JPH11116340A - Silicon nitride sintered product having high strength and high toughness and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly improve the strength and toughness of a silicon nitride sintered product light in weight and excellent in heat resistance. SOLUTION: This silicon nitride sintered product is obtained by adding 5-30 vol.% of needle-like silicon nitride particles 3 having diameters of 550-1000 μm and lengths of 2500-4000 μm and containing a sintering auxiliary to silicon nitride particles containing a sintering auxiliary and used for a matrix and subsequently simultaneously sintering the components in the mixture in a nitrogen gas atmosphere. In the produced silicon nitride sintered product, 5-30 vol.% of the needle-like silicon nitride particles 3 having diameters of 400-750 μm and lengths of 2,000-3,500 μm are dispersed in the silicon nitride matrix 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a silicon nitride sintered body which is lightweight and has excellent heat resistance and high strength and toughness (fracture toughness).
(Silicon nitride sintered body) suitable for imparting a material and a method for producing the same, for example, a structural member used for a member for an automobile, a member for an electronic device, a member for a chemical device, a member for an aerospace device, etc. Is provided.

[0002]

2. Description of the Related Art In order to expand the use of high-strength ceramics, which are lightweight and excellent in heat resistance, for machine parts, etc., the price is reduced, and the performance of machine parts, etc. is increased by applying ceramics. It is necessary to improve it.

[0003] Therefore, for example, a method of improving the hardness and toughness of a ceramic matrix by adding a second phase to improve ingot-like performance, and a material for improving strength by reducing the diameter of particles have been developed. In addition, a material that improves the thermal conductivity by selectively growing some of the particles based on the opposite idea has been developed.

A material having the best balance of mechanical performance is silicon nitride, and a composite material using silicon nitride as a matrix has been actively developed. A method of improving mechanical performance for a long time is to add a second phase while reinforcing the strength of silicon nitride or to strengthen it with fibers to increase the hardness and strength, thereby increasing the tool and component. Development for use in materials and the like has been performed since about 1970.

[0005] Recently, a method of adding a columnar metal has been reported (JP-A-8-26837), but it is difficult to use at a temperature of 1000 ° C or more which is a characteristic of ceramics. There is also a method of improving the high-temperature strength by compounding silicon carbide with silicon nitride (Japanese Patent Laid-Open No. 8-33).
7476, JP-A-8-73270, JP-A-8-67
568).

[0006] In order to obtain high strength, there has been reported a method of reducing the particle size of a starting material to about 0.1 µm (Japanese Patent Application Laid-Open No. 8-12306). And the production efficiency decreases.

Similarly, a process has been proposed in which powder is uniformly ground to a diameter of about 0.2 μm and sintered (JP-A-8-48564). In this case, there is a disadvantage that the strength is high but the toughness is low.

On the other hand, there is a method of improving the strength by reducing the amount of halogen in the raw material (JP-A-9-25168).

As a technique for improving the strength and toughness of silicon nitride itself, a technique for improving the strength and toughness at a high temperature by crystallizing a grain boundary phase (Japanese Patent Laid-Open No. 8-319165).
Also, a material in which coarse silicon nitride powder and needle-like particles are dispersed in fine silicon nitride powder has been proposed (Japanese Patent Application Laid-Open No. Hei 8-
133842). In this case, although the toughness is improved, the strength is hardly changed.

As a method of simultaneously obtaining high toughness and high strength, there is also a method of laminating sheet-formed silicon nitride and orienting and growing particles in a direction perpendicular to the load to increase the strength and toughness in one direction (Japanese Patent Application Laid-Open No. 8-108). No. 143400).

As a method for improving the thermal conductivity of silicon nitride, a method disclosed by the Ceramic Society of Japan, 1989, January
A technique for sintering an auxiliary agent as Y ₂ O ₃ and a technique for reducing the amount of aluminum have been disclosed on pages 56 to 62 of the monthly publication (JP-A-4-175268, JP-A-4-2193).
No. 71), or a method of sintering an auxiliary agent as a plurality of rare earth oxides has been reported (JP-A-9-308).
No. 66).

[0012]

In the composite material manufacturing process mainly used in the past, a method of compounding a second phase powder into a raw material matrix powder and then sintering the composite material is used. However, there is a problem that residual stress remains around the added phase when the alloy is introduced, and the matrix may have defects to reduce the strength. Further, there is a disadvantage that the process becomes complicated and expensive due to the addition of expensive fibers.

