JPH08225311A - Silicon nitride/silicon carbide complex powder, complex molding, their production and production of sintered compact of silicon nitride/silicon carbide complex - Google Patents

Abstract

PURPOSE: To obtain silicon nitride/silicon carbide complex powder having excellent sintering properties, capable of forming a high-strength sintered compact. CONSTITUTION: This silicon nitride/silicon carbide complex powder is obtained by blending silicon powder with carbonaceous powder and a sintering auxiliary, heat-treating the prepared mixed powder under a nitrogen gas-containing atmosphere and causing nitrogenation and carbonization of silicon and has >=30% αtype silicon nitride content based on the whole silicon nitride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride / silicon carbide composite powder and a composite molded body, a method for producing the same, and a method for producing a silicon nitride / silicon carbide composite sintered body. The present invention relates to a composite powder suitable for producing a silicon nitride / silicon carbide nanocomposite having thermal shock resistance, abrasion resistance and the like, a composite molded body, a method for producing them, and a method for producing a composite sintered body.

[0002]

2. Description of the Related Art Silicon nitride ceramics sintered bodies have severe operating conditions at high temperatures because of their high strength, high heat resistance, high thermal shock resistance, and high wear resistance. It is expected to be used as various structural ceramics. Also, various components are added for the purpose of improving the physical properties. Among them, silicon carbide is a ceramic component capable of exhibiting good oxidation resistance, high-temperature strength, and mechanical strength, and a ceramic sintered body in which silicon nitride is mixed with silicon carbide has been proposed. However, a sintered body obtained by simply mixing a silicon nitride powder and a silicon carbide powder does not have a nanocomposite structure, and the silicon carbide powder (on the order of microns) exists at a grain boundary of silicon nitride. Stay in. Therefore, various methods have been proposed in order to obtain a sintered body having a nanocomposite structure in which silicon carbide is finely dispersed in silicon nitride.

In Japanese Patent Laid-Open No. 2-160669, silicon carbide having an average particle size of 1 μm or less is dispersed in grain boundaries, and fine particles of silicon carbide having a size of several nanometers to several hundreds of nanometers are dispersed in silicon nitride particles. Disclosed is a silicon nitride-silicon carbide composite sintered body having a fine structure. This composite sintered body uses amorphous silicon nitride-silicon carbide composite powder or silicon nitride-silicon carbide mixed powder that produces fine silicon carbide having an average particle size of 0.5 μm or less in a liquid phase sintering system. 15 in the presence of sintering aid
It is manufactured by sintering at a temperature of 00-2300 ° C. However, the amorphous silicon nitride-silicon carbide composite powder is obtained by a vapor phase reaction method of an organic silicon compound, is very expensive, and is inferior in mass productivity. Further, there is a problem that the amorphous powder is inferior in moldability. Further, what is specifically disclosed as a silicon nitride-silicon carbide mixed powder is a mixed powder of an amorphous silicon nitride powder and a silicon carbide powder obtained by the same formulation as above, and the same problem still occurs. is there.
In addition, all that is disclosed is firing by hot pressing which does not require molding.

Japanese Patent Application Laid-Open No. Hei 3-261611 discloses a method for producing a silicon nitride composite powder for producing a silicon nitride / silicon carbide composite sintered body, comprising mixing a metal silicon powder and a carbonaceous powder, The resulting mixture in a nitrogen-containing inert gas atmosphere,
Disclosed is a method characterized in that the carbonization reaction and the nitridation reaction of the metal silicon powder are simultaneously performed by heating at a temperature of 1400 ° C. or lower. However, since this composite powder does not contain a sintering aid in the starting material, the silicon nitride generated by the heat treatment has β
It was difficult to form a mold, and it was difficult to increase the α-type silicon nitride content in the composite powder. In addition, since the β-type silicon nitride grows in a needle-like shape, the resulting powder has a large particle size and is difficult to pulverize. From the viewpoint of improving the sinterability, the silicon nitride raw material powder is required to have a high α-type silicon nitride content and to be fine particles. However, the disclosed method cannot satisfy these conditions, and the sinterability is There is a problem that it is inferior to.

A method for firing a β-type silicon nitride raw material powder to obtain a sintered body having high characteristics has been reported (F
C report, 1994 (5), pp. 130-133), in this method, it is necessary to control the particle size distribution of the β-type silicon nitride powder, to make the powder finer and to have a uniform particle size, Since high-temperature sintering by a sintering method is required, the process is expected to be complicated. It was also confirmed from this report that the β-type silicon nitride powder was a powder having low sinterability.

Accordingly, an object of the present invention is to provide a silicon nitride / silicon carbide composite powder and a composite compact having good sinterability and capable of forming a high-strength sintered body, a method for producing the same, and silicon nitride / silicon carbide. An object of the present invention is to provide a method for manufacturing a composite sintered body.

[0007]

Means for Solving the Problems As a result of intensive studies in view of the above objects, the present inventors have found that using silicon powder, carbonaceous powder and a sintering aid as starting materials and subjecting them to heat treatment under specific conditions. To obtain a silicon nitride / silicon carbide composite powder or composite molded body having a high α-type silicon nitride content, and thereby to obtain a composite powder or composite molded body having high sinterability, and completed the present invention. .

That is, in the silicon nitride / silicon carbide composite powder of the present invention, carbon powder and a sintering aid are mixed with silicon powder, and the obtained mixed powder is heat treated in an atmosphere containing nitrogen gas to obtain silicon. Is obtained by nitriding and carburizing, and the content of α-type silicon nitride in the composite powder is 30% or more of the total silicon nitride.

Further, the silicon nitride / silicon carbide composite molded article of the present invention is obtained by mixing a carbonaceous powder and a sintering aid with a silicon powder,
A molded body formed from the obtained mixed powder is heat-treated in a nitrogen gas-containing atmosphere to cause silicon nitriding and carbonization, and the content of α-type silicon nitride in the composite molded body is entirely It is characterized by being 30% or more of silicon nitride.

