JP2517249B2 - High-strength zirconia-based HIP sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to hydrothermal stability and thermal stability, which are composed of zirconia containing yttrium oxide and cerium oxide as stabilizers and alumina, spinel, and mullite as dispersion components. The invention relates to a high-strength zirconia-based sintered body with significantly improved properties and high-temperature stability.

[Prior Art] A zirconia sintered body undergoes a phase transition from a cubic system to a tetragonal system to a monoclinic system in a high temperature region, but with a volume change at that time, especially the volume of the phase transition from the tetragonal system to the monoclinic system. The change is large, so that there is a drawback that the sintered body is destroyed by this volume change. To eliminate this drawback, ZrO ₂ was
A large number of stabilized zirconia consisting of cubic crystals or partially stabilized zirconia consisting of cubic crystals and monoclinic crystals are disclosed at room temperature to prevent the transition by solid solution of O, MgO, Y ₂ O _3, etc. In addition, it has been announced that partially stabilized zirconia obtained by allowing a tetragonal crystal, which is a metastable phase, to exist in a sintered body at room temperature exhibits high strength. This is partly because, when a mechanical external stress is applied, a phase transition from a metastable tetragonal crystal to a monoclinic crystal that is a room temperature stable phase is induced and the stress is absorbed.

Thus, at room temperature, as a stabilizer for obtaining a zirconia sintered body in which the tetragonal crystal is kept metastable, Y ₂ O ₃ has been mainly used conventionally, and it has a significantly high strength,
It has attracted attention because of its high toughness. Further, there is disclosed a method for producing a high-strength zirconia-based sintered body in which alumina or the like is dispersed in partially stabilized zirconia having Y ₂ O ₃ as a stabilizer.
60-235762.

In the present invention, by mixing alumina in a specific ratio to zirconia containing tetragonal crystals to which a small amount of yttria is added, and by performing hot isostatic pressing treatment, the strength characteristics are further significantly improved as compared with the conventional partially stabilized zirconia. It was discovered that a sintered body can be obtained.

On the other hand, partially stabilized zirconia consisting of tetragonal crystal containing only a small amount (5 mol% or less) of yttrium oxide (Y ₂ O ₃ ) as a stabilizer is a tetragonal crystal that is stable at high temperature and is controlled up to room temperature by controlling the microstructure. It is provided as a metastable phase, and high strength is obtained by preventing the occurrence of cracks resulting from volume expansion due to the phase transformation into monoclinic crystals. As a result, its structure and properties change over time, especially under thermal stress.
By heating at a relatively low temperature of ℃ to 400 ℃ for a long time, a phase transition from tetragonal to monoclinic occurs, and deterioration of strength with time occurs. Further, the strength deterioration due to this phase transition is remarkably accelerated in the presence of water or the like, and such deterioration with time is a serious problem.

This means that in the invention of the above-mentioned JP-A-60-235762, Y
Zirconia using only ₂ O ₃ as a stabilizer, even in a high-strength zirconia sintered body partially containing alumina, as with the partially stabilized zirconia, the problem of deterioration over time is included, and Nothing is disclosed about improvement in so-called hot water stability when heated in the presence for a long time. On the other hand, the zirconia porcelain and manufacturing method disclosed in JP-A-60-141673 disclose a method for improving thermal stability by allowing yttrium oxide and cerium oxide to coexist. However, this zirconia sintered body composed of yttrium oxide and cerium oxide has a drawback of low mechanical strength, and although the thermal stability is improved, the hot water stability in the presence of water is touched. Not yet, still inadequate. As described above, there has been a long-awaited demand for zirconia-based ceramics having high strength and excellent heat and hot water stability without deterioration over time.

Therefore, the applicants of the present invention filed the invention of a high-strength zirconia-based sintered body and a method for producing the same on September 22, 1986 as a method for achieving this. In the above invention, zirconia containing a predetermined amount of yttrium oxide and cerium oxide as a stabilizer, and alumina, which controls the crystal phase and the crystal particle size, the theoretical density and bending strength by HIP treatment than conventional products. It has been found that, by maintaining a high level, the zirconia sintered body has higher strength than conventional zirconia sintered bodies and is excellent in heat and hot water stability.

However, in the above-mentioned invention, the most general HIP processing method in which a carbon heating element is used as a manufacturing method and an inert gas such as Ar gas is used as a pressure medium has been used. Therefore, when the capsules are not used, the sintered body is colored due to the atmosphere, especially the reducing atmosphere, and due to the difference in the reduction state, the coloring is different between the surface and the inside of the sintered body. Was strongly received.

This phenomenon was also highly dependent on the temperature of HIP treatment.
That is, when the HIP treatment is performed at a higher temperature, the zirconia crystal undergoes a phase transition from a tetragonal crystal to a monoclinic crystal, the phenomenon of so-called destabilization proceeds, and the strength rapidly decreases with the decrease in the density of the sintered body. To do. This is because cerium, which is one of the stabilizers for zirconia, is reduced to a chemical non-stoichiometric value between tetravalent and tetravalent or trivalent or trivalent, and the ionic radius of the cerium ion changes. It is assumed that the main cause is occurrence. In addition, the conventional HIP sintered body obtained by using the carbon heating element has a problem that the trace amount of carbon contained in the sintered body is oxidized during heat treatment or high temperature use, and the characteristics are likely to deteriorate. Had.