On the other hand, the method of using fine particles or reducing the particle diameter cannot cope with the process of handling fine particles. As a result, although the strength can be slightly improved, the yield in the process is deteriorated, and the ordinary ceramics manufacturing process is difficult. There is also a disadvantage that it can no longer be used. Above all, there is no means with good manufacturability that can simultaneously improve both strength and toughness.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of such prior art, and has been made to improve both the strength and toughness of a silicon nitride sintered body which is lightweight and excellent in heat resistance. The purpose is to be able to do things.

[0015]

Means for Solving the Problems The invention proposed here is:
Introducing a new domain into the matrix eliminates the problem of insufficient bonding strength between different materials, and achieves both strength and toughness.

In the present invention, attention has been paid to a particle group sintering technique utilizing a coarse particle group which has been eliminated as an agglomerate causing a reduction in strength in the prior art, and a silicon nitride sphere for a matrix containing a rare earth-based sintering aid is used. Particles and needle-shaped silicon nitride particles obtained by extruding spherical silicon nitride powder containing a rare earth-based sintering aid and an oxide-based sintering aid into an acicular shape by an extrusion method or the like are blended at a predetermined ratio, and simultaneously sintered. By doing so, a silicon nitride sintered body is manufactured. Then, the above problem is solved by providing a particle group dispersed structure that exhibits excellent functions by minimizing the addition ratio of the silicon nitride needle-like particles. The silicon nitride sintered body thus obtained has not only thermal conductivity but also considerable mechanical strength, toughness and hardness characteristics.

That is, the high-strength and high-toughness silicon nitride sintered body according to the present invention has a diameter of 400 to 750 μm in a silicon nitride matrix.
And 3 to 30% by volume of silicon nitride needle-shaped particles having a length of 2000 to 3500 μm.

Further, according to a second aspect of the present invention, there is provided a method for producing a high-strength and high-toughness silicon nitride sintered body. 5 to 3 μm of silicon nitride needle-like particles having a diameter of 550 to 1000 μm and a length of 2500 to 4000 μm.
It is characterized in that sintering is performed simultaneously in a nitrogen gas atmosphere after adding 0% by volume.

In the embodiment of the method for producing a high-strength and high-toughness silicon nitride sintered body according to the present invention, as described in claim 3, the silicon nitride particles for the matrix include yttrium oxide and neodymium oxide. Lanthanum oxide, ytterbium oxide, at least one rare earth oxide, and one or more oxides selected from silicon oxide, magnesium oxide, at least one non-rare earth oxide. It may contain from 1 to 8% by weight of a binder.

Similarly, in an embodiment of the method for producing a high-strength and high-toughness silicon nitride sintered body according to the present invention, as described in claim 4, the silicon nitride particles for the matrix include β-type silicon nitride. It is possible to use a β-type silicon nitride raw material powder having a content of 90% by weight or more and an average particle diameter of 0.5 to 0.7 μm.

Similarly, in an embodiment of the method of manufacturing a high-strength and toughness silicon nitride sintered body according to the present invention, as described in claim 5, the silicon nitride needle-like particles are added to yttrium oxide and neodymium oxide. Lanthanum oxide, ytterbium oxide, at least one rare earth oxide, and one or more oxides selected from silicon oxide, magnesium oxide, at least one non-rare earth oxide. It may contain from 1 to 8% by weight of a binder.

Similarly, in an embodiment of the method for producing a high-strength, high-toughness silicon nitride sintered body according to the present invention, as described in claim 6, the silicon nitride needle-like particles contain α-type silicon nitride. 90% by weight or more of α-type silicon nitride raw material powder and / or β-type silicon nitride having a content of 90% by weight or more and an average particle diameter of 0.5 to 0.8 μm.
Thus, a β-type silicon nitride raw material powder having an average particle diameter of 0.5 to 0.7 μm can be used.

Similarly, in an embodiment of the method for producing a high-strength and high-toughness silicon nitride sintered body according to the present invention, as described in claim 7, silicon nitride needle-like particles are used as the matrix silicon nitride particles. 1950-21 after addition
At a temperature of 00 ° C. and a partial pressure of nitrogen of 0.08 to 1.0 MPa
Gas pressure sintering in nitrogen gas.

Similarly, in an embodiment of the method for producing a high-strength and high-toughness silicon nitride sintered body according to the present invention, as described in claim 8, silicon nitride needle-like particles are used as matrix silicon nitride particles. 1950-20 after addition
Hot press sintering can be performed in a nitrogen gas at a temperature of 50 ° C. and a nitrogen partial pressure of 0.2 to 10 MPa.

Similarly, in an embodiment of the method for producing a high-strength and high-toughness silicon nitride sintered body according to the present invention, after the sintering, 2100 to 22
Hot isostatic press sintering can be performed in a nitrogen gas at a temperature of 00 ° C. and a nitrogen partial pressure of 30 to 200 MPa.