The method for producing a silicon nitride / silicon carbide composite powder in which the content of α-type silicon nitride of the present invention is 30% or more of the total silicon nitride is the mixing of carbonaceous powder and sintering aid with silicon powder. Then, the obtained mixed powder is heat-treated under a nitrogen gas-containing atmosphere to cause nitriding and carbonization of silicon, in which case the nitriding carbonization reaction is performed at a temperature of 1000 ° C to 1450 ° C, and at least the temperature before the start of the reaction. It is characterized in that the rate of temperature rise from when the temperature reaches the holding temperature to less than 2 ° C./min.

[0011] The method of the present invention for producing a silicon nitride / silicon carbide composite molded article in which the content of α-type silicon nitride is 30% or more of the total silicon nitride is as follows. After mixing, a compact is formed from the obtained mixed powder, and the compact is heat-treated in an atmosphere containing nitrogen gas to cause nitridation and carbonization of silicon.
The process is carried out at a temperature of 11450 ° C., and the rate of temperature rise from at least the temperature before the start of the reaction to the holding temperature is set to less than 2 ° C./min.

A first method of the present invention for producing a silicon nitride / silicon carbide composite sintered body is to form a molded body from the above silicon nitride / silicon carbide composite powder, and the molded body is subjected to 1600 in an atmosphere containing nitrogen gas. It is characterized by being sintered at ℃ ~ 2200 ℃.

The second method of the present invention for producing a silicon nitride / silicon carbide composite sintered body is to sinter the above silicon nitride / silicon carbide composite compact at 1600 ° C. to 2200 ° C. in an atmosphere containing nitrogen gas. Is characterized by.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. [1] Starting Material (a) Silicon Powder The silicon powder used in the present invention has an average particle size of 0.2 to 20 μm.
It is preferably m, particularly 0.3 to 10 μm. Average particle size is
If it is less than 0.2 μm, the powder surface is highly oxidized, and if it is more than 20 μm, uniform dispersion becomes difficult and the reactivity becomes poor.

As the silicon powder, relatively low purity and inexpensive powder as defined in JIS G 2312,
A wide range of materials can be used, such as a high-purity material obtained by crushing a crushed material of a semiconductor silicon wafer. When high-purity silicon powder is used, Fe, Cr, Co
It is also possible to accelerate the reaction by adding a compound such as

When the total amount of the silicon powder and the carbonaceous powder in the starting material is 100% by weight, the content of the silicon powder is 81.2%.
9 to 97.6% by weight is preferable, and 84.2 to 93.2% by weight is more preferable. If the amount of silicon powder is less than 81.2% by weight, the sintered body becomes difficult to be densified and the desired composite sintered body cannot be obtained. Also
If it exceeds 97.6% by weight, the combined effect of silicon carbide becomes insufficient.

(B) Carbonaceous powder The carbonaceous powder used in the present invention is not particularly limited as long as it is fine, but graphite powder or carbon black powder such as acetylene black or Ketjen black is preferable. Carbonaceous powder has an average particle size of 20 μm or less, especially
It is preferably 10 μm or less. If the average particle size is larger than 20 μm, uniform dispersion becomes difficult.

When the total amount of the silicon powder and the carbonaceous powder in the starting material is 100% by weight, the content of the carbonaceous powder is 2.
4 to 18.8% by weight is preferable, and 6.8 to 15.8% by weight is more preferable. If the carbonaceous powder is less than 2.4% by weight, the composite effect cannot be obtained, and if it is more than 18.8% by weight, the sintered body is not densified.

(C) Silicon nitride powder In order to improve the moldability of the mixed powder and to use it as a nucleus for silicon nitride formation, 0.1 to 5 μm, preferably 0.1 to 3 μm.
Silicon nitride powder having an average particle size of m may be added.
The addition amount of the silicon nitride powder is 0 to 100% by weight of the total of the silicon nitride formed by the heat treatment and the added silicon nitride.
The content is preferably 10% by weight, more preferably 0 to 5% by weight. If the amount of silicon nitride powder added is too large (the ratio of silicon nitride powder to silicon powder is too high), Si
The reaction sintering is insufficient and the combined effect cannot be obtained.

(D) Silicon Carbide Powder Silicon carbide powder may be added in a small amount for the same purpose as silicon nitride powder, that is, to improve the moldability of the silicon powder mixed powder and to serve as a nucleus for silicon carbide formation. Good. The preferable addition amount of silicon carbide powder is as follows: the total amount of silicon carbide formed by heat treatment and silicon carbide to be added is 100% by weight.
It is 0 to 10% by weight, more preferably 0 to 5% by weight. If the addition amount of silicon carbide is too large, the reaction sintering of silicon becomes insufficient, and a combined effect cannot be obtained.

(E) Sintering aid powder The sintering aid powder at the time of producing the composite powder is selected from the group consisting of (a) oxides of elements of Group 3A and 4A of the periodic table.
At least one kind of compound, or (a) and (b) aluminum nitride. Among them, (a) Y ₂ O ₃ and Lu ₂ O
_3, Yb ₂ O _3, at least one compound selected from the group consisting of HfO ₂ are preferred, Y ₂ O ₃ alone is particularly preferred.

The sintering aid powder used in the production of the composite compact is (a)
It comprises at least one compound selected from the group consisting of oxides of Group 3A elements and Group 4A elements of the Periodic Table, or (b) aluminum nitride and / or silicon oxide, and (a) above.
Among them, (a) Y ₂ O ₃ , Lu ₂ O ₃ , Yb ₂ O ₃ , H
At least one compound selected from the group consisting of fO ₂ , or (a) and silicon oxide are preferable, and Y ₂ O ₃
Alone or Y ₂ O ₃ and silicon oxide are particularly preferable.

The content of the sintering aid powder is preferably from 5 to 20% by weight, more preferably from 7 to 15% by weight, based on 100% by weight of the total amount of the composite powder or composite compact produced by the heat treatment. And If the amount of the sintering aid powder is less than 5% by weight, the sinterability of the obtained composite powder is insufficient, and
If it is more than 10% by weight, the high-temperature strength of the sintered body decreases.

The sintering aid is mixed with silicon powder and carbonaceous powder for nitriding / carbonization treatment. By adding the sintering aid from the beginning, the content of α-type silicon nitride in the composite powder or composite molded body increases, the dispersion state of the sintering aid improves, and the characteristics of the sintered body improve. .

