JPH11116358A - Processing of superplastic ceramic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a superplastic ceramic to be processed at far much lower temperature than the conventional processing temperature, additionally at an equal to or higher strain rate than the conventional rate. SOLUTION: A ceramic that is mainly composed of complex crystalline structure of calcium silicate and lithium aluminosilicate, has an average crystal particle size of <=2 μm, the maximum crystal particle size of <=20 μm, a density of more than 98% theoretical density and contains 2-98 wt.% of lithium aluminosilicate based on the total amount of calcium silicate and lithium aluminosilicate is subjected to plastic working at a temperature of 800-1,100 deg.C at a strain rate of 10<-5> -5×10<-3> /sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to various low- and high-temperature parts / jigs / equipments requiring thermal shock resistance, various precision mold materials / precision inspection equipment parts / high-temperature instrument parts requiring low thermal expansion properties, and heat insulating properties. The present invention relates to a method for processing superplastic ceramics suitable for heat insulating materials for semiconductors requiring high precision processing and various precision parts requiring high precision processing, and more particularly to a method for processing superplastic ceramics capable of processing at low temperature and high speed.

[0002]

2. Description of the Related Art Ceramics are brittle materials, but it has been found that plastic processing similar to that of metal can be performed by reducing the crystal structure of a sintered body. Such ceramics that can be plastically processed are called superplastic ceramics. Representative examples thereof include zirconia, zirconia containing alumina, silicon nitride, and silicon nitride containing silicon carbide. (JP-A-62-91480, JP-A-63-182279, JP-A-4-1279)
03303, JP-A-8-12443).

[0003] However, these conventional techniques have a problem that the plastic working temperature actually requires a very high temperature of about 1400 ° C, and at a temperature lower than that, superplasticity is not exhibited. For example, in the example of Japanese Patent Application Laid-Open No. 62-91480, the plastic working temperature is 1400 to 1500 ° C., which is remarkably compared to the plastic working temperature of a metal such as 550 ° C. for aluminum alloy and 850 ° C. for titanium alloy. High temperature. At such a high temperature, it is necessary to make all the ancillary equipment such as a mold for performing plastic working made of ceramics, or to use carbon jigs and tools in a device having a vacuum system. It is what you need.

[0004] Another problem is that the strain rate during processing is low. In general, the strain rate during plastic working of superplastic ceramics is extremely small compared to metals, so that the production rate is inferior to metals. Therefore, there is no mention that plastic working of ceramics having a higher strain rate and good productivity is desired.

[0005]

As described above, in the prior art, the plastic working temperature of ceramics is extremely high, and the working speed is not sufficient. Accordingly, an object of the present invention is to provide a method for processing a superplastic ceramic which can be processed at a temperature much lower than the conventional one and at a strain rate equal to or greater than the conventional one.

[0006]

Under such circumstances, the present inventors have conducted intensive studies and as a result, have found that a high-density composite sintered body having a small crystal grain size composed of a fixed ratio of calcium silicate and lithium aluminosilicate has the following problems. The present inventors have found that plastic working at a low temperature and at a sufficiently large speed is possible, and have completed the present invention.

That is, the present invention mainly comprises a crystal structure composed of calcium silicate and lithium aluminosilicate, and has an average crystal grain size of 2 μm or less and a maximum crystal grain size of 20 μm or less.
μm or less, the density is at least 98% of theoretical density, a ceramic lithium aluminosilicate to the total amount of calcium silicate and lithium aluminosilicate is contained 2 to 98 wt%, a temperature of 800 to 1100 ° C., 10 ^-5 ~ 5 × 10
An object of the present invention is to provide a method for processing superplastic ceramics, which is characterized by performing plastic processing at a strain rate of ^-3 / sec.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The superplastic ceramic used in the present invention is a composite sintered body mainly composed of calcium silicate and lithium aluminosilicate. If only one of calcium silicate and lithium aluminosilicate is used, plastic working at low temperature and high speed cannot be performed, and characteristics as a ceramic material will be inferior.

The average crystal grain size of the superplastic ceramic must be 2 μm or less, and preferably 1 μm or less. When the average crystal grain size exceeds 2 μm, the superplastic behavior itself appears, but it is not preferable because the critical strain amount of plastic working decreases.

