JPH01290558A - Zirconia sintered body - Google Patents

Abstract

PURPOSE:To prepare a zirconia sintered body having high strength and thermal stability and to prevent chipping during processing and generation of crack in the sintered body by specifying a content of Y2O3 and CeO2, crystal particle size, crystal structure and particle size of cubic crystal of zirconia. CONSTITUTION:The title zirconia sintered body consists primarily of zirconia of tetragonal crystals consisting of 2-3.5mol.% Y2O3, 0.1-<0.5mol.% CeO2 and having <=1mu mean crystal particle size, wherein <=10vol.% monoclinic crystals and 0 or <=5vol.% cubic crystal having <=1mu particle size are contained. If the content of Y2O3 is out of the above-described range, high strength is not attained. If the content of CeO2 is below the above described lower limit, the thermal stability is not improved. If it is > the upper limit, exhibition of the strength attains insufficiently. If the mean crystal particle size of the sintered body exceeds 1mu, the stability of the tetragonal crystal decreases. When cubic crystals are contained and the crystal particle size exceeds 1mu, the strength decreases remarkably and the processability deteriorates.

Description

[Detailed Description of the Invention] Industrial Field of Application This invention is applicable to various types of cutlery, medical equipment, tableware, sliding members, etc. that are exposed to steam, hot water, and other corrosive environments in the mid- to high-temperature range during use. This invention relates to a zirconia sintered body suitable for various uses.

Conventional Technology There are various types of zirconia sintered bodies, but the so-called high-strength zirconia sintered bodies use Y2O3 to make all or part of the zirconia square.
Stabilizers such as these are added.

However, the square product obtained by adding Y2O3 has low thermal stability, and the sintered body is
When exposed to temperatures of ~500°C or placed in high-temperature water for long periods of time, the tetragonal product gradually transforms into monoclinic crystals and its strength deteriorates.

Therefore, the invention of JP-A-162173M in 1982 and the invention of JP-A-162173M in 1982
- In the invention of No. 108367, Y2 is used as a stabilizer.
It is proposed to use CeO2 instead of O3.

These inventions focus on the fact that CeO2 has a great effect on stabilizing tetragonal crystals. However, originally, so-called high-strength zirconia sintered bodies develop strength by utilizing so-called stress-induced transformation, in which the tetragonal shape transforms into monoclinic crystal when stress is applied to it. Therefore, excessive stabilization of the tetragonal crystal by CeO2 makes it difficult for stress-induced transformation to occur, or even if it occurs, it narrows the transformation region, and there is a problem that the strength development mechanism cannot function sufficiently. Also, Ce
Zirconia sintered bodies made of tetragonal crystals stabilized using O2 have a considerably large average crystal grain size due to significant grain growth during sintering, which also inhibits the development of strength. .

Therefore, for example, the invention of JP-A-60-137870,
JP-A-60-141671 Invention, JP-A-62-153
In the invention No. 163, Y2O3 and C are used as stabilizers.
It is used together with eO2.

In both of these inventions, the upper limit of CeO2 is defined so as not to cause a decrease in strength. however,
Even if the amount of CeO2 added is within the specified range, the strength of the sintered body is lower than that of one in which only an appropriate amount of Y2O3 is added.

In addition, these sintered bodies have coarse cubic grains mixed in a fine square matrix, which promotes a decrease in strength. After all, it is difficult to say that any of these sintered bodies simultaneously satisfy the two properties of strength and thermal stability. In addition, if coarse cubic grains are mixed, there is also the problem that chips and cracks are likely to occur during processing.

Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned problems of conventional sintered bodies, and to improve the high strength of sintered bodies made by adding only Y2O3, and by adding only CeO2. It is an object of the present invention to provide a zirconia sintered body that not only has the feature of excellent thermal stability of a sintered body, but also can prevent the occurrence of chips and cracks that occur during processing.

