JPS62252368A - Zirconia sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a zirconia sintered body.

There are various conventional zirconia sintered bodies, but JP-A-59-2
In Japanese Patent No. 27770, a zirconia sintered body is obtained by hot pressing or hot isostatic pressing a zirconia powder containing a stabilizer in a graphite mold in an inert atmosphere.

There is a description that this sintered body exhibits a black color and has high heat resistance and toughness. However, because this sintered body uses a graphite mold and is sintered in an inert atmosphere, carbon remains, and this carbon remains when the sintered body is used at high temperatures of 600'C or higher. When this happens, it evaporates into carbon dioxide gas, creating pores and greatly reducing its strength.

Furthermore, JP-A-60-191056 discloses zirconia with a cubic crystal structure (cubic zirconia) and zirconia with a tetragonal crystal structure (tetragonal zirconia).
A zirconia sintered body is described in which (a) coexists with tetragonal zirconia and in which tetragonal zirconia is precipitated within the grains of cubic zirconia.

When this sintered body is subjected to thermal shock or external stress, the tetragonal zirconia transforms into zirconia with a monoclinic structure (monoclinic zirconia), expands, and causes compressive stress in the vicinity. It is said that mechanical properties, particularly toughness and strength, are improved because it acts to alleviate applied thermal shock and stress by generating microscopic cracks. This is a relaxation effect due to a so-called stress-induced transformation mechanism. However, since the tetragonal zirconia at the grain boundaries of cubic zirconia, where the stress-induced transformation mechanism acts most prominently, is not taken into consideration, the above-mentioned improvement effect is not so great.

In general, Japanese Patent Application Laid-open No. 57-111278 discloses that the zirconia contains 5 to 70 mol% of tetragonal zirconia and has a porosity of 2 to 1.
0% zirconia sintered body is described. It is said that this sintered body also has improved thermal shock strength and mechanical strength due to the stress-induced transformation mechanism. However, the improvement in mechanical strength is not so remarkable because the porosity is relatively high at 2 to 10%, and the variation is large. It also has the disadvantage of low toughness. Furthermore, its corrosion resistance is low due to its high porosity.

Problems to be Solved by the Invention The purpose of the invention is to solve the above-mentioned drawbacks of conventional sintered bodies,
To provide a zirconia sintered body that not only has high mechanical properties, particularly toughness and strength, and has extremely small variations, but also shows almost no decrease in strength even when used at high temperatures of 600'C or higher, and has excellent corrosion resistance. I'm in the middle of the day.

Means for Solving the Problems In order to achieve the above object, in this invention, zirconia having a cubic crystal structure and zirconia having a tetragonal crystal structure coexist, and zirconia having a tetragonal crystal structure coexists. Zirconia, which has a crystal structure of The amount of zirconia with a tetragonal crystal structure present in
．． Contains 5 mol%, contains substantially no carbon, and has a porosity of 0.
Provided is a zirconia sintered body characterized in that the content of zirconia is 6% or less.

Hereinafter, the zirconia sintered body of the present invention will be explained in detail along with its manufacturing method.

In this invention, first, an aqueous solution of zirconium chloride with a purity of 99.9% or more and an aqueous solution of yttrium chloride with a purity of 99.5% or more are mixed in an amount of 3.5 to 5.5 yttrium as yttrium. After mixing so that the average particle size is 0.1 μm or less using a well-known coprecipitation method, hydrolysis method, thermal decomposition method, metal alkoxide method, sol-gel method, gas phase method, etc. A zirconia powder is prepared. Alternatively, it is possible to use an aqueous solution of zirconium nitrate and yttrium nitrate, or to mix zirconia powder and yttrium powder.

Next, the above powder was calcined at 800 to 1000'C,
Grind with a ball mill, attrition mill, etc. The calcination and pulverization are repeated as necessary to obtain a raw material powder. This raw material powder forms a solid solution in which zirconia powder and ittria powder are uniformly mixed. Zirconia in a solid solution usually forms a mixed phase of monoclinic and tetragonal systems, although this varies depending on the purity of the zirconia or yttria used, the particle size, the amount of yttria, the calcination temperature, the calcination time, etc. There is.

