JPH0769732A - High-tenacity ceramic and its production - Google Patents

Abstract

PURPOSE:To obtain a high-tenacity ceramic by mixing a nonoxide ceramic such as SiC, zirconia or the like and a sintering auxiliary in a prescribed proportion. CONSTITUTION:One or more nonoxide ceramics (A) are obtained from SiC, Si3N4, AlN, ZrSi2, VSi2, NbSi2, TaSi2, CrSi2 and MoSi2. Then, one or more compounds (B) are obtained from zirconia and rare earth oxides. Further, 3 to 79wt.% of Ln4Al2O9 (Ln is one or more selected from Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu) (C) is mixed with 20 to 96wt.% of the component A and 1 to 40wt.% of the component B to prepare a mixed powder (D). The mixture (D) is heated at 1,300 to 1,900 deg.C in a nonoxidative atmosphere for 0.1 to 2,000 minutes to produce high-tenacity ceramics.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to high toughness ceramics and a method for producing the same. Generally, ceramic materials are
In recent years, its importance is being re-recognized because it has excellent properties that metal materials and plastic materials do not have.
In particular, since it can be used even if it is heated to a temperature of 1000 ° C or higher in an oxidizing atmosphere, it is now indispensable as a material for high efficiency gas turbine engines and other high temperature materials. ing. By the way, the biggest drawback of this ceramic is low toughness,
Improving this is the key to the development of ceramic materials. The present invention proposes a high toughness ceramic obtained by toughening a non-oxide ceramic having excellent properties as a high temperature material by a new mechanism, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In order to make non-oxide ceramics into a dense sintered body, conventionally, oxide-based sintering aids such as
It is common to add Al ₂ O ₃ , Y ₂ O _3, etc. This is because the toughness of the non-oxide ceramics can be improved to some extent by adding these sintering aids. However, the addition of this conventional sintering aid is still insufficient for improving the toughness.

It is well known that among the ceramics, the one having the highest toughness is zirconia which undergoes martensitic transformation. The toughening mechanism of this zirconia is
It is believed to be due to the stress-induced transformation mechanism. From this, it is considered that the addition of zirconia is effective for increasing the toughness value of the non-oxide ceramics. However, since this zirconia does not sinter with non-oxide ceramics, this zirconia cannot be used as a toughening additive. In addition to this, since zirconia tends to have a significantly low toughness in the temperature range of 700 ° C. or higher, it is rather difficult to say that it is suitable as a toughening additive for high temperature materials.

[0004]

Generally, non-oxide ceramics achieve an improvement in strength through the promotion of densification by adding a sintering aid, and, at the same time, are more advantageous than those in a single-phase state. The toughness can be improved. However, regarding the known additives that have been used to date, since there is no toughening mechanism like zirconia,
A remarkable improvement in toughness cannot be expected.

The object of the present invention is to establish a technique capable of overcoming the problems of the above-mentioned conventional techniques. In particular, it not only has a normal action as a sintering aid for non-oxide ceramics, It is an object of the present invention to provide a high toughness ceramics and an advantageous manufacturing method thereof by adopting a novel sintering aid also having a toughening mechanism.

[0006]

[Means for Solving the Problems] As a result of intensive studies to achieve the above-mentioned object, the inventors have found that Ln undergoing a ferroelastic phase transition.
₄ Al ₂ O ₉ (However, Ln is Y, Sm, Eu, Gd, Tb, Dy, Ho,
Any one or two selected from Er, Yb and Lu
(Comprising more than one kind) compounds are non-oxide ceramics such as SiC, Si ₃ N ₄ , AlN, ZrSi ₂ , VSi ₂ , NbSi ₂ , TaSi
_The present invention has been completed by finding that it acts extremely effectively for firing of ₂ , CrSi ₂ and MoSi ₂ . However, since this compound (Ln ₄ Al ₂ O ₉ ) easily reacts with the non-oxide ceramics, there is a problem that it is very difficult to control the firing temperature and time. As a result of further research on the problem, the inventors of the present invention have found that compounds that are difficult to react with non-oxide ceramics; that is, zirconia and rare earth oxides (Sc ₂ O ₃ , Y ₂ O ₃ , La ₂ O). ₃ , CeO ₂ , Pr ₂ O ₃ , Nd ₂ O
₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₄ O ₉ , Dy ₂ O ₃ ,, Ho ₂ O ₃ ,
It was found that this can be solved by adding Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ , and Lu ₂ O ₃ ) together.