Means for Solving the Problems In order to achieve the above object, in this invention, Y2O
3 in a range of 2 mol% or more and less than 3.5 mol%, C
Zirconia that contains eO2 in a range of 0.1 mol% or more and less than 0.5 mol%, has an average crystal grain size of 1 μm or less, has a mainly tetragonal zirconia crystal structure, and has a monoclinic crystal structure. is 10% by volume or less, and does not contain zirconia with a cubic crystal structure, or even if it does contain zirconia, it contains 5% by volume or less.
There is provided a zirconia sintered body characterized in that the crystal grain size of zirconia having a cubic crystal structure is 1 μm or less. In this invention, regarding zirconia with a monoclinic crystal structure and zirconia with a cubic crystal structure, there are cases in which they are not contained at all, and cases in which they are contained in extremely small amounts within the ranges mentioned above. Sometimes there are. Regarding zirconia having a cubic crystal structure, if it is included, the cubic crystal grain size must be 1 μm or less.

To explain this invention in more detail, this invention
The reason why 3 is included is because, as mentioned above, doing so causes the precipitation of square parts, which is convenient for developing strength. However, if the old content is less than 2 mol%,
Not only does the amount of tetragonal crystals decrease, but the monoclinic crystals increase too much to achieve high strength. Moreover, if it exceeds 3.5 mol %, a large amount of coarse cubic grains will be mixed in the matrix of the square product, resulting in a significant decrease in strength and workability.

In addition, the reason why this invention contains CeO2 is to stabilize the tetragonal product appropriately, improve thermal stability, and prevent the decrease in strength of the sintered body due to gradual transformation of the tetragonal crystal to monoclinic crystal. This is to prevent this. In addition, the sintered body is Zro2-Y2
By becoming a three-component system of O3-Ce02, the tetragonal region expands and cubic crystals are less likely to coexist.
This is because it is possible to prevent a decrease in strength and improve workability. However, the amount of CeO2 is 0.1 mol%
If the amount is less than that, such an effect cannot be obtained. Moreover, if it exceeds 0.5 mol %, the stability of the tetragonal product becomes too high, and the strength development mechanism by stress-induced transformation from the tetragonal product to monoclinic crystal does not function sufficiently.

The reason why the average crystal grain size of the sintered body is set to 1 μm or less in this invention is because if the average crystal grain size is larger than 1 μm, the stability of the square product becomes excessively small. In addition, cubic crystals are not contained at all, or even if they are contained, they are limited to 5% by volume or less, but if cubic crystals are contained, the crystal grain size does not cause the disadvantages due to the coarse grains mentioned above. Therefore, it must be 1 μm or less. Here, the average crystal particle diameter is measured by an intercept method. In this method, the surface of the sintered body is etched, an arbitrary straight line is drawn on a micrograph of the etched surface, the intersection of the straight line and the grain boundary is determined, and the average length of the straight line divided by the grain boundary is determined. is the average crystal grain size. Further, the cubic crystal grain size is defined as the average value of the maximum length of each cubic grain in the same direction determined from a microscopic photograph of the etched surface of the sintered body.

In the sintered body of the present invention, the crystal structure of zirconia is mainly square. That is, if monoclinic crystals or cubic crystals are present, the amount of tetragonal crystals that have a strength-producing effect due to stress-induced transformation will be reduced accordingly, and the strength of the sintered body will be low.

In addition, the large number of monoclinic crystals means that microcracks are generated around or in the vicinity of the monoclinic crystal when it transforms from a tetragonal crystal, and these microcranks become the nucleus of a tetragonal crystal. Since the product easily transforms into monoclinic crystal, it must be limited to 10% by volume or less. Roughly speaking, when cubic crystals are precipitated, the cubic crystals contain excess Y2O3 and CeO2, so the amount of Y2O3 and CeO2 in the surrounding tetragonal matrix decreases, and the stability of the tetragonal product decreases. It will decrease excessively. Also,
The larger the amount of cubic crystals, the larger the crystal grains.
It becomes coarse particles, which reduces strength and causes chips and cracks. Therefore, in the present invention, cubic crystals are not contained at all, or even if they are contained, they are limited to 5% by volume or less.