Next, the above raw material powder is processed by rubber press method, injection molding method,
A molded body is obtained by molding into a desired shape using a well-known molding method such as a mold molding method, an extrusion molding method, or a doctor blade 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 30-50''C/hour above that.
Raise the temperature to 1100-1550'C at a rate of 'C/hour, hold at that temperature for several hours, then increase the temperature to 200-500'C.
The presintered body is cooled at a rate of C/hour to obtain a presintered body having a key density of at least 95% of the theoretical density, preferably at least 97.5%. In the process of increasing temperature, the crystal structure of zirconia transforms from a monoclinic and tetragonal coexistence state to a cubic system or a tetragonal and cubic coexistence state. The temperature and speed of such crystal structure transformation vary depending on the amount of ittria, the amount of impurities, etc. Therefore, while referring to the phase diagram, the preliminary sintering temperature to obtain the above-mentioned crystal structure is determined within the above-mentioned range. During the cooling process, some of the tetragonal zirconia may transform into monoclinic zirconia.

Next, the preliminary sintered body is subjected to so-called main sintering using a hot isostatic pressing method (HIP method) in an oxidizing atmosphere. That is, the pre-sintered body is heated in a controlled oxygen atmosphere, that is, in an oxidizing atmosphere.
1100~ under pressure of 1000~2000KO/cm2
Heat at 1500°C for several hours to sinter. The oxygen concentration during sintering is 11,000 pp to 40% by volume. 1100
If it is less than 0pp, the oxygen concentration is too low and the sintered body will be reduced by the gas released from the constituent materials of the furnace.
Carbon and carbon monoxide will remain in the sintered body. In addition, in a high concentration oxygen atmosphere exceeding 40% by volume,
This is not practical because the ignition point of the members constituting the processing furnace is significantly lowered and the life of the furnace is significantly shortened.

By the way, there are two methods for processing using the HIP method.

One method is to place the compact into a glass or metal container (capsule) and subject it to treatment, and the other method is to obtain a pre-sintered compact whose key density is 95% or more of the theoretical density, as described above. This method involves subjecting it to processing after it has been processed. The former has the advantage of being able to obtain a dense sintered body even at relatively low temperatures and does not require a high-density pre-sintered body. Not suitable for manufacturing. Although the latter does not have such shape restrictions, it is necessary that the pores of the preliminary sintered body be closed pores rather than open pores because of pressurization with gas. In this respect, there is no problem because most of the pores in a pre-sintered body whose key density is 95% or more of the theoretical density are closed pores.

According to such a HIP method, the bond between crystal grains becomes strong, and a dense sintered body can be obtained even at low temperatures, and the mechanical properties of the sintered body are improved. In the former case, the raw material powder may be placed in the container instead of the molded body. In that case, of course, no molding operation is required.

In any case, the HIP process is performed in an oxidizing atmosphere. This is because the HIP method uses a heater made of carbon or other material and is normally carried out in an inert atmosphere such as an argon atmosphere, but when doing so, trace amounts of carbon and carbon monoxide may remain in the sintered body. Become. However, when such a sintered body is used at a high temperature of 6oo'c or higher, the remaining carbon and carbon monoxide become carbon dioxide gas and evaporate, creating pores in the sintered body and causing the failure of the sintered body at high temperatures. The strength and room temperature strength after use at high temperatures are significantly reduced.

During the above-mentioned sintering, zirconia again assumes a cubic system or a mixed phase of a tetragonal system and a cubic system. Cooling (the crystal structure of poly
During the cooling process, a part or most of the cubic zirconia changes to tetragonal zirconia, and roughly a part of the tetragonal zirconia changes to monoclinic zirconia, although this varies depending on the cooling rate of the sintering process. In the coexistence state of tetragonal zirconia and cubic zirconia, a part of the tetragonal zirconia changes to monoclinic zirconia, a part or a large part of the cubic zirconia changes to tetragonal zirconia, and then the tetragonal zirconia changes to monoclinic zirconia. A portion of it turns into monoclinic zirconia. Eventually, the zirconia sintered body changes to a state in which tetragonal, monoclinic, and cubic zirconia coexist. However,
The amount of square zirconia varies depending on various conditions such as the purity, particle size, and composition of the pigment powder, the density of the pre-sintered body, the temperature and time of the main sintering, and the cooling conditions after the main sintering. Therefore, it is necessary to strictly control these conditions during manufacturing.