[2] Method for producing composite powder (1) Preparation of mixed powder First, the respective components are blended so as to have the above blending ratio and thoroughly mixed with a ball mill, a kneader or the like. The mixing may be dry or wet. In the case of wet mixing, a dispersion medium such as water, ethanol or butanol is added to the powder mixture. Also, a suitable organic or inorganic binder can be added.
Examples of the organic binder include ethyl silicate, polyethylene glycol, polyvinyl alcohol (PV
A), acrylic emulsion, polyurethane emulsion and the like. Also, an inorganic binder can be added.

(2) Nitriding / Carburizing Treatment Next, the mixed powder is heated in a nitrogen-containing atmosphere to nitride and carbonize the silicon powder in the mixed powder. The nitridation rate and carbonization rate are determined by the amount of C in the starting material. That is, since substantially all of C is combined with silicon to form silicon carbide, substantially all unreacted silicon is converted to silicon nitride. For example, if Si and C are mixed at a molar ratio of 100: 7, the molar ratio of silicon nitride to silicon carbide is 31: 7.

The conditions of the nitriding / carbonizing treatment need to be slightly changed depending on the composition of the mixed powder, but the temperature is set to 1450 ° C. or less. Heating to a temperature exceeding 1450 ° C. is not preferable because silicon elutes or silicon evaporates. The lower limit of the nitriding / carbonizing treatment temperature is preferably set to 1000 ° C. If it is less than 1000 ° C, nitriding / carbonization reaction does not occur or the reaction rate is too low even if it occurs. A more preferred reaction temperature is 1100-1380 ° C.

In the present invention, the rate of temperature rise near the reaction temperature (holding temperature) of the nitriding reaction is reduced. Specifically, when the atmospheric temperature is 900 to 1300 ° C or higher, the heating rate is 2 ° C /
Min, preferably 0.5 ° C / min or less. If the rate of temperature rise is 2 ° C./minute or more, the nitriding reaction becomes vigorous, the content of α-type silicon nitride in the produced composite powder decreases, and the sinterability of the composite powder decreases, which is not preferable.
The preferred content of α-type silicon nitride is at least 30%, particularly preferably at least 40%, based on the total silicon nitride in the composite powder.

The pressure of the nitrogen-containing atmosphere is preferably 1 kgf / cm ² or more, more preferably 5 to 2000 kgf / cm ^{2.
Assume 2} . If the pressure of the nitrogen-containing atmosphere is less than 1 kgf / cm ² , nitriding does not proceed well. The reaction time of the nitriding / carbonizing treatment varies slightly depending on the treatment temperature and the like, but is generally 1 to 10
It is preferable to set it to about an hour. The nitrogen-containing atmosphere is a nitrogen-containing gas atmosphere, and examples of the nitrogen-containing gas include nitrogen gas, a mixed gas of nitrogen and hydrogen, a mixed gas of nitrogen and ammonia, and the like.

(3) Pulverization of powder The obtained silicon nitride / silicon carbide composite is pulverized into a composite powder. The pulverization can be performed by using a ball mill, a jet mill, an attrition mill or the like. The average particle size of the composite powder obtained by pulverization is preferably from 0.1 to 5 μm, more preferably from 0.3 to 3 μm.

When the nitriding / carburizing treatment is carried out under the above conditions, the silicon particles in the mixed powder react with carbon to produce silicon particles as a starting material and fine particles of silicon carbide finer than the carbon particles, and at the same time, nitride Thus, silicon nitride containing a high proportion of α-silicon nitride finer than the starting material silicon particles is generated.

[3] Manufacturing Method of Composite Molded Product (1) Preparation of Molded Product First, the respective components are blended and mixed by the same method as described in the above section [2] (1). The obtained mixed powder is molded into a desired shape. As a molding method, press molding, slip casting molding, injection molding or the like can be used.

In the case of press molding, molding is performed using a desired press mold after removing the dispersion medium. In the case of slip casting, it is poured into a hygroscopic mold together with the dispersion medium. In the case of injection molding, a suitable organic or inorganic binder is added and injection is performed in a mold. Examples of the organic binder include ethyl silicate, polyethylene glycol, polyvinyl alcohol (PVA), acrylic emulsion, polyurethane emulsion and the like. Inorganic binders can also be added. Slip casting molding or injection molding is preferable for producing a molded body having a complicated shape.

(2) Nitriding / Carburizing Treatment The conditions of nitriding / carburizing treatment may be almost the same as those described in the section [2] (2) above, but the thickness of the compact, the particle size of the starting raw material powder, etc. Therefore, the temperature should be 1450 ° C or lower. Heating above 1450 ° C. is not preferable because silicon is eluted. The lower limit of nitriding / carbonization temperature is 10
It is preferably set to 00 ° C. If the temperature is lower than 1000 ° C, nitriding /
The carbonization reaction does not occur, or if it does, the reaction rate is too low. A more preferred reaction temperature is 1200-1400 ° C.

In the present invention, the rate of temperature rise near the reaction temperature (holding temperature) of the nitriding reaction is reduced. Specifically, when the atmospheric temperature is 900 to 1300 ° C or higher, the heating rate is 2 ° C /
Min, preferably 0.5 ° C / min or less. If the rate of temperature rise is 2 ° C./min or more, the nitridation reaction becomes violent, the content of α-type silicon nitride in the formed composite decreases, and the sinterability of the composite decreases. The preferred content of α-type silicon nitride is at least 30%, particularly preferably at least 40%, based on the total silicon nitride in the composite molded body.

When the nitriding / carburizing treatment is performed under the above conditions, the silicon particles in the molded body react with carbon to form silicon carbide particles that are finer than the starting material silicon particles and carbon particles, and are also nitrided. Α- finer than the starting silicon particles
Silicon nitride containing silicon nitride is generated.

[4] Method for producing composite sintered body (1) The first method of the present invention for producing a silicon nitride / silicon carbide composite sintered body is as follows. The silicon carbide composite powder is molded by the same method as described in the section [3] (1) above. The shaped body is sintered at a temperature of 1600 to 2200 ° C, preferably at a temperature of 1800 to 2000 ° C. If the sintering temperature is less than 1600 ° C., the densification of the sintered body will be insufficient and desired characteristics cannot be obtained. Further, if the sintering temperature exceeds 2200 ° C, decomposition of silicon nitride begins, which is not preferable. Sintering is performed in a non-oxidizing atmosphere, preferably a nitrogen gas atmosphere. At this time, the atmospheric gas pressure is preferably about 5 to 2000 kgf / cm ² . Also, the sintering temperature holding time is 1 to
It is preferably about 5 hours. Hot pressing or HIP is preferred to achieve good sintered compact density. Particularly when firing with HIP, a sintered body having a complicated shape can be manufactured.

