JP3007731B2 - Silicon carbide-mixed oxide sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention eliminates pores and micro-cracks in ceramics that cause a reduction in strength and reliability, thereby enabling the sintering of silicon carbide (SiC) -based oxide ceramics having high strength and reliability. With regard to union,
This paper proposes an organically uniform SiC- (Ln-Al-Si) oxide-based sintered body (where Ln is a rare earth element and a mixture thereof) and a method for producing the same.

[0002]

2. Description of the Related Art In general, ceramic materials are promising as structural materials because of their high strength at high temperatures and excellent heat resistance, oxidation resistance and corrosion resistance. In particular, there is a great deal of interest in the application of such ceramics to structural materials used in a temperature range exceeding the usage limit of metals. Among these ceramics, SiC is one of the most promising structural materials that can be used at high temperatures because of its excellent heat resistance and oxidation resistance.

[0003] However, SiC is difficult to be sintered, so that it is extremely difficult to obtain a dense sintered body without adding an auxiliary agent. For this reason, conventionally, SiC powder has been fired by adding Al ₂ O ₃ as a sintering aid. However, a SiC sintered body obtained by using Al ₂ O ₃ as a sintering aid becomes a dense sintered body by liquid phase sintering, but pores are generated due to the reaction between Al ₂ O ₃ and SiC. easy. As a result, the strength is 600M
Pa or less, the fracture toughness value is as small as 5 MPa · m ^1/2, and the m value of the Weibull coefficient, which is an index indicating the reliability of ceramics, is as small as 10 or less. It could be said.

On the other hand, a technique for improving the strength and toughness of a SiC sintered body and improving reliability by compounding SiC with other ceramics has been previously described by one of the present inventors. Proposed. For example, a technique for producing a dense SiC-rare earth oxide-alumina composite sintered body by sintering under no pressure is described in Omori and Takei et al., J. Am. Ceram. Soc., 65 ( 1982) C-92) ". Further, in the sintering, a technique of producing a dense SiC-rare earth oxide-alumina-based composite sintered body by increasing a sintering temperature to 2150 ° C. and generating Al metal and a Si semiconductor has also been proposed. (Omori, Takei, J. Mater.Sc
i, 23 (1988) 3744-3749).

[0005]

However, in the case of the SiC sintered body synthesized by this method, small defects always exist inside the sintered body, and destruction starts from this defect, so that the reliability as a material is low. And had a serious problem in practical use.

The mechanism of forming the SiC-rare earth oxide-alumina sintered body is considered as follows. First, in a first step, an oxide solid solution or an oxide compound is generated from a rare earth oxide and alumina. Next, in the second stage, the SiC is dissolved and diffused in the oxide, and the SiC grains are grown and shrunk to form a dense sintered body.

However, in the second step, the SiC powder dissolves in the oxide and undergoes a chemical reaction at the same time as the SiC reacts with the alumina to generate gases such as CO, CO ₂ and SiO. As a result, defects such as voids and pores are generated in the sintered body, resulting in a disadvantage that the strength of the interface between SiC and the oxide is reduced.

An object of the present invention is to provide a sintered body of SiC-based oxide ceramics obtained by firing SiC and a rare-earth oxide-alumina-based oxide without further defects such as voids and pores as described above. It is an object of the present invention to provide a highly reliable sintered body having high strength and high toughness, and to propose a novel technique for an advantageous production method thereof.

[0009]

As a result of diligent research to achieve the above object, the present inventors have found that rare earth oxides
By mixing silica with the alumina-based oxide, a mixture of rare earth oxide-alumina-silica-based powder and SiC is fired. In such a mixture firing, the reaction between SiC and alumina is suppressed, so that the formation of pores is reduced and the sintering of SiC and oxide proceeds gently, so that a dense sintered body can be obtained. It turned out to be easy.

