JPH05221738A - Ceramic having oriented macrodome crystal and its production - Google Patents

Abstract

PURPOSE:To improve fracture toughness and strength by compressing and deforming a specified ceramic presintered body in one direction at a temp. where the presintered body can be plastic-deformed under pressure and expansion-deforming the body in the other direction. CONSTITUTION:Ceramics such as Si3N4, a sintering assistant, a solvent and a dispersant are mixed in a specified molar ratio to prepare argil. The argil is filled in the carbon die lined with a mold releasing agent of a hot press, cold-rolled under gaseous N2 pressure, then heated to a specified temp. and presintered to obtain a ceramic presintered body having a macrodome crystal or crystal nucleus. The presintered body is kept at high temp. and pressure, compression-deformed in the microdome crystal direction and then expansion- deformed in the orthogonal direction to form a two-dimensionally oriented secondary sintered body. The body is subjected to HIP to obtain a sintered body having >=8-9 MPam<1/2> fracture toughness and >=1200-1300 MPa strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel ceramic sintered body having oriented (in particular, two-dimensionally oriented) long-axis crystals (for example, columnar or acicular crystals or plate-like crystals having long axes) and its production. The present invention relates to a method, in particular, a method in which such a long-axis two-dimensional oriented crystal is formed in a sintering process (in-situ), and an ultra-high toughness and ultra-high strength material that can withstand a harsh working environment is provided. Is provided.

[0002]

[Technical background] In recent years, the need for ultrahigh-strength materials that can withstand even harsh operating environments is increasing, and great expectations are placed on improving the toughness and reliability of ceramics. In particular, ceramics are highly promising as in-vehicle engine parts and members because they have higher strength than metals and are excellent in heat resistance.

However, ceramics have a very low fracture toughness value as compared with metals, and fracture is brittle, so that the problem of still lacking reliability has not been completely overcome.

That is, since ceramics are essentially brittle, a method of dispersing or precipitating a heterogeneous phase as an energy dissipation source in the material is used for improving the toughness thereof.
That is, it has been considered that compounding is basically effective. Various toughness improving mechanisms by particle dispersion or fiber dispersion have been proposed so far, and research is underway to find conditions under which high strength and high toughness can be achieved by fundamentally pursuing each mechanism. It has been done vigorously.

Silicon nitride-based ceramics are an example of high-strength materials that can withstand use at high temperatures. However, silicon nitride-based ceramics have been attracting attention for their excellent strength characteristics and are being studied as structural materials. It has been put to practical use in some areas. However, like other ceramic materials, silicon nitride has a major problem as a structural material that lacks reliability in strength characteristics (has large variations) and low toughness, and therefore its practical application has not been accelerated. The current situation.

[0006]

2. Description of the Related Art Ken Kawashima et al., "Si by fiber control
Diversification of ₃ N ₄ ceramics "Silicon nitride ceramics (2), pp. 135-146, the drawbacks of such silicon nitride ceramics are mentioned, and the results of attempts to improve them by the HIP method are reported. That is, as bending strength, Sinter (gas pressure sintering) is 680 to 1079M.
953-1230MP with Pa and Sinter + HIP
a, Sinter / HIP (gas pressure sintering to HIP continuous treatment) reports 1000 to 1227 MPa and fracture toughness values of 5.3, 5.2 and 5.7 MPa · m ^1/2 respectively ( 135-138, Table).

[0007]

However, when a material having a high bending strength is sought, the K _IC becomes small, and conversely, when a material having a high K _IC is sought, the bending strength tends to be low. That is, bending strength and fracture toughness have opposite tendencies and it is extremely difficult to combine them (No. 143).
Page Fig. 15-Fig. 17).

Therefore, as a method for improving both of the above characteristics, "gas pressure sintering (Sinter) + HI" is used.
P ”or“ gas pressure sintering / HIP ”(from gas pressure sintering to H
It requires a complicated process such as continuous processing up to IP, and it is considered that there are still great difficulties in its practical application. Some improvement was achieved by this method, but bending strength was 1074 MPa, K _{IC was} 6.7MPm.
The combination of ^1/2 is the highest, and if one of the characteristic values is tried to be raised above this, the other will decrease, so there was no choice but to compromise the characteristic values of both.

On the other hand, as a conventional method for increasing strength and toughness, a method based on so-called fiber reinforcement by adding and dispersing fibers in a ceramic matrix has been mainly used. In the case of this method, it is difficult to uniformly disperse the fibers in the matrix, it is difficult to ensure the matching or bonding between the fibers and the matrix phase, and further, the strength of the fibers is deteriorated during the sintering process. There are various problems such as careful selection of fibers and sintering conditions that do not occur.

Therefore, it is a first object of the present invention to provide a novel manufacturing method capable of orienting the long-axis crystals of a ceramic sintered body.

A second object of the present invention is to provide a novel ceramic sintered body having both high strength and high toughness, and to provide a manufacturing method therefor.

A third object of the present invention is to provide a silicon nitride-based ultra high strength and ultra high toughness ceramic sintered body in which both orientation and growth of long-axis crystals are controlled.

