JPS6126560A - Zirconia ceramics - 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 application field] The present invention relates to zirconia ceramics.

[Conventional technology]

Conventionally, sizirconia has been used as a highly corrosion-resistant high-temperature material, but in order to prevent or reduce the catastrophic expansion and contraction that accompanies its transformation, so-called stabilized zirconia or partially stabilized zirconia, in which stabilizing elements are dissolved in solid solution, is used. It is common that This stabilized zirconia or partially stabilized zirconia is a composite of equiaxed and monoclinic crystals with a thermally stable structure, and has excellent thermal shock properties, but is resistant to mechanical stress. It did not have sufficient strength.

In contrast, recently, metastable ceramics such as tetragonal zirconia have been researched and developed, and are attracting attention as materials that are resistant to mechanical stress and have high toughness.

Ceramics such as tetragonal zirconia are, for example, (1) stabilized zirconia ceramics consisting only of conventional equiaxed crystals, or partially stabilized zirconia ceramics consisting of mixed crystals of monoclinic and equiaxed crystals. After long-term aging treatment in a thermally stable temperature range, the tetragonal crystals are frozen by rapid cooling (9), or (2) neutralization coprecipitation and hydrolysis of the zirconium compound and the compound of the stabilizing element.・
It can be produced using a so-called wet method fine powder produced by spray pyrolysis without performing the aging or quenching treatment.

However, although it is possible to prepare small samples with the former method, cracks may occur in samples large enough to be used as industrial materials due to rapid cooling, and in the latter case, In the wet process fine powder produced,
There are also problems with the quality of the final product and the manufacturing process, such as the presence of zirconia particles that do not contain stabilizing elements as a solid solution, and the formation of relatively hard secondary particles that are agglomerated fine primary particles. Not a few.

[Problem that the invention seeks to solve]

The present invention relates to a zirconia ceramic material that does not crack even if it is rapidly cooled to a size that is suitable for use as an industrial material, and that does not contain zirconia particles that do not contain stabilizing elements as a solid solution. , yzo, , 3.2~
Powder containing monoclinic zirconia by causing martensitic transformation of tetragonal zirconia ceramics obtained by melting and rapidly cooling a composition containing 7% by weight and the remainder being substantially ZrO2. The present invention relates to a zirconia ceramic in which the monoclinic crystal is restored to a tetragonal crystal while the powder is molded and sintered by a conventional method.

[Means for solving problems]

The present invention has been made in view of the above points, and the central technical idea of the present invention is to melt a composition containing 3.2 to 7% by weight of Y2O3 and the remainder substantially consisting of ZrO2. After that, a solidified body containing tetragonal zirconia was formed by rapid cooling,
A solidified body containing tetragonal zirconia is crushed and crushed, and by this operation, a powder containing monoclinic zirconia obtained by causing martensitic transformation is formed. This is a sintered body in which monoclinic zirconia has been restored to tetragonal form. Y2O
Fused zirconia using 3 as a stabilizing element is known, and has a two-phase structure of monoclinic and tetragonal crystals at 1 mole of Y2O3 (148 folds), and a tetragonal structure at 3 mole% (5.4 wts) or more. There are also reports that cubic crystals exist.

According to the inventor Go, when a Y2O3-ZrO2 composition melt was slowly cooled, a solidified body consisting of monoclinic crystals and equiaxed crystals was obtained, and when rapidly cooled, a solidified body consisting of monoclinic crystals and tetragonal crystals was obtained.

Therefore, it can be presumed that both the slowly cooled portion and the rapidly cooled portion were present in the above-mentioned sample.

The present inventors have found that if Y2O3 is less than 3.2% by weight, a sufficient amount of tetragonal crystals involved in martensitic transformation will not be formed in the rapidly cooled body, and the mechanical strength will not be sufficient, and the sinterability of the pulverized powder will be poor. It was defective.

