JPS6186466A - Spinel 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 The present invention relates to spinel ceramics that have both high strength and high toughness.

[Industrial application field]

In general, spinel ceramics have superior corrosion resistance compared to alumina ceramics, but due to their inferior strength and toughness, in reality they are susceptible to tensile stress and impact forces.
It's just being used in areas where it doesn't belong. Therefore,
If the toughness of the spinel ceramics can be improved to increase its strength, it will be possible to use it in a wide range of fields such as corrosion-resistant and wear-resistant parts such as various nozzles and pulps, and artificial teeth.

[Conventional technology]

Many researchers have attempted to improve the strength and toughness of brittle objects such as ceramics, and one of the methods is to suppress grain growth by adding sintering aids. . However, this method does not provide a satisfactory toughness improvement effect. Next, there is a method of suppressing the growth of cracks by dispersing fine particles in the sintered body, but if it is difficult to uniformly disperse the fine particles in the sintered body, this method will not be sufficiently effective. Not yet.

[Problem that the invention seeks to solve]

From the above-mentioned viewpoints, the present inventors have conducted intensive research in order to solve the problems of conventional spinel-based ceramics and thereby obtain spinel-based ceramics that have high strength and high toughness.

[Means for solving problems]

As a result, the tetragonal crystal thread Zr containing spinel-based ceramics as a matrix and containing Y2O3 as a stabilizer.
It has been discovered that the strength and toughness of spinel ceramics can be improved by dispersing O□ without special particle size control, and the present invention has been achieved based on this knowledge.

That is, the present invention provides component A: MgO function nAJL203
Spinel 20 to 95 volumes represented by (1 excitation),
Component B: Tetragonal ceramic containing 2 to 3.5%/L/% of Y2O3.

[Effect]

The mechanism for improving the strength and toughness of the spinel ceramics of the present invention is that when an external force is applied, the tetragonal Zr02, which exists metastably in the spinel ceramics, transforms into the monoclinic Zro2 due to the stress at the crack tip. This improves strength and toughness by absorbing fracture energy.

Furthermore, if a spinel ceramic containing an excessive amount of At203 as a solid solution is used as a matrix, and metastable tetragonal ZrO2 containing Y2O3 as a solid solution is dispersed therein, heat treatment is performed at a temperature lower than the spinel solid solution formation temperature. It has been found that the addition of microscopic mechanisms to spinel-based ceramics has the effect of improving strength and toughness.

In the present invention, the reason why the component composition range is limited as described above will be explained below.

(a) Spinel (Z0, cough 20,) Zr02 generally undergoes a transition from tetragonal to monoclinic at a temperature of about 850°C during cooling from a high temperature, accompanied by a volume expansion of about 4. Now. According to research by the present inventors, if ZrO2 particles are dispersed in a matrix that does not react with ZrO□ and sintered, and the matrix suppresses the volume expansion during ZrO2 transition, the tetragonal → monoclinic transition does not occur. zu, 85
Tetragonal ZrO2 can exist metastablely from temperatures below 0° C. to room temperature.

In this case, the tetragonal ZrO 2 particles existing metastably in the matrix are in a compressive stress state or a tensile stress state due to the difference in thermal expansion coefficient with the matrix. In order to obtain good strength and toughness improvement effects due to the phase transition of the tetragonal Zr0z, it is desirable that the tetragonal ZrO□ particles existing metastably in the matrix be in a tensile stress state. Zr
The stress state of O□heton is the matrix and tetragonal ZrO
This is caused by the difference in the coefficient of thermal expansion between the ZrO□ particles and the tetragonal ZrO□ particles when the IJ-Fuchs coefficient of thermal expansion is smaller. The coefficient of thermal expansion of tetragonal ZrO2 is 11 x 10'''6/℃, but the coefficient of thermal expansion of spinel is as small as s Nowadays, a sintered body in which tetragonal ZrO□ is metastably dispersed in a spinel matrix, that is, a spinel ceramic, has a good strength and toughness improvement effect of 14T.
It is something that can be done.

