JPS6242878B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a silicon carbide sintered body, and particularly to a method for manufacturing a dense, non-porous silicon carbide sintered body. Silicon carbide is a material that has many excellent characteristics such as excellent chemical stability, high strength at high temperatures, and corrosion resistance and oxidation resistance. For this reason, silicon carbide is promising as a high-temperature structural material, particularly as a blade material for high-temperature gas turbines. Conventionally, silicon carbide sintered bodies have been manufactured by hot pressing, reaction sintering, and gas phase reaction methods. Among these, the gas phase reaction method is a method in which carbon and silicon compounds (mainly organic compounds or halogen compounds) are introduced into a reaction chamber along with a carrier gas, and are thermally decomposed to produce silicon carbide on a suitable substrate. be. Although a homogeneous and dense silicon carbide sintered body can be obtained by this method, it is difficult to obtain a thin film with a thickness of about 1 mm at most. In addition, silicon carbide sintered bodies produced by the reaction sintering method are usually obtained by mixing carbon and silicon or silicon dioxide powder and firing the mixture. Silicon sintered bodies are difficult to obtain. At present, there is no method other than the hot press method to produce dense and large-sized products. Silicon carbide has traditionally been known as a material that is difficult to sinter, but Alliegro et al. (J.am.Ceram.Soc.,
39386-389 (1956) reported that a sintered body close to the theoretical density (3.21 g/cm ³ ) could be obtained by hot pressing with the addition of aluminum, iron, etc. Since then, various additives have been investigated. Furthermore, the particle size of the raw material silicon carbide powder has also been studied. For example, General Electric Company's Savante Prochatka is published in Published Patent Publication No. 49-
99308, 0.5 to 3.0 parts (by weight) of boron is added to 100 parts (by weight) of silicon carbide, and the ceramic is hot pressed to obtain a ceramic having a theoretical density of 98%.
Products using boron or boron carbide as an additive are also described in Japanese Unexamined Patent Publications Nos. 50-78609 and 52-6716. Also, Weaver K. Gierard et al. of Norton Corporation published patent publication No. 49-7311
In No. 1, we obtained products with theoretical densities exceeding 99% for products to which 0.5 to 5.0% by weight of aluminum or aluminum oxide was added as an additive. Also, aluminum or aluminum oxide, iron,
Published Patent Publication No. 51- uses silicon as an additive.
65111. According to the above-mentioned conventional technology, in order to obtain a dense silicon carbide body, a submicron fine powder of silicon carbide or a fine powder having a particle size of several microns or less is used, and the same fine powder is used as an additive. I had to use powder. Additionally, operations were required to obtain a uniform dispersion of fine additive powder and silicon carbide powder, which generally required a ball milling process in a suitable container containing tungsten carbide spheres. . An object of the present invention is to provide a method for producing a simple and dense sintered body of silicon carbide, and to reduce variations in strength and improve reliability. The present invention is an element in the first to fourth periods of the Periodic Table of Elements, in which at least one element selected from Group A, Group B, Group A, and Group A is dissolved as a solid solution in an amount of more than 1.0% and not more than 10.0% by weight. The process involves hot pressing silicon carbide powder in a vacuum or inert gas at a temperature of 1900°C to 2050°C and a pressure of 100 to 700 kg/ ^cm2 for 5 to 60 minutes, resulting in dense carbonization. A sintered body of silicon can be produced.
(The elements of groups a, b, a in the first to fourth periods are Be, Mg, Ca, Cr, Fe, Co, Ni, B,
Al, Ga, etc. ) Furthermore, a sintered body of silicon carbide having a theoretical density of 95% or more can be obtained. This can be used as a high-temperature structural material, such as a material for high-temperature gas turbines. As mentioned above, silicon carbide is a material that is difficult to sinter, so it is necessary to add additives. Conventionally, additive powder was prepared separately from silicon carbide powder and mixed uniformly by ball milling means, but according to the present invention, such a milling step is not necessary. In the present invention, when obtaining fine powder of silicon carbide, in advance,
The above-mentioned elements may be dissolved in solid solution. Such silicon carbide can be easily synthesized by a conventional method. Although the effect of additives in obtaining a silicon carbide sintered body is not precisely understood, it is generally considered as follows. This is because when a mixture of silicon carbide and additives is heated to about 2000°C under pressure, the atoms of the additives diffuse into the crystal lattice of silicon carbide, and as a result, the crystal grains of the silicon carbide body are separated from each other. It is thought that the bonding progresses, resulting in a dense sintered body. In this case, it is essential that the additives be uniformly dispersed; poor dispersion will result in areas where sintering will not proceed. In the conventional method, additives are added separately from silicon carbide powder, so for example, FF
As stated by Lange [J. Mater. Sci., 10, 314-320 (1975)], aluminum is unevenly distributed in silicon carbide grains. For example, when a silicon carbide sintered body is exposed to a high temperature of 1500° C. or higher, it causes deterioration in areas where additive components are unevenly distributed. In the method of the present invention, since the additive components are dissolved in silicon carbide in advance, local non-uniformity is less likely to occur. In addition, since the additive components in silicon carbide mutually diffuse within the particles when heated to approximately 2000°C under pressure, it is almost impossible for the additive components to be unevenly distributed in the sintered body. Are better. There are several important conditions for hot pressing silicon carbide to obtain a dense sintered body. Regarding the silicon carbide powder that is the starting material, the first factor is the amount of additive components dissolved in the silicon carbide raw material powder. If this amount is less than 1.0% by weight, it is difficult to obtain a dense silicon carbide sintered body, and if it is more than 10% by weight, densification is easily achieved, but the progress of grain growth is significant, resulting in poor strength and oxidation resistance. will decrease. The optimum amount added is 2-5% by weight. Note that two or more kinds of silicon carbide raw material powders having different amounts of solid solution of additive components may be blended, or powders containing no additives in solid solution may be used together. However, in this case, it is important to be careful to avoid uneven distribution. Second, the average particle size of the silicon carbide powder is also an important condition; the smaller the particle size, the better; however, densification is possible if the particle size is 10 microns or less. However, as long as the amount is within the range of 20% by weight, powder having a particle size of 20 to 70 microns may be mixed. Next, as conditions for hot pressing, temperature, pressure and time are important, and these are interrelated. In order to obtain a dense silicon carbide sintered body, first of all it is necessary to raise the temperature to 1900°C or higher. At temperatures lower than this, the additive components do not diffuse sufficiently and a dense sintered body cannot be obtained. Also, 2050
If the temperature exceeds ℃, excessive grain growth tends to occur. The second factor is pressure, which is largely limited by the material of the die used. When using graphite dies, the pressure of 700Kg/ ^cm2 is almost the upper limit, but by adjusting the temperature and time,
It is possible to obtain a dense sintered body even at 100Kg/cm ² . Furthermore, the sintering time is also one of the important conditions, and the optimum time is determined from the relationship between temperature and pressure. In general, temperature (over 2000℃), pressure (over 400℃)
Kg/cm ² ) is high, sintering takes 5 to 15 minutes,
If the temperature and pressure are low, it will take 30 to 60 minutes. However, if the sintering time is kept longer than this, the sintered density will not improve any further, and excessive grain growth will occur. A more important condition is the atmosphere during sintering; an oxidizing atmosphere cannot be used because it oxidizes silicon carbide and produces silicon dioxide. For this purpose, a vacuum or an inert gas atmosphere is used. By hot-pressing silicon carbide powder under the above-mentioned conditions, a sintered body of silicon carbide having a density of 95% or more of the theoretical density can be obtained. Next, the present invention will be explained with reference to examples. Example 1 Chemical analysis was conducted on the components of silicon carbide powder containing aluminum as a solid solution and having an average particle size of 3 microns. The analysis table was as shown in Table 1.