Next, the zirconia sintered body of the present invention is cooled from the above sintering temperature to 1100 to 1400° C. at a rate of 60 to 500° C./hour and heat-treated at that temperature to obtain 1 q of zirconia sintered body of the present invention. However, this heat treatment may be performed by cooling the sintered body at a rate of -H200 to 500'C/hour and then heating it again to the above temperature. By this heat treatment, tetragonal zirconia precipitates at the grain boundaries of cubic zirconia grows, and tetragonal zirconia precipitates within the grains. However, if the heat treatment is performed at too low a temperature and for a short time, the precipitation and growth of the tetragonal zirconia will be insufficient.On the other hand, if the heat treatment is performed at a high temperature for a long time, the crystal grains will grow and become coarse.
When carried out at a relatively low temperature of 1200° C., the time is preferably 1000 hours or more, and when carried out at a relatively high temperature of 1250 to 1400'C, it is preferably within several hundred hours.

In the zirconia sintered body of this invention, cubic zirconia is used as a so-called matrix, and each crystal grain has a fine grain shape, plate shape, lath shape, spherical shape, ellipse shape, or a complex combination of these shapes. Tetragonal zirconia in a geometric mosaic shape is dispersed and precipitated. Further, at the grain boundaries of cubic zirconia, tetragonal zirconia, which is smaller than the cubic zirconia but has a similar shape, is precipitated.

When a thermal shock or external stress is applied to the sintered body, the tetragonal zirconia in the grains undergoes martensitic transformation to monoclinic zirconia, growing a compressive stress field and fine cracks, and relaxing the applied stress. , improve the mechanical properties of the sintered body, especially the toughness and strength. However, tetragonal zirconia in the grains is stable against the martensitic transformation at temperatures above 600'C, and although strength development due to this cannot be expected, as a result of suppressing the growth of microcracks, toughness and Improve strength. However, this inhibitory effect has very little temperature dependence. The most effective size of square zirconia is 0.03 to 0.2 μm.

On the other hand, tetragonal zirconia existing in the grain boundaries of cubic zirconia exhibits excellent strength development effects due to stress-induced transformation mechanism at temperatures below 1000'C, but its temperature dependence is large, and as the temperature increases The effectiveness decreases rapidly as the temperature increases. The preferred size of the grain boundaries of tetragonal zirconia is 0.
It is 1 to 0.7 μm.

The total amount of square zirconia in the zirconia sintered body must be 30 to 80 mol%.

That is, if it is less than 30 mol%, the stress-induced transformation mechanism will not work sufficiently, and the mechanical properties will not improve. On the other hand, if it exceeds 80 mol%, the amount of cubic zirconia in particular becomes too small, martensitic transformation becomes too significant when the sintered body is used at high temperatures, and the mechanical strength also decreases significantly.

Now, as mentioned above, the tetragonal zirconia is precipitated within the grains and at the grain boundaries of the cubic zirconia, and it is necessary that the amount of the tetragonal zirconia at the grain boundaries is 5 to 60 mol %. Preferably it is 5 to 40 mol%. In other words, if it is less than 5 mol%, no improvement in strength at room temperature due to the stress-induced transformation mechanism can be expected, while if it exceeds 60 mol%, the amount of intragranular tetragonal zirconia will be too small, resulting in poor thermal stability and strength at high temperatures. The decline becomes significant. Therefore, the total amount of tetragonal zirconia and the amount of tetragonal zirconia within the grains and at the grain boundaries are determined by taking into consideration, for example, the variation between room temperature strength and high temperature strength, and the balance between stability and strength.

Here, it is difficult to determine the amount of tetragonal zirconia at the grain boundaries separately from that within the grains using general X-ray diffraction methods. Therefore, the following measurement method is adopted.

That is, the sintered body is optically polished to a roughness of 150 to 180
After etching with sulfuric acid at °C for 20 to 30 minutes, the amount of ittria was analyzed using an X-ray microanalyzer with a scanning electron microscope. Then, it can be divided into crystal grains in which the amount of iso1 to ria is 2 to 4 mol% and crystal grains in which the amount is 6 to 8 mol%.

Therefore, the amount of tetragonal zirconia at the grain boundary is defined as a crystal grain containing 2 to 4 mol % of ittria. Note that the difference between the total amount of tetragonal zirconia obtained by the X-ray diffraction method described below and the tetragonal zirconia at the grain boundary is the amount of tetragonal zirconia within the grain.

Total strength of square zirconia in zirconia sintered body C
The mol% is determined as follows.

That is, the sintered body is polished with a #150 to #300 grindstone and further polished with a diamond paste. Then, the surface of the polished sintered body was subjected to X-ray diffraction, and the diffraction intensity (area intensity; hereinafter the same) of the tetragonal zirconia 111 plane was determined.
, the diffraction intensity B of the monoclinic zirconia 111 plane, and the diffraction intensity C of the monoclinic zirconia 111 plane are determined, and the calculation is made from them using the following equation. However, for the diffraction intensity, the value after correction by the Lorentz factor is used.

