JP2006062918A - Zirconia-alumina-based ceramic and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zirconia-alumina-based ceramic having excellent wear resistance in addition to high strength and high toughness and a method of manufacturing the same. <P>SOLUTION: The zirconia-alumina-based ceramic comprises 67-89.5 mass% zirconia crystal phase containing 8-12 mol% CeO<SB>2</SB>, 10-30 mass% alumina phase and 0.5-3 mass% zinc oxide and contains a needle crystal deposited by dissolving a part of CeO<SB>2</SB>and zinc oxide in alumina to form a solid solution and the average crystal diameter of the zirconia crystal phase and alumina phase is ≤1 μm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zirconia-alumina ceramic and a method for producing the same, and more particularly to a zirconia-alumina ceramic having a high strength, high toughness and high wear resistance suitable for structural parts and the like, and a method for producing the same.

In recent years, ceramics have been applied to various structural parts for reasons such as excellent mechanical properties and corrosion resistance. For example, there are various blades and tools, mechanical parts such as bearings, and biological members. In order to apply to such applications, in Patent Document 1 below, zirconia-based composite ceramics are selected, and such ceramics contain an additive (CeO ₂ ) that stabilizes tetragonal crystals in the zirconia crystal phase. It is described that the weather resistance such as the mechanical properties and the heat deterioration test can be improved.
Japanese Examined Patent Publication No. 5-35103

  However, although the zirconia composite ceramic described in Patent Document 1 has high mechanical strength and toughness as described above, since this composite ceramic is fired at a relatively high temperature of 1500 to 1600 ° C., zirconia. The crystal phase grows and the variation of the crystal grain size becomes large. For this reason, when the wear resistance test is performed on the above composite ceramic, the crystal particles are likely to be missing, and the missing part has a large volume. For this reason, there has been a problem that the speed of wear increases rapidly.

  Accordingly, an object of the present invention is to provide a zirconia-alumina ceramic having excellent wear resistance in addition to high strength and high toughness, and a method for producing the same.

According to the present invention, it comprises 67 to 89.5% by mass of zirconia containing 8 to 12% by mol of CeO ₂ , 10 to 30% by mass of alumina, and 0.5 to 3% by mass of zinc oxide. A portion of the CeO ₂ and zinc oxide is dissolved and precipitated, has a needle crystal, a zirconia crystal phase, and an alumina phase, and an average crystal diameter of the zirconia crystal phase and the alumina phase is 1 μm or less. A zirconia-alumina-based ceramic is provided.

In the zirconia-alumina ceramic of the present invention, it is preferable that the maximum crystal diameter of the zirconia crystal phase is 2 μm or less, and the needle-like crystal is ZnCeAl ₁₁ O ₁₉ .

Further, according to the present invention, a step of preparing a Ce-stabilized zirconia powder, an alumina powder, and a zinc oxide powder, each having an average particle size of 1 μm or less, the Ce-stabilized zirconia powder, the alumina powder, and the oxidation The following conditions (a) and (b): (a) Ce-stabilized zirconia powder 67 to 89.5 mass%, alumina powder 10 to 30 mass%, zinc oxide 0.5 to 3 mass %, (B) a step of preparing a mixed powder for molding by mixing so that the CeO ₂ concentration in the Ce-stabilized zirconia powder is 8 to 12 mol%, and the predetermined powder mixture There is provided a process for producing a zirconia-alumina ceramic, characterized by comprising a step of forming into a shape and a step of firing the obtained molded body in an air atmosphere at 1450 ° C. or lower. Furthermore, it is preferable to perform hot isostatic baking at a temperature of 1400 ° C. or less after the baking, and to perform heat treatment at a temperature of 1100 ° C. to 1250 ° C. in the air after the baking.

  The zirconia-alumina ceramic of the present invention is a zirconia-rich zirconia-alumina ceramic, and since it has a high zirconia content, it has a high bending strength and an excellent fracture toughness value. Since the average crystal diameter of the crystal phase and the alumina phase is suppressed to 1 μm or less, it is possible to effectively avoid a decrease in the bending strength due to the increase in zirconia.

  Further, according to the present invention, the bending strength can be increased even in the point that the zirconia crystal phase is a crystal phase in which the Ce component is dissolved, and according to the zirconia crystal phase to which Ce is added, Further, the omission of particles can be suppressed and the wear resistance can be improved.

Furthermore, in the ceramic according to the present invention, since a needle-like crystal in which a part of CeO ₂ and zinc oxide is dissolved and precipitated in the alumina phase is formed, the fracture toughness can be improved.

In particular, if the needle-like crystal is ZnCeAl ₁₁ O ₁₉ , the fracture toughness can be further increased due to the flat crystal strengthening: crack bowing effect of the needle-like crystal.

  Furthermore, according to the present invention, if the maximum crystal diameter of the zirconia crystal phase is 2 μm or less, the bending strength can be further increased.

  As described above, the zirconia-alumina ceramic of the present invention has high strength, high toughness, high hardness, excellent wear resistance, and excellent hot water deterioration resistance. This is extremely useful for applications such as parts, various cutting tools and tools, structural parts such as bearings, and biological members.