In the range of 5.2 to 7% by weight of Y2OB, the L1 quenched body contained a sufficient amount of tetragonal crystals, and the thin plate quenched body with a thickness of 1+w had such strength that it was difficult to break it with fingers.

When the rapidly cooled body is crushed and crushed, the tetragonal crystal changes to monoclinic crystal due to martensitic transformation, resulting in an easily sinterable powder that does not contain secondary particles and has a relatively uniform particle size.

The particle size of the powder is preferably 3 μm or less.

When Y2O3 is 7% by weight or more, the quenched body is almost 100% tetragonal, and almost no monoclinic crystals are formed even by the mechanical stress caused by crushing, and in the end most of the quenched body is tetragonal. , it cannot contribute to martensitic transformation.

The distinction between tetragonal crystals that contribute to martensitic transformation and tetragonal crystals that do not, and the mechanism of their formation, are not clear. Phenomenologically, if a part that should exist as an equiaxed crystal if it is slowly cooled, becomes a tetragonal crystal due to rapid cooling, the tetragonal crystal will undergo martensitic transformation and change to a monoclinic crystal even if it is subjected to mechanical stress. There is no company. Conversely, it can be said that the tetragonal crystal that can contribute to martensitic transformation should exist as a monoclinic crystal in a slowly cooled body.

In the present invention, slow cooling refers to an operation such as casting approximately 18 kl of the molten material into a graphite mold, immediately removing it from the mold, immersing it in fine alumina powder, and slowly cooling it. This refers to an operation in which the material is poured onto a plate to a thickness of about 1.5 on, then transferred onto another cooled graphite plate and rapidly cooled.

In the slow cooling operation, the cooling time to room temperature takes all day and night,
Rapid cooling operations can be completed within a few hours.

〔Example〕

Example The zirconia raw material used in the present invention was obtained by chlorinating and refining Nobulite ore from South Africa (ZrO
299% or more), and an industrial reagent was used for Y2O3. A 300 KVA single phase arc furnace was used for melting. Moreover, the Xa diffraction of the slowly cooled body and the rapidly cooled body did not depend on the pulverized sample, but used a polished surface. This is due to the fact that phase change occurs due to martensitic transformation when a pulverized sample is prepared, so we investigated a sample preparation method that would avoid this. Polishing was performed using a D1200 mesh diamond grinder. In X@ diffraction, the integrated intensity of each phase and its peak was measured and the ratio thereof was determined.

Table 1 lists examples and experimental examples, including samples 1 to 1.
6 is an example.

One of the aspects of the present invention is that zirconia ceramics is a quenched body and contains metastable tetragonal crystals, which when subjected to mechanical stress,
Another aspect of the present invention is a powder that is pulverized by applying mechanical stress and undergoes a tetragonal-monoclinic transformation, which is characterized by easy sintering. It is a powder with uniform particle size.

Regarding the compositions of Examples 1 to 6 and Experimental Examples A to D, ceramic pins for mounting ceramic 7-in-ones as shown in Japanese Patent Publication No. 58-4271 were cast using a graphite mold. The graphite plate used was a graphite plate having a thickness of 50 mm and had a sufficient size to satisfy the above-mentioned quenching conditions.) The quenched body reached room temperature within 1 hour after casting.

The ceramic pins with the compositions of Examples 1-6 were apparently sound cast bodies with no cracks, whereas the ceramic pins with the compositions of Experiments A-D were broken into two to three pieces and were not sound. I couldn't get something with a certain shape.

The quenched body was crushed using a show crusher, and then crushed to 3 μm or less using a stamp mill and a gel mill.

The ratio of each phase of the obtained powder was determined by X-ray diffraction. This is shown in Table-2.

Comparing Tables 1 and 2, it is clearly recognized in Samples 1 to 6 that the pulverization caused martinsite transformation and the tetragonal crystals changed to monoclinic crystals.

Next, the powder was placed on a 50 x 50 x 6 m plate.
2-hole press molding under a pressure of 1400'
A sintered body was obtained by heating at 1600° C. for 2 hours in the air.