[Problems to be Solved by the Invention] The present invention is directed to such Y ₂ O ₃ -ZrO ₂ system partially stabilized zirconia mainly consisting of tetragonal crystals or a sintered body mainly composed of this, which is deteriorated with time. It was made to solve the problems in water and the problems such as destabilization phenomenon in high temperature HIP treatment of the invention and deterioration during high temperature use. Dramatically increased,
It provides a zirconia-based sintered body that has no deterioration over time, is highly durable, and has extremely high strength, and is not affected by a reducing atmosphere at the same time. An object of the present invention is to provide an extremely excellent zirconia-based sintered body that is free from strength deterioration.

[Means for Solving Problems] The high-strength zirconia-based HIP sintered body of the present invention is mainly tetragonal or tetragonal containing yttrium oxide (Y ₂ O ₃ ) or cerium oxide (CeO ₂ ) as a stabilizer. moiety and stabilized zirconia 50-98 wt% consisting of cubic and alumina (Al ₂ O ₃₎ as a dispersion component, a spinel _{(MgO · Al 2 O 3)} , at least of the mullite _{(3Al 2 O 3 · 2SiO 2} ) 50 or more
2% by weight, and the average crystal grain size of the sintered body is 2 μm
In the following, the gist is that the bulk density of the sintered body is 99% or more of the theoretical density or the porosity is 1% or less, and a similar color to that of the sintered product of the composition in the atmosphere is exhibited.

[Operation] The high-strength zirconia-based sintered body of the present invention has significantly higher strength than conventional yttria-containing partially stabilized zirconia-based sintered bodies, and has extremely high thermal stability and hot water stability, and Even if it is used for a long time, it does not show a deterioration phenomenon such as a change in shape or a decrease in strength, and has extremely excellent durability. As described above, the high-strength zirconia-based sintered body of the present invention having high thermal stability and high hydrothermal stability while maintaining extremely high strength is the result of the inventors' earnest studies, It was completed based on such knowledge.

The present inventors have made extensive studies on zirconia sintered bodies containing cerium oxide and yttrium oxide. As a result, by using cerium oxide as a stabilizing agent coexist with yttrium oxide, the crystal structure of tetragonal zirconia than conventional tetragonal zirconia stabilized with Y ₂ O _3, high temperature stability of the zirconia Included as a stabilizer in zirconia based on the finding that the thermodynamic stability region of the tetragonal crystal becomes closer to the crystal structure of the cubic phase and the thermodynamic stability region of the tetragonal crystal expands to low temperatures, while the thermodynamic stability of the tetragonal crystal increases. Cerium oxide and yttrium oxide in the composition range of the present invention are found.

In addition, alumina (Al ₂ O 3) for zirconia sintered bodies containing yttrium oxide and cerium oxide as stabilizers
₃ ), spinel (MgO ・ Al ₂ O ₃ ), mullite (3Al ₂ O ₃・ 2Si)
The effect of addition of O ₂ ) was also examined. As a result, the addition of these oxides increases the content of tetragonal crystals, contributes to the increase of fracture energy due to the increase of elastic modulus, shows high strength in combination with the application of HIP treatment, and strengthens the grain boundary part of ZrO _2. It has been found that the stability of the metastable tetragonal zirconia is further enhanced, and as a result of the synergistic effect with the stability due to the presence of the CeO ₂ component, the hot water stability is significantly improved.

In the present invention, by using a hot isostatic press, it is possible to control the size of the pores contained in the sintered body to be less than 30 μm, which is denser than the conventional sintering at atmospheric pressure. Furthermore, sintering can be completed at lower temperatures. Therefore, the average crystal grain size of the sintered body can be further reduced, and the bulk density of 99% or more of the theoretical density or 1% or less of the porosity can be obtained. As a result
While having a strength of 150 kgf / mm ² or more, it is possible to obtain a crystalline body that is extremely excellent in thermal and hydrothermal stability in combination with the composition control of each component of yttrium oxide, cerium oxide, zirconia, alumina, spinel, and mullite. Made possible

Further, in the present invention, by using a gas containing oxygen as a pressurizing medium for HIP treatment in particular, a carbon heating element that is generally used in the past is used, and an inert gas such as Ar gas is used as a pressure medium. Compared to the HIP treatment used as, it is not affected by the reducing atmosphere.

For this reason, firstly, there is no coloring due to the influence of the reducing atmosphere, such as different coloring on the surface and inside of the sintered body.

Secondly, cerium, which is one of the stabilizers contained in the partially stabilized zirconia composition of the present invention, is tetravalent to tetravalent and trivalent.
A destabilization phenomenon, which is considered to be mainly caused by a change in ionic radius due to a stoichiometric non-stoichiometric value between valences or trivalence, that is, a phenomenon in which a zirconia crystal undergoes a phase transition from tetragonal to monoclinic Does not happen. Therefore, the properties such as strength, heat and hot water stability are further improved, and the effect of the HIP treatment, which is the object of the present invention, is completely obtained.

