JPH10194824A - Alumina sintered body containing zirconia - Google Patents

Abstract

(57) Abstract: Provided is a zirconia-containing alumina sintered body having high bending strength and excellent thermal shock resistance. SOLUTION: This is mainly composed of alumina and has an average crystal particle diameter of 0.1 mm.
In addition to containing 2 to 30% by volume of zirconia of 2 to 2 μm, the zirconia particles are uniformly dispersed in an alumina matrix in a state where the zirconia particles are not substantially aggregated, and 10 to 85% of the zirconia at room temperature (25 ° C.) In the form of monoclinic zirconia.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zirconia-containing alumina sintered body having high bending strength and excellent thermal shock resistance, and is used as a bearing, a thread guide, a member for a pump, an insulator for a CVD apparatus, and the like. It can be suitably used.

[0002]

2. Description of the Related Art Conventionally, zirconia-containing alumina sintered bodies in which zirconia particles are dispersed in an alumina matrix have been attracting attention and studied in order to improve the strength of the alumina sintered bodies.

For example, Japanese Patent Publication No. 59-24475 and Japanese Patent Publication No. 8-13701 disclose a zirconia-containing alumina sintered body in which metastable tetragonal zirconia particles are dispersed in an alumina matrix. . When an external force is applied to this zirconia-containing alumina sintered body, the metastable tetragonal zirconia particles undergo a phase transition to monoclinic, and the stress is relaxed by fine microcracks generated due to volume expansion occurring at this time. This improves the strength and fracture toughness of the sintered body, and utilizes the stress-induced transformation mechanism of zirconia.

Japanese Patent Publication No. 59-25748 discloses a zirconia-containing alumina sintered body in which agglomerated particles composed of unstabilized zirconia particles are dispersed in an alumina matrix. The zirconia-containing alumina sintered body has micro-cracks formed around the aggregated zirconia particles, and when an external force is applied to the sintered bodies, the cracks generated by the stress are branched by the micro-cracks to reduce the stress. The fracture toughness value of the sintered body is improved by absorption and relaxation, and utilizes micro cracks due to unstabilized zirconia particles.

[0005]

However, any zirconia-containing alumina sintered body has been studied mainly for the purpose of improving the mechanical properties, and the thermal shock properties have not been sufficiently studied. It was not satisfactory in terms of thermal shock resistance.

First, in a structure in which tetragonal zirconia is dispersed in an alumina matrix, such as a zirconia-containing alumina sintered body disclosed in Japanese Patent Publication Nos. Since the stress-induced transformation mechanism of zirconia does not act on the stress generated instantaneously due to the impact, and most of the tetragonal zirconia does not undergo a phase transition, it is not possible to form fine microcracks in the sintered body. For this reason, there has been a problem that the stress caused by the thermal shock cannot be absorbed or reduced, and the strength is greatly deteriorated. Although the thermal shock resistance of the sintered body can be increased by increasing the content of tetragonal zirconia significantly and increasing the strength, the production cost is high when the content is increased since zirconia is an expensive material. It was too uneconomical.

On the other hand, in Japanese Patent Publication No. 59-25748, since microcracks exist inside the sintered body,
Although the stress due to thermal shock can be relieved, the zirconia particles dispersed in the alumina matrix are 2-1 to zirconia particles.
Because of the 5 μm agglomerated particles, large cracks are ubiquitous in the sintered body together with fine micro cracks, so that the strength of the sintered body cannot be increased so much, and the stress accompanying thermal shock Therefore, there was a problem that the strength was greatly deteriorated.

An object of the present invention is to provide a zirconia-containing alumina sintered body having high bending strength and excellent thermal shock resistance.

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention has been made in consideration of the above-mentioned problems, and mainly comprises alumina and zirconia in an amount of 2 to 30%.
%, And the zirconia particles are uniformly dispersed in the alumina matrix in a state where they are not substantially aggregated.
85% is monoclinic zirconia, this sintered body is heated so that the temperature difference from the water temperature becomes 250 ° C., and the zirconia-containing alumina sintered body having a transverse rupture strength of 250 MPa or more after being dropped into water. It is what constitutes the body.

In the present invention, the zirconia particles have an average crystal particle diameter of 0.2 to 2 μm.

