JPH0317786B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) This invention is a pressureless sintered silicon carbide material that can produce silicon carbide sintered bodies without pressure, which is one of the representative ceramics that have been attracting attention in recent years. The present invention relates to a method for producing a quality sintered body. (Prior art) Conventionally, as a method for manufacturing a silicon carbide sintered body,
There are reaction sintering methods, hot press methods, pressureless sintering methods, etc. Of these, the reactive sintering method tends to contain excess silicon (Si), and the hot pressing method has the drawbacks of making it difficult to manufacture products with complex shapes, whereas the pressureless sintering method has the disadvantages of being difficult to manufacture products with complex shapes. Since it can be sintered under pressure, it has the advantage of being able to manufacture products with complex shapes and eliminating the problem of excess silicon. A conventional method for producing a pressureless sintered silicon carbide sintered body having such advantages is to compact a mixed powder obtained by adding boron and carbon or a compound thereof to silicon carbide powder, and to press the obtained compact. There was a method of heating and sintering a powder compact at 1900 to 2300°C in an inert atmosphere, especially an argon atmosphere at 1 atm (for example, Japanese Patent Application Laid-open No.
78609, JP-A-56-92167). In this manufacturing method, carbon has the effect of removing the SiO ₂ film formed on the surface of the silicon carbide powder through a reducing action, improving the surface energy of the silicon carbide powder, and increasing atomic diffusion between particles. , boron diffuses onto the surface of silicon carbide powder at the beginning of the sintering process, lowers the surface energy of silicon carbide powder, suppresses evaporation, condensation, and surface diffusion of silicon carbide, and promotes mass transfer, that is, densification of silicon carbide. It is thought that boron and carbon have the effect of solid-dissolving in silicon carbide in the latter stage of the sintering process and have the effect of further promoting sintering. However, in the conventional pressureless sintering method for producing a silicon carbide sintered body, in order to obtain a dense sintered body with high density, especially 95% or more of the theoretical density, it is necessary to replace boron with silicon carbide. Solid solubility limit (approximately 0.2% by weight)
Because boron must be added in amounts greater than is β of silicon carbide
→ α transformation occurs and abnormal coarse crystals (200~
400 μm), which caused a problem in that the strength of the sintered body was significantly reduced. (Purpose of the Invention) The present invention was made by focusing on such conventional problems, and even when boron is added in silicon carbide at a solid solubility limit of approximately 0.2% by weight or more, crystal grain growth does not occur. It is dense with a theoretical density ratio of 85% or more, and the crystal grains are significantly finer than conventional silicon carbide sintered bodies. Furthermore, it is an object of the present invention to provide a method for manufacturing a silicon carbide sintered body that can obtain a silicon carbide sintered body with excellent strength. (Structure of the Invention) A method for producing a silicon carbide sintered body according to the present invention includes silicon carbide powder having an average particle size of 0.2 μm or less and containing a β phase of 90% by weight or more, 2.0% by weight of elemental boron and/or a boron-containing compound corresponding to said weight%;
1.49 wt% elemental carbon and/or the wt%
A carbon-containing compound corresponding to 0.1 to 1.0% by weight of titanium nitride is mixed and then molded, and if necessary, after generating elemental boron or carbon from the boron-containing compound or carbon-containing compound, The molded body is heated to a temperature of 1,900 to 2,200°C in a non-oxidizing atmosphere such as a vacuum, a nitrogen atmosphere, an inert atmosphere, etc. at atmospheric pressure or a pressure higher than atmospheric pressure, so that the density becomes 85% or more of the theoretical value. The feature is that a sintered body is obtained. The silicon carbide powder used in this invention is
It has an average particle size of 0.2 μm or less and contains 90% by weight or more of β phase. Here, silicon carbide powder is
100% β-SiC is more desirable, but α
-SiC, SiO ₂ Even if it contains other free Si, Fe, Al, Ca, Mg, etc., there is no problem as long as β-SiC is 90% by weight or more. Furthermore, if the particle size of the silicon carbide powder is too large, it becomes difficult to sinter and increase the density, so it is preferable to use a silicon carbide powder with an average particle size of 0.2 μm or less. In addition, the amounts of boron and carbon added are 0.4 to 2.0% by weight of boron and 0.4 to 2.0% by weight of carbon, based on the silicon carbide powder.