The phase structure, density, and three-point bending strength of zirconia in the sintered body were measured, and the results are shown in Table 3.

〔effect〕

The sintered body obtained by shaping and firing the powder containing ZrO2, which has been transformed from metastable tetragonal to monoclinic under mechanical stress, is heat-treated again and transformed from monoclinic to tetragonal. On the other hand, the tetragonal crystals in the powder that do not participate in martensitic transformation are converted into equiaxed crystals in the sintered body.

From Tables 1 to 3, the proportion of tetragonal crystals in the quenched body, the proportion of monoclinic crystals in the powder obtained by pulverizing this quenched body, and the proportion of tetragonal crystals in the sintered body obtained by shaping and firing this pulverized powder are determined. Figure 1 shows the bending strength of the sintered body.

The pulverized powder obtained by pulverizing a rapidly solidified body containing a monostable tetragonal crystal and transforming it into a monoclinic crystal is easily sinterable and can achieve sufficient density even at a relatively low sintering temperature of 1400°C to 1500°C, and is highly bendable. You can gain strength.

[Brief explanation of drawings]

Figure 1 is a graph showing bending strength Procedural amendment September 12, 1980 Patent application No. 145609 3, Relationship with the case of the person making the amendment Patent applicant 4, agent Address: 160 Telephone 03- 354-4084
6. Number of inventions increased by amendment None. Corrected as shown in the attached sheet. Amendment Statement 1, Title of Invention Zirconia Ceramics 2, Ivj Claims (11Y2O33, 2 to 7% by weight balance is substantially ZrO
2. Powder containing monoclinic zirconia obtained by crushing and pulverizing a V solid containing tetragonal crystals obtained by melting and rapidly cooling a different composition, and causing martensitic transformation through this operation. A zirconia ceramic characterized in that the monoclinic crystal is restored to a tetragonal crystal while the powder is molded and sintered by a conventional method. (21Y2O33, 2 to 7% by weight the remainder is substantially ZrO
2. The zirconia ceramic according to claim 1, comprising a metastable tetragonal crystal that can be transformed into a monoclinic type by mechanical stress obtained by melting and then rapidly cooling the composition. (3) The easily sinterable zirconia ceramic according to claim 1, which is obtained by applying mechanical stress to the zirconia ceramic according to claim 2 and transforming into a monoclinic shape. 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to zirconia ceramics. [Prior Art] Zirconia has traditionally been used as a highly corrosion-resistant high-temperature material, but in order to prevent or reduce the catastrophic expansion and contraction associated with its transformation, so-called stabilized zirconia or Partially stabilized zirconia is commonly used. This stabilized zirconia or partially stabilized zirconia is composed of a composite of equiaxed crystals and monoclinic crystals, which have a thermally stable structure, and has excellent thermal shock properties, but has insufficient resistance to mechanical stress. It had no strength. In contrast, recently, ceramics made of metastable tetragonal zirconia have been researched and developed, which are resistant to mechanical stress and
It is attracting attention as a material with high toughness. Ceramics made of this tetragonal zirconia are, for example, (1) stabilized zirconia ceramics made only of conventional equiaxed crystals, or partially stabilized zirconia ceramics made of a mixed crystal of monoclinic crystals and equiaxed crystals. After aging treatment for a long time in a stable temperature range, the tetragonal crystals are frozen by rapid cooling, or (neutral coprecipitation, hydrolysis, and
It can be produced by using a so-called wet method fine powder produced by spray pyrolysis without performing the aging and quenching treatment. However, even if the former method is possible to prepare a small sample, if the sample is large enough to be used as an industrial material, cracks may occur during the rapid cooling process, and in the latter case, In the wet process fine powder produced,