(2) The second method of the present invention for producing a silicon nitride / silicon carbide composite sintered body is the same as the above-mentioned [4] ( Sinter in the same way as described in column 1). Before sintering, the silicon nitride / silicon carbide composite molded body may be heat-treated in an oxidizing atmosphere. The silicon nitride /
The surfaces of silicon nitride and silicon carbide constituting the silicon carbide composite molded body are oxidized to form a silicon oxide film. As with the case where silicon oxide is added as a sintering aid, this film reacts with silicon oxide and the sintering aid to promote sintering.
The temperature of the heat treatment is preferably less than 1300 ° C.

(3) Silicon Nitride / Silicon Carbide Composite Sintered Body The silicon nitride / silicon carbide composite sintered body obtained by the above method is
It has a so-called nanocomposite structure in which fine silicon carbide particles are dispersed in silicon nitride particles. Since silicon carbide particles have a higher coefficient of thermal expansion than silicon nitride particles, it is considered that residual stress acts on the silicon nitride particles. Further, it is considered that the fine silicon carbide particles dispersed in the grain boundaries of silicon nitride act like a wedge to suppress the grain boundary sliding of silicon nitride.

Therefore, when the silicon carbide / silicon nitride ratio is small, the above effect cannot be sufficiently obtained. On the other hand, silicon carbide /
If the ratio of silicon nitride is too large, too many silicon carbide particles are dispersed and the grain growth of silicon nitride is suppressed, and the sintered body density does not increase sufficiently. From the above points, the weight ratio of silicon carbide / silicon nitride is preferably 5/95 to 50/50, and 15/85 to 40
/ 60 is more preferable.

[0041]

EXAMPLES The present invention will now be described in more detail with reference to specific examples, but the present invention is not limited thereto.

Example 1 (1) Preparation of Composite Powder A silicon powder (JIS MSi 1) having an average particle size of 0.5 μm, a carbon powder having a particle size of 5 μm or less as carbonaceous material, and a nitride having an average particle size of 0.1 μm Silicon powder, silicon carbide powder having an average particle size of 0.2 μm, Y ₂ O ₃ powder having an average particle size of 1.4 μm,
An AlN powder having an average particle diameter of 2 μm was mixed at a ratio shown in Table 1 (however, the mixing ratio of the silicon powder and the carbonaceous carbon powder was determined based on the proportion of silicon nitride, silicon carbide, and sintering aid in the produced composite powder). It is a value calculated according to a reaction formula for producing silicon nitride and silicon carbide so that the ratio becomes the target compounding ratio shown in Table 10.)
The mixture was mixed with 80 parts by weight of balls using 18 parts by weight of ethanol as a solvent for 18 hours and dried.

The obtained raw material powder was placed in a reaction vessel, and 1300
The temperature was raised from 1 ° C to 1380 ° C at a heating rate of 0.5 ° C / minute, and then the temperature was maintained for 60 minutes. Nitrogen gas atmosphere was used as a nitrogen gas atmosphere to cause nitriding / carburizing reaction under a gas pressure of 9 kgf / cm ² , then put it in a 2 liter polyethylene pot together with 200 parts by weight of alcohol and 200 parts by weight of silicon nitride balls, and use a ball mill for 7 Milling was carried out for a day to prepare a composite powder.

X-ray diffraction of the obtained composite powder was measured, and α
The crystal phases of type silicon nitride and β type silicon nitride were identified, and the content rate of α type silicon nitride in the total silicon nitride was determined by the following equation. Content of α-type silicon nitride (%) = 100 x (102) plane and (210)
Total diffraction intensity of plane (α-type silicon nitride) / ((102) plane and (21)
0) plane total diffraction intensity (α-type silicon nitride) + (101) plane and (21) plane
Table 7 summarizes the results of the (0) plane total diffraction intensity (β-type silicon nitride).

Table 1 Raw material powder composition Weight (g) Blending ratio (wt%) Silicon powder 270.7 69.9 Carbon powder 43.7 11.3 Silicon nitride powder 14.9 3.9 Silicon carbide powder 7.7 2.0 Y ₂ O ₃ powder 35.0 9.0 AlN powder 15.0 3.9

(2) Preparation of composite sintered body The composite powder obtained in (1) was formed into a shape of 55 × 35 × 6 mm under a pressure of 200 k.
After preforming with a gf / cm ² mold press, an isotropic pressure of 4 ton / square cm was applied by CIP. Then the maximum holding temperature
HI at 1850 ° C, maximum nitrogen gas pressure 1000kgf / cm ²
P sintering was performed to obtain a silicon nitride / silicon carbide composite sintered body.
When the structure of the obtained sintered body was observed with an electron microscope,
It was found to have a nanocomposite structure.

(3) Physical Properties of Composite Sintered Body The density of the obtained sintered body was measured by the Archimedes method. JI
According to S R-1601, the sintered body was cut into a size of 3 mm × 4 mm × 40 mm to obtain a test piece, and a three-point bending strength test (room temperature and 1400 ° C.) and a fracture toughness value K ₁ c were measured as follows. The results obtained under the conditions are shown in Table 7. (i) Three-point bending strength test: At room temperature, a span of 30 mm and a crosshead speed of 0.5 mm / min were used. In the case of 1400 ° C., the temperature was raised to 1400 ° C. and the temperature was maintained for 1 hour, and then the above conditions were used. (ii) Fracture toughness: SENB method (Single Edge Notched Be
am Method).

Example 2 Using the silicon nitride / silicon carbide composite powder obtained in Example 1,
Molded under the same conditions as in Example 1, and HIP under the same conditions as in Example 1.
After the treatment, normal pressure sintering was performed at 1500 ° C. for 2 hours under a nitrogen gas atmosphere to obtain a sintered body. A strength test was performed on the sintered body in the same manner as in Example 1, and the results are shown in Table 7.

