JP2004352548A - Composite ceramic and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite ceramic having excellent wear resistance in addition to high strengths and high toughness and a method for manufacturing the same. <P>SOLUTION: In the composite ceramic constituted of a zirconia crystal phase 1 containing 2.8-4.5 mol% Y<SB>2</SB>O<SB>3</SB>and a metallic phase 3 composed of one of Mo and W or a mixture of Mo with W, the average particle diameter of the zirconia crystal phase 1 is ≤0.35 μm, the average particle diameter of the metallic phase 3 is ≤1 μm, the content of the metallic phase 3 in the composite ceramic is 5-25 mass% and ≥95% of metallic phase 3 exists in the grain boundary of the zirconia crystal phase 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００３５】
表１に結果から、本発明の複合セラミックスである試料Ｎｏ．２〜５、８〜１１、１３、１４、１６では、３点曲げ強度が１３２０ＭＰａ以上、靭性が５以上となり、比摩耗量が０．３５以下であった。特に、粒界に第３相として平均粒径０．５μｍ以下のアルミナ相を含有させた試料Ｎｏ．２〜５、８〜１１、１３、１４では、３点曲げ強度が１３７０ＭＰａ以上、靭性を５．８ＧＰａ以上と高まり、比摩耗量が０．３以下とさらに改善できた。
【００３６】
一方、本発明外の試料では、３点曲げ強度、靭性、比摩耗量ともに本発明よりも劣っていた。
【００３７】
【発明の効果】
以上詳述したように、本発明によれば、複合セラミックスを構成するジルコニア結晶相の平均粒径が金属相の平均粒径よりも小さいために、ジルコニア結晶相中に金属相の一部を取り込むことがないことから粒成長が抑制され、このため、この複合セラミックスについて耐摩耗試験を行った場合にジルコニア結晶相の欠落が抑制され、欠落してもこの部分の質量が小さいために摩耗する速さが遅く、このため耐摩耗性を高めることができる。
【図面の簡単な説明】
【図１】本発明の複合セラミックスの内部の模式図である。
【符号の説明】
１ ジルコニア結晶相
３ 金属相[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a composite ceramic and a method for producing the same, and more particularly to a composite ceramic suitable for a structural material having wear resistance and a method for producing the same.
[0002]
[Prior art]
In recent years, ceramics have been applied to various structural parts because of their excellent mechanical properties and corrosion resistance. For example, various cutting tools and tools, mechanical parts such as bearings, and living body-related members. In order to apply to such applications, in Patent Document 1 below, a zirconia-based composite ceramic is selected, and by including a high melting point metal in the composite ceramic, it is possible to enhance particularly the toughness among the mechanical properties. It states that it can.
[0003]
[Patent Document 1]
JP-A-6-172026
[0004]
[Problems to be solved by the invention]
However, in the zirconia-based composite ceramics described in Patent Literature 1, although the toughness is high as described above, the zirconia crystal phase constituting the composite ceramics takes in a part of the metal phase and grows grains. In addition, when a wear resistance test is performed on such a composite ceramic, for example, there is a problem that crystal grains are likely to be lost, and the speed of abrasion is rapidly increased because the missing portion has a large volume.
[0005]
Accordingly, an object of the present invention is to provide a composite ceramic having excellent wear resistance in addition to high strength and high toughness, and a method for producing the same.
[0006]
[Means for Solving the Problems]
The composite ceramics of the present invention is a composite ceramic containing a zirconia crystal phase containing 2.8 to 4.5 mol% of Y ₂ O ₃ and a metal phase composed of any of Mo and W or a mixture of Mo and W. In the above, the average particle size of the zirconia crystal phase is 0.35 μm or less, the average particle size of the metal phase is 1 μm or less, the content of the metal phase is 5 to 25% by mass in the total amount, and the metal It is characterized in that 95% or more of the phase exists at the grain boundary of the zirconia crystal phase.
[0007]
According to such a configuration, since the average particle diameter of the zirconia crystal phase constituting the composite ceramics is smaller than the average particle diameter of the metal phase, it is difficult to incorporate a part of the metal phase into the zirconia crystal phase. Therefore, when a wear resistance test is performed on such a composite ceramic, the loss of the zirconia crystal phase is suppressed. However, the wear resistance can be increased.
[0008]
In the above-mentioned composite ceramics, it is desirable that the zirconia crystal phase and the metal phase have an alumina phase having an average particle size of 0.5 μm or less at the grain boundaries. Abrasion resistance can be further enhanced by including an alumina phase having a higher hardness than the zirconia crystal phase in a grain boundary which is a boundary particularly when the crystal phase is missing.