[0026]

The high-strength, high-toughness silicon nitride sintered body and the method for producing the same according to the present invention have the above-mentioned construction. The method for producing the concrete is as follows.

Silicon nitride powder for matrix (β-type silicon nitride content of 90% by weight or more and average particle size of 0.5%
Sintering aid (1 to 8% by weight of one or more rare earth oxides and / or 1 to 8% by weight of one or more non-rare earth oxides). Then, the mixture is pulverized and mixed by a ball mill and dried to obtain a matrix powder.

On the other hand, as an additive phase, silicon nitride powder for acicular particles (α-type mainly containing 90% by weight or more of α-type silicon nitride and having an average particle diameter of 0.5 to 0.8 μm, Sintering aid (1 to 8% by weight of one or more rare earth oxides) in a silicon nitride containing 90% by weight or more and having an average particle diameter of 0.5 to 0.7 μm. and/
Or one or more non-rare earth oxides in an amount of 1 to 8% by weight), pulverize and mix in an alcohol with a ball mill, and then dry. Add methyl cellulose to the dry powder and knead the mixture. Particles.

Next, the silicon nitride particles for a matrix and the silicon nitride needle-like particles are mixed in a predetermined volume ratio (the needle-like particles are 5 to 5).
30% by volume) with a V-shaped blender to obtain a "needle-like particle mixed powder", and then sintered in a nitrogen gas atmosphere.

Here, the reason why it is desirable to determine the range with respect to the particle size and the added amount of the raw material powder when the above-mentioned “needle particle mixed powder” is formed is as follows.

If the particle size of the silicon nitride powder for the matrix is too large, sintering in the temperature range described in the present invention becomes difficult, and if it is too small, it is difficult to handle and similarly sintering with the acicular particles is difficult. Therefore, the thickness is preferably set to 0.5 to 0.7 μm.

Further, β of silicon nitride powder for matrix
If the conversion is less than 90% by weight, sintering in the temperature range described in the present invention becomes difficult.

Further, if the amount of the sintering aid added to the silicon nitride for the matrix is too small, the sintering of the silicon nitride will be insufficient, and if it is too large, the glass phase will increase and the strength and toughness will decrease. % By weight.

Next, if the particle size of the silicon nitride powder for acicular particles is large, sintering in the temperature range described in the present invention is difficult, and if it is small, production becomes difficult depending on the ability of the extruder. 0.5 to 0.8 for α-type silicon nitride
In the case of μm and β-type silicon nitride, the thickness is preferably 0.5 to 0.7 μm.

On the other hand, if the amount of the silicon nitride powder for acicular particles is large, spaces are generated and mechanical properties become insufficient. If the amount is small, the effect is not exhibited.
And

Further, if the β-formation ratio of the silicon nitride powder for acicular particles is small, sintering becomes excessive, coarse particles are formed and the strength is reduced. Therefore, the content is preferably 90% by weight or more.

Further, if the amount of the auxiliary agent added to the silicon nitride powder for acicular particles is small, the acicular particles cannot be sintered, and if the amount is too large, the glass phase increases and the strength and toughness of the acicular particles decrease. Therefore, the content is preferably set to 1 to 8% by weight.

If the diameter of the silicon nitride needle-like particles as a raw material is less than 550 μm, a shearing force is exerted at the time of extrusion to make extrusion difficult, and if the diameter exceeds 1000 μm, the matrix may have excessive silicon nitride needle-like particles. And the strength tends to decrease.

When the length of the silicon nitride needle-shaped particles as a raw material is less than 2500 μm, the particles cannot be uniformly arranged in the fracture path. When the length is more than 4000 μm, the matrix is partially silicon nitride needles. The strength tends to decrease due to the formation of vacancies in the form of particles.

Further, when the volume fraction of the silicon nitride needle-like particles is less than 5% by volume, the matrix tends to partially become silicon nitride needle-like particles and the strength tends to decrease. If there is, the matrix tends to be silicon nitride needle-like particles and the strength tends to decrease.

Next, sintering of the above-mentioned “needle-like particle mixed powder” is carried out by appropriately performing press molding, and
A nitrogen atmosphere (nitrogen partial pressure 0.2-10
Hot press sintering under MPa) or 1950-210
A nitrogen atmosphere in a temperature range of 0 ° C (nitrogen partial pressure 0.08 to 1.
Gas pressure sintering under a pressure of 0 MPa).
a to 200 MPa) can be used.