[0013]

The first object of the present invention is to provide a ceramic pre-sintered body containing long-axis crystals or long-axis crystal nuclei in the temperature range where the plastic deformation under pressure is possible. Columnar or acicular crystals characterized by compressing and compressing in one axial direction sufficient to orient the crystals to cause compressive deformation in the compressive axial direction and at the same time expand and deform in a direction different from the compressive axis It is achieved by a method for manufacturing a ceramic sintered body having As a result, a ceramic sintered body containing a long-axis crystal substantially oriented in one-dimensional or two-dimensional direction can be obtained, and the orientation of the crystal can be controlled so as to have both high strength and high toughness. ..

[0014] Further preferred specific developments of the manufacturing method of the present invention are shown in the dependent claims from claim 2.

That is, by further including a crystal growth step of controlling and growing a long-axis crystal (or a long-axis crystal nucleus) in an oriented state subsequent to or at the same time as the above-mentioned orientation step, optimal for both strength and toughness. It is possible to control the orientation and control the crystal length (or the crystal growth degree, and optionally the aspect ratio in consideration of the growth of the thickness) (claim 2).

In the crystal growth step, in the oriented state of the aspect ratio of the major axis crystal, a first predetermined curve showing a change in toughness as the aspect ratio increases, and a change in strength also as the aspect ratio increase. According to the second predetermined curve showing the above, by controlling and growing until a predetermined aspect ratio is reached (claim 3), a product of uniform quality with high yield, which is designed in advance by test and industrially controlled, is obtained. Obtained (see FIG. 5).

It is preferable for orientation that the amount of expansion deformation is at least an amount corresponding to the amount of shrinkage of the pre-sintered body from the green compact (claim 4).

The expansion and deformation are carried out in at least one-dimensional direction (preferably two-dimensional direction) orthogonal to the pressure-compression axis (claims 5 and 6).

Further, a pre-sintering step of sintering the pre-sintered body without substantially applying a compressive pressure (that is, a force for forcibly compressing the material to be fired such as hot press pressure and HIP) is further added. The pre-sintered body containing the fired and shrunk material is loaded into the hot press machine with a gap and hot pressed under a pressure sufficient to substantially orient the long axis crystal, and the long axis crystal in the oriented state. Of the pre-sintered body is continued in the hot press machine, for example, in the hot press machine or separately, by continuously applying the hot press pressurization for a sufficient time to grow the steel to reach a predetermined aspect ratio. It can be pre-sintered (for example, by gas pressure sintering, other ordinary sintering, etc.) without performing it, and the growth of the long-axis crystal after orientation can be controlled according to the purpose. If pre-sintering is performed using a hot press machine (but without HP treatment), the pre-sintered body is manufactured (from cold press forming to the pre-sintered body or pre-sintering) to compressive deformation. The crystal orientation step by can be continuously performed by one hot press machine. Note that, instead of the hot press machine, the crystal orientation by compression deformation can be performed by hot pressing a sheet-shaped pre-sintered body (for example, hot rolling with a roll),
As long as it is a plastic deformation means by hot pressing, other means can be used. In the case of hot pressing, there is an advantage that densification is achieved by crystal growth under pressure after orientation.

The method further comprises the step of further crystal-growing the ceramic sintered body having oriented long-axis crystals, that is, a secondary sintered body, by HIP processing until a predetermined aspect ratio is reached (claim 8). From the state reached by, the strength and toughness are increased by further growth of the long-axis crystal without deterioration of the strength.

By making the pre-sintered body in a state of containing a glass phase together with a long-axis crystal (or a nucleus thereof, which may be in a non-oriented state), the orientation treatment can be facilitated and, as much as possible, A pre-sintered body having sufficient high strength and high toughness can be obtained.

The term "long-axis crystal" includes not only columnar or needle-like crystals (including, of course, rod-like or fibrous crystals) but also plate-like crystals having a long axis. It is essential that these crystals include at least those that can be further grown in the processing steps after pre-sintering, and may be crystal nuclei as long as they can be oriented.

The oriented long-axis crystals (particularly columnar or needle-like crystals) can achieve an increase in toughness due to deflection enhancement without addition of fibers or whiskers. However, the present invention
Further strengthening by compounding (fiber or whisker reinforcement,
(For example, particle dispersion strengthening) is not excluded.

By using silicon nitride, which is a columnar crystal, as an example of the long-axis crystal, a suitable sintered body can be obtained (claim 9). As the long-axis crystal ceramic material capable of crystal orientation, in addition to silicon nitride, SbSI, SbSOI, Pb
Bi ₂ Nb ₂ O ₉ , Bi ₄ Ti ₃ O ₁₂ , (Pb, K) Nb
₂ O ₆ , (Sr, Ba) Nb ₂ O ₆ , (Pb, Ba, La) Nb ₂ O ₆ etc. (above columnar or needle-like), and other cordierite (above long axis tabular) etc.

In the case of silicon nitride, the columnar crystals are β-Si.
₃ N ₄ , but the starting powder is α-Si ₃ N ₄ or
It may be a composition (or crystal nucleus) capable of forming β-Si ₃ N ₄ during presintering. The same applies to other types of ceramic materials, and it is not always necessary to use the long-axis crystal as a starting powder in the presintering step, and a state suitable for presintering can be selected.

A second object of the present invention is achieved by a ceramic sintered body characterized in that it comprises long-axis crystals oriented by hot pressing deformation and substantially oriented in at least one-dimensional direction. It (Claim 10).

