JPH11116341A - Highly heat-conductive silicon nitride sintered product and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to impart improved high heat conductivity and breaking toughness to a silicon nitride sintered product light in weight and excellent in heat resistance. SOLUTION: Silicon nitride powder 2 containing 1-7 wt.% of a sintering auxiliary is mixed with 0.5-8.5 wt.% of silicon nitride whiskers 3 and subsequently sintered to obtain the highly heat-conductive silicon nitride sintered product having an average heat conductivity of >=90 W/m.K in mutually orthogonal directions X, Y and Z and having a heat conductivity of ±10 W/m.K in the directions X, Y and Z.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a highly thermally conductive ceramic (silicon nitride sintered body) suitable for imparting even higher thermal conductivity and fracture toughness to a silicon nitride sintered body that is lightweight and excellent in heat resistance. Body) and a method for producing the same, for example, a member for an automobile, a member for an electronic device,
An object of the present invention is to provide a structural member used for a member for a chemical device, a member for aerospace equipment, and the like.

[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 for improving the mechanical performance by increasing the hardness and toughness of the ceramic matrix by adding a second phase, and a material for improving the strength by reducing the diameter of the particles have been developed. Have been done.

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] As a method for improving the thermal conductivity of silicon nitride, there is a method disclosed in 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).

Recently, a method of adding a columnar metal has been reported (Japanese Patent Application Laid-Open No. 8-26837), but it cannot be used 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).

[0007] In order to obtain high strength, a method of reducing the particle size of a starting material to about 0.1 µm has been reported (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 for 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 for simultaneously obtaining high toughness and high strength, there is 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 Laid-Open No. 8-108). No. 143400).

[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, in the production method for obtaining a high thermal conductivity, although the thermal conductivity can be improved by changing the auxiliary agent, the toughness value is lowered, and there is also a disadvantage that the characteristic values cannot be compatible.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of such prior art, and is intended to provide a silicon nitride sintered body which is lightweight and excellent in heat resistance and has a small direction dependency of thermal conductivity. It is an object of the present invention to provide a silicon nitride sintered body having high thermal conductivity, high strength and high toughness, and excellent mechanical properties.

[0015]

Means for Solving the Problems The invention proposed here is:
By introducing a new domain into the matrix, this method eliminates sintering problems between different materials and achieves both strength and thermal conductivity.

In the present invention, attention is paid to a sintering technique utilizing silicon nitride single crystal whiskers, which is considered as a coarse particle which causes a decrease in strength in the prior art, and the surface is oxidized by a hydrothermal treatment method to form SiO _{2 on the} surface. A silicon nitride sintered body is manufactured by a method of adding a predetermined ratio of silicon nitride whiskers on which is precipitated and simultaneously sintering. The above problem is solved by providing a particle group dispersed structure that exhibits excellent functions by minimizing the addition ratio of silicon nitride whiskers. The silicon nitride sintered body thus obtained has excellent thermal conductivity and considerable mechanical strength, toughness and hardness characteristics.

In the high thermal conductivity silicon nitride sintered body according to the present invention, as described in claim 1, silicon nitride whiskers are contained in a silicon nitride matrix in an amount of 0.5 to 8.5.
The average value of the thermal conductivity in the X, Y, and Z directions orthogonal to each other is 90 W / m · K or more, and the value of the thermal conductivity in the X, Y, and Z directions is ± 10 W. /
m · K or less.

In the embodiment of the high thermal conductive silicon nitride sintered body according to the present invention, as described in claim 2, among the silicon nitride whiskers, the diameter is 3 μm.
m, the ratio of whiskers occupying 10 m or more is 10 to 65 area%.

According to a third aspect of the present invention, there is provided a method for producing a silicon nitride sintered body having a high thermal conductivity, wherein silicon nitride powder containing 1 to 7% by weight of a sintering aid is added to silicon nitride powder. The mixed powder to which whiskers are added in an amount of 0.5 to 8.5% by weight is sintered, and the average value of the thermal conductivity in the X, Y, and Z directions orthogonal to each other is 90 W / m · K or more, and , Y, and Z thermal conductivity values are ± 10 W / m ·
It is characterized in that a silicon nitride sintered body having a temperature within K is obtained.

In a preferred embodiment of the method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention, claim 4
As described in the above, the silicon nitride whisker to be added is β-type silicon nitride and has a diameter of 2 to 5 μm and a length of 2 μm.
It can be made to be 0 to 50 μm.