Third, HIP that has been generally used
The sintered body obtained by the treatment has a high strength zirconia of the present invention, whereas the trace amount of carbon that has penetrated into the sintered body during the HIP treatment is likely to be oxidized during heat treatment or high temperature use to cause deterioration of properties. There is no characteristic deterioration of the sintered body during such heat treatment or high temperature use, and the strength of the sintered body does not deteriorate even after holding it in the atmosphere at 1000 ° C for a long time, and it can be used at high temperature for a long time. It does not deteriorate at all.

Thus, the sintered body of the composition of the present invention to which the conventional HIP treatment is applied is further superior. Further, it has excellent characteristics that are about twice or more the high temperature strength of the conventional partially stabilized zirconia. Furthermore, it has extremely excellent thermal shock resistance.

Further, in the present invention, by setting the average crystal particle size of the zirconia sintered body to 2 μm or less, a sintered body excellent in strength and hot water stability could be obtained.

Furthermore, the high-strength zirconia sintered body of the present invention has excellent wear resistance of zirconia and also improves the creep characteristics of the zirconia sintered body at high temperatures.

Contained in the sintered body of the present invention, in order tetragonal zirconia does not exhibit a stable degradation by thermal Y ₂ O ₃ -CeO ₂ -ZrO ₂ system, there metastable tetragonal, ZrO ₂ particles near When subjected to stress concentration on, the transformation to the monoclinic system which is a low temperature stable phase occurs,
It has the effect of relieving stress. Therefore, the high-strength zirconia-based sintered body of the present invention exhibits remarkably high strength and high toughness.

In the present invention, Y ₂ O ₃ and Ce are used as zirconia stabilizers.
Requires O ₂ . The compounding ratios of the three components of Y ₂ O ₃ , CeO ₂ and ZrO ₂ of the present invention are shown by mol% of ZrO ₂ , YO _1.5 and CeO _{2 on} the three axes intersecting the equilateral triangle as shown in FIG. Point A (ZrO ₂ 87.5mol%, YO _1.5 12mol%, CeO ₂ 0.5mol)
%) Point B (ZrO ₂ 95.5mol%, YO _1.5 4mol%, CeO ₂ 0.5mol%) Point C (ZrO ₂ 95.5mol%, YO _1.5 2mol%, CeO ₂ 2.5mol%) Point D (ZrO ₂ 92.5mol% , YO _1.5 0.5mol%, CeO ₂ 7.0mol
%) Point E (ZrO ₂ 85mol%, YO _1.5 0.5mol%, CeO ₂ 14.5mol
%), And the composition is preferably within the range surrounded by the line connecting the five specific composition groups. If the zirconia composition is selected within this range, the amount of monoclinic crystals when the sintered body is held in 180 ° C. (10 atm) saturated steam for 20 hours can be 30% by volume or less. Further, the amount of monoclinic crystals when kept in the atmosphere of 200 ° C. for 3000 hours can be 20% by volume or less.

However, if the amount of the stabilizer is less than this range, the stability of the tetragonal zirconia will be low. That is, in the three-sided coordinate of FIG. 1, when CeO ₂ is less than the line AB, the thermal stability is inferior, and Y ₂ O _{3 is} less than the line DE.
If the amount is small, the strength is low and the thermal stability is poor. Also, line AE
If the amount of Y ₂ O ₃ or CeO ₂ is larger than that, sufficient mechanical properties cannot be obtained. When the amount of the stabilizer is smaller than that of the line BCD, the stability of the tetragonal zirconia is low.

Further, in order to make the present invention more effective, the compounding amounts of the above three components are represented by point F (ZrO ₂ 88 mol%, YO _1.5 10 mol%, CeO _{2 2} mol%) point on the triangular coordinates of FIG. _{G (ZrO 2 89mol%, YO} 1.5 10mol%, CeO 2 1mol%) point _{H (ZrO 2 93mol%, YO} 1.5 6mol%, CeO 2 1mol%) point _{I (ZrO 2 94.5mol%, YO} 1.5 2mol%, CeO ₂ 3.5 mol%) point _{J (ZrO 2 91mol%, YO} 1.5 1mol%, CeO 2 8mol%) point _{K (ZrO 2 86mol%, YO} 1.5 1mol%, a specific 5 composition point indicated by CeO ₂ 13 mol%) Select within the range enclosed by the connecting lines. If the composition of zirconia is selected within this range, the amount of monoclinic crystals when the sintered body is held in saturated steam at 180 ° C (10 atm) for 20 hours can be 20% by volume or less. Further, the amount of monoclinic crystal when kept in the atmosphere of 200 ° C. for 3000 hours can be 10% by volume or less.