That is, the present invention relates to SiC, Si ₃ N ₄ , AlN, Z
_{rSi 2, VSi 2, NbSi 2} , TaSi 2, CrSi 2 and MoSi non-oxide selected of one kind or two or more kinds from among ₂ Ceramics: 20~96wt% (preferably 20 to 80 wt% ), Powder of one or two of zirconia and rare earth oxides: 1 to 40 wt%, and Ln ₄ Al ₂ O ₉ (however,
Ln is any one or more selected from Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu) powder:
3 to 79 wt% (preferably 19 to 79 wt%) is mixed, and the mixed powder is heated to a temperature of 1300 to 1900 ° C in a non-oxidizing atmosphere and held for 0.1 to 2000 minutes for firing. A method for producing a characteristic high toughness ceramics, and a high toughness ceramics synthesized by this production method; namely, SiC, Si ₃ N ₄ ,
_{AlN, ZrSi 2, VSi 2,} NbSi 2, TaSi 2, CrSi 2 and MoSi ₂
20 to 96 wt% (preferably 20 to 80 wt%) of any one or more non-oxide ceramics selected from among
, 1 to 40 wt% of any one or more selected from zirconia and rare earth oxides, and Ln
₄ Al ₂ O ₉ (However, Ln is Y, Sm, Eu, Gd, Tb, Dy, Ho, E
High toughness ceramics comprising 3 to 79 wt% (preferably 19 to 79 wt%) of any one or more selected from r, Yb and Lu).

[0008]

In the present invention, Ln ₄ Al ₂ O _{9 which} has attracted attention as a sintering aid for non-oxide ceramics is a ferroelastic compound which undergoes a ferroelastic phase transition at 1000 ° C. or higher and exhibits a rapid volume change there. . The temperature of the phase transition of this compound varies depending on the rare earth oxide contained in this compound, and is, for example, Y ₄ Al.
For ₂ O ₉ to about 1400 ° C., a phase transition at about 1150 ° C. For Gd ₄ Al ₂ O _9, and generates a plurality of domains in the phase transition temperature or less. On the other hand, the generated domain has a characteristic of being capable of absorbing stress energy because it has a function of transition due to stress. Therefore, in the sintered body containing the ferroelastic compound, the crack propagation energy in the sintered body is absorbed by the domain transition, and the effect of inhibiting the development becomes strong, and as a result, the toughness of the sintered body becomes large. It will be.

Since the toughness of a ceramic material using such a ferroelastic compound becomes large at a temperature below the ferroelastic phase transition temperature, for example, one using Y ₄ Al ₂ O ₉ has a toughness in a temperature range of 1400 ° C. or lower. growing. Therefore, it is less likely to be destroyed from room temperature to high temperature, and can be used as a highly reliable material.

According to the experiments conducted by the present inventors, a non-oxide type cell
Lamix, zirconia, rare earth oxides and Ln_FourAl₂
O₉Was added to synthesize a sintered body,
It was confirmed that the toughness of the knot was improved about 1.5 times or more.
And this improvement in toughness is _FourAl₂O₉Ferroelastic phase of sintering aid
It was clarified that it was due to the transposition effect.

The ceramics according to the present invention are SiC, Si ₃
N ₄ , AlN, ZrSi ₂ , VSi ₂ , NbSi ₂ , TaSi ₂ , CrSi ₂ and
It contains 20 to 96 wt% of one or more non-oxide ceramics selected from MoSi ₂ . The reason for including this non-oxide ceramics in an amount of 20 wt% or more is that if it is less than 20 wt%, the properties as a non-oxide are lost, while the reason for limiting it to 96 wt% or less is that it contains a large amount. This is because the toughness is deteriorated. In addition, in order to obtain a highly reliable material having high toughness, it is preferable to set it to 20 to 80 wt%.

Next, 10 kinds of rare earth elements (Ln: Y, Sm, Eu, Gd, Tb, Dy, H) were used as Ln ₄ Al ₂ O ₉ used as a sintering aid.
The reason for limiting to O, Er, Yb and Lu) is that other rare earth elements do not form stable Ln ₄ Al ₂ O ₉ . And, the reason for limiting the content of Ln ₄ Al ₂ O ₉ to 3 wt% or less is that when it is less than 3 wt%, it has almost no effect on increasing the toughness, while when it exceeds 79 wt%, it is regarded as a non-oxide. The characteristics of ceramics are diminished. In addition, if it is preferably 20 to 79 wt%, highly reliable ceramics can be obtained.

Next, in the present invention, zirconia and a rare earth oxide are added together with Ln ₄ Al ₂ O ₉ , but if these amounts are less than 1%, the non-oxide ceramics react with Ln ₄ Al ₂ O _9. This is because it is not possible to effectively suppress this, and on the other hand, the suppression effect reaches saturation even if it is contained in a large amount exceeding 40%.

Next, the manufacturing method of the present invention will be described. The manufacturing method of the present invention is as follows.First, in the mixing ratio of the raw material powder as described above, the non-oxide ceramics SiC, Si ₃ N ₄ , AlN, ZrSi ₂ , VSi ₂ , NbSi
_2, one or a more of the powder either selected from among TaSi _2, CrSi ₂ and MoSi _2, and any one or more of powders selected from among zirconia and rare earth oxides , Any one selected from Ln ₄ Al ₂ O ₉
One kind or two or more kinds of powders are mixed and molded. In this step, if pressureless sintering is performed thereafter,
Although molding is required, this molding step is not necessary in the hot press sintering method, HIP sintering method, and discharge plasma sintering method.

Next, the mixed molded body is fired.
This firing is performed in a controlled atmosphere at a temperature of 1300 to 1900 ° C. for 0.1 to 2000 minutes. If the firing temperature is lower than 1300 ° C, a dense sintered body cannot be obtained, and if it exceeds 1900 ° C, Ln ₄ Al ₂ O ₉ melts and the reaction with non-oxide ceramics becomes violent. Because. The firing time varies depending on the sintering method. For example, it may be sufficient that the sintering temperature is reached in a few minutes and the sintering temperature is maintained for 1 minute or less. However, the sintering time is 0.
If it is shorter than 1 minute, a dense sample cannot be obtained. On the other hand, even if the sintering time is increased to 2000 minutes or more, not only improvement in densification above a certain level cannot be expected, but also the cost becomes high. Moreover, the firing atmosphere is preferably a non-oxidizing atmosphere in which the non-oxide ceramics are not oxidized, and it must be in an inert gas or in a vacuum. Furthermore, the speed of reaching the sintering temperature varies depending on the sintering method, but when using a discharge plasma sintering machine and a microwave sintering machine,
Short as a few minutes.

In this sintering process, when the pressureless sintering method is adopted, if the sample is sent to the hot zone, it is possible to reach a predetermined temperature in a short time of 1 minute. is there. Further, in order to avoid the reaction between the non-oxide ceramics and Ln ₄ Al ₂ O ₉ , it is sometimes preferable that the temperature rising rate is short.

[0017]

【Example】

Example 1 40 g of Si ₃ N ₄ powder, 30 g of Y ₄ Al ₂ O ₉ powder and 60 g of CeO ₂ powder were mixed with alcohol in a ball mill for 24 hours. After mixing, heat to remove alcohol, fill in a graphite mold of 50 mmφ, and use a spark plasma sintering machine to 1500
℃ until the temperature was raised at 5 minutes, 1 minute hold at that temperature, Si ₃ N
₄ sintered bodies were obtained. Flexural strength of the sintered body is 1500 MPa, the fracture toughness value at room temperature is 12 MPa · m ^1/2, 10
It was 11 MPa · m ^1/2 at 00 ° C.

Example 2 50 g of SiC powder, 38 g of Y ₄ Al ₂ O ₉ powder and 11 g of CeO ₂ powder and
1g of La ₂ O ₃ powder and alcohol in a ball mill
Mix for 24 hours. After mixing, remove alcohol and 4x
Molded to 20 x 40 mm ³ . The temperature of this green body was raised to 1700 ° C. in 5 minutes in argon gas and kept at that temperature for 5 minutes to obtain a SiC sintered body. The bending strength of this sintered body is 1200 M
Pa and the fracture toughness value at room temperature is 9 MPa · m ^1/2 .
The bending strength at 1000 ° C was 900 MPa, and the fracture toughness value was 8 MPa · m ^1/2 .

Example 3 30 g of AlN powder, ₂ g of ZrO ₂ (3Y) powder and 15 g of Yb ₄ Al ₂ O ₉ powder
And were mixed for 1 hour using a Menor mortar. This mixed powder was molded, heated to 1500 ° C. in argon gas for 2 hours, and kept at that temperature for 30 minutes to obtain a sintered body.
The bending strength of this sintered body was 900 MPa, and the fracture toughness value at room temperature was 9 MPa · m ^1/2 . The fracture toughness value at 1000 ° C was 7 MPa · m ^1/2 .