The mechanical pressing force in the case of hot pressing is preferably about 20 MPa. In hot press sintering, if the temperature is lower than 1950 ° C., the density does not increase and is not suitable as a structural material. In this case, the particles grow excessively and the strength is reduced. In this case, the gas pressure must be set to a nitrogen atmosphere pressure of 0.2 MPa or more in order to prevent silicon nitride in the matrix from being decomposed, and is preferably 10 MPa or less from the viewpoint of sintering equipment specifications. On the other hand, in hot isostatic sintering, the nitrogen atmosphere is preferably 30 to 200 MPa for recrystallization / grain growth.

In the microstructure after sintering, in a silicon nitride sintered body 1 schematically shown in FIG. 1, needle-like silicon nitride particles (group) 3 are dispersed in a silicon nitride matrix 2 while maintaining a needle shape. In addition, needle-like particles of silicon nitride corresponding to the diameter and length of the added particles are present. In this case, if the dispersion amount of the silicon nitride needle-like particles is less than 5% by volume, the amount is not necessary for contacting the particles, and the specific gravity increases, which is not preferable. If the dispersion amount exceeds 30% by volume, voids are generated. This is not preferable because the mechanical strength is significantly reduced.

Next, in the evaluation of the silicon nitride sintered body according to the present invention, the evaluation of the particle group microstructure was carried out using an optical microscope after polishing the sample with diamond particles (particle diameter 0.26 μm). Also, the strength is JIS-R
The four-point bending test method according to 1601 was used, and the fracture toughness was evaluated using the SEPB method according to JIS-R1607. Further, the particle diameter was 4 mm × 4 mm in the micrograph.
Were determined by averaging the diameters of the particles contained in the area of Furthermore, the thermal conductivity is 10 mm in diameter according to JIS-R1611.
X Measured with a 2 mm thick disk.

Here, in addition to the derivative technology of the present invention, after the silicon nitride containing the second phase particles used in the present invention is formed into acicular particles, and then added to the powder in the form of particles, the method is as follows. This is a novel manufacturing technique that can impart different characteristics to ceramics without using a normal sintering process, without causing deviations in characteristic values, with no problem in mass productivity, and without increasing costs.

[0046]

According to the present invention, the high-strength and high-toughness silicon nitride sintered body according to the present invention has a diameter of 400 to 750 μm and a length of 2000 to 3500 μm in a silicon nitride matrix. 5 to 5 needle-shaped silicon nitride particles
Since the dispersion is 30% by volume, the silicon nitride sintered body which is lightweight and excellent in heat resistance can simultaneously impart higher strength and higher toughness (fracture toughness). This is a great effect that it is suitable as a structural member used for a member for electronic equipment, a member for electronic equipment, a member for chemical equipment, a member for aerospace equipment, and the like.

According to a second aspect of the present invention, there is provided a method for producing a high-strength and high-toughness silicon nitride sintered body, comprising: adding a sintering aid to silicon nitride particles for marix containing a sintering aid. Included diameter is 550-1000 μm and length is 250
After adding 5 to 30% by volume of silicon nitride needle-like particles of 0 to 4000 μm and sintering simultaneously in a nitrogen gas atmosphere, the silicon nitride sintered is lightweight, has excellent heat resistance, and has high strength and toughness. The great effect of being able to manufacture the body is brought about.

And, as described in claim 3,
Silicon nitride particles for matrix, yttrium oxide,
One or more rare earth oxides selected from neodymium oxide, lanthanum oxide, ytterbium oxide, and one or more oxides selected from one or more non-rare earth oxides selected from silicon oxide and magnesium oxide By containing 1 to 8% by weight of the system sintering aid, sintering can be performed sufficiently well, the formation of a glass phase can be prevented, and the strength and toughness of the silicon nitride matrix can be further improved. Is a great effect.

Further, as described in claim 4, the silicon nitride particles for the matrix have a β-type silicon nitride content of 90% by weight or more and an average particle diameter of 0.5 to 0.7 μm.
By using the β-type silicon nitride raw material powder that is the main component, sintering can be performed sufficiently well, and the strength and toughness of the silicon nitride matrix can be further improved. There is a great effect that there is.

Still further, as described in claim 5, the silicon nitride needle-like particles include at least one rare earth oxide selected from the group consisting of yttrium oxide, neodymium oxide, lanthanum oxide and ytterbium oxide; One or more oxide-based sintering aids selected from one or more non-rare earth oxides selected from silicon and magnesium oxide
By containing 8% by weight, it is possible to perform sintering sufficiently well, prevent the formation of a glass phase, and further improve the strength and toughness of the silicon nitride needle-like particles. The effect is brought.

Further, as described in claim 6, the needle-like particles of silicon nitride have a content of α-type silicon nitride of 90% by weight or more and an average particle diameter of 0.5 to 0.8 μm. The content of the α-type silicon nitride raw material powder and / or β-type silicon nitride is 90% by weight or more and the average particle size is 0.1%.
By using a β-type silicon nitride raw material powder having a particle size of 5 to 0.7 μm, sintering can be sufficiently performed, and the strength and toughness of silicon nitride needle-like particles are further improved. The great effect of being able to do so is brought about.