Similarly, in an embodiment of the method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention,
As described above, the silicon nitride whiskers to be added can be subjected to hydrothermal treatment at 110 to 140 ° C.

Similarly, in an embodiment of the method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention, claim 6
As described in the above, the sintering aid contained in the silicon nitride powder includes at least one rare earth oxide selected from yttrium oxide, neodymium oxide, lanthanum oxide, and ytterbium oxide, and silicon oxide and magnesium oxide. And at least one selected from one or more non-rare earth oxides selected from the group consisting of:

Similarly, in an embodiment of the method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention, claim 7
As described in the above, a mixed powder of a silicon nitride powder containing a sintering aid and a silicon nitride whisker is 1950-
Gas pressure sintering can be performed in a nitrogen gas at a temperature of 2100 ° C. and a nitrogen partial pressure of 0.2 to 1 MPa.

Similarly, in an embodiment of the method for producing a silicon nitride sintered body having high thermal conductivity according to the present invention, claim 8
As described in the above, a mixed powder of a silicon nitride powder containing a sintering aid and a silicon nitride whisker is 1950-
After gas pressure sintering in a nitrogen gas at a temperature of 2100 ° C. and a nitrogen partial pressure of 0.2 to 1 MPa, 2100 to 220
Hot isostatic sintering can be performed under a nitrogen atmosphere of 30 to 200 MPa at a temperature of 0 ° C.

[0025]

The high thermal conductive silicon nitride sintered body and the method of manufacturing the same according to the present invention have the above-mentioned construction. The method of manufacturing the silicon nitride sintered body will be specifically described as follows.

Silicon nitride powder for matrix (When the content of β-type silicon nitride is 90% by weight or more and the average particle size is 0.5 to
0.7 μm), a sintering aid (total of 1 to 7% by weight of one or more rare earth oxides and / or one or more non-rare earth oxides) is added and pulverized by a ball mill in alcohol. After mixing, the mixture is dried to obtain a matrix powder.

On the other hand, as an additional phase,
0.5 to 8. Silicon nitride whiskers that have been hydrothermally treated at
5% by weight is added, mixed in an alcohol by a ball mill, and dried by a rotary evaporator to obtain a raw material powder.

Next, the mixed powder of the silicon nitride powder containing the sintering aid and the silicon nitride whisker is sintered in a nitrogen gas atmosphere.

Here, the reason why it is desirable to determine the range with respect to the diameter and the amount of the raw material when forming the mixed powder is as follows.

If the particle size of the silicon nitride powder for the matrix is too large, sintering within the temperature range described in the present invention becomes difficult, and if it is too small, it is difficult to handle, and similarly, it is difficult to simultaneously sinter with silicon nitride whiskers. 0.5 ~
The thickness is preferably 0.7 μm.

Further, β of silicon nitride powder for matrix
If the conversion ratio is small, sintering in the temperature range described in the present invention becomes difficult, so it is preferable to set the content to 90% by weight or more.

Further, if the amount of the sintering aid added to the silicon nitride powder for the matrix is 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. The content is preferably set to 7% by weight.

Next, the silicon nitride whiskers for acicular particles are preferably single crystals. If the diameter of the silicon nitride whiskers is larger than 5 μm, sintering in the temperature range described in the present invention is difficult. If it is smaller than 3 μm, it is not preferable because it dissolves during liquid phase sintering and cannot exert its effect.

The length of the silicon nitride whiskers is 20.
If the length is shorter than μm, the effect cannot be exerted.

Further, if the addition amount of the silicon nitride whisker is more than 8.5% by volume, the specific gravity becomes large and the mechanical properties become insufficient, which is not preferable. If it is less than 0.5% by weight, the effect cannot be exhibited. It is not preferable.

Next, when sintering the mixed powder of the silicon nitride powder for matrix containing the above-mentioned sintering aid and the silicon nitride whisker, after appropriately performing press molding, the mixed powder is heated at a temperature of 1950 to 2100 ° C. Atmosphere (0.2
Gas pressure sintering method of sintering under a pressure of 1 to 220 MPa, or the gas pressure sintered body obtained here is again subjected to a pressure of 2100 to 220 MPa under a nitrogen atmosphere of 30 to 200 MPa.
A hot isostatic sintering method of sintering at a temperature of 0 ° C. can be employed. In this case, in gas pressure sintering, if the temperature is lower than 1950 ° C., the density does not increase and is not suitable as a structural material.
If the temperature is higher than 00 ° C., the particles grow excessively and the strength is reduced, which is not preferable.