Further, in order to make the present invention most effective, the above 3
In the triangular coordinate of FIG. 1 the amount of component, the point _{F (ZrO 2 88mol%, YO} 1.5 10mol%, CeO 2 2mol%) point _{G (ZrO 2 89mol%, YO} 1.5 10mol%, CeO 2 1mol%) point _{L (ZrO 2 93.5mol%, YO} 1.5 4mol%, CeO 2 2.5mol%) point _{M (ZrO 2 93mol%, YO} 1.5 2mol%, CeO 2 5mol%) point _{N (ZrO 2 88mol%, YO} 1.5 1mol%, CeO ₂ 11mol%) It is recommended to select within the range surrounded by the solid line connecting the points K (ZrO ₂ 86mol%, YO _1.5 1mol%, CeO ₂ 13mol%). If the composition of zirconia is selected within this range, the amount of monoclinic crystals when the sintered body is held in saturated steam at 180 ° C (10 atm) for 20 hours can be 20% by volume or less. Also, in the atmosphere of 200 ℃ 3
The amount of monoclinic crystals when kept for 000 hours can be reduced to 5% by volume or less.

In the present invention, zirconia (ZrO ₂ ) containing yttrium oxide and cerium oxide is 50 to 98% by weight, and alumina (Al ₂ O ₃ ) and spinel (MgO.Al) are dispersed components.
_At least 1 of ₂ O ₃ ) and mullite (3Al ₂ O ₃ · 2SiO ₂ ).
It contains 50% to 2% by weight of seeds or more. If the proportion of these dispersing components is less than 2% by weight, it is difficult to obtain the effect of increasing the strength and improving the stability of heat and hot water by adding the dispersing components.
If it exceeds 50% by weight, the strengthening mechanism due to tetragonal zirconia decreases and the expected strength cannot be obtained. In order to make the present invention more effective, it is advisable to select the content of these dispersion components in the range of 5 to 40% by weight. More preferably, the range of 10-35% by weight is good. That is, if the dispersion component is selected in this range, the heat and hot water stability will be extremely excellent due to the synergistic effect with the CeO ₂ component which is a stabilizer of zirconia.

The sintered body of the present invention must have a three-point bending strength of 150 kgf / mm ² or more. Within the composition of the present invention, yet satisfy the heat and hot water stability shown in the present invention, and the strength is 150k
This is because a sintered body having a gf / mm ² or more is considered to be remarkably excellent.

Further, it is necessary that the bulk density of the sintered body is 99% or more of the theoretical density or the porosity is 1% or less. When the theoretical density is lower than 99% or the porosity is higher than 1%, the strength of the sintered body is low, and the heat and hydrothermal stability is low. That is, the higher the bulk density, the more stable the tetragonal zirconia contained in the sintered body, and the more excellent the heat resistance and the hot water stability.

The pores contained in the sintered body are preferably 30 μm or less. If it has large pores of 30 μm or more, a high strength sintered body cannot be obtained. More preferably, it is 20 μm or less.

Further, the color of the sintered body of the present invention is similar to the color of the sintered body of the composition in the air, that is, white or milky white or light yellow, and is colored by a reducing or non-oxidizing atmosphere, that is, reddish brown or It is necessary that it does not appear dark brown or black. That is, this is the result of performing the HIP treatment using a gas containing oxygen as a pressure medium, by defining the color of the sintered body in this manner, the high-strength zirconia-based ceramics of the present invention and the conventional HIP treatment. It can be completely distinguished from the high-strength zirconia-based sintered body used.

Since the zirconia sintered body having the composition of the present invention is a partially stabilized zirconia mainly composed of tetragonal crystals, it exhibits high strength and high toughness. Since the tetragonal system is a metastable phase by nature, a part of the sample surface is transformed into a monoclinic structure by grinding and the residual compressive stress of the surface layer contributes to strengthening of the sintered body. The degree of this strengthening depends on the surface roughness due to grinding and the grain size of the sintered body. Therefore, the partially stabilized zirconia mainly composed of tetragonal crystals according to the present invention means zirconia containing at least 50% or more of tetragonal system in a mirror state in the measurement of the crystal phase by X-ray diffraction.

The content of each sill phase in the zirconia sintered body is measured by X-ray diffraction based on the polymorphic crystal quantification method. X
Hereinafter, the integrated intensity of the line diffraction peak is simply referred to as the integrated intensity. Since the lattice constants of tetragonal and cubic crystals of zirconium oxide are close to each other, the peaks are very close to each other in low-angle diffraction and cannot be separated.Therefore, the integrated intensity of the monoclinic peak and the tetragonal and cubic peaks cannot be separated. The quantitative ratio of the integrated intensity sum (monoclinic / tetragonal + cubic) is measured, and the quantitative ratio of both is obtained from the integrated intensity of the tetragonal and cubic peaks at a high angle where the tetragonal and cubic peaks are separated. (Tetragonal + cubic) is measured,
Calculate the amount of each crystal. The specific calculation method of each crystal amount of zirconia by X-ray diffraction is as follows.

(1) Measurement of integrated intensity Mixed integral intensity of tetragonal <111> and cubic <111>
I _{T + C} 〈111〉 Integrated intensity of monoclinic crystals 〈11〉 and 〈111〉 ・ ・ ・ I _{M + C} 〈11
〉, I _M 〈III〉 Integral intensity of tetragonal 〈004〉 and 〈400〉 ・ ・ ・_IT 〈00
4>, I _T <400> Integral intensity of cubic <400> ... I _C <400> (2) The content of each crystal phase was determined as the volume% by the following formula.