The ceramic sintered body containing the oriented columnar or acicular crystals as the main phase does not necessarily require the fiber-reinforced phase added from the beginning, which is different from the main phase, and has a predetermined high strength. -High toughness can be achieved (claim 10)
~ 12).

The oriented long-axis crystals may be included as a dispersed phase with respect to the matrix constituent phase.

By including the oriented long-axis crystals substantially oriented in a two-dimensional direction, a ceramic sintered body having higher strength and higher toughness can be obtained (claim 11).

By using a silicon nitride crystal as the oriented long-axis crystal, a high-strength and high-toughness silicon nitride sintered body can be obtained (claim 12).

Aspect ratio 4 of the oriented long-axis crystals
The above is preferable (claim 13).

Typically, according to the present invention, a strength of 900 M
A silicon nitride-based sintered body having a columnar silicon nitride crystal having a Pa of 2 or more and a fracture toughness value of 4 MPam ^1/2 or more and being substantially two-dimensionally oriented is obtained (claim 14). Further strength 1
A combination of unprecedented values of 100 MPa or more, fracture toughness K _{IC of} about 7 MPam ^1/2 or more, maximum strength of 1200 to 1300 MPa or more, fracture toughness K _{IC of} 8 to 9 MPam ^1/2 or more (claim 15) , 16). A ceramic sintered body having an ultrahigh strength and an ultrahigh fracture toughness value can be obtained by having a two-dimensionally oriented long-axis crystal and an aspect ratio of 8 to 12 (claim 17).

In other words, by including a long-axis crystal that is substantially two-dimensionally oriented and isotropically growth-controlled at a predetermined aspect ratio, both strength and toughness are theoretically predicted from the substance. The highest standards are achieved.
(Claim 18).

[0034]

DETAILED DESCRIPTION OF THE INVENTION Silicon nitride will be described below as a typical example of a material for forming a typical long-axis crystal.

Factors that improve the fracture toughness value can be roughly classified into two. (1) Direct interaction between the main crack and dispersed particles (2) Mechanism of forming a process zone near the tip of the main crack (1) includes bending of the leading edge of the main crack and deflection of the main crack surface. , (2) include microcracking, stress-induced phase transition, and fracture surface crosslinking.

In silicon nitride capable of forming columnar crystals in the sintering process, crack deflection is considered to be a major factor as a mechanism for increasing toughness. According to the calculation of Faber et al., The fracture toughness (theoretical value) is about four times that of the matrix in the dispersion of the columnar crystals with the aspect ratio of 12, but the measured value is smaller than that. (KT Fiber et al., Acta).
Metal. 31 , 565, 577 (1983),
"Ceramic Reinforced Composite Ceramics", Industrial Technology Service Center Co., Ltd. (1991), pp. 68-72).

However, it is not known how to produce such a sintered body. Therefore, in the present invention, it is possible to obtain a fracture toughness value higher than the conventional one by orienting the long-axis (columnar or rod-shaped) crystal of silicon nitride in two dimensions or one dimension, or by controlling the crystal growth. It was done. In order to realize the orientation of the long-axis crystal, the pre-sintered body (or the primary sintered body) containing the long-axis crystal is compressed and deformed with respect to one axis at a predetermined high temperature, and at the same time, it is different (especially orthogonal). )) One-dimensional or two-dimensional expansion deformation (that is, hot plastic deformation)
By doing so, it became clear that the crystal can be oriented one-dimensionally or two-dimensionally. as a result,
For example, the fracture toughness value is about 4 MPam ^1/2 to about 8 corresponding to the aspect ratio of 4 to 12 from 3 MPam ^{1/2 in the} non-oriented state.
It is possible to obtain those having a pressure of at least ¹ MPam ^1/2 .

The following two mechanisms are considered to act in the present invention. That is, (1) orientation of long-axis crystals (2) growth control of oriented long-axis crystals

(1) <Mechanism of Increasing Fracture Toughness Value Due to Orientation> As a mechanism of increasing the toughness of silicon nitride formed by long-axis crystals in the sintering process, crack deflection is the largest factor. For that purpose, it is essential to control the long-axis crystal.
Moreover, it is considered possible to obtain the maximum fracture toughness value indicated by silicon nitride if both orientation control and growth control of long-axis crystals are possible (this is also true for other ceramic materials). Applicable to). Generally, in the following cases regarding orientation control and growth control, the maximum crack deflection occurs and a high fracture toughness value is exhibited. Preferably, the maximum effect is obtained by realizing both the orientation control and the growth control. Both controls are based on a stepwise basic process (long-axis crystal formation by pre-sintering, and subsequent crystal orientation by hot pressure plastic deformation), and by adding a subsequent HIP,
It is surprising to bring about a dramatic improvement in the properties of both.

As shown in FIG. 3, when a crack propagates in the sintered body, the two-dimensional orientation material shown in ii) is clearly in a direction substantially orthogonal to that of the three-dimensional orientation material shown in i). The propagating crack is less likely to propagate. Therefore, the two-dimensionally oriented material is considered to be more advantageous for increasing the toughness against cracks in a specific direction.

