3 wt%, the titanium oxide powder 0.2 to 2 wt%, were mixed so as to satisfy, it is 8 to 12 mol% (b) the Ce-stabilized zirconia powder per, CeO ₂ concentration preparing a molding mixed powder, steps of molding the molding mixed powder into a predetermined shape, and the resulting molded body was fired in the air atmosphere at 1350 ° C. to 1550 ° C., then, than baked formed temperature There is provided a process for producing an alumina / zirconia ceramic characterized by comprising a step of performing hot isostatic firing at a low temperature.

The alumina / zirconia ceramic of the present invention is an alumina-rich alumina / zirconia ceramic, and since it has a high alumina content, it has high hardness and excellent wear resistance, and the zirconia crystal phase is stabilized by CeO _2. Mainly composed of tetragonal crystals, and the average crystal diameter of the zirconia crystal phase is suppressed to 1 μm or less, and the presence of the zirconia crystal phase dispersed in the porcelain effectively avoids a decrease in strength due to an increase in alumina. It can also be excellent in strength and toughness. For example, it can have a Vickers hardness of 1600 Hv or higher and a fracture toughness value of 4.1 MPa · m ^1/2 or higher. Further, since it contains a small amount of titanium oxide in addition to the above components, the strength can be further increased by increasing the anisotropic crystal of tetragonal ZrO ₂ by Ce . In this case, the titanium oxide is preferably 0.5 to 1% by mass.

  Furthermore, according to the present invention, the toughness can be further improved by the flat crystal strengthening by acicular crystals of a composite oxide having Zn, Ce and Al as constituent elements in the porcelain. In this case, the amount of zinc oxide is preferably 0.4 to 2% by mass, and particularly preferably 0.5 to 1.5% by mass in terms of precipitating acicular crystals and high strength, high toughness, and high hardness.

  Furthermore, if the average crystal diameter of the alumina phase is 2 μm or less, the bending strength can be further increased.

  As described above, the alumina / zirconia ceramic of the present invention has high strength, high toughness, high hardness, and excellent wear resistance. Therefore, various structural parts, various blades and tools, Or it is very useful for uses, such as structural parts, such as a bearing, and a bio-related member.

Further, according to the production method of the present invention, the addition of titanium oxide to the mixed powder promotes the metastabilization of tetragonal ZrO ₂ by Ce and the generation of anisotropic crystals, resulting in lower temperatures. Sintering is possible.

  FIG. 1 is a schematic view showing the internal structure of the alumina / zirconia ceramic of the present invention.

The alumina / zirconia ceramic of the present invention has a basic structure of having a zirconia crystal phase and an alumina phase as crystal phases and being rich in alumina. That is, it is composed of a zirconia crystal phase 1 containing CeO ₂ , an alumina phase 3, and zinc oxide. In particular, according to the present invention, the acicular crystal 5 in which CeO ₂ and a part of zinc oxide are dissolved and precipitated on alumina is formed. The composition is characterized by being precipitated, and the composition thereof is 5 to 30% by mass of zirconia crystal phase 1 containing CeO ₂ in the range of 8 to 12% by mol, and 67 to 90% by mass of alumina phase 3. %, Zinc oxide is 0.3 to 3% by mass, and titanium oxide is 0.2 to 2% by mass.

The content of CeO ₂ contained in the zirconia crystal phase is 9 to 10 mol% in order to stabilize the zirconia crystal phase 1 as tetragonal crystals and to suppress the precipitation of monoclinic crystals and cubic crystals. desirable. Here, it is desirable that the needle-like crystal 5 is ZnCeAl ₁₁ O ₁₉ from the viewpoint of further improving toughness.

  In the crystal phase of the alumina / zirconia ceramic of the present invention, titanium oxide is desirable in terms of low-temperature firing.

When CeO ₂ contained in the zirconia crystal phase, which is the main component of the alumina / zirconia ceramic of the present invention, is less than 8 mol%, a monoclinic crystal that is a metastable phase tends to precipitate, whereas 12 mol%. When the amount is larger, cubic crystals increase, and bending strength, toughness, and hardness decrease.

  Further, when the proportion of the zirconia crystal phase constituting the alumina / zirconia ceramic is less than 5% by mass and the proportion of the alumina phase is more than 90% by mass, the toughness is reduced particularly in the mechanical properties, and the strength To lower.

  On the other hand, when the proportion of the zirconia crystal phase 1 is more than 30% by mass and the proportion of the alumina phase 3 is less than 67% by mass, the bending strength and the Vickers hardness are particularly lowered among the mechanical properties. Further, when the amount of zinc oxide is less than 0.5%, the toughness is lowered, and when it exceeds 3%, the strength is lowered.