Cubic Zirconium Oxide (Volume)% C = 100-MT ... (III) The sintered body of the present invention has an average crystal grain diameter of 2 μm.
It must be: It is preferably 1 μm or less. This is because when the average crystal grain size exceeds 2 μm, the transformation from tetragonal to monoclinic is likely to occur in a hot and hot water environment. The thermal stability of the zirconia sintered body largely depends on the particle diameter of the sintered body, and the smaller the particle diameter, the more improved the stability. In the case of the sintered body of the present invention, since it contains cerium oxide (CeO ₂ ) as a stabilizer, as compared with yttrium oxide partially stabilized zirconia that does not contain this, the critical particle diameter depends on the composition, The size is several times to about 5 times, and the stability is extremely high.

In addition, in the present invention, 20 ° C in steam at 180 ° C (10 atm) is used.
The amount of monoclinic crystals of zirconia crystals on the surface of the sintered body after holding for a while
It is necessary to be 30% by volume or less, preferably 20% by volume or less. More preferably, it is 10% by volume or less. Further, the amount of monoclinic zirconia crystals on the surface of the sintered body after being kept in the air at 200 ° C. for 3000 hours needs to be 20% by volume or less, preferably 10% by volume or less, more preferably 5% by volume or less. Is good. Because under these conditions,
By setting the upper limit of the deterioration with time, it is possible to completely distinguish it from the conventional yttria-based high-strength zirconia sintered body.

In addition, the strength of the sintered body after holding for 1500 hours in the atmosphere at 1000 ° C
It must be 150 kgf / mm ² or more. This is because it can be distinguished from the conventional zirconia-based sintered body using general HIP sintering.

The average particle size of the sintered body is measured by the following method.

The average particle diameter is determined by the following formula after observing with a scanning electron microscope after etching a sintered body having a mirror surface.

Average particle size; average length of 50 or more particles that cross a line segment that is arbitrarily drawn.

The present invention is characterized by hot isostatic pressing (hereinafter abbreviated as HIP), and in particular, the present invention is characterized by performing HIP treatment using a gas containing oxygen as a pressurizing medium. . A carbon heater is used for general HIP, but for HIP treatment in an oxidizing atmosphere using the gas containing oxygen of the present invention as a pressure medium, it is used in an electric furnace used in the atmosphere. A heating element, for example, iron-chromium-aluminum-cobalt-based or nickel-chromium-based heating can be used for use at 1400 ° C or lower, and a silicon carbide-based or molybdenum disilicide-based heating element or platinum for higher temperatures. A heating element or a zirconia-based heating element can be used.

Regarding the temperature and pressure conditions for HIP processing, 1200 to 1600
The temperature is preferably in the range of 50 to 500 MPa. Under the conditions of pressure less than 50 MPa and temperature less than 1200 ° C, it is difficult to obtain the expected high strength sintered body. Also. At temperatures above 1600 ° C, it is possible to obtain high strength, but the sintered body particles grow into grains, resulting in inferior heat and hydrothermal stability, and industrial use as a practical material. Not suitable as a material. The present invention is characterized in that a gas containing oxygen is used as the pressurizing medium, and a gas containing 0.1% or more of oxygen is preferable.

The pre-sintered body to be subjected to the HIP treatment must have a relative density of 95% or more. Relative density is 95
If it is less than%, open pores will remain in the sintered body, and sufficient densification by HIP treatment cannot be achieved.

In order to obtain a sintered body composed of such dense and fine particles, it is preferable to use fine powder having excellent sinterability as a starting material. That is, as a mixed powder,
It is preferable to use a powder obtained by finely pulverizing a thermal decomposition product of an oxide of zirconium, yttrium, cerium, aluminum, magnesium, silicon or a compound thereof. Specifically, as a zirconia raw material, fine powder obtained by a wet method having a primary particle diameter of 0.1 μm or less is used.
Further, it is desirable to use a high-purity fine powder having a primary particle diameter of 0.5 μm or less as a raw material for the dispersion component of alumina, spinel, and mullite. Further, a sol of zirconium oxide and / or a water-soluble salt containing zirconium, Y ₂ O ₃ ,
It is also preferable to use a fine powder synthesized by a coprecipitation method from an aqueous solution containing a water-soluble salt of CeO ₂ . As for alumina, alumina sol and / or
Alternatively, it can be prepared by a coprecipitation method in addition to zirconium oxide as a salt of aluminum.

The mullite (3Al ₂ O ₃ .2SiO ₂ ) used in the present invention may be either a natural raw material or a synthetic raw material, but is preferably fine powder and easily sinterable. Such fine and easily sinterable raw material powder is obtained by, for example, mixing a solution containing an aluminum compound and a solution containing a silicic acid compound in a liquid phase, followed by drying, calcination at 800 to 1500 ° C., and pulverization. .

The partially-stabilized zirconia contained in the sintered body of the present invention is prepared by uniformly mixing a sol of ZrO ₂ and / or a water-soluble salt with a water-soluble salt of a stabilizer in a solution state, and then precipitating Since the raw material obtained by separating in a form is used, the stabilizer can be uniformly dispersed in ZrO _2, and the easily sinterable powder made of extremely fine particles can be used as the raw material. As a result, a sintered body having a fine powder and a uniform composition and almost no micropores can be obtained, and desired values can be obtained for mechanical and thermal characteristics.