[0009]
And in the said composite ceramics, it is desirable to contain the said alumina phase in the ratio of 30 mass% or less.
[0010]
The method for producing the composite ceramics of the present invention includes: a zirconia powder containing 2.8 to 4.5 mol% of Y ₂ O ₃ and having an average particle diameter of 0.3 μm or less; a Mo powder having an average particle diameter of 0.3 to 1 μm; Forming a mixed powder obtained by mixing any one of the W powders or Mo powder and the W powder; and forming a pre-sintered body by firing the formed body at normal pressure in a humidified nitrogen-hydrogen mixed atmosphere. And firing the pre-sintered body under hot isostatic pressure.
[0011]
According to such a manufacturing method, the atmosphere during sintering is made to be a humidified nitrogen-hydrogen mixed atmosphere, so that the oxidation of Mo powder and W powder is suppressed more than the case where the sintering atmosphere is not humidified. Reduction and nitriding of the powder can be suppressed, and sinterability can be improved. Thus, in the method for producing a composite ceramic, the relative density of the pre-sintered body can be increased to 95% or more. Further, it is desirable that alumina powder is further added to the composite ceramics of the present invention at a ratio of 30% by mass or less.
[0012]
In this case, it is preferable that the maximum temperature in the normal pressure firing and the maximum temperature in the hot isostatic pressing firing are 1550 ° C. or less, respectively. Further, in the present invention, the average particle size of the zirconia crystal phase and the metal phase such as the Mo phase and the W phase constituting the composite ceramics is set to 0.35 μm or less and 1 μm or less, respectively, by setting the maximum temperature in sintering to 1550 ° C. or less. Can be.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail. FIG. 1 is a schematic view of the inside of the composite ceramics of the present invention. The composite ceramics of the present invention comprises a partially stabilized zirconia crystal phase 1 containing 2.8 to 4.5 mol% of Y ₂ O ₃ and one of a Mo phase and a W phase, or both of them. And a certain metal phase 3. The content of Y ₂ O ₃ contained in the zirconia crystal phase 1 may be _{3 to} 3.3 mol% in terms of stabilizing the tetragonal crystal of the zirconia crystal phase 1 or suppressing monoclinic crystal and cubic crystal. desirable. It is important that the zirconia crystal phase 1 has an average particle size of 0.35 μm or less. In particular, it is desirable that the thickness be 0.25 μm or less. The lower limit is preferably 0.1 μm or more, particularly preferably 0.15 μm or more. In order to make the particle diameter smaller than this, it is necessary to use a zirconia powder having an average particle diameter smaller than the lower limit, which causes difficult points such as moldability.
[0014]
On the other hand, the metal phase 3 preferably has an average particle size of 1 μm or less, particularly 0.8 μm or less, in both the Mo phase and the W phase. On the other hand, the lower limit is preferably 0.4 μm or more.
[0015]
It is important that the content of the metal phase 3 in the composite ceramic is 5 to 25% by mass. In particular, the content is more preferably from 10 to 20% by mass. The metal phase 3 may include at least one of the Mo phase and the W phase, and the Mo phase is particularly preferable.
[0016]
In the present invention, the metal phase 3 is less likely to be taken into the zirconia crystal phase 1 by making the average particle size of the zirconia crystal phase 1 smaller than that of the metal phase 3 as described above. Does not grow so much as to take in the metal phase, so that the metal phase 3 exists at the grain boundary of the zirconia crystal phase 1. In this regard, when the average particle diameter of the zirconia crystal phase 1 is D1 and the average particle diameter of the metal phase 3 is D2, it is desirable that the relationship of 0.3 ≦ D1 / D2 ≦ 0.5 is satisfied. Further, the metal phase 3 present in the composite ceramic of the present invention does not form an elongated continuous phase as in the case where the content of the metal phase 3 is increased, and the zirconia crystal phase 1 and the metal phase 3 are not formed. And exist in a form in which particles are bonded to each other. It is important that 95% or more of the metal phase 3 is present at the grain boundary of the zirconia crystal phase 1 because grain growth of the zirconia crystal phase 1 is not required, and 98% or more is particularly desirable.
[0017]
When the amount of Y ₂ O ₃ contained in the zirconia crystal phase 1 which is a main component of the composite ceramics of the present invention is less than 2.8 mol%, the mechanical properties at the initial stage are improved but the monostable phase which is a metastable phase is improved. For example, mechanical properties after autoclaving are reduced by half because the clinics are likely to precipitate (the phase stability is reduced). On the other hand, when it is more than 4.5 mol%, cubic crystals increase.