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

The zirconia-alumina ceramic of the present invention has a zirconia crystal phase 1, an alumina phase 3, and an acicular crystal 5 as crystal phases, and has a zirconia-rich basic composition. That is, it is composed of zirconia containing CeO ₂ , alumina, and a zinc oxide compound. In particular, according to the present invention, the needle-like crystal 5 is formed by solid solution of CeO ₂ and zinc oxide on alumina and precipitation. As its composition, 67 to 89.5% by mass of zirconia containing CeO ₂ in the range of 8 to 12% by mol, 10 to 30% by mass of alumina, and 0.8% of zinc oxide. It is important to consist of 5 to 3% by mass.

The content of CeO ₂ contained in the zirconia crystal phase according to the present invention is 9 to 10 mol% in order to stabilize this zirconia crystal phase as a tetragonal crystal and suppress the precipitation of monoclinic crystals and cubic crystals. It is desirable that the needle-like crystal is ZnCeAl ₁₁ O ₁₉ from the viewpoint of further improving toughness.

When CeO ₂ contained in the zirconia crystal phase, which is the main component of the zirconia-alumina ceramic of the present invention, is less than 8 mol%, a monoclinic crystal which 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 zirconia-alumina ceramic of the present invention is less than 67% by mass and the proportion of the alumina phase is more than 30% by mass, the toughness is reduced particularly among the mechanical properties. .

  On the other hand, when the proportion of the zirconia crystal phase is more than 89.5% by mass and the proportion of the alumina phase is less than 10% by mass, the bending strength and 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, while when it exceeds 3%, the strength is lowered. The amount of zinc oxide is preferably 0.5 to 1.5% by mass, particularly in terms of increasing strength.

  In the zirconia-alumina ceramic of the present invention, the alumina phase 3 is preferably present at the grain boundary 7 of the zirconia crystal phase 1 in that the wear resistance due to the high hardness of the alumina phase 3 can be enhanced.

  Further, it is important that both the zirconia crystal phase 1 and the alumina phase 3 of the present invention have an average particle size of 1 μm or less, and they are more preferably 0.3 to 0.8 μm in terms of increasing the bending strength and toughness. desirable.

  When the average particle size of the zirconia crystal phase 1 and the alumina phase 3 is larger than 1 μm, the zirconia crystal phase 1 changes from tetragonal to monoclinic and the toughness decreases. When crystals having a large particle size are sometimes present in such ceramics, the lack of zirconia crystal phase or alumina phase particles tends to occur during the wear resistance test, resulting in a decrease in wear resistance. Therefore, it is desirable that the maximum crystal diameters of the zirconia crystal phase 1 and the alumina phase 3 are 2 μm or less.

And according to the zirconia-alumina ceramic according to the present invention having the above configuration, the bending strength is 1000 MPa or more, the Vickers hardness is 1200 or more, the fracture toughness value is 8 or more, and the specific wear amount is 0.3 × 10 ^−10. mm ² / N or less.

  Next, a method for producing the zirconia-alumina 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. In this case, the composition is characterized by mixing 67 to 89.5% by mass of the zirconia powder and 10 to 30% by mass of alumina powder and 0.5 to 3% by mass of zinc oxide powder. In particular, it is preferable that 74 to 85% by mass of zirconia powder, 15 to 24% by mass of alumina powder, and 1 to 2% by mass of zinc oxide powder.

  That is, the zirconia powder and the alumina powder are set for the purpose of increasing the toughness of the ceramic obtained after firing, and the amount of zinc oxide is acicular crystals that contain and precipitate this zinc oxide. This defines the amount of precipitation. This is because a large amount of these acicular crystals precipitates leads to a decrease in the hardness of the ceramic.

  In addition, it is important that the average particle diameters of the zirconia powder and the alumina powder used in the present invention are both 1 μm or less, particularly 0.8 μm or less, particularly 0.1 to 0.6 μm. When 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 zirconia-alumina ceramic becomes large, leading to a decrease in bending strength.

The purity of the zirconia powder and alumina powder used in the present invention is desirably 99.9% or more. Furthermore, as for zirconia powder, CeO ₂ and zirconia powder added individually, or obtained by calcination after mixing CeO ₂ and zirconia powder, or a metal salt or alkoxide of Ce and zirconia Any of those obtained by mixing (hydrolysis method) in a pH-adjusted aqueous solution can be suitably used, but water is added in that a more stable zirconia having a more uniform particle size can be obtained. A powder synthesized by a decomposition method is more preferable.

  Furthermore, in the ceramics according to the present invention, powders such as alkaline earth metal oxides can be used as a sintering aid as necessary in order to enhance the sinterability. These sintering aids are not limited to oxides, and can also be used in the form of compounds such as carbonates that form oxides upon firing. 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 such a sintering aid is 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 terms of maintaining high bending strength and fracture toughness. It is good.