According to the present invention, alumina sintering is carried out by dispersing zirconia particles having a phase transition in an alumina matrix and allowing a part of the zirconia particles to exist in a monoclinic zirconia state at room temperature (25 ° C.). Very fine microcracks are formed in the body, which can enhance the thermal shock resistance of the alumina sintered body.

That is, zirconia exists as metastable tetragonal zirconia at a temperature of about 1100 ° C. or higher,
At a temperature lower than 0 ° C., it exists in a monoclinic zirconia state. Also, since zirconia undergoes a volume expansion when undergoing a phase transition from tetragonal zirconia to monoclinic zirconia, by dispersing monoclinic zirconia in an alumina matrix, fine microcracks are formed around the monoclinic zirconia. Since the microcracks can prevent the progress of the cracks due to the thermal stress, the thermal shock resistance of the alumina sintered body can be improved.

However, in order to do so, zirconia is added to
0% by volume, and the proportion of monoclinic zirconia dispersed in the alumina matrix is 10 to 8%.
It is important to make it 5%.

If the zirconia content is less than 2% by volume, the microcracks formed in the sintered body are too small even if all the zirconia is monoclinic zirconia. On the other hand, when the zirconia content is more than 30% by volume, the microcracks formed in the sintered body become too large, and the sintering becomes difficult. This is because the strength of the body is greatly reduced.

On the other hand, when the proportion of monoclinic zirconia is less than 10%, since the microcracks formed in the sintered body are too small, the stress accompanying the thermal shock cannot be absorbed, and the thermal shock resistance is enhanced. Conversely, when the proportion of monoclinic zirconia exceeds 85%,
This is because the strength of the sintered body itself is greatly reduced due to too many micro cracks formed in the sintered body at room temperature.

Preferably, zirconia is added in an amount of 10 to 20.
% Of the monoclinic zirconia dispersed in the alumina matrix.
%, And if zirconia is contained in this range, the strength of the sintered body at room temperature is 500 MPa or more,
Further, an alumina sintered body having a transverse rupture strength of 400 MPa or more against a thermal shock at 250 ° C. and excellent in thermal shock resistance can be obtained.

It is important that the monoclinic zirconia particles dispersed in the alumina matrix be dispersed almost uniformly without agglomeration.

This is because, when monoclinic zirconia particles are present in the alumina matrix in an agglomerated state, microcracks formed around each monoclinic zirconia particle are combined, and large cracks are unevenly distributed. Therefore, the effect of increasing the strength of the sintered body is small, and because the strength is significantly deteriorated by thermal shock, as in the present invention, the monoclinic zirconia particles are not aggregated in the alumina matrix. By uniformly dispersing, fine microcracks can be formed uniformly, so that stress due to thermal shock can be absorbed and reduced, and the thermal shock resistance of the alumina sintered body can be increased.

However, when the average crystal particle diameter of the zirconia particles is larger than 2 μm, the strength cannot be increased because fine microcracks cannot be uniformly formed around the monoclinic zirconia, and the strength cannot be sufficiently increased. No thermal shock resistance is obtained. In addition, it is difficult to make the average crystal particle diameter of the zirconia particles smaller than 0.2 μm in production.

Therefore, the average crystal particle diameter of the zirconia particles dispersed in the alumina matrix is 0.2 to 2 μm.
Is good.

On the other hand, the main constituent alumina may be contained in the range of 70 to 98% by volume, and a sintering aid such as SiO ₂ , MgO, CaO or the like is added in an amount of 1% by volume or less in order to enhance sinterability. You may contain in the range.

The average crystal particle diameter of alumina is 1-2.
The average crystal grain size of alumina is preferably 0 μm, because it is difficult to make the average crystal grain size of alumina smaller than 1 μm. When the average crystal grain size of alumina is larger than 20 μm, the strength of the alumina sintered body is greatly reduced. Because you do.

Incidentally, in order to obtain the zirconia-containing alumina sintered body according to the present invention, the average particle diameter is 0.5 to 10 μm.
Of alumina at 70 to 98% by volume, Y ₂ O ₃ and Ca
Zirconia having an average particle size of 0.5 to 2.0 μm, which is not stabilized or partially stabilized by a stabilizer such as O
30% by volume is added and mixed with a vibration mill, a bead mill or the like.