The content is preferably 1.01 to 1.49% by weight. The reason for this is
If the amount of boron is too small, silicon carbide will evaporate during sintering.
If the effect of boron, which increases the densification of silicon carbide by suppressing agglomeration and surface diffusion, is insufficient and the amount of carbon is too low, the SiO ₂ film formed on the surface of the silicon carbide powder will be removed by reducing action. This is because carbon's effect of increasing atomic diffusion between particles cannot be obtained sufficiently, and as a result, high density of the sintered body cannot be achieved. This is because, in this case, the sintered body cannot achieve high density. In this case, boron can be partially or entirely added as a boron-containing compound in an amount corresponding to the amount of boron added, and carbon can be partially or entirely added as a carbon-containing compound. It is also possible to add within the range of the amount corresponding to the amount added. Furthermore, in this invention, in addition to the addition of boron and carbon, titanium nitride is added in a range of 0.1 to 1.0% by weight. This titanium nitride has the effect of promoting densification of silicon carbide, and
By absorbing excess boron as a compound, it prevents boron from being unevenly distributed at grain boundaries and has the effect of suppressing the growth of crystal grains, thereby significantly increasing the strength of silicon carbide sintered bodies. It has an effect. It has been found from various experiments that in order to obtain such effects, it is preferable to set the content in the range of 0.1 to 1.0% by weight. Thus, silicon carbide powder, boron or a boron-containing compound, or boron and a boron-containing compound, carbon or a carbon-containing compound, or carbon and a carbon-containing compound, and titanium nitride are mixed and homogenized, and then formed into a predetermined shape. . Next, when a boron-containing compound or a carbon-containing compound is used as the boron or carbon source, elemental boron or carbon is generated from the boron-containing compound or carbon-containing compound in the compact, and then the carbonization is performed. Silicon, boron, carbon and titanium nitride are sintered by heating to a temperature of 1900-2200°C in a non-oxidizing atmosphere. Examples of the non-oxidizing atmosphere used at this time include vacuum, nitrogen atmosphere, and inert atmosphere. After this sintering, a high-density sintered body with a density of 85% or more of the theoretical value is obtained. (Function) For example, by mixing silicon carbide powder, boron powder, carbon powder, and titanium nitride powder, and then uniformly mixing them using a ball mill or the like, the carbon powder can be uniformly distributed on the surface of the silicon carbide powder. It is covered with. Furthermore, when a liquid phenolic resin is used as a carbon source, the phenolic resin is uniformly mixed between the silicon carbide powder using a ball mill, and carbon is uniformly distributed on the surface of the silicon carbide powder through the subsequent carbonization process. It is covered with. This free carbon removes the oxide film SiO ₂ of the silicon carbide powder by a reducing action at 1000 to 1650°C (SiO ₂ +3C→SiC+2CO) and increases the surface energy of the silicon carbide particles. On the other hand, boron diffuses onto the surface of the silicon carbide particles activated as described above in the initial stage of sintering, lowers the surface energy of the silicon carbide particles, and suppresses coalescence of the silicon carbide particles. In other words, surface diffusion, evaporation, and condensation of atoms in silicon carbide particles are reduced to suppress coalescence and coarsening of silicon carbide particles, and volumetric diffusion and grain boundary diffusion in silicon carbide particles are promoted to make the silicon carbide particles densified. promote. In this case, the surface of titanium nitride also volatilizes (1550℃
10 ^-4 mmHg), diffuses onto the surface of silicon carbide particles,