  Next, the ceramic manufacturing method according to the present invention is characterized in that the compact is fired in an air atmosphere at 1450 ° C. or lower. This is because when calcination is performed at a temperature higher than 1450 ° 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 the toughness tends to be lowered and the wear resistance is particularly lowered. As a minimum, 1300 degreeC or more is preferable from the reason of improving sinterability.

  Furthermore, in the present invention, it is desirable to perform heat treatment in the air at 1100 ° C. to 1250 ° C. after the firing, and by adding such heat treatment, particularly hardness and wear resistance can be enhanced.

  In the present invention, it is desirable to perform hot isostatic firing at 1400 ° C. or lower in an oxidizing atmosphere before the heat treatment after the atmospheric firing. Thereby, it is possible to increase the density while suppressing grain growth of the zirconia crystal phase and the alumina phase constituting the zirconia-alumina ceramic. 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 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), and alumina powder (average particle size 0.3 μm, purity 99.9%) Were blended so as to have the composition shown in Table 1. The mixing was performed using a high-purity wear-resistant alumina ball and a polyethylene container, and using a wet ball mill for 24 hours with IPA as a solvent. Thereafter, the mixed powder obtained by drying was press-molded and fired in air at 1300 to 1550 ° C. for 2 hours to produce a rod-shaped primary sintered body. Next, as shown in Table 1, the prepared sample was heat-treated at a temperature of 1200 ° C. in the atmosphere.

  Some sintered bodies (those having a relative density of 95% or more) were subjected to hot isostatic firing at a maximum temperature of 1350 ° C. with an oxygen partial pressure of 20%. 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 along the diagonal line of the obtained electron micrograph, and the average crystal diameter and its variation were determined using a measuring microscope. Measurement points were 10 points each. Further, the bending strength at room temperature according to JIS-R1601 and the fracture toughness value were measured by the SEPB method according to JIS-R1607. In the present invention, the blended zirconia powder and alumina powder composition was reflected as the crystal phase composition. Furthermore, abrasion resistance was evaluated using a pin-on-disk test method (JIS-T0303). Note that needle-like crystals were confirmed in the sample containing zinc oxide of the present invention. The obtained results are shown in Table 1.

From the results of Table 1, sample No. which is the zirconia-alumina ceramic of the present invention is shown. In 2 to 5, 8 to 10, 13 to 15, 17, 18, and 20 to 27, the average crystal diameter of each of the zirconia crystal phase and the alumina phase is 1 μm or less, the maximum crystal diameter is 2 μm or less, and the bending strength is 1030 MPa. As described above, the fracture toughness value was 8.1 or more, the Vickers hardness was 1210 or more, and the specific wear amount in the wear resistance test was 0.3 mm ² / N (× 10 ⁻¹⁰ ) or more. In particular, in the case where the maximum crystal diameter is 2 μm or less and the ceramic is formed with acicular ZnCeAl ₁₁ O ₁₉ containing 0.5 to 1.5 mass% of zinc oxide, the bending strength is 1120 MPa or more. there were.

  On the other hand, sample No. In 1, 6, 7, 11, 12, 16, and 19, any one of the bending strength, fracture toughness value, Vickers hardness, and specific wear amount in the abrasion resistance test was lower than the product of the present invention.

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

Explanation of symbols

1 Zirconia crystal phase 3 Alumina phase 5 Acicular crystals

Claims (6)

And 67 to 89.5% by weight of zirconia containing 8-12 mol% of CeO _2, and 10 to 30 wt% alumina, with of zinc 0.5 to 3 wt% and the oxide, the CeO ₂ and zinc oxide alumina A zirconia-alumina system characterized by having a needle crystal, a zirconia crystal phase, and an alumina phase that are partly dissolved and precipitated, and an average crystal diameter of the zirconia crystal phase and the alumina phase is 1 μm or less Ceramics. 2. The zirconia-alumina ceramic according to claim 1, wherein the maximum crystal diameter of the zirconia crystal phase is 2 μm or less. The zirconia-alumina ceramic according to claim 1 or 2, wherein the needle-like crystal is ZnCeAl ₁₁ O ₁₉ . In any case, the step of preparing Ce-stabilized zirconia powder, alumina powder, and zinc oxide powder having an average particle size of 1 μm or less, the Ce-stabilized zirconia powder, alumina powder, and zinc oxide powder under the following conditions: Conditions (a) and (b): (a) Ce stabilized zirconia powder 67 to 89.5 mass%, alumina powder 10 to 30 mass%, zinc oxide 0.5 to 3 mass%, (b) Ce stabilization A step of preparing a mixed powder for molding by mixing so that the CeO ₂ concentration in the zirconia powder is 8 to 12 mol%, a step of forming the mixed powder for molding into a predetermined shape, and obtaining Firing the resulting molded body in an air atmosphere of 1450 ° C. or lower,
A process for producing a zirconia-alumina ceramic, characterized by comprising: The method for producing a zirconia-alumina ceramic according to claim 4, wherein hot isostatic firing is performed at a temperature of 1400 ° C or less after the firing. The method for producing a zirconia-alumina ceramic according to claim 4 or 5, wherein heat treatment is performed at a temperature of 1100C to 1250C in the air after the firing.

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