In the microstructure after sintering, in a silicon nitride sintered body 1 schematically shown in FIG. 1, silicon nitride whiskers 3 are dispersed in a silicon nitride matrix 2 while maintaining a needle shape. There are silicon nitride needle-like particles corresponding to the diameter and length of the particles. In this case, if the added amount of the silicon nitride whisker is less than 0.5% by volume, the amount of the grown particles is not required, and if the added amount exceeds 8.5% by volume, the coarse particles become large and the mechanical property value becomes large. Is remarkably reduced, which is not preferable.

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 further,
The thermal conductivity was measured on a disk having a diameter of 10 mm and a thickness of 2 mm according to JIS-R1611.

Here, in addition to the derivative technology of the present invention, the method of forming the silicon nitride containing the second phase particles used in the present invention into needle-like particles, and then adding the silicon nitride to the powder in the form of particles is described. 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.

[0040]

According to the high thermal conductivity silicon nitride sintered body of the present invention, the silicon nitride whisker is contained in the silicon nitride matrix in the range of 0.5 to 8.5.
The average value of the thermal conductivity in the X, Y, and Z directions orthogonal to each other is 90 W / m · K or more, and the value of the thermal conductivity in the X, Y, and Z directions is ± 10 W. /
m · K or less, it is possible to simultaneously provide even higher thermal conductivity and more excellent fracture toughness to a silicon nitride sintered body that is lightweight and has excellent heat resistance,
For example, a remarkable effect is obtained that the material is suitable as 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, and the like.

And, as described in claim 2,
By setting the proportion of the whiskers having a diameter of 3 μm or more in the silicon nitride whiskers to be 10 to 65 area%, it is possible to obtain higher thermal conductivity and more excellent fracture toughness at the same time. That is a great effect.

According to a third aspect of the present invention, there is provided a method for producing a silicon nitride sintered body having a high thermal conductivity, wherein a silicon nitride whisker is added to a silicon nitride powder containing 1 to 7% by weight of a sintering aid. Of 0.5 to 8.5% by weight is sintered, and the average value of the thermal conductivity in the X, Y, and Z directions orthogonal to each other is 90 W / m · K or more and the X,
Since a silicon nitride sintered body having a thermal conductivity value within ± 10 W / m · K in the Y and Z directions is obtained, it is lightweight, has excellent heat resistance, and has high strength and high toughness and has thermal conductivity. A remarkable effect that it is possible to manufacture a silicon nitride sintered body having excellent heat conduction characteristics with small direction dependence of the rate.

And, as described in claim 4,
Silicon nitride whiskers to be added are β-type silicon nitride, having a diameter of 2 to 5 μm and a length of 20 to 50 μm, thereby simultaneously providing higher thermal conductivity and more excellent fracture toughness. This is a great effect that is possible.

As described in claim 5, by subjecting the silicon nitride whiskers to be added to hydrothermal treatment at 110 to 140 ° C., the surface of the silicon nitride whiskers is oxidized and SiO ₂ is formed on the surface. By being sintered at the same time as the precipitated silicon nitride particles, the silicon nitride whisker should be added to the necessary minimum amount to obtain a silicon nitride sintered body having high thermal conductivity and high fracture toughness at the same time. This is a great effect that is possible.

Further, as described in claim 6,
The sintering aid contained in the silicon nitride powder is 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. By using one or more selected from among the non-rare earth oxides described above, sintering can be performed sufficiently well and the strength and toughness of the silicon nitride matrix are further improved. A great effect is obtained.

Further, as described in claim 7, the mixed powder of the silicon nitride powder containing the sintering aid and the silicon nitride whisker is mixed at a temperature of 1950 to 2100 ° C. and a nitrogen partial pressure of 0.1%. By performing gas pressure sintering in a nitrogen gas of 2 to 1 MPa, it is possible to simultaneously sinter the silicon nitride powder for the matrix and the silicon nitride whisker, and to obtain excellent heat conduction characteristics with small direction dependence. This has a remarkable effect that it is possible to produce a silicon nitride sintered body having high strength and high toughness as well as having a high strength.