Further, the crystal grain size of the present superplastic ceramic must be at most 20 μm, preferably at most 10 μm, particularly preferably at most 5 μm. If there is a crystal that is significantly larger than the average crystal grain size, the crystal grain acts as a defect, which causes voids or breakage during plastic working.

Further, the density of the present superplastic ceramic must be 98% or more of the theoretical density, and more preferably 99% or more. If the density is less than this, voids existing in the sintered body become large voids during plastic working, and the limit strain amount is significantly reduced, which is not preferable. The sintered body may contain up to about 2% by weight of impurities contained in the raw material and unavoidable impurities in the production process. Therefore, 98% or more of the theoretical density is
Strictly speaking, it is necessary to consider the impurity of 2% by weight or less, but here, the numerical value converted by considering that it is composed only of calcium silicate and lithium aluminosilicate is used.

The ratio of calcium silicate and lithium aluminosilicate in the present superplastic ceramic must be 2 to 98% by weight as the ratio of lithium aluminosilicate to the total amount of both, and is preferably 5 to 95% by weight. More preferred. When the content of lithium aluminosilicate is less than 2% by weight or more than 98% by weight, the sintered body is not densified to 98% of the theoretical density and many pores remain, so that superplasticity is impaired.

As the calcium silicate constituting the superplastic ceramic, CaO is abbreviated as C, SiO ₂ is abbreviated as S, and C
S, C ₂ S, C ₃ S, C ₃ S _{2 and the} like. Among them, CS wollastonite is preferable, and wollastonite has two types of α and β. Knight is most preferred. C ₂ S, C ₃ S and the like may be contained, but if the amount is large, the superplasticity phenomenon is impaired, so that it is preferably up to 2% by weight.

As the lithium aluminosilicate constituting the superplastic ceramic, Li ₂ O is L, Al ₂ O ₃ is A, S
iO ₂ is abbreviated as S and includes eucryptite of LAS ₂ , spodumene of LAS ₄ , and solid solution of spodumene. Of these, spojumen are preferred in terms of cost and the like as compared with eucryptite. There are two types of spodumene, α and β, with β-spodumene being most preferred.

In addition to these, the superplastic ceramics
Fe as an unavoidable impurity component_TwoO _Three, TiO_Two, MgO, Mn
O, Na_TwoOK_TwoO, P_TwoO_FiveEtc. may be contained up to 2% by weight.
I don't know.

The superplastic ceramics may include, for example, at least one kind of wollastonite having an average particle diameter of less than 1 μm or calcium silicate which transforms to wollastonite upon firing, and at least one of lithium aluminosilicate having an average particle diameter of less than 1 μm. Forming a raw material mixture containing seeds,
This can be manufactured by firing at 1000 to 1150 ° C.

The starting materials for calcium silicate include wollastonite as well as CSH (a precursor of calcium silicate crystalline hydrate, and a molar ratio of Ca to Si of Ca).
/ Si is a general term for amorphous hydrates that can have various ratios), tobermorite, zonotolite, gyrolite, orkenite, and the like. Any of these can be used alone or in combination of two or more. Among them, CSH, zonotolite and wollastonite are preferable, CSH having a Ca / Si molar ratio of about 0.5 to 1.5 is preferable, and wollastonite is preferably natural β-wollastonite.

As the other starting material, lithium aluminosilicate, L: A: S = 1: 1: 2, 1: 1: 3, 1: 1: 4,
1: 1: 6, 1: 1: 8, 1: 1: 10, 1: 1: 12, 1: 1: 15, etc., either of which is used alone or in combination of two or more. be able to. Of these, LAS ₂ eucryptite,
The LAS ₄ spodumene and the LAS ₈ petalite are preferred, and from the viewpoint of cost and the like, naturally-occurring α-spodumene, β-spodumene obtained by calcining the α-spodumene, and natural petalite are preferred. Petalite becomes a β-spodumene solid solution at high temperatures.