Suppresses surface diffusion, evaporation, and condensation of atoms on the surface of silicon carbide particles. Furthermore, as titanium nitride diffuses onto the surface of silicon carbide particles, many lattice defects are induced on the surface of silicon carbide crystal particles, and in the latter stage of the sintering process, various atoms are generated through these lattice defects. Generates a base for diffusion. As described above, boron and titanium nitride promote volumetric diffusion within silicon carbide particles and promote densification. In the latter stage of the sintering process, each of the boron becomes a solid solution in the silicon carbide particles, but the boron that is not completely dissolved is combined with titanium and the compounds TiB ₂ (melting point 2900℃) and TiB (melting point
2550℃) and Ti ₂ B (melting point 2200℃), and these compounds significantly strengthen the grain boundaries of silicon carbide than boron alone. In addition, nitrogen is responsible for the growth of silicon carbide crystal particles and β
Since the effect of suppressing the transformation from phase to α phase is remarkable, the crystal grain size of the sintered body is very small, 1 to 2 μm, and no abnormally grown coarse grains are produced. In this way, titanium nitride not only induces volumetric diffusion of silicon carbide under certain abundance conditions and promotes sintering, but also forms compounds consisting of boron and titanium at the grain boundaries to strengthen the grain boundaries. Furthermore, it has the effect of making the crystals of the sintered body finer and significantly improving the strength of the sintered body, and a high-density and high-strength silicon carbide sintered body can be obtained. (Example 1) Next, an example of the present invention will be described together with a comparative example. 100 g of silicon carbide powder (Beta Random Ultra Fine, average particle size 0.3 μm, β phase approximately 100% by weight; manufactured by IBIDEN Co., Ltd.) and boron powder (Amorphous,
Average particle size: 0.3 μm; manufactured by Seratsuku Co., Ltd.) 0.3 to 2.5 g,
Phenol resin (PR50404, carbon yield 27% by weight;
3.0 to 6.0 g (manufactured by Sumitomo Bakelite Co., Ltd.) and 0.1 to 1.2 g of titanium nitride powder (-325mesh; manufactured by Cerac Co., Ltd.)
and using acetone 200c.c. as the solvent.
Mixed in a ball mill for 25 hours. Next, the slurry obtained by ball mill mixing was heated and dried in a vacuum to remove acetone, and the obtained mixed powder was crushed in an agate mortar.
The particles were sized to particles of 105 μm or less using a standard sieve. Next, put the sized particles into the mold and apply a pressure of 500 kg.
The powder was compacted at f/cm ² and then re-compacted using a cold isostatic pressure device at a pressure of 2000Kgf/cm ² to form 13 x 6 x 32 mm.
A powder compact was molded. Next, the powder compact formed in this manner was placed in a vacuum furnace and heated to convert the phenolic resin into carbon. At this time, in a carbonization treatment in which the compact was heated to 900°C at a heating rate of 100°C/hr in a vacuum with a degree of vacuum of 10 ^-3 mmHg and held at 900°C for 1 hour, the carbon yield was 27% by weight. It was hot. Next, the molded body after carbonization treatment is placed in a vacuum degree of 10 ^-3
The molded body was sintered by heating and holding at 2100° C. for 30 minutes in a vacuum of mmHg or less.
The heating temperature during sintering at this time is 1500℃→
1650℃ for 20 minutes, held at 1650℃ for 30 minutes,
1650℃→2100℃; 3 hours. Next, the surface of the silicon carbide sintered body thus obtained was polished with a #600 diamond grindstone, and then finished polished using a diamond paste with a particle size of 1 μm. The silicon carbide sintered body thus obtained (8×4
When examining the density and bending strength of
The results are shown in the table.

【table】

[Table] As shown in Table 1, it was confirmed that the density ratio was lower than 85% when the amount of boron, carbon, and titanium nitride added to the silicon carbide powder were outside the scope of this invention. Ta. On the other hand, in all cases where the scope of this invention is satisfied, the density ratio is 85%.