ZrO ₂ of the zirconia sintered body of the present invention is part of HfO ₂
Even if it is replaced by, the same characteristics are exhibited.

[Examples] Examples of the present invention will be described in detail below to clarify the effects of the present invention.

(Example 1) Aluminum nitrate and ethyl silicate were mixed with water and ethanol so as to have a mullite composition, and the mixed solution was spray-dried at 600 ° C. 1000-130 the obtained synthetic powder
By calcination at 0 ℃ and crushing, the specific surface area is 50
〜10m ² / g, Al ₂ O ₃ / SiO ₂ ratio 71.8 / 28.2 mullite (3Al ₂
O ₃ · 2SiO ₂ ) was prepared. In addition, this synthetic mullite is 160
Sintering at 0 ° C showed a density of 3.17.

Next, add 99.9% pure yttrium chloride and 99.9% pure cerium chloride to an aqueous solution of 99.9% pure zirconium oxychloride, and mix them uniformly so that the powders obtained are in the proportions shown in Tables 1 and 2. The solution was coagulated with alkali (6N ammonia water) to form a hydroxide precipitate, which was washed, dehydrated and dried, calcined at 900 ° C for 2 hours, and wet-ground in a ball mill for 48 hours to partially stabilize zirconia powder. Got This powder had an average particle size of 0.5 μm and a specific surface area of 25 m ² / g.

This powder contains Al with an average particle size of 0.3 μm and a purity of 99.9%.
₂ O _3, an average particle diameter of 0.3 [mu] m, in addition 99.9% pure MgO · Al ₂ O _3, and a synthetic mullite powder as described above at a ratio in Table 1 and Table 2, the molding aid added after the wet mixing and drying The resulting powder is isotropically molded at a pressure of 1.5 ton / cm ² and 1200 to 1500 ℃
It was baked in the atmosphere at the temperature of. The samples shown in Table 1 (1) and (2) were all pre-sintered at 1400 ° C. The obtained pre-sintered body had a relative density of 95% or more with respect to the theoretical density and an average particle diameter of 0.1 to 0.5 μm.

The pre-sintered body thus obtained has a temperature of 1200 to 1600 ° C.
550kgf / cm ² (53.9MPa), 1000k in an Ar gas atmosphere containing 0.1 to 5% oxygen as a pressurizing medium using a platinum heating element.
gf / cm ² (98MPa), 1500kgf / cm ² (147MPa), 2000kgf / cm
Hot isostatic pressing (HIP) treatment was performed at a pressure of ² (196 MPa). Further, as a comparative example, HIP treatment using a carbon heating element was performed in an Ar gas atmosphere containing no oxygen.

The obtained sintered body was measured for bulk density, porosity, flexural strength, average particle size, crystal phase before and after heat and hot water deterioration test by X-ray diffraction. The various physical properties were measured as follows.

a) The bending strength is 3 × 4 × 40m according to JIS-1601-1981
m sample piece, span 30 mm, crosshead speed 0.5 mm
Bending was performed at 3 points / min.

b) The quantification of the crystal phase is based on the X-ray diffraction method described above.

c) For the bulk density, the Archimedes method was used.

d) The porosity was measured by image processing.

e) In the hot water deterioration test, the physical properties of the sample that was autoclaved in saturated steam at 180 ° C (10 atm) for a certain period of time according to the heating cycle shown in Fig. 2 and kept at 180 ° C for a total of 20 hours were measured. did. The quantification of the monoclinic crystals after the hot water deterioration test was performed on the surface of the sintered body by the X-ray diffraction (I) formula.

f) In the heat deterioration test, the sample was taken out after being kept in an electric furnace at 200 ° C. for 3000 hours, and the physical properties of the sample subjected to the treatment were measured. After the heat deterioration test, the monoclinic crystal was quantified on the surface of the sintered body by the X-ray diffraction (I) formula.

g) In the high temperature aging test, the sintered body sample was taken out after being held in the air in an electric furnace at 1000 ° C. for 1500 hours, and the bending strength was measured.

The results of the above measurements are also shown in Tables 1 and 2.

Table 1 shows the composition of YO _1.5 , CeO ₂ and ZrO ₂ in this order from left to right (2.5, 6, 91.5) or (4, 4, 9).
2) Keep it constant and disperse components Al ₂ O ₃ , MgO ・ Al ₂ O ₃ , 3A
The porosity, the average particle size, the crystal phase of ZrO ₂ , and the bending strength were measured by changing the pre-sintering temperature and the HIP treatment conditions while gradually increasing the addition amount of l ₂ O ₃ · 2SiO ₂ . Samples in Table 1
No1, No8, No10, No12 are comparative examples without HIP treatment, sample No2 is a comparative example containing no dispersant component,
In both cases, the strength of the sintered body is low. Samples No17 and No19 are comparative examples in which HIP processing was performed using a carbon heater.
The sample is colored dark brown and has a lower strength than that of the present invention, and at a temperature near 1600 ° C., grain growth occurs and the strength is significantly reduced. Sample No. 20 is a comparative example in which the HIP treatment temperature is higher than the range of the present invention, and it can be seen that the bending strength is reduced due to grain growth. Sample Nos. 25 to 27 are
This is a comparative example in which the amount of the dispersed component is larger than the range of the present invention, and the bending strength is low. On the other hand, Sample No. 3 which is an example of the present invention
7, 9, 11, 13 to 16, 18, 21 to 24, 28 to 41 have a porosity of 1% or less, and are sintered bodies made of fine particle crystals, and have a high bending strength of 150 kgf / mm ² or more. It was confirmed to show. Further, when the sintered body of the present invention was observed by an electron microscope.
No pores larger than 30 μm were found.