As described above, starting materials such as Y ₂ O ₃ and C
The use of zirconia powder that is not stabilized or partially stabilized by a stabilizer such as aO is 2 to 30 when a stabilized or partially stabilized zirconia powder is used.
This is because even if the content is within the range of volume%, the proportion of monoclinic zirconia present in the alumina matrix is too small, so that a sufficient amount of microcracks cannot be formed in the sintered body. When mixing the raw materials, it is important to mix the alumina powder and the zirconia powder using a vibration mill, a bead mill or the like in order to uniformly mix the alumina powder and the zirconia powder. That is, by uniformly mixing the alumina powder and the zirconia powder, the zirconia particles are prevented from aggregating when the sintered body is formed, and the zirconia particles can be uniformly dispersed in the alumina matrix. is there.

Then, a binder is further added to the mixed raw material to prepare a slurry, and the mixture is spray-dried with a spray drier to form granules. The granules are filled in a mold and subjected to a uniaxial pressure molding method or the like. The molded body is formed by a pressure and pressure molding method, or the molded body is formed by a usual ceramic molding method such as a tape molding method, a cast molding method, or an injection molding method.

Thereafter, the compact was fired at a firing temperature of 1500 to 1650 ° C. in an air atmosphere or a vacuum atmosphere.
What is necessary is just to bake for several hours.

The reason why the firing temperature was set to 1500 to 1650 ° C. is that the proportion of monoclinic zirconia has a correlation with the firing temperature, and as shown in FIG. The proportion of clonic zirconia can be increased. However, if the firing temperature is lower than 1500 ° C., the proportion of monoclinic zirconia cannot be increased to 10% or more,
In addition, the strength cannot be increased because of the poor sintering property and the densification cannot be performed. Conversely, when the temperature exceeds 1650 ° C., the alumina particles cannot suppress the abnormal grain growth of zirconia, and This is because the strength is reduced.

The zirconia-containing alumina sintered body thus formed is contained in an alumina matrix in an amount of 2 to 30% by volume.
Zirconia particles are uniformly dispersed without substantially aggregating, and 10 to 85% of the zirconia can be present in a monoclinic zirconia state.

[0029]

EXAMPLE A zirconia-dispersed alumina sintered body was formed in which the zirconia content and the ratio of monoclinic zirconia were respectively changed, and the bending strength and thermal shock resistance at room temperature were measured by a three-point bending test.

First, to prepare the raw materials, alumina powder and zirconia powder were weighed and added at a ratio shown in Table 1 so that the total would be 1 kg, and wet-mixed with a vibration mill for about 24 to 48 hours. A slurry was prepared by adding a binder, and dried with a spray drier to prepare granules (raw material) in which alumina powder and zirconia powder were uniformly mixed. In addition, No. shown in Table 1 As the zirconia powder of No. 4, a zirconia powder partially stabilized with ₃ mol of Y ₂ O ₃ was used, and other zirconia powders which were not stabilized or partially stabilized by a stabilizer were used.

Next, the granules are filled in a mold, formed into a prism at a pressure of 1 ton / cm ² by a uniaxial pressing method, and the formed body is fired at a temperature of 1500 to 1650 ° C. 3x4 by grinding the obtained prismatic sintered body
Fifteen bending test pieces of 40 mm each were manufactured.

First, the surface of each bending test piece was measured with an X-ray diffractometer, and the peak intensity I of monoclinic zirconia was measured.
_m and peak intensity I of zirconia other than monoclinic zirconia
_{After obtaining t} , calculating the ratio of monoclinic zirconia based on Equation 1, the transverse rupture strength at room temperature (25 ° C.) was measured. Next, the temperature difference from the water temperature is 200 ° C., 250 ° C.
Each bending test piece was heated to a temperature of ° C., then dropped into water and subjected to a thermal shock, the bending strength was measured, and the thermal shock resistance was measured.

An alumina sintered body having a purity of 99% was prepared as a comparative reference test piece, and an experiment was conducted in the same manner.

[0034]

(Equation 1)

Table 1 shows the characteristics of the sintered body constituting each bending test piece and the results thereof.