These starting materials have an average particle size of less than 1 μm,
In particular, it is preferably 0.5 μm or less. This superplastic ceramic has an average crystal grain size of 2 μm or less and a maximum crystal grain size of 20 μm.
This is necessary because the size of the crystal grain in the sintered body depends on the grain size of the starting material used and the firing temperature. That is, if a raw material having a large particle size is used, it is natural that the crystal grain size of the sintered body structure becomes large, and even if a raw material having a small particle size is used, grain growth occurs during sintering. In the form, the crystal grain size of the sintered body becomes larger than the grain size of the raw material. Therefore, it is desirable that the raw material particle size used is smaller.

As a method for easily obtaining ultrafine particles of less than 1 μm of these starting materials, for example, the following methods can be mentioned.

That is, ultra-fine wollastonite particles are obtained by hydrothermally treating a slurry in which the Ca / Si molar ratio of the Si raw material and the Ca raw material is adjusted to 0.5 to 1.5 to synthesize calcium silicate hydrate. By firing at 1200 ° C and pulverizing if necessary,
Β-spodumene can be manufactured by sintering the spodumene at 1000 to 1300 ° C. and subjecting it to a phase transition to pulverize the obtained β-spodumene.

By calcination as described above, the former provides fine particles of β-wollastonite or an aggregate thereof, and the latter obtains a polycrystalline structure having fine crystal grain boundaries of β-spodumene, In each case, ultrafine particles can be easily obtained by a ball mill or the like without using a special ultrafine pulverizer such as an attritor.

The composition of the raw material blend may be such that the lithium aluminosilicate is 2-98% by weight based on the total amount of calcium silicate and lithium aluminosilicate in the crystal phase of the sintered body after firing. When a raw material having an impurity component content of 2% by weight or less is used, the lithium aluminosilicate raw material may be blended at a ratio of 2 to 98% by weight based on the total amount of the calcium silicate raw material and the lithium aluminosilicate raw material. it can.

By baking the above raw material mixture,
The superplastic ceramic used in the present invention is obtained. The firing temperature is preferably from 1000 to 1150 ° C. Firing temperature
If the temperature is lower than 1000 ° C., the sintered body is hardly densified, and the pores increase, so that the superplasticity performance is easily deteriorated. When the temperature exceeds 1150 ° C., the average particle diameter is liable to be 2 μm or more because the grain growth increases, depending on the raw material particle diameter. Superplasticity is impaired for reasons such as The firing time varies depending on the size of the target sintered body, but usually about 60 minutes is sufficient.

In the present invention, the above plastic working of the ceramics is performed at a temperature of 800 to 1100 ° C. and a strain rate of 10 ^{−5 to} 5 × 10 ⁻³ / sec. Although plastic working is possible even when the temperature is lower than 800 ° C., it is industrially disadvantageous because the strain rate is too low to be lower than 10 ⁻⁵ / sec. The temperature is 1100 ℃
When the temperature exceeds sintering temperature, the sintering temperature is approached and grain growth of the sintered body occurs.
It causes destruction and is not preferred.

[0026] Even if the strain rate is less than 10 ^-5 / sec, there is no inconvenience, but it is not industrial in terms of low efficiency.
On the other hand, when the strain rate exceeds 5 × 10 ⁻³ / sec, it is not preferable in that the pressure increases and a large-sized apparatus is required, and voids are formed in the sintered body.

The working pressure (stress) of the plastic working is different between a case where the pressure is controlled by a certain fixed pressure such as gas pressure and a case where the displacement is controlled by a certain fixed displacement speed. In the case of displacement control, the processing pressure depends on the deformation speed. That is, when the deformation speed is low, the saturation occurs at a lower processing pressure, and when the deformation speed is high, the saturation pressure becomes higher. The preferred working pressure is 1 to 50 MPa, and if less than this lower limit, it depends on the temperature at which the plastic working is performed, but in general, the strain rate is too low for industrial use, and when exceeding the upper limit,
The strain rate becomes too high, and voids are formed in the sintered body, which is not preferable.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the invention is limited thereto.

In each of the examples, when one of β-wollastonite and β-spodumene is small, it is difficult to completely identify the crystal phase of the sintered body. The crystal phase of the sintered body obtained with the ratio of β-wollastonite and β-spodumene used at 50:50 was confirmed. The crystal phases were β-wollastonite and β-spodumene. Nothing was found. Therefore, taking into account the weight loss (ignition loss) of each starting material at a high temperature, the ratio of the crystal phase of the sintered body is almost the same as that of the starting material, but the ratio of the crystal phase in the following examples is The numerical value of the ratio indicates a value as a pure content excluding this impurity.