  In the alumina / zirconia-based ceramic of the present invention, the zirconia crystal phase is preferably present at the grain boundary of the alumina phase 3 in terms of increasing toughness due to the zirconia crystal phase 1.

  And it is important that the zirconia crystal phase 1 of the present invention has an average particle size of 1 μm or less, and 0.3 to 0.8 μm is more desirable in terms of enhancing the bending strength and toughness. When the average particle diameter of the zirconia crystal phase 1 is larger than 1 μm, the zirconia crystal phase 1 changes from tetragonal to monoclinic and the toughness is greatly reduced. When crystals having a large average particle size are present in such ceramics, the lack of particles of the zirconia crystal phase 1 or the alumina phase 3 is likely to occur during the wear resistance test, resulting in a decrease in wear resistance. Therefore, the average crystal diameter of the alumina phase is desirably 2 μm or less.

The alumina / zirconia-based ceramics according to the present invention having the above-described configuration can have characteristics of a bending strength of 1000 MPa or more, a Vickers hardness of 1700 or more, and a fracture toughness value of 4 MPa · m ^1/2 or more.

  Next, a method for producing the alumina / zirconia ceramic of the present invention will be described.

In the present invention, first, after preparing a zirconia-based mixed powder obtained by mixing zirconia powder containing 8 to 12 mol% of Ce ₂ O ₃ and alumina powder, mixed powder obtained by mixing this zirconia-based mixed powder and zinc oxide powder. Then, this mixed powder is formed into a desired shape. Furthermore, titanium oxide is mixed with the mixed powder containing zinc oxide.

According to the present invention, 5 to 30 wt% the zirconia powder, alumina powder 67-90 wt%, zinc oxide powder 0. It is characterized by using 3 to 3% by mass of titanium oxide powder mixed at a rate of 0.2 to 2% by mass . In particular, a 10 to 25 wt% zirconia powder, alumina powder from 68.5 to 79 wt%, 1-2 wt% of zinc oxide powder, it is preferable that the titanium oxide powder and 0.5 to 1 wt%.

  That is, the zirconia powder and the alumina powder are set for the purpose of achieving high strength and high hardness of the ceramic sintered body, and the amount of zinc oxide is acicular that contains and precipitates this zinc oxide. The amount of precipitation of crystal 5 is specified. This is because a large amount of these acicular crystals precipitates leads to a decrease in the hardness of the ceramic.

  In this case, it is important that the average particle size of the zirconia powder is 1 μm or less, particularly 0.8 μm or less, while the average crystal size of the alumina phase 3 is 2 μm or less, particularly 1. 5 μm or less is preferable. If a material having an average particle size larger than this is used, the average particle size of the zirconia crystal phase and the alumina phase constituting the sintered alumina / zirconia ceramic may be increased.

The purity of the zirconia powder and alumina powder used in the present invention is desirably 99.9% or more. The zirconia powder used in the present invention, those that have been added and CeO ₂ and zirconia powder individually, also those obtained by calcining after mixing the CeO ₂ and zirconia powder, or, Ce and zirconia metal Any of those obtained by mixing (hydrolyzing) a salt or alkoxide in an aqueous solution adjusted in pH can be suitably used, but a more uniform zirconia having a more uniform particle size is obtained. The powder synthesized by the hydrolysis method is more preferable.

  Furthermore, in the ceramic according to the present invention, a powder such as an alkaline earth metal oxide can be used as a sintering aid, if necessary, in order to enhance the sinterability. These sintering aids are not limited to oxides, and can be used as a form of a compound that forms an oxide by firing, or as a carbonate. The average particle size of the powder of these sintering aids is also preferably 1 μm or less, like the main raw material. The amount of the sintering aid is preferably 2 parts by mass or less per 100 parts by mass of the mixed powder of zirconia powder, alumina powder and zinc oxide powder which are main raw materials.

  In the method for producing a ceramic according to the present invention, the compact is fired in an air atmosphere at 1350 ° C. to 1550 ° C., and then hot isostatic firing is performed at a temperature lower than the firing temperature. . This is because when calcination is performed at a temperature higher than 1550 ° C., the zirconia crystal phase 1 and the alumina phase 3 grow and become larger than the average crystal diameter defined in the present invention, and the zirconia crystal phase 1 changes from tetragonal to monoclinic. This is because it transitions to crystals and the toughness tends to decrease, and in particular, the wear resistance decreases. Densification cannot be achieved at 1350 ° C. or lower.

  In the present invention, after the normal pressure firing, hot isostatic firing is performed at a temperature lower than the temperature of the normal pressure firing. Thus, the zirconia crystal phase 1 and the alumina phase constituting the alumina / zirconia ceramics 3 can be increased in density while suppressing grain growth.