In the above, the amount of monoclinic crystal is determined by the following formula from the intensity obtained by performing X-ray diffraction on the carefully polished surface of the sintered body and integrating the representative diffraction peaks of monoclinic crystal, tetragonal crystal, and cubic crystal. Find it by In the formula, Qm is the amount of monoclinic crystal (volume %), IrrN 11 is the strength of the 111 plane of monoclinic crystal, Irr
N1 King is the intensity of the 111 plane of the monoclinic crystal, and Itclll is the intensity of the 111 plane of the tetragonal and cubic crystals.

Cm= [(1ml 11 +1m111)/(■t
C111+■m111 +Imt 1T)]x100 Further, the amount of cubic crystals is determined as follows.

That is, the sintered body is heat treated at 1300'C for 130 minutes, roughly immersed in 160'C sulfuric acid for 1 hour to etch the polished surface, and any surface of the etched surface is exposed to a microscope at 2000x magnification. Observe with. If cubic grains exist, that part will be preferentially corroded and can be easily distinguished from other crystals, so the ratio of the area of the cubic grain to the area of the other parts is determined. However, since the observation plane is an arbitrary plane and the cubic grains have no orientation, the area ratio is regarded as the volume ratio, and the amount of cubic crystals ( Volume %) is calculated. Hey, if you find the amount of monoclinic and cubic crystals,
The remainder is a square product.

The sintered body of this invention can be manufactured by various methods. Next, a suitable example will be explained.

That is, first, an aqueous solution of zirconium chloride with a purity of 99.9% or more, an aqueous solution of yttrium chloride with a purity of 99.5% or more, and an aqueous solution of cerium chloride with a purity of 99.5% or more are predetermined. After mixing in the ratio of , well-known coprecipitation method, hydrolysis method, thermal decomposition method, alkoxide method,
Using a sol-gel method, gas phase method, etc., a predetermined proportion of Y2O
A zirconia powder containing 3 and CeO2 is prepared. Alternatively, an aqueous solution of zirconium nitrate, yttrium nitrate, and cerium nitrate may be used, or a mixed powder of zirconia powder, yttrium powder, and ceria powder may be used as the so-called starting material.

Next, the above powder is calcined at 800 to 1000°C and pulverized. The calcination and pulverization are repeated as necessary to obtain a raw material powder. This raw material powder forms a solid solution in which itria and ceria are uniformly mixed in zirconia.

Next, the above raw material powder is processed by rubber press method, injection molding method,
A molded article is obtained by molding into a desired shape using a well-known molding method such as a mold molding method or an extrusion molding method.

Next, the above molded body is placed in a heating furnace at a rate of 50-100'C/hour up to about 900'C, and at a rate of 30-100'C/hour above that.
The temperature was raised to 1200-1550°C at a rate of 50'C/hour, cooled in a variable furnace and held at that temperature for several hours, and sintered. This sintered body has a bulk density of 95% or more, preferably 97.5% or more of the theoretical density, and after sintering, it is subjected to hot isostatic pressing (HIP) to make it rough. It is also possible to increase the density.

Examples Example Zirconia powder having an average particle diameter of 0.1 μm was prepared in which Y2O3 and CeO2 were uniformly dissolved in solid solution to have the composition shown in the table.

That is, an aqueous solution of zirconium oxychloride with a purity of 99.9%, an aqueous solution of yttrium chloride with a purity of 99.9%, and an aqueous solution of cerium chloride with a purity of 99.9% are mixed into a sintered body. The amounts of Y2O3 and CeO2 in are mixed so that they have the composition shown in the table, and the mixed aqueous solution is gradually heated to 100°C.
The temperature was raised to 9oo'c at a rate of roughly 100°C/hour, and the calcined powder was heated for 3 hours to obtain a calcined powder. It was ground in a strained ball mill to obtain a powder with an average particle size of 0.1 μm.

Next, each of the above powders was rubber press molded at a pressure of 1 ton/cm2 to obtain a molded body.

Next, each of the above-mentioned molded bodies was placed in a heating furnace, and the temperature was raised to 1400'C at a rate of 50'C/hour up to 900'C, and at a rate of 30'C/hour beyond that temperature, and the temperature was raised to 1400'C at a rate of 30'C/hour. After holding for a period of time, the mixture was cooled in a furnace to obtain a sintered body. However, for N and 11, the heating temperature was 1600'C.