Examples 1-4 (1) Raw Materials Used As a lithium aluminosilicate raw material, natural α-spodumene (Li ₂ O: 7.6% by weight, Al ₂ O ₃ : 26.5% by weight,
SiO ₂ : 64.5% by weight, other: 1.2% by weight, ignition loss 0.2% by weight)
- wollastonite (CaO: 46.2 wt%, SiO _2: 51.1 wt%, Other: 1.6 wt%, ignition loss 1.1 wt%) was used.

(2) Production of raw material fine particles (a) The natural α-spodumene used has an average particle diameter of 200
The temperature was raised to 1100 ° C. at a rate of 5 ° C./min, baked at this temperature for 1 hour, and then gradually cooled to obtain β-spodumene. The β-spodumene contained many fine cracks, and a kind of grain boundary appeared at a size of about 0.5 μm. When this powder was wet-pulverized by a ball mill for 72 hours, ultrafine particles having an average particle diameter of 0.45 μm were easily obtained. Milling conditions are mill volume: 400 liters,
Mill rotation speed: 100 rpm, media: 400 kg of alumina balls having a diameter of 5 mm, 100 kg of the above-mentioned β-spodumene coarse particles, and 100 kg of water were added to make a slurry concentration of 50%. (b) On the other hand, the natural β-wollastonite used had an average particle size of 2.5 μm, which was pulverized for 72 hours to obtain an average particle size of 0.5 μm.
2 μm ultrafine particles were obtained. Grinding conditions are as follows:
It is the same as in the case of spojumen except that 15% by weight of the dispersant is added to 00% by weight.

(3) Firing / grinding Raw materials of β-wollastonite and β-spodumene are collected from the respective slurries at various ratios, and 3% by weight of polyvinyl alcohol is added as a binder to the slurries and mixed. And granulated with a spray dryer. The granules are put into a mold and molded at 1 t / cm ² , and the obtained molded body is heated at a temperature of 5 ° C./min to a temperature shown in Table 1, held for 1 hour, and then cooled to a room temperature and cooled in a furnace to a diameter of 50 mm and a thickness of 4 mm. Was obtained. Both surfaces of this sintered body were ground using a # 400 diamond wheel (Okamoto Machine Tool Co., Ltd., precision surface grinder PSG-52D
X).

(4) Various measuring methods Density: Calculated by Archimedes' method. Flexural strength: Processing a sintered body to 3 × 4 × 40mm, JIS R 1601
Was measured by Crystal grain size: measured by scanning electron microscope (SEM) observation of the structure of the sintered body.

(5) Plastic Working The above JIS R 0601 test piece was subjected to plastic working by three-point bending at a temperature and a deformation rate shown in Table 1 in the atmosphere until it was deformed by 5 mm in the load direction. The tensile strain rate was 6tδ /
Calculated from S ² (t: thickness of test piece, δ: deformation speed of test piece, S: distance between lower fulcrums of bending).

(6) Results As shown in Table 1, the results all showed superplasticity at a much lower temperature and pressure than those of the prior art, and the strain rate was higher than that of the conventional one. After bending, when the tensile surface of the test piece was observed with a microscope, no crack was observed in any case.

Examples 5 to 8 Diatomaceous earth and slaked lime for industrial use were mixed at a Ca / Si molar ratio of 1 to prepare a slurry having a water / solids ratio (W / S) of 10.0.
For 1 hour to synthesize CSH. After drying this CSH at 120 ° C., it was baked at 1000 ° C. for 1 hour. When the crystal phase was identified by X-ray diffraction, it contained no impurities
It was β-wollastonite that was 100% transformed. This was an aggregate of ultrafine particles having an average particle size of 0.25 μm. The weight loss at this time is 13%. The β-spodumene before pulverization that had undergone a phase transition in the same manner as in Examples 1 to 4 and β-wollastonite obtained from the CSH were blended so that the solid content became 50:50. This was ground with a ball mill in the same manner as in Examples 1 to 4 to obtain a raw material having an average particle size of 0.15 μm. this
It was fired at 1050 ° C. in the same manner as in Example 1 to obtain a sintered body, and various characteristic values were measured. Then, the resultant was subjected to plastic working in the air under the conditions shown in Table 1, and as a result, as shown in Table 1, each of them exhibited superplasticity at a much lower temperature and lower pressure than the conventional one, and the strain rate was higher than the conventional one. Was. After bending, when the tensile surface of the test piece was observed with a microscope, no crack was observed in any case.