Example 3 (1) Preparation of Composite Powder A silicon powder (JIS MSi 1) having an average particle size of 0.5 μm, an acetylene black powder having an average particle size of 500 Å as carbonaceous material, and an average particle size of 0.1 μm Silicon nitride powder, silicon carbide powder having an average particle size of 0.2 μm,
1.4 μm of Y ₂ O ₃ powder was weighed in the ratio shown in Table 2 (however, calculated from the target compounding ratio shown in Table 10 in the same manner as in Example 1), and 200 parts by weight by a ball mill. With 80 parts by weight of ethanol as solvent
Mix for 18 hours and dry.

Table 2 Raw material powder composition Weight (g) Blending ratio (wt%) Silicon powder 274.9 72.9 Acetylene black powder 39.4 10.4 Silicon nitride powder 16.1 4.3 Silicon carbide powder 6.9 1.8 Y ₂ O ₃ powder 40.0 10.6

The obtained raw material powder was placed in a reaction vessel, and 1300
After the temperature was raised to 1380 ° C. at a rate of 0.5 ° C./min from the temperature, the treatment was terminated without maintaining the temperature at 1380 ° C. The nitriding / carbonization reaction was performed under a gas pressure of 9 kgf / cm ^{2 in} a nitrogen gas atmosphere, and then 200 parts by weight of alcohol and 200 parts by weight
The mixture was placed in a 2 liter polyethylene pot together with parts by weight of silicon nitride balls and pulverized by a ball mill for 7 days to prepare a composite powder. The α-type silicon nitride content of the obtained composite powder was determined in the same manner as in Example 1. The results are shown in Table 7.

(2) Preparation of Composite Sintered Body The composite powder obtained in (1) was filled in a graphite die having a diameter of 42 mm and heated to a maximum of 1850 ° C. under a nitrogen gas atmosphere of 9 kgf / cm ² at a load of 4.8 tons and a load of 4.8 tons. The temperature was raised and hot press sintering was performed to obtain a silicon nitride / silicon carbide composite sintered body. Observation of the structure of the obtained sintered body with an electron microscope revealed that the structure had a nanocomposite structure. The physical properties of the obtained composite sintered body were determined in the same manner as in Example 1. The results are shown in Table 7.

Example 4 A silicon nitride / silicon carbide composite powder and a sintered body were obtained in the same manner as in Example 3 except that silicon powder (JIS MSi 1) having an average particle size of 3.4 μm was used. The content of α-type silicon nitride in the obtained powder was determined in the same manner as in Example 1, and the results are shown in Table 7. The physical properties of the obtained composite sintered body were determined in the same manner as in Example 1. The results are shown in Table 7.

Comparative Example 1 The same raw material powder as in Example 1 was used, and the nitriding / carbonization reaction was carried out under the same heat treatment conditions and nitrogen atmosphere as in Example 1 except that the heating rate from 1300 ° C. was changed to 2 ° C./min. Awakened. After the heat treatment, the mixture was ground in a ball mill for 7 days in the same manner as in Example 1.

Using the obtained silicon nitride / silicon carbide composite powder, molding was performed under the same conditions as in Example 1, and HIP sintering was performed under the same conditions as in Example 1 to obtain a sintered body. A strength test of the sintered body and measurement of K ₁ c were performed in the same manner as in Example 1. The results are shown in Table 7.
Shown in

Comparative Example 2 The same raw material powder as in Example 1 was used except that acetylene black powder was used as the carbonaceous powder, and the nitriding / carbonization reaction was caused under the same heat treatment conditions as in Comparative Example 1. After the heat treatment, the mixture was pulverized in a ball mill for 7 days in the same manner as in Example 1 to prepare a composite powder.

Using the obtained silicon nitride / silicon carbide composite powder, molding was performed under the same conditions as in Example 1, and HIP sintering was performed under the same conditions as in Example 1 to obtain a sintered body. A strength test was performed on the sintered body in the same manner as in Example 1, and the results are shown in Table 7.

Comparative Example 3 Using the silicon nitride / silicon carbide composite powder obtained in Comparative Example 2,
Molded under the same conditions as in Example 1, and HIP under the same conditions as in Example 1.
After the treatment, pressureless sintering was performed under the same conditions as in Example 2 to obtain a sintered body. The strength test and the fracture toughness value K ₁ c of the sintered body were measured in the same manner as in Example 1, and the results are shown in Table 7.

Comparative Example 4 The same powder as in Example 1 was weighed at the ratio shown in Table 3 except that the Y ₂ O ₃ powder and the AlN powder were not added, mixed by a ball mill under the same conditions as in Example 1, and dried. did.

Table 3 Raw material powder composition Weight (g) Blending ratio (wt%) Silicon powder 300.6 80.4 Carbon powder 48.5 13.0 Silicon nitride powder 16.5 4.4 Silicon carbide powder 8.5 2.3

The obtained raw material powder was placed in a reaction vessel, and a nitriding / carbonization reaction was caused under the same conditions as in Example 1. Assuming that the composite powder after heat treatment is 90% by weight, the average particle size is 1.4μ
7% by weight of Y ₂ O ₃ powder and Al having an average particle size of 2 μm
3% by weight of N powder and 200% by weight of alcohol and 200% by weight.
The resulting mixture was placed in a 2 liter polyethylene pot together with the silicon nitride ball at a weight ratio of 7% and mixed and ground by a ball mill for 7 days to prepare a composite powder having the same composition as in Example 1. The α-type silicon nitride content of the obtained composite powder was determined in the same manner as in Example 1. The results are summarized in Table 7.

Using the obtained silicon nitride / silicon carbide composite powder, molding was performed under the same conditions as in Example 1, and H was formed under the same conditions as in Example 1.
IP sintering was performed to obtain a silicon nitride / silicon carbide composite sintered body. A strength test was performed on the obtained sintered body, and the results are shown in Table 7.

Example 5 (1) Preparation of composite powder Silicon powder (JIS MSi 1) having an average particle size of 0.7 μm, carbon powder having a particle size of 5 μm or less as carbonaceous material, and Lu ₂ having an average particle size of 1 μm O ₃ powder was weighed at a ratio shown in Table 4 (however, the value was calculated from the target compounding ratio shown in Table 10 as in Example 1), and 200 parts by weight of ethanol was used as a solvent by a ball mill. It was mixed with 100 parts by weight of balls for 18 hours and dried.