CT= [A/ (A+B+C)]

CC= [D/ (D10E10F>] X100 However,
D = Diffraction intensity of 400 planes of vertical cubic zirconia E: Diffraction intensity of 004 planes of tetragonal zirconia F: Diffraction intensity of 400 planes of tetragonal zirconia Once the amounts of tetragonal zirconia and cubic zirconia are determined,
The remainder is monoclinic zirconia, but since monoclinic zirconia forms microcracks and compressive stress fields around it, if the amount thereof becomes extremely large, the strength and toughness of the sintered body will decrease.

Therefore, it is preferable that the amount of monoclinic zirconia is 10 mol% or less. Furthermore, the presence of cubic zirconia improves the thermal stability of the sintered body, since cubic zirconia has the highest thermal stability among zirconias.

The sintered body in this invention contains 3.5 to 5.5 mol% of ittria as a zirconia stabilizer.

This range of 3.5 to 5.5 mol% is a necessary condition for making the total amount of tetragonal zirconia 30 to 80 mol% and setting the tetragonal zirconia in the grain boundaries to 5 to 60 mol%. However, this is not a sufficient condition. In other words, the amount of square zirconia is determined by the amount of raw material powder,
It also varies depending on the preliminary sintering conditions, main sintering conditions, etc.

Only when these conditions and the amount of ittria work together will the total amount of tetragonal zirconia be 30 to 80 mol%,
Further, the amount of tetragonal zirconia at the grain boundaries is 5 to 60 mol%. The use of ittria has the advantage of enabling sintering at a relatively low temperature and obtaining a dense sintered body, but does not exclude the use of other stabilizers in combination.

For example, magnesia, calcia, ceria, and other oxides that form a solid solution with zirconia can be used together as stabilizers.

The zirconia sintered body of the present invention does not substantially contain carbon, which causes a decrease in strength at temperatures above 600°C. Here, a sintered body that does not substantially contain carbon is
It is defined as follows.

That is, to analyze the amount of carbon in the zirconia sintered body, combustion infrared method, secondary ion mass spectrometry called SIMS,
Various methods are used, such as laser Raman spectroscopy, but in this invention, laser Raman spectroscopy was used, and an argon laser was used to excite the sintered body with light of wavelengths 4,880 and 4,579. In this case, if the presence of carbon detected as amorphous carbon is not recognized, the sintered body is defined as containing substantially no carbon.

It is essential that the zirconia sintered body of this invention has a porosity P of 0.6% or less. Here, the porosity P(
%) is defined by the formula: P=[1-(Kazadensity/Theoretical Density>]X100. In other words, the strength of the sintered body and its variation are greatly influenced by the porosity.

This is because the presence of pores causes stress concentration in those areas.

The decrease in strength and variations are not so great when the porosity is low, but they sharply increase when the porosity exceeds 0.6%. Therefore, in this invention, the porosity is set to 0.6% or less to avoid such inconvenience. The preferred porosity is 0.3% or less. Note that in this field, the Weibull coefficient is used as an index that statistically represents variations in strength. Therefore, the larger the Weibull coefficient, the smaller the variation and the higher the reliability.

Furthermore, the porosity has a great effect on the corrosion resistance of the zirconia sintered body, and when the porosity exceeds 0.6%, the corrosion resistance is greatly reduced. In other words, pores are mainly formed at the grain boundaries of cubic zirconia, but when moisture acts on the pores, it becomes a stimulus and the tetragonal zirconia at the grain boundaries easily transforms into monoclinic zirconia, resulting in the formation of microcracks. As a result of propagation along the grain boundaries, the grain boundary bonds are separated and the strength is greatly reduced.

Hereinafter, the present invention will be roughly described in detail based on Examples.

Example 1 An aqueous solution of zirconium oxychloride with a purity of 99.9% and an aqueous solution of yttrium chloride with a purity of 99.9% were mixed so that the amount of yttrium was 5 mol %.

Next, the above aqueous solution was gradually heated to 100'C, kept at that temperature for about 150 hours to drive off the water, and the solution was heated to about 100'C.
The calcined powder is heated to about 900'C at a rate of 0'C/hour and held at that temperature for about 3 hours.

This calcined powder was roughly ground in a ball mill lined with urethane to obtain a raw material powder having an average particle size of about 0.07 μm.

