JPH04367563A - Sic-based oxide sintered compact and its production - Google Patents

Abstract

PURPOSE:To improve strength and reliability by forming a mixture of a rare earth oxide with SiC at a specific weight ratio, rapidly heating the formed mixture to a specific temperature, holding the formed mixture at the temperature for a prescribed time and synthesizing the subject sintered compact. CONSTITUTION:With 95-5wt.% rare earth oxide powder such as Y2O3, is mixed 5-95wt.% Al2O3 powder. The resultant mixed oxide powder in an amount of 80-10wt.% is then mixed with 20-90wt.% SiC powder and the obtained mixture is added and mixed with an aqueous solution of a polymer such as PVA at 2-30wt.% concentration. The prepared mixture is subsequently dried and formed. The formed compact is then rapidly heated to 1700-2100 deg.C in a nonoxidizing atmosphere such as Ar gas and kept at the aforementioned temperature for 0.1-30min to provide an SiC-based oxide sintered compact. The resultant sintered compact is further subjected to hot isostatic pressing treatment at 1600-2000 deg.C under 0.2-10 MPa in a nonoxidizing atmosphere. Thereby, the objective SiC-based oxide sintered compact free of fine defects is obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention creates structurally uniform SiC-based oxide ceramics with high strength and reliability by eliminating pores and microcracks in ceramics that cause a decrease in strength and reliability. Sintered bodies, especially SiC
-Rare earth oxide-alumina sintered body and method for producing the same.

0002

[Prior Art] Ceramic materials are considered promising as structural materials because they have high strength at high temperatures and are excellent in heat resistance, oxidation resistance, and corrosion resistance. In particular, there is a great deal of interest in the application of ceramics to structural materials that are used at temperatures exceeding the service limits of metals. Among these ceramics, SiC has excellent heat resistance and oxidation resistance, so it is extremely promising as a structural material that can be used even at high temperatures.

However, since SiC is generally difficult to sinter, it is extremely difficult to obtain a dense sintered body without adding an auxiliary agent. For example, as a technique to overcome such difficulties, a conventional technique in which metal Al is added as a sintering aid to SiC powder and then hot pressed has been proposed by R. A. Al
Liegro and L. B. It has been proposed by Coffin et al. (J. Am. CERAM. Soc., 39 (
1956) 386-89). However, by simply adding metal Al to SiC, it is not possible to produce a sintered body having excellent properties by sintering under no pressure.

[0004] Furthermore, an example of a SiC sintered body synthesized under no pressure by adding boron and carbon is S. Procha
reported by zka (Special C
eramics No. 6 P171-182, 19
75). Furthermore, a technology that allows SiC powder to be sintered without pressure by adding carbon together with metal Al as a sintering aid was developed by W. Bocker and H. Landferman
“Powder Met.
t. , 11 (1979) 83-85).

[0005] Also, Al2O is added to SiC powder as a sintering aid.
A technique has been proposed that allows synthesis of a dense sintered body by hot pressing even if 3 is added (U.S.P.
at. No. 3520656). Furthermore, Al2O3 was added as a sintering aid to the SiC powder, and the
97-9 by holding at a temperature below 0℃ for 10 hours
A technique to obtain an 8% dense body has also been proposed (Keiichiro Suzuki, Silicon Carbide Ceramics, P. 345-366
, Uchida, Rokakuba).

However, when boron and carbon or Al and carbon are used as sintering aids, pores tend to remain during solid phase sintering. In addition, SiC obtained using Al2O3 as a sintering aid
Although the sintered body becomes a dense sintered body by liquid phase sintering,
Pores are generated due to the reaction between 12O3 and SiC. As a result, the strength was 600 MPa or less, and the fracture toughness was 5 MPa.
- Both m1/2 were small, and the Weibull coefficient m value, which is an index showing the reliability of ceramics, was small at 10 or less, so it could be said that it was a material with poor reliability.

[0007] On the other hand, one of the present inventors previously proposed a technique for improving the strength and toughness of a SiC sintered body and improving its reliability by compositing SiC with other ceramics. Proposed. For example, a technology for producing a dense SiC-rare earth oxide-alumina composite sintered body by sintering under no pressure was reported by Omori and Takei et al. in "J, Am. Ceram. Soc., 65.
(1982) C-92). Furthermore, a technique has been proposed in which a dense SiC-rare earth oxide-alumina composite sintered body is manufactured by increasing the firing temperature to 2150°C to generate Al metal and Si semiconductor in the sintering process. (Omori, Takei, J.M.
ater. Sci, 23 (1988) 3744-3
749).