Table 2 shows that the amount of dispersed components was fixed at 20%, the pre-sintering temperature and HIP treatment conditions were kept constant, and the composition of the stabilizers YO _1.5 and CeO ₂ contained in zirconia were changed to obtain porosity, ZrO
After measuring the crystalline phase of ₂ (monoclinic ZrO ₂ content) and bending strength,
00 were measured crystal phase change after holding change of ZrO ₂ crystal phase (monoclinic ZrO ₂ amount) and 180 ° C. 10 atm in saturated steam 20 hours after holding in 3000 hours electric furnace at ° C. It is a thing. Sample No. 1 in Table 2, 3-4, 9-10, 15-16, 21-2
2, 27, 31, 35, 37 are comparative examples in which the composition of the stabilizer contained in zirconia is outside the scope of the present invention, sufficient bending strength is not obtained, or heat deterioration test or heat Before and after the water deterioration test, the amount of monoclinic zirconia was large and the deterioration was remarkable.

On the other hand, sample Nos. 2 to 5 and 8 to 11 which are examples of the present invention
4, 17-20, 23-26, 28-30, 32-34, 36 have a porosity of 1% or less, the amount of monoclinic zirconia is almost zero, there is no heat deterioration, and there is little hot water deterioration. It was confirmed to show excellent strength. Also, when observed with an electron microscope,
No pores larger than 30 μm were found.

(Example 2) The sintered body produced by the method described in Example 1 was subjected to a heat deterioration test at 200 ° C for 3000 hours and at 180 ° C.
Autoclave treatment was performed for 20 hours in saturated steam at 10 atm, and a hydrothermal deterioration test was performed. Changes in the zirconia crystal phase before and after the test (changes in the amount of monoclinic zirconia crystal phase) and changes in the strength of the sintered body were performed. The measurement was carried out and the results are shown in Table 3. In addition,
In this example, in order to grasp the extent of deterioration from the sample surface to the inside, the bending strength of the sintered body was measured according to JIS standard 1
The test was performed using a sample (1.0 × 4.0 × 40 mm) with a thickness of / 3.

Table 3 shows the thermal deterioration and hot water deterioration test results of the HIP-treated sintered bodies for the main compositions. Sample No
2, 17 is a comparative example of partially stabilized zirconia sintered body not subjected to HIP treatment outside the composition of the present invention, but both have low bending strength, No2 does not contain a dispersant component, so in the hot water deterioration test Deterioration is remarkable. Further, No17 does not contain a CeO ₂ component as a stabilizer, and does not contain a dispersing component such as Al ₂ O ₃ ,
Heat deterioration and hot water deterioration are remarkable. Sample No14 ~ 15, No18 ~
No. 19 does not contain a CeO ₂ component as a stabilizer, and is a sintered body obtained by the conventional HIP treatment using a carbon heater, but its thermal deterioration and hot water deterioration are remarkable. Sample No16
Is a high-strength zirconia sintered body containing alumina, which does not contain CeO ₂ as a stabilizer, in an atmosphere containing oxygen.
Although it is a comparative example subjected to HIP treatment, it shows excellent strength before the test, but since it does not contain CeO ₂ as a stabilizer, it is significantly deteriorated by heat and hot water.

In comparison with this, Sample No. 1, No. 3 to 13, Sample No. 20, which are examples of the present invention, have excellent strength of 150 kgf / mm ² or more, and even after heat and hot water deterioration test, they are monoclinic from tetragonal zirconia. It was confirmed that the amount of transition of the crystalline phase to the crystalline zirconia was zero or extremely small, and the strength was 150 kgf / mm ² or more even after the test, and the thermal stability and the hot water stability were excellent.

(Example 3) The sintered body produced by the method described in Example 1 was subjected to a high temperature thermal deterioration test in which it was kept in an electric furnace at 1000 ° C for 1500 hours, and the strength of the sintered body at room temperature before and after the test was measured. The results are shown in Table 4.

Table 4 shows the pre-sintering temperature, HI
P treatment temperature, HIP pressure constant, using the platinum heater is an example of the present invention, when performing the HIP treatment using a gas containing oxygen as a pressurizing medium, and using a carbon heater as a comparative example In the case where the HIP treatment of No. 2 was performed, each sintered body was held at high temperature for a long time and the change in strength was examined. As is clear from Table 4, the strength of all the HIP-treated bodies using the carbon heaters of the comparative examples is significantly reduced after the test. On the other hand, HI using the oxygen-containing gas of the present invention as a pressure medium
It was confirmed that the P-treated body maintained high strength.