Table 4 Raw material powder composition Weight (g) Mixing ratio (% by weight) Silicon powder 270.1 71.2 Carbon powder 38.7 10.2 Lu ₂ O ₃ powder 70.5 18.6

The obtained raw material powder was placed in a reaction vessel, and 1150
After the temperature was raised to 1230 ° C. at a rate of 0.5 ° C./min from the temperature, the temperature was maintained for 60 minutes. Nitrogen gas atmosphere was used as a nitrogen gas atmosphere to cause nitriding / carburizing reaction under a gas pressure of 9 kgf / cm ² , then put it in a 2 liter polyethylene pot together with 200 parts by weight of alcohol and 200 parts by weight of silicon nitride balls, and use a ball mill for 7 Milling was carried out for a day to prepare a composite powder.
The α-type silicon nitride content of the obtained composite powder was determined in the same manner as in Example 1. The results are shown in Table 7.

(2) Preparation of Composite Sintered Body Using the composite powder obtained in (1), it was molded under the same conditions as in Example 1. This compact was sintered in a nitrogen gas atmosphere of 9 kgf / cm ² at 2000 ° C. for 4 hours under normal pressure, and then 1000 kgf / cm ²
HIP sintering was performed at 1850 ° C. for 1 hour in a nitrogen gas atmosphere.
A strength test was performed on the composite sintered body obtained in the same manner as in Example 1, and the results are shown in Table 7.

Example 6 (1) Preparation of Composite Powder A silicon powder (JIS MSi 1) having an average particle size of 0.7 μm, a carbon powder having a particle size of 5 μm or less as carbonaceous material, and Lu ₂ having an average particle size of 1 μm O ₃ powder and Al with an average particle size of 2 μm
N powder was weighed at a ratio shown in Table 5 (however, the value was calculated from the target compounding ratio shown in Table 10 as in Example 1), and 200 parts by weight of ethanol was used as a solvent to make 100 It was mixed with 18 parts by weight of balls for 18 hours and dried.

Table 5 Raw material powder composition Weight (g) Mixing ratio (% by weight) Silicon powder 266.3 69.9 Carbon powder 38.1 10.0 Lu ₂ O ₃ powder 61.7 16.2 AlN powder 15.0 3.9

The obtained raw material powder was subjected to a nitriding / carbonization reaction in the same manner as in Example 5, and then put into a 2-liter polyethylene pot together with 200 parts by weight of alcohol and 200 parts by weight of silicon nitride balls. For 7 days to prepare a composite powder. The α-type silicon nitride content of the obtained composite powder was determined in the same manner as in Example 1. The results are shown in Table 7.
Shown in

(2) Preparation of Composite Sintered Body The composite powder obtained in (1) was molded under the same conditions as in Example 1 and then subjected to normal pressure sintering and HIP sintering in the same manner as in Example 5. Was done. A strength test was performed on the composite sintered body obtained in the same manner as in Example 1, and the results are shown in Table 7.

Comparative Example 5 An average particle size of 1 μm was used instead of Lu ₂ O ₃ powder as a sintering aid.
Except for using In ₂ O ₃ powder, the same raw material powders as in Example 6 in the proportions indicated in Table 6 (provided that the value calculated from the object compounding ratio shown in the same manner as Table 10 in Example 1. ) Weighed and mixed with 200 parts by weight of ethanol as a solvent together with 100 parts by weight of a ball by a ball mill for 18 hours and dried.

Table 6 Raw material powder composition Weight (g) Mixing ratio (% by weight) Silicon powder 278.0 74.0 Carbon powder 39.8 10.6 In ₂ O ₃ powder 43.0 11.4 AlN powder 15.0 4.0

The obtained raw material powder was subjected to a nitriding / carbonization reaction in the same manner as in Example 5, then put into a 2 liter polyethylene pot together with 200 parts by weight of alcohol and 200 parts by weight of silicon nitride balls, and then ball milled. For 7 days to prepare a composite powder. The α-type silicon nitride content of the obtained composite powder was determined in the same manner as in Example 1. The results are shown in Table 7.
Shown in

The obtained composite powder was molded under the same conditions as in Example 1, and then pressureless sintering and HIP sintering were performed in the same manner as in Example 5. A strength test was performed on the composite sintered body obtained in the same manner as in Example 1, and the results are shown in Table 7.

[0075]

[Table 7]

As can be seen from Table 7, in the composite powders of Comparative Examples 1 to 3 in which the heating rate during the nitriding / carbonization reaction was 2 ° C./min, Examples 1 to 3 in which the heating rate was 0.5 ° C./min. Α compared to 4
The content of type silicon nitride was greatly reduced. Further, Comparative Example 4 containing no sintering aid and In ₂ O ₃
In Comparative Example 5 using powder, Examples 1 and 5 and 6 were used.
, The content of α-type silicon nitride was greatly reduced.

Example 7 (1) Preparation of Composite Molded Product A silicon powder (JIS MSi 1) having an average particle size of 0.5 μm, a carbon powder having a particle size of 5 μm or less as carbonaceous material, and a carbon powder having an average particle size of 0.1 μm A silicon nitride powder, a silicon carbide powder having an average particle diameter of 0.2 μm, and a Y ₂ O ₃ powder having an average particle diameter of 1.4 μm were mixed at the ratio shown in Table 8 (however, Table 1 was used in the same manner as in Example 1).
It is a value calculated from the target compounding ratio shown in 0. ) Weighed, mixed with a ball mill for 100 hours using 200 parts by weight of ethanol as a solvent together with 100 parts by weight of balls, and dried.

Table 8 Raw material powder composition Weight (g) Blending ratio (wt%) Silicon powder 274.9 72.9 Carbon powder 39.4 10.4 Silicon nitride powder 16.1 4.3 Silicon carbide powder 6.9 1.8 Y ₂ O ₃ powder 40.0 10.6

After the obtained raw material powder was preformed into a shape of 55 × 35 × 6 mm, an isotropic pressure of 4 tons / cm 2 was applied by a CIP device. The obtained molded body was placed in a reaction vessel, heated to 1450 ° C. at a rate of 0.5 ° C./min from 1200 ° C., and held for 30 minutes. The atmosphere was a mixed gas atmosphere of 20% by volume of hydrogen gas and 80% by volume of nitrogen gas, and a nitriding / carbonization reaction was caused under a gas pressure of 9 kgf / cm ² to prepare a composite molded body. The content rate of α-type silicon nitride of the obtained composite molded body was determined in the same manner as in Example 1. The results are shown in Table 11.