However, in products synthesized by this method, small defects exist inside the sintered body, and destruction starts from these defects, resulting in a lack of reliability as a material and a major problem in practical use. Ta.

[0009]

[Problems to be Solved by the Invention] The formation mechanism of this SiC-rare earth oxide-alumina based sintered body is thought to be as follows. First, in the first step, an oxide solid solution or an oxide compound is generated from the rare earth oxide and alumina, and then, in the second step, the SiC is solid-dissolved in the oxide.
The SiC grains are diffused, grow, and contracted to form a dense sintered body.

However, in the second stage, a chemical reaction occurs at the same time that the SiC powder is dissolved in the oxide, and SiC reacts with alumina to generate gases such as CO, CO2 and Si0. As a result, defects such as voids and pores occur in the sintered body, resulting in a decrease in the strength of the interface between SiC and the oxide.

The object of the present invention is to develop this SiC-rare earth oxide-alumina sintered body into a high-strength, high-toughness, and highly reliable sintered body free of defects such as voids and pores as described above. At the same time, it is an object of the present invention to propose a new technique for an advantageous manufacturing method thereof.

0012

[Means for Solving the Problems] As a result of intensive research in order to achieve the above object, it was found that the heating rate of the sintered body is an important factor, and the present invention has been developed as follows. completed. That is, the present invention combines 80-10% by weight of mixed oxide powder consisting of 95-5% by weight of rare earth oxide and 5-95% by weight of Al2O3;
After mixing 0 to 90% by weight and shaping the mixture, heating is performed in a non-oxidizing atmosphere at a rapid temperature increase in which the time to reach a temperature of 1700 to 2100 ° C. is within 60 minutes, and then A method for producing a SiC-based oxide sintered body, characterized in that the synthesis is carried out by holding the temperature at that temperature for 0.1 to 30 minutes, a SiC-based oxide sintered body synthesized thereby, and this SiC-based oxide sintered body. Add another 160 sintered bodies.
Provided is a method for producing a SiC-based oxide sintered body characterized by HIP treatment at a temperature of 0 to 2000°C and a pressure of 0.2 to 10 MPa, and a SiC-based oxide sintered body synthesized thereby. do.

[0013]

[Operation] The present inventors have discovered that in composite materials such as SiC-based oxide sintered bodies, it is important to control the interface and structure between SiC and oxide, and that this bonding can be controlled by the firing temperature conditions. As a result of further intensive research, we found that sintering at an appropriate firing temperature and in a short time due to rapid heating can eliminate pores and voids in the sintered body, which can cause a decrease in strength and reliability. The present invention was developed based on the discovery that it is effective in preventing.

[0014] In the first method of the present invention, first, 95 to 5% by weight of rare earth oxide powder and 5 to 95% by weight of Al2O3 powder are
80 to 10% by weight of mixed oxide powder consisting of SiC powder 2
0 to 90% by weight.

Here, as the rare earth oxide, Sc2O
3, Y2O3, La2O3, CeO2, Pr2O
3, Nd2O3, Sm2O3, Eu2O3, Gd
2O3, Tb2O3, Dy2O3, Ho2O3,
Er2O3, Tm2O3, Yb2O3, Lu2O
3 is used.

Rare earth oxide powder in the mixed oxide powder and A
The mixing ratio with l2O3 powder is rare earth oxide powder 95-5
% by weight and Al2O3 powder is preferably 5 to 95% by weight. This is because if the Al2O3 powder content is less than 5%, the sintering effect is small, and if it exceeds 95%, a dense sintered body cannot be obtained. The mixing ratio of the SiC powder and the mixed oxide powder is 80 to 10% by weight of the mixed oxide powder.
and SiC powder is preferably 20 to 90% by weight. This is because if the SiC powder content is less than 20%, the composite effect of SiC is not exhibited, and if the content exceeds 90%, the SiC content increases and a dense sintered body cannot be obtained.

[0017] For mixing the mixed oxide powder and SiC powder, a conventional machine used for mixing or kneading powders can be used. In addition, this mixture is 2 to 3
0% by weight of organic polymers (polyethylene glycol,
It is preferable to mix it in a solution containing polyvinyl alcohol, starch, etc.). The reason for this is that if it is less than 2%, the binding effect of the organic polymer is small, and if it is more than 30%, it is difficult to remove this polymer.

Next, the mixed raw material obtained as described above is dried and molded to obtain a desired shaped product. For molding at this time, conventional molding techniques that are generally used can be applied. Moreover, the pressurization used during this molding can be performed using conventional single-press presses, double-press presses, isostatic presses, or other methods.