EFFECTS OF THE INVENTION The high-strength zirconia-based small sintered body of the present invention is, as described above, at least one selected from zirconia containing a predetermined amount of yttrium oxide and cerium oxide as a stabilizer, alumina, spinel, and mullite. As a result, the theoretical density and bending strength could be maintained at higher levels than conventional products by controlling the crystal phase and crystal particle size, and by HIP processing using oxygen-containing gas as a pressurizing medium. Further, it has an effect that it has higher strength than the conventional zirconia sintered body, has no change in strength even after being kept at high temperature for a long time, and has excellent heat and hot water stability.

The high-strength zirconia-based sintered body of the present invention is a conventional cutting tool, a die, a nozzle, a mechanical structural material such as a bearing, of course, among them, a field requiring strength and durability, that is, thermal stress, Parts subject to mechanical stress or thermal stress such as thermal shock stress, repeated thermal stress, such as abrasion-resistant ceramics screw for thermoplastic resin or ceramics injection molding machine, brass rod or copper pipe shell, or heat of aluminum, aluminum alloy, etc. It is the most suitable material for hot extrusion dies.

It can also be used for engine parts such as engine cylinder liners, piston caps, cylinder heads, valves, valve guides, exhaust ports, rocker arms, tip auxiliary combustion chambers, tappets, cams, bearings, and gas turbine parts.

Furthermore, parts exposed to chemicals such as acids or alkalis, for example, rotors of acid-resistant pumps, sealing materials, and cutting tools such as scalpels, scissors, knives, knives, industrial cutters, etc., parts for crushing machines, sliding members, Artificial bones, artificial joints, artificial tooth crowns, bridge teeth materials for artificial teeth made of cast ceramics, artificial tooth roots, artificial tooth root core materials, cutting tools, application to machine tools such as gauges and practical application, and greatly contributing to performance improvement It is widely used as an industrial material. It is extremely useful industrially.

[Brief description of drawings]

Fig. 1 shows ZrO ₂ and Y on three axes intersecting an equilateral triangle.
Triangular coordinates showing the composition range of the present invention by displaying mol% of O _1.5 and CeO ₂ , and FIG. 2 is a diagram showing a relationship between temperature and time showing a heating cycle of a hot water deterioration test.

Claims (5)

(57) [Claims] 1. 50 to 98% by weight of partially stabilized zirconia mainly containing tetragonal crystals or tetragonal and cubic crystals containing yttrium oxide (Y ₂ O ₃ ) and cerium oxide (CeO ₂ ) as a stabilizer, and a dispersion component. alumina (Al ₂ O _3), spinel _{(MgO · Al 2 O 3)} , consists of a 50-2% by weight of at least one or more of mullite _{(3Al 2 O 3 · 2SiO 2} ), the average crystal of the sintered body By hot isostatic pressing using a gas having a particle size of 2 μm or less, a bulk density of the sintered body of 99% or more of the theoretical density or a porosity of 1% or less, and a gas containing oxygen as a pressurizing medium. A high-strength zirconia-based HIP sintered body characterized by exhibiting a color similar to that of a sintered product of the composition in air. 2. Partially stabilized zirconia has three axes in which yttrium oxide (Y ₂ O ₃ ) and cerium oxide (CeO ₂ ) contained therein intersect in an equilateral triangle as shown in the accompanying drawings.
Point A (ZrO ₂ 87.5mol%, YO _1.5 12mol%, CeO ₂ 0.5mol%) Point B (ZrO ₂ 95.5mol%, YO _1.5 4mol%, in the triangular coordinates showing ZrO ₂ , YO _1.5 , CeO ₂ CeO ₂ 0.5mol%) Point C (ZrO ₂ 95.5mol%, YO _1.5 2mol%, CeO ₂ 2.5mol%) Point D (ZrO ₂ 92.5mol%, YO _1.5 0.5mol% CeO ₂ 7.0mol%) Point E (ZrO ₂ 85mol%, YO _1.5 0.5mol%, CeO ₂ 14.5mol%) The high-strength zirconia according to claim 1, which has a composition within a range surrounded by a line connecting specific 5 composition points. System HIP sintered body. 3. The high strength according to claim 1 or 2, wherein the amount of monoclinic crystals of the zirconia crystals after holding in saturated steam at 180 ° C (10 atm) for 20 hours is 30% by volume or less. Zirconia-based HIP sintered body. 4. A zirconia crystal having a monoclinic amount of 20% by volume or less after being kept at 200 ° C. in the atmosphere for 3000 hours, according to any one of claims 1, 2 and 3. High-strength zirconia-based HIP sintered body. 5. The three-point bending strength of the sintered body at room temperature is 150 k.
gf / mm ² or more, and the three-point bending strength of the sintered body after holding for 1500 hours in the air at 1000 ° C. is 150 kgf / mm ² or more. Claims 1, 2, 3 or The high-strength zirconia-based HIP sintered body according to any one of items 4.