(2) <Mechanism of increasing fracture toughness value by controlling long-axis crystal growth> As shown in FIG. 4, even when only the two-dimensional oriented material is considered, (i) when the long-axis crystal is short ( When the long-axis crystal of ii) is long, the crack deflection is larger and the crack is less likely to propagate in the direction intersecting with the long-axis crystal. Also, regarding the thickness, it can be seen that there should be an optimum thickness that is neither too thick nor too thin. Therefore, to show maximum crack deflection,
There should be an optimal aspect ratio for it. From this viewpoint, the present invention was conducted by experiments and confirmed its effectiveness.

Due to the synergistic effect of the above two mechanisms (1) and (2), a sintered body of silicon nitride having a strength and toughness value suitable for the purpose of use can be obtained. The strength and toughness value can be adjusted according to the purpose. Controlled sintered bodies can be obtained respectively.

Based on this viewpoint, the orientation of the long-axis crystal was controlled for the purpose of improving the fracture toughness value of silicon nitride which forms the long-axis crystal in the sintering process.

In the conventional sintering method, the long-axis crystal of silicon nitride was three-dimensionally non-oriented (random state) and the fracture toughness value was about 3-5. Therefore, in the present invention, for the purpose of improving the fracture toughness value, when a pre-sintered body of silicon nitride containing a long-axis crystal together with a glass phase is uniaxially compressed and compressed by hot pressing at a temperature at which it can be plastically deformed by pressure. At the same time, this was expanded and deformed in the other two axial directions orthogonal to each other to orient the long-axis crystals two-dimensionally (hereinafter referred to as "HP treatment").
As a result, the fracture toughness value could be improved to about 8 MPam ^1/2 . As a result, the bending strength is 800
What was around MPa improved to around 1200 MPa.

In the present invention, "substantially oriented" means
The state in which the effect is significantly exhibited by the orientation of the long-axis crystal in a predetermined direction. Further, as the oriented long-axis crystal, in the case of silicon nitride, the aspect ratio ranges from 4 or more to 12 or more, preferably about 6.5 to 12 (more preferably 8).
~ 12).

In the case of a silicon nitride sintered body, it is sufficient that the HP treatment temperature is basically within the sintering temperature range. The conditions for the HP treatment are a temperature of 1700 to 180.
It is preferable that the range is 0 ° C., the pressure is 100 to 500 kg / cm ² , and the holding time is 0.5 to 3 hours. Pressure is 1
If it is less than 00 kg / cm ² , the orientation is insufficient, and 500
If it exceeds kg / cm ² , the crystal growth rate in the oriented state tends to be rather slow.

The optimum conditions for orientation by HP treatment are as follows: temperature of about 1750 ° C. and pressure of about 3 under the conditions of the examples of the present application.
It is 30 ± 50 kg / cm ² and the holding time is about 1 to 2 hours.

The firing shrinkage of the pre-sintered body from the state before sintering (cold press molding volume or green or dry compact) is about 10 to 20% (volume%) in the case of silicon nitride. The amount of expansion deformation in the non-compressed axial direction during the HP treatment for orientation is preferably at least an amount corresponding to this firing shrinkage.

Pre-sintering is thus carried out until a sufficiently high temperature is reached and until long-axis crystals are formed and grown to an extent sufficient for orientation. It is not preferable to apply a compression action by external pressure such as hot pressing before reaching such a state.

Although a sintering method by hot pressing itself is known, in this case, generally, hot pressing is started from the temperature at which sintering starts (about 1500 ° C. for silicon nitride). However, in the present invention, about 17
Sufficient pre-sintering until reaching a temperature of 00 ° C. or higher is preferable for free long-axis crystal growth.

For orientation by hot pressure plastic deformation,
A long-axis crystal (or its nucleus) exists in the pre-sintered body in an orientable state. Therefore, (1) the aspect ratio of the long-axis crystal (or nucleus) of the pre-sintered body is preferably 1.5 or more (more preferably 2-3),
(2) For plastic deformation, it is necessary that a predetermined flowable phase (generally a glass phase or a liquid phase) is present. In order to secure sufficient orientation possibility, the pre-sintered body has a direct compression action such as hot pressing and is a product to be fired (molded body).
It is preferable to sinter and crystallize in a natural state without applying the above.

The silicon nitride sintered body preferably contains a predetermined sintering aid in addition to silicon nitride. First, Y ₂ O ₃ will be indispensable for producing a glass phase and then a specific crystal phase (Y ₂ Si ₃ O ₃ N ₄ ) at grain boundaries. The more sintering aids, Al ₂ O _3, the _{outer, La 2 O 3, Nd 2} O 3, CeO
It is preferred to use one or more rare earth oxides such as ₂ together with Y ₂ O ₃ .

The ratio of silicon nitride: sintering aid = 98: 2-9
It is preferable that the range is 0:10 mol% and the content of Y ₂ O ₃ is 1 mol% or more. When the amount of the sintering aid (or the component other than the component that constitutes silicon nitride at the time of sintering) exceeds 10 mol 5, the production and growth of β-Si ₃ N ₄ that should be a long-axis crystal tend to be inhibited. There is one, so be careful.

As a result of such HP treatment, a combination of high strength and high toughness with a bending strength of about 1100 Pa or more and a fracture toughness value KIC of about 6.7 MPam ^1/2 was obtained. It was FIG. 5 shows sample N of Table 1 described later.
o. The measured values of 1 to 4 are shown.

It should be noted that, by the HP treatment, long-axis crystals (columnar crystals) grow together with (or after) the orientation, and as shown in FIG. 5, substantially linear (or slightly curved) crystals are formed on each other. The two curves intersect to show strength (flexural strength) and fracture toughness. The toughness y is y = 2.8 + 0.54x, where x is the aspect ratio.
(MPam ^1/2 ) (Formula I), strength y ′ is y ′ = 1459−
It is represented by 52x (MPa) (formula II).

According to these expressions I and II, HP treatment is performed until a predetermined aspect ratio is reached, and a sintered body having desired strength and toughness values can be obtained. This fact is due to the design of the material,
It is extremely useful in production.

That is, the toughness value K _IC has an aspect ratio of 4 to 10
Shows a curve of about 5 to about 8 MPam ^1/2 , and the strength is about 1250 to 950 M for the same aspect ratio.
The value of Pa is shown.

Although this is an effect of the HP treatment (that is, by the orientational growth), according to the present invention, the controlled orientational growth of the long-axis crystal (its state and process) is further controlled by growth as described later. It was found to be extremely useful as a basis for

(2) <Control of Growth of Long-Axis Crystals> When silicon nitride is sintered, a sintering aid is generally mixed, but growth of long-axis (columnar) crystals occurs during HP sintering depending on the kind of the aid. There will be a considerable difference. In the present invention, as a sintering aid, La ₂ O ₃ —Y ₂ O ₃ system, Al ₂ O ₃ —Y ₂ O ₃ system, Nd are used.
As a result of testing the ₂ O ₃ —Y ₂ O ₃ system and the CeO ₂ —Y ₂ O ₃ system, Nd ₂ O ₃ —Y ₂ O, which produces the largest major axis crystal, has a difference in the degree of growth of the major axis crystal. It was revealed that the fracture toughness value of the ₃ type silicon nitride reached 8 MPam ^1/2 by the HP treatment. As a sintering aid for silicon nitride, Al
_{In addition} to rare earth oxides including ₂ O ₃ and Y ₂ O ₃ , MgO and Ca
Known materials such as O can be used.

The pre-sintered body is subjected to HP treatment once and then isotropic pressure of high pressure is applied to silicon nitride (secondary sintered body) at high temperature (HIP
Treatment) further grows the long-axis crystal,
Not only can it be possible to control the degree of growth by changing the pressure, but it also prevents the decrease in strength that accompanies an increase in the aspect ratio as seen during HP treatment, and not only the toughness but also the strength. It was also found that can be further increased.

(2-1) Specific Example of Growth Control of Long-Axis Crystals (Sintering Aid, Growth Control by Changing Sintering Conditions) The following is performed depending on the difference between the sintering aid and the sintering conditions during hot press treatment. There was a difference in the major axis (columnar) crystals.

[0062]

[Table 1]

From the above, columnar crystal growth control (thickness and length, by changing the sintering aid and HIP processing conditions)
It can be seen that especially aspect ratio control) is possible. The pre-sintering conditions for obtaining the pre-sintered body also affect the aspect ratio, but the pre-sintering includes moderate long-axis crystal growth achieved by gas pressure sintering or the like and is as high as possible. A sintered state is achieved.

In addition, in addition, if the raw material of the pre-sintered body is formed by using long-axis (columnar) crystal silicon nitride (β type) or the like and is sintered (gas pressure sintering, etc.), the density of Is very low (and therefore bulky), that is, sufficient sintering does not proceed, and therefore the density, strength, and fracture toughness values are all amorphous (generally rounded particles). It is far inferior to what was formed and fired using finely divided starting particle powder.

This fact is effective for silicon nitride, except that long-axis crystals (columnar or rod-shaped crystals) are produced from the above-mentioned fine powder starting particles during the sintering process (in-situ) and contained. No method has been found at this time.

Sintering of the pre-sintered body is preferably carried out in the same HP apparatus for performing the HP treatment (orientation treatment) in the subsequent stage for the sake of work efficiency, but it may be pre-sintered in another furnace or HP apparatus. , If necessary.

(B) (2-2) <Strength based on growth control by HIP process-
Toughness Value Control> Curves A and B shown by arrows in FIG. 5 show the effect of the HIP treatment, and respectively represent curves of toughness value and strength value (first and second) that change with the increase of the aspect ratio. .. Curves A and B are both values A in the state after HP treatment (secondary sintered body)
1B1 (Sample No. 2 in Table 1) as a starting point, 1-5
The change in toughness and strength values when HIP treatment of hr is performed under a pressure of 1800 ° C. × 100 kg / cm ² is shown.
A temperature substantially equal to or higher than the temperature of this HIP treatment (preferably, further at a high temperature of 10 to 50 ° C., for example, 1750 to 185
It can be carried out at 0 ° C, preferably at a pressure of 100 to 300 atm, and at a pressure of 100 to 300 atm.

Quite surprisingly, the tendency for the decrease in strength caused by the continuation of the HP treatment after orientation is interrupted and both curves show an increase. With continued HIP treatment, the toughness value K _IC increases uniformly with increasing aspect ratio, reaching a maximum value of about 9.7 MPam ^1/2 . On the other hand, the strength increased to more than 1300 MPa with the increase of the aspect ratio of 7 to 9, and after drawing the top portion with the aspect ratio of 9 to 10,
Although it is slightly lowered, an aspect ratio of 11 or more shows about 1240 MPa.

This data shows that the 2
Long-axis (columnar) crystals that are dimensionally oriented and grown to a predetermined aspect ratio are grown by controlling the aspect ratio in the direction of increasing the aspect ratio by HIP processing. The combination of values is to be achieved in a very controlled manner.

This finding is extremely important not only for practical use in the future but also as a model mechanism for increasing strength-toughness not only for silicon nitride but also for general ceramics that produces long-axis crystals. It is no exaggeration to say that it is a breakthrough.

[0071]

EXAMPLE An example of controlling the orientation of the long-axis crystal (two-dimensional orientation control by HP treatment) will be shown below.

(1) Preparation of pre-sintered body i) The following materials were used as raw materials. Silicon nitride: Ube Industries, Ltd. E-10 (average particle size 0.25 μm) (α type) Hermann See Stark LC12-S (average particle size 0.77 μm) Electrochemical Co., Ltd. SN-P21B (average particle size) Diameter 0.80 μm), SN-P21C (average particle size 0.69 μm), SN-P21C3 (average particle size 0.52 μm) Sintering aid: (A): Mitsubishi Kasei Co., Ltd. Y ₂ O ₃ (average particle size) Diameter 0.8 μm) (B): Nissan Rare Element Chemical Co., Ltd. La ₂ O ₃ (average particle size 0.5 μm), Nd ₂ O ₃ (average particle size 7.3 μm), CeO ₂ (average particle size 6. 8 μm) (B): Sumitomo Chemical Co., Ltd. Al ₂ O ₃ (average particle size 0.37 μm) Solvent: Toagosei Co., Ltd. trichloroethylene (trichlene R) (125 wt% based on solid content) Dispersant: Ajinomoto AL-M (organic) (2 wt% based on solid content)

Ii) Mixing ratio of raw materials Si ₃ N ₄ : sintering aid B: Y ₂ O ₃ = 92: 5: 3 mol% As the sintering aid B, La ₂ O ₃ , Al ₂ O ₃ , Nd ₂ O ₃ ,
Any one of CeO ₂ was used.

Iii) The kneaded material was prepared in the following steps (a) to (f). (A) Weighing Si ₃ N ₄ + sintering aid B + Y ₂ O ₃ solvent, dispersant, cobblestone (Si ₃ N ₄ ) (b) Wet mixing 16 hours (ball mill) (c) Drying oven 100 ° C × 18 hours ( d) Dry grinding 48 hours (ball mill) (e) Screening (150 μm mesh through) (f) Kneaded clay

Iv) Pre-sintering A hot press device (inner diameter 280 mm) equipped with a carbon mold coated with a release agent (BN) on the inner surface was filled with kneaded clay and cold-pressed to a height of 12 mm at a pressure of 330 kg / cm ² . It was compression molded. Then, heat under a N ₂ gas pressure of 9 kg / cm ² for 13
The temperature was raised to 1750 ° C. at a temperature rising rate of ° C./min, and pre-sintering was performed by holding the temperature for 1 or 2 hours to obtain a pre-sintered body (columnar β-silicon nitride). The presintered body has a density of 2.5 g / cm ³ (70% of theoretical density ratio), and the aspect ratio of columnar crystals is 3 (2
~ 5).

This process is schematically shown in (1) to (2a) of FIG. 1. In (2a), the pre-sintered body is in a state of spontaneous shrinkage due to sintering in the hot press machine (shrinkage rate of about 20). %).

(2) Orientation control of long-axis crystal (two-dimensional orientation control by HP treatment) The pre-sintered body was then hot-pressed to 330 kg / cm.
Under a pressure of ^{2 for} a predetermined time (1 hour or 2 hours), an atmosphere of N ₂ gas pressure and normal pressure (1 kg / cm ² ) is maintained to orient the long-axis (columnar) crystal and grow the crystal in the oriented state. I went. See (3) and (3a) in FIG. The result of hot pressing (secondary sintered body) is shown in (3a). In addition, in FIG. 2, the pre-sintered body (2a), the secondary sintered body (HP processing result) of FIG. 1 (3
The state of crystal orientation in the state of a) is schematically shown.

By subjecting the silicon nitride pre-sintered body to the HP treatment, the long-axis (columnar) crystals can be oriented two-dimensionally, and the fracture toughness and the strength are greatly improved as described below. No. Nos. 1 to 4 correspond to the samples shown in Table 1, and Nos. 1a to 4a are Nos. It is a non-oriented comparative example corresponding to Nos. 1 to 4, and No.
It was obtained by sintering under the same conditions as those of Nos. 1 to 4 (however, including the HP time of Nos. 1 to 4 without hot pressing) for the same time.

[0079]

[Table 2]

The values of strength and toughness shown in Table 2 are based on JIS
3-point bending method and single-edge V-notch beam method (S
EVNB method), No. 1 to
The measured value of the anisotropic sintered body of No. 4 was about 10% lower in the direction (weak direction) orthogonal to the two-dimensional orientation direction. In addition, No. 1 to 4 and Comparative Example No. The densities of 1a to 4a are 3.3 to 3.5 and 2.5 to 2.7 g / cm ^{3, respectively.}
Met.

(3) The effects of controlling the growth of the long-axis (columnar) crystal are as shown in Table 1 and FIG. Table 1 shows the relationship between the length, thickness, aspect ratio of the long-axis (columnar) crystal, the HP treatment conditions, and the components of the sintering aid.

(3-1) That is, by the HP treatment after pre-sintering, the fracture toughness value increases as the aspect ratio increases from 4 to 10, but the strength decreases in accordance with a tendency that is almost inversely proportional to it. It became clear. However, noting that this aspect ratio can control the growth of long-axis crystals by the present invention, by selecting the aspect ratio in a preferable range, it is possible to achieve high fracture toughness while maintaining high strength. Indicates that is possible. That is, a fracture toughness value of about 6 at an aspect ratio of 6 to 8
An excellent combination of ˜7 MPam ^1/2 and strength of about 1100 MPa or more is achieved. According to the present invention, there is an extremely advantageous advantage in that the control of the orientation of the long-axis crystal and the control of the aspect ratio can be simultaneously achieved by combining them. Of course, it is also possible to obtain one of high strength or high toughness particularly intentionally.

(3) <HIP treatment after orientation> Further, the secondary sintered body (H
By subjecting the P-treated body) to the HIP treatment, a further increase in both strength and toughness is achieved on the basis of the secondary sintered body without causing a decrease in strength. By controlling the aspect ratio in this way, the strength,
The highest level of toughness is surely obtained.

That is, as shown in FIG. 5, sample No. 1 to 1800 ° C for 2 (aspect ratio 6.8)
As a result of HIP treatment for 5 hours under a N ₂ gas atmosphere at a pressure of 100 kg / cm ² , the strength of the secondary sintered body was B.
_It increases along with the increase of the aspect ratio in the direction of the arrow along the curve B from _one point, and it increases to 130 in the vicinity of the aspect ratio of 9-10.
It showed a peak exceeding 0 MPa. This is in contrast to the case where the aspect ratio increases with continued hot pressing. Further, the toughness further increased along with the increase of the aspect ratio along the curve A from the point A _{1 of the} secondary sintered body in the direction of the arrow, and showed a peak at the aspect ratio of 11 (9.7 MPam ^1/2 ).

That is, the aspect ratio is theoretically calculated by combining the growth of a fixed long-axis (columnar) crystal under hot pressing in a two-dimensional orientation state with the crystal growth under isotropic pressure by HIP treatment. The maximum toughness value was achieved near the value (12) that results in the predicted maximum toughness, with the consequent increase in strength rather than strength deterioration.

[0086]

By the one-dimensional or two-dimensional orientation treatment (so-called HP treatment) of the present invention, the long-axis crystals contained in the pre-sintered body are oriented in a predetermined direction and controlled to a predetermined aspect ratio. As a result, either or both the fracture toughness value and the strength are easily improved. (Claims 1 and 10)

Further, by controlling the growth of the long-axis crystal of the present invention (the aspect ratio can also be controlled), it is possible to quantitatively increase both the fracture toughness value and the strength without causing a large decrease. became. As a result, it is possible to obtain a long-axis crystal base sintered body having desired strength and fracture toughness value.
(Claim 1)

According to the features of the dependent claims 2 to 9, the intended high-strength, high-toughness ceramic sintered body can be obtained in a specific and defined manner. In particular, by further applying HIP to the secondary sintered body (resultant of HP treatment),
An increase in aspect ratio (long-axis crystal growth) can be achieved without causing a decrease in strength, and an unprecedented ultra-high toughness and ultra-high strength ceramic sintered body can be obtained. (Claims 8, 16 to 1
8)

In the concrete implementation of the present invention, by combining the crystal orientation and the growth control, a ceramic sintered body having both high strength and high toughness, which has been conventionally regarded as difficult, can be obtained, and the development of the advanced technology. It has led to a rapid development of ceramic materials for the industry, and further development in each direction is expected based on this.

Although the embodiments have been described with silicon nitride as an example, the present invention is naturally applicable to a ceramic material and a composite material thereof capable of producing long-axis crystals in a sintering process.

Although the dispersion strengthening of the fibers such as whiskers is not carried out in the examples, the present invention can be similarly applied to the composite material to which the fiber reinforcing is added according to the present invention, and the dispersion of particles and the like. There is no arguing that the strength effect due to the compounding of can be further added.

In the present invention, columnar (including rod-shaped) crystals have been described as examples, but needle-shaped ones or long plate-shaped ones are naturally included as one mode of long-axis crystals, and orientation and aspect ratio are included. Can be controlled.

Silicon nitride is the most suitable material for embodying the present invention in that it has heat resistance, can form long-axis (columnar) crystals, and its growth can be controlled. In particular, the powder starting particles are granular (α-Si ₃ N _{4 in} the case of silicon nitride) or starting component particles that generate silicon nitride in the sintering process, and long-axis (columnar) crystals are generated during presintering. Are advantageous in the present invention, and the present invention is applicable to similar ceramic materials.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an embodiment of a manufacturing method of the present invention step by step,

FIG. 2 is a schematic view showing an orientation state of long-axis (columnar) crystals of the sintered body in the states (2a) and (3a) of FIG.