Further, as described in claim 7, after the silicon nitride needle-like particles are added to the silicon nitride particles for the matrix, the temperature is 1950-2100 ° C. and the nitrogen partial pressure is 0.08-1. By gas pressure sintering in nitrogen gas of 0 MPa, it is possible to simultaneously sinter the silicon nitride particles for the matrix and the silicon nitride needle-like particles, and produce a silicon nitride sintered body having high strength and high toughness. The great effect that it is possible is brought about.

Further, as described in claim 8, after the silicon nitride needle-like particles are added to the silicon nitride particles for the matrix, the temperature is 1950 to 2050 ° C. and the nitrogen partial pressure is 0.2 to 10 MPa. By performing hot press sintering in nitrogen gas, it is possible to simultaneously sinter the silicon nitride particles for the matrix and the needle-shaped silicon nitride particles, and obtain a high-strength and high-toughness silicon nitride sintered body. The great effect that it can be manufactured is brought about.

Further, as described in claim 9, after the sintering, hot isostatic press sintering is performed in a nitrogen gas having a temperature of 2100 to 2200 ° C. and a nitrogen partial pressure of 30 to 200 MPa. By doing so, a remarkable effect that a high-strength and high-toughness silicon nitride sintered body with further improved mechanical properties can be produced is brought about.

[0055]

【Example】

(Examples 1 to 5, Comparative Examples 1 and 2)-Amount of Silicon Nitride Needle Particles-(1) Raw Material Adjustment When obtaining silicon nitride needle particles, commercially available silicon nitride powder (P21FC manufactured by Denki Kagaku Kogyo Kogyo) When the content of β-type silicon nitride is 90% by weight or more and the average particle size is 0.5 to 0.5%.
Those) of 7 [mu] m, the sintering aid (manufactured by Shin-Etsu Chemical Co., Y ₂ 0 ₃ 2
Wt. And 2 wt.% Of Nd ₂ O ₃ ) were added, pulverized and mixed by a ball mill in alcohol for 24 hours, and then dried. Thereafter, 40% by weight of water and 5% by weight of methylcellulose are mixed to form a kneaded body, and the kneaded body is extruded through a mesh having predetermined holes to form needle-like particles having a diameter of 800 μm and a length of 3000 μm. did.

On the other hand, when obtaining silicon nitride particles for a matrix, 2% by weight of Nd ₂ O ₃ and 2% by weight of Y ₂ O ₃ were added to a commercially available silicon nitride powder (P21FC manufactured by Denki Kagaku Kogyo) as a sintering aid. %, And the mixture was ground and mixed by a ball mill in alcohol for 96 hours and then dried.

Then, silicon nitride needle-like particles were prepared in the same manner as in Example 1 of Tables 1 and 2 than the silicon nitride spherical particles for matrix.
As shown in the columns of Nos. 1 to 5 and Comparative Examples 1 and 2, they were blended in the range of 0 to 35% by weight, and then mixed with a V-type blender to obtain "needle-shaped particle group mixed powder".

(2) Sintering Conditions and Specimen Shape During sintering, the sintering was performed in a nitrogen atmosphere (0.9 MPa).
“Acicular particle group sintered body” was obtained by using gas pressure sintering at 0 ° C. for 4 hours. The shape of the “sintered needle particle group” was 4 × 5 × 45 mm. Then, a JIS-shaped test piece was prepared from the flat plate having the above-mentioned shape.

(3) Observation of Microstructure and Evaluation of Characteristics Evaluation of the microstructure of the particle group was performed using an optical microscope after polishing the sample with diamond particles (particle diameter 0.26 μm). The strength test uses a four-point bending test method according to JIS-R1601, and the fracture toughness test uses JIS-R160.
7 using the SEPB method. Further, the thermal conductivity was measured using a disk according to JIS-R1611.

(4) Results As shown in Tables 1 and 2, the acicular particle group sintered bodies of Examples 1 to 5 in which acicular particles were added in an amount of 5 to 30% by weight had a thermal conductivity of 90 W / m · K or more and mechanical strength of 650
MPa or more, the fracture toughness value is 6.5 MPaＭＰm or more, and when used for turbine applications or engine applications, it has sufficient mechanical strength characteristics to suppress the generation of thermal stress and to have a fracture probability of 1 / 100,000 or less. Ceramic material. On the other hand, Comparative Example 1 containing no needle-like particles and Comparative Example 2 containing excessive needle-like particles had unfavorable results.