On the other hand, spinel forms a spinel solid solution in the At203-excess region, and its formation temperature is very low. When a sintered body of spinel solid solution is heat-treated at a low temperature, the Kita At2 in the sintered body is
O8 particles are uniformly precipitated, and the effect of improving strength and toughness due to particle dispersion is obtained. The spinel solid solution composition range in which the effect of improving strength and toughness due to such dispersion of precipitated AA203 particles is observed is AL20a/MgO≦4 (molar ratio).

For the above reasons, in the present invention spinel is MgO-cough 4
o3 (1≦n≦4) is a suitable foil.

(b) Y,03 Zr02 generally takes a transformation phase from a high-temperature cubic crystal to a tetragonal crystal and a monoclinic crystal as the temperature decreases.

According to the research of the present inventors, 3 Y2O3 was added to ZrO2.
, 5 molti, Zr0z stably exists in the form of a high-temperature cubic crystal up to room temperature. Even if external force is applied to the spinel ceramic in which the cubic ZrO2 particles are dispersed, the cubic 2102 particles in the ceramic do not transform into monoclinic, so the strength and toughness improvement effect of the spinel ceramic is not effective. I can't get it. In addition, when the amount of YO is less than 2 molt, Zr02 exists in a monoclinic form, so
Even if this is dispersed in spinel ceramics, the effect of improving the strength and toughness of the ceramics cannot be obtained. In other words, when Y2O3 is added in an amount within the range of 2 to 3.5 mol relative to ZrO□, ZrO□ can be made to exist metastablely in a tetragonal system, and for the first time, it has the effect of improving the strength and toughness of spinel ceramics. It shows itself.

(e) ZrO□ The main strength and toughness improvement mechanism of spinel ceramics in the present invention is the phase transition of tetragonal ZrO2, which exists metastably in spinel ceramics, to monoclinic Zr0z when external force is applied. It is based on stress absorption by Therefore, in order to obtain a greater effect of improving strength and toughness, it is necessary to have a greater number of tetragonal ZrO□ particles present in a metastable manner in the spinel ceramic. According to the research conducted by the present inventors, the amount of ZrO2 is 5 vol.
If it is less than that, there is no effect of improving strength and toughness, and there is no point in adding it.

In addition, when the amount of ZrO□ exceeds 80 vol. H, the thermal stability of the tetragonal ZrOO in the spinel ceramics decreases significantly, and the thermodynamically stable monoclinic temperature range (approximately 850 degrees Celsius or less) is maintained for a long time. If this is maintained, most of the metastable tetragonal ZrO2 in the spinel ceramic will transform to monoclinic, and the effect of improving strength and toughness will no longer be obtained. That is, the effect of improving strength and toughness is exhibited when the amount of ZRO2 added is in the range of 5 to 80 vol.

The manufacturing method for obtaining the high-strength, high-toughness spinel-based ceramics of the present invention may be carried out by following the usual powder metallurgy method, but in order to further improve the strength and toughness, ZrO□ particles may be added. Must be evenly distributed,
For mixing, wet ball mill mixing or attritor mixing is preferable. Further, the firing is performed in the air or in vacuum, preferably in a reduced pressure nitrogen atmosphere, at a temperature of 1400-1700°C.
Sintering can be done by holding the temperature in the temperature range of 'C for (9) minutes to 5 hours, and when using spinel solid solution raw material, it can be sintered by holding it in the temperature range of 1,000 to 1,300 degrees Celsius for (to) minutes to 2 hours during cooling after sintering. , it is necessary to perform heat treatment to precipitate At, 03. In particular, when high-density ceramics are required, high-density ceramics can be obtained by hot isostatic sintering or hot pressing.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Commercially available Mgo-At2o3 powder was used as the raw material powder, and Zr0Ct2'8)i
20 Add ycz, 6H20 aqueous solution to the aqueous solution so that Y2O3 is 1 to 4 molt with respect to ZrO□, drop ammonia water to this mixed solution to co-precipitate, filter dry, and grow at 900 ° C. ZrO2(-Y2O3
) Powder was used. These raw material powders were
Blend the composition shown in the table, add ethyl alcohol as a solvent, mix in a ball mill for 15 hours, and then dry. Then, this mixed powder is 1toTV/cpR2
After isostatic pressing at a pressure of
-3 were produced. Comparative ceramics have compositions outside the scope of the present invention.