There are also problems with the quality of the final product and the manufacturing process, such as the presence of zirconia particles that do not contain stabilizing elements as a solid solution, and the formation of relatively hard secondary particles that are agglomerated fine primary particles. Not a few. [Problems to be solved by the invention] According to the present invention, cracks do not occur even when a glass of a size suitable for use as an industrial material is rapidly cooled, and zirconia particles with no stabilizing element dissolved therein are mixed. This relates to zirconia ceramics with no Y2O3 of 3.2 to 7
% by weight, the remainder being substantially ZrO2, and then rapidly cooled to cause martensitic transformation of the obtained tetragonal zirconia ceramic to form a powder containing monoclinic zirconia. This invention relates to a zirconia ceramic in which the monoclinic crystal is restored to a tetragonal crystal while the powder is molded and sintered by a conventional method. [Means for Solving the Problems] The present invention has been made in view of the above points, and the central technical idea of the present invention is that Y2O3 is 3.2 to 7% by weight, the remainder being substantially After melting a composition made of ZrO2, a solidified body containing tetragonal zirconia obtained by rapidly cooling is produced.
A solidified body containing tetragonal zirconia is crushed and crushed, and by this operation, a powder containing monoclinic zirconia obtained by causing martensitic transformation is formed. It is a sintered body in which monoclinic zirconia has been restored to a tetragonal structure. Y2
Fused zirconia using O3 as a stabilizing element is known, and has a two-phase structure of monoclinic and tetragonal crystals at 1 mol% (1.8% by weight) of Y2O3 and 3 mol% (5.4% by weight) or less. There are also reports that there are tetragonal and cubic crystals. According to the present inventors, when a Y2O3-ZrO2 composition melt was slowly cooled, a solidified body consisting of monoclinic crystals and equiaxed crystals was obtained, and when rapidly cooled, a solidified body consisting of monoclinic crystals and tetragonal crystals was obtained. Therefore, it can be inferred that the above-mentioned known fact indicates that both a slowly cooled portion and a rapidly cooled portion were present in the sample. The present inventors have found that if the content is less than 720332% by weight, a sufficient amount of tetragonal crystals involved in martensitic transformation will not be formed in the quenched body, the mechanical strength will not be sufficient, and the sinterability of the pulverized powder will be poor. there were. In the range of 2 to 7% by weight of Y2O3, the quenched body contained a sufficient amount of tetragonal crystals, and the quenched body of a thin plate with a thickness of 1j1 ml had such strength that it was difficult to break it with fingers. When the rapidly cooled body is crushed and crushed, the tetragonal crystal transforms into monoclinic crystal due to martensitic transformation, which is accompanied by volume expansion.
It becomes a highly active state with internal strain accumulated, and the resulting powder is sinterable and does not form secondary particles that are tightly aggregated primary particles like wet method powder. Particle size of powder is 3
It is desirable that it is less than μm. A sintered body made from a powder containing monoclinic crystals produced by this martensitic transformation is in a high energy state containing metastable tetragonal crystals produced by reverse transition of monoclinic crystals, and therefore has a high fracture strength. is large enough. When Y2O3 is more than 7% by weight, the quenched body becomes almost 100% tetragonal, and almost no monoclinic crystals are produced even by the mechanical stress caused by crushing, and in the end most of the quenched body is tetragonal. , it becomes impossible to enrich the martensitic metamorphosis. The distinction between the tetragonal crystals that contribute to the martensitic transformation and the tetragonal crystals that contribute to the martensitic transformation and the mechanism of their formation are not clear. Phenomenologically, if a part that should exist as an equiaxed crystal by slow cooling becomes a tetragonal crystal by rapid cooling, even if subjected to mechanical stress, this tetragonal crystal undergoes martensitic transformation [7] and changes to a monoclinic crystal. There isn't. Conversely, it can be said that the tetragonal crystal that can contribute to martensitic transformation should exist as a monoclinic crystal in a slowly cooled body. As stated above, the inventors of the present application do not believe that it is sufficient to simply include a large number of tetragonal