That is, the present invention relates to a mixed oxide of 99.9 to 90% by weight of Ln4Al2O9 or LnAlO3 (where Ln is a rare earth element and a mixture thereof) and 0.1 to 10% by weight of silica; A mixture of 95 to 5 wt% of silicon carbide SiC according to the mixture is formed, and then the formed body is heated in a non-oxidizing atmosphere at a temperature rising rate of 5 to 2000 ° C./min.
A method for producing a SiC- (Ln-Al-Si) oxide-based sintered body, characterized in that firing is performed at a temperature of 2100 ° C. for 0.1 to 600 minutes, and the SiC- (Ln -Al-Si) An oxide-based sintered body.

[0011]

In general, it is considered that silica added to other oxide ceramics has a low melting point of 1550 ° C., becomes a glassy state, and precipitates at grain boundaries, lowering high-temperature strength.
Therefore, this silica was rather one of the compounds that one did not want to add.

On the other hand, in the present invention, attention is paid to this silica, and sintering becomes possible by forming a mixture of SiC and (rare earth oxide-alumina-silica-based powder). If it does not precipitate and become glass, and further forms a solid solution in the rare earth oxide-alumina system, or if it exists in a solid solution amount or more, it reacts with the rare earth oxide or alumina to form a silicate compound. It was found that there was no problem of lowering the strength.

According to the findings of the present inventors, the addition of this silica to other compounds effectively acts to obtain a dense sintered body, rather than the oxide portion of the sintered body. It is effective for improving the strength and toughness of the steel.

The minute amount of silica present on the surface of unoxidized SiC is insufficient to increase the strength and toughness of the oxide by itself.

Next, the SiC- (Ln-Al-Si) oxide-based sintered body of the present invention contains 5 to 95% by weight of rare earth oxide powder and 94.9 to 100% of alumina.
A mixed oxide consisting of 4.9 wt% and silica 0.1 to 10 wt%, that is, a mixed oxide consisting of 99.9 to 90 wt% of Ln 4 Al 2 O 9 or LnAlO 3 (where Ln is a rare earth element and a mixture thereof) and 0.1 to 10 wt% of silica 5 to 95 wt% %When;
SiC powder, or whisker, or a mixture of these
It is obtained by mixing and baking 95 to 5 wt%.

Here, when the rare earth oxide powder is less than 5 wt%, the characteristics of the mixed oxide are deviated from the characteristics of alumina alone, and the sinterability with SiC deteriorates. If the content of alumina is less than 4.9 wt%, the characteristics of the mixed oxide are almost deviated from those of the rare earth oxide alone, and the sinterability with SiC is deteriorated.

On the other hand, if the amount of the rare earth oxide powder exceeds 95 wt%, the amount of the rare earth oxide is too large, and the sinterability with SiC deteriorates. If the amount of alumina exceeds 94.9 wt%, the properties of the rare earth are lost. Therefore, the rare earth oxide powder and alumina are limited to the above range.

If the amount of silica is less than 0.1 wt%, abnormal growth of crystal grains of the sintered body cannot be suppressed, so that the strength and toughness of the oxide portion of the sintered body are small, and Can not get. On the other hand, the amount of silica added is
If it exceeds 10 wt%, the effect of addition does not change, but silica, which is larger than the amount of solid solution, reacts with the rare earth oxide or alumina to form a silicate compound, which is rather undesirable.
Therefore, the amount of silica added is limited to the above range of 0.1 to 10% by weight.

Further, when the amount of the mixed oxide is less than 5 wt%, the sinterability with SiC is deteriorated and a dense sintered body cannot be obtained. On the other hand, if the amount of SiC is less than 5 wt%, that is, if the amount of the mixed oxide is more than 95 wt%, a sintered body excellent in hardness and high-temperature strength, which is the effect of adding SiC, cannot be obtained. Therefore, the mixing ratio of the mixed oxide and SiC is limited as described above.

The rare earth oxide (Ln ₂ O ₃ ) includes
For example, 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 ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ ,
Yb ₂ O ₃ and Lu ₂ O ₃ are preferably used.

The mixed oxide and SiC powder or Si
For mixing with the C whisker, an ordinary machine used for mixing or kneading powder can be used.
This mixing may be either a dry method or a wet method. Particularly in the case of the wet method, mixing can be effectively performed by using a surfactant such as ethylamine or fish oil.

Next, the mixed raw material obtained as described above is dried once, and then continuously formed into a predetermined shape. In this molding step, an organic polymer (polyethylene glycol, polyvinyl alcohol, or the like) is added as a molding aid to the above-mentioned mixed raw material, and molding can be performed by applying a commonly known molding technique.

Next, the production method of the present invention will be described.
In the method of the present invention, first, a mixture of SiC and (Ln-Al-Si) mixed oxide is formed at the above-described mixing ratio. Next, the formed body is heated at a heating rate of 5 to 2000 ° C./min, and subjected to a baking treatment at a temperature of 1600 to 2100 ° C. for 0.1 to 200 minutes to obtain a sintered body.

A sintered body can be obtained at a heating rate of less than 5 ° C./min, but the density becomes low. On the other hand, it is impossible to raise the temperature faster than 2000 ° C / min.
/ Min.

If the sintering temperature is lower than 1600 ° C., a dense sintered body cannot be obtained due to insufficient sintering. On the other hand, if the sintering temperature is higher than 2100 ° C., SiC reacts with alumina. To form pores and not be densified. For this reason, the range of the appropriate firing temperature is limited to the range of 1600 to 2100 ° C.

Next, the calcination time is related to the calcination temperature, and it is preferable that the calcination temperature is long when the calcination temperature is low and short when the calcination temperature is high. No sintered body can be obtained, while the sintering effect hardly changes after more than 200 minutes, or
Since SiC and alumina react with each other to form pores, the time is limited to a range of 0.1 to 10 hours.

It is preferable that a non-oxidizing atmosphere (for example, an inert gas such as a nitrogen gas, an argon gas, or a helium gas) is used as the atmosphere during the firing because SiC is oxidized in an oxidizing atmosphere. Moreover, you may bake in a vacuum.

[0028] The thus obtained SiC-
(Ln, Al, Si) oxide-based sintered body has good sintering of SiC and oxide, and the toughness and strength of oxide are remarkably improved. More than 50% larger.

[0029] Next, the above-described technique of firing an oxide containing silica and SiC to produce an oxide sintered body which is excellent in strength and toughness and can be used even at a high temperature produces martensite transformation during firing. This is particularly effective in the case of a rare earth oxide-alumina-silica-based sintered body containing a compound of Ln ₄ Al ₂ O ₉ or LnAlO ₃ as a main component. That is, a mixed powder 9 of a rare earth oxide and alumina having a composition of Ln ₄ Al ₂ O ₉ or LnAlO ₃
9.9 to 90 wt%, mixed oxide of 5 to 95 wt% consisting of silica powder of 0.1 to 10 wt%, and 95 to 5 wt% of SiC or SiC whiskers or a mixture thereof are synthesized by the above-described method. SiC-Ln ₄ Al ₂ O ₉ sintered body or SiC-LnAlO ₃ sintered, the crystal grain size is controlled to 30μm or less, without generating a twinning by martensitic transformation, excellent in strength and toughness It was.

The reason is that twins are not formed in the constituent particles in the sintered body, but only a small number of twins are formed with the progress of cracks to absorb the energy of strain, and this twin is not formed. Since the energy of strain can be absorbed by the movement of the crystal plane, it is considered that the strength and toughness of the sintered body are increased. This is a previously unknown mechanism of toughening, and is a novel discovery of the inventors.

[0031]

【Example】

(Example 1) SiC powder 60 in 140 ml of ethyl alcohol
g, Y ₂ O ₃ powder 71.2 g, Al ₂ O ₃ powder 16.1 g and SiO ₂ powder 2.7 g
g of the mixed powder was added, 2 ml of diethylamine was further added, and the mixture was wet-mixed using a ball mill for 48 hours. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Thereafter, it was formed into a formed body having a size of 45 × 20 × 5 mm ³ . Next, the formed body is heated to 500 ° C. in air at a rate of 2 ° C./min.
And calcined for 2 hours. Next, this calcined sample was
The temperature was raised to 1775 ° C. at a rate of 50 ° C./min in nitrogen gas, and the temperature was maintained at 1775 ° C. for 10 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 800 MPa, and the fracture toughness value K _IC = 10 MP · m
It was ^1/2 .

(Example 2) In 90 ml of ethyl alcohol, 49.75 g of SiC powder, 44.05 g of Yb ₂ O ₃ powder, and 5.70 g of Al ₂ O ₃ powder
g and 0.5 g of SiO ₂ powder were added, and 1 ml of diethylamine was further added, followed by wet mixing using a ball mill for 48 hours. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45
It was molded into a green compact having a size of × 20 × 5 mm ³ . Next, the formed product is heated in air at a rate of 2 ° C./min.
The temperature was raised to 0 ° C., and the temperature was maintained at 500 ° C. for 2 hours for calcination. Next, the calcined sample was heated to 1830 ° C. at a rate of 100 ° C./min in nitrogen gas, and kept at 1830 ° C. for 5 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body was 900 MPa, and the fracture toughness value K _IC = 10 MP · m
It was ^1/2 . Further, a transmission electron micrograph of this sample is shown in FIG. As is clear from this figure, it was confirmed that the white SiC particles were well bonded to the oxide matrix and were finely dispersed.

Example 3 39.88 g of SiC powder, 52.45 g of Gd ₂ O ₃ powder, and 7.38 of Al ₂ O ₃ powder in 90 ml of ethyl alcohol
It was charged with a mixed powder of g and SiO ₂ powder 0.3 g, further added diethylamine 1 ml, were mixed for 48 hours wet in a ball mill. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45
It was molded into a green compact having a size of × 20 × 5 mm ³ . Next, the formed product is heated in air at a rate of 2 ° C./min.
The temperature was raised to 0 ° C., and the temperature was maintained at 500 ° C. for 2 hours for calcination. The calcined sample was heated to 1870 ° C. at a rate of 150 ° C./min in nitrogen gas and kept at 1870 ° C. for 10 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body was 1100 MPa, and the fracture toughness value K _IC = 12MP ·
m ^1/2 .

Example 4 A mixed powder of 60 g of SiC powder, 32.64 g of Y ₂ O ₃ powder, 5.76 g of Al ₂ O ₃ powder and 1.6 g of SiO ₂ powder was placed in 90 ml of ethyl alcohol. Diethylamine was added and wet-mixed using a ball mill for 48 hours. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45 × 20
It was formed into green product of the magnitude of × 5 mm ^3. Next, this formed body is heated to 500 ° C. in air at a rate of 2 ° C./min.
The temperature was raised to 500 ° C. for 2 hours, and calcined. The calcined sample was heated to 1950 ° C. at a rate of 100 ° C./min in argon gas, and kept at 1950 ° C. for 10 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 800 MPa, and the fracture toughness value K _IC = 9 MP · m
It was ^1/2 .

Example 5 A mixed powder of 90 g of SiC powder, 6.96 g of Nd ₂ O ₃ powder, 2.10 g of Al ₂ O ₃ powder and 0.93 g of SiO ₂ powder was placed in 90 ml of ethyl alcohol, and further mixed with 1 ml of ethyl alcohol. Diethylamine was added and wet-mixed using a ball mill for 48 hours. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45 × 20 ×
It was molded into a green compact having a size of 5 mm ³ . Next, the formed body was heated to 500 ° C. in air at a rate of 2 ° C./min, and calcined at 500 ° C. for 2 hours. Then
The calcined sample was heated to 1950 ° C. at a rate of 60 ° C./min in argon gas, and kept at 1950 ° C. for 5 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 650 MPa, and the fracture toughness value K _IC = 7 MP · m
It was ^1/2 .

Example 6 10 g of SiC powder, 78.74 g of H ₂ O ₃ powder and 10.62 g of Al ₂ O ₃ powder in 90 ml of ethyl alcohol
Then, a mixed powder of 0.64 g of SiO ₂ powder was added, 1 ml of diethylamine was further added, and the mixture was wet-mixed using a ball mill for 48 hours. After completion of the mixing, the mixture was heated to 60 ° C. to evaporate the alcohol, and then stirred and mixed in a 5% aqueous polyethylene glycol solution, followed by drying. Then 45x
It was molded into a green compact having a size of 20 × 5 mm ³ . Next, the formed product is heated in air at a rate of 2 ° C./min.
The temperature was raised to 500 ° C., and calcined at 500 ° C. for 2 hours. Next, the calcined sample was heated in air at a heating rate of 80 ° C./min for 18 minutes.
The temperature was raised to 00 ° C. and maintained at 1800 ° C. for 10 minutes to obtain a sintered body.

The obtained sintered body was densely sintered, and almost no pores were observed. The bending strength of the sintered body is 1000 MPa, and the fracture toughness value K _IC = 11MP ·
m ^1/2 .

As described above, the SiC- obtained by the method of the present invention
The (Ln-Al-Si) oxide-based sintered body is dense, has no pores, and is composed of particles having an average crystal grain size of 30 μm or less. Moreover, the sintered body of the present invention has sufficient strength and fracture toughness for practical use. In particular, the fracture toughness value is about three times that of the conventional SiC sintered body or its composite material, and the strength is 50% or more larger.

[0044]

As described above, according to the present invention, the rare earth oxide-alumina-silica mixed oxide and SiC are fired to control the crystal grain size of the sintered body to 30 μm or less, and By preventing the formation of oxides, the dense and high strength and toughness of both the excellent toughness of the oxide sintered body and the high-temperature strength of SiC, and the structurally uniform SiC- (Ln-Al-
Si) An oxide-based sintered body can be easily obtained.

Therefore, according to the present invention, the engine parts,
Gas turbine blades, parts for gas turbines, parts for corrosion-resistant equipment, parts for crucibles, parts for ball mills, heat exchangers for high-temperature furnaces, heat-resistant materials, heat-resistant materials for high-altitude flying objects, combustion pipes, parts for die casting,
Insulation materials, fusion reactor materials, nuclear reactor materials, solar reactor materials,
Tools, heat shielding materials, electronic circuit substrates, sealing materials, fittings and valve parts, biomaterials such as artificial bones and artificial roots, dielectric materials, blades and cutter blades, sporting goods, pumps, nozzles, magnetic heads, rollers, Guides, bearings, ferrules, and other materials that can be effectively used in a wide range of fields can be provided.

[Brief description of the drawings]

FIG. 1 is a transmission micrograph showing a crystal structure of a SiC— (Ln—Al—Si) oxide-based sintered body.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C04B 35/565 C04B 35/10 C04B 35/44 C04B 35/50

Claims (2)

(57) [Claims] 1. 95-5 wt% of silicon carbide, Ln4Al2O9
Or LnAlO3 (where Ln is a rare earth element and
Mixture) 99.9~90wt% and silica 0.1 mixture and oxide 5 to 95 wt% consisting of 10 wt%, silicon carbide formed of a sintered body of al - mixed oxide-based sintered body. 2. 95-5 wt% of silicon carbide, Ln4Al2O9
Or LnAlO3 (where Ln is a rare earth element and
Molding a mixture of a mixture) 99.9~90wt% and silica 0.1 10 wt% mixed oxide 5 to 95 wt% consisting of al, then, in the resulting mixture molded body in a non-oxidizing atmosphere, 5 to 2000 ° C. / Min at a heating rate of 1600-2100
A method for producing a silicon carbide-mixed oxide-based sintered body, characterized in that the firing is carried out while maintaining the temperature in a temperature range of 0.1 to 600 minutes.