Next, the raw material powder is molded using a rubber press method,
A molded body was obtained. Pressure force during molding is approximately 101,000 KCI
10 and shita.

Next, the above-mentioned molded body is placed in a heating furnace and heated at a rate of about 0°C/hour up to about 900'C, and thereafter at a rate of about 0°C/hour up to about 1500°C. The temperature was maintained for about 2 hours to obtain a pre-sintered body having a bulk density of about 98% of the theoretical density.

Next, the preliminary sintered body was main sintered using the HIP method. That is, using a platinum heater, the pre-sintered body was heated at a temperature of M to about 1450'C at a rate of about 450'C/hour in an oxidizing atmosphere containing about 3% oxygen and the balance being argon gas.
At the same time, the pressure was increased to 2000 K Cl/Cm2, held for about 1.5 hours, and then cooled at a rate of about 400'C/hour to obtain a sintered body.

Next, the temperature of the sintered body was raised to about 1200"C in air at a rate of 300"C/hour, maintained at that temperature for about 200 hours, and cooled at a rate of 300"C/hour.

Regarding the sintered body thus obtained, the amount of cubic zirconia, the total amount of tetragonal zirconia, the amount of tetragonal zirconia at grain boundaries, the porosity, the presence or absence of carbon, and the bending strength at room temperature (room temperature strength) and bending strength (high temperature strength) and fracture toughness after holding at 1000'C for 1000 hours,
The Weibull coefficient was measured. In addition, the bending strength is measured using J
According to IS-R1601. Fracture toughness was measured using the MI method (
(Minute indenter shakuhachi method). In this method, a Vickers indentation is made on the surface of a test piece, the length of the crack that occurs at that time is measured, and the length is calculated using Shinryo's formula.

Roughly speaking, the Weibull coefficient was determined by setting n to 20.

The measurement results were as follows.

Cubic zirconia: 40 mol% Total amount of tetragonal zirconia: 58 mol% m of tetragonal zirconia at grain boundary: 30 mol% Porosity
20.4% Carbon presence: Not detected Room temperature strength: 900MPa High temperature strength
:900MPa Fracture toughness : 5
．． A sintered body of the present invention was obtained in the same manner as in Example 1, except that the heat treatment in air was carried out at 1300'C for 100 hours. The same measurements as in Example 1 were performed on this sintered body, and the results are shown below.

Amount of cubic zirconia: 49 mol% Total amount of tetragonal zirconia = 46 mol% ffi of tetragonal zirconia at grain boundary: 30 mol% Porosity = 0.5% Presence or absence of carbon 2 No detection room temperature strength Near 00 MPa high temperature strength
Near 20MPa fracture toughness: 4.
Weibull coefficient: 7 MPa fi': 12 Example 3 A sintered body of the present invention was obtained in the same manner as in Example 1, except that the amount of ittria was changed so that it was 4 mol% in the sintered body. Ta. The results of measuring this sintered body in the same manner as in Example 1 are shown below.

Amount of cubic zirconia: 28 mol% Total amount of tetragonal zirconia: 265 mol% Amount of tetragonal zirconia at grain boundaries: 55 mol% Porosity
20.3% Carbon presence: Not detected Room temperature strength: 1400MPa High temperature strength
:1380MPa fracture toughness
: 5.6 MPa 〃W Weibull coefficient = 13 Comparative Example 1 A sintered body was prepared in the same manner as in Example 1 except that the amount of yttoria in the sintered body was adjusted to 6 mol %.

The results of measuring this sintered body in the same manner as in Example 1 are shown below.

ffl of cubic zirconia: 30 mol% Total amount of tetragonal zirconia: 25 mol% Amount of tetragonal zirconia at grain boundaries: 5 mol% Porosity
20.5% Carbon presence: Not detected Room temperature strength: 420MPa High temperature strength
:440MPa Fracture toughness :a,
avpa $ Weibull coefficient: 10 A sintered body was obtained in the same manner as in Example 1, except that a carbon heater was used for the heat treatment, the heat treatment was performed in an argon atmosphere, and the heat treatment in air was not performed. . The results of measuring this sintered body in the same manner as in Example 1 are shown below. just,
Although the presence of carbon was confirmed by laser Raman fractional analysis, its absolute direction was below the detection limit by combustion analysis, so it is considered to be extremely small.