[Table] To 100 parts by weight of this silicon carbide powder, 10 parts by volume of silicone oil and 10 parts by volume of xylene were added and kneaded. This was placed in a mold and molded at a pressure of 1 ton/cm ² , and then placed in a graphite die. The density of the molded product after molding was 1.71 g/cm ³ . The hot press was carried out in an induction heating furnace at a reduced pressure of 1×10 ^{to 4} torr or less. A pressure of 200 Kg/cm ² was applied and maintained until the hot pressing was completed. The temperature was raised from room temperature to the predetermined temperature of the hot press in about 2 hours, and maintained at the predetermined temperature for 5 to 100 minutes. Thereafter, the furnace was allowed to cool to room temperature. Figure 1 shows the density of the sintered body when the sintering time is constant and the sintering temperature is changed, and Figure 2 shows the density of the sintered body when the sintering temperature is constant and the sintering time is changed. shows the density of From these two figures, the temperature is 1900
It can be seen that a dense sintered body can be obtained within the range of 5 to 60 minutes at a temperature of 5 to 2050 degrees Celsius. Example 2 The same operation as in Example 1 was carried out using silicon carbide powder with an average particle size of 3 microns in which the type and concentration of elements dissolved in silicon carbide were varied, and a silicon carbide sintered body was obtained. Obtained. The hot pressing conditions at this time were a temperature of 2000° C., a pressure of 200 Kg/cm ² and a time of 30 minutes. Table 2 shows the relationship between the type and weight % of added elements and the density of the sintered body.

【table】

[Table] No. 6, in which the sum of elements dissolved in silicon carbide is 1.0% by weight or less, has a significantly low density of the sintered body. Example 3 A sintered body of silicon carbide was prepared in the same manner as in Example 1 using silicon carbide powder (average particle size 3 microns) containing the elements shown in Table 3. Obtained. In order to investigate the influence of hot press pressure, the temperature during sintering was 2000℃ and the time was 30 minutes.
Changed the pressure.