crystals; It needs to be able to transform into a monoclinic crystal. (Even a 100-inch tetragonal crystal is useless if this transformation is small.) (2) In powder, the tetragonal crystal in the solidified body transforms into martensitic crystal. (3) In the sintered body, it is desirable that the powder contains a large amount of metastable tetragonal crystals produced by reverse transition of the monoclinic crystals in the powder. These three points It is an essential condition for the present invention to satisfy the following conditions, and it is for this reason that the Y2O3 content of the present invention is set to 3.2 to 7 times. After casting the molten material in 18 to 7 into a graphite mold, it is immediately removed from the mold and slowly cooled by immersing it in fine alumina powder. This refers to an operation in which after pouring into a JJF of /TRI, it is transferred to another cooled graphite plate and then rapidly cooled.The slow cooling operation requires more than 12 days and nights to cool down to room temperature, while the rapid cooling operation In the slow cooling operation, it takes 24 hours or more to cool the melt from the start of solidification to normal temperature, and in the rapid cooling operation, it takes less than 24 hours, but preferably 10 hours or less. In addition to the above-mentioned methods, quenching operations can also be carried out by applying a trickle of the molten material to a rotating object that is rotating at high speed, or by blowing a jet stream of air to cool it down to room temperature in a few seconds (or less). [Example] The zirconia raw material used in the present invention was obtained by subjecting baddellite ore from South Africa to chlorination and refining treatment (Zr
O2 99% or more), Y2O3 used an industrial reagent. A 300 KVA single-phase arc furnace was used for melting and melting. The slowly cooled body is produced by using the above method and takes 30 hours to reach a temperature that can be touched by hand after casting, and the rapidly cooled body is produced by pouring the molten body onto a graphite plate to a thickness of 2 to 3 crn. 5 hours after the start of solidification, it was cooled to a temperature that could be touched by hand. Furthermore, X-ray diffraction of the slowly cooled body and the rapidly cooled body was performed using a polished surface, regardless of the crushed sample. This is due to the fact that phase change occurs due to martensitic transformation when a pulverized sample is prepared, so we investigated a sample preparation method that would avoid this. The polishing was done using a 1200 mesh diamond grinder. The results of X-ray diffraction show that the slowly cooled body consists of monoclinic + equiaxed crystals when the Y2O3 content is low, and as the Y2O3 content increases, the equiaxed crystals increase, and when Y2O3 content is 7.9% by weight or more, equiaxed crystals are formed. It becomes 100% axial crystal, and in the rapidly cooled body, Y2O
When the 3 content is low, it is formed from monoclinic tetragonal crystals, Y2O3
As the content increases, the number of square items increases, and Y2O34,5
It was shown that when the weight percentage is higher than 100%, the tetragonal crystal structure becomes 100%. Furthermore, each phase was quantified by X-ray diffraction. This quantification is for monoclinic (111). (111) Integrated intensity of diffraction line 1 m (111), Im
(111), integrated intensity of tetragonal (111) diffraction line It(
1111, equiaxed product (integrated intensity Ic of 1111 diffraction line
111), flavie and N1chols
This was carried out using the following formula indicated by on. Annealing body X100 (volume) ・・・・・・・・・・・・(1
)X100 (body bond) ・・・・・・・・・・・・
・(2) Quenched body X100 (volume%) ・・・・・・・・・・・・・(
3)X100 (volume%) ・・・・・・・・・・・・
- (4) The measurement results are shown in Table 1. Table 1 shows actual M'4 (+) and experimental examples, and samples 1 to 6 are examples. One of the aspects of the present invention is that zirconia ceramics is a rapidly solidified body and has a metastable tetragonal structure. containing, which is subjected to mechanical stress,
Another aspect of the present invention is a powder that is pulverized by applying mechanical stress and undergoes a tetragonal-monoclinic transformation, which is characterized by easy sintering. It is a powder with uniform particle size. About the compositions of Examples 1 to 6 and Experimental Examples A to D