Examples 9 to 11 β-Wollastonite starting from CSH as in Examples 5 to 8 and commercially available β-eucryptite (loss on ignition: 0.4% by weight) were used as in Examples 1 to 4. Similarly, pulverization was performed with a ball mill to obtain raw materials having an average particle size of 0.15 μm and 0.21 μm, respectively. These were blended so as to have a solid content of 50:50. this
It was fired at 1000 ° C. in the same manner as in Example 1 to obtain a sintered body, and various characteristic values were measured. Next, as a result of plastic working under the conditions shown in Table 1 in the atmosphere, as shown in Table 1, each of them showed superplasticity at a much lower temperature and lower pressure than the conventional one, and the strain rate was higher than the conventional one. Was. After bending, when the tensile surface of the test piece was observed with a microscope, no crack was observed in any case.

Comparative Examples 1 to 5 Except that the blending conditions and firing conditions were as shown in Table 1, fired bodies were obtained in the same manner as in Examples 1 to 4. Next, plastic working was performed under the conditions shown in Table 1, respectively. As a result, cracks were observed in Comparative Examples 1, 2 and 5 after the processing test. The sintered bodies used in Comparative Examples 3 and 4 were the same as those in Example 2. However, in Comparative Example 3, the processing temperature was too low, plastic deformation could not catch up with the deformation speed, and the sample broke during the test. Was too hot to carry the load and creeped.

Comparative Example 6 A fired body was obtained in the same manner as in Example 2 except that the average particle size of the starting materials was 1.1 μm and the firing temperature was 1100 ° C. It broke during the plastic working test due to the coarse grain size.

Comparative Example 7 The same as Example 2 except that the plastic working speed was 10 mm / min. It broke in the middle of the test because the speed was too high and the pressure increased significantly.

COMPARATIVE EXAMPLE 8 A partially stabilized zirconia sintered body of 3 mol% yttria solid solution having an average crystal grain size of 0.3 μm and almost 100% densified was subjected to plastic working under the conditions shown in Table 1. At the temperature, it showed little deformation and broke brittlely.

Comparative Example 9 An alumina / zirconia composite sintered body having an average crystal grain size of 0.4 μm obtained by adding 20 wt% alumina powder to zirconia powder in which 3 mol% yttria is dissolved was subjected to plastic working under the conditions shown in Table 1. However, it did not show any deformation at this temperature and broke brittlely.

[0043]

[Table 1]

[0044]

According to the present invention, it is possible to process superplastic ceramics at a temperature much lower than the conventional one and at a strain rate which is equal to or greater than the conventional one.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihiko Misaki 6276 Onoda, Onoda-shi, Yamaguchi Prefecture Chichibu Onoda Central Research Laboratory (72) Inventor Masahiko Suzuki 1-29 Showa-cho, Aoba-ku, Sendai City, Miyagi Prefecture

Claims (2)

[Claims] 1. A crystal structure mainly composed of a composite of calcium silicate and lithium aluminosilicate, having an average crystal grain size of 2 μm or less, a maximum crystal grain size of 20 μm or less, and a density of 98% or more of the theoretical density. Ceramics containing 2 to 98% by weight of lithium aluminosilicate based on the total amount of lithium aluminosilicate,
A method for processing superplastic ceramics, wherein plastic processing is performed at a temperature of 800 to 1100 ° C. and a strain rate of 10 ^{−5 to} 5 × 10 ⁻³ / sec. 2. The processing method according to claim 1, wherein the calcium silicate is wollastonite, and the lithium aluminosilicate is at least one selected from eucryptite, spodumene, and spodumene solid solution.