[Table] Figure 3 shows the density of the sintered body when the pressure is changed. Density is 3.10g/cm ³ or more at 100Kg/cm ² or less. Example 4 Using the sample of Example 3, various silicon carbide powders with different particle sizes were prepared. For the hot press, a sample was prepared using the same procedure as in Example 1, and the sample was heated at 2000°C.
The test time was 200Kg/cm ² for 30 minutes. Figure 4 shows the relationship between average particle size and density. It can be seen that when the average particle size is 10 microns or less, the density of the sintered body becomes high. The particle size distribution of silicon carbide with an average particle size of 9.4 microns is shown in Table 4, and if the particles with a particle size of 20 to 70 microns exceed about 20% by weight, the sintered body The density is 2.8g/ ^cm3 .

[Table] Example 5 Silicon carbide powder No. 6 used in Example 2 was mixed with other silicon carbide powders in various proportions, and the same operation as in Example 1 was performed to form a sintered body of silicon carbide. Obtained. The hot press conditions at this time were 2000℃, 200Kg/cm ² ,
It was set as 30 minutes. Table 5 shows the relationship between the mixing ratio of silicon carbide powder and the density of the obtained sintered body of silicon carbide.

【table】

[Table] Items with non-uniform parts in the sintered body
It was seen. In addition, the density of the sintered body also decreases.
Example 6 Among the silicon carbide sintered bodies described above,
For those with a high density sintered body of 3.20 g/cm3 or ^more , a test piece with a cross-sectional area of 2 mm x 2 mm and a length of 5 cm was prepared, polished with diamond paste with a particle size of 1 micron, and spun. A three-point bending test was performed with a device having a length of 3 cm. Simple average bending strength: 50 measurements Room temperature: 75 to 109 Kg/mm ² 1300°C: 70 to 105 Kg/mm ² Example 7 1.5% by weight of Al in No. 7 of Table 2, 5% of Al in No. 8
No. 11 and No. 12 were mixed by weight% and kneaded in a bow mill.
shall be. In addition, No. 13 and No. 13 were prepared by mixing 1% by weight and 3% by weight of B with No. 6 in Table 2 and kneading them in a ball mill.
Set it as No.14. Sintered bodies were prepared from the above Nos. 7, 8, 11 to 14 by hot pressing in the same manner as in Example 1. The hot press conditions were 2000°C, 200Kg/cm ² , and 30 minutes. The obtained sintered body was subjected to a bending test (at room temperature) according to the method shown in Example 6. The test was conducted on 100 pieces of each, and the simple average strength and Weibull coefficient, which is an index of dispersion, were calculated and shown in Table 6. Note that there is inherent variation in the fracture strength of brittle materials such as sintered bodies, which follows the Weibull distribution, so in order to handle it using statistical methods, the following Weibull distribution function is applied, and P(σ )=1−Q(σ)=exp[−σ ^m /σ ₀ ] m is the Weibull coefficient. However, P(σ) is the probability of non-destruction under stress σ, and σ ₀ indicates a parameter of the scale. The larger the Weibull coefficient, the smaller the variation in strength and the higher the reliability.

[Table] In Table 6, Nos. 11 to 14 are additives mixed using the conventional method, and No. 1 using the method of the present invention.
The Weibull coefficient is smaller than 7 and 8. According to the present invention, it is possible to obtain a silicon carbide sintered body having a Weibull coefficient unprecedentedly large and close to the theoretical density. In addition, in the present invention, it is necessary to form a solid solution of 1 to 10% by weight of elements belonging to groups a, b, a, and groups of the first to fourth periods of the periodic table, but other elements are not included. Even if it is a solid solution, it makes no difference.

[Brief explanation of the drawing]

The first is a curve diagram showing the relationship between sintering temperature and the density of silicon carbide sintered body, Figure 2 is a curve diagram showing the relationship between sintering time and density of silicon carbide sintered body, and Figure 3 is a curve diagram showing the relationship between sintering time and density of silicon carbide sintered body. FIG. 4 is a curve diagram showing the relationship between the pressure during compaction and the density of the silicon carbide sintered body. FIG. 4 is a curve diagram showing the relationship between the average particle size of silicon carbide powder and the density of the silicon carbide sintered body. 1...Sintering time 5 minutes, 2...Sintering time 30 minutes, 3
...Sintering time 60 minutes, 4...1900℃, 5...2050
℃, 6...2100℃.

Claims (1)

[Claims] 1 An element in the 1st to 4th period of the periodic table of elements, in which at least one element selected from group a, group b, group a, and group is dissolved in a solid solution of more than 1.0% by weight and 10.0% by weight or less Silicon carbide powder is heated to 1900℃ in vacuum or inert gas.
A silicon carbide sintered body characterized by hot pressing at 2050°C and a pressure of 100Kg/ ^mm2 to 700Kg/ ^mm2 for 5 minutes or more to obtain a sintered body with a density of 95% or more of the theoretical density and a Weibull coefficient of 19 or more. manufacturing method.