Next, square bar-shaped test pieces were cut out from each of the above sintered bodies and polished with a #400 grindstone to a thickness of 3 mm and a width of 4 m.
m, length 3f 3mm.

Next, using each of the above test pieces, the amount of tetragonal, monoclinic, and cubic crystals, average crystal grain size, and bending strength were determined.
The amount of monoclinic crystals opened and the bending strength were measured after heating at 0'C for 3000 hours. The amount of monoclinic crystals was measured after the surface of the test piece was roughly mirror-finished with diamond paste.

The bending strength was determined by the well-known three-point bending test method. The measurement results are shown in the table below. In the table, sintered bodies of N, 1 to 4 are the sintered bodies of the present invention.

From the above table, it can be seen that the sintered body of the present invention has high bending strength in the initial stage, and also has high thermal stability, so that the strength decreases very little after being held at high temperature for a long time.

Fig. 1 shows a scanning electron micrograph (magnification: 5000x) of the sintered body of N, 3, but there are no cubic grains.
It can be seen that a fine square uniform structure was obtained.

On the other hand, N.5 has low thermal stability because the amount of Y2O3 is below the lower limit defined by the present invention.

In addition, in the case of N, 6, since the amount of CeO2 is below the lower limit specified by the present invention, coarse cubic grains are mixed and the thermal stability is low. A scanning electron micrograph (magnification: 5,000 times) of this sintered body is shown in FIG. 2, and coarse cubic grains (crystal grains that appear large) are present within the square matrix. Furthermore, the one with N, 7.8 has too much CeO2, the one with N, 9 has too much Y2O3, the one with N, 10 has too little Y2O3,
Because there are too many CeO2 deposits, the initial bending strength is low in all cases. Also, the one with N and 11 is Y
Although the amount of 2O3 and Ce0z is within the range of this invention, the average crystal grain size exceeds 1 μm due to the high firing temperature, and monoclinic crystals and coarse cubic grains are also present. Both characteristics are very low.

Effects of the Invention The sintered body of this invention contains Y2O3 at 2 mol% or more, 3.5% by mole or more.
Contains CeO2 in a range of less than mol%, contains CeO2 in a range of 0.1 mol% or more and less than 0.5 mol%, and has an average crystal grain size of 1
μm or less, the crystal structure of zirconia is mainly tetragonal, the amount of zirconia with a monoclinic crystal structure is 10% by volume or less, and it does not contain zirconia with a cubic crystal structure, or even if it contains zirconia with a cubic crystal structure. 5% by volume or less, and the crystal grain size of zirconia with a cubic crystal structure is 1 μm or less, so as shown in the examples, it has very high strength and is thermally stable. Excellent quality. In addition, it does not contain zirconia with a cubic crystal structure, or even if it does contain it, the amount is less than 5% by volume, and the cubic crystal grain size is less than 1 μm, so it does not cause chips or cracks during processing. It becomes possible to prevent the occurrence of

As mentioned above, the sintered body of the present invention has high mechanical strength and excellent thermal stability, and can be precisely processed by preventing chipping and cracking, so it can be used for various cutlery tools, It is very suitable as a constituent material for items such as medical equipment, tableware, and sliding parts that are exposed to steam, hot water, and other corrosive environments in the medium and high temperature range during use.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph (magnification: 5000 times) showing the crystal structure of a sintered body according to an example of the present invention, and FIG. 2 is a sintered body according to a comparative example.

Claims (1)

[Claims] Contains Y_2O_3 in a range of 2 mol% or more and less than 3.5 mol%, contains CeO_2 in a range of 0.1 mol% or more and less than 0.5 mol%, has an average crystal grain size of 1 μm or less, and is a zirconia The crystal structure is mainly tetragonal, the amount of zirconia with a monoclinic crystal structure is 10% by volume or less, and there is no zirconia with a cubic crystal structure,
A zirconia sintered body characterized in that the amount of zirconia contained therein is 5% by volume or less, and the crystal grain size of zirconia having a cubic crystal structure is 1 μm or less.