Ceramic pins for ceramic fiber attachment, as shown in No. 8-4271, were cast using a graphite mold. The graphite plate used was a graphite plate with a thickness of 50 cm, which had a sufficient size to satisfy the above-mentioned quenching conditions, and the quenched material reached room temperature within 1 hour after casting. The ceramic bottles with the compositions of Examples 1-6 were apparently sound cast bodies with no cracks, whereas the ceramic bottles with the compositions of Experimental Examples A-D were divided into 2 to 3 pieces and were not sound. I couldn't get something with a certain shape. The quenched body is crushed using a show crusher, then a stamp mill, and then a stamp mill. - Grinding to 3 μm or less using Lumir 1
-It is. When the constituent phases of the obtained powders were identified by X-ray diffraction, all compositions were composed of monoclinic tetragonal crystals, but the amount of monoclinic crystals tended to decrease as the Y2O3 content increased. was there. Garvie-N1c)+ol as previously described for phase quantification.
sonO formula (3). (4) was used. This is shown in Table-2. Comparing Tables 1 and 2, it is clearly recognized in Samples 1 to 6 that martensitic transformation occurred due to pulverization and the tetragonal crystals changed to monoclinic crystals. The amount of monoclinic crystals produced by the martensitic transformation of the tetragonal crystals in this rapidly solidified body is also listed in Table 2.
In the range of 1% by weight (Examples 1 to 6), the amount produced is 20 volumes or more, and in particular, in the range of 0 to 5.0% by weight of Y2O3, the amount is maximum. Next, the powder was rubber-pressed into a 50x50x6 plate material under a pressure of 1 ton/d, and heated at 1550C for 2 hours in the air to obtain a sintered body. The phase structure, density, and three-point strength of zirconia in the sintered body were measured, and the results are shown in Table 3. According to X-ray diffraction, Y2O3 content is 2.0-3.4% by weight.
In the range of
Then it becomes a 100-chi tetragonal crystal. Thereafter, as Y2O3 increased, equiaxed crystals were generated, and as Y2O3 increased, the amount thereof also increased. Quantification of phase is Garv for monoclinic tetragonal phase.
ie-Nicholson (7) Equations (31 and (41) were used, but in the case of a tetragonal equiaxed crystal, both (1
11) Since the diffraction lines are very close and cannot be separated, Gar
The formula vie -N1cholson cannot be used as is. Therefore, in the present invention, the determination of these two phases is carried out using Garvie-Ni.
When Cholson's formula is derived, monoclinic (111)
, the content of the integrated intensity of the (111) diffraction line is said to be equal to the integrated intensity IH(111) of the transition tetragonal or equiaxed crystal when it is heated to a high temperature. Returning to the original idea of making assumptions, we carried out the work based on the assumptions shown in "1" below. In other words, the tetragonal (3
11), (113) and equiaxed (311) diffraction lines can be separated and their integrated intensity values can be measured. X10, assuming that the content is equal to the integrated intensity of the equiaxed (311) diffraction line that transitions from tetragonal to high temperature.
0 (volume chi) Equiaxed crystal content = 100 - tetragonal crystal content (volume chi) It was determined by the formula. Here Ii (311), It (113)
. Ic(311) are tetragonal (311) and (1
13) Equiaxed crystals of diffraction lines (This is the integrated intensity value of 3111 diffraction lines. The equiaxed crystals generated in the sintered body are tetragonal crystals in the rapidly solidified body, and when crushed and crushed, they do not undergo martinsite transformation and are turned into powder as they are. It is thought that the tetragonal crystals that remained in the powder were formed by dislocation, but on the other hand, the tetragonal crystals were formed by reverse transition of the monoclinic crystals generated by the martensitic transformation in the powder, and some of the tetragonal crystals were formed by the reverse transition of the monoclinic crystals that were generated by the martensitic transformation in the powder. It is thought that the tetragonal crystals remained as they are, and the two can be quantitatively distinguished.Table 3 shows the amount of tetragonal crystals produced by reverse transition of the monoclinic crystals in this powder. Also written, but Y2O3 content 3.4