FIG. 3 is a schematic diagram showing the relationship between deflection and orientation due to long-axis (columnar) crystals during crack development,

FIG. 4 is a schematic view showing a state of crack deflection with respect to a short length and a large thickness of an oriented long-axis (columnar) crystal,

FIG. 5 is a graph showing the relationship between aspect ratio, strength, and fracture toughness value in HP.
Graphs showing processing and HP processing + HIP processing are respectively shown.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI technical display location // C04B 35/58 102 X 8821-4G (72) Inventor Kenji Oshima Miyoshi-cho, Nishikamo-gun, Aichi Fukuya character fox 66 66 (72) Inventor Tsuguo Ito 5 Shintocho, Seto-shi, Aichi (72) Inventor Yoshiki Kato 3-18 Ushimaki-cho, Mizuho-ku, Nagoya-shi, Aichi 5701 Room 72 (Inventor) Seo Ito 15-3 Nakamichi, Kurosaki-cho, Okazaki-shi, Aichi (72) Inventor Misao Iwata 1-601, Tenshiro-cho, Tenpaku-ku, Nagoya-shi, Aichi 2 Building 206, Nishidaira Nishi Nishi Room (72) Inventor Kiyoshi Sato 1-3-1 Nishitsurugaoka, Oi-cho, Iruma-gun, Saitama Prefecture Tonen Corporation Research Institute (72) Inventor Nao Suzuki 1-3-1 Nishi-tsurugaoka, Oi-cho, Iruma-gun, Saitama Prefecture Research house (72) inventor Isoda, Takeshi Saitama Prefecture Iruma-gun Oi-cho, Nishitsurugaoka 1-chome third No. 1 Tonen Co., Ltd. Research Institute in

Claims (18)

[Claims] 1. A ceramic pre-sintered body containing a long-axis crystal or a long-axis crystal nucleus is applied in one axial direction in an amount sufficient to orient the long-axis crystal in a temperature range in which it can be plastically deformed under pressure. A ceramic sintered body having substantially oriented long-axis crystals, characterized by including a crystal orientation process of compressing and compressing and deforming in the direction of the compression axis and simultaneously expanding and deforming in a direction different from the compression axis. Production method. 2. The manufacturing method according to claim 1, further comprising a crystal growth step of controlling and growing a long-axis crystal in an oriented state subsequent to or simultaneously with the orientation step. 3. In the crystal growth step, in the oriented state of the aspect ratio of the major axis crystal, a first predetermined curve showing a change in toughness as the aspect ratio increases, and a strength also as the aspect ratio increase. 3. The manufacturing method according to claim 2, wherein the growth is controlled and controlled until a predetermined aspect ratio is reached according to a second predetermined curve indicating the change of. 4. The manufacturing method according to claim 1, wherein the amount of expansion deformation is at least an amount corresponding to the amount of shrinkage of the pre-sintered body from the unfired compact. 5. The manufacturing method according to claim 1, wherein the expansion and deformation are substantially performed in a one-dimensional direction orthogonal to the pressure and compression axis. 6. The manufacturing method according to claim 1, wherein the expansion and deformation are substantially performed in a two-dimensional direction orthogonal to the compression and compression axis. 7. A pre-sintering step of sintering the pre-sintered body without substantially applying a compressive pressure, wherein the pre-sintered body in a state of being fired and contracted is allowed to enter a hot press machine. And press hot pressing under a pressure sufficient for the substantial orientation of the long-axis crystals, and continue hot-pressing for a sufficient time to grow the oriented long-axis crystals until a predetermined aspect ratio is reached. 7. The method according to claim 1, wherein
The manufacturing method according to 1. 8. The method according to claim 1, further comprising the step of crystal-growing the ceramic sintered body having oriented long-axis crystals, that is, a secondary sintered body, by a HIP process until a predetermined aspect ratio is reached. Manufacturing method. 9. The method according to claim 1, wherein the long-axis crystal is a columnar or needle-like crystal or a plate-like crystal having a long axis. 10. A ceramic sintered body comprising long-axis crystals oriented by hot pressure deformation substantially oriented in at least one-dimensional direction. 11. The ceramic sintered body according to claim 10, wherein the oriented long-axis crystals are substantially oriented in a two-dimensional direction. 12. The ceramic sintered body according to claim 10, wherein the oriented long-axis crystals are columnar silicon nitride crystals. 13. The ceramic sintered body according to claim 10, wherein the oriented long-axis crystals have an aspect ratio of 4 or more. 14. A strength of 900 MPa or more and a fracture toughness value of 4.
The ceramic sintered body according to claim 12 or 13, which has a pillar-shaped silicon nitride crystal having a MPam ^1/2 or more and being substantially two-dimensionally oriented. 15. A fracture toughness value K with a strength of 1100 MPa or more.
The ceramic sintered body according to claim 12, which has an _{IC of} about 7 MPam ^1/2 or more. 16. A strength of 1200 MPa or more and a fracture toughness value of 8.
The ceramic sintered body according to any one of claims 12 to 15, which has a MPam ^1/2 or more. 17. The ceramic sintered product according to claim 10, comprising a long-axis crystal having a substantially two-dimensionally oriented long-axis crystal having an aspect ratio of 8-12. body. 18. The ceramic sintered body according to claim 10, which comprises a long-axis crystal that is substantially two-dimensionally oriented and isotropically growth-controlled.