(Example 6-10, Comparative Example 3-6)-Diameter and Length of Silicon Nitride Particles-(1) Raw Material Adjustment To obtain silicon nitride needle-like particles, commercially available silicon nitride powder (electrochemical The content of industrial P21FC β-type silicon nitride is 90% by weight or more and the average particle size is 0.5 to 0.5%.
Those) of 7 [mu] m, the sintering aid (manufactured by Shin-Etsu Chemical Co., Y ₂ 0 ₃ 2
Wt. And 2 wt.% Of Nd ₂ O ₃ ) were added, pulverized and mixed by a ball mill in alcohol for 24 hours, and then dried. Then, after mixing 40% by weight of water and 5% by weight of methylcellulose to obtain a kneaded body, the kneaded body was extruded through a mesh having predetermined holes, thereby obtaining Examples 6 to 10 of Tables 3 and 4 and As shown in the columns of Comparative Examples 3 to 6, the diameter was 500 to 1000 μm, and the length was 2000 to 2000.
Needle-shaped particles of 6000 μm were obtained.

On the other hand, commercially available silicon nitride powder (P21F manufactured by Denki Kagaku Kogyo)
C), 2% by weight of Nd ₂ O ₃ as a sintering aid and Y ₂ O
₃ was added in an amount of 2% by weight, and the mixture was ground and mixed by a ball mill in an alcohol for 96 hours and then dried.

Then, 80% by weight of the above-mentioned silicon nitride spherical particles for matrix and 20% by weight of silicon nitride needle-like particles were mixed, and then mixed with a V-type blender to obtain a "needle-like particle group mixed powder". Conditions and test piece shape During sintering, 200 in a nitrogen atmosphere (0.9 MPa)
Table 3 by using gas pressure sintering at 0 ° C for 4 hours.
As shown in the columns of Examples 6 to 10 and Comparative Examples 3 to 6, the diameter of the acicular particles was 375 to 750 μm and the length was 150.
A “needle-shaped particle group sintered body” of 0 to 4800 μm was obtained. The shape of the “sintered needle particle group” was 4 × 5 × 45 mm. Then, a JIS-shaped test piece was prepared from the flat plate having the above-mentioned shape.

(3) Microstructure Observation and Characteristic Evaluation The microstructure of the particle group was evaluated using an optical microscope after polishing the sample with diamond particles (particle diameter 0.26 μm). The strength test uses a four-point bending test method according to JIS-R1601, and the fracture toughness test uses JIS-R160.
7 using the SEPB method. Further, the thermal conductivity was measured using a disk according to JIS-R1611.

(4) Results As shown in Tables 3 and 4, the diameter was 600 to 1000 μm,
In the acicular particle group sintered bodies of Examples 6 to 10 to which 20% by weight of acicular particles having a length in the range of 3000 to 4000 μm were added, the diameter of the acicular particle groups in the sintered body was 450 to 750 μm.
m, the length is 2400-3200 μm, the thermal conductivity is 90 W / m · K or more, and the mechanical strength is 650 M
Pa or more, the fracture toughness value is 6.5 MPaＭＰm or more,
When used for turbine applications or engine applications, the ceramic material has sufficient mechanical strength characteristics that suppresses the generation of thermal stress and has a fracture probability of 1 / 100,000 or less. On the other hand, the length of the acicular particle group is 4000 μm.
In Comparative Examples 4 and 5, the sintering was hindered, the density was reduced, and the strength and thermal conductivity were reduced due to the introduction of holes. Comparative Example 3 having a small diameter
In Comparative Example 6 having a short length, the effect of stopping the propagation of cracks was small and the toughness value was reduced.

(Examples 11 to 17, Comparative Examples 7 and 8) Influence of Sintering Conditions (1) Raw Material Adjustment In obtaining silicon nitride needle-like particles, commercially available silicon nitride powder (P21FC β manufactured by Denki Kagaku Kogyo Kogyo) When the content of the silicon nitride is 90% by weight or more and the average particle size is 0.5 to 0.5%.
Those) of 7 [mu] m, the sintering aid (manufactured by Shin-Etsu Chemical Co., Y ₂ 0 ₃ 2
Wt. And 2 wt.% Of Nd ₂ O ₃ ) were added, pulverized and mixed by a ball mill in alcohol for 24 hours, and then dried. Thereafter, 40% by weight of water and 5% by weight of methylcellulose are mixed to form a kneaded body, and the kneaded body is extruded through a mesh having predetermined holes to form acicular particles having a diameter of 800 μm and a length of 3000 μm. did.