  In the present invention, the relative density of the pre-sintered body before hot isostatic firing is preferably 95% or more, particularly preferably 97% or more. The atmosphere in the case of this hot isostatic pressing is preferably argon or an oxygen concentration of 15 to 20%.

First, partially stabilized zirconia powder containing CeO ₂ prepared by a hydrolysis method (purity 99.9%, average particle size 0.2 μm, (0.7 μm for sample No. 28, purity 99.9% was used) )), And alumina powder (average particle size 0.3 μm, purity 99.9% (for sample No. 28, use 0.8 μm, purity 99.9%)), zinc oxide, titanium oxide in Table 1 It mix | blended so that it might become the composition shown. The mixing was carried out using a high-purity wear-resistant alumina ball and a polyethylene container, using IPA as a solvent, and a wet ball mill for 24 hours. Thereafter, the mixed powder obtained by drying is press-molded and fired in air at 1300 to 1600 ° C. for 2 hours to produce a rod-shaped primary sintered body, followed by hot isostatic pressing (HIP). The temperature conditions shown in Table 1 were used. The relative density after this treatment was 99.5% or more.

Next, the obtained sintered body was ground to produce a 4 × 3 × 35 mm sample. The crystal structure was observed using an electron microscope. The average crystal diameter and the maximum crystal diameter of the zirconia crystal phase and the alumina crystal phase were determined using a measuring microscope for the average crystal diameter of the crystals present along the diagonal line of the obtained electron micrograph. Measurement points were 10 points each. Further, the bending strength at room temperature according to JIS-R1601, Vickers hardness according to JIS 2244, and fracture toughness value according to SEPB method according to JIS-R1607 were measured. In the present invention, the blended zirconia powder and alumina powder composition was reflected as the crystal phase composition. The obtained results are shown in Table 1.

From the results shown in Table 1, specimen No. 2 to 4, 7 to 10, 13 to 15, 17 to 20, 23 to 26, the average crystal diameter of the zirconia crystal phase is 1 μm or less, the average crystal diameter of the alumina phase is 2 μm or less, and the bending strength is 1010 MPa or more. The fracture toughness value was 4.1 or more, and the Vickers hardness was 1705 or more. Sample No. containing 0.2 to 2 mass% of titanium oxide of the present invention . In 17 to 20, the firing temperature in spite 1350~1,4 5 0 ℃ low, had the same characteristics as the above sample.

  On the other hand, sample No. In 1, 5, 6, 11, 12, 16, 21, 22, 27, and 28, any one of the bending strength, fracture toughness value, and Vickers hardness was lower than the product of the present invention.

It is a schematic diagram which shows the internal structure of the alumina zirconia ceramic of this invention.

Explanation of symbols

1 Zirconia crystal phase 3 Alumina phase 5 Acicular crystals

Claims (4)

Zirconia 5 to 30 mass% containing 8 to 12 mol% of CeO _2, and from 67 to 90 wt% alumina, zinc oxide from 0.3 to 3 wt%, it becomes a titanium oxide 0.2 to 2% by weight, characterized in that said alumina has the CeO ₂ and the portion of the zinc oxide solid solution precipitated needles and zirconia crystal phase and an alumina phase, and the average crystal size of the zirconia crystal phase is 1μm or less Alumina-zirconia ceramics. 2. The alumina / zirconia ceramic according to claim 1, wherein an average crystal diameter of the alumina phase is 2 μm or less. 3. The alumina / zirconia ceramic according to claim 1, wherein the needle-like crystal is ZnCeAl ₁₁ O ₁₉ . A step of preparing a Ce-stabilized zirconia powder in which Ce ₂ O ₃ is solid solution, an alumina powder, a zinc oxide powder, and a titanium oxide powder, each having an average particle size of 1 μm or less, the Ce-stabilized zirconia powder and the alumina powder and the zinc oxide powder and the titanium oxide powder, the conditions of the following conditions (a), (b): (a) the Ce-stabilized zirconia powder 5-30 mass%, the alumina powder 67 to 90 wt%, the zinc oxide powder 0. 3-3 wt%, the titanium oxide powder 0.2 to 2 wt%, were mixed so as to satisfy, it is 8 to 12 mol% (b) the Ce-stabilized zirconia powder per, CeO ₂ concentration preparing a molding mixed powder, steps of molding the molding mixed powder into a predetermined shape, and the resulting molded body was fired in the air atmosphere at 1350 ° C. to 1550 ° C., then, than baked formed temperature A process for producing an alumina / zirconia ceramic, characterized by comprising a step of hot isostatic firing at a low temperature.

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