[0018]
When the average particle size of the zirconia crystal phase 1 is larger than 0.35 μm or when the average particle size of the metal phase 3 is larger than 1 μm, the metal phase 3 is taken into the zirconia crystal phase 1 and the grains grow. In a sliding test such as an abrasion resistance test, the volume of the missing part of the particles becomes large, and the abrasion resistance decreases.
[0019]
Further, when the content of the metal phase 3 in the composite ceramics is less than 5% by mass, the effect of improving the mechanical strength and toughness of the zirconia-based ceramics cannot be obtained. On the other hand, when the content is more than 25% by mass, the metal phase 3 forms an elongated continuous phase as described above. In the abrasion test, the metal phase 3 tends to be missing, and the abrasion resistance is reduced.
[0020]
In addition, the composite ceramic of the present invention desirably contains an alumina phase in addition to the zirconia crystal phase and the metal phase in that the wear resistance due to the high hardness of the alumina phase can be enhanced. Preferably, the alumina phase is also present at the grain boundaries of the zirconia crystal phase. Therefore, the average particle size of the alumina phase is 0.5 μm or less, particularly 0.4 μm or less, and the lower limit is more preferably 0.1 μm or more, particularly 0.15 μm or more, and the content is 30% by mass or less. In particular, the content is more preferably 15 to 25% by mass.
[0021]
Next, a method for producing the composite ceramic of the present invention will be described.
[0022]
The composite ceramic of the present invention is obtained by mixing a zirconia powder containing 2.8 to 4.5 mol% of Y ₂ O ₃ with any one of Mo powder and W powder, or a mixed powder obtained by mixing Mo powder and W powder. It is characterized by being formed into a desired shape and sintering in a specific atmosphere.
[0023]
In this case, it is important that the zirconia powder and the two types of metal powder have an average particle diameter of 0.3 μm or less and 0.3 to 1 μm, respectively. When the average particle diameter is larger than the above, the average particle diameter of the zirconia crystal phase and the metal phase constituting the composite ceramic after sintering may be increased. The suitable range of the average particle size is preferably from 0.15 to 0.25 μm for zirconia powder and from 0.4 to 0.8 μm for metal powder.
[0024]
The purity of the ceramic powder such as zirconia powder and the metal powder used in the present invention is desirably 99.9% or more.
[0025]
Further, the present invention is characterized in that two-stage firing is performed. First, a preliminary sintered body is formed by firing at normal pressure. In this case, it is important to use a humidified nitrogen-hydrogen mixed atmosphere as the firing atmosphere in that the oxidation of the Mo powder and the W powder is suppressed and the reduction of the zirconia powder is suppressed.
[0026]
It is important that the relative density of the pre-sintered body thus obtained is 95% or more. In particular, 96% or more is more preferable from the viewpoint of promoting densification during the subsequent hot isostatic pressing and firing.
[0027]
The present invention is characterized in that the pre-sintered body is then subjected to hot isostatic pressing and firing. As the firing temperature at this time, it is important that both the maximum temperature in the normal pressure firing and the maximum temperature in the hot isostatic pressing firing are 1550 ° C. or less. By suppressing the maximum temperature during sintering to 1550 ° C. or less, the grain growth of the zirconia crystal phase and the metal phase constituting the composite ceramic of the present invention can be suppressed. From the viewpoint of increasing the density after sintering, the firing temperature is preferably 1350 to 1550 ° C for normal pressure sintering and 1250 to 1450 ° C for hot isostatic pressing. Furthermore, the atmosphere in the case of the hot isostatic pressurization firing is preferably in argon gas and the pressure is in the range of 1000 to 3000 atm.
[0028]
The zirconia powder used in the present invention is obtained by powder-mixing Y ₂ O ₃ and zirconia powder and then calcining, or mixed in a pH-adjusted aqueous solution of Y and zirconia metal salts or alkoxides. Any of those obtained by hydrolysis (hydrolysis method) may be used, but a powder synthesized by a hydrolysis method is preferred in that zirconia having a uniform particle diameter and more stabilized is obtained.
[0029]
The alumina powder contained as the third phase in the composite ceramics of the present invention has an average particle size of 0.6 μm or less, particularly 0.4 μm or less, and the lower limit is preferably 0.1 μm or more, particularly preferably 0.15 μm or more. .
[0030]
In the present invention, other ceramic powders can be added instead of the alumina powder or together with the alumina powder as long as the properties such as wear resistance of the ceramics are not reduced.
[0031]
【Example】
First, partially stabilized zirconia powder (purity 99.9%, average particle size 0.2 μm) containing Y ₂ O ₃ prepared by a hydrolysis method and having a predetermined mol%, Mo powder, and W powder (each having an average particle size of 0. 4 μm, purity of 99.9% or more) and alumina powder (average particle size: 0.3 μm, purity: 99.9%) were blended to have the composition shown in Table 1. Mixing was performed using a high-purity abrasion-resistant alumina ball and a polyethylene container using a wet ball mill for 24 hours using IPA as a solvent. Thereafter, the mixed powder obtained by drying was press-molded, and sintered at a humidified nitrogen-hydrogen atmosphere of H ₂ / N ₂ = 0.25 and a dew point of 30 ° C. and 1400 ° C. to produce a rod-shaped primary sintered body.
[0032]
Next, among these sintered bodies, those having a relative density of 95% or more were subjected to hot isostatic firing at a maximum temperature of 1350 ° C. under a pressure of 2000 atm to obtain a dense sintered body having a relative density of 99.9% or more. . Next, the obtained sintered body was ground to prepare a 4 × 3 × 35 mm sample.
[0033]
The three-point bending strength at room temperature according to JIS-R1601 and the fracture toughness value of the obtained sample were measured by the SEPB method according to JIS-R1607. X-ray diffraction was used for identification and quantification of the crystal phase. For the crystal structure observation, the ratio between the metal phase and the zirconia phase was determined using an analytical electron microscope. Further, wear resistance was evaluated using a pin-on-disk test method (JIS-T0303). Table 1 shows the obtained results.
[0034]
[Table 1]

[0035]
From the results in Table 1, it can be seen from the results of Sample No. In 2 to 5, 8 to 11, 13, 14, and 16, the three-point bending strength was 1320 MPa or more, the toughness was 5 or more, and the specific wear amount was 0.35 or less. In particular, Sample No. 3 in which an alumina phase having an average particle size of 0.5 μm or less was contained as a third phase in the grain boundary. In 2 to 5, 8 to 11, 13, and 14, the three-point bending strength was increased to 1370 MPa or more, the toughness was increased to 5.8 GPa or more, and the specific wear amount was further improved to 0.3 or less.
[0036]
On the other hand, the samples outside the present invention were inferior to the present invention in all of the three-point bending strength, toughness and specific wear.
[0037]
【The invention's effect】
As described above in detail, according to the present invention, since the average particle size of the zirconia crystal phase constituting the composite ceramics is smaller than the average particle size of the metal phase, a part of the metal phase is incorporated into the zirconia crystal phase. As a result, grain growth is suppressed, and therefore, when a wear resistance test is performed on this composite ceramic, the loss of the zirconia crystal phase is suppressed. However, the wear resistance can be increased.
[Brief description of the drawings]
FIG. 1 is a schematic view of the inside of a composite ceramic of the present invention.
[Explanation of symbols]
1 Zirconia crystal phase 3 Metal phase

Claims (7)

Zirconia crystal phase containing Y ₂ O ₃ 2.8 to 4.5 mol%, Mo, either W, or in a composite ceramic containing a metal phase consisting of a mixture of Mo and W, of the zirconia crystal phase The average particle size is 0.35 μm or less, the average particle size of the metal phase is 1 μm or less, the content of the metal phase is 5 to 25% by mass in the total amount, and 95% or more of the metal phase is 95% or more. A composite ceramic, which is present at a grain boundary of the zirconia crystal phase. 2. The composite ceramic according to claim 1, wherein the composite ceramic has an alumina phase having an average particle size of 0.5 μm or less at a grain boundary between a zirconia crystal phase and a metal phase. 3. The composite ceramic according to claim 1, wherein the alumina phase is contained in a proportion of 30% by mass or less. A zirconia powder having an average particle size of 0.3 μm or less containing 2.8 to 4.5 mol% of Y ₂ O _3, and a Mo powder or a W powder having an average particle size of 0.3 to 1 μm, or A step of forming a mixed powder obtained by mixing the Mo powder and the W powder; a step of sintering the formed body under normal pressure in a humidified nitrogen-hydrogen mixed atmosphere to form a pre-sintered body; A method for producing a composite ceramics, which comprises firing under isostatic pressure. The method for producing a composite ceramic according to claim 4, wherein the relative density of the pre-sintered body is 95% or more. 6. The method for producing a composite ceramic according to claim 4, wherein the maximum temperature in normal pressure firing and the maximum temperature in hot isostatic pressure firing are 1550 ° C. or less. The method for producing a composite ceramic according to any one of claims 4 to 6, wherein the alumina powder is added at a ratio of 30% by mass or less.

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