It was confirmed that the material had a high density and a high value of strength. Furthermore, the crystal grain size of the sintered body obtained by this invention example was very small, 1 to 2 μm, whereas in the case of the sintered body that did not contain titanium nitride,
It was 10 to 20 μm, which was considerably larger than the case containing titanium nitride. Furthermore, in the sintered body obtained according to this invention, no abnormally grown coarse grains were observed, whereas in the case of the sintered body that did not contain titanium nitride, coarse particles with a grain size of 200 μm were observed. were often observed, and it became clear that these coarse particles were often the starting point of fracture. (Example 2) Next, another example of the present invention will be described together with a comparative example. 100 g of silicon carbide powder (Beta Random Ultra Fine, average particle size 0.3 μm, almost 100% by weight of β phase; manufactured by IBIDEN Co., Ltd.) and boron carbide powder (manufactured by Syuutark; −325 mesh) were ball milled for 100 hours. ), 2.5 g of furan resin (V-901, carbon yield 48% by weight; manufactured by Hitachi Chemical Co., Ltd.), and 0.4 g of titanium nitride powder (-325 mesh; manufactured by Serac Co., Ltd.) were added, Ball mill mixing was performed for 25 hours using 250 c.c. of benzene as a solvent. The slurry thus obtained was then injected into liquid nitrogen to form frozen particles with a particle size of 1 to 3 mm. Subsequently, the frozen particles are placed in a vacuum container, the degree of vacuum is maintained at 5 to 10 mmHg, and the temperature is maintained at 25°C to sublimate and dry the benzene to obtain a powder. The particles were sized using a sieve. Thereafter, the mixed powder was compacted and carbonized in the same manner as in Example 1 to prepare a test piece. Then, the obtained specimen was placed in vacuum (10 ^-3 mm
Hg or less) or by heating and holding at 2100° C. for 30 minutes in an argon gas atmosphere of 1 atm to obtain a silicon carbide sintered body. Then, the obtained sintered compact test piece was polished in the same manner as in Example 1, and the density ratio and bending strength were examined.
The results are shown in the table. Also, for comparison, the same silicon carbide powder as above
To 100 g, 1.0 g of the same boron carbide powder as above and 2.5 g of furan resin were added and mixed, and then the density ratio and bending strength of test pieces obtained in the same manner as above were examined in the same manner. The results are also shown in Table 2.

[Table] As shown in Table 2, when titanium nitride is added, a sintered body with excellent density ratio and strength is obtained, whereas when titanium nitride is not added, the bending strength is low. That was the result. Note that the freeze-drying method adopted in this example allows various sintering aids to be dispersed extremely uniformly in the silicon carbide powder, making it possible to obtain a mixed powder with extremely excellent sinterability. It has the advantage of (Effects of the Invention) As explained above, according to the method for producing a silicon carbide sintered body of the present invention, silicon carbide powder having an average particle size of 0.2 μm or less and containing 90% by weight or more of β phase; 0.4 to 2.0% by weight of elemental boron or a boron-containing compound corresponding to this weight%, 1.01 to 1.49% by weight of elemental carbon or a carbon-containing compound corresponding to this weight%, and 0.1% by weight of the silicon carbide powder. ~1.0% by weight of titanium nitride is mixed and molded, and the molded body is heated at 1900~2200°C in a non-oxidizing atmosphere.
Since the sintered body was heated to a temperature of It is highly dense and dense with a theoretical density ratio of 85% or more, and its crystal grains are extremely fine, making it different from conventional silicon carbide. This has the remarkable effect that it is possible to obtain a silicon carbide sintered body that is even stronger in strength than a silicon carbide sintered body.

Claims (1)

[Claims] 1 Silicon carbide powder with an average particle size of 0.2 μm or less and containing 90% by weight or more of β phase, and 0.4 to 2.0% by weight of elemental boron or the weight% of the silicon carbide powder.
boron-containing compounds equivalent to 1.01-1.49% by weight
of elemental carbon or a carbon-containing compound corresponding to this weight % and 0.1 to 1.0 weight % of titanium nitride are mixed and then molded, and the molded body is heated to a temperature of 1900 to 2200°C in a non-oxidizing atmosphere. A method for producing a silicon carbide sintered body, characterized in that a sintered body having a density of 85% or more of the theoretical value is obtained.