[0019] Next, the above-mentioned formed body is
The temperature is rapidly increased within 60 minutes to reach a temperature of 0° C., and the temperature is maintained for 0.1 to 30 minutes to form a sintered body. In such a firing method, an oxide solid solution or an oxide compound consisting of a rare earth oxide and Al2O3 plays an important role in sintering. That is, this oxide solid solution or compound has high reactivity with SiC near the firing temperature, and when kept at the firing temperature for a long time, gases such as CO, CO2, and SiO are generated by the reaction between SiC and alumina. As a result, the generated gas becomes defects such as voids and pores in the sintered body. And such defects are
This extremely reduces the reliability of the sintered body as a material, and causes a decrease in strength and toughness.

[0020] That is, in the present invention, the reason for rapidly increasing the temperature is precisely to prevent the occurrence of the above-mentioned defects, and it is necessary to strictly control the sintering time, including the appropriate firing temperature and heating time. This is why.

[0021] In this way, rare earth oxides and Al2O3
In order to quickly generate a solid solution or compound by reaction with SiC, uniformly bond grains of SiC, and control the reaction between SiC and oxide, it is necessary to rapidly raise the temperature from room temperature to the firing temperature. It must be done. Preferably, it is necessary that the time required to reach the firing temperature is in the range of 1 to 60 minutes. The lower limit of this range is the shortest possible time (less than 1 minute), and the upper limit of 60 minutes is limited because if the time exceeds this, the decomposition of SiC becomes noticeable and the above-mentioned defects are likely to occur.

[0022] Next, the firing temperature is 1700 to 2100°C.
A range of is preferred. If the temperature is lower than 1700°C, a dense sintered body cannot be obtained, while if the temperature is higher than 2100°C, Si
This is because the decomposition of C becomes noticeable and many of the above defects occur. Note that this firing temperature depends on the type of rare earth oxide, A
It differs depending on the mixing ratio with 12O3 and the mixing ratio between SiC and mixed oxide.

Next, the atmosphere during firing is preferably a non-oxidizing atmosphere such as nitrogen gas, argon gas, helium gas, etc. with a low oxygen content, or vacuum.

Next, the holding time at the firing temperature is 0.1
It is preferable that it is in the range of 30 minutes. This is because if the holding time exceeds 30 minutes, the decomposition of SiC becomes noticeable and the above-mentioned defects are likely to occur. be.

The sintered body synthesized by the first method of the present invention has almost no large defects, is extremely reliable, and has high average strength and toughness values. Furthermore, the ``Weibull coefficient (m)'', which is an index indicating the reliability of ceramics, obtained by Weibull plotting the bending strength of the sintered body of the present invention is 20 or more, which is different from the normal sintering method. Weibull coefficient m of the obtained SiC sintered body
is around 10, so the Si synthesized by the method of the present invention
It was found that the m value of the C sintered body was improved by more than twice that value. Furthermore, the structure of the sintered body obtained by such a method was uniform. This is considered to be because the uniformly mixed powder was rapidly sintered due to the rapid temperature rise, so no segregation of the structure occurred.

Next, in applications where even a few small defects occurring in the SiC-based oxide sintered body are a problem, the SiC-based rare earth oxide-alumina-based sintered body synthesized by the second method of the present invention is used. Solids are preferably used.

That is, in the second method of the present invention, the SiC-based oxide sintered body synthesized in the first method is further subjected to hot isostatic pressing (HIP) treatment, thereby improving the sintered body. This removes minute defects.

Normally, HIP processing 8 The higher the pressure, the easier it is to remove even large defects. However, if the pressure is high, the equipment becomes expensive and it becomes difficult to maintain the pressure. Since the SiC-based oxide sintered body synthesized by the first method of the present invention has small and very few defects, it is not possible to completely remove the defects by HIP treatment at low pressure. can. That is, the synthesized SiC-based oxide sintered body was heated at a temperature of 1600 to 2000°C and a pressure of 0.2
By HIPing with ~10MPa inert gas,
Such defects can be removed.

Here, the pressure of the inert gas is 0.2 to 1
A range of 0 MPa is preferred. This is because defects cannot be removed even by HIP treatment at less than 0.2 MPa. Moreover, if the pressure exceeds 10 MPa, the price of the pressure vessel becomes high and it is not practical.

[0030] In the sintered body synthesized by the second method of the present invention, even a few minute defects are completely removed, and the reliability as a material for the sintered body described above is further increased, and the sintered body is relatively The average intensity increases.