A large value is obtained for compositions in the range of ~5.0% by weight, which roughly corresponds to the magnitude of the bending strength of the sintered body. The present invention has been described above; the amount of tetragonal crystals in the rapidly solidified body, the amount of monoclinic crystals generated by martensitic transformation in the powder, and the amount of tetragonal crystals generated by reverse transformation of monoclinic crystals in the sintered body. It is shown in FIG. 1K7j that the present invention is achieved in zirconia compositions containing Y2O3 in the range of 3.2 to 7% by weight. Next, we will discuss the material that was cooled and solidified at a faster rate than the rapid cooling of the Curzen plate. Y2O3 content is 4.0 weight-f? :
A mixture of refined baddellite ore and industrial-grade ittria powder blended at was applied to a disk with a diameter of 300 nm rotating at 300 rpm to obtain two types of coagulated bodies. The cooling rate at this time is about several seconds from the start of solidification to room temperature. This solidified material had a hollow spherical shape when blown with air, and a flaky shape when applied to a rotating disk. The phase composition of these coagulates and powders obtained by crushing the coagulates in the same manner as above, and zirconia ceramics made from these powders as raw materials, as well as the three-point strength of the ceramics, are shown in Table 4. The following results were obtained. This result shows that both compressed air quenching and rotating disk quenching are somewhat more effective at quenching than the cardan plate quenching shown earlier, and although the amount of tetragonal crystals in the solidified body is larger, the powder and sintered body obtained from this solidified body are approximately Having similar characteristics, the rjk-shaped bit tip made of this sintered body in the shape of 5NP432 is less likely to cause betting when used for rough cutting of cast iron compared to conventional alumina-based ones, and is more suitable for high-speed heavy cutting. Ta. In this way, the present invention is achieved by using a rapidly solidified body, and if a slowly cooled body that requires 24 hours or more from the start of solidification of the molten material is used, even a composition containing Y2O3 in the same range can be achieved according to the present invention. However, the strength of the solidified body is weak and it does not contain tetragonal crystals, so the powder obtained from this solidified body does not contain monoclinic crystals generated by martensitic transformation, and therefore it is a highly concentrated powder containing a large amount of strain energy. Since it is difficult to achieve an active state and the sintering properties are poor, sintered bodies made from this powder do not contain reverse transition tetragonal crystals and have low strength. [Effect] The sintered body obtained by molding and firing, which is a powder containing ZrO2 which has been converted from metastable tetragonal to monoclinic due to mechanical stress, is heat-treated again and converted from monoclinic to tetragonal. On the other hand, the tetragonal crystals in the powder, which do not participate in the martensitic transformation, are transformed into equimediate convex crystals in the sintered body. From Tables 1 to 3 and Figure 1, the proportion of tetragonal crystals in the quenched body,
The proportion of monoclinic crystals in the powder obtained by pulverizing this rapidly cooled body, and the proportion of tetragonal crystals generated by reverse transition in the sintered body obtained by shaping and firing this pulverized powder, determine the bending strength of the sintered body. Shown in Figure 1. A pulverized powder obtained by pulverizing a rapidly solidified body containing a metastable tetragonal crystal and transforming it into a monoclinic crystal is easily sinterable and can achieve a sufficient density, as well as high bending strength. 4. Brief explanation of the drawings Figure 1 is a graph showing the phase composition (volume ratio) of solidified bodies, powders, and sintered bodies, and Figure 2 is a graph showing bending strength. 0h mape)

Claims (1)

[Claims] Y_2O_3 3.2 to 7% by weight The remainder is substantially ZrO
Powder powder containing monoclinic zirconia obtained by crushing and pulverizing a solidified body containing tetragonal crystals obtained by melting and rapidly cooling a composition consisting of _2, and causing martensitic transformation through this operation. A zirconia ceramic characterized in that the monoclinic crystal is restored to a tetragonal crystal while being molded and sintered by a conventional method.