Further, as described in claim 8, a mixed powder of a silicon nitride powder containing a sintering aid and a silicon nitride whisker is prepared at a temperature of 1950-2100 ° C. and a nitrogen partial pressure of 0.1 wt. After gas pressure sintering in a nitrogen gas of 2 to 1 MPa, a temperature of 2100 to 2200 ° C.
By performing hot isostatic sintering in a nitrogen atmosphere of 200 MPa, a remarkable effect that a highly thermally conductive silicon nitride sintered body with further improved mechanical properties can be obtained is brought about. .

[0048]

【Example】

(Examples 1 to 5, Comparative Examples 1 and 2)-Addition amount of surface-treated silicon nitride whisker-(1) Raw material adjustment To obtain silicon nitride acicular particles, a commercially available β-type silicon nitride whisker (E10 manufactured by Ube Industries) 3μ in diameter
m, having a length of 30 μm) was subjected to hydrothermal treatment at 120 ° C. for 96 hours, and then dried to obtain silicon nitride whiskers as a raw material.

On the other hand, when obtaining a silicon nitride powder for a matrix, commercially available silicon nitride powder (P21FC β type manufactured by Denki Kagaku Kogyo having a content of 90% by weight or more and an average particle size of 0.5 to 0.7 μm) is used. ), 2% by weight of Nd ₂ O ₃ and 2% by weight of Y ₂ O ₃ were added as sintering aids to form a mixture.
The mixture was pulverized and mixed by a ball mill in alcohol for an hour, and then dried.

Then, silicon nitride whiskers were added to the silicon nitride powder in Examples 1 to 5 and Comparative Examples 1 and 2 shown in Tables 1 and 2.
As shown in column 2, after mixing in a range of 0 to 10% by weight, the mixture was mixed with a V-type blender to obtain "surface-treated whisker mixed powder".

(2) Sintering Conditions and Specimen Shape During sintering, the sintering was performed in a nitrogen atmosphere (0.9 MPa).
By performing gas pressure sintering at 0 ° C. for 4 hours, a “surface-treated whisker mixed sintered body” was obtained. The shape of the “sintered whisker-mixed sintered body” 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-R1607.
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, 0.5% silicon nitride whiskers were used.
In the sintered bodies of Examples 1 to 5 in which ８8% by weight was added, the orientation dependence of the thermal conductivity was small, and an excellent value of 90 W / m · K or more was obtained on average. The mechanical strength is 650MP
a, the fracture toughness value is 6.5 MPa√m or more, and when used for turbine or engine applications, sufficient mechanical strength characteristics to suppress the generation of thermal stress and to reduce the probability of fracture to 1 / 100,000 or less Ceramic material. On the other hand, in the sintered body of Comparative Example 1 in which no silicon nitride whisker was added, the strength, toughness, and thermal conductivity were inferior, and the addition amount of the silicon nitride whisker was 10% by weight. In the sintered body of Example 2, since the grain growth was excessively promoted, the strength was greatly reduced, and the orientation dependency of the thermal conductivity was slightly large.

(Examples 6 to 10, Comparative Examples 3 and 4)-Hydrothermal treatment temperature of surface-treated silicon nitride whiskers (1) Preparation of raw material To obtain silicon nitride needle-like particles, commercially available β-type silicon nitride whiskers ( Ube Industries E10 3μ in diameter
m, having a length of 10 μm) in Examples 6 to 1 of Tables 3 and 4.
0 and 100 to 16 as shown in the columns of Comparative Examples 3 and 4.
Particles subjected to a hydrothermal treatment at a temperature of 0 ° C. for 96 hours and particles subjected to a hydrothermal treatment at a temperature of 120 ° C. for 48 hours and 144 hours were prepared and dried to obtain a raw material silicon nitride whisker.

On the other hand, when obtaining a silicon nitride raw material powder for a matrix, a commercially available silicon nitride powder (P21FC manufactured by Denki Kagaku Kogyo Co., Ltd.) was added with 2% by weight of Nd ₂ O ₃ and 2% by weight of Y ₂ O ₃ as sintering aids. The mixture was pulverized and mixed by a ball mill in an alcohol for 96 hours and then dried.

Then, 4% by weight of silicon nitride whiskers were blended with the silicon nitride powder and mixed with a V-type blender to obtain "surface-treated whisker mixed powder".