[0031]

【Example】

(Example 1) α-type SiC powder 500g, Y2O3 powder 4
25 g and 75 g of Al2O3 powder were placed in a 5% polyethylene glycol aqueous solution, wet mixed for 10 hours, and then dried. Next, this dry powder is molded to obtain a green body, which is placed in an electric furnace and heated from room temperature to 1950°C in 10 minutes in argon gas, and held at this temperature for 5 minutes to sinter. I got a body.

The obtained sintered body was polished and examined for the presence of defects using an optical microscope, but no defects were found. In addition, as a result of the bending strength test, the Weibull coefficient obtained by Weibull plotting the strength values was m = 21, and the strength and fracture toughness values were 1200 MPa and 10 MPa, respectively.
It was m1/2. When this sample was subjected to HIP treatment at 1850° C. for 1 hour under an Ar gas pressure of 0.9 MPa, the m value increased to 25.

(Example 2) α-type SiC powder 250g, S
700 g of m2O3 powder and 50 g of Al2O3 powder were placed in a 4% polyethylene glycol aqueous solution, mixed with stirring, and then dried. Next, this dry powder is molded to obtain a green body, which is placed in an electric furnace and heated from room temperature to 1920 m
The temperature was raised to .degree. C. over 40 minutes and maintained at this temperature for 1 minute to obtain a sintered body.

As a result of the bending strength test of the obtained sintered body, the value of the Weibull coefficient was m=22, and the strength and fracture toughness values were 1100 MPa and 11 MP·m1, respectively.
/2. This sample was heated under an Ar gas pressure of 10 MPa.
As a result of HIP treatment at 1800℃ for 30 minutes, the m value was 28.
rose to

(Example 3) β-type SiC powder 700g, L
228 g of a2O3 powder and 72 g of Al2O3 powder were placed in a 3% polyethylene glycol aqueous solution, mixed with stirring, and then dried. Next, this dry powder is molded to obtain a green body, which is placed in an electric furnace and heated in nitrogen gas from room temperature to 1900°C in 30 minutes, and held at this temperature for 2 minutes to sinter. I got a body.

The obtained sintered body was processed to prepare a sample for bending strength, and a bending strength test was conducted. As a result, the Weibull coefficient value was m=22, and the strength and fracture toughness values were 1100 MPa and 11 MP·m1/2, respectively. This sample was heated under Ar gas pressure of 0.9 MPa at 185
As a result of HIP treatment at 0° C. for 10 minutes, the m value increased to 26.

(Example 4) α-type SiC powder (average particle size 0
．． 3 μm) 200 g, 720 g of Yb2O3 powder, and 80 g of Al2O3 powder were mixed with alcohol, wet mixed using a ball mill for 24 hours, and then the alcohol was removed and dried. Next, this dry powder was added to a 6% polyethylene glycol aqueous solution and mixed by stirring, and then dried. Then, this dry powder is molded to obtain a green body, which is placed in an electric furnace and heated from room temperature to 1950°C in 30 minutes in argon gas, and held at this temperature for 1 minute to form a sintered body. I got it.

As a result of the bending strength test of the obtained sintered body, the value of the Weibull coefficient was m=23, and the strength and fracture toughness values were 1050 MPa and 10 MP·m1, respectively.
/2. As a result of HIPing this sample at 1700°C for 2 hours under Ar gas pressure of 0.8 MPa, the m value was 2.
It rose to 7.

(Example 5) α-type SiC powder 800g, H
40 g of o2O3 powder and 160 g of Al2O3 powder were mixed with alcohol, wet mixed using a ball mill for 24 hours, and then dried. Next, this dry powder was molded to obtain a green body, which was placed in an electric furnace and heated from room temperature to 2000°C in 3 minutes in nitrogen gas, and then heated to this temperature at 0.
．． A sintered body was obtained by holding for 1 minute. The obtained sintered body was heated at 1800°C for 30 minutes under an argon gas pressure of 98 MPa.
HIP treatment was performed for 1 minute.

As a result of conducting a bending strength test on the obtained sintered body, the value of the Weibull coefficient was m=28, and the strength and fracture toughness values were 1500 MPa and 12 MP·m1, respectively.
/2.

In this way, SiC obtained by the conventional method
The value of the Weibull coefficient of the sintered body is m = 10 or less, and the strength and fracture toughness values are respectively 600 MPa or less, 5
Considering that the SiC sintered body according to the present invention obtained in this example had a value of MP·m1/2, it was confirmed that all the physical property values of the SiC sintered body according to the present invention obtained in this example were superior to conventional materials.

