JP2006104024A - Zirconia composite sintered compact and biomaterial using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zirconia composite sintered compact which is improved in respective defects of Y-TZP carrying out solid solution of Y<SB>2</SB>O<SB>3</SB>and comprising tetragonal crystal (or tetragonal and cubic crystal) sintered at a temperature in a stable range of tetragonal zirconia (t-ZrO<SB>2</SB>), and of Ce-TZP carrying out solid solution of CeO<SB>2</SB>and comprising tetragonal crystal (or tetragonal and cubic crystal), and which is also excellent in wear resistance; and to provide a biomaterial formed of the zirconia composite sintered compact. <P>SOLUTION: The zirconia composite sintered compact is the one containing Al<SB>2</SB>O<SB>3</SB>, which contains, by mol, 0.2-1.5% Y<SB>2</SB>O<SB>3</SB>and 4.7-12% CeO<SB>2</SB>to the total amount of ZrO<SB>2</SB>, and further contains, by mass, 1-30% Al<SB>2</SB>O<SB>3</SB>, and MgO and/or CaO in an amount of 0.15-7.5% in total, based on the total amount. The zirconia composite sintered compact is characterized in that Al<SB>2</SB>O<SB>3</SB>-based deposits are dispersed and the deposits equal to or more than 3% of the number of total Al<SB>2</SB>O<SB>3</SB>-based deposits satisfy that the major axis is 1-10 μm and the ratio of minor axis to major axis is ≤0.5. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zirconia composite sintered body that can be suitably used as a structural material such as a sliding member, a blade, a medical device, tableware, or a machine part, or a biomaterial such as an artificial bone, an artificial joint, or an artificial tooth root. Is.

Pure zirconia (ZrO ₂ ) exhibits three crystal phases of cubic, tetragonal, and monoclinic in order from the high temperature side. According to the equilibrium theory, monoclinic crystals are formed at low temperatures of 1170 ° C. or lower, tetragonal crystals are formed between 1170 and 2370 ° C., and cubic crystals are formed from 2370 ° C. to the melting point (2715 ° C.). The phase transition between monoclinic and tetragonal is a martensitic transformation with a volume change of about 4.6%. Pure zirconia lacks stability because it breaks due to the volume change as it passes through the transition temperature. Therefore, in general, by adding about 1.5 to 15 mol% of an oxide such as Y ₂ O ₃ , CaO, or MgO as a stabilizer with respect to ZrO ₂ , it is stable that hardly undergoes transition even when heated as a cubic crystal. Widely used as modified ZrO ₂ .

Among these, partially stabilized zirconia that has left part of the metastable tetragonal crystals has been shown to have high strength and high toughness, and is attracting attention. For example, tetragonal zirconia polycrystal (Tetragonal Zirconia Polycrystal: TZP), in particular Y ₂ O _3, is dissolved and sintered at a temperature in the stable region of tetragonal zirconia (t-ZrO ₂ ) (1300 to 1550 ° C.). Y-TZP composed of tetragonal crystals (or tetragonal crystals and cubic crystals) is used as a structural member because of its high strength and high toughness. The development of this high strength and high toughness is brought about by stress-induced phase transformation. In other words, because the fracture energy is reduced by phase transformation from the metastable phase tetragonal to monoclinic at the crack tip in the stress field generated during use of structural members, high strength and high toughness are exhibited. is there. However, since such TZP causes volume expansion at the same time as t-ZrO ₂ changes to monoclinic zirconia, there is a problem that if it is transformed too much, the surface properties are roughened and the strength is lowered. In particular, phase transformation is likely to occur in a temperature range near 100 to 300 ° C. in the presence of moisture (hereinafter sometimes referred to as “in a hydrothermal environment”).

In addition, tetragonal (or tetragonal and cubic) Ce-TZP in which CeO ₂ is solid-solved has a low threshold value for causing phase transformation under stress, so that phase transformation can be performed at relatively low stress. Is induced, and a wider phase transformation zone is obtained at the crack tip than in the case of stabilization with Y ₂ O ₃ . Therefore Y ₂ O ₃ with stabilized ZrO ₂ (i.e., Y-TZP) compared to, ZrO ₂ (i.e., Ce-TZP) stabilized with CeO ₂ is, 10 MPa · m ^1/2 or more high fracture toughness Indicates. Ce-TZP is also known as a material having excellent characteristics such as almost no phase transformation even in a temperature range near 100 to 300 ° C. in the presence of moisture and having a wider solid solution range. However, since the threshold value causing the stress-induced phase transformation is low, the strength tends to decrease, and the strength may be insufficient as compared with Y-TZP.

  Accordingly, the present inventors have sought to provide a zirconia sintered body having high strength and high toughness that does not deteriorate characteristics even in a hydrothermal environment by improving the respective disadvantages of Y-TZP and Ce-TZP. Proposed the technique of Patent Document 1. In this technique, by containing the Y-TZP and Ce-TZP at a specific ratio, it is difficult to cause phase transformation in a hydrothermal environment, and it is possible to achieve both high strength and high toughness. However, in this technique, the wear resistance of the zirconia sintered body is not taken into consideration, and when the present inventors have further studied, the zirconia sintered body may be worn when used in a sliding portion. It was.

Patent Document 2 proposes a zirconia-alumina composite ceramic material having wear resistance. This composite ceramic material includes a first phase composed of zirconia particles containing ceria and a second phase composed of alumina particles. According to this document, it is described that if the content of alumina is increased, the wear resistance of the composite ceramic material is improved. However, as a result of studies by the present inventors, wear resistance may not be improved even when the alumina content is increased.
JP 2004-75532 A (see [Claims] and [0007]) Japanese Unexamined Patent Application Publication No. 2004-51481 (see [Claims] and [0006])

  The present invention has been made in view of such a situation, and the object thereof is to improve the above-mentioned drawbacks of Y-TZP and Ce-TZP, and to further improve the wear resistance. The present invention also provides a structural member, a sliding member, particularly a biomaterial formed by the zirconia composite sintered body.

The inventors of the present invention have made extensive studies in order to realize a zirconia composite sintered body having both the strength level of Y-TZP and the toughness level of Ce-TZP, and further excellent in wear resistance. As a result, Y ₂ O ₃ and CeO ₂ are used in combination as stabilizers, and a predetermined amount of Al ₂ O ₃ is blended to further increase the strength, and Al ₂ O ₃ contained in the zirconia composite sintered body. It has been found that if the form of the system precipitate is appropriately controlled, a zirconia composite sintered body in which these problems are solved brilliantly, and a structural member, a sliding member, particularly a biomaterial using the same can be provided. Was completed.

That is, the zirconia composite sintered body according to the present invention is a zirconia composite sintered body containing Al ₂ O ₃ , and based on the total ZrO ₂ , Y ₂ O ₃ : 0.2 to 1.5 mol%, In addition to containing CeO ₂ : 4.7 to 12 mol%, Al ₂ O ₃ : 1 to 30% by mass and MgO and / or CaO: 0.15 to 7.5% by mass in the total amount In addition, Al ₂ O ₃ -based precipitates are dispersed, and 3% or more of the total number of Al ₂ O ₃ -based precipitates has a major axis of 1 to 10 μm and a minor axis / major axis ratio of 0. The point is that it is 5 or less.

From the viewpoint of promoting precipitation of Al ₂ O ₃ -based precipitates that satisfy the above range, La ₂ O ₃ : 2% by mass or less (not including 0% by mass) is further included in the total amount. Is preferred. From the viewpoint of reducing the phase transformation under the stress load condition, it is preferable to further contain TiO ₂ : 1 mol% or less (excluding 0 mol%) with respect to all ZrO ₂ . Note that the scope of the present invention includes a biomaterial formed by the zirconia composite sintered body.

According to the present invention, zirconia that can achieve both high strength and high toughness by using Y ₂ O ₃ and CeO ₂ in combination as a zirconia stabilizer, and further increases the strength by containing Al ₂ O _3. A composite sintered body can be provided. Moreover, according to the present invention, the zirconia composite sintered body improved in wear resistance by appropriately controlling the form of the Al ₂ O ₃ -based precipitates contained in the zirconia composite sintered body, and the same are used. Biomaterials can be provided.

As a result of various studies by the present inventors, it has been found that the crystal phase of the zirconia sintered body is important in order to increase both the strength and toughness of the zirconia sintered body. In order to further increase the strength, it is effective to combine a predetermined amount of Al ₂ O ₃ with the zirconia sintered body. However, when Al ₂ O ₃ is combined, the wear resistance may deteriorate. Therefore, further investigation was made to improve the wear resistance of the zirconia composite sintered body, and it was found that the shape control of the Al ₂ O ₃ -based precipitates contained in the zirconia composite sintered body is important. Hereinafter, the function and effect of the present invention will be described.

  First, means for increasing the strength and toughness of the zirconia composite sintered body will be described. In order to increase the strength and toughness of the zirconia composite sintered body, the key point is how the zirconia tetragonal crystals exist. When a stabilizer is contained in a large amount, both the strength and toughness are lowered due to an increase in cubic crystals. On the other hand, when the stabilizer is insufficient, phase transformation from tetragonal to monoclinic crystals tends to occur in a hydrothermal environment or under stress load conditions, and the strength of the zirconia composite sintered body is deteriorated.

Therefore, the present inventors examined how zirconia tetragonal crystals should exist in the zirconia composite sintered body. As a result, it has been found that if Y ₂ O ₃ and CeO ₂ are used in combination as stabilizers for zirconia, both high strength and high toughness can be achieved.

Since oxide-based ceramics have strong ionic bondability, the degree of stabilization of the crystal structure is determined to some extent by the radius ratio between the cation and anion and the valence of the ion. According to Shannon, the ionic radii of the main elements are as follows. O ²⁻ : 140 pm, Zr ⁴⁺ : 84 pm, Y ³⁺ : 101.5 pm, Ce ⁴⁺ : 114.3 pm, Ti ⁴⁺ : 60.5 pm. Therefore, the ionic radius ratio of Zr ^{4+ to} O ²⁻ is 0.6. On the other hand, since the ideal ionic radius ratio of cubic crystals of zirconia is 0.732, the ionic radius ratio of Zr ^{4+ to} O ²⁻ is considerably smaller than the ideal ionic radius ratio of cubic crystals, and the crystal phase Becomes unstable. Therefore, in order to stabilize the crystal phase, Y ₂ O ₃ or CeO ₃ is added as a stabilizer.

For Y ₂ O ₃ , the ionic radius ratio of Y ^{3+ to} O ²⁻ is 0.725, which is almost equal to the ideal ionic radius ratio (0.732) of zirconia cubic crystals, Strain hardly occurs, and the threshold stress that causes stress-induced phase transformation increases, so that the strength is increased. On the other hand, the toughness decreases.

On the other hand, for CeO ₂ , the ionic radius ratio of Ce ^{4+ to} O ²⁻ is 0.816, which is slightly larger than the ideal ionic radius ratio (0.732) of zirconia cubic crystals. Distorts the structure. As a result, the threshold stress causing stress-induced phase transformation is lowered and the toughness is improved. On the other hand, the strength is reduced.

Therefore, the present inventors have thought that if Y ₂ O ₃ and CeO ₂ are used in combination as stabilizers, the disadvantages of adding each stabilizer alone can be compensated for each other. That is, the strength is increased by adding Y ₂ O _3, and the toughness is increased by adding CeO ₂ .

Based on these findings, further a result of our research to clarify the preferred amount of stabilizer, relative to the total _{ZrO 2, Y 2 O 3:} 0.2~1.5mol% and CeO _2: 4. It has been found that it is preferable to contain 7 to 12 mol%. Hereinafter, the reason for setting such a range will be described.

Y ₂ O _3: 0.2~1.5mol%
Y ₂ O ₃ is a stabilizer that is contained to ensure the strength of the zirconia sintered body, and is 0.2 mol% or more. Preferably it is 0.5 mol% or more. However, if the amount is too large, the toughness of the zirconia sintered body is lowered, and further, phase transformation in a hydrothermal environment is induced, so the content is made 1.5 mol% or less. Preferably it is 1.0 mol% or less.

CeO _2: 4.7~12mol%
CeO ₂ is a stabilizer that is contained to ensure the toughness of the zirconia sintered body and prevent phase transformation in a hydrothermal environment, and is 4.7 mol% or more. Preferably it is 5 mol% or more, More preferably, it is 7 mol% or more. However, if the amount is too large, cubic crystals are formed and the strength and toughness of the zirconia sintered body are lowered. Preferably it is 11 mol% or less.

Next, the present inventors studied to further increase the strength of the zirconia composite sintered body. As a result, it has been found that it is effective to contain 1 to 30% by mass of Al ₂ O ₃ in the ratio of the total amount of the zirconia composite sintered body. The reason for setting such a range is as follows.

Al ₂ O ₃ : 1 to 30% by mass
When Al ₂ O ₃ is mixed and dispersed, zirconia particles and Al ₂ O ₃ particles are combined to increase the strength of the zirconia composite sintered body. In order to exert such effects, it is necessary to contain 1% by mass or more. Preferably it is 3 mass% or more. However, if Al ₂ O ₃ exceeds 30% by mass, the Al ₂ O ₃ itself tends to aggregate, and instead the strength and toughness are reduced. Preferably it is 20 mass% or less.

Note that the zirconia sintered body of the present invention, Al ₂ O ₃ nanoparticles or particles are dispersed in ZrO ₂ within the particle, or ZrO ₂ particles are dispersed in Al ₂ O ₃ within the particle composite, or they In some cases, a mutual nanocomposite structure in which these are combined is observed, but the presence of these structures does not adversely affect the characteristics of the present invention.

By the way, when Al ₂ O ₃ is contained, the wear resistance of the zirconia composite sintered body may deteriorate. Therefore, the present inventors examined a phenomenon in which the wear resistance of the zirconia composite sintered body deteriorates. As a result, when Al ₂ O ₃ is included as a component constituting the zirconia composite sintered body, Al ₂ O ₃ -based precipitates are generated in the zirconia composite sintered body. It has been found that the wear resistance deteriorates due to detachment from ZrO ₂ ). That is, the Al ₂ O ₃ -based precipitates that have fallen from the matrix act as an abrasive and promote wear on the surface of the zirconia composite sintered body. Cause of attrition Al ₂ O ₃ based precipitate from the matrix is where there is no consistency in the Al ₂ O ₃ based precipitates and ZrO ₂ crystal grain boundary crystal structure is different for each other. For example zirconia shearing stress acts on the phase transformation to the Al ₂ O ₃ based precipitates and ZrO ₂ grain boundaries, this time Al ₂ O ₃ based precipitates and the ZrO ₂ grain boundaries because there is no consistency The binding force becomes weak, and the Al ₂ O ₃ -based precipitates are easily peeled off from the matrix and fall off.

Therefore, the present inventors examined a means for preventing the Al ₂ O ₃ -based precipitates from falling off the matrix and improving the wear resistance of the zirconia composite sintered body. As a result, it was found that in order to improve the wear resistance of the zirconia composite sintered body, it is important to control the form of the Al ₂ O ₃ -based precipitates dispersed in the zirconia composite sintered body. .

That is, in the zirconia composite sintered body of the present invention, Al ₂ O ₃ -based precipitates are dispersed, and 3% or more of the total number of Al ₂ O ₃ -based precipitates has a major axis of 1 to 10 μm. It is important that the ratio of the major axis to the minor axis (short axis / major axis ratio) is 0.5 or less.

The Al ₂ O ₃ -based precipitate as used herein refers to an oxide containing Al among the precipitates dispersed in the zirconia composite sintered body. Al ₂ O ₃ system and the of, as described later, because it may like MgO and CaO is solved in Al ₂ O ₃ precipitates, consisting of Al ₂ O ₃ (ie, Al ₂ O ₃ and not the 100% by weight) precipitates, the ratio of Al ₂ O ₃ occupying the precipitate is confirmed by scanning electron microscopy as described below (SEM) but, ZrO ₂ is a matrix during the analysis This is because it is difficult to strictly confirm the proportion of Al ₂ O _{3 in} the precipitate.

The zirconia composite sintered body of the present invention, among these Al ₂ O ₃ based precipitates, long axis by a ratio of major axis and a minor axis with 1 to 10 [mu] m (minor axis / Nagajikuhi) is 0.5 or less It is important that the number of some is 3% or more of the total number of Al ₂ O ₃ -based precipitates. By forming the Al ₂ O ₃ -based precipitate into a long and narrow bar, the contact area between the precipitate and ZrO ₂ is increased, and the precipitate is firmly fixed in the matrix together with the anchor effect. Therefore, even if friction occurs or phase transformation occurs, it is difficult for the precipitate to fall off the matrix.

However, if the length of the major axis is less than 1 μm, the size of the Al ₂ O ₃ -based precipitate is too small, so that such an effect cannot be obtained and the wear resistance is not improved. On the other hand, if the length exceeds 10 μm, the size of the Al ₂ O ₃ -based precipitate is too large, so that the toughness may be impaired. During the zirconia composite sintered body of the present invention, Al ₂ O ₃ based precipitates whose length exceeds 10μm is preferably not been possible variance, the number of such Al ₂ O ₃ based precipitate the total Al 1% or less with respect to the number of ₂ O ₃ -based precipitates is acceptable.

When the minor axis / major axis ratio of the Al ₂ O ₃ -based precipitate exceeds 0.5, the precipitate becomes nearly spherical, and such an effect cannot be exhibited effectively.

In the zirconia composite sintered body of the present invention, the number of such elongated Al ₂ O ₃ -based precipitates is 3% or more of the total number of Al ₂ O ₃ -based precipitates. This is because if the above-mentioned elongated Al ₂ O ₃ -based precipitates are too small, the wear resistance improving effect cannot be exhibited. Preferably it is 5% or more.

The total volume of the Al ₂ O ₃ -based precipitate can be controlled by adjusting the amount of Al ₂ O ₃ added. At this time, many Al ₂ O ₃ -based precipitates having a major axis length of less than 1 μm may be precipitated. However, since the form of the Al ₂ O ₃ -based precipitate to be controlled in the present invention is large and coarse, for example, the major axis is 1 to 10 μm and the ratio of the major axis to the minor axis (minor axis / major axis ratio) is the number of not more than 0.5 is even 3% of the total number of the Al ₂ O ₃ based precipitates, the total volume of Al ₂ O ₃ based precipitates to be controlled, the zirconia composite sintered body in Occupies most of the total volume of all Al ₂ O ₃ -based precipitates present in the substrate. Therefore, even if a large number of Al ₂ O ₃ -based precipitates having a major axis length of less than 1 μm are present, the effect of the present invention is not hindered.

The shape and number of such Al ₂ O ₃ -based precipitates can be observed by photographing a cut surface of the zirconia composite sintered body with a scanning electron microscope (SEM) and analyzing the image. Details will be described in an embodiment described later.

As described above, in the zirconia composite sintered body of the present invention, it is important to appropriately control the form of the Al ₂ O ₃ -based precipitates contained in the sintered body, but to appropriately control the form. Is a ratio in the total amount of the zirconia composite sintered body, and it is necessary to contain MgO and / or CaO: 0.15 to 7.5% by mass in total. The reason for setting this range is as follows.

MgO and / or CaO: 0.15-7.5 mass% in total
MgO and CaO have the effect of controlling the morphology of the precipitate by dissolving in the Al ₂ O ₃ -based precipitate. The reason is not clear, but when MgO or CaO is dissolved in the Al ₂ O ₃ -based precipitate, the form of the precipitate changes. MgO and CaO also act as sintering aids, increasing the density of the zirconia composite sintered body and improving both strength and toughness. In order to exhibit such an action effectively, it is necessary to contain 0.15% by mass or more in total. Preferably it is 0.5 mass% or more. However, if it is excessively contained, it aggregates and, on the contrary, causes a decrease in strength and toughness. Therefore, the upper limit is set to 7.5% by mass in total. Preferably it is 5 mass% or less. Even if MgO or CaO is added alone, the effect is sufficiently exerted, but of course they may be used in combination.

In order to appropriately control the form of the Al ₂ O ₃ -based precipitate, the mixing ratio [Al ₂ O ₃ / (MgO + CaO)] of the Al ₂ O ₃ and the MgO and / or CaO is 4 on a mass basis. It is preferable to set to ~ 6. The reason is not clear, but if the blending ratio is less than 4, the blending amount of MgO or CaO becomes excessive. On the other hand, if the blending ratio exceeds 6, the blending amount of Al ₂ O ₃ becomes excessive. The form of the Al ₂ O ₃ -based precipitate cannot be sufficiently controlled.

Note that, as described above, MgO and CaO are sufficiently effective even when used alone, so when using MgO alone, the blending ratio of Al ₂ O ₃ and MgO is expressed by the following formula (1): In the case of using CaO alone, the blending ratio of Al ₂ O ₃ and CaO is calculated by the following equation (2).
Compounding ratio = [Al ₂ O ₃ / MgO] (1)
Compounding ratio = [Al ₂ O ₃ / CaO] (2)

In order to promote precipitation of Al ₂ O ₃ -based precipitates that satisfy the above range, La ₂ O ₃ : 2% by mass or less (not including 0% by mass) is further included in the total amount. Is preferred.

La ₂ O ₃ : 2% by mass or less (excluding 0% by mass)
La ₂ O ₃ is an oxide that effectively acts to promote the precipitation of Al ₂ O ₃ -based precipitates as elongated rods. However, if the amount added is too large, it aggregates and lowers the strength and toughness of the zirconia composite sintered body, so the upper limit is made 2 mass%. In addition, in order to exhibit such an effect effectively, it is good to contain 0.005 mass% or more.

By the way, the zirconia composite sintered body of the present invention contains Y ₂ O ₃ and CeO ₂ as zirconia stabilizers. However, when Y ₂ O ₃ is used, Y ³⁺ is an element having a lower valence than Zr ^{4+. Therefore} , in order to maintain electrical neutrality, oxygen ions are added depending on the amount of Y ₂ O ₃ added. Try to form holes based on Therefore, in a hydrothermal environment, the vacancies based on oxygen ions react with moisture to generate H ⁺ , so that the Zr—O bond is broken and lattice distortion occurs, and this distortion facilitates the nucleation of transformation. Phase transformation is likely to occur.

On the other hand, when CeO ₂ is used, Ce ⁴⁺ is an equivalent element to Zr ⁴⁺ , so that it can be electrically neutral. For this reason, pores based on oxygen ions are not formed to maintain an electrical balance, and as a result, the Zr—O bond is not broken, and phase transformation hardly occurs even in a hydrothermal environment.

As described above, when Y ₂ O ₃ and CeO ₂ are used in combination as stabilizers, the disadvantages of adding each stabilizer alone can be compensated for each other. That is, when only Y ₂ O ₃ is used as a stabilizer, phase transformation is likely to occur in a hydrothermal environment, but if CeO ₂ that does not easily cause phase transformation in a hydrothermal environment is used in combination, the added component Only the amount of Y ₂ O ₃ used can be reduced. When viewed Therefore the entire zirconia composite sintered body can be a Y ₂ O ₃ as a stabilizer in comparison to using solely reduce the degree to cause phase transformation under hydrothermal environment.

Similarly, with regard to the phase transformation that occurs under stress loading conditions, if Y ₂ O ₃ that causes almost no distortion in the crystal structure and CeO ₂ that causes distortion are used in combination, it is stable when viewed as a whole zirconia composite sintered body. As compared with the case where CeO ₂ is used alone as the agent, the phase transformation occurring under the stress load environment can be suppressed. However, even if Y ₂ O ₃ and CeO ₂ are used in combination, this is not a fundamental solution for preventing phase transformation under a stress load environment. In other words, CeO ₂ has a ionic radius ratio of Ce ^{4+ to} O ²⁻ that is slightly larger than the ideal ionic radius ratio of cubic crystals of zirconia, so that the crystal structure is distorted, but Y ₂ O ₃ is O ^{2 Since} the ionic radius ratio of Y ³⁺ to-and the ideal ionic radius ratio of zirconia cubic crystals are almost equal, no distortion occurs in the crystal structure. Therefore, even if CeO ₂ and Y ₂ O ₃ are used in combination, the amount of distortion of the crystal structure caused by adding CeO ₂ cannot be reduced.

Therefore, the present inventors examined a method for alleviating the distortion of the crystal structure due to the difference in the ion radius ratio caused by adding CeO ₂ . In the course of the study, it is thought that the distortion of the crystal structure due to the addition of CeO ₂ can be alleviated if a stabilizer having an ionic radius ratio slightly smaller than the ideal ionic radius ratio of cubic crystals of zirconia is used in combination. The investigation was repeated focusing on the ionic radius ratio of the stabilizer. As a result, it has been found that TiO ₂ can be an excellent stabilizer meeting these purposes.

TiO ₂ has an ionic radius ratio of Ti ^{4+ to} O ²⁻ of 0.432, which is smaller than the ideal ionic radius ratio of zirconia cubic crystals (0.732). Therefore, as described above, distortion of the crystal lattice due to the addition of CeO ₂ can be relaxed, and the crystal phase is stabilized.

Moreover, since Ti ⁴⁺ is an equivalent element to Zr ⁴⁺ , it can be electrically neutral. For this reason, voids based on oxygen ions are not formed so as to maintain an electrical balance. As a result, the Zr—O bond is not broken, and a phase transformation is not caused in a hydrothermal environment. Therefore, even when TiO ₂ is used in combination, the phase transformation under the hydrothermal environment is not induced, so that only the resistance to the stress-induced phase transformation is appropriately exhibited.

As a result of further research to clarify the preferred blending amount of the stabilizer based on such knowledge, it is preferable to contain TiO ₂ : 1 mol% or less (not including 0 mol%) with respect to all ZrO _2. I found out.

TiO ₂ : 1 mol% or less (excluding 0 mol%)
TiO ₂ is a stabilizer that reduces distortion of the crystal structure due to the addition of CeO ₂ and suppresses stress-induced phase transformation. In order to exhibit such an effect effectively, it is contained at least 0.01 mol%. Preferably it is 0.03 mol% or more. However, since the ionic radius ratio of Ti ^{4+ to} O ²⁻ of TiO ₂ is smaller than the ideal ionic radius ratio of cubic zirconia, excessive addition of TiO ₂ causes distortion in the crystal structure and stress loading It is easy to cause phase transformation below. Therefore, the upper limit of TiO ₂ was set to 1 mol%. A preferable upper limit is 0.5 mol%.

The zirconia composite sintered body of the present invention is preferably formed only from the above-mentioned components, and it is better that there are as few inevitable impurities as possible. However, the range that does not affect the characteristics is about 3% by mass or less. Inevitable impurities can be included. In particular, mixing of, for example, HfO ₂ which is present in the ZrO ₂ raw material and is difficult to separate does not affect the characteristics at all.

  The production method of the zirconia composite sintered body according to the present invention is not particularly limited. For example, (1) mixing of raw material powder, (2) compacting of mixed powder, (3) sintering of the molded body, It is manufactured through each process. Each of these steps will be described in turn.

(1) The raw material powder may be mixed in accordance with a conventional method. After wet mixing, drying and granulation are preferably used as secondary particles, which is preferable in terms of workability and prevention of component segregation. That is, (a) Y ₂ O ₃ powder, CeO ₂ powder, Al ₂ O ₃ powder, and mixed zirconia powder containing MgO powder and / or CaO powder are prepared in advance by a wet method. Depending on the case, a powder obtained by mixing La ₂ O ₃ powder or TiO ₂ powder may be used as the raw material powder. In addition, (b) Y zirconia powder containing Y ₂ O ₃ by wet method, Ce zirconia powder containing CeO ₂ , Al ₂ O ₃ powder, and MgO powder and / or CaO powder (if necessary, La A powder prepared by mixing ₂ O ₃ powder or TiO ₂ powder in advance and drying it may be used as the raw material powder. It is also possible to use a powder containing TiO ₂ as the Y zirconia powder and Ce zirconia powder. At this time, the TiO ₂ powder may be mixed according to the amount of TiO ₂ contained in the Y zirconia powder or Ce zirconia powder. Further, (c) a zirconia powder containing Y ₂ O ₃ and CeO ₂ (optionally TiO ₂ ) is prepared in advance by a wet method, and the Al ₂ O ₃ powder, MgO powder and / or Alternatively, CaO powder may be mixed by a wet method (a powder containing La ₂ O ₃ powder, if necessary), dried, and used as a raw material powder. Note that La ₂ O ₃ may also be included in the zirconia powder in advance.

  When the methods (a) to (c) are compared, in the present invention, it is recommended to adjust the raw material powder by adopting the method (b). The zirconia sintered body obtained by using the raw material powder obtained by the method (b) has a high strength and a high toughness, and hardly causes hydrothermal transformation.

  When preparing the raw material powder by the method (b), it is preferable to mix the Y zirconia powder and the Ce zirconia powder in a volume ratio of 1: 9 to 4: 6. More preferably, it is in the range of 2: 8 to 3: 7.

When using a Y zirconia powder, it is preferable that the Y ₂ O ₃ containing 2~5mol%. The specific surface area (BET value) of this Y zirconia powder is recommended to be about 10 to 20 m ² / g. When using a Ce zirconia powder, it preferably contains CeO ₂ 8~15mol%. The specific surface area (BET value) of this Ce zirconia powder is recommended to be about 10 to 20 m ² / g. The Al ₂ O ₃ powder is not limited as long as the purity is 2N (nine) or more, but it is recommended that the specific surface area (BET value) is about 10 to 20 m ² / g.

The form of adding MgO or CaO is not particularly limited, and for example, it may be added in the form of a compound such as MgCO ₃ , Mg (OH) ₂ , CaCO ₃ , Ca (OH) ₂ . When adding as these compounds, the addition amount should just be 8 mass% or less in the quantity converted into MgO or CaO.

The La ₂ O ₃ powder is not limited as long as the purity is 2N (nine) or more. The TiO ₂ powder is not limited as long as the purity is 2N (ine) or higher, but a powder having a specific surface area (BET value) of about 25 to 100 m ² / g is recommended.

  In the wet method, it is preferable to mix using a mixing ball having a diameter of about 10 mm or less. This is because if it is too large, it is difficult to mix uniformly. As the mixed balls, those made of zirconia are preferably used. The mixing time is not particularly limited, but is preferably 10 hours or more for uniform mixing.

(2) The raw material powder blended and mixed to have a desired composition is compacted by a hydrostatic pressing method at a compacting pressure of 98 to 196 MPa (1 to ² ton / cm ² ). If the molding pressure is too low, the density of the molded body will not increase. On the other hand, if the molding pressure is too high, it becomes difficult for the binder component to escape from the molded body during degreasing.

(3) The zirconia shaped body is sintered in a tetragonal stable region of about 1350 to 1550 ° C. (preferably about 1450 to 1550 ° C.) for about 1 to 4 hours (for example, about 2 hours), and is sintered. Next, hot isostatic pressing (HIP) is performed. However, HIP is preferably performed in an oxygen-containing atmosphere because CeO ₂ is reduced and cracks occur on the surface when HIP is performed in an atmosphere containing only Ar. Specifically, the sintered body may be subjected to HIP sintering in an atmosphere of 1400 ° C., 1500 atm and 80% Ar-20% O ₂ for 2 hours.

  The zirconia composite sintered body of the present invention can be used as a structural material such as a sliding member, a blade, a medical device, tableware, or a machine part, but is also suitable as a biomaterial such as an artificial bone, an artificial joint, or an artificial tooth root. Can be used. The zirconia composite sintered body of the present invention can be suitably used as a material for a part having a sliding part such as an artificial joint.

  When the zirconia composite sintered body of the present invention is used as a biomaterial, for example, a porous layer is preferably formed on the surface portion of the material in order to strengthen the bondability between the implant and the bone. The porous layer formed on the surface portion of the zirconia composite sintered body preferably has a thickness of 0.1 to 3 mm and a porosity of about 25 to 75%.

  Although the manufacturing method of a porous layer (porous structure) is not specifically limited, The following methods are employable. For example, the pore forming agent may be removed by molding together with the raw material powder and an organic substance (pore forming agent) such as acrylic resin or polyethylene, and then heating during sintering. The porosity and the pore diameter can be controlled by the size (particle diameter) of the pore-forming agent and the amount added.

  Further, a foaming agent such as lauryl betaine or a nonylphenol surfactant may be added at the time of mixing the raw material powder, and this foaming agent may be heated and fired during sintering to form pores. In this case as well, the porosity and pore diameter can be controlled by the amount of foaming agent added.

  When the zirconia composite sintered body of the present invention is used as a biomaterial, it is recommended to have a coating layer formed of a biocompatible material on the surface of the porous layer. Biocompatibility can be improved by forming a coating layer on the surface of the porous layer with a calcium phosphate material such as hydroxyapatite.

  The method for coating the surface of the porous layer is not particularly limited, and the following methods are exemplified. In order to coat only the surface of the surface layer portion of the porous layer, a plasma spray method or a plasma spraying method can be applied. Further, in order to coat the inner surface of the surface layer portion of the porous layer, a method in which a coating agent is applied by a slurry application method or a sol-gel method and then sintered is preferable. Can be formed. In order to ensure coating strength, it is desirable to roughen the surface of the sintered body by sandblasting, chemical etching, or the like as pretreatment for coating.

  Hereinafter, the present invention will be described in more detail with reference to experimental examples, but the following experimental examples are not intended to limit the present invention, and may be implemented with appropriate modifications within a range that can meet the purpose described above and below. These are all possible and are within the scope of the present invention.

Experimental example 1
Y zirconia powder containing ₃ mol% of Y ₂ O ₃ , Ce zirconia powder containing 12 mol% of CeO ₂ , Y ₂ O ₃ powder, CeO ₂ powder, ZrO ₂ powder, Al ₂ O ₃ powder, MgO powder and CaCO ₃ powder La ₂ O ₃ powder and TiO ₂ powder were prepared.

The Y zirconia powder has a specific surface area (about the specific surface area, the BET value, the same applies hereinafter) of 16 m ² / g. The specific surface area of the Ce zirconia powder is 11 m ² / g. The Y ₂ O ₃ powder has a specific surface area of 4 m ² / g and a purity of 2N (nine). The CeO ₂ powder has a specific surface area of 4 m ² / g and a purity of 2N (nine). The ZrO ₂ powder has a specific surface area of 15.6 m ² / g and a purity of 98% or more. The Al ₂ O ₃ powder has a specific surface area of 14.5 m ² / g and a purity of 3N (nine). The MgO powder has a specific surface area of 160 m ² / g and a purity of 3N (nine). The CaCO ₃ powder has a specific surface area of 2.5 m ² / g and a purity of 3N (nine). Table 1 shows the amount of CaO converted.

The purity of the La ₂ O ₃ powder is 3N (nine). The specific surface area of the TiO ₂ powder is 50 m ² / g, and the purity is 2N (nine).

Sample No. in Table 1 below. For 1 to 12, 20 to 21, 23 to 25, Y zirconia powder and Ce zirconia powder blended in the volume ratio shown in Table 1, Al ₂ O ₃ powder, MgO powder, CaCO ₃ powder, La ₂ O ₃ powder and TiO ₂ powder were put into a polyethylene container together with a zirconia ball having a diameter of 3 mm so as to have the component composition shown in Table 2 below, and wet-mixed with an ethanol solvent for 24 hours. After wet mixing, the dried product was passed through a mesh to obtain a raw material powder.

Sample No. in Table 1 below. For Nos. 13, 14 and 22, when Y ₂ O ₃ powder, CeO ₂ powder and ZrO ₂ powder were mixed as a pretreatment by a wet method, the powder wet-mixed for 24 hours with an ethanol solvent was dried, and then at 1000 ° C. A powder is obtained by calcining for 3 hours, and this powder is pulverized and mesh-passed, and then mixed with Al ₂ O ₃ powder or MgO powder so as to have the component composition shown in Table 2 below. Were placed in a polyethylene container together with zirconia balls and wet mixed with an ethanol solvent for 24 hours. After wet mixing, the dried product was passed through a mesh to obtain a raw material powder.

In addition, among the component compositions shown in Table 2 below, the amount of Y ₂ O _{3, the} amount of CeO _{2 and the} amount of TiO ₂ are mol% based on the total ZrO ₂ , and the amount of Al ₂ O _{3, the} amount of MgO, the amount of CaO, and La _The amount of ₂ O ₃ is shown by mass% with respect to the total amount of powder. Table ₂ shows the compounding ratio ([Al ₂ O ₃ ] / [MgO + CaO]) calculated from the Al ₂ O ₃ content, the MgO content, and the CaO content in the table.

The obtained raw material powder was molded at 147 MPa (1.5 ton / cm ² ) by cold isostatic pressing. Subsequently, the obtained molded body was sintered at 1450 ° C. for 2 hours in the air to obtain a sintered body.

Next, sample No. in Table 1 below. For 1 to 14, the obtained sintered body was further subjected to HIP sintering for 2 hours in an atmosphere of 1350 ° C., 1500 atm and 80% Ar-20% O ₂ .

A part of the sintered zirconia sintered body was pulverized, and the component composition was confirmed by the following ICP method. As a result, it was confirmed that the component composition of the obtained zirconia sintered body was equal to the component composition of the raw material powder shown in Table 2 below. The specific measurement procedure is as follows. The test material is measured in a platinum crucible, and an alkali flux (Na ₂ CO ₃ + Na ₂ B ₄ O ₇ ) is added and melted. The melt is extracted with hydrochloric acid, and then transferred to a measuring flask to obtain a measurement solution. The measurement solution is subjected to quantitative analysis of metal components with an ICP mass spectrometer (“SPQ8000” manufactured by Seiko Instruments Inc.), and the value is converted into an oxide to determine the amount of each oxide.

Next, the density of various zirconia composite sintered bodies produced as described above was measured by the Archimedes method, and it was confirmed that the relative density was 99% or more. The form of the dispersed Al ₂ O ₃ -based precipitate was observed with a scanning electron microscope (SEM). The observation conditions are as follows.

The specimen was cut out and the cut surface was mirror polished. The cross section after polishing was observed with a scanning electron microscope (SEM: “S-4500” manufactured by Hitachi, Ltd.). The acceleration voltage during observation was 20 kV, and a 0.002 mm ² region was photographed at a magnification of 5000 times. Sample No. 12 SEM photographs are shown in FIG.

Next, the SEM photograph was subjected to image analysis and binarized into a ZrO ₂ portion and an Al ₂ O ₃ portion. For the image analysis, “Nano Hunter NS2K-Lt” manufactured by Nanosystem Corporation was used. The SEM photograph after image analysis is shown in FIG. In the figure, the white part is ZrO ₂ and the black part is Al ₂ O ₃ .

From SEM photograph of image analysis, to the number of the total Al ₂ O ₃ based precipitates, the ratio of the number of long axis short axis / long axis ratio 1~10μm 0.5 following Al ₂ O ₃ based precipitates The results are shown in Table 2 below. At this time, the number of Al ₂ O ₃ precipitates whose major axis is less than 0.03 μm is not included. This is because it is below the detection limit, and even if such fine precipitates fall off, the wear resistance is hardly affected.

  Next, (1) bending test, (2) toughness test, and (3) sliding test were performed using various zirconia composite sintered bodies whose relative density was confirmed to be 99% or more.

  (1) The bending test was performed according to JIS R1601. That is, the zirconia composite sintered body was processed into a 3 × 4 × 40 mm test piece, and a four-point bending test was performed with an upper span of 10 mm and a lower span of 30 mm. Fifteen test pieces were prepared, and the average value of these was used as the result of the bending test.

  (2) The toughness test was performed according to JIS R1607. As a test piece, a sample in which the above zirconia composite sintered body was ground with a surface grinder and then the surface was mirror-finished with 3 μm diamond abrasive grains was used. The average value of 5 points was taken as the result of the toughness test.

  (3) The sliding test was conducted by a pin-on-disk test. As for the size of the pin of the test piece, a convex part of diameter: 1.5 mm × length: 2 mm was provided at the tip of the test piece of diameter: 5 mm × height: 15 mm in order to increase the contact surface pressure. On the other hand, the disk has a diameter of 40 mm and a thickness of 5 mm. The pin (test piece) and the friction surface of the disk were mirror-polished to Ra = 0.01 μm.

  As a wear tester, a friction wear T tester manufactured by Shinko Engineering is used, and three test pieces are mounted on the upper anvil at an equal interval on a circumference of 40 mm in diameter and fixed to the bottom of the container. A load of 343 N (35 kgf) was applied to the disc, and the anvil was rotated by bringing the surface pressure into contact with 64.7 MPa. The sliding time was 40 hours and the sliding speed was 120 mm / sec. Note that physiological saline was circulated in the container.

  Table 2 shows the test results.

As apparent from Table 2, the sample No. Nos. 1 to 14 can achieve high strength of 900 MPa or more and high toughness of 8 MPa · m ^1/2 or more, and can suppress the amount of wear of the pin to 50 mg or less, and are excellent in wear resistance. In contrast, sample no. In 20-25, either intensity | strength, toughness, or abrasion resistance is inferior.

Sample No. 12 is a drawing-substituting photograph obtained by image analysis of a photograph of No. 12 taken with an electron microscope.

Claims (4)

A zirconia composite sintered body containing Al ₂ O ₃ ,
For all ZrO ₂ ,
Y ₂ O ₃ : 0.2 to 1.5 mol%,
CeO ₂ : In addition to 4.7 to 12 mol%,
As a percentage of the total amount,
Al ₂ O ₃ : 1 to 30% by mass,
MgO and / or CaO: 0.15 to 7.5% by weight in total, and
While Al ₂ O ₃ -based precipitates are dispersed, 3% or more of the total number of Al ₂ O ₃ -based precipitates has a major axis of 1 to 10 μm and a minor axis / major axis ratio of 0.5 or less. A zirconia composite sintered body characterized by that. 2. The zirconia composite sintered body according to claim 1, further comprising La ₂ O ₃ : 2% by mass or less (not including 0% by mass) as a ratio in the total amount. Furthermore, all to ZrO _2, TiO _2: zirconia composite sintered body according to claim 1 or 2 are those containing 1 mol% or less (not including 0 mol%).   The biomaterial formed with the zirconia composite sintered compact in any one of Claims 1-3.

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