[0036]

[Table 1]

As a result, first, the sample No. Although No. 1 contained zirconia, the transverse rupture strength at room temperature could be improved as compared with the alumina sintered body as a reference sample, but the content of zirconia was as small as 1% by volume, and Since the ratio of clonal zirconia is small, 250
The transverse rupture strength was significantly reduced to 90 MPa against a thermal shock of ℃.

Sample No. In No. 10, the zirconia content was more than 35% by volume and more than 30% by volume, and the ratio of monoclinic zirconia was more than 85% and 91.2%. Was lower than the alumina sintered body.

On the other hand, the sample No. 2,3
Nos. 6 to 9 all have a zirconia content of 2 to 30% by volume and a monoclinic zirconia ratio of 10 to 85%, so that the transverse rupture strength at room temperature is 500 MPa or more;
The transverse rupture strength was significantly improved as compared with the alumina sintered body as the reference sample, and the transverse rupture strength of 250 MPa or more was obtained even with a thermal shock of 250 ° C. In particular, the sample No. 3, 6 to 8 have a zirconia content of 1
0 to 20% by volume and the proportion of monoclinic zirconia is 50
Since it is in the range of ８０80%, a transverse rupture strength of 400 MPa or more with respect to a thermal shock at 250 ° C. was obtained, and excellent thermal shock resistance was obtained.

The sample No. Comparison of Sample Nos. 3 and 4 shows that Sample Nos. No. 4 had the highest transverse rupture strength at room temperature because partially stabilized zirconia was used as a raw material, but the ratio of monoclinic zirconia in the sintered body was as small as 0.5%, so that heat at 250 ° C. When an impact was applied, the transverse rupture strength was reduced to 168 MPa, and significant strength deterioration was observed.

On the other hand, the sample No. Sample No. 3 has a flexural strength at room temperature of Sample No. 3. Although slightly inferior to that of No. 4, the ratio of monoclinic zirconia was 55.1% and the micro-cracks were fine in the sintered body.
It had a high transverse rupture strength of 465 MPa even with a thermal shock of 50 ° C.

From the above, in order to enhance the thermal shock resistance of the sintered body, it is better to exist in the state of monoclinic zirconia which generates microcracks than to disperse tetragonal zirconia having a stress-induced transformation mechanism. It turns out good.

Further, the sample No. Comparison of Sample Nos. 3, 5, and 6 shows that Sample Nos. 5 has a monoclinic zirconia ratio of 72.2.
%, But the average crystal particle diameter of zirconia is 2 μm.
Strength at room temperature is low due to
The flexural strength when a thermal shock of 0 ° C. was applied was as low as 108 MPa. 3, 6 have a transverse rupture strength of 500 MPa or more at room temperature since the average crystal particle diameter of zirconia is 2 μm or less;
No significant deterioration in strength was observed even when a thermal shock of ℃ was applied.

This indicates that the average crystal particle diameter of the zirconia particles is preferably 2 μm or less.

[0045]

As described above, the zirconia-containing alumina sintered body of the present invention contains 2 to 30% by volume of zirconia having an average crystal particle diameter of 0.2 to 2 μm, mainly containing alumina, and an alumina matrix. The zirconia particles are uniformly dispersed in a state in which the zirconia particles are not substantially aggregated.
When 5% is present in the state of monoclinic zirconia, the transverse rupture strength at room temperature can be increased, and a sintered body having excellent thermal shock resistance can be obtained.

Therefore, the alumina sintered body containing zirconia of the present invention can be suitably used as a material requiring thermal shock resistance, such as a bearing, a thread guide, a member for a pump, and an insulator for a CVD apparatus.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the ratio of monoclinic zirconia in a zirconia-containing alumina sintered body and the firing temperature.

Claims (2)

[Claims] (1) Mainly composed of alumina and zirconia in an amount of 2-3.
0 volume%, and the zirconia particles are uniformly dispersed in the alumina matrix in a state where they are not substantially aggregated. At room temperature (25 ° C.), 10 to 85% of the zirconia is monoclinic zirconia. A zirconia-containing alumina sintered body characterized in that the sintered body is heated so that the temperature difference from the water temperature becomes 250 ° C. and has a transverse rupture strength of 250 MPa or more after being dropped into water. 2. The zirconia-containing alumina sintered body according to claim 1, wherein the zirconia particles have an average crystal particle diameter of 0.2 to 2 μm.