(2) Production of Composite Sintered Body The composite molded body obtained in (1) was sintered at 2050 ° C. for 4 hours under a nitrogen gas atmosphere of 9 kgf / cm ² at normal pressure, and then 1000 kgf / cm 2
HIP sintering was performed at 1900 ° C. for 1 hour in a nitrogen gas atmosphere of No. ² . Observation of the structure of the obtained sintered body with an electron microscope revealed that the structure had a nanocomposite structure. A strength test was performed on the composite sintered body obtained in the same manner as in Example 1,
The results are shown in Table 11.

Example 8 (1) Preparation of Composite Molded Article The raw material powder obtained in Example 7 was molded under the same conditions as in Example 7, and a nitriding / carbonization reaction was caused under the same conditions as in Example 7. A composite molded article was prepared. Α of the obtained composite molded body
The content of type silicon nitride was determined in the same manner as in Example 1. The results are shown in Table 11.

(2) Preparation of Composite Sintered Body After the composite molded body obtained in (1) was treated in an oxidizing atmosphere at 700 ° C. for 24 hours, normal pressure sintering and HIP were performed under the same conditions as in Example 7.
Sintering was performed. The composite sintered body obtained in the same manner as in Example 1 was subjected to a strength test, and the results are shown in Table 11.

Example 9 (1) Production of Composite Molded Product The raw material powder used in Example 7 was mixed with S having an average particle size of 1 μm.
iO ₂ powder at a ratio shown in Table 9 (however,
It is a value calculated from the target compounding ratio shown in Table 10 in the same manner as in. ) Weighed, mixed and dried under the same conditions as in Example 7.
The obtained raw material powder was formed into a compact in the same manner as in Example 7,
Under the same conditions as in Example 7, a nitriding / carbonization reaction was caused to prepare a composite molded body. The content rate of α-type silicon nitride of the obtained composite molded body was determined in the same manner as in Example 1. The results are shown in Table 11.

Table 9 Raw material powder composition Weight (g) Blend ratio (wt%) Silicon powder 164.6 72.7 Carbon powder 23.6 10.4 Silicon nitride powder 9.7 4.3 Silicon carbide powder 4.1 1.8 Y ₂ O ₃ powder 24.0 10.6 SiO ₂ powder 0.4 0.2

(2) Production of composite sintered body The composite molded body obtained in (1) was subjected to normal pressure sintering and HIP sintering under the same conditions as in Example 7. The composite sintered body obtained in the same manner as in Example 1 was subjected to a strength test, and the results are shown in Table 11.

Comparative Example 6 (1) Preparation of Composite Molded Body The raw material powder obtained in Example 7 was used for molding under the same conditions as in Example 7, and a nitriding / carbonization reaction was caused under the same conditions as in Example 7. , A composite molded body was prepared. Α of the obtained composite molded body
The content of type silicon nitride was determined in the same manner as in Example 1. The results are shown in Table 11.

(2) Preparation of Composite Sintered Body The composite molded body obtained in (1) was treated in an oxidizing atmosphere at 1300 ° C. for 24 hours, and then pressureless sintering was carried out under the same conditions as in Example 7. Since the sintered body was decomposed and the density measurement became difficult, the experiment was stopped.

Table 10 Objective mixing ratio of the produced composite powder or composite molded body Sintering aid: Base material (SiCN) Silicon nitride: Silicon carbide Example 1 7% by weight Y ₂ O ₃ 90% by weight 66% by weight 34% by weight % ⁽¹⁾ 3 wt% AlN Example 2 7 wt% Y ₂ O ₃ 90 wt% 66 wt% 34 wt% ⁽¹⁾ 3 wt% AlN Example 3 8 wt% Y ₂ O ₃ 92 wt% 70 wt% 30 wt% ⁽¹⁾ Example 4 8 wt% Y ₂ O ₃ 92 wt% 70 wt% 30 wt% ⁽¹⁾ Example 5 14.1 wt% Lu ₂ O ₃ 85.9 wt% 70 wt% 30 wt% Example 6 12.34 wt% Lu ₂ O ₃ 84.66 wt% 70 wt% 30 wt% 3 wt% AlN Example 7 8 wt% Y ₂ O ₃ 92 wt% 70 wt% 30 wt% ⁽¹⁾ Example 8 8 wt% Y ₂ O ₃ 92% by weight 70% by weight 30% by weight ⁽¹⁾ Example 9 8% by weight Y ₂ O ₃ 91.86% by weight 70% by weight 30% by weight ⁽¹⁾ 0.14% by weight SiO ₂ Comparative example 1 7% by weight Y ₂ O ₃ 90% by weight 66% by weight 34% by weight ⁽¹⁾ 3% by weight AlN Comparative Example 2 7% by weight Y ₂ O ₃ 90% by weight 66% by weight 34% by weight ⁽¹⁾ 3% by weight AlN Comparative Example 3 7% by weight Y ₂ O ₃ 90% by weight 66 wt% 34 wt% ⁽¹⁾ 3% by weight AlN Comparative example 4 - 100 wt% 66 wt% 34 wt% ⁽¹⁾ Comparative example 5 8.61 wt% an In ₂ O ₃ 88.39 wt% 70 wt% 30 wt% 3 wt% AlN Comparative example 6 8 wt% Y ₂ O ₃ 92 wt% 70 wt% 30 wt% ⁽¹⁾ Note (1): containing 5 wt% increments added silicon nitride and silicon carbide as seed crystals to the raw material powder.