Amount of cubic zirconia: 45 mol% Total a of tetragonal zirconia: 50 mol% ffi of tetragonal zirconia at grain boundary: 30 mol% Porosity
20.5% Room temperature strength Near 00MPa high temperature strength
:80MPa Fracture toughness: 4. oMpa li Weibull coefficient: 12 Comparative Example 3 A sintered body was prepared in the same manner as in Example 1, except that the amount of yttria in the sintered body was adjusted to 2.5 mol %, and the heat treatment was performed for 1200″C120O hours. The results of measuring this sintered body in the same manner as in Example 1 are shown below. However, regarding the porosity, the sintered body had many cracks due to the transformation from a tetragonal to a monoclinic crystal. was.

Amount of cubic zirconia: 11 mol% Total ffinia of tetragonal zirconia 0 mol% Amount of tetragonal zirconia at grain boundaries: 65 mol% Porosity: 26% Presence or absence of carbon: Not detected Room temperature strength: 300 MPa High temperature strength
: 170MPa Fracture toughness : 4
．． Weibull coefficient at 5 MPa: 4.3 Comparative Example 4 The sintered body was made to contain 5.5 mol% of yttria, and the sintering temperature was 1600'C.

A sintered body was obtained in the same manner as in Example 1, except that the heat treatment was performed at 1300° C. for 1000 hours. The results of measuring this sintered body in the same manner as in Example 1 are shown below.

Amount of cubic zirconia = 6262 mol% Total ffi of tetragonal zirconia: 30 mol% Amount of tetragonal zirconia at grain boundaries: 3 mol% Porosity 20
．． 5% Presence of carbon: Not detected Room temperature strength: 300MPa high temperature strength
:300MPa Fracture toughness :3.
8 MPa (FFr Weibull coefficient: 12 Effects of the invention In this invention, tetragonal zirconia exists in the grains and grain boundaries of cubic zirconia, the amount of tetragonal zirconia is 30 to 80 mol%, and the amount of tetragonal zirconia is 30 to 80 mol%. The amount of tetragonal zirconia present is 5-60 mol%, with 3.5
Since it is a zirconia sintered body containing ~5.5 mol%, substantially free of carbon, and having a porosity of 0.6% or less,
It has high mechanical properties, especially toughness and strength, with very little variation in these properties, and high corrosion resistance. Furthermore, since it does not substantially contain carbon, there is almost no decrease in strength even when used at high temperatures of 600° C. or higher.

As mentioned above, the sintered body of the present invention has high strength and high toughness, and has very little variation and is highly reliable.
Moreover, there is almost no decrease in strength even when used at high temperatures of 600'C or higher. Therefore, it can be used for various purposes. An example is shown below.

A. Sub-combustion chamber, turbocharger, piston cap, cylinder, cylinder liner, plate nitrogen seat valve head, gas turbine blade, combustor, nose cone,
As a material for internal combustion openings such as shrads, exhaust valves, and various insulation materials.

B. Dice, nozzles, capillaries, precision measurement blocks and gauges, rings, heating cylinders, heat insulating spacers,
Insulating sleeves, mechanical seals, coil springs, drawing tools, bearings, balls for bearings, balls for crushers, guide rolls, rolling rolls, slurry pump impellers, screws, sleeves, valves, orifices, tiles, wire wrapping. Various industries such as sleeves, drivers, and thread guides are used as mechanical materials.

C. As a cutter material for cutters (slitters and round blades) for textiles, paper, film, magnetic tape, etc., razors, clipper blades, various scissors, various knives, various kitchen knives, etc.

D. As medical equipment materials or medical materials such as scalpels, tweezers, tooth roots, dental crowns, closures, bone fixation materials, etc.

E. Artificial jewelry, seals, tie pins, crow buttons,
As a decorative material for watch parts, etc., or as a jewelry substitute material.

F. As a material for sports and leisure equipment such as Go stones, golf clubs, and fishing line guides.

G. As a material for tableware such as spoons, forks, plates, etc.

H. As a material for writing instruments such as ballpoint pen balls and nibs.

Claims (1)

[Claims] Zirconia with a cubic crystal structure and zirconia with a tetragonal crystal structure coexist; The total amount of zirconia, which exists in the world and has a tetragonal crystal structure, is 30 to 80 mol%.
The amount of zirconia with a tetragonal crystal structure existing in the grain boundaries is 5 to 60 mol%, and the amount of zirconia present in the grain boundaries is 5 to 60 mol%.
A zirconia sintered body containing 5 to 5.5 mol%, substantially free of carbon, and having a porosity of 0.6% or less.