As a result, for each ceramic obtained, the state% 3
Point bending strength and fracture toughness were measured using the notched beam method, and the results are also shown in Table 1. As shown in Table 1, inventive ceramics 1 to 4 all have high strength and high toughness, whereas comparative ceramics 1 to 3, which have compositions outside the inventive range, have high strength and high toughness. Both toughness and toughness are inferior.

Example 2 Commercially available MgQ/At2o3 powder was used as raw material powder, and commercially available Zr was added with 3 molti Y2O3 as a stabilizer.
O2 (tetragonal) powder is blended so that the amount of Zr02 is from o to 90 vol. Ethyl alcohol was added to these formulations, mixed in a ball mill for 15 hours and dried, and the resulting mixed powder was isostatically pressed at a pressure of 1.5 tons/cm' and kept at a temperature of 1500°C for 3 hours in the air. Ceramics are created by firing under certain conditions.

For each of the obtained ceramics, three-point bending strength at room temperature and fracture toughness by the notched beam method were measured and shown in Table 2. In addition, in order to investigate the thermal stability of these ceramics, the amount of monoclinic ZrO□ formed and the three-point bending strength after being maintained at 200° C. for 100 hours were measured and are shown in Table 3.

As shown in Table 2, when the amount of ZrO2 exceeds 80 vol.-, the strength cannot be increased by the amount of ZrO2, and as shown in Table 3, when the amount of ZrO2 exceeds 80 vol. The thermal stability of spinel ceramics is extremely high.
Moreover, as shown in Table 2, when the amount of ZrO2 is less than 5 vol. h, there is almost no effect of improving the strength and toughness.

In this way, a high-strength, high-toughness spinel-based ceramic can be obtained in which the amount of ZrO2 added is 5 to 80 vol. defined in the present invention and has excellent thermal stability.

Example 3 Spinel (solid solution) powder represented by MgO-nAt203 manufactured so that n = 1.2, 3.4.5 was used as raw material powder, and 3 mol qbY2 as a stabilizer.
Commercially available zr02 (tetragonal) powder added with
It was blended so that the amount of ZrO□ was 50 vol. This was mixed and pulverized using an attritor mill, then wasostatically molded at a pressure of 1 ton and 40°C, and then heated to a temperature of 1650°C in the atmosphere.
After firing under conditions of holding for a long time, 1200℃ during cooling.
Heat treatment was performed at a temperature of 2 hours to precipitate fine AL203, followed by cooling to obtain spinel ceramics.

The theoretical density ratio, three-point bending strength, and fracture toughness by notched beam method were measured for the obtained ceramics, and the results are shown in Table 4.

As shown in Table 4, spinel (
Spinel ceramics using powder raw materials (1≦n≦4) have both high strength and high toughness, but spinel ceramics outside the scope of the present invention are found to have significantly inferior strength and toughness.

Table 1 Table 2 *1) 99% or more of the ZrO2 phase before heating is a tetragonal phase.

Table 4 [Effects of the Invention] As explained above, the spinel ceramics of the present invention have excellent corrosion resistance, excellent thermal stability, and significantly improved strength and toughness. It is expected to be used in a wide range of fields, including corrosion-resistant and wear-resistant parts such as loincloth nozzles and valves, and artificial teeth.

Claims (1)

[Scope of Claims] A high-strength, high-toughness spinel ceramic made by sintering 20 to 95% by volume of component A and 5 to 80% by volume of component B. A component: spinel represented by MgO・nAl_2O_3 (1≦n≦4) B component: tetragonal ZrO_2 containing 2 to 3.5 mol% of Y_2O_3