Example 4 70 g of SiC powder, 20 g of Y ₄ Al ₂ O ₉ powder and 10 g of ZrO ₂ (3Y) powder
Was mixed on a ball mill for 24 hours using alcohol as the solvent. After mixing, remove alcohol, bury this mixed powder in a graphite mold, use a hot press machine to raise the temperature to 1700 ° C in argon gas for 30 minutes, hold at that temperature for 15 minutes and sinter. Got the body The bending strength of this sintered body is 1500MP
The fracture toughness value at room temperature is 10 MPa · m ^1/2 , 1000 ° C.
The fracture toughness value at was 7 MPa · m ^1/2 .

Example 5 Si ₃ N ₄ powder 10 g, Ho ₄ Al ₂ O ₉ powder 35 g and ZrO ₂ (3Y) powder 5 g
And were mixed in a ball mill for 24 hours using ethanol as a solvent. After completion of mixing, ethanol was removed to obtain a green product. The product form, in nitrogen gas was heated to 10 ° C. / min 1650 ° C. at a heating rate of, and held at this temperature for 400 minutes, Si ₃ N
₄ sintered bodies were obtained. The bending strength of this sintered body was 1400 MPa, and the fracture toughness value at room temperature was 12 MPa · m ^1/2 . The fracture toughness value at 1000 ° C was 9 MPa · m ^1/2 .

Example 6 20 g of SiC powder, 30 g of Si ₃ N ₄ powder, 40 g of Yb ₄ Al ₂ O ₉ powder and 10 g of CeO ₂ powder were mixed with alcohol as a solvent in a ball mill for 24 hours. After the mixing was completed, the alcohol was removed to obtain a green product. This green body was heated at 1700 ° C in nitrogen gas.
It was fed into the hot zone heated to 2 minutes in 2 minutes and kept at this temperature for 2 minutes to obtain a sintered body. The bending strength of this sintered body is 1600 MPa, and the fracture toughness value at room temperature is 12 MPa ・ m ^1/2
The fracture toughness value at 1000 ° C. was 9 MPa · m ^1/2 .

The above examples and comparative examples are summarized in the following table.

[Table 1]

[0024]

As described above, according to the present invention, Ln
By utilizing the ferroelastic phase transition of ₄ Al ₂ O ₉ , it is possible to obtain a dense non-oxide ceramic having high strength and high toughness at room temperature and high temperature. Thus, the present invention provides engine parts, gas turbine blades, gas turbine parts, corrosion resistant device parts, crucibles, ball mill parts, insulating materials, IC substrates, fusion reactor materials, nuclear reactor materials, die casting parts, combustion tubes, Heating elements, heat-resistant materials for high-flying objects, heat exchangers, heat-resistant materials, electronic circuit substrates, sealing materials, joint and valve parts, heat shield materials, biomaterials such as artificial bones and artificial roots, dielectric materials, blades, Cutter blade, tool, sports equipment, pump, nozzle, roller, guide, bearing,
It is possible to advantageously provide a high toughness ceramic that is effectively used in a wide range of fields such as ferrules.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location C04B 35/565 35/584 35/581 C04B 35/56 101 K 35/58 102 D 102 H 104 B

Claims (2)

[Claims] 1. SiC, Si ₃ N ₄ , AlN, ZrSi ₂ , VSi ₂ , NbSi ₂ , T
Any one selected from aSi ₂ , CrSi ₂ and MoSi ₂
20-96wt of one or more non-oxide ceramics
%, 1 to 40 wt% of one or more selected from zirconia and rare earth oxides, and Ln ₄ Al ₂ O ₉ (where Ln is Y, Sm, Eu, Gd, Tb, Dy, Ho,
A high toughness ceramic containing 3 to 79 wt% of any one or more selected from Er, Yb and Lu). 2. SiC, Si ₃ N ₄ , AlN, ZrSi ₂ , VSi ₂ , NbSi ₂ , T
Any one selected from aSi ₂ , CrSi ₂ and MoSi ₂
Type or 2 or more types of non-oxide ceramics: 20 ~ 96wt
%, Powder of one or more of zirconia and rare earth oxides: 1 to 40 wt%, and Ln ₄ Al ₂ O ₉ (where Ln is Y, Sm, Eu, Gd, Tb, Dy , Ho,
Powder of any one or more selected from Er, Yb and Lu): 3 to 79 wt% is mixed, and the mixed powder is heated to a temperature of 1300 to 1900 ° C in a non-oxidizing atmosphere. A method for producing a high-toughness ceramics, which comprises heating to a temperature of 0.1 to 2000 minutes and then firing.