On the other hand, when obtaining the silicon nitride particles for the matrix, 2% by weight of Nd ₂ O ₃ and 2% by weight of Y ₂ O ₃ as sintering aids were added to a commercially available silicon nitride powder (P21FC manufactured by Denki Kagaku Kogyo). %, And the mixture was ground and mixed by a ball mill in alcohol for 96 hours and then dried.

Then, after mixing 80% by weight of the silicon nitride spherical particles for matrix and 20% by weight of silicon nitride needle-like particles, they were mixed with a V-type blender to obtain a "needle-like particle group mixed powder".

(2) Sintering Conditions and Specimen Shapes In sintering, a nitrogen atmosphere (0.9 MPa) was used.
As shown in the columns of Examples 11 to 14 of Comparative Example 6, the gas pressure sintering at 1900 to 2100 ° C. for 4 hours as shown in the column of Comparative Example 7, and shown in the columns of Examples 16 and 17 and Comparative Example 8 in Tables 5 and 6. Gas pressure hot press sintering at a temperature of 1900 to 2050 ° C. for 4 hours and hot isostatic sintering (HIP) after gas pressure sintering as shown in the column of Example 15 in Tables 5 and 6. As a result, an "acicular particle group sintered body" was obtained. The shape of the “sintered needle particle group” was 4 × 5 × 45 mm. Then, a JIS-shaped test piece was prepared from the flat plate having the above-mentioned shape.

(3) Observation of Microstructure and Evaluation of Characteristics Evaluation of the microstructure of the particle group was performed using an optical microscope after polishing the sample with diamond particles (particle diameter 0.26 μm). The strength test uses a four-point bending test method according to JIS-R1601, and the fracture toughness test uses JIS-R160.
7 using the SEPB method. Further, the thermal conductivity was measured using a disk according to JIS-R1611.

(4) Results As shown in Tables 5 and 6, needle-like particles of Examples 11 to 17 were obtained by adding 20% by weight of needle-like particles and sintering them under the conditions of the present invention. Has a thermal conductivity of 90 W / m · K or more, a mechanical strength of 650 MPa or more, and a fracture toughness of 6.
When it is used as a turbine or an engine, the ceramic material has sufficient mechanical strength characteristics that suppresses generation of thermal stress and has a fracture probability of 1 / 100,000 or less. On the other hand, in Comparative Examples 7 and 8 in which the sintering temperature was 1900 ° C., the sintering was hindered, the density was reduced, and holes were introduced, so that the strength, toughness, and thermal conductivity were reduced. I was

(Examples 18 to 23, Comparative Examples 9 and 10)
Kinds and Additions of Sintering Aids (1) Raw Material Adjustment When obtaining silicon nitride needle-like particles, a commercially available silicon nitride powder (P21FC β-type silicon nitride manufactured by Denki Kagaku Kogyo Co., Ltd.) having an average content of 90% by weight or more is used. Particle size is 0.5-0.
Those) of 7 [mu] m, the sintering aid (manufactured by Shin-Etsu Chemical Co., Y ₂ 0 _3,
Nd ₂ O ₃ , La ₂ O ₃ , Yb ₂ O ₃ , MgO, SiO
₂ in Examples 18 to 23 and Comparative Examples 9 and 10 in Tables 5 and 6), and the mixture was pulverized and mixed by a ball mill in alcohol for 24 hours and then dried.
Thereafter, 40% by weight of water and 5% by weight of methylcellulose are mixed to form a kneaded body, and the kneaded body is extruded through a mesh having predetermined holes to obtain a diameter of 80%.
Needle-shaped particles having a thickness of 0 μmm and a length of 3000 μm were obtained.

[0073] On the other hand, in obtaining a matrix for silicon nitride particles it is a commercially available silicon nitride powder (manufactured by Denki Kagaku Kogyo P21FC), sintering aid (manufactured by Shin-Etsu Chemical Co., Y ₂ 0 _3,
Nd ₂ O ₃ , La ₂ O ₃ , Yb ₂ O ₃ , MgO, SiO
₂ were added as shown in the columns of Examples 18 to 23 and Comparative Examples 9 and 10 in Tables 7 and 8), pulverized and mixed by a ball mill in alcohol for 96 hours, and then dried.

Then, 80% by weight of the above-mentioned silicon nitride spherical particles for matrix and 20% by weight of silicon nitride needle-like particles were mixed, and then mixed with a V-type blender to obtain "needle-like particle group mixed powder".

(2) Sintering conditions and test piece shape Sintering was performed in a nitrogen atmosphere (0.9 MPa) for 200 minutes.
By performing gas pressure sintering at 0 ° C. for 4 hours, “a needle-shaped particle group sintered body” was obtained. The shape of the “sintered needle particle group” was 4 × 5 × 45 mm. Then, a JIS-shaped test piece was prepared from the flat plate having the above-mentioned shape.

(3) Observation of microstructure and evaluation of characteristics Evaluation of the microstructure of the particle group was performed using an optical microscope after polishing the sample with diamond particles (particle diameter 0.26 μm). The strength test uses a four-point bending test method according to JIS-R1601, and the fracture toughness test uses JIS-R160.
7 using the SEPB method. Further, the thermal conductivity was measured using a disk according to JIS-R1611.

(4) Results As shown in Tables 7 and 8, the needle-like particle group sintering of Examples 18 to 23 in which 20% by weight of the needle-like particles were added and 1 to 8% by weight of the sintering aid were added. The body has a thermal conductivity of 90 W / m · K or more, a mechanical strength of 650 MPa or more, and a fracture toughness of 6.5 MPaＭＰm or more, and suppresses the generation of thermal stress when used for turbine or engine applications. It has been a ceramic material having sufficient mechanical strength characteristics with a breaking probability of 1 / 100,000 or less. On the contrary,
In Comparative Example 9 in which the amount of the sintering aid was less than 1% by weight, the sintering was hindered, the density was reduced, and the thermal conductivity was reduced due to the introduction of holes. Further, in Comparative Example 10 in which the amount of the sintering aid exceeded 8% by weight, the glass phase was increased and the strength and the thermal conductivity were reduced.

[0078]

[Table 1]

[0079]

[Table 2]

[0080]

[Table 3]

[0081]

[Table 4]

[0082]

[Table 5]

[0083]

[Table 6]

[0084]

[Table 7]

[0085]

[Table 8]

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing the structure of a high-strength, high-toughness silicon nitride sintered body according to the present invention.

Claims (9)

[Claims] 1. The method of claim 1 wherein the silicon nitride matrix has a diameter of 4
00-750 μm and length of 2000-3500 μm
High-strength and high-toughness silicon nitride sintered body, wherein 5 to 30% by volume of silicon nitride needle particles are dispersed. 2. A needle-like silicon nitride particle having a diameter of 550 to 1000 μm and a length of 2500 to 4000 μm containing a sintering agent is added to silicon nitride particles for marix containing a sintering agent in an amount of 5 to 30% by volume. And then simultaneously sintering in a nitrogen gas atmosphere. 3. The silicon nitride particles for a matrix include one or more rare earth oxides selected from yttrium oxide, neodymium oxide, lanthanum oxide and ytterbium oxide, and one or more selected from silicon oxide and magnesium oxide. The method for producing a high-strength and high-toughness silicon nitride sintered body according to claim 2, comprising 1 to 8% by weight of one or more oxide-based sintering aids selected from the group consisting of non-rare earth oxides. . 4. The method according to claim 1, wherein a β-type silicon nitride raw material powder having a β-type silicon nitride content of 90% by weight or more and an average particle diameter of 0.5 to 0.7 μm is used as the silicon nitride particles for the matrix. The method for producing a high-strength, high-toughness silicon nitride sintered body according to claim 2 or 3, wherein: 5. The silicon nitride needle-like particles include at least one rare earth oxide selected from yttrium oxide, neodymium oxide, lanthanum oxide, and ytterbium oxide, and at least one selected from silicon oxide and magnesium oxide. The method for producing a high-strength and high-toughness silicon nitride sintered body according to claim 2, comprising 1 to 8% by weight of one or more oxide-based sintering aids selected from the group consisting of non-rare earth oxides. . 6. A β-type silicon nitride raw material powder having a β-type silicon nitride content of 90% by weight or more and an average particle size of 0.5 to 0.7 μm.
Or the method for producing a high-strength, high-toughness silicon nitride sintered body according to item 5. 7. Addition of needle-like particles of silicon nitride to silicon nitride particles for a matrix, followed by gas pressure sintering in a nitrogen gas at a temperature of 1950 to 2100 ° C. and a nitrogen partial pressure of 0.08 to 1.0 MPa. 7. The method according to claim 2, wherein
The method for producing a high-strength and high-toughness silicon nitride sintered body according to any one of the above. 8. A method comprising adding silicon nitride needle-like particles to the silicon nitride particles for a matrix, followed by hot press sintering in a nitrogen gas at a temperature of 1950 to 2050 ° C. and a nitrogen partial pressure of 0.2 to 10 MPa. The method for producing a high-strength and high-toughness silicon nitride sintered body according to any one of claims 2 to 6. 9. The hot isostatic press sintering in nitrogen gas at a temperature of 2100 to 2200 ° C. and a nitrogen partial pressure of 30 to 200 MPa after sintering. For producing a high-strength, high-toughness silicon nitride sintered body.