(2) Sintering Conditions and Specimen Shape During sintering, the sintering was performed in a nitrogen atmosphere (0.9 MPa).
By performing gas pressure sintering at 0 ° C. for 4 hours, a “surface-treated whisker mixed sintered body” was obtained. The shape of the “sintered whisker-mixed sintered body” 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 carried out 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-R1607.
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, silicon nitride whiskers were
In the sintered bodies of Examples 6 to 10 using the acicular particles subjected to hydrothermal treatment at a temperature of up to 140 ° C., the orientation dependence of the thermal conductivity was small, and an excellent value exceeding 90 W / m · K on average. was gotten. In addition, the mechanical strength is 650 MPa or more, and the fracture toughness is 6.5 MPa√m or more. When used for turbine applications and engine applications, the generation of thermal stress is suppressed and the fracture probability is reduced to 1 / 100,000 or less. Ceramic material having excellent mechanical strength characteristics. When the hydrothermal treatment temperature is 120 ° C., 48 hours and 1 hour
The same effect was obtained by any of the treatments for 44 hours. On the other hand, the strength and toughness of the sintered body of Comparative Example 3 having a low hydrothermal treatment temperature of 100 ° C. are low, and the strength of the sintered body of Comparative Example 4 having a high hydrothermal treatment temperature of 160 ° C. Was low.

(Examples 11 to 15 and Comparative Examples 4 to 6)-Sintering Conditions of Silicon Nitride Mixed Powder-(1) Preparation of Raw Materials In order to obtain silicon nitride needle-like particles, commercially available β-type silicon nitride whiskers (Ube Kosan E10 diameter 3μ
m, having a length of 30 μm) was subjected to hydrothermal treatment at 120 ° C. for 96 hours, and then dried to obtain silicon nitride whiskers as a raw material.

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

Then, 4% by weight of silicon nitride whiskers were blended with the silicon nitride powder and mixed with a V-type blender to obtain "surface-treated whisker mixed powder".

(2) Sintering Conditions and Specimen Shapes In sintering, a nitrogen atmosphere (0.9 MPa) was used.
6, Examples 11 to 13 and Comparative Examples 4 and 5
(However, as shown in the column of sheet molding and sintering, gas pressure sintering at 1950-2100 ° C. for 4 hours, and gas pressure sintering as shown in the columns of Examples 14 and 15) By performing hot isostatic sintering after sintering, and further performing gas pressure hot press sintering at 2000 ° C. for 1 hour as shown in the column of Comparative Example 6, a “surface-treated whisker mixed sintered body” was obtained. . The shape of the “sintered whisker-mixed sintered body” was 4 × 5 × 45 mm. And
A test piece having a JIS shape was prepared from the flat plate having the above 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-R1607.
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, the "surface-treated whisker mixed powder" was gas-pressure sintered at a temperature of 1950 to 2100 ° C. and the sintered bodies of Examples 11 to 13 and hot isostatic pressure In the sintered bodies of Examples 14 and 15 in which sintering was performed, the orientation dependency of the thermal conductivity was small, and an excellent value exceeding 90 W / m · K on average was obtained. The mechanical strength is also 650MPa
As described above, the fracture toughness value is 6.5 MPa√m or more, and has sufficient mechanical strength characteristics to suppress the generation of thermal stress and reduce the probability of fracture to 1 / 100,000 or less when used for turbine and engine applications. Ceramic material. On the other hand, the sintered body of Comparative Example 4 having a low sintering temperature of 1900 ° C. has low strength and toughness and not very good thermal conductivity, and the sintered body of Comparative Example 5 which is extruded and then sintered. In the sintered body of Comparative Example 6 in which hot press sintering was performed during the sintering or in the sintering, a relatively large anisotropy occurred in the thermal conductivity.

(Examples 16 to 23)-Kinds and Additions of Sintering Aids-(1) Raw Material Adjustment To obtain silicon nitride needle-like particles, a commercially available β-type silicon nitride whisker (E10 having a diameter of E10 manufactured by Ube Industries) 3μ
m, having a length of 50 μm) at a temperature of 120 ° C. for 96 hours.
After hydrothermal treatment for an hour, it was dried to obtain silicon nitride whiskers as a raw material.

On the other hand, when obtaining a silicon nitride raw material powder for a matrix, commercially available silicon nitride powder (P21FC manufactured by Denki Kagaku Kogyo Co., Ltd.) was used as a sintering aid as shown in the columns of Examples 16 to 23 of Tables 7 and 8. And yttrium oxide,
A rare earth oxide selected from neodymium oxide, lanthanum oxide and ytterbium oxide and a non-rare earth oxide selected from silicon oxide and magnesium oxide are combined in a total of 4% by weight, and added to a ball mill in alcohol for 96 hours. After crushing and mixing, it was dried.