(Example 6) α-type SiC powder 45g, Y2O
After mixing and molding 44.9 g of Al2O3 powder and 10.1 g of Al2O3 powder according to a conventional method,
Raise the temperature to 1950℃ at a heating rate of 0℃/min,
A sintered body was obtained by maintaining the temperature at 950°C for 10 minutes. The obtained sintered body was polished, and a scanning electron micrograph of the polished surface of this sample is shown in FIG. As is clear from this photo, SiC
The black particles are uniformly dispersed in the white oxide matrix with no visible pores. Furthermore, as a result of conducting a bending strength test on the obtained sintered body, the value of the Weibull coefficient was m = 21, and the strength and fracture toughness values were each 800 MP.
a, 8MP・m1/2. When this sample was subjected to HIP treatment at 1800° C. for 30 minutes under an Ar gas pressure of 3 MPa, the m value increased to 26.

(Comparative Example) A green body made from the same raw materials as in Example 6 was heated to 1950°C at a heating rate of 6°C/min and held at 1950°C for 10 minutes to obtain a sintered body. . The obtained sintered body was polished, and a scanning electron micrograph of the polished surface of this sample is shown in FIG. As is clear from this photo,
There are many pores generated by the reaction between the white oxide matrix and SiC. Moreover, as a result of conducting a bending strength test on the obtained sintered body, it was found that the strength was significantly lowered to 150 MPa.

[0044]

As described above, according to the present invention, the generation of pores and voids in ceramics, which cause a decrease in strength and reliability, can be prevented by sintering at an appropriate sintering temperature and in a short time by rapid temperature rise. By applying this method, it is possible to easily obtain a dense, structurally uniform SiC-rare earth oxide-alumina sintered body having high strength and reliability. Moreover, the SiC-rare earth oxide-alumina-based sintered body of the present invention is economical because it can be made into a product by pressureless sintering.

[0045] The SiC-rare earth oxide-alumina composite silicon carbide sintered compact of the present invention can be used for gas turbine blades,
Spherical bodies, gas turbine parts, equipment parts for corrosive liquids,
Crucibles, ball mill linings, heat exchangers and refractories for high-temperature reactors, heating elements, combustion tubes, die-casting pumps, thin-walled tubes, fusion reactor materials, nuclear reactor materials, solar reactor materials, tools and their parts, for grinding Materials, heat shields, single crystal substrate electronic materials,
It is effectively used in a wide range of fields including electronic circuit substrates, insulating materials, and other fields.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the crystal structure of the polished surface of a sintered body obtained by the method of the present invention.

FIG. 2 is an electron micrograph showing the crystal structure of a polished surface of a sintered body obtained by a conventional method.

Claims (4)

[Claims] Claim 1: 95-5% by weight of rare earth oxide and A
Mixed oxide 80-1 consisting of 5-95% by weight of l2O3
After molding a mixture of 0% by weight and 20 to 90% by weight of SiC, a mixture of
Heating is carried out at a rapid temperature increase that takes less than 60 minutes to reach a temperature of 2100 °C, and then the temperature is increased by 0.1 to 3
SiC-based oxide sintered body synthesized by holding for 0 minutes. Claim 2: 95-5% by weight of rare earth oxide and A
Mixed oxide 80-1 consisting of 5-95% by weight of l2O3
After molding a mixture of 0% by weight and 20 to 90% by weight of SiC, a mixture of
Heating is carried out at a rapid temperature increase that takes less than 60 minutes to reach a temperature of 2100 °C, and then the temperature is increased by 0.1 to 3
The SiC-based oxide sintered body synthesized by holding for 0 minutes was further heated at a temperature of 1600 to 2000°C for 0.5 to 10 minutes.
A SiC-based oxide sintered body manufactured by HIP treatment at a pressure of MPa. 3. 95-5% by weight of rare earth oxide and A
Mixed oxide powder consisting of 5-95% by weight of l2O3 80~
After mixing 10% by weight of SiC powder and 20 to 90% by weight of SiC powder and molding the mixed powder, it takes 6 hours to reach a temperature of 1700 to 2100°C in a non-oxidizing atmosphere.
1. A method for producing a SiC-based oxide sintered body, characterized in that synthesis is carried out by applying rapid temperature rise within 0 minutes and then maintaining that temperature for 0.1 to 30 minutes. 4. The SiC-based oxide sintered body produced by the method according to claim 3 is further heated to a temperature of 1,600 to 200
A method for producing a SiC-based oxide sintered body, comprising performing HIP treatment at a temperature of 0° C. and a pressure of 0.2 to 10 MPa.