Table 11 Example 7 Example 8 Example 9 Comparative Example 6 α-type silicon nitride content of composite molded body (%) ⁽¹⁾ 100 100 100 100 Three-point bending strength (MPa) Room temperature bending strength 575.1 730.3 563.6 − 1400 ° C bending strength 491.2 606.6 629.8 − Sintered body density (g / cm ³ ) 3.27 3.29 3.30 (not measured) Note (1): α-type silicon nitride content (%) = 100 × (102) Total diffraction intensity of (210) plane (α-type silicon nitride) / total diffraction intensity of ((102) plane and (210) plane (α-type silicon nitride) + total diffraction intensity of (101) plane and (210) plane ( β-type silicon nitride))

As described above, the composite compacts of Examples 7 to 9 exhibited a high α-type silicon nitride content, and the composite sintered compacts thereof exhibited high bending strength and sintered density.

[0091]

As described in detail above, according to the present invention,
Using a mixed powder containing a silicon powder, a carbonaceous powder, and a sintering aid as a starting material, and causing nitridation and carbonization of silicon by heat treatment in a nitrogen gas-containing atmosphere and at a specific temperature increasing rate, A composite powder and a composite compact having an α-type silicon nitride content are obtained. Therefore, the composite sintered body composed of the composite powder or composite molded body obtained by the method of the present invention has excellent high-temperature strength, static fatigue resistance, wear resistance, and hardness. The silicon nitride / silicon carbide composite sintered body having such characteristics is suitable for a structural member or the like used at a high temperature.

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Claims (15)

[Claims] 1. A silicon nitride obtained by mixing silicon powder with carbonaceous powder and a sintering aid, and heat-treating the obtained mixed powder in an atmosphere containing nitrogen gas to cause nitriding and carbonization of silicon. And a silicon carbide composite powder, wherein the content of α-type silicon nitride in the composite powder is 30% or more of the total silicon nitride, the silicon nitride / silicon carbide composite powder. 2. The silicon nitride / silicon carbide composite powder according to claim 1, wherein the sintering aid is selected from the group consisting of (a) oxides of Group 3A elements and Group 4A elements of the Periodic Table. A silicon nitride / silicon carbide composite powder comprising the above compound or (b) aluminum nitride and the above (a). 3. The silicon nitride / silicon carbide composite powder according to claim 1, wherein the content of the sintering aid is 100% by weight based on the total amount of the composite powder produced by the heat treatment.
A silicon nitride / silicon carbide composite powder characterized by being 5 to 20% by weight. 4. The silicon nitride / silicon carbide composite powder according to claim 1, wherein the mixed powder is silicon powder, carbonaceous powder, a sintering aid, silicon nitride and / or silicon nitride. A silicon nitride / silicon carbide composite powder characterized by being mixed with silicon carbide. 5. The silicon nitride / silicon carbide composite powder according to any one of claims 1 to 4, wherein the weight ratio of silicon carbide / silicon nitride is 5/95 to 50/50. / Silicon carbide composite powder. 6. A silicon powder is mixed with a carbonaceous powder and a sintering aid, and a compact formed from the resulting mixed powder is heat treated in an atmosphere containing nitrogen gas to cause nitriding and carbonization of silicon. In the composite molded body of silicon nitride and silicon carbide obtained as described above, the content of α-type silicon nitride in the composite molded body is 30% or more of the total silicon nitride. body. 7. The silicon nitride / silicon carbide composite molded body according to claim 6, wherein the sintering aid is (a) Periodic Table 3A.
One or more compounds selected from the group consisting of oxides of Group 4 elements and Group 4A elements, or (b) aluminum nitride and / or
Alternatively, a silicon nitride / silicon carbide composite molded body comprising silicon oxide and the above (a). 8. The silicon nitride / silicon carbide composite molded body according to claim 6 or 7, wherein the content of the sintering aid is 5 to 100% by weight of the total amount of the composite molded body produced by the heat treatment. 20% by weight of a silicon nitride / silicon carbide composite molded body. 9. The silicon nitride / silicon carbide composite molded body according to claim 6, wherein the mixed powder is silicon powder, carbonaceous powder, a sintering aid, silicon nitride and / or
Alternatively, a silicon nitride / silicon carbide composite molded body characterized by being mixed with silicon carbide. 10. The silicon nitride / silicon carbide composite molded body according to claim 6, wherein the weight ratio of silicon carbide / silicon nitride is 5/95 to 50/50. Silicon / silicon carbide composite molded body. 11. In a method for producing a silicon nitride / silicon carbide composite powder, wherein the content of α-type silicon nitride is 30% or more of the total silicon nitride, a carbonaceous powder and a sintering aid are mixed with silicon powder, The obtained mixed powder is heat-treated in a nitrogen gas-containing atmosphere to cause nitriding and carbonization of silicon, in which case the nitriding carbonization reaction is performed at a temperature of 1000 ° C to 1450 ° C, and at least maintained from the temperature before the start of the reaction. A method characterized in that the rate of temperature increase until the temperature is reached is less than 2 ° C / min. 12. A method for producing a silicon nitride / silicon carbide composite compact having an α-type silicon nitride content of 30% or more of the total silicon nitride, wherein carbon powder and a sintering aid are mixed with silicon powder. A molded body is formed from the obtained mixed powder, and the molded body is heat-treated in an atmosphere containing nitrogen gas to cause nitriding and carbonization of silicon, at which the nitriding carbonization reaction is performed at 1000 ° C to
A method which is carried out at a temperature of 1450 ° C., and at least the temperature rising rate from the temperature before the start of the reaction until the temperature reaches the holding temperature is less than 2 ° C./minute. 13. A method for producing a silicon nitride / silicon carbide composite sintered body, wherein a molded body is formed from the silicon nitride / silicon carbide composite powder according to claim 1, and the molded body is subjected to a nitrogen gas-containing atmosphere. A method characterized by sintering at 1600 ° C to 2200 ° C in a medium. 14. A method for producing a silicon nitride / silicon carbide composite sintered body, wherein the silicon nitride / silicon nitride according to claim 6 is used.
The silicon carbide composite compact was placed in an atmosphere containing nitrogen gas.
A method comprising sintering at 00 ° C to 2200 ° C. 15. The method for producing a silicon nitride / silicon carbide composite sintered body according to claim 14, wherein
After heat-treating a silicon carbide composite compact at a temperature of less than 1300 ° C. in an oxidizing atmosphere, then perform 1600 in an atmosphere containing nitrogen gas.
A method characterized by sintering at ℃ ~ 2200 ℃.