Then, 4% by weight of silicon nitride whiskers were blended with the silicon nitride powder and mixed with a V-type blender to obtain "surface-treated whisker mixed powder".

(2) Sintering conditions and test piece shape During sintering, the sintering was performed in a nitrogen atmosphere (0.9 MPa).
By performing gas pressure sintering at 0 ° C. for 4 hours, a “surface-treated whisker mixed sintered body” was obtained. In addition, the shape of the surface-treated whisker mixed sintered body 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-R1607.
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, even when the sintering aid was changed within an appropriate range, the combination of the sintering aid in Examples 16 to 23 was the same as in the previous example. In this case, the orientation dependence of the thermal conductivity was small, and an excellent value exceeding 90 W / m · K on average was obtained. In addition, the mechanical strength is 650 MPa or more, and the fracture toughness is 6.5 MPa√m or more. When used for turbine applications and engine applications, the generation of thermal stress is suppressed and the fracture probability is reduced to 1 / 100,000 or less. Ceramic material having excellent mechanical strength characteristics.

[0072]

[Table 1]

[0073]

[Table 2]

[0074]

[Table 3]

[0075]

[Table 4]

[0076]

[Table 5]

[0077]

[Table 6]

[0078]

[Table 7]

[0079]

[Table 8]

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing the structure of a highly thermally conductive silicon nitride sintered body according to the present invention.

Claims (8)

[Claims] 1. Silicon nitride whiskers are dispersed in a silicon nitride matrix in an amount of 0.5 to 8.5% by volume, and the average thermal conductivity in X, Y, and Z directions orthogonal to each other is 9%.
A highly thermally conductive silicon nitride sintered body characterized by being at least 0 W / m · K and having a value of thermal conductivity within ± 10 W / m · K in the X, Y, and Z directions. 2. A silicon nitride whisker having a diameter of 3
The high thermal conductive silicon nitride sintered body according to claim 1, wherein the proportion of the whiskers having a size of at least μm is 10 to 65 area%. 3. A mixed powder in which 0.5 to 8.5% by weight of silicon nitride whiskers are added to silicon nitride powder containing 1 to 7% by weight of a sintering aid, and X, X
A silicon nitride sintered body having an average value of thermal conductivity in the Y, Z directions of 90 W / m · K or more and a value of thermal conductivity in the X, Y, Z directions within ± 10 W / m · K. A method for producing a silicon nitride sintered body having high thermal conductivity, characterized by obtaining: 4. The silicon nitride whisker to be added is β-type silicon nitride, having a diameter of 2 to 5 μm and a length of 20 to 50.
The method for producing a highly thermally conductive silicon nitride sintered body according to claim 3, wherein the thickness is set to be μm. 5. The silicon nitride whisker to be added is 110
The method for producing a highly thermally conductive silicon nitride sintered body according to claim 3, wherein the heat treatment is performed at a temperature of 140 ° C. to 140 ° C. 6. 6. The sintering aid contained in the silicon nitride powder,
One or more rare earth oxides selected from yttrium oxide, neodymium oxide, lanthanum oxide, ytterbium oxide, and one or more non-rare earth oxides selected from silicon oxide and magnesium oxide
The method for producing a highly thermally conductive silicon nitride sintered body according to any one of claims 3 to 5, wherein the method is one or more kinds. 7. A mixed powder of a silicon nitride powder and a silicon nitride whisker containing a sintering aid is mixed with 1950-2100
7. The high thermal conductive silicon nitride sintered body according to claim 3, wherein gas-pressure sintering is performed in a nitrogen gas at a temperature of ℃ and a nitrogen partial pressure of 0.2 to 1 MPa. Production method. 8. A mixed powder of a silicon nitride powder containing a sintering aid and a silicon nitride whisker,
Gas pressure sintering in nitrogen gas at a temperature of 200 ° C. and a nitrogen partial pressure of 0.2 to 1 MPa, and then hot isostatic sintering at a temperature of 2100 to 2200 ° C. in a nitrogen atmosphere of 30 to 200 MPa. The method for producing a silicon nitride sintered body having high thermal conductivity